JP2022140284A - Printing device, printing system and printing method - Google Patents

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

The present invention relates to a technique of printing by ejecting ink from an ejection head, and more particularly, by collecting ink supplied from a supply tank to an ejection head in a recovery tank and sending the ink from the recovery tank to the supply tank by a circulation pump. , relates to a technique for cyclically supplying ink to an ejection head.

The printing apparatus described in Patent Document 1 includes a supply tank and a recovery tank that are connected to the ejection head, respectively. Ink is sent to the recovery tank via Additionally, the printing apparatus includes a circulation pump that delivers ink from the collection tank to the supply tank. As a result, an ink circulation path for returning the ink that has reached the collection tank from the supply tank via the ejection head to the supply tank is generated.

This printing apparatus also has an electromagnetic valve between the recovery tank and the supply tank. This electromagnetic valve shuts off the recovery tank and the supply tank when energized, and communicates the recovery tank and the supply tank when not energized. With such a configuration, when the circulation pump stops due to a power failure 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. As a result, the ink can be prevented from overflowing from the collection tank.

Japanese Patent Application Laid-Open No. 2020-44823

By the way, in the above printing apparatus, the negative pressure in the collection tank increases as the collection tank and the supply tank are communicated with each other. As a result, the negative pressure in the collection tank may be insufficient with respect to the head pressure between the collection tank and the ejection head, causing ink to leak from the ejection head.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is intended to prevent ink leakage from an 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. The purpose is to provide a technology that enables prevention.

A printing apparatus according to the present invention includes an ejection head that ejects ink from nozzles, a recovery tank that stores ink recovered from the ejection head, a buffer section that communicates with the recovery tank, and a supply that stores ink to be supplied to the ejection head. a tank, a first pressure applying section that applies a first pressure to the inside of the supply tank, a second pressure applying section that applies a second pressure that is a negative pressure lower than the first pressure to the inside of the recovery tank and the buffer section, and the recovery tank A circulation pump is provided between the supply tank and the recovery tank, and the supply tank and the recovery tank are cut off from each other when energized. , a bypass solenoid valve that communicates the supply tank and the recovery tank when not energized, and a power supply section that supplies power to the circulation pump and the bypass solenoid valve. When the bypass solenoid valve is not energized, it communicates with the recovery tank and the 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 the supply tank. prevents ink from leaking from the nozzles against the head pressure between the collection and supply tanks and the nozzles of the ejection head.

In a printing method according to the present invention, while applying a first pressure to a supply tank connected to an ejection head that executes printing by ejecting ink from nozzles, applying a second pressure, which is a negative pressure lower than the first pressure, to the communicating buffer portion 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; At the same time, the buffer unit communicates with the recovery tank and the 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 the supply tank, and the third pressure is recovered. preventing ink from leaking out of the nozzle against the head pressure between the tank and the supply tank and the nozzle of the ejection head.

In the present invention (printing apparatus and printing method) configured as described above, a buffer section communicating with the collection tank is provided. When the recovery tank and the supply tank are shut off from each other, the first pressure is applied to the supply tank, and the second pressure, which is a negative pressure lower than the first pressure, is applied to the recovery tank and the buffer section. be done. In such a 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 rises. do. However, since the buffer section is provided separately from the recovery tank, the range of pressure increase in the recovery tank is suppressed compared to the case where 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 is applied to the recovery tank, the supply tank, and the ejection head. To prevent ink from leaking from a nozzle against the head pressure between the nozzle. 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.

Further, the first pressure application 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 first pressure tank. The first solenoid valve communicates the supply tank and the first pressure tank when energized, and shuts off the supply tank and the first pressure tank when not energized. The pressure application 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 via the second solenoid valve. The second solenoid valve communicates the recovery tank and the second pressure tank when energized, and isolates the recovery tank and the second pressure tank from each other when the second solenoid valve is not energized. You may In such a configuration, the first and second pressure tanks are cut off from the supply tank, the recovery tank, and the buffer section as the supply tank and the recovery tank are communicated with each other. Therefore, the third pressure necessary for preventing leakage of ink from the ejection head can be reliably generated in each of the supply tank, the recovery tank, and the buffer section.

