JP2006247899A5 - - Google Patents

Description

Droplet discharge device

  The present invention relates to a droplet discharge device that discharges droplets, and more particularly to a droplet discharge device that is optimal for forming an image by forming a line head and discharging ink droplets.

  In an ink jet recording apparatus, bubbles generated in ink are a cause of ejection failure and an increase in flow path resistance, and it is important for removing the bubbles to improve the reliability of the apparatus. Conventionally, as a countermeasure for removing the bubbles, it is known to discharge the bubbles by circulating the ink in the ink supply path (see, for example, Patent Documents 1 to 4).

  By the way, in recent years, line heads for the purpose of speeding up have been advanced. If this line head is advanced, it is necessary to provide a large number of discharge nozzles. For this reason, at the time of printing, there is a problem in that pressure loss (flow path resistance) increases when ink is supplied corresponding to a large number of ejection nozzles. In particular, this problem becomes serious when the above-described measures for discharging bubbles are taken.

This problem is not limited to the case of using a line head as described above, but often occurs in a droplet discharge apparatus that circulates a discharge liquid after providing a large number of discharge nozzles.
JP-A-6-24000 JP-A-4-53754 Japanese Patent Publication No. 3-71021 Japanese Patent Laid-Open No. 11-342634

  In view of the above fact, an object of the present invention is to provide a droplet discharge device in which pressure loss generated when a liquid flows is reduced.

  According to the first aspect of the present invention, a liquid chamber and a discharge nozzle that communicates with the liquid chamber are formed, a liquid droplet discharge head that discharges liquid droplets from the discharge nozzle, a tank that stores liquid, the liquid chamber, A switch for switching the liquid flow direction of the second line, a first line that connects the tank and can flow liquid from the tank to the liquid chamber, a second line that connects the liquid chamber and the tank, and And the switching means includes a pump for flowing the liquid from the liquid chamber toward the tank, and an on-off valve connected in parallel to the pump, and the droplet discharge head A plurality of liquid chambers, and the first line includes a first main line and a plurality of first branch lines branched from the first main line and communicating with the liquid chambers, respectively. The two lines are the second main line and the second A plurality of second branch lines that branch from the main line and communicate with the liquid chambers, respectively, and when discharging droplets, the pump is stopped and the on-off valve is opened to open the second line. The liquid flow direction of the second line is changed to the direction of flowing from the tank to the liquid chamber, and when the liquid is circulated, the pump is driven and the on-off valve is closed to change the liquid flow direction of the second line to the liquid chamber. The flow direction is from to the tank.

  The tank may be a sub tank (reservoir tank).

  At the time of discharging a droplet, the liquid flow directions of the first line and the second line are both directions from the tank to the liquid chamber. When the liquid is circulated, the liquid flow direction of the first line is a direction that flows from the liquid chamber to the tank, and the liquid flow direction of the second line is a direction that flows from the liquid chamber to the tank.

  Therefore, at the time of discharging a droplet, the liquid flows from the two lines into the liquid chamber of the droplet discharge head. Thereby, even if the liquid pressure is reduced as compared with the conventional case, the flow rate of the liquid to the liquid chamber at the time of discharge can be maintained, and the pressure loss is greatly reduced as compared with the conventional case. Moreover, since it is not necessary to increase the pipe diameters of the first line and the second line, the apparatus does not increase in size.

  The switching means includes a pump for causing the liquid to flow from the liquid chamber toward the tank, and an on-off valve connected in parallel to the pump. When the liquid is circulated, the pump is driven and the on-off valve is closed, and the pump during the circulation is driven in a direction in which negative pressure is generated in the flow paths such as the first line and the second line. Air bubbles are discharged. Therefore, compared to the case where the liquid is pumped and circulated through the flow paths such as the first line and the second line, liquid leakage due to the application of pressure does not occur from the connection part or the joint part of the flow path. Further, the configuration of the switching means can be a simple configuration with one pump and one valve.

  Further, the liquid droplet ejection head includes a plurality of liquid chambers, and the first line includes a first main line and a plurality of first branch lines branched from the first main line and communicating with the liquid chambers. The second line includes a second main line and a plurality of second branch lines that branch from the second main line and communicate with the respective liquid chambers. Each channel resistance of the channel becomes uniform, and it is easy to suppress variations in refill amount during ejection and variations in suction amount during recovery operation.

  According to a second aspect of the present invention, the first main line and the second main line are both arranged so as to have an upward slope from the upstream side to the downstream side of the liquid flow during the circulation of the liquid. It is characterized by that.

