EP4600042A1

EP4600042A1 - Ink circulation device, inkjet recording device equipped with same, and ink pump

Info

Publication number: EP4600042A1
Application number: EP24780894.2A
Authority: EP
Inventors: Naoki Kobayashi
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2023-03-30
Filing date: 2024-03-29
Publication date: 2025-08-13
Also published as: WO2024204800A1; JPWO2024204800A1; CN120225363A; JP7822519B2; WO2024202241A1

Abstract

An ink circulation device includes a circulation channel that carries ink including a pigment, a supplier located at the circulation channel to supply the ink to a predetermined destination, and a pump located at the circulation channel to pump the ink flowing through the destination to the supplier. The ink in the pump has a maximum flow velocity less than or equal to a predetermined velocity. A product of a smallest cross-sectional area of a channel of individual channels included in an ink head as the destination and a number of the individual channels is greater than or equal to a smallest cross-sectional area of a channel in the pump.

Description

TECHNICAL FIELD

The present disclosure relates to an ink circulation device, an inkjet recording apparatus including the ink circulation device, and an ink pump.

BACKGROUND OF INVENTION

Patent Literature 1 describes an inkjet recording apparatus including an assembly for circulating ink between a recording head and an ink tank. The inkjet recording apparatus with this technique includes the tank for storing ink, the recording head for ejecting ink supplied from the tank, a supply channel for supplying ink from the tank to the recording head, a collection channel for collecting ink from the recording head to the tank, and a pump. During a recording operation, the pump is driven at a first speed to circulate ink in a circulation channel including the tank, the supply channel, the recording head, and the collection channel. The pump is driven at a second speed faster than the first speed for a predetermined time after ink circulation is started.

CITATION LIST

PATENT LITERATURE

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2022-51952

SUMMARY

PROBLEM TO BE SOLVED

One or more aspects of the present disclosure are directed to an ink circulation device that can avoid blockage of a circulation channel including a head and a tank, an inkjet recording apparatus including the ink circulation device, and an ink pump.

SOLUTION TO PROBLEM

In one aspect of the present disclosure, an ink circulation device includes a circulation channel, a supplier, and a pump. The circulation channel carries ink including a pigment. The supplier is located at the circulation channel and supplies the ink to a predetermined destination. The pump is located at the circulation channel and pumps the ink flowing through the destination to the supplier. The destination is an ink head that ejects the ink. The ink head includes a plurality of nozzles that ejects the ink, and a plurality of individual channels each for a corresponding nozzle of the plurality of nozzles. Each of the plurality of individual channels includes a channel that supplies the ink to the corresponding nozzle and a channel that collects the ink from the corresponding nozzle. The ink in the pump has a maximum flow velocity less than or equal to a predetermined velocity. A product of a smallest cross-sectional area of a channel of the plurality of individual channels and a number of the plurality of individual channels is greater than or equal to a smallest cross-sectional area of a channel in the pump.
In another aspect of the present disclosure, an ink circulation device includes a circulation channel, a supplier, and a pump. The circulation channel carries ink including a pigment. The supplier is located at the circulation channel and supplies the ink to a predetermined destination. The pump is located at the circulation channel and pumps the ink flowing through the destination to the supplier. The ink in the pump receives a shearing stress less than or equal to 30 Pa.
In another aspect of the present disclosure, an inkjet recording apparatus includes a circulation channel, an ink head, a supplier, and a pump. The circulation channel carries ink including a pigment. The ink head ejects the ink. The supplier is located at the circulation channel. The supplier supplies the ink to the ink head. The pump is located at the circulating path and pumps the ink collected from the destination to the supplier. The ink head includes a plurality of nozzles that ejects the ink, and a plurality of individual channels each for a corresponding nozzle of the plurality of nozzles. Each of the plurality of individual channels includes a channel that supplies the ink to the corresponding nozzle and a channel that collects the ink from the corresponding nozzle. The ink in the circulation channel has a maximum flow velocity less than or equal to a predetermined velocity. A product of a smallest cross-sectional area of a channel of the plurality of individual channels and a number of the plurality of individual channels is greater than or equal to a smallest cross-sectional area of a channel in the pump.
In another aspect of the present disclosure, an inkjet recording apparatus includes a circulation channel, an ink head, a supplier, and a pump. The circulation channel carries ink including a pigment. The ink head ejects the ink. The supplier is located at the circulation channel and supplies the ink to the ink head. The pump is located at the circulation channel and pumps the ink collected from the ink head to the supplier. The ink in the pump receives a shearing stress less than or equal to 30 Pa.
In another aspect of the present disclosure, an ink pump is to be located at a circulation channel for carrying ink including a pigment. The ink pump pumps, to a supplier located at the circulation channel to supply the ink to a predetermined destination, the ink flowing through the destination. The ink in the pump has a maximum flow velocity less than or equal to a predetermined velocity.
In another aspect of the present disclosure, an ink pump is to be located at a circulation channel for carrying ink including a pigment. The ink pump pumps, to a supplier located at the circulation channel to supply the ink to a predetermined destination, the ink flowing through the destination. The ink in the pump receives a shearing stress less than or equal to 30 Pa.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a recording apparatus according to one embodiment of the present disclosure, illustrating its overall structure.
FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1.
FIG. 3 is an enlarged perspective view of a carriage shown in FIG. 1.
FIG. 4 is a schematic diagram illustrating the flow of ink near ink heads in one embodiment of the present disclosure.
FIG. 5 is a schematic diagram of a supply subtank and a collection subtank in one embodiment of the present disclosure.
FIG. 6 is a graph showing the relationship between the flow velocity in a pump and the number of coarse particles for working examples and comparative examples compared with the working examples of a pump according to one embodiment of the present disclosure.
FIG. 7 is a graph showing the relationship between the shearing stress in a pump and the number of coarse particles for the working examples and the comparative examples compared with the working examples of the pump according to one embodiment of the present disclosure.
FIG. 8A is a schematic cross-sectional view of a pump in one embodiment of the present disclosure, illustrating its internal structure.
FIG. 8B is a schematic cross-sectional view of the pump in one embodiment of the present disclosure, illustrating a part of its internal structure.
FIG. 8C is a schematic cross-sectional view of the pump in one embodiment of the present disclosure, illustrating a part of its internal structure.

