Patent Description:
This disclosure relates to a droplet discharge head and a droplet discharge apparatus.

With regard to a droplet discharge head, <CIT> discloses a head that includes a piezoelectric element mainly made of lead zirconate titanate (PZT) and discharges a liquid as droplets.

In a piezo-type droplet discharge head, a non-lead based piezoelectric material having a reduced lead (Pb) content, which is substituted for PZT, is desired from the viewpoint of reducing an environmental load. In such a non-lead based piezoelectric material, it is known that potassium sodium niobate (KNN)-based materials have relatively excellent piezoelectric characteristics, and components and characteristics thereof are studied. Here, the image quality of printing performed by the piezo-type droplet discharge head and life of the droplet discharge head change not only depending on the components and characteristics of the piezoelectric material but also depending on use conditions such as a liquid viscosity and a driving frequency of the droplet discharge head. In addition, in general, as compared with PZT, the KNN-based material has characteristics different from those of PZT, such as a small displacement amount when a voltage is applied and high temperature dependency of the displacement amount. When the KNN-based material is used as the piezoelectric material of the droplet discharge head, it is not sufficiently studied to implement good image quality and long life by considering the above-described characteristics of the KNN-based material and the use conditions of the droplet discharge head. <CIT> discloses a droplet discharge head according to the pre-characterising clause of appended claim <NUM>, and a droplet discharge apparatus including the droplet discharge head.

A first aspect of the present disclosure provides a droplet discharge head. The droplet discharging head includes: a nozzle configured to discharge a liquid as droplets; a pressure chamber defining substrate defining a pressure chamber communicating with the nozzles; a piezoelectric element; and a vibration plate disposed between the pressure chamber defining substrate and the piezoelectric element, forming a part of a wall surface of the pressure chamber, and configured to vibrate by driving of the piezoelectric element. The piezoelectric element includes a first electrode, a second electrode, and a piezoelectric layer disposed between the first electrode and the second electrode, the piezoelectric layer containing a perovskite-type composite oxide containing potassium, sodium, and niobium as a main component. A driving frequency f [Hz] representing a frequency at which the piezoelectric element is driven, a piezoelectric constant d<NUM> [m/v] of the piezoelectric element, a ratio x of a sodium molar fraction to a total value of a potassium molar fraction and the sodium molar fraction in the piezoelectric layer, and a viscosity µ [Pa·s] of the liquid at <NUM> satisfy a relationship represented by a following formula (<NUM>).

A second aspect of the present disclosure provides a droplet discharge apparatus. The droplet discharge apparatus includes: the droplet discharging head of the above aspect; a moving mechanism configured to change a relative position between the droplet discharge head and a medium; and a control unit configured to control the droplet discharge head and the moving mechanism.

<FIG> is a schematic view showing a schematic configuration of a droplet discharge apparatus <NUM> as a first embodiment. <FIG> shows arrows along X, Y, and Z directions which are orthogonal to one another. The X, Y, and Z directions are directions along an X axis, a Y axis, and a Z axis that are three spatial axes orthogonal to one another, and each direction includes a direction on one side along a corresponding one of the X axis, the Y axis, and the Z axis, and a direction opposite thereto. Specifically, positive directions along the X axis, the Y axis, and the Z axis are a +X direction, a +Y direction, and a +Z direction, respectively, and negative directions along the X axis, the Y axis, and the Z axis are a -X direction, a -Y direction, and a -Z direction, respectively. In <FIG>, the X axis and the Y axis are axes along a horizontal plane, and the Z axis is an axis along a vertical line. Therefore, in the embodiment, the -Z direction is a direction of gravity. In other drawings, the arrows along the X, Y, and Z directions are also appropriately represented. The X, Y, and Z directions in <FIG> and X, Y, and Z directions in the other drawings represent the same directions. In the present specification, the term "orthogonal" includes a range of <NUM>° ± <NUM>°.

The droplet discharge apparatus <NUM> discharges a liquid as droplets. The term "droplet" refers to a state of the liquid discharged from the droplet discharge apparatus <NUM>, and includes granular-shaped droplets with a tail, teardrop-shaped droplets with a tail, and thread-shaped droplets with a tail. The term "liquid" used herein may be any material that can be consumed by the droplet discharge apparatus <NUM>. For example, the "liquid" may be a material when a substance is in a liquid phase, and the "liquid" also includes a material in a liquid state such as a material in a liquid state having a high or low viscosity, and sol, gel water, other inorganic solvents, organic solvents, solutions, liquid resins, and liquid metals such as metal melts. Further, the "liquid" includes not only the liquid as a state of the substance but also a liquid in which particles of a functional material made of a solid substance such as a pigment or a metal particle are dissolved, dispersed or mixed in a solvent. Typical examples of the liquids include ink and a liquid crystal. Here, the ink includes general water-based ink, oilbased ink, and various liquid compositions such as gel ink and hot melt ink.

The droplet discharge apparatus <NUM> according to the embodiment is an inkjet printer that prints an image on a medium P by discharging the ink as droplets. The droplet discharge apparatus <NUM> discharges droplets onto the medium P such as paper based on print data indicating ON/OFF of dots to the medium P, and forms dots at various positions on the medium P, thereby printing an image on the medium P. As the medium P, in addition to paper, for example, a material capable of holding a liquid, such as plastic, film, fiber, cloth, leather, metal, glass, wood, or ceramics, can be used.

The droplet discharge apparatus <NUM> includes a droplet discharge head <NUM>, a moving mechanism <NUM>, an ink cartridge <NUM>, and a control unit <NUM>.

The control unit <NUM> is implemented by a computer including one or more processors, a main storage device, and an input and output interface that inputs and outputs a signal to and from outside. The control unit <NUM> controls the droplet discharge head <NUM> and the moving mechanism <NUM> according to print data, thereby discharging droplets from the droplet discharge head <NUM> onto the medium P and printing an image on the medium P. That is, the control unit <NUM> controls a discharge operation of the droplet discharge head <NUM> that discharges droplets.

The moving mechanism <NUM> changes a relative position between the droplet discharge head <NUM> and the medium P. The moving mechanism <NUM> in the embodiment has a head moving mechanism <NUM> that moves the droplet discharge head <NUM>, and a conveyance motor <NUM> that conveys the medium P. The head moving mechanism <NUM> includes a carriage <NUM> that holds the droplet discharge head <NUM>, and a drive motor <NUM> and a drive belt <NUM> for driving the carriage <NUM>.

