Liquid droplet ejection head and liquid droplet ejection device

Abstract

The present invention provides a droplet ejection head and a droplet ejection device that achieve good image quality and long life by taking into account the characteristics of the piezoelectric layer and the use conditions of the droplet ejection head. The droplet ejection head comprises: a nozzle that ejects liquid as droplets; a pressure chamber forming substrate that forms a pressure chamber connected to the nozzle; a piezoelectric element having a first electrode, a second electrode, and a piezoelectric layer mainly composed of a perovskite-type composite oxide including potassium (K), sodium (Na), and niobium; and a vibration plate that forms a part of the wall surface of the pressure chamber and vibrates when driven by the piezoelectric element. The driving frequency f [Hz] of the piezoelectric element and the piezoelectric constant d of the piezoelectric element are respectively 31 [m / v], the ratio x of the molar fraction of sodium to the total molar fraction of potassium and sodium in the piezoelectric layer, and the viscosity μ [Pa·s] of the liquid at 25° C. satisfy the relationship shown in formula (1).

Description

Technical Field

[0001] The present disclosure relates to a liquid drop ejection head and a liquid drop ejection device. Background Art

[0002] Regarding a liquid droplet ejection head, Patent Document 1 discloses a head that includes a piezoelectric element whose main material is lead zirconate titanate (PZT) and ejects liquid as liquid droplets.

[0003] In a piezoelectric droplet ejection head, from the perspective of reducing the environmental burden, a lead-free piezoelectric material that suppresses the lead (Pb) content is desired to replace PZT. Among such lead-free piezoelectric materials, potassium sodium niobate (KNN)-based materials are known to have relatively excellent piezoelectric properties, and research has been conducted on their composition and properties. Here, the image quality of the print performed by the piezoelectric droplet ejection head and the life of the droplet ejection head will not only change according to the composition and properties of the piezoelectric material, but also according to the use conditions such as the viscosity of the liquid and the drive frequency of the droplet ejection head. In addition, in general, KNN-based materials have the following characteristics that are different from PZT, that is, compared with PZT, the displacement when voltage is applied is smaller, and the temperature dependence of the displacement is higher. When using KNN-based materials as piezoelectric materials for droplet ejection heads, there has been insufficient research on technologies that achieve good image quality and long life by taking into account the characteristics of such KNN-based materials and the use conditions of the droplet ejection head.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-58169 Summary of the Invention

[0005] According to a first embodiment of the present disclosure, a droplet ejection head is provided. The droplet ejection head comprises: a nozzle that ejects liquid as droplets; a pressure chamber forming substrate that forms a pressure chamber connected to the nozzle; a piezoelectric element; and a vibration plate that is arranged between the pressure chamber forming substrate and the piezoelectric element, forms a part of the wall surface of the pressure chamber, and vibrates by the drive of the piezoelectric element. The piezoelectric element comprises a first electrode, a second electrode, and a piezoelectric layer arranged between the first electrode and the second electrode, wherein the piezoelectric layer comprises a perovskite-type composite oxide containing potassium, sodium, and niobium as a main component. The driving frequency f [Hz] representing the frequency at which the piezoelectric element is driven, the piezoelectric constant d of the piezoelectric element 31 [m / v], the ratio x of the molar fraction of sodium to the total molar fraction of potassium and sodium in the piezoelectric layer, and the viscosity μ [Pa·s] of the liquid at 25° C. satisfy the relationship shown in the following formula (1).

[0006] 5.3×10-11 ≤(d 31 ·x) / (μ·f)≤3.0×10 -9 ……(1)

[0007] According to a second aspect of the present disclosure, a droplet ejection device is provided, comprising: the droplet ejection head of the above aspect; a moving mechanism for changing the relative position of the droplet ejection head and a medium; and a control unit for controlling the droplet ejection head and the moving mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is an explanatory diagram showing the schematic structure of a liquid droplet ejection device.

[0009] Figure 2 This is an exploded perspective view showing the structure of a droplet ejection head.

[0010] Figure 3 Schematic diagram showing a cross section of a main portion of a droplet ejection head along the Y direction and the Z direction.

[0011] Figure 4 To express Figure 3 Ⅳ-Ⅳ cross-sectional view of the pressure chamber and the piezoelectric part.

[0012] Figure 5 This is the first diagram showing the results of a performance evaluation test of a liquid droplet ejection head.

[0013] Figure 6 This is the second diagram showing the results of the performance evaluation test of the droplet ejection head.

[0014] Figure 7 The third diagram shows the results of the performance evaluation test of the liquid droplet ejection head. DETAILED DESCRIPTION

[0015] A. First embodiment:

[0016] Figure 1 1 is an explanatory diagram showing a schematic structure of a liquid droplet ejection device 100 according to a first embodiment. Figure 1 , arrow marks along mutually orthogonal X, Y, and Z directions are shown. The X, Y, and Z directions are directions along three mutually orthogonal spatial axes, namely, the X axis, the Y axis, and the Z axis, and include directions along one side of the X axis, the Y axis, and the Z axis and opposite directions thereof. Specifically, the positive directions along the X axis, the Y axis, and the Z axis are respectively the +X direction, the +Y direction, and the +Z direction, and the negative directions along the X axis, the Y axis, and the Z axis are respectively the -X direction, the -Y direction, and the -Z direction. In addition, in Figure 1In the diagram, the X-axis and the Y-axis are axes along the horizontal plane, and the Z-axis is an axis along the vertical line. Therefore, in this embodiment, the -Z direction is the direction of gravity. In other figures, arrows along the X, Y, and Z directions are also shown as appropriate. Figure 1 The X, Y, and Z directions in FIG. 1 and the X, Y, and Z directions in other figures represent the same directions. In this specification, the term "orthogonal" means including a range of 90 degrees ± 10 degrees.

[0017] The droplet ejection device 100 ejects liquid in the form of droplets. "Droplets" refers to the state of the liquid ejected from the droplet ejection device 100, including states such as granular, tear-like, and linear trailing forms. Furthermore, the term "liquid" as used herein refers to any material that can be consumed by the droplet ejection device 100. For example, "liquid" refers to any material in a liquid phase. Liquids with high or low viscosity, as well as liquid metals such as sols, gel water, other inorganic solvents, organic solvents, solutions, liquid resins, and molten metals are also included in the term. Furthermore, "liquid" encompasses not only liquids as a state of matter but also materials composed of solid functional material particles, such as pigments and metal particles, dissolved, dispersed, or mixed in a solvent. Representative examples of liquids include inks and liquid crystals. Ink includes various liquid compositions, such as general water-based inks, oil-based inks, gel inks, and hot-melt inks.

[0018] The droplet ejection device 100 in this embodiment is an inkjet printer that prints an image on a medium P by ejecting ink as droplets. The droplet ejection device 100 ejects droplets onto a medium P, such as paper, based on print data indicating the presence / absence (ON / OFF) of dots on the medium P, thereby forming dots at various locations on the medium P and printing an image on the medium P. In addition to paper, the medium P can also include materials capable of retaining liquids, such as plastic, film, fiber, cloth, leather, metal, glass, wood, and ceramics.

