Liquid ejection head

Abstract

To provide a liquid discharge head capable of, by discharging liquid, causing a meniscus of the liquid in a nozzle to return, the meniscus projecting outward after the discharge.SOLUTION: A liquid discharge head of an embodiment includes a nozzle part, a pressure chamber, an actuator, a first liquid chamber, and a second liquid chamber. The nozzle part forms a plurality of nozzles that discharge liquid. The plurality of pressure chambers respectively communicate with the nozzles. The actuator changes volumes of the pressure chambers and causes a pressure change in the pressure chambers due to liquid column resonance in a longitudinal direction in the pressure chambers. The first liquid chamber communicates with one opening ends of the longitudinal direction of the pressure chambers and also communicates with a liquid supply path. The second liquid chamber communicates with each of the other opening ends of the longitudinal direction of the pressure chambers and forms dead ends that are separate for each of the pressure chambers.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] Embodiments of the present invention relate to a liquid ejection head.

Background Art

[0002] A liquid ejection head that supplies a predetermined amount of liquid to a predetermined position is known. The liquid ejection head is mounted on, for example, an inkjet printer, a 3D printer, a dispensing device, or the like. An inkjet printer ejects ink droplets from an inkjet head to form an image or the like on the surface of a recording medium. A 3D printer ejects droplets of a modeling material from a modeling material ejection head and cures them to form a three-dimensional object. A dispensing device ejects droplets of a sample and supplies a predetermined amount to a plurality of containers or the like.

[0003] The liquid ejection head has a plurality of channels for ejecting liquid. Each channel includes a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and an actuator for changing the volume of the pressure chamber. The liquid ejection head selects a channel for ejecting liquid from among the plurality of channels and drives it by applying a drive signal to the actuator. When the actuator is driven, the volume of the pressure chamber filled with liquid changes, and liquid is ejected from the nozzle. In a liquid ejection head having such a configuration, the meniscus of the liquid in the nozzle may rise outward immediately after ejection. In particular, when liquid is repeatedly ejected, the meniscus is likely to rise. When the next liquid is ejected in a state where the meniscus has risen, the ejection speed may slow down, and the ejection of the liquid may not be stable.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a liquid ejection head capable of returning the meniscus of the liquid in the nozzle that has swelled outward after ejection by ejecting the liquid.

Means for Solving the Problems

[0006] The liquid ejection head according to an embodiment of the present invention includes a nozzle portion, a pressure chamber, an actuator, a first liquid chamber, and a second liquid chamber. The nozzle portion forms a plurality of nozzles for ejecting liquid. The plurality of pressure chambers communicate with each of the nozzles respectively. The actuator changes the volume of each of the pressure chambers, and causes a pressure change due to longitudinal liquid column resonance in the pressure chamber in each of the pressure chambers. The first liquid chamber communicates with one open end in the longitudinal direction of each of the pressure chambers, and further communicates with a liquid supply path. The second liquid chamber communicates with the other open end in the longitudinal direction of each of the pressure chambers respectively, and is a dead-end path separated for each pressure chamber.

Brief Description of the Drawings

[0007]

Figure 1

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Mode for Carrying Out the Invention

[0008] Hereinafter, a liquid ejection head according to an embodiment will be described in detail with reference to the accompanying drawings. In each figure, the same components are denoted by the same reference numerals.

[0009] As an example of an image forming apparatus equipped with the liquid ejection head of the embodiment, an inkjet printer 10 that prints an image on a recording medium will be described. FIG. 1 shows a schematic configuration of the inkjet printer 10. The inkjet printer 10 includes, inside a housing 11, a cassette 12 for storing a sheet S which is an example of a recording medium, an upstream conveyance path 13 of the sheet S, a conveyance belt 14 for conveying the sheet S taken out from the cassette 12, a plurality of inkjet heads 100 to 103 for ejecting ink droplets toward the sheet S on the conveyance belt 14, a downstream conveyance path 15 of the sheet S, a discharge tray 16, and a control board 17. An operation unit 18 which is a user interface is arranged on the upper side of the housing 11.

