Inkjet recording device for textile printing

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

[Technical Field]

[0001] The present disclosure relates to an ink circulation device, an inkjet recording apparatus including the same, and an ink pump. [Background technology]

[0002] 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 for storing ink, a recording head for ejecting ink supplied from the tank, a supply flow path for supplying ink from the tank to the recording head, a recovery flow path for recovering 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 through a circulation path including 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-51952 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide an ink circulation device capable of preventing clogging of a circulation path including a head and a tank, an ink jet recording apparatus including the same, and an ink pump. [Means for solving the problem]

[0005] An ink circulation device according to one aspect of the present disclosure comprises a circulation path through which ink containing a pigment flows, a supply unit located on the circulation path and supplying the ink to a predetermined destination, and a pump located on the circulation path and sending the ink to the supply unit after passing through the destination, wherein the destination is an ink head capable of ejecting the ink, the ink head including 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 maximum flow velocity of the ink in the pump is set to a predetermined velocity or less, and the product of the smallest flow path cross-sectional area in the individual flow path and the number of the individual flow paths is greater than or equal to the smallest flow path cross-sectional area in the pump.

[0006] In addition, an ink circulation device according to another 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 that has passed through the destination to the supply unit, wherein the shear stress generated in the ink within the pump is 30 (Pa) or less.

[0007] 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, wherein 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 maximum flow velocity of the ink in the circulation path is set to be equal to or less than the predetermined velocity, and the product of the smallest flow path cross-sectional area within the individual flow path and the number of the individual flow paths is equal to or greater than the smallest flow path cross-sectional area within the pump.

[0008] 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 ink head to the supply unit, wherein the shear stress generated in the ink within the pump is 30 (Pa) or less.

[0009] 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 to a supply section located in the circulation path that supplies the ink to a predetermined supply destination via the supply destination, and the maximum flow rate of the ink within the pump is set to a predetermined speed or less.

[0010] 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 section located in the circulation path that supplies the ink to a predetermined supply destination, and the shear stress generated in the ink within the pump is 30 (Pa) or less. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing the overall configuration of a recording apparatus according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is an enlarged perspective view of the carriage shown in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the flow of ink around an ink head according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a schematic diagram showing a supply sub-tank and a recovery sub-tank according to an embodiment of the present disclosure. [Figure 6]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. [Figure 7] 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. [Figure 8A] FIG. 7A is a schematic cross-sectional view showing the internal structure of a pump according to an embodiment of the present disclosure. [Figure 8B] FIG. 7B is a schematic cross-sectional view showing a portion of the internal structure of a pump according to an embodiment of the present disclosure. [Figure 8C] 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. DETAILED DESCRIPTION OF THE INVENTION

[0012] A recording apparatus according to an embodiment of the present disclosure will be described below 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 the recording apparatus. 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 apparatus according to the present disclosure can also be used to print various images on recording media such as paper sheets and resin sheets.

[0013] [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 uses an inkjet method to print images on a wide and long workpiece W (recording medium). As an example, the width of the workpiece W is several meters. The printer 1 includes a device frame 10, and a workpiece transport unit 20 and carriage 3 that are incorporated into this device frame 10. In this embodiment, the left-to-right direction is the main scanning direction S (FIG. 3) when printing on the workpiece W, and the direction from rear to front is the sub-scanning direction (the transport direction F of the workpiece W, which intersects with the main scanning direction S).

[0014] 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 a printing area where inkjet printing processing 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 and right direction) that intersects with the transport direction F of the work W during the inkjet printing processing.

[0015] 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-to-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.

[0016] 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 heads 4, pre-treatment liquid head 5, and post-treatment liquid head 6, and caps are also fitted. The left frame 113 forms a return area 14 for the carriage 3. The return 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 across the printing area 12 from right to left during the printing process.

[0017] A carriage guide 15 is attached to the upper side of the device frame 10 to allow the carriage 3 to reciprocate in the left-right direction. The carriage guide 15 is a flat plate-shaped member that is long in the left-right direction, and is disposed above the work transport unit 20. A timing belt 16 is attached to the carriage guide 15 so as to be able to 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.

[0018] 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 that allows it to move back and forth in the main scanning direction S. The carriage 3 is engaged with the guide rails 17. The carriage 3 is also fixed to a timing belt 16. As the timing belt 16 moves orbitally left or right, the carriage 3 moves left or right along the carriage guide 15 while being guided by the guide rails 17.

[0019] 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 about its axis and performs the operation of winding up the work W.

[0020] 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 workpiece W. Arranged on this transport path, in order from upstream, are 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. The first tension roller 23 applies a predetermined tension to the workpiece W on the upstream side of the transport roller 25. The work guide 24 changes the transport direction of the workpiece W from upward to forward, allowing the workpiece W to enter the printing area 12.

[0021] 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 around 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 so as to face the transport roller 25 from above, and forms a transport nip portion with the transport roller 25.

[0022] The turn-back roller 27 changes the transport direction of the workpiece W that has passed through the printing area 12 from forward to downward, and guides the workpiece W after printing to the take-up roller 22. The second tension roller 28 applies a predetermined tension to the workpiece W downstream of the transport roller 25. A platen 29 is disposed below the transport path of the workpiece W in the printing area 12.

[0023] The carriage 3 is cantilevered by the guide rail 17 and moves back and forth in a main scanning direction S (left and right in this embodiment) that intersects (is perpendicular to) the transport direction F. The carriage 3 includes 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 (FIG. 3) that are mounted on the carriage frame 30. The carriage frame 30 includes a head support frame 31 and a back frame 32.

[0024] The head support frame 31 is a horizontal plate that holds the heads 4 to 6. The back frame 32 is a vertical plate that extends upward from the rear end 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 by the engagement portion.

[0025] 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 of 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 arranged 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 arranged in the transport direction F.

[0026] [Carriage Details] The carriage 3 will now be further described. Fig. 3 is an enlarged perspective view of the carriage 3 shown in Fig. 1. Fig. 3 shows the transport direction F (sub-scanning direction) of the workpiece W and the main scanning direction S, which is the direction of movement of the carriage 3. Fig. 3 shows an example in which the carriage 3 is equipped with a plurality of ink heads 4 that eject ink for image formation onto the workpiece W, a pre-treatment liquid head 5 and a post-treatment liquid head 6 that eject non-color-forming treatment liquid, and a plurality of sub-tanks 7 that supply the ink and treatment liquid to these heads 4 to 6.