Also, the printing apparatus may be configured such that the first pressure is a positive pressure. In other words, the above-described problem of ink leakage tends to become prominent in the configuration in which positive pressure is generated in the supply tank. Therefore, it is particularly suitable to apply the present invention to such a configuration.

Also, the printing apparatus may be configured so that the ink is white ink. In other words, white ink is often used for printing a so-called solid image that constitutes a background or the like. When printing such a solid image, if the amount of white ink ejected from the ejection head is insufficient, an image defect such as streaky areas where white ink does not adhere may occur. On the other hand, by applying a positive pressure to the inside of the supply tank, a sufficient amount of white ink can be ejected from the ejection head, and a suitable solid image can be printed.

A printing system according to the present invention includes the printing device described above and a drying device that dries ink ejected onto a printing medium by the printing device. In such a printing system as well, 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 the ink from the ejection head is eliminated. .

As described above, according to the present invention, leakage of ink from the ejection head is prevented when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers the ink from the ejection head is eliminated. becomes possible.

1 is a front view schematically showing an example of a printing system according to the present invention; FIG. FIG. 2 is a front view schematically showing a printing device included in the printing system of FIG. 1; FIG. 2 is a diagram schematically showing the configuration of an ejection head and an ink supply mechanism that supplies ink to the ejection head; FIG. 2 is a diagram schematically showing the configuration of an ejection head and an ink supply mechanism that supplies ink to the ejection head;

FIG. 1 is a front view schematically showing an example of a printing system according to the invention. In FIG. 1 and the following figures, the horizontal direction X and the vertical direction Z are indicated where appropriate. As shown in FIG. 1, the printing system 1 comprises a printing device 3 and a drying device 6 arranged in the horizontal direction X. As shown in FIG. This printing system 1 transports a long band-shaped print medium M from a delivery roll 11 to a take-up roll 12 in a roll-to-roll manner. The material of the print medium M is a film such as OPP (oriented polypropylene) or PET (polyethylene terephthalate). However, the material of the print medium M is not limited to film, and may be paper or the like. Such a print medium M has flexibility. Further, hereinafter, of the two surfaces of the printing medium M, the surface on which an image is printed is referred to as a surface M1, and the surface opposite to the surface M1 is referred to as a back surface M2.

The printing device 3 prints an image on the surface M1 of the printing medium M by ejecting water-based ink onto the surface M1 of the printing medium M transported from the delivery roll 11 to the take-up roll 12 by an inkjet method. A detailed configuration of the printing device 3 will be described later. The print medium M on which the image is printed in this way is transported in the horizontal direction X from the printing device 3 toward the drying device 6 .

The drying device 6 includes a drying oven 60 and dries the print medium M transported from the printing device 3 as it is transported from the supply roll 11 to the take-up roll 12 . Inside the drying furnace 60, there are 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 middle blowing units 61m arranged in the horizontal direction X below the upper blowing units 61u. Two lower blower units 61l arranged in the horizontal direction X below the blower unit 61m are provided.

The print medium M ejected from the ejection port 312 of the printing device 3 passes through the two upper blower units 61u in the horizontal direction X, and then is folded back toward the two middle blower units 61m by the pair of rollers 62. . Subsequently, the print medium M passes through the two middle blower units 61m in the horizontal direction X, and is turned back by the pair of air turn bars 63 toward the second lower blower unit 61l. Further, the print medium M is transported out of the drying device 6 after passing through the two lower blower units 61l in the horizontal direction X. As shown in FIG.

The upper blower unit 61u has two blower chambers 64 arranged so as to sandwich the printing medium M passing in the horizontal direction X from the vertical direction Z. As shown in FIG. Each blowing chamber 64 has a plurality of nozzles 65 arranged in the horizontal direction X, and hot air (gas of 60° C. or higher) is jetted onto the printing medium M from each nozzle 65 . In this way, the print medium M is dried by hot air jetted from the nozzles 65 of the two blowing chambers 64 while passing between the two blowing chambers 64 provided above and below. Each of the middle blowing unit 61m and the lower blowing unit 61l also has two blowing chambers 64 sandwiching the print medium M in the vertical direction Z, similarly to the upper blowing unit 61u.