[0010] Image data to be printed on the sheet S is generated by, for example, a computer 200 which is an external connection device. The image data generated by the computer 200 is sent to the control board 17 of the inkjet printer 10 through a cable 201 and connectors 202 and 203.

[0011] The pickup roller 204 supplies the sheets S one by one from the cassette 12 to the upstream conveyance path 13. The upstream conveyance path 13 is composed of the feed roller pair 131, 132 and the sheet guide plates 133, 134. The sheet S is sent to the upper surface of the conveyance belt 14 via the upstream conveyance path 13. The arrow 104 in the figure indicates the conveyance path of the sheet S from the cassette 12 to the conveyance belt 14.

[0012] The conveyance belt 14 is a net-shaped endless belt having a large number of through holes formed on its surface. The three rollers of the drive roller 141, the driven rollers 142, 143 rotatably support the conveyance belt 14. The motor 205 rotates the conveyance belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive device. The 105 in the figure indicates the rotation direction of the conveyance belt 14. A negative pressure container 206 is arranged on the back side of the conveyance belt 14. The negative pressure container 206 is connected to a decompression fan 207. The fan 207 creates a negative pressure in the negative pressure container 206 by the airflow formed, and adsorbs and holds the sheet S on the upper surface of the conveyance belt 14. The 106 in the figure indicates the flow of the airflow.

[0013] The inkjet heads 100 to 103, which are examples of liquid ejection heads, are arranged to face the sheet S adsorbed and held on the conveyance belt 14 with a slight gap of, for example, 1 mm therebetween. The inkjet heads 100 to 103 eject ink droplets toward the sheet S, respectively. The inkjet heads 100 to 103 print an image when the sheet S passes below. Each of the inkjet heads 100 to 103 has the same structure except that the color of the ejected ink is different. The colors of the ink are, for example, cyan, magenta, yellow, and black.

[0014] The inkjet heads 100 to 103 are each connected to the ink tanks 315 to 318 and the ink supply pressure regulators 321 to 324 via the ink flow paths 311 to 314. Each of the ink tanks 315 to 318 is disposed above each of the inkjet heads 100 to 103. During standby, each of the ink supply pressure regulators 321 to 324 adjusts the pressure inside each of the inkjet heads 100 to 103 to a negative pressure, for example, -1.2 kPa, with respect to the atmospheric pressure so that ink does not leak from the nozzles 3 (see FIG. 2) of the inkjet heads 100 to 103. During image formation, the ink in each of the ink tanks 315 to 318 is supplied to each of the inkjet heads 100 to 103 by the ink supply pressure regulators 321 to 324.

[0015] After image formation, the sheet S is sent from the conveyance belt 14 to the downstream conveyance path 15. The downstream conveyance path 15 includes pairs of feed rollers 151, 152, 153, 154 and sheet guide plates 155, 156 that define the conveyance path of the sheet S. The sheet S is sent from the downstream conveyance path 15 to the discharge tray 16 through the discharge port 157. The arrow 107 in the figure indicates the conveyance path of the sheet S.

[0016] Next, the configuration of the inkjet heads 100 to 103 will be described. The following describes the inkjet head 100 with reference to FIGS. 2 to 6, but the inkjet heads 101 to 103 have the same structure as the inkjet head 100.

[0017] As shown in FIG. 2, the inkjet head 100 includes a head portion 2 which is an example of a liquid ejection portion. The head portion 2 is connected to a flexible printed wiring board 21. The head portion 2 includes a nozzle plate 22, an actuator substrate 23, and an ink supply portion 24 which is an example of a liquid supply portion. The ink supply portion 24 is connected to the ink supply pressure regulator 321 in FIG. 1 via the ink flow path 311.

[0018] The flexible printed wiring board 21 mounts a driving IC (Integrated Circuit) 25 which is a driver chip (hereinafter referred to as the driving IC). The driving IC as a control unit temporarily stores the print data sent from the control board 17 of the inkjet printer 10 and gives a driving signal to each channel to eject ink at a predetermined timing.