The carriage <NUM> reciprocates in the main scanning direction by a driving force transmitted from the drive motor <NUM> to the carriage <NUM> via the drive belt <NUM>. As a result, the droplet discharge head <NUM> reciprocates in the main scanning direction together with the carriage <NUM>. The conveyance motor <NUM> conveys the medium P along the sub scanning direction intersecting the main scanning direction by driving a roller (not shown). As described above, the moving mechanism <NUM> in the embodiment changes the relative position between the droplet discharge head <NUM> and the medium P by moving both the droplet discharge head <NUM> and the medium P. In the embodiment, the main scanning direction is a direction along the Y direction. The sub scanning direction is a direction 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.

In other embodiments, the moving mechanism <NUM> may move neither the droplet discharge head <NUM> nor the medium P, and may change the relative position between the droplet discharge head <NUM> and the medium P by only moving, for example, the medium P. More specifically, for example, the droplet discharge head <NUM> may be implemented as a head that extends over the entire width of the medium P, and the moving mechanism <NUM> may be implemented by a roller, a motor, or the like that conveys the medium P with respect to the head. Such a printing method in which printing is performed by conveying the medium P without driving the droplet discharge head <NUM> is also referred to as a single-path method.

The ink cartridge <NUM> stores the ink as a liquid to be supplied to the droplet discharge head <NUM>. In the embodiment, four ink cartridges <NUM> are attachable to and detachable from the carriage <NUM>, and four types of ink having different colors are stored as liquids in the four ink cartridges <NUM>. For example, the ink cartridge <NUM> may be attached to a main body of the droplet discharge apparatus <NUM> instead of being attached to the carriage <NUM>. In other embodiments, a mechanism for storing the ink may be, for example, an ink tank, or a bag-shaped liquid pack formed of a flexible film, and a type of the mechanism for storing the ink and the number of mechanisms and a type of the stored ink and the quantity of stored ink are not particularly limited.

The droplet discharge head <NUM> in the embodiment discharges the ink, in a form of droplets, supplied from the ink cartridge <NUM> onto the medium P conveyed along the sub scanning direction while reciprocating in the main scanning direction. The droplet discharge head <NUM> is electrically coupled to the control unit <NUM> via a flexible cable <NUM>. The droplet discharge apparatus <NUM> may include two or more droplet discharge heads <NUM>.

<FIG> is an exploded perspective view showing a configuration of the droplet discharge head <NUM> according to the embodiment. The droplet discharge head <NUM> in the embodiment is formed by stacking a nozzle plate <NUM>, a pressure chamber defining substrate <NUM>, a piezoelectric portion <NUM>, and a sealing portion <NUM> in the Z direction. A drive circuit <NUM> is provided on a surface of the sealing portion <NUM> on a +Z direction side.

The nozzle plate <NUM> in the embodiment is a thin plate-shaped member, and is disposed such that a plate surface thereof is along the X direction and the Y direction. In the nozzle plate <NUM>, the plurality of nozzles <NUM> are arranged side by side in a row along the X direction. The droplet discharge head <NUM> ejects a liquid as droplets from these nozzles <NUM>. In the embodiment, the nozzle plate <NUM> is made of stainless steel (SUS). The nozzle plate <NUM> may be formed of, for example, another type of metal such as a nickel (Ni) alloy, a resin material such as polyimide or a dry film resist, or an inorganic material such as a silicon (Si) single crystal substrate or glass ceramics. In addition, two or more rows of nozzles <NUM> may be formed in the nozzle plate <NUM>.

The pressure chamber defining substrate <NUM> is a plate-shaped member that defines a flow path of the pressure chamber <NUM> and the like. The pressure chamber defining substrate <NUM> is, directly or via an adhesive, a thermal welding film, or the like, bonded to a surface of the nozzle plate <NUM> in the +Z direction. The pressure chamber defining substrate <NUM> is formed with a hole HL penetrating the pressure chamber defining substrate <NUM> in the Z direction for defining the pressure chamber <NUM>, an ink supply path <NUM>, and a communication portion <NUM>. In the embodiment, the pressure chamber defining substrate <NUM> is formed of a Si single crystal substrate. The pressure chamber defining substrate <NUM> may be, for example, a substrate formed of another material containing Si as a main component, another ceramic material, a glass material, or the like. In the present specification, the main component refers to a component contained in a certain material, member, or the like at a ratio of <NUM>% by mass or more, preferably <NUM>% by mass or more.

In the embodiment, a plurality of pressure chambers <NUM> are arranged side by side along the X direction. By stacking the pressure chamber defining substrate <NUM> on the nozzle plate <NUM>, the plurality of pressure chambers <NUM> communicate with the plurality of nozzles <NUM>, respectively. Each pressure chamber <NUM> has a substantially parallelogram shape whose longitudinal direction is the Y direction when viewed from the Z direction. Ink as a liquid flows in the pressure chamber <NUM>.

The communication portion <NUM> is an empty portion common to each of the plurality of pressure chambers <NUM>, and communicates with the plurality of pressure chambers <NUM> and the like to form a common liquid chamber to be described later. The communication portion <NUM> communicates with each of the plurality of pressure chambers <NUM> via the ink supply path <NUM>. The ink supply path <NUM> has a portion having a width smaller than that of the pressure chamber <NUM>, and reduces a loss of pressure generated in the pressure chamber <NUM> and prevents an occurrence of so-called crosstalk, which is a phenomenon in which the pressure generated in each pressure chamber <NUM> propagates to another pressure chamber <NUM> via the common liquid chamber.

The piezoelectric portion <NUM> is formed by stacking a vibration plate <NUM> and a piezoelectric element <NUM> on the pressure chamber defining substrate <NUM>. The piezoelectric portion <NUM> vibrates the vibration plate <NUM> provided between the piezoelectric element <NUM> and the pressure chamber defining substrate <NUM> by driving the piezoelectric element <NUM>, and changes a volume of the pressure chamber <NUM>. Details of the piezoelectric portion <NUM> will be described later. The piezoelectric portion <NUM> may also be referred to as a piezoelectric device or an actuator.