DESCRIPTION OF EMBODIMENTS

A recording apparatus according to one embodiment of the present disclosure will now be described below with reference to the drawings. In one or more embodiments below, an inkjet printer including an ink head for ejecting ink for forming an image onto a wide and long recording medium will be described as a specific example of the recording apparatus. The inkjet printer may be used for digital textile printing to print images such as letters or patterns on a recording medium including a textile such as woven fabric or knitted fabric. In one or more embodiments of the present disclosure, the recording apparatus is also used for printing various images on a recording medium such as a paper sheet or a resin sheet. Overall Structure of Inkjet Printer
FIG. 1 is a perspective view of an inkjet printer 1 according to a first embodiment of the present disclosure, illustrating its overall structure. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. The inkjet printer 1 is a printer for printing an image on a wide and long workpiece W (recording medium) by inkjet printing. An example workpiece W is several meters wide. The printer 1 includes an apparatus frame 10, and a workpiece feeder 20 and a carriage 3 incorporated in the apparatus frame 10. Note that, in the present embodiment, a lateral direction is a main scanning direction S (FIG. 3) in printing on the workpiece W, and a direction from rear to front is a subscanning direction (a feed direction F of the workpiece W intersecting with the main scanning direction S).
The apparatus frame 10 is a frame on which various components of the inkjet printer 1 are mounted. The workpiece feeder 20 is an assembly that intermittently feeds (transports) the workpiece W to allow the workpiece W to move in the feed direction F from rear to front in a printing area in which an inkjet printing process is performed. The carriage 3 carries an ink head 4, a pretreatment liquid head 5, a post-treatment liquid head 6, and a subtank 7, and reciprocates in the main scanning direction S (lateral direction) intersecting with the feed direction F of the workpiece W during the inkjet printing process.
The apparatus frame 10 includes a center frame 111, a right frame 112, and a left frame 113. The center frame 111 is a frame on which various components of the inkjet printer 1 are mounted and has a lateral width corresponding to the workpiece feeder 20. The right frame 112 stands on the right of the center frame 111, and the left frame 113 stands on the left of the center frame 111. A printing area 12 in which the printing process is performed on the workpiece W is defined between the right frame 112 and the left frame 113.
The right frame 112 defines a maintenance area 13. The maintenance area 13 is an area into which the carriage 3 is retracted when the printing process described above is not performed. In the maintenance area 13, the ink head 4 and nozzles (ejection orifices) of the pretreatment liquid head 5 and the post-treatment liquid head 6 are, for example, cleaned, purged, or capped. The left frame 113 defines a turn-back area 14 for the carriage 3. The turn-back area 14 is an area for the carriage 3 that has scanned the printing area 12 from right to left in the printing process to enter temporarily before performing main scanning in the reverse direction.
The apparatus frame 10 receives, on its upper portion, a carriage guide 15 for guiding the carriage 3 to reciprocate in the lateral direction. The carriage guide 15 is a flat plate elongated in the lateral direction and is located above the workpiece feeder 20. The carriage guide 15 receives a timing belt 16 rotatable in the lateral direction (main scanning direction). The timing belt 16 is an endless belt that is driven to rotate in the lateral direction.
The carriage guide 15 includes a pair of upper and lower guide rails 17 holding the carriage 3 in a manner reciprocable in the main scanning direction S. The pair of guide rails 17 extend parallel to each other in the lateral direction. The carriage 3 is engaged with the guide rails 17. The carriage 3 is fixed to the timing belt 16. The carriage 3, while being guided by the guide rails 17, moves in the left direction or in the right direction along the carriage guide 15 as the timing belt 16 rotates in the left direction or in the right direction.
Referring mainly to FIG. 2, the workpiece feeder 20 includes a feed roller 21 that unwinds the workpiece W before printing, and a take-up roller 22 that winds the workpiece W after printing. The feed roller 21 is located in a lower rear portion of the apparatus frame 10. The feed roller 21 is a winding shaft of a feed roll WA as a wound roll of the workpiece W before printing. The take-up roller 22 is located in a lower front portion of the apparatus frame 10. The take-up roll is a winding shaft of a take-up roll WB as a wound roll of the printed workpiece W. The take-up roller 22 includes a first motor M1 that rotates the take-up roller 22 about its axis to wind the workpiece W.
A path extending through the printing area 12 between the feed roller 21 and the take-up roller 22 is a feed path of the workpiece W. This feed path includes, in the order from the upstream, a first tension roller 23, a workpiece guide 24, a transport roller 25 and a pinch roller 26, a turn roller 27, and a second tension roller 28. The first tension roller 23 applies a predetermined tension to the workpiece W upstream from the transport roller 25. The workpiece guide 24 redirects the workpiece W from upward to frontward and feeds the workpiece W into the printing area 12.
The transport roller 25 generates a feed force for feeding the workpiece W intermittently in the printing area 12. The transport roller 25, which is driven by a second motor M2, rotates about its axis and intermittently feeds the workpiece W frontward (in the predetermined feed direction F) to allow the workpiece W to pass through the printing area 12 (image formation position) facing the carriage 3. The pinch roller 26 faces the transport roller 25 from above and forms a feed nip with the transport roller 25.
The turn roller 27 redirects the workpiece W that has passed through the printing area 12 from frontward to downward, and guides the printed workpiece W to the take-up roller 22. The second tension roller 28 applies a predetermined tension to the workpiece W downstream from the transport roller 25. A platen 29 is located below the feed path of the workpiece W in the printing area 12.
The carriage 3 reciprocates, while being held by the guide rails 17 in a cantilevered manner, in the main scanning direction S (the lateral direction in the present embodiment) intersecting with (in the present embodiment, perpendicular to) the feed direction F. The carriage 3 includes a carriage frame 30 as well as the ink head 4, the pretreatment liquid head 5, the post-treatment liquid head 6, and the subtanks 7 mounted on the carriage frame 30 (FIG. 3). The carriage frame 30 includes a head support frame 31 and a back frame 32.
The head support frame 31 is a horizontal plate holding the heads 4 to 6 described above. The back frame 32 is a vertical plate extending upward from a rear edge of the head support frame 31. As described above, the timing belt 16 is fixed to the back frame 32. The guide rails 17 are engaged with the back frame 32. In other words, the back frame 32 is an engaging portion held by the guide rails 17 in a cantilevered manner in the present embodiment. The head support frame 31 is a horizontal plate including a rear end portion held by the guide rails 17 in a cantilevered manner with the engaging portion.
Note that being held in a cantilevered manner refers to the state in which the engaging portion (back frame 32) in the carriage 3 held by the guide rails 17 as holding members is located upstream or downstream alone from the middle of the carriage 3 in the feed direction F, with no other engaging portion in an area opposite to the area including the engaging portion. The engaging portion may also be located outside an area including the ink head 4 and the treatment heads in the feed direction F. In other words, the engaging portion may be located upstream or downstream alone from the area including the ink head 4 and the treatment heads in the feed direction F.

