Liquid ejecting device and liquid ejecting head

Abstract

The present disclosure relates to a liquid ejection device, comprising: a liquid storage unit capable of storing liquid; a liquid ejection unit including an ejection port capable of ejecting the liquid; and a pressure control unit that receives liquid from the liquid storage unit and allows liquid having a pressure controlled within a predetermined pressure range to be supplied to the liquid ejection unit. Furthermore, the liquid ejection device comprises: a first circulation unit that supplies liquid having a pressure controlled by the pressure control unit to the ejection port while circulating the liquid between the liquid ejection unit and the pressure control unit; and a second circulation unit that circulates the liquid between the liquid storage unit and the pressure control unit. The present disclosure also relates to a liquid ejection head.

Description

[0001] This application is a divisional application of the invention patent application with the application date of June 18, 2021, application number 202110675636.6, and invention name “Liquid injection device and liquid injection head”. Technical Field

[0002] The present disclosure relates to a liquid ejecting device and a liquid ejecting head. Background Art

[0003] A liquid ejection device for performing printing by using a liquid ejection head has been proposed, which includes a circulation mechanism for circulating liquid between the liquid ejection head and a liquid storage unit as a measure to solve problems such as liquid thickening, colorant precipitation, and retention of bubbles and foreign matter in the liquid ejection head and the liquid supply flow path.

[0004] Japanese Patent Laid-Open No. 2017-7108 discloses a liquid ejecting device that circulates liquid in a liquid ejecting head by means of a circulation pump installed above the liquid ejecting head. Summary of the Invention

[0005] The present disclosure provides a liquid injection device, which includes: a liquid storage unit capable of storing liquid; a liquid injection unit, the liquid injection unit including an injection port capable of injecting liquid; a pressure control unit, the pressure control unit receiving liquid from the liquid storage unit and allowing liquid with a pressure controlled within a predetermined pressure range to be supplied to the liquid injection unit; a first circulation unit, the first circulation unit supplying liquid with a pressure controlled by the pressure control unit to the injection port while circulating the liquid between the liquid injection unit and the pressure control unit; and a second circulation unit, the second circulation unit circulating the liquid between the liquid storage unit and the pressure control unit.

[0006] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic diagram showing a schematic configuration of a liquid ejecting device in an embodiment of the present invention;

[0008] Figure 2 is a schematic diagram showing a circulation path of the liquid ejecting device in the first embodiment;

[0009] Figure 3 is a schematic diagram showing the state of the circulation path and the flow of ink in the case of printing;

[0010] Figure 4is a schematic diagram showing the state of the circulation path and the flow of ink in the case of a high printing load;

[0011] Figure 5 1 is a schematic diagram showing a circulation path of a liquid ejecting device in a second embodiment;

[0012] Figure 6 is a schematic diagram showing a state in which the flow of ink is reversed in the liquid ejecting head;

[0013] Figure 7 is a schematic diagram showing a modified example of the second embodiment;

[0014] Figure 8 is a cross-sectional perspective view showing a printing element substrate;

[0015] Figure 9A and 9B is a perspective view showing a circulation unit in a second embodiment;

[0016] Figure 10A and 10B yes Figure 9A and 9B An exploded perspective view of the circulation unit is shown;

[0017] Figure 11A and 11B is a diagram schematically showing a cross section of a switching valve;

[0018] Figure 12A and 12B yes Figure 10A and 10B perspective and cross-sectional views of the head circulation pump shown;

[0019] Figure 13A and 13B yes Figure 12A and 12B An exploded perspective view of the head circulation pump is shown;

[0020] Figure 14 yes Figure 9A and 9B a cross-sectional view taken along line XIV-XIV in the illustrated circulation unit;

[0021] Figure 15 It is along Figure 14 A cross-sectional view taken along line XV-XV in FIG.

[0022] Figure 16A and 16B It is along Figure 14 A cross-sectional view taken along line XVI-XVI in FIG.

[0023] Figure 17is a graph showing the relationship between the flow resistance in the valve unit and the valve opening degree of the pressure regulator; and

[0024] Figure 18 Schematic diagram showing a schematic configuration of a liquid ejecting device in a comparative example. DETAILED DESCRIPTION

[0025] In the configuration disclosed in Japanese Patent Laid-Open No. 2017-7108, liquid thickening, colorant precipitation, and retention of bubbles and foreign matter in the liquid ejection head can be reduced by circulating the liquid in the liquid ejection head by a circulation pump. However, colorant precipitation and retention of bubbles and foreign matter may still occur in the liquid flow path from the liquid storage unit to the liquid ejection head. This results in the need to perform a long suction recovery operation to suck and discharge the liquid from the ejection port of the liquid ejection head before starting printing, thereby causing a large amount of waste ink and long downtime. Such problems are particularly prominent in liquid ejection devices used for commercial printing (which use ink that is easy to precipitate, such as white ink).

[0026] In view of these circumstances, a configuration can be considered in which the liquid in the liquid storage unit is circulated sequentially through a supply pipe, a circulation pump, a liquid ejecting head, a collection pipe, and the liquid storage unit. However, in such a configuration, the collection pipe will vibrate during the reciprocating scanning of the liquid ejecting head, and negative pressure changes will occur in the liquid ejecting head. This will lead to instability in the ejection characteristics and the amount of ejected droplets of the liquid ejecting head. Therefore, there is a risk of image quality degradation due to streaks and unevenness in the printed image. As the scanning speed of the liquid ejecting head increases to improve printing productivity, this impact on image quality becomes more significant.

[0027] Therefore, it is difficult for conventional technologies to simultaneously achieve reductions in waste ink and downtime as well as high-speed and high-image-quality printing characteristics.

[0028] In view of these circumstances, an object of the present disclosure is to provide a liquid ejecting apparatus and a liquid ejecting head capable of achieving efficient liquid ejecting operation while suppressing colorant precipitation and foreign matter retention in a liquid flow path.

[0029] Embodiments of the present invention are described below with reference to the accompanying drawings. The scope of the present invention should be determined based on the scope of the claims, and the following description should not be construed as limiting the scope of the present invention. Furthermore, the shapes, layouts, and other aspects described below should not be construed as limiting the scope of the present invention. In this embodiment, an inkjet printing device is used as an example of a liquid ejecting device that ejects liquid and prints on a print medium. Therefore, in the following description, the liquid ejected from the inkjet printing device is referred to as ink, and the liquid ejecting head that ejects the ink is referred to as a print head.

[0030] [First embodiment]

[0031] (Overall Configuration of Printing Device)

[0032] Figure 1 This is a schematic diagram illustrating the general configuration of an inkjet printing device 1000 (hereinafter referred to as the printing device) according to an embodiment of the present invention. A printhead 1 is mounted on a carriage 1005 movably supported by a slide shaft 1004. The carriage 1005 reciprocates along the slide shaft 1004 above a platen 1008 driven by a carriage motor (not shown). A print medium 1007 is transported to the upper surface of the platen 1008 by a transport roller (not shown). The printhead 1 ejects ink while reciprocating above the print medium 1007 supported on the upper surface of the platen 1008. As the printhead 1 reciprocates, the print medium 1007 is intermittently transported by the transport roller. The printhead 1 is electrically connected to a control unit (not shown), which transmits power, ejection control signals, and other signals to the printhead 1. The printing device 1000 ejects ink onto the print medium 1007 under the control of the control unit in response to the operation of transporting the print medium 1007. This operation of the printhead 1 allows an image to be printed on the print medium 1007. The control unit in this embodiment includes a computer having a CPU, ROM, RAM, etc. According to the control program stored in the ROM, the CPU performs various processes such as calculations and controls while using data stored in the RAM. The RAM also serves as a work area for the CPU to perform calculations.

[0033] The printing apparatus 1000 includes a main tank 2000, a sub-tank (liquid storage unit) 2001 that stores ink supplied from the main tank 2000, and a supply pipe 1001 and a collection pipe 1002 that allow fluid communication between the print head 1 and the sub-tank 2001. Such a configuration is provided for each type of ink (each color of ink) used in the printing apparatus 1000. In this embodiment, four colors of ink, namely black (Bk), cyan (C), magenta (M), and yellow (Y), are used, and the above-mentioned configuration is provided for each ink. To simplify the drawings, Figure 1 1 and 2. The supply pipe 1001 and the collection pipe 1002 for two of the four color inks are shown. A supply pump 1003 is connected to the supply pipe 1001, and ink is supplied from the sub-tank 2001 to the print head 1 through the supply pump 1003. The portion of ink supplied to the print head 1 is controlled by a differential pressure valve 2004 (see FIG. 2 ). Figure 2 ) and the collection pipe 1002 return to the auxiliary tank 2001.

[0034] (Schematic layout of the print head)

[0035] Next, a schematic configuration of the print head 1 of the printing apparatus 1000 in this embodiment and an ink flow path (liquid flow path) formed in the print head 1 will be described. Figures 2 to 4is a schematic diagram showing an ink flow path and ink flow of one color of ink of the printing apparatus 1000 in this embodiment, wherein Figure 2 Shows the print standby state, Figure 3 shows the print operation status, and Figure 4 The state in which the printing operation is performed with a high printing load is shown. Figures 2 to 4 , only a flow path through which ink of one color flows is shown; however, circulation paths for inks of a plurality of colors are actually provided in each print head 1 and the main body portion of the printing apparatus 1000.