[0027] Each of the ink heads 4 has a large number of nozzles (ink ejection holes) that eject ink droplets using an ejection method such as a piezo method using a piezo element or a thermal method using a heating element.

[0028] Each of the ink heads 4 includes, for example, a plurality of ejection units including nozzles, a common supply flow path that supplies ink to the plurality of ejection units, and a common recovery flow path that recovers ink from the plurality of ejection units. This common recovery flow path recovers ink that is supplied to the ejection units but not ejected from the nozzles.

[0029] The ejection unit includes an individual flow path connecting the common supply flow path and the common recovery flow path, a pressure applying unit such as a piezoelectric element or a heating element, and a nozzle. The portion of the individual flow path facing the pressure applying unit is called a pressure chamber. The pressure chamber and the nozzle may be arranged in this order from the common supply flow path, 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 not ejected from the nozzle. The cross-sectional area of ​​the smallest portion of the individual flow path 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 located midway between the pressure chamber and one of the common flow paths. Note that ink traveling from the common supply flow path to the common recovery flow path does not pass through the nozzle, so the nozzle is not included in the individual flow path when considering the minimum cross-sectional area of ​​the individual flow path.

[0030] Regarding the structure of each ink head, ink that flows into the ink head flows into the common supply channel through a forward flow channel formed in the inlet section (also called the back end). The ink is then supplied to each nozzle through individual flow channels provided in each ejection section. Some of the ink is ejected from the nozzle, while the remaining ink flows from the individual flow channels into the common recovery flow channel and then flows out of the ink head through a return flow channel formed in the inlet section. Each of the multiple individual flow channels is branched off from the common supply flow channel. Each of the multiple individual flow channels is connected to the common recovery flow channel and converges into the common recovery flow channel. That is, in one ink head 4, the multiple individual flow channels provided corresponding to each ejection section (nozzle) are arranged in parallel in terms of flow channel structure.

[0031] Each ink head 4 may further include a filter. The filter is disposed, for example, within the common supply flow path or upstream thereof, and prevents foreign matter and coarse particles in the ink from flowing downstream to prevent clogging of the nozzles or the individual flow paths. A filter may also be disposed in the flow path of the introduction section (back end) (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.

[0032] As the ink, for example, a water-based pigment ink containing a water-based solvent, a pigment, and a binding resin (binder) can be used.

[0033] The binder resin may be present in a dispersed state in an aqueous medium. The binder resin functions to bond the subject to be printed to the pigment. Therefore, 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 binder resin content 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, relative to the mass of the ink.

[0034] In this embodiment, the multiple ink heads 4 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 as to be aligned in two rows in the main scanning direction S. Each color of ink head 4 has two heads.

[0035] Specifically, the ink heads 4 include 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 include 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 shifted from each other in the transport direction F and the main scanning direction S. These two ink heads 4 form a group, and a total of eight groups of ink heads 4 (41A to 48A, 41B to 48B) eject inks of different colors.

[0036] The pre-treatment liquid head 5 and the post-treatment liquid head 6 are disposed at positions different from the ink heads 4 in the transport direction F. The pre-treatment liquid head 5 is disposed upstream of the ink heads 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 heads 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, a plurality of pre-treatment liquid heads 5 or a plurality of post-treatment liquid heads 6 may be disposed. It is desirable that the carriage 3 be equipped with at least one pre-treatment liquid head 5 and at least one post-treatment liquid head 6, but in other embodiments, a pre-treatment liquid head 5 and a post-treatment liquid head 6 may not be disposed.

[0037] A series of heads along the main scanning direction S, which are made up of the ink heads 4, pre-treatment liquid heads 5, and post-treatment liquid heads 6, will be referred to as a row of heads, or simply as a row. Also, a series of heads along the transport direction F, which are made up of the ink heads 4, pre-treatment liquid heads 5, and post-treatment liquid heads 6, will be referred to as a row of heads, or simply as a row.

[0038] The pretreatment liquid head 5 ejects a 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 to which ink has not yet been ejected from the ink head 4. The pretreatment liquid is a non-color-forming 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 or the coagulation of ink pigments. Examples of such pretreatment liquids that can be used include a treatment liquid in which a binder resin is blended into a solvent, or a treatment liquid in which a positively charged cationic resin is blended into a solvent.

[0039] The post-treatment liquid head 6 ejects a post-treatment liquid for performing a predetermined post-treatment on the workpiece W to which ink has adhered. The post-treatment liquid is ejected from the post-treatment liquid head 6 onto a position on the workpiece W after the ink has been ejected from the ink head 4. The post-treatment liquid is also a non-color-forming treatment liquid that does not develop color even when it adheres to the workpiece W, and is a treatment liquid that exhibits the function of improving the fixation 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 components contained in the post-treatment liquid and the pre-treatment liquid are different.

[0040] Here, a non-color-forming treatment liquid refers to a treatment liquid that, when printed alone on a recording medium, is not perceived as having a color by the naked eye. Colors here include colors with a saturation of zero, such as black, white, and gray. A non-color-forming treatment liquid is essentially a transparent liquid; however, when viewed in its liquid form, for example, 1 liter of treatment liquid may not be completely transparent, but may appear slightly white. Such colors are so faint that, when printed alone on a recording medium, they are not perceived as having a color by the naked eye. Note that, depending on the type of treatment liquid, when printed alone on a recording medium, changes such as gloss may appear on the recording medium, but such a state is not considered color-forming.

[0041] In this embodiment, the pre-treatment liquid and the post-treatment liquid may be ejected onto almost 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.

[0042] Next, a case where the pretreatment liquid and the posttreatment liquid are selectively ejected will be described. As described above, the pretreatment liquid, ink, and posttreatment liquid are ejected in this order onto the portion of the workpiece W where a color is to be printed in accordance with the image. In this case, the ink may be of one color or multiple colors. In portions where no color is to be printed, i.e., portions where no ink is ejected, the pretreatment liquid and the posttreatment liquid are basically not ejected either. Note that, in order to adjust the image quality of the image to be printed and the texture of the workpiece W, the selection of ejection of the pretreatment liquid and the posttreatment liquid may be made to differ from the ejection of the ink.

