Liquid discharge head and liquid discharge system

Abstract

To improve performance of discharging air bubble mixing in liquid in individual flow paths, without increasing flow rates of liquid flowing through the individual flow paths.SOLUTION: A liquid discharge head 1 comprises: first substrates 11c and 11d having lower surfaces to which a nozzle 21 opens and having a pressure chamber 23 communicated with the nozzle formed therein; and a piezoelectric element 12 arranged on an upper surface of the first substrate to oppose to the pressure chamber. The pressure chamber extends in a first direction, which has liquid inflow port 23x and a liquid outflow port 23y at one end side and at the other end side in the first direction. The nozzle is arranged between the inflow port and the outflow port in the first direction. When viewed from a second direction orthogonal to the first direction, an upper wall 23a of the pressure chamber is curved to protrude downward, in a state where voltages are not yet applied to the piezoelectric element.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a liquid ejection head that ejects liquid from nozzles, and a liquid ejection system that includes the liquid ejection head. [Background technology]

[0002] As a liquid ejection head, an ink jet recording head (see Patent Document 1) is known that includes a nozzle, a pressure chamber communicating with the nozzle, an ink supply path connected to one end of the pressure chamber, and an ink discharge path connected to the other end of the pressure chamber. In this ink jet recording head, ink is circulated through the ink supply path, the pressure chamber, and the ink discharge path. This makes it possible to prevent ink components from settling in the ink flow path and ink from drying up near the nozzle. In addition, air bubbles that have become mixed in the ink within the ink flow path can be expelled. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-158552 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the ink jet recording head having the above configuration, when the flow rate of ink in the pressure chamber is increased, the ejection direction of ink droplets ejected from the nozzle may be tilted from the desired direction to a certain direction. Specifically, the ejection direction of ink droplets may be tilted from the desired direction (e.g., vertical direction) to the direction in which ink flows in the pressure chamber (direction from one end of the pressure chamber to the other end of the pressure chamber). For this reason, it is not preferable to increase the flow rate of ink in the pressure chamber. However, if the flow rate of ink in the pressure chamber is not increased, it becomes difficult to efficiently expel air bubbles mixed in the ink in the pressure chamber.

[0005] The present invention aims to improve the ability to expel air bubbles that have become mixed into the liquid in a pressure chamber, without increasing the flow rate of the liquid flowing through the pressure chamber, in a liquid ejection head having a configuration for circulating the liquid in the pressure chamber. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a liquid ejection head comprising: a first substrate having a lower surface through which a nozzle opens, and in which a pressure chamber communicating with the nozzle is formed; and a piezoelectric element arranged on an upper surface of the first substrate so as to face the pressure chamber, the pressure chamber extending in a first direction parallel to the lower surface of the first substrate, having an inlet for liquid at one end side in the first direction, and having an outlet for the liquid at the other end side in the first direction, the nozzle being arranged between the inlet and the outlet in the first direction, and when viewed from a second direction parallel to the lower surface of the first substrate and perpendicular to the first direction, an upper wall of the pressure chamber is curved so as to be convex downward when no voltage is applied to the piezoelectric element.

[0007] In the liquid ejection head according to this aspect of the present invention, the upper wall of the pressure chamber is curved so as to be convex downward when viewed from the second direction in a state in which no voltage is applied to the piezoelectric element, and liquid flows from the inlet to the outlet in the pressure chamber. Therefore, even if air bubbles get mixed in with the liquid in the pressure chamber from the nozzle, the air bubbles can be easily moved along the upper wall of the pressure chamber to the outlet. In other words, in a liquid ejection head having a configuration for circulating the liquid in the pressure chamber, it is possible to improve the discharge of air bubbles mixed in the liquid in the pressure chamber without increasing the flow rate of the liquid flowing through the pressure chamber. Effect of the Invention

[0008] According to the liquid ejection head of the present invention, it is possible to improve the ability to expel air bubbles that have become mixed into the liquid in the pressure chamber, without increasing the flow rate of the liquid flowing through the pressure chamber. [Brief description of the drawings]

[0009] [Figure 1] 1 is a plan view of a printer equipped with a head according to an embodiment of the present invention. [Diagram 2] FIG. [Diagram 3] 3 is a cross-sectional view of the head taken along line III-III in FIG. 2. [Figure 4] FIG. 2 is a block diagram showing the electrical configuration of the printer. [Diagram 5] 7 is a cross-sectional view corresponding to FIG. 3 of a head according to a modified example. [Figure 6] 7 is a cross-sectional view corresponding to FIG. 3 of a head according to another modified example. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The schematic configuration of a printer 100 equipped with a head 1 according to an embodiment of the present invention will be described with reference to FIG.

