JP2017128099A - Inkjet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet head that can increase durability of an actuator and stably discharge an ink droplet.SOLUTION: The inkjet head includes: an oscillation plate; a pressure chamber provided on one face side of the oscillation plate; a discharge hole communicated to the pressure chamber and penetrating through the oscillation plate; an actuator for oscillating the oscillation plate to discharge an ink droplet from the discharge hole; a protective layer provided at a surface of the oscillation plate on an opposite side to the pressure chamber while being superposed on the actuator; and a liquid repellent layer provided at a surface of the protective layer.SELECTED DRAWING: Figure 4

Description

  Embodiments described herein relate generally to an inkjet head that changes the volume of a pressure chamber filled with ink and ejects ink droplets from an ink meniscus of a nozzle provided in the pressure chamber.

  2. Description of the Related Art Conventionally, ink jet printers that form images and characters by ejecting ink droplets onto a medium such as paper are known. This type of ink jet printer has, for example, an ink jet head including a plurality of sets of pressure chambers and actuators filled with ink.

  The actuator includes, for example, a diaphragm that forms part of the wall of the pressure chamber, a piezoelectric element attached to the diaphragm, and a wiring that supplies power to the piezoelectric element. When the actuator is operated by supplying power to the piezoelectric element, the diaphragm is deformed to change the volume of the pressure chamber, pressure vibration is generated in the ink in the pressure chamber, and ink droplets are ejected from the nozzles provided on the diaphragm.

In this type of ink jet head, a protective film that covers the piezoelectric element is provided on the diaphragm so as to increase the durability of the actuator. The protective film is made of, for example, a relatively hard material such as SiO ₂ or SiN, and prevents cracks from occurring in the piezoelectric body and electrodes of the piezoelectric element.

JP 2011-56939 A

However, if a protective film formed of a relatively hard material such as SiO ₂ or SiN is provided on the diaphragm, the deformation of the diaphragm may be hindered, making it difficult to eject ink droplets. For this reason, if the protective film is thinly provided so as not to adversely affect the ejection of ink droplets, there is a problem that moisture in the air reaches the electrode through the protective film and corrodes.

  Therefore, development of an ink jet head that can enhance the durability of the actuator and can stably eject ink droplets is desired.

  An ink jet head according to an embodiment includes a vibration plate, a pressure chamber provided on one surface side of the vibration plate, a discharge hole provided through the vibration plate so as to communicate with the pressure chamber, and a vibration plate. An actuator that ejects ink droplets from the ejection holes, a protective layer of an inorganic insulating material provided on the surface of the diaphragm opposite to the pressure chamber, and a liquid repellent layer provided on the surface of the protective layer. .

FIG. 1 is a perspective view illustrating an inkjet head according to an embodiment. FIG. 2 is a plan view showing an actuator substrate of the inkjet head of FIG. FIG. 3 is a partially enlarged plan view in which a part of the actuator substrate of FIG. 2 is enlarged. 4 is a partially enlarged cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a partially enlarged cross-sectional view taken along line V-V in FIG. FIG. 6 is a bottom view of the flow path substrate of the inkjet head of FIG. 1 as viewed from the ink supply member side. 7 is a partially enlarged bottom view in which the bottom surface of the flow path substrate of FIG. 6 is partially enlarged. FIG. 8 is a plan view of the ink supply member of the inkjet head of FIG. 1 as viewed from the flow path substrate side.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is an external perspective view showing the inkjet head 1. The inkjet head 1 has a structure in which an actuator substrate 2, a flow path substrate 3, and an ink supply member 4 are stacked. In addition, the inkjet head 1 includes a driver IC 5.

  The actuator substrate 2, the flow path substrate 3, and the ink supply member 4 are bonded to each other by, for example, an epoxy adhesive. The actuator substrate 2 and the driver IC 5 are electrically connected by an anisotropic conductive film (ACF).

  A large number of actuators 6 are formed in an array on the actuator substrate 2. Each actuator 6 has a nozzle 7 (ejection hole) for ejecting ink droplets.