  Thereby, at the time of circulation of a liquid, a bubble can be reliably discharged | emitted with a smaller flow volume using the buoyancy of a bubble. Therefore, it is possible to save the power and reduce the size of the pump, and to reduce the power consumption and size of the device. Moreover, the backflow of bubbles can also be prevented.

  According to a third aspect of the present invention, a connection flow path that is directly connected to the second main line and communicates the flow path is provided at the downstream end of the first main line, and the flow resistance of the connection flow path is The total flow resistance of the first branch line and the second branch line connected to the one liquid chamber is larger.

  Thereby, at the time of circulation, the flow velocity in a connection flow path becomes large, and bubble discharge | emission can be performed easily. As a result, the required pump capacity can be greatly reduced. At the time of discharge, the liquid can sufficiently flow through the first branch line and the second branch line on the downstream end side of the first main line.

  According to a fourth aspect of the present invention, an image is formed using an ink liquid as a liquid.

  Thereby, an image forming apparatus capable of forming a good image can be realized.

  According to the present invention, it is possible to realize a droplet discharge device that reduces pressure loss that occurs when a liquid flows.

  Hereinafter, an ink jet recording apparatus will be exemplified as a droplet discharge apparatus, and an embodiment of the present invention will be described. In the second and subsequent embodiments, the same components as those already described are denoted by the same reference numerals and description thereof is omitted.

[First Embodiment]
First, the first embodiment will be described.

(overall structure)
FIG. 1 shows an ink jet recording apparatus 12 according to a first embodiment of the present invention. A paper feed tray 16 is provided in the lower part of the casing 14 of the ink jet recording apparatus 12, and the sheets P stacked in the paper feed tray 16 can be taken out one by one by a pickup roll 18. The taken paper P is transported by a plurality of transport roller pairs 20 constituting a predetermined transport path 22. Hereinafter, the term “transport direction” simply refers to the transport direction of the paper P that is a recording medium.

  Above the paper feed tray 16, an endless transport belt 28 stretched around a drive roll 24 and a driven roll 26 is disposed. A recording head array 30 is disposed above the conveyor belt 28 and faces the flat portion 28F of the conveyor belt 28. This opposed area is an ejection area SE where ink droplets are ejected from the recording head array 30. The sheet P transported along the transport path 22 is held by the transport belt 28 and reaches the discharge area SE, and ink droplets corresponding to image information are attached from the recording head array 30 in a state of facing the recording head array 30. The

  Then, by rotating the paper P while being held by the transport belt 28, the paper P can be passed through the discharge region SE a plurality of times, and so-called multipass image recording can be performed. Therefore, the surface of the conveyance belt 28 is a circulation path of the paper P in the present invention.

  As an example, the conveying belt 28 is formed by molding a semiconductive polyimide material (surface resistance value 1010 to 1013 Ω / □, volume resistance value 109 to 1012 Ω · cm) to a thickness of 75 μm, a width of 380 mm, and a circumferential length of 1000 mm. Can be used. Moreover, as the drive roll 24 and the driven roll 26, as an example, a φ50 mm SUS roll can be used.

  Further, without providing the conveyor belt 28, for example, a recording medium (paper P) may be sucked and held on the outer periphery of a conveyance roller formed in a cylindrical shape or a columnar shape and rotated. However, when the conveyor belt 28 is used as in the present embodiment, the flat portion 28F is formed, so that the recording head array 30 can be arranged corresponding to the flat portion 28F, which is preferable.

In this embodiment, the recording head array 30 has a long shape in which the effective recording area is equal to or larger than the width of the paper P (the length in the direction orthogonal to the transport direction), and is yellow (Y) and magenta (M). , Sian (C), and Black (K), four inkjet recording head units 32 (hereinafter simply referred to as head units 32) corresponding to the four colors are arranged along the transport direction to record full-color images. It is possible. The method for ejecting ink droplets in each head unit 32 is not particularly limited, and a known method such as a so-called thermal method or piezoelectric method can be applied.

  The inkjet recording head 33 (see FIGS. 5 and 6) constituting each head unit 32 is controlled by a head controller 60. For example, the head controller 60 determines the ejection timing of the ink droplets and the ink ejection port (nozzle) to be used according to the image information, and sends a drive signal to the inkjet recording head 33.

  The recording head array 30 may be stationary in a direction orthogonal to the transport direction. However, if the recording head array 30 is configured to move as necessary, an image with higher resolution can be obtained by multi-pass image recording. Or failure of the ink jet recording head 33 is not reflected in the recording result.