[0036] First, a general configuration of the print head 1 in this embodiment will be described. The print head 1 includes: a printing element substrate 10 as a liquid ejecting unit; a support member 11 that supports the printing element substrate 10; and a circulation unit 200 to which the support member 11 is fixed.

[0037] The circulation unit 200 functions as a pressure control mechanism that receives ink from a sub-tank 2001 as a liquid storage unit and supplies the ink having a pressure controlled within a predetermined pressure range to the printing element substrate 10 through the supporting member 11 and has the following configuration.

[0038] The circulation unit 200 includes a filter 201, a pressure regulator 202 serving as a pressure control unit, a head circulation pump 203, a negative pressure compensation valve 204, and a flow path that allows communication between these components. The pressure regulator 202 includes a supply chamber 2025, a negative pressure chamber 2026 capable of fluid communication with the supply chamber 2025 via an orifice 2028, and a pressure control valve 2027 that controls the flow resistance of ink through the orifice 2028. The pressure control valve 2027 is arranged to be movable back and forth relative to the orifice 2028 and is biased in the direction of closing the orifice 2028 by the biasing force of a biasing member (biasing unit) 2021 including a spring.

[0039] The supply chamber 2025 communicates with the supply pipe 1001 and the collection pipe 1002 via a flow path formed in the body 206, which forms the framework of the circulation unit 200. The negative pressure chamber 2026 communicates with the discharge port 2038 of the head circulation pump 203 via a flow path formed in the body 206, and also with a flow path 11c formed in the support member 11. The side surface of the negative pressure chamber 2026 is formed partially by a flexible membrane 2023, and a pressure plate 2022 is fixed to the inner surface of the flexible membrane 2023. One end portion of a shaft 2024, which is provided on the pressure control valve 2027, contacts the pressure plate 2022 via a biasing member 2021. The pressure plate 2022 can shift along with the flexible membrane in response to changes in pressure in the negative pressure chamber 2026. This displacement of the pressure plate 2022 is transmitted to the pressure control valve 2027 via the shaft 2024. Therefore, the position of the pressure control valve 2027 is changed by the combined force of the pressing pressure from the pressure receiving plate 2022 and the biasing force of the biasing member 2021, and thus controls the flow resistance of the ink in the orifice 2028. The filter 201 has a function of removing dust and bubbles contained in the ink supplied from the sub-tank 2001 by the supply pump 1003.

[0040] The head circulation pump 203 includes a discharge port 2038 for discharging liquid and a suction port 2039 for sucking liquid. The discharge port 2038 communicates with the pressure regulator 202, which serves as a pressure control unit, via a flow path, while the suction port 2039 communicates with the flow path 11d formed in the support member 11. The head circulation pump 203 discharges ink sucked through the suction port 2039 from the discharge port 2038, supplies the ink to the pressure regulator 202 via the flow path, and thus serves as a drive source for forming a circulating flow of ink in a first circulation path R1, which will be described later.

[0041] Negative pressure compensation valve 204 is provided in bypass passage R3, allowing communication between the discharge port 2038 and the suction port 2039 of head circulation pump 203. When a pressure differential develops between the upstream and downstream sides of negative pressure compensation valve 204, negative pressure compensation valve 204 opens, allowing communication through bypass passage R3. This negative pressure compensation valve 204 functions to suppress the increase in negative pressure generated downstream of the ejection port during continuous printing of images with a high print load. The print load in this context refers to the ratio of the amount of ink actually applied per unit area of ​​the print medium to the maximum amount of ink that can be applied per unit area. A higher print load results in a greater amount of ink applied per unit area.

[0042] In the printing element substrate 10, ejection ports 103 (through which ink is ejected) are formed, and flow paths communicating with the ejection ports 103 are also formed. Each of these flow paths is formed by a pressure chamber 106 communicating with a corresponding one of the ejection ports 103, a supply flow path 105a communicating with the pressure chamber 106, and a collection flow path 105b. Figure 8The structure of the printing element substrate 10 is described in detail.

[0043] Flow paths 11c and 11d that allow communication between the printing element substrate 10 and the circulation unit 200 are formed in the support member 11. In the flow path 11c, one end portion thereof communicates with the flow path of the circulation unit 200 via the communication port 11a, while the other end portion communicates with the supply flow path 105a via an opening 109 formed in the printing element substrate 10. On the other hand, in the flow path 11d, one end portion thereof communicates with the flow path of the circulation unit 200 via the communication port 11b, while the other end portion communicates with the collection flow path 105b via the opening 109 formed in the printing element substrate 10.

[0044] With the print head 1 having the above configuration, a first circulation path R1 circulating through the circulation unit 200 , the supporting member 11 , and the printing element substrate 10 and a second circulation path R2 circulating through the circulation unit 200 and the sub-tank 2001 are formed in the printing apparatus 1000 .

[0045] Hereinafter, the flow of ink in the first circulation passage R1 and the second circulation passage R2 will be described in detail.

[0046] (Flow of Ink in the First Circulation Path)

[0047] First, the flow of ink in the first circulation path R1 will be described. When the head circulation pump (first pump) 203 is driven, ink is supplied from the discharge port 2038 of the head circulation pump 203 to the negative pressure chamber 2026 in the pressure regulator 202. The pressure regulator 202 is a so-called pressure-reducing regulating mechanism and has the function of stabilizing the pressure within the negative pressure chamber 2026 within a certain range through the operation of the pressure control valve 2027 and the biasing member 2021, even when the flow rate changes. The details of the pressure control operation will be described later.

[0048] The ink whose pressure is adjusted to a predetermined slightly negative pressure range (preferably, -20 to -1000 mmAq) in the negative pressure chamber 2026 in the pressure regulator 202 passes through the negative pressure chamber 2026 and flows into the flow path formed in the printing element substrate 10 via the flow path 11c formed in the support member 11. As described above, the flow path includes the supply flow path 105a, the pressure chamber 106, the collection flow path 105b, etc. The ink flowing from the flow path 11c of the support member 11 into the supply flow path 105a is as follows: Figure 2 As shown by the arrow in , the ink passes through the pressure chamber 106 and the collection flow path 105b, and then returns to the head circulation pump 203 again through the flow path 11d of the support member 11. A part of the ink flowing in the pressure chamber 106 is supplied to a corresponding one of the ejection ports 103.

[0049] Thus, a first circulation flow (hereinafter also referred to as "in-head circulation flow") is generated in the print head 1, circulating between the pressure regulator 202 and the printing element substrate 10. Consequently, precipitation of the ink pigment in the first circulation path R1 is suppressed. Furthermore, since bubbles, thickened ink, foreign matter, and the like can be discharged to the outside of the printing element substrate 10, proper ejection can be performed without performing a preliminary ejection operation, and reliable printing can be achieved.

[0050] exist Figure 2 In the illustrated printhead 1, the first circulation flow formed by ink (liquid) flowing through the first circulation path R1 should pass through the pressure chamber 106 of the printing element substrate 10. In this case, the ink flow rate is set within a range that enables proper ejection operation. In a typical inkjet printhead, the flow path near the ejection ports 103 is an extremely fine micropath, measuring tens of micrometers; therefore, the pressure drop is considerable. Therefore, if the flow rate is set too high, the negative pressure in the ejection ports 103 becomes excessively high, and there is a risk that the meniscus suitable for ejection operation cannot be maintained. In particular, in a printing element substrate 10 in which the ejection ports 103 are arranged at a density of 300 dpi or higher, it is preferable to set the ink flow rate to be equal to or less than the ejection flow rate when ejecting from all ejection ports 103 simultaneously. Furthermore, it is also preferable to form a bypass flow path in the printing element substrate 10 or the support member 11, or in the boundary between the printing element substrate 10 and the support member 11, to increase the number of paths through which circulation can occur without passing through the pressure chamber 106.

[0051] As long as the flow rate and pressure required for conveying liquid can be ensured, the form of the head circulation pump 203 to be applied can be any of the positive displacement type and the negative displacement type. For example, a diaphragm pump, a tube pump, a piston pump, etc. can be applied as a positive displacement type. On the other hand, an axial flow pump can be an example of an applicable negative displacement type pump. In addition, it is preferred to select a driving method from a variety of methods such as motor drive, piezoelectric drive, and pneumatic drive. Taking into account the use of the pump (the pump is to be installed on the print head 1 and to move back and forth at high speed) and the cost of the pump, it is preferred to select a small, light, and small number of parts pump. More preferably, the pump should have a small pressure pulsation. A piezoelectric diaphragm pump can be an example of a preferred pump with the above characteristics. In addition, it is also preferred to apply such a pump: the pump is connected to the front and rear of the pump chamber by a pipeline with a flow resistance difference (the internal pressure in the pump chamber changes at high frequency due to the piezoelectric element, the foaming caused by boiling, etc.) to produce a fluid inertia effect to convey liquid. In this embodiment, the above-mentioned head circulation pump 203 and the first circulation path R1 constitute the first circulation unit.

