Printing device

Abstract

To provide a printing device that cyclically heats ink and yet has a flow passage that bypasses a printing head, which can shorten a length of the flow passage and increase flow volumes to heat up ink in a short time.SOLUTION: In a printing device according to the present invention, a supply tank is communicated with one end of a manifold space of a supply-side manifold part and second bypass piping is communicated with the other end of the space, and supply piping through which the supply-side manifold part is connected to a printing head is communicated with a space between both ends. Further, a recovery tank is communicated with one end of a manifold space of a collection-side manifold part and first bypass piping is communicated with the other end, and recovery piping through which the printing head is connected to the recovery-side manifold part is communicated with a space between both ends.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a printing device that prints by ejecting ink from a print head, and more particularly to an ink circulation system that heats the ink to an appropriate temperature for printing. [Background technology]

[0002] Printing devices that print by ejecting ink from a print head sometimes employ an ink circulation system in which ink is circulated while being supplied to the print head, in order to prevent the nozzles that eject the ink from drying out, etc. In this type of technology, a bypass flow path that does not pass through the print head is sometimes provided in order to circulate ink while temporarily stopping the supply of ink to the print head.

[0003] For example, in the technology described in Patent Document 1, an ink circulation flow path passes through a supply-side pressure adjustment tank, a supply-side manifold, a print head, a recovery-side manifold, and a recovery-side tank in that order, but a bypass flow path that does not pass through the print head is configured by connecting the supply-side manifold and the recovery-side manifold. Furthermore, in the technology described in Patent Document 2, for example, three-way valves provided before and after the print head switch between a flow path that passes through the print head and a bypass flow path that does not. Furthermore, in the technology described in Patent Document 3, for example, a bypass flow path is provided that short-circuits the supply-side tank and the recovery-side tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-144611 [Patent Document 2] Japanese Patent Application Publication No. 2024-035849 [Patent Document 3] Japanese Patent Application Publication No. 2023-139837 Summary of the Invention [Problem to be solved by the invention]

[0005] In an inkjet printing device having an ink circulation channel that circulates ink, increasing the ink flow rate in the circulation channel and shortening the channel length are effective ways of raising the ink temperature to the required level in a short period of time. However, all of the above-mentioned conventional technologies focus solely on bypassing the print head, and do not incorporate any proactive measures to increase the flow rate in the bypass channel or shorten its length. In this sense, the above-mentioned conventional technologies leave room for improvement.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a printing device that circulates and heats ink and has a flow path that bypasses the print head, thereby shortening the flow path length and increasing the flow rate, thereby constructing a bypass flow path that can heat the ink in a short period of time. [Means for solving the problem]

[0007] A printing device according to the present invention includes a print head that ejects ink, a supply tank that stores the ink to be supplied to the print head, a supply-side manifold unit having a manifold space that communicates with the internal space of the supply tank, a supply pipe that transfers the ink from the manifold space to the print head, a supply-side valve inserted in the supply pipe, a recovery tank that stores the ink recovered from the print head, a recovery-side manifold unit having a manifold space that communicates with the internal space of the recovery tank, a recovery pipe that transfers the ink from the print head to the manifold space of the recovery-side manifold unit, a recovery valve inserted in the recovery pipe, and a valve that transfers the ink from the recovery tank to the supply tank. a return pipe for returning ink, a heater inserted in the return pipe for heating the ink, a temperature detection unit for detecting the temperature of the ink flowing through the return pipe, a first bypass pipe for transferring the ink from the supply tank to the manifold space of the recovery manifold unit, a first bypass valve inserted in the first bypass pipe, a second bypass pipe for transferring the ink from the manifold space of the supply manifold unit to the recovery tank, a second bypass valve inserted in the second bypass pipe, and a control unit for controlling the supply-side valve, the recovery-side valve, the heater, the first bypass valve, and the second bypass valve based on the detection result of the temperature detection unit.

[0008] Here, the supply tank is connected to one end of the manifold space of the supply side manifold section, and the second bypass pipe is connected to the other end, with the supply pipe connecting between them, and the recovery tank is connected to one end of the manifold space of the recovery side manifold section, and the first bypass pipe is connected to the other end, with the recovery pipe connecting between them.

[0009] Another aspect of the printing device according to the present invention includes a print head that ejects ink, a supply tank that stores the ink to be supplied to the print head, a supply-side manifold unit having a supply-side manifold space that communicates with the internal space of the supply tank, a supply pipe that transfers the ink from the manifold space to the print head, a supply-side valve inserted in the supply pipe, a recovery tank that stores the ink recovered from the print head, a recovery-side manifold unit having a recovery-side manifold space that communicates with the internal space of the recovery tank, a recovery pipe that transfers the ink from the print head to the manifold space of the recovery-side manifold unit, a recovery-side valve inserted in the recovery pipe, and a valve that connects the recovery pipe to the recovery manifold space. the ink supply system includes a return pipe for returning the ink from a tank to the supply tank, a heater inserted in the return pipe for heating the ink, a temperature detection unit for detecting the temperature of the ink flowing through the return pipe, a first bypass pipe for transferring the ink from the supply tank to the recovery manifold space, a first bypass valve inserted in the first bypass pipe, a second bypass pipe for transferring the ink from the supply manifold space to the recovery tank, a second bypass valve inserted in the second bypass pipe, and a control unit for controlling the supply valve, the recovery valve, the heater, the first bypass valve, and the second bypass valve based on the detection result of the temperature detection unit.

[0010] Here, the first bypass piping forms a bypass flow path that transports the ink from the supply tank to the recovery side manifold space without passing through the print head, while the second bypass piping forms a bypass flow path that transports the ink from the supply side manifold space to the recovery tank without passing through the print head.

[0011] In the invention configured in this way, a circulation flow path is formed for ink that is delivered from the supply tank, passes through the supply manifold, the print head, the recovery manifold, and the recovery tank, and returns to the supply tank. Here, when the control unit closes the supply valve and the recovery valve and opens the first bypass valve and the second bypass valve, a bypass flow path that does not pass through the print head is formed.

[0012] More specifically, when the first bypass valve is opened, a bypass flow path is formed from the supply tank through the first bypass pipe and the recovery manifold to the recovery tank. At this time, the first bypass pipe bypasses the print head and the supply manifold. On the other hand, when the second bypass valve is opened, a bypass flow path is formed from the supply manifold to the recovery tank through the second bypass pipe. At this time, the second bypass pipe bypasses the print head and the recovery manifold.

[0013] Therefore, two bypass flow paths are formed between the supply tank and the recovery tank: a first bypass flow path that passes through the first bypass pipe and the recovery manifold, and a second bypass flow path that passes through the supply manifold and the second bypass pipe. These flow paths are parallel to each other. This allows for a higher flow rate than when a flow path is provided that simply bypasses the print head. For example, if the diameter of the pipes that make up the flow path is the same, the flow path cross-sectional area is doubled, which is expected to increase the flow rate.

[0014] The first bypass flow path bypasses not only the print head but also the supply-side manifold. Similarly, the second bypass flow path bypasses not only the print head but also the recovery-side manifold. This allows the flow path length to be shorter than a flow path that simply bypasses the print head, i.e., a flow path that passes through both the supply-side manifold and the recovery-side manifold.

[0015] In this way, the ink flow path formed in the present invention to bypass the print head can have a higher flow rate and a shorter flow path length than a flow path that goes through the print head, making it possible to circulate a large amount of ink while heating it, thereby reducing the time required to heat the ink to a temperature suitable for printing compared to conventional methods.