  Four maintenance units 34 corresponding to the respective head units 32 are arranged in the vicinity of the recording head array 30 (in this embodiment, both sides in the transport direction). When performing maintenance on the head unit 32, as shown in FIG. 2, the recording head array 30 moves upward, and the maintenance unit 34 moves into the gap formed between the conveyance belt 28 and enters. . Then, a predetermined maintenance operation (vacuum, dummy jet, wiping, capping, etc.) is performed in a state of facing the nozzle surface 33N (see FIGS. 3 and 7) which is a discharge surface.

  As shown in FIG. 8, the maintenance unit 34 includes a cap 88 that receives ink from the nozzle surface 33 </ b> N and a drain line 92 that discharges ink received by the cap 88 during the recovery operation of the inkjet recording apparatus 12. Yes. A waste ink tank 96 is provided through a valve 94 at the downstream end of the ink flow in the drainage line 92. Further, the ink jet recording apparatus 12 includes a second pump 98 (a pump for recovery operation of the ink jet recording head 33) 98 that gives ink delivery force (ink suction force) from the cap 88 to the drainage line 92, and a second pump 98. A motor to be driven (not shown). This motor is controlled by the controller 56 in the same manner as the motor that drives the pump 74.

  In the present embodiment, the four maintenance units 34 are divided into two sets of two, and the recording head array 30 is arranged on the upstream side in the transport direction and the downstream side in the transport direction of the recording head array 30 during image recording. I am doing so.

  As shown in detail in FIG. 3, a charging roll 36 to which a power source 38 is connected is disposed on the upstream side in the transport direction of the recording head array 30. The charging roll 36 is driven while sandwiching the conveyance belt 28 and the paper P with the driven roll 26, and moves between a pressing position for pressing the paper P against the conveyance belt 28 and a separation position separated from the conveyance belt 28. It is possible. At the pressing position, a predetermined potential difference is generated between the grounded driven roll 26 and the sheet P can be charged and electrostatically attracted to the transport belt 28.

  As the charging roll 36, for example, a roll having a diameter of 14 mm in which conductive carbon is coated on the surface of silicone rubber and the volume resistance value is adjusted to about 10 6 to 10 7 Ω · cm can be used.

  As the power source 38, a DC power source is shown in FIG. 3, but an AC power source may be used as long as the paper P can be charged to a predetermined potential.

  A registration roll (not shown) is provided further on the upstream side in the transport direction than the charging roll 36, and the paper P is aligned before reaching between the transport belt 28 and the charging roll 36.

  A peeling plate 40 (see FIGS. 1 and 2) is disposed on the downstream side in the transport direction of the recording head array 30, and the paper P can be peeled from the transport belt 28. As the peeling plate 40, for example, an aluminum plate having a thickness of 0.5 mm, a width of 330 mm, and a length of 100 mm can be used.

  The peeled paper P is transported by a plurality of rotatable discharge roller pairs 42 constituting a discharge path 44 on the downstream side in the transport direction of the peeling plate 40, and is discharged to a paper discharge tray 46 provided at the upper part of the housing 14. Discharged.

  Below the peeling plate 40, a cleaning roll 48 is disposed so that the conveyance belt 28 can be sandwiched between the drive roll 24 and the surface of the conveyance belt 28 is cleaned.

  A reversing path 52 including a plurality of reversing roller pairs 50 is provided as a reversing unit between the paper feed tray 16 and the conveying belt 28, and the sheet P on which an image is recorded on one side is reversed and conveyed. By holding the belt 28, image recording on both sides of the paper P can be easily performed.

  Between the transport belt 28 and the paper discharge tray 46, there are provided an ink tank 54 for storing each of the four color inks, and a reservoir tank 64 connected to the downstream side of the ink tank 54. The reservoir tank 64 is provided with an air release portion 65, and the liquid level in the reservoir tank 64 is at atmospheric pressure. The ink in the reservoir tank 64 is supplied to each head unit 32 via a first ink line 69 and a second ink line 70 which will be described later. As the ink, various known inks such as water-based ink, oil-based ink, and solvent-based ink can be used.

  As shown in FIG. 4, the entire inkjet recording apparatus 12 is controlled by a controller 56, and operations including image recording, discharging, and maintenance are performed from taking out the paper P. Various data relating to the recorded image is sent from the image controller 58 to the controller 56. For example, as will be described later, the applied voltage and the like in the first charging mode and the second charging mode are controlled by the controller 56 in accordance with the data of the recorded image. The inkjet recording head 33 is controlled by a head controller 60, and a signal is transmitted from the controller 56 to the head controller 60. The controller 56, the head controller 60, and the charging roll 36 are supplied with power from a power source 38.

