Inkjet printing apparatus

Abstract

To provide a technique capable of discharging ink that may have deteriorated due to overheating when ink circulation is stopped and reducing a discharge amount.SOLUTION: An ink partition region 79 is set in a partial region including a heater in a return pipe 65 that connects an internal recovery tank 52 and a supply tank 51 in a circulation path 41 of ink. The ink partition region 79 is a region in which, when ink circulation is stopped, the ink in the circulation path 41 is separated from the ink in other regions of the return pipe 65. Before restarting ink circulation in the circulation path 41, a control unit selectively executes a normal restart mode in which the ink partition region 79 and other regions of the return pipe 65 are immediately brought into communication to each other, or a post-discharge restart mode in which at least a part of the ink in the ink partition region 79 is discharged to an external recovery tank 53, and thereafter the ink partition region 79 and other regions of the return pipe 65 are brought into communication to each other on the basis of the temperature of the ink in the ink partition region 79.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an inkjet printing apparatus that performs printing by ejecting ink onto a print medium such as paper. [Background technology]

[0002] Conventionally, inkjet printing devices have sometimes been provided with an ink circulation path that supplies ink to an ejection head that ejects ink onto a print medium, and then recovers ink that is not ejected from the ejection head and supplies it again to the ejection head. An inkjet printing device provided with such an ink circulation path is described in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-006261 Summary of the Invention [Problem to be solved by the invention]

[0004] The image recording device (1) in Patent Document 1 has an ink circulation unit (3a). The ink circulation unit (3a) is composed of a first ink circulation path (14) and a second ink circulation path (15), which circulate two types of ink. An image recording unit (4) is connected to the first ink circulation path (14) and the second ink circulation path (15), and ink is supplied to each nozzle row (11) of the image recording unit (4) by circulating ink through each of them (paragraph 0027). A heat exchanger (23a) is also disposed across the first ink circulation path (14) and the second ink circulation path (15) (paragraph 0028, Figure 2).

[0005] Here, for example, when image recording is performed while circulating ink only through the first ink circulation path (14) filled with K ink, and ink is ejected from the nozzle array (11), drive heat is generated in the image recording unit (4), gradually increasing the temperature of the ink being pumped through the first ink circulation path (14). At this time, the heat exchanger (23) cools the ink inside by dissipating heat through the heat dissipation fins (65), but the cooling performance gradually deteriorates (see paragraphs 0041 and 0042). Therefore, the control unit (2) starts circulating ink through the second ink circulation path (15), which is not used for image recording (see paragraph 0043). Here, the ink in the second ink circulation path (15) is not used for image recording, so its temperature is low. By pumping the low-temperature ink to the heat exchanger (23), the heat can be absorbed and the temperature can be reduced (see paragraph 0044).

[0006] However, if the image recording device (1) or the ink circulation unit (3a) were to stop due to a power outage or other reason, the ink in the second ink circulation path (15) would also stop being sent to the heat exchanger (23). In this case, the ink in the first ink circulation path (14) would remain at a high temperature, potentially causing deterioration or degradation. If the deteriorated or degraded ink were used for image recording, the ink would not be ejected properly from the nozzle array (11) or the desired color gamut would not be achieved. For this reason, when the image recording device (1) or the ink circulation unit (3a) is restored after a stoppage, the deteriorated or degraded ink must be disposed of as waste liquid. However, if all of the ink in the first ink circulation path (14) were to be disposed of as waste liquid, significant losses would occur and workability would be reduced.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a technology that, when ink circulation stops, can discharge ink that may have been altered or deteriorated due to overheating to the outside when the ink is subsequently restored, and that can reduce the amount of ink discharged at that time. [Means for solving the problem]

[0008] To solve the above problems, the first invention of the present application is an inkjet printing device that prints by ejecting ink onto a print medium, and includes an ink circulation path, an external recovery tank, a circulation pump, a heater, a control unit, and an ink compartment area. The circulation path includes an ejection head that ejects ink, a supply tank that stores ink supplied to the ejection head, an internal recovery tank that stores ink recovered from the ejection head, and a return pipe that connects the internal recovery tank to the supply tank. The external recovery tank recovers ink that is discharged to the outside of the circulation path. The circulation pump is inserted in the return pipe and sends ink from the internal recovery tank to the supply tank via the return pipe. The heater is inserted in the return pipe between the circulation pump and the supply tank and heats the ink flowing from the internal recovery tank to the supply tank. The control unit is capable of controlling the ejection head, the circulation pump, and the heater, and is capable of detecting whether ink is circulating in the circulation path. The ink compartment area is set to a portion of the return pipe that includes the heater, and when the circulation of ink in the circulation path stops, the ink in the circulation path is separated from the ink in the other areas of the return pipe. Before resuming the circulation of ink in the circulation path, the control unit selectively executes a normal restart mode, based on the temperature of the ink in the ink compartment area, in which the ink compartment area is immediately connected to the other areas of the return pipe, or a post-drain restart mode, in which the ink compartment area is connected to the other areas of the return pipe after at least a portion of the ink in the ink compartment area is drained to the external recovery tank.

[0009] A second aspect of the present invention is the inkjet printing device of the first aspect, further comprising an on-off valve and a switching valve in the ink compartment area. The on-off valve is interposed in the return pipe between the circulation pump and the heater and allows or blocks the flow of ink from the internal recovery tank to the supply tank. The switching valve is interposed in the return pipe between the heater and the supply tank and is switchable between a state in which the heater is connected to the supply tank and a state in which the heater is disconnected from the supply tank and the internal space of the circulation path is connected to the external recovery tank. The controller is further capable of controlling the on-off valve and the switching valve. The controller controls the on-off valve to close and the switching valve to connect the ink compartment area to the external recovery tank, thereby separating the ink in the ink compartment area from the ink in the other return pipe areas.

[0010] A third invention of the present application is the inkjet printing device of the second invention, wherein in the post-discharge restart mode, the control unit controls the opening and closing valve, and the switching valve connects the ink compartment area to the external recovery tank, and the circulation pump is driven to discharge at least a portion of the ink in the ink compartment area into the external recovery tank.

[0011] The fourth invention of the present application is an inkjet printing device according to any one of the first to third inventions, wherein the control unit determines whether the temperature of the ink in the ink compartment area is below a predetermined threshold or above the predetermined threshold, and if it determines that the temperature is below the predetermined threshold, executes the normal resume mode, and if it determines that the temperature is above the predetermined threshold, executes the post-discharge resume mode.

[0012] A fifth invention of the present application is an inkjet printing device according to the fourth invention, wherein the control unit determines whether the temperature of the ink in the ink compartment area is below the predetermined threshold value or above the predetermined threshold value based on the duty value of the heater during a first predetermined period prior to the point at which it is detected that the circulation of ink in the circulation path has stopped.

[0013] A sixth aspect of the present invention is the inkjet printing apparatus of the fourth aspect, further comprising a temperature sensor interposed between the heater and the switching valve in the return pipe to detect the temperature of the ink in the return pipe, and the control unit determines whether the temperature of the ink in the ink compartment area is below the predetermined threshold or above the predetermined threshold based on the detection result of the temperature sensor.

[0014] The seventh invention of the present application is an inkjet printing device according to any one of the first to sixth inventions, wherein when the control unit executes the post-discharge restart mode, it stops driving the heater at least until the ink compartment area is connected to the area of ​​the other return pipe.

