Liquid dispensing head

Abstract

To provide a liquid discharge head equipped with a vibration plate that can transmit force from an actuator uniformly.SOLUTION: A liquid discharge head according to an embodiment comprises pressure chambers, a vibration plate, hard particles, and an actuator. The pressure chambers communicate with a nozzle that discharges liquid. The vibration plate forms portions of bulkheads of the plurality of pressure chambers. The hard particles are distributed in a resin layer formed on an outer surface of the vibration plate. The actuator applies force to the vibration plate through the hard particles. The resin layer in which the hard particles are dispersed is formed on the outer surface of the vibration plate, ranging from a region contacting the actuator up to positions of the bulkheads separating the adjacent 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 for supplying 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, etc. 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, a diaphragm constituting a part of the partition wall of the pressure chamber, and an actuator for applying a force to the diaphragm to change 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 applies a force to the diaphragm, the volume of the pressure chamber filled with liquid changes, and liquid is ejected from the nozzle. However, since the diaphragm is formed of a material that is easily bent, it is difficult for the force from the actuator to be transmitted.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem that this invention aims to solve is to provide a liquid discharge head equipped with a diaphragm capable of uniformly transmitting force from an actuator. [Means for solving the problem]

[0006] An embodiment of the present invention comprises a liquid discharge head, a diaphragm, hard particles, an actuator, and a support column. The pressure chamber communicates with a nozzle for discharging liquid. The diaphragm forms part of the partition walls of a plurality of the pressure chambers. The hard particles are distributed in a resin layer formed on the outer surface of the diaphragm. The actuator extends toward the diaphragm and applies force to the diaphragm via the hard particles. The support column uses a common piezoelectric element and internal electrodes. Applying force to the diaphragm An actuator that is not used for discharging liquid, formed together with the actuator, and adjacent to the aforementioned Applying force to the diaphragm It is provided between actuators via a groove. The resin layer in which the hard particles are dispersed is the Applying force to the diaphragm The resin layer, in which the hard particles are dispersed, is formed on the outer surface of the diaphragm from the area in contact with the actuator to the position of the partition wall separating the adjacent pressure chambers, and the diaphragm is sandwiched between the support column and the partition wall. [Brief explanation of the drawing]

[0007] [Figure 1] This is an overall configuration diagram of an inkjet printer equipped with an inkjet head according to an embodiment. [Figure 2] The above is a perspective view of the inkjet head. [Figure 3] This is a partially enlarged cross-sectional view of the head portion of the inkjet head shown above. [Figure 4] This is a partially enlarged cross-sectional view of the head portion of the inkjet head shown above. [Figure 5] This is a partially enlarged plan view of the head portion of the inkjet head shown above. [Figure 6] This diagram illustrates the assembly process of the inkjet head shown above. [Figure 7]This is a circuit diagram of the control system for the inkjet head shown above. [Figure 8] This is the drive waveform applied to the actuator of the inkjet head described above. [Figure 9] This is a diagram illustrating the operation of the actuator described above. [Modes for carrying out the invention]

[0008] The liquid discharge head according to the embodiment will be described in detail below with reference to the attached drawings. In each drawing, identical components are denoted by the same reference numerals.

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

[0010] The image data to be printed on sheet S is generated, for example, by an externally connected device, such as a computer 200. The image data generated by the computer 200 is sent to the control board 17 of the inkjet printer 10 via cable 201 and connectors 202 and 203.

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

[0012] The conveyor belt 14 is a mesh-like endless belt with numerous through holes formed on its surface. Three rollers, a drive roller 141 and driven rollers 142 and 143, rotatably support the conveyor belt 14. A motor 205 rotates the conveyor belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive device. In the figure, 105 indicates the direction of rotation of the conveyor belt 14. A negative pressure container 206 is placed on the back side of the conveyor belt 14. The negative pressure container 206 is connected to a pressure-reducing fan 207. The fan 207 creates negative pressure inside the negative pressure container 206 with the airflow it generates, causing the sheet S to adhere to and hold on the upper surface of the conveyor belt 14. In the figure, 106 indicates the flow of the airflow.

[0013] Inkjet heads 100-103, which are examples of liquid ejection heads, are positioned opposite a sheet S held by suction on a transport belt 14, with a small gap of, for example, 1 mm between them. Each inkjet head 100-103 ejects droplets of ink toward the sheet S. The inkjet heads 100-103 print an image as the sheet S passes below them. Each inkjet head 100-103 has the same structure except that it ejects a different color of ink. The ink colors are, for example, cyan, magenta, yellow, and black.