[0019] The droplet ejection device 100 includes a droplet ejection head 200 , a moving mechanism 40 , an ink cartridge 80 , and a control unit 110 .

[0020] The control unit 110 is comprised of a computer equipped with one or more processors, a main memory device, and an input / output interface for external signal input and output. The control unit 110 controls the droplet ejection head 200 and the movement mechanism 40 according to print data, thereby ejecting droplets from the droplet ejection head 200 onto the medium P, thereby printing an image on the medium P. In other words, the control unit 110 controls the droplet ejection operation of the droplet ejection head 200.

[0021] The moving mechanism 40 changes the relative position between the droplet ejection head 200 and the medium P. In this embodiment, the moving mechanism 40 includes a head moving mechanism 41 that moves the droplet ejection head 200 and a transport motor 51 that transports the medium P. The head moving mechanism 41 includes a carriage 42 that holds the droplet ejection head 200, a drive motor 46 for driving the carriage 42, and a drive belt 47.

[0022] The carriage 42 moves back and forth in the main scanning direction due to the driving force transmitted to it from the drive motor 46 via the drive belt 47. Consequently, the droplet ejection head 200 moves back and forth in the main scanning direction together with the carriage 42. The transport motor 51 drives rollers (not shown) to transport the medium P along a sub-scanning direction that intersects the main scanning direction. In this manner, the moving mechanism 40 in this embodiment changes the relative position of the droplet ejection head 200 and the medium P by moving both the droplet ejection head 200 and the medium P. In this embodiment, the main scanning direction is along the Y direction. The sub-scanning direction is along the X direction and is orthogonal to the main scanning direction. In other embodiments, the main scanning direction and the sub-scanning direction may not be orthogonal to each other.

[0023] In other embodiments, the moving mechanism 40 may not move both the droplet ejection head 200 and the medium P. For example, the relative position of the droplet ejection head 200 and the medium P may be changed by moving only the medium P. More specifically, for example, the droplet ejection head 200 may be configured to span the entire width of the medium P, while the moving mechanism 40 may be comprised of rollers and a motor that transport the medium P relative to the head. This printing method, in which printing is performed by transporting the medium P without driving the droplet ejection head 200, is referred to as a single-pass method.

[0024] The ink cartridges 80 store ink, which is the liquid to be supplied to the droplet ejection head 200. In this embodiment, the four ink cartridges 80 are detachably mounted on the carriage 42, and each of the four ink cartridges 80 stores four types of ink having different colors as liquid. Alternatively, the ink cartridges 80 may be mounted on the main body of the droplet ejection device 100, rather than on the carriage 42. Furthermore, in other embodiments, the ink storage mechanism may be, for example, an ink tank or a bag-shaped liquid bag formed from a flexible film. The type and number of ink storage mechanisms, as well as the type and amount of stored ink, are not particularly limited.

[0025] The droplet ejection head 200 in this embodiment ejects ink supplied from the ink cartridge 80 in the form of droplets onto the medium P being transported in the sub-scanning direction while reciprocating in the main scanning direction. The droplet ejection head 200 is electrically connected to the control unit 110 via a flexible cable 48. The droplet ejection device 100 may include two or more droplet ejection heads 200.

[0026] Figure 2 This is an exploded perspective view showing the structure of the droplet ejection head 200 in this embodiment. The droplet ejection head 200 in this embodiment is composed of a nozzle plate 210, a pressure chamber forming substrate 220, a piezoelectric portion 230, and a sealing portion 250 stacked in the Z direction. Furthermore, a drive circuit 90 is provided on the +Z-side surface of the sealing portion 250.

[0027] The nozzle plate 210 in this embodiment is a thin plate-shaped component, and is configured so that its plate surface is along the X direction and the Y direction. On the nozzle plate 210, a plurality of nozzles 211 are formed so as to be arranged in a row along the X direction. The droplet ejection head 200 ejects the liquid as droplets from the nozzles 211. In this embodiment, the nozzle plate 210 is formed of stainless steel (SUS). In addition, the nozzle plate 210 can also be formed of other types of metals, such as nickel (Ni) alloy, or resin materials such as polyimide and dry film resist, single crystal substrates of silicon (Si), inorganic materials such as glass ceramics, etc. In addition, more than two rows of nozzles 211 can also be formed on the nozzle plate 210.

[0028] The pressure chamber forming substrate 220 is a plate-shaped component that defines flow paths such as the pressure chambers 221. The pressure chamber forming substrate 220 is bonded to the +Z surface of the nozzle plate 210, for example, via an adhesive or hot melt film, or directly bonded to the +Z surface of the nozzle plate 210. The pressure chamber forming substrate 220 has holes HL formed therein, extending through the pressure chamber forming substrate 220 in the Z direction, for forming the pressure chambers 221, the ink supply paths 223, and the communication portions 225. In this embodiment, the pressure chamber forming substrate 220 is formed from a single crystal Si substrate. Alternatively, the pressure chamber forming substrate 220 may be formed from another material, such as another ceramic material or a glass material, primarily Si. In this specification, the term "primary component" refers to a component present in a material or component at a proportion of 50% by mass or greater, preferably 80% by mass or greater.

[0029] In this embodiment, multiple pressure chambers 221 are arranged side by side along the X-direction. A pressure chamber-forming substrate 220 is stacked on the nozzle plate 210, thereby connecting the multiple pressure chambers 221 to the multiple nozzles 211. When viewed from the Z-direction, each pressure chamber 221 has a substantially parallelogram shape with the Y-direction as its longitudinal direction. Ink, as a liquid, circulates within the pressure chambers 221.

[0030] The communication portion 225 is a hollow space shared by the multiple pressure chambers 221. It communicates with the multiple pressure chambers 221, thereby forming a common liquid chamber, described later. The communication portion 225 communicates with each of the multiple pressure chambers 221 via the ink supply path 223. The ink supply path 223 has a portion narrower than the width of the pressure chambers 221. This prevents pressure loss within the pressure chambers 221 and prevents the pressure generated in each pressure chamber 221 from propagating to other pressure chambers 221 via the common liquid chamber, a phenomenon known as cross-flow.

[0031] The piezoelectric section 230 is constructed by laminating a vibration plate 231 and a piezoelectric element 240 on a pressure chamber-forming substrate 220. When the piezoelectric element 240 is driven, the vibration plate 231, which is positioned between the piezoelectric element 240 and the pressure chamber-forming substrate 220, vibrates, thereby changing the volume of the pressure chamber 221. Details of the piezoelectric section 230 are described below. The piezoelectric section 230 is also sometimes referred to as a piezoelectric device or an actuator.

[0032] The sealing portion 250 is bonded to the piezoelectric portion 230 via an adhesive. The sealing portion 250 includes a piezoelectric element holding portion 251, which is a space for holding the piezoelectric element 240, and a manifold portion 252 that is connected to the connecting portion 225 of the pressure chamber forming substrate 220 and forms a common liquid chamber. In this embodiment, the sealing portion 250 is formed using a Si single crystal substrate. In addition, the sealing portion 250 can also be formed from other ceramic materials or glass materials. In this case, the sealing portion 250 is preferably formed from a material having a thermal expansion coefficient substantially the same as that of the pressure chamber forming substrate 220.