[0015] An eighth aspect of the present invention is the inkjet printing apparatus of the second aspect, wherein the heaters include a first heater and a second heater that are adjacent to each other along the circulation path and inserted into the return pipe. The second heater is located downstream of the circulation path from the first heater, and the duty value of the second heater is greater than the duty value of the first heater. Before restarting the circulation of ink in the circulation path, the control unit determines whether the temperature of the ink in the first heater is less than a predetermined first threshold or greater than or equal to the first threshold, and whether the temperature of the ink in the second heater is less than a predetermined second threshold or greater than or equal to the second threshold. When the control unit determines that the temperature of the ink in the first heater is lower than the first threshold and that the temperature of the ink in the second heater is equal to or higher than the second threshold, the control unit sets the discharge-restart mode by causing the switching valve to communicate the internal space of the circulation path with the external recovery tank and driving the circulation pump for a specific time to discharge the ink in the ink compartment area to the external recovery tank, and then causing the switching valve to communicate the ink compartment area with the other area of ​​the return pipe. The specific time is obtained by dividing a specific volume calculated based on the volume of ink that can pass through the second heater by the amount of ink delivered per unit time of the circulation pump. [Effects of the Invention]

[0016] According to the first to eighth aspects of the present invention, when the ink circulation stops, ink that may have been altered or deteriorated due to overheating can be discharged to the outside based on the ink temperature when the ink is subsequently restored. Furthermore, since a smaller amount of ink than the total amount of ink present in the circulation path can be discharged, the amount of ink to be discharged can be reduced.

[0017] In particular, according to the second aspect of the present invention, the ink in the ink compartment area is separated from the ink in the other areas of the return pipe using an on-off valve and a switching valve, so that the ink can be securely separated.

[0018] In particular, according to the third aspect of the present invention, in the post-discharge restart mode, the ink is discharged to the external recovery tank by driving the circulation pump, so that the ink can be reliably discharged.

[0019] In particular, according to the fifth aspect of the present invention, ink can be discharged based on the result of determining whether the ink temperature is below or above a threshold value, taking into consideration the amount of heat generated by the heater.

[0020] In particular, according to the sixth aspect of the present invention, the temperature of the ink in the ink compartment area is detected using a temperature sensor, so that the temperature of the ink can be detected more accurately.

[0021] In particular, according to the seventh aspect of the present invention, overheating of the ink can be further suppressed.

[0022] In particular, according to the eighth aspect of the present invention, ink that may have been altered or deteriorated due to overheating by the second heater can be discharged to the outside based on the ink temperature. Furthermore, the ink to be discharged can be limited to ink that may have been altered or deteriorated due to overheating by the second heater. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram conceptually illustrating the configuration of an inkjet printing device. [Figure 2] FIG. 2 is a diagram conceptually illustrating the configuration of an ink supply unit and an ejection head. [Figure 3] FIG. 2 is a block diagram showing connections between a control unit and each unit of the inkjet printing device. [Figure 4] 10 is a flowchart showing the flow of transporting continuous paper, printing on continuous paper, circulating ink, and discharging ink to the outside. [Figure 5] FIG. 10 is a diagram showing the relationship between the temperature of ink passing through a heater and the duty value of the heater corresponding to that temperature. [Figure 6] 10 is a flowchart showing a procedure for executing post-recovery processing. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the components described in these embodiments are merely examples and are not intended to limit the scope of the present invention. Furthermore, in the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary to facilitate understanding.

[0025] <1. Configuration of inkjet printing device> FIG. 1 is a conceptual diagram illustrating the configuration of an inkjet printing apparatus 1 according to one embodiment of the present invention. This inkjet printing apparatus 1 is an inkjet printer that conveys a long strip of continuous paper 10 while ejecting droplets of aqueous ink from multiple ejection heads 35 toward the continuous paper 10, thereby recording characters and images on the surface of the continuous paper 10. Note, however, that the long strip of continuous paper 10 is merely one example of a print medium. The print medium may be cut paper, plastic film, cardboard, metal foil, or a glass substrate, among others. In other words, the inkjet printing apparatus 1 may be any apparatus that ejects ink onto a print medium to perform printing. As shown in FIG. 1, the inkjet printing apparatus 1 includes a conveying unit 2, a printing unit 3, and a control unit 9.

[0026] The transport unit 2 is a mechanism that transports the continuous paper 10 in a transport direction along its longitudinal direction along a predetermined transport path. The continuous paper 10 is passed over multiple transport rollers 12. The continuous paper 10 is transported along a transport path formed by the multiple transport rollers 12. Each transport roller 12 rotates around an axis extending perpendicular to the transport direction, thereby guiding the continuous paper 10 downstream along the transport path. In addition, tension is applied to the continuous paper 10 in the transport direction. This prevents the continuous paper 10 from sagging or wrinkling during transport.

[0027] The printing unit 3 has a plurality of (four in this embodiment) ejection heads 35 and a plurality of (four in this embodiment) ink supply units 4. The four ejection heads 35 have the same structure. The four ink supply units 4 also have the same structure.

[0028] The four ejection heads 35 are arranged at intervals from one another in the transport direction. Each of the four ejection heads 35 ejects ink droplets from a nozzle 83 (see FIG. 2, described later) toward the surface (top surface) of the continuous paper 10. In this embodiment, the four ejection heads 35 eject ink of different colors (for example, cyan, magenta, yellow, and black) to record a single-color image on the surface (top surface) of the continuous paper 10. Then, a multi-color image is formed on the top surface of the continuous paper 10 by superimposing the four single-color images.

[0029] FIG. 2 is a conceptual diagram showing the configuration of one ink supply unit 4 and one ejection head 35. In this embodiment, each ejection head 35 has multiple (five in this embodiment) heads 80. The five heads 80 have the same structure. For this reason, FIG. 2 shows only one of the five heads 80 in detail, and the remaining four heads 80 are shown in a simplified manner. As shown in FIG. 2, each of the five heads 80 has a housing 81, an internal tank 82, and multiple nozzles 83.

[0030] The housing 81 forms the outer frame of the head 80. The internal tank 82 is disposed inside the housing 81 and is capable of temporarily storing ink. The multiple nozzles 83 are arranged at equal intervals in the transport direction and width direction of the continuous paper 10 in the lower part of the housing 81. Each of the multiple nozzles 83 communicates with the internal tank 82. Each of the multiple nozzles 83 has multiple piezoelectric elements 831 as pressure generating elements, an ink chamber 832, and an ejection port 830. The ink chamber 832 communicates with the internal tank 82.

[0031] When ink is ejected, the ink flows down from the internal tank 82 to the ink chamber 832. Then, by controlling the piezoelectric element 831, the ink in the ink chamber 832 is pressurized, causing the ink to be ejected as droplets from the ejection port 830. However, the nozzle 83 may be of a so-called thermal type, in which the ink in the ink chamber 832 is heated to generate bubbles, thereby pressurizing the ink.

[0032] Next, the ink supply unit 4 will be described. The ink supply unit 4 is a device that supplies ink to the ejection head 35 while circulating a portion of the ink. As described above, the inkjet printing apparatus 1 of this embodiment has four ink supply units 4. Since the four ink supply units 4 have the same structure, the following will describe the structure of only one ink supply unit 4.