  The ink supply member 4 includes an ink supply pipe 8 for supplying ink to the inkjet head 1 and an ink discharge pipe 9 for collecting ink that has not been ejected from the nozzle 7. A tube for feeding liquid (not shown) is connected to the ink supply pipe 8 and the ink discharge pipe 9.

  The driver IC 5 generates a drive signal for each actuator 6 in response to a control signal from the ink jet printer. Each actuator 6 causes ink droplets to be ejected through the nozzle 7 in response to the drive signal.

  The ink supplied to the ink supply member 4 via the ink supply pipe 8 is supplied to the actuator substrate 2 via the flow path substrate 3. Ink droplets are ejected from the nozzles 7 in accordance with the drive signal generated by the driver IC 5. The ink that has not been ejected from the nozzles 7 is collected by the ink supply member 4 through the flow path substrate 3 and discharged through the ink discharge pipe 9.

  FIG. 2 is a partially enlarged plan view of the actuator substrate 2 viewed from the ink ejection direction. The actuator substrate 2 is provided with a plurality of actuators 6 and a plurality of extraction electrodes 31. The plurality of extraction electrodes 31 are formed of a conductive material, and a mounting pad 10 is provided at one end (the lower end in the drawing) of each extraction electrode 31. The plurality of extraction electrodes 31 include a plurality of individual electrodes 11 individually extracted from each actuator 6 and a plurality of (in this embodiment, eight) actuators 6 connected in a straight line. A common electrode 12.

  The individual electrode 11 electrically connects a lower electrode 14 (described later) of each actuator 6 and the mounting pad 10. The individual electrodes 11 are electrically independent from each other. Further, the common electrode 12 connects upper electrodes 16 (described later) of the plurality of actuators 6 in series and is electrically connected to the mounting pad 10.

  The plurality of mounting pads 10 provided on the plurality of extraction electrodes 31 are electrically connected to the driver IC 5. An anisotropic conductive film (ACF) can be used for the connection between the mounting pad 10 and the driver IC 5. In addition, the mounting pad 10 may be connected to the driver IC 5 by a method such as wire bonding.

FIG. 3 is a partially enlarged plan view showing the actuator 6 further enlarged. FIG. 4 is a cross-sectional view of the actuator substrate 2 taken along the line IV-IV in FIG.
The actuator 6 includes a vibration plate 13, a lower electrode 14, a piezoelectric body 15, an upper electrode 16, an insulating layer 17, a common electrode 12, a protective layer 18, and a liquid repellent layer 19. A nozzle 7 is provided at the center of the actuator 6. The nozzle 7 is a circular discharge hole that penetrates the diaphragm 13. The lower electrode 14, the piezoelectric body 15, and the upper electrode 16 have a substantially annular shape surrounding the nozzle 7.

  The diaphragm 13 is supported by the actuator substrate 2. In the present embodiment, the pressure chamber 20 is formed in the actuator substrate 2 by etching the constituent material of the actuator substrate 2 from the back side while the diaphragm 13 is stacked on the actuator substrate 2. That is, a cylindrical internal space that functions as the pressure chamber 20 is provided on the back side of the actuator 6. The nozzle 7 provided in the vibration plate 13 communicates with the internal space of the pressure chamber 20.

  The inner diameter of the nozzle 7 and the inner diameter of the pressure chamber 20 are determined in consideration of the desired ink discharge volume, driving frequency, and driving voltage. In this embodiment, the inner diameter of the nozzle 7 is 20 μm, and the inner diameter of the pressure chamber 20 is 200 μm. The nozzle 7 and the pressure chamber 20 are disposed concentrically along the central axis C.

  The actuator substrate 2 is made of single crystal silicon having a thickness of 50 μm. The thickness of the actuator substrate 2 is desirably 1/2 or less of the diameter of the pressure chamber 20. As a result, when ink flowing from the individual ink supply path 21 described later flows out to the individual ink discharge path 22 described later, the entire ink in the pressure chamber 20 flows, and bubbles in the pressure chamber 20 can be easily discharged.