[0011] The printer 100 (an example of a liquid ejection system) includes a head unit 1x including four heads 1 (an example of a liquid ejection head), a platen 3, a transport mechanism 4, and a controller 5.

[0012] A sheet of paper 9 is placed on the upper surface of the platen 3 .

[0013] The transport mechanism 4 includes two roller pairs 4a and 4b. When the transport motor 4m is driven under the control of the controller 5, the roller pairs 4a and 4b rotate while sandwiching the paper 9, and the paper 9 is transported in the transport direction (an example of a first direction). The two roller pairs 4a and 4b are disposed so as to sandwich the platen 3 in the transport direction.

[0014] The head unit 1x is of a line type (a type in which ink is ejected onto the paper 9 from nozzles 21 (see FIGS. 2 and 3) with the position fixed) and is long in the paper width direction (an example of the second direction). The four heads 1 are arranged in a staggered pattern in the paper width direction.

[0015] Here, the paper width direction is perpendicular to the transport direction, and both the paper width direction and the transport direction are perpendicular to the vertical direction.

[0016] The controller 5 has a ROM (Read Only Memory), a RAM (Random Access Memory), and an ASIC (Application Specific Integrated Circuit). The ASIC executes recording processing and the like in accordance with a program stored in the ROM. In the recording processing, the controller 5 controls the driver IC 1d (see FIG. 4) and the conveying motor 4m of each head 1 based on a recording command (including image data) input from an external device such as a PC, and records an image on the paper 9. Furthermore, the controller 5 controls a positive pressure pump 7P and a negative pressure pump 7Q (see FIGS. 2 and 4) to circulate ink between the ink tank 7 and each head 1, as described below.

[0017] Next, the configuration of the head 1 will be described with reference to FIGS.

[0018] The head 1 has a flow path substrate 11 and a plurality of piezoelectric elements 12 .

[0019] As shown in Fig. 3, the flow path substrate 11 has four plates 11a to 11d bonded to each other. All of the plates 11a to 11d are made of silicon, but the upper surface side of the plate 11c is made of silicon oxide by baking when forming the piezoelectric layer 12b described later. A common flow path 30 is formed in the plate 11a. A plurality of individual flow paths 20 are formed in the plates 11b to 11d. The plurality of individual flow paths 20 are located below the common flow path 30. The plates 11c and 11d bonded to each other are an example of a first substrate. The plates 11a and 11b bonded to each other are an example of a second substrate.

[0020] 2, the common flow path 30 includes return flow paths 31, 32 and a supply flow path 33 arranged in the transport direction. The return flow paths 31, 32 and the supply flow path 33 each extend in the paper width direction. The supply flow path 33 is disposed between the return flow path 31 and the return flow path 32 in the transport direction.

[0021] The supply flow path 33 communicates with the ink tank 7 via a supply port 33x. The return flow paths 31 and 32 communicate with the ink tank 7 via exhaust ports 31y and 32y, respectively. The supply port 33x is formed at one end of the supply flow path 33 in the paper width direction (upper in FIG. 2). The exhaust ports 31y and 32y are formed at the other end of the return flow paths 31 and 32 in the paper width direction (lower in FIG. 2). The supply port 33x and the exhaust ports 31y and 32y open on the upper surface of the plate 11a.

[0022] In the ink tank 7, ink to be supplied to the head 1 is stored.

