WO2024204800A1 - Ink circulation device, inkjet recording device equipped with same, and ink pump - Google Patents

Abstract

This inkjet recording device is provided with: a circulation path through which ink containing a pigment flows; a supply unit that is positioned in the circulation path and supplies the ink to a prescribed supply destination; and a pump that is positioned in the circulation path and sends the ink, which has passed through the supply destination, to the supply unit, wherein the maximum flow velocity of the ink in the pump is set to be equal to or less than a prescribed velocity, and the product of the minimum flow passage cross-sectional area in an individual flow passage of an ink head being the supply destination and the number of individual flow passages is equal to or greater than the minimum flow passage cross-sectional area in the pump.

Description

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

This disclosure relates to an ink circulation device, an inkjet recording device equipped with the same, and an ink pump.

Patent Document 1 discloses an inkjet recording device equipped with a mechanism for circulating ink between a recording head and an ink tank. In this technology, the inkjet recording device includes a tank that contains ink, a recording head that ejects ink supplied from the tank, a supply flow path that supplies ink from the tank to the recording head, a recovery flow path that recovers 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 path that includes the tank, supply flow path, recording head, and recovery flow path, while the pump is driven at a second speed faster than the first speed until a predetermined time has elapsed since the start of ink circulation.

JP 2022-51952 A

The objective of this disclosure is to provide an ink circulation device capable of preventing clogging of the circulation path including the head and tank, as well as an inkjet recording device and an ink pump that are equipped with the same.

An ink circulation device according to one aspect of the present disclosure includes a circulation path through which ink containing a pigment flows, a supply unit located in the circulation path and supplying the ink to a predetermined destination, and a pump located in the circulation path and sending the ink via the destination to the supply unit, the destination being an ink head capable of ejecting the ink, the ink head including a plurality of nozzles ejecting the ink, and a plurality of individual flow paths provided for each of the plurality of nozzles, the individual flow paths including a flow path for supplying the ink to the nozzle and a flow path for recovering the ink from the nozzle, the maximum flow velocity of the ink in the pump is set to a predetermined velocity or less, and the product of the minimum flow path cross-sectional area in the individual flow paths and the number of the individual flow paths is greater than or equal to the minimum flow path cross-sectional area in the pump.

An ink circulation device according to another aspect of the present disclosure includes a circulation path through which pigment-containing ink flows, a supply unit located in the circulation path and supplying the ink to a predetermined destination, and a pump located in the circulation path and sending the ink via the destination to the supply unit, and the shear stress generated in the ink within the pump is 30 (Pa) or less.

In addition, an inkjet recording device according to another aspect of the present disclosure includes a circulation path through which ink containing a pigment flows, an ink head capable of ejecting the ink, a supply unit located in the circulation path and supplying the ink to the ink head, and a pump located in the circulation path and sending the ink recovered from the supply destination to the supply unit, the ink head includes a plurality of nozzles that eject the ink, and a plurality of individual flow paths provided for each of the plurality of nozzles, including a flow path that supplies the ink to the nozzle and a flow path that recovers the ink from the nozzle, the maximum flow speed of the ink in the circulation path is set to be equal to or lower than the predetermined speed, and the product of the minimum flow path cross-sectional area in the individual flow path and the number of the individual flow paths is equal to or greater than the minimum flow path cross-sectional area in the pump.

An inkjet recording device according to another aspect of the present disclosure includes a circulation path through which pigment-containing ink flows, an ink head capable of ejecting the ink, a supply unit located in the circulation path for supplying the ink to the ink head, and a pump located in the circulation path for sending the ink recovered from the ink head to the supply unit, and the shear stress generated in the ink within the pump is 30 (Pa) or less.

Furthermore, an ink pump according to another aspect of the present disclosure is an ink pump located in a circulation path through which ink containing a pigment flows, and is capable of sending the ink via a supply destination to a supply section located in the circulation path that supplies the ink to a predetermined supply destination, and the maximum flow rate of the ink in the pump is set to a predetermined speed or less.

Furthermore, an ink pump according to another aspect of the present disclosure is an ink pump located in a circulation path through which ink containing a pigment flows, and is capable of sending the ink via a supply destination to a supply section located in the circulation path that supplies the ink to a specified supply destination, and the shear stress generated in the ink within the pump is 30 (Pa) or less.

FIG. 1 is a perspective view showing the overall configuration of a recording apparatus according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. FIG. 3 is an enlarged perspective view of the carriage shown in FIG. FIG. 4 is a schematic diagram showing the flow of ink around an ink head according to an embodiment of the present disclosure. FIG. 5 is a schematic diagram showing a supply sub-tank and a recovery sub-tank according to an embodiment of the present disclosure. FIG. 6 is a graph showing the relationship between the flow velocity in the pump and the amount of coarse particles in an example of a pump according to an embodiment of the present disclosure and a comparative example compared to the example. FIG. 7 is a graph showing the relationship between the shear stress in the pump and the amount of coarse particles in an example of a pump according to an embodiment of the present disclosure and a comparative example compared to the example. FIG. 7A is a schematic cross-sectional view showing an internal structure of a pump according to an embodiment of the present disclosure. FIG. 7B is a schematic cross-sectional view showing a portion of the internal structure of the pump according to one embodiment of the present disclosure. FIG. 7C is a schematic cross-sectional view showing a portion of the internal structure of a pump according to an embodiment of the present disclosure.

Below, a recording device according to an embodiment of the present disclosure will be described with reference to the drawings. In the following embodiment, an inkjet printer equipped with an ink head that ejects ink for forming an image onto a wide, long recording medium will be exemplified as a specific example of a recording device. Inkjet printers are suitable for digital textile printing, which uses an inkjet method to print images such as letters and patterns onto a recording medium made of fabric such as woven or knitted fabric. Of course, the recording device according to the present disclosure can also be used to print various images onto recording media such as paper sheets and resin sheets.

[Overall configuration of inkjet printer]
FIG 1 is a perspective view showing the overall configuration of an inkjet printer 1 according to a first embodiment of the present disclosure, and FIG 2 is a schematic cross-sectional view taken along line II-II in FIG 1. The inkjet printer 1 is a printer that prints images on a wide and long workpiece W (recording medium) using an inkjet method. As an example, the width of the workpiece W is several meters. The printer 1 includes a device frame 10, and a work transport section 20 and a carriage 3 that are incorporated into this device frame 10. Note that in this embodiment, the left-right direction is the main scanning direction S ( FIG. 3 ) when printing on the workpiece W, and the direction from the rear to the front is the sub-scanning direction (the transport direction F of the workpiece W, which is a direction that intersects with the main scanning direction S).

The device frame 10 forms a framework for mounting various components of the inkjet printer 1. The work transport unit 20 is a mechanism that intermittently feeds (transports) the work W so that the work W progresses in a transport direction F from rear to front in the printing area where the inkjet printing process is performed. The carriage 3 is equipped with an ink head 4, a pre-treatment liquid head 5, a post-treatment liquid head 6, and a sub-tank 7, and moves back and forth in a main scanning direction S (left-right direction) that intersects with the transport direction F of the work W during the inkjet printing process.

The device frame 10 includes a central frame 111, a right frame 112, and a left frame 113. The central frame 111 forms a framework for mounting various components of the inkjet printer 1, and has a left-right width corresponding to the work transport section 20. The right frame 112 and the left frame 113 are erected to the right and left of the central frame 111, respectively. Between the right frame 112 and the left frame 113 is the printing area 12 where printing processing is performed on the work W.

The right frame 112 forms the maintenance area 13. The maintenance area 13 is an area where the carriage 3 is retracted when the printing process is not being performed. In the maintenance area 13, cleaning processes, purging processes, etc. are performed on the nozzles (ejection holes) of the ink head 4, pre-treatment liquid head 5, and post-treatment liquid head 6, and caps are also fitted. The left frame 113 forms the turn-around area 14 for the carriage 3. The turn-around area 14 is an area where the carriage 3 temporarily enters when it performs a main scan in the opposite direction after performing a main scan in the opposite direction from right to left in the printing process.

A carriage guide 15 is attached to the upper side of the device frame 10 to allow the carriage 3 to move back and forth in the left-right direction. The carriage guide 15 is a flat member that is long in the left-right direction, and is disposed above the work transport section 20. A timing belt 16 is attached to the carriage guide 15 so that it can move in a circular motion in the left-right direction (main scanning direction). The timing belt 16 is an endless belt that is driven to move in a circular motion in the left or right direction.

The carriage guide 15 is equipped with a pair of upper and lower guide rails 17 that extend parallel to the left and right and that hold the carriage 3 in a state in which it can move back and forth in the main scanning direction S. The carriage 3 engages with the guide rails 17. The carriage 3 is also fixed to a timing belt 16. As the timing belt 16 moves orbitally to the left or right, the carriage 3 moves left or right along the carriage guide 15 while being guided by the guide rails 17.