  On the other hand, if the thickness of the actuator substrate 2 is larger than ½ of the diameter of the pressure chamber 20, the ink flow near the back surface of the vibration plate 13 becomes poor, and it becomes difficult to remove bubbles that enter from the nozzle 7.

The diaphragm 13 is laminated integrally with the actuator substrate 2 so as to cover the upper surface of the pressure chamber 20. The material of the diaphragm 13 is SiO ₂ and can be formed by heating a silicon wafer to be the actuator substrate 2 at a high temperature. In the present embodiment, the thickness of the diaphragm 13 is 4 μm.

  On the surface side of the diaphragm 13, a lower electrode 14, a piezoelectric body 15, and an upper electrode 16 are formed in a donut shape with the nozzle 7 as a center. The inner diameter of the piezoelectric body 15 and the upper electrode 16 was 30 μm, and the outer diameter of the piezoelectric body 15 and the upper electrode 16 was 140 μm. The lower electrode 14 and the upper electrode 16 are made of a conductive material. In this embodiment, Pt is deposited by sputtering to form the lower electrode 14 and the upper electrode 16.

  The piezoelectric body 15 is made of a piezoelectric material. In this example, the piezoelectric body 15 was formed by depositing PZT (lead zirconate titanate) by sputtering. PZT may be formed by a sol-gel method or the like. The material of the piezoelectric body 15 is not limited to PZT, and KNN (potassium sodium niobate) or the like may be used. The thicknesses of the upper electrode 16 and the lower electrode 14 are 0.1 to 0.2 μm. The thickness of the piezoelectric body 15 was 2 μm.

  When a voltage is applied between the lower electrode 14 and the upper electrode 16, an electric field acts on the piezoelectric body 15, and the piezoelectric body 15 expands in the film thickness direction due to the inverse piezoelectric effect, and as a result, is orthogonal to the film thickness direction. Shrink in the direction you want. Due to the contraction of the piezoelectric body 15, the upper surface of the vibration plate 13 is contracted, and the actuator 6 is deformed in a direction in which the actuator 6 protrudes toward the pressure chamber 20 in a movable region of the actuator 6, that is, a region where the vibration plate 13 faces the pressure chamber 20. To do. As a result, the vibration plate 13 is deformed to cause a pressure fluctuation in the ink in the pressure chamber 20, and an ink droplet is ejected through the nozzle 7.

An insulating layer 17 made of an insulating inorganic material is provided on the surface of the upper electrode 16. The insulating layer 17 can be formed by depositing SiO ₂ by TEOS-CVD. In the present embodiment, the thickness of the insulating layer 17 is 0.5 μm. The insulating layer 17 is provided between the lower electrode 14 and the common electrode 12 in order to ensure insulation between the lower electrode 14 and the common electrode 12 in the outer peripheral portion of the piezoelectric body 15.

  If the insulating layer 17 is present in the movable region of the actuator 6, the operation of the actuator 6 is hindered. Therefore, it is desirable to make the portion of the insulating layer 17 that overlaps the movable region of the actuator 6 as small as possible. Therefore, in this embodiment, the insulating layer 17 is not formed in most of the movable region of the actuator 6.

  The presence of the insulating layer 17 affects the shape when the actuator 6 is deformed. That is, the deformation of the actuator 6 is small at the portion where the insulating layer 17 overlaps, and the deformation is large at the other portion. Therefore, when the insulating layer 17 is formed in an asymmetric shape with respect to the center of the nozzle 7 so as to overlap the movable region of the actuator 6, the deformation of the actuator 6 becomes asymmetric with respect to the center of the nozzle 7. There is a possibility that the flying direction of the ejected ink droplet is inclined. Therefore, it is necessary to arrange the insulating layer 17 so as to overlap with the symmetrical shape with respect to the center of the nozzle 7 in the movable region of the actuator 6.

  In the present embodiment, as shown in FIG. 3, an insulating layer 17 is disposed between two actuators 6 adjacent to each other along the common electrode 12, and the insulating layer 17 is placed symmetrically with respect to the center of each actuator 6. Each actuator 6 was overlaid. In order to ensure the symmetry of the layout, for example, a dummy insulating layer 17a that does not flow current is provided over the actuator 6a disposed at the end of the row of the actuators 6.