Details of Carriage

The carriage 3 will be described further. FIG. 3 is an enlarged perspective view of the carriage 3 illustrated in FIG. 1. In FIG. 3, the feed direction F (the subscanning direction) of the workpiece W and the main scanning direction S in which the carriage 3 moves are illustrated. In the example illustrated in FIG. 3, the carriage 3 carries multiple ink heads 4 for ejecting ink for image formation on the workpiece W, the pretreatment liquid head 5 and the post-treatment liquid head 6 for ejecting noncolor-developing treatment liquids, and multiple subtanks 7 for supplying these heads 4 to 6 with the ink and the treatment liquids.
Each of the ink heads 4 includes many nozzles (ink ejection orifices) for ejecting ink droplets by, for example, piezoelectric ejection using piezoelectric elements or thermal ejection using heating elements.
Each of the ink heads 4 includes, for example, multiple ejection portions including nozzles, a common supply channel for supplying ink to the multiple ejection portions, and a common collection channel for collecting ink from the multiple ejection portions. The common collection channel collects ink that is not ejected from the nozzles after being supplied to the ejection portions.
Each of the ejection portions includes an individual channel connecting the common supply channel and the common collection channel, a pressure applier such as a piezoelectric element or a heating element, and a nozzle. A portion of the individual channel facing the pressure applier is referred to as a pressure chamber. The individual channel may include the pressure chamber and the nozzle in this order from a potion near the common supply channel. However, this arrangement may be reversed. In the individual channel, the channel from the common supply channel to the nozzle supplies ink to the nozzle, and the channel from the nozzle to the common collection channel collects ink that is not ejected from the nozzle. In the individual channel, a cross-sectional area of a portion having the smallest cross section that is orthogonal to a direction of the flow of ink is referred to as a smallest cross-sectional area of the individual channel. The smallest cross-sectional area may be in a channel connecting the pressure chamber and either of the common channels. Note that ink flowing from the common supply channel to the common collection channel does not flow through the nozzle. Thus, in determining the smallest cross-sectional area of the individual channel, the nozzle is excluded from the individual channel.
The structure of each of the ink heads will be described additionally. Ink flowing into an ink head flows into the common supply channel through a flow-in channel defined in an introduction portion (also referred to as a backend). Then, the ink is supplied, through the individual channels defined in the respective ejection portions, into the corresponding nozzles. Part of the ink is ejected from the nozzles, and the rest of the ink flows through the individual channels into the common collection channel, and then flows out of the ink head through a flow-out channel defined in the introduction portion. The multiple individual channels branch from the common supply channel. The respective individual channels are connected to the common collection channel to merge into the common collection channel. In other words, a single ink head 4 has a channel structure in which the multiple individual channels corresponding to the respective ejection portions (nozzles) are arranged in parallel.
Each of the ink heads 4 may further include a filter. The filter is located, for example, in or upstream from the common supply channel and reduces foreign substances or coarse particles in ink flowing downstream to reduce clogging of the nozzles or the individual channels. The filter (backend filter) may be located in the channel in the introduction portion (backend). Ink supplied to the ink head all flows through the backend filter, and the ink through the backend filter flows toward the common supply channel.
Examples of the ink include water-based pigment ink containing a water-based solvent, a pigment, and a bonding resin (binder).
The bonding resin may be dispersed in an aqueous medium. The bonding resin binds the pigments on a printing subject. Thus, ink containing the bonding resin can provide a printed object on which the pigments are more stably fixed. Examples of the bonding resin include a polyurethane resin, a (meth)acrylic resin, a styrene-(meth)acrylic resin, a styrenemaleic acid copolymer, a vinyl naphthalene-(meth)acrylic acid copolymer, and a vinyl naphthalene-maleic acid copolymer. The content of the bonding resin may be 1 to 20 mass% inclusive, or more specifically, 2 to 10 mass% inclusive of the mass of ink.
In the present embodiment, the multiple ink heads 4 can eject eight colors of ink. The ink heads 4 are mounted on the head support frame 31 in the carriage 3 in two arrays in the main scanning direction S. Two ink heads 4 are used for each of the colors.
More specifically, the ink heads 4 as a first upstream ink head 41A and a first downstream ink head 41B eject yellow ink. The ink heads 4 as a second upstream ink head 42A and a second downstream ink head 42B eject magenta ink. In the same or similar manner, two ink heads 4 for ejecting the same color of ink are arranged in a manner displaced from each other in the feed direction F and in the main scanning direction S as illustrated in FIG. 3. With these two ink heads 4 being paired, a total of eight pairs of ink heads 4 (41A to 48A and 41B to 48B) eject different colors of ink.
The pretreatment liquid head 5 and the post-treatment liquid head 6 are at different positions from the ink heads 4 in the feed direction F. The pretreatment liquid head 5 is upstream from the ink heads 4 in the feed direction F. In FIG. 3, a single pretreatment liquid head 5 is located adjacent to the left end of an array of ink heads 4. In the same or similar manner, the post-treatment liquid head 6 is downstream from the ink heads 4 in the feed direction F. In FIG. 3, a single post-treatment liquid head 6 is located adjacent to the right end of an array of ink heads 4. In another embodiment, multiple pretreatment liquid heads 5 or multiple post-treatment liquid heads 6 may be arranged. Although the carriage 3 may carry at least one pretreatment liquid head 5 and at least one post-treatment liquid head 6, the carriage 3 may carry none of the pretreatment liquid head 5 or the post-treatment liquid head 6 in another embodiment.
A series of heads including the ink heads 4, the pretreatment liquid head 5, and the post-treatment liquid head 6 aligned in the main scanning direction S is referred to as an array of heads, or simply an array. A series of heads including the ink heads 4, the pretreatment liquid head 5, and the post-treatment liquid head 6 aligned in the feed direction F is referred to as a line of heads, or simply a line.
The pretreatment liquid head 5 ejects a pretreatment liquid for a predetermined pretreatment of the workpiece W. The pretreatment liquid is ejected from the pretreatment liquid head 5 to an area of the workpiece W on which no ink has been ejected from the ink heads 4. The pretreatment liquid is a noncolor-developing treatment liquid that develops no color on the workpiece W, and improves, for example, fixation of ink on the workpiece W or facilitates agglomeration of ink pigments. Examples of the pretreatment liquid may include a treatment liquid of a solvent containing a bonding resin or a treatment liquid of a solvent containing a positively charged cationic resin.
The post-treatment liquid head 6 ejects a post-treatment liquid for a predetermined post-treatment of the workpiece W with ink applied. The post-treatment liquid is ejected from the post-treatment liquid head 6 to an area of the workpiece W on which ink has been ejected from the ink heads 4. The post-treatment liquid is also a noncolor-developing treatment liquid that develops no color on the workpiece W. The post-treatment liquid improves the fixation and the toughness (durability against rubbing or scratching) of an ink image printed on the workpiece W by the ink heads 4. Examples of the post-treatment liquid include a silicone treatment liquid. Note that the post-treatment liquid is different from the pretreatment liquid. More specifically, the post-treatment liquid and the pretreatment liquid contain different components.
The noncolor-developing treatment liquid refers to a liquid that is not perceptible as having developed a color to the naked eye when printed on a recording medium alone. The color includes colors with zero saturation, such as black, white, and gray. Although the noncolor-developing treatment liquid is basically a transparent liquid, a liter of treatment liquid in a liquid state may appear slightly white or another color. Such a faint color is not perceptible as having developed a color to the naked eye when printed on a recording medium alone. Note that, although a type of treatment liquid printed alone on the recording medium may cause a change such as adding gloss to the recording medium, such a change is not referred to as developing a color.
In the present embodiment, the pretreatment liquid and the post-treatment liquid may be ejected across substantially the entire surface of the workpiece W, or may be selectively ejected based on an image to be printed in the same manner as or in a similar manner to the ink.
Selective ejecting of the pretreatment liquid and the post-treatment liquid will now be described. As described above, the pretreatment liquid, the ink, and the post-treatment liquid are ejected in this order on an area of the workpiece W on which colors are printed based on an image. In this case, the ink may have one color or multiple colors. For an area on which no color is printed, or in other words, an area on which no ink is ejected, no pretreatment liquid or the post-treatment liquid is basically ejected. Note that, to adjust the quality of an image to be printed or the texture of the workpiece W, the pretreatment liquid and the post-treatment liquid may be selectively ejected in a manner partially different from that of ink ejecting.
As illustrated in FIG. 3, the head support frame 31 includes openings 31H in its area carrying the heads. The head support frame 31 receives the ink heads 4, the pretreatment liquid head 5, and the post-treatment liquid head 6 fitted into the respective openings 31H. The nozzles on the lower end faces of the heads 4, 5, and 6 are exposed through the openings 31H.
The multiple subtanks 7 are supported by the carriage 3 with a holding frame (not illustrated) above the heads 4, 5, and 6. The multiple subtanks 7 correspond to the respective heads 4, 5, and 6. Each of the subtanks 7 receives supply of the ink or the treatment liquid from a main tank 90 (described later) containing the ink or the treatment liquid, and supplies the ink or the treatment liquid to the head 4, 5, or 6. The subtanks 7 are connected to the corresponding heads 4, 5, and 6 with pipes (not illustrated in FIG. 3).
More specifically, the multiple subtanks 7 include a first supply subtank 71A to an eighth supply subtank 78A, a pretreatment supply subtank 7FA, and a post-treatment supply subtank 7RA arranged rearward in the main scanning direction S. The first to eighth supply subtanks are arranged at an ink circulation channel to supply ink to predetermined supply destinations (ink heads). The multiple subtanks 7 also include a first collection subtank 71B to an eighth collection subtank 78B, a pretreatment collection subtank 7FB, and a post-treatment collection subtank 7RB arranged frontward in the main scanning direction S. The first to eighth collection subtanks are arranged at the ink circulation channel to collect ink from the ink heads 4.
The first supply subtank 71A and the first collection subtank 71B located leftmost in the carriage 3 store yellow ink containing pigments. The first supply subtank 71A supplies the yellow ink to the first upstream ink head 41A and the first downstream ink head 41B (each referred to as a supply destination). The first collection subtank 71B stores the yellow ink collected from the first upstream ink head 41A and the first downstream ink head 41B. As described above, part of the yellow ink is ejected from the first upstream ink head 41A and the first downstream ink head 41B onto the workpiece W. In the same or similar manner, the second supply subtank 72A supplies magenta ink to the second upstream ink head 42A and the second downstream ink head 42B. The second collection subtank 72B stores the magenta ink collected from the second upstream ink head 42A and the second downstream ink head 42B. The remaining third to eighth subtanks also have the same or similar structures and functions as described above.
The pretreatment supply subtank 7FA supplies the pretreatment liquid to the pretreatment liquid head 5, and the pretreatment collection subtank 7FB collects the pretreatment liquid from the pretreatment liquid head 5. The post-treatment supply subtank 7RA supplies the post-treatment liquid to the post-treatment liquid head 6, and the post-treatment collection subtank 7RB collects the post-treatment liquid from the post-treatment liquid head 6.
As described above, the inkjet printer 1 according to the present embodiment is an all-in-one printer including three types of heads, or the ink heads 4, the pretreatment liquid head 5, and the post-treatment liquid head 6, on the single carriage 3. This inkjet printer 1 can achieve, for example, in digital textile printing, a printing process of inkjet printing on a textile in which the pretreatment liquid ejection is performed integrally with the post-treatment liquid ejection. This can simplify the textile printing process, and can downsize textile printing apparatuses.
Note that the inkjet printer 1 according to the present embodiment performs printing on the workpiece W by serial printing. More specifically, for a wide workpiece W, the workpiece W cannot undergo printing while moving continuously. The serial printing includes repeatedly reciprocating the carriage 3 carrying the ink heads 4 of the respective colors in the main scanning direction S and intermittently feeding the workpiece W in the feed direction F.
More specifically, the carriage 3 moving in an outgoing direction, which is one direction of the main scanning direction S, prints a strip of image. During the main scanning in this outgoing direction, the feed of the workpiece W is stopped. The workpiece W on which the strip of image has been printed is then fed forward in the feed direction F by a predetermined pitch. During the feed, the carriage 3 stays in the turn-back area 14 at the left end. After the workpiece W is fed forward, the carriage 3 turns back in a return direction opposite to the outgoing direction, as the timing belt 16 rotates in the reverse direction. The workpiece W is stopped. The carriage 3 then moves in the return direction and prints a subsequent strip of image upstream from the strip of image described above. The same or similar movement is repeated subsequently.