[0014] Each of the inkjet heads 100-103 is connected to ink tanks 315-318 and ink supply pressure regulators 321-324 via ink channels 311-314. Each ink tank 315-318 is positioned above each of the inkjet heads 100-103. To prevent ink leakage from the nozzles 24 (see Figure 2) of the inkjet heads 100-103 during standby, each ink supply pressure regulator 321-324 adjusts the pressure inside each inkjet head 100-103 to a negative pressure relative to atmospheric pressure, for example, -1.2kPa. During image formation, the ink from each ink tank 315-318 is supplied to each of the inkjet heads 100-103 by the ink supply pressure regulators 321-324.

[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 is composed of feed roller pairs 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 discharge port 157 to the discharge tray 16 via the downstream conveyance path 15. Arrow 107 in the figure indicates the conveyance path of the sheet S.

[0016] Subsequently, the configuration of the inkjet heads 100 to 103 will be described. The following describes the inkjet head 100 while referring to FIGS. 2 to 9, but the inkjet heads 101 to 103 also 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 which is an example of a film wiring board. The flexible printed wiring board 21 is connected to a printed board 22 which is an example of a relay board. The head portion 2 includes a nozzle plate 23 which is an example of a nozzle portion. The head portion 2 is connected to the ink supply pressure adjustment device 321 in FIG. 1 via an ink flow path 311.

[0018] The nozzles 24 of each channel for ejecting ink are arranged along, for example, the X direction in the first direction of the nozzle plate 23. The nozzle density is set, for example, within the range of 150 to 1200 dpi. The nozzles 24 are not limited to a single row and may be multiple rows. The detailed configuration of the head portion 2 will be described later.

[0019] The flexible printed circuit board 21 is a flexible printed circuit board made of a synthetic resin film such as polyimide. The flexible printed circuit board 21 is equipped with a driver chip, which is an integrated circuit (IC) 3 (hereinafter referred to as the driver IC). The printed circuit board 22 is a rigid through-hole board made by laminating multiple layers of glass fiber-reinforced epoxy resin and copper wiring layers. The driver IC 3, acting as a control unit, temporarily stores the print data sent from the control board 17 of the inkjet printer 10 via the printed circuit board 22 and provides drive signals to each channel to eject ink at predetermined timings.

[0020] Figures 3 to 5 are partial cross-sectional views of the head portion 2. The nozzle plate 23 is bonded to one surface of the pressure chamber substrate 4. The nozzle plate 23 is a rectangular plate formed of, for example, a resin such as polyimide or a metal such as stainless steel. The diaphragm 41 is bonded to one surface of the pressure chamber substrate 4 opposite to the nozzle plate 23. The diaphragm 41 is flexible and deforms when an external force is applied. The diaphragm 41 is a thin plate formed of, for example, a metal such as stainless steel. The thickness of the diaphragm 41 is, for example, 4 μm. The material of the diaphragm 41 may be something other than metal, such as a polyimide film.

[0021] The pressure chambers 42 are formed in the pressure chamber substrate 4. Multiple pressure chambers 42 are arranged at the positions of each nozzle 24 and communicate with each nozzle 24. The pressure chamber substrate 4 is made of a metal such as stainless steel. As an example, the pressure chambers 42 are formed by creating a rectangular opening in the pressure chamber substrate 4 that penetrates in a second direction, for example in the Z direction, and closing the openings on both sides with a nozzle plate 23 and a diaphragm 41, respectively. That is, the diaphragm 41 is shared by multiple pressure chambers 42 and constitutes part of the partition wall of each of the multiple pressure chambers 42 (see Figure 4).

[0022] The pressure chamber 42 communicates with a guide channel 43 having a constricted section, and further communicates with an ink supply manifold 45 via an ink supply port 44, which is an opening that penetrates the diaphragm 41 and the resin layer 5. The guide channel 43 is formed in a groove shape in a third direction, for example in the Y direction, on one surface of the pressure chamber substrate 4 on the diaphragm 41 side, for each pressure chamber 42. The ink supply manifold 45 is formed within a frame 46 joined to one surface of the diaphragm 41 with the resin layer 5 in between. The ink supply manifold 45 extends in the X direction and communicates with the pressure chamber 42 of each channel via the ink supply port 44 and guide channel 43 of each channel. The ink supply manifold 45, as a common ink chamber, communicates with the ink channel 311 (see Figures 1 and 2).

