JP2017018845A - Ink discharge device and ink discharge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink discharge device that can suppress a variation in temperatures of ink even when flow rates of the ink to be supplied to an inkjet head vary.SOLUTION: Ink circulates in a first path. A second path branches off from a branching position of the first path, and then returns to a merging position of the first path. A first pump inserted into the first path transfers ink. A heater heats the ink circulating in the first path. An inkjet head inserted into the second path changes the ink circulating in the second path into a liquid-droplet shape and discharges the ink. A second pump inserted into the second path transfers the ink.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ink ejection apparatus and an ink ejection method for ejecting heated ink from an inkjet head.

  Japanese Patent Application Laid-Open Publication No. 2004-228561 discloses an ink discharge apparatus that discharges ink (liquid thin film material) from an ink jet head (nozzle head). In this ink ejection device, ink is supplied from the tank for storing ink to the inkjet head, and excess ink is collected from the inkjet head to the tank. In order to reduce the viscosity of the ink, the ink is heated in the tank and in the ink transport path.

International Publication No. 2013/015093

  When the ejection amount from the ink jet head fluctuates, the flow rate of ink circulating in the transport path also fluctuates. As the flow rate of the ink passing through the heater fluctuates, the ink temperature also fluctuates. When the temperature of the ink supplied to the inkjet head fluctuates, the ejection of ink from the inkjet head becomes unstable.

  An object of the present invention is to provide an ink ejection apparatus and an ink ejection method capable of suppressing fluctuations in ink temperature even when the flow rate of ink supplied to an inkjet head varies.

According to one aspect of the invention,
A first path through which ink circulates;
A second path that branches off from the branch point of the first path and then returns to the meeting point of the first path;
A first pump inserted into the first path to transfer the ink;
A heater for heating the ink circulating in the first path;
An ink-jet head that is inserted into the second path and discharges the ink flowing through the second path as droplets;
There is provided an ink ejection device having a second pump inserted into the second path and transporting the ink.

According to another aspect of the invention,
A first path through which ink circulates;
A second path that branches off from the branch point of the first path and then returns to the meeting point of the first path;
A heater for heating the ink circulating in the first path;
A method of ejecting the ink using an ink ejection device that is inserted into the second path and has an inkjet head that ejects the ink in droplets,
The ink is heated by the heater while circulating the ink through the first path, and a part of the ink in the first path is caused to flow through the second path to the inkjet head. Supply ink,
An ink ejection method is provided in which the ink supplied to the inkjet head is made into droplets and ejected from the inkjet head.

  When the flow rate of ink flowing through the second path changes, the flow rate of ink flowing through the first path also changes. At this time, the ratio of the change amount with respect to the total flow rate of the ink flowing through the first path is smaller than the ratio of the change amount with respect to the total flow rate of the ink flowing through the second path. Since the heater warms the ink flowing through the first path, the temperature variation of the ink can be suppressed.

FIG. 1 is a schematic diagram of an ink ejection apparatus according to an embodiment. FIG. 2 is a schematic diagram of an ink ejection apparatus according to another embodiment. FIG. 3 is a schematic diagram more specifically showing a part of the first path of the ink ejection apparatus according to the embodiment shown in FIG. FIG. 4 is a schematic diagram of an ink ejection apparatus according to still another embodiment. FIG. 5 is a flowchart of an ink ejection method using the ink ejection apparatus shown in FIG.

With reference to FIG. 1, an ink ejection apparatus according to an embodiment will be described.
FIG. 1 is a schematic diagram of an ink discharge apparatus according to an embodiment. The ink ejection apparatus according to the embodiment includes a first path 10 through which ink circulates. At the branch point 31 of the first route 10, the second route 20 branches from the first route 10. The second path 20 merges with the first path 10 at the merge point 32.

  A heater 11 and a first pump 12 are inserted into the first path 10. For example, an electric heater can be used as the heater 11. As the first pump 12, for example, a diaphragm pump can be used. The heater 11 and the first pump 12 are preferably inserted in a path from the junction point 32 to the branch point 31. The first pump 12 transfers the ink in the first path 10. When the ink is transferred by the first pump 12, the ink circulates through the first path 10. The heater 11 heats the ink circulating in the first path 10.

  The first temperature sensor 13 measures the temperature of the ink circulating in the first path 10. The measurement result is input to the control device 50.