Incidentally, the specific configuration of the upper blower unit 61u is not limited to this example. For example, a plurality of rollers arranged in the horizontal direction X may be provided instead of the lower blowing chamber 64 of the upper and lower blowing chambers 64 of the upper blowing unit 61u. In such a configuration, hot air can be jetted from the upper air blowing chamber 64 to the front surface M1 of the print medium M while supporting the back surface M2 of the print medium M from below by the plurality of rollers.

FIG. 2 is a front view schematically showing a printing device included in the printing system of FIG. 1. FIG. In FIG. 2, one side X1 and the other side X2 in the horizontal direction X are shown as appropriate. Here, 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 of 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 transports the print medium M using a plurality of rollers arranged.

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

Also, the white printing section 33 has a single ejection head 331 arranged above the print medium M conveyed by the conveying section 4 . The ejection head 331 has nozzles facing from above the surface M1 of the print medium M passing therebelow, 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.

A carry-in port 311 opens in the side wall of the housing 31 on the other side X2, while a carry-out port 312 opens in the side wall of the housing 31 on the one side X1. Then, the transport unit 4 transports the printing medium M from the inlet 311 to the outlet 312 while passing through the color printing unit 32 and the white printing unit 33 .

The conveying unit 4 includes a carry-in unit 41 provided below the color printing unit 32, an ascending conveying unit 42 provided on one side X1 of the color printing unit 32, and a It has an upper transport section 43 and a lower transport section 44 provided on the other side X<b>2 of the color printing section 32 . The carry-in unit 41 conveys the print medium M carried in from the carry-in port 311 to the one side X1 by the rollers 411, and the ascending transport unit 42 carries the print medium M transported by the carry-in unit 41 upward by the rollers 421. Then, the upper transport section 43 transports the print medium M transported by the ascending transport section 42 to the other side X2 by the rollers 431, and the descending transport section 44 transports the print medium M transported by the upper transport section 43. It is conveyed downward by rollers 441 .

Further, the transport unit 4 has a color transport unit 45 that supports the print medium M facing the color print unit 32 from below. The color conveying 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 print medium M from below. Thus, the surface M1 of the print 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 the surface M1 from above.

Further, the transport section 4 has rollers 461, 462, and 463 arranged between the color transport section 45 and the descending transport section 44 in the direction in which the print medium M advances. A roller 461 is a drive roller that drives the print medium M. As shown in FIG. Rollers 462 and 463 are driven rollers that are driven by the print medium M to rotate.

Further, the conveying section 4 has a reversing conveying section 47 that vertically inverts the printing medium M conveyed from the color conveying section 45 to the one side X1 twice. The reversing transport unit 47 has a plurality of rollers 471 to 477 including a driving roller 471, and these rollers 471 to 477 invert the print medium M upside down twice while contacting the back surface M2 of the print medium M. As shown in FIG. That is, the reversing conveying unit 47 conveys the printing medium M conveyed from the color conveying 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 rollers 472. The front surface M1 and the back surface M2 of the print medium M are turned upside down by conveying the print medium M. Subsequently, the reversing conveying unit 47 conveys the print medium M from the one side X1 toward the other side X2 with a plurality of rollers 473, and then conveys the print medium M upward with the rollers 474-476. Further, the reversing conveying unit 47 changes the traveling direction of the printing medium M to the one side X1 by the rollers 476, thereby vertically inverting the front surface M1 and the back surface M2 of the printing medium M again, and the printing medium M by the rollers 477. is conveyed from the other side X2 toward the one side X1.

The transport unit 4 also has a white transport unit 48 that supports the print medium M facing the white print unit 33 from below. enter in. The white conveying unit 48 has a roller 481 that contacts the back surface M2 of the print medium M from below. Thus, the surface M1 of the print medium M supported by the white conveying section 48 faces upward, and the ejection head 331 of the white printing section 33 ejects white ink while facing the surface M1 from above.