[0023] The hard particles 50 are laid out on the outer surface of the diaphragm 41 as viewed from the pressure chamber 42, and the gaps are filled with binder resin 51 to fix the particles in place. In other words, the hard particles 50 are dispersed within the resin layer 5 formed by the binder resin 51. The resin layer 5 in which the hard particles 50 are dispersed is formed, for example, by applying a fluid binder resin 51 mixed with the hard particles 50 to the outer surface of the diaphragm 41 and curing the binder resin 51. A thermosetting epoxy resin is preferred for the binder resin 51. The hard particles 50 only need to be randomly dispersed on the outer surface of the diaphragm 41. However, it is desirable that the particles do not overlap in the thickness direction (i.e., the Z direction) of the resin layer 5. The average particle diameter of the hard particles 50 is, for example, 4 μm.

[0024] The hard particles 50 are particles that are at least harder than the binder resin 51 (after curing). The material of the hard particles 50 may be metal, glass, silica, etc. Particles of these materials have the advantage of being easy to standardize in size. A metal example is nickel (Ni). When conductive hard particles 50 such as metal are used, they may be used, for example, in electrodes or wiring. The hard particles 50 may contain particles of different materials as long as the particle sizes are uniform.

[0025] The actuator 6 is positioned on the outer surface of the diaphragm 41 with hard particles 50 interposed between them. That is, the hard particles 50 are in contact with both the actuator 6 and the diaphragm 41. Therefore, the particle diameter of the hard particles 50 determines the distance between the diaphragm 41 and the actuator 6. As mentioned above, if the diaphragm 41 is made of stainless steel with a thickness of, for example, 4 μm, then the diameter of the hard particles 50 and the thickness of the diaphragm 41 are the same.

[0026] The actuators 6 for each channel are arranged in positions facing the pressure chamber 42 and the guide channel 43, with the diaphragm 41 and hard particles 50 in between. The actuators 6 and the diaphragm 41 may be joined using the binder resin 51 that forms the resin layer 5 as an adhesive. Each actuator 6 is fixed by joining one side opposite to the diaphragm 41 in the Z direction to the support member 47. The frame 46 may also be joined using the binder resin 51 that forms the resin layer 5 as an adhesive. In Figure 3, the hard particles 50 are dispersed across the entire upper surface of the diaphragm 41, but for example, by using different adhesives, the area where the frame 46 is placed may be covered only with the binder resin 51.

[0027] The actuator 6 is a laminated piezoelectric actuator formed by alternately stacking piezoelectric elements 61, such as a piezo element, a first internal electrode 62, and a second internal electrode 63 in layers (see Figure 3 in particular). Each piezoelectric element 61 is arranged with its polarization direction opposite to that of the other in the Z direction, for example, and is deformed in d33 mode. The first internal electrode 62 and the second internal electrode 63 are conductive films formed on the main surface of the piezoelectric element 61, respectively. The first internal electrode 62 is formed to one end face of the actuator 6 in the Y direction and is connected to a first external electrode 64 formed on this end face. The second internal electrode 63 is formed to the other end face of the actuator 6 in the Y direction and is connected to a second external electrode 65 formed on this end face. The dummy layer 68 is made of the same material as the piezoelectric element 61. However, the dummy layer 68 does not deform because it has internal electrodes on only one side and no electric field is applied to it. The dummy layer 68 serves as a base for fixing the actuator 6 to the support member 47 (see Figure 4 in particular), or as a polishing surface to achieve accuracy during or after assembly.

[0028] In an actuator 6 formed by stacking multiple piezoelectric elements 61, as an example, a first internal electrode 62 and a second internal electrode 63 are deposited on the main surface of each piezoelectric element 61, which has been processed into a thin plate shape. The piezoelectric elements 61 are then stacked and fired, and a voltage is applied between the first internal electrode 62 and the second internal electrode 63 to polarize the piezoelectric elements 61. Subsequently, a first external electrode 64 and a second external electrode 65 are deposited. The piezoelectric elements 61 are formed from lead-containing piezoelectric materials such as lead zirconate titanate (PZT) or lead-free piezoelectric materials such as sodium potassium niobate. The first internal electrode 62 and the second internal electrode 63 are deposited from a sinterable conductive material such as silver palladium. The first external electrode 64 and the second external electrode 65 are deposited from Ni, Cr, Au, etc., using known methods such as plating or sputtering.