[0033] As shown in FIG. 2, each ink supply unit 4 includes a supply tank 51, an internal recovery tank 52, an external recovery tank 53, a supply side manifold 61, a plurality (five in this embodiment) of supply side thin pipes 62, a plurality (five in this embodiment) of recovery side thin pipes 63, a recovery side manifold 64, a return pipe 65, a discharge pipe 66, a circulation pump 71, a plurality (five in this embodiment) of supply side opening / closing valves 73, a plurality (five in this embodiment) of head outlet side opening / closing valves 74, a return side opening / closing valve 75, a first heater 76, a second heater 77, a switching valve 78, a first temperature sensor 84, a second temperature sensor 85, a third temperature sensor 86, a filter 87, and a degassing unit 88.

[0034] The supply tank 51 is a container for temporarily storing ink to be supplied to the ejection head 35. An internal chamber 510 capable of temporarily storing ink is disposed inside the supply tank 51. The supply tank 51 may be equipped with a liquid level sensor for detecting the height of the liquid surface of the ink stored in the internal chamber 510 of the supply tank 51.

[0035] The supply-side manifold 61 and the five supply-side thin pipes 62 are pipes that connect the supply tank 51 and the five heads 80 of one discharge head 35. The supply-side manifold 61 is a thick pipe whose upstream end is connected to communicate with the internal chamber 510 of the supply tank 51. The five supply-side thin pipes 62 are thin pipes that branch off from the supply-side manifold 61. The upstream end of each of the five supply-side thin pipes 62 is connected to communicate with the internal passage of the supply-side manifold 61, and the downstream end is connected to communicate with the internal tank 82 of one head 80.

[0036] In this embodiment, a supply-side on-off valve 73 is inserted in each of the supply-side thin pipes 62. The supply-side on-off valve 73 may be, for example, a solenoid valve that opens and closes under the control of the control unit 9. However, the supply-side on-off valve 73 may also be a manually opened and closed on-off valve. When the supply-side on-off valve 73 is closed, communication between the internal passages of the supply-side thin pipes 62 is blocked. That is, when the supply-side on-off valve 73 is closed, the flow of ink from the supply tank 51 to the head 80 is blocked. On the other hand, when the supply-side on-off valve 73 is open, communication between the internal passages of the supply-side thin pipes 62 is permitted. However, the supply-side on-off valve 73 is not necessarily provided. A filter or the like may be inserted in the supply-side manifold 61 or the five supply-side thin pipes 62.

[0037] The five recovery side thin pipes 63 and the recovery side manifold 64 are pipes that connect the five heads 80 of one discharge head 35 to the internal recovery tank 52. Each of the five recovery side thin pipes 63 is a thin tube that branches off from the recovery side manifold 64. The upstream end of each of the five recovery side thin pipes 63 is connected to communicate with the internal tank 82 of one head 80, and the downstream end is connected to communicate with an internal passage of the recovery side manifold 64. The recovery side manifold 64 is a thick pipe that is connected to communicate with an internal chamber 520 (described later) of the internal recovery tank 52 at its downstream end.

[0038] In this embodiment, a head outlet-side on-off valve 74 is inserted in each recovery-side thin pipe 63. The head outlet-side on-off valve 74 may be, for example, a solenoid valve that opens and closes under the control of the control unit 9. However, a manually opened and closed on-off valve may also be used for the head outlet-side on-off valve 74. When the head outlet-side on-off valve 74 is closed, communication between the internal passages of the recovery-side thin pipes 63 is blocked. That is, when the head outlet-side on-off valve 74 is closed, the flow of ink from the head 80 to the internal recovery tank 52 is blocked. On the other hand, when the head outlet-side on-off valve 74 is open, communication between the internal passages of the recovery-side thin pipes 63 is permitted. However, the head outlet-side on-off valve 74 is not necessarily provided. Furthermore, a filter or the like may be inserted in each of the five recovery-side thin pipes 63 or the recovery-side manifold 64.

[0039] The internal recovery tank 52 is a container for temporarily storing ink recovered from the ejection head 35. An internal chamber 520 capable of temporarily storing ink is disposed inside the internal recovery tank 52. The internal recovery tank 52 may be equipped with a liquid level sensor for detecting the height of the liquid surface of the ink stored in the internal chamber 520 of the internal recovery tank 52.

[0040] 2, a pressurizing mechanism 515 is connected to the supply tank 51. The pressurizing mechanism 515 pressurizes the inside of the supply tank 51 and adjusts the air pressure in the internal chamber 510 of the supply tank 51 to a positive pressure (pressure higher than atmospheric pressure). The pressurizing mechanism 515 is composed of, for example, a compressor, a pressurized buffer tank, a pressure adjustment mechanism (regulator), etc. Furthermore, a depressurizing mechanism 524 is connected to the internal recovery tank 52. The depressurizing mechanism 524 depressurizes the inside of the internal recovery tank 52 and adjusts the air pressure in the internal chamber 520 of the internal recovery tank 52 to a negative pressure (pressure lower than atmospheric pressure). The depressurizing mechanism 524 is composed of, for example, a vacuum pump, a depressurized buffer tank, a pressure adjustment mechanism (regulator), etc.

[0041] The operations of the pressurizing mechanism 515 and the decompression mechanism 524 are configured to be controllable by the control unit 9. When the pressurizing mechanism 515 and the decompression mechanism 524 are driven, a pressure difference is created between the internal chamber 510 of the supply tank 51 and the internal chamber 520 of the internal recovery tank 52. This allows the ink stored in the supply tank 51 to be supplied to the ejection head 35, and further allows the ink remaining in the ejection head 35 (ink not ejected from the ejection head 35) to be recovered in the internal recovery tank 52.

[0042] The return pipe 65 is a pipe that connects the internal chamber 520 of the internal recovery tank 52 and the internal chamber 510 of the supply tank 51 so that they can communicate with each other. That is, the return pipe 65 connects the internal recovery tank 52 and the supply tank 51. As shown in FIG. 2 , the upstream end of the internal passage of the return pipe 65 is connected in communication with the internal chamber 520 of the internal recovery tank 52. In addition, the downstream end of the internal passage of the return pipe 65 is connected in communication with the internal chamber 510 of the supply tank 51.

[0043] With the above configuration, an ink circulation path 41 is formed that runs from the supply tank 51 via the supply-side manifold 61, the supply-side thin pipe 62, the internal tank 82 of the ejection head 35, the recovery-side thin pipe 63, the recovery-side manifold 64, the internal recovery tank 52, and the return pipe 65, and returns to the supply tank 51 again. That is, the ink circulation path 41 includes the supply tank 51, the ejection head 35, the internal recovery tank 52, and the return pipe 65.

[0044] In addition, a circulation pump 71, a return-side opening / closing valve 75, a first heater 76, a second heater 77, a switching valve 78, a first temperature sensor 84, a second temperature sensor 85, a third temperature sensor 86, a filter 87, and a degassing unit 88 are inserted in the return pipe 65. As will be described in detail later, a discharge pipe 66 is also connected to the switching valve 78 provided in the ink circulation path 41.

[0045] The circulation pump 71 is a device that performs a liquid transfer operation to transfer ink from the internal recovery tank 52 to the supply tank 51 via the return pipe 65. The circulation pump 71 generates a flow of ink in the internal passage of the return pipe 65 from the internal recovery tank 52 to the supply tank 51 in accordance with an operation signal from the control unit 9. The circulation pump 71 in this embodiment is a pump, such as a diaphragm pump, that is less likely to generate foreign matter such as dust when driven. The circulation pump 71 applies pressure to the ink inside the circulation pump 71 by the reciprocating movement of an internal piston, and ejects the ink from an outlet that communicates with the internal passage of the return pipe 65. The circulation pump 71 is also electrically connected to the control unit 9. The circulation pump 71 outputs data related to its operating status to the control unit 9.