The sealing portion <NUM> is bonded onto the piezoelectric portion <NUM> via an adhesive. The sealing portion <NUM> includes a piezoelectric element holding portion <NUM> which is a space for holding the piezoelectric element <NUM>, and a manifold portion <NUM> which communicates with the communication portion <NUM> of the pressure chamber defining substrate <NUM> to form the common liquid chamber. In the embodiment, the sealing portion <NUM> is formed of a Si single crystal substrate. The sealing portion <NUM> may be formed of another ceramic material, a glass material, or the like. In this case, the sealing portion <NUM> is preferably formed of a material having substantially the same thermal expansion coefficient as a thermal expansion coefficient of the pressure chamber defining substrate <NUM>.

The drive circuit <NUM> supplies a drive signal for driving the piezoelectric element <NUM> to the piezoelectric element <NUM>. As the drive circuit <NUM>, for example, a circuit substrate or a semi-conductor integrated circuit (IC) can be used. The drive circuit <NUM> and the piezoelectric element <NUM> are electrically coupled to each other via a lead electrode <NUM> and an electric wiring (not shown). The drive circuit <NUM> and the control unit <NUM> are electrically coupled to each other via an electric wiring (not shown).

<FIG> is a schematic view showing a cross section of a main part of the droplet discharge head <NUM> along the Y direction and the Z direction. As shown in <FIG>, by stacking the above-described members, the manifold portion <NUM> and the communication portion <NUM> communicate with each other, and a manifold <NUM> which is a common liquid chamber of each of the plurality of pressure chambers <NUM> is formed. Further, the nozzle <NUM>, the pressure chamber <NUM>, the ink supply path <NUM>, and the manifold <NUM> communicate with one another, thereby forming an ink flow path. The droplet discharge head <NUM> discharges the liquid supplied to the pressure chamber <NUM> through the above-described flow path as droplets from the nozzle <NUM> by the piezoelectric portion <NUM> changing the volume of the pressure chamber <NUM>. The manifold <NUM> may be referred to as the common liquid chamber or a reservoir.

<FIG> is a cross-sectional view taken along a line IV-IV of the pressure chamber <NUM> and the piezoelectric portion <NUM> in <FIG>. As described above, the piezoelectric portion <NUM> includes the vibration plate <NUM> and the piezoelectric element <NUM>. As shown in <FIG>, the piezoelectric element <NUM> includes a piezoelectric layer <NUM>, a plurality of first electrodes <NUM>, and a second electrode <NUM>.

As shown in <FIG>, the vibration plate <NUM>, the piezoelectric layer <NUM>, the first electrode <NUM>, and the second electrode <NUM> are stacked along a thickness direction of the piezoelectric layer <NUM>, more specifically, along the Z direction. The first electrode <NUM> is disposed between the piezoelectric layer <NUM> and the vibration plate <NUM>. The piezoelectric layer <NUM> is disposed between the first electrode <NUM> and the second electrode <NUM>. That is, in the embodiment, the vibration plate <NUM>, the first electrode <NUM>, the piezoelectric layer <NUM>, and the second electrode <NUM> are stacked in this order along the Z direction. In general, the droplet discharge head <NUM> is used when the nozzles <NUM> are located in a vertically downward direction as in the embodiment. In this case, the first electrode <NUM> is also referred to as a lower electrode, and the second electrode <NUM> is also referred to as an upper electrode. In other embodiments, for example, the nozzle plate <NUM> may function as a vibration plate.

As described above, the vibration plate <NUM> vibrates by driving the piezoelectric element <NUM>. As shown in <FIG>, the vibration plate <NUM> according to the embodiment includes an elastic layer <NUM> and an insulating layer <NUM>. The elastic layer <NUM> is located on the pressure chamber defining substrate <NUM> and the pressure chamber <NUM>, and the insulating layer <NUM> is located on the elastic layer <NUM>. In the embodiment, the elastic layer <NUM> is formed as an elastic film containing silica (SiO<NUM>) as a main component, and the insulating layer <NUM> is formed as an insulating film containing zirconia (ZrO<NUM>) as a main component. The insulating layer <NUM> is also referred to as a protective layer.

In the embodiment, the plurality of first electrodes <NUM> are individually provided for the plurality of pressure chambers <NUM>. The second electrode <NUM> is provided in common to the plurality of pressure chambers <NUM>. The electrodes provided individually for the plurality of pressure chambers <NUM> may be referred to as individual electrodes, and the electrode provided in common may be referred to as a common electrode. That is, in the embodiment, the first electrode <NUM>, which is the lower electrode, is the individual electrode, and the second electrode <NUM>, which is the upper electrode, is the common electrode. As shown in <FIG>, in the embodiment, the first electrodes <NUM> are arranged side by side along the X direction such that the longitudinal direction of each first electrode <NUM> is along the Y direction. The second electrode <NUM> is provided continuously in the X direction and the Y direction over the plurality of pressure chambers <NUM> so as to cover the piezoelectric layer <NUM> from above.

The first electrode <NUM> and the second electrode <NUM> are formed of various metals such as platinum (Pt), iridium (Ir), titanium (Ti), tungsten (W), and tantalum (Ta), a conductive metal oxide such as lanthanum nickelate (LaNiO<NUM>), or the like. The first electrode <NUM> and the second electrode <NUM> may be formed of a plurality of layers made of the above-described various metals, conductive metal oxide, or the like. The first electrode <NUM> and the second electrode <NUM> may be formed of different materials.

In other embodiments, an adhesion layer that improves adhesion between the first electrode <NUM> and the vibration plate <NUM> may be provided between the first electrode <NUM> and the vibration plate <NUM>. The adhesion layer is formed of titanium (Ti), titanium oxide, or the like.

As shown in <FIG>, the piezoelectric layer <NUM> has a first active portion Ac and a second active portion NAc. In the embodiment, the first active portion Ac corresponds to a portion of the piezoelectric layer <NUM> that overlaps both the first electrode <NUM> and the second electrode <NUM> when viewed along the Z direction. The second active portion NAc corresponds to a portion of the piezoelectric layer <NUM> that does not overlap one or both first electrode <NUM> and the second electrode <NUM> when viewed along the Z direction.

The piezoelectric element <NUM> is driven by applying a voltage to the piezoelectric layer <NUM> via the first electrode <NUM> and the second electrode <NUM>. More specifically, the piezoelectric element <NUM> is displaced by piezoelectric strain generated in the first active portion Ac of the piezoelectric layer <NUM> when the voltage is applied to the piezoelectric layer <NUM>. The displacement of the piezoelectric element <NUM> causes the vibration plate <NUM> to vibrate, and changes the volume of the pressure chamber <NUM>. Piezoelectric strain generated in the second active portion NAc of the piezoelectric layer <NUM> when the voltage is applied to the piezoelectric layer <NUM> is smaller than the piezoelectric strain generated in the first active portion Ac of the piezoelectric layer <NUM> when the voltage is applied to the piezoelectric layer <NUM>.