[0023] The individual flow paths 20 include a plurality of first individual flow paths 20a connecting the return flow path 31 and the supply flow path 33, and a plurality of second individual flow paths 20b connecting the return flow path 32 and the supply flow path 33. The plurality of first individual flow paths 20a are arranged at equal intervals in the paper width direction. Similarly, the plurality of second individual flow paths 20b are also arranged at equal intervals in the paper width direction. The plurality of first individual flow paths 20a are shifted by a half pitch in the paper width direction with respect to the plurality of second individual flow paths 20b. Each of the first individual flow paths 20a straddles the return flow path 31 and the supply flow path 33 in the transport direction. Each of the second individual flow paths 20b straddles the return flow path 32 and the supply flow path 33 in the transport direction.

[0024] 2, the ink in the ink tank 7 is supplied from the supply port 33x to the supply flow path 33 by driving the positive pressure pump 7P under the control of the controller 5. The ink supplied to the supply flow path 33 moves from one side to the other in the paper width direction within the supply flow path 33, and is supplied to each of the multiple first individual flow paths 20a and the multiple second individual flow paths 20b. The ink supplied to the first individual flow paths 20a flows out into the return flow path 31 and moves in the return flow path 31 from one side to the other in the paper width direction. The ink is discharged from the return flow path 31 through the outlet 31y and returned to the ink tank 7 by driving the negative pressure pump 7Q under the control of the controller 5. The ink supplied to the second individual flow paths 20b flows out into the return flow path 32 and moves in the return flow path 32 from one side to the other in the paper width direction. The ink is discharged from the return flow path 32 through the outlet 32y and returned to the ink tank 7 by driving the negative pressure pump 7Q under the control of the controller 5. By circulating the ink between the head 1 and the ink tank 7 in this way, air bubbles in the ink are removed and the ink is prevented from thickening. Note that the thick arrows in FIG. 2 indicate the flow of ink.

[0025] Each individual flow path 20 includes a nozzle 21, a pressure chamber 23, and two connection flow paths 25. As shown in FIG. 3, the nozzle 21 is configured as a through hole formed in the plate 11d, and opens to the lower surface of the plate 11d. As shown in FIG. 2, the pressure chamber 23 has a substantially rectangular planar shape that is elongated in the transport direction. Also, as shown in FIG. 3, the pressure chamber 23 has a substantially rectangular cross-sectional shape that is elongated in the transport direction. A recess 11cx is formed in the lower surface of the plate 11c at a position facing the nozzle 21, and the pressure chamber 23 is defined by the recess 11cx and the plate 11d bonded to the lower surface of the plate 11c. That is, the upper wall 23a of the pressure chamber 23 is formed by the thin-walled portion of the plate 11c (the portion whose thickness is reduced by the recess 11cx). On the other hand, the lower wall 23b of the pressure chamber 23 is formed by the plate 11d. Moreover, side walls 23c, 23d of the pressure chamber 23 are formed by the thick portion of the plate 11c (portion where the recess 11cx is not formed). As shown in Fig. 3, the connecting flow path 25 is composed of a through hole formed in the plate 11b and the upper wall 23a of the pressure chamber 23. Recesses 11bx are formed in the lower surface of the plate 11b at positions facing each pressure chamber 23. The plate 11b is bonded to the upper surface of the plate 11c so that a plurality of piezoelectric elements 12, which will be described later, are housed in the recesses 11bx.

[0026] As shown in FIG. 2 and FIG. 3, one end 231 and the other end 232 in the transport direction of the pressure chamber 23 constituting the second individual flow path 20b overlap with the supply flow path 33 and the return flow path 32 in the vertical direction, respectively. An inlet 23x and an outlet 23y are formed in the upper wall 23a of the pressure chamber 23 constituting the second individual flow path 20b. Specifically, the inlet 23x is disposed on the one end 231 side of the pressure chamber 23 in the transport direction, and the outlet 23y is disposed on the other end 232 side of the pressure chamber 23 in the transport direction. The inlet 23x and the outlet 23y of the pressure chamber 23 constituting the second individual flow path 20b are connected to the supply flow path 33 and the return flow path 32 via the connection flow path 25, respectively. Similarly, the other end and one end in the transport direction of the pressure chamber 23 constituting the first individual flow path 20a overlap with the supply flow path 33 and the return flow path 31 in the vertical direction, respectively. The inlet 23x and the outlet 23y of the pressure chamber 23 constituting the first individual flow path 20a are connected to the supply flow path 33 and the return flow path 31 via the connecting flow path 25, respectively.