[0052] (Flow of Ink in the Second Circulation Path)

[0053] Next, we will describe the flow of ink in the second circulation path R2 formed in the printhead 1. The ink in the replaceable main tank 2000 is supplied to the sub-tank 2001 via the replenishment pump 2003, and then to the circulation unit 200 of the printhead 1 via the supply tube 1001. The sub-tank 2001 includes an atmospheric communication port 2002, which allows air bubbles in the ink to be discharged to the outside. Furthermore, since the sub-tank 2001 can store ink, printing can continue while the main tank 2000 is being replaced mid-print, thereby improving the convenience of the printing apparatus 1000.

[0054] In the event that ink consumed by ejecting (discharging) ink from the ejection ports 103 of the print head 1 during a printing operation, suction recovery, or the like needs to be replenished, the replenishing pump 2003 transfers ink from the main tank 2000 to the sub-tank 2001. The sub-tank 2001 is connected to the print head 1 so that ink can be supplied to the print head 1 through the supply tube 1001. In addition, the sub-tank 2001 is connected to the print head 1 so that ink from the print head 1 can be collected through the collection tube 1002.

[0055] When the supply pump (second pump) 1003 is driven, the ink in the sub-tank 2001 is Figure 2 As shown by the arrow in , the ink passes through the supply pipe 1001 and the filter 201, and then flows into the supply chamber 2025 of the pressure regulator 202. The ink flowing in the supply chamber 2025 returns to the sub-tank 2001 via the collection pipe 1002. Therefore, a second circulation path R2 is formed in the printing device 1000, which forms a second circulation flow (hereinafter also referred to as "tank circulation flow") starting from the sub-tank 2001 and returning to the sub-tank 2001 again via the print head 1. Therefore, the precipitation of ink pigment in the second circulation path R2 including the sub-tank 2001, the supply chamber 2025, the supply pipe 1001 and the collection pipe 1002 is suppressed. In this embodiment, the above-mentioned supply pump 1003 and the second circulation path R2 constitute a second circulation unit.

[0056] A differential pressure valve (second pressure control unit) 2004 is provided on the collection tube 1002. The differential pressure valve 2004 opens only when a differential pressure equal to or greater than a certain pressure appears between the upstream and downstream sides of the differential pressure valve, so as to allow ink to flow through the collection tube 1002. Since the sub-tank 2001 is connected downstream of the differential pressure valve 2004, a hydraulic head pressure relative to the sub-tank 2001 is applied downstream of the differential pressure valve 2004. The upstream side of the differential pressure valve 2004 is maintained at a pressure equal to or greater than a certain pressure by the pressure regulator 202. This pressure value on the upstream side of the differential pressure valve 2004 does not necessarily have to be a positive pressure, but may also be a negative pressure, as long as the pressure is equal to or greater than the minimum pressure at which normal pressure control can be performed by the design of the pressure regulator 202. The differential pressure valve 2004 can be attached to a position on the downstream side of the collection tube 1002, that is, close to the sub-tank 2001. In order to further reduce the pressure change caused by the ink vibration caused by the sliding of the collection tube 1002, it is preferable to provide a differential pressure valve 2004 near the print head 1. In order to suppress the pressure change, it is more preferable to adopt a configuration in which the differential pressure valve 2004 is inserted into the connector pin connecting the print head 1 and the collection tube 1002.

[0057] exist Figure 2 In the illustrated state, printing is not performed, so the pressure control valve 2027 in the pressure regulator 202 is closed. Accordingly, the ink supplied to the pressure regulator 202 passes through the supply chamber 2025 at a pressure equal to or greater than a certain pressure and flows back to the sub-tank 2001 through the collection pipe 1002.

[0058] As described above, in this embodiment, in the print standby state, two circulation flows are formed with the pressure control valve 2027 in the pressure regulator 202 as a pressure boundary.

[0059] Specifically, the following two circulation flows are formed:

[0060] 1) A first circulation flow generated between the pressure regulator 202 and the printing element substrate 10; and

[0061] 2) A second circulation flow is generated between the pressure regulator 202 and the sub-tank 2001.

[0062] Therefore, even when using ink that easily settles, such as white ink, density changes caused by colorant settling can be suppressed. Accordingly, in this embodiment, the printing apparatus 1000 does not need to perform a suction recovery operation when resuming printing, thereby not causing waste ink and downtime.

[0063] Because the pressure changes caused by ink vibrations in the supply pipe 1001 and collection pipe 1002 during printing are sufficiently reduced by the action of the regulator, the pressure changes are never transmitted to the first circulation flow side. Therefore, even when the reciprocating scanning speed of the print head 1 is increased and printing is performed at high speed, the ejection performance of the print head 1 remains stable, thereby enabling the printing of high-quality images with less streaking and unevenness.

[0064] Next, the state of ink flow in the case where a printing operation is started is described. Figure 3 1 is a schematic diagram showing the flow state of one color ink in the printing apparatus 1000 of this embodiment. Once the amount of ink is reduced by ejection, the negative pressure in the negative pressure chamber 2026 increases, and the pressure receiving plate 2022 of the pressure regulator 202 is Figure 3 2022. As the pressure plate 2022 moves, the pressure control valve 2027 moves to the left away from the orifice 2028. As a result, an amount of ink corresponding to the amount of ink ejected flows from the supply chamber 2025 into the negative pressure chamber 2026 as indicated by the arrow A1, thereby replenishing the ink to the first circulation flow. During this process, the pressure in the negative pressure chamber 2026 is maintained at a predetermined slight negative pressure by the action of the biasing member 2021, and the first circulation flow is also maintained. Therefore, even when the ejection port 103 is in a non-ejecting state, no precipitation of the colorant will occur, and the ejection port 103 can be maintained in a state capable of ejecting at any time without performing a pre-ejection operation. Since the second circulation flow is also continuously maintained during this process, the precipitation of the colorant is also suppressed between the sub-tank 2001 and the print head 1. Accordingly, ink with a continuously stable density can be supplied to the print head 1.

[0065] In order to achieve high-speed printing, the print head 1 needs to perform reciprocating scanning at high speed, and thus increase the vibration of the ink in the supply pipe 1001 and / or the collection pipe 1002. However, in this embodiment, the pressure change transmitted to the pressure control valve 2027 due to the vibration of the ink is transmitted to the negative pressure chamber in an attenuated state. That is, as in Figure 3 As can be seen in the figure, the pressure change transmitted to pressure control valve 2027 is attenuated according to the ratio (S1 / S2) of the pressure receiving area (S1) of pressure control valve 2027 and the pressure receiving area (S2) of pressure receiving plate 2022. The attenuated pressure change is then transmitted to negative pressure chamber 2026. Therefore, the negative pressure change can be sufficiently reduced in the first circulation flow, thereby stabilizing the amount of ejected droplets and ejection performance. Accordingly, high-speed and high-quality printing without streaks or unevenness can be performed.

[0066] Once the printing operation stops, the pressure control valve 2027 is closed again, and the two flows of the second circulation flow and the first circulation flow are autonomously separated from each other; however, since the circulation flows continue to be maintained separately, precipitation of the colorant is suppressed.

[0067] Figure 4 105a, as well as the ink from the collection flow path 105b. Figure 4 As shown by the arrow shown in the pressure chamber 106. Even in this state, backflow does not occur because a piezoelectric diaphragm pump of a positive displacement type is used as the head circulation pump 203 in this example. Therefore, if many ejection ports 103 of the printing element substrate 10 continue to print with a high printing load, the pressure in the collection flow path 105b decreases, and eventually the replenishment of ink to the ejection ports 103 will become insufficient. In this case, there is a possibility that the amount of ejected droplets will become less than the design, and the image may fade or blur. In addition, if there are few ejection ports 103 in the non-printing state, the flow rate of the ink in those ejection ports 103 will increase significantly, and the negative pressure will increase and the temperature will drop abnormally. This will affect ink jetting and reduce image quality.

[0068] To prevent such image quality degradation during high-load printing, a negative pressure compensation valve (negative pressure compensation unit) 204 is provided in the circulation unit 200 in this embodiment. Negative pressure compensation valve 204 is designed to open when the differential pressure between its upstream and downstream sides becomes equal to or greater than a predetermined differential pressure. If the pressure in the collection flow path 105b decreases excessively due to continuous printing with a high print load, negative pressure compensation valve 204 opens to supply ink from pressure regulator 202, thereby suppressing any excessive increase in negative pressure. Consequently, stable ink ejection can be performed even during high-load printing, enabling the formation of high-quality images.

[0069] Return Reference Figure 2In the print standby state, it can be seen that no circulation flow is generated in the negative pressure compensation valve 204 and the detour passage R3. To suppress the precipitation of ink pigment in these areas, it is preferable to make the flow rate of the head circulation pump 203 in the print standby state greater than the flow rate during printing, thereby reducing the pressure in the suction port 2039 of the head circulation pump 203. This is preferable because opening the negative pressure compensation valve 204 in this manner can generate an ink flow that suppresses the precipitation of pigment in these areas. There is a possibility that this operation will cause the pressure in the pressure chamber 106 of the printing element substrate 10 to decrease, and this pressure reduction may be detrimental to the designed ejection drive; however, as long as the meniscus in the ejection port 103 is maintained, the print standby state is maintained, so there is no problem.