The piezoelectric layer <NUM> contains a so-called potassium sodium niobate (KNN)-based composite oxide as a main component. The KNN-based composite oxide refers to a perovskite-type composite oxide represented by a general formula ABO<NUM> containing potassium (K), sodium (Na), and niobium (Nb). The KNN-based oxide is represented by the following formula (c1).

Since the KNN-based composite oxide is a non-lead based piezoelectric material in which a content of lead (Pb) or the like is reduced, the KNN-based composite oxide is excellent in biocompatibility and has a small environmental load. In addition, since the KNN-based composite oxide is excellent in piezoelectric characteristics among non-lead based piezoelectric materials, it is advantageous for improving various characteristics. In addition, the KNN-based composite oxide has a relatively high Curie temperature as compared with other non-lead based piezoelectric materials such as BNT-BKT-BT; [(Bi,Na)TiO<NUM>]-[(Bi,K)TiO<NUM>]-[BaTiO<NUM>], and is less likely to undergo depolarization due to a temperature rise, and thus, the KNN-based composite oxide can be used at a high temperature.

The "non-lead based" material may not be a material containing no Pb at all, but may be a material containing substantially no Pb, and may contain Pb as, for example, an inevitable component. From the viewpoint of reducing the environmental load, in the droplet discharge head <NUM>, the content of Pb in the piezoelectric portion <NUM>, that is, the content of Pb in the vibration plate <NUM> and the piezoelectric element <NUM>, is preferably, for example, <NUM> mass% or less. As a result, the piezoelectric portion <NUM> is excellent in biocompatibility, and the environmental load due to the piezoelectric portion <NUM> is reduced. From the same viewpoint, it is preferable that the piezoelectric portion <NUM> do not substantially contain bismuth (Bi).

In the above formula (c1), a content of Na is preferably <NUM> mol% or more and <NUM> mol% or less with respect to a total amount of metal elements constituting an A site. That is, in the above formula (<NUM>), it is preferable that <NUM> ≤ X ≤ <NUM>. Accordingly, a composite oxide having a composition advantageous for the piezoelectric characteristics is obtained. In addition, the content of Na is preferably <NUM> mol% or more and <NUM> mol% or less, and still more preferably <NUM> mol% or more and <NUM> mol% or less with respect to the total amount of metal elements constituting the A site. That is, in the above formula (<NUM>), it is more preferable that <NUM> ≤ X ≤ <NUM>, and it is still more preferable that <NUM> ≤ X ≤ <NUM>. Accordingly, a composite oxide having a composition more advantageous for the piezoelectric characteristics is obtained.

Alkali metals at the A site of the KNN, that is, K and Na, may be added excessively with respect to a stoichiometric composition, or may be insufficient with respect to the stoichiometric composition. Therefore, the composite oxide in the embodiment can also be expressed by the following formula (c2).

In the formula (c2), M represents an amount of the alkali metal that is excessively added or insufficient with respect to the stoichiometric composition. For example, when M = <NUM>, it means that when the amount of K and Na in the stoichiometric composition is <NUM> mol%, a total of <NUM> mol% of K and Na is contained. When M = <NUM>, it means that when the amount of K and Na in the stoichiometric composition is <NUM> mol%, a total of <NUM> mol% of K and Na is contained. When the alkali metal at the A site is not excessive or insufficient with respect to the stoichiometric composition, A = <NUM>. From the viewpoint of improving the characteristics of the piezoelectric layer <NUM>, it is preferable that <NUM> ≤ A ≤ <NUM>, it is more preferable that <NUM> ≤ A ≤ <NUM>, and it is still more preferable that <NUM> ≤ A ≤ <NUM>.

The piezoelectric material constituting the piezoelectric layer <NUM> may be a KNN-based composite oxide, and is not limited to the composition represented by the above formula (<NUM>). For example, another metal element (additive) different from potassium, sodium, and niobium may be contained in the A site or a B site of the 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 may contain two or more of these other metal elements. An addition amount of such an additive is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less with respect to a total amount of elements serving as the main component. A reason for this is that the addition of the additive makes it easy to improve various characteristics of the piezoelectric layer <NUM> to diversify a configuration and function, while the addition of the additive makes it easy to exhibit the characteristics derived from the KNN of the piezoelectric layer <NUM> when the amount of the additive is smaller. Even when the piezoelectric layer <NUM> contains these additives, it is preferable that the piezoelectric layer <NUM> have an ABO tri-type perovskite structure.

The piezoelectric layer <NUM> preferably contains Cu, in particular, as the additive. As a result, it is possible to prevent a discharge failure of droplets in the droplet discharge head <NUM>. The piezoelectric layer <NUM> preferably contains Mn, in particular, as the additive. As a result, it is possible to prevent an occurrence of a leakage current in the piezoelectric element <NUM>. Therefore, heat generation of the piezoelectric element <NUM> can be prevented, and a life of the piezoelectric element <NUM> can be extended.

The piezoelectric layer <NUM> in the embodiment is formed as a polycrystalline body of the KNN-based composite oxide composed of a plurality of single crystals. Accordingly, as compared with when the piezoelectric layer <NUM> is formed as, for example, a single crystal body, when stress is generated in the piezoelectric element <NUM>, the stress in a plane of the piezoelectric element <NUM> is likely to be dispersed and equalized, and thus stress fracture of the piezoelectric element <NUM> is less likely to occur, and reliability is improved.

When the piezoelectric layer <NUM> is formed as a polycrystalline body, the various additives described above may be contained in a grain boundary in the piezoelectric layer <NUM>. In particular, Mn is preferably contained in the grain boundary in the piezoelectric layer <NUM> in a state of being, for example, a manganese oxide. As a result, it is possible to fill voids in the grain boundary in the piezoelectric layer <NUM>, and it is possible to effectively prevent the occurrence of the leakage current when the voltage is applied to the piezoelectric element <NUM>.

