Piezoelectric actuator, liquid discharge head, and liquid discharge apparatus

Abstract

To reduce residual stress of a vibration member.SOLUTION: A piezoelectric actuator 39 includes: a base material 32 having openings 41a and partition walls 48 each partitioning the openings 41a; a vibration member 33 which is provided on the partition walls 48 so as to cover the openings 41a; and a piezoelectric element 40 provided on a surface, which is opposite to a side of the base material 32, of the vibration member 33. The vibration member 33 has recessed parts 55, penetrating through the vibration member 33, on the partition walls 48 each of which is disposed along at least a portion, which extends in a longitudinal direction, of the opening 41a.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric actuator, a liquid ejection head, and a liquid ejection apparatus. [Background technology]

[0002] 2. Description of the Related Art A liquid ejection head mounted on a liquid ejection apparatus is known to use a piezoelectric actuator including a piezoelectric element to eject liquid.

[0003] Generally, in this type of liquid ejection head, a portion of the wall of the liquid chamber is made up of a vibrating member, and a piezoelectric element is attached to the vibrating member. When the piezoelectric element is deformed by passing electricity through the vibrating member, the deformation of the piezoelectric element causes the vibration of the vibrating member, which changes the pressure within the liquid chamber and ejects liquid from the liquid chamber.

[0004] Furthermore, Patent Document 1 (JP 2016-165816 A) proposes a configuration in which a recess is formed in a position on the vibration plate other than the liquid chamber forming area, and the lower electrode has an anchor portion inserted into the recess, in order to prevent the lower electrode formed on the vibration plate from peeling off from the vibration plate.

[0005] Incidentally, residual stress may occur in the vibrating member after molding. If residual stress exists in the vibrating member, when the vibrating member deforms during liquid ejection, stress accompanying the deformation is generated in addition to the residual stress, which causes a large stress to act on the vibrating member, potentially resulting in damage to the vibrating member. Furthermore, if residual stress causes warping in the vibrating member, the warping is corrected when the vibrating member is joined to another component, which places a load on the vibrating member and may result in damage to the component. Furthermore, when the vibrating member is transported or adsorbed during the manufacturing process, the warping of the vibrating member may cause transport and adsorption problems. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to reduce the residual stress in the vibrating member. [Means for solving the problem]

[0007] In order to solve the above problems, the piezoelectric actuator of the present invention comprises a substrate having an opening and a partition wall that separates the opening, a vibration member provided on the partition wall so as to cover the opening, and a piezoelectric element provided on the surface of the vibration member opposite the substrate side, wherein the vibration member has a recess on the partition wall that penetrates the vibration member and is arranged along at least a portion extending longitudinally of the opening. [Effects of the Invention]

[0008] According to the present invention, the residual stress in the vibrating member can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing an overall configuration of an image forming apparatus according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a control block diagram of the image forming apparatus according to the first embodiment of the present invention. [Figure 3] FIG. 1 is a plan view of a liquid ejection unit according to a first embodiment of the present invention. [Figure 4] 1 is an exploded perspective view of a liquid ejection head according to a first embodiment of the present invention. [Figure 5] 1 is a cross-sectional view in the short side direction of a liquid ejection head according to a first embodiment of the present invention. [Figure 6] 1 is a cross-sectional view of a piezoelectric actuator according to a first embodiment of the present invention. [Figure 7] 1 is a plan view of a piezoelectric actuator according to a first embodiment of the present invention, as viewed from the vibration member side. [Figure 8] FIG. 4 is a cross-sectional view of a piezoelectric actuator according to a second embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional view of a piezoelectric actuator according to a third embodiment of the present invention. [Figure 10] FIG. 1 is a diagram illustrating an example of a serial type liquid ejection unit. [Figure 11] FIG. 10 is a cross-sectional view of a piezoelectric actuator according to another reference example of the present invention. [Figure 12] FIG. 10 is a cross-sectional view of a piezoelectric actuator according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and once they have been described, their description will be omitted.

[0011] <Configuration of image forming device> First, an inkjet image forming apparatus, which is an example of a liquid ejection apparatus according to the present invention, will be described with reference to Fig. 1. Fig. 1 is a diagram showing the overall configuration of an image forming apparatus according to a first embodiment of the present invention.

[0012] As shown in FIG. 1, an image forming apparatus 100 according to the first embodiment of the present invention includes a sheet supply unit 1, a sheet conveying unit 2, an image forming unit 3, a drying unit 4, and a sheet recovery unit 5.

[0013] The sheet supply unit 1 is a part that supplies the sheet S. Specifically, the sheet supply unit 1 has a supply roller 11 and a tension adjustment mechanism 12. A long sheet S is wound around the supply roller 11 in a roll shape. When the supply roller 11 rotates, the sheet S is unwound from the supply roller 11. The tension adjustment mechanism 12 is a mechanism that adjusts the tension of the sheet S so that the sheet S is supplied with a constant tension. Specifically, the tension adjustment mechanism 12 has multiple rollers around which the sheet S is stretched. By moving some of the multiple rollers that the tension adjustment mechanism 12 has, the tension of the sheet S is adjusted, and the sheet S is supplied with a constant tension.

[0014] The sheet conveying unit 2 is a part that conveys the sheet S supplied from the sheet supply unit 1 to the image forming unit 3. Specifically, the sheet conveying unit 2 has a plurality of conveying rollers 15 as a conveying means for conveying the sheet S. The sheet conveying means may be a conveying belt or the like in addition to the conveying rollers 15. With the sheet S stretched across each of the conveying rollers 15, the sheet S is conveyed to the image forming unit 3 by the rotation of each of the conveying rollers 15.