[0070] This embodiment includes a first circulation path R1, through which ink circulates between the printing element substrate 10 and the negative pressure chamber 2026 of the pressure regulator 202; and a second circulation path R2, through which ink circulates between the supply chamber 2025 of the pressure regulator 202 and the sub-tank 2001. With this configuration, a pressure control valve 2027, which allows for communication and blocking between the negative pressure chamber 2026 and the supply chamber 2025, opens and closes according to the ejection volume. This maintains a constant negative pressure in the negative pressure chamber 2026 even during high-speed printing, effectively suppressing pressure fluctuations caused by tube vibration during scanning by the printhead 1. Consequently, high-speed and high-quality printing is achieved. Furthermore, because the pressure control valve 2027 autonomously closes in the print standby state, the first circulation path R1 (maintaining negative pressure) and the second circulation path R2 (with pressure isolated from that of the first circulation path R1) are autonomously formed within the head, and circulation continues uninterrupted in each path. Therefore, even with ink that easily settles, such as white ink, a recovery operation by sucking a large amount of ink, which would otherwise be performed, is no longer necessary.

[0071] [Second embodiment]

[0072] The fluid passage corresponding to one color of ink in the printing apparatus 1000 in the second embodiment of the present invention is Figure 5 and Figure 6 The second embodiment differs from the first embodiment in that the second embodiment includes two switching valves (switching units) 205 in the circulation unit 200 to switch the flow direction of ink in the printing element substrate 10 .

[0073] In this embodiment, a three-way valve is used as the switching valve 205; however, the present embodiment is not limited thereto. The switching valve 205 may have a Figure 5 and Figure 6Configurations different from the one shown in the figure can be used as long as they have the function of reversing the flow in the printing element substrate 10, especially the flow in the pressure chamber 106. For example, a five-way valve using a sliding valve can be applied. In the case of using the switching valve 205, it is necessary to consider that the pressure in the print head 1 does not exceed the negative pressure range capable of maintaining the meniscus in the ejection port 103 by operating the pressure control valve 2027 during the switching of the switching valve 205. For this reason, it is preferable to design the stroke in the opening and closing operation of the pressure control valve 2027 to be very short or to use a "rocker valve" type. The specific structure of the rocker valve type will be described below.

[0074] like Figure 5 As shown, in the two switching valves 205, Figure 5 One port of the switching valve 205 on the left side is connected to the pressure regulator 202, while one port of the switching valve 205 on the right side is connected to the head circulation pump 203. The remaining two ports of the two switching valves 205 are selectively connected to the two flow paths 11c and 11d of the support member 11. Specifically, Figure 5 In the state shown, the left switching valve 205 is connected to the flow path 11c, and the communication with the flow path 11d is blocked. Figure 5 In the state shown, the switching valve on the left supplies ink flowing out of the negative pressure chamber 2026 of the pressure regulator 202 to the flow path 11c in the support member 11, while the switching valve 205 on the right collects ink from the flow path 11d in the support member 11 to the head circulation pump 203.

[0075] Figure 6 The communication state between the switching valve 205 and the flow paths 11c and 11d is shown. Figure 5 The state shown is switched. In this state, the switching valve 205 on the left is connected to the flow path 11d, and the connection with the flow path 11c is blocked. At the same time, the switching valve 205 on the right is connected to the flow path 11c, and the connection with the flow path 11d is blocked. In this case, the switching valve 205 on the left supplies the ink flowing out of the negative pressure chamber 2026 of the pressure regulator 202 to the flow path 11d in the support member 11, while the switching valve 205 on the right collects the ink from the flow path 11c in the support member 11 to the head circulation pump 203. Figure 5 and Figure 6 In FIG, a dotted-line arrow indicates a state where no ink flows through the flow path (blocked state).

[0076] Therefore, in the second embodiment, the direction of flow of ink in the pressure chamber 106 of the print head 1 can be switched to reverse. This process should achieve the following results. Generally, the width dimension of the flow path (independent communication holes 104a and 104b) directly connected to the pressure chamber 106 of the printing element substrate 10 is several tens of μm, and this width dimension is narrower than the supply flow path 105a and the collection flow path 105b. For this reason, in the case where bubbles are generated or flow into the supply flow path 105a, if the ink is only as Figure 5 If the state shown in FIG. 1 is circulated, it is difficult to discharge bubbles through the pressure chamber 106. In this case, Figure 6 As shown, by reversing the flow direction of the ink in the pressure chamber 106 , the bubbles in the supply flow path 105 a can be discharged to the outside of the printing element substrate 10 .

[0077] Because in Figure 5 and Figure 6 In both illustrated in-head circulation states, the negative pressure in the print head 1 is maintained within an appropriate range by the pressure regulator 202, allowing printing to commence while continuing in-head circulation. Therefore, in addition to the functions and effects achieved in the first embodiment, this embodiment also allows printing to continue while air bubbles and foreign matter are expelled to the exterior of the printing element substrate 10. Consequently, downtime of the printing apparatus 1000 can be further reduced.

[0078] [Modification of the Second Embodiment]

[0079] Next, refer to Figure 7 A modification of the second embodiment described above is described. In the second embodiment, as Figure 6 As shown, the supply flow path 105a and the collection flow path 105b are independently communicated with independent communication holes 104a and 104b respectively communicating with the pressure chamber 106. In contrast, this modification has a configuration in which a single flow path 105c is communicated with the independent communication holes 104a and 104b.

[0080] Therefore, in this modification, although a portion of the ink supplied from the support member 11 is supplied to the pressure chamber 106 through the independent communication holes 104a and 104b, most of the ink flowing in the flow path 105c flows again into the support member 11 through the flow path 105c without passing through the pressure chamber 106. In other words, in this modification, a first circulation path that does not pass through the pressure chamber 106 is formed.

[0081] With this configuration, since the in-head circulating flow does not pass through small portions such as the pressure chamber 106 and the independent communication holes 104a and 104b communicating with the pressure chamber 106, the flow resistance of the ink is reduced, and it is possible to more reliably avoid the precipitation of the colorant in the print head 1. In addition, bubbles and foreign matter included in the ink can be more reliably discharged to the outside of the printing element substrate 10.

[0082] Since no flow is formed through the pressure chamber 106 in the print standby state, there is a possibility that pigment precipitation occurs in the independent communication holes 104a and 104b communicating with the pressure chamber 106. However, since these portions have a small size as described above, the pigment precipitation in these portions can be removed by a small number of preliminary ejection operations.

[0083] Furthermore, in this modification, since there is no circulation flow through the pressure chamber 106, evaporation of water from the ejection ports 103 is suppressed. Consequently, even when the in-head circulation continues for a long period of time, the concentration of the entire ink is suppressed, and the number of concentrated ink discharge processes performed can be reduced, further reducing waste ink.

[0084] Hereinafter, the configuration of the constitution in the above embodiment is described in more detail. The description is based on the configuration of the above second embodiment, and the configuration including the switching valve 205 is described, while the other configurations are similar to those of the constitution in the first embodiment.

[0085] (Printing element substrate)

[0086] The configuration of the printing element substrate 10 in this embodiment will be described. Figure 8 1 is a perspective view showing a cross section taken in the longitudinal direction (Y direction) of an ejection port array 103L including a plurality of ejection ports 103 formed in the printing element substrate 10. In the printing element substrate 10, a substrate 107 made of Si and an ejection port forming member 102 formed of a photosensitive resin are laminated together. A cover member 108 is bonded to the rear surface of the substrate 107. A printing element 111 is formed on one side ( Figure 8 The upper surface side in the middle), grooves constituting the supply flow path 105a and the collection flow path 105b extending along the ejection port array are formed on the opposite side ( Figure 8 Four ejection port arrays are formed on the ejection port forming member 102 of the printing element substrate 10.

[0087] A printing element 111, a heating element for bubbling liquid using thermal energy, is arranged at a position corresponding to each ejection port 103. The printing element 111 is electrically connected to the terminal 110 via an electrical wiring (not shown) provided inside the substrate 107. The printing element 111 generates heat based on a pulse signal input from the control unit of the printing apparatus 1000 via the electrical wiring substrate and the flexible wiring substrate, and causes the liquid filled in the pressure chamber 106 to boil. The liquid is ejected from the ejection port 103 by the bubbling force generated by the boiling.

[0088] The supply flow path 105a and the collection flow path 105b are flow paths extending in the column direction of the ejection ports 103 provided on the printing element substrate 10 and are connected to the pressure chamber 106 through the independent communication hole 104a and the independent communication hole 104b, respectively. A plurality of openings 109 are provided in the cover member 108. In this embodiment, three openings 109 for one supply flow path 105a and two openings 109 for one collection flow path 105b are provided in the cover member 108 at predetermined intervals. Each opening 109 is connected to the flow path in the support member 11, as shown in FIG. Figure 5 As shown. The cover member 108 has a function as a cover of a part of the wall forming the supply flow path 105a and the collection flow path 105b. It is preferable that the cover member 108 has sufficient corrosion resistance to the liquid (ink). In terms of suppressing color mixing, the opening shape and opening position of the opening 109 are required to be accurate. The cover member 108 is used to transform the spacing of the flow path from the printing element substrate 10 to the flow path of the support member 11 through the opening 109, and considering the pressure loss, it is ideal that the thickness of the cover member 108 is thin. Therefore, it is preferable to use a photosensitive resin material or a silicon wafer as the material of the cover member 108, and provide the opening 109 by a photolithography process.