Referring primarily to FIG. 2, the work transport section 20 includes a feed roller 21 that pays out the work W before printing, and a take-up roller 22 that takes up the work W after printing. The feed roller 21 is located at the rear lower part of the device frame 10, and is a take-up shaft for the feed roll WA, which is a wound body of the work W before printing. The take-up roller 22 is located at the front lower part of the device frame 10, and is a take-up shaft for the take-up roll WB, which is a wound body of the work W after the printing process. A first motor M1 is attached to the take-up roller 22, which drives the take-up roller 22 to rotate around its axis and perform the winding operation of the work W.

The path between the delivery roller 21 and the take-up roller 22 and passing through the printing area 12 is the transport path for the work W. On this transport path, in order from the upstream side, a first tension roller 23, a work guide 24, a transport roller 25 and a pinch roller 26, a turn-back roller 27, and a second tension roller 28 are arranged. The first tension roller 23 applies a predetermined tension to the work W on the upstream side of the transport roller 25. The work guide 24 changes the transport direction of the work W from upward to forward, allowing the work W to enter the printing area 12.

The transport roller 25 is a roller that generates a transport force that intermittently feeds the workpiece W in the printing area 12. The transport roller 25 is driven to rotate about its axis by the second motor M2, and intermittently transports the workpiece W forward (predetermined transport direction F) so that the workpiece W passes through the printing area 12 (image forming position) facing the carriage 3. The pinch roller 26 is disposed to face the transport roller 25 from above, and forms a transport nip portion with the transport roller 25.

The turn-back roller 27 changes the transport direction of the work W that has passed through the printing area 12 from the forward direction to the downward direction, and guides the work W after the printing process to the take-up roller 22. The second tension roller 28 applies a predetermined tension to the work W downstream of the transport roller 25. A platen 29 is disposed below the transport path of the work W in the printing area 12.

The carriage 3 is supported at one end by the guide rail 17 and moves back and forth in the main scanning direction S (left and right in this embodiment) that intersects (orthogonal in this embodiment) with the transport direction F. The carriage 3 comprises a carriage frame 30, and an ink head 4, a pre-treatment liquid head 5, a post-treatment liquid head 6, and a sub-tank 7 (Figure 3) that are mounted on the carriage frame 30. The carriage frame 30 includes a head support frame 31 and a back frame 32.

The head support frame 31 is a horizontal plate that holds the heads 4 to 6 described above. The back frame 32 is a vertical plate that extends upward from the rear edge of the head support frame 31. As described above, the timing belt 16 is fixed to the back frame 32. The guide rail 17 is engaged with the back frame 32. That is, in this embodiment, the back frame 32 is an engagement portion that is held in a cantilevered state by the guide rail 17. The head support frame 31 is a horizontal plate whose rear end side is supported in a cantilevered state by the guide rail 17 via the engagement portion.

Note that the cantilevered state refers to a state in which the engagement portion (back frame 32), which is the portion of the carriage 3 that is held by the guide rail 17, which is a holding member, is present only on one side, either upstream or downstream, from the center of the carriage 3 in the transport direction F, and no other engagement portion is present on the opposite side to the side where the engagement portion is present. The engagement portion may also be located outside the range in which the ink head 4 and processing head are located in the transport direction F. In other words, the engagement portion may be located only upstream or only downstream of the range in which the ink head 4 and processing head are located in the transport direction F.

[Carriage details]
The carriage 3 will be further described. Fig. 3 is an enlarged perspective view of the carriage 3 shown in Fig. 1. Fig. 3 shows a transport direction F (sub-scanning direction) of the work W and a main scanning direction S which is a moving direction of the carriage 3. Fig. 3 shows an example in which a plurality of ink heads 4 which eject ink for forming an image onto the work W, a pre-treatment liquid head 5 and a post-treatment liquid head 6 which eject a non-coloring treatment liquid, and a plurality of sub-tanks 7 which supply the ink and the treatment liquid to these heads 4 to 6 are mounted on the carriage 3.

Each ink head 4 has a large number of nozzles (ink ejection holes) that eject ink droplets using an ejection method such as a piezoelectric method using a piezoelectric element or a thermal method using a heating element.

Each of the ink heads 4 includes, for example, a plurality of ejection sections including nozzles, a common supply flow path that supplies ink to the plurality of ejection sections, and a common recovery flow path that recovers ink from the plurality of ejection sections. This common recovery flow path recovers ink that is supplied to the ejection sections and not ejected from the nozzles.

The ejection unit includes an individual flow path connecting the common supply flow path and the common recovery flow path, a pressure unit such as a piezoelectric element or a heating element, and a nozzle. In the individual flow path, the portion facing the pressure unit is called a pressure chamber. The pressure chamber and the nozzle may be arranged in the individual flow path from the common supply flow path side, but this arrangement order may be reversed. In the individual flow path, the flow path from the common supply flow path to the nozzle supplies ink to the nozzle, and the flow path from the nozzle to the common recovery flow path recovers ink that has not been ejected from the nozzle. In the individual flow path, the cross-sectional area of the portion with the smallest cross-sectional area perpendicular to the ink flow direction is called the minimum cross-sectional area of the individual flow path. This minimum cross-sectional area may be arranged in the middle of the flow path connecting the pressure chamber and any of the common flow paths. Note that the ink heading from the common supply flow path to the common recovery flow path does not pass through the nozzle, so when considering the minimum cross-sectional area of the individual flow path, the nozzle is not included in the individual flow path.

In addition, to add a note about the structure of each ink head, the ink that flows into the ink head flows into the above-mentioned common supply flow path through a forward flow path formed in the introduction section (also called the back end). The ink is then supplied to each nozzle through individual flow paths provided in each ejection section. Some of the ink is ejected from the nozzle, while the remaining ink flows from the individual flow paths into the common recovery flow path and then flows out of the ink head through a return flow path formed in the introduction section. Each of the multiple individual flow paths is provided by branching off from the common supply flow path. Each of the multiple individual flow paths is connected to the common recovery flow path and is arranged to converge at the common recovery flow path. In other words, in one ink head 4, the multiple individual flow paths provided corresponding to each ejection section (nozzle) are arranged in parallel in terms of flow path structure.

Each ink head 4 may further include a filter. The filter is, for example, placed in the common supply flow path or upstream of it, and makes it difficult for foreign matter or coarse particles in the ink to flow downstream so that the nozzle or the individual flow paths are less likely to become clogged. The filter may also be placed in the flow path of the introduction section (back end) mentioned above (back end filter). All ink supplied to the ink head passes through the back end filter, and the ink that has passed through the back end filter then heads toward the common supply flow path.

As the ink, for example, a water-based pigment ink containing a water-based solvent, pigment, and binding resin (binder) can be used.

The binder resin may be present in a dispersed state in the aqueous medium. The binder resin has the function of binding the printing object and the pigment. For this reason, by including a binder resin in the ink, a printed product with excellent pigment fixation can be obtained. Examples of binder resins include urethane resins, (meth)acrylic resins, styrene-(meth)acrylic resins, styrene-maleic acid copolymers, vinylnaphthalene-(meth)acrylic acid copolymers, and vinylnaphthalene-maleic acid copolymers. The content of the binder resin is preferably 1% by mass or more and 20% by mass or less, and more preferably 2% by mass or more and 10% by mass or less, based on the mass of the ink.

The ink heads 4 in this embodiment are capable of ejecting eight colors of ink. The ink heads 4 are mounted on the head support frame 31 of the carriage 3 so that they are aligned in two rows in the main scanning direction S. Each color of ink head 4 has two heads.

Specifically, the ink heads 4 have a first upstream ink head 41A and a first downstream ink head 41B. These ink heads 4 eject yellow ink. The ink heads 4 also have a second upstream ink head 42A and a second downstream ink head 42B. These ink heads 4 eject magenta ink. Similarly, as shown in FIG. 3, two ink heads 4 that eject ink of the same color are arranged at positions offset from each other in the transport direction F and the main scanning direction S. These two ink heads 4 form a set, and a total of eight sets of ink heads 4 (41A-48A, 41B-48B) eject ink of different colors.

The pre-treatment liquid head 5 and the post-treatment liquid head 6 are disposed at positions different from the ink head 4 in the transport direction F. The pre-treatment liquid head 5 is disposed upstream of the ink head 4 in the transport direction F. FIG. 3 shows an example in which one pre-treatment liquid head 5 is disposed near the left end of the array of ink heads 4. Similarly, the post-treatment liquid head 6 is disposed downstream of the ink head 4 in the transport direction F. FIG. 3 shows an example in which one post-treatment liquid head 6 is disposed at the right end of the array of ink heads 4. In other embodiments, multiple pre-treatment liquid heads 5 or multiple post-treatment liquid heads 6 may be disposed. It is desirable that the carriage 3 is provided with at least one pre-treatment liquid head 5 and at least one post-treatment liquid head 6, but in other embodiments, the pre-treatment liquid head 5 and the post-treatment liquid head 6 may not be disposed.