Circulation Channel of Ink and Treatment Liquid

The flow of the ink and the treatment liquids in the inkjet printer 1 according to the present embodiment will now be described. Although the flow of ink is described in detail below, the same or a similar structure is used for the treatment liquids. FIG. 4 is a schematic diagram illustrating the flow of ink near a liquid ejecting head in the present embodiment. FIG. 5 is a schematic diagram of the supply subtank and the collection subtank in the present embodiment. In the respective figures, the lines connecting the components indicate pipes (tubes) for carrying a gas or a liquid.
In the present embodiment, a pressure is applied, with a gas (air), to the first supply subtank 71A to the post-treatment supply subtank 7RA (each also referred to as a supply tank or a supplier) and the first collection subtank 71B to the post-treatment collection subtank 7RB (each also referred to as a collection tank or a collector) mounted on the carriage 3 in FIG. 3. This causes the supply subtanks to supply liquids (the ink, the pretreatment liquid, and the post-treatment liquid) to the ink heads 4, the pretreatment liquid head 5, and the post-treatment liquid head 6.
A circulation channel including supply and collection paths of yellow ink to and from the first upstream ink head 41A and the first downstream ink head 41B will be described with reference to FIG. 4. Note that the same or a similar structure as in FIG. 4 is applicable to the ink heads for other colors. The inkjet printer 1 further includes, on the carriage 3, filters 81, 82, 83, and 84, a circulation pump 85 (a pump or an ink pump), a check valve 86, and a degasser 87. The inkjet printer 1 further includes, outside the carriage 3 and on the apparatus frame 10 (FIG. 1), the main tank 90, a capacitive sensor 91, a main tank valve 92, a main supply pump 93, and a controller 100.
Yellow ink flowing from the first supply subtank 71A into an ink supply channel QA splits into a first ink path Q1 extending through the first upstream ink head 41A and a second ink path Q2 extending through the first downstream ink head 41B. The filter 81 is located upstream from the first upstream ink head 41A, and the filter 82 is located upstream from the first downstream ink head 41B. The filter 83 is located downstream from the first upstream ink head 41A, and the filter 84 is located downstream from the first downstream ink head 41B. These filters remove, for example, foreign substances or dust in the ink. After the first upstream ink head 41A and the first downstream ink head 41B eject part of the yellow ink on the workpiece W, the remaining ink is collected through an ink collection channel QB into the first collection subtank 71B. The collected yellow ink is further supplied to the first supply subtank 71A through an ink return channel Q3.
As illustrated in FIG. 4, the circulation pump 85 is a part of a yellow ink circulation channel that starts from the first supply subtank 71A and returns to the first supply subtank 71A through the first upstream ink head 41A, the first downstream ink head 41B, and the first collection subtank 71B. In the present embodiment, the circulation pump 85 pumps yellow ink from the first collection subtank 71B to the first supply subtank 71A. Note that the circulation pump 85, together with the ink circulation channel and the subtanks, forms an ink circulation device according to one or more embodiments of the present disclosure. The circulation pump 85 located at the ink circulation channel pumps the ink flowing through the ink heads 4 to the supply subtank.
The check valve 86 prevents backflow of ink from the first supply subtank 71A to the first collection subtank 71B through the ink return channel Q3. The degasser 87 degasses ink (remove air bubbles) in the ink return channel Q3.
The main tank 90 is mounted on the apparatus frame 10 of the inkjet printer 1 and stores yellow ink. Note that the same or similar main tanks 90 are also provided for other colors of ink.
The capacitive sensor 91 detects the amount of yellow ink remaining in the main tank 90.
The main tank valve 92 can open or close an ink refill channel Q4 extending from the main tank 90 to the first supply subtank 71A. The main tank valve 92 may be opened or closed manually or automatically in response to a command signal input from the controller 100.
The main supply pump 93 operates to supply the yellow ink in the main tank 90 to the first supply subtank 71A.
The controller 100 centrally controls the operation of the inkjet printer 1, and electrically controls the components illustrated in FIG. 4.
In one example as illustrated in FIG. 5, the first supply subtank 71A with a box-like structure stores yellow ink with a supply tank gas area SA and a supply tank ink area SB defined inside. The supply tank gas area SA is a space above the level of yellow ink in the first supply subtank 71A, and the supply tank ink area SB is an area defined with the yellow ink. The supply tank gas area SA is connected to a supply pressure channel P11. The supply pressure channel P11 is connected to a pressure source (not illustrated) and maintains the supply tank gas area SA in the first supply subtank 71A at a predetermined pressure. The supply tank ink area SB is connected to the ink supply channel QA (the first ink path Q1 and the second ink path Q2), to the ink return channel Q3, and to the ink refill channel Q4.
The first supply subtank 71A also includes a capacitive sensor 71A1 that can detect the level of the yellow ink (the amount of ink) in the first supply subtank 71A.
In the same or similar manner, the first collection subtank 71B with a box-like structure stores yellow ink with a collection tank gas area SC and a collection tank ink area SD defined inside. The collection tank gas area SC is a space above the level of the yellow ink in the first collection subtank 71B, and the collection tank ink area SD is an area defined with the yellow ink. The collection tank gas area SC is connected to a collection pressure channel P12. The collection pressure channel P12 is connected to a pressure source (not illustrated) and maintains the collection tank gas area SC in the first collection subtank 71B at a predetermined pressure. The collection tank ink area SD is also connected to the ink collection channel QB (the first ink path Q1 and the second ink path Q2) and to the ink return channel Q3.
The first collection subtank 71B further includes a capacitive sensor 71B1 that can detect the level of the yellow ink (the amount of ink) in the first collection subtank 71B.
In the present embodiment, the supply tank gas area SA in the first supply subtank 71A is maintained at, for example, +2 kPa (with respect to the atmospheric pressure, the same or similar applies hereafter), and the collection tank gas area SC in the first collection subtank 71B is maintained at, for example, -15kPa. This generates a flow of yellow ink from the first supply subtank 71A in FIG. 4 to the first collection subtank 71B through the ink supply channel QA (the first ink path Q1 and the second ink path Q2) and the ink collection channel QB (the first ink path Q1 and the second ink path Q2). Note that both the supply tank gas area SA and the collection tank gas area SC may be maintained at a positive pressure higher than 0 kPa. Both the supply tank gas area SA and the collection tank gas area SC may also be maintained at a negative pressure lower than 0 kPa. The difference between the pressures in the supply tank gas area SA and the collection tank gas area SC may be 5 to 20 kPa.
When the controller 100 determines that, in response to an output signal from the capacitive sensor 71A1 (FIG. 5), the ink level in the first supply subtank 71A is low, the circulation pump 85 operates in response to a command signal input from the controller 100. Part of the yellow ink in the first collection subtank 71B is then supplied to the first supply subtank 71A through the ink return channel Q3. Note that the circulation pump 85 operates independently of whether printing by the inkjet printer 1 is being performed or is stopped.
Additionally, when the controller 100 determines, based on the detection results from the capacitive sensors 71A1 and 71B1, that the amount of yellow ink in both the subtanks, or the first supply subtank 71A and the first collection subtank 71B, has fallen below a predetermined threshold, the controller 100 operates the main supply pump 93 to refill the first supply subtank 71A with yellow ink from the main tank 90 through the ink refill channel Q4. During this operation, the main tank valve 92 opens to adjust the maximum refill amount (refilling rate) to the first supply subtank 71A. When the capacitive sensor 91 detects that the amount of yellow ink remaining in the main tank 90 is low, the controller 100 causes a display (not illustrated) of the inkjet printer 1 to display an ink refill message.
Yellow ink is ejected from the first upstream ink head 41A and from the first downstream ink head 41B based on an image to be formed on the workpiece W. Yellow ink also circulates in, as illustrated in FIG. 4, the circulation channel including the ink supply channel QA, the first ink path Q1, the second ink path Q2, the ink collection channel QB, and the ink return channel Q3. In this case, some yellow ink continues to circulate in the circulation channel without being ejected from the ink heads.
In the structure in which ink circulates as described above, long use causes agglomerated ink pigments (coarse particles) in the circulation channel including the heads, damaging the circulation pump 85 or blocking the paths. In particular, in the present embodiment, the inkjet printer 1 prints images on the wide and long workpiece W (recording medium) by inkjet printing. In this printer, the flow rate of ink flowing through the circulation channel is relatively greater than that in a common home printer. Thus, agglomerated substances are likely to form. The inventors of the present disclosure have noticed that a factor for formation of such agglomerated substances is the flow velocity of ink in the respective channels including the circulation pump 85, and evaluated the production of coarse particles (the number of coarse particles) against the flow velocities of various pumps.
Table 1 shows the relationship between the pump characteristics and the number of coarse particles for various pumps used as the circulation pump 85. The pump characteristics include the smallest cross-sectional area of the channel, the maximum flow rate, the maximum flow velocity, and the shearing stress. The smallest cross-sectional area of the channel is the cross-sectional area of a portion having the smallest cross section in the path for carrying ink in the pump. In a diaphragm pump or a piezoelectric pump, the smallest cross-sectional area of the channel corresponds to the area of a passage through a valve, which is the cross-sectional area of a channel in a valve portion in the pump. Note that the cross-sectional area of the valve portion including a closed valve is 0. Thus, the area of a passage through the valve is a cross-sectional area with an open valve.
The maximum flow rate corresponds to the maximum flow rate of ink in the pump. The flow rate of ink in the pump is obtained by measuring the flow rate of ink at the outlet or the inlet of the pump. The maximum flow rate is the greatest one of the flow rates obtained as described above. Although the amount of circulating ink is controlled to maintain a predetermined amount, the actual flow rate at the pump outlet fluctuates by a certain degree depending on the operation principles of the respective pumps. The maximum flow rate is the maximum flow rate of a pump operating while printing is being performed, and is a value accommodating the fluctuations resulting from the operation of the pump described above. The maximum flow rate is generated when, for example, the circulation pump 85 delivers ink in the first collection subtank 71B to the first supply subtank 71A containing a smaller amount of ink. The maximum flow velocity is less than or equal to a predetermined velocity at least during continuous printing. The maximum flow velocity may also be less than or equal to the predetermined velocity when no printing is performed and ink is circulating in the idle inkjet printer 1. Note that, although the flow velocity may be temporarily greater than the predetermined velocity during irregular operations such as a process of restoring the inkjet printer 1 in which a trouble has occurred, the flow velocity may also be less than or equal to the predetermined velocity during such irregular operations.