[0046] The return-side on-off valve 75 is disposed in the return pipe 65 downstream of the circulation pump 71 and upstream of the first heater 76, the second heater 77, and the switching valve 78. That is, the return-side on-off valve 75 is disposed in the return pipe 65 between the circulation pump 71 and the first and second heaters 76 and 77. The return-side on-off valve 75 corresponds to the "on-off valve" of the present invention. For example, a solenoid valve that opens and closes under the control of the control unit 9 is used as the return-side on-off valve 75. In addition, a normally closed solenoid valve is used as the return-side on-off valve 75 in this embodiment. Therefore, the return-side on-off valve 75 is closed when no power is supplied. However, a manually opened and closed on-off valve may be used as the return-side on-off valve 75.

[0047] When the return-side on-off valve 75 is closed, communication with the internal passage of the return pipe 65 is blocked. That is, when the return-side on-off valve 75 is closed, the flow of ink from the internal recovery tank 52 to the supply tank 51 and the backflow of ink from the switching valve 78 to the circulation pump 71 are prevented. On the other hand, when the return-side on-off valve 75 is open, communication with the internal passage of the return pipe 65 is permitted. That is, the return-side on-off valve 75 allows or blocks the flow of ink from the internal recovery tank 52 to the supply tank 51.

[0048] The first heater 76 is a device that heats the ink being pumped through the internal passage of the return pipe 65. The first heater 76 is located in the return pipe 65 between the internal recovery tank 52 and the switching valve 78. The first heater 76 has a heating element such as a carbon heater, and is connected to a power source via an ON / OFF circuit (not shown). The first heater 76 can heat the ink by generating heat when the power is turned on. As will be described in detail later, the first heater 76 is switched between the ON state and the OFF state, thereby controlling the temperature of the ink passing through the first heater 76 to, for example, a first target temperature T1°C that is higher than room temperature.

[0049] The second heater 77 is a device that heats the ink being pumped through the internal passage of the return pipe 65. The second heater 77 is located in the return pipe 65 between the first heater 76 and the switching valve 78. That is, the second heater 77 is located downstream of the first heater 76 along the circulation path 41. In other words, in this embodiment, the first heater 76 and the second heater 77 are provided adjacent to each other along the circulation path 41 and inserted into the return pipe 65. The second heater 77 has a heating element made up of a carbon heater or the like, and is connected to a power source via an ON / OFF circuit (not shown). The second heater 77 can heat the ink by generating heat when the power is turned on. As will be described in detail later, the second heater 77 is controlled, for example, by switching between an ON state and an OFF state, so that the temperature of the ink passing through the second heater 77 becomes a second target temperature T2°C that is higher than the first target temperature T1 (for example, about 5°C higher than the first target temperature T1). In other words, the proportion of time that the second heater 77 is in the ON state per unit time (for example, 1 second) (hereinafter referred to as the "duty value") is greater than the duty value of the first heater 76.

[0050] However, in the present invention, the number of heaters interposed in the return pipe 65 between the internal recovery tank 52 and the switching valve 78 may be one or may be three or more. The heater may be any heater that is interposed in the return pipe 65 between the circulation pump 71 and the supply tank 51 and heats the ink flowing from the internal recovery tank 52 to the supply tank 51.

[0051] A first temperature sensor 84 is inserted in the return pipe 65 downstream of the return-side on-off valve 75 in the ink feed direction and upstream of the first heater 76 in the ink feed direction. The first temperature sensor 84 detects the temperature of the ink flowing into the first heater 76. The first temperature sensor 84 is also electrically connected to the control unit 9. The first temperature sensor 84 outputs data related to the detection result of the ink temperature to the control unit 9.

[0052] A second temperature sensor 85 is inserted in the return pipe 65 downstream of the first heater 76 in the ink feed direction and upstream of the second heater 77 in the ink feed direction. The second temperature sensor 85 detects the temperature of the ink flowing out from the first heater 76. The second temperature sensor 85 is also electrically connected to the control unit 9. The second temperature sensor 85 outputs data related to the detection result of the ink temperature to the control unit 9.

[0053] A third temperature sensor 86 is inserted in the return pipe 65 downstream of the second heater 77 in the ink feeding direction and upstream of the switching valve 78 in the ink feeding direction. The third temperature sensor 86 detects the temperature of the ink flowing out from the second heater 77. The third temperature sensor 86 is also electrically connected to the control unit 9. The third temperature sensor 86 outputs data related to the detection result of the ink temperature to the control unit 9.

[0054] That is, the ink supply unit 4 of this embodiment has temperature sensors 85 and 86 that are interposed in the return pipe 65 between the first and second heaters 76 and 77 and the switching valve 78, and detect the temperature of the ink in the return pipe 65. However, the first temperature sensor 84, the second temperature sensor 85, and the third temperature sensor 86 do not necessarily have to be provided.

[0055] The switching valve 78 is inserted in the return pipe 65 downstream of the first and second heaters 76 and 77 and the temperature sensors 84, 85, and 86, and upstream of the filter 87. That is, the switching valve 78 is inserted in the return pipe 65 between the first and second heaters 76 and 77 and the supply tank 51. The switching valve 78 is a three-way valve that switches the ink circulation path 41 in the internal passage of the return pipe 65 to an ink waste path via the discharge pipe 66. The switching valve 78 may be, for example, an electromagnetic valve that performs a switching operation under the control of the control unit 9. The switching valve 78 has a built-in solenoid (not shown) for switching the ink outflow destination. However, the switching valve 78 may be a manually switched switching valve. The switching valve 78 has an inlet 781, a first outlet 782, and a second outlet 783.

[0056] The inlet 781 communicates with the first and second heaters 76 and 77 and the temperature sensors 84, 85, and 86 (upstream side of the circulation path 41). The first outlet 782 communicates with the filter 87 (downstream side of the circulation path 41). The second outlet 783 communicates with the internal passage of the discharge pipe 66. Normally, the second outlet 783 is closed, and the inlet 781 and the first outlet 782 communicate with each other. That is, when power is supplied to the switching valve 78 and the solenoid is ON (excited), the destination of the ink flow from the switching valve 78 is the first outlet 782. This allows the internal passage of the return pipe 65 to communicate with each other. On the other hand, by closing the first outlet 782 and connecting the inlet 781 and the second outlet 783, the ink flowing in from the inlet 781 can be directed to a waste path via the discharge pipe 66 and discharged to the outside of the inkjet printing apparatus 1. That is, when no power is supplied to the switching valve 78 and the solenoid is OFF (demagnetized), the destination of the ink from the switching valve 78 is the second outlet 783. In other words, the switching valve 78 can switch between a state in which the first and second heaters 76, 77 communicate with the supply tank 51 and a state in which the communication between the first and second heaters 76, 77 and the supply tank 51 is blocked and the internal space of the circulation path 41 communicates with an external recovery tank 53 (described later).

