JP2014058169A - Liquid ejecting head, liquid ejecting apparatus, and actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid ejecting head in which displacement characteristics of a piezoelectric element is improved, and to provide a liquid ejecting apparatus and an actuator.SOLUTION: A piezoelectric element is driven in a condition in which relationship between minimum voltage Vmin and maximum voltage Vmax which are applied to the piezoelectric element, and peak voltage Vsatisfies an expression (1) Vmin<V<Vmax. In this expression (1), the peak voltage Vis a voltage value at which a primary differential coefficient of displacement by voltage, which is obtained from a displacement-voltage curve, becomes a maximum value.

Description

  The present invention relates to a liquid ejecting head and a liquid ejecting apparatus that eject liquid droplets from a nozzle by displacement of a piezoelectric element, and an actuator including a piezoelectric element.

  A typical example of the liquid ejecting head is an ink jet recording head that ejects ink droplets from ink by generating pressure in a pressure generating chamber by pressure generating means. Examples of the pressure generating means constituting the ink jet recording head include a piezoelectric element in which a piezoelectric layer made of a piezoelectric material exhibiting an electromechanical conversion function is sandwiched between two electrodes, and the piezoelectric element is bent and deformed. Thus, pressure is applied to the pressure generating chamber to eject ink droplets from the nozzles.

  As a material for the piezoelectric layer used for the piezoelectric element, for example, a material having a perovskite structure such as PZT is preferably used. When formed of such a material, the piezoelectric layer is mainly composed of rhombohedral or tetragonal crystals. For example, there is one in which the composition Zr / Ti of zirconia and titanium contained in the piezoelectric layer is adjusted and the crystal is tetragonal (see, for example, Patent Document 1).

  Thus, by adjusting the composition and crystal system of the piezoelectric layer, the piezoelectric characteristics of the piezoelectric layer can be improved, and the displacement characteristics of the piezoelectric element can be improved.

JP 2005-119166 A

  However, there is a limit in improving the piezoelectric characteristics only by adjusting the composition and crystal system of the piezoelectric layer, and there is a problem that the displacement characteristics of the piezoelectric element cannot be sufficiently improved. In recent years, further improvement in the displacement characteristics of piezoelectric elements has been desired, and it has become difficult to satisfy the demands.

  Such problems are not limited to piezoelectric elements used in ink jet recording heads, but also exist in piezoelectric elements used in liquid ejecting heads that eject other liquid droplets. Furthermore, devices other than liquid ejecting heads The same applies to the actuator used in the above.

  SUMMARY An advantage of some aspects of the invention is that it provides a liquid ejecting head, a liquid ejecting apparatus, and an actuator that have improved displacement characteristics of a piezoelectric element.

The present invention for solving the above-described problems is a flow path forming substrate in which a pressure generating chamber communicating with a nozzle for ejecting droplets is formed, and a pressure change is generated in the pressure generating chamber provided on the flow path forming substrate. A piezoelectric element, the piezoelectric element comprising a piezoelectric layer, a first electrode provided on one side of the piezoelectric layer, and a second electrode provided on the opposite side of the piezoelectric layer. and said piezoelectric element, characterized in that the relationship between the minimum voltage Vmin and the maximum voltage Vmax and the peak voltage V ₀ to be applied to the piezoelectric element is intended to be driven under the condition satisfying the following formula (1) It is in the liquid jet head.
Vmin <V ₀ <Vmax (1) (In the above formula (1), the peak voltage V ₀ is a voltage value at which the first-order differential coefficient based on the displacement voltage obtained from the displacement-voltage curve becomes the maximum value. .)
In the present invention, the piezoelectric element can be efficiently displaced using a voltage range in which the change rate of the displacement amount of the piezoelectric element is large. Accordingly, the droplet ejection characteristics can be improved.

Here, to the extent that the maximum voltage Vmax is greater than the peak voltage V _0, it is preferable that the minimum voltage Vmin is set to a value smaller than the peak voltage V _0. Thereby, the piezoelectric element can be displaced more efficiently.