The maximum flow velocity corresponds to the maximum velocity of ink in the pump. Ink flows fastest in the pump in its portion having the smallest cross-sectional area in the path for carrying ink. Thus, the maximum flow velocity is obtained by dividing the maximum flow rate by the smallest cross-sectional area of a channel. The number of coarse particles is the number of particles having 5 µm or more diameters counted until each pump has pumped about 1000 L or more volume of fluid cumulatively.

Table 1

No.	Comparative Example 1	Comparative Example 2	Comparative Example 3	Working Example 1	Working Example 2	Working Example 3
Pump	Diaphragm pump	Diaphragm pump	Process pump	Peristaltic pump	Piezoelectric pump	Diaphragm pump
Smallest cross-sectional area of channel (m²)	1.96E-06	1.96E-06	7.07E-06	1.26E-05	6.28E-06	2.20E-06
Maximum flow rate (m³/sec)	1.24E-05	1.24E-05	5.00E-05	3.33E-06	6.67E-06	7.75E-06
Maximum flow velocity (m/sec)	6.3	6.3	7.1	0.3	1.1	3.5
Shearing stress (Pa)	48	48	-	1	5	25
Number of coarse particles (count/mL)	129667	80006	271311	3863	1164	20015

FIG. 6 is a graph showing the relationship between the maximum flow velocity (flow velocity in the pump in FIG. 6) in Table 1 and the number of coarse particles.
As shown in Table 1 and FIG. 6, the inventors of the present disclosure have noticed that the production of coarse particles tends to increase with the flow velocity in the pump. This phenomenon may be caused by accelerated agglomeration (shear agglomeration) of the particles of pigments, as viscous ink generates velocity gradient at the cross-sections of each channel, thus causing the particles to have different velocities and collide more frequently with one another. The velocity gradient mainly results from the particles near the inner wall of the channel (pipe) flowing relatively slower than the particles near the center of the channel.
Note that the flow velocity in the pump may be slowed by increasing the duty ratio of the pump operation. In such control of a pump, the controller 100 operates the pump intermittently to change the duty ratio (the ratio of pump operation in a predetermined period), and thus can set the amount of ink delivered per time. To deliver a predetermined amount of ink per time, a pump with a slower maximum flow velocity may be used to increase the duty ratio. This can reduce coarse particle production. Note that the duty ratio may be greater than or equal to 30%, or specifically, greater than or equal to 40%, or more specifically, greater than or equal to 50%. The duty ratio may be closer to 100% to address the above. However, control with the duty ratio close to 100% cannot increase the amount of ink to be delivered. Thus, the duty ratio may be less than or equal to 80%, or more specifically, less than or equal to 60%.
The treatment liquids such as the pretreatment liquid and the post-treatment liquid typically include no substance that may agglomerate like pigments, or may include a smaller amount of such a substance than ink. Thus, the flow velocity in the pump for circulating the treatment liquids may be faster than the flow velocity of the pump for circulating the ink. In this manner, when the circulating treatment liquids have faster flow velocities than the circulating ink, the duty ratio is typically lower and the delivery amount can be changed within a wider range. However, when the circulating treatment liquids have the same velocity as or a similar velocity to that of the circulating ink, the same pump can be used for the treatment liquids and the ink, allowing the circulation control to be the same or similar as well.
In the circulation channel with the pump pumping ink directly into the ink heads 4, the amount of circulating ink is, despite any pulsation, substantially constant in the channels from the pump to the ink heads 4, and decreases by the amount of ink ejected from the ink heads 4 in the channels downstream from the ink heads 4. Thus, the maximum flow rate of the circulating ink corresponds to the maximum flow rate of the ink delivered from the pump.
In the present embodiment, the circulation pump 85 delivers ink from the first collection subtank 71B to the first supply subtank 71A. The ink is delivered from the first supply subtank 71A to the first collection subtank 71B through the ink heads 4 using the difference in the pressures of gases supplied to the subtanks. The amount of delivery from the circulation pump 85 is greater than the amount of ink delivered from the first supply subtank 71A to the first collection subtank 71B when the ink heads 4 eject no ink. Thus, the amount of ink in the first collection subtank 71B does not increase while the circulation pump 85 is operating. This is achieved with the maximum flow rate (the maximum flow rate per unit time excluding fluctuations such as pulsation) from the circulation pump 85 being greater than the maximum flow rate of the ink flowing from the first supply subtank 71A to the ink heads 4. In other words, during continuous printing, the pressure difference between the first supply subtank 71A and the first collection subtank 71B allows the flow rate of ink flowing from the first supply subtank 71A to the ink heads 4 to be less than the maximum flow rate of ink delivered from the circulation pump 85. Additionally, the flow rate of ink flowing from the ink heads 4 to the first collection subtank 71B is less than the flow rate of the ink flowing from the first supply subtank 71A to the ink heads 4 by the amount of ink ejected from the ink heads 4. Thus, the maximum flow rate of circulating ink corresponds to the maximum flow rate of ink delivered from the circulation pump 85.
The flow rate of ink flowing in the circulation channel is directly measurable when the ink flows through, for example, a tube. The flow rate of ink can also be obtained through calculation (including simulation) using, for example, the dimensions of the channel, the pressure applied, or the physical properties of the ink. When the flow rate of ink flowing in an individual component is obtained, the flow velocity in the component can be obtained by dividing the flow rate by the cross-sectional area.
In each of the ink heads 4, the flow velocity is fastest in, for example, the individual channels connecting the common supply channel and the corresponding pressure chambers. These portions of the individual channel tend to have the smallest cross-sectional areas in the ink head 4. The individual channels are as many as the nozzles. The ink flowing into the ink head 4 is typically distributed into the individual channels connected in parallel. Thus, the ink flowing in each of the individual channels has a lower flow rate and a slower flow velocity. The flow velocity of the ink is, for example, 0.2 m/sec. Although the smallest cross-sectional area of the individual channel is smaller than the smallest cross-sectional area of the channel in the circulation pump 85, the maximum flow velocity in the individual channel is faster than the maximum flow velocity in the circulation pump 85.
More specifically, in each of the ink heads, the product of the smallest cross-sectional area of a channel of the individual channels and the number of individual channels is greater than or equal to the smallest cross-sectional area of the channel in the circulation pump 85. In each of the ink heads, the product of the smallest cross-sectional area of a channel in the individual channels and the number of individual channels is greater than the smallest cross-sectional area of the channel in the circulation pump 85. Note that, as described above, a single ink head 4 has a channel structure in which the multiple individual channels corresponding to the ejection portions (nozzles) are arranged in parallel. When the smallest cross-sectional area of a channel differs among the individual channels, the product of the smallest cross-sectional area of a channel in the individual channels and the number of individual channels corresponds to, and thus be calculated as, the sum of the smallest cross-sectional areas of the respective channels of the entire individual channels.
Note that the maximum flow velocity of ink in the circulation pump 85 may be less than or equal to 30 times, or specifically, less than or equal to 25 times, or more specifically, less than or equal to 15 times, or still more specifically, less than or equal to 10 times the flow velocity of the ink flowing in the individual channels in the ink head 4 described above (the maximum flow velocity of ink in the ink head).
Note that the circulation channel may include a valve, such as an electromagnetic valve, for stopping the flow of ink. When being open, such a valve defines a channel having a smaller cross-sectional area. The flow velocity in such a valve is, for example, 1.0 m/sec.
Note that the flow velocity of ink flowing in the circulation pump 85 may be less than or equal to 6 times, or specifically, less than or equal to 5 times, or more specifically, less than or equal to 3 times, or still more specifically, less than or equal to 2 times the flow velocity of ink in the valve described above. In other words, in the channel of the ink circulation channel extending from a collection port to a supply port through the circulation pump 85 and the supply subtank, the maximum flow velocity of ink in the circulation pump 85 may be less than or equal to 6 times, or specifically, less than or equal to 5 times, or more specifically, less than or equal to 3 times, or still more specifically, less than or equal to 2 times the maximum flow velocity of ink in the portion other than the circulation pump 85.
For the ink head 4 including filters, the total cross-sectional area of the filters is greater than the total cross-sectional area of the smallest portions of the individual channels. Thus, the flow velocity of ink in the individual channels is faster than the flow velocity of ink at the filters. The total cross-sectional area of the filters in the circulation channel is greater than the cross-sectional area of the valve such as the electromagnetic valve. Thus, the flow velocity of ink at the valve such as the electromagnetic valve is faster than the flow velocity of ink at the filters. This relationship is not limited for the ink, and is also applicable for the treatment liquids. In particular, for the ink head 4 including a filer inside (for example, the backend filter described above), the total open area of the filter may be greater than or equal to, or more specifically, greater than the smallest cross-sectional area of the channel in the circulation pump 85.
In the structure described above, setting the maximum flow velocity of ink in the circulation pump 85 at less than or equal to the predetermined velocity can reduce ink agglomeration and coarse particles. This can avoid damage on the circulation pump 85 or blockage of the paths.
In particular, in the present embodiment, the first collection subtank 71B located at the ink circulation channel stores ink collected from the respective ink heads. The circulation pump 85, located at the channel being a part of the circulation channel and connecting the first collection subtank 71B and the first supply subtank 71A (between the first collection subtank 71B and the first supply subtank 71A in an upstream-downstream positional relationship in the channel), pumps ink from the first collection subtank 71B to the first supply subtank 71A. This structure including the subtank for supply and the subtank for collection independently of the ink heads can reliably supply ink to the ink heads and collect ink from the ink heads. This structure also includes the circulation pump 85 located at the channel between the subtanks which is farthest from the ink heads, and thus can facilitate ink circulation without affecting ink ejection. This arrangement can reduce ink agglomeration and coarse particles.
Additionally, ink containing a binder as in the present embodiment has a natural tendency to agglomerate. However, limiting the maximum flow velocity of ink as described above can reduce agglomeration of ink containing a binder.
Ink being textile printing ink as in the present embodiment has a greater binder content to print images such as letters or patterns on a recording medium including a textile such as woven fabric or knitted fabric. In this case, agglomeration described above is more likely to occur. However, limiting the maximum flow velocity of ink in the same or similar manner can reduce agglomeration of ink containing a larger amount of binder.
Note that, when operating, the pump in the inkjet printer 1 according to the present embodiment provides a flow rate greater than or equal to 1.7 × 10^-7 m³/sec for ink flowing in the pump, as the pumps shown in Table 1. Ink circulating at such a greater flow rate is more likely to generate the velocity gradient described above, and thus accelerates agglomeration and coarse particle production. In this case, however, agglomeration of ink circulating at a greater flow rate can be reduced by limiting the maximum flow velocity of ink in the same manner or similar manner.
As shown in Table 1 and FIG. 6, the circulation pump 85 may be a peristaltic pump (working example 1 in Table 1). However, the peristaltic pump operates with rollers compressing a tube, deteriorating the tube gradually, and thus may have a lower flow rate over a long time. The peristaltic pump also operates with pulsation based on its operation principle. Thus, the peristaltic pump may be used as the circulation pump 85 within a range in which the above concerns are not apparent.
A piezoelectric pump (working example 2 in Table 1) as the circulation pump 85 can circulate ink while eliminating the concerns described above. As shown in Table 1, the piezoelectric pump can have a flow velocity less than or equal to a predetermined velocity. The piezoelectric pump is a type of diaphragm pumps that drives a diaphragm with a piezoelectric member. In a common diaphragm pump in which the diaphragm is driven mechanically or, for example, hydraulically, the amount of the displacement of the diaphragm over a single stroke (a single round of vibration) is substantially constant. The amount of ink pumped out by the displacement may also be relatively close to a specific amount. However, in a diaphragm pump in which the diaphragm is driven by a piezoelectric member, the diaphragm receiving substantially the same driving force is not displaced by the same amount. Although unknown in detail, when ink is not easily pumped out, the diaphragm receiving the same driving force may be displaced by a smaller amount, and thus may have a little lower flow rate and a little slower maximum flow velocity. Additionally, the piezoelectric pump does not cause pulsation described above, and thus can stably circulate ink. However, the piezoelectric pump has a relatively poor load characteristic, and may not achieve an intended flow rate depending on the resistance or inertance of the circulation channel. Thus, the piezoelectric pump may be used as the circulation pump 85 within a range in which these concerns are not apparent.