  In the ink jet recording apparatus 12 of the present embodiment configured as described above, the paper P taken out from the paper feed tray 16 is transported to the transport belt 28 as described above. Then, it is pressed against the conveyor belt 28 by the charging roll 36 and is held by being attracted (contacted) to the conveyor belt 28 by the voltage applied from the charging roll 36. In this state, while the paper P passes through the ejection area SE by circulation of the transport belt, ink droplets are ejected from the recording head array 30 and an image is recorded on the paper P. When an image is recorded in only one pass, the paper P is peeled off from the transport belt 28 by the peeling plate 40, transported by the discharge roller pair 42, and discharged to the paper discharge tray 46. On the other hand, when performing image recording by multi-pass, after the paper P is circulated and passed through the ejection area SE until the required number of times is reached, the paper P is peeled off from the transport belt 28 by the paper P with the peeling plate 40, The paper is conveyed by the discharge roller pair 42 and discharged to the paper discharge tray 46.

(Ink flow line)
Hereinafter, one color (for example, yellow) will be described with respect to ink flow, and the other colors have the same configuration and function, and thus description thereof will be omitted.

  The ink jet recording head 33 is formed with a plurality of ink chambers 72 and discharge nozzles 78 (see FIG. 7) communicating with the respective ink chambers 72, and discharges ink droplets by increasing the pressure in the ink chamber 72. It discharges from the nozzle 78. That is, as shown in FIG. 7, the lower surface side of the inkjet recording head 33 is a discharge surface, and 1024 discharge nozzles 78 are arranged.

  As shown in FIGS. 5 and 6, the ink jet recording apparatus 12 is provided with a first ink line 69 and a second ink line 70 that connect the ink chamber 72 and the reservoir tank 64. A pump 74 and an on-off valve 76 are connected in parallel to the second ink line 70 so that the ink flow direction can be switched. The pump 74 is provided so as to apply a fluid force from the ink chamber 72 to the reservoir tank 64 to the ink liquid. The ink jet recording apparatus 12 is provided with a motor (not shown) for driving the pump 74, and this motor is controlled by the controller 56. The controller 56 also controls the opening / closing of the on / off valve 76.

  The first ink line 69 includes a first main ink line 79 and a first branch line 81 branched from the first main ink line 79 and connected to each ink chamber 72. Similarly, the second ink line 70 includes a second main ink line 80 and a second branch line 82 branched from the second main ink line 80 and connected to each ink chamber 72.

  At the time of ink discharge, the pump 74 is stopped and the on-off valve 76 is opened. As the ink chamber 72 is depressurized by the ejection of ink droplets, the ink liquid flows from the reservoir tank 64 to the ink chamber 72 in both the first ink line 69 and the second ink line 70. Accordingly, since the ink liquid flows into the ink chamber 72 from the two ink lines, the pressure loss is greatly reduced as compared with the case of one ink line, and the allowable pressure loss value for each ink line is set to about twice. Is possible. Thereby, a supply channel cross-sectional area can be made small. Accordingly, it is possible to reduce the volume of the piping, and further reduce the size and cost of the apparatus. In addition, during the ink circulation described below, the flow rate becomes faster and the pump 74 does not require excessive performance, so that the pump 74 can be downsized.

  At the time of ink circulation, the pump 74 is driven and the on-off valve 76 is closed. As a result, in the first ink line 69, the ink liquid flows from the reservoir tank 64 to the ink chamber 72, and in the second ink line 70, the ink liquid flows from the ink chamber 72 to the reservoir tank 64, and the ink liquid circulates. Accordingly, it is possible to circulate ink using the second ink line 70 in which the ink liquid is allowed to flow into the ink chamber 72 when ink is ejected. By this ink circulation, bubbles in the ink liquid can be discharged in the reservoir tank 64 and further discharged from the atmosphere opening portion 65 to the atmosphere.

  Further, the first ink line 69 functions as a circulation path main flow forward path, and the second ink line 70 functions as a circulation path main flow return path. In the present embodiment, the first main ink line 79 is located below the second main ink line 80. Accordingly, the bubble discharge performance is further improved by the buoyancy effect of the bubbles. In addition, it is easy to prevent backflow of bubbles.