Further, the transport section 4 has an unloading section 49 provided above the upper transport section 43 . The carry-out section 49 has a plurality of rollers 491 arranged from the other side X2 in the horizontal direction X to the one side X1. The unloading unit 49 transports the print medium M conveyed by the white conveying unit 48 to the one side X<b>1 with a plurality of rollers 491 , thereby unloading the print medium M from the unloading port 312 of the housing 31 to the drying device 6 .

As described above, the color printing section 32 and the white printing section 33 of the printing device 3 have ejection heads 321 and 331 . Next, an ink supply mechanism for supplying ink to these ejection heads 321 and 331 will be described. Note that the basic configuration of the ink supply mechanism is common to the ejection heads 321 and 331 . Therefore, the description will focus on the ejection head 331 that ejects white ink. Also, the ejection heads 321 and 331 are hereinafter referred to as an ejection head H as appropriate.

3 and 4 are diagrams schematically showing the configuration of an ejection head and an ink supply mechanism that supplies ink to the ejection head. FIG. 3 shows power transmission, and FIG. 4 shows power failure. As shown in both figures, the ejection head H has a housing Ha, and a plurality of nozzles N are arranged and opened at the bottom of the housing Ha. Inside the housing Ha, there are provided a plurality of cavities Hb communicating with the plurality of nozzles N and an ink supply chamber Hc communicating with the plurality of cavities Hb. Stored in Hb. A piezoelectric element provided in the cavity Hb pushes the ink out of the cavity Hb, whereby the ink is ejected from the nozzle N communicating with the cavity Hb. A specific method for ejecting ink may be a thermal method for heating ink instead of a method using a piezoelectric element. An ink inlet Hd and an ink outlet He are opened above the ejection head H, and ink flows from the ink supply mechanism 9 through the ink inlet Hd into the ink supply chamber Hc, whereupon the ink is supplied. The ink flows out from the chamber Hc to the ink supply mechanism 9 through the ink outlet He.

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. The supply tank 91 and the recovery tank Ink is stored in each of 92 . The supply tank 91 and recovery tank 92 are arranged above the ejection head H, respectively. The ink supply mechanism 9 is arranged in a pipe 932 that connects the recovery tank 92 and the supply tank 91, and includes a circulation pump 93 that sends ink from the recovery tank 92 to the supply tank 91, the circulation pump 93, and the supply tank 91. and a degassing filter 931 positioned in line 932 at a location between the degassing filter 931 to remove gas from the ink before it exits the circulation pump 93 and enters the supply tank 91 .

The ink supply mechanism 9 has a power supply circuit 94 that supplies power to each part of the apparatus. Then, the circulation pump 93 sends ink from the recovery tank 92 to the supply tank 91 by power supplied from the power supply circuit 94 (liquid sending operation). As a result, the circulation pump 93 performs an ink circulation operation in which the ink is circulated through the circulation path C from the recovery tank 92 to the ink supply chamber Hc of the ejection head H via the supply tank 91 and then back to the recovery tank 92 . .

Further, the ink supply mechanism 9 is arranged in a main tank 951 capable of storing a large amount of ink, and a pipe 953 that connects the main tank 951 and the recovery tank 92 in a flow path. and a main pump 952 for feeding. When the amount of ink circulating in the circulation path C decreases due to ejection of ink from the nozzles N, the main pump 952 supplies ink from the main tank 951 to the recovery tank 92 with power supplied from the power supply circuit 94 .

Further, the ink supply mechanism 9 includes a supply-side pressure application section 96 (hereinafter referred to as “pressure application section 96” as appropriate) that applies the positive pressure P<b>1 to the supply tank 91 . The pressure application unit 96 includes a pressure tank 961, a pump 962 that supplies a gas (air) to the pressure tank 961 to apply a positive pressure P1 to the inside of the pressure tank 961, and one end of which is connected to the pressure tank 961. A flexible tube 963 is provided. In the pressure application unit 96 , the pump 962 supplies the gas to the pressure tank 961 by power supplied from the 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 the pipe 934 .

On the other hand, in the supply tank 91, gas (air) is accumulated above the liquid surface of the ink. That is, in the supply tank 91, the ink is stored below the gas-liquid interface, and the gas exists above the gas-liquid interface. Therefore, the positive pressure P<b>1 is applied to the gas-liquid interface in the supply tank 91 by the pressure application unit 96 .