[0029] The first external electrode 64 of each actuator 6 is connected to the individual wiring 66 of the flexible printed circuit board 21 (see Figure 3). The flexible printed circuit board 21 has a base material 26, individual wiring 66, an adhesive layer 27, and an insulating layer 28. The flexible printed circuit board 21 is arranged so that the area where the solder plating layer 29 is formed faces the first external electrode 64, and the first external electrode 64 and individual wiring 66 of each channel are electrically and mechanically connected by melting solder. On the other hand, the second external electrode 65 of each channel is connected to a common wiring (not shown) and is connected to a common potential, for example, via the flexible printed circuit board 21.

[0030] Between the actuators 6 of each channel, actuators 60 with a similar configuration to actuator 6 are arranged via grooves 69, and may, for example, serve as support columns. Actuators 6 and 60 are formed together using a common piezoelectric element 61, a first internal electrode 62, and a second internal electrode 63, and are separated into individual actuators 6 and 60 by forming grooves 69. The actuators 60 that serve as support columns are positioned at the partition wall 40 between adjacent pressure chambers 42 (see Figure 4). Hard particles 50 are also laid between these support columns and the diaphragm 41. This allows the support columns to be supported by hard particles 50 that are harder than the binder resin 51. Actuators 60 are not used for ink ejection, but may be used for ink ejection. Therefore, the actuators 60 that serve as support columns do not necessarily need to have a first external electrode 64 and a second external electrode 65, but may also have them. Note that the support columns may be formed from a different material instead of being composed of actuators 60 with a similar configuration to actuator 6. For example, the support member 47 may be integrally formed with the support column.

[0031] As an example, the head section 2 described above is manufactured by forming a first structure by joining a nozzle plate 23, a pressure chamber substrate 4 with a pressure chamber 42, and a diaphragm 41 to each other, and a second structure by joining an actuator 6, a support column (actuator 60), and a support member 47 to each other, as shown in Figure 6. After applying an uncured binder resin 51 containing hard particles 50 to the diaphragm 41, positioning the actuator 6 so that its position coincides with the center of the pressure chamber 42, and then heat-curing the binder resin 51. When joining the first structure and the second structure, the actuator 6 presses against the uncured binder resin 51 containing the hard particles 50, so that the hard particles 50 do not overlap in the thickness direction.

[0032] Figure 7 is a circuit diagram of the control system of the inkjet head 100. As shown in Figure 7, the actuator 6 connects the first external electrode 64 to individual wiring 66, and connects to the output terminal of the drive IC 3 via the individual wiring 66. The connection point between the first external electrode 64 and the individual wiring 66 is the individual terminal of the actuator 6. The second external electrode 65 is connected to common wiring 67, and connects to a common potential via the common wiring 67. The connection point between the second external electrode 65 and the common wiring 67 is the common terminal of the actuator 6.

[0033] The individual wiring 66 from the individual terminals of each actuator 6 is connected to the output terminals of the drive driver D (i.e., the drive circuit) of the drive IC 3. The drive IC 3 is connected to the power supply 7 for the drive voltage V1 and the power supply 71 for the drive voltage V2 supplied to the actuator 6. The positive terminals of power supplies 7 and 71 are connected to the drive IC 3, and the negative terminals are connected to ground (GND). The drive IC 3 is connected to the signal lines of the print data sent from the control board 17 (see Figure 1) of the inkjet printer 10. Print data is an example of a control signal. The common wiring 67 from the common terminal of each actuator 6 is connected to ground (GND).

[0034] Next, the ink ejection operation will be explained with reference to Figures 8 and 9. Each drive driver D of the drive IC3 uses drive voltages V1, V2 and ground (GND) to provide a drive waveform to the individual terminals of each actuator 6. Voltage V1 is, for example, 20V. Voltage V2 is, for example, 10V. Ground (GND) is, for example, 0V. Which actuator 6 to drive is determined, for example, based on the print data. Figure 8 is an example of a drive waveform provided to the actuator 6.