[0089] Next, the flow of liquid in the printing element substrate 10 is described. The supply flow path 105a and the collection flow path 105b formed by the substrate 107 and the cover member 108 are connected to the flow path of the support member 11, respectively. Figure 5 In the case of the drive head circulation pump 203, the liquid in the supply flow path 105a flows into the collection flow path 105b (by the independent communication hole 104a, the pressure chamber 106 and the independent communication hole 104b) Figure 8 By this flow, ink precipitation in the printing element substrate 10 can be suppressed in the pressure chamber 106 where the ejection operation is suspended. At the same time, thickened ink, bubbles, foreign matter, etc. generated by evaporation from the ejection port 103 can be discharged to the collection flow path 105b.

[0090] The ink collected in the collection flow path 105b passes through the opening 109 of the cover member 108 and the flow paths 11c and 11d of the support member 11 (see FIG. Figure 5 and Figure 6 ) returns to the head circulation pump 203. In this process, when the switching valve 205 is Figure 6 When the flow direction in the printing element substrate 10 is switched, the flow direction in the printing element substrate 10 is along the same direction as the Figure 8 Even when a circulation flow in the direction of arrow C is generated, bubbles, foreign matter, etc. larger than the independent communication hole 104a are retained in the supply flow path 105a. Figure 6 In the case where a circulation flow in the reverse direction is generated as shown, relatively large bubbles and foreign matter remaining in the supply flow path 105 a can be discharged to the outside of the printing element substrate 10 through the opening 109 .

[0091] (Cyclic Unit)

[0092] Figure 9A and 9B This is a perspective view showing the appearance of a specific configuration example of a circulation unit 200 for one color. The circulation unit 200 includes a pressure regulator 202 and a switching valve 205 installed in a body 206, in which an ink flow path is provided, and a head circulation pump 203 attached to the body 206. In this embodiment, the pressure regulator 202 and switching valve 205 are integrated with the body 206 to reduce costs. Similar to the head circulation pump 203, the pressure regulator 202 and switching valve 205 can also be attached to the body 206 as separate units. In this case, the advantage is that each unit can be used universally regardless of the shape of the body 206.

[0093] like Figure 9B As shown, a coupling hole 206a through which ink is received from the sub-tank 2001 and a coupling hole 206b through which ink returns to the sub-tank 2001 are provided on the upper portion of the body 206. A hole 206c through which ink is supplied to the printing element substrate 10 via the support member 11 and a hole 206d through which ink is collected from the printing element substrate 10 are provided on the lower portion of the body 206.

[0094] Figure 10A and 10B is an exploded view of the circulation unit 200. Figure 10A In the embodiment, a filter chamber 2060 is provided in the upper portion of the body 206, and the filter 201 is inserted and welded to the filter chamber 2060. The negative pressure compensation valve 204 is inserted next to the filter chamber 2060. The lower portion of the negative pressure compensation valve 204 communicates with the pump supply port 2061 inside the body 206. The flow path structure inside the body 206 is described below.

[0095] The pressure control valve 2027, the biasing member 2021, and the spring retainer 2029 are inserted in this stacked order into the supply chamber 2025 provided on the side surface of the body 206. The biasing member 2021 is compressed to a designed length between the pressure control valve 2027 and the spring retainer 2029 to apply a certain biasing force to the pressure control valve 2027. The spring retainer 2029 has a function as a cover for the supply chamber 2025 and a function as a fixing member to fix the biasing member 2021, and is welded or joined to the body 206.

[0096] Two switching chambers 2053 are provided in the lower portion of the side surface of the body 206, and the rocker valves 2051 are respectively inserted into the switching chambers 2053. The switching valve 205 is formed when the flexible film 2052 is bonded to the body 206 and the two rocker valves 2051 by a method such as bonding or welding so as to cover the entire switching chambers 2053. The structure and switching operation of the switching valve 205 will be described later.

[0097] exist Figure 10B , a negative pressure chamber 2026 is formed on the opposite surface side of the supply chamber 2025 in the body 206. The biasing member 2021, the pressure plate 2022 and the flexible membrane 2023 are inserted into the negative pressure chamber 2026 in this stacked order. The biasing member 2021 is compressed to a designed length between the bottom of the negative pressure chamber 2026 and the pressure plate 2022 to apply a certain load to the pressure plate 2022. The flexible membrane 2023 is welded or bonded to the body 206. The flexible membrane serves as a cover for the negative pressure chamber 2026 while deforming without hindering the movement of the pressure plate 2022. In addition, in terms of production aspects such as molding, a flow path in the form of a groove is formed in the body 206, and therefore the sealing film 208 is adhered or welded to the body 206 in the step of assembling the circulation unit 200 to cover the opening portion of the flow path.

[0098] (Switching valve)

[0099] Figure 11A and 11B is schematically shown along Figure 9AXI-XI in the figure is a cross-sectional view of the switching valve 205. The rocker valve 2051 is inserted into the switching chamber 2053 provided in the housing 2036 while being capable of pivoting around the rotation axis 2054. The flexible membrane 2052 is welded to the rocker valve 2051. The end portion of the flexible membrane 2052 is welded to the peripheral portion of the switching chamber 2053 to seal the switching chamber 2053. In addition, a cover 2059 is attached to the housing 2036 so as to cover the flexible membrane 2052. A biasing member 2057 that biases a portion close to one end portion of the rocker valve 2051 is attached to the inner surface (surface facing the membrane) of the cover 2059. In addition, a pressing member 2058 that is configured to be able to press or move away from a portion close to the other end portion of the rocker valve 2051 is attached to the inner surface of the cover 2059 and the flexible membrane 2052 is arranged therebetween. In Figure 10A , the biasing member 2057, the pressing member 2058, and the cover 2059 are not shown.

[0100] In this embodiment, a three-way valve of a so-called rocker valve type is used as the switching valve 205. Figure 11A and 11B As shown, a rotational force about the rotation axis 2054 is generated in the rocker valve 2051 according to the biasing force of the biasing member 2057. Therefore, the rocker valve 2051 closes the opening and closing port 2056L and opens the other opening and closing port 2056R. In this case, if the pressing member 2058 is pressed downward by the pressurized air to exceed the biasing force of the biasing member 2057, as shown in FIG. Figure 11B As shown, the rocker valve 2051 closes the opening and closing port 2056R and opens the other opening and closing port 2056L. Therefore, the communication relationship between the common port 2055 set at the center of the switching chamber 2053 and the opening and closing port 2056L or 2056R can be switched according to the position of the rocker valve 2051.

[0101] In this embodiment, pneumatic drive is applied as a driving method of the rocker valve 2051; however, the driving method is not limited thereto, and another driving method may be applied. For example, a mechanical mechanism using a magnetic coil and a motor may also be preferably adopted.

[0102] In addition to the rocker valve 2051, a three-way valve can also be formed by using multiple direct-acting pressure control valves 2027. In this case, the ink is pressed out and sucked in as the pressure control valve 2027 is opened and closed; therefore, pressure changes are caused in the flow path within the head, and this can affect the meniscus of the ejection port 103. If the state of the meniscus changes, the volume of the ejected droplets changes. Therefore, if the amount of change is large, there is a risk that the concentration difference on the printed image will lead to a decrease in image quality. In order to suppress this risk, it can be considered to significantly reduce the stroke of the valve or to provide a large buffer chamber. However, in this case, a possible disadvantage is that a strong circulation pump is required (because the flow resistance in the valve unit increases) or the size of the circulation unit 200 is increased.

[0103] On the other hand, in the case of using the rocker valve 2051 as in this embodiment, the ink is pushed out and sucked simultaneously during the switching operation; therefore, the change in negative pressure is small, and the influence on the meniscus in the ejection port 103 can be suppressed. It should be noted that even in the case of applying the rocker valve 2051, there may be a case where the pressure change during opening and closing cannot be sufficiently suppressed in a single switching chamber because the rotation axis 2054 of the rocker valve 2051 is not necessarily arranged center-symmetrically due to design limitations of the spring for opening and closing the valve, etc. However, in this embodiment, as Figure 5 As shown, the switching valves 205 are arranged on the upstream and downstream sides of the ejection port 103, respectively. Therefore, the volume change during switching between the two switching chambers 2053 can be compensated by using the switching valves 205 having the same shape and arranged so that the valve elements move in opposite phases. Therefore, the negative pressure change in the in-head circulation flow path (first circulation flow path) during the switching operation can be sufficiently reduced.

[0104] (Head circulation pump)

[0105] Figure 12A is a diagram showing the appearance of the head circulation pump 203. In this embodiment, a piezoelectric diaphragm pump is used as the head circulation pump 203. Generally speaking, compared with motor-type diaphragm pumps, piezoelectric diaphragm pumps have the characteristics of having fewer parts, being smaller and lighter, being quieter, and having less pressure pulsation. Therefore, it can be said that piezoelectric diaphragm pumps are suitable for installation in the print head 1. However, there are problems with piezoelectric diaphragm pumps. Because the displacement of the diaphragm 2031 is small, it is difficult to make the pump self-sufficient, and if a large number of bubbles are mixed in the pump, the liquid delivery volume will be reduced.