  An ink jet head 21 and a second pump 22 are inserted into the second path 20. As the second pump 22, for example, a diaphragm pump can be used similarly to the first pump 12. The second pump 22 transfers the ink in the second path 20. When the second pump 22 is operated, a part of the ink circulating in the first path 10 flows into the second path 20 at the branch point 31. The ink that has flowed into the second path 20 flows through the second path 20 and then merges with the ink flowing through the first path 10 at the merge point 32.

  The ink jet head 21 discharges ink flowing from the second path 20 in droplets. The ink that was desired to be discharged flows out of the inkjet head 21 and returns to the first path 10 via the second path 20. The stage 40 holds the substrate 41 at a position facing the inkjet head 21. When ink droplets ejected from the inkjet head 21 land on the substrate 41, the ink is applied to the substrate 41.

  Next, the excellent effect of the above embodiment will be described. The flow rate of ink flowing through the first path 10 from the branch point 31 to the merge point 32 is denoted by Q1, and the flow rate of ink flowing through the second path 20 is denoted by Q2. The flow rate of the ink flowing through the first path 10 from the junction point 32 to the branch point 31 is equal to Q1 + Q2. When ink is ejected from the inkjet head 21, the ink flow rate is different between the second path 20 on the upstream side of the inkjet head 21 and the second path 20 on the downstream side. Here, a state where ink is not ejected from the inkjet head 21 will be described.

  The flow rate of the ink flowing through the heater 11 is Q1 + Q2. When the flow rate Q2 of the ink flowing through the inkjet head 21 changes and becomes Q2 + ΔQ2, the flow rate of the ink flowing through the heater 11 also changes by ΔQ2. The ratio (change rate) of the change amount with respect to the total flow rate flowing through the heater 11 is represented by ΔQ2 / (Q1 + Q2).

  As a comparative example, consider a configuration in which an inkjet head is inserted into one circulation path. An inkjet head and a heater are inserted into one circulation path. If the flow rate of ink flowing through the inkjet head is represented by Q2, the flow rate of ink flowing through the heater is also equal to Q2. When the flow rate of ink flowing through the inkjet head varies by ΔQ2, the flow rate of ink flowing through the heater also varies by ΔQ2. At this time, the ratio (change rate) of the change amount with respect to the total flow rate of the ink flowing through the heater 11 is represented by ΔQ2 / Q2.

  The change rate ΔQ2 / (Q1 + Q2) in the example is smaller than the change rate ΔQ2 / Q2 in the comparative example. As described above, when the configuration of the embodiment is employed, the rate of change in the flow rate of the ink flowing through the heater is smaller than that of the configuration of the comparative example. For this reason, the fluctuation range of the temperature of the ink when the flow rate of the ink flowing through the inkjet head 21 is changed can be reduced. Since the temperature fluctuation range is small, the stability of ink ejection can be increased.

  In order to reduce the rate of change in the flow rate of the ink flowing through the heater 11, it is preferable that the flow rate Q1 is larger than the flow rate Q2. This flow rate can be realized by controlling the operations of the first pump 12 and the second pump 22.

  Next, as another comparative example, a configuration in which a large-capacity ink tank is inserted into one circulation path and a heater is disposed in the ink tank will be considered. Also in this comparative example, by controlling the temperature of the ink in the large-capacity ink tank to be constant, the temperature change range when the ink flow rate is changed can be reduced. However, as the ink temperature increases, the deterioration of the ink progresses faster. As the ink deteriorates, the ink must be replaced. If a large amount of ink is stored in a heated state, a large amount of ink must be discarded when the ink is replaced.

  In the above embodiment, since it is not necessary to store a large volume of ink in a heated state, the amount of ink to be discarded can be reduced when replacing the ink.

  Next, the procedure from the start of the ink temperature rise to the ink discharge operation at the start of operation of the ink discharge apparatus according to the embodiment will be described.

  First, the first pump 12 and the heater 11 are operated to heat the ink while circulating the ink in the first path 10. At this time, the second pump 22 is stopped. For this reason, ink does not flow into the second path 20. When the temperature of the ink flowing through the first path 10 reaches the first target temperature, the ink is caused to flow into the second path 20 by operating the second pump 22. Thereafter, the inkjet head 21 is operated to discharge ink.