[0016] However, if the objective is simply to increase the cross-sectional area of ​​the flow path and shorten the flow path length, it is possible to install a bypass pipe that bypasses the supply tank and the recovery tank. However, in this case, ink will accumulate in the manifold spaces of the supply manifold and the recovery manifold. Such ink cannot be heated and may aggregate due to a drop in temperature.

[0017] In the present invention, a flow path that bypasses the supply-side manifold but passes through the recovery-side manifold, and a flow path that bypasses the recovery-side manifold but passes through the supply-side manifold are provided in parallel, so that the flow path length can be shortened while ink circulation can be achieved in both manifolds.

[0018] In particular, when the second bypass pipe is configured to communicate with the manifold space at a position as close as possible to the end of the supply-side manifold section opposite the end that communicates with the supply-side tank, the flow of ink in the supply-side manifold section is the same regardless of whether or not a bypass is provided for the print head. Similarly, when the first bypass pipe is configured to communicate with the manifold space at a position as close as possible to the end of the recovery-side manifold section opposite the end that communicates with the recovery tank, the flow of ink in the recovery-side manifold section is the same regardless of whether or not a bypass is provided for the print head. This prevents the flow of ink in the manifold space from changing when switching between the presence and absence of a bypass, making it possible to maintain smooth circulation. [Effects of the Invention]

[0019] As described above, according to the present invention, a bypass flow path that bypasses the supply manifold and print head, and a bypass flow path that bypasses the print head and recovery manifold are formed in parallel between the supply tank and the recovery tank. This increases the ink flow rate in the bypass flow path and shortens the flow path length, making it possible to quickly raise the temperature of ink circulated via these bypass flow paths. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing the configuration of an inkjet printing apparatus according to this embodiment. [Figure 2] FIG. 2 is a diagram conceptually showing the configuration of an ink supply unit and a head unit. [Figure 3] FIG. 2 is a perspective view showing a part of a head unit and an ink supply unit. [Figure 4] FIG. 2 is a block diagram showing the electrical configuration of the inkjet printing device. [Figure 5] FIG. 4 is a diagram showing the temperature dependency of ink viscosity. [Figure 6] FIG. 2 is a diagram schematically illustrating a piping system related to ink circulation. [Figure 7] 10 is a flowchart illustrating an example of an ink circulation process. [Figure 8] FIG. 10 is a diagram showing the flow of ink in a first circulation mode. [Figure 9] FIG. 10 is a diagram showing the flow of ink in a second circulation mode. [Figure 10] FIG. 1 is a more generalized schematic diagram of an ink circulation flow path. [Figure 11] FIG. 10 is a diagram showing a first modified example. [Figure 12] FIG. 10 is a diagram showing another modified example. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the components described in the embodiment are merely examples and are not intended to limit the scope of the present invention. In the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary to facilitate understanding.

[0022] FIG. 1 shows the configuration of an inkjet printing apparatus according to this embodiment. The inkjet printing apparatus 1 is an inkjet printer that conveys a long strip of continuous paper 10 while ejecting droplets of water-based ink from multiple head units 35 toward the continuous paper 10, thereby recording characters and images on the surface of the continuous paper 10. The continuous paper 10 is an example of a printing medium. The printing medium may be cut paper, or a substrate made of plastic film, cardboard, metal foil, or glass. In the inkjet printing apparatus 1, the head units 35 eject ink such as water-based ink. However, the ink ejected by the head units 35 may also be oil-based ink, UV ink, or the like.

[0023] As shown in FIG. 1, the inkjet printing apparatus 1 includes an unwinding roller 11, a take-up roller 12, a conveying unit 2, a printing unit 3, and a control unit 9.

[0024] The unwinding roller 11 holds the continuous paper 10 wound in a roll. The unwinding roller 11 unwinds the continuous paper 10 by rotating, and supplies the continuous paper 10 to the transport section 2. The take-up roller 12 takes up the continuous paper 10 in a roll. In the inkjet printing device 1, the unwinding roller 11 and the take-up roller 12 transport the continuous paper 10 roll-to-roll.

[0025] The transport unit 2 transports the continuous paper 10 supplied from the unwind roller 11 to the take-up roller 12. The transport unit 2 has a drive roller 21, a nip roller 23, and multiple transport rollers 25. The drive roller 21 is connected to a motor (not shown) and is actively rotated by the motor's power. The nip roller 23, together with the drive roller 21, pinches the continuous paper 10. The nip roller 23 presses against the drive roller 21 via the continuous paper 10, thereby generating a grip force that allows the drive roller 21 to transport the continuous paper 10. The multiple transport rollers 25 rotate passively. Note that at least some of the multiple transport rollers 25 may be configured to be actively rotatable.

[0026] The printing section 3 has four head units 35 and four ink supply sections 4. The four head units 35 have the same structure as one another, and the four ink supply sections 4 have the same structure as one another.

[0027] The four head units 35 are arranged at intervals from one another in the transport direction. Each of the four head units 35 ejects ink droplets from a nozzle 83 (FIG. 2) toward the surface of the continuous paper 10. The four head units 35 eject ink of different colors (for example, cyan, magenta, yellow, and black) to record a single-color image on the surface of the continuous paper 10. A multi-color image is formed on the top surface of the continuous paper 10 by superimposing the four single-color images.

[0028] FIG. 2 is a diagram conceptually illustrating the configuration of one ink supply unit and one head unit. In this embodiment, each head unit 35 has multiple ejection heads 80. In this example, each head unit 35 has five ejection heads 80. The multiple ejection heads 80 have the same structure. In FIG. 2, only one ejection head 80 is illustrated in detail, and the remaining four ejection heads 80 are illustrated in a simplified manner. As shown in FIG. 2, the ejection head 80 has a housing 81, an internal tank 82, and multiple nozzles 83.

[0029] The housing 81 forms the outer frame of the ejection head 80. The internal tank 82 is disposed inside the housing 81 and is capable of temporarily storing ink. A plurality of 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. The plurality of nozzles 83 each communicate with the internal tank 82. Each nozzle 83 has a piezoelectric element 831, an ink chamber 832, and an ejection port 830. The piezoelectric element 831 is a pressure generating element. The ink chamber 832 communicates with the internal tank 82.

[0030] The ink in the internal tank 82 flows down into the ink chamber 832. Then, the ink in the ink chamber 832 is pressurized by the piezoelectric element 831, causing ink droplets to be ejected from the ejection port 830. The ink ejection method may be a so-called thermal method, in which a heater is used as a pressure generating element.

[0031] The ink supply unit 4 is a device that circulates ink by supplying ink to the head unit 35 and collecting ink that has not been ejected from the head unit 35. The four ink supply units 4 have the same structure.

[0032] 2, the ink supply unit 4 includes a supply tank 51, a recovery tank 52, a refill tank 53, a supply manifold 61, a plurality (five in this embodiment) of supply branch pipes 62, a plurality (five in this embodiment) of recovery branch pipes 63, a recovery manifold 64, a connection pipe 65, a refill pipe 66, a circulation pump 71, a refill pump 72, a backflow prevention on-off valve 73, a heater 74, a first filter 75, a second filter 76, and a degassing unit 77. In Fig. 2, the supply manifold 61 and the recovery manifold 64 are indicated by thick lines to distinguish them from the other pipes.