[0043] 3, openings 31H are provided in the head support frame 31 at positions where the heads are arranged. The ink heads 4, the pre-treatment liquid heads 5, and the post-treatment liquid heads 6 are attached to the head support frame 31 so as to be fitted into the respective openings 31H. Nozzles arranged on the lower end surfaces of the heads 4, 5, and 6 are exposed from the respective openings 31H.

[0044] The multiple sub-tanks 7 are supported by the carriage 3 above the heads 4, 5, and 6 via a holding frame (not shown). The multiple sub-tanks 7 are provided corresponding to each of the heads 4, 5, and 6. Ink or treatment liquid is supplied to each sub-tank 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 sub-tank 7 and the heads 4, 5, and 6 are connected by pipes (not shown in FIG. 3).

[0045] Specifically, the multiple sub-tanks 7 include a first supply sub-tank 71A to an eighth supply sub-tank 78A, a pre-treatment supply sub-tank 7FA, and a post-treatment supply sub-tank 7RA, which are arranged on the rear side along the main scanning direction S. The first to eighth supply sub-tanks are located on the ink circulation path and supply ink to predetermined destinations (ink heads). Furthermore, the multiple sub-tanks 7 include a first recovery sub-tank 71B to an eighth recovery sub-tank 78B, a pre-treatment recovery sub-tank 7FB, and a post-treatment recovery sub-tank 7RB, which are arranged on the front side along the main scanning direction S. The first to eighth recovery sub-tanks are located on the ink circulation path and recover ink from the ink heads 4.

[0046] The first supply sub-tank 71A and first recovery sub-tank 71B, located on the far left side of the carriage 3, store yellow ink containing 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). The first recovery sub-tank 71B stores yellow ink recovered from the first upstream ink head 41A and the first downstream ink head 41B. As described above, some of the yellow ink is ejected from the first upstream ink head 41A and the first downstream ink head 41B toward the workpiece W. Similarly, the second supply sub-tank 72A supplies magenta ink to the second upstream ink head 42A and the second downstream ink head 42B. The second recovery sub-tank 72B stores magenta ink recovered from the second upstream ink head 42A and the second downstream ink head 42B. The other sub-tanks, from the third sub-tank to the eighth sub-tank, each have the same structure and function as above.

[0047] The pre-treatment supply sub-tank 7FA supplies the pre-treatment liquid to the pre-treatment liquid head 5, and the pre-treatment recovery sub-tank 7FB recovers the pre-treatment liquid from the pre-treatment liquid head 5. The post-treatment supply sub-tank 7RA supplies the post-treatment liquid to the post-treatment liquid head 6, and the post-treatment recovery sub-tank 7RB recovers the post-treatment liquid from the post-treatment liquid head 6.

[0048] 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 pre-treatment liquid head 5, and the post-treatment liquid head 6 - are mounted on a single carriage 3. With this inkjet printer 1, for example, in the printing process of performing inkjet printing on fabric in digital textile printing, the process of ejecting the pre-treatment liquid and the process of ejecting the post-treatment 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.

[0049] 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 in which a carriage 3 carrying ink heads 4 of each color moves back and forth in the main scanning direction S, and the workpiece W is intermittently fed in the transport direction F, repeatedly.

[0050] Specifically, the band-shaped image is printed while the carriage 3 moves in the forward direction, which is one of the main scanning directions S. During this forward main scanning, the feeding of the workpiece W is stopped. After the band-shaped 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 the reverse direction. The workpiece W is in a stopped state. Then, while moving in the return direction, the carriage 3 prints the next band-shaped image upstream of the previous band-shaped image. Similar operations are repeated thereafter.

[0051] <Ink and processing liquid circulation paths> 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 the supply sub-tank and recovery sub-tank according to this embodiment. Note that in each figure, the lines connecting components indicate conduits (tubes) through which gas or liquid flows.

[0052] In this embodiment, pressure is applied via gas (air) to each of the first supply sub-tank 71A to the post-treatment supply sub-tank 7RA (also referred to as a supply tank or a supply section, respectively) and the first recovery sub-tank 71B to the post-treatment recovery sub-tank 7RB (also referred to as a recovery tank or a 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, the pre-treatment liquid head 5, and the post-treatment liquid head 6.

[0053] Referring to Figure 4, a circulation path including paths for supplying and recovering 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 shown in Figure 4 is also provided for the ink heads of other colors. The inkjet printer 1 further includes filters 81, 82, 83, and 84, a circulation pump 85 (pump, ink pump), a check valve 86, and a degasser 87, which are arranged on the carriage 3. The inkjet printer 1 also includes a main tank 90, a capacitance sensor 91, a main tank valve 92, a main supply pump 93, and a control unit 100, which are arranged on the device frame 10 (Figure 1) outside the carriage 3.

[0054] Yellow ink flowing from the first supply subtank 71A into the ink supply path QA is split into a first ink path Q1 via the first upstream ink head 41A and a second ink path Q2 via the first downstream ink head 41B. A filter 81 is located upstream of the first upstream ink head 41A, and a filter 82 is located upstream of the first downstream ink head 41B. A filter 83 is located downstream of the first upstream ink head 41A, and a filter 84 is located downstream of the first downstream ink head 41B. These filters function to remove foreign matter, dust, and other contaminants 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 through the ink collection path QB into the first collection subtank 71B. The collected yellow ink is then supplied to the first supply subtank 71A via the ink return path Q3.

[0055] As shown in FIG. 4, the circulation pump 85 constitutes part of a circulation path for yellow ink that flows from the first supply sub-tank 71A via the first upstream ink head 41A, the first downstream ink head 41B, and the first recovery sub-tank 71B before returning to the first supply sub-tank 71A. In this embodiment, the circulation pump 85 sends yellow ink from the first recovery sub-tank 71B to the first supply sub-tank 71A. The circulation pump 85, together with the ink circulation path and each sub-tank, 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 sub-tank.

[0056] The check valve 86 prevents ink from flowing back from the first supply sub-tank 71A to the first recovery sub-tank 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.

[0057] 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.

[0058] The capacitance sensor 91 detects the remaining amount of yellow ink in the main tank 90 .