[0033] The drive circuit 90 supplies a drive signal to the piezoelectric element 240 to drive the piezoelectric element 240. For example, a circuit board or a semiconductor integrated circuit (IC) can be used as the drive circuit 90. The drive circuit 90 and the piezoelectric element 240 are electrically connected via lead electrodes 295 and electrical wiring (not shown). Furthermore, the drive circuit 90 and the control unit 110 are electrically connected via electrical wiring (not shown).

[0034] Figure 3Schematic diagram showing a cross section of the main part of the droplet ejection head 200 along the Y direction and the Z direction. Figure 3 As shown, by stacking the aforementioned components, the manifold portion 252 and the connecting portion 225 are connected, forming a manifold 293 that serves as a common liquid chamber for each of the multiple pressure chambers 221. Furthermore, the nozzles 211, the pressure chambers 221, the ink supply path 223, and the manifold 293 are connected, forming an ink flow path. The droplet ejection head 200 uses the piezoelectric portion 230 to change the volume of the pressure chambers 221, thereby ejecting liquid supplied to the pressure chambers 221 via the flow path as droplets from the nozzles 211. The manifold 293 is sometimes referred to as a common liquid chamber or a reservoir.

[0035] Figure 4 for Figure 3 The pressure chamber 221 and the piezoelectric part 230 are shown in a IV-IV cross-sectional view. As described above, the piezoelectric part 230 includes a vibration plate 231 and a piezoelectric element 240. Figure 3 as well as Figure 4 As shown, the piezoelectric element 240 includes a piezoelectric layer 260 , a plurality of first electrodes 270 , and a second electrode 280 .

[0036] like Figure 3 as well as Figure 4 As shown, the vibration plate 231, the piezoelectric layer 260, the first electrode 270, and the second electrode 280 are stacked along the thickness direction of the piezoelectric layer 260, more specifically, along the Z direction. The first electrode 270 is arranged between the piezoelectric layer 260 and the vibration plate 231. The piezoelectric layer 260 is arranged between the first electrode 270 and the second electrode 280. That is, in this embodiment, the vibration plate 231, the first electrode 270, the piezoelectric layer 260, and the second electrode 280 are stacked in sequence along the Z direction. In addition, generally speaking, the droplet ejection head 200 is used in a state where the nozzle 211 is located vertically below, as in this embodiment. In this case, the first electrode 270 is also called the lower electrode, and the second electrode 280 is also called the upper electrode. In addition, in other embodiments, for example, the nozzle plate 210 can also function as a vibration plate.

[0037] As described above, the vibration plate 231 is configured to vibrate when driven by the piezoelectric element 240. Figure 3 as well as Figure 4As shown, the vibration plate 231 in this embodiment includes an elastic layer 232 and an insulating layer 233. The elastic layer 232 is located on the pressure chamber forming substrate 220 and on the pressure chamber 221, while the insulating layer 233 is located on the elastic layer 232. In this embodiment, the elastic layer 232 is formed as an elastic film primarily composed of silicon dioxide (SiO2), while the insulating layer 233 is formed as an insulating film primarily composed of zirconium oxide (ZrO2). The insulating layer 233 is also called a protective layer.

[0038] In this embodiment, a plurality of first electrodes 270 are provided in a separate manner relative to the plurality of pressure chambers 221. The second electrode 280 is provided in a common manner relative to the plurality of pressure chambers 221. In addition, the electrodes provided in a separate manner relative to the plurality of pressure chambers 221 are sometimes referred to as separate electrodes, and the electrodes provided in a common manner are sometimes referred to as common electrodes. That is, in this embodiment, the lower electrode, i.e., the first electrode 270, is a separate electrode, and the upper electrode, i.e., the second electrode 280, is a common electrode. Figure 3 as well as Figure 4 As shown, in this embodiment, the first electrodes 270 are arranged side by side in the X direction with their longitudinal directions along the Y direction. The second electrode 280 is provided continuously in the X and Y directions across the plurality of pressure chambers 221 so as to cover the piezoelectric layer 260 from above.

[0039] The first electrode 270 and the second electrode 280 are formed of, for example, various metals such as platinum (Pt), iridium (Ir), titanium (Ti), tungsten (W), and tantalum (Ta), or conductive metal oxides such as lanthanum nickelate (LaNiO3). The first electrode 270 and the second electrode 280 may also be formed of, for example, multiple layers composed of the aforementioned various metals or conductive metal oxides. In addition, the first electrode 270 and the second electrode 280 may be formed of different materials.

[0040] In other embodiments, an adhesion layer for improving the adhesion between the first electrode 270 and the vibration plate 231 may be provided between the first electrode 270 and the vibration plate 231. The adhesion layer is formed of, for example, titanium (Ti) or titanium oxide.

[0041] like Figure 4 As shown, the piezoelectric layer 260 includes a first active portion Ac and a second active portion NAc. In this embodiment, the first active portion Ac corresponds to the portion of the piezoelectric layer 260 that overlaps with both the first electrode 270 and the second electrode 280 when viewed along the Z direction. Furthermore, the second active portion NAc corresponds to the portion of the piezoelectric layer 260 that does not overlap with either or both of the first electrode 270 and the second electrode 280 when viewed along the Z direction.

[0042] The piezoelectric element 240 is driven by applying a voltage to the piezoelectric layer 260 via the first electrode 270 and the second electrode 280. More specifically, the piezoelectric element 240 is displaced by piezoelectric deformation generated in the first active portion Ac of the piezoelectric layer 260 when a voltage is applied to the piezoelectric layer 260. This displacement of the piezoelectric element 240 causes the vibration plate 231 to vibrate, thereby changing the volume of the pressure chamber 221. Furthermore, the piezoelectric deformation generated in the second active portion NAc of the piezoelectric layer 260 when a voltage is applied to the piezoelectric layer 260 is smaller than the piezoelectric deformation generated in the first active portion Ac of the piezoelectric layer 260 when a voltage is applied to the piezoelectric layer 260.

[0043] The piezoelectric layer 260 is primarily composed of a potassium sodium niobate (KNN)-based composite oxide. KNN-based composite oxides are perovskite-type composite oxides composed of potassium (K), sodium (Na), and niobium (Nb), represented by the general formula ABO₃. KNN-based oxides are represented by the following formula (c1).

[0044] (K 1-X , Na X )NbO3…(c1)

[0045] KNN-based composite oxides are lead-free piezoelectric materials that contain a reduced content of lead (Pb), resulting in excellent biocompatibility and a low environmental impact. Furthermore, since KNN-based composite oxides exhibit superior piezoelectric properties even among lead-free piezoelectric materials, they contribute to improved properties. Furthermore, KNN-based composite oxides have a higher Curie temperature than other lead-free piezoelectric materials, such as BNT-BKT-BT and [(Bi, Na)TiO3]-[(Bi, K)TiO3]-[BaTiO3], and are less susceptible to depolarization due to temperature increases, allowing them to be used at higher temperatures.