[0019] A nozzle plate 22 which is an example of the nozzle part is a rectangular plate formed of a resin such as polyimide or a metal such as stainless steel. The nozzles 3 of each channel for ejecting ink are arranged along the longitudinal direction (X direction) of the nozzle plate 22. The nozzle density is set, for example, within the range of 150 to 1200 dpi. The discharge holes 31 are formed in the nozzle plate 22. The discharge holes 31 communicate with the individual negative pressure ink chambers 5 described later and are used, for example, when filling the inkjet head 100 with ink. That is, the discharge holes 31 do not eject ink during printing. The discharge holes 31 are formed as holes smaller than the nozzles 3 and are arranged along the Y direction for one nozzle 3. The nozzles 3 and a set of three discharge holes 31 may be formed in a plurality of rows in the Y direction of the nozzle plate 22. The discharge holes 31 are an example of the opening holes formed on the same surface as the nozzles 3 (the XY plane in the example of the figure).

[0020] Particularly, as shown in FIGS. 3 to 6, the nozzle plate 22 formed with the nozzles 3 is attached to the actuator substrate 23 via, for example, a frame member 26. The actuator substrate 23 is a substrate formed of, for example, insulating ceramics. The frame member 26 is formed of, for example, resin. The pressure chambers 4 for the ink of each channel are arranged alternately with the air chambers 40, for example, in the longitudinal direction (X direction) of the nozzle plate 22, in the space surrounded by the nozzle plate 22, the frame member 26, and the actuator substrate 23. The pressure chambers 4 for the ink of each channel for ejecting ink communicate with the nozzles 3 of each channel, respectively.

[0021] The pressure chamber 4 is formed by, for example, notching two piezoelectric members 41 laminated on the surface of the actuator substrate 23 in directions where the polarization directions are opposite (for example, the opposing directions), for example, in a rectangular groove shape (see FIG. 6). That is, the piezoelectric member 41 is formed such that its longitudinal direction extends in the short side direction (Y direction) of the actuator substrate 23. The piezoelectric member 41 is formed at a height that contacts the surface of the nozzle plate 22. Therefore, the pressure chamber 4 has side walls of the piezoelectric members 41 standing on both sides in its short side direction, and is, for example, an elongated space with both ends in its longitudinal direction open. Note that the piezoelectric member 41 is formed, for example, to have a trapezoidal shape in side view, but the shape in side view is not limited to a trapezoid.

[0022] The air chambers 40 are arranged on both sides adjacent to the pressure chamber 4 with the piezoelectric members 41 interposed therebetween. Similar to the pressure chamber 4, the air chambers 40 are formed by notching the piezoelectric members 41, for example, in a rectangular groove shape, and further, the openings at both ends in the longitudinal direction are closed with, for example, convex wall members 27 extending inward from a frame-like member 26 to form a sealed space into which ink is not introduced. The wall member 27 is, for example, a resin wall.

[0023] One of the openings at both longitudinal ends of the pressure chamber 4 communicates with the ink standby chamber 42. The ink standby chamber 42 as a liquid standby chamber is an example of the first liquid chamber. Each ink standby chamber 42 is partitioned from the ink standby chamber 42 of an adjacent channel by a convex wall member 27 extending from, for example, the frame-shaped member 26. That is, the ink standby chambers 42 are separated for each channel that discharges ink. The ink standby chamber 42 expands the space in the lateral direction more than the width of the opening of the pressure chamber 4 by the width of the piezoelectric members 41 on both sides in plan view. Further, when viewed in a longitudinal section, the space expands in the longitudinal direction, for example, along the extension line of the inclined surface of the piezoelectric member 41. By thus making the space of the ink standby chamber 42 larger than the opening at the end of the pressure chamber 4, one opening of the pressure chamber 4 is made an open end where the pressure change due to the liquid column resonance described later is small. However, it is not always necessary to expand the space of the ink standby chamber 42 in both the lateral and longitudinal directions, and either one may be sufficient. Also, as an example, a configuration is cited in which the wall member 27 that partitions the ink standby chamber 42 of an adjacent channel is shared with the wall member 27 that closes the opening of the air chamber 40, but they may be formed separately. Further, the wall member 27 may be formed of another member such as a plate.

