Printing device, printing system, and printing method

Abstract

To prevent ink from leaking out from a discharge head when eliminating a pressure differential between a supply tank that supplies ink to the discharge head and a collection tank that collects ink from the discharge head.SOLUTION: A printing device is provided with a buffer tank 98 (a buffer part) communicated with a collection tank 92. In a state where the collection tank 92 and a supply tank 91 are shut off from each other, positive pressure P1 (first pressure) is applied into the supply tank 91 and negative pressure P2 (second pressure) that is lower than the positive pressure P1 is applied into the collection tank 92 and into the buffer tank 98. Once the supply tank 91 is communicated with the collection tank 92, negative pressure P3 (third pressure) that is higher than the negative pressure P2 and lower than the positive pressure P1 is generated in the supply tank 91, in the collection tank 92 and in the buffer tank 98, and the negative pressure P3 prevents ink from leaking out from a nozzle N of a discharge head H against hydraulic head pressure among the collection tank 92 and the supply tank 91 and the nozzle N.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] This invention relates to a technology for printing by ejecting ink from an ejection head, and in particular to a technology for recovering ink supplied to the ejection head from a supply tank in a recovery tank, while sending ink from the recovery tank to the supply tank using a circulation pump, thereby circulating ink to the ejection head. [Background technology]

[0002] The printing device described in Patent Document 1 includes a supply tank and a recovery tank, each connected to the ejection head, and sends ink from the supply tank to the recovery tank via the ejection head by making the pressure in the recovery tank lower than the pressure in the supply tank. Furthermore, this printing device includes a circulation pump that sends ink from the recovery tank to the supply tank. This creates an ink circulation path that returns the ink that has reached the recovery tank from the supply tank via the ejection head to the supply tank.

[0003] This printing device also includes a solenoid valve between the recovery tank and the supply tank. This solenoid valve isolates the recovery tank from the supply tank when power is applied, but connects the recovery tank to the supply tank when power is not applied. With this configuration, if the circulation pump stops due to a power outage or the like, the pressure difference between the recovery tank and the supply tank is eliminated, and the flow of ink from the supply tank to the recovery tank can be stopped. This makes it possible to prevent ink from overflowing from the recovery tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2020-44823 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the printing device described above, as the recovery tank and the supply tank communicate with each other, the negative pressure in the recovery tank increases, and as a result, the negative pressure in the recovery tank becomes insufficient relative to the head pressure between the recovery tank and the ejection head, causing ink to leak from the ejection head.

[0006] This invention has been made in consideration of the above-mentioned problems, and aims to provide technology that makes it possible to prevent ink leakage from the ejection head when the pressure difference between a supply tank that supplies ink to the ejection head and a recovery tank that recovers ink from the ejection head is eliminated. [Means for solving the problem]

[0007] The printing device according to the present invention includes an ejection head which ejects ink from nozzles, a recovery tank which stores ink recovered from the ejection head, a buffer section which communicates with the recovery tank, a supply tank which stores ink to be supplied to the ejection head, a first pressure applying section which applies a first pressure to the inside of the supply tank, a second pressure applying section which applies a second pressure which is a negative pressure lower than the first pressure to the inside of the recovery tank and the buffer section, a circulation pump which performs a liquid transfer operation to transfer ink from the recovery tank to the supply tank by using supplied power, and a circulation pump which is provided between the supply tank and the recovery tank and which increases the pressure of the supply tank when power is applied. the recovery tank is disposed above the ejection head, and the buffer unit communicates with the recovery tank and the supply tank when the bypass solenoid valve is not energized, and generates a third pressure in the recovery tank and the supply tank, which is a negative pressure higher than the second pressure and lower than the first pressure, and the third pressure resists a head pressure between the recovery tank and the supply tank, and the nozzle of the ejection head, to prevent ink leakage from the nozzle.

[0008] The printing method of the present invention includes the steps of applying a first pressure in a supply tank connected to an ejection head that ejects ink from nozzles to perform printing, while applying a second pressure, which is a negative pressure lower than the first pressure, in a recovery tank connected to the ejection head and in a buffer section communicating with the recovery tank, to supply ink from the supply tank to the ejection head and recover ink from the ejection head to the recovery tank; supplying power to a circulation pump provided between the recovery tank and the supply tank to send ink from the recovery tank to the supply tank; and, when the supply of power to the circulation pump is stopped, communicating the recovery tank and supply tank with each other and communicating the buffer section with the recovery tank and supply tank to generate a third pressure, which is a negative pressure higher than the second pressure and lower than the first pressure, in the recovery tank and supply tank, and the third pressure resists head pressure between the recovery tank and supply tank and the nozzle of the ejection head to prevent ink leakage from the nozzle.