  The piezoelectric layer is preferably made of a material having a perovskite structure, for example, the piezoelectric layer is made of lead zirconate titanate (PZT). In particular, the crystal structure of the piezoelectric layer is preferably rhombohedral. This further improves the displacement efficiency of the piezoelectric layer when a predetermined voltage is applied. Therefore, the piezoelectric element can be displaced more efficiently.

According to another aspect of the present invention, there is provided a flow path forming substrate in which a pressure generating chamber communicating with a nozzle for ejecting droplets is formed, and a piezoelectric element provided on the flow path forming substrate and causing a pressure change in the pressure generating chamber. A liquid ejecting head comprising: a piezoelectric layer; a piezoelectric layer; a first electrode provided on one side of the piezoelectric layer; and a second electrode provided on the opposite side of the piezoelectric layer. And drive means for driving the piezoelectric element under the condition that the relationship between the minimum voltage Vmin and the maximum voltage Vmax applied to the piezoelectric element and the peak voltage V ₀ satisfies the following formula (1): The liquid ejecting apparatus is characterized.
Vmin <V ₀ <Vmax (1) (In the above formula (1), the peak voltage V ₀ is a voltage value at which the first-order differential coefficient based on the displacement voltage obtained from the displacement-voltage curve becomes the maximum value. .)
In the present invention, the piezoelectric element can be efficiently displaced using a voltage range in which the change rate of the displacement amount of the piezoelectric element is large. Accordingly, the droplet ejection characteristics can be improved.

The present invention further includes a piezoelectric element including a piezoelectric layer and a first electrode and a second electrode provided on both sides of the piezoelectric layer, and the piezoelectric element is applied to the piezoelectric element. The actuator is characterized in that the relationship between the minimum voltage Vmin and the maximum voltage Vmax and the peak voltage V ₀ is driven under a condition satisfying the following expression (1).
Vmin <V ₀ <Vmax (1) (In the above formula (1), the peak voltage V ₀ is a voltage value at which the first-order differential coefficient based on the displacement voltage obtained from the displacement-voltage curve becomes the maximum value. .)
In the present invention, the piezoelectric element can be efficiently displaced using a voltage range in which the change rate of the displacement amount of the piezoelectric element is large.

FIG. 2 is an exploded perspective view illustrating a schematic configuration of the recording head according to the first embodiment. 2A and 2B are a plan view and a cross-sectional view of the recording head according to the first embodiment. It is a graph which shows the relationship between the voltage applied to a piezoelectric element, and a displacement. It is a graph which shows the relationship between the applied voltage to a piezoelectric element, and the differential coefficient of displacement. It is a graph which shows the relationship between the minimum voltage applied to a piezoelectric element, and a displacement width. 1 is a diagram illustrating a schematic configuration of a recording apparatus according to an embodiment.

Hereinafter, the present invention will be described in detail based on embodiments.
(Embodiment 1)
FIG. 1 is an exploded perspective view illustrating a schematic configuration of an ink jet recording head that is an example of a liquid ejecting head according to Embodiment 1 of the present invention. FIG. 2 illustrates a longitudinal direction of a pressure generation chamber of the ink jet recording head, and FIG. It is the top view and sectional drawing in the width direction.

  The flow path forming substrate 10 constituting the ink jet recording head is made of, for example, a silicon single crystal substrate having a plane orientation (110), and as shown in FIGS. (Short direction). In addition, a communication portion 13 is formed in a region outside the longitudinal direction of the pressure generation chamber 12 of the flow path forming substrate 10, and the communication portion 13 and each pressure generation chamber 12 are provided for each pressure generation chamber 12. Communication is made via a supply path 14 and a communication path 15. The communication part 13 communicates with a reservoir part 32 of a protective substrate, which will be described later, and constitutes a part of the reservoir 100 that serves as a common ink chamber for the pressure generating chambers 12. The ink supply path 14 plays a role of maintaining a constant flow path resistance of the ink flowing into the pressure generation chamber 12 from the communication portion 13, and is formed with a width narrower than that of the pressure generation chamber 12 in this embodiment.