[0015] The image forming unit 3 is a part that forms an image on the sheet S. Specifically, the image forming unit 3 has a liquid ejection unit 13 and a transport guide member 14. The liquid ejection unit 13 is a means for ejecting liquid ink onto the sheet S. The transport guide member 14 is a guide member that is disposed below the liquid ejection unit 13 so as to face the liquid ejection unit 13. When the sheet S is transported onto the transport guide member 14, the sheet S is guided along the transport guide member 14. Then, an image is formed on the sheet S by ejecting ink from the liquid ejection unit 13 onto the sheet S on the transport guide member 14.

[0016] The drying unit 4 is a section that dries the sheet S onto which the ink has been ejected. Specifically, the drying unit 4 has a heating roller 16 that heats the sheet S. The heating roller 16 is a cylindrical roller that has a heat source such as a halogen heater inside. As the sheet S is transported while being wrapped around the outer circumferential surface of the heating roller 16, the sheet S is heated, and the liquid components contained in the ink evaporate, thereby drying the sheet S. Note that the heating means for heating the sheet S may be a contact-type heating means such as the heating roller 16, or a non-contact-type heating means such as a hot air generator that blows hot air onto the sheet S.

[0017] The sheet collection unit 5 is a section that collects the sheet S. Specifically, the sheet collection unit 5 has a collection roller 17 and a tension adjustment mechanism 18. When the sheet S is transported to the sheet collection unit 5, the rotating collection roller 17 winds the sheet S into a roll and collects it. The tension adjustment mechanism 18 has multiple rollers, similar to the tension adjustment mechanism 12 of the sheet supply unit 1. The tension of the sheet S is adjusted by moving some of the multiple rollers of the tension adjustment mechanism 18, and the sheet S is wound up by the collection roller 17 at a constant tension.

[0018] <Control configuration of image forming apparatus> FIG. 2 is a control block diagram of the image forming apparatus according to the first embodiment of the present invention.

[0019] As shown in FIG. 2, the image forming apparatus 100 according to the first embodiment of the present invention includes a CPU (Central Processing Unit) 501, a ROM (Read Only Memory) 502, a RAM (Random Access Memory) 503, an NVRAM (Non-Volatile Random Access Memory) 504, an external device connection I / F 505, a network I / F 506, a bus line 507, and an operation panel 508.

[0020] The CPU 501 controls the overall operation of the image forming apparatus 100. Specifically, the CPU 501 controls the ejection operation of the liquid ejection unit 13, the rotation speeds of the supply roller 11, the recovery roller 17, and the transport roller 15, the temperature of the heating roller 16, and the tension adjustment operation of the tension adjustment mechanisms 12 and 18. The ROM 502 stores programs used to drive the CPU 501, such as the IPL. The RAM 503 is used as a work area for the CPU 501. The NVRAM 504 stores various data, such as programs, and retains the various data even when the image forming apparatus 100 is powered off.

[0021] The external device connection I / F 505 is connected to a PC (Personal Computer) via a USB (Universal Serial Bus) cable or the like, and communicates control signals and image data to be printed with the PC. The network I / F 506 is an interface for communicating data using a communication network such as the Internet. The bus line 507 is an address bus and a data bus or the like for electrically connecting the components such as the CPU 501.

[0022] The operation panel 508 displays current setting values, a selection screen, etc., and is configured with a touch panel that receives input from an operator, an alarm lamp, etc. The CPU 501 controls various operations of the image forming apparatus 100 based on information such as image information, sheet conveying speed, and sheet type input through the operation panel 508.

[0023] <Configuration of liquid ejection unit> FIG. 3 is a plan view of the liquid ejection unit 13 according to the first embodiment of the present invention.

[0024] 3, the liquid ejection unit 13 according to the first embodiment of the present invention includes two liquid ejection heads 20 aligned in a sheet transport direction A in which a sheet S is transported. Each liquid ejection head 20 includes a plurality of head bodies 21 that eject ink, a base member 22 that holds each head body 21, and the like.

[0025] In this case, the head bodies 21 extend elongatedly in the sheet width direction B, which is a direction perpendicular to the sheet conveying direction A, and are arranged two by two adjacent to each other in the sheet conveying direction A. Furthermore, four sets of adjacent head bodies 21 are arranged in both the sheet conveying direction A and the sheet width direction B. In FIG. 3, the two upper sets of head bodies 21 and the two lower sets of head bodies 21 are arranged offset from each other in the sheet width direction B. In this way, by arranging the head bodies 21 offset in the sheet width direction B, the liquid ejection unit 13 can eject ink across the entire width of the image forming area of the sheet S. Therefore, when the sheet S is conveyed to a position facing the liquid ejection unit 13, ink is ejected from each head body 21 and an image is formed on the sheet S without the liquid ejection unit 13 moving relative to the conveyed sheet S. Note that FIG. 3 shows an example of the configuration of the liquid ejection unit 13, and the arrangement and number of the head bodies 21 are not limited to this example.

[0026] <Configuration of liquid ejection head> FIG. 4 is an exploded perspective view of the liquid ejection head 20 according to the first embodiment of the present invention.

[0027] As shown in Figure 4, the liquid ejection head 20 according to the first embodiment of the present invention comprises a plurality of head bodies 21, a base member 22, a cover member 23, a heat dissipation member 24, a manifold 25, a printed circuit board (PCB) 26, a module case 27, a flexible wiring member 50, etc.

[0028] The multiple head bodies 21 are held by being fixed to a base member 22. Methods for fixing the head bodies 21 to the base member 22 include fastening with screws, adhesive bonding, caulking, and the like. One surface of the base member 22 is covered by a cover member 23. The cover member 23 has holes 23a at positions corresponding to the respective head bodies 21. As a result, the liquid ejection surfaces of the respective head bodies 21 are arranged so as to be exposed through the holes 23a. A module case 27 is attached to the base member 22 on the side opposite to the side where the respective head bodies 21 are exposed. The module case 27 accommodates the heat dissipation member 24, the manifold 25, the printed circuit board 26, and a portion of the flexible wiring member 50 including the driver IC 53.