Also, the pressure application unit 96 includes an electromagnetic valve 964 provided between the other end of the tube 963 and one end of the pipe 934 . This solenoid valve 964 is of a normally closed type. Therefore, at the time of power transmission shown in FIG. is provided inside supply tank 91 via tube 963 , solenoid valve 964 and piping 934 . On the other hand, at the time of power failure shown in FIG. 4, the power supply from the power supply circuit 94 to the solenoid valve 964 is lost, so the solenoid valve 964 forms an atmosphere cutoff state between the pressure tank 961 and the supply tank 91, and the pressure tank Application of the positive pressure P1 from 961 to the supply tank 91 is cut off.

The pressure application unit 96 has a check filter 965 between the pipe 934 and the solenoid valve 964 . This non-return filter 965 prohibits passage of ink from the supply tank 91 to the pressure tank 961 while permitting the passage of gas from the supply tank 91 to the pressure tank 961 . In this way, the non-return filter 965 prevents the ink from flowing into the tube 963 from the supply tank 91 .

The ink supply mechanism 9 also includes a recovery-side pressure applying section 97 (hereinafter referred to as “pressure applying section 97” as appropriate) that applies a negative pressure to the recovery tank 92 . The pressure application unit 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 of tube 973 . Then, in the pressure application unit 97 , the pump 972 discharges gas from the pressure tank 971 by power supplied from the power supply circuit 94 . The negative pressure P2 generated in the pressure tank 971 by the pump 972 in this way is applied to the recovery tank 92 via the tube 973 and the pipe 944 .

On the other hand, in the recovery tank 92, gas (air) is accumulated above the liquid surface of the ink. That is, in the recovery tank 92, the ink is stored below the gas-liquid interface, and the gas exists above the gas-liquid interface. Therefore, the negative pressure P<b>2 is applied to the gas-liquid interface in the recovery tank 92 by the pressure application unit 97 .

Also, the pressure application unit 97 includes an electromagnetic valve 974 provided between the other end of the tube 973 and one end of the pipe 944 . This solenoid valve 974 is of the normally closed type. Therefore, during the power transmission shown in FIG. is provided to the inside of recovery tank 92 via tube 973 , solenoid valve 974 and piping 944 . On the other hand, at the time of power failure shown in FIG. 4, the power supply from the power supply circuit 94 to the solenoid valve 974 is lost, so the solenoid valve 974 forms an atmosphere cutoff state between the pressure tank 971 and the recovery tank 92, and the pressure tank Application of the negative pressure P2 from 971 to the recovery tank 92 is cut off.

The pressure application unit 97 has a check filter 975 between the pipe 944 and the solenoid valve 974 . This non-return filter 975 prohibits the passage of ink from the collection tank 92 to the pressure tank 971 while permitting the passage of gas from the collection tank 92 to the pressure tank 971 . In this way, the non-return filter 975 prevents the ink from flowing into the tube 973 from the collection tank 92 .

Furthermore, the ink supply mechanism 9 has a buffer tank 98 that communicates with the recovery tank 92 through a pipe 988 . The buffer tank 98 communicates with the recovery tank 92 above the gas-liquid interface (that is, the gas layer). In other words, gas moves between the buffer tank 98 and the recovery tank 92 . On the other hand, the ink does not move between the buffer tank 98 and the recovery tank 92 and no ink exists in the buffer tank 98 . Both during power transmission (FIG. 3) and during power failure (FIG. 4), the buffer tank 98 and recovery tank 92 communicate with each other, and the pressure in the buffer tank 98 and the pressure in the recovery tank 92 are always equal. .

That is, during the power transmission shown in FIG. is provided to the inside of buffer tank 98 via tube 973 , solenoid valve 974 , piping 944 and piping 988 . On the other hand, at the time of power failure shown in FIG. 4, the power supply from the power supply circuit 94 to the solenoid valve 974 is lost, so the solenoid valve 974 forms an atmosphere cutoff state between the pressure tank 971 and the buffer tank 98, and the pressure tank Application of the negative pressure P2 from 971 to the buffer tank 98 is cut off.