An average grain size of crystal grains in the piezoelectric layer <NUM> is preferably <NUM> or more and <NUM> or less. Accordingly, since the average grain size is <NUM> or more, it is possible to prevent a decrease in the piezoelectric characteristics of the piezoelectric layer <NUM> due to fairly small crystal grains. Therefore, the piezoelectric characteristics can be further improved. In addition, since the average grain size is <NUM> or less, it is possible to further prevent an occurrence of cracks in the piezoelectric layer <NUM>. The average grain size of the crystal grains can be determined based on a SEM image of the piezoelectric layer <NUM> obtained by a scanning electron microscope (SEM). More specifically, the average grain size of the crystal grains is calculated by measuring grain sizes of, for example, <NUM> or more crystal grains in the SEM image of the piezoelectric layer <NUM> having the same magnification and calculating an arithmetic average of the measured grain sizes. In other embodiments, the average grain size of the crystal grains may be, for example, less than <NUM> or more than <NUM>.

The KNN may also be a mixed crystal having the ABO tri-type perovskite structure with other composite oxides different from the KNN. That is, in the present specification, the "perovskite-type composite oxide containing K, Na, and Nb" includes a piezoelectric material represented as a mixed crystal containing a composite oxide having the ABO tri-type perovskite structure containing K, Na, and Nb and another composite oxide having the ABO tri-type perovskite structure. The other composite oxide is not particularly limited, but is preferably a non-lead based piezoelectric material, so that the piezoelectric layer <NUM> can be formed as the non-lead based piezoelectric material. In addition, it is preferable that the composite oxide do not substantially contain bismuth (Bi).

The piezoelectric material includes a material having a composition in which a part of an element is missing, a material having a composition in which a part of an element is excessive, and a material having a composition in which a part of an element is substituted with another element. As long as basic characteristics of the piezoelectric layer <NUM> do not change, a material deviated from the stoichiometric composition due to deficiency or excess, or a material in which a part of an element is substituted with another element is also contained in the piezoelectric material according to the embodiment.

In the piezoelectric element <NUM>, it is preferable that a thickness of the elastic layer <NUM> be <NUM> or more and <NUM> or less, a thickness of the insulating layer <NUM> be <NUM> or more and <NUM> or less, a thickness of the piezoelectric layer <NUM> be <NUM> or more and <NUM> or less, a thickness of the first electrode <NUM> be <NUM> or more and <NUM> or less, and a thickness of the second electrode <NUM> be <NUM> or more and <NUM> or less. It should be noted that the thickness of each of these elements is an example, and can be changed within a range that does not change the scope of the present disclosure.

When the piezoelectric portion <NUM> in the embodiment is manufactured, first, the vibration plate <NUM> is prepared. The elastic layer <NUM> of the vibration plate <NUM> is formed at the pressure chamber defining substrate <NUM> by, for example, thermally oxidizing the Si substrate, more specifically, the pressure chamber defining substrate <NUM> in which the holes HL are not formed. The insulating layer <NUM> is formed at the elastic layer <NUM> by, for example, a CVD method. Accordingly, the vibration plate <NUM> is formed. In other embodiments, the elastic layer <NUM> may be formed at the pressure chamber defining substrate <NUM> by, for example, the CVD method. The holes HL of the pressure chamber defining substrate <NUM> are formed by, for example, anisotropic etching using an alkaline solution such as potassium hydroxide (KOH) after the vibration plate <NUM> is formed at the pressure chamber defining substrate <NUM>. More specifically, in the embodiment, the holes HL are formed after the completion of the piezoelectric portion <NUM>.

Next, the first electrode <NUM> is formed at the vibration plate <NUM> by patterning by sputtering, etching, or the like.

Next, the piezoelectric layer <NUM> is formed at the first electrode <NUM> and the vibration plate <NUM>. The piezoelectric layer <NUM> in the embodiment is formed in a thin film shape by a solution method such as an MOD method or a sol-gel method. The solution method such as the MOD method or the sol-gel method is also referred to as a wet method or a liquid phase method. By forming the piezoelectric layer <NUM> by the solution method in this manner, productivity of the piezoelectric layer <NUM> can be increased. In other embodiments, the piezoelectric layer <NUM> may be formed by, for example, a gas phase method such as sputtering or a solid phase method such as powder compacting.

When the piezoelectric layer <NUM> is formed by the solution method, for example, first, a precursor solution containing a predetermined metal complex is prepared. The precursor solution is a sol or a solution containing a metal element as a raw material of the piezoelectric layer <NUM>, and is, for example, a solution obtained by dissolving or dispersing a metal complex capable of forming a composite oxide containing K, Na, and Nb by firing in an organic solvent. When the above additive such as Cu or Mn is added to the piezoelectric layer <NUM>, a metal complex or the like containing the additive may be further mixed with the precursor solution.

Examples of the metal complex containing K include potassium <NUM>-ethylhexanoate and potassium acetate. Examples of the metal complex containing Na include sodium <NUM>-ethylhexanoate and sodium acetate. Examples of metal complex containing Nb include niobium <NUM>-ethylhexanoate and niobium pentaethoxy. When Mn is added as the additive, examples of the metal complex containing Mn include manganese <NUM>-ethylhexanoate. When Cu is added as the additive, examples of metal complex containing Cu include copper acetate. Two or more metal complexes may be used in combination. For example, potassium <NUM>-ethylhexanoate and potassium acetate may be used in combination as the metal complex containing K. Examples of the solvent include <NUM>-n-butoxyethanol, n-octane, and mixed solvents thereof. The precursor solution may contain an additive that stabilizes the dispersion of the metal complex containing K, Na, and Nb. Examples of such additives include <NUM>-ethylhexanoic acid.

After the above-described precursor solution is prepared, a coating step of coating the first electrode <NUM> and the vibration plate <NUM> with the precursor solution to form a precursor film is executed. In the coating step, the first electrode <NUM> and the vibration plate <NUM> are coated with the precursor solution by, for example, a spin coating method. Next, a drying step of heating the precursor film at a predetermined temperature, for example, about <NUM> to <NUM> and drying the precursor film for a certain period of time is executed. Next, a degreasing step of degreasing the dried precursor film by heating the dried precursor film at a predetermined degreasing temperature, for example, <NUM> to <NUM> is executed. Then, a firing step of crystallizing the degreased precursor film by heating the degreased precursor film at a higher predetermined firing temperature, for example, <NUM> to <NUM> is executed. Examples of a heating device used in the drying step, the degreasing step, and the firing step include a rapid thermal annealing (RTA) device that performs heating by irradiation with an infrared lamp and a hot plate. By executing the coating step to the firing step described above, a piezoelectric film formed of KNN as a main component and formed as a polycrystalline body is formed. Further, in the firing step, Mn contained in the precursor solution is precipitated at the grain boundary between the KNN crystals.