[0046] In addition, "lead-free" materials do not necessarily need to be materials that do not contain Pb at all. As long as they are materials that basically do not contain Pb, for example, they may also contain Pb as an unavoidable component. From the perspective of reducing the environmental burden, in the droplet ejection head 200, the Pb content in the piezoelectric portion 230, that is, the Pb content in the vibration plate 231 and the piezoelectric element 240, is preferably, for example, 0.1% by mass or less. As a result, the piezoelectric portion 230 is excellent in biocompatibility, and the environmental burden caused by the piezoelectric portion 230 is reduced. In addition, from the same point of view, the piezoelectric portion 230 is preferably not to contain bismuth (Bi).

[0047] In the above formula (c1), the content of Na is preferably 10 mol% or more and 90 mol% or less relative to the total amount of the metal elements constituting the A site. That is, in the above formula (1), it is preferably 0.1≤X≤0.9. Accordingly, a composite oxide having a composition that is favorable for piezoelectric properties is obtained. In addition, the content of Na is more preferably 30 mol% or more and 80 mol% or less relative to the total amount of the metal elements constituting the A site, and further preferably 40 mol% or more and 75 mol% or less. That is, in the above formula (1), it is more preferably 0.3≤X≤0.8, and further preferably 0.4≤X≤0.75. Accordingly, a composite oxide having a composition that is more favorable for piezoelectric properties is obtained.

[0048] The alkali metals at the A site of KNN, namely K and Na, may be added in excess or in deficiency relative to the stoichiometric composition. Therefore, the composite oxide in this embodiment is also represented by the following formula (c2).

[0049] (K M(1-X) , Na MX )NbO3…(c2)

[0050] M in the above formula (c2) represents the amount of alkali metal added in excess or insufficient relative to the stoichiometric composition. For example, if M = 1.1, it means that when the amount of K and Na in the stoichiometric composition is set to 100 mol%, a total of 110 mol% of K and Na are contained. If A = 0.9, it means that when the amount of K and Na in the stoichiometric composition is set to 100 mol%, a total of 90 mol% of K and Na are contained. In addition, when the alkali metal at the A site is neither excessive nor insufficient relative to the stoichiometric composition, M = 1.0. From the viewpoint of improving the characteristics of the piezoelectric layer 260, it is preferably 0.85≤M≤1.20, more preferably 0.90≤M≤1.15, and even more preferably 0.95≤M≤1.10.

[0051] The piezoelectric material constituting the piezoelectric layer 260 only needs to be a KNN-based composite oxide and is not limited to the composition shown by the above formula (1). It can also be, for example, a metal element (additive) other than potassium, sodium, or niobium included in the A site or B site of KNN. Examples of such additives include manganese (Mn), lithium (Li), barium (Ba), calcium (Ca), strontium (Sr), zirconium (Zr), titanium (Ti), bismuth (Bi), tantalum (Ta), antimony (Sb), iron (Fe), cobalt (Co), silver (Ag), magnesium (Mg), zinc (Zn), and copper (Cu). The piezoelectric material may contain one of these other metal elements or two or more. The amount of such additives added is preferably less than 20% by mass relative to the total amount of the element as the main component, more preferably less than 15% by mass, and even more preferably less than 10% by mass. The reason for this is that the addition of additives improves the various properties of the piezoelectric layer 260, making it easier to diversify its structure and functions. On the other hand, the fewer additives, the easier it is to utilize the KNN properties of the piezoelectric layer 260. Furthermore, even when the piezoelectric layer 260 contains these additives, it is preferably configured to have an ABO3-type perovskite structure.

[0052] The piezoelectric layer 260 preferably contains Cu as an additive. This can suppress droplet ejection defects in the droplet ejection head 200. Furthermore, the piezoelectric layer 260 preferably contains Mn as an additive. This can suppress leakage current in the piezoelectric element 240. This can suppress heat generation in the piezoelectric element 240 and extend the life of the piezoelectric element 240.

[0053] In this embodiment, the piezoelectric layer 260 is formed as a polycrystal of a KNN-based composite oxide composed of multiple single crystals. Therefore, compared to a case where the piezoelectric layer 260 is formed as a single crystal, when stress is generated in the piezoelectric element 240, the stress is dispersed and more evenly distributed within the surface of the piezoelectric element 240. This reduces stress failure in the piezoelectric element 240, thereby improving reliability.

[0054] When the piezoelectric layer 260 is formed as a polycrystalline body, the various additives described above may also be included in the grain boundaries of the piezoelectric layer 260. In particular, Mn is preferably included in the form of, for example, manganese oxide, in the grain boundaries of the piezoelectric layer 260. This fills the vacancies in the grain boundaries of the piezoelectric layer 260, effectively suppressing leakage current when voltage is applied to the piezoelectric element 240.

[0055] The average particle size of the crystal grains in the piezoelectric layer 260 is preferably not less than 0.15 μm and not more than 3 μm. Accordingly, since the average particle size is not less than 0.15 μm, the reduction in the piezoelectric characteristics of the piezoelectric layer 260 caused by the crystal grains being too small can be suppressed. Therefore, the piezoelectric characteristics can be further improved. In addition, since the average particle size is not more than 3 μm, the occurrence of cracks in the piezoelectric layer 260 can be further suppressed. In addition, the average particle size of the crystal grains can be obtained based on the SEM image of the piezoelectric layer 260 obtained using a scanning electron microscope (SEM). In more detail, the average particle size of the crystal grains is calculated by measuring the particle sizes of, for example, more than 100 crystal grains in the SEM image of the piezoelectric layer 260 at the same magnification, and calculating the arithmetic mean of the measured particle sizes. In addition, in other embodiments, the average particle size of the crystal grains may be, for example, less than 0.15 μm or may exceed 3 μm.

[0056] In addition, KNN can also be a mixed crystal with other composite oxides having an ABO3 type perovskite structure that are different from KNN. That is, in this specification, "a perovskite type composite oxide containing K, Na, and Nb" includes a piezoelectric material represented as a mixed crystal, wherein the mixed crystal includes a composite oxide having an ABO3 type perovskite structure containing K, Na, and Nb, and other composite oxides having an ABO3 type perovskite structure. Although other composite oxides are not particularly limited, they are preferably non-lead piezoelectric materials so that the piezoelectric layer 260 can be configured as a non-lead piezoelectric material. In addition, it is preferred that the composite oxide contains substantially no bismuth (Bi).

[0057] Piezoelectric materials also include materials having a composition in which a portion of an element is missing, materials having a composition in which a portion of an element is in excess, and materials having a composition in which a portion of an element is substituted with another element. Materials whose compositions deviate from the stoichiometric composition due to missing / excessive elements, and materials in which a portion of an element is substituted with another element, are also included in the piezoelectric material of this embodiment, as long as the basic properties of the piezoelectric layer 260 are not changed.