[0106] In summary, in the circulation unit 200, the head internal circulation flow F turns downward (Z2 direction) along the vertical direction (Z direction) before entering the pump collection port 2062, as shown in FIG. Figure 16AWith this configuration, the bubbles exhausted from the printing element substrate 10 are guided to gather in the upper portion of the circulation unit 200 to prevent them from flowing into the head circulation pump 203 .

[0107] like Figure 12A As shown, the discharge port 2038 and the suction port 2039 are provided on one surface of the head circulation pump 203. The discharge port 2038 and the suction port 2039 are respectively connected to the pump supply port 2061 and the pump collection port 2062 formed in the body 206 of the circulation unit 200. In this case, the discharge port 2038 is arranged above the suction port 2039 (Z1 direction) along the vertical direction (Z direction). This configuration is preferred because it facilitates the discharge of bubbles mixed in the head circulation pump 203 and can ensure a stable flow rate.

[0108] Another measure to suppress the entry of bubbles into the head circulation pump 203 may be to provide a filter 201 or a net as a bubble trapping material in the pump collection port 2062 or in front of or behind the pump collection port 2062. In this case, it is necessary to appropriately set the mesh size and area of ​​the filter 201 so as to prevent an excessive pressure drop in the filter 201 and to capture bubbles of a size that affects pump operation.

[0109] Figure 12B It is along Figure 12A A cross-sectional view taken along line XIIB-XIIB in FIG. Figure 12B , the hollow arrows indicate the direction of ink flow. Two check valves 2035, a pump drive circuit 2040, and a diaphragm 2031 are attached to a housing 2036. An electrode plate 2032 and a piezoelectric element 2033 are connected to the diaphragm 2031.

[0110] The pump drive circuit 2040 is electrically connected to the main control unit (not shown). The pump drive circuit 2040 includes a built-in boost circuit that generates the voltage required to drive the piezoelectric element 2033. The pump drive circuit 2040 is electrically connected to the piezoelectric element 2033 and the electrode plate 2032 via a TAB 2041 and should be able to generate a potential difference between the piezoelectric element 2033 and the electrode plate 2032 at a certain frequency based on a signal from the control unit. This potential difference causes the piezoelectric element 2033 to Figure 12B The displacement in the vertical direction (X direction) of the electrode plate 2032 and the diaphragm 2031 connected to the electrode plate 2032 are displaced accordingly. Figure 12B In the case of the downward displacement (in the X2 direction), the check valve 2035 on the right side opens and sucks ink. In this process, the check valve 2035 on the left side closes. On the other hand, when the diaphragm 2031 is in the Figure 12BWhen the ink is displaced upward (in the X1 direction), the check valve 2035 on the left side opens and discharges ink. During this process, the check valve 2035 on the right side closes.

[0111] Generally speaking, the displacement of the piezoelectric element 2033 is very small, approximately tens of μm; however, by performing this operation at a frequency of tens to hundreds of Hz, a flow rate of approximately several to several tens of mL / min can be generated. Furthermore, a pump injection pressure or suction pressure of approximately several to several tens of kPa can be generated. The flow rate and pressure can be adjusted based on the dimensions of the piezoelectric element 2033 and pump chamber 2034, the thickness of the piezoelectric element 2033, the electrode plate 2032, and the diaphragm 2031, the voltage / frequency supplied to the piezoelectric element 2033, the drive waveform (sinusoidal or square wave), and the like.

[0112] For example, by applying a high voltage of several hundred V within a range equal to or less than the breakdown voltage between the piezoelectric element 2033 and the electrode plate 2032, the displacement of the piezoelectric element 2033 can be increased, and the flow rate and pressure of the pump can be increased. Therefore, from the perspectives of measures against high voltage and suppression of ink adhesion, it is possible to Figure 12B In the illustrated structure, the cover 2037 is bonded to a position covering the piezoelectric element 2033. It is more preferable to provide the cover 2037 to a position covering the pump drive circuit 2040.

[0113] Figure 13A and 13B 2 is an exploded perspective view of the head circulation pump 203. As described above, a pair of check valves 2035 are attached to the housing 2036, with the housing 2036 positioned therebetween. In this embodiment, the check valves 2035 are secured by inserting their legs into holes in the housing 2036. The diaphragm 2031, electrode plate 2032, and piezoelectric element 2033 are attached to the pump chamber 2034 of the housing 2036 in this stacked order. It is preferred that the diaphragm 2031 have chemical resistance to ink and sufficient rigidity to follow the deformation of the piezoelectric element 2033. Therefore, a resin such as PPS or PPE formed with a thickness of approximately 0.2 to 0.5 mm can be used as the diaphragm 2031. Furthermore, the pump drive circuit 2040, the TAB 2041 electrically connecting the piezoelectric element 2033 and electrode plate 2032 to the pump drive circuit 2040, and the cover 2037 are attached to the housing 2036. Wire leads, solder, etc. can replace TAB 2041.

[0114] (Pressure Regulator)

[0115] Details of the structure and pressure control operation of the pressure regulator 202 provided in the circulation unit 200 will be described. Figure 14 It is along Figure 9BA cross-sectional view taken along line XIV-XIV in . A general pressure reducing regulator is used as the pressure regulator 202 provided in this embodiment. The pressure regulator 202 includes a negative pressure chamber 2026 sealed by a flexible membrane (flexible member) 2023. The negative pressure chamber 2026 is formed between the flexible membrane 2023 including a peripheral portion joined to the surface of the body 206 and a wall portion 2063 of the body 206 covered by the flexible membrane 2023. The pressure plate 2022 is fixed to the inner surface of the flexible membrane 2023. The orifice 2028 is formed in the central portion of the wall portion 2063 covered by the flexible membrane 2023 so as to penetrate the wall portion 2063. In the body 206, the supply chamber 2025 is formed at a position on the side of the wall portion 2063 opposite to the pressure plate 2022.

[0116] The pressure plate 2022 is biased by the biasing member (spring) 2021 in the negative pressure chamber 2026. Figure 14 The pressure control valve 2027 is biased in the direction of right movement of the head (i.e., the direction in which the volume of the negative pressure chamber 2026 increases). A pressure control valve 2027 capable of closing the orifice 2028 is provided in the supply chamber 2025. The shaft 2024 is fixed to the pressure control valve 2027, and one end of the shaft 2024 is capable of contacting the pressure plate 2022. These pressure control valve 2027, the shaft 2024 and the pressure plate 2022 are configured to move integrally during head driving. The pressure control valve 2027 is biased in the direction of right movement of the head (i.e., the direction in which the volume of the negative pressure chamber 2026 increases). Figure 14 The pressure control valve 2027 is biased in the direction of rightward movement (i.e., the direction in which the pressure control valve 2027 closes the orifice 2028).

[0117] The pressure control valve 2027 operates to change the flow resistance by changing the gap between the pressure control valve 2027 and the orifice 2028. To stop the circulation of ink, the pressure control valve 2027 contacts the orifice 2028 to close the gap and fluidically seal the orifice 2028. It is preferable to use an elastic material such as rubber or elastomer that has sufficient corrosion resistance to ink as the material of the pressure control valve 2027.

[0118] exist Figure 14 2028, the pressure control valve 2027 is provided on the right side of the orifice 2028 so that the gap between the orifice 2028 and the pressure control valve 2027 is reduced when the pressure receiving plate 2022 moves to the left. The pressure of the ink flowing from the filter 201 into the supply chamber 2025 during the printing operation is reduced due to the pressure drop in the gap portion between the pressure control valve 2027 and the orifice 2028 as the ink passes through the gap, and then the ink flows into the negative pressure chamber 2026. Thereafter, the ink is switched to the negative pressure chamber 2026 by the switching valve 205 (see FIG. Figure 5 ) Ink is supplied from the negative pressure chamber 2026 to the printing element substrate 10.

[0119] The pressure P2 in the negative pressure chamber 2026 is determined based on the following relationship, which represents the balance of forces applied to the structure:

[0120] P2=P0-(P1Sv+k1x) / Sd …… (Expression 1), where

[0121] Sd is the pressure receiving area of ​​the pressure receiving plate, Sv is the pressure receiving area of ​​the pressure control valve, P0 is atmospheric pressure, P1 is the pressure in the supply chamber [Pa], P2 is the pressure in the negative pressure chamber, k1 is the composite spring constant of the biasing member, and x is the spring displacement.

[0122] The second term on the right side of Expression 1 is always a positive value, and thus it can be concluded that pressure P2<pressure P0, and pressure P2 is a negative pressure.

[0123] The pressure P2 can be set to a desired control pressure by varying the force of the biasing member 2021. To vary the force of the biasing member 2021, the spring constant K or the free length of the spring can be varied.

[0124] Assuming that the flow resistance in the gap portion between the pressure control valve 2027 and the orifice 2028 is R, and the flow rate through the orifice 2028 is Q, the following expression can be obtained:

[0125] P2=P1-QR...(Expression 2)

[0126] In this case, the flow resistance R and the gap between the valve and the orifice 2028 (hereinafter referred to as "valve opening") are designed to have, for example Figure 17 That is, as the valve opening increases, the flow resistance R decreases. The pressure P2 is determined by the valve opening determined to satisfy (Expression 1) and (Expression 2) at the same time.