The piezoelectric layer <NUM> in the embodiment is formed by repeatedly executing the coating step to the firing step a plurality of times to form a plurality layers of piezoelectric films. In the embodiment, a portion of the piezoelectric layer <NUM> formed at the first electrode <NUM> corresponds to the above-described first active portion Ac, and a portion of the piezoelectric layer <NUM> formed not on the first electrode <NUM> but on the vibration plate <NUM> corresponds to the above-described second active portion NAc. In a series of steps from the coating step to the firing step, the firing step may be performed after repeating the steps from the coating step to the degreasing step a plurality of times. A heating rate in the drying step is preferably <NUM>/sec to <NUM>/sec. In the solution method, by firing the piezoelectric film at such a heating rate, the piezoelectric layer <NUM> which is not a pseudo-cubic crystal can be formed. The term "heating rate" as used herein defines a rate of change over time in the temperature from the degreasing temperature to the firing temperature in the firing step.

Thereafter, the piezoelectric layer <NUM> including a plurality of piezoelectric films is patterned. Dry etching such as reactive ion etching or ion milling, and wet etching using an etching solution are performed as the patterning. Thereafter, the second electrode <NUM> is formed at the piezoelectric layer <NUM> by, for example, the same method as that of the first electrode <NUM>. Before and after the second electrode <NUM> is formed at the piezoelectric layer <NUM>, reheating treatment may be appropriately performed in a temperature range of <NUM> to <NUM>. By performing the reheating treatment in this manner, it is possible to form a good interface between the piezoelectric layer <NUM> and the first electrode <NUM> or between the piezoelectric layer <NUM> and the second electrode <NUM>, and to improve crystallinity of the piezoelectric layer <NUM>. The reheating treatment is also referred to as post-annealing.

Through the above steps, the piezoelectric element <NUM> including the first electrode <NUM>, the piezoelectric layer <NUM>, and the second electrode <NUM>, and the piezoelectric portion <NUM> including the vibration plate <NUM> are completed. In each of the steps described above, for example, etching may be appropriately performed in order to smooth a surface of each member or adjust the thickness.

The inventors of the present disclosure intensively studied improvement in image quality of printing performed by the droplet discharge head <NUM> and extension of the life of the droplet discharge head <NUM>. As a result, it is found that in the droplet discharge head <NUM>, when a driving frequency f [Hz] representing a frequency at which the piezoelectric element <NUM> is driven, a piezoelectric constant d<NUM> [m/v] of the piezoelectric element <NUM>, a ratio x of Na in the piezoelectric layer <NUM>, and a liquid viscosity µ [Pa·s] satisfy a relationship represented by the following formula (<NUM>), good image quality and long life can be implemented.

More specifically, the ratio x represents a ratio of a Na molar fraction to a total value of a K molar fraction and the Na molar fraction in the piezoelectric layer <NUM>. That is, the ratio x is the same value as X in the above formula (c1). The viscosity µ represents a viscosity of the liquid discharged as droplets from the droplet discharge head <NUM> at <NUM>. Hereinafter, (d<NUM>·x)/(µ·f) is also referred to as a parameter P<NUM>.

The inventors of the present disclosure have further found that, the piezoelectric layer <NUM> contains Cu, and the driving frequency f, the piezoelectric constant d<NUM>, the ratio x, the viscosity µ, and an atomic percentage y [at%] of Cu in the piezoelectric layer <NUM> satisfy a relationship represented by the following formula (<NUM>), it is possible to prevent a discharge failure of the droplet discharge head <NUM>, and it is possible to implement even better image quality. Hereinafter, (d<NUM>·x·y)/(µ·f) is also referred to as a parameter P<NUM>.

The inventors of the present disclosure have further found that, the piezoelectric layer <NUM> contains Mn, and the driving frequency f, the piezoelectric constant d<NUM>, the ratio x, the viscosity µ, and an atomic percentage z [at%] of Mn in the piezoelectric layer <NUM> satisfy a relationship represented by the following formula (<NUM>), it is possible to implement a further longer life of the droplet discharge head <NUM>. Hereinafter, (d<NUM>·x·z)/(µ·f) is also referred to as a parameter P<NUM>.

In order to verify an effect of the droplet discharge head <NUM> in the embodiment, a plurality of samples were evaluated by a performance evaluation test. More specifically, a plurality of samples belonging to a sample group Sg1, a plurality of samples belonging to a sample group Sg2, and a plurality of samples belonging to a sample group Sg3 were used as the samples of the performance evaluation test.

As the samples belonging to the sample group Sg1, the droplet discharge head <NUM> including the piezoelectric element <NUM> having the piezoelectric layer <NUM> to which the additive described above was not added was used. Among the samples belonging to the sample group Sg1, a part of or all of the driving frequency f, the piezoelectric constant d<NUM>, the ratio x, and viscosity µ described above were made different from one another. As the samples belonging to the sample group Sg2, the droplet discharge head <NUM> including the piezoelectric element <NUM> having the piezoelectric layer <NUM> to which Cu was added as the additive was used. Among the samples belonging to the sample group Sg2, a part of or all of the driving frequency f, the piezoelectric constant d<NUM>, the ratio x, the viscosity µ, and the atomic percentage y described above were made different from one another. As the samples belonging to the sample group Sg3, the droplet discharge head <NUM> including the piezoelectric element <NUM> having the piezoelectric layer <NUM> to which Mn was added as the additive was used. Among the samples belonging to the sample group Sg3, a part of or all of the driving frequency f, the piezoelectric constant d<NUM>, the ratio x, the viscosity µ, and the atomic percentage z described above were made different from one another.

The piezoelectric portion <NUM> of the droplet discharge head <NUM> as a sample belonging to each sample group was prepared by the procedure described above. Specifically, first, the first electrode <NUM> was formed at the insulating layer <NUM> of the vibration plate <NUM> by sputtering and etching. Next, a coating step was executed using a sol containing a raw material of the piezoelectric layer <NUM> as the precursor solution, and then the drying step, the degreasing step, and the firing step were executed to form the piezoelectric film. Thereafter, the coating step to the firing step were repeated to form the piezoelectric layer <NUM> including a plurality of layers of piezoelectric films. Then, the second electrode <NUM> was formed at the piezoelectric layer <NUM> by, for example, the same method as that of the first electrode <NUM>. When the piezoelectric portions <NUM> of the samples belonging to the sample group Sg2 were prepared, a precursor solution containing Cu was used as the precursor solution. When the piezoelectric portions <NUM> of the samples belonging to the sample group Sg3 were prepared, a precursor solution containing Mn was used as the precursor solution. In addition, the piezoelectric portion <NUM> of the sample belonging to each sample group was prepared as the piezoelectric portion <NUM> not containing Pb.