[0024] Each ink waiting chamber 42 communicates with an ink supply manifold 44 via a constriction 43 respectively. That is, the constriction 43 is provided for each ink waiting chamber 42 of each channel. The constriction 43 is, for example, a rectangular ink passage. The constriction 43 is formed, for example, to penetrate the actuator substrate 23 in the thickness direction from the bottom surface of the convex portion on the outer side of the ink waiting chamber 42. The ink supply manifold 44 is formed, for example, in a groove shape on the surface of the ink supply section 24 along the arrangement direction (X direction) of the constrictions 43. The ink supply manifold 44 communicates with the ink flow path 311 (see FIG. 2). By laminating the actuator substrate 23 and the ink supply section 24, the constrictions 43 of each channel communicate with the ink supply manifold 44. The opening area of the constriction 43 is made smaller than at least the cross-sectional area of the ink waiting chamber 42. Usually, it is further made smaller than the opening area of the pressure chamber 4. That is, the cross-sectional area through which the ink passes through the constriction 43 is preferably smaller than the cross-sectional area through which the ink passes through the ink waiting chamber 42 and also smaller than the cross-sectional area through which the ink passes through the pressure chamber 4. The length of the constriction 43 is the thickness of the actuator substrate 23. The resistance when the ink passes through the constriction 43 is determined by the opening area and the length of the constriction 43. The smaller the opening area and the longer the length, the greater the resistance. The ink supply manifold 44 and the constriction 43 are an example of a liquid supply path that supplies ink to the ink waiting chamber 42 as the first liquid chamber.

[0025] Of the openings at both longitudinal ends of the pressure chamber 4, the other one communicates with the individual negative pressure ink chamber 5. The individual negative pressure ink chamber 5 as the individual negative pressure liquid chamber is an example of the second liquid chamber. Each individual negative pressure ink chamber 5 is partitioned from the individual negative pressure ink chamber 5 of the adjacent channel by, for example, a convex wall member 51 extending from the frame-shaped member 26. That is, the individual negative pressure ink chambers 5 are separated for each channel that discharges ink. The individual negative pressure ink chamber 5 expands the space in the lateral direction more than the width of the opening of the pressure chamber 4 by the width of the piezoelectric members 41 on both sides in plan view. Further, when viewed in the longitudinal section, the space expands in the longitudinal direction, for example, along the extension line of the inclined surface of the piezoelectric member 41. By thus enlarging the space of the individual negative pressure ink chamber 5 compared to the opening at the end of the pressure chamber 4, the other opening in the longitudinal direction of the pressure chamber 4 is made an open end with a small pressure change due to liquid column resonance described later. However, it is not always necessary to expand the space of the individual negative pressure ink chamber 5 in both the lateral and longitudinal directions, and either one of them may be sufficient. Also, as an example, a configuration is cited in which the wall member 51 that partitions the individual negative pressure ink chamber 5 of the adjacent channel is shared with the wall member 51 that closes the opening of the air chamber 40, but they may be formed separately. Further, the wall member 51 may be formed of another member such as a plate, for example.

[0026] The individual negative pressure ink chamber 5 is a dead end where ink does not enter or exit except through the opening of the pressure chamber 4. The discharge hole 31 is used, for example, when filling the inkjet head 100 with ink, but there is no ink entry or exit through this discharge hole 31 during printing. That is, since the individual negative pressure ink chamber 5 communicates with the open end of the pressure chamber 4, the ink pressure does not rise like in the pressure chamber 4, and ink is not ejected from the discharge hole 31. Further, since the individual negative pressure ink chamber 5 is intended to make the interior negative pressure, the size of the hole is made smaller than that of the nozzle 3 so as not to suck air from the discharge hole 31. The shape of the discharge hole 31 is preferably a stepped cylinder. The discharge hole 31 has a smaller hole size to prevent air from being sucked in when the individual negative pressure ink chamber 5 becomes negative pressure, while increasing the number of holes to facilitate air discharge when filling the ink. Of course, the number of discharge holes 31 formed in one individual negative pressure ink chamber 5 is not limited to three and may be increased or decreased. Also, it is preferably arranged along the extension line in the longitudinal direction (Y direction) of the pressure chamber 4, but the arrangement direction may be changed.