[0058] Preferably, in the piezoelectric element 240, the thickness of the elastic layer 232 is set to 0.1 μm to 2.0 μm, the thickness of the insulating layer 233 is set to 0.01 μm to 1.0 μm, the thickness of the piezoelectric layer 260 is set to 0.1 μm to 5.0 μm, the thickness of the first electrode 270 is set to 0.01 μm to 1.0 μm, and the thickness of the second electrode 280 is set to 0.01 μm to 1.0 μm. The thicknesses of these elements are merely examples and can be varied without departing from the spirit of the present disclosure.

[0059] When manufacturing the piezoelectric portion 230 in this embodiment, first, the vibration plate 231 is prepared. The elastic layer 232 of the vibration plate 231 is formed on the pressure chamber forming substrate 220 by, for example, thermally oxidizing a Si substrate, more specifically, a pressure chamber forming substrate 220 in a state where the hole HL is not formed. The insulating layer 233 is formed on the elastic layer 232 by, for example, a CVD (chemical vapor deposition) method. Thus, the vibration plate 231 is formed. In other embodiments, the elastic layer 232 may also be formed on the pressure chamber forming substrate 220 by, for example, a CVD method. In addition, the hole HL of the pressure chamber forming substrate 220 is formed by, for example, anisotropic etching using an alkaline solution such as potassium hydroxide (KOH) after the vibration plate 231 is formed on the pressure chamber forming substrate 220. More specifically, in this embodiment, the hole HL is formed after the piezoelectric portion 230 is completed.

[0060] Next, the first electrode 270 is formed on the vibration plate 231 by patterning, etching, or the like.

[0061] Next, a piezoelectric layer 260 is formed on the first electrode 270 and the vibration plate 231. The piezoelectric layer 260 in this embodiment is formed into a thin film by a solution method such as MOD (Metal Organic Deposition) or a sol-gel method. Solution methods such as MOD and sol-gel are also called wet methods or liquid phase methods. In this way, by forming the piezoelectric layer 260 using a solution method, the productivity of the piezoelectric layer 260 can be improved. In other embodiments, the piezoelectric layer 260 can also be formed by, for example, a gas phase method such as sputtering or a solid phase method such as powder compacting.

[0062] When forming the piezoelectric layer 260 using a solution method, for example, a precursor liquid containing a predetermined metal complex is first prepared. The precursor liquid is a sol or solution containing the metal elements that will form the raw materials for the piezoelectric layer 260. For example, a metal complex that forms a composite oxide containing K, Na, and Nb upon firing is dissolved or dispersed in an organic solvent. If additives such as Cu and Mn are to be added to the piezoelectric layer 260, the metal complex containing the additive may be further mixed into the precursor liquid.

[0063] Examples of metal complexes containing K include potassium 2-ethylhexanoate and potassium acetate. Examples of metal complexes containing Na include sodium 2-ethylhexanoate and sodium acetate. Examples of metal complexes containing Nb include niobium 2-ethylhexanoate and pentaethoxyniobium. When Mn is added as an additive, examples of metal complexes containing Mn include manganese 2-ethylhexanoate. When Cu is added as an additive, examples of metal complexes containing Cu include copper acetate. In this case, two or more metal complexes may be used in combination. For example, potassium 2-ethylhexanoate and potassium acetate may be used in combination as metal complexes containing K. Examples of solvents include 2-n-butoxyethanol or n-octane, or mixed solvents thereof. The precursor solution may contain additives that stabilize the dispersion of metal complexes containing K, Na, and Nb. Examples of such additives include 2-ethylhexanoic acid.

[0064] After the precursor liquid is prepared as described above, a coating process is performed in which the precursor liquid is coated on the first electrode 270 and the vibration plate 231 to form a precursor film. In the coating process, the precursor liquid is coated on the first electrode 270 and the vibration plate 231 by, for example, spin coating. Next, a drying process is performed in which the precursor film is heated to a predetermined temperature, for example, about 130°C to 250°C, and dried for a fixed time. Next, a degreasing process is performed in which the dried precursor film is degreased by heating it at a predetermined degreasing temperature, for example, 300°C to 450°C. Then, a firing process is performed in which the degreased precursor film is crystallized by heating it at a higher predetermined firing temperature, for example, 600°C to 800°C. Examples of heating devices used in the drying, degreasing, and firing steps include RTA (Rapid Thermal Annealing) devices or hot plates that utilize infrared lamp irradiation for heating. By performing the aforementioned coating through firing steps, a piezoelectric film composed primarily of KNN and formed as a polycrystalline structure is formed. Furthermore, during the firing step, the Mn contained in the precursor liquid precipitates at the grain boundaries between the KNN crystals.

[0065] The piezoelectric layer 260 in this embodiment is formed by repeatedly performing the coating process to the firing process to form a multi-layer piezoelectric film. In this embodiment, the portion of the piezoelectric layer 260 formed on the first electrode 270 corresponds to the above-mentioned first active portion Ac, and the portion not formed on the first electrode 270 but formed on the vibration plate 231 corresponds to the above-mentioned second active portion NAc. In addition, in a series of processes from the coating process to the firing process, the firing process can also be performed after repeating the coating process to the degreasing process multiple times. In addition, the heating rate in the drying process is preferably set to 30°C to 350°C / sec. In the solution method, by firing the piezoelectric film at such a heating rate, a non-quasi-cubic piezoelectric layer 260 can be achieved. The "heating rate" mentioned here specifies the time rate of change of temperature from the degreasing temperature to the firing temperature in the firing process.

[0066] Thereafter, the piezoelectric layer 260 composed of a plurality of piezoelectric films is patterned. As patterning, for example, dry etching such as reactive ion etching or ion milling, or wet etching using an etching solution is performed. Thereafter, the second electrode 280 is formed on the piezoelectric layer 260, for example, by the same method as the first electrode 270. It is also possible to appropriately perform a reheating treatment in a temperature range of 600°C to 800°C before and after the second electrode 280 is formed on the piezoelectric layer 260. In this way, by performing the reheating treatment, a good interface can be formed between the piezoelectric layer 260 and the first electrode 270 and the second electrode 280, and the crystallinity of the piezoelectric layer 260 can be improved. The reheating treatment is also called a post-annealing treatment.

[0067] Through the above steps, the piezoelectric portion 230 including the piezoelectric element 240 having the first electrode 270, the piezoelectric layer 260, and the second electrode 280, and the vibration plate 231 is completed. In each of the above steps, etching may be performed as appropriate to smooth the surface of each component or adjust its thickness.

[0068] The inventors of the present disclosure have conducted extensive research to improve the image quality of printing performed by the droplet ejection head 200 and to extend the life of the droplet ejection head 200. As a result, they have found that in the droplet ejection head 200, the driving frequency f [Hz] indicating the frequency at which the piezoelectric element 240 is driven, the piezoelectric constant d of the piezoelectric element 240, and the piezoelectric constant d of the piezoelectric element 240 are the same. 31 When [m / v], the ratio x of Na in the piezoelectric layer 260, and the viscosity μ [Pa·s] of the liquid satisfy the relationship represented by the following formula (1), good image quality and a long life can be achieved.