  Further, in the present embodiment, the insulating layer 17 between the two adjacent actuators 6 is continuously formed without a break. Thereby, the level | step difference which arises in the common electrode 12 formed on the insulating layer 17 can be decreased, the malfunction that the common electrode 12 is disconnected at the level | step difference part of the cut | interruption of the insulating layer 17 can be reduced, and a high yield inkjet. Head can be provided.

  A common electrode 12 made of a conductive material is formed on the diaphragm 13, the upper electrode 16, and the insulating layer 17. A mounting pad 10 is provided at one end of the common electrode 12. The common electrode 12 electrically connects the upper electrodes 16 of the plurality of actuators 6 in the same row to the mounting pad 10. The common electrode 12 is electrically insulated from the lower electrode 14 of each actuator 6 through an insulating layer 17.

  On the other hand, the individual electrode 11 having conductivity is formed on the diaphragm 13 and the lower electrode 14. A mounting pad 10 is provided at one end of the individual electrode 11. The individual electrode 11 electrically connects the lower electrode 14 of each actuator 6 to the mounting pad 10. The individual electrodes 11 are electrically insulated from each other.

  In the present embodiment, the individual electrode 11 and the common electrode 12 are formed by depositing gold by a sputtering method. Each of the individual electrode 11 and the common electrode 12 has a thickness of 0.1 μm to 0.5 μm.

A protective layer 18 made of an insulating inorganic material is provided on the diaphragm 13, the lower electrode 14, the piezoelectric body 15, the upper electrode 16, the insulating layer 17, the individual electrode 11, and the common electrode 12. The protective layer 18 is provided on the entire surface of the actuator substrate 2 except for the region where the mounting pad 10 is formed. The protective layer 18 was formed by depositing SiO ₂ by TEOS-CVD. The thickness of the protective layer 18 is desirably 0.1 μm to 1 μm. In the present embodiment, the thickness of the protective layer 18 is 0.5 μm.

Since SiO ₂ is a relatively hard film made of an inorganic material, the lower electrode 14, the piezoelectric body 15, and the upper electrode 16 are covered with the protective layer 18, so that stress of the members 14, 15, 16 is increased by the stress accompanying the driving of the actuator 6. It can prevent that a crystal structure shifts and a crack enters. On the other hand, if the protective layer 18 is too thick, the deformation operation of the actuator 6 is hindered, causing a problem in the ink droplet ejection operation.

  The protective layer 18 protects the electrodes 14 and 16 and the piezoelectric body 15 inside the actuator 6 from ink and moisture in the air. However, if the thickness of the protective layer 18 is set to a thickness that does not hinder the operation of the actuator 6, the effect of protecting the inside of the actuator 6 from moisture cannot always be sufficiently achieved. Therefore, in this embodiment, the protective layer 18 is thinned, and a relatively soft liquid-repellent layer 19 made of resin is provided on the protective layer 18 so that moisture is not absorbed by the protective layer 18.

As material of the protective layer 18, in addition to SiO _2, for example, it may be an inorganic material such as SiN. Since SiN is less hygroscopic than SiO _2, it has a high protective effect against moisture. However, since the Young's modulus of SiO ₂ is smaller than that of SiN, the deformation operation of the actuator 6 is not easily inhibited. Therefore, the material of the protective layer 18 is appropriately selected according to requirements.

  A liquid repellent layer 19 formed of a resin having liquid repellency is provided on the entire surface of the protective layer 18. The liquid repellent layer 19 was formed by forming an amorphous fluororesin by spin coating. As the amorphous fluororesin, for example, Cytop (registered trademark) manufactured by Asahi Glass was used. The contact angle of the liquid repellent layer 19 with respect to water is 90 degrees or more. The thickness of the liquid repellent layer 19 is 0.5 μm to 5 μm. In this embodiment, the thickness of the liquid repellent layer 19 is 1 μm.