A diaphragm pump as the circulation pump 85 can circulate ink while eliminating the concerns described above. For the inkjet printer 1 according to the present embodiment including the diaphragm pump, the smallest cross-sectional area of the circulation channel in the pump is set to greater than or equal to 2.0 × 10^-6 m², and the maximum flow rate of ink is set to less than or equal to 1.7 × 10^-5 m³/sec. As described above, among diaphragm pumps, a piezoelectric pump may be used.
Table 1 shows working example 3 including a diaphragm pump and comparative examples 1 and 2 compared with working example 1. Comparative example 2 differs from comparative example 1 in that an external damper is attached.
Comparison of the working example 3 and the comparative examples 1 and 2 has revealed that slowing the maximum flow velocity reduces coarse particle production. The diaphragm pump has a relatively enhanced load characteristic compared with other pumps, and thus can be used appropriately to achieve an intended flow rate of ink flowing through the circulation channel.
FIG. 7 is also a graph showing the relationship between the shearing stress and the number of coarse particles in Table 1. The shearing stress refers to shearing stress on the ink (liquid) in each pump. The shearing stress in Table 1 and FIG. 7 is calculated with Formula 1, where the flow velocity distribution between parallel plates (Couette flow) is applicable in a pipe channel. $Shearing stress τ (in Pa) = μ \times v / r$ In Formula 1, µ (in Pa·s) is the viscosity of ink, and v (in m/s) is the flow velocity of ink. In this case, the flow velocity corresponds to the maximum flow velocity described above. Additionally, r (in m) corresponds to the radius of a circular tube as the channel, and can be calculated as the radius of a circle having an area of a passage through the valve in Table 1. In the examples above, the ink viscosity µ is 6 mPa·s.
The inventors of the present disclosure have noticed a tendency that the production of coarse particles increase or decrease depending on the shearing stress acting on ink in the pump. As described above, this phenomenon may be caused by accelerated agglomeration (shear agglomeration) of the particles of pigments, as viscous ink generates velocity gradient at the cross-sections of each channel, thus causing the particles to have different velocities and collide more frequently with one another. As shown in FIG. 7, ink agglomeration and coarse particles can be stably reduced within a range in which the shearing stress is less than or equal to 30 Pa. Such an expected boundary is added in FIG. 7 as a dashed line along an area of a shearing stress of 30 Pa. As shown in Table 1, for working examples 1, 2, and 3, the shearing stress is less than or equal to 30 Pa, and the number of coarse particles are also fewer than those of comparative examples.
The results have revealed that the shearing stress is a major cause of coarse particle production, and that setting the shearing stress within a range less than or equal to 30 Pa can stably reduce ink agglomeration and coarse particles.
In other words, during ink delivery with a pump that applies substantially the same pressure on ink, although ink with a higher viscosity tends to receive a greater shearing stress based on Formula 1, the flow velocity of the ink in the pipe is slower and the particles collide one another less frequently. In contrast, although ink with a lower viscosity tends to receive a smaller shearing stress based on Formula 1, the flow velocity of the ink is faster and the particles collide one another more frequently. Thus, independently of the ink viscosity, setting the shearing stress within a range less than or equal to 30 Pa as described above can stably reduce ink agglomeration and coarse particles.
To avoid a faster flow velocity of ink in the diaphragm pump, the inventors of the present disclosure have further focused on the valve structure for increasing the cross-sectional area. FIG. 8A is a schematic cross-sectional view of the circulation pump 85 in the present embodiment, illustrating its internal structure.
The circulation pump 85 includes a pump body 850, a pump chamber 851 defined in the pump body 850 to store ink, a displacement member 852, an inflow channel 85A, an outflow channel 85B, an inflow check valve 853, and an outflow check valve 854.
The displacement member 852 is a part of the pump chamber 851 (the upper surface of the pump chamber 851 in FIG. 8A) and is displaceable to switch inflow and outflow of ink in the circulation pump 85. The displacement member 852 is displaced to change the volume of the pump chamber 851. In the present embodiment, the displacement member 852 includes a piezoelectric vibrator and vibrates in accordance with an input drive voltage.
The inflow channel 85A communicates with an upstream portion of the ink circulation channel. In other words, the inflow channel 85A is located upstream from the pump chamber 851. In the same or similar manner, the outflow channel 85B communicates with a downstream portion of the ink circulation channel. In other words, the outflow channel 85B is located downstream from the pump chamber 851. The inflow check valve 853 is a displaceable check valve between the inflow channel 85A and the pump chamber 851. In the same or similar manner, the outflow check valve 854 is a displaceable check valve between the pump chamber 851 and the outflow channel 85B.
FIGs. 8B and 8C are schematic cross-sectional views of the outflow check valve 854 and its surrounding components in the circulation pump 85 in FIG. 8A. A check valve support 850H in FIG. 8B is a part of the pump body 850 in FIG. 8A and supports the outflow check valve 854. The check valve support 850H includes a flat surface 855 (a facing surface). The flat surface 855 faces the outflow check valve 854 and is connected to an inlet of the outflow channel 85B.
When the displacement member 852 in FIG. 8A is displaced to increase the pressure in the pump chamber 851, the outflow check valve 854 is displaced from a position in FIG. 8B to a position in FIG. 8C. This allows ink to flow from the pump chamber 851 to the outflow channel 85B. However, when the pump chamber 851 has a lower pressure than the outflow channel 85B, the outflow check valve 854 blocks the channel as in FIG. 8B, thus preventing backflow of ink from the outflow channel 85B to the pump chamber 851.
In the present embodiment, when the circulation pump 85 pumps ink, the outflow check valve 854 comes in contact with the flat surface 855 as in FIG. 8C. In this manner, the cross-sectional area of the channel near the outflow check valve 854 in the ink circulation channel is greater than when the check valve support 850H includes a protrusion as illustrated in FIG. 8B with a dashed line. Note that, in place of the flat surface 855, a curved surface, for example, may be located as the facing surface.
Note that the inflow check valve 853 in FIG. 8A and its surrounding components also have the same or a similar structure as the outflow check valve 854 and its surrounding components in FIGs. 8B and 8C. In this case, the pump chamber 851 in FIGs. 8B and 8C is replaced with the inflow channel 85A in FIG. 8A. The outflow channel 85B in FIGs. 8B and 8C is replaced with the pump chamber 851 in FIG. 8A. Thus, when the displacement member 852 in FIG. 8A is displaced to decrease the pressure in the pump chamber 851, the inflow check valve 853 allows ink to flow from the inflow channel 85A to the pump chamber 851. However, when the pump chamber 851 has a higher pressure than the inflow channel 85A, the inflow check valve 853 prevents backflow of ink from the pump chamber 851 to the inflow channel 85A.
Additionally, in the present embodiment, the channel in the circulation pump 85 has the smallest cross-sectional area in at least one of the channel in a portion including the inflow check valve 853 or the channel in a portion including the outflow check valve 854. In other words, in the circulation pump 85, the channel other than the portions including the inflow check valve 853 and the outflow check valve 854 are designed not to be thinner than the channels in the portions including the inflow check valve 853 and the outflow check valve 854. In other words, the smallest cross-sectional area of the channel in the circulation pump 85 is the cross-sectional area of the channel in the portions including the respective check valves. Note that the smallest cross-sectional area of the channel in the circulation pump 85 may be at least one of the cross-sectional area of the channel in the portion including the inflow check valve 853 or the cross-sectional area of the channel in the portion including the outflow check valve 854.
In the present embodiment, at least one of the inflow check valve 853 or the outflow check valve 854 defines, when being open, a channel having a cross-sectional area greater than or equal to 2.0 × 10^-6 m². Note that, in FIG. 8B, two arrows indicate the flow of ink allowed by the displacement of the outflow check valve 854. The flow of ink for the appropriate cross-sectional area as described above will be described in detail below.
For channels having the same cross-sectional areas, the shearing stress acting on ink has a greater effect as below in a structure having an elongated cross section than in a structure having a circular cross-section. In the elongated structure, the wall of the channel, at which the flow velocity is 0, is closer to a middle portion of the channel, at which the flow velocity is maximum. Thus, the shearing stress is greater. The shearing stress also has a greater effect in an area near the wall of the channel than in the middle portion of the channel. Thus, in the elongated structure in which the wall of the channel extends longer, the shearing stress has a greater effect in a larger area.
Thus, in the present embodiment, the cross-sectional area of the channel for the open outflow check valve 854 is set as described above to allow the opening defined by the open outflow check valve 854 to have an elongated shape. This can particularly reduce ink agglomeration in the circulation channel.
In the circulation channel using each of the pumps described above, the flow velocity of ink may be less than or equal to 6 m/sec, or more specifically, less than or equal to 5 m/sec. The flow velocity of the ink may also be less than or equal to 3 m/sec, or more specifically, less than or equal to 2 m/sec. In this manner, limiting the predetermined velocity for limiting the maximum flow velocity of ink can further reduce ink agglomeration and coarse particles.
The portion in the circulation channel in which the flow velocity of ink is set to less than or equal to the predetermined velocity may be a portion in the circulation pump 85 alone or a portion of the circulation channel except the respective ink heads. In other words, the ink circulation channel in FIG. 4 includes the supply ports Q1A and Q2A connected to the respective ink heads. The ink circulation channel also includes collection ports Q1B and Q2B connected to the respective ink heads. In the circulation channel, the maximum flow velocity of ink may be set to less than or equal to the predetermined velocity from the collection ports Q1B and Q2B to the supply ports Q1A and Q2A through the first collection subtank 71B, the circulation pump 85, and the first supply subtank 71A. In the present embodiment, the maximum flow velocity of ink from the collection ports to the supply ports through the circulation pump 85 and the supply subtank in the ink circulation channel is the flow velocity of ink in the circulation pump 85. More specifically, the maximum flow velocity of ink from the collection ports to the supply ports through the circulation pump 85 and the supply subtank in the ink circulation channel and the maximum flow velocity of ink in the ink heads 4 correspond to the flow velocity in the circulation pump 85. Additionally, the portion of the ink circulation channel in which the flow velocity of ink is set to less than or equal to the predetermined velocity may be the entire circulation channel including the respective ink heads. The maximum flow velocity of ink in the circulation pump 85 may also be faster than the maximum flow velocity of ink in the multiple individual channels in the ink head 4.
The nozzles for ejecting liquid in the ink head, or the individual channels for supplying and collecting ink to and from the nozzles include portions having smaller cross-sectional areas, and may thus be clogged with coarse particles or agglomerated coarse particles. Setting filters in the ink heads or in the ink circulation channel can reduce clogging in the nozzles or the individual channels. However, many coarse particles may clog the filters over a long time. Thus, in the circulation channel of ink, setting the flow velocity of ink to less than or equal to the predetermined velocity can reduce clogging in the nozzles, the individual channels, or the filters. The nozzles and the individual channels for supplying and collecting ink to and from the nozzles include a structure in which a nozzle is attached to an individual channel carrying ink from an ink supply source to an ink collection destination. In this structure, the individual channel is connected to the basal end of a cylindrical nozzle. When ink flows in the individual channel with this structure, ink in the nozzle starts flowing and mixes. With the flow of ink in the nozzle, part of the ink flowing in the individual channel is supplied to the nozzle, and part of the ink in the nozzle is collected to the individual channel.
Note that, in a channel structure in which the flow velocity is fastest inside the ink heads 4, coarse particles form in the ink heads 4 and are likely to cause clogging or other phenomena. Thus, a structure in which the flow velocity is fastest outside the ink heads 4 may be used and monitored to avoid formation of many coarse particles at the flow velocity.
Additionally, for a pump with at least a valve, the opening defined with the closed valve may be smaller, as the opening greater than an appropriate size may cause unstable liquid pumping volume due to external factors such as the pressure on the liquid or the flow velocity.
In the present embodiment as described above, the inkjet printer 1 (the inkjet recording apparatus), the ink circulation device, and the ink pump circulate ink to reduce overuse of ink and can also avoid blockage of the circulation channel including the heads and the tanks. Note that the embodiments of the present disclosure are not limited to the above embodiment and may include embodiments as below.