The series of heads arranged along the main scanning direction S, which is made up of the ink heads 4, pretreatment liquid heads 5, and posttreatment liquid heads 6, is referred to as a row of heads, or simply as a row. The series of heads arranged along the transport direction F, which is made up of the ink heads 4, pretreatment liquid heads 5, and posttreatment liquid heads 6, is referred to as a row of heads, or simply as a row.

The pretreatment liquid head 5 ejects pretreatment liquid for performing a predetermined pretreatment on the workpiece W. The pretreatment liquid is ejected from the ink head 4 onto a position on the workpiece W where ink has not yet been ejected from the ink head 4. The pretreatment liquid is a non-coloring treatment liquid that does not develop color even when it adheres to the workpiece W, and is a treatment liquid that exhibits functions such as increasing the fixation of ink to the workpiece W and the coagulation of ink pigments. As such a pretreatment liquid, a treatment liquid in which a binding resin is mixed into a solvent, or a treatment liquid in which a positively charged cationic resin is mixed into a solvent, can be used.

The post-treatment liquid head 6 ejects post-treatment liquid for performing a predetermined post-treatment on the workpiece W to which ink has been attached. The post-treatment liquid is ejected from the post-treatment liquid head 6 to a position on the workpiece W after the ink has been ejected from the ink head 4. The post-treatment liquid is a non-coloring treatment liquid that does not develop color even when it adheres to the workpiece W, and has the function of increasing the fixability and robustness (resistance to rubbing and scraping) of the ink image printed on the workpiece W by the ink head 4. A silicone-based treatment liquid or the like can be used as such a post-treatment liquid. Note that the post-treatment liquid and the pre-treatment liquid are different treatment liquids. Specifically, the post-treatment liquid and the pre-treatment liquid contain different components.

Here, non-color-forming processing liquid refers to a liquid that, when printed alone on a recording medium, is not recognized as having color by the naked eye. Colors here include colors with a saturation of zero, such as black, white, and gray. Non-color-forming processing liquids are basically transparent liquids, but for example, when 1 liter of processing liquid is viewed in liquid form, it is not completely transparent and may appear slightly white. Such colors are very light, so when printed alone on a recording medium, it is not recognized as having color by the naked eye. Note that, depending on the type of processing liquid, when printed alone on a recording medium, changes such as the appearance of gloss on the recording medium may occur, but such a state is not color-forming.

In this embodiment, the pre-treatment liquid and the post-treatment liquid may be ejected onto substantially the entire surface of the workpiece W, or the pre-treatment liquid and the post-treatment liquid may be ejected selectively in accordance with the image to be printed, similar to ink.

Next, a case where the pretreatment liquid and posttreatment liquid are selectively ejected will be described. As described above, the pretreatment liquid, ink, and posttreatment liquid are ejected in that order onto the workpiece W in the portion where the color is to be printed according to the image. In this case, the ink may be of one color or of multiple colors. In the portion where the color is not to be printed, i.e., the portion where the ink is not ejected, the pretreatment liquid and posttreatment liquid are basically not ejected either. Note that in order to adjust the image quality of the printed image and the texture of the workpiece W, the selection of the ejection of the pretreatment liquid and posttreatment liquid may be made to differ from the ejection of the ink.

As shown in FIG. 3, openings 31H are provided at the locations of the heads on the head support frame 31. The ink head 4, pre-treatment liquid head 5, and post-treatment liquid head 6 are attached to the head support frame 31 so that they fit into the respective openings 31H. Nozzles arranged on the bottom end surface of each of the heads 4, 5, and 6 are exposed from each opening 31H.

The multiple subtanks 7 are supported by the carriage 3 above the heads 4, 5, and 6 via a holding frame (not shown). The multiple subtanks 7 are provided corresponding to each of the heads 4, 5, and 6. Ink or treatment liquid is supplied to each subtank 7 from a main tank 90 (described below) that contains ink and treatment liquid, and these are supplied to each of the heads 4, 5, and 6. Each subtank 7 and the heads 4, 5, and 6 are connected by pipelines (not shown in FIG. 3).

Specifically, the multiple subtanks 7 have a first supply subtank 71A to an eighth supply subtank 78A, a pre-treatment supply subtank 7FA, and a post-treatment supply subtank 7RA arranged on the rear side along the main scanning direction S. The first to eighth supply subtanks are located in the ink circulation path and supply ink to a specified destination (ink head). Furthermore, the multiple subtanks 7 have a first recovery subtank 71B to an eighth recovery subtank 78B, a pre-treatment recovery subtank 7FB, and a post-treatment recovery subtank 7RB arranged on the front side along the main scanning direction S. The first to eighth recovery subtanks are located in the ink circulation path and recover ink from the ink head 4.

The first supply sub-tank 71A and the first recovery sub-tank 71B located on the far left side of the carriage 3 store yellow ink containing a pigment. The first supply sub-tank 71A supplies yellow ink to the first upstream ink head 41A and the first downstream ink head 41B (both of which are also referred to as supply destinations). On the other hand, the first recovery sub-tank 71B stores the yellow ink recovered from the first upstream ink head 41A and the first downstream ink head 41B. As mentioned above, a portion of the yellow ink is ejected toward the workpiece W from the first upstream ink head 41A and the first downstream ink head 41B. Similarly, the second supply sub-tank 72A supplies magenta ink to the second upstream ink head 42A and the second downstream ink head 42B. On the other hand, the second recovery sub-tank 72B stores the magenta ink recovered from the second upstream ink head 42A and the second downstream ink head 42B. Each of the other sub-tanks, from the third sub-tank to the eighth sub-tank, has the same structure and function as described above.

The pre-treatment supply sub-tank 7FA supplies pre-treatment liquid to the pre-treatment liquid head 5, and the pre-treatment recovery sub-tank 7FB recovers pre-treatment liquid from the pre-treatment liquid head 5. The post-treatment supply sub-tank 7RA supplies post-treatment liquid to the post-treatment liquid head 6, and the post-treatment recovery sub-tank 7RB recovers post-treatment liquid from the post-treatment liquid head 6.

As described above, the inkjet printer 1 according to this embodiment is an all-in-one printer in which three types of heads - the ink head 4, the pretreatment liquid head 5, and the posttreatment liquid head 6 - are mounted on a single carriage 3. With this inkjet printer 1, for example, in the printing process in digital textile printing where inkjet printing is performed on fabric, the process of ejecting the pretreatment liquid and the process of ejecting the posttreatment liquid can be carried out in an integrated manner. This makes it possible to simplify the textile printing process and make the textile printing device more compact.

The inkjet printer 1 according to this embodiment uses a serial printing method to print on the workpiece W. Specifically, if the workpiece W is wide, it is not possible to print on the workpiece W while continuously feeding it. The serial printing method is a printing method that repeats the reciprocating movement of a carriage 3 carrying ink heads 4 of each color in the main scanning direction S and the intermittent feeding of the workpiece W in the transport direction F.

Specifically, the strip image is printed while the carriage 3 moves in the forward direction, which is one of the main scanning directions S. During this main scanning in the forward direction, the feeding of the workpiece W is stopped. After the strip image is printed, the workpiece W is sent out in the transport direction F by a predetermined pitch. At this time, the carriage 3 waits in the turn-back area 14 on the left end side. After the workpiece W is sent out, the carriage 3 turns back in the return direction, which is opposite to the forward direction, as the timing belt 16 moves in reverse. The workpiece W is in a stopped state. Then, while moving in the return direction, the carriage 3 prints the next strip image upstream of the strip image. Similar operations are repeated thereafter.

<Circulation paths for ink and processing liquid>
Next, the flow of ink and treatment liquid in the inkjet printer 1 according to this embodiment will be described. Note that, although the flow of ink will be described in detail below, a similar structure is provided for each treatment liquid. Fig. 4 is a schematic diagram showing the flow of ink around the liquid ejection head according to this embodiment. Fig. 5 is a schematic diagram showing a supply sub-tank and a recovery sub-tank according to this embodiment. Note that in each figure, the lines connecting members indicate pipes (tubes) through which gas or liquid flows.

In this embodiment, pressure is applied via gas (air) to each of the first supply sub-tank 71A through post-treatment supply sub-tank 7RA (also referred to as a supply tank or supply section, respectively) and the first recovery sub-tank 71B through post-treatment recovery sub-tank 7RB (also referred to as a recovery tank or recovery section, respectively) mounted on the carriage 3 in FIG. 3. As a result, liquid (ink, pre-treatment liquid, post-treatment liquid) is supplied from each supply sub-tank to the ink head 4, pre-treatment liquid head 5, and post-treatment liquid head 6.