[0059] 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 or closed manually, or automatically in response to a command signal input from the control unit 100.

[0060] The main supply pump 93 operates to supply the yellow ink in the main tank 90 to the first supply sub-tank 71A.

[0061] The control unit 100 controls the overall operation of the inkjet printer 1, and electrically controls each of the components shown in FIG.

[0062] As shown in FIG. 5, for example, the first supply sub-tank 71A has a box-like structure. When yellow ink is stored therein, a supply tank gas region SA and a supply tank ink region SB are formed. The supply tank gas region SA is a space above the liquid surface of the yellow ink in the first supply sub-tank 71A, and the supply tank ink region SB is a region formed by the yellow ink. The supply tank gas region SA is connected to a 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 region SA of the first supply sub-tank 71A at a predetermined pressure. The supply tank ink region 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.

[0063] The first supply sub-tank 71A also has a capacitance sensor 71A1 that can detect the liquid level (ink amount) of yellow ink in the first supply sub-tank 71A.

[0064] Similarly, the first recovery sub-tank 71B has a box-like structure, and when yellow ink is stored therein, a recovery tank gas region SC and a recovery tank ink region SD are formed. The recovery tank gas region SC is a space above the liquid surface of the yellow ink in the first recovery sub-tank 71B, and the recovery tank ink region SD is a region formed by the yellow ink. The recovery tank gas region SC communicates with the recovery-side pressure supply path P12. The recovery-side pressure supply path P12 communicates with a pressure source (not shown) and maintains the recovery tank gas region SC of the first recovery sub-tank 71B at a predetermined pressure. The recovery tank ink region SD also communicates with the ink recovery path QB (first ink path Q1, second ink path Q2) and the ink return path Q3.

[0065] The first collection sub-tank 71B also has a capacitance sensor 71B1 that can detect the liquid level (ink amount) of yellow ink in the first collection sub-tank 71B.

[0066] In this embodiment, the supply tank gas region SA of the first supply sub-tank 71A is maintained at, for example, +2 kPa (relative to atmospheric pressure; the same applies below), and the recovery tank gas region SC of the first recovery sub-tank 71B is maintained at, for example, -15 kPa. As a result, a flow of yellow ink is formed from the first supply sub-tank 71A shown 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 sub-tank 71B. Note that both the supply tank gas region SA and the recovery tank gas region SC may be maintained at a positive pressure greater than 0 kPa. Alternatively, both the supply tank gas region SA and the recovery tank gas region SC may be maintained at a negative pressure less than 0 kPa. The pressure difference between the supply tank gas region SA and the recovery tank gas region SC may be 5 to 20 kPa.

[0067] When the control unit 100 receives an output signal from the capacitance sensor 71A1 (FIG. 5) and determines that there is little ink in the first supply sub-tank 71A, 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. The circulation pump 85 operates whether the inkjet printer 1 is in the middle of or is stopped from printing.

[0068] 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 replenishment amount (replenishment 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 displays an ink refill message on a display unit (not shown) of the inkjet printer 1.

[0069] 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 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, as shown in Figure 4. In this case, some ink continues to circulate through the circulation path without being ejected from the ink heads.

[0070] In a structure in which ink is circulated as described above, there is a problem that, over long periods of use, pigment ink aggregates (coarse particles) 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 uses an inkjet method to print images on a wide and long workpiece W (recording medium), and compared to a typical home printer, the flow rate of ink flowing through the circulation path is relatively high, making it more likely to produce aggregates. The present inventors focused on the ink flow speed in each flow path, including the circulation pump 85, as a factor in the generation of such aggregates, and evaluated the amount of coarse particles produced (amount of coarse particles) relative to the flow speed of various pumps.

[0071] 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 ​​are shown as 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 ink flows within 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 section within the pump. Note that since the cross-sectional area of ​​the valve section is considered to be 0 (zero) when the valve is closed, the valve passage area is the cross-sectional area when the valve is open.

[0072] The maximum flow rate corresponds to the maximum flow rate of ink in the pump. The flow rate of ink in the pump can be obtained by measuring the ink flow rate at the pump outlet or inlet. The maximum flow rate is the largest of these flow rates. Even when the ink circulation rate 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 refers to the maximum flow rate when the pump is operated during printing and includes the fluctuations that occur depending on the pump operation described above. The maximum flow rate occurs, for example, when the circulation pump 85 transfers ink from the first recovery subtank 71B to the first supply subtank 71A, which has run low on ink. The maximum flow rate is kept below a predetermined speed at least during continuous printing. The maximum flow rate may also be kept below a predetermined speed when circulating ink while the inkjet printer 1 is paused and not printing. It should be noted that during non-routine operations, such as the process of restoring an inkjet printer 1 that has experienced some kind of trouble, it is acceptable to temporarily increase the flow rate above the specified speed, but even in such cases, it is best to keep the flow rate below the specified speed.

[0073] The maximum flow rate corresponds to the maximum velocity of the ink inside the pump. It is believed that the point where the ink velocity inside the pump is greatest is the part with the smallest cross-sectional area of ​​the ink flow path. 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 particles was calculated by counting the number of particles with a diameter of 5 μm or more that were generated by each pump until a cumulative flow rate of approximately 1,000 L was delivered.

[0074] [Table 1]

[0075] FIG. 6 is a graph showing the relationship between the maximum flow velocity in Table 1 (flow velocity inside the pump in FIG. 6) and the amount of coarse particles.

[0076] As shown in Table 1 and Figure 6, the present inventors have discovered that the amount of coarse particles generated tends to increase depending on the flow velocity inside the pump. This phenomenon is thought to be caused by a velocity gradient occurring at the cross section of each flow path due to the viscosity of the ink, which increases the frequency of collisions between particles that make up the pigment due to the difference in velocity between those particles, promoting the generation of agglomerates (shear agglomeration). Note that this velocity gradient is mainly caused by the velocity of particles near the inner wall of the flow path (pipe) being relatively slower than the velocity of particles near the center of the flow path.