[0057] When the control unit 9 (described later) closes the return-side on-off valve 75 and connects the inlet 781 and the second outlet 783 of the switching valve 78, the circulation path 41 is divided into a section from the return-side on-off valve 75 to the switching valve 78 and other sections. Hereinafter, this section of the circulation path 41 from the return-side on-off valve 75 to the switching valve 78 will be referred to as the "ink compartment region 79." That is, the ink compartment region 79 is defined as a portion of the return pipe 65 that includes the first and second heaters 76 and 77. When the return-side on-off valve 75 is closed and the circulation of ink in the circulation path 41 stops, the ink compartment region 79 is divided into the ink in the circulation path 41 and the ink in the other sections of the return pipe 65 by connecting the inlet 781 and the second outlet 783 of the switching valve 78. In this state, the ink flow between the ink compartment region 79 and other sections of the return pipe 65 is restricted. Furthermore, since the switching valve 78 has flow path resistance, even if the ink flows out of the switching valve 78 to the first ink outlet 782, the ink in the ink compartment area 79 is restricted from flowing with the ink downstream thereof, and the ink compartment area 79 is separated from other areas of the return pipe 65.

[0058] The external recovery tank 53 is a container for recovering ink that is discharged to the outside of the circulation path 41. The external recovery tank 53 is provided outside the circulation path 41 of the ink that circulates between the supply tank 51 and the internal recovery tank 52. An internal chamber 530 capable of storing ink is provided inside the external recovery tank 53.

[0059] The discharge pipe 66 is a pipe that connects the internal chamber 530 of the external recovery tank 53 and the second outlet 783 of the switching valve 78 so that they can communicate with each other. The internal passage of the discharge pipe 66 is connected at its upstream end to the second outlet 783 of the switching valve 78. The internal passage of the discharge pipe 66 is connected at its downstream end to the internal chamber 530 of the external recovery tank 53. As described above, by switching the switching valve 78 to connect the internal space of the circulation path 41 to the external recovery tank 53, ink can be sent to the internal chamber 530 of the external recovery tank 53 via the internal passage of the return pipe 65, the internal space of the switching valve 78, and the internal passage of the discharge pipe 66.

[0060] As described above, in this embodiment, the return-side on-off valve 75 and the switching valve 78 are provided in the ink compartment area 79. Furthermore, under the control of the control unit 9, the return-side on-off valve 75 is closed and the ink outlet from the switching valve 78 is switched to the second outlet 783, thereby connecting the ink compartment area 79 to the external recovery tank 53, thereby separating the ink in the ink compartment area 79 from the ink in the other areas of the return pipe 65.

[0061] The filter 87 is inserted in the return pipe 65 downstream of the switching valve 78 and upstream of the degassing unit 88. The filter 87 filters the ink being sent through the internal passage of the return pipe 65, and removes foreign matter contained in the ink.

[0062] The degassing unit 88 is inserted in the return pipe 65 downstream of the filter 87 and upstream of the supply tank 51. The degassing unit 88 in this embodiment is a so-called hollow fiber membrane degassing module. The degassing unit 88 removes air bubbles from the ink being pumped through the internal passage of the return pipe 65.

[0063] Next, the control unit 9 will be described. The control unit 9 is an information processing device for controlling each part of the inkjet printing apparatus 1. FIG. 3 is a block diagram showing the connection between the control unit 9 and each part of the inkjet printing apparatus 1. As conceptually shown in FIG. 3, the control unit 9 has a processor 91 such as a CPU, a memory 92 such as RAM, and a storage unit 93 such as a hard disk drive. The storage unit 93 stores a computer program 9P for executing a printing process while transporting the continuous paper 10, supplying ink to the ejection head 35 while circulating a portion of the ink, and discharging the ink to outside the circulation path 41.

[0064] 3, the control unit 9 is communicatively connected to the transport unit 2, the four ejection heads 35 of the printing unit 3, the circulation pumps 71 of each of the four ink supply units 4 of the printing unit 3, the five supply-side on-off valves 73, the five head outlet-side on-off valves 74, the return-side on-off valve 75, the first heater 76, the second heater 77, the switching valve 78, the temperature sensors 84, 85, 86, the pressurizing mechanism 515, and the decompression mechanism 524. The control unit 9 controls the operation of each of these units in accordance with a computer program 9P.

[0065] That is, the control unit 9 can control the transport unit 2, the four ejection heads 35 of the printing unit 3, the circulation pumps 71 of each of the four ink supply units 4 of the printing unit 3, the five supply-side on-off valves 73, the five head outlet-side on-off valves 74, the return-side on-off valves 75, the first heater 76, the second heater 77, the switching valve 78, the temperature sensors 84, 85, and 86, the pressurizing mechanism 515, and the decompression mechanism 524. By controlling the operation of each of these units, the control unit 9 transports the continuous paper 10 and the printing process progresses, and ink is supplied to the internal tanks 82 of each ejection head 35 while some of the ink circulates. Furthermore, under certain conditions, ink is discharged to the outside of the circulation path 41. As described above, the circulation pump 71 outputs data related to its operating status to the control unit 9. The control unit 9 can detect whether ink is circulating within the circulation path 41 based on the data input from the circulation pump 71.

[0066] <2. Continuous paper transport, printing, ink circulation, and ink discharge> Next, we will explain the procedures for transporting the continuous paper 10, printing on the continuous paper 10, circulating ink, and discharging ink to the outside, which are performed in the inkjet printing device 1. Figure 4 is a flowchart showing the flow of transporting the continuous paper 10, printing on the continuous paper 10, circulating ink, and discharging ink to the outside.

[0067] First, when transporting the continuous paper 10, printing the continuous paper 10, and circulating the ink, the control unit 9 operates the transport unit 2 to transport the continuous paper 10 in a transport direction along the longitudinal direction along a predetermined transport path, while controlling the multiple nozzles 83 of each of the four ejection heads 35 to eject droplets of ink onto the surface of the continuous paper 10, thereby recording an image on the surface of the continuous paper 10 (step S1).

[0068] Here, a sufficient amount of ink is stored in the internal chamber 510 of the supply tank 51 as preparation for transporting the continuous paper 10, printing the continuous paper 10, and circulating the ink. The control unit 9 also opens the five supply-side on-off valves 73, the five head outlet-side on-off valves 74, and the return-side on-off valve 75. The control unit 9 also closes the second outlet 783 of the switching valve 78 to connect the inlet 781 and the first outlet 782.

[0069] The control unit 9 then drives the circulation pump 71, first heater 76, second heater 77, pressurizing mechanism 515, and decompression mechanism 524 of each of the four ink supply units 4. That is, the control unit 9 drives the circulation pump 71 to circulate ink in the ink circulation path 41, while driving the pressurizing mechanism 515 and decompression mechanism 524 to supply ink to the internal tank 82 of each ejection head 35. The control unit 9 also turns on the power of the first temperature sensor 84, second temperature sensor 85, and third temperature sensor 86, causing these sensors to start measuring.

[0070] More specifically, by driving the pressurizing mechanism 515 and the decompressing mechanism 524, a pressure difference is created between the internal chamber 510 of the supply tank 51 and the internal chamber 520 of the internal recovery tank 52. This allows the ink stored in the supply tank 51 to be supplied to the ejection head 35, and further allows the ink remaining in the ejection head 35 (ink not ejected from the ejection head 35) to be recovered in the internal recovery tank 52. Furthermore, by driving the circulation pump 71, a flow of ink is generated in the internal passage of the return pipe 65, from the internal recovery tank 52 to the supply tank 51.

[0071] Furthermore, by driving the first and second heaters 76, 77, the ink being sent through the internal passage of the return pipe 65 can be heated and then sent to the supply tank 51. More specifically, the control unit 9 first controls the temperature of the ink passing through the first heater 76 to be, for example, a first target temperature T1°C by switching the first heater 76 between an ON state and an OFF state. As described above, the second temperature sensor 85 detects the temperature of the ink flowing out from the first heater 76 and outputs data related to the detection result to the control unit 9. The control unit 9 adjusts the drive amount of the first heater 76 based on the ink temperature detection result input from the second temperature sensor 85.