With reference to FIG. 4, the circulation path including the supply and recovery paths for yellow ink to the first upstream ink head 41A and the first downstream ink head 41B will be described. Note that a structure similar to that of FIG. 4 is also provided for the ink heads of other colors. The inkjet printer 1 further includes filters 81, 82, 83, and 84 arranged on the carriage 3, a circulation pump 85 (pump, ink pump), a check valve 86, and a degasser 87. The inkjet printer 1 further includes a main tank 90 arranged on the device frame 10 (FIG. 1) outside the carriage 3, a capacitance sensor 91, a main tank valve 92, a main supply pump 93, and a control unit 100.

The yellow ink that flows into the ink supply path QA from the first supply sub-tank 71A is divided into a first ink path Q1 that passes through the first upstream ink head 41A and a second ink path Q2 that passes through the first downstream ink head 41B. The filter 81 is disposed upstream of the first upstream ink head 41A, and the filter 82 is disposed upstream of the first downstream ink head 41B. The filter 83 is disposed downstream of the first upstream ink head 41A, and the filter 84 is disposed downstream of the first downstream ink head 41B. These filters have the function of removing foreign matter, dust, etc. from the ink. After a portion of the yellow ink is ejected from the first upstream ink head 41A and the first downstream ink head 41B onto the workpiece W, the remaining ink is collected from the ink collection path QB to the first collection sub-tank 71B. Furthermore, the collected yellow ink is supplied to the first supply sub-tank 71A through the ink return path Q3.

As shown in FIG. 4, the circulation pump 85 constitutes part of a circulation path for yellow ink that flows from the first supply subtank 71A via the first upstream ink head 41A and the first downstream ink head 41B, and the first recovery subtank 71B, and returns to the first supply subtank 71A. In this embodiment, the circulation pump 85 sends yellow ink from the first recovery subtank 71B to the first supply subtank 71A. The circulation pump 85, together with the ink circulation path and each subtank, constitutes the ink circulation device of the present disclosure. The circulation pump 85 is located in the ink circulation path, and sends ink that has passed through the ink head 4 to the supply subtank.

The check valve 86 prevents the backflow of ink from the first supply subtank 71A to the first recovery subtank 71B via the ink return path Q3. The degasser 87 has the function of degassing the ink (removing air bubbles) in the ink return path Q3.

The main tank 90 is mounted on the device frame 10 of the inkjet printer 1 and stores yellow ink. Similar main tanks 90 are provided for the other colors.

The capacitance sensor 91 detects the remaining amount of yellow ink in the main tank 90.

The main tank valve 92 is a valve that can open or close the ink refill path Q4 that extends from the main tank 90 to the first supply sub-tank 71A. The main tank valve 92 can be opened and closed manually or automatically in response to a command signal input from the control unit 100.

The main supply pump 93 operates to supply the yellow ink in the main tank 90 to the first supply sub-tank 71A.

The control unit 100 controls the overall operation of the inkjet printer 1, and electrically controls each of the components shown in FIG. 4.

As shown in FIG. 5, for example, the first supply sub-tank 71A has a box-shaped structure, and when yellow ink is stored inside, a supply tank gas area SA and a supply tank ink area SB are formed. The supply tank gas area SA is a space above the liquid level of the yellow ink in the first supply sub-tank 71A, and the supply tank ink area SB is an area formed by the yellow ink. The supply tank gas area SA is connected to the supply side pressure supply path P11. The supply side pressure supply path P11 is connected to a pressure source (not shown) and maintains the supply tank gas area SA of the first supply sub-tank 71A at a predetermined pressure. The supply tank ink area SB is also connected to the ink supply path QA (first ink path Q1, second ink path Q2), the ink return path Q3, and the ink refill path Q4.

The first supply sub-tank 71A also has a capacitance sensor 71A1 that can detect the liquid level (ink amount) of the yellow ink in the first supply sub-tank 71A.

Similarly, the first recovery subtank 71B has a box-like structure, and when yellow ink is stored inside, a recovery tank gas area SC and a recovery tank ink area SD are formed. The recovery tank gas area SC is the space above the liquid level of the yellow ink in the first recovery subtank 71B, and the recovery tank ink area SD is an area formed by the yellow ink. The recovery tank gas area SC is connected to the recovery side pressure supply path P12. The recovery side pressure supply path P12 is connected to a pressure source (not shown) and maintains the recovery tank gas area SC of the first recovery subtank 71B at a predetermined pressure. In addition, the recovery tank ink area SD is connected to the ink recovery path QB (first ink path Q1, second ink path Q2) and the ink return path Q3.

The first collection sub-tank 71B also has a capacitance sensor 71B1 that can detect the liquid level (ink amount) of the yellow ink in the first collection sub-tank 71B.

In this embodiment, the supply tank gas area SA of the first supply subtank 71A is maintained at, for example, +2 kPa (relative to atmospheric pressure, the same applies below), and the recovery tank gas area SC of the first recovery subtank 71B is maintained at, for example, -15 kPa. As a result, a flow of yellow ink is formed from the first supply subtank 71A in FIG. 4 through the ink supply path QA (first ink path Q1, second ink path Q2) and the ink recovery path QB (first ink path Q1, second ink path Q2) to the first recovery subtank 71B. Both the supply tank gas area SA and the recovery tank gas area SC may be maintained at a positive pressure greater than 0 kPa. Both the supply tank gas area SA and the recovery tank gas area SC may be maintained at a negative pressure less than 0 kPa. The pressure difference between the supply tank gas area SA and the recovery tank gas area SC may be 5 to 20 kPa.

When the control unit 100 determines that there is little ink in the first supply sub-tank 71A upon receiving an output signal from the capacitance sensor 71A1 (Figure 5), the circulation pump 85 operates in response to a command signal input from the control unit 100. As a result, some of the yellow ink in the first recovery sub-tank 71B is supplied to the first supply sub-tank 71A through the ink return path Q3. Note that the circulation pump 85 operates whether the inkjet printer 1 is in the middle of a printing operation or not.

Furthermore, when the control unit 100 determines based on the detection results of the capacitance sensors 71A1, 71B1 that the amount of yellow ink in both the first supply subtank 71A and the first recovery subtank 71B has fallen below a preset threshold, the control unit 100 operates the main supply pump 93 to replenish yellow ink from the main tank 90 to the first supply subtank 71A through the ink refill path Q4. At this time, the main tank valve 92 opens to adjust the maximum refill amount (refill speed) for the first supply subtank 71A. Furthermore, when the capacitance sensor 91 detects that the remaining amount of yellow ink in the main tank 90 is low, the control unit 100 causes the display unit (not shown) of the inkjet printer 1 to display an ink refill message.

Yellow ink is ejected from the first upstream ink head 41A and the first downstream ink head 41B in accordance with the image to be formed on the workpiece W, while as shown in FIG. 4, the yellow ink circulates through a circulation path formed by the ink supply path QA, the first ink path Q1, the second ink path Q2, the ink recovery path QB, and the ink return path Q3. In this case, there is ink that continues to circulate through the circulation path without being ejected from each ink head.

In a structure in which ink is circulated as described above, there is a problem that, over a long period of use, pigment ink aggregates (coarse powder) form in the circulation path including the head, causing damage to the circulation pump 85 and clogging of each path. In particular, in this embodiment, the inkjet printer 1 is a printer that prints images on a wide and long workpiece W (recording medium) using an inkjet method, and compared to a typical home printer, the flow rate of ink flowing through the circulation path is relatively large, making it easier for aggregates to form. The disclosers of this disclosure have focused on the flow speed of ink in each flow path including the circulation pump 85 as a cause of such aggregates, and have evaluated the amount of coarse powder generated (amount of coarse powder) in relation to the flow speed of various pumps.

Table 1 shows the relationship between pump characteristic values and the amount of coarse powder when various pumps are used as the circulation pump 85. The pump characteristic values shown are the minimum flow path cross-sectional area, maximum flow rate, maximum flow velocity, and shear stress. The minimum flow path cross-sectional area is the cross-sectional area of the smallest section of the path through which the ink flows inside the pump. In diaphragm pumps and piezoelectric pumps, the minimum flow path cross-sectional area corresponds to the valve passage area, which is the cross-sectional area of the flow path in the valve part inside the pump. Note that since the cross-sectional area of the valve part when the valve is closed is considered to be 0 (zero), the valve passage area is the cross-sectional area when the valve is open.