  The liquid repellent layer 19 can prevent ink from adhering to the actuator 6, and can prevent the protective layer 18 from absorbing moisture. Further, since the liquid repellent layer 19 is made of resin, the Young's modulus is relatively small, and the deformation operation of the actuator 6 is difficult to be inhibited. In addition, the liquid repellent layer 19 prevents ink from adhering to the actuator 6, and can prevent the ink 7 from being blocked by the ink adhering to the surface of the actuator 6 and hindering the ejection of ink.

  FIG. 5 is a cross-sectional view of the actuator substrate 2, the flow path substrate 3, and the ink supply member 4 along VV in FIG. 3. FIG. 6 is a bottom view of the flow path substrate 3 as viewed from the ink supply member 4 side. FIG. 7 is a partially enlarged bottom view in which the bottom surface of the flow path substrate 3 is partially enlarged. FIG. 8 is a plan view of the ink supply member 4 as viewed from the flow path substrate 3 side.

  The flow path substrate 3 includes a plurality of sets of individual ink supply paths 21 (supply paths) and a plurality of individual ink discharge paths 22 (discharge paths) respectively corresponding to the plurality of pressure chambers 20 of the actuator substrate 2. Each of the plurality of sets of individual ink supply paths 21 and individual ink discharge paths 22 has a substantially semicircular cross-sectional shape, and is provided through the flow path substrate 3. Therefore, the plurality of sets of individual ink supply paths 21 and individual ink discharge paths 22 are arranged in an array in the same pattern as the plurality of pressure chambers 20.

  When attention is paid to the pair of individual ink supply paths 21 and the individual ink discharge paths 22 facing each pressure chamber 20, the pair of flow paths 21 and 22 has a height along the thickness direction of the flow path substrate 3 over the entire length thereof. It is divided by the partition wall 29 which has. The partition walls 29 are not individually provided so as to face the plurality of pressure chambers 20, and are continuously arranged in a meander shape through the passages 21 and 22 of each set. Both ends of the partition wall 29 in the height direction are disposed on both surfaces of the flow path substrate 3.

  A shared ink supply path 23 that communicates with the plurality of individual ink supply paths 21 and a shared ink discharge path 24 that communicates with the plurality of individual ink discharge paths 22 are provided on the bottom surface of the flow path substrate 3 on the ink supply member 4 side. Is provided. The shared ink supply path 23 and the shared ink discharge path 24 have a depth less than ½ of the thickness of the flow path substrate 3. Each of the shared ink supply path 23 and the shared ink discharge path 24 has a comb-like complicated shape, and is opposed to each other with a meander-shaped partition wall 29 interposed therebetween.

  The shared ink supply path 23 includes a basic ink supply path 25 extending in the longitudinal direction of the flow path substrate 3. The shared ink discharge path 24 includes a basic ink discharge path 26 extending in the longitudinal direction of the flow path substrate 3.

  Focusing on one pressure chamber 20, the cross-sectional areas of the individual ink supply path 21 and the individual ink discharge path 22 are the same as the cross-sectional area of the pressure chamber 20. Further, by making the cross-sectional area of the individual ink supply path 21 and the cross-sectional area of the individual ink discharge path 22 the same, the ink is distributed most efficiently. If the cross-sectional area of the individual ink supply path 21 and the cross-sectional area of the individual ink discharge path 22 are greatly different, the efficiency of ink distribution is limited to the narrower cross-sectional area. Further, by making the length of the individual ink supply path 21 and the length of the individual ink discharge path 22 the same, the ink can be circulated most efficiently. If the length of the individual ink supply path 21 and the length of the individual ink discharge path 22 are significantly different, the efficiency of ink distribution is limited in the longer direction. In other words, in the present embodiment, the cross-sectional areas of the individual ink supply path 21 and the individual ink discharge path 22 communicating with each pressure chamber 20 are designed to be sufficiently large so that the ink can easily flow through each pressure chamber 20. Therefore, it is not necessary to increase the size of a pump (not shown), and power consumption can be suppressed.