[0072] FIG. 5 is a diagram showing an example of the temperature of ink passing through the first and second heaters 76, 77 and the ratio of the time the heaters are in an ON state per unit time (e.g., 1 second) when the heaters are driven (i.e., "duty value") corresponding to the ink temperature. As shown in FIG. 5, when the temperature of the ink passing through the first heater 76 is below the "first target temperature T1-2.5°C," the control unit 9 drives the first heater 76 at a duty value of 100%. Then, when the temperature of the ink passing through the first heater 76 becomes equal to or higher than the "first target temperature T1-2°C," the control unit 9 gradually reduces the duty value. When the temperature of the ink passing through the first heater 76 becomes equal to or higher than the "first target temperature T1-2°C," the control unit 9 drives the first heater 76 at a duty value of 50% or less. When the temperature of the ink passing through the first heater 76 becomes equal to or higher than the "first target temperature T1°C," the control unit 9 drives the first heater 76 at a duty value of 0%. In other words, when the temperature of the ink passing through the first heater 76 becomes equal to or higher than the "first target temperature T1°C," the control unit 9 stops driving the first heater 76. By controlling in this way, the temperature of the ink passing through the first heater 76 can be adjusted to the "first target temperature T1°C."

[0073] Furthermore, the control unit 9 controls the temperature of the ink passing through the second heater 77 to, for example, a second target temperature T2°C by switching the second heater 77 between an ON state and an OFF state. As described above, the third temperature sensor 86 detects the temperature of the ink flowing out from the second heater 77 and outputs data related to the detection result to the control unit 9. The control unit 9 adjusts the drive amount of the second heater 77 based on the ink temperature detection result input from the third temperature sensor 86. Here, as described above, the duty value of the second heater 77 is greater than the duty value of the first heater 76.

[0074] As shown in FIG. 5, when the temperature of the ink passing through the second heater 77 is below the first target temperature T1 + 3°C (second target temperature T2 - 2°C), the control unit 9 drives the second heater 77 at a 100% duty value. Then, when the temperature of the ink passing through the second heater 77 reaches or exceeds the first target temperature T1 + 3°C (second target temperature T2 - 2°C), the control unit 9 gradually reduces the duty value. When the temperature reaches or exceeds the first target temperature T1 + 4°C (second target temperature T2 - 1°C), the control unit 9 drives the second heater 77 at a duty value of 50% or less. When the temperature reaches or exceeds the first target temperature T1 + 5°C (second target temperature T2°C), the control unit 9 drives the second heater 77 at a duty value of 0%. That is, when the temperature reaches or exceeds the first target temperature T1 + 5°C (second target temperature T2°C), the control unit 9 stops driving the second heater 77. By controlling in this manner, the temperature of the ink passing through the second heater 77 can be adjusted to the second target temperature T2°C. Furthermore, by adjusting the temperature of the ink passing through the second heater 77 to the second target temperature T2° C., the ink can then be ejected from the ejection head 35 in a satisfactory manner.

[0075] As described above, the first temperature sensor 84 detects the temperature of the ink flowing into the first heater 76 and outputs data related to the detection result to the control unit 9. By referring to the data related to the detection result by the first temperature sensor 84, the control unit 9 can know what the temperature of the ink flowing into the first heater 76 was in the first place. This can be used as a guide to determine whether the first heater 76 and the second heater 77 are operating normally.

[0076] Furthermore, by passing the ink flowing through the internal passage of the return pipe 65 through a filter 87, small impurities remaining in the ink can be removed, and the ink can be sent to the supply tank 51. Furthermore, by passing the ink flowing through the internal passage of the return pipe 65 through a degassing unit 88, the ink can be degassed before being sent to the supply tank 51.

[0077] If, for example, a power outage occurs and the power supply to the inkjet printing apparatus 1 is cut off, the power supply to the circulation pump 71 is also cut off, and the operation of the circulation pump 71 is stopped. Furthermore, if an operator discovers that ink is leaking from the ink circulation path 41, that the ink level stored in the internal chamber 510 of the supply tank 51 has dropped excessively, or that the ink stored in the internal chamber 530 of the external recovery tank 53 has overflowed, the operator will stop the operation of the circulation pump 71. In these cases, the circulation of ink in the circulation path 41 is stopped, and ink will stagnate inside the first and second heaters 76 and 77.

[0078] As described above, the first and second heaters 76, 77 each have a heating element made of a carbon heater or the like. The heating element remains at a high temperature even after the power supply to the first and second heaters 76, 77 is cut off. Therefore, if the ink circulation is stopped for a certain period of time, the ink remaining inside the first and second heaters 76, 77 may be excessively heated and may be altered or deteriorated. If the altered or deteriorated ink is subsequently used, the ink may not be ejected properly from the ejection head 35, or the desired color gamut may not be obtained.

[0079] Therefore, the control unit 9 first detects whether the circulation pump 71 has stopped operating (step S2). This includes cases where a power outage occurs, cutting off the power supply to the circulation pump 71 and causing the circulation pump 71 to automatically stop operating, or where an operator stops the circulation pump 71 themselves. The control unit 9 continues to transport the continuous paper 10, print on the continuous paper 10, and circulate ink until it detects that the circulation pump 71 has stopped operating (step S2: No). On the other hand, if it detects that the circulation pump 71 has stopped operating (step S2: Yes), it executes the ink partition step S21 described below.

[0080] As described above, the return-side on-off valve 75 is a normally closed solenoid valve, and therefore closes automatically when a power outage or the like occurs and the power supply to the return-side on-off valve 75 stops. However, when the control unit 9 detects that the ink circulation in the circulation path 41 has stopped, the control unit 9 may send a control signal to the return-side on-off valve 75 to block the flow of ink. Alternatively, an operator may manually close the return-side on-off valve 75. In this way, when the circulation of ink in the circulation path 41 stops due to a power outage or the like, the ink compartment area 79 is separated from the other return pipes 65 (step S21).

[0081] Furthermore, as described above, when the solenoid built into the switching valve 78 is demagnetized (OFF), the ink outflow destination is switched to the second outlet 783. Therefore, if a power outage or the like occurs and the power supply to the switching valve 78 is stopped, the ink outflow destination is automatically switched to the second outlet 783. However, when the control unit 9 detects that the ink circulation in the circulation path 41 has stopped, the control unit 9 may send a control signal to the switching valve 78 to switch the ink outflow destination to the second outlet 783. Alternatively, an operator may manually switch the ink outflow destination of the switching valve 78 to the second outlet 783. In this manner, the ink compartment step S21 is executed.

[0082] After executing the ink compartment step S21, the control unit 9 performs post-recovery processing (step S3) when it recovers from a power outage, fixes ink leakage, etc., and then transports the continuous paper 10, prints the continuous paper 10, and circulates the ink again.

[0083] FIG. 6 is a flowchart showing the procedure for executing the post-recovery process. As will be described in detail below, when executing the post-recovery process, the control unit 9 can selectively execute a "normal resume mode" or a "post-discharge resume mode." That is, after executing ink partition step S21, the control unit 9 selectively executes the "normal resume mode" or the "post-discharge resume mode" after the power outage is restored or the ink leakage or other problem is resolved. The control unit 9 can determine whether the power outage has been resolved or the ink leakage or other problem has been resolved based on whether the power supply to the inkjet printing apparatus 1 has been resumed or input by an operator, etc.