  In the above procedure, the low-temperature ink before heating does not flow into the second path 20. Since the low temperature ink has a high viscosity, when the low temperature ink flows into the second path 20, the pressure loss increases and the flow rate of the ink decreases. For this reason, the amount of heat released from the ink during the period flowing through the second path 20 increases. As a result, it takes a long time for the temperature of the ink in the inkjet head 21 to reach the target temperature. In the embodiment, since the heated ink flows into the second path 20, the ink flow rate can be increased from the beginning. For this reason, the time until the ink in the inkjet head 21 reaches the target temperature can be shortened.

  Next, an ink ejection apparatus according to another embodiment will be described with reference to FIGS. Hereinafter, differences from the embodiment shown in FIG. 1 will be described, and descriptions of common configurations will be omitted.

  FIG. 2 shows a schematic diagram of an ink ejection apparatus according to the present embodiment. The second temperature sensor 24 measures the temperature of the ink in the inkjet head 21. The measurement result of the second temperature sensor 24 is input to the control device 50.

  The pressure sensor 26 measures the pressure of the ink in the second path 20 connected to the entrance side of the inkjet head 21. The pressure sensor 27 measures the pressure of the ink in the second path 20 connected to the outlet side of the inkjet head 21. Measurement results of the pressure sensors 26 and 27 are input to the control device 50. The control device 50 can calculate the pressure of the ink in the inkjet head 21 based on the measurement results of the pressure sensors 26 and 27.

  A supply tank 15 stores ink to be supplied to the first path 10. A supply valve 14 is inserted in the first path 10. Ink is supplied from the supply tank 15 to the first path 10 via the supply valve 14. The supply valve 14 can switch between a supply state in which ink is supplied from the supply tank 15 to the first path 10 and a non-supply state in which ink is not supplied. The control device 50 controls the heater 11, the first pump 12, and the supply valve 14.

  FIG. 3 is a schematic diagram more specifically showing a part of the first path 10 of the ink ejection apparatus according to the present embodiment. A supply tank 60 is inserted in the first path 10. A first chamber 61, a second chamber 62, and a third chamber 63 are provided in the supply tank 60. After the ink flowing through the first path 10 flows into the supply tank 60, it flows into the first chamber 61 from the lower end of the first chamber 61. The heater 11 is disposed in the first chamber 61. When the ink flows in the first chamber 61 from the bottom to the top, the ink is warmed by the heater 11.

  When the liquid level of the ink flowing into the first chamber 61 rises and exceeds a certain height, the ink overflows from the first chamber 61 and flows into the second chamber 62. The upstream end of the second path 20 is connected to the lower end of the second chamber 62. A connection point between the second chamber 62 and the second path 20 corresponds to the branch point 31 (FIG. 2). Ink in the second chamber 62 flows through the second path 20 and is supplied to the inkjet head 21. A second path 20 from the upstream end to the inkjet head 21 is covered with a heat insulating cover 23. A plurality of nozzle holes 25 are provided on the surface facing the lower side of the inkjet head 21. From each nozzle hole 25, the ink droplets are ejected.

  When the liquid level of the ink in the second chamber 62 exceeds a certain height, the ink overflows from the second chamber 62 and flows into the third chamber 63. The ink flowing out from the lower end of the third chamber 63 returns to the supply tank 60 through the first path 10. The first chamber 61, the second chamber 62, and the third chamber 63 constitute a part of the first path 10.

  The downstream end of the second path 20 is connected to the side surface of the third chamber 63. The ink that has flowed through the second path 20 flows into the third chamber 63. The connection location between the second path 20 and the third chamber 63 corresponds to the junction location 32 (FIG. 2).

  A buffer tank 34 is inserted in the second path 20 between the inkjet head 21 and the second pump 22. The buffer tank 34 suppresses the pulsation of the ink flow rate generated by the second pump 22 from being transmitted to the inkjet head 21.

  An air valve 65 is attached to the upper surface of the supply tank 60. With the air valve 65 opened, atmospheric pressure is applied to the ink level in the first chamber 61, the second chamber 62, and the third chamber 63. In this embodiment, the air valve 65 is opened during the operation of the ink ejection device.

  The first pump 12 and the first pump 12 are arranged so that the flow rate of ink flowing into the supply tank 60 through the first path 10 is larger than the flow rate of ink supplied from the second chamber 62 to the inkjet head 21. Two pumps 22 are controlled. For this reason, the ink always overflows from the second chamber 62 to the third chamber 63. Thereby, the height of the ink level in the second chamber 62 is kept constant. The level of the liquid level in the third chamber 63 varies vertically depending on the amount of ink in a range lower than the level of the liquid level in the second chamber 62.