  The individual ink supply path 21 and the individual ink discharge path 22 have a length of 200 μm to 1000 μm. Thereby, an inertial resistance can be imparted to the ink filling the individual ink supply path 21, and an inertial resistance can be imparted to the ink filling the individual ink discharge path 22. Therefore, according to the present embodiment, when the actuator 6 generates pressure vibration in the ink inside the pressure chamber 20, the pressure vibration escapes from the pressure chamber 20 via the individual ink supply path 21 and the individual ink discharge path 22. This can be suppressed, and ink can be easily ejected from the nozzle 7. In the present embodiment, the lengths of the individual ink supply path 21 and the individual ink discharge path 22 are each 400 μm.

  In order to give inertial resistance to the ink in the individual ink supply path 21 and the individual ink discharge path 22, the flow path connecting the individual ink supply path 21, the pressure chamber 20, and the individual ink discharge path 22 needs to be filled with ink. There is. In this case, a slight amount of bubbles generated in the pressure chamber 20 due to ejection of ink droplets may be included in the ink. That is, “the length of the individual ink supply path 21 (supply path)” and “the length of the individual ink discharge path 22 (discharge path)” in the claims and the detailed description of the invention are “filled with ink”. This means the length of the “part”.

The length required for the individual ink supply path 21 or the individual ink discharge path 22 for giving inertial resistance is obtained by applying the theory disclosed in Japanese Patent No. 5659198 to this embodiment. That is, the length of the nozzle 7 that ejects ink droplets is L1, the opening area of the nozzle 7 is S1, the lengths of the individual ink supply path 21 and the individual ink discharge path 22 are L2, and the individual ink supply path 21 When the sum of the opening areas of the individual ink discharge paths 22 is S2,
(Formula 1) L2 / S2> = L1 / S1 / 3
The length L2 of the individual ink supply path 21 and the individual ink discharge path 22 and the sum S2 of the opening areas may be set so as to satisfy the above.

For example, L1 is set to 5.5 × 10 ⁻⁶ [m], S1 is set to 3.14 × 10 ⁻¹⁰ [m ² ], L2 is set to 4 × 10 ⁻⁴ [m], and S2 is set to 3.14 × 10. ^{In the case of −8} [m ² ], L1 / S1 / 3 is 5.84 × 10 ³ [1 / m], L2 / S2 is 1.27 × 10 ⁴ [1 / m], and the formula 1 Meet. In this case, the ink in the individual ink supply path 21 and the individual ink discharge path 22 can have sufficient inertial resistance, and the ink in the pressure chamber 20 is ejected from the individual ink supply path 21 or the individual ink when ejecting ink droplets. It is possible to prevent the ink from flowing into the ink discharge path 22 and to stabilize the ejection of ink droplets.

  The partition between the individual ink supply path 21 and the individual ink discharge path 22 is defined by a partition wall 29, and the sum of the opening area of the individual ink supply path 21 and the opening area of the individual ink discharge path 22 is the cross-sectional area of the pressure chamber 20. In order to make them substantially the same, the opening diameter D (FIG. 7) of the substantially circular hole that combines the individual ink supply path 21 and the individual ink discharge path 22 is larger than the inner diameter of the pressure chamber 20. The partition wall 29 is formed so as to pass through a substantially circular center including the individual ink supply path 21 and the individual ink discharge path 22. In this embodiment, while the inner diameter of the pressure chamber 20 is 200 μm, the substantially circular opening diameter D including the individual ink supply path 21 and the individual ink discharge path 22 is 220 μm. That is, in this case, the width of the partition wall 29 is 20 μm.

  As a result, a positional deviation of up to 10 μm can be allowed along the joint surface between the actuator substrate 2 and the flow path substrate 3, the change in the opening area of the pressure chamber 20 can be suppressed, and the ink accompanying the change in the opening area Variations in ejection characteristics can be suppressed, and deterioration in print quality can be prevented.