[0127] If the ejection flow rate changes during printing operation and the flow rate Q increases instantaneously, the ink flow rate based on this change is supplied from the supply chamber 2025 to the negative pressure chamber 2026. Therefore, the flow resistance in the collection pipe 1002 decreases, and accordingly, the load on the supply pump 1003 decreases. As a result, the pressure P1 in the supply chamber 2025 decreases, and thus the force P1Sv attempting to close the pressure control valve 2027 decreases, while the pressure P2 increases instantaneously according to (Expression 1).

[0128] In addition, according to (Expression 2), R = (P1-P2) / Q. In this case, the flow rate Q and pressure P2 increase, and the pressure P1 decreases; therefore, the flow resistance R decreases. Once R decreases, the valve opening is adjusted according to Figure 17 As shown in Figure 14As can be seen in , since the length of the biasing member (spring) 2021 decreases when the valve opening increases, the displacement x from the free length increases. Therefore, the force k1x of the spring increases. Therefore, the pressure P2 decreases instantaneously according to (Expression 1). On the other hand, if the flow rate Q decreases and the pressure P1 increases instantaneously, P2 decreases instantaneously through the opposite action to the above. By instantaneously repeating these operations, the valve opening changes according to the flow rate Q, and at this time (Expression 1) and (Expression 2) should be satisfied at the same time, so that the pressure P2 in the negative pressure chamber 2026 is autonomously controlled to be constant.

[0129] In the case where the pressure P1 decreases, R decreases to make the pressure P2 constant, as can be seen in (Expression 2). That is, the valve opening increases. However, as in Figure 17 As can be seen in Figure 2, even when the valve opening is increased, a flow resistance R equal to or lower than a certain value (≈ the flow resistance of the orifice 2028) cannot be achieved. Therefore, in order to allow the pressure regulator 202 to stably control the pressure P2 to be constant, a value P1 equal to or greater than a certain value needs to be continuously applied to the supply chamber 2025. Therefore, the capacity of the supply pump 1003, the pressure drop in the supply pipe 1001 and the filter 201, the valve opening pressure of the differential pressure valve 2004, etc. need to be designed based on the maximum ejection flow rate of the print head 1 and the minimum operating pressure of the pressure regulator 202.

[0130] In this embodiment, two coupling springs are used as the springs of the biasing member 2021. By adopting a configuration of two coupling springs similar to this embodiment, the following preferred side effects can be obtained.

[0131] That is, the pressure-receiving plate 2022 and the shaft 2024 are configured to be separated from each other within the negative-pressure chamber 2026. Furthermore, even when the pressure-receiving plate 2022 and the shaft 2024 are separated from each other, this configuration allows a biasing force to be applied to the pressure-receiving plate 2022 in a direction that increases the internal volume of the negative-pressure chamber 2026 by the spring within the negative-pressure chamber 2026. Therefore, even if bubbles in the flow path of the print head 1 expand due to changes in the ambient temperature, the increased internal volume of the negative-pressure chamber 2026 can be absorbed by the increase in the internal volume of the negative-pressure chamber 2026, thereby generating a predetermined negative pressure within the negative-pressure chamber 2026. Consequently, ink leakage from the ejection ports 103 can be suppressed.

[0132] However, as long as the spring has an elastic force that can satisfy the required negative pressure value, there will be no difficulty in the pressure regulation function. Therefore, a configuration using only one spring or three or more springs can be applied.

[0133] (Negative pressure compensation valve)

[0134] The negative pressure compensation valve 204 has a function of suppressing the increase in negative pressure generated in the supply flow path 105a or the collection flow path 105b on the downstream side of the ejection port 103 of the printing element substrate 10 to be equal to or lower than a certain value in the case of continuous printing of an image with a high print load, thereby maintaining image quality. Figure 16A A conventional differential pressure valve is shown as the negative pressure compensation valve 204. The negative pressure compensation valve 204 includes a pressure control valve 2041, an orifice 2042, and a biasing member (spring) 2043 that biases the pressure control valve 2041 so as to contact the orifice 2042. The pressure control valve 2041 should open when the differential pressure between the upstream and downstream sides of the negative pressure compensation valve 204 is equal to or greater than a certain value and the pressure in the opening direction of the pressure control valve 2041 becomes greater than the biasing force of the biasing member 2043. Figure 16A shows the state where the pressure control valve 2041 is closed, and Figure 16B The pressure control valve 2041 is shown in an open state. The valve opening pressure of the pressure control valve 2041 can be set to a desired value according to the biasing force of the spring and the pressure receiving area of ​​the pressure control valve 2041.

[0135] It should be noted that since the flow resistance of a differential pressure valve generally changes as the flow rate through it increases, it is not suitable for consistently maintaining the pressure downstream of the differential pressure valve within a certain range. When the maximum ejection flow rate of the printhead 1 is relatively low, the differential pressure valve 2004, with its simple and compact structure, is suitable as the negative pressure compensation valve 204. However, for printheads 1 with relatively high maximum ejection flow rates, it is advantageous to use a differential pressure valve having the same structure as the pressure regulator 202 as the negative pressure compensation valve 204. In this case, there is a risk of increasing the size of the circulation unit 200.

[0136] (Flow of Ink in Circulation Unit)

[0137] exist Figures 14 to 16A In FIG. 16 and FIG. 16B , the tank circulation flow (second circulation flow) E and the head circulation flow (first circulation flow) F generated in the circulation unit 200 of this embodiment are indicated by arrows. Figure 14 It is along Figure 9B A cross-sectional view taken along line XIV-XIV in FIG. Figure 15 It is along Figure 14 A cross-sectional view taken along line XV-XV in FIG. Figure 16A and 16B It is along Figure 14 For simplicity of description, the communication state between the communication port and the switching chamber 2053 is shown in FIG. Figure 16A and 16BIn other words, the white circle represents the state where the communication port is opened by the rocker valve 2051, and the black circle represents the state where the communication port is closed by the rocker valve 2051.

[0138] exist Figure 14 and Figure 15 , the tank circulation flow (first circulation flow) indicated by arrow E passes through the filter 201, flows into the supply chamber 2025, passes around the pressure control valve 2027 and the biasing member 2021, and then flows back from the circulation unit 200 to the sub-tank 2001. Therefore, even in the print standby state, the flow of ink suppresses the sedimentation of colorant between the sub-tank 2001 and the supply chamber 2025 and between the supply chamber 2025 and the sub-tank 2001.

[0139] Pressure changes associated with ink vibrations in the supply tube 1001 and / or collection tube 1002 that occur during high-speed printing are attenuated according to the ratio (S1 / S2) of the pressure receiving area (S1) of the pressure control valve 2027 to the pressure receiving area (S2) of the pressure receiving plate 2022, as described above. Figure 14 In the illustrated configuration, this ratio is 3% or less, and negative pressure changes occurring in the tank circulation flow are sufficiently attenuated in the head circulation flow. Therefore, the printing apparatus 1000 of this embodiment enables high-speed printing with high image quality and no streaking or unevenness.

[0140] Depend on Figure 16A and 16B The head internal circulation flow indicated by the arrow F in FIG. 2 flows from the pump supply port 2061 through the flow path in the body 206 by driving the head circulation pump 203 to flow into the negative pressure chamber 2026. Then, after flowing between the pressure plate 2022 and the orifice 2028, the head internal circulation flow flows to the outside of the circulation unit 200 through the switching valve 205. Thereafter, as shown in FIG. Figure 5 As shown, the head internal circulation flow passes through the support member 11 and the printing element substrate 10 and flows back to the circulation unit 200 again. Then, the head internal circulation flow passes through the switching valve 205 again and returns to the pump collection port 2062.

[0141] exist Figure 16A In the embodiment, this configuration allows the in-head circulating flow to flow from the upper side (Z1) to the lower side (Z2) along the vertical direction (Z direction) of the negative pressure chamber 2026, which is an example for achieving size reduction of the circulation unit 200. Since the precipitated colorant accumulates on the vertical lower side, in order to shorten the time required to resolve the precipitation problem, it is preferable to adopt a configuration in which the in-head circulating flow flows from the lower side to the upper side along the vertical direction of the negative pressure chamber 2026.

[0142] Figure 16B The operating state of the rocker valve 2051 is shown, and the communication state between the communication port and the switching chamber 2053 is shown. Figure 16A By switching the communication state of the communication port as described above, a flow in the opposite direction can be generated in the printing element substrate 10 (eg Figure 6 As shown), while maintaining the circulating flow F in the head.

[0143] exist Figure 16A In the illustrated state, negative pressure compensation valve 204 is closed, and no ink flows in the area indicated by dashed arrow F'. Therefore, there is a risk of pigment precipitation in this area. If pigment precipitation in this area affects image quality, the pressure in pump collection port 2062 is reduced by increasing the flow rate of head circulation pump 203. Therefore, negative pressure compensation valve 204 is opened, forming a branch flow F' that branches off from the internal head circulation flow F, thereby suppressing pigment precipitation.

[0144] exist Figure 16A In the print standby state, the pressure control valve 2027 is in contact with the orifice 2028, and the tank circulation flow E and the in-head circulation flow F are independent circulation flows. In this case, the in-head circulation flow F flows under a negative pressure state, which begins with the slight negative pressure generated in the negative pressure chamber 2026. The tank circulation flow E flows into the supply chamber 2025 at a higher pressure than the pressure of the in-head circulation flow. It is preferable to set the flow rate of the tank circulation flow E to be greater than the maximum ejection flow rate of the in-head circulation flow F and the print head 1 so that the flow from the circulation unit 200 to the sub-tank 2001 does not stop.