[0027] Each individual negative pressure ink chamber 5 forms a concave air reservoir portion 52 at a position facing the discharge hole 31, for example. When using the inkjet head 100 with the nozzle 3 positioned on the bottom surface side as illustrated in FIG. 1, the air reservoir portion 52 is located on the upper side of the discharge hole 31. That is, the air reservoir portion 52 is formed on one surface (in this case, the ceiling surface) in the direction opposite to the direction in which gravity acts inside the individual negative pressure ink chamber 5 so that the air remaining inside the chamber accumulates. As a preferable example, the shape of the air reservoir portion 52 is, for example, elliptical in plan view. Further, when viewed in cross section, the outer periphery of the air reservoir portion 52 preferably has an inclined shape without providing a step.

[0028] Although FIGS. 3 to 5 are not shown, as shown in FIG. 6, the electrode 45 is integrally formed on, for example, the bottom surface and both side surfaces of the pressure chamber 4. The electrodes 45 of each pressure chamber 4 are respectively connected to the wiring electrodes 46 as individual electrodes. The electrode 47 is integrally formed on, for example, the bottom surface and both side surfaces of the air chamber 40. The electrodes 47 of each air chamber 40 are connected to the wiring electrode 48 as a common electrode. The piezoelectric member 41 and the electrodes 45 and 47 sandwiching the piezoelectric member 41 constitute an actuator 6 that changes the volume of the pressure chamber 4 by shear mode deformation. The electrodes 45 and 47 and the wiring electrodes 46 and 48 are formed of, for example, a nickel thin film by electroless plating or the like. In particular, the electrode 45 of the pressure chamber 4 may be covered with a protective film (not shown) so as not to come into contact with the ink. The wiring electrode 46 from the pressure chamber 4 is connected to the flexible printed wiring board 21 at, for example, the end of the actuator substrate 23 and is connected to the drive driver (that is, the drive circuit) of the drive IC 25. The drive driver of each channel respectively gives a drive voltage, for example, as a drive signal, to the actuator 6 of each channel. On the other hand, the wiring electrode 48 from the air chamber 40 is connected to, for example, the ground (GND). With such a configuration, in the actuator 6 to which a drive voltage is applied, an electric field is applied in a direction intersecting (preferably, orthogonal) to the polarization axis of the piezoelectric member 41, and the piezoelectric member 41 serving as the side walls on both sides of the pressure chamber 4 deforms in a shear mode.

[0029] FIG. 7 shows a drive waveform (DRP waveform) as an example of a drive waveform for driving the actuator 6. FIG. 7 also shows the changes in the pressure of the ink in the pressure chamber 4 and the flow velocity of the ink during driving. The drive waveform sequentially applies a voltage of negative potential (-V) during period t1, a ground potential (GND) during period t2, and a voltage of positive potential (+V) during period t3 to the actuator 6. The period t1 is set to, for example, half the time of the pressure vibration period of the head unit 2. When the pressure vibration period is, for example, 4.8 [μs], the period t1 is 2.4 [μs]. The period t2 is, for example, 3.25 [μs], and the period t3 is 0.7 [μs] shorter than the period t2. At this time, the center interval between the period t1 and the period t3 is t1 / 2 + t2 + t3 / 2 = (pressure vibration period).

[0030] Figure 8(a) shows a state where the potentials of the electrodes 45 and 47 of the adjacent pressure chamber 4 and air chamber 40 are both at the ground potential (GND). In this state, the piezoelectric members 41 on both sides of the pressure chamber 4 are not subjected to any distortion effect. Figure 8(b) shows a state where a voltage (-V) with a negative potential is applied to the electrode 45 of the pressure chamber 4 during the period t1 of the driving waveform in FIG. 7. In this state, an electric field acts on the piezoelectric members 41 on both sides of the pressure chamber 4 in a direction orthogonal to the polarization direction, and the piezoelectric members 41 are deformed in the outer side in a shear mode, so that the volume of the pressure chamber 4 expands.