[0033] The supply tank 51 is a container for temporarily storing ink to be supplied to the head unit 35. The supply tank 51 has an internal chamber. The internal chamber is capable of temporarily storing ink.

[0034] Fig. 3 is a perspective view showing a part of the head unit and the ink supply section. A supply-side manifold 61 and five supply-side branch pipes 62 connect the supply tank 51 to five ejection heads 80 of one head unit 35. Note that Fig. 3 shows only one of the five ejection heads 80 of the head unit 35, only one of the five supply-side branch pipes 62 connected to the supply-side manifold 61, and only one of the five recovery-side branch pipes 63 connected to the recovery-side manifold 64.

[0035] As shown in Figures 2 and 3, the upstream end of the supply-side manifold 61 is connected to the internal chamber of the supply tank 51. Five supply-side branch pipes 62 branch off from the supply-side manifold 61. The supply-side manifold 61 is a pipe that is thicker than the supply-side branch pipes 62. The upstream end of each supply-side branch pipe 62 is connected to the internal passage of the supply-side manifold 61. The downstream end of each supply-side branch pipe 62 is connected to the internal tank 82 of one of the ejection heads 80. As will be described later, a solenoid valve 621 is inserted in the supply-side branch pipe 62. A filter may also be provided.

[0036] The five recovery side branch pipes 63 and the recovery side manifold 64 connect the five ejection heads 80 of one head unit 35 to the recovery tank 52. As shown in FIGS. 2 and 3 , the five recovery side branch pipes 63 are thin tubes branching off from the recovery side manifold 64. The upstream end of each recovery side branch pipe 63 is connected to an internal tank 82 of one ejection head 80. The downstream end of each recovery side branch pipe 63 is connected to an internal passage of the recovery side manifold 64. The downstream end of the recovery side manifold 64 is connected to an internal chamber of the recovery tank 52. The recovery side manifold 64 is a thicker pipe than the recovery side branch pipe 63. As will be described later, a solenoid valve 631 is inserted in the recovery side branch pipe 63. A filter may also be provided.

[0037] The recovery tank 52 temporarily stores the ink recovered from the head unit 35. The recovery tank 52 has an internal chamber for storing the ink.

[0038] 3, the supply-side manifold 61 extends horizontally directly from the lower side of the supply tank 51, i.e., without piping, and their internal spaces are connected to each other. On the other hand, the recovery-side manifold 64 extends horizontally directly from the lower side of the recovery tank 52, and their internal spaces are connected to each other.

[0039] The extension direction D1 in which the supply-side manifold 61 extends from the supply tank 51 and the extension direction D2 in which the recovery-side manifold 64 extends from the recovery tank 52 are parallel to each other and are opposite directions. Furthermore, in the horizontal direction perpendicular to the extension directions D1 and D2, i.e., the direction perpendicular to the paper surface, the supply-side manifold 61 and the recovery-side manifold 64 are disposed close to each other. In the vertical direction, the supply-side manifold 61 and the recovery-side manifold 64 can be at the same height. In other words, the supply-side manifold 61 and the recovery-side manifold 64 are disposed at a fixed distance in the horizontal direction.

[0040] 2, the ink supply unit 4 has a pressure difference generating unit 55. The pressure difference generating unit 55 is connected to the supply tank 51 and the recovery tank 52. The pressure difference generating unit 55 generates a pressure difference between the internal chambers of the supply tank 51 and the recovery tank 52 by adjusting the pressure (internal pressure) in the internal chamber of the supply tank 51 and the pressure (internal pressure) in the internal chamber of the recovery tank 52.

[0041] Specifically, pressure difference generating unit 55 has pressurizing unit 551 and depressurizing unit 553. Pressurizing unit 551 and depressurizing unit 553 are controlled by control unit 9. Pressurizing unit 551 makes the internal pressure of supply tank 51 a positive pressure higher than atmospheric pressure by, for example, supplying gas to the internal chamber of supply tank 51. Depressurizing unit 553 makes the internal pressure of recovery tank 52 a negative pressure lower than atmospheric pressure by, for example, sucking gas from the internal chamber of recovery tank 52.

[0042] Due to the pressure difference formed by the pressure difference forming unit 55, ink stored in the supply tank 51 is sent to the internal tank 82 of each ejection head 80 via the supply-side manifold 61 and each supply-side branch pipe 62. Furthermore, due to the pressure difference formed by the pressure difference forming unit 55, ink not ejected from each ejection head 80 is sent to the recovery tank 52 via each recovery-side branch pipe 63 and recovery-side manifold 64.

[0043] The connection pipe 65 connects the internal chamber of the supply tank 51 and the internal chamber of the recovery tank 52 so that they can communicate with each other. As shown in Fig. 2, the upstream end of the connection pipe 65 is connected to the internal chamber of the recovery tank 52. The downstream end of the connection pipe 65 is connected to the internal chamber of the supply tank 51. A circulation pump 71, a backflow prevention on-off valve 73, a heater 74, a second filter 76, and a degassing unit 77 are attached to the connection pipe 65. The refill pipe 66 is connected to a connection point 655 in the connection pipe 65 between the backflow prevention on-off valve 73 and the heater 74.

[0044] The circulation pump 71 performs a liquid transfer operation to transfer ink from the recovery tank 52 to the supply tank 51. The circulation pump 71 generates a flow of ink from the recovery tank 52 to the supply tank 51 in the internal passage of the connection pipe 65. The circulation pump 71 is preferably a diaphragm pump that is less likely to generate foreign matter such as dust when it is driven. The flow rate of the circulation pump 71 is changed in multiple stages by a control signal output by the control unit 9. The flow rate of the circulation pump 71 is changed in at least three stages: zero (second circulation flow rate), a basic circulation flow rate greater than zero, and a high circulation flow rate (first circulation flow rate) greater than the basic circulation flow rate.

[0045] The backflow prevention on-off valve 73 is located in the connecting pipe 65 downstream of the circulation pump 71 and upstream of the connection point 655. When the backflow prevention on-off valve 73 closes, the connecting pipe 65 is shut off. In other words, when the backflow prevention on-off valve 73 is closed, the backflow of ink from the connection point 655 toward the circulation pump 71 is prevented. When the backflow prevention on-off valve 73 opens, the connecting pipe 65 is opened.

[0046] The heater 74 heats the ink passing through the connection pipe 65. The heater 74 is located in the connection pipe 65 between the connection point 655 and the supply tank 51. The heater 74 has a temperature sensor 741. The temperature sensor 741 measures the temperature of the ink flowing into the heater 74. The temperature sensor 741 may also measure the temperature of the ink that has passed through the heater 74. The heater 74 is electrically connected to the control unit 9. The heater 74 outputs data indicating the temperature measured by the temperature sensor 741 to the control unit 9. The control unit 9 controls the heater 74 based on the temperature measured by the temperature sensor 741.

[0047] The second filter 76 is located in the connection pipe 65 between the connection point 655 and the supply tank 51. The second filter 76 filters the ink flowing through the connection pipe 65 to remove foreign matter contained in the ink. The filtration diameter of the second filter 76 (the size of the holes in the second filter 76) is, for example, 4 to 6 μm.

[0048] The degassing unit 77 is located in the connection pipe 65 between the connection point 655 and the supply tank 51. The degassing unit 77 in this embodiment is, for example, a hollow fiber membrane degassing module. The degassing unit 77 removes air bubbles from the ink flowing inside the connection pipe 65.