The ratio x of Na, the atomic percentage y of Cu, and the atomic percentage z of Mn described above were adjusted by adjusting an amount of each raw material charged into the precursor solution. Thus, in each sample, the ratio x was adjusted to <NUM> or more and <NUM> or less, the atomic percentage y was adjusted to a value of <NUM> or more and <NUM> or less, and the atomic percentage z was adjusted to <NUM> or more and <NUM> or less. The ratio x, the atomic percentage y, and the atomic percentage z in the completed piezoelectric element <NUM> were measured by energy dispersive X-ray spectroscopy (EDX) analysis. For the EDX analysis, JEM-ARM200F manufactured by JEOL Ltd.

As the performance evaluation test, an image quality evaluation test and a life evaluation test were performed. In the image quality evaluation test, a mixed color black ink was discharged from the droplet discharge head <NUM> for each sample, an image having a highlight portion and a shadow portion was printed on a white printing paper, and a degree of graininess in the highlight portion and a degree of blurring and bleeding in the shadow portion were visually evaluated. Print data for printing an image in the image quality evaluation test was the same among the samples. The higher the graininess in a certain portion of the image, the stronger roughness and unevenness when the portion is visually recognized. The mixed color black ink is ink exhibiting black by mixing cyan, yellow, and magenta colors, and is also referred to as a composite black ink.

In the image quality evaluation test, when neither the graininess in the highlight portion nor the blurring and bleeding in the shadow portion was recognized, an evaluation result was "A". When any one of the graininess in the highlight portion and the blurring and bleeding in the shadow portion was hardly recognized and the other one was slightly recognized, the evaluation result was "B". When both the graininess in the highlight portion and the blurring and bleeding in the shadow portion were slightly recognized, the evaluation result was "C". When at least one of the graininess in the highlight portion and the blurring and bleeding in the shadow portion was remarkably recognized, the evaluation result was "D".

In the life evaluation test, a first piezoelectric constant representing the piezoelectric constant d<NUM> of the piezoelectric element <NUM> of the droplet discharge head <NUM> immediately after the manufacture and a second piezoelectric constant representing the piezoelectric constant d<NUM> of the piezoelectric element <NUM> of the droplet discharge head <NUM> after <NUM>,<NUM> times of use were compared for each sample. Each of the first piezoelectric constant and the second piezoelectric constant was calculated based on a measurement result of displacement due to piezoelectric strain of a strip sample. More specifically, first, the piezoelectric element <NUM> was cut into a strip shape having a length of <NUM> and a width of <NUM> when viewed along the Z direction, thereby preparing the strip sample. Next, when one end portion of the strip sample in a longitudinal direction was fixed, a voltage waveform having a sine difference of <NUM> V, a positive voltage, and <NUM> V was continuously applied to one electrode of the strip sample to cause the piezoelectric strain in the strip sample. At this time, displacement of an end portion of the strip sample on an opposite side from the fixed end portion was measured by a laser displacement meter, and the piezoelectric constant was calculated based on the measured displacement. The first piezoelectric constant was used as the piezoelectric constant d<NUM> in the above formulae (<NUM>) to (<NUM>).

In the life evaluation test, the evaluation result was "A" when a ratio of the second piezoelectric constant to the first piezoelectric constant was <NUM> or more, the evaluation result was "B" when the ratio was <NUM> or more and less than <NUM>, the evaluation result was "C" when the ratio was <NUM> or more and less than <NUM>, and the evaluation result was "D" when the ratio was less than <NUM>. Note that the certain droplet discharge head <NUM> after "<NUM>,<NUM> times of use" refers to that printing similar to the image quality evaluation test described above is executed <NUM>,<NUM> times by the droplet discharge head <NUM>.

In the performance evaluation test, the driving frequency f of each sample was adjusted to a constant frequency of <NUM> × <NUM><NUM> Hz or more and <NUM> × <NUM><NUM> Hz or less by adjusting a frequency of the drive signal. In the performance evaluation test, the viscosity µ of each sample was adjusted to <NUM> × <NUM>-<NUM> Pa·s or more and <NUM> × <NUM>-<NUM> Pa·s or less by adjusting a ratio of a dye component and a solvent in the mixed color black ink used as a liquid in the performance evaluation test.

<FIG> is a first diagram showing results of the performance evaluation tests of the droplet discharge head <NUM> in the embodiment. <FIG> shows a performance evaluation result of the sample group Sg1 described above. As shown in <FIG>, in the sample group Sg1, when the parameter P<NUM> was less than <NUM> × <NUM>-<NUM>, the evaluation results of the image quality and the life were both D. Similarly, when the parameter P<NUM> exceeded <NUM> × <NUM>-<NUM>, the evaluation results of the image quality and the life were both D. On the other hand, when the parameter P<NUM> was <NUM> × <NUM>-<NUM> or more and <NUM> × <NUM>-<NUM> or less, the evaluation result of the image quality was B, and the evaluation result of the life was C. That is, it was found that when the piezoelectric constant d<NUM>, the ratio x, the viscosity µ, and the driving frequency f satisfy the relationship represented by the above formula (<NUM>), good image quality and long life are implemented.

<FIG> is a second diagram showing results of the performance evaluation tests of the droplet discharge head <NUM> in the embodiment. <FIG> shows performance evaluation results of samples satisfying the relationship of the above formula (<NUM>) in the sample group Sg2. As shown in <FIG>, when the parameter P<NUM> was less than <NUM> × <NUM>-<NUM>, the evaluation result of the image quality was B, and the evaluation result of the life was C. In addition, when the parameter P<NUM> exceeded <NUM> × <NUM>-<NUM>, the evaluation results of the image quality and the life were both D. On the other hand, when the parameter P<NUM> was <NUM> × <NUM>-<NUM> or more and <NUM> × <NUM>-<NUM> or less, the evaluation result of the image quality was A, and the evaluation result of the life was C. That is, it was found that when the piezoelectric constant d<NUM>, the ratio x, the viscosity µ, the driving frequency f, and the atomic percentage y satisfy the relationship represented by the above formula (<NUM>), even better image quality is implemented. This is considered to be an effect due to the prevention of the discharge failure by the addition of Cu to the piezoelectric layer <NUM>. Although not shown, the evaluation results of the image quality and the life of the samples that do not satisfy the relationship of the above formula (<NUM>) in the sample group Sg2 were both D.