[0029] FIG. 5 is a cross-sectional view in the width direction of the liquid ejection head 20 according to the first embodiment of the present invention.

[0030] 5, in the liquid ejection head 20 according to the first embodiment of the present invention, the head main body 21 is housed in the hole 22c of the base member 22. The head main body 21 has a nozzle plate 31, a piezoelectric actuator 39, a holding substrate 34, and a common flow path member 35. The piezoelectric actuator 39 includes a flow path substrate 32, a vibration member 33, and a piezoelectric element 40. The piezoelectric element 40 is connected to the printed circuit board 26 via a flexible wiring member 50.

[0031] The nozzle plate 31 is a plate-shaped member having nozzles 30 that eject ink. The peripheral edge of the nozzle plate 31 excluding the nozzles 30 is joined to the cover member 23. On the other hand, the nozzles 30 are arranged so as to be exposed through holes 23a in the cover member 23.

[0032] The flow path substrate 32 is a base material on which the nozzle plate 31, the vibration member 33, and the piezoelectric element 40 are attached. More specifically, the nozzle plate 31 is bonded to the liquid ejection side of the flow path substrate 32, and the vibration member 33 and the piezoelectric element 40 are bonded in this order to the opposite side. The flow path substrate 32 is also provided with individual liquid chambers 41 that communicate with the nozzles 30 of the nozzle plate 31, supply-side individual flow paths 42 that communicate with the individual liquid chambers 41, and recovery-side individual flow paths 43 that communicate with the individual liquid chambers 41 on the side opposite to the supply-side individual flow path 42.

[0033] The holding substrate 34 is a member that holds the nozzle plate 31 and the piezoelectric actuator 39. More specifically, by bonding the vibration member 33 to the holding substrate 34, the nozzle plate 31, the flow path substrate 32, the vibration member 33, and the piezoelectric element 40 are held by the holding substrate 34. The holding substrate 34 is also provided with a supply-side intermediate individual flow path 44 that communicates with the supply-side individual flow path 42 via one hole 33a provided in the vibration member 33, and a recovery-side intermediate individual flow path 45 that communicates with the recovery-side individual flow path 43 via the other hole 33b provided in the vibration member 33.

[0034] The supply flow path member 35 is a flow path member that fixes the holding substrate 34 to the base member 22. The holding substrate 34 is joined to the common flow path member 35, and the common flow path member 35 is further fixed to the base member 22, thereby holding the entire head main body 21 to the base member 22. The common flow path member 35 is also provided with a supply-side common flow path 46 that communicates with the supply-side intermediate individual flow path 44, and a recovery-side common flow path 47 that communicates with the recovery-side intermediate individual flow path 45. The supply-side common flow path 46 is arranged to communicate with the supply port 28 via one flow path 51 of the manifold 25, and the recovery-side common flow path 47 is arranged to communicate with the recovery port 29 via the other flow path 52 of the manifold 25.

[0035] The base member 22 is preferably formed from a material with a low linear expansion coefficient. Examples of materials for the base member 22 include 42 alloy (iron alloy) with added nickel, and invar. By forming the base member 22 from such a material, the amount of thermal expansion of the base member 22 when the liquid ejection head 20 generates heat can be reduced. This reduces misalignment of the nozzles 30 due to thermal expansion of the base member 22, thereby reducing misalignment of the ink ejection position relative to the sheet. Alternatively, the nozzle plate 31 and the vibration member 33 may be formed from single-crystal silicon, with their linear expansion coefficients approximately equal to that of the base member 22. By making the linear expansion coefficients of the nozzle plate 31 and the vibration member 33 approximately equal to that of the base member 22, it is possible to further reduce misalignment of the nozzles 30 due to thermal expansion.

[0036] <Head body configuration> FIG. 6 is a cross-sectional view of a piezoelectric actuator 39 according to a first embodiment of the present invention.

[0037] 6, in a piezoelectric actuator 39 according to the first embodiment of the present invention, a flow path substrate 32 has a plurality of individual liquid chambers 41 and partition walls 48 that separate each individual liquid chamber 41. Also, one nozzle 30 is disposed below each individual liquid chamber 41 in Fig. 6. Therefore, a plurality of nozzles 30 are arranged in the same direction as the arrangement direction of each individual liquid chamber 41.

[0038] A vibration member 33 is provided on the partition wall 48 of the flow path substrate 32 so as to cover the opening 41a of each individual liquid chamber 41. The vibration member 33 is provided so as to cover the entire upper opening 41a in FIG. 6, so that one surface of the individual liquid chamber 41 is formed by the vibration member 33.

[0039] The flow path substrate 32 is formed using, for example, single crystal silicon with a thickness of 80 μm. When single crystal silicon is used as the material for the flow path substrate 32, the individual liquid chambers 41 can be formed finely and with high precision using semiconductor processing techniques such as photolithography. Furthermore, the material for the flow path substrate 32 is not limited to silicon, and any material suitable for processing the individual liquid chambers 41 can be selected from metals, alloys, ceramics, semiconductors, etc.

[0040] A piezoelectric element 40 is provided on the surface of the vibration member 33 opposite to the flow path substrate 32 side. The piezoelectric element 40 has, in this order from the vibration member 33 side, a first electrode 36, a piezoelectric body 37, and a second electrode 38. The first electrode 36 is an individual electrode provided individually for each individual liquid chamber 41. On the other hand, the second electrode 38 is a common electrode provided in common across all of the individual liquid chambers 41. The piezoelectric body 37 is interposed between the first electrode 36 and the second electrode 38.