[0077] The flow rate within the pump may be slowed by increasing the duty of the pump operation. For example, the control unit 100 can control the pump 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. To achieve a predetermined amount of transfer per unit time, a pump with a slow maximum flow rate may be used to increase the duty. This reduces the generation of coarse particles. The duty may be 30% or more, further 40% or more, and particularly 50% or more. From the above perspective, it is preferable for the duty to be close to 100%. However, if the duty is set close to 100%, it becomes impossible to increase the amount of ink transferred by control. Therefore, the duty may be set to 80% or less, particularly 60% or less.

[0078] Furthermore, treatment liquids such as pre-treatment liquid and post-treatment liquid generally do not contain substances that may aggregate, such as pigments, and even if they do contain such substances, the amount is smaller than that of ink. Therefore, the flow rate of the pump that circulates the treatment liquid may be faster than the flow rate of the pump that circulates the ink. In this way, if the flow rate of the treatment liquid is made faster than the flow rate of the ink, the duty basically decreases, thereby widening the range in which the transfer amount can be changed. On the other hand, if the flow rate of the treatment liquid is made similar to the flow rate of the ink, the same pump can be used for both the treatment liquid and the ink, and the circulation control can be the same or similar.

[0079] When 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 is almost constant, even if there is pulsation, and in the flow path from the ink head 4, the amount of ink circulating is reduced 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 pump.

[0080] In this embodiment, the circulation pump 85 transfers ink from the first collection sub-tank 71B to the first supply sub-tank 71A. The transfer of ink from the first supply sub-tank 71A to the first collection sub-tank 71B via the ink head 4 is achieved by the difference in gas pressure applied to the sub-tank. By setting the transfer rate of the circulation pump 85 to be greater than the rate of ink transfer from the first supply sub-tank 71A to the first collection sub-tank 71B when no ink is being ejected from the ink head 4, the amount of ink in the first collection sub-tank 71B can be prevented from increasing while the circulation pump 85 is operating. To achieve this, the maximum flow rate of ink delivered by the circulation pump 85 (maximum flow rate per unit time, not including fluctuations such as pulsation) is set to be greater than the maximum flow rate of ink from the first supply sub-tank 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 delivered by the circulation pump 85. Furthermore, 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 delivered from the circulation pump 85.

[0081] 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.

[0082] In the ink head 4, the flow velocity is fastest, for example, in the individual flow paths connecting the common supply flow path and the pressure chamber. The individual flow paths in this portion are often the flow paths with the smallest 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 connected in parallel. Therefore, the flow rate of ink flowing through the individual flow paths is small, and the ink flow velocity is slow. This ink flow velocity is, for example, 0.2 m / sec. Here, the minimum flow path cross-sectional area of ​​the individual flow paths is smaller than the minimum flow path cross-sectional area of ​​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.

[0083] More specifically, in each ink head, the product of the smallest flow path cross-sectional area within an individual flow path and the number of individual flow paths is equal to or larger than the smallest flow path cross-sectional area within the circulation pump 85. Furthermore, in each ink head, the product of the smallest flow path cross-sectional area within an individual flow path and the number of individual flow paths is larger than the smallest flow path cross-sectional area within the circulation pump 85. As described above, in one ink head 4, the multiple individual flow paths provided corresponding to each ejection unit (nozzle) are arranged in parallel in terms of flow path structure. Furthermore, when individual flow paths with different smallest flow path cross-sectional areas are mixed, the product of the smallest flow path cross-sectional area within an individual flow path and the number of individual flow paths corresponds to the sum of the smallest flow path cross-sectional areas for all the individual flow paths, and may be calculated in this manner.

[0084] Furthermore, the maximum flow velocity of the ink within the circulation pump 85 is preferably 30 times or less, more preferably 25 times or less, more preferably 15 times or less, and even more preferably 10 times or less than the flow velocity of the ink flowing through the individual flow paths of the ink head 4 (maximum flow velocity of the ink within the ink head).

[0085] The circulation path may be provided with a valve, such as an electromagnetic valve, that can stop the flow of ink. Such a valve keeps the cross-sectional area of ​​the flow path small even when open. The flow rate through such a valve is, for example, 1.0 m / sec.

[0086] The flow rate of ink flowing through 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 than the flow rate of ink in the valve. In other words, in the ink circulation path from the recovery port via circulation pump 85 and the supply sub-tank to the supply port, the maximum flow rate of ink in 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 than the maximum flow rate of ink in the portion other than circulation pump 85.

[0087] Furthermore, if a filter is provided inside the ink head 4, the total cross-sectional area of ​​the filter is greater than the total cross-sectional area of ​​the smallest portions 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. Since the total cross-sectional area of ​​the filters provided in the circulation path is greater than the cross-sectional area of ​​a valve such as a solenoid valve, 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 also applies to each treatment liquid. In particular, if a filter is provided inside the ink head 4 (for example, the aforementioned back-end filter), it is desirable that the total opening area of ​​the filter be equal to or greater than the smallest flow path cross-sectional area in the circulation pump 85, and more desirably, be greater than that area.

[0088] In the above configuration, if the maximum flow rate of the ink in the circulation pump 85 is set to a predetermined rate or less, it is possible to suppress the ink from coagulating and becoming coarse. As a result, damage to the circulation pump 85 and blockage of each path can be prevented.

[0089] In particular, in this embodiment, the first collection subtank 71B is disposed midway along the ink circulation path and stores ink collected from each ink head. The circulation pump 85 is disposed in a flow path that connects the first collection subtank 71B and the first supply subtank 71A, which constitutes part of the circulation path (located between the first collection subtank 71B and the first supply subtank 71A in terms of upstream and downstream positional relationship in the flow path), and sends ink from the first collection subtank 71B to the first supply subtank 71A. This configuration, by providing a supply subtank and a collection subtank independent of the ink heads, allows for a stable supply of ink to the ink heads and stable collection of ink from the ink heads. Furthermore, by disposing the circulation pump 85 in the flow path between the subtanks farthest from the ink heads, it is possible to promote ink circulation without affecting ink ejection. This location also helps prevent ink from coagulating and becoming coarse.

[0090] Furthermore, when the ink contains a binder as in this embodiment, aggregation is likely to occur due to its characteristics, but by limiting the maximum flow velocity of the ink as described above, it is possible to suppress aggregation of ink containing a binder.