[0069] 5.3×10 -11 ≤(d 31 ·x) / (μ·f)≤3.0×10 -9 …(1)

[0070] More specifically, the ratio x represents the ratio of the mole fraction of Na in the piezoelectric layer 260 to the total mole fraction of K and Na. That is, the ratio x is the same as X in the above formula (c1). In addition, the viscosity μ represents the viscosity of the liquid ejected as droplets from the droplet ejection head 200 at 25°C. In the following, (d 31 ·x) / (μ·f) is also expressed as parameter P1.

[0071] Furthermore, the inventors of the present disclosure have further discovered that when the piezoelectric layer 260 contains Cu, the driving frequency f and the piezoelectric constant d 31When the ratio x, the viscosity μ, and the atomic percentage y [at%] of Cu in the piezoelectric layer 260 satisfy the relationship shown in the following formula (2), it is possible to suppress ejection defects of the droplet ejection head 200, thereby achieving better image quality. 31 ·x·y) / (μ·f) is also expressed as parameter P2.

[0072] 5.3×10 -12 ≤(d 31 ·x·y) / (μ·f)≤6.0×10 -9 …(2)

[0073] Furthermore, the inventors of the present disclosure have further discovered that when the piezoelectric layer 260 contains Mn, the driving frequency f and the piezoelectric constant d 31 When the ratio x, the viscosity μ, and the atomic percentage z [at%] of Mn in the piezoelectric layer 260 satisfy the relationship shown in the following formula (3), the life of the droplet ejection head 200 can be further extended. 31 ·x·z) / (μ·f) is also expressed as parameter P3.

[0074] 5.3×10 -12 ≤(d 31 ·x·z) / (μ·f)≤6.0×10 -9 …(3)

[0075] To verify the effectiveness of the droplet ejection head 200 in this embodiment, a performance evaluation test was conducted on multiple samples. More specifically, the performance evaluation test used samples belonging to sample group Sg1, sample group Sg2, and sample group Sg3.

[0076] As samples belonging to the sample group Sg1, the droplet ejection head 200 having the piezoelectric element 240 having the piezoelectric layer 260 without the above-mentioned additives was used. 31 , ratio x, and viscosity μ are partially or completely different. As samples belonging to the sample group Sg2, a droplet ejection head 200 having a piezoelectric element 240 having a piezoelectric layer 260 to which Cu is added as an additive was used. The driving frequency f, piezoelectric constant d 31, ratio x, viscosity μ, and atomic percentage y are partially or entirely different. As samples belonging to sample group Sg3, a droplet ejection head 200 having a piezoelectric element 240 having a piezoelectric layer 260 to which Mn is added as an additive was used. The driving frequency f, piezoelectric constant d 31 , ratio x, viscosity μ, and atomic percentage z are different in part or in whole.

[0077] The piezoelectric portion 230 of the droplet ejection head 200, serving as a sample for each sample group, was fabricated using the above-described steps. Specifically, first, a first electrode 270 was formed on the insulating layer 233 of the vibration plate 231 by sputtering and etching. Next, a coating process was performed using a sol containing the raw materials for the piezoelectric layer 260 as a precursor liquid. Drying, degreasing, and sintering were then performed to form a piezoelectric film. The coating and sintering processes were then repeated to form a piezoelectric layer 260 composed of multiple layers of piezoelectric film. Furthermore, a second electrode 280 was formed on the piezoelectric layer 260 using the same method as for the first electrode 270. In the fabrication of the piezoelectric portion 230 for the sample belonging to sample group Sg2, a precursor liquid containing Cu was used. Furthermore, in the fabrication of the piezoelectric portion 230 for the sample belonging to sample group Sg3, a precursor liquid containing Mn was used. Furthermore, the piezoelectric portion 230 of the sample belonging to each sample group was produced as the piezoelectric portion 230 not containing Pb.

[0078] The aforementioned Na ratio x, Cu atomic percentage y, and Mn atomic percentage z were adjusted by adjusting the amount of each raw material added to the precursor solution. Thus, the ratio x in each sample was adjusted to a value between 0.3 and 0.8, the atomic percentage y was adjusted to a value between 0.01 and 2.50, and the atomic percentage z was adjusted to a value between 0.01 and 2.50. Furthermore, the ratio x, atomic percentage y, and atomic percentage z in the completed piezoelectric element 240 were measured using EDX (Energy Dispersive X-ray Spectroscopy) analysis. A JEM-ARM200F manufactured by JEOL Ltd. was used for the EDX analysis.

[0079] As performance evaluation tests, image quality evaluation tests and life evaluation tests were conducted. In the image quality evaluation test, for each sample, mixed color black ink was ejected from the droplet ejection head 200, and an image with highlight and shadow parts was printed on a white printing paper, and the degree of granularity in the highlight part and the degree of blur and blurring in the shadow part were visually evaluated. The printing data used to print the image in the image quality evaluation test was set to be the same between each sample. In addition, the higher the granularity in a certain part of the image, the stronger the roughness or concave-convex feeling when visually confirming the part. In addition, mixed color black ink refers to an ink that appears black by mixing cyan, yellow and magenta colors, and is also called composite black ink.

[0080] In the image quality evaluation test, if both granularity in highlights and blurring and shading in shadows are barely noticeable, the evaluation result is set to "A." If either granularity in highlights or blurring and shading in shadows is barely noticeable, while the other is slightly noticeable, the evaluation result is set to "B." If both granularity in highlights and blurring and shading in shadows are barely noticeable, the evaluation result is set to "C." If at least one of granularity in highlights, blurring and shading in shadows is noticeably noticeable, the evaluation result is set to "D."

[0081] In the life evaluation test, the piezoelectric constant d of the piezoelectric element 240 of the droplet ejection head 200 immediately after manufacture was measured for each sample. 31 The first piezoelectric constant and the piezoelectric constant d of the piezoelectric element 240 of the droplet ejection head 200 after being used ten thousand times are shown. 31 The first piezoelectric constant and the second piezoelectric constant are compared. The first piezoelectric constant and the second piezoelectric constant are respectively calculated based on the measurement results of the displacement caused by the piezoelectric deformation of the long strip sample. In more detail, first, when observing along the Z direction, the piezoelectric element 240 is cut into a long strip shape with a length of 15 mm and a width of 4 mm, thereby making a long strip sample. Next, with one end of the long side direction of the long strip sample fixed, a voltage waveform of 0V, positive voltage, and 0V sinusoidal difference is continuously applied to one electrode of the long strip sample to cause piezoelectric deformation of the long strip sample. The displacement of the end of the long strip sample on the opposite side of the fixed end at this time is measured by a laser displacement meter, and the piezoelectric constant is calculated based on the measured displacement. In addition, as the piezoelectric constant d in the above formulas (1) to (3), 31 , the first piezoelectric constant was used.

[0082] In the life evaluation test, if the ratio of the second piezoelectric constant to the first piezoelectric constant is 0.95 or greater, the evaluation result is designated "A," if it is 0.90 or greater but less than 0.95, the evaluation result is designated "B," if it is 0.80 or greater but less than 0.90, the evaluation result is designated "C," and if it is less than 0.80, the evaluation result is designated "D." Furthermore, "using a certain droplet ejection head 200 10,000 times" means that the same printing as in the above-mentioned image quality evaluation test was performed 10,000 times using the droplet ejection head 200.