  A nozzle plate 20 in which nozzles 21 communicating with the pressure generating chambers 12 are arranged on one side of the flow path forming substrate 10 is joined by an adhesive, a heat welding film, or the like. The nozzle plate 20 is made of, for example, glass ceramics, a silicon single crystal substrate, stainless steel, or the like.

  On the other hand, an elastic film 50 made of an oxide film is formed on the surface of the flow path forming substrate 10 opposite to the nozzle plate 20, and a material different from that of the elastic film 50 is formed on the elastic film 50. An insulator film 55 made of an oxide film is formed. Further, on the insulator film 55, a piezoelectric element 300 composed of the first electrode 60, the piezoelectric layer 70, and the second electrode 80 is formed. In general, one of the electrodes of the piezoelectric element 300 is a common electrode common to the plurality of piezoelectric elements 300, and the other electrode is patterned into a region facing each pressure generating chamber 12 together with the piezoelectric layer 70 to individually It is an electrode. In this embodiment, the first electrode 60 is used as a common electrode for the piezoelectric element 300, and the second electrode 80 is used as an individual electrode for the piezoelectric element 300. Absent.

  Note that such a piezoelectric element 300 and a vibration plate that is a portion where displacement is generated by driving the piezoelectric element 300 are collectively referred to as an actuator. In the example described above, the elastic film 50, the insulator film 55, and the first electrode 60 function as a diaphragm, but the configuration of the diaphragm is not particularly limited. For example, the elastic film 50 and the insulator film 55 are provided. Instead, only the first electrode 60 may function as a diaphragm. Further, for example, the piezoelectric element 300 itself may substantially double as a diaphragm.

Here, the material of the first and second electrodes 60 and 80 constituting the piezoelectric element 300 is not particularly limited, and examples thereof include platinum (Pt) and iridium (Ir). The piezoelectric layer 70 is a piezoelectric material having an electromechanical conversion action, for example, a ferroelectric material having a perovskite structure and containing Zr or Ti as a metal, for example, a ferroelectric such as lead zirconate titanate (PZT). It is made of a material or a material added with a metal oxide such as niobium oxide, nickel oxide or magnesium oxide. Specifically, lead zirconate titanate (Pb (Zr, Ti) O ₃ ), barium zirconate titanate (Ba (Zr, Ti) O ₃ ), lead lanthanum zirconate titanate ((Pb, La) ( Zr, Ti) O ₃ ) or lead magnesium niobate zirconium titanate (Pb (Zr, Ti) (Mg, Nb) O ₃ ).

  The crystal structure of the piezoelectric layer 70 may be any of a rhombohedral system, a tetragonal system, and a monoclinic system, but is preferably a rhombohedral system. . The piezoelectric layer 70 may be preferentially oriented in any of the (100) plane, (110) plane, or (111) plane, but is preferably preferentially oriented in the (100) plane.

  This is because it corresponds to an engineered domain structure in which the amount of piezoelectric displacement becomes maximum when the direction of the polarization moment is inclined at a certain angle with respect to the direction of the applied electric field. That is, when a predetermined voltage is applied to the piezoelectric element 300 and the piezoelectric layer 70 is deformed, the rhombohedral crystal transitions to a tetragonal crystal, and the piezoelectric displacement is maximized. Therefore, the piezoelectric layer 70 having such a crystal structure is excellent in displacement characteristics, and an extremely large displacement amount can be obtained by applying a predetermined voltage as will be described later.

  Incidentally, the “priority orientation” means a state in which the orientation direction of the crystal is not disordered and a specific crystal plane is oriented in a substantially constant direction. For example, “preferentially oriented in the (100) plane” means the ratio of diffraction intensities of the (100) plane, the (110) plane, and the (111) plane generated when the piezoelectric layer is measured by the X-ray diffraction wide angle method ( 100) / ((100) + (110) + (111)) means greater than 0.5.