[0041] The vibration member 33, the first electrode 36, the piezoelectric body 37, and the second electrode 38 are sequentially stacked on the flow path substrate 32. Examples of methods for forming these include a method in which the vibration member 33, the first electrode 36, the piezoelectric body 37, and the second electrode 38 are formed on the flow path substrate 32 by using a CVD (Chemical Vapor Deposition) method, a sputtering method, an ALD (Atomic Layer Deposition) method, or a spin coating method, and then patterned by photolithography.

[0042] In the actuator 39 configured as described above, when a predetermined drive voltage is applied to the first electrode 36 and the second electrode 38, the piezoelectric body 37 is deformed, and the deformation of the piezoelectric body 37 causes the vibration member 33 to deform so as to protrude into the individual liquid chamber 41. As a result, the ink in the individual liquid chamber 41 is pressurized, and ink is ejected from the nozzle 30.

[0043] The vibrating member 33 can be made of, for example, a silicon-based compound or a zirconium-based compound. Silicon-based compounds are preferably made of materials containing at least silicon oxides such as silicon dioxide (SiO2) because they are easy to manufacture. Other silicon-based compounds include single crystal silicon, polycrystalline silicon, silicon nitride (Si3N4), and silicon carbide (SiC). Zirconium-based compounds include zirconium oxide (ZrO2). The thickness of the vibrating member 33 is set to an appropriate value depending on the vibration characteristics and strain required of the piezoelectric actuator. For example, the appropriate thickness of the vibrating member 33 is preferably in the range of 1 μm to 3 μm.

[0044] Examples of materials that can be used for the first electrode 36 and the second electrode 38 include metals such as platinum (Pt) and iridium (Ir), and conductive oxides such as iridium oxide (IrO2), tin monoxide (SnO), and indium oxide (InO2). Examples of materials that can be used for the piezoelectric body 37 include lead zirconate titanate (PZT). Lead zirconate titanate, in which the ratio of zinc (Zn) to titanium (Ti) is adjusted to 53:47, exhibits particularly favorable characteristics. The ratio of the constituent elements of lead zirconate titanate may be adjusted appropriately depending on the molding method, molding conditions, and desired performance of the piezoelectric body 37. For example, adjusting the ratio of zinc to titanium within the range of 43:57 to 63:37 can achieve favorable piezoelectric characteristics. Furthermore, lead zirconate titanate may be doped with elements such as manganese (Mn), niobium (Nb), molybdenum (Mo), and cobalt (Co).

[0045] The widths of the first electrode 36 and the piezoelectric body 37 can be set appropriately depending on the desired deformation amount and processing method of the piezoelectric actuator. For example, if the width of the opening 41a of the individual liquid chamber 41 is 60 μm, good displacement characteristics can be obtained by setting the width of the piezoelectric body 37 to 50 μm and the width of the first electrode 36 to 40 μm. Furthermore, the thickness of the piezoelectric body 37 can be set appropriately depending on the performance required of the piezoelectric actuator. The thickness of the piezoelectric body 37 is preferably set, for example, in the range of 1 μm to 4 μm.

[0046] The width between the openings 41a of adjacent individual liquid chambers 41 is set to, for example, 85 μm. The width of the openings 41a in the arrangement direction (the horizontal direction in FIG. 6) in which the openings 41a are arranged is set to, for example, 60 μm. The width of the openings 41a in the direction perpendicular to the arrangement direction of the openings 41a (the direction perpendicular to the paper surface in FIG. 6) is set to, for example, 600 μm. The widths of the openings 41a in the arrangement direction and the direction perpendicular thereto may be set to appropriate sizes depending on the specifications required for the piezoelectric actuator and the liquid ejection head.

[0047] <Issues with liquid ejection heads> Here, the problems with the liquid ejection head 20 will be described using the configuration according to the first embodiment of the present invention as an example.

[0048] The vibration member 33 provided in the liquid ejection head 20 is generally formed by a method such as CVD, PVD (Physical Vapor Deposition), or thermal oxidation of the flow path substrate 32. In either method, the vibration member 33 is processed in a heated space, and therefore residual stress occurs in the vibration member 33 after molding.

[0049] At this time, if the residual stress generated in the vibrating member 33 is large, stress caused by the deformation of the vibrating member 33 during liquid ejection is also added, resulting in a large stress acting on the vibrating member 33, which may cause damage such as cracks to the vibrating member 33. For example, if tensile stress is generated in the vibrating member 33 from its surroundings, and the vibrating member 33 deforms so as to protrude toward the individual liquid chamber 41 during liquid ejection, large stress acts on the vibrating member 33, particularly around the opening 41a of the individual liquid chamber 41. This may cause damage to the vibrating member 33. Conversely, if compressive stress is generated in the vibrating member 33, the vibrating member 33 will attempt to stretch, causing deformation such as buckling. If the vibrating member 33 deforms during liquid ejection in this state, the deformation of the vibrating member 33 will be uneven, which may cause damage to the vibrating member 33.

[0050] Furthermore, if the residual stress causes warping in the vibration member 33, the warping is corrected when the vibration member 33 is bonded to the flow path substrate 32 and the piezoelectric element 40, and a load is applied to the vibration member 33, the flow path substrate 32, and the piezoelectric element 40. This may cause damage to these bonded members.

[0051] Furthermore, if the warp generated in the vibration member 33 is large, there is a risk that transportation and suction problems will occur when the vibration member 33 is transported or sucked during the manufacturing process.

[0052] As described above, in the liquid ejection head 20, residual stress generated in the vibrating member 33 may cause damage to the vibrating member 33 and other components, as well as problems such as poor transport and poor suction during the manufacturing process. These problems can be addressed by selecting a material for the vibrating member 33 that is less prone to residual stress and warping. However, selecting a material for the vibrating member 33 from a limited range of materials narrows the range of material choices. Because the material for the vibrating member 33 significantly contributes to the crystalline state of the piezoelectric element 37, as well as to manufacturing costs and ease of manufacture, a wide range of materials for the vibrating member 33 is preferable in order to ensure a good crystalline state. Therefore, selecting a material for the vibrating member 33 from a limited range of materials is difficult to adopt in order to ensure a wide range of material choices.