  Further, as in this embodiment, a plurality of individual ink supply paths 21 are connected by a shared ink supply path 23, a plurality of individual ink discharge paths 22 are connected by a shared ink discharge path 24, and the basic ink supply of the shared ink supply path 23 is performed. By making the path 25 and the ink supply groove 27 of the ink supply member 4 face each other, and the basic ink discharge path 26 of the shared ink discharge path 24 and the ink discharge groove 28 of the ink supply member 4 are made to face each other, Even when the joint surface with the ink supply member 4 is displaced, the flow rate of the ink flowing through each individual ink supply path 21 and each individual ink discharge path 22 can be made constant. As a result, variations in the flow rate of ink flowing through the individual ink supply path 21 and the individual ink discharge path 22 can be suppressed, variations in ink ejection characteristics can be suppressed, and deterioration in print quality can be prevented.

  As shown in FIG. 8, an ink supply groove 27 and an ink discharge groove 28 are provided on the surface of the ink supply member 4 on the flow path substrate 3 side. The ink supply groove 27 and the ink discharge groove 28 extend along the longitudinal direction of the ink supply member 4. The ink supply groove 27 and the ink discharge groove 28 are fluidly connected to the basic ink supply path 25 and the basic ink discharge path 26 of the flow path substrate 3 in a state where the flow path substrate 3 and the ink supply member 4 are joined. . The ink supply pipe 8 is fluidly connected to one end of the ink supply groove 27, and the ink discharge pipe 9 is fluidly connected to one end of the ink discharge groove 28.

  In this embodiment, the basic ink supply path 25 and the basic ink discharge path 26 are provided on the flow path substrate 3, and the ink supply groove 27 and the ink discharge groove 28 are provided on the ink supply member 4. The supply path 25 and the basic ink discharge path 26 or the ink supply groove 27 and the ink discharge groove 28 of the ink supply member 4 may be omitted. For example, the ink supply groove 4 and the ink discharge groove 28 of the ink supply member 4 may be eliminated, the ink supply pipe 8 may be connected to the basic ink supply path 25, and the ink discharge pipe 9 may be connected to the basic ink discharge path 26. .

Subsequently, the operation of the inkjet head 1 of the present embodiment will be described.
When ink is injected from the ink supply pipe 8, the pressure chamber 20 is filled with ink through the ink supply groove 27, the basic ink supply path 25, the shared ink supply path 23, and the individual ink supply path 21. Further, the ink is discharged from the ink discharge pipe 9 through the individual ink discharge path 22, the shared ink discharge path 24, the basic ink discharge path 26, and the ink discharge groove 28.

  By making the pressure of the ink flowing through the ink supply pipe 8 higher than the pressure of the ink flowing through the ink discharge pipe 9 and adjusting the average value of both pressures to about −1000 Pa from the atmospheric pressure, the ink meniscus is placed inside the nozzle 7. Is formed. In this state, the ink from the ink supply pipe 8 to the ink discharge pipe 9 is described above without causing ink to leak from the nozzle 7 or sucking outside air through the nozzle 7 (with the ink meniscus shape stabilized). Ink can be circulated stably through the flow path.

  In this state, when the driver IC 5 generates a drive signal, the voltage between the individual electrode 11 and the common electrode 12 changes. As a result, the voltage between the lower electrode 14 and the upper electrode 16 changes, and the actuator 6 is displaced. When the actuator 6 is displaced, pressure vibration is generated in the ink in the pressure chamber 20, and an ink droplet is ejected from the nozzle 7. At this time, since the ink in the individual ink supply path 21 and the individual ink discharge path 22 has an inertial resistance, the ink can be prevented from flowing out of the pressure chamber 20 due to the pressure vibration, and the ink droplets can be ejected from the nozzle 7. Can be discharged efficiently.

  Bubbles may enter the pressure chamber 20 from the nozzle 7 during the ink ejection operation. If bubbles enter the pressure chamber 20, even if the actuator 6 is displaced, sufficient pressure vibration is not applied to the ink, and the ink is not ejected from the nozzle 7. However, since the ink inside the inkjet head 1 is constantly flowing, the bubbles that have entered the pressure chamber 20 are discharged to the shared ink discharge path 24 via the individual ink discharge path 22.