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 pump outlet or the pump inlet. The maximum flow rate is the maximum of such flow rates. Even if the amount of ink circulated is controlled to be constant, the actual flow rate at the pump outlet varies to some extent depending on the operating principle of each pump. The maximum flow rate here is the maximum flow rate when the pump is operated while printing work is being performed, and is a value that includes the fluctuations that occur depending on the operation of the pump described above. The maximum flow rate occurs, for example, when ink in the first recovery subtank 71B is transferred by the circulation pump 85 to the first supply subtank 71A, which has a low ink amount. The maximum flow rate is set to a predetermined speed or less at least while continuous printing is being performed. In addition, when ink is circulated while printing is not being performed and the inkjet printer 1 is paused, the maximum flow rate may also be set to a predetermined speed or less. In addition, during non-routine work, such as the process of recovering an inkjet printer 1 that has had some kind of trouble, it is acceptable for the flow rate to temporarily exceed the specified speed, but even in such cases, it is best to keep the flow rate below the specified speed.

The maximum flow rate corresponds to the maximum speed of the ink inside the pump. It is considered that the ink speed inside the pump is greatest at the part with the smallest cross-sectional area of the path through which the ink flows. Therefore, the maximum flow rate is the maximum flow rate divided by the smallest cross-sectional area of the flow path. The amount of coarse powder was calculated by counting the number of particles with a diameter of 5 μm or more that were generated until a cumulative flow rate of approximately 1000 L was delivered by each pump.

Figure 6 is a graph showing the relationship between the maximum flow velocity in Table 1 (flow velocity inside the pump in Figure 6) and the amount of coarse powder.

As shown in Table 1 and Figure 6, the present inventors have discovered that the amount of coarse powder generated tends to increase depending on the flow speed inside the pump. This phenomenon is believed to occur because a velocity gradient occurs at the cross section of each flow path due to the viscosity of the ink, and the difference in speed between the particles that make up the pigment increases the frequency of collisions between those particles, promoting the generation of agglomerates (shear agglomeration). Note that the velocity gradient is mainly brought about by the velocity of particles close to the inner wall of the flow path (tube) being relatively slower than the velocity of particles close to the center of the flow path.

The flow rate in the pump may be slowed by increasing the duty of the pump operation. For example, the control unit 100 may control the pump in this way by operating the pump intermittently and varying the duty (the rate at which the pump operates within a certain period of time) to determine the amount of ink transferred per unit time. When the amount of ink transferred per unit time is to be a predetermined amount, a pump with a slow maximum flow rate may be used to increase the duty. In this way, the generation of coarse powder can be reduced. The duty may be 30% or more, further 40% or more, and especially 50% or more. From the above perspective, it is better for the duty to be close to 100%, but on the other hand, if it is close to 100%, it will not be possible to increase the amount of ink transferred by control, so the duty may be 80% or less, especially 60% or less.

Furthermore, processing liquids such as pre-processing liquid and post-processing liquid do not generally contain substances that may aggregate, such as pigments, and even if such substances are contained, the amount is smaller than that of ink. Therefore, the flow rate of the pump that circulates the processing liquid may be faster than the flow rate of the pump that circulates the ink. In this way, if the flow rate of the processing liquid circulation is made faster than the flow rate of the ink circulation, the duty is basically lowered, and the range in which the transport amount can be changed can be made wider. On the other hand, if the flow rate of the processing liquid circulation is made approximately the same as the flow rate of the ink circulation, the same pump can be used for both the processing liquid and the ink, and the circulation control can be the same or similar.

When the ink transported by the pump is supplied directly to the ink head 4, the amount of ink circulating in the flow path from the pump to the ink head 4 in the circulation path is almost constant even if there is pulsation, and in the flow path exiting the ink head 4, the amount of ink circulating is reduced by the amount ejected by the ink head 4. Therefore, the maximum flow rate of circulating ink is the maximum flow rate of ink sent out from the pump.

In this embodiment, the circulation pump 85 transfers ink from the first recovery subtank 71B to the first supply subtank 71A. The transfer of ink from the first supply subtank 71A to the first recovery subtank 71B via the ink head 4 is performed by the difference in gas pressure applied to the subtank. By making the transfer amount of the circulation pump 85 greater than the amount of ink transferred from the first supply subtank 71A to the first recovery subtank 71B when there is no ejection from the ink head 4, it is possible to prevent the amount of ink in the first recovery subtank 71B from increasing as long as the circulation pump 85 is operating. To achieve this, the maximum flow rate of ink sent by the circulation pump 85 (maximum flow rate per unit time, not including fluctuations such as pulsation) is made greater than the maximum flow rate of ink from the first supply subtank 71A to the ink head 4. In other words, when printing is being performed continuously, the pressure difference between the first supply subtank 71A and the first recovery subtank 71B is set so that the flow rate of ink from the first supply subtank 71A to the ink head 4 is less than the maximum flow rate of ink sent out by the circulation pump 85. Also, the flow rate of ink from the ink head 4 to the first recovery subtank 71B is less than the flow rate of ink from the first supply subtank 71A to the ink head 4 by the amount of ink ejected from the ink head 4. Therefore, the maximum flow rate of circulating ink is the maximum flow rate of ink sent out from the circulation pump 85.

The flow rate of ink flowing through the circulation path can be measured directly if it is flowing through a tube, etc. The ink flow rate can also be calculated (including simulation) from the dimensions of the flow path, the applied pressure, the physical properties of the ink, etc. If the flow rate of ink flowing through each part is known, the flow velocity of each part can be obtained by dividing the flow rate by the cross-sectional area.

In the ink head 4, the individual flow paths that connect the common supply flow path and the pressure chamber have the fastest flow velocity, for example. These individual flow paths are often the flow paths with the narrowest cross-sectional area in the ink head 4. There are the same number of individual flow paths as there are nozzles. The ink that flows into the ink head 4 is basically distributed and flows among the individual flow paths that are connected in parallel. Therefore, the flow rate of the ink flowing through the individual flow paths is small, and the ink flow velocity is slow. The ink flow velocity is, for example, 0.2 m/sec. Here, the minimum flow path cross-sectional area in the individual flow paths is smaller than the minimum flow path cross-sectional area in the circulation pump 85, but the maximum flow velocity of the individual flow paths is faster than the maximum flow velocity of the circulation pump 85.

More specifically, in each ink head, the product of the minimum flow path cross-sectional area in an individual flow path and the number of individual flow paths is equal to or greater than the minimum flow path cross-sectional area in the circulation pump 85. Furthermore, in each ink head, the product of the minimum flow path cross-sectional area in an individual flow path and the number of individual flow paths is greater than the minimum flow path cross-sectional area in the circulation pump 85. As described above, in one ink head 4, the multiple individual flow paths provided corresponding to each ejection section (nozzle) are arranged in parallel in terms of the flow path structure. Furthermore, when individual flow paths with different minimum flow path cross-sectional areas are mixed, the product of the minimum flow path cross-sectional area in an individual flow path and the number of individual flow paths corresponds to the sum of the minimum flow path cross-sectional areas for all individual flow paths, and may be calculated in this manner.

The maximum flow velocity of the ink in the circulation pump 85 is preferably 30 times or less, more preferably 25 times or less, even more preferably 15 times or less, and even more preferably 10 times or less, the flow velocity of the ink flowing through the individual flow paths of the ink head 4 described above (the maximum flow velocity of the ink in the ink head).

In addition, the circulation path may be provided with a valve such as an electromagnetic valve that can stop the flow of ink. With such a valve, the cross-sectional area of the flow path is small even when it is open. The flow rate through such a valve is, for example, 1.0 m/sec.

The flow rate of the ink flowing through the circulation pump 85 is preferably 6 times or less, more preferably 5 times or less, more preferably 3 times or less, and even more preferably 2 times or less, the flow rate of the ink in the valve. In other words, in the ink circulation path from the recovery port through the circulation pump 85 and the supply sub-tank to the supply port, the maximum flow rate of the ink in the circulation pump 85 is preferably 6 times or less, more preferably 5 times or less, more preferably 3 times or less, and even more preferably 2 times or less, the maximum flow rate of the ink in the parts other than the circulation pump 85.

Furthermore, when a filter is provided in the ink head 4, the total cross-sectional area of the filter is greater than the total cross-sectional area of the smallest portion of the individual flow paths, so the flow rate of ink in the individual flow paths is faster than the flow rate of ink in the filter. The total cross-sectional area of the filter provided in the circulation path is greater than the cross-sectional area of a valve such as a solenoid valve, so the flow rate of ink in a valve such as a solenoid valve is faster than the flow rate of ink in the filter. This relationship is not limited to ink, but is similar for each processing liquid. In particular, when a filter is provided in the ink head 4 (for example, the back-end filter mentioned above), it is desirable for the total opening area of the filter to be equal to or greater than the smallest flow path cross-sectional area in the circulation pump 85, and it is even more desirable for it to be greater than that area.

In the above configuration, if the maximum flow rate of the ink in the circulation pump 85 is set to a predetermined speed or lower, it is possible to suppress the ink from coagulating and becoming coarse. As a result, damage to the circulation pump 85 and blockages in each path can be prevented.