[0009] In the present invention (printing device and printing method) configured as described above, a buffer section communicating with the recovery tank is provided. Then, in a state in which the recovery tank and the supply tank are mutually cut off, a first pressure is applied in the supply tank, and a second pressure, which is a negative pressure lower than the first pressure, is applied in the recovery tank and the buffer section. In this configuration, when the supply tank and the recovery tank are communicated with each other, the difference between the first pressure in the supply tank and the second pressure in the recovery tank and the buffer section is eliminated, and the pressure in the recovery tank increases. However, since the buffer section is provided separately from the recovery tank, the increase in pressure in the recovery tank is suppressed compared to a case in which there is no buffer section. Specifically, a third pressure, which is a negative pressure higher than the second pressure and lower than the first pressure, is generated in the recovery tank and the supply tank, and this third pressure prevents ink from leaking from the nozzles against the head pressure between the recovery tank and the supply tank and the nozzles of the ejection head. In this way, it is possible to prevent ink from leaking from the ejection head when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers ink from the ejection head is eliminated.

[0010] The printing device may be configured such that the first pressure applying unit has a first solenoid valve and a first pressure tank connected to the supply tank via the first solenoid valve, and applies a first pressure generated in the first pressure tank to the supply tank via the first solenoid valve, and the first solenoid valve communicates the supply tank with the first pressure tank when energized and isolates the supply tank from the first pressure tank when deenergized, and the second pressure applying unit has a second solenoid valve and a second pressure tank connected to the collection tank via the second solenoid valve, and applies a second pressure generated in the second pressure tank to the collection tank via the second solenoid valve, and the second solenoid valve communicates the collection tank with the second pressure tank when energized and isolates the collection tank from the second pressure tank when deenergized. In this configuration, as the supply tank and the collection tank are communicated, the first and second pressure tanks are isolated from the supply tank, the collection tank, and the buffer unit. Therefore, the third pressure required to prevent leakage of ink from the ejection head can be reliably generated in each of the supply tank, the recovery tank, and the buffer section.

[0011] The printing device may also be configured so that the first pressure is a positive pressure. In other words, in a configuration in which a positive pressure is generated in the supply tank, the problem of ink leakage described above tends to become more pronounced. Therefore, it is particularly suitable to apply the present invention to such a configuration.

[0012] The printing device may also be configured so that the ink is white ink. That is, white ink is often used to print so-called solid images that form backgrounds, etc. When printing such solid images, if the amount of white ink ejected from the ejection head is insufficient, image defects such as streaks appearing in areas where the white ink does not adhere can occur. In response to this, applying positive pressure to the supply tank allows a sufficient amount of white ink to be ejected from the ejection head, making it possible to print a suitable solid image.

[0013] A printing system according to the present invention includes the above-mentioned printing device and a drying device that dries the ink ejected onto a print medium by the printing device. This printing system also makes it possible to prevent ink leakage from the ejection head when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers ink from the ejection head is eliminated. Effect of the Invention

[0014] As described above, according to the present invention, it is possible to prevent ink leakage from the ejection head when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers ink from the ejection head is eliminated. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a front view showing a schematic diagram of an example of a printing system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a front view showing a schematic diagram of a printing device included in the printing system shown in FIG. [Diagram 3] FIG. 2 is a diagram illustrating a schematic configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head. [Figure 4] FIG. 2 is a diagram illustrating a schematic configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] FIG. 1 is a front view showing a schematic example of a printing system according to the present invention. In FIG. 1 and the following figures, a horizontal direction X and a vertical direction Z are appropriately indicated. As shown in FIG. 1, the printing system 1 includes a printing device 3 and a drying device 6 arranged in the horizontal direction X. This printing system 1 transports a long strip-shaped printing medium M from a pay-out roll 11 to a take-up roll 12 in a roll-to-roll manner. The material of the printing medium M is a film such as OPP (oriented polypropylene) or PET (polyethylene terephthalate). However, the material of the printing medium M is not limited to a film, and may be paper or the like. Such a printing medium M is flexible. In the following description, the surface on which an image is printed of both sides of the printing medium M is appropriately referred to as the front surface M1, and the surface opposite to the front surface M1 is appropriately referred to as the back surface M2.

[0017] The printing device 3 prints an image on the surface M1 of the printing medium M by ejecting water-based ink by an inkjet method onto the surface M1 of the printing medium M being transported from the pay-out roll 11 to the take-up roll 12. A detailed configuration of the printing device 3 will be described later. The printing medium M on which the image has been printed in this manner is transported in the horizontal direction X from the printing device 3 towards the drying device 6.

[0018] The drying device 6 includes a drying furnace 60, and dries the printing medium M discharged from the printing device 3 as it is transported from the pay-out roll 11 to the take-up roll 12. The drying furnace 60 includes two upper blowing units 61u arranged in the horizontal direction X, two middle blowing units 61m arranged in the horizontal direction X below the upper blowing units 61u, and two lower blowing units 61l arranged in the horizontal direction X below the middle blowing units 61m.

[0019] The printing medium M discharged from the discharge port 312 of the printing device 3 passes through two upper-stage blowing units 61u in the horizontal direction X, and is then turned back toward the two middle-stage blowing units 61m by a pair of rollers 62. Next, the printing medium M passes through two middle-stage blowing units 61m in the horizontal direction X, and is then turned back toward the two lower-stage blowing units 61l by a pair of air turn bars 63. Furthermore, the printing medium M passes through two lower-stage blowing units 61l in the horizontal direction X, and is then discharged to the outside of the drying device 6.