[0053] In view of the above circumstances, in the first embodiment of the present invention, in order to reduce the residual stress generated in the vibrating member 33, the vibrating member 33 is configured as follows.

[0054] <Configuration of the vibrating member according to the first embodiment of the present invention> Hereinafter, the configuration of the vibrating member 33 according to the first embodiment of the present invention will be described with reference to FIGS.

[0055] 6 , in the first embodiment of the present invention, the vibration member 33 has a recess 55. The recess 55 is provided on the partition wall 48 of the flow path substrate 32. The recess 55 is also provided so as to penetrate the vibration member 33. That is, the recess 55 penetrates the vibration member 33 in a direction intersecting with one surface of the vibration member 33 that is joined to the flow path substrate 32. Furthermore, since the vibration member 33 has the recess 55, the second electrode 38 that covers the vibration member 33 is formed so as to enter the recess 55 and cover the recess 55.

[0056] Fig. 7 is a plan view of the piezoelectric actuator 39 according to the first embodiment of the present invention, as viewed from the vibration member 33 side. However, the second electrode 38 is omitted in Fig. 7. The cross-sectional view taken along line CC in Fig. 7 is Fig. 6.

[0057] 7, the recess 55 is provided so as to surround the entire opening 41a of the individual liquid chamber 41. In the first embodiment of the present invention, the openings 41a are arranged adjacent to each other, and therefore the recess 55 is provided so as to surround each opening 41a. Each opening 41a is formed in a rectangular shape having two short side portions 411 extending in the short direction X and two long side portions 412 extending in the longitudinal direction Y. Therefore, the recess 55 is provided so as to surround the entire opening 41a along each of the short side portions 411 and each of the long side portions 412 of the opening 41a.

[0058] In this way, in the first embodiment of the present invention, the vibrating member 33 has the recess 55 that entirely surrounds each opening 41a, so that the residual stress of the vibrating member 33 around each opening 41a can be reduced.

[0059] Therefore, the configuration according to the first embodiment of the present invention makes it possible to suppress damage to the vibration member 33. Furthermore, by reducing the residual stress of the vibration member 33, warping of the vibration member 33 is also suppressed, which reduces the load generated at the joint between the vibration member 33 and the flow path substrate 32 and at the joint between the vibration member 33 and the piezoelectric element 40, making it possible to suppress damage to the vibration member 33, the flow path substrate 32, and the piezoelectric body 37. Furthermore, by reducing the warping of the vibration member 33, it becomes possible to suppress the occurrence of transport problems and suction problems of the vibration member 33 during the manufacturing process.

[0060] In particular, in the first embodiment of the present invention, the recesses 55 are provided so as to penetrate the vibrating member 33, and therefore the residual stress in the vibrating member 33 can be reduced more effectively than in the configuration having the recesses 55 that do not penetrate the vibrating member 33 as shown in Fig. 11. Therefore, with the configuration according to the first embodiment of the present invention, it is possible to reliably prevent problems caused by the residual stress in the vibrating member 33.

[0061] The magnitude of the residual stress occurring in the vibration member 33 is preferably within the range of -400 MPa to 200 MPa. The magnitude of the residual stress can be calculated, for example, from the magnitude (radius of curvature) of the warp occurring in the vibration member 33 formed on the flow path substrate 32 using the following formula: In the formula, σ is the residual stress occurring in the vibration member 33, E is the elastic modulus of the flow path substrate 32, ν is the Poisson's ratio of the flow path substrate 32, and t a is the thickness of the flow path substrate 32, t b is the thickness of the vibration member 33, R a is the radius of curvature of the flow path substrate 32 alone, R b is the radius of curvature when the vibration member 33 is formed on the flow path substrate 32.

[0062]

number

[0063] The magnitude of the residual stress occurring in the vibrating member 33 can also be calculated from the diffraction pattern observed by X-ray diffraction, Raman spectroscopy, or nanobeam electron diffraction (NBED). When residual stress occurs in the vibrating member 33, the lattice spacing changes depending on the angle between the lattice plane and the stress direction. Therefore, by changing the tilt angle of the vibrating member 33 in X-ray diffraction, it is possible to measure the lattice plane tilted relative to the vibrating member 33, and calculate the residual stress occurring in the vibrating member 33. Raman spectroscopy is a spectroscopic method based on inelastic scattering of light. When residual stress occurs in the vibrating member 33, the interatomic distance changes as stress is applied to the crystal. Generally, the bonding force between atoms depends on the interatomic distance, and the frequency of lattice vibrations (phonons) changes due to stress. In the case of compressive stress, the phonon lines shift to the higher wavenumber side, while in the case of tensile stress, the phonon lines shift to the lower wavenumber side. Therefore, the residual stress of the measurement sample can be calculated by measuring the difference in the peak value of the phonon lines with respect to the vibration member 33 where no residual stress occurs. In the ultrafine electron beam diffraction method, a transmission electron microscope (TEM) is used to incident an electron beam on the vibration member 33 at a predetermined angle, and the lattice spacing is measured from the obtained diffraction spot. Then, the residual stress can be calculated by measuring the lattice strain from the difference between the measured lattice spacing and the lattice spacing of the vibration member 33 where no residual stress occurs.

[0064] The recesses 55 may be provided over the entire periphery of each opening 41 a, or may be provided over a portion of the periphery of each opening 41 a. However, in order to effectively reduce residual stress in the vibrating member 33, it is preferable that the recesses 55 be provided on the partition wall 48 (the hatched portion in FIG. 7) that is arranged along at least the portion of the opening 41 a that extends in the longitudinal direction Y (the long side portion 412).