In particular, in this embodiment, the first recovery subtank 71B is disposed in the middle of the ink circulation path and stores the ink recovered from each ink head. The circulation pump 85 is disposed in a flow path that connects the first recovery subtank 71B and the first supply subtank 71A, which constitutes part of the circulation path (located between the first recovery subtank 71B and the first supply subtank 71A in terms of the upstream and downstream positional relationship in the flow path), and sends ink from the first recovery subtank 71B to the first supply subtank 71A. With this configuration, by providing a supply subtank and a recovery subtank independent of the ink head, it is possible to stably supply ink to the ink head while stably recovering ink from the ink head. By disposing the circulation pump 85 in the flow path between the subtanks that are farthest from the ink head in the flow path, it is possible to promote the circulation of ink without affecting the ejection of ink. In addition, at such a position, it is possible to suppress the aggregation and coarse powdering of ink.

Furthermore, when the ink contains a binder as in this embodiment, the ink is prone to aggregation due to its characteristics, but by limiting the maximum ink flow speed as described above, it is possible to suppress aggregation of ink containing a binder.

Furthermore, when the ink is a textile printing ink as in this embodiment, the binder content is high in order to print images such as characters and patterns on a recording medium made of fabric such as woven or knitted fabric. In this case, aggregation as described above is likely to occur, but by similarly limiting the maximum ink flow speed, it is possible to suppress aggregation of ink that contains a large amount of binder.

In the inkjet printer 1 according to this embodiment, the flow rate of ink flowing through the pump when the pump is operating is 1.7×10 ^-7 (m ³ /sec) or more, as shown in Table 1. When ink circulates at a high flow rate like this, the velocity gradient described above is likely to occur, which results in aggregation and the generation of coarse powder being promoted. However, even in such a case, it is possible to suppress aggregation of ink circulating at a high flow rate by similarly limiting the maximum flow speed of the ink.

Here, as shown in Table 1 and FIG. 6, a tube pump (Example 1 in Table 1) can be used as the circulation pump 85. However, in a tube pump, the rollers crush the tube as it works, which gradually deteriorates the tube and may cause a decrease in flow rate over a long period of time. In addition, due to the operating principle of the tube pump, pulsation occurs. Therefore, it is desirable to use a tube pump as the circulation pump 85 to the extent that these concerns do not become apparent.

On the other hand, by using a piezoelectric pump (Example 2 in Table 1) as the circulation pump 85, it is possible to circulate the ink while eliminating the above concerns. By using a piezoelectric pump, it is possible to keep the flow rate low below a certain level, as shown in Table 1. A piezoelectric pump is a type of diaphragm pump, and the diaphragm is driven by a piezoelectric body. In a typical diaphragm pump, the diaphragm is driven mechanically or hydraulically, so the amount of displacement of the diaphragm in one drive (one back-and-forth vibration) is almost constant. It is thought that the amount of ink pushed out due to the displacement is also relatively close to a constant amount. In contrast, when the diaphragm is driven by a piezoelectric body, the driving force applied to the diaphragm becomes almost constant, but instead the amount of displacement is not constant. Although the details are unknown, in a situation where it is difficult to push out the ink, it is thought that the amount of displacement of the diaphragm will be smaller even with the same driving force, so the flow rate will be slightly smaller and the maximum flow rate will be slightly slower. Furthermore, in the case of a piezoelectric pump, the ink can be circulated stably because no pulsation as described above occurs. However, the load characteristics of a piezoelectric pump are relatively poor, and depending on the resistance and inertance of the circulation path, it may not be possible to achieve the required flow rate, so it is desirable to use a piezoelectric pump for the circulation pump 85 to the extent that these concerns do not become apparent.

On the other hand, by using a diaphragm pump as the circulation pump 85, it is possible to circulate ink while eliminating the above-mentioned concerns. When a diaphragm pump is used in the ink jet printer 1 according to this embodiment, the minimum cross-sectional area of the circulation path in the pump is set to 2.0×10 ^-6 (m ² ) or more, and the maximum flow rate of the ink is set to 1.7×10 ^-5 (m ³ /sec) or less. Furthermore, for the reasons mentioned above, it is preferable to use a piezoelectric pump among diaphragm pumps.

Table 1 shows Example 3 as a diaphragm pump, and Comparative Examples 1 and 2 for comparison. Comparative Example 2 differs from Comparative Example 1 in that an external damper is attached to the pump.

In contrast, in Example 3, it was confirmed that the generation of coarse powder was suppressed by reducing the maximum flow velocity compared to Comparative Examples 1 and 2. Diaphragm pumps have better load characteristics than other pumps, so they can be used preferably when it is necessary to ensure the flow rate of ink flowing through the circulation path.

Furthermore, Figure 7 is a graph showing the relationship between the shear stress in Table 1 and the amount of coarse powder. The shear stress in question refers to the shear stress that occurs in the ink (liquid) inside each pump. The shear stress in Table 1 and Figure 7 is calculated based on the following formula 1, which assumes that the flow velocity distribution inside the pipe is between parallel plates (Couette flow).

Shear stress τ (unit: Pa) = μ × v / r ... (Equation 1)
In formula 1, μ (unit: Pa·s) is the viscosity of the ink, and v (unit: m/s) is the flow velocity of the ink. In this case, the flow velocity corresponds to the maximum flow velocity mentioned above. Furthermore, r (unit: m) corresponds to the radius of a circular tube when the flow path is assumed to be a circular tube, and can be calculated as the radius when the valve passage area in Table 1 is taken as the area of a circle. In the above example, the viscosity μ of the ink is 6 (mPa·s).

The present inventors have found that the increase or decrease in the amount of coarse powder generated tends to depend on the shear stress acting on the ink in the pump. This phenomenon is believed to be caused by the velocity gradient occurring at the cross section of each flow path due to the viscosity of the ink as described above, and the velocity difference between the particles that make up the pigment increases the frequency of collisions between the particles, promoting the generation of agglomerates (shear agglomeration). As shown in Figure 7, the ink can be stably suppressed from agglomerating and becoming coarse when the shear stress is in the range of 30 (Pa) or less. In order to show such a desirable boundary, a dashed line is added to the area of shear stress 30 (Pa) in Figure 7. As shown in Table 1, in Examples 1, 2, and 3, the shear stress is 30 (Pa) or less in all cases, and the amount of coarse powder is also reduced compared to the comparative example.

These results show that shear stress is the main cause of coarse powder generation, and that by setting the shear stress to a range of 30 Pa or less, ink aggregation and coarse powder generation can be stably suppressed.

As another idea, when ink is transported using a pump where the pressure applied to the ink is nearly constant, if the viscosity of the ink is high, the shear stress tends to increase according to Equation 1, but the ink flow rate in the pipe decreases and the frequency of collisions between particles decreases. On the other hand, if the viscosity of the ink is low, the shear stress tends to decrease according to Equation 1, but the ink flow rate increases and the frequency of collisions between particles increases. As a result, it was found that by setting the shear stress to a range of 30 (Pa) or less as described above, regardless of the viscosity of the ink, ink aggregation and coarse powdering can be stably suppressed.

Furthermore, the present inventors have focused on expanding the cross-sectional area by improving the valve structure in order to prevent the ink flow rate in the diaphragm pump from becoming too fast. Figure 8A is a schematic cross-sectional view showing the internal structure of the circulation pump 85 according to this embodiment.

The circulation pump 85 has a pump body 850, a pump chamber 851 formed within the pump body 850 and capable of storing ink, a displacement portion 852, an intake flow path 85A, an exhaust flow path 85B, an intake side check valve 853, and an exhaust side check valve 854.

The displacement portion 852 constitutes a part of the pump chamber 851 (the upper surface of the pump chamber 851 in FIG. 8A), and displaces to switch the suction and discharge of ink in the circulation pump 85. The volume of the pump chamber 851 changes depending on the displacement of the displacement portion 852. In this embodiment, the displacement portion 852 is composed of a piezoelectric vibrator, and vibrates in response to the input drive voltage.

The suction flow path 85A communicates with the upstream side of the ink circulation path. That is, the suction flow path 85A is located upstream of the pump chamber 851. Similarly, the delivery flow path 85B communicates with the downstream side of the ink circulation path. That is, the delivery flow path 85B is located downstream of the pump chamber 851. The suction side check valve 853 is located between the suction flow path 85A and the pump chamber 851, and is a displaceable check valve. Similarly, the delivery side check valve 854 is located between the pump chamber 851 and the delivery flow path 85B, and is a displaceable check valve.

FIGS. 8B and 8C are schematic cross-sectional views showing the vicinity of the delivery side check valve 854 of the circulation pump 85 in FIG. 8A. The check valve support portion 850H in FIG. 8B is part of the pump body 850 in FIG. 8A, and has a structure that supports the delivery side check valve 854. The check valve support portion 850H has a flat portion 855 (opposing surface). The flat portion 855 is disposed opposite the delivery side check valve 854, and is connected to the inlet of the delivery flow path 85B.