[0020] The upper blowing unit 61u has two blowing chambers 64 arranged to sandwich the printing medium M passing in the horizontal direction X in the vertical direction Z. Each blowing chamber 64 has a plurality of nozzles 65 arranged in the horizontal direction X, and each nozzle 65 sprays hot air (gas at 60 degrees or higher) onto the printing medium M. In this way, the printing medium M is dried by the hot air sprayed from the nozzles 65 of these blowing chambers 64 while passing between the two blowing chambers 64 arranged above and below. Similarly to the upper blowing unit 61u, each of the middle blowing unit 61m and the lower blowing unit 61l has two blowing chambers 64 that sandwich the printing medium M in the vertical direction Z.

[0021] Incidentally, the specific configuration of the upper blower unit 61u is not limited to this example. For example, instead of the lower blower chamber 64 of the upper and lower blower chambers 64 of the upper blower unit 61u, multiple rollers arranged in the horizontal direction X may be provided. In this configuration, hot air can be sprayed onto the front surface M1 of the printing medium M from the upper blower chamber 64 while the back surface M2 of the printing medium M is supported from below by the multiple rollers.

[0022] Fig. 2 is a front view showing a schematic diagram of a printing device provided in the printing system of Fig. 1. In Fig. 2, one side X1 and the other side X2 of the horizontal direction X are appropriately shown. Here, the one side X1 is the side facing the drying device 6 from the printing device 3, and the other side X2 is the opposite side to the one side X1. The printing device 3 includes a housing 31, a color printing unit 32 arranged in the housing 31, a white printing unit 33 arranged above the color printing unit 32 in the housing 31, and a transport unit 4 that transports the printing medium M by a plurality of rollers arranged in the housing 31.

[0023] The color printing unit 32 has a plurality of (six) ejection heads 321 arranged in the traveling direction of the printing medium M (direction from the other side X2 to the one side X1) above the printing medium M transported by the transport unit 4. The plurality of ejection heads 321 have nozzles facing from above the surface M1 of the printing medium M passing below each of them, and eject color inks of different colors from the nozzles by an inkjet method. Here, color ink means ink other than white, and includes inks such as cyan, magenta, yellow, and black. In this way, the plurality of ejection heads 321 of the color printing unit 32 print a color image on the surface M1 of the printing medium M by ejecting color inks from above onto the surface M1 of the printing medium M passing below each of them.

[0024] The white printing unit 33 also has a single ejection head 331 arranged above the printing medium M transported by the transport unit 4. The ejection head 331 has nozzles facing from above the surface M1 of the printing medium M passing below it, and ejects white ink from the nozzles by an inkjet method. In this way, the ejection head 331 of the white printing unit 33 prints a white image on the surface M1 of the printing medium M by ejecting white ink from above onto the surface M1 of the printing medium M passing below it.

[0025] An inlet 311 opens in a side wall on the other side X2 of the housing 31, while an outlet 312 opens in a side wall on the one side X1 of the housing 31. The transport unit 4 transports the print medium M from the inlet 311 to the outlet 312, passing through the color printing unit 32 and the white printing unit 33.

[0026] The transport section 4 has an entrance section 41 provided below the color printing section 32, an upward transport section 42 provided on one side X1 of the color printing section 32, an upward transport section 43 provided above the color printing section 32, and a downward transport section 44 provided on the other side X2 of the color printing section 32. The entrance section 41 transports the printing medium M carried in from the entrance 311 to the one side X1 by rollers 411, the upward transport section 42 transports the printing medium M transported by the entrance section 41 to the upward side by rollers 421, the upward transport section 43 transports the printing medium M transported by the upward transport section 42 to the other side X2 by rollers 431, and the downward transport section 44 transports the printing medium M transported by the upward transport section 43 to the downward side by rollers 441.

[0027] Furthermore, the transport unit 4 has a color transport unit 45 that supports the printing medium M facing the color printing unit 32 from below, and the printing medium M that has passed through the downward transport unit 44 enters the color transport unit 45. This color transport unit 45 has a plurality of rollers 451 arranged from the other side X2 to the one side X1, and each roller 451 contacts the back surface M2 of the printing medium M from below. In this way, the front surface M1 of the printing medium M supported by the color transport unit 45 faces upward, and each ejection head 321 of the color printing unit 32 ejects color ink while facing this front surface M1 from above.

[0028] The transport unit 4 also has rollers 461, 462, and 463 arranged between the color transport unit 45 and the downward transport unit 44 in the traveling direction of the printing medium M. The roller 461 is a drive roller that drives the printing medium M. The rollers 462 and 463 are driven rollers that rotate following the rotation of the printing medium M.