[0027] In each individual flow path 20, one of the two connecting flow paths 25 extends upward from the pressure chamber 23 and is connected to the supply flow path 33. The other of the two connecting flow paths 25 extends upward from the pressure chamber 23 and is connected to the return flow path 31 or the return flow path 32. In each individual flow path 20, the nozzle 21 is disposed between one end and the other end of the pressure chamber 23 in the transport direction.

[0028] The ink supplied to the supply flow path 33 moves downward through one of the connecting flow paths 25, and is supplied to the pressure chamber 23. The ink supplied to the pressure chamber 23 moves horizontally, and a portion of the ink is ejected from the nozzle 21, while the remainder moves upward through the other connecting flow path 25 and flows into the return flow path 31 or the return flow path 32. The arrows in Fig. 3 each indicate the flow of ink.

[0029] The piezoelectric elements 12 are disposed on the upper surface of the plate 11c so as to face the pressure chambers 23 formed in the plate 11c, respectively.

[0030] As shown in FIG. 3, each piezoelectric element 12 includes, from the bottom, a common electrode 12a, a piezoelectric layer 12b, and an individual electrode 12c. The common electrode 12a is made of a metal material and is provided so as to be common to the multiple pressure chambers 23. The piezoelectric layer 12b is formed by firing (annealing) a piezoelectric material mainly composed of lead zirconate titanate (PZT). The piezoelectric layer 12b is provided so as to be common to the multiple pressure chambers 23, and covers the upper and side surfaces of the common electrode 12a. The individual electrode 12c is made of a metal material and has a substantially rectangular planar shape that is long in the transport direction. The individual electrode 12c is provided for each pressure chamber 23, and is formed on the upper surface of the piezoelectric layer 12b so as to face the pressure chamber 23.

[0031] Each individual electrode 12c is electrically connected to a driver IC1d (see FIG. 4) via an individual wiring 13. The common electrode 12a is also electrically connected to the driver IC1d via a common wiring (not shown). The driver IC1d maintains the potential of the common electrode 12a at the ground potential, while changing the potential of the individual electrode 12c.

[0032] Here, when no voltage is applied to the individual electrodes 12c, the piezoelectric layer 12b is deformed to be convex downward due to residual stress during firing, as shown in Fig. 3. As a result, the upper wall 23a of the pressure chamber 23 and the common electrode 12a are curved to be located at the lowest position near the center of the pressure chamber 23 in the transport direction when viewed from the paper width direction. Therefore, the upper surface 23a1 of the pressure chamber 23 is also curved to be located at the lowest position near the center of the transport direction. Specifically, when viewed from the paper width direction, the height from the lower surface 23b1 to the upper surface 23a1 of the pressure chamber 23 is continuously lowered along the transport direction from the inlet 23x to the part 23z (hereinafter referred to as the bottom part 23z) that protrudes most downward of the upper wall 23a of the pressure chamber, and is continuously higher along the transport direction from the bottom part 23z to the outlet 23y.

[0033] The vertical displacement D of the bottom portion 23z from the non-curved portion of the upper wall 23a of the pressure chamber 23 (the portion where the piezoelectric element 12 is not formed) is, for example, about 200 to 800 nm. Note that a tensile stress is generated in the piezoelectric layer 12b, and a compressive stress is generated in the vibration plate 12a.

[0034] The nozzle 21 is located at the same position in the transport direction as the bottom portion 23z. In other words, when viewed from the paper width direction, the nozzle 21 is located directly below the bottom portion 23z.