When the pressure in the pump chamber 851 increases with the displacement of the displacement portion 852 in FIG. 8A, the delivery side check valve 854 is displaced from FIG. 8B to FIG. 8C. As a result, ink is permitted to flow from the pump chamber 851 to the delivery flow path 85B. On the other hand, when the pressure in the pump chamber 851 is lower than the delivery flow path 85B, the delivery side check valve 854 blocks the flow path as shown in FIG. 8B, preventing ink from flowing back from the delivery flow path 85B to the pump chamber 851.

In this embodiment, when the circulation pump 85 delivers ink, the delivery side check valve 854 abuts against the flat surface portion 855 as shown in FIG. 8C. This makes it possible to increase the cross-sectional area of the flow path around the delivery side check valve 854 in the ink circulation path, compared to when the check valve support portion 850H has a protrusion as shown by the dashed line in FIG. 8B. Note that instead of the flat surface portion 855, a curved surface or the like may be disposed as the opposing surface.

Note that a structure similar to that around the delivery side check valve 854 in Figs. 8B and 8C is also provided around the suction side check valve 853 in Fig. 8A. In this case, the pump chamber 851 in Figs. 8B and 8C is replaced with the suction flow path 85A in Fig. 8A, and the delivery flow path 85B in Figs. 8B and 8C is replaced with the pump chamber 851 in Fig. 8A. As a result, when the pressure in the pump chamber 851 decreases with the displacement of the displacement portion 852 in Fig. 8A, the suction side check valve 853 allows ink to flow from the suction flow path 85A to the pump chamber 851. On the other hand, when the pressure in the pump chamber 851 is higher than that of the suction flow path 85A, the suction side check valve 853 prevents ink from flowing back from the pump chamber 851 to the suction flow path 85A.

Furthermore, in this embodiment, at least one of the flow paths in the circulation pump 85 has the smallest cross-sectional area: the flow path in the suction side check valve 853 and the flow path in the delivery side check valve 854. In other words, in the circulation pump 85, the flow paths other than the flow paths in the suction side check valve 853 and the delivery side check valve 854 are designed not to be narrower than the flow paths in the flow paths in the suction side check valve 853 and the delivery side check valve 854. In other words, the cross-sectional area of the flow paths in the circulation pump 85 is smallest in the flow paths in the check valves. Note that at least one of the cross-sectional areas of the flow paths in the circulation pump 85 may be smallest: the cross-sectional area of the flow path in the suction side check valve 853 and the cross-sectional area of the flow path in the delivery side check valve 854.

In this embodiment, at least one of the suction side check valve 853 and the delivery side check valve 854 is set to have a flow path cross-sectional area of 2.0×10 ^-6 (m ² ) or more when the check valve is open. In Fig. 8B, the ink flow permitted by the displacement of the delivery side check valve 854 is shown by two arrows. The ink flow when the suitable cross-sectional area is set as described above will be described in detail below.

When considering the shear stress acting on the ink, even if the cross-sectional area of the flow path is the same, a long and thin cross-sectional shape has a greater effect than a circle in the following ways. A long and thin shape has a greater shear stress because the distance between the flow path wall, where the flow velocity is zero, and the center of the flow path, where the flow velocity is at its maximum, is closer. Also, since the effect of shear stress is greater in the area near the flow path wall than in the center of the flow path, the area where the effect of shear stress is greater is wider for a long and thin shape due to the longer length of the flow path wall.

For this reason, in this embodiment, the size of the cross-sectional area of the flow path when the delivery side check valve 854 is open is set as described above so that the opening that is created when the delivery side check valve 854 is open tends to have an elongated shape. As a result, it is possible to particularly suppress ink aggregation within the circulation path.

It is preferable that the ink flow velocity in the circulation path using each of the above pumps be kept to 6 m/sec or less, and more preferable that it be kept to 5 m/sec or less. Furthermore, it is preferable that the ink flow velocity be kept to 3 m/sec or less, and more preferable that it be kept to 2 m/sec or less. In this way, by suppressing the specified speed for limiting the maximum ink flow velocity, it is possible to further suppress the ink from coagulating and powdering.

The area of the ink circulation path where the ink flow rate is set to less than the predetermined speed may be only within the circulation pump 85, or may be an area of the circulation path excluding each ink head. That is, in FIG. 4, the ink circulation path includes supply ports Q1A and Q2A connected to each ink head. The ink circulation path also includes recovery ports Q1B and Q2B connected to each ink head. The maximum ink flow rate from the recovery ports Q1B and Q2B to the supply ports Q1A and Q2A via the first recovery subtank 71B, the circulation pump 85, and the first supply subtank 71A may be set to less than the predetermined speed. In this embodiment, the maximum ink flow rate from the recovery port to the supply port via the circulation pump 85 and the supply subtank is the flow rate within the circulation pump 85. More specifically, the maximum flow speed of the ink in the ink circulation path from the recovery port through the circulation pump 85 and the supply sub-tank to the supply port, and in the ink head 4, is the flow speed in the circulation pump 85. Furthermore, the region in the ink circulation path where the ink flow speed is set to be equal to or lower than the predetermined speed may be the entire circulation path including each ink head. Also, the maximum flow speed of the ink in the circulation pump 85 may be faster than the maximum flow speed of the ink in the multiple individual flow paths in the ink head 4.

Nozzles that eject liquid in an ink head, or individual flow paths that supply and collect ink from the nozzles, have small cross-sectional areas and may become clogged with coarse powder or coarse powder aggregates. If a filter is provided in the ink head or ink circulation path, clogging of the nozzle or individual flow path is less likely to occur, but if a large amount of coarse powder is generated, the filter may become clogged with coarse powder in the long term. For this reason, if the ink flow rate in the ink circulation path is set to be equal to or lower than the above-mentioned specified speed, clogging of the nozzle, individual flow path, or filter can be made less likely to occur. Here, the nozzle and the individual flow paths that supply and collect ink from the nozzle also include a structure in which a nozzle is attached to an individual flow path through which ink flows from the ink supply source to the ink collection destination. In such a structure, the individual flow path is attached to the base of the cylindrical shape of the nozzle. When ink flows in an individual flow path with such a structure, a flow occurs in the ink in the nozzle, and the ink in the nozzle is agitated. As a flow occurs in the ink inside the nozzle, some of the ink flowing in the individual flow paths is supplied to the nozzle, and some of the ink in the nozzle is collected in the individual flow paths.

In addition, if the flow path structure is such that the fastest flow speed is inside the ink head 4, coarse powder will be generated inside the ink head 4, which can easily cause clogging. For this reason, the flow path structure may be such that the fastest flow speed is outside the ink head 4, and monitoring may be performed to ensure that not a lot of coarse powder is generated even at that flow speed.

In addition, at least in pumps with a valve mechanism, if the opening when the valve is closed is larger than necessary, the amount of liquid delivered may vary due to external factors such as the pressure applied to the liquid and the flow rate, so it is desirable to make the opening relatively small.

The inkjet printer 1 (inkjet recording device), ink circulation device, and ink pump according to the present embodiment described above can circulate the ink, eliminating waste of the ink while preventing clogging of the circulation path including the head and tank. Note that the present disclosure is not limited to the above embodiment, and can take the following forms.

(1) The ink heads 4 are not limited to being arranged in two rows on the carriage 3. The ink heads 4 may be arranged in a single row, or in three or more rows. Furthermore, the inkjet printer 1 is not limited to being configured to be capable of ejecting ink of multiple colors onto the workpiece W, and may be configured to eject ink of a single color.

(2) In the above embodiment, the inkjet printer 1 may not have the pre-treatment liquid head 5 that ejects the pre-treatment liquid, the post-treatment liquid head 6 that ejects the post-treatment liquid, or any of the components associated with these.

(3) In the above embodiment, a recovery tank is provided in the ink circulation path, but the recovery tank may be omitted. In this case, the ink circulation path is provided so that the ink flows from the supply tank to the ink head (supply destination) and then back to the supply tank. The circulation pump 85 constitutes a part of the circulation path and sends out the ink. In this case, the maximum flow rate of the ink in the circulation pump 85 may be set to be equal to or lower than the predetermined speed. Furthermore, assuming that the first recovery sub-tank 71B does not exist in FIG. 4, the maximum flow rate of the ink in the circulation path from the recovery ports Q1B, Q2B through the circulation pump 85 and the first supply sub-tank 71A to the supply ports Q1A, Q2A may be set to be equal to or lower than the predetermined speed, or the maximum flow rate of the ink in the entire circulation path including each ink head may be set to be equal to or lower than the predetermined speed.

(4) The configurations disclosed in each of the above embodiments can be combined with each other to form a single disclosure.