[0029] Furthermore, the transport unit 4 has a reversing transport unit 47 that turns upside down the printing medium M transported from the color transport unit 45 to the one side X1 twice. The reversing transport unit 47 has a plurality of rollers 471 to 477 including a drive roller 471, and turns upside down the printing medium M twice while these rollers 471 to 477 contact the back side M2 ​​of the printing medium M. That is, the reversing transport unit 47 transports the printing medium M transported from the color transport unit 45 downward by the rollers 471 and 472, and further changes the traveling direction of the printing medium M to the other side X2 by the roller 472 and transports it, thereby turning upside down the front surface M1 and the back surface M2 of the printing medium M. Next, the reversing transport unit 47 transports the printing medium M from the one side X1 to the other side X2 by the plurality of rollers 473, and then transports the printing medium M upward by the rollers 474 to 476. Furthermore, the inversion and transport section 47 changes the direction of travel of the printing medium M to one side X1 using rollers 476, thereby again inverting the front surface M1 and back surface M2 of the printing medium M, and transports the printing medium M from the other side X2 to the one side X1 using rollers 477.

[0030] The transport unit 4 also has a white transport unit 48 that supports the printing medium M facing the white printed unit 33 from below, and the printing medium M that has been turned upside down twice by the reversing transport unit 47 enters the white transport unit 48. This white transport unit 48 has a roller 481 that contacts the back surface M2 of the printing medium M from below. Thus, the front surface M1 of the printing medium M supported by the white transport unit 48 faces upward, and the ejection head 331 of the white printed unit 33 ejects white ink while facing this front surface M1 from above.

[0031] The conveying unit 4 also has an unloading unit 49 provided above the upper conveying unit 43. The unloading unit 49 has a plurality of rollers 491 arranged from the other side X2 to one side X1 in the horizontal direction X. The unloading unit 49 conveys the print medium M conveyed by the white conveying unit 48 to the one side X1 by the plurality of rollers 491, thereby unloading the print medium M from the unloading opening 312 of the housing 31 to the drying device 6.

[0032] As described above, the color printing unit 32 and the white printing unit 33 of the printing device 3 have ejection heads 321, 331. Next, an ink supply mechanism that supplies ink to these ejection heads 321, 331 will be described. The basic configuration of the ink supply mechanism is common to the ejection heads 321, 331. Therefore, the description will focus on the ejection head 331 that ejects white ink. In addition, hereinafter, the ejection heads 321, 331 will be referred to as ejection heads H as appropriate.

[0033] 3 and 4 are diagrams showing the configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head, with FIG. 3 showing the state during power transmission and FIG. 4 showing the state during a power outage. As shown in both figures, the discharge head H has a housing Ha, and a plurality of nozzles N are arranged and open at the bottom of the housing Ha. Inside the housing Ha, a plurality of cavities Hb each communicating with the plurality of nozzles N and an ink supply chamber Hc communicating with the plurality of cavities Hb are provided, and ink supplied from the ink supply chamber Hc is stored in the cavity Hb. Then, a piezoelectric element provided in the cavity Hb pushes ink out of the cavity Hb, so that ink is discharged from the nozzle N communicating with the cavity Hb. Note that the specific method of discharging ink does not have to be a method using a piezoelectric element, and may be a thermal method of heating ink. In addition, an ink inlet Hd and an ink outlet He are opened at the top of the ejection head H, and ink flows from the ink supply mechanism 9 into the ink supply chamber Hc via the ink inlet Hd and flows out from the ink supply chamber Hc to the ink supply mechanism 9 via the ink outlet He.

[0034] The ink supply mechanism 9 includes a supply tank 91 connected to the ink inlet Hd via a pipe 911, and a recovery tank 92 connected to the ink outlet He via a pipe 922, and ink is stored in each of the supply tank 91 and the recovery tank 92. Each of the supply tank 91 and the recovery tank 92 is disposed above the ejection head H. The ink supply mechanism 9 includes a circulation pump 93 disposed in a pipe 932 that connects the flow path between the recovery tank 92 and the supply tank 91, and that sends ink from the recovery tank 92 to the supply tank 91, and a degassing filter 931 disposed in the pipe 932 at a position between the circulation pump 93 and the supply tank 91, and the degassing filter 931 removes gas from the ink before it flows out of the circulation pump 93 and into the supply tank 91.

[0035] The ink supply mechanism 9 has a power supply circuit 94 that supplies power to each component of the device. The circulation pump 93 sends ink from the recovery tank 92 to the supply tank 91 using the power supplied from the power supply circuit 94 (liquid sending operation). As a result, the circulation pump 93 executes an ink circulation operation that circulates ink through a circulation path C that passes from the recovery tank 92 through the supply tank 91 to the ink supply chamber Hc of the ejection head H and then returns to the recovery tank 92.

[0036] The ink supply mechanism 9 also includes a main tank 951 capable of storing a large amount of ink, and a main pump 952 that is disposed in piping 953 that connects the main tank 951 and the recovery tank 92 through a flow path and sends ink from the main tank 951 to the recovery tank 92. When the ink circulating through the circulation path C decreases due to the ejection of ink from the nozzles N, the main pump 952 uses power supplied from a power supply circuit 94 to replenish ink from the main tank 951 to the recovery tank 92.