[0049] The refill tank 53 stores the ink to be refilled into the supply tank 51. The refill tank 53 has an internal chamber capable of storing ink. The refill tank 53 is located outside the circulation flow path of the ink that circulates between the supply tank 51 and the recovery tank 52.

[0050] The replenishment pipe 66 connects the internal chamber of the replenishment tank 53 and the connection pipe 65 so that they can communicate with each other. As shown in FIG. 2 , the replenishment pipe 66 is connected to the internal chamber of the replenishment tank 53 at its upstream end. The replenishment pipe 66 is also connected to the connection pipe 65 at a connection point 655 at its downstream end. The connection point 655 is located on the connection pipe 65 between the circulation pump 71 and the supply tank 51. The connection point 655 is located on the connection pipe 65 between the check valve 73 and the supply tank 51. The replenishment pipe 66 is also equipped with a replenishment pump 72 and a first filter 75.

[0051] The refill pump 72 performs a liquid transfer operation to transfer ink from the refill tank 53 to the connecting pipe 65. The refill pump 72 is, for example, a diaphragm pump. The flow rate of the refill pump 72 is changed in multiple stages by a control signal output by the control unit 9. Hereinafter, the flow rate of the refill pump 72 will be referred to as the "refill flow rate." The refill flow rate is changed in at least three stages: a basic refill flow rate which is zero; a high refill flow rate (first refill flow rate) which is greater than the basic refill flow rate; and a low refill flow rate (second refill flow rate) which is greater than the basic refill flow rate and less than the high refill flow rate.

[0052] The first filter 75 is located in the refill pipe 66 between the refill pump 72 and the connection point 655. The first filter 75 filters the ink flowing through the refill pipe 66 to remove foreign matter contained in the ink. The filtration diameter of the first filter 75 (the size of the holes in the first filter 75) is, for example, approximately 10 to 30 μm. That is, the filtration diameter of the first filter 75 is equal to or larger than the filtration diameter of the second filter 76. However, the filtration diameter of the first filter 75 may be smaller than the filtration diameter of the second filter 76.

[0053] A first bypass pipe 67 is provided to connect the supply tank 51 and the recovery side manifold 64. A solenoid valve 671 is inserted in the first bypass pipe 67. Meanwhile, a second bypass pipe 68 is provided to connect the supply side manifold 61 and the recovery tank 52. A solenoid valve 681 is inserted in the second bypass pipe 68. The functions of these will be described later.

[0054] The control unit 9 is an information processing device for controlling each part of the inkjet printing device 1. As shown in Fig. 1, 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 program 931 for executing a process for executing a printing process while transporting the continuous paper 10, and a process for supplying ink to the head unit 35. The storage unit 93 also stores print data 933 that indicates an image to be printed on the continuous paper 10.

[0055] Figure 4 is a block diagram showing the electrical configuration of this inkjet printing device. As shown in Figure 4, the control unit 9 is communicatively connected to the transport unit 2, each head unit 35, the valves (backflow prevention valve 73) of each ink supply unit 4, the pumps (circulation pump 71, replenishment pump 72), the heater 74, sensors such as a temperature sensor 741, and the pressure difference generating unit 55. The control unit 9 controls the operation of each of these units in accordance with a program 931. As a result, the transport and printing process of the continuous paper 10 progress, and ink is supplied to the internal tank 82 of each ejection head 80.

[0056] In the inkjet printing device 1 configured as described above, ink supplied from the ink supply unit 4 to the ejection head 80 is ejected from the nozzles 83 to print on the continuous paper 10, which is the print medium. As will be explained below, the viscosity of the ink is temperature-dependent, and the ink needs to be heated to maintain a viscosity suitable for printing.

[0057] FIG. 5 is a diagram showing the temperature dependence of the ink viscosity. As shown in FIG. 5, the ink used in the inkjet printing apparatus 1 has a general property that its viscosity V decreases as the temperature T rises. In an inkjet printing apparatus that ejects ink droplets by utilizing the fluidity of the ink, it is required that the value of the viscosity of the ink supplied to the ejection head 80 falls within a range suitable for printing (herein referred to as the "printing appropriate viscosity range"). As shown in FIG. 5, if the range of "V3 < V < V2" is taken as the printing appropriate viscosity range, the range of the temperature T of the ink suitable for printing (herein referred to as the "printing appropriate temperature range") is represented by "T3 < T < T2".

[0058] In the ink supply unit 4, the temperature of the ink is maintained within the appropriate range by heating with the heater 74 while circulating the low-temperature ink. However, the supply-side branch pipe 62 and the recovery-side branch pipe 63 that are directly connected to the ejection head 80 among the ink flow paths are particularly thin pipes and may be constituted by, for example, resin tubes. Therefore, they are not suitable for pumping high-viscosity ink, and ink aggregation may occur in the pipes, or the tubes may be damaged or detached. Also, since the ink flow rate is small, it takes a long time to circulate the ink.

[0059] Thus, the circulation of the ink via the ejection head 80 is not preferable because there is a risk of damaging the apparatus and it takes a long time to raise the temperature of the ink. Therefore, in this embodiment, as is also done in the prior art, a circulation flow path that bypasses the ejection head 80 is formed to perform ink circulation.

[0060] FIG. 6 is a diagram showing a schematic diagram of a piping system involved in ink circulation. More specifically, FIG. 4 is a diagram showing selected components of the ink flow path shown in FIGS. 2 and 3 that are involved in ink circulation. In FIG. 6, the supply tank 51, supply-side manifold 61, recovery tank 52, and recovery-side manifold 64 correspond to a cross-sectional view of their horizontal cross sections viewed from above. Note that, in this diagram, the supply-side manifold 61 and the recovery-side manifold 64 are shown separated vertically in order to show the piping around the ejection head 80. However, as mentioned above, in an actual device, these are arranged adjacent to each other in the horizontal direction.

[0061] 6, the internal spaces of the supply tank 51 and the supply-side manifold 61 communicate directly with each other without piping, and the internal space of the supply-side manifold 61 extends toward the right in the drawing. That is, the internal space of the supply-side manifold 61 communicates with the supply tank 51 at its left end. Also, the internal spaces of the recovery tank 52 and the recovery-side manifold 64 communicate directly with each other without piping, and the internal space of the recovery-side manifold 64 extends toward the left in the drawing. That is, the internal space of the recovery-side manifold 64 communicates with the recovery tank 52 at its right end.

[0062] The supply tank 51 and the left end of the recovery side manifold 64 in the drawing, i.e., the end opposite the recovery tank 52, are connected by a first bypass pipe 67 having an electromagnetic valve 671 inserted therein. The right end of the supply side manifold 61 in the drawing, i.e., the end opposite the supply tank 51, are connected to the recovery tank 52 by a second bypass pipe 68 having an electromagnetic valve 681 inserted therein.

[0063] Both the first bypass pipe 67 and the second bypass pipe 68 have the function of bypassing the ejection head 80 from the ink flow path that normally passes through the ejection head 80. In other words, by using the first bypass pipe 67 and the second bypass pipe 68, it is possible to form a circulation flow path (hereinafter referred to as a "bypass flow path") that does not pass through the ejection head 80.

[0064] The first bypass pipe 67 and the second bypass pipe 68 are provided to form a bypass flow path, and therefore their flow path cross-sectional area can be determined arbitrarily. To ensure a sufficient ink flow rate in the bypass flow path, it is desirable to increase the flow path cross-sectional area. This makes it possible to raise the ink temperature to the optimum temperature range for printing in a short period of time.