  The pump 74 is driven in a direction in which a negative pressure is generated in the flow paths such as the first line and the second line to discharge bubbles. Therefore, compared to the case where the ink liquid is pumped and circulated through the flow paths such as the first line and the second line, ink leakage due to application of pressure does not occur from the connection part or the joint part of the flow path.

  In addition, the ink flow direction of the second ink line 70 can be switched with a simple configuration of the pump 74 and the on-off valve 76.

[Second Embodiment]
Next, a second embodiment will be described. In the present embodiment, the structure of the line head is different from that of the first embodiment.

  As shown in FIGS. 9 and 10, the ink jet recording head 103 provided in the ink jet recording apparatus according to the present embodiment is a single line head, and a common ink chamber 102 that communicates in common with each discharge nozzle. Is provided.

  A first ink line 105 is provided instead of the first ink line 69, and a second ink line 106 is provided instead of the second ink line 70. In the present embodiment, since the ink chambers are provided as one common ink chamber 102 instead of a plurality, the first ink line 105 and the second ink line 106 do not need to be formed with branch lines.

  Thereby, the same effect as the first embodiment can be obtained. That is, at the time of ink ejection shown in FIG. 9, the pump 74 is stopped and the on-off valve 76 is opened. As the ink chamber 102 is depressurized by the ejection of ink droplets, the ink liquid flows from the reservoir tank 64 to the ink chamber 102 in both the first ink line 105 and the second ink line 106. Accordingly, since the ink liquid flows into the ink chamber 102 from the two ink lines, the pressure loss is greatly reduced as compared with the case of one ink line, and the allowable pressure loss value for each ink line is set to about twice. Is possible. Thereby, a supply channel cross-sectional area can be made small. Accordingly, it is possible to reduce the volume of the piping, and further reduce the size and cost of the apparatus. In addition, during the ink circulation described below, the flow rate becomes faster and the pump 74 does not require excessive performance, so that the pump 74 can be downsized.

  During the ink circulation shown in FIG. 10, the pump 74 is driven and the on-off valve 76 is closed. As a result, in the first ink line 105, the ink liquid flows from the reservoir tank 64 to the ink chamber 102, and in the second ink line 106, the ink liquid flows from the ink chamber 102 to the reservoir tank 64, and the ink liquid circulates. Accordingly, it is possible to circulate ink using the second ink line 106 in which the ink liquid is allowed to flow into the ink chamber 102 when ink is ejected. By this ink circulation, bubbles in the ink liquid can be discharged in the reservoir tank 64 and further discharged from the atmosphere opening portion 65 to the atmosphere.

[Third Embodiment]
Next, a third embodiment will be described. As shown in FIG. 12, in the present embodiment, compared with the first embodiment, the first main ink line 79 and the second main ink line 79 and the second main ink line 79 have an upward gradient from the upstream side to the downstream side of the ink flow during ink circulation. The main ink lines 80 are arranged to be inclined.

  According to this embodiment, when ink is circulated, the bubbles can be reliably discharged with a smaller flow rate by utilizing the buoyancy of the bubbles. Therefore, it is possible to save the power and reduce the size of the pump 74 and to reduce the power consumption and size of the device. Moreover, the backflow of bubbles can also be prevented.

  As shown in FIG. 11, the same effects as those of the first embodiment can be obtained during ink ejection.

[Fourth Embodiment]
Next, a fourth embodiment will be described. As shown in FIGS. 13 and 14, in this embodiment, compared to the first embodiment, the downstream end 79 </ b> T of the first main ink line 79 is directly connected to the second main ink line 80 to communicate the flow path. A connection channel 110 is provided. The flow path resistance of the connection flow path 110 is larger than the total flow path resistance of the connected first branch line 81 and second branch line 82 for any ink chamber 72.

  As a result, the flow velocity in the connection flow path during ink circulation is increased, and bubbles can be discharged more easily than in the first embodiment. Accordingly, the required flow rate can be reduced, and the pumping force required to flow the ink liquid during ink circulation can be further reduced.

  Similarly to the first embodiment, during ink circulation, the first ink line 69 functions as a circulation main flow forward path, and the second ink line 70 functions as a circulation main flow return path. In the present embodiment, the first main ink line 79 is located below the second main ink line 80. Accordingly, the bubble discharge performance is further improved by the buoyancy effect of the bubbles. In addition, it is easy to prevent backflow of bubbles.