[0035] Next, the operation of the piezoelectric element 12 when ink is ejected from a specific nozzle 21 will be described. First, in a state where ink is not ejected from the nozzle 21 (standby state), the common electrode 12a is maintained at ground potential, and a predetermined voltage is applied to the individual electrode 12c corresponding to the pressure chamber 23 communicating with the nozzle 21. At this time, an electric field parallel to the polarization direction is generated in the piezoelectric layer 12b between the individual electrode 12c and the common electrode 12a. As a result, the piezoelectric layer 12b contracts in a horizontal direction perpendicular to the polarization direction and deforms so as to be convex toward the pressure chamber 23. As a result, the common electrode 12a and the upper wall 23a of the pressure chamber 23 are curved so as to be convex further downward compared to a state where a predetermined voltage is not applied to the individual electrode 12c. Specifically, the lowest portion 23z is displaced downward, for example, by about 0.5 to 1.5 μm, from the non-curved portion of the upper wall 23a of the pressure chamber 23 (the portion where the piezoelectric element 12 is not formed). Here, as shown in FIG. 3, the wiring 13 extends from the individual electrode 12c in a direction from the outlet 23y to the inlet 23x. Therefore, the end of the piezoelectric layer 12b on the inlet 23x side is less likely to deform than the other parts. As a result, the downward displacement of the upper wall 23a of the pressure chamber 23 is greater near the outlet 23y than near the inlet 23x. This causes the bottom part 23z to shift from the center of the pressure chamber 23 to the outlet 23y side in the transport direction. In other words, the bottom part 23z is located between the center of the pressure chamber 23 and the outlet 23y in the transport direction. In the standby state, as described above, the controller 5 drives the positive pressure pump 7P and the negative pressure pump 7Q to circulate the ink between the head 1 and the ink tank 7. Therefore, in the pressure chamber 23, a flow of ink is generated from the inlet 23x to the outlet 23y.

[0036] When ink is to be ejected from the nozzle 21, the potential of the individual electrode 12c corresponding to the pressure chamber 23 communicating with the nozzle 21 is first switched to the ground potential. As a result, the piezoelectric layer 12b between the individual electrode 12c and the common electrode 12a is restored to the state when the specific voltage is not applied to the individual electrode 12c. As a result, the downward displacement of the upper wall 23a of the pressure chamber 23 becomes smaller than when the specific voltage is applied to the individual electrode 12c, and the volume of the pressure chamber 23 increases. Next, a specific voltage is applied to the individual electrode 12c again. At this time, the piezoelectric layer 12b between the individual electrode 12c and the common electrode 12a is deformed to be convex toward the pressure chamber 23 again. As a result, the downward displacement of the upper wall 23a of the pressure chamber 23 becomes larger than when the specific voltage is not applied to the individual electrode 12c, and the volume of the pressure chamber 23 decreases. As a result, the pressure of the ink in the pressure chamber 23 increases, and the ink is ejected from the nozzle 21. When ejecting the ink, the controller 5 drives the positive pressure pump 7P and the negative pressure pump 7Q to circulate the ink between the head 1 and the ink tank 7. Therefore, within the pressure chamber 23, a flow of ink is generated from the inlet 23x toward the outlet 23y.

[0037] As described above, the upper wall 23a of the pressure chamber 23 is curved so as to be convex downward when viewed from the paper width direction in a state where a predetermined voltage is not applied to the individual electrode 12c. Air bubbles mixed in the ink in the pressure chamber 23 move toward the upper surface 23a1 of the pressure chamber 23. According to this embodiment, the upper surface 23a1 of the pressure chamber 23 is inclined upward from the lowermost portion 23z toward the outlet 23y. Therefore, the air bubbles that reach the upper surface 23a1 of the pressure chamber 23 can be smoothly moved along the upper surface 23a1 to the outlet 23y. From the above, it is possible to efficiently discharge the air bubbles mixed in the ink in the pressure chamber 23 without increasing the flow rate of the ink flowing through the pressure chamber 23.

[0038] In this embodiment, the inflow port 23x and the outflow port 23y are formed in the upper wall 23a of the pressure chamber 23. Therefore, air bubbles that get mixed into the ink inside the pressure chamber 23 and move toward the upper surface 23a1 of the pressure chamber 23 can be efficiently discharged from the outflow port 23y.

[0039] In this embodiment, the two connecting channels 25 connected to each pressure chamber 23 extend upward from the inlet 23x and the outlet 23y, respectively. The two connecting channels 25 are then each connected to a common channel 30 located further above. For this reason, air bubbles mixed in the ink inside the pressure chamber 23 can be efficiently discharged to the common channel 30 via the outlet 23y and the connecting channels 25.