[0065] Furthermore, in an actual device, the supply-side manifold 61 and the recovery-side manifold 64 are disposed close to each other, so it is possible to extremely shorten the lengths of the first bypass pipe 67 and the second bypass pipe 68. This allows the flow path length of the bypass pipe to be shortened, further shortening the time required to heat the ink to the temperature range appropriate for printing.

[0066] 7 is a flowchart showing an example of ink circulation processing. This processing is realized by the processor 91 of the control unit 9 executing a program 931 stored in advance in the storage unit 93 to cause each unit of the device to perform a predetermined operation. In this processing, the operation differs depending on the temperature of the ink detected by the temperature sensor 741.

[0067] That is, when the ink temperature T detected by the temperature sensor 741 is lower than the first temperature T1, that is, when it is in the first temperature range shown in FIG. 5 (YES in step S100), the ink is in a high-viscosity state in which the viscosity V is higher than the value V3 corresponding to the first temperature T1. Therefore, the ink is not suitable for circulating through the ejection head 80. Therefore, a bypass flow path is formed (step S101), and with the heater 74 turned on (step S102), the circulation pump 71 is operated to circulate the ink (step S103). Here, this operation is referred to as the "first circulation mode."

[0068] Figure 8 is a diagram showing the flow of ink in the first circulation mode. In Figure 8 and Figure 9 described below, solenoid valves that are filled in black represent those in the closed state. Other solenoid valves that are white represent those in the open state. As shown in Figure 8, in the first circulation mode, solenoid valve 671 on the first bypass pipe 67 and solenoid valve 681 on the second bypass pipe 68 are opened, while solenoid valve 621 on the supply-side branch pipe 62 connected to the ejection head 80 and solenoid valve 631 on the recovery-side branch pipe 63 are closed.

[0069] Solid arrows indicate the flow of ink. Considering the supply tank 51 as the starting point, the ink in the supply tank 51 flows through two bypass paths: one that runs from the first bypass pipe 67 to the recovery tank 52 via the recovery manifold 64, and the other that runs from the supply manifold 61 to the recovery tank 52 via the second bypass pipe 68, before flowing into the recovery tank 52. The ink flowing out of the recovery tank 52 is sent to the heater 74 by the connecting pipe 65 and the circulation pump 71 inserted in the connecting pipe 65.

[0070] At this time, the heater 74 is on, so the ink is heated and returns to the supply tank 51 via the connection pipe 65. By circulating the ink while heating it in this way, the temperature of the ink can be raised. Because there is no need to circulate low-temperature ink through the ejection head 80 and a circulation flow path with a high flow rate and a short flow path length can be formed, it is possible to raise the temperature of the ink from an initial ink temperature that is lower than the first temperature T1 to a temperature equal to or higher than the first temperature T1 in a short period of time.

[0071] On the other hand, if the ink temperature T exceeds the first temperature T1 (NO in step S100) but does not exceed the second temperature T2 (YES in step S110), that is, if the ink temperature T is in the second temperature range shown in FIG. 5, a circulation flow path (referred to as the "head-via-flow path" in FIG. 7) that passes through the ejection head 80 is formed (step S111). Then, with the heater 74 turned on (step S112), the circulation pump 71 is operated to circulate the ink (step S103). This operation is referred to as the "second circulation mode."

[0072] 9 is a diagram showing the flow of ink in the second circulation mode. In the second circulation mode, the solenoid valve 671 on the first bypass pipe 67 and the solenoid valve 681 on the second bypass pipe 68 are opened, and instead the solenoid valve 621 on the supply branch pipe 62 connected to the ejection head 80 and the solenoid valve 631 on the recovery branch pipe 63 are opened. As a result, the ink flows from the supply manifold 61 through each ejection head 80 into the recovery manifold 64, and then returns from the recovery tank 52 to the supply tank 51. At this time, the heater 74 is turned on, so the ink is further heated.

[0073] When the second circulation mode is executed, the ink temperature T exceeds the first temperature T1, and the ink viscosity V is below the value V1. In this way, the ink viscosity V decreases due to heating, and circulation via the ejection head 80 begins to function. This also increases the temperature of the ink in the supply-side branch pipe 62 and the recovery-side branch pipe 63 connected to the ejection head 80.

[0074] When the ink temperature T reaches the second temperature, which is the lower limit of the optimum temperature range for printing (NO in step S110), the ink has reached a temperature T and viscosity V suitable for printing. As in the second circulation mode, the solenoid valve 671 on the first bypass pipe 67 and the solenoid valve 681 on the second bypass pipe 68 are opened, and the solenoid valve 621 on the supply-side branch pipe 62 connected to the ejection head 80 and the solenoid valve 631 on the recovery-side branch pipe 63 are opened, forming a head-passing flow path (step S121). Because the ink temperature T has reached the optimum temperature range for printing, the heater 74 is turned off (step S122). This operation is referred to as the "third circulation mode."

[0075] The third circulation mode is a variation of the second circulation mode described above, in which the heater 74 is turned off, and the open / close states of each solenoid valve are the same. Therefore, the ink flow is the same as that shown in Figure 9. Because the ink has reached the optimum temperature range for printing, the ink is circulated via the ejection head 80 and ejected from the nozzles 83 as needed, allowing for printing with good image quality.

[0076] Because the heater 74 is turned off, the temperature rise is suppressed and the ink is prevented from overheating. If the ink temperature T subsequently falls below the second temperature T2, the printer switches back to the second circulation mode and the heater is turned on, suppressing the temperature drop and, as a result, maintaining the ink temperature T within the optimum temperature range for printing. In this way, the ink can be circulated while the ink temperature T is maintained within the optimum temperature range for printing.

[0077] The above operation is repeated until the printing process is completed (step S104), thereby maintaining the ink temperature T within the optimum temperature range for printing during the printing process. This also prevents low-temperature, highly viscous ink from flowing into the ejection head 80.

[0078] 8 and 9, the flow of ink from the supply tank 51 through the supply-side manifold 61 is the same in the first circulation mode shown in Fig. 8 and the second and third circulation modes shown in Fig. 9. In other words, the flow of ink in the supply-side manifold 61 is always to the right in the figure, regardless of whether the ink passes through the ejection head 80. Similarly, the flow of ink from the recovery-side manifold 64 to the recovery tank 52 is always to the right, regardless of whether the ink passes through the ejection head 80.

[0079] If the ink flow differs between when it circulates via the ejection head 80 and when it circulates via the bypass flow path, turbulence such as eddies will occur in the ink flow when switching between these two states. Such turbulence will cause ink to accumulate in the piping and not participate in circulation, slowing down the temperature rise of the ink throughout the entire piping system.

[0080] For example, if we only consider the speed of circulation, it would be advantageous to form a bypass flow path that directly bypasses the supply tank to the recovery tank. However, doing so would cause the ink in the manifold to deviate from the circulation flow path, resulting in ink stagnation in this area. It is also possible to form a bypass flow path that connects the supply manifold to the recovery manifold in order to bypass only the ejection head 80. In this case, ink stagnation in the manifold would not occur. However, because the two manifolds are connected in series, the overall flow path length of the circulation flow path becomes longer, and it takes longer for the ink to heat up to the optimum temperature range for printing.