[0091] Furthermore, in the case of the present embodiment where the ink is a textile printing ink, the binder content is large in order to print images such as letters and patterns on a recording medium made of fabric such as woven fabric or knitted fabric. In this case, aggregation as described above is likely to occur, but by similarly limiting the maximum ink flow velocity, it is possible to suppress aggregation of ink that contains a large amount of binder.

[0092] In the ink jet printer 1 according to this embodiment, as shown in Table 1, the flow rate of ink flowing through the pump when the pump is in operation is 1.7×10 -7 (m 3 / sec) or more. When ink circulates at a high flow rate, the velocity gradient described above is likely to occur, which results in the promotion of aggregation and the generation of coarse particles. 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 ink flow velocity.

[0093] 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 compress the tube as it operates, which can gradually deteriorate the tube and cause a decrease in flow rate over time. Furthermore, 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.

[0094] On the other hand, using a piezoelectric pump (Example 2 in Table 1) as the circulation pump 85 makes it possible to circulate ink while eliminating the above concerns. Using a piezoelectric pump makes it possible to maintain a low flow rate 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 element. In a typical diaphragm pump, the diaphragm is driven mechanically or hydraulically, so the amount of diaphragm displacement per drive (one back-and-forth vibration) is nearly constant. The amount of ink pushed out due to the displacement is also thought to be relatively constant. In contrast, when the diaphragm is driven by a piezoelectric element, the driving force applied to the diaphragm is nearly constant, but the amount of displacement is not constant. Although the details are unknown, it is thought that in situations where it is difficult to push the ink out, the amount of diaphragm displacement will be smaller even with the same driving force, resulting in a slightly lower flow rate and a slightly slower maximum flow rate. Furthermore, since a piezoelectric pump does not generate the pulsation described above, ink can be circulated stably. However, piezoelectric pumps have relatively poor load characteristics and may not be able to achieve the required flow rate depending on the resistance and inertance of the circulation path, so it is desirable to use a piezoelectric pump for circulation pump 85 to the extent that these concerns do not become apparent.

[0095] On the other hand, by using a diaphragm pump as the circulation pump 85, it is possible to circulate ink while eliminating the above concerns. When a diaphragm pump is used in the inkjet printer 1 according to this embodiment, the minimum cross-sectional area of ​​the circulation path within the pump is 2.0×10 -6 (m 2 ) or more, and the maximum flow rate of the ink is 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.

[0096] Table 1 shows a diaphragm pump, Example 3, and Comparative Examples 1 and 2. Comparative Example 2 differs from Comparative Example 1 in that an external damper is attached to the pump.

[0097] In contrast, it was confirmed that the generation of coarse particles was suppressed in Example 3 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 favorably when it is necessary to ensure a sufficient flow rate of ink flowing through the circulation path.

[0098] Furthermore, Figure 7 is a graph showing the relationship between the shear stress in Table 1 and the amount of coarse particles. The shear stress refers to the shear stress generated 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 that between parallel plates (Couette flow).

[0099] Shear stress τ (unit: Pa) = μ × v / r (Equation 1) In Equation 1, μ (unit: Pa·s) is the viscosity of the ink, and v (unit: m / s) is the ink flow velocity. In this case, the flow velocity corresponds to the maximum flow velocity mentioned above. Furthermore, r (unit: m) corresponds to the radius of the circular pipe when the flow path is assumed to be a circular pipe, and can be calculated as the radius when the valve passage area in Table 1 is taken to be the area of ​​a circle. In the above example, the ink viscosity μ is 6 (mPa·s).

[0100] The present inventors have discovered that 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 that occurs at the cross section of each flow path due to the viscosity of the ink, as described above. The velocity difference between pigment particles increases the frequency of collisions between the particles, promoting the formation of agglomerates (shear agglomeration). As shown in Figure 7, ink agglomeration and coarse powder generation can be stably suppressed when the shear stress is in the range of 30 Pa or less. To indicate this desirable boundary, a dashed line is added to the shear stress range of 30 Pa in Figure 7. As shown in Table 1, in Examples 1, 2, and 3, the shear stress was 30 Pa or less, and the amount of coarse powder was reduced compared to the comparative example.

[0101] These results indicate 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.

[0102] Alternatively, if we consider the transport of ink using a pump where the pressure applied to the ink is nearly constant, when 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, when 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 discovered that, regardless of the viscosity of the ink, ink aggregation and coarse powder formation can be stably suppressed by setting the shear stress in the range of 30 Pa or less as described above.

[0103] Furthermore, the present inventors have focused on increasing the cross-sectional area by devising a 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 circulation pump 85 according to this embodiment.

[0104] 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 section 852, an intake flow path 85A, an exhaust flow path 85B, an intake side check valve 853, and an exhaust side check valve 854.

[0105] The displacement portion 852 constitutes a part of the pump chamber 851 (the upper surface of the pump chamber 851 in FIG. 8A), and is displaced to switch between 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 made up of a piezoelectric vibrator, and vibrates in response to an input drive voltage.

[0106] The suction flow path 85A communicates with the upstream side of the ink circulation path. In other words, 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. In other words, 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.

[0107] 8B and 8C are schematic cross-sectional views showing the periphery of delivery-side check valve 854 of circulation pump 85 of FIG. 8A. Check valve support portion 850H of FIG. 8B is part of pump body 850 of FIG. 8A and has a structure that supports delivery-side check valve 854. Check valve support portion 850H has a flat surface 855 (opposing surface). Flat surface 855 is disposed opposite delivery-side check valve 854 and is connected to the inlet of delivery flow path 85B.

[0108] 8A, the pressure in the pump chamber 851 increases, and 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 that of the delivery flow path 85B, the delivery-side check valve 854 closes the flow path as shown in FIG. 8B, and thus the backflow of ink from the delivery flow path 85B to the pump chamber 851 is prevented.

[0109] In this embodiment, when ink is delivered by the circulation pump 85, the delivery-side check valve 854 comes into contact with the flat surface portion 855 as shown in Fig. 8C. Therefore, compared to when the check valve support portion 850H has a protrusion as shown by the dashed line in Fig. 8B, the cross-sectional area of ​​the flow path around the delivery-side check valve 854 in the ink circulation path can be increased. Note that instead of the flat surface portion 855, a curved surface or the like may be arranged as the opposing surface.