[0083] In the performance evaluation test, the driving frequency f of each sample was adjusted to 5.0×10 3 Hz and above and 30×10 3 In addition, in the performance evaluation test, the viscosity μ of each sample was adjusted to 1.0×10 -3 Pa·s or above and 30×10 -3 Pa·s or less.

[0084] Figure 5 This is the first diagram showing the results of a performance evaluation test of the liquid droplet ejection head 200 according to the present embodiment. Figure 5 The performance evaluation results of the sample group Sg1 are shown. Figure 5 As shown, in the sample group Sg1, when the parameter P1 is less than 5.3×10 -11 In the case of , the evaluation results of image quality and life are both D. In addition, similarly, when the parameter P1 exceeds 3.0×10 -9 In the case of , the evaluation results of image quality and lifespan are both D. On the other hand, when the parameter P1 is 5.3×10 -11 Above and 3.0×10 -9 In the following case, the image quality evaluation result is B, and the life evaluation result is C. That is, it can be seen that the piezoelectric constant d 31 When , the ratio x, the viscosity μ, and the driving frequency f satisfy the relationship shown in the above formula (1), good image quality and long life can be achieved.

[0085] Figure 6 This is a second diagram showing the results of a performance evaluation test of the liquid droplet ejection head 200 according to this embodiment. Figure 6 The performance evaluation results of the samples satisfying the relationship of the above formula (2) in the sample group Sg2 are shown. Figure 6 As shown, when the parameter P2 is less than 5.3×10 -12In the case of , the image quality evaluation result is B, and the life evaluation result is C. In addition, when the parameter P2 exceeds 6.0×10 -9 In the case of , the evaluation results of image quality and lifespan are both D. On the other hand, when the parameter P2 is 5.3×10 -12 Above and 6.0×10 -9 In the following case, the image quality evaluation result is A, and the life evaluation result is C. That is, it can be seen that the piezoelectric constant d 31 When the ratio x, viscosity μ, drive frequency f, and atomic percentage y satisfy the relationship shown in equation (2), better image quality can be achieved. This is believed to be due to the effect of suppressing ejection defects by adding Cu to the piezoelectric layer 260. Although not shown in the figure, the image quality and life evaluation results of the samples in sample group Sg2 that did not satisfy the relationship in equation (1) were all D.

[0086] Figure 7 FIG3 is a third diagram showing the results of a performance evaluation test of the liquid droplet ejection head 200 according to the present embodiment. Figure 7 The performance evaluation results of the samples satisfying the relationship of the above formula (3) in the sample group Sg3 are shown. Figure 7 As shown, when the parameter P3 is less than 5.3×10 -12 In the case of , the image quality evaluation result is B, and the life evaluation result is C. In addition, when the parameter P3 exceeds 6.0×10 -9 In the case of , the evaluation results of image quality and lifespan are both D. On the other hand, when the parameter P3 is 5.3×10 -12 Above and 6.0×10 -9 In the following cases, the evaluation results of image quality and lifespan are both A. In other words, it can be seen that the piezoelectric constant d 31 When the ratio x, viscosity μ, drive frequency f, and atomic percentage z satisfy the relationship shown in equation (3), better image quality and longer life can be achieved. This is believed to be the result of the addition of Mn to the piezoelectric layer 260, which suppresses leakage current and heat generation in the piezoelectric layer 260. Although not shown in the figure, the image quality and life evaluation results of the samples in sample group Sg3 that did not satisfy the relationship in equation (1) were all D.

[0087] The parameters P1, P2, and P3 can be referenced, for example, when the droplet ejection head 200 is manufactured or when the droplet ejection head 200 is used. For example, when the driving frequency f and the type of liquid used are predetermined, the piezoelectric constant d can be adjusted when the droplet ejection head 200 is manufactured so as to satisfy the relationships shown in the above equations (1), (2), and (3) for the viscosity μ of the liquid and the predetermined driving frequency f.31 , ratio x, atomic percentage y, and atomic percentage z are adjusted. In this case, the driving frequency f and viscosity μ can be determined to have a range with a lower limit and an upper limit, so that when the driving frequency f and viscosity μ are determined, no matter how the driving frequency f and viscosity μ change within the predetermined range, as long as the piezoelectric constant d is adjusted in a manner that satisfies the relationship shown in the above formulas (1), (2), and (3), 31 , ratio x, atomic percentage y, and atomic percentage z can be adjusted. Thus, a droplet ejection head 200 having a piezoelectric element 240 with a preferred composition and piezoelectric characteristics can be manufactured. In addition, for example, when using a piezoelectric element 240 having a specific piezoelectric constant d 31 When the droplet ejection head 200 includes the piezoelectric element 240 with a ratio x, the control unit 110 may control the driving frequency f within the range of 5 to 30 kHz according to the viscosity μ of the liquid to satisfy the relationship shown in the above formula (1).

[0088] According to the liquid droplet ejection head 200 in the present embodiment described above, the driving frequency f and the piezoelectric constant d 31 The ratio x of , Na, and the viscosity μ satisfy the relationship shown in the above formula (1). Thus, when the driving frequency f is within the range of 5 to 30 kHz, it is possible to achieve good image quality and extend the life of the droplet ejection head 200 by taking into account the relationship between the ink viscosity μ and the driving frequency f, which are the operating conditions of the droplet ejection head 200, and the composition and piezoelectric properties of the piezoelectric layer 260.

[0089] In this embodiment, the piezoelectric layer 260 contains copper, and the driving frequency f and the piezoelectric constant d 31 The ratio x of Na, the viscosity μ, and the atomic percentage y of copper satisfy the relationship shown in the above formula (2). This can suppress ejection defects and achieve better image quality.

[0090] In this embodiment, the piezoelectric layer 260 contains manganese, and the driving frequency f and the piezoelectric constant d 31 , the Na ratio x, the viscosity μ, and the manganese atomic percentage z satisfy the relationship shown in the above formula (3). This suppresses the occurrence of leakage current in the piezoelectric layer 260. Therefore, the life of the droplet ejection head 200 can be further extended, and ejection defects caused by heat generation in the piezoelectric layer 260 can be suppressed.

[0091] Furthermore, in this embodiment, manganese is contained in the grain boundaries of the piezoelectric layer 260 having a polycrystalline structure. This can suppress voids at the grain boundaries in the piezoelectric layer, thereby further extending the life of the droplet ejection head 200.

[0092] Furthermore, in this embodiment, the average grain size of the crystal grains in the piezoelectric layer 260 is greater than or equal to 0.15 μm and less than or equal to 3 μm. This 0.15 μm average grain size further improves the piezoelectric properties of the piezoelectric layer 260. Furthermore, the 3 μm average grain size further suppresses the occurrence of cracks in the piezoelectric layer 260.