  In order to preferentially orient the piezoelectric layer 70 in the (100) plane or the (110) plane, an orientation control layer having a predetermined crystal orientation is provided below or above the first electrode 60, or the first electrode Titanium or the like that invalidates the orientation is provided on 60 and the heat treatment temperature or the like when forming the piezoelectric layer 70 is adjusted. In addition, the piezoelectric layer 70 preferentially oriented in the (111) plane is formed directly on the first electrode 60 preferentially oriented in the (111) plane, for example, to follow the crystallinity of the first electrode 60. The piezoelectric layer 70 preferentially oriented on the (111) plane by epitaxial growth can be formed.

  The piezoelectric layer 70 can be formed by a sol-gel method, a MOD (Metal-Organic Decomposition) method, a PVD (Physical Vapor Deposition) method such as a sputtering method or a laser ablation method.

  Further, each second electrode 80 that is an individual electrode of the piezoelectric element 300 is drawn from the vicinity of the end on the ink supply path 14 side and extended to the insulator film 55, for example, gold (Au) or the like. The lead electrode 90 which consists of is connected.

  A protective substrate 30 having a piezoelectric element holding portion 31 that is a space for protecting the piezoelectric element 300 is bonded onto the flow path forming substrate 10 on which the piezoelectric element 300 is formed. Further, the protective substrate 30 is provided with a reservoir portion 32. The reservoir portion 32 is communicated with the communication portion 13 of the flow path forming substrate 10 as described above, and is shared by the ink chambers common to the pressure generating chambers 12. This constitutes a reservoir 100. Further, the protective substrate 30 is provided with a through hole 33 that penetrates the protective substrate 30 in the thickness direction, and the vicinity of the end portion of the lead electrode 90 drawn from each piezoelectric element 300 is exposed in the through hole 33. It is provided to do.

  A driving circuit 120 as a driving means for driving the piezoelectric element 300 is fixed on the protective substrate 30. The driving circuit 120 and the lead electrode 90 are connected to each other by a conductive wire such as a bonding wire. It is electrically connected via 121. A compliance substrate 40 including a sealing film 41 and a fixing plate 42 is bonded onto the protective substrate 30. The sealing film 41 is made of a material having low rigidity and flexibility, and one surface of the reservoir portion 32 is sealed by the sealing film 41. The fixed plate 42 is made of a relatively hard material. A region of the fixing plate 42 facing the reservoir 100 is an opening 43 that is completely removed in the thickness direction, and one surface of the reservoir 100 is sealed only with a flexible sealing film 41. ing.

  In the ink jet recording head of the present embodiment having the above-described configuration, the ink is taken in from the ink introduction port connected to the external ink supply means, and the interior from the reservoir 100 to the nozzle 21 is filled with ink, and then the drive circuit In accordance with a recording signal from 120, a voltage is applied to each piezoelectric element 300 corresponding to the pressure generation chamber 12 to bend and deform, thereby increasing the pressure in each pressure generation chamber 12 and ejecting ink droplets from the nozzles 21.

As described below, the piezoelectric element 300 of the present invention mounted on such an ink jet recording head has a minimum voltage Vmin and a maximum voltage Vmax applied to the piezoelectric element 300 at the time of driving. It is driven under conditions that satisfy (1). That is, the voltages (minimum voltage Vmin and maximum voltage Vmax) applied to the piezoelectric element 300 by the drive circuit 120 as drive means are set so as to satisfy the relationship of the following formula (1).
Vmin <V ₀ <Vmax (1)
(In the above formula (1), the peak voltage V ₀ is a voltage value at which the first-order differential coefficient based on the displacement voltage obtained from the displacement-voltage curve becomes the maximum value.)

More specifically, as shown in FIG. 3, the displacement amount of the piezoelectric element 300 tends to increase as the voltage applied to the piezoelectric element 300 increases. As can be seen from this graph, the rate of change (inclination) of the displacement with respect to the voltage applied to the piezoelectric element 300 is not constant but sequentially changes. Then, when the primary differential coefficient (change rate) of the displacement amount is obtained based on the result of the graph of FIG. 3, the result is as shown in FIG. That is, as shown in FIG. 4, the first derivative (change rate) of the change amount of the piezoelectric element 300 rapidly increases until the peak voltage V ₀ is reached as the voltage applied to the piezoelectric element 300 increases. Then decrease.