[0037] Furthermore, the ink supply mechanism 9 includes a supply-side pressure applying unit 96 (hereinafter, appropriately referred to as the "pressure applying unit 96") that applies a positive pressure P1 to the supply tank 91. The pressure applying unit 96 includes a pressure tank 961, a pump 962 that applies a positive pressure P1 inside the pressure tank 961 by supplying gas (air) to the pressure tank 961, and a flexible tube 963 having one end connected to the pressure tank 961. In the pressure applying unit 96, the pump 962 supplies gas to the pressure tank 961 using power supplied from a power supply circuit 94. The positive pressure P1 thus generated in the pressure tank 961 by the pump 962 is applied to the supply tank 91 via the tube 963 and further the piping 934.

[0038] In contrast, gas (air) accumulates above the ink surface inside the supply tank 91. That is, ink is stored below the gas-liquid interface inside the supply tank 91, and gas exists above the gas-liquid interface. Therefore, the pressure applying unit 96 applies a positive pressure P1 to the gas-liquid interface inside the supply tank 91.

[0039] Further, the pressure applying unit 96 includes an electromagnetic valve 964 provided between the other end of the tube 963 and one end of the piping 934. This electromagnetic valve 964 is of a normally closed type. Therefore, during the power transmission shown in FIG. 3, the electromagnetic valve 964 forms a state of communication between the atmosphere of the pressure tank 961 and the supply tank 91 by the power supplied from the power supply circuit 94, and the positive pressure P1 inside the pressure tank 961 is applied to the inside of the supply tank 91 through the tube 963, the electromagnetic valve 964, and the piping 934. On the other hand, during the power outage shown in FIG. 4, the power supply from the power supply circuit 94 to the electromagnetic valve 964 is lost, so that the electromagnetic valve 964 forms a state of blocking the atmosphere between the pressure tank 961 and the supply tank 91, and the application of the positive pressure P1 from the pressure tank 961 to the supply tank 91 is blocked.

[0040] The pressure applying unit 96 has a check filter 965 between the pipe 934 and the solenoid valve 964. This check filter 965 allows the passage of gas from the supply tank 91 to the pressure tank 961, while prohibiting the passage of ink from the supply tank 91 to the pressure tank 961. In this way, the check filter 965 prevents ink from flowing from the supply tank 91 into the tube 963.

[0041] The ink supply mechanism 9 also includes a recovery-side pressure application section 97 (hereinafter, appropriately referred to as the "pressure application section 97") that applies a negative pressure to the recovery tank 92. The pressure application section 97 includes a pressure tank 971, a pump 972 that reduces the pressure inside the pressure tank 971 by sucking gas (air) from the pressure tank 971, and a flexible tube 973 having one end connected to the pressure tank 971. In the pressure application section 97, the pump 972 exhausts gas from the pressure tank 971 using power supplied from a power supply circuit 94. The negative pressure P2 thus generated in the pressure tank 971 by the pump 972 is applied to the recovery tank 92 via the tube 973 and further the piping 944.

[0042] In contrast, gas (air) accumulates above the ink surface in the recovery tank 92. That is, ink is stored below the gas-liquid interface in the recovery tank 92, and gas exists above the gas-liquid interface. Therefore, the pressure applying unit 97 applies a negative pressure P2 to the gas-liquid interface in the recovery tank 92.

[0043] Further, the pressure applying unit 97 includes an electromagnetic valve 974 provided between the other end of the tube 973 and one end of the piping 944. This electromagnetic valve 974 is of a normally closed type. Therefore, during the power transmission shown in FIG. 3, the electromagnetic valve 974 forms a state of communication between the atmospheres of the pressure tank 971 and the collection tank 92 by the power supplied from the power supply circuit 94, and the negative pressure P2 inside the pressure tank 971 is applied to the inside of the collection tank 92 through the tube 973, the electromagnetic valve 974, and the piping 944. On the other hand, during the power outage shown in FIG. 4, the power supply from the power supply circuit 94 to the electromagnetic valve 974 is lost, so that the electromagnetic valve 974 forms a state of blocking the atmosphere between the pressure tank 971 and the collection tank 92, and the application of the negative pressure P2 from the pressure tank 971 to the collection tank 92 is blocked.

[0044] The pressure applying unit 97 has a check filter 975 between the pipe 944 and the solenoid valve 974. This check filter 975 allows the passage of gas from the recovery tank 92 to the pressure tank 971, while prohibiting the passage of ink from the recovery tank 92 to the pressure tank 971. In this way, the check filter 975 prevents ink from flowing from the recovery tank 92 into the tube 973.

[0045] Furthermore, the ink supply mechanism 9 has a buffer tank 98 that communicates with the recovery tank 92 through a pipe 988. This buffer tank 98 communicates with the recovery tank 92 above the gas-liquid interface (i.e., the gas layer). In other words, gas moves between the buffer tank 98 and the recovery tank 92. On the other hand, ink does not move between the buffer tank 98 and the recovery tank 92, and no ink is present in the buffer tank 98. During both the power transmission (FIG. 3) and the power outage (FIG. 4), the buffer tank 98 and the recovery tank 92 are in communication with each other, and the pressure in the buffer tank 98 and the pressure in the recovery tank 92 are always equal.