  A level sensor 66 is installed in the supply tank 60. The level sensor 66 measures the height of the ink level in the third chamber 63. As the level sensor 66, for example, an ultrasonic level sensor, a float type level sensor, or the like can be used. The measurement result of the level sensor 66 is input to the control device 50 (FIG. 2).

  A first temperature sensor 13 is further installed in the supply tank 60. For example, the first temperature sensor 13 measures the temperature of the ink in the second chamber 62.

  A water head pressure depending on the height difference from the nozzle hole 25 to the liquid level of the second chamber 62 is applied to the position of the nozzle hole 25 of the inkjet head 21. By adjusting this height difference, the hydraulic head pressure applied to the position of the nozzle hole 25 can be adjusted. When the total amount of ink flowing through the first path 10 and the second path 20 changes, the level of the ink level in the third chamber 63 changes, but the level of the ink level in the second chamber 62 changes. The height is kept constant. For this reason, even if the total amount of ink flowing through the first path 10 and the second path 20 increases or decreases, the water head pressure at the position of the nozzle hole 25 of the inkjet head 21 can be maintained constant.

  Next, still another embodiment will be described with reference to FIGS. Hereinafter, differences from the embodiment shown in FIGS. 2 to 3 will be described, and description of common configurations will be omitted.

  FIG. 4 shows a schematic diagram of an ink ejection apparatus according to this embodiment. In the embodiment shown in FIGS. 2 and 3, the second pump 22 is inserted into the second path 20 on the downstream side of the inkjet head 21. In the embodiment shown in FIG. 4, in addition to the second pump 22, a third pump 28 is also inserted into the second path 20 upstream of the inkjet head 21. A buffer tank 29 is inserted in the second path 20 between the third pump 28 and the inkjet head 21.

  By controlling the outputs of the second pump 22 and the third pump 28, the meniscus pressure at the position of the nozzle hole 25 of the inkjet head 21 can be adjusted.

  FIG. 5 shows a flowchart of an ink discharge method using the ink discharge apparatus of FIG. In step S <b> 1, the control device 50 operates the first pump 12 to circulate ink in the first path 10. In step S2, the control device 50 determines whether or not ink replenishment is necessary. Whether or not ink replenishment is necessary can be determined based on the level of the ink level in the third chamber 63 measured by the level sensor 66 attached to the supply tank 60. If the liquid level is less than a preset reference value, it is determined that ink replenishment is necessary. If the liquid level is equal to or higher than the reference value, it is determined that ink replenishment is unnecessary.

  If it is determined that ink replenishment is necessary, ink is replenished to the first path 10 in step S3. Specifically, the control device 50 switches the supply valve 14 to the supply state. As a result, ink is supplied from the supply tank 15 to the first path 10. When the ink level in the third chamber 63 exceeds the reference value, ink replenishment is stopped. Specifically, the control device 50 switches the supply valve 14 from the supply state to the non-supply state.

  If it is determined in step S2 that ink replenishment is unnecessary, or if ink replenishment is completed in step S2, the temperature rise of the ink in the first path 10 is started in step S4. Specifically, the control device 50 operates the heater 11.

  In step S5, it is determined whether or not the temperature of the ink in the first path 10 has reached the first target temperature. This determination can be made by the control device 50 based on the measurement result of the first temperature sensor 13. When the temperature of the ink does not reach the first target temperature, the ink is continuously circulated through the first path 10 until the first target temperature is reached.

  When the temperature of the ink circulating in the first path 10 reaches the first target temperature, ink starts to flow through the second path 20 in step S6. Specifically, the control device 50 operates the second pump 22 and the third pump 28. Thereby, the supply of ink to the inkjet head 21 is started. At this time, the second pump 22 and the third pump 28 are controlled to operate at a preset output.

  At the start of ink supply to the second path 20, the temperatures of the pipes constituting the second path 20, the inkjet head 21, and the like are lower than the first target temperature. For this reason, the temperature of the ink flowing into the second path 20 decreases as the ink flows through the second path 20. At this time, the pipe line of the second path 20, the inkjet head 21, and the like are warmed by ink.

  In step S7, it is determined whether the temperature of the ink in the inkjet head 21 has reached the second target temperature. This determination is performed by the control device 50 based on the measurement result of the second temperature sensor 24. The second target temperature is set substantially the same as the first target temperature. When the temperature of the ink in the inkjet head 21 has not reached the second target temperature, the ink is continuously circulated through the second path 20 until the temperature of the ink reaches the second target temperature.