[0081] In contrast to this, the bypass flow path in this embodiment consists of two systems, one from the supply tank 51 bypassing the supply-side manifold 61 and the discharge head 80 to the recovery tank 52, and the other from the supply tank 51 bypassing the discharge head 80 and the recovery-side manifold 64 to the recovery tank 52, which are in a parallel relationship. Also, due to the relative positions of the supply tank 51, supply-side manifold 61, recovery-side manifold 64, and recovery tank 52 shown in Figure 3, the first bypass pipe 67 and the second bypass pipe 68 can be configured to be extremely short.

[0082] For example, if the supply side manifold 61 and the recovery side manifold 64 are arranged at the same position in the vertical direction, the first bypass piping 67 and the second bypass piping 68 can also be constructed using horizontal piping with a simple structure.

[0083] Furthermore, in the manifold spaces inside the supply manifold 61 and the recovery manifold 64, ink flows in from one end and flows out from the other end, so ink does not stagnate in the manifold spaces.

[0084] In this way, this embodiment realizes a structure in which a bypass flow path with a short flow path length is connected in parallel, allowing the ink to circulate in the piping system at a high flow rate, and the ink temperature can be raised to the optimum temperature range for printing in a short period of time.

[0085] 3, the ink supply unit 4 of this embodiment is configured such that the supply tank 51 and the supply-side manifold 61 are directly connected, and the recovery tank 52 and the recovery-side manifold 64 are directly connected, and further, the extension direction D1 of the supply-side manifold 61 from the supply tank 51 and the extension direction D2 of the recovery-side manifold 64 from the recovery tank 52 are parallel to but opposite to each other, thereby maximizing the effects of the present invention. However, as will be explained next, the present invention is also effective when the ink supply unit does not have such a structure.

[0086] Figure 10 is a more generalized schematic diagram of the ink circulation flow path. The circulation flow path in the present invention can be illustrated in a generalized manner as shown in Figure 10(a). Note that the ejection head 80 and the pipes 62 and 63 connected thereto are the same as those shown in Figure 6, so a description of these parts will be omitted.

[0087] 10(a), the supply tank 51 and one end (the left end in the figure) of the supply-side manifold 61 are connected, while the other end (the right end in the figure) of the supply-side manifold 61 is connected to the recovery tank 52 by a second bypass pipe 68. Furthermore, one end (the right end in the figure) of the recovery-side manifold 64 is connected to the recovery tank 52, and the other end (the left end in the figure) is connected to the supply tank 51 by a first bypass pipe 67. A heater 74 having a temperature sensor 741 is inserted in the connection pipe 65, which serves as a return pipe from the recovery tank 52 to the supply tank 51. This structure is the same as in the above-described embodiment.

[0088] 10(b), two bypass flow paths are formed that connect the supply tank 51 and the recovery tank 52 and do not pass through the ejection head 80: one that passes through the supply-side manifold 61 but not through the recovery-side manifold 64, and the other that passes through the recovery-side manifold 64 without passing through the supply-side manifold 61, and these are in a parallel relationship. As shown in FIG. 10(a), the ink flows in the same direction in the supply-side manifold 61 and the recovery-side manifold 64, regardless of whether the ink passes through the ejection head 80 or the bypass flow path.

[0089] Therefore, the effects of the above-described embodiment, i.e., the effect of shortening the circulation time by forming bypass flow paths with high flow rates and short flow path lengths in parallel, and the effect of preventing ink retention by keeping the ink flow direction constant within the manifold and allowing ink to flow from one end of the manifold space to the other, can be obtained regardless of the relative positions of the tank and the manifold. Among these, the structure of the above-described embodiment can be said to be the most excellent in that it allows the first and second bypass pipes to be extremely short.

[0090] However, certain effects can also be obtained by the following modified examples: In the following modified examples, components having the same structure and function as those in the above embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0091] 11 is a diagram showing a first modified example. In this modified example, a first bypass pipe 67a corresponding to the first bypass pipe 67 in the above embodiment is connected to a position approximately midway in the longitudinal direction of the recovery side manifold 64. Similarly, a second bypass pipe 68a corresponding to the second bypass pipe 68 in the above embodiment is connected to a position approximately midway in the longitudinal direction of the supply side manifold 61. In FIG. 11 and the following figures, solid arrows indicate the flow direction of ink during bypass.

[0092] Even with this configuration, the manifold space can be used to form parallel bypass flow paths with high flow rates and short flow path lengths, thereby reducing the time required for ink circulation. In terms of the effect of promoting ink circulation in the manifold space, it is best to connect the bypass flow paths to the ends of the manifold space, as in the above embodiment. However, if the ink flow when the bypass flow path is formed passes through at least a portion of the manifold space, it is possible to improve ink retention in the manifold space.

[0093] The connection position of the bypass pipe to the manifold space is based on the following considerations. To prevent ink from accumulating by flowing in the manifold space when forming a bypass flow path, it is preferable to allow ink to flow over as wide a range as possible within the manifold space. Therefore, it is preferable to connect the first bypass pipe 67a to the recovery manifold 64 as far upstream as possible in the ink flow direction (to the right in FIG. 11), that is, as far away as possible from the recovery tank 52.

[0094] In this sense, it is ideal to connect the first bypass pipe 67a to the upstream end of the recovery side manifold 64, as in the above embodiment. However, in terms of generating some kind of ink flow in the manifold space, it is possible to connect the first bypass pipe 67a to any position on the recovery side manifold 64. According to the knowledge of the inventors of the present application, a sufficient retention suppression effect can be achieved by connecting the first bypass pipe 67a upstream of the midpoint between both ends of the manifold space.

[0095] In particular, when at least one recovery branch pipe 63 is connected to the manifold space upstream of the intermediate position, even when a bypass flow path is formed, ink can flow up to the connection position of the recovery branch pipe 63. This effect is effective for the recovery branch pipe 63 connected to the manifold space upstream of the connection position of the first bypass pipe 67a.

[0096] The same can be said for the second bypass pipe 68a. That is, it is preferable that the second bypass pipe 68a be connected to the supply-side manifold 61 as downstream as possible in the ink flow direction (to the right in FIG. 11), that is, at a position as far away as possible from the supply tank 51. The second bypass pipe 68a can be connected to any position on the supply-side manifold 61, but it is more preferable that it be connected downstream of the midpoint between both ends of the manifold space. If the supply-side branch pipe 62 is connected to the manifold space upstream of the midpoint, ink can flow up to the connection position of the supply-side branch pipe 62 even when a bypass flow path is formed. This effect is effective for the supply-side branch pipe 62 connected to the manifold space upstream of the connection position of the second bypass pipe 68a.

[0097] Figure 12 shows another modified example. In a second modified example shown in Figure 12(a), a first bypass pipe 67b is connected to one recovery branch pipe 63 downstream of the solenoid valve 631. Therefore, when a bypass flow path is formed via the first bypass pipe 67b, ink flows from the first bypass pipe 67b through the recovery branch pipe 63 to the manifold space of the recovery manifold 64. In this case, it is desirable that the recovery branch pipe 63 downstream of the junction with the first bypass pipe 67b has a sufficiently large pipe diameter so as to be able to handle a large ink flow rate during bypass.