[0031] In the subsequent period t2, by setting the potential of the electrode 45 of the pressure chamber 4 to the ground potential (GND), the expanded volume of the pressure chamber 4 returns to the state of FIG. 8(a). By returning the volume of the pressure chamber 4 at the end of the period t1 set to half of the pressure vibration cycle in this way, as shown in FIG. 7, the pressure of the ink in the pressure chamber 4 increases, and the ink droplets are ejected from the nozzle 3. This pressure change utilizes the liquid column resonance in the longitudinal direction of the pressure chamber, which will be described in detail later.

[0032] In the further subsequent period t3, a voltage (+V) with a positive potential is applied to the electrode 45 of the pressure chamber 4. In this state, as shown in FIG. 8(c), an electric field acts on the piezoelectric members 41 on both sides of the pressure chamber 4 in a direction opposite to that in FIG. 8(b), and the piezoelectric members 41 are deformed inward, so that the volume of the pressure chamber 4 contracts. After the elapse of the period t3, by setting the potential of the electrode 45 of the pressure chamber 4 to the ground potential (GND), the contracted volume of the pressure chamber 4 returns to the state of FIG. 8(a). This contraction and return attenuate the residual vibration.

[0033] In this way, ink ejection is performed by driving the actuator 6 to control the pressure in the pressure chamber 4. When the longitudinal ends of the pressure chamber 4 are open ends, the liquid column resonance in the longitudinal direction of the pressure chamber generated when the actuator 6 is driven is utilized for ink ejection. That is, it is different from an inkjet head configured to utilize Helmholtz resonance. The liquid column resonance has a wavelength equal to the value obtained by multiplying the sound velocity of the ink in the pressure chamber 4 by the pressure oscillation period described above. When both longitudinal ends of the pressure chamber 4 are open, it becomes a 1 / 2 wavelength resonance tube of this wavelength.

[0034] In the case of a 1 / 2 wavelength resonance tube, when the pressure amplitude and the flow velocity amplitude are represented by a standing wave as shown in FIG. 9, the central portion in the longitudinal direction of the pressure chamber has the maximum pressure amplitude and the minimum flow velocity amplitude. On the other hand, at the open end of the standing wave, the pressure amplitude is the minimum and the flow velocity amplitude is the maximum. Therefore, the nozzle 3 is arranged at the central portion in the longitudinal direction where the pressure amplitude becomes the largest. It is not limited to the position where the pressure amplitude is exactly the largest, and it may be in the vicinity thereof. An example of the vicinity is within a range of 1 / 10 wavelength. The nozzle 3 preferably has a tapered shape in which the diameter becomes smaller toward the tip side. The diameter on the base end side of the nozzle 3 is, for example, 40 to 55 μm. The diameter on the tip side of the nozzle 3 is, for example, 20 to 30 μm.

[0035] The nozzle 3 forms an ink meniscus M near its opening (see FIG. 10), introduces the pressure change due to the liquid column resonance generated when the actuator 6 is driven into the nozzle 3, and ejects the ink. The nozzle 3 having a tapered shape increases the ink flow velocity by narrowing the tip side to a narrow opening, and applies a load to the pressure chamber 4 by the wide opening on the base end side. When at rest without ejecting ink, a negative pressure is applied to the pressure chamber 4 to keep the meniscus M concave. That is, as described above, the inside of the inkjet head 100 is adjusted to a negative pressure with respect to the atmospheric pressure by the ink supply pressure adjusting device 321.