Therefore, in the present invention, the minimum voltage Vmin applied to the piezoelectric element 300 is set to a value smaller than the peak voltage V ₀ , and the maximum voltage Vmax applied to the piezoelectric element 300 is set to a value larger than the peak voltage V _0. I tried to do it. That is, the voltage applied to the piezoelectric element 300 satisfies the relationship of the above formula (1). Accordingly, the piezoelectric element 300 can be efficiently displaced using a voltage range in which the rate of change of the displacement amount of the piezoelectric element 300 is large. Therefore, the ink droplet ejection characteristics can be improved.

  In addition, since the piezoelectric element 300 can be efficiently displaced in this way, for example, even when the piezoelectric characteristics of the piezoelectric element 300 vary between the heads and it is necessary to adjust the applied voltage, the voltage can be reduced. By adjusting, the displacement amount of the piezoelectric element 300 can be easily made uniform.

  Furthermore, the minimum voltage Vmin and the maximum voltage Vmax are applied to the piezoelectric element 300 with a voltage difference (Vmax−Vmin) between the minimum voltage Vmin and the maximum voltage Vmax applied to the piezoelectric element 300 being a constant value (for example, 20V, 25V), The result of measuring the difference in displacement (displacement width) at that time is shown in FIG. As shown in FIG. 5, when the voltage difference is constant, the displacement width is basically larger as the minimum voltage Vmin is smaller and smaller as the minimum voltage Vmin is larger, regardless of whether the voltage difference is 20V or 25V. The tendency to become.

For this reason, when the voltage difference between the minimum voltage Vmin and the maximum voltage Vmax applied to the piezoelectric element 300 is set to a predetermined value, the intermediate value of this voltage difference is preferably smaller than the peak voltage V ₀ , more preferably the maximum to the extent that the voltage Vmax greater than the peak voltage _{V 0,} to set the minimum voltage Vmin to a value smaller than the peak voltage _{V 0.} Thereby, the piezoelectric element 300 can be displaced more efficiently.

(Other embodiments)
As mentioned above, although one Embodiment of this invention was described, of course, this invention is not limited to embodiment mentioned above. In the above-described embodiment, the piezoelectric element 300 is defined by the relationship between the minimum voltage Vmin and the maximum voltage Vmax to be applied and the peak voltage V ₀ , but for example, the minimum value of the electric field strength applied to the piezoelectric element 300 (minimum electric field strength). Emin) and the maximum value of the electric field strength (maximum electric field strength Emax) and the peak electric field strength E ₀ may be specified. The peak electric field intensity E ₀ is an electric field intensity value at which the first-order differential coefficient based on the electric field intensity of the strain obtained from the strain-electric field intensity curve becomes a maximum value.

That is, the piezoelectric element 300 may be driven under the condition that the minimum electric field intensity Emin and the maximum electric field intensity Emax applied to the piezoelectric element 300 satisfy the following formula (2).
Emin <E ₀ <Emax (2)

The strain-field strength curve substantially matches the displacement-voltage curve. Therefore, the relationship of the minimum value of the intensity of the electric field applied to the piezoelectric element 300 (the minimum field strength Emin) and a maximum value of the electric field strength (maximum electric field strength Emax) and peak electric field intensity _{E 0,} and the minimum voltage Emin and the maximum voltage Emax substantially coincides with the relationship of the peak voltage V _0. For this reason, the minimum electric field intensity Emin and the maximum electric field intensity Emax applied to the piezoelectric element 300 and the peak electric field intensity E ₀ satisfy the relationship of the above formula (2). The piezoelectric element 300 can be efficiently displaced using the range of electric field strength in which the rate of change of the displacement amount of the piezoelectric element 300 is large.