[0065] 7, the recess 55 is preferably provided over a range H wider than the width region W1 of the opening 41a in the longitudinal direction Y. By providing the recess 55 over a range H wider than the width region W1 of the opening 41a in the longitudinal direction Y, the residual stress of the vibrating member 33 can be further reduced.

[0066] Furthermore, the width W2 of the recess 55 is preferably equal to or less than half the width W3 of the partition wall 48. Note that the width W2 of the recess 55 and the width W3 of the partition wall 48 herein refer to the widths on the surface of the partition wall 48 on which the recess 55 is provided, in a direction intersecting the direction in which the recess 55 and the partition wall 48 extend along the edge of the opening 41 a. By setting the width W2 of the recess 55 to equal to or less than half the width W3 of the partition wall 48, the distance from the opening 41 a to the recess 55 can be secured, thereby preventing ink from flowing from the individual liquid chamber 41 into the recess 55.

[0067] <Configuration of other embodiments> Next, another embodiment of the present invention that is different from the first embodiment will be described. Below, differences from the first embodiment of the present invention will be mainly described, and descriptions of the same parts will be omitted as appropriate.

[0068] Second Embodiment of the Present Invention FIG. 8 is a cross-sectional view of a piezoelectric actuator 39 according to a second embodiment of the present invention.

[0069] As shown in FIG. 8 , in the second embodiment of the present invention, a recess 55 of a vibrating member 33 is filled with a filler 56 having a stress opposite to the stress generated in the vibrating member 33. The material of the filler 56 is preferably a material containing at least lead zirconate titanate. The stress of the filler 56 may have an absolute value smaller than the stress (residual stress) generated in the vibrating member 33. For example, if the stress of the vibrating member 33 is −300 MPa, the stress of the filler 56 may have an absolute value smaller than the stress of the vibrating member 33, such as −100 MPa. In this case, the second electrode 38 is disposed so as to cover the surface of the filler 56. The other configurations are the same as those of the first embodiment of the present invention.

[0070] As described above, in the second embodiment of the present invention, the recess 55 is filled with the filler 56 having a stress in the opposite direction to the stress generated in the vibrating member 33, thereby further reducing the residual stress generated in the vibrating member 33. In other words, the opposite stress of the filler 56 cancels out part or all of the residual stress in the vibrating member 33, further reducing the stress generated in the vibrating member 33. Therefore, the configuration according to the second embodiment of the present invention makes it possible to more effectively prevent damage to the vibrating member 33 and other components caused by residual stress, as well as problems such as poor transport and poor suction during the manufacturing process.

[0071] To make the filler member 56 have a stress in the opposite direction to the stress of the vibrating member 33, for example, the vibrating member 33 can be made of silicon dioxide and the filler member 56 can be made of lead zirconate titanate. In other words, by making the filler member 56 from lead zirconate titanate, which has a stress in the opposite direction to that of silicon dioxide, the stress of the filler member 56 can be made to be a stress in the opposite direction to the stress of the vibrating member 33.

[0072] Whether the stress of the filler member 56 is smaller than the stress of the vibrating member 33 can be determined by the magnitude of the warp that occurs in the vibrating member 33 described above or by X-ray diffraction, etc. Furthermore, if the piezoelectric body 37 and the filling member 56 are both formed of the same material, such as lead zirconate titanate, the magnitude relationship of the stress between the filler member 56 and the vibrating member 33 can be determined by checking the state of bending of the joint between the vibrating member 33 and the piezoelectric body 37 toward the individual liquid chamber 41 or toward the piezoelectric body 37. If the joint between the vibrating member 33 and the piezoelectric body 37 protrudes toward the individual liquid chamber 41, it can be determined that the stress of the filler member 56 is larger than the stress of the vibrating member 33. Conversely, if the joint between the vibrating member 33 and the piezoelectric body 37 protrudes toward the piezoelectric body 37, it can be determined that the stress of the filler member 56 is smaller than the stress of the vibrating member 33.

[0073] Furthermore, in order to form the filling member 56 from the same material as the piezoelectric body 37, first, a recess 55 is formed in the vibration member 33 before the piezoelectric body 37 is laminated on the vibration member 33. Then, the piezoelectric body 37 is formed on the entire surface of the vibration member 33, including the recess 55, by a method such as spin coating or sputtering, and photolithography and etching are performed to leave the piezoelectric body 37 only in necessary areas, thereby forming the filling member 56 made of the same material as the piezoelectric body 37 in the recess 55.

[0074] Third Embodiment of the Present Invention FIG. 9 is a cross-sectional view showing a part of a piezoelectric actuator 39 according to a third embodiment of the present invention.

[0075] 9, the recess 55 of the vibration member 33 is a recess that does not penetrate the vibration member 33. The recess 55 is filled with a filler member 56 that has a stress in the opposite direction to the stress generated in the vibration member 33. Therefore, also in the third embodiment of the present invention, the second electrode 38 is arranged so as to cover the surface of the filler member 56. The other configurations are the same as those in the first embodiment of the present invention.

[0076] As described above, in the third embodiment of the present invention, the recesses 55 do not penetrate the vibrating member 33, and therefore are less effective in reducing the residual stress in the vibrating member 33 than in a configuration having recesses 55 that penetrate the vibrating member 33. However, in the third embodiment of the present invention, the recesses 55 are filled with the filler 56, which has a stress opposite to the stress generated in the vibrating member 33, and therefore the effect of reducing the residual stress in the vibrating member 33 can be improved. As a result, the third embodiment of the present invention can also reduce the residual stress generated in the vibrating member 33, and effectively prevent damage to the vibrating member 33 and other components caused by the residual stress, as well as problems such as poor transport and poor suction during the manufacturing process.

[0077] <Durability test of piezoelectric actuator> Next, a durability test performed using the piezoelectric actuator according to the embodiment of the present invention and a piezoelectric actuator according to a comparative example will be described.