  The bubbles discharged to the shared ink discharge path 24 are discharged out of the inkjet head 1 through the basic ink discharge path 26, the ink discharge groove 28, and the ink discharge pipe 9. That is, the bubbles that have entered one pressure chamber 20 are discharged out of the inkjet head 1 without entering the other pressure chamber 20. As described above, the ink jet head 1 according to the present embodiment can automatically and effectively discharge the bubbles that have entered the pressure chamber 20, so that the ink jet head 1 with high reliability can be provided.

Then, the effect of the inkjet head 1 of this invention is demonstrated.
The ink jet 1 of the present invention is opened on the lower surface of the actuator substrate 2, and the pressure chamber 20 formed in the thickness direction of the actuator substrate 2 and the actuator 6 formed on the upper surface of the actuator substrate 2 to change the volume of the pressure chamber 20. And a nozzle 7 that is formed in the actuator 6 and ejects ink in the pressure chamber 20. The actuator 6 includes the vibration plate 13, the lower electrode 14, the piezoelectric body 15, the upper electrode 16, and the insulating layer 17. The lead electrode 31, the protective layer 18 made of an inorganic material, and the liquid repellent layer 19 made of a resin material are laminated. Since the liquid repellent layer 19 prevents ink from adhering to the surface of the actuator 6 and prevents moisture from entering the protective layer 18, the thickness of the protective layer 18 can be reduced while preventing corrosion of the electrode. Drive voltage can be reduced. Since the liquid repellent layer 19 is a resin material, it has a small Young's modulus and does not hinder the deformation of the actuator 6. That is, the present invention can achieve both reduction in driving voltage and long-term durability.

  According to the inkjet head 1 of the embodiment described above, since the liquid repellent layer 19 is provided on the protective layer 18 covering the actuator 6, the durability of the actuator 6 can be enhanced and ink droplets can be stably ejected. be able to.

  The above-described embodiments are presented as examples and are not intended to limit the scope of the invention. The above-described embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. The above-described embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and spirit of the invention.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet head, 2 ... Actuator board, 3 ... Flow path board, 4 ... Ink supply member, 5 ... Driver IC, 6 ... Actuator, 7 ... Nozzle, 8 ... Ink supply pipe, 9 ... Ink discharge pipe, 10 ... Mounting Pad 11, individual electrode, 12 common electrode, 13 diaphragm, 14 lower electrode, 15 piezoelectric body, 16 upper electrode, 17 insulating layer, 18 protective layer, 19 liquid repellent layer, 20 Pressure chamber, 21 ... Individual ink supply path, 22 ... Individual ink discharge path, 23 ... Shared ink supply path, 24 ... Shared ink discharge path, 25 ... Basic ink supply path, 26 ... Basic ink discharge path, 27 ... Ink supply groove 28 ... Ink discharge grooves, 29 ... Partitions, 31 ... Extraction electrodes.

Claims (5)

A diaphragm,
An ink pressure chamber provided on one side of the diaphragm;
An ejection hole provided through the diaphragm in communication with the ink pressure chamber;
An actuator that vibrates the diaphragm and ejects ink droplets from the ejection holes;
A protective layer of an inorganic insulating material provided on the surface of the diaphragm opposite to the pressure chamber so as to overlap the actuator;
A liquid repellent layer provided on the surface of the protective layer;
An inkjet head having The protective layer has a thickness of 0.1 μm to 1 μm.
The inkjet head according to claim 1. The liquid repellent layer is formed of a resin having a contact angle with water of 90 degrees or more.
The inkjet head according to claim 1 or 2. The thickness of the liquid repellent layer is 1 μm to 5 μm.
The inkjet head according to claim 3.   The actuator is formed by laminating a lower electrode, a piezoelectric body, and an upper electrode in order from the diaphragm side, and is formed on a part of the upper surface of the upper electrode and a part of the side surface of the piezoelectric body. An insulating layer made of an inorganic insulating material, and an extraction electrode made of a conductive material formed on the surface of the upper electrode and the insulating layer and electrically connected to the upper electrode. The inkjet head of 1-4.