[0040] In this embodiment, when a voltage is applied to the individual electrode 12c, the upper wall 23a of the pressure chamber 23 is deformed to be more downwardly convex than when no voltage is applied to the individual electrode 12c. Therefore, air bubbles mixed in the ink in the pressure chamber 23 can be efficiently moved toward the outlet 23y without increasing the flow rate of ink flowing through the pressure chamber 23. As a result, air bubbles mixed in the ink in the pressure chamber 23 can be efficiently discharged.

[0041] In this embodiment, the bottom portion 23z of the upper wall 23a of the pressure chamber 23 is located at the same position in the transport direction as the nozzle 21. Air bubbles that have entered the ink in the pressure chamber 23 from the nozzle 21 move from the nozzle 21 toward the bottom portion 23z directly above the nozzle 21, but are caused to flow toward the outlet 23y from the bottom portion 23z by the flow of ink in the pressure chamber 23. For this reason, according to this embodiment, air bubbles that have entered the ink in the pressure chamber 23 from the nozzle 21 can be reliably moved toward the outlet 23y from the bottom portion 23z, and can be efficiently discharged from the outlet 23y.

[0042] In this embodiment, when viewed from the paper width direction, the height from the lower surface 23b to the upper surface 23a of the pressure chamber 23 increases continuously along the transport direction from the lowest part 23z to the outlet 23y. Therefore, air bubbles that have entered the nozzle inside the pressure chamber 23 can be efficiently moved toward the outlet 23y. As a result, air bubbles that have entered the ink inside the pressure chamber 23 can be efficiently discharged.

[0043] [Variations] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various design modifications are possible within the scope of the claims.

[0044] In the above embodiment, the bottom part 23z is located at the same position as the nozzle 21 in the transport direction, but this is not limited thereto. For example, the nozzle 21 may be disposed between the bottom part 23z and the outlet 23y in the transport direction. In the above embodiment, as shown in FIG. 3, the wiring 13 extends from the individual electrode 12c as a starting point, in a direction from the outlet 23y toward the inlet 23x, and further extends along the transport direction, bypassing the connecting flow path 25. Therefore, the end of the piezoelectric layer 12b on the inlet 23x side is less likely to deform than the other parts. As a result, when a predetermined voltage is applied to the individual electrode 12c, the downward displacement of the upper wall 23a of the pressure chamber 23 is slightly larger near the outlet 23y than near the inlet 23x. That is, the bottom part 23z is shifted from the center of the pressure chamber 23 toward the outlet 23y in the transport direction. Therefore, the position of the nozzle 21 in the transport direction may be the same as the bottom part 23z in a state where a predetermined voltage is applied to the individual electrode 12c, or may be between the bottom part 23z and the outlet 23y in a state where a predetermined voltage is applied to the individual electrode 12c as in the head 1A shown in Fig. 5. This makes it possible to easily move air bubbles mixed in the ink in the pressure chamber 23 from the nozzle 21 to the outlet 23y, regardless of whether a predetermined voltage is applied to the individual electrode 12c.

[0045] In the above embodiment, the inlet 23x and the outlet 23y are formed in the upper wall 23a of the pressure chamber 23, but this is not limited thereto. For example, as in the head 1B shown in FIG. 6, the inlet 23x and the outlet 23y may be formed in the upper end of the side wall 23c on one side in the transport direction and the upper end of the side wall 23d on the other side of the pressure chamber 23, respectively. In this case, air bubbles mixed in the ink in the pressure chamber 23 can be efficiently discharged. In this case, the connection flow path 25 connected to the inlet 23x and the supply flow path 33 communicating with the pressure chamber 23 via the connection flow path 25, and the connection flow path 25 connected to the outlet 23y and the return flow paths 31 and 32 communicating with the pressure chamber 23 via the connection flow path 25 may be formed in the plate 11c.

[0046] In the above embodiment, the positive pressure pump 7P and the negative pressure pump 7Q may be set so that the absolute value of the positive pressure by the positive pressure pump 7P is smaller than the absolute value of the negative pressure by the negative pressure pump 7Q. This makes it possible to maintain a negative pressure inside the pressure chamber 23 and easily curve the upper wall 23a of the pressure chamber 23 so as to be convex downward.

[0047] In the above embodiment, one supply flow path 33 is sandwiched between two return flow paths 31 and 32 in the transport direction, but this is not limited thereto. For example, one return flow path may be sandwiched between two supply flow paths in the transport direction.