[0084] 6, before restarting the circulation of ink in the circulation path 41, the control unit 9 first determines whether the temperature of the ink in the ink compartment area 79 is below a predetermined threshold or above a predetermined threshold (step S31). In making this determination, the control unit 9 references the duty values ​​of the first heater 76 and the second heater 77 during a first predetermined period (e.g., one second) before detecting that the circulation of ink in the circulation path 41 has stopped. Note that, because the duty values ​​may change as described above, the control unit 9 may set the first predetermined period to a period of several minutes and reference the integral of the duty values ​​of the first and second heaters 76 and 77 over that period.

[0085] The control unit 9 determines that the duty value was large during the first predetermined period before detecting that the ink circulation had stopped, which means that the heating elements inside the first and second heaters 76, 77 continued to generate a large amount of heat even during the period when the ink circulation had stopped.The control unit 9 then determines that the ink remaining inside the first and second heaters 76, 77 is likely to have been excessively heated and altered or deteriorated.The control unit 9 then determines, based on the result of referencing the duty value, whether the temperature of the ink in the ink compartment area 79 is below or above the threshold value.

[0086] More specifically, after detecting that the circulation of ink in the circulation path 41 has stopped, the control unit 9 determines whether the temperature of the ink in the first heater 76 is less than a predetermined first threshold value or equal to or greater than the first threshold value before restarting the circulation of ink in the circulation path 41. Furthermore, after detecting that the circulation of ink in the circulation path 41 has stopped, the control unit 9 determines whether the temperature of the ink in the second heater 77 is less than a predetermined second threshold value or equal to or greater than the second threshold value before restarting the circulation of ink in the circulation path 41. In this way, in this embodiment, ink can be discharged as described below based on the result of determining whether the temperature of the ink is less than a predetermined threshold value or equal to or greater than a predetermined threshold value, taking into account the heat generation amounts of the first and second heaters 76, 77.

[0087] However, the control unit 9 may determine whether the temperature of the ink in the ink compartment area 79 is below a predetermined threshold or above a predetermined threshold based on the detection results of the second temperature sensor 85 located downstream of the first heater 76 and the detection results of the third temperature sensor 86 located downstream of the second heater 77. When discharging ink (described below), the control unit 9 may stop discharging the ink to the outside at that point if it determines that the ink temperature is sufficiently low based on the detection results of the temperature sensors 85 and 86.

[0088] If the controller 9 determines that the temperature of the ink in the ink compartment area 79 is below a predetermined threshold (step S31: YES), it executes the "normal restart mode" (step S32). More specifically, if the controller 9 determines that the temperature of the ink in the first heater 76 is below a predetermined first threshold and that the temperature of the ink in the second heater 77 is below a predetermined second threshold, it executes the "normal restart mode." That is, the controller 9 executes the "normal restart mode" based on the temperature of the ink in the ink compartment area 79. In this case, as the "normal restart mode," the controller 9 immediately connects the ink compartment area 79 to other areas of the return pipe 65. That is, the controller 9 closes the second outlet 783 of the switching valve 78 and connects the inlet 781 and the first outlet 782, thereby connecting the first and second heaters 76 and 77 to the supply tank 51. The controller 9 also opens the return-side on-off valve 75. Next, the control unit 9 drives the circulation pump 71 to restart the circulation of the ink, and then transports the continuous paper 10, prints on the continuous paper 10, and circulates the ink.

[0089] On the other hand, if the control unit 9 determines that the temperature of the ink in the ink compartment area 79 is equal to or higher than the predetermined threshold (step S31: NO), it executes the "post-drain restart mode" (step S33). For example, if the control unit 9 determines that the temperature of the ink in the first heater 76 is lower than the first predetermined threshold and the temperature of the ink in the second heater 77 is equal to or higher than the second predetermined threshold, it executes the "post-drain restart mode." That is, the control unit 9 executes the "post-drain restart mode" based on the temperature of the ink in the ink compartment area 79. In this case, as the "post-drain restart mode," the control unit 9 closes the first outlet 782 of the switching valve 78 and connects the inlet 781 and the second outlet 783, thereby connecting the internal space of the circulation path 41 to the external recovery tank 53. The control unit 9 also opens the return-side opening / closing valve 75. Then, the control unit 9 drives the circulation pump 71 for a "specific time" to discharge the ink in the ink compartment area 79 into the external recovery tank 53. Thereafter, as will be described later, the control unit 9 again connects the ink compartment region 79 with another region of the return pipe 65.

[0090] Here, the "specific period" is a value obtained by, for example, dividing the sum of the volume of the section of the internal passage of the return pipe 65 from the switching valve 78 to the second heater 77 and the volume of the internal space of the second heater 77 by the amount of liquid delivered per unit time by the circulation pump 71. In other words, the "specific period" is a value obtained by dividing a specific volume calculated based on the volume of ink that can pass through the second heater 77 by the amount of liquid delivered per unit time by the circulation pump 71. This makes it possible to discharge ink that may have deteriorated due to overheating of the second heater 77 to the outside of the circulation path 41. Furthermore, the ink to be discharged in this case can be limited to ink that may have deteriorated due to overheating of the second heater 77.

[0091] However, the amount of ink discharged to the external recovery tank 53 may be all of the ink in the ink compartment area 79, or a smaller amount determined by referring to the temperatures of the ink in the first heater 76 and the second heater 77. That is, based on the temperature of the ink in the ink compartment area 79, the control unit 9 sets the "discharge-and-restart mode" to open the return-side on-off valve 75, sets the switching valve 78 to connect the ink compartment area 79 to the external recovery tank 53, and drives the circulation pump 71 to discharge at least a portion of the ink in the ink compartment area 79 to the external recovery tank 53, and then, as described below, reconnects the ink compartment area 79 to another area of ​​the return pipe 65.

[0092] Furthermore, when the control unit 9 determines that the temperature of the ink in the first heater 76 is equal to or higher than a predetermined first threshold and that the temperature of the ink in the second heater 77 is equal to or higher than a predetermined second threshold, the control unit 9 similarly executes the "post-discharge restart mode." In this case, the control unit 9 similarly switches the switching valve 78, opens the return-side opening / closing valve 75, and drives the circulation pump 71 for a "specific time." In this case, the "specific time" is, for example, a value obtained by dividing the sum of the volume of the section of the internal passage of the return pipe 65 from the switching valve 78 to the first heater 76, the volume of the internal space of the second heater 77, and the volume of the internal space of the first heater 76, by the amount of liquid delivered per unit time by the circulation pump 71.

[0093] That is, when the control unit 9 determines that the temperature of the ink in the ink compartment area 79 is equal to or higher than a predetermined threshold, it causes the switching valve 78 to connect the ink compartment area 79 to the external recovery tank 53. The control unit 9 also opens the return-side on-off valve 75. The control unit 9 then drives the circulation pump 71 for a "specific time" to drain the ink in the ink compartment area 79 to the external recovery tank 53. This allows ink that may have been altered or degraded due to overheating to be drained to the outside based on the ink temperature when the ink circulation stops and is subsequently restored. Furthermore, even when draining ink to the external recovery tank 53, not all of the ink in the circulation path 41 is drained. In this embodiment, only ink in the ink compartment area 79 that may have been altered or degraded due to excessive heating by the second heater 77, or ink that may have been altered or degraded due to excessive heating by both the first heater 76 and the second heater 77, is drained to the external recovery tank 53. This reduces the amount of ink to be drained.