[0110] 8A。 In this case, pump chamber 851 in FIGS. 8B and 8C is replaced by suction flow path 85A in FIG. 8A, and delivery flow path 85B in FIGS. 8B and 8C is replaced by pump chamber 851 in FIG. 8A. As a result, when the pressure in pump chamber 851 decreases with the displacement of displacement portion 852 in FIG. 8A, suction side check valve 853 allows ink to flow from suction flow path 85A to pump chamber 851. On the other hand, when the pressure in pump chamber 851 is higher than the pressure in suction flow path 85A, suction side check valve 853 prevents ink from flowing back from pump chamber 851 to suction flow path 85A.

[0111] Furthermore, in this embodiment, the cross-sectional area of ​​the flow paths in circulation pump 85 is smallest in at least one of the flow paths in suction-side check valve 853 and the flow paths in delivery-side check valve 854. In other words, circulation pump 85 is designed so that the flow paths other than those in suction-side check valve 853 and delivery-side check valve 854 are not narrower than the flow paths in suction-side check valve 853 and delivery-side check valve 854. That is, the cross-sectional area of ​​the flow paths in circulation pump 85 is smallest in the flow paths in the areas of each check valve. Note that the cross-sectional area of ​​the flow paths in circulation pump 85 may be smallest in at least one of the flow paths in suction-side check valve 853 and the flow paths in delivery-side check valve 854.

[0112] In this embodiment, at least one of the suction-side check valve 853 and the delivery-side check valve 854 has a cross-sectional area of ​​a flow path of 2.0×10 when the check valve is open. -6 (m2 ) or more. 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 preferable cross-sectional area is set as described above will be described in detail below.

[0113] When considering the shear stress acting on the ink, even if the cross-sectional area of ​​the flow channel is the same, a long and thin cross-sectional shape has a greater effect than a circular one, as follows: With a long and thin shape, the distance between the flow channel wall, where the flow velocity is zero, and the center of the flow channel, where the flow velocity is at its maximum, is closer, so the shear stress is greater. Also, since the effect of shear stress is greater in the region near the flow channel wall than in the center of the flow channel, the region where the effect of shear stress is greater with a long and thin shape is wider due to the longer length of the flow channel wall.

[0114] For this reason, in this embodiment, 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 is likely to have an elongated shape. As a result, it is possible to particularly suppress aggregation of ink in the circulation path.

[0115] The ink flow velocity in the circulation path using each of the above pumps is preferably kept to 6 m / sec or less, and more preferably 5 m / sec or less. Furthermore, the ink flow velocity is preferably kept to 3 m / sec or less, and more preferably 2 m / sec or less. By limiting the predetermined speed for limiting the maximum ink flow velocity in this way, it is possible to further suppress ink aggregation and coarse powder formation.

[0116] Furthermore, the region of the ink circulation path where the ink flow velocity is set to be equal to or less than the predetermined velocity may be only within the circulation pump 85, or may be a region of the circulation path excluding the ink heads. That is, in FIG. 4, the ink circulation path includes supply ports Q1A and Q2A connected to the ink heads. The ink circulation path also includes recovery ports Q1B and Q2B connected to the ink heads. The maximum ink flow velocity in the circulation path from the recovery ports Q1B and Q2B via the first recovery sub-tank 71B, the circulation pump 85, and the first supply sub-tank 71A to the supply ports Q1A and Q2A is set to be equal to or less than the predetermined velocity. In this embodiment, the maximum ink flow velocity in the ink circulation path from the recovery ports via the circulation pump 85 and the supply sub-tank to the supply ports is the flow velocity within the circulation pump 85. More specifically, the maximum ink flow rate in the ink circulation path from the recovery port via the circulation pump 85 and the supply sub-tank to the supply port, and within the ink head 4, is the flow rate in the circulation pump 85. Furthermore, the region of the ink circulation path where the ink flow rate is set to be equal to or lower than the predetermined rate may be the entire circulation path including each ink head. Furthermore, the maximum ink flow rate in the circulation pump 85 may be faster than the maximum ink flow rate in the multiple individual flow paths within the ink head 4.

[0117] In an ink head, nozzles that eject liquid or individual flow paths that supply and recover ink to the nozzles have small cross-sectional areas, which can lead to clogging with coarse particles or aggregates of coarse particles. While providing a filter in the ink head or ink circulation path reduces clogging in the nozzles or individual flow paths, if a large amount of coarse particles is generated, the filter may become clogged with coarse particles over the long term. Therefore, by setting the ink flow velocity in the ink circulation path to a predetermined velocity or less, clogging in the nozzles, individual flow paths, or filters can be reduced. Here, the terms "nozzle" and "individual flow paths that supply and recover ink to the nozzles" also refer to a structure in which a nozzle is attached to an individual flow path through which ink flows from an ink supply source to an ink recovery destination. In such a structure, the individual flow path is attached to the base of the cylindrical nozzle. When ink flows through an individual flow path in such a structure, a flow occurs in the ink within the nozzle, stirring the ink within the nozzle. As a result of the ink flowing in the nozzles, some of the ink flowing in the individual flow paths is supplied to the nozzles, and some of the ink in the nozzles is collected in the individual flow paths.

[0118] If the flow path structure is such that the fastest flow rate is achieved inside the ink head 4, coarse particles are likely to be generated inside the ink head 4, causing clogging and other problems. For this reason, the flow path structure may be such that the fastest flow rate is achieved outside the ink head 4, and monitoring may be performed to prevent the generation of large amounts of coarse particles even at that flow rate.

[0119] In addition, at least in pumps having 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 somewhat small.

[0120] The inkjet printer 1 (inkjet recording device), ink circulation device, and ink pump according to the present embodiment described above can circulate ink to eliminate ink waste 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.

[0121] (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 one 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.

[0122] (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 therewith.

[0123] (3) In the above embodiment, a recovery tank is provided in the ink circulation path. However, a recovery tank is not required. 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 part of the circulation path and pumps out the ink. In this case, the maximum ink flow rate in the circulation pump 85 may be set to be equal to or less than the predetermined speed. Furthermore, assuming that the first recovery sub-tank 71B is not present in FIG. 4, the maximum ink flow rate in the circulation path from the recovery ports Q1B and Q2B through the circulation pump 85 and the first supply sub-tank 71A to the supply ports Q1A and Q2A may be set to be equal to or less than the predetermined speed. Alternatively, the maximum ink flow rate in the entire circulation path, including each ink head, may be set to be equal to or less than the predetermined speed.