  When the temperature of the ink in the inkjet head 21 reaches the second target temperature, control for increasing the pressure of the ink in the inkjet head 21 is started in step S8. For example, the control device 50 can increase the pressure of the ink in the inkjet head 21 by decreasing the output of the second pump 22 (FIGS. 2 and 3). At this time, the flow rate of the ink flowing through the second path 20 decreases. The second pump 22 is controlled to decrease to a preset output.

  In addition, the outputs of both the second pump 22 and the third pump 28 may be reduced. When the output decrease amount of the second pump 22 is made larger than the output decrease amount of the third pump 28, the ink pressure in the ink jet head 21 increases. Also in this case, the flow rate of the ink flowing through the second path 20 decreases.

  In step S9, it is determined whether or not the ink pressure in the inkjet head 21 has increased to the target pressure. This determination is performed by the control device 50 based on the measurement results of the pressure sensors 26 and 27 (FIG. 2). When the pressure of the ink in the inkjet head 21 has not increased to the target pressure, the outputs of the second pump 22 and the third pump 28 are controlled until the target pressure is reached. For example, the control device 50 increases / decreases the output by a preset step size.

  When the pressure of the ink in the inkjet head 21 reaches the target pressure, in step S10, the second pressure is measured based on the measurement results of the pressure sensors 26 and 27 so that the pressure of the ink in the inkjet head 21 is within the allowable range. Feedback control of the outputs of the pump 22 and the third pump 28 is performed. The inkjet head 21 is operated while performing feedback control of the outputs of the second pump 22 and the third pump 28. Thereby, ink droplets are ejected from the inkjet head 21.

  Next, the excellent effect of the embodiment shown in FIGS. 4 to 5 will be described. In this embodiment, the ink flowing into the second path 20 is heated to the first target temperature (step S5). Since the viscosity of the ink is lowered by heating, the flow rate of the ink flowing through the second path 20 can be increased from the beginning. For this reason, similarly to the embodiment shown in FIG. 1, it is possible to shorten the time until the temperature of the ink in the inkjet head 21 reaches the second target temperature.

  Furthermore, in the embodiment shown in FIGS. 4 to 5, the period from the time when ink starts to flow through the second path 20 (step S <b> 6) to the time when the pressure of ink in the inkjet head 21 is increased (step S <b> 8). The ink pressure in the inkjet head 21 becomes lower than the final target pressure. For this reason, it is possible to prevent the ink from leaking from the inkjet head 21 until the ejection of the ink from the inkjet head 21 is started.

  During the period from step S6 to step S8, as described above, the output of the second pump 22 or the outputs of both the second pump 22 and the third pump 28 is the output during the ink ejection operation (step S11). Set higher. For this reason, the flow rate of the ink flowing through the second path 20 is larger than the flow rate during the ink ejection operation. By increasing the flow rate of the ink flowing through the second path 20, it is possible to shorten the period until the temperature of the ink in the inkjet head 21 reaches the second target temperature.

  Furthermore, in the embodiment shown in FIGS. 4 to 5, after the pressure of the ink in the inkjet head 21 reaches the target pressure, feedback control is performed to keep the pressure in the inkjet head 21 within an allowable range. If this feedback control is started in a state where the difference between the ink pressure in the inkjet head 21 and the target pressure is large, the feedback control may become unstable. In the above embodiment, instability of feedback control can be avoided.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 10 1st path | route 11 Heater 12 1st pump 13 1st temperature sensor 14 Supply valve 15 Supply tank 20 2nd path | route 21 Inkjet head 22 2nd pump 23 Thermal insulation cover 24 2nd temperature sensor 25 Nozzle hole 26 27 Pressure sensor 28 Third pump 29 Buffer tank 31 Branching point 32 Junction point 34 Buffer tank 40 Stage 41 Substrate 50 Control device 60 Supply tank 61 First chamber 62 Second chamber 63 Third chamber 65 Air valve 66 Level sensor

The ink jet head 21 discharges ink flowing from the second path 20 in droplets. The ink that has not been ejected flows out of the inkjet head 21 and returns to the first path 10 via the second path 20. The stage 40 holds the substrate 41 at a position facing the inkjet head 21. When ink droplets ejected from the inkjet head 21 land on the substrate 41, the ink is applied to the substrate 41.