[0078] Durability tests were conducted using the piezoelectric actuator according to the first embodiment of the present invention shown in FIG. 6, the piezoelectric actuator according to the second embodiment of the present invention shown in FIG. 8, and the piezoelectric actuator according to the comparative example shown in FIG. 12. The piezoelectric actuator according to the comparative example has a configuration in which no recesses 55 are provided in the vibrating member 33. In both configurations, the thickness of the vibrating member 33 was 2 μm, and the magnitude of the residual stress generated in the vibrating member 33 was 100 MPa. Furthermore, in the piezoelectric actuators according to the first and second embodiments of the present invention, the width of the recesses 55 was 20 μm. Furthermore, in the piezoelectric actuator according to the second embodiment of the present invention, the stress of the filling member 56 was -100 MPa.

[0079] Then, in each of the piezoelectric actuators configured in this manner, an AC voltage was applied to the first electrode 36 and the second electrode 38 under the conditions described below, and the vibration member 33, the piezoelectric body 37, etc. were checked under a microscope to see if there were any cracks or damage due to discharge. Voltage: 0V to 40V Pulse frequency: 120[kHz] Pulse duty: 50% (time ratio of 40V voltage per pulse period) Number of pulses applied: 10 11 times

[0080] The voltage applied to the first electrode 36 and the second electrode 38 is not limited to an AC voltage, but may be a DC voltage. Also, an accelerated test may be performed by changing the applied voltage, temperature, and humidity. The test for examining the durability of a piezoelectric actuator is not limited to the conditions of this test, and appropriate test conditions can be set depending on the application and desired performance of the piezoelectric actuator.

[0081] As a result of carrying out a durability test under the above conditions, the piezoelectric actuator according to the comparative example was found to have a high resistance when the number of applied pulses was 5 11In contrast, in the piezoelectric actuators according to the first and second embodiments of the present invention, cracks occurred when the number of applied pulses was 10 11 No cracks were generated even after the test cycle reached 100 times. Furthermore, when the warpage of the vibrating member 33 was compared, the piezoelectric actuator according to the first embodiment of the present invention had less warpage than the piezoelectric actuator according to the comparative example, and the piezoelectric actuator according to the second embodiment of the present invention had even less warpage than the piezoelectric actuator according to the first embodiment of the present invention.

[0082] From the above, it has been confirmed that in the piezoelectric actuators according to the first and second embodiments of the present invention, warping of the piezoelectric element 40 including the vibrating member 33 can be reduced and the occurrence of cracks can be suppressed compared to the piezoelectric actuator according to the comparative example. Therefore, it can be said that according to each embodiment of the present invention, warping and breakage of the piezoelectric element 40 due to residual stress in the vibrating member 33 can be suppressed.

[0083] The present invention is not limited to the above-described embodiments, and various design modifications are possible within the scope of the invention.

[0084] For example, the present invention is not limited to the line-type liquid ejection unit 13 shown in Fig. 3, but can also be applied to a serial-type liquid ejection unit 60 shown in Fig. 10. Below, the configuration and operation of the serial-type liquid ejection unit 60 will be briefly described with reference to Fig. 10.

[0085] The serial type liquid ejection unit 60 shown in Figure 10 includes a carriage 62 that carries a liquid ejection head 61, a guide member 63 for guiding the carriage 62 in the sheet width direction B, and a drive device 64 that moves the carriage 62.

[0086] The drive device 64 includes, for example, a motor 65 as a drive source, and a timing belt 68 wound around a drive pulley 66 and a driven pulley 67. When the motor 65 is driven and the drive pulley 66 rotates, the timing belt 68 moves in an orbital motion, and the carriage 62 moves in the sheet width direction B along the guide member 63.

[0087] In such a serial type liquid ejection unit 60, ink is ejected from the liquid ejection head 61 in accordance with an image signal while the carriage 62 moves in the sheet width direction B, thereby forming an image of one line on the stationary sheet S. Then, while the sheet S is transported in the sheet transport direction A by a predetermined amount at a time, the carriage 62 repeatedly moves back and forth and ejects ink, thereby forming an image on the sheet S.

[0088] Furthermore, the "liquid ejection device" according to the present invention includes not only an inkjet image forming apparatus, which is one example of a liquid ejection device, but also various other liquid ejection devices that have a liquid ejection unit and eject liquid onto a sheet by driving the liquid ejection unit. Therefore, the "liquid ejection device" according to the present invention is not limited to devices that visualize meaningful images such as letters and figures using ejected liquid. For example, the "liquid ejection device" also includes devices that form patterns that have no meaning in themselves, devices that create three-dimensional images, and even treatment liquid ejection devices that eject treatment liquid onto the surface of a sheet for purposes such as modifying the surface of the sheet.

[0089] Furthermore, the "liquid ejection device" according to the present invention may include means for feeding, conveying, and discharging sheets, pre-processing devices, and post-processing devices. Furthermore, the "liquid ejection device" may be one in which the liquid ejection unit moves relative to the sheet, or one in which the liquid ejection unit does not move relative to the sheet. Specific examples include a serial type liquid ejection device as shown in FIG. 10 and a line type liquid ejection device as shown in FIG. 3. The liquid ejection head may be one that includes multiple head bodies, or one that includes a single head body.

[0090] The "sheet" onto which the liquid is ejected includes any material to which the liquid can adhere at least temporarily, such as a material to which the liquid can adhere and stick, or a material to which the liquid can adhere and penetrate. Specific examples include recording media such as paper, recording paper, film, and cloth, and electronic substrates. The "sheet" may be made of any material to which the liquid can adhere, even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, or ceramics. The "sheet" may be a long sheet wound into a roll (such as roll paper), or a sheet cut to a predetermined size in the sheet transport direction (such as cut paper).