[0036] Based on the operating principle of the liquid column resonance tube, it is desirable that there is no pressure change at the open end position of the pressure chamber 4. Therefore, an ink standby chamber 42 and an individual negative pressure ink chamber 5 are provided, and both ends of the pressure chamber 4 are open ends. However, in reality, due to the flow of ink entering and leaving between the pressure chamber 4 and the ink standby chamber 42, and between the pressure chamber 4 and the individual negative pressure ink chamber 5 when the actuator 6 is driven, pressure changes may occur at both ends of the pressure chamber 4. If the pressure vibration caused by this pressure change propagates to the surrounding channels, a crosstalk problem may occur. However, by separating the ink standby chamber 42 and the individual negative pressure ink chamber 5 for each pressure chamber 4, the propagation of pressure vibration to the surrounding channels is suppressed. The ink standby chambers 42 of each channel communicate with each other through an ink supply manifold 44. Therefore, a constriction 43 is provided between the ink standby chamber 42 and the ink supply manifold 44 to suppress the propagation of pressure vibration through the ink supply manifold 44.

[0037] As described above, when liquid column resonance is used for ink ejection, in the time domain of the pressure vibration, the ink standby chamber 42 and the individual negative pressure ink chamber 5 act as open ends. However, when looking at the ejection operation over a slightly longer time span, in the channels where ink is repeatedly ejected, the meniscus M of the ink formed at the nozzle 3 gradually bulges outward convexly as shown by the dashed line in Fig. 10. At the same time, the average pressures of the pressure chamber 4, the ink standby chamber 42, and the individual negative pressure ink chamber 5 decrease. Since the ink standby chamber 42 is replenished with ink from the ink supply manifold 44 when the pressure inside the chamber becomes negative, the negative pressure is eliminated. On the other hand, the individual negative pressure ink chamber 5, which is a dead end, maintains its negative pressure state for a longer time than the ink standby chamber 42 because it is not replenished with ink. And due to this negative pressure, the meniscus M of the ink at the nozzle 3 can be pulled back, and as a result, the swelling of the meniscus M after ejection can be suppressed.

[0038] The shape of the discharge hole 31 is preferably a hole smaller than the nozzle 3 and having a cylindrical portion without being tapered like the nozzle 3 because it is suitable for maintaining the negative pressure state of the above-described individual negative pressure ink chambers 5. That is, even if the individual negative pressure ink chambers 5 become negative pressure and the meniscus M of the discharge hole 31 retreats as shown by the broken line in FIG. 10, the meniscus force remains unchanged if it is a cylindrical portion, and it is possible to prevent air from being sucked in.

[0039] The swelling of the meniscus M of the ink in the nozzle 3 does not occur in the channels where ink is not being discharged, but occurs in the channels where ink is being discharged. In particular, it is likely to occur in the channels where ink is repeatedly discharged. Therefore, the individual negative pressure ink chambers 5 are separated for each pressure chamber 4, making it possible both to quickly restore the swelling of the meniscus M and to suppress the above-described crosstalk between the channels. If the state of the meniscus M of the ink in the nozzle 3 is stabilized, stable high-quality high-speed printing becomes possible. Therefore, for example, even when high-speed continuous discharge is performed at a frequency of 50 kHz, the discharge state of the ink is stabilized.

[0040] Next, the filling of ink into the inkjet head 100 will be described. FIG. 11 schematically shows the state in which the pressure chamber 4, the ink standby chamber 42, and the individual negative pressure ink chambers 5 are filled with ink when the inkjet head 100 is arranged in the posture where the nozzle 3 is located on the bottom surface side as illustrated in FIG. 1. The ink is filled, for example, by supplying ink from the ink supply pressure adjusting device 321 in FIG. 1. The ink from the ink supply manifold 44 flows into the ink standby chamber 42 through the constriction 43 as shown in FIG. 11(a), filling the interior of the ink standby chamber 42. Further, as shown in FIG. 11(b), the interior of each pressure chamber 4 is filled, and a meniscus M of ink is formed in the nozzle 3. Further, as shown in FIG. 11(c), the ink fills the interior of the individual negative pressure ink chambers 5. However, for example, the air remaining in the chamber due to the discharge hole 31 being wetted with ink accumulates in the concave air reservoir portion 51 thereafter.