[0048] The head unit 1x is not limited to the line type, but may be a serial type (a type in which liquid is ejected from nozzles onto an ejection target while moving in a scanning direction parallel to the paper width direction).

[0049] The ejection target is not limited to paper, but may be, for example, cloth, a substrate, etc.

[0050] The liquid ejected from the nozzles is not limited to ink, and may be any liquid (for example, a treatment liquid that aggregates or precipitates components in the ink, etc.).

[0051] The present invention is not limited to printers, but can also be applied to facsimiles, copy machines, multifunction machines, etc. The present invention can also be applied to liquid ejection heads used for purposes other than image recording (for example, liquid ejection heads that eject conductive liquid onto a substrate to form a conductive pattern). [Explanation of symbols]

[0052] 1 Head 5. Controller 7 Ink Tank 7P positive pressure pump 7Q Negative Pressure Pump 12 Piezoelectric element 20 Individual Channels 21 Nozzle 23 Pressure Chamber 23x inlet 23y outlet 25 Connecting Channel 30 Common flow path 31,32 Return channel 31y,32y outlet 33 Supply Channel 33x supply ports 100 Printers

Claims

1. A liquid ejection head, a first substrate having a lower surface on which a nozzle is opened and in which a pressure chamber communicating with the nozzle is formed; a piezoelectric element disposed on an upper surface of the first substrate so as to face the pressure chamber; the pressure chamber extends in a first direction parallel to a lower surface of the first substrate, has an inlet for liquid on one end side in the first direction, and has an outlet for liquid on the other end side in the first direction; the nozzle is disposed between the inlet and the outlet in the first direction, when viewed from a second direction that is parallel to a lower surface of the first substrate and perpendicular to the first direction, an upper wall of the pressure chamber is curved so as to be convex downward when no voltage is applied to the piezoelectric element, the piezoelectric element has a first electrode disposed on an upper surface of the first substrate, a piezoelectric layer disposed on the upper surface of the first electrode so as to face the pressure chamber, and a second electrode disposed on the upper surface of the piezoelectric layer so as to face the pressure chamber; A liquid ejection head, characterized in that a vertical displacement of a lowermost portion of the upper wall of the pressure chamber that protrudes most downward from a non-curved portion of the upper wall of the pressure chamber is 200 to 800 nm.

2. The liquid ejection head according to claim 1 , wherein the inlet and the outlet are formed in an upper wall of the pressure chamber.

3. a second substrate on which a supply flow path through which the liquid supplied to the pressure chamber flows, a first connection flow path connecting the supply flow path and the inlet, a return flow path through which the liquid flowing out of the pressure chamber flows, a second connection flow path connecting the return flow path and the outlet, and a recess are formed, The liquid ejection head according to claim 2 , wherein the second substrate is laminated on the upper surface of the first substrate such that the piezoelectric element is housed in the recess of the second substrate.

4. the pressure chamber has a first side wall on the one end side and a second side wall on the other end side, The inlet is formed at an upper end of the first side wall, The liquid ejection head according to claim 1 , wherein the outlet is formed at an upper end of the second side wall.

5. The liquid ejection head according to claim 4, further comprising a supply flow path connected to the inlet and through which the liquid supplied to the pressure chamber flows, and a return flow path connected to the outlet and through which the liquid flowing out of the pressure chamber flows.

6. A liquid ejection head as described in any one of claims 1 to 5, wherein when viewed from the second direction, the upper wall of the pressure chamber deforms so as to be more convex downward when a voltage is applied to the piezoelectric element than when no voltage is applied to the piezoelectric element.

7. 2. A liquid ejection head as described in claim 1, wherein when viewed from the second direction, the nozzle is positioned at the same position as the downwardly most protruding part of the upper wall of the pressure chamber in the first direction, or between the downwardly most protruding part of the upper wall of the pressure chamber and the outlet.

8. 2 . The liquid ejection head according to claim 1 , wherein, when viewed from the second direction, the nozzle is disposed at the same position as a portion of an upper wall of the pressure chamber that protrudes most downward in the first direction.