  The ink jet recording head described above constitutes a part of a recording head unit having an ink flow path communicating with an ink cartridge or the like, and is mounted on the ink jet recording apparatus. As shown in FIG. 6, in the recording head units 1A and 1B having the ink jet recording head, cartridges 2A and 2B constituting ink supply means are detachably provided, and a carriage 3 on which the recording head units 1A and 1B are mounted. Is provided on a carriage shaft 5 attached to the apparatus body 4 so as to be movable in the axial direction. The recording head units 1A and 1B, for example, are configured to eject a black ink composition and a color ink composition, respectively.

  The driving force of the driving motor 6 is transmitted to the carriage 3 via a plurality of gears and timing belt 7 (not shown), so that the carriage 3 on which the recording head units 1A and 1B are mounted is moved along the carriage shaft 5. The On the other hand, the apparatus body 4 is provided with a platen 8 along the carriage shaft 5, and a recording sheet S that is a recording medium such as paper fed by a paper feed roller (not shown) is wound around the platen 8. It is designed to be transported.

  In the above-described embodiment, the configuration in which the drive circuit 120 as the drive unit is mounted on the ink jet recording head is exemplified. However, the drive unit may be provided on the recording apparatus side.

  Further, in the above-described embodiments, the present invention has been described by taking an ink jet recording head and a liquid ejecting apparatus as an example of the liquid ejecting head and the liquid ejecting apparatus. The present invention is intended for the entire apparatus, and can of course be applied to a liquid ejecting head that ejects liquid other than ink. Other liquid ejecting heads include, for example, various recording heads used in image recording apparatuses such as printers, color material ejecting heads used in the manufacture of color filters such as liquid crystal displays, organic EL displays, and FEDs (field emission displays). Examples thereof include an electrode material ejection head used for electrode formation, a bioorganic matter ejection head used for biochip production, and the like.

  The present invention can be applied not only to a liquid jet head typified by an ink jet recording head but also to an actuator mounted on another apparatus.

  10 flow path forming substrate, 12 pressure generating chamber, 20 nozzle plate, 21 nozzle, 30 protective substrate, 40 compliance substrate, 41 sealing film, 42 fixing plate, 50 elastic film, 55 insulator film, 60 first electrode, 70 piezoelectric layer, 80 second electrode, 90 lead electrode, 300 piezoelectric element

Claims (7)

A flow path forming substrate in which a pressure generating chamber communicating with a nozzle for ejecting liquid droplets is formed; and a piezoelectric element provided on the flow path forming substrate and causing a pressure change in the pressure generating chamber. The element includes a piezoelectric layer, a first electrode provided on one side of the piezoelectric layer, and a second electrode provided on the opposite side of the piezoelectric layer,
The piezoelectric element is driven under the condition that the relationship between the minimum voltage Vmin and the maximum voltage Vmax applied to the piezoelectric element and the peak voltage V ₀ satisfies the following formula (1). Jet head.
Vmin <V ₀ <Vmax (1) (In the above formula (1), the peak voltage V ₀ is a voltage value at which the first-order differential coefficient based on the displacement voltage obtained from the displacement-voltage curve becomes the maximum value. .) The maximum range of voltage Vmax is greater than the peak voltage V _0, the liquid jet head according to claim 1, wherein the minimum voltage Vmin is characterized in that it is set to a value smaller than the peak voltage V ₀ .   The liquid jet head according to claim 1, wherein the piezoelectric layer is made of a material having a perovskite structure.   The liquid ejecting head according to claim 3, wherein the piezoelectric layer is formed of lead zirconate titanate (PZT).   The liquid jet head according to claim 3, wherein a crystal structure of the piezoelectric layer is a rhombohedral system. A flow path forming substrate in which a pressure generating chamber communicating with a nozzle for ejecting liquid droplets is formed; and a piezoelectric element provided on the flow path forming substrate and causing a pressure change in the pressure generating chamber. A liquid ejecting head in which the element includes a piezoelectric layer, a first electrode provided on one side of the piezoelectric layer, and a second electrode provided on the opposite side of the piezoelectric layer;
Drive means for driving the piezoelectric element under the condition that the relationship between the minimum voltage Vmin and the maximum voltage Vmax applied to the piezoelectric element and the peak voltage V ₀ satisfies the following formula (1): Liquid ejecting device.
Vmin <V ₀ <