[0124] (4) The multiple configurations disclosed in the above embodiments can be combined with each other to form a single disclosure. [Explanation of symbols]

[0125] 1. Inkjet printer 3 Carriage 3 4 ink heads 41A 1st upstream ink head 41B 1st downstream ink head 42A Second upstream ink head 42B Second downstream ink head 5 Pre-treatment liquid head 6 Post-treatment liquid head 7 Subtank 71A 1st supply sub-tank 71A1 Capacitive Sensor 71B First recovery subtank 71B1 Capacitive Sensor 72A Second supply sub-tank 72B Second recovery subtank 85 Circulation pump 850 pump body 850H Check valve support 851 Pump Room 852 Displacement section 853 Suction side check valve 854 Delivery side check valve 855 Plane section 85A Suction passage 85B Outlet channel 90 Main Tank 91 Capacitive Sensor 92 Main tank valve 93 Main supply pump P11 Supply side pressure supply line P12 Recovery side pressure supply line QA ink supply path QB ink recovery channel Q1 First ink path Q2 Second ink path Q3 Ink return path Q4 Ink refill path

Claims

1. a circulation path through which a printing ink containing a pigment and a binder flows; an ink head located in the circulation path and capable of ejecting the ink, the ink head including 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 supply unit located in the circulation path and supplying the ink to the ink head; a pump located in the circulation path and configured to send the ink collected from the plurality of individual flow paths of the ink head to the supply unit; Equipped with the flow rate of the ink flowing through the pump is 1.7×10 −7 (m 3 / sec) or more; a maximum flow velocity of the ink in the circulation path is set to 6 m / sec or less; the product of the smallest flow path cross-sectional area within the individual flow path and the number of the individual flow paths is equal to or larger than the smallest flow path cross-sectional area within the pump; The pump 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 flow path and the pump chamber; a displaceable delivery-side check valve located between the pump chamber and the delivery flow path; and The inkjet textile printing recording device, wherein at least one of the cross-sectional areas of the flow passage 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.

2. a circulation path through which a printing ink containing a pigment and a binder flows; an ink head located in the circulation path and capable of ejecting the ink, the ink head including 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 supply unit located in the circulation path and supplying the ink to the ink head; a pump located in the circulation path and configured to send the ink collected from the plurality of individual flow paths of the ink head to the supply unit; Equipped with the flow rate of the ink flowing through the pump is 1.7×10 −7 (m 3 / sec) or more; a maximum flow velocity of the ink in the circulation path is set to 6 m / sec or less; the product of the smallest flow path cross-sectional area within the individual flow path and the number of the individual flow paths is equal to or larger than the smallest flow path cross-sectional area within the pump; The pump 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 flow path and the pump chamber; a displaceable delivery-side check valve located between the pump chamber and the delivery flow path; and At least one of the suction side check valve and the delivery side check valve has a cross-sectional area of ​​2.0 x 10 when the check valve is open. －６ (m ２ ) The inkjet recording apparatus for textile printing.

3. a circulation path through which a printing ink containing a pigment and a binder flows; an ink head located in the circulation path and capable of ejecting the ink, the ink head including 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 supply unit located in the circulation path and supplying the ink to the ink head; a pump located in the circulation path and configured to send the ink collected from the plurality of individual flow paths of the ink head to the supply unit; Equipped with the flow rate of the ink flowing through the pump is 1.7×10 −7 (m 3 / sec) or more; a maximum flow velocity of the ink in the circulation path is set to 6 m / sec or less; the product of the smallest flow path cross-sectional area within the individual flow path and the number of the individual flow paths is equal to or larger than the smallest flow path cross-sectional area within the pump; The pump 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 flow path 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; and the delivery-side check valve abuts against the opposing surface when the ink is delivered by the pump.

4. 4. The inkjet textile printing recording apparatus according to claim 1, wherein a shear stress generated in the ink in the pump is 30 (Pa) or less.

5. 4. The inkjet recording apparatus for textile printing according to claim 1, wherein the pump is a piezoelectric pump.

6. The pump is a diaphragm pump, and the minimum cross-sectional area of ​​the circulation path in the pump is 2.0×10 －６ (m ２ ) or more, and the maximum flow rate of the ink is 1.7 × 10 －５ (m ３ 4. The ink-jet recording apparatus for textile printing according to claim 1, wherein the ink jet speed is set to 1 / sec or less.

7. a recovery unit located in the circulation path and configured to recover the ink from the ink head; The inkjet recording apparatus for textile printing 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.

8. the pump has a displaceable check valve; 4. The inkjet textile recording apparatus according to claim 1, wherein the cross-sectional area of ​​the flow path in the pump is smallest at a portion of the check valve.

9. 4. The inkjet recording apparatus for textile printing 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.

10. The inkjet textile printing recording device according to claim 1 , wherein the minimum cross-sectional area of ​​the individual flow path is smaller than the minimum cross-sectional area of ​​the pump.

11. 11. The inkjet recording apparatus for textile printing according to claim 10, wherein the ink head has a filter therein, and the total opening area of ​​the filter is equal to or larger than the smallest cross-sectional area of ​​the flow path in the pump.

12. the circulation path includes a supply port and a recovery port connected to the ink head; 4. The inkjet textile recording 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 unit to the supply port is set to 6 m / sec or less.

13. the circulation path includes a supply port and a recovery port connected to the ink head; 4. The inkjet textile recording apparatus according to claim 1, wherein a maximum flow rate of the ink in the circulation path from the recovery port through the pump and the supply unit to the supply port is a flow rate within the pump.

14. the circulation path includes a supply port and a recovery port connected to the ink head; 4. The inkjet textile recording device according to claim 1, wherein a maximum flow velocity of the ink in the circulation path from the recovery port via the pump and the supply unit to the supply port, and in the ink head, is equal to a flow velocity in the pump.

15. The inkjet textile recording apparatus 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.

16. the circulation path includes a supply port and a recovery port connected to the ink head; 4. The inkjet textile recording 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 a portion other than the pump.

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