As a comparative example, consider a configuration in which an inkjet head is inserted into one circulation path. An inkjet head and a heater are inserted into one circulation path. If the flow rate of ink flowing through the inkjet head is represented by Q2, the flow rate of ink flowing through the heater is also equal to Q2. When the flow rate of the ink flowing through the ink jet head is varied by [Delta] Q2, varying only the flow rate also [Delta] Q2 of ink flowing through the heater. At this time, the ratio (change rate) of the change amount with respect to the total flow rate of the ink flowing through the heater 11 is represented by ΔQ2 / Q2.

Claims (9)

A first path through which ink circulates;
A second path that branches off from the branch point of the first path and then returns to the meeting point of the first path;
A first pump inserted into the first path to transfer the ink;
A heater for heating the ink circulating in the first path;
An ink-jet head that is inserted into the second path and discharges the ink flowing through the second path as droplets;
And an ink ejection device having a second pump that is inserted into the second path and transports the ink. further,
A replenishment tank for storing the ink replenished to the first path;
A replenishing valve that switches between a replenishing state in which the ink is replenished from the replenishing tank to the first path and a non-replenishing state in which the ink is not replenished;
A first temperature sensor that measures the temperature of the ink circulating in the first path;
A controller for controlling the refill valve, the heater, the first pump, and the second pump;
The controller is
The replenishing valve is set to the replenishing state, the first pump is operated, the ink is circulated through the first path, the heater is controlled to warm the ink,
Whether or not the temperature of the ink circulating in the first path has reached the first target temperature based on the measurement result of the first temperature sensor after the supply valve is switched to the non-supply state. Determine
2. The ink discharge according to claim 1, wherein when it is determined that the temperature of the ink has reached the first target temperature, the second pump is operated to start supplying the ink to the second path. apparatus.   The first pump and the second pump so that the flow rate of the ink flowing through the first path from the branch point to the merge point is larger than the flow rate of the ink flowing through the second path. The ink discharge device according to claim 1, further comprising a control device that controls the operation of the ink jet. The second pump is inserted into the second path on the downstream side of the inkjet head,
further,
A third pump inserted into the second path upstream of the inkjet head;
A second temperature sensor that measures the temperature of the ink flowing through the second path,
The controller is
Based on the measurement result of the second temperature sensor, it is determined whether or not the temperature of the ink flowing through the second path has reached a second target temperature,
If it is determined that the temperature of the ink flowing through the second path has reached the second target temperature, the second pump and the third pump are set so that the pressure of the ink in the inkjet head increases. The ink ejection device according to claim 3, wherein the ink ejection device controls the pump. And a pressure sensor for measuring the pressure of the ink in the inkjet head.
The controller is
After controlling the second pump so that the pressure of the ink in the ink jet head increases, the pressure of the ink in the ink jet head increases to a target pressure based on the measurement result of the pressure sensor. Whether or not
When it is determined that the pressure of the ink in the inkjet head has increased to the target pressure, the first pressure is adjusted so that the pressure of the ink in the inkjet head is within an allowable range based on the measurement result of the pressure sensor. The ink discharge apparatus according to claim 4, wherein feedback control of the second pump and the third pump is performed. A first path through which ink circulates;
A second path that branches off from the branch point of the first path and then returns to the meeting point of the first path;
A heater for heating the ink circulating in the first path;
A method of ejecting the ink using an ink ejection device that is inserted into the second path and has an inkjet head that ejects the ink in droplets,
The ink is heated by the heater while circulating the ink through the first path, and a part of the ink in the first path is caused to flow through the second path to the inkjet head. Supply ink,
An ink ejection method in which the ink supplied to the inkjet head is made into droplets and ejected from the inkjet head. Before supplying the ink to the inkjet head,
Heating the ink with the heater while circulating the ink in the first path without flowing the ink in the second path;
The part of the ink that circulates through the first path is caused to flow through the second path when the temperature of the ink that circulates through the first path reaches a first target temperature. Ink ejection method.   After the temperature of the ink flowing through the second path reaches a second target temperature after a part of the ink circulating in the first path starts flowing through the second path, The ink discharge method according to claim 7, wherein the pressure of the ink is increased.   After increasing the pressure of the ink in the inkjet head, while controlling the flow rate of the second path so that the pressure of the ink in the inkjet head falls within an allowable range, The ink ejection method according to claim 8, wherein the ink is ejected in droplets.

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