[0098] Here, the first bypass pipe 67b is connected to one of the multiple recovery side branch pipes 63 that is connected to the recovery side manifold 64 on the most upstream side in the ink flow direction. Therefore, an ink flow effect is obtained substantially throughout the entire manifold space. However, the pipe to which the first bypass pipe 67b is connected is not limited to this, and it may be any of the multiple recovery side branch pipes 63. Furthermore, the first bypass pipe 67b may be branched and connected to two or more recovery side branch pipes 63. Similarly, the second bypass pipe 68b is connected to at least one of the supply side branch pipes 62 upstream of the solenoid valve 621.

[0099] 12(b), the first bypass pipe 67c is connected to a three-way valve 632 inserted in the recovery branch pipe 63. Similarly, the second bypass pipe 68c is connected to a three-way valve 622 inserted in the supply branch pipe 62. In this configuration, the control unit 9 controls the three-way valves 622 and 632 to switch between the ink flow path via the ejection head 80 and the ink flow path via the first bypass pipe 67c and the second bypass pipe 68c (i.e., the bypass flow path). In this case, too, it is arbitrary to which or how many recovery branch pipes 63 the first bypass pipe 67c is connected to and which or how many supply branch pipes 62 the second bypass pipe 68c is connected to.

[0100] As described above, in the printing device 1 of the above embodiment, the ejection head 80, the supply tank 51, the recovery tank 52, the heater 74, the first bypass pipe 67 (67a, 67b, 67c), the second bypass pipe 68 (68a, 68b, 68c) and the control unit 9 function as the "print head," "supply tank," "recovery tank," "heater," "first bypass pipe," "second bypass pipe," and "control unit" of the present invention, respectively.

[0101] Furthermore, the supply-side branch pipe 62 corresponds to the "supply pipe" of the present invention, and the solenoid valve 621 corresponds to the "supply-side valve" of the present invention. Furthermore, the recovery-side branch pipe 63 corresponds to the "recovery pipe" of the present invention, and the solenoid valve 631 corresponds to the "recovery-side valve" of the present invention. Furthermore, the supply-side manifold 61 corresponds to the "supply-side manifold portion" of the present invention, and the recovery-side manifold 64 corresponds to the "recovery-side manifold portion" of the present invention, and the internal space of each corresponds to the "manifold space" of the present invention.

[0102] Furthermore, solenoid valve 671 corresponds to the "first bypass valve" of the present invention, and solenoid valve 681 corresponds to the "second bypass valve" of the present invention. Furthermore, connection pipe 65 corresponds to the "reflux pipe" of the present invention. Furthermore, temperature sensor 741 functions as the "temperature detection unit" of the present invention.

[0103] Furthermore, the first circulation mode in the above embodiment corresponds to the "first circulation mode" of the present invention, while the second circulation mode and the third circulation mode in the above embodiment both correspond to the "second circulation mode" of the present invention. That is, the "second circulation mode" of the present invention does not limit the on / off of the heater. The second circulation mode of the present embodiment corresponds to the "second circulation mode" of the present invention that involves heater heating, and the third circulation mode corresponds to the "second circulation mode" of the present invention that does not involve heater heating.

[0104] In the above embodiment, the extension direction D1 of the supply-side manifold 61 corresponds to the "first direction" of the present invention, and the extension direction D2 of the recovery-side manifold 64 corresponds to the "second direction" of the present invention. The horizontal direction perpendicular to these directions corresponds to the "third direction" of the present invention. The optimum temperature range for printing in the above embodiment corresponds to the "optimum temperature range" of the present invention.

[0105] The present invention is not limited to the above-described embodiment, and various modifications other than those described above are possible without departing from the spirit of the present invention. For example, in the above-described embodiment, the temperature sensor 741 is integrated with the heater 74, but these may be configured separately and inserted into the return pipes. Furthermore, multiple sets of heaters and temperature sensors may be connected in series.

[0106] Furthermore, for example, in the above embodiment, a mode in which ink is circulated using only the bypass flow path without passing through the ejection head 80, and a mode in which ink is circulated using the ejection head 80 without using the bypass flow path, may be selectively executed. Alternatively or in addition to this, a circulation mode in which ink is diverted between the flow path passing through the ejection head 80 and the bypass flow path may be provided.

[0107] Furthermore, although each solenoid valve in the above embodiment functions as an on-off valve that switches the flow of ink on and off, at least some of them may also have a flow rate control function.

[0108] As described above with reference to specific embodiments, in the printing device according to the present invention, for example, the internal space of the supply tank and the manifold space of the supply-side manifold may be directly connected without piping, and the internal space of the recovery tank and the manifold space of the recovery-side manifold may be directly connected without piping. With this configuration, the cross-sectional areas of the flow paths from the supply tank to the supply-side manifold and the flow paths from the recovery-side manifold to the recovery tank can be increased and the flow paths can be reduced in length, allowing the temperature of the ink to be raised to a temperature range suitable for printing in a short period of time.

[0109] In this case, the manifold space of the supply-side manifold section may be configured to extend horizontally from the supply tank in a first direction, while the manifold space of the recovery-side manifold section may be configured to extend horizontally from the recovery tank in a second direction opposite to the first direction. With this configuration, it is possible to significantly shorten the flow path lengths of the bypass flow paths formed between the supply tank and the recovery-side manifold section and between the recovery tank and the supply-side manifold section.

[0110] For example, the supply-side manifold section and the recovery-side manifold section may be arranged horizontally and side by side in a third direction perpendicular to the first direction. With this configuration, the first bypass pipe and the second bypass pipe can be configured as simple horizontal pipes.

[0111] Alternatively, for example, multiple print heads may be provided, with multiple supply pipes and multiple recovery pipes provided corresponding to each print head. With this configuration, printing can be performed efficiently using multiple print heads.

[0112] Alternatively, for example, a higher pressure may be applied to the ink in the supply tank than to the ink in the recovery tank, and with this configuration, the pressure difference between the two can cause ink to flow from the supply tank to the recovery tank.

[0113] In addition, for example, in a printing device according to the present invention, the control unit may be configured to execute a first circulation mode in which the supply-side valve and the recovery-side valve are closed while the first and second bypass valves are opened to circulate ink without passing through the print head, and a second circulation mode in which the supply-side valve and the recovery-side valve are opened while the first and second bypass valves are closed to circulate ink via the print head. With this configuration, it is possible to switch between circulation via the print head and circulation without passing through the print head as needed.

[0114] In this case, for example, when the ink temperature detected by the temperature detection unit is lower than a first temperature that is lower than the appropriate temperature range for printing, the control unit can execute the first circulation mode while heating the ink with the heater. Furthermore, when the ink temperature exceeds the first temperature, the control unit can execute the second circulation mode while heating the ink with the heater. This configuration prevents low-temperature, high-viscosity ink from flowing to the print head, while allowing ink whose temperature has risen and its viscosity to decrease to circulate through the print head. As a result, the temperature of the print head and the ink in the piping connected to it can also be efficiently raised.

[0115] Furthermore, the control unit may be configured to stop heating by the heater and execute the second circulation mode when the ink temperature reaches the appropriate temperature range, thereby preventing the ink from overheating.

[0116] In a second aspect of the printing device according to the present invention, a supply tank may be connected to one end of the supply manifold space, the second bypass pipe may be connected to the supply manifold space at a position closer to the other end than the midpoint between the one end and the opposite end of the supply manifold space, and a recovery tank may be connected to one end of the recovery manifold space, and the first bypass pipe may be connected to the recovery manifold space at a position closer to the other end than the midpoint between the one end and the opposite end of the recovery manifold space. This configuration also provides the effect of generating a flow of ink within the manifold space when the bypass flow path is formed.