9. The liquid ejection head according to claim 2 , wherein when viewed from the second direction, the height from the lower surface to the upper surface of the pressure chamber increases continuously from the downwardly most protruding part of the upper wall of the pressure chamber towards the outlet.

10. the piezoelectric element has a first electrode disposed on an upper surface of the first substrate, a piezoelectric layer disposed on an upper surface of the first electrode so as to face the pressure chamber, and a second electrode disposed on an upper surface of the piezoelectric layer so as to face the pressure chamber; 2. The liquid ejection head according to claim 1, wherein, when no voltage is applied to the piezoelectric element, a tensile stress is generated in the piezoelectric layer, and a compressive stress is generated in the upper wall of the pressure chamber.

11. A liquid ejection system, comprising: a first substrate having a lower surface on which a nozzle is opened and in which a pressure chamber communicating with the nozzle is formed; a piezoelectric element disposed on an upper surface of the first substrate so as to face the pressure chamber; a second substrate formed with a supply flow path through which liquid supplied to the pressure chamber flows, a return flow path through which the liquid flowing out of the pressure chamber flows, and a recess, the second substrate being laminated on an upper surface of the first substrate such that the piezoelectric element is accommodated in the recess; A tank for storing the liquid; a positive pressure pump connected to the tank and the supply line; a negative pressure pump connected to the return flow path and the tank; the pressure chamber extends in a first direction parallel to a lower surface of the first substrate, has an inlet for the liquid on one end side in the first direction, and has an outlet for the liquid on the other end side in the first direction; the nozzle is disposed between the inlet and the outlet in the first direction, when viewed from a second direction that is parallel to a lower surface of the first substrate and perpendicular to the first direction, an upper wall of the pressure chamber is curved so as to be convex downward when no voltage is applied to the piezoelectric element, a vertical displacement of a most downwardly protruding lowermost portion of the upper wall of the pressure chamber from a non-curved portion of the upper wall of the pressure chamber is between 200 and 800 nm; the piezoelectric element has a first electrode disposed on an upper surface of the first substrate, a piezoelectric layer disposed on the upper surface of the first electrode so as to face the pressure chamber, and a second electrode disposed on the upper surface of the piezoelectric layer so as to face the pressure chamber; the inlet and the outlet are formed in an upper wall of the pressure chamber, The second substrate is further provided with a first connection channel connecting the supply channel and the inlet, and a second connection channel connecting the return channel and the outlet, The liquid ejection system, wherein the pressure chamber is maintained at a negative pressure when no voltage is applied to the piezoelectric element.

12. A liquid ejection system, comprising: a first substrate having a lower surface in which a nozzle opens, and in which a pressure chamber communicating with the nozzle, a supply flow path through which a liquid supplied to the pressure chamber flows, and a return flow path through which the liquid flowing out of the pressure chamber flows; a piezoelectric element disposed on an upper surface of the first substrate so as to face the pressure chamber; A tank for storing the liquid; a positive pressure pump connected to the tank and the supply line; a negative pressure pump connected to the return flow path and the tank; the pressure chamber extends in a first direction parallel to a lower surface of the first substrate, and has a first side wall at one end in the first direction and a second side wall at the other end in the first direction; an inlet for the liquid is formed at an upper end of the first side wall of the pressure chamber; an outlet for the liquid is formed at an upper end of the second side wall of the pressure chamber, the nozzle is disposed between the inlet and the outlet in the first direction, when viewed from a second direction that is parallel to a lower surface of the first substrate and perpendicular to the first direction, an upper wall of the pressure chamber is curved so as to be convex downward when no voltage is applied to the piezoelectric element, a vertical displacement of a most downwardly protruding lowermost portion of the upper wall of the pressure chamber from a non-curved portion of the upper wall of the pressure chamber is between 200 and 800 nm; the piezoelectric element has a first electrode disposed on an upper surface of the first substrate, a piezoelectric layer disposed on the upper surface of the first electrode so as to face the pressure chamber, and a second electrode disposed on the upper surface of the piezoelectric layer so as to face the pressure chamber; The first substrate further includes a first connection channel connecting the supply channel and the inlet, and a second connection channel connecting the return channel and the outlet, The liquid ejection system, wherein the pressure chamber is maintained at a negative pressure when no voltage is applied to the piezoelectric element.

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