During power transmission in FIG. 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, so that the ink flows through the circulation path C to the supply tank 91. to the recovery tank 92 . 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, so that the necessary meniscus in the nozzles N of the ejection head H will not be generated. Therefore, the circulation pump 93 circulates the ink from the recovery tank 92 to the supply tank 91 to keep the liquid levels of the supply tank 91 and the recovery tank 92 constant.

In addition, the ink supply mechanism 9 includes an electromagnetic valve 99 provided in a pipe 999 connecting the recovery tank 92 and the supply tank 91 so as to communicate the atmosphere between the recovery tank 92 and the supply tank 91 . A solenoid valve 99 is provided in parallel with the circulating pump 93 between . This solenoid valve 99 is of a normally open type. Therefore, during the power transmission shown in FIG. 3, the electromagnetic valve 99 is opened by the power supplied from the power supply circuit 94, and the communication state of the atmosphere between the collection tank 92 and the supply tank 91 via the electromagnetic valve 99 is cut off. there is On the other hand, during a power failure shown in FIG. communicate with. As a result, the upper side of the gas-liquid interface (that is, the gas layer) in the recovery tank 92 and the upper side of the gas-liquid interface (that is, the gas layer) in the supply tank 91 communicate with each other.

In this way, when the electromagnetic valve 99 communicates the recovery tank 92 and the supply tank 91 during a power failure (FIG. 4), the pressure in the recovery tank 92 and the pressure in the supply tank 91 become a predetermined negative pressure P3. The negative pressure P3 is higher than the negative pressure P2 and lower than the positive pressure P1. Incidentally, a negative pressure P2 is applied in advance in the buffer tank 98 during power transmission (FIG. 3), and the buffer tank 98 communicates with the recovery tank 92 and the supply tank 91 during power failure (FIG. 4). Due to the function of the buffer tank 98, a certain degree of negative pressure P3 is maintained in the recovery tank 92 and the supply tank 91 during a power failure. On the other hand, each of the supply tank 91 and the recovery tank 92 is arranged above the ejection head H as described above. Therefore, between the gas-liquid interfaces of the recovery tank 92 and the supply tank 91 and the nozzles N of the ejection head H, a head pressure corresponding to the height difference is generated. Therefore, the buffer tank 98 is provided with a volume sufficient to generate the negative pressure P3 that maintains the ink against this head pressure.

The ink supply mechanism 9 according to the present embodiment described above sends ink from the recovery tank 92 to the supply tank 91 by the circulation pump 93, whereby the ink reaches the ejection head H from the recovery tank 92 via the supply tank 91. The ink is circulated through a circulation path C that returns to the recovery tank 92 later. A solenoid valve 99 is provided between the supply tank 91 and the recovery tank 92, and this solenoid valve 99 shuts off the atmosphere between the supply tank 91 and the recovery tank 92 when energized (Fig. 3). Therefore, the electromagnetic valve 99 does not hinder the generation of the pressure difference (=P2-P1) between the supply tank 91 and the recovery tank 92. On the other hand, the solenoid valve 99 communicates the atmosphere between the supply tank 91 and the recovery tank 92 when de-energized (FIG. 4). Therefore, when the circulation pump 93 stops due to a power failure, the pressure difference between the supply tank 91 and the recovery tank 92 is quickly eliminated, and the ink is recovered from the supply tank 91 via the ink supply chamber Hc of the ejection head H. Ink can be prevented from flowing into the tank 92 .