[0046] That is, during power transmission as shown in Fig. 3, the solenoid valve 974 creates a state of atmospheric communication between the pressure tank 971 and the buffer tank 98 by the power supplied from the power supply circuit 94, and the negative pressure P2 inside the pressure tank 971 is applied to the inside of the buffer tank 98 via the tube 973, the solenoid valve 974, the piping 944, and the piping 988. On the other hand, during a power outage as shown in Fig. 4, the power supply from the power supply circuit 94 to the solenoid valve 974 is lost, so that the solenoid valve 974 creates a state of blocking the atmosphere between the pressure tank 971 and the buffer tank 98, and the application of the negative pressure P2 from the pressure tank 971 to the buffer tank 98 is blocked.

[0047] 3, the pressure P2 inside the recovery tank 92 and the buffer tank 98 is lower than the pressure P1 inside the supply tank 91, which causes the ink to move from the supply tank 91 to the recovery tank 92 via the circulation path C. If this state continues, the liquid level in the supply tank 91 will drop and the liquid level in the recovery tank 92 will rise, and the meniscus required for the nozzle N of the ejection head H will no longer be generated. Therefore, the circulation pump 93 circulates the ink from the recovery tank 92 to the supply tank 91, thereby keeping the liquid levels in the supply tank 91 and the recovery tank 92 constant.

[0048] The ink supply mechanism 9 also includes an electromagnetic valve 99 provided in a pipe 999 that connects the atmosphere between the recovery tank 92 and the supply tank 91 so that the atmosphere between the recovery tank 92 and the supply tank 91 can be communicated with each other. In other words, the electromagnetic valve 99 is provided in parallel with the circulation pump 93 between the recovery tank 92 and the supply tank 91. This electromagnetic valve 99 is of a normally open type. Therefore, during power transmission as shown in FIG. 3, the electromagnetic valve 99 is opened by power supplied from the power supply circuit 94, and the communication state of the atmosphere between the recovery tank 92 and the supply tank 91 via the electromagnetic valve 99 is cut off. On the other hand, during a power outage as shown in FIG. 4, the power supply from the power supply circuit 94 to the electromagnetic valve 99 is lost, so the electromagnetic valve 99 is closed, and the atmosphere between the recovery tank 92 and the supply tank 91 is communicated with each other via the electromagnetic valve 99. As a result, the upper side of the gas-liquid interface in the recovery tank 92 (i.e., the gas layer) and the upper side of the gas-liquid interface in the supply tank 91 (i.e., the gas layer) are communicated with each other.

[0049] Thus, when the solenoid valve 99 communicates the collection tank 92 with the supply tank 91 during a power outage (FIG. 4), the pressure in the collection tank 92 and the pressure in the supply tank 91 become a predetermined negative pressure P3. This negative pressure P3 is higher than the negative pressure P2 and lower than the positive pressure P1. Incidentally, the negative pressure P2 is applied in advance to the buffer tank 98 during power transmission (FIG. 3), and the buffer tank 98 communicates with the collection tank 92 and the supply tank 91 during a power outage (FIG. 4). Due to the function of the buffer tank 98, a certain degree of negative pressure P3 is maintained in the collection tank 92 and the supply tank 91 during a power outage. Meanwhile, as described above, each of the supply tank 91 and the collection tank 92 is disposed above the discharge head H. Therefore, a head pressure according to the difference in height is generated between the gas-liquid interfaces of the collection tank 92 and the supply tank 91 and the nozzle N of the discharge head H. Therefore, the buffer tank 98 is provided with a volume sufficient to generate a negative pressure P3 that maintains the ink against this head pressure.

[0050] The ink supply mechanism 9 according to the present embodiment described above circulates the ink through a circulation path C in which the ink travels from the recovery tank 92 to the supply tank 91 by the circulation pump 93, and the ink travels from the recovery tank 92 to the ejection head H via the supply tank 91, and then returns to the recovery tank 92. In addition, an electromagnetic valve 99 is provided between the supply tank 91 and the recovery tank 92, and this electromagnetic valve 99 isolates the atmospheres between the supply tank 91 and the recovery tank 92 when energized (FIG. 3). Therefore, the electromagnetic valve 99 does not inhibit the generation of a pressure difference (=P2-P1) between the supply tank 91 and the recovery tank 92. On the other hand, this electromagnetic valve 99 communicates the atmospheres between the supply tank 91 and the recovery tank 92 when not energized (FIG. 4). Therefore, when the circulation pump 93 stops due to a power outage, the pressure difference between the supply tank 91 and the recovery tank 92 is quickly eliminated, and the ink can be prevented from flowing into the recovery tank 92 from the supply tank 91 via the ink supply chamber Hc of the ejection head H.