[0117] In this case, it is preferable that at least one supply pipe communicates between one end of the supply-side manifold space and the intermediate position, and at least one recovery pipe communicates between one end of the recovery-side manifold space and the intermediate position. With this configuration, the supply pipe or recovery pipe is connected to a position in the manifold space where ink flows even during bypass, and can contribute to the effect of ink circulation during bypass.

[0118] For example, the first bypass pipe may be connected to the recovery pipe downstream of the recovery valve in the ink flow direction in the recovery pipe, and the second bypass pipe may be connected to the supply pipe upstream of the supply valve in the ink flow direction in the supply pipe. With this configuration, it is possible to circulate ink by using parts of the recovery pipe and the supply pipe as bypass flow paths. [Industrial Applicability]

[0119] The present invention can be applied to printing devices in general that perform printing using ink, and is particularly suitable for printing devices that circulate ink in order to heat the ink in advance. [Explanation of symbols]

[0120] 1 Printing device 9 Control Unit 51 Supply Tank 52 Recovery Tank 61 Supply side manifold (supply side manifold part) 62 Supply side branch piping (supply piping) 63 Recovery branch piping (recovery piping) 64 Recovery side manifold (recovery side manifold part) 65 Connection piping (return piping) 67, 67a, 67b, 67c First bypass piping 68, 68a, 68b, 68c Second bypass piping 74 Heater 80 Discharge head (print head) 621 Solenoid valve (supply side valve) 631 Solenoid valve (recovery side valve) 671 Solenoid valve (first bypass valve) 681 Solenoid valve (second bypass valve) 741 Temperature sensor (temperature detection part) D1 1st direction D2 2nd direction

Claims

1. a print head that ejects ink; a supply tank that stores the ink to be supplied to the print head; a supply-side manifold portion having a manifold space communicating with the internal space of the supply tank; a supply pipe for conveying the ink from the manifold space to the print head; a supply-side valve inserted in the supply pipe; a recovery tank that stores the ink recovered from the print head; a recovery side manifold portion having a manifold space communicating with the internal space of the recovery tank; a recovery pipe that conveys the ink from the print head to the manifold space of the recovery manifold portion; a recovery side valve inserted in the recovery pipe; a return pipe for returning the ink from the recovery tank to the supply tank; a heater inserted in the reflux pipe for heating the ink; a temperature detection unit that detects the temperature of the ink flowing through the return pipe; a first bypass pipe that transfers the ink from the supply tank to the manifold space of the recovery side manifold portion; a first bypass valve inserted in the first bypass pipe; a second bypass pipe that transfers the ink from the manifold space of the supply-side manifold portion to the recovery tank; a second bypass valve inserted in the second bypass pipe; a control unit that controls the supply-side valve, the recovery-side valve, the heater, the first bypass valve, and the second bypass valve based on the detection result of the temperature detection unit; Equipped with one end of the manifold space of the supply-side manifold portion communicates with the supply tank, and the other end of the manifold space communicates with the second bypass pipe, and the supply pipe communicates therebetween; The printing device, wherein the recovery tank communicates with one end of the manifold space of the recovery side manifold portion, the first bypass pipe communicates with the other end, and the recovery pipe communicates between them.

2. a print head that ejects ink; a supply tank that stores the ink to be supplied to the print head; a supply-side manifold portion having a supply-side manifold space communicating with the internal space of the supply tank; a supply pipe for conveying the ink from the manifold space to the print head; a supply-side valve inserted in the supply pipe; a recovery tank that stores the ink recovered from the print head; a recovery side manifold portion having a recovery side manifold space communicating with the internal space of the recovery tank; a recovery pipe that conveys the ink from the print head to the manifold space of the recovery manifold portion; a recovery side valve inserted in the recovery pipe; a return pipe for returning the ink from the recovery tank to the supply tank; a heater inserted in the reflux pipe for heating the ink; a temperature detection unit that detects the temperature of the ink flowing through the return pipe; a first bypass pipe that transfers the ink from the supply tank to the recovery manifold space; a first bypass valve inserted in the first bypass pipe; a second bypass pipe that transfers the ink from the supply manifold space to the recovery tank; a second bypass valve inserted in the second bypass pipe; a control unit that controls the supply-side valve, the recovery-side valve, the heater, the first bypass valve, and the second bypass valve based on the detection result of the temperature detection unit; Equipped with a first bypass pipe that forms a bypass flow path for transporting the ink from the supply tank to the recovery manifold space without passing through the print head, and a second bypass pipe that forms a bypass flow path for transporting the ink from the supply manifold space to the recovery tank without passing through the print head.

3. the supply tank is in communication with one end of the supply-side manifold space, and the second bypass pipe is in communication with the supply-side manifold space at a position closer to the other end than a midpoint between the one end and the other end of the supply-side manifold space, 3. The printing device according to claim 2, wherein the recovery tank is connected to one end of the recovery side manifold space, and the first bypass pipe is connected to the recovery side manifold space at a position closer to the other end than a midpoint between the one end and the other end of the recovery side manifold space on the opposite side.

4. At least one of the supply pipes communicates between the one end of the supply manifold space and the intermediate position, The printing apparatus according to claim 3 , wherein at least one recovery pipe communicates between the one end of the recovery manifold space and the intermediate position.

5. the first bypass pipe is connected to the recovery pipe downstream of the recovery side valve in a flow direction of the ink in the recovery pipe, 5. The printing apparatus according to claim 2, wherein the second bypass pipe is connected to the supply pipe upstream of the supply-side valve in the direction of flow of the ink in the supply pipe.

6. the internal space of the supply tank and the manifold space of the supply-side manifold portion are directly connected without piping, The printing apparatus according to claim 1 or 2, wherein the internal space of the recovery tank and the manifold space of the recovery manifold portion are directly connected without using piping.

7. 7. The printing device according to claim 6, wherein the manifold space of the supply-side manifold section extends from the supply tank in a horizontal first direction, while the manifold space of the recovery-side manifold section extends from the recovery tank in a horizontal second direction opposite to the first direction.

8. The printing apparatus according to claim 7 , wherein the supply-side manifold section and the recovery-side manifold section are arranged horizontally and side by side in a third direction perpendicular to the first direction.

9. 3. The printing apparatus according to claim 1, further comprising a plurality of the print heads, and a plurality of the supply pipes and a plurality of the recovery pipes are provided corresponding to each of the print heads.

10. 3. The printing device according to claim 1, wherein a higher pressure is applied to the ink in the supply tank than to the ink in the recovery tank.

11. The control unit a first circulation mode in which the supply side valve and the recovery side valve are closed, while the first bypass valve and the second bypass valve are opened, thereby circulating the ink without passing through the print head; a second circulation mode in which the supply-side valve and the recovery-side valve are opened, while the first bypass valve and the second bypass valve are closed, to circulate the ink via the print head; and 5. The printing device according to claim 1, wherein the printing device executes the following steps.

12. The control unit When the temperature of the ink detected by the temperature detection unit is lower than a first temperature that is lower than an appropriate temperature range suitable for printing, the first circulation mode is executed while heating is performed by the heater; The printing apparatus according to claim 11 , wherein when the temperature of the ink exceeds the first temperature, the second circulation mode is executed while heating is performed by the heater.

13. The printing device according to claim 12 , wherein the control unit stops heating by the heater and executes the second circulation mode when the temperature of the ink reaches the appropriate temperature range.

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