(1) The ink heads 4 are not limited to those arranged in two arrays on the carriage 3. The ink heads 4 may be in a single array or in three or more arrays. The inkjet printer 1 is not limited to eject multiple colors of ink onto the workpiece W, and may eject a single color of ink.
(2) In the above embodiments, the inkjet printer 1 may not include the pretreatment liquid head 5 for ejecting the pretreatment liquid, the post-treatment liquid head 6 for ejecting the post-treatment liquid, or any components associated with these heads.
(3) In the above embodiments, the ink circulation channel includes the collection tank. However, the collection tank may be eliminated. In this case, the ink circulation channel extending from the supply tank returns to the supply tank through the ink heads (supply destinations). The circulation pump 85 is a part of the circulation channel and pumps ink. In this case, the maximum flow velocity of ink in the circulation pump 85 may also be less than or equal to the predetermined velocity. Additionally, assuming that the first collection subtank 71B is eliminated in FIG. 4, the maximum flow velocity of ink from the collection ports Q1B and Q2B to the supply ports Q1A and Q2A through the circulation pump 85 and the first supply subtank 71A in the circulation channel may be set to less than or equal to the predetermined velocity, or the maximum flow velocity of ink in the entire circulation channel including the respective ink heads may be set to less than or equal to the predetermined velocity.
(4) The multiple structures described in each of the above embodiments may be combined with one another to provide an embodiment of the present disclosure.