[0051] In particular, a buffer tank 98 (buffer section) that communicates with the atmosphere is provided in the recovery tank 92. In a state in which the atmospheres between the recovery tank 92 and the supply tank 91 are blocked from each other, a positive pressure P1 (first pressure) is applied to the supply tank 91, and a negative pressure P2 (second pressure) that is lower than the positive pressure P1 is applied to the recovery tank 92 and the buffer tank 98. In this configuration, when the atmospheres between the supply tank 91 and the recovery tank 92 are communicated, the difference between the positive pressure P1 in the supply tank 91 and the negative pressure P2 in the recovery tank 92 is eliminated, and the pressure in the recovery tank 92 rises. However, since the buffer tank 98 is provided separately from the recovery tank 92, the increase in pressure in the recovery tank 92 is suppressed compared to when the buffer tank 98 is not provided. Specifically, a negative pressure P3 (third pressure) that is higher than the negative pressure P2 and lower than the positive pressure P1 is generated in the recovery tank 92 and the supply tank 91, and this negative pressure P3 resists the head pressure between the recovery tank 92 and the supply tank 91 and the nozzles N of the ejection head H, thereby preventing ink leakage from the nozzles N. In this way, it is possible to prevent ink leakage from the ejection head H when the pressure difference between the supply tank 91 that supplies ink to the ejection head H and the recovery tank 92 that recovers ink from the ejection head H is eliminated.

[0052] The pressure applying unit 96 (first pressure applying unit) has a solenoid valve 964 (first solenoid valve) and a pressure tank 961 (first pressure tank) that allows the atmosphere to communicate with the supply tank 91 via the solenoid valve 964, and applies a positive pressure P1 generated in the pressure tank 961 to the supply tank 91 via the solenoid valve 964. The solenoid valve 964 allows the atmosphere between the supply tank 91 and the pressure tank 961 to communicate with each other when energized, and blocks the atmosphere between the supply tank 91 and the pressure tank 961 from each other when not energized. The pressure applying unit 97 (second pressure applying unit) has a solenoid valve 974 (second solenoid valve) and a pressure tank 971 (second pressure tank) that allows the atmosphere to communicate with the recovery tank 92 (and the buffer tank 98) via the solenoid valve 974, and applies a negative pressure P2 generated in the pressure tank 971 to the recovery tank 92 and the buffer tank 98 via the solenoid valve 974. The solenoid valve 974 communicates the atmosphere between the recovery tank 92 and the buffer tank 98 and the pressure tank 971 when energized, and blocks the atmosphere between the recovery tank 92 and the buffer tank 98 and the pressure tank 971 when de-energized. In this configuration, as the atmosphere between the supply tank 91 and the recovery tank 92 is communicated during a power outage, the pressure tank 961 and the pressure tank 971 are blocked from the atmosphere between the supply tank 91, the recovery tank 92 and the buffer tank 98. Therefore, the negative pressure P3 required to prevent leakage of ink from the ejection head H can be reliably generated in each of the supply tank 91, the recovery tank 92 and the buffer tank 98.

[0053] 3, a positive pressure P1 is applied to the supply tank 91. In this manner, in a configuration in which the positive pressure P1 is generated in the supply tank 91, the problem of ink leakage described above tends to become more pronounced. Therefore, a configuration in which the buffer tank 98 is provided as described above is particularly suitable.

[0054] Furthermore, in the ink supply mechanism 9 for the ejection head H that ejects white ink, applying a positive pressure P1 to the supply tank 91 has the following advantages. That is, white ink is often used to print so-called solid images that form backgrounds and the like. When printing such solid images, if the amount of white ink ejected from the ejection head H is insufficient, image defects such as streaks appearing in areas where the white ink does not adhere can occur. In response to this, applying a positive pressure P1 inside the supply tank 91 allows a sufficient amount of white ink to be ejected from the ejection head H, making it possible to print a suitable solid image.

[0055] In the embodiment described above, the printing system 1 corresponds to an example of the "printing system" of the present invention, the printing device 3 corresponds to an example of the "printing device" of the present invention, the drying device 6 corresponds to an example of the "drying device" of the present invention, the supply tank 91 corresponds to an example of the "supply tank" of the present invention, the recovery tank 92 corresponds to an example of the "recovery tank" of the present invention, the circulation pump 93 corresponds to an example of the "circulation pump" of the present invention, the power supply circuit 94 corresponds to an example of the "power supply unit" of the present invention, the pressure applying unit 96 corresponds to an example of the "first pressure applying unit" of the present invention, the pressure tank 961 corresponds to an example of the "first pressure tank" of the present invention, and the solenoid valve 964 corresponds to an example of the "first the pressure applying section 97 corresponds to an example of a "second pressure applying section" of the present invention, the pressure tank 971 corresponds to an example of a "second pressure tank" of the present invention, the solenoid valve 974 corresponds to an example of a "second solenoid valve" of the present invention, the buffer tank 98 corresponds to an example of a "buffer section" of the present invention, the solenoid valve 99 corresponds to an example of a "bypass solenoid valve" of the present invention, the discharge head H corresponds to an example of an "discharge head" of the present invention, the nozzle N corresponds to an example of a "nozzle" of the present invention, the positive pressure P1 corresponds to an example of a "first pressure" of the present invention, the negative pressure P2 corresponds to an example of a "second pressure" of the present invention, and the negative pressure P3 corresponds to an example of a "third pressure" of the present invention.