[0035] As shown in Figure 8, the actuator 6 is put into a standby state by applying a voltage V2 to its individual terminals. When a voltage V2 is applied, an electric field is applied in the direction of the polarization axis of the piezoelectric element 61, and as shown in Figure 9(a), the actuator 6 extends in the stacking direction (Z direction), causing the volume of the pressure chamber 42 to contract. Then, at time t1 in Figure 8, the potential of the individual terminals is lowered to ground (GND), causing the actuator 6 to return to its original position, as shown in Figure 9(b), and the volume of the pressure chamber 42 to expand relatively. Due to the expansion of the volume of the pressure chamber 42, ink flows into the pressure chamber 42 via the guide channel 43. Then, for example, after a time elapsed of half the pressure oscillation period of the head unit 2, when a voltage V2 is applied to the individual terminals at time t2 in Figure 8, as shown in Figure 9(c), the actuator 6 extends in the stacking direction (Z direction), causing the volume of the pressure chamber 42 to contract, and ink droplets R are ejected from the nozzle 24. For example, after half the pressure vibration period of the head unit 2 has elapsed, when a voltage V1 is applied to the individual terminals at time t3 in Figure 8, the actuator 6 extends further in the stacking direction (Z direction), as shown in Figure 9(d), causing the volume of the pressure chamber 42 to contract. Then, at time t4, the actuator 6 and pressure chamber 42 are returned to the initial state shown in Figure 9(a), thereby damping the residual vibration. In this way, the volume of the pressure chamber 42 changes in accordance with the longitudinal vibration of the actuator 6 in the stacking direction, enabling ink to be ejected. After that, a voltage V2 is applied to the individual terminals to put the printer into standby mode.

[0036] As schematically shown in Figures 9(a) to (d), when the actuator 6 contracts in the stacking direction (Z direction), the diaphragm 41 deforms, particularly in the area corresponding to the groove 69. For example, when the nozzle density is 300 dpi, the pitch of the pressure chamber 42 is 169 μm. The width of the pressure chamber 42 is approximately 80 μm, the width of the actuator 6 is approximately 40 μm, and the width of the groove 69 is 20 μm. Multiple hard particles 50 are also present in the groove 69. The diaphragm 41, in which a resin layer 5 formed of hard particles 50 and binder resin 51 is formed on the outer surface from the area in contact with the actuator 6 to the position of the partition wall 40 separating adjacent pressure chambers 42, is easily deflected in the deflection direction due to the elasticity of the binder resin 51, and therefore deformation is not easily hindered. Subsequently, when the actuator 6 extends in the stacking direction (Z direction) to eject ink, the diaphragm 41 is pushed by the actuator 6. However, because the diaphragm 41, which has a resin layer 5 formed of hard particles 50 and binder resin 51 on its outer surface, is hard in the thickness direction, the force received from the actuator 6 is easily transmitted. As a result, the force from the actuator 6 can be transmitted uniformly. The same is true when the actuator 6 is extended to dampen residual vibrations.

[0037] As described above, according to the above embodiment, it is possible to provide an inkjet head 100 equipped with a diaphragm 41 that can uniformly transmit force from the actuator 6. Since the stacked piezoelectric actuator with the above configuration has a large amount of deformation in the Z direction, the effect of this embodiment is significant.

[0038] Furthermore, the actuator 6 is not limited to a stacked type in which multiple piezoelectric elements 61 are stacked. It may also be an actuator with a single layer of piezoelectric elements 61. In addition, the operation of the actuator when a drive voltage is applied is not limited to longitudinal vibration. Moreover, it may be applied not only to the drop-on-demand piezo method but also to the continuous method.

[0039] In the above-described embodiment, the inkjet head 100 of the inkjet printer 10 was described as an example of a liquid ejection device, but the liquid ejection device may also be the material ejection head of a 3D printer or the sample ejection head of a dispensing device.

[0040] 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 carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0041] 10 Inkjet Printers 100-103 Inkjet head 2 Head section 24 nozzles 3. Drive IC 41 Vibration plate 50 hard particles 51 Binder resin 6 Actuators 60 Actuator (support column) D Drive driver (drive circuit)

Claims

1. A pressure chamber communicating with a nozzle that discharges liquid, A diaphragm that forms part of the partition wall of multiple pressure chambers, Hard particles dispersed in the resin layer formed on the outer surface of the diaphragm, An actuator that extends toward the diaphragm and applies force to the diaphragm via the hard particles, An actuator that applies force to the diaphragm using a common piezoelectric element and internal electrodes, and an actuator that is not used for discharging liquid, formed together, comprising a support column provided between adjacent actuators that apply force to the diaphragm via a groove, The resin layer in which the hard particles are dispersed is formed on the outer surface of the diaphragm from the region in contact with the actuator that applies force to the diaphragm to the position of the partition wall separating the adjacent pressure chambers. A liquid dispensing head characterized in that the resin layer in which the hard particles formed up to the position of the partition wall are dispersed, and the diaphragm, are sandwiched between the support column and the partition wall.

2. The liquid discharge head according to claim 1, characterized in that the hard particles dispersed in the resin layer have the same particle size and each is in contact with both the diaphragm and the actuator that applies force to the diaphragm.

3. The liquid dispensing head according to claim 1, characterized in that the hard particles are randomly dispersed.

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