REFERENCE SIGNS

1: inkjet printer
3: carriage 3
4: ink head
41A: first upstream ink head
41B: first downstream ink head
42A: second upstream ink head
42B: second downstream ink head
5: pretreatment liquid head
6: post-treatment liquid head
7: subtank
71A: first supply subtank
71A1: capacitive sensor
71B: first collection subtank
71B1: capacitive sensor
72A: second supply subtank
72B: second collection subtank
85: circulation pump
850: pump body
850H: check valve support
851: pump chamber
852: displacement member
853: inflow check valve
854: outflow check valve
855: flat surface
85A: inflow channel
85B: outflow channel
90: main tank
91: capacitive sensor
92: main tank valve
93: main supply pump
P11: supply pressure channel
P12: collection pressure channel
QA: ink supply channel
QB: ink collection channel
Q1: first ink path
Q2: second ink path
Q3: ink return channel
Q4: ink refill channel

Claims

An ink circulation device, comprising:
a circulation channel configured to carry ink including a pigment;

a supplier located at the circulation channel, the supplier being configured to supply the ink to a predetermined destination; and

a pump located at the circulation channel, the pump being configured to pump the ink flowing through the destination to the supplier,

wherein the destination is an ink head configured to eject the ink,

the ink head includes
a plurality of nozzles configured to eject the ink, and

a plurality of individual channels each for a corresponding nozzle of the plurality of nozzles, each of the plurality of individual channels including a channel configured to supply the ink to the corresponding nozzle and a channel configured to collect the ink from the corresponding nozzle,

the ink in the pump has a maximum flow velocity less than or equal to a predetermined velocity, and

a product of a smallest cross-sectional area of a channel of the plurality of individual channels and a number of the plurality of individual channels is greater than or equal to a smallest cross-sectional area of a channel in the pump.
An ink circulation device, comprising:
a circulation channel configured to carry ink including a pigment;

a supplier located at the circulation channel, the supplier being configured to supply the ink to a predetermined destination; and

a pump located at the circulation channel, the pump being configured to pump the ink flowing through the destination to the supplier,

wherein the ink in the pump receives a shearing stress less than or equal to 30 Pa.
The ink circulation device according to claim 1 or claim 2, wherein
the ink further includes a binder.
The ink circulation device according to claim 3, wherein
the ink is a textile printing ink.
The ink circulation device according to any one of claims 1 to 4, wherein
the ink flowing in the pump has a flow rate greater than or equal to 1.7 × 10^-7 m³/sec.
The ink circulation device according to any one of claims 1 to 5, wherein
the pump is a piezoelectric pump.
The ink circulation device according to any one of claims 1 to 5, wherein
the pump is a diaphragm pump, the circulation channel in the pump has a smallest cross-sectional area greater than or equal to 2.0 × 10^-6 m², and the ink in the pump has a maximum flow rate greater than or equal to 1.7 × 10^-5 m³/sec.
The ink circulation device according to any one of claims 1 to 7, further comprising:
a collector located at the circulation channel, the collector being configured to collect the ink from the destination,

wherein the pump is located between the collector and the supplier to pump the ink from the collector to the supplier.
The ink circulation device according to any one of claims 1 to 8, wherein
the pump includes a check valve being displaceable, and

the pump has a smallest cross-sectional area of a channel in a portion including the check valve.
The ink circulation device according to any one of claims 1 to 5, wherein
the pump includes
a pump chamber configured to store the ink,

a displacement member being a part of the pump chamber and displaceable to change a volume of the pump chamber,

an inflow channel upstream from the pump chamber,

an outflow channel downstream from the pump chamber,

an inflow check valve being displaceable and between the inflow channel and the pump chamber, and

an outflow check valve being displaceable and between the pump chamber and the outflow channel, and

the pump includes a channel with a smallest cross-sectional area being at least one of a cross-sectional area in a portion including the inflow check valve or a cross-sectional area in a portion including the outflow check valve.
The ink circulation device according to any one of claims 1 to 5, wherein
the pump includes
a pump chamber configured to store the ink,

a displacement member being a part of the pump chamber and displaceable to change a volume of the pump,

an inflow channel upstream from the pump chamber,

an outflow channel downstream from the pump chamber,

an inflow check valve being displaceable and between the inflow channel and the pump chamber, and

an outflow check valve being displaceable and between the pump chamber and the outflow channel, and

at least one of the inflow check valve or the outflow check valve being open has a cross-sectional area of 2.0 × 10^-6 m².
The ink circulation device according to any one of claims 1 to 5, wherein
the pump includes
a pump chamber configured to store the ink,

a displacement member being a part of the pump chamber and displaceable to change a volume of the pump chamber,

an inflow channel upstream from the pump chamber,

an outflow channel downstream from the pump chamber,

an inflow check valve being displaceable and between the inflow channel and the pump chamber,

an outflow check valve being displaceable and between the pump chamber and the outflow channel, and

a facing surface facing the outflow check valve and connecting to an inlet of the outflow channel, and

the outflow check valve comes in contact with the facing surface when the pump pumps the ink.
The ink circulation device according to any one of claims 1 to 12, wherein
the ink in the pump has a maximum flow velocity less than or equal to 6 m/sec.
The ink circulation device according to any one of claims 1 to 13, wherein
the destination is an ink head configured to eject the ink, and

the ink in the pump has a maximum flow velocity less than or equal to 30 times a maximum flow velocity of the ink in the ink head.
The ink circulation device according to any one of claims 1 to 13, wherein
the destination is an ink head configured to eject the ink,

the ink head includes
a plurality of nozzles configured to eject the ink, and

a plurality of individual channels each for a corresponding nozzle of the plurality of nozzles, each of the plurality of individual channels including a channel configured to supply the ink to the corresponding nozzle and a channel configured to collect the ink from the corresponding nozzle, and

the plurality of individual channels includes a channel with a smallest cross-sectional area being smaller than a smallest cross-sectional area of a channel in the pump.
The ink circulation device according to claim 15, wherein
the ink head includes a filter inside, and a total of open areas of the filter is greater than or equal to the smallest cross-sectional area of the channel in the pump.
The ink circulation device according to any one of claims 1 to 13, wherein
the destination is an ink head configured to eject the ink,

the circulation channel includes a supply port and a collection port connected to the ink head, and

the ink has, in the circulation channel from the collection port to the supply port through the pump and the supplier, a maximum flow velocity less than or equal to the predetermined velocity.
The ink circulation device according to any one of claims 1 to 13, wherein
the destination is an ink head configured to eject the ink,

the circulation channel includes a supply port and a collection port connected to the ink head, and

the ink has, in the circulation channel from the collection port to the supply port through the pump and the supplier, a maximum flow velocity being a flow velocity in the pump.
The ink circulation device according to any one of claims 1 to 13, wherein
the destination is an ink head configured to eject the ink,

the circulation channel includes a supply port and a collection port connected to the ink head, and

the ink has, in the circulation channel from the collection port to the supply port through the pump and the supplier and in the ink head, a maximum flow velocity being a flow velocity in the pump.
The ink circulation device according to any one of claims 1 to 13, wherein
the destination is an ink head configured to eject the ink,

the ink head includes
a plurality of nozzles configured to eject the ink, and

a plurality of individual channels each for a corresponding nozzle of the plurality of nozzles, each of the plurality of individual channels including a channel configured to supply the ink to the corresponding nozzle and a channel configured to collect the ink from the corresponding nozzle, and

the ink in the pump has a greater maximum flow velocity than in the plurality of individual channels.
The ink circulation device according to any one of claims 1 to 13, wherein
the destination is an ink head configured to eject the ink,

the circulation channel includes a supply port and a collection port connected to the ink head, and

the ink in the pump has a maximum flow velocity less than or equal to six times a maximum flow velocity of the ink in a portion other than the pump in a channel of the circulation channel from the collection port to the supply port through the pump and the supplier.
An inkjet recording apparatus, comprising:
a circulation channel configured to carry ink including a pigment;

an ink head configured to eject the ink;

a supplier located at the circulating path, the supplier being configured to supply the ink to the ink head; and

a pump located at the circulating path, the pump being configured to pump the ink collected from the ink head to the supplier,

wherein the ink head includes
a plurality of nozzles configured to eject the ink, and

a plurality of individual channels each for a corresponding nozzle of the plurality of nozzles, each of the plurality of individual channels including a channel configured to supply the ink to the corresponding nozzle and a channel configured to collect the ink from the corresponding nozzle,

the ink in the circulation channel has a maximum flow velocity less than or equal to a predetermined velocity, and

a product of a smallest cross-sectional area of a channel of the plurality of individual channels and a number of the plurality of individual channels is greater than or equal to a smallest cross-sectional area of a channel in the pump.
An inkjet recording apparatus, comprising:
a circulation channel configured to carry ink including a pigment;

an ink head configured to eject the ink;

a supplier located at the circulating path, the supplier being configured to supply the ink to the ink head; and

a pump located at the circulating path, the pump being configured to pump the ink collected from the ink head to the supplier,

wherein the ink in the pump receives a shearing stress less than or equal to 30 Pa.
An ink pump to be located at a circulation channel for carrying ink including a pigment, the ink pump being configured to pump, to a supplier located at the circulation channel to supply the ink to a predetermined destination, the ink flowing through the destination, wherein the ink in the pump has a maximum flow velocity less than or equal to a predetermined velocity.
An ink pump to be located at a circulation channel for carrying ink including a pigment, the ink pump being configured to pump, to a supplier located at the circulation channel to supply the ink to a predetermined destination, the ink flowing through the destination, wherein the ink in the pump receives a shearing stress less than or equal to 30 Pa.