<FIG> is a third diagram showing results of the performance evaluation tests of the droplet discharge head <NUM> in the embodiment. <FIG> shows performance evaluation results of samples satisfying the relationship of the above formula (<NUM>) in the sample group Sg3. As shown in <FIG>, when the parameter P<NUM> was less than <NUM> × <NUM>-<NUM>, the evaluation result of the image quality was B, and the evaluation result of the life was C. In addition, when the parameter P<NUM> exceeded <NUM> × <NUM>-<NUM>, the evaluation results of the image quality and the life were both D. On the other hand, when the parameter P<NUM> was <NUM> × <NUM>-<NUM> or more and <NUM> × <NUM>-<NUM> or less, both the evaluation result of the image quality and the evaluation result of the life were A. That is, it was found that when the piezoelectric constant d<NUM>, the ratio x, the viscosity µ, the driving frequency f, and the atomic percentage z satisfy the relationship represented by the above formula (<NUM>), even better image quality and longer life are implemented. This is considered to be an effect due to the prevention of the occurrence of the leakage current and the prevention of heat generation of the piezoelectric layer <NUM> by the addition of Mn to the piezoelectric layer <NUM>. Although not shown, the evaluation results of the image quality and the life of the samples that do not satisfy the relationship of the above formula (<NUM>) in the sample group Sg3 were both D.

The parameter P<NUM>, the parameter P<NUM>, and the parameter P<NUM> may be referred to during manufacturing the droplet discharge head <NUM>, or may be referred to during using the droplet discharge head <NUM>, for example. For example, when the driving frequency f and the type of liquid to be used are determined in advance, the piezoelectric constant d<NUM>, the ratio x, the atomic percentage y, and the atomic percentage z can be adjusted so as to satisfy the relationships represented by the above formulas (<NUM>), (<NUM>), and (<NUM>) with respect to the liquid viscosity µ and the driving frequency f determined in advance during manufacturing the droplet discharge head <NUM>. The driving frequency f and the viscosity µ in this case may be determined as, for example, a range having a lower limit value and an upper limit value, and in a case of determining the driving frequency f and the viscosity µ in this manner, the piezoelectric constant d<NUM>, the ratio x, the atomic percentage y, and the atomic percentage z may be adjusted so as to satisfy the relationships represented by the formula (<NUM>), the formula (<NUM>), and the formula (<NUM>), regardless of how the driving frequency f and the viscosity µ are changed within a predetermined range. As a result, it is possible to manufacture the droplet discharge head <NUM> including the piezoelectric element <NUM> having a preferable composition and piezoelectric characteristics. In addition, for example, when the droplet discharge head <NUM> including the piezoelectric element <NUM> having an identified piezoelectric constant d<NUM>, an identified ratio x, or the like is used, the control unit <NUM> may control the driving frequency f thereof in a range of <NUM> to <NUM> in accordance with the liquid viscosity µ so as to satisfy the relationship represented by the above formula (<NUM>) or the like.

According to the droplet discharge head <NUM> in the embodiment described above, the driving frequency f, the piezoelectric constant d<NUM>, the ratio x of Na, and the viscosity µ satisfy the relationship represented by the above formula (<NUM>). As a result, when the driving frequency f is in the range of <NUM> to <NUM>, it is possible to implement good image quality and long life of the droplet discharge head <NUM> by considering the relationship between the viscosity µ of the ink and the driving frequency f as use conditions of the droplet discharge head <NUM> and components and piezoelectric characteristics of the piezoelectric layer <NUM>.

In the embodiment, the piezoelectric layer <NUM> contains copper, and the driving frequency f, the piezoelectric constant d<NUM>, the ratio x of Na, the viscosity µ, and an atomic percentage y of copper satisfy a relationship represented by the above formula (<NUM>). As a result, it is possible to prevent a discharge failure and to implement even better image quality.

In the embodiment, the piezoelectric layer <NUM> contains manganese, and the driving frequency f, the piezoelectric constant d<NUM>, the ratio x of Na, the viscosity µ, and an atomic percentage z of manganese satisfy a relationship represented by the above formula (<NUM>). As a result, it is possible to prevent an occurrence of a leakage current in the piezoelectric layer <NUM>. Therefore, a life of the droplet discharge head <NUM> can be further extended, and a discharge failure caused by heat generation of the piezoelectric layer <NUM> can be prevented.

In the embodiment, manganese is contained in the grain boundary of the piezoelectric layer <NUM> having a polycrystalline structure. As a result, it is possible to reduce voids in the grain boundary in the piezoelectric layer, and it is possible to implement a further longer life of the droplet discharge head <NUM>.

In the embodiment, an average grain size of crystal grains in the piezoelectric layer <NUM> is <NUM> or more and <NUM> or less. As a result, since the average grain size is <NUM> or more, piezoelectric characteristics of the piezoelectric layer <NUM> can be further improved. In addition, since the average grain size is <NUM> or less, it is possible to further prevent an occurrence of cracks in the piezoelectric layer <NUM>.

Claim 1:
A droplet discharge head (<NUM>) comprising:
a liquid;
a nozzle (<NUM>) configured to discharge the liquid as droplets;
a pressure chamber defining substrate (<NUM>) defining a pressure chamber (<NUM>) communicating with the nozzle;
a piezoelectric element (<NUM>) including a first electrode (<NUM>), a second electrode (<NUM>), and a piezoelectric layer (<NUM>) disposed between the first electrode and the second electrode, the piezoelectric layer containing a perovskite-type composite oxide containing potassium, sodium, and niobium as a main component; and
a vibration plate (<NUM>) disposed between the pressure chamber defining substrate (<NUM>) and the piezoelectric element (<NUM>), forming a part of a wall surface of the pressure chamber, and configured to vibrate by driving of the piezoelectric element, characterised in that:
a driving frequency f [Hz] representing a frequency at which the piezoelectric element (<NUM>) is driven, a piezoelectric constant d<NUM> [m/v] of the piezoelectric element, a ratio x of a sodium molar fraction to a total value of a potassium molar fraction and the sodium molar fraction in the piezoelectric layer, and a viscosity µ [Pa·s] of the liquid at <NUM> satisfy a relationship represented by a following formula (<NUM>). <MAT>