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 Pre-treatment liquid head 6 Post-treatment liquid head 7 Sub-tank 71A First supply sub-tank 71A1 Capacitance sensor 71B First recovery sub-tank 71B1 Capacitance sensor 72A Second supply sub-tank 72B Second recovery sub-tank 85 Circulation pump 850 Pump body 850H Check valve support portion 851 Pump chamber 852 Displacement portion 853 Suction side check valve 854 Delivery side check valve 855 Flat portion 85A Suction flow path 85B Delivery flow path 90 Main tank 91 Capacitance sensor 92 Main tank valve 93 Main supply pump P11 Supply side pressure supply path P12 Recovery side pressure supply path QA Ink supply path QB Ink recovery path Q1 First ink path Q2 Second ink path Q3 Ink return path Q4 Ink refill path

Claims (25)

a circulation path through which ink containing a pigment flows;
a supply unit located in the circulation path and configured to supply the ink to a predetermined destination;
a pump located in the circulation path and configured to send the ink that has passed through the supply destination to the supply unit;
Equipped with
the supply destination is an ink head capable of ejecting the ink,
the ink head includes a plurality of nozzles that eject the ink, and a plurality of individual flow paths provided for each of the plurality of nozzles, the individual flow paths including a flow path that supplies the ink to the nozzle and a flow path that recovers the ink from the nozzle;
a maximum flow velocity of the ink in the pump is set to a predetermined velocity or less;
An ink circulation device, wherein a product of a minimum flow path cross-sectional area within the individual flow path and the number of the individual flow paths is equal to or greater than a minimum flow path cross-sectional area within the pump. a circulation path through which ink containing a pigment flows;
a supply unit located in the circulation path and configured to supply the ink to a predetermined destination;
a pump located in the circulation path and configured to send the ink that has passed through the supply destination to the supply unit;
Equipped with
An ink circulation device, wherein a shear stress generated in the ink within the pump is 30 (Pa) or less. The ink circulation device according to claim 1 or 2, wherein the ink further contains a binder. The ink circulation device according to claim 3, wherein the ink is a printing ink. 5. The ink circulation device according to claim 1, wherein a flow rate of the ink flowing through the pump is 1.7×10 ^-7 (m ³ /sec) or more. 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 minimum cross-sectional area of the circulation path within the pump is set to 2.0 x 10 ^-6 (m ² ) or more, and the maximum flow rate of the ink is set to 1.7 x 10 ^-5 (m ³ /sec) or less. a recovery unit that is located on the circulation path and that recovers the ink from the supply destination,
The ink circulation device according to claim 1 , wherein the pump is located between the collection section and the supply section, and sends the ink from the collection section to the supply section. the pump having a displaceable check valve;
9. The ink circulation device according to claim 1, wherein a cross-sectional area of the flow passage in the pump is minimum at a portion of the check valve. The pump comprises:
a pump chamber capable of containing the ink;
a displacement portion that constitutes a part of the pump chamber and displaces so as to change the volume of the pump chamber;
a suction passage located upstream of the pump chamber;
an outlet flow path located downstream of the pump chamber;
a displaceable suction-side check valve located between the suction passage and the pump chamber;
a displaceable delivery-side check valve located between the pump chamber and the delivery flow path;
having
6. The ink circulation device according to claim 1, wherein at least one of the cross-sectional areas of the flow passages in the pump, the cross-sectional area of the flow passage in the suction side check valve portion and the cross-sectional area of the flow passage in the delivery side check valve portion, is the smallest. The pump comprises:
a pump chamber capable of containing the ink;
A displacement portion that constitutes a part of the pump chamber and displaces so as to change the volume of the pump;
a suction passage located upstream of the pump chamber;
an outlet flow path located downstream of the pump chamber;
a displaceable suction-side check valve located between the suction passage and the pump chamber;
a displaceable delivery-side check valve located between the pump chamber and the delivery flow path;
having
6. The ink circulation device according to claim 1, wherein at least one of the suction side check valve and the delivery side check valve has a cross-sectional area of 2.0×10 ^-6 (m ² ) or more when the check valve is open. The pump comprises:
a pump chamber capable of containing the ink;
a displacement portion that constitutes a part of the pump chamber and displaces so as to change the volume of the pump chamber;
a suction passage located upstream of the pump chamber;
an outlet flow path located downstream of the pump chamber;
a displaceable suction-side check valve located between the suction passage and the pump chamber;
a displaceable delivery-side check valve located between the pump chamber and the delivery flow path;
an opposing surface disposed opposite the delivery-side check valve and connected to an inlet of the delivery flow path;
having
6. The ink circulation device according to claim 1, wherein the delivery-side check valve abuts against the opposing surface when the ink is delivered by the pump. An ink circulation device according to any one of claims 1 to 12, wherein the maximum flow rate of the ink in the pump is 6 m/sec or less. the supply destination is an ink head capable of ejecting the ink,
14. The ink circulation device according to claim 1, wherein a maximum flow velocity of the ink in the pump is 30 times or less than a maximum flow velocity of the ink in the ink head. the supply destination is an ink head capable of ejecting the ink,
the ink head includes a plurality of nozzles that eject the ink, and a plurality of individual flow paths provided for each of the plurality of nozzles, the individual flow paths including a flow path that supplies the ink to the nozzle and a flow path that recovers the ink from the nozzle;
The ink circulation device according to claim 1 , wherein a minimum flow path cross-sectional area in the individual flow path is smaller than a minimum flow path cross-sectional area in the pump. The ink circulation device according to claim 15, wherein the ink head has a filter therein, and the total opening area of the filter is equal to or greater than the minimum flow path cross-sectional area in the pump. the supply destination is an ink head capable of ejecting the ink,
the circulation path includes a supply port and a recovery port connected to the ink head,
The ink circulation device according to claim 1 , wherein a maximum flow speed of the ink in the circulation path from the recovery port through the pump and the supply portion to the supply port is set to be equal to or lower than the predetermined speed. the supply destination is an ink head capable of ejecting the ink,
the circulation path includes a supply port and a recovery port connected to the ink head,
The ink circulation device according to claim 1 , wherein a maximum flow velocity of the ink in the circulation path from the recovery port through the pump and the supply portion to the supply port is a flow velocity in the pump. the supply destination is an ink head capable of ejecting the ink,
the circulation path includes a supply port and a recovery port connected to the ink head,
14. The ink circulation device according to claim 1, wherein a maximum flow velocity of the ink in the circulation path from the recovery port through the pump and the supply portion to the supply port, and in the ink head, is the flow velocity in the pump. the supply destination is an ink head capable of ejecting the ink,
the ink head includes a plurality of nozzles that eject the ink, and a plurality of individual flow paths provided for each of the plurality of nozzles, the individual flow paths including a flow path that supplies the ink to the nozzle and a flow path that recovers the ink from the nozzle;
The ink circulation device according to claim 1 , wherein a maximum flow velocity of the ink in the pump is faster than a maximum flow velocity of the ink in the plurality of individual flow paths. the supply destination is an ink head capable of ejecting the ink,
the circulation path includes a supply port and a recovery port connected to the ink head,
14. An ink circulation device according to claim 1, wherein in a flow path of the circulation path from the recovery port via the pump and the supply part to the supply port, a maximum flow velocity of the ink in the pump is six times or less than a maximum flow velocity of the ink in parts other than the pump. a circulation path through which ink containing a pigment flows;
an ink head capable of ejecting the ink;
a supply unit located in the circulation path and configured to supply the ink to the ink head;
a pump located in the circulation path and configured to send the ink collected from the ink head to the supply unit;
Equipped with
the ink head includes a plurality of nozzles that eject the ink, and a plurality of individual flow paths provided for each of the plurality of nozzles, the individual flow paths including a flow path that supplies the ink to the nozzle and a flow path that recovers the ink from the nozzle;
a maximum flow velocity of the ink in the circulation path is set to a predetermined velocity or less;
an ink jet recording apparatus, wherein a product of a minimum flow path cross-sectional area in the individual flow path and the number of the individual flow paths is equal to or greater than a minimum flow path cross-sectional area in the pump. a circulation path through which ink containing a pigment flows;
an ink head capable of ejecting the ink;
a supply unit located in the circulation path and configured to supply the ink to the ink head;
a pump located in the circulation path and configured to send the ink collected from the ink head to the supply unit;
Equipped with
An ink jet recording apparatus, wherein a shear stress generated in the ink within the pump is 30 (Pa) or less. An ink pump located in a circulation path through which ink containing a pigment flows, capable of sending the ink via a specified destination to a supply section located in the circulation path that supplies the ink to the specified destination, and in which the maximum flow rate of the ink in the pump is set to a specified speed or less. An ink pump located in a circulation path through which ink containing a pigment flows, the ink pump being capable of sending the ink to a supply section located in the circulation path and supplying the ink to a specified supply destination via the supply destination, and a shear stress generated in the ink within the pump being 30 (Pa) or less.

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