In particular, a buffer tank 98 (buffer section) is provided in which the atmosphere communicates with the recovery tank 92 . In a state where the atmosphere between the recovery tank 92 and the supply tank 91 is shut off from each other, a positive pressure P1 (first pressure) is applied to the supply tank 91 and a negative pressure lower than the positive pressure P1 is applied. A pressure P2 (second pressure) is applied within the recovery tank 92 and within the buffer tank 98 . In such a configuration, when the atmosphere between the supply tank 91 and the recovery tank 92 is 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 recovery tank is closed. The pressure within 92 rises. However, since the buffer tank 98 is provided separately from the recovery tank 92, the pressure increase in the recovery tank 92 is suppressed compared to the case where 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 Also, it prevents the ink from leaking from the nozzles N against the head pressure between the supply tank 91 and the nozzles N of the ejection head H. Thus, it is possible to prevent leakage of ink 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 the ink from the ejection head H is resolved. It's becoming

The pressure application unit 96 (first pressure application unit) includes an electromagnetic valve 964 (first electromagnetic valve) and a pressure tank 961 (first pressure The positive pressure P1 generated in the pressure tank 961 is applied to the supply tank 91 via the electromagnetic valve 964. The solenoid valve 964 communicates the atmosphere between the supply tank 91 and the pressure tank 961 when energized, and shuts off the atmosphere between the supply tank 91 and the pressure tank 961 when not energized. In addition, the pressure application unit 97 (second pressure application unit) includes an electromagnetic valve 974 (second electromagnetic valve) and a pressure that allows the atmosphere to communicate with the collection tank 92 (and the buffer tank 98) via the electromagnetic valve 974. The negative pressure P2 generated in the pressure tank 971 is applied to the collection tank 92 and the buffer tank 98 via the electromagnetic valve 974. The electromagnetic valve 974 communicates the atmosphere between the recovery tank 92 and the buffer tank 98 and the pressure tank 971 when energized, and communicates the atmosphere between the recovery tank 92 and the buffer tank 98 and the pressure tank 971 when not energized. Atmospheres are isolated from each other. In such a configuration, the pressure tank 961 and the pressure tank 971 move between the supply tank 91, the recovery tank 92 and the buffer tank 98 as the atmosphere between the supply tank 91 and the recovery tank 92 is communicated during a power failure. isolated from the atmosphere of Therefore, the negative pressure P3 necessary for preventing leakage of ink from the ejection head H can be reliably generated in each of the supply tank 91, recovery tank 92 and buffer tank 98. FIG.

Further, during power transmission in FIG. 3, the supply tank 91 is supplied with a positive pressure P1. In this way, in the configuration in which the positive pressure P1 is generated in the supply tank 91, the above-described problem of ink leakage tends to become prominent. Therefore, the configuration in which the buffer tank 98 is provided as described above is particularly suitable.

Further, in the ink supply mechanism 9 for the ejection head H that ejects white ink, applying the positive pressure P1 to the supply tank 91 has the following advantages. In other words, white ink is often used for printing a so-called solid image that constitutes a background or the like. If the amount of white ink ejected from the ejection head H is insufficient when printing such a solid image, an image defect may occur, such as streaky areas where no white ink adheres. On the other hand, by applying the positive pressure P1 to the inside of the supply tank 91, a sufficient amount of white ink can be ejected from the ejection head H, and a suitable solid image can be printed.

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, and the drying device 6 corresponds to the "printing device" of the present invention. The supply tank 91 corresponds to one example of the "supply tank" of the present invention, the recovery tank 92 corresponds to one example of the "recovery tank" of the present invention, and the circulation pump 93 corresponds to one example of the "recovery tank" of the present invention. The power supply circuit 94 corresponds to an example of the "power supply section" of the present invention, the pressure applying section 96 corresponds to an example of the "first pressure applying section" of the present invention, and the pressure tank 961 corresponds to an example of the "first pressure tank" of the present invention, the solenoid valve 964 corresponds to an example of the "first solenoid valve" of the present invention, and the pressure applying section 97 corresponds to the "second pressure applying section" of the present invention. , the pressure tank 971 corresponds to an example of the "second pressure tank" of the present invention, the solenoid valve 974 corresponds to an example of the "second solenoid valve" of the present invention, and the buffer tank 98 corresponds to an example of the "second solenoid valve" of the present invention. The solenoid valve 99 corresponds to an example of the "buffer section" of the present invention, the solenoid valve 99 corresponds to an example of the "bypass solenoid valve" of the present invention, the ejection head H corresponds to an example of the "ejection head" of the present invention, and the nozzle N corresponds to an example of the "ejection head" of the present invention. The positive pressure P1 corresponds to an example of the "first pressure" of the present invention, the negative pressure P2 corresponds to an example of the "second pressure" of the present invention, and the negative pressure P3. corresponds to an example of the "third pressure" of the present invention.