[0093] B. Other methods:

[0094] The present disclosure is not limited to the above-mentioned embodiments and can be implemented in various ways without departing from its main purpose. For example, the present disclosure can also be implemented in the following ways. In order to solve part or all of the problems of the present disclosure, or to achieve part or all of the effects of the present disclosure, the technical features in the above-mentioned embodiments corresponding to the technical features in the various methods described below can be appropriately replaced or combined. In addition, if the technical feature is not described as a necessary technical feature in this specification, it can be appropriately deleted.

[0095] (1) According to the first embodiment of the present disclosure, a droplet ejection head is provided. The droplet ejection head comprises: a nozzle that ejects liquid as droplets; a pressure chamber forming substrate that forms a pressure chamber connected to the nozzle; a piezoelectric element; and a vibration plate that is arranged between the pressure chamber forming substrate and the piezoelectric element, forms a part of the wall surface of the pressure chamber, and vibrates by the drive of the piezoelectric element. The piezoelectric element comprises a first electrode, a second electrode, and a piezoelectric layer arranged between the first electrode and the second electrode, wherein the piezoelectric layer comprises a perovskite-type composite oxide containing potassium, sodium, and niobium as a main component. The driving frequency f [Hz] representing the frequency at which the piezoelectric element is driven, the piezoelectric constant d of the piezoelectric element, 31 [m / v], the ratio x of the molar fraction of sodium to the total molar fraction of potassium and sodium in the piezoelectric layer, and the viscosity μ [Pa·s] of the liquid at 25° C. satisfy the relationship shown in the following formula (1).

[0096] 5.3×10 -11 ≤(d 31 ·x) / (μ·f)≤3.0×10 -9 …(1)

[0097] According to this aspect, the relationship between the ink viscosity and driving frequency, which are the use conditions of the droplet ejection head, and the composition and piezoelectric characteristics of the piezoelectric layer can be taken into consideration, thereby achieving good image quality and extending the life of the droplet ejection head.

[0098] (2) In the above embodiment, the piezoelectric layer may contain copper, and the driving frequency f and the piezoelectric constant d may be 31 , the ratio x, the viscosity μ, and the atomic percentage y [at %] of copper in the piezoelectric layer satisfy the relationship shown in the following formula (2).

[0099] 5.3×10 -12 ≤(d 31 ·x·y) / (μ·f)≤6.0×10 -9 …(2)

[0100] According to such an aspect, ejection defects can be suppressed, thereby achieving better image quality.

[0101] (3) In the above embodiment, the piezoelectric layer may contain manganese, and the driving frequency f and the piezoelectric constant d may be 31 , the ratio x, the viscosity μ, and the atomic percentage z [at %] of manganese in the piezoelectric layer satisfy the relationship shown in the following formula (3).

[0102] 5.3×10 -12 ≤(d 31 ·x·z) / (μ·f)≤6.0×10 -9 …(3)

[0103] According to this aspect, the occurrence of leakage current in the piezoelectric layer can be suppressed, thereby further extending the life of the droplet ejection head and suppressing ejection defects caused by heat generation in the piezoelectric layer.

[0104] (4) In the above embodiment, the piezoelectric layer may be formed as a polycrystalline body, and manganese may be contained at the grain boundaries of the piezoelectric layer. According to this embodiment, pores at the grain boundaries of the piezoelectric layer can be suppressed, thereby further extending the life of the droplet ejection head.

[0105] (5) In the above embodiment, the average particle size of the crystal grains in the piezoelectric layer may be greater than or equal to 0.15 μm and less than or equal to 3 μm. According to this embodiment, since the average particle size is greater than or equal to 0.15 μm, the piezoelectric properties of the piezoelectric layer can be further improved. Furthermore, since the average particle size is less than or equal to 3 μm, cracks in the piezoelectric layer can be further suppressed.

[0106] (6) According to a second aspect of the present disclosure, there is provided a droplet ejection device comprising: a droplet ejection head according to the above aspect; a moving mechanism for changing the relative position of the droplet ejection head and a medium; and a control unit for controlling the droplet ejection head and the moving mechanism.

[0107] Explanation of symbols

[0108] 40…moving mechanism; 41…head moving mechanism; 42…slide; 46…driving motor; 47…driving belt; 48…flexible cable; 51…conveying motor; 80…ink cartridge; 90…driving circuit; 100…droplet ejecting device; 110…control unit; 200…droplet ejecting head; 210…nozzle plate; 211…nozzle; 220…pressure chamber forming substrate; 221…pressure chamber; 223…ink supply path; 225…connecting portion; 230…piezoelectric portion; 231…vibrating plate; 232…elastic layer; 233…insulating layer; 240…piezoelectric element; 250…sealing portion; 251…piezoelectric element holding portion; 252…manifold portion; 260…piezoelectric layer; 270…first electrode; 280…second electrode; 293…manifold; 295…lead electrode.

Claims

1. A droplet ejection head comprising: a nozzle, which ejects the liquid as droplets; a pressure chamber forming substrate, which forms a pressure chamber communicating with the nozzle; A piezoelectric element comprising a first electrode, a second electrode, and a piezoelectric layer disposed between the first electrode and the second electrode, wherein the piezoelectric layer contains a perovskite-type composite oxide containing potassium, sodium, and niobium as a main component; a vibration plate disposed between the pressure chamber forming substrate and the piezoelectric element, forming a portion of the wall surface of the pressure chamber, and vibrating when driven by the piezoelectric element; The driving frequency f represents the frequency at which the piezoelectric element is driven, and the piezoelectric constant d represents the piezoelectric element. 31 The ratio x of the mole fraction of sodium in the piezoelectric layer to the total mole fraction of potassium and the mole fraction of sodium and the viscosity μ of the liquid at 25° C. satisfy the relationship represented by the following formula (1): 5.3×10 -11 ≤(d 31 ·x) / (μ·f)≤3.0×10 -9 …(1)。 2. The liquid drop ejection head according to claim 1, wherein The piezoelectric layer contains copper, The driving frequency f, the piezoelectric constant d 31 , the ratio x, the viscosity μ, and the atomic percentage y of copper in the piezoelectric layer satisfy the relationship shown in the following formula (2): 5.3×10 -12 ≤(d 31 ·x·y) / (μ·f)≤6.0×10 -9 …(2)。 3. The liquid drop ejection head according to claim 1, wherein The piezoelectric layer contains manganese, The driving frequency f, the piezoelectric constant d 31 , the ratio x, the viscosity μ, and the atomic percentage z of manganese in the piezoelectric layer satisfy the relationship shown in the following formula (3): 5.3×10 -12 ≤(d 31 ·x·z) / (μ·f)≤6.0×10 -9 …(3)。 4. The liquid drop ejection head according to claim 3, wherein: The piezoelectric layer is formed as a polycrystalline body. Manganese is contained at grain boundaries in the piezoelectric layer.

5. The liquid drop ejection head according to claim 4, wherein: The average grain size of crystal grains in the piezoelectric layer is not less than 0.15 μm and not more than 3 μm.

6. A liquid droplet ejection device comprising: The liquid drop ejection head according to any one of claims 1 to 5; a moving mechanism for changing the relative position of the droplet ejection head and the medium; A control unit controls the liquid droplet ejection head and the moving mechanism.

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