  At the time of ejection, the total flow path resistance of the connected first branch line 81 and second branch line 82 is smaller than the flow path resistance of the connection flow path 110 for any ink chamber 72. Therefore, even if the connection flow path 110 is provided, the ink liquid flows through the first branch line 81 and the second branch line 82 without any problem as in the first embodiment.

  The embodiments of the present invention have been described above with reference to the embodiments. However, these embodiments are merely examples, and various modifications can be made without departing from the scope of the invention. Needless to say, the scope of rights of the present invention is not limited to the above embodiment.

It is a front sectional view showing the configuration of the ink jet recording apparatus of the first embodiment in an image recording state. It is a front sectional view showing the composition of the ink jet recording device of a 1st embodiment in a maintenance state. It is a conceptual diagram which shows the structure of the conveyance belt of the inkjet recording device of 1st Embodiment, and its vicinity. FIG. 2 is a block diagram illustrating a configuration of a control system of the ink jet recording apparatus according to the first embodiment. FIG. 3 is a schematic diagram illustrating an ink flow during ink ejection in the ink jet recording apparatus according to the first embodiment. FIG. 3 is a schematic diagram illustrating an ink flow during ink circulation in the ink jet recording apparatus according to the first embodiment. It is a rear view which shows the structure of the inkjet recording head in 1st Embodiment. It is a schematic diagram which shows the structure of a maintenance unit in 1st Embodiment. It is a schematic diagram which shows the ink flow at the time of ink discharge with the inkjet recording device of 2nd Embodiment. It is a schematic diagram showing an ink flow during ink circulation in the ink jet recording apparatus according to the second embodiment. It is a schematic diagram which shows the ink flow at the time of ink discharge in the inkjet recording device of 3rd Embodiment. It is a schematic diagram which shows the ink flow at the time of ink circulation in the inkjet recording device of 3rd Embodiment. It is a schematic diagram which shows the ink flow at the time of ink discharge in the inkjet recording device of 4th Embodiment. FIGS. 14A and 14B are schematic diagrams showing the ink flow during ink circulation in the inkjet recording apparatus of the fourth embodiment, respectively, and the ink flow in the direction of arrows 14B-14B in FIG. 14A. It is sectional drawing which shows a path | route.

Explanation of symbols

12 Inkjet recording device (droplet ejection device)
33 Inkjet recording head (droplet ejection head)
64 Reservoir tank (tank)
69 First ink line (first line)
70 Second ink line (second line)
72 Ink chamber (liquid chamber)
74 Pump 76 On-off valve 78 Discharge nozzle 79 First main ink line (first line)
79T Downstream end 80 Second main ink line (second line)
81 First branch line 82 Second branch line 102 Common ink chamber (liquid chamber)
103 Inkjet recording head (droplet ejection head)
105 First ink line (first line)
106 Second ink line (second line)
110 Connection channel

Claims (4)

A liquid discharge head for forming a liquid chamber and a discharge nozzle communicating with the liquid chamber and discharging liquid droplets from the discharge nozzle;
A tank for storing liquid;
A first line connecting the liquid chamber and the tank, and capable of flowing liquid from the tank to the liquid chamber;
A second line connecting the liquid chamber and the tank;
Switching means for switching the liquid flow direction of the second line;
With
The switching means includes a pump for flowing the liquid from the liquid chamber toward the tank, and an on-off valve connected in parallel to the pump,
The droplet discharge head is provided with a plurality of the liquid chambers,
The first line includes a first main line and a plurality of first branch lines that branch from the first main line and communicate with the liquid chambers, respectively.
The second line includes a second main line and a plurality of second branch lines branched from the second main line and communicating with the liquid chambers, respectively.
At the time of discharging a droplet, by stopping the pump and opening the on-off valve, the liquid flow direction of the second line is changed to the direction of flowing from the tank to the liquid chamber,
When the liquid is circulated, the liquid droplet is characterized in that the liquid flow direction of the second line is changed from the liquid chamber to the tank by driving the pump and closing the on-off valve. Discharge device.   The first main line and the second main line are both arranged so as to have an upward gradient from the upstream side to the downstream side of the liquid flow during the circulation of the liquid. Item 2. A droplet discharge device according to Item 1. At the downstream end of the first main line, a connection flow path is provided that connects the flow path directly connected to the second main line,
The flow path resistance of the connection flow path is larger than the total flow path resistance of the first branch line and the second branch line connected to one liquid chamber. Or the droplet discharge device of 2.   The liquid droplet ejection apparatus according to claim 1, wherein image formation is performed using an ink liquid as a liquid.