[0091] Furthermore, the "liquid ejection device" according to the present invention is not limited to a device that ejects liquid onto an object onto which the liquid can be attached, but may also be a device that ejects liquid into air or liquid.

[0092] Furthermore, the "liquid" ejected by the "liquid ejection device" may have any viscosity or surface tension that allows it to be ejected from the liquid ejection unit. While not particularly limited, it is preferable for the viscosity of the liquid to be 30 mPa·s or less at room temperature and pressure, or upon heating or cooling. More specifically, the liquid may be a solution, suspension, emulsion, or the like containing a solvent such as water or an organic solvent, a colorant such as a dye or pigment, a functionalizing material such as a polymerizable compound, a resin, or a surfactant, a biocompatible material such as DNA, amino acids, proteins, or calcium, or an edible material such as a natural dye. These liquids can be used, for example, in inkjet inks, surface treatment solutions, components of electronic devices and light-emitting devices, liquids for forming electronic circuit resist patterns, and material liquids for 3D modeling.

[0093] To summarize the above-described aspects of the present invention, the present invention includes at least the following aspects.

[0094] [First aspect] The first aspect is a piezoelectric actuator comprising a substrate having an opening and a partition wall that separates the opening, a vibration member provided on the partition wall so as to cover the opening, and a piezoelectric element provided on the surface of the vibration member opposite the substrate side, wherein the vibration member has a recess on the partition wall that penetrates the vibration member and is arranged along at least a portion extending longitudinally of the opening.

[0095] [Second aspect] A second aspect is the piezoelectric actuator of the first aspect, wherein the recess is filled with a filler member that has a stress in the opposite direction to the stress generated in the vibration member.

[0096] [Third aspect] A third aspect is a piezoelectric actuator comprising a substrate having an opening and a partition wall that separates the opening, a vibration member provided on the partition wall so as to cover the opening, and a piezoelectric element provided on the surface of the vibration member opposite the substrate side, wherein the vibration member has a recess on the partition wall that is arranged along at least a portion extending longitudinally of the opening and does not penetrate the vibration member, and the recess is filled with a filling member that has a stress in the opposite direction to the stress generated in the vibration member.

[0097] [Fourth aspect] A fourth aspect is a piezoelectric actuator according to the second or third aspect, wherein the stress of the filling member has an absolute value smaller than the stress generated in the vibrating member.

[0098] [Fifth aspect] A fifth aspect is any one of the first to fourth aspects, wherein the recess is a piezoelectric actuator provided so as to surround the entire opening.

[0099] [Sixth aspect] A sixth aspect is a piezoelectric actuator according to any one of the first to fifth aspects, wherein the recess is provided over a range wider than the width of the opening in the longitudinal direction.

[0100] [Seventh aspect] A seventh aspect is the piezoelectric actuator according to any one of the first to sixth aspects, wherein the width of the recess is equal to or less than half the width of the partition wall.

[0101] [Eighth aspect] An eighth aspect is a piezoelectric actuator according to the second or third aspect, wherein the vibration member contains at least silicon oxide, and the filling member contains at least lead zirconate titanate.

[0102] [Ninth aspect] A ninth aspect is a liquid ejection head comprising: a nozzle plate having nozzles for ejecting liquid; and the piezoelectric actuator of any one of the first to eighth aspects having a liquid chamber communicating with the nozzles.

[0103] [Tenth aspect] A tenth aspect is a liquid ejection device including the liquid ejection head of the ninth aspect. [Explanation of symbols]

[0104] 20 Liquid ejection head 30 nozzles 31 Nozzle plate 32 Flow path substrate (base material) 33 Vibration member 39 Piezoelectric Actuator 40 Piezoelectric element 41 Individual liquid chamber 41a opening 48 Bulkhead 55 recess 56 Filler material 100 Image forming device (liquid ejection device) [Prior art documents] [Patent documents]

[0105] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-165816

Claims

1. a substrate having an opening and a partition wall that defines the opening; a vibration member provided on the partition wall so as to cover the opening; a piezoelectric element provided on a surface of the vibration member opposite to the substrate, The piezoelectric actuator according to claim 1, wherein the vibration member has a recess on the partition wall that is disposed along at least a portion of the opening that extends in the longitudinal direction and that penetrates the vibration member.

2. 2. The piezoelectric actuator according to claim 1, wherein the recess is filled with a filler member having a stress in an opposite direction to the stress generated in the vibration member.

3. a substrate having an opening and a partition wall that defines the opening; a vibration member provided on the partition wall so as to cover the opening; a piezoelectric element provided on a surface of the vibration member opposite to the substrate, the vibration member has a recess on the partition wall that is disposed along at least a portion of the opening extending in the longitudinal direction and does not penetrate the vibration member; A piezoelectric actuator, characterized in that the recess is filled with a filler member having a stress in an opposite direction to the stress generated in the vibration member.

4. 4. The piezoelectric actuator according to claim 2, wherein the absolute value of the stress in the filling member is smaller than the absolute value of the stress generated in the vibration member.

5. The piezoelectric actuator according to claim 1 or 3, wherein the recess is provided so as to surround the entire opening.

6. 4. The piezoelectric actuator according to claim 1, wherein the recess is provided over a range wider than a width area of the opening in the longitudinal direction.

7. 4. The piezoelectric actuator according to claim 1, wherein the width of the recess is equal to or less than half the width of the partition wall.

8. the vibration member includes at least silicon oxide; 4. The piezoelectric actuator according to claim 2, wherein the filling member contains at least lead zirconate titanate.

9. A liquid ejection head comprising: a nozzle plate having nozzles for ejecting liquid; and the piezoelectric actuator according to claim 1 or 3, having a liquid chamber communicating with the nozzles.

10. A liquid ejection apparatus comprising the liquid ejection head according to claim 9.

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