[0145] Once printing starts, the volume of ink in the area of ​​the in-head circulation flow decreases, the pressure control valve 2027 opens, and a branch flow is generated from the tank circulation flow E to the in-head circulation flow F. In this case, although there is a pressure difference between the tank circulation flow and the in-head circulation flow, due to the difference in pressure drop caused by the gap between the orifice 2028 and the pressure control valve 2027, a negative pressure suitable for ejection in the in-head circulation flow is stably maintained.

[0146] As described above, the printing apparatus 1000 of this embodiment can print at high speed with high image quality, and even for inks that easily precipitate, such as white ink, the precipitation suppression effect of the cycle can significantly reduce the need for recovery operations. Consequently, the amount of waste ink and downtime caused by recovery operations can be reduced.

[0147] (Comparative Example)

[0148] Figure 18Schematic diagram illustrating the print head and ink path of an inkjet printing device 1000a in a comparative example to this embodiment. This comparative example differs from the first embodiment described above in that a circulation flow path is formed, in which ink is driven by the supply pump 1003 through the interior of the printing element substrate 10 and circulated between the sub-tank 2001 and the print head 1. Specifically, in the comparative example, a circulation flow path is formed, in which ink supplied from the sub-tank 2001 via the supply tube 1001 to the pressure regulator 202 passes through the printing element substrate 10 and then returns to the sub-tank 2001 via the collection tube 1002. Thus, the comparative example has a configuration in which a circulation flow is formed through the sub-tank and the print head, thereby suppressing colorant precipitation in the flow path.

[0149] However, in the comparative example, ink circulation is performed within a single circulation flow path. Therefore, if the ink in the supply tube 1001 and the collection tube 1002 vibrates due to the reciprocating scanning of the print head during printing operation, a new problem arises: the ink pressure changes caused by the vibration are transmitted to the interior of the printing element substrate 10. That is, in the configuration of the comparative example, the pressure changes from the supply tube 1001 are reduced by the pressure regulator 202, but the pressure changes from the collection tube 1002 side are transmitted to the pressure chamber 106 without being reduced. This can cause the ejection volume and ejection characteristics of the print head to become unstable, resulting in streaks and unevenness in the printed image, and thus reducing image quality. This problem becomes more prominent as the print head scanning speed increases. Therefore, in the comparative example, although the precipitation of colorant can be suppressed, a new problem of reduced image quality and productivity arises.

[0150] On the other hand, according to the printing apparatus of this embodiment, it is possible to suppress the precipitation of the toner in the flow path without degrading the image quality and productivity.

[0151] (Other embodiments)

[0152] In the above embodiments, a serial printing device that allows a print head to scan back and forth while performing printing is described as an example; however, the present invention is not limited to this. The present invention is also effective for a so-called full-line printing device (which includes a long print head in which a plurality of printing elements are arranged within a range corresponding to the page width). In a full-line printing device, the print head does not move during the printing operation; therefore, negative pressure changes are not generated due to the vibration of the tube connecting the liquid storage unit and the print head as in a serial printing device. However, since the circulation flow rate required to suppress the precipitation of the colorant increases according to the size of the print head, the pulsation of the circulation pump may increase and the image quality may deteriorate. The configuration of the present invention forms two circulation flows with pressures separated from each other through a pressure control unit; therefore, if the present invention is applied to a full-line printing device, the pulsation of the circulation pump can be suppressed from being transmitted to the print head. Therefore, high-speed printing with high image quality can be achieved while suppressing the precipitation of the pigment.

[0153] In the above embodiment, a liquid ejecting head that ejects liquid by the heat energy generated by a heating element and a liquid ejecting device using the liquid ejecting head are described. However, the present invention is also applicable to a liquid ejecting head that ejects liquid by an electromechanical transducer element (piezoelectric element) and a liquid ejecting device using the liquid ejecting head.

[0154] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A liquid ejection device, comprising: a liquid storage unit capable of storing liquid; a liquid ejecting head configured to perform a reciprocating motion along a predetermined direction; as well as a tube that allows fluid communication between the liquid ejection head and the liquid storage unit, The liquid ejecting head comprises: a liquid ejecting unit, the liquid ejecting unit comprising an ejection port capable of ejecting liquid; a pressure control unit configured to receive the liquid from the liquid storage unit and allow the liquid having a pressure controlled within a predetermined pressure range to be supplied to the liquid ejecting unit; a liquid flow for circulating liquid between the liquid ejecting unit and the pressure control unit; The pressure control unit comprises: a supply chamber, the supply chamber receiving the liquid from the liquid storage unit; a negative pressure chamber configured to communicate with the liquid ejecting unit; and A pressure control valve is configured to control the communication state between the supply chamber and the negative pressure chamber according to the pressure difference between the supply chamber and the negative pressure chamber, wherein when the pressure control valve is closed, the circulation flow between the liquid injection unit and the negative pressure chamber is separated from the flow between the liquid storage unit and the supply chamber. 2 . The liquid ejecting device according to claim 1 , wherein the liquid flow does not pass through the liquid storage unit.

3. The liquid ejecting device according to claim 1, wherein The liquid flow is configured to circulate liquid between the liquid ejecting unit and the pressure control unit in a state in which the pressure control valve closes the communication between the supply chamber and the negative pressure chamber.

4. The liquid ejecting device according to claim 1, wherein The pressure control valve is arranged to be movable forward and backward relative to an orifice that allows communication between the supply chamber and the negative pressure chamber, and a gap between the orifice and the pressure control valve is changed according to a pressure difference between the supply chamber and the negative pressure chamber.

5. The liquid ejecting device according to claim 4, wherein The negative pressure chamber includes a pressure receiving plate that can be displaced according to the pressure inside the negative pressure chamber, and The pressure receiving plate applies a pressing pressure to the pressure control valve to press the pressure control valve in a direction to separate the pressure control valve from the orifice. The liquid ejecting device according to claim 5 , wherein The pressure control valve is biased in a direction to close the orifice by a biasing force of a biasing unit, and changes the gap by a combined force of the biasing force and a pressing pressure of the pressure receiving plate.

7. The liquid ejecting device according to claim 5, wherein A portion of the negative pressure chamber is formed by a flexible member that is displaced according to the pressure in the negative pressure chamber, and The pressure receiving plate is displaced together with the flexible member.

8. The liquid ejecting device according to any one of claims 1 to 7, wherein The liquid flow includes a circulation flow path that allows liquid to circulate between the negative pressure chamber and the liquid ejecting unit, and a pump that allows liquid to flow through the circulation flow path.

9. The liquid ejecting device according to claim 1, wherein The liquid ejection head includes a bypass flow path that enables liquid to circulate without passing through a pressure chamber communicating with the ejection port.

10. The liquid ejecting device according to claim 1, wherein The liquid ejection head is configured to eject inks of a plurality of colors.

11. The liquid ejecting device according to claim 1, wherein The liquid ejection head is configured to eject white ink.

12. The liquid ejecting device according to claim 8, wherein The pump is a piezoelectric diaphragm pump.

13. The liquid ejecting device according to any one of claims 1 to 7, wherein The liquid flow forms a circulation flow passing through a pressure chamber that generates pressure to eject the liquid from an ejection port of the liquid ejecting unit.

14. The liquid ejecting device according to any one of claims 1 to 7, wherein The liquid flow includes a negative pressure compensation unit that compensates for pressure in the liquid ejecting unit by supplying liquid to the liquid ejecting unit if pressure on a downstream side of the liquid ejecting unit becomes lower than a certain pressure.

15. The liquid ejecting device according to claim 14, wherein The liquid flow causes the flow rate of the liquid circulating in the printing standby state to be greater than the flow rate of the liquid circulating in the printing operation state.

16. The liquid ejecting device according to any one of claims 1 to 7, wherein The liquid flow and the pressure control unit are integrally provided in a liquid ejection head supporting the liquid ejection unit. 17 . The liquid ejecting device according to claim 1 , wherein the liquid ejecting unit includes a heating element for ejecting the liquid from the ejection port.

18. The liquid ejecting device according to claim 8, wherein In the pump, the discharge port is arranged vertically above the suction port.

19. A liquid ejection head configured to perform reciprocating motion in a predetermined direction and configured to communicate with a liquid storage unit through a tube, the liquid ejection head comprising: a liquid ejecting unit, the liquid ejecting unit comprising an ejection port capable of ejecting liquid; a pressure control unit connectable to the liquid storage unit, receiving liquid from the liquid storage unit, and allowing the liquid having a pressure controlled within a predetermined pressure range to be supplied to the liquid ejecting unit; a liquid flow for circulating liquid between the liquid ejecting unit and the pressure control unit; The pressure control unit comprises: a supply chamber, the supply chamber receiving the liquid from the liquid storage unit; a negative pressure chamber, the negative pressure chamber being in communication with the liquid ejecting unit; and A pressure control valve, which controls the communication state between the supply chamber and the negative pressure chamber according to the pressure difference between the supply chamber and the negative pressure chamber, wherein when the pressure control valve is closed, the circulation flow between the liquid injection unit and the negative pressure chamber is separated from the flow between the liquid storage unit and the supply chamber.

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