[0094] When the "restart after discharge mode" is executed, the control unit 9 stops driving the first and second heaters 76, 77 at least until the ink compartment area 79 is connected to another area of ​​the return pipe 65, as will be described later. This makes it possible to further prevent the ink from overheating.

[0095] As described above, after driving the circulation pump 71 for the "specific time" to discharge the ink in the ink compartment area 79 into the external recovery tank 53, the control unit 9 again closes the second outlet 783 of the switching valve 78 and connects the inlet 781 and the first outlet 782, thereby connecting the first and second heaters 76, 77 to the supply tank 51. That is, the control unit 9 again connects the ink compartment area 79 to the other area of ​​the return pipe 65. The control unit 9 also opens the return-side on-off valve 75. The control unit 9 then drives the circulation pump 71 to resume ink circulation, transporting the continuous paper 10, printing the continuous paper 10, and circulating the ink. The control unit 9 also drives the first and second heaters 76, 77 again and adjusts the drive amounts of the first and second heaters 76, 77 based on the ink temperature detection results input from the temperature sensors 85, 86.

[0096] 4, the control unit 9 then determines whether or not to end the transport and printing of the continuous paper 10 (step S4). If image data to be printed remains, the control unit 9 continues transport and printing of the continuous paper 10 (step S4: No). When there is no more image data to print (step S4: Yes), the control unit 9 stops the operation of each unit and ends the transport of the continuous paper 10, printing on the continuous paper 10, and circulation of ink.

[0097] <3. Modifications> Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0098] In the above embodiment, when ink in the ink compartment area 79 is discharged to the external recovery tank 53 in the "discharge-restart mode," the return-side on-off valve 75 is opened and the circulation pump 71 is driven. However, without opening the return-side on-off valve 75 or driving the circulation pump 71, a separate pressurizing mechanism and decompression mechanism may be provided to pressurize the circulation path 41 side and decompress the external recovery tank 53 side, thereby discharging ink in the internal space of the circulation path 41 to the external recovery tank 53.

[0099] Furthermore, the elements appearing in the above-described embodiments and modifications may be combined as appropriate within the scope of not causing any contradiction. [Explanation of symbols]

[0100] 1. Inkjet printing device 2. Conveyor section 3 Printing Department 4 Ink supply unit 9 Control Unit 10 Continuous Paper 35 Discharge head 41 Circulation Route 51 Supply Tank 52 Internal recovery tank 53 External recovery tank 65 Return piping 66 Discharge piping 71 Circulation Pump 75 Return side opening / closing valve 76 First heater 77 Second heater 78 Switching valve 79 Ink Compartment Area 84 First temperature sensor 85 Second temperature sensor 86 Third temperature sensor 781 (Switching valve) inlet 782 (Switching valve) First outlet 783 (Switching valve) Second outlet

Claims

1. An inkjet printing device that prints by ejecting ink onto a print medium, an ink circulation path including an ejection head that ejects ink, a supply tank that stores ink to be supplied to the ejection head, an internal recovery tank that stores ink recovered from the ejection head, and a return pipe that connects the internal recovery tank and the supply tank; an external recovery tank that recovers ink discharged to the outside of the circulation path; a circulation pump inserted in the return pipe to send ink from the internal recovery tank to the supply tank via the return pipe; a heater interposed between the circulation pump and the supply tank in the return pipe, for heating the ink flowing from the internal recovery tank to the supply tank; a control unit that can control the ejection head, the circulation pump, and the heater, and that can detect whether or not ink is circulating in the circulation path; an ink partition area that is set in a partial area of ​​the return pipe including the heater, and that separates the ink in the circulation path from the ink in the other areas of the return pipe when the circulation of ink in the circulation path stops; and The control unit before restarting the circulation of the ink in the circulation path, based on the temperature of the ink in the ink compartment area, a normal restart mode in which the ink compartment region is immediately connected to the other return pipe region; a post-drain restart mode in which, after at least a portion of the ink in the ink compartment area is drained to the external recovery tank, the ink compartment area is communicated with the other area of ​​the return pipe; An inkjet printing device that selectively performs the above.

2. 10. The inkjet printing apparatus of claim 1, In the ink compartment area, an on-off valve interposed between the circulation pump and the heater in the return pipe, for allowing or blocking the flow of ink from the internal recovery tank to the supply tank; a switching valve that is interposed between the heater and the supply tank in the return pipe and is switchable between a state in which the heater and the supply tank are in communication with each other and a state in which the communication between the heater and the supply tank is interrupted and an internal space of the circulation path is in communication with the external recovery tank; is further established, the control unit is capable of further controlling the on-off valve and the switching valve, an ink jet printing device in which the control unit controls the on-off valve to close, and the ink compartment area is connected to the external recovery tank via the switching valve, thereby separating the ink in the ink compartment area from the ink in the area of ​​the other return pipe.

3. 3. The inkjet printing apparatus of claim 2, In the inkjet printing device, in the post-discharge restart mode, the control unit opens the on-off valve, and the switching valve connects the ink compartment area to the external recovery tank, and the circulation pump is driven to discharge at least a portion of the ink in the ink compartment area into the external recovery tank.

4. 4. The inkjet printing apparatus according to claim 1, The control unit determining whether the temperature of the ink in the ink compartment area is below a predetermined threshold or above the predetermined threshold; If it is determined that the value is less than the predetermined threshold, the normal resume mode is executed; When it is determined that the value is equal to or greater than the predetermined threshold, the inkjet printing apparatus executes the post-discharge restart mode.

5. 5. The inkjet printing apparatus of claim 4, The control unit determines whether the temperature of the ink in the ink compartment area is below the predetermined threshold or above the predetermined threshold based on the duty value of the heater during a first predetermined period before detecting that the circulation of ink in the circulation path has stopped.

6. 5. The inkjet printing apparatus of claim 4, a temperature sensor that is interposed between the heater and the switching valve in the return pipe and detects the temperature of the ink in the return pipe; and The control unit determines whether the temperature of the ink in the ink compartment area is less than the predetermined threshold value or greater than or equal to the predetermined threshold value based on the detection result from the temperature sensor.

7. 10. The inkjet printing apparatus of claim 1, When the ink-restart mode is executed, the control unit stops driving the heater at least until the ink compartment area and the area of ​​the other return pipe are connected to each other.

8. 3. The inkjet printing apparatus of claim 2, The heaters include a first heater and a second heater that are adjacent to each other along the circulation path and are inserted into the return pipe. and the second heater is located downstream of the first heater in the circulation path, and a duty value of the second heater is greater than a duty value of the first heater; The control unit before restarting the circulation of the ink in the circulation path, determining whether the temperature of the ink in the first heater is less than a predetermined first threshold value or greater than or equal to the first threshold value, and whether the temperature of the ink in the second heater is less than a predetermined second threshold value or greater than or equal to the second threshold value, when it is determined that the temperature of the ink in the first heater is lower than the first threshold value and the temperature of the ink in the second heater is equal to or higher than the second threshold value, the switch valve is caused to communicate the internal space of the circulation path with the external recovery tank, the circulation pump is driven for a specific time to discharge the ink in the ink compartment area to the external recovery tank, and then the switch valve is caused to communicate the ink compartment area with an area of ​​the other return pipe, An inkjet printing apparatus, wherein the specific time is obtained by dividing a specific volume calculated based on the volume of ink that can pass through the second heater by the amount of ink delivered per unit time by the circulation pump.

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