[0041] That is, even if air remains in the individual negative pressure ink chamber 5 during ink filling, it can be accumulated in the air reservoir portion 52. As a result, for example, it is possible to suppress the influence on the ink ejection operation such as air entering the pressure chamber 4. Furthermore, the air in the individual negative pressure ink chamber 5 can also be expected to function as a buffer for suppressing residual vibration when the ink is ejected. The air reservoir portion 52 is preferably formed at a position as far as possible from the open end of the pressure chamber 4. In addition, when the residual air is so small that it can be ignored, such as when the pressure chamber 4, the ink standby chamber 42, and the individual negative pressure ink chamber 5 are depressurized and filled with ink, the air reservoir portion 52 and the discharge hole 31 may be omitted.

[0042] According to the above-described embodiment, it is possible to return the meniscus M of the ink in the nozzle 3 that has swelled outward due to ejection. Note that the ink standby chamber 42 side does not necessarily have to be separated for each channel, and may be a common ink chamber that communicates between the channels. In this case, the constriction portion 43 and the ink supply manifold 44 may also be omitted, and the common ink chamber and the ink flow path 311 may be communicated.

[0043] The inkjet head 100 is not limited to a form in which the nozzle 3 is used in a posture where the nozzle 3 is located on the bottom surface side as illustrated in FIG. 1. The inkjet head 100 may be used, for example, in a posture where the nozzle 3 faces the lateral direction, or may face a direction other than the lateral direction. When the nozzle 3 is not vertically downward, in order to minimize the volume of the gas remaining in the individual negative pressure ink chamber 5 after filling, the position of the discharge hole 31 is arranged far from the pressure chamber 4 and at a high position on the side opposite to the direction of gravity as much as possible, and it is desirable to abolish the air reservoir portion 52 or arrange it at a position higher than the discharge hole 31. The position and presence or absence of the discharge hole 31 and the air reservoir portion 52 can be determined in consideration of the posture of the inkjet head 100 during use and the direction in which gravity acts.

[0044] The inkjet head 100 is not limited to the shear mode actuator 6 in which a plurality of pressure chambers 4 are arranged. It may be a drop-on-demand piezo type actuator or the like.

[0045] In the above embodiment, the inkjet head 100 of the inkjet printer 10 has been described as an example of a liquid ejection head. However, the liquid ejection head may be a modeling material ejection head of a 3D printer or a sample ejection head of a dispensing device.

[0046] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0047] 10 Inkjet printer 100 to 103 Inkjet head 2 Head unit 22 Nozzle plate 23 Actuator substrate 3 Nozzle 31 Discharge hole 4 Pressure chamber 41 Piezoelectric member 42 Ink standby chamber 43 Constriction 44 Ink supply manifold 5 Individual negative pressure ink chamber 52 Air reservoir part 6 Actuator

Claims

1. A nozzle section forming a plurality of nozzles for discharging liquid, A plurality of pressure chambers respectively communicating with each of the nozzles, An actuator that changes the volume of each of the pressure chambers and causes a pressure change due to longitudinal liquid column resonance in the pressure chamber in each of the pressure chambers, A first liquid chamber communicating with one open end in the longitudinal direction of each of the pressure chambers and further communicating with a liquid supply passage, A second liquid chamber of a dead end separated for each of the pressure chambers and communicating with the other open end in the longitudinal direction of each of the pressure chambers. A liquid discharge head characterized by comprising.

2. The liquid discharge head according to claim 1, wherein the second liquid chamber forms an opening hole smaller than the nozzle on the same surface as the nozzle.

3. The liquid discharge head according to claim 1 or 2, wherein the second liquid chamber forms a concave air reservoir portion at a position opposite to the direction in which gravity acts.

4. The liquid discharge head according to claim 3, wherein the outer periphery of the concave air reservoir portion is formed in an inclined shape.

5. The liquid discharge head according to any one of claims 1 to 4, wherein the first liquid chamber is formed separately for each of the pressure chambers and communicates with a liquid supply manifold via a constriction.

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