[0056] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the pressure applied from the pressure tank 961 of the pressure applying unit 96 to the supply tank 91 does not need to be a positive pressure, and may be a negative pressure. In particular, in the ink supply mechanism 9 that supplies ink to the ejection head H that ejects color ink, a negative pressure (first pressure) higher than the negative pressure P2 may be applied to the supply tank 91 during power transmission.

[0057] Moreover, during power transmission, a redundant pipe may be provided instead of the buffer tank 98 as a "buffer section" to which the negative pressure P2 is applied in advance.

[0058] Furthermore, it is not necessary for the above-mentioned solenoid valves 974, 964 and 99 to be configured as single valves, but they may be collectively configured as a multi-way valve. [Industrial Applicability]

[0059] The present invention is applicable to the printing technology in general. [Explanation of symbols]

[0060] 1. Printing system 3...Printing device 6...Drying device 91…Supply tank 92…Recovery tank 93…Circulation pump 94...Power supply circuit (power supply section) 96...pressure applying portion (first pressure applying portion) 961…Pressure tank (first pressure tank) 964...Solenoid valve (first solenoid valve) 97...pressure applying portion (second pressure applying portion) 971…Pressure tank (second pressure tank) 974...Solenoid valve (second solenoid valve) 98...Buffer tank (buffer section) 99...Solenoid valve (bypass solenoid valve) H…Discharge head N…Nozzle P1…Positive pressure (first pressure) P2: Negative pressure (second pressure) P3: Negative pressure (third pressure)

Claims

1. an ejection head that ejects ink from a nozzle; a recovery tank that stores ink recovered from the ejection head; A buffer section communicating with the recovery tank; a supply tank that stores ink to be supplied to the ejection head; a first pressure applying unit that applies a first pressure to the inside of the supply tank; a second pressure applying unit that applies a second pressure, which is a negative pressure lower than the first pressure, to the inside of the recovery tank and the inside of the buffer unit; a circulation pump that uses the supplied power to perform a liquid transfer operation for transferring ink from the collection tank to the supply tank; a bypass solenoid valve provided between the supply tank and the recovery tank, for isolating the supply tank and the recovery tank from each other when energized, and for connecting the supply tank and the recovery tank to each other when deenergized; a power supply unit for supplying power to the circulation pump and the bypass solenoid valve; Equipped with The recovery tank is disposed above the ejection head, A printing device in which the buffer unit is connected to the recovery tank and the supply tank when the bypass solenoid valve is not energized, and generates a third pressure in the recovery tank and the supply tank, which is a negative pressure higher than the second pressure and lower than the first pressure, and the third pressure resists the head pressure between the recovery tank and the supply tank and the nozzle of the ejection head to prevent ink leakage from the nozzle.

2. the first pressure applying unit has a first solenoid valve and a first pressure tank connected to the supply tank via the first solenoid valve, and applies the first pressure generated in the first pressure tank to the supply tank via the first solenoid valve; the first solenoid valve, when energized, connects the supply tank and the first pressure tank, and, when deenergized, isolates the supply tank and the first pressure tank from each other; the second pressure applying unit has a second solenoid valve and a second pressure tank connected to the recovery tank via the second solenoid valve, and applies the second pressure generated in the second pressure tank to the recovery tank via the second solenoid valve; 2. The printing apparatus according to claim 1, wherein the second solenoid valve connects the collection tank and the second pressure tank when energized, and isolates the collection tank and the second pressure tank from each other when deenergized.

3. 3. The printing apparatus according to claim 1, wherein the first pressure is a positive pressure.

4. 4. The printing apparatus according to claim 3, wherein the ink is a white ink.

5. A printing device according to any one of claims 1 to 4, a drying device that dries the ink ejected onto the printing medium by the printing device; A printing system comprising:

6. a step of applying a first pressure to a supply tank connected to a discharge head that discharges ink from nozzles to perform printing, while applying a second pressure, which is a negative pressure lower than the first pressure, to a recovery tank connected to the discharge head and to a buffer section communicating with the recovery tank, thereby supplying ink from the supply tank to the discharge head and recovering ink from the discharge head to the recovery tank; supplying power to a circulation pump disposed between the recovery tank and the supply tank to send ink from the recovery tank to the supply tank; when the supply of power to the circulation pump is stopped, the recovery tank and the supply tank are communicated with each other, and the buffer unit is communicated with the recovery tank and the supply tank to generate a third pressure in the recovery tank and the supply tank, the third pressure being a negative pressure higher than the second pressure and lower than the first pressure, and the third pressure acts against a head pressure between the recovery tank and the supply tank and the nozzle of the ejection head to prevent ink from leaking from the nozzle; A printing method comprising:

Images