The present invention is not limited to the above-described embodiments, and various modifications other than those described above 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 application unit 96 to the supply tank 91 does not need to be positive pressure, and may be 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.

Further, redundant piping may be provided as a "buffer section" to which the negative pressure P2 is applied in advance during power transmission instead of the buffer tank 98 described above.

Further, the electromagnetic valve 974, the electromagnetic valve 964, and the electromagnetic valve 99 described above do not have to be configured as single valves, and may be collectively configured as multi-way valves.

The present invention is applicable to printing technology in general.

REFERENCE SIGNS LIST 1 printing system 3 printing device 6 drying device 91 supply tank 92 recovery tank 93 circulation pump 94 power supply circuit (power supply unit)
96... Pressure applying section (first pressure applying section)
961... Pressure tank (first pressure tank)
964... Solenoid valve (first solenoid valve)
97... Pressure applying section (second pressure applying section)
971... Pressure tank (second pressure tank)
974... Solenoid valve (second solenoid valve)
98... Buffer tank (buffer section)
99... Solenoid valve (bypass solenoid valve)
H...Ejection head N...Nozzle P1...Positive pressure (first pressure)
P2... Negative pressure (second pressure)
P3... Negative pressure (third pressure)

Claims (6)

an ejection head that ejects ink from nozzles;
a recovery tank that stores the ink recovered from the ejection head;
a buffer unit communicating with the recovery tank;
a supply tank that stores ink to be supplied to the ejection head;
a first pressure applying section 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;
a circulation pump that uses supplied electric power to perform a liquid transfer operation for sending ink from the recovery tank to the supply tank;
a bypass electromagnetic valve provided between the supply tank and the recovery tank, which isolates the supply tank and the recovery tank from each other when energized, and communicates the supply tank and the recovery tank when the supply tank is not energized; ,
A power supply unit that supplies power to the circulation pump and the bypass solenoid valve,
The recovery tank is arranged above the ejection head,
The buffer section communicates with the recovery tank and the supply tank when the bypass electromagnetic valve is not energized, and recovers a third pressure that is a negative pressure higher than the second pressure and lower than the first pressure. A printing apparatus according to claim 1, wherein said third pressure is generated in said tank and said supply tank, and wherein said third pressure resists head pressure between said recovery tank and said supply tank and said nozzle of said ejection head to prevent ink from leaking from said nozzle. The first pressure application unit has a first electromagnetic valve and a first pressure tank connected to the supply tank via the first electromagnetic valve, and applies the first pressure generated in the first pressure tank. , given to the supply tank through the first solenoid valve,
the first solenoid valve communicates the supply tank and the first pressure tank when energized, and disconnects the supply tank and the first pressure tank when not energized;
The second pressure application unit has a second electromagnetic valve and a second pressure tank connected to the recovery tank via the second electromagnetic valve, and applies the second pressure generated in the second pressure tank. , given to the recovery tank through the second solenoid valve,
2. The printing apparatus according to claim 1, wherein the second solenoid valve allows communication between the recovery tank and the second pressure tank when energized, and isolates the recovery tank and the second pressure tank from each other when not energized. . 3. The printing apparatus according to claim 1, wherein said first pressure is positive pressure. 4. The printing apparatus according to claim 3, wherein said ink is white ink. a printing apparatus according to any one of claims 1 to 4;
and a drying device that dries ink ejected onto a print medium by the printing device. While applying a first pressure to a supply tank connected to an ejection head that ejects ink from nozzles to perform printing, a first pressure is applied to a recovery tank connected to the ejection head and to a buffer section communicating with the recovery tank. applying a second pressure, which is a negative pressure lower than the first pressure, 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;
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 communicates with the recovery tank and the supply tank so that the pressure is higher than the second pressure. to generate a third pressure, which is a negative pressure lower than the first pressure, in the recovery tank and the supply tank, and the third pressure is between the recovery tank and the supply tank and the nozzle of the ejection head. and preventing leakage of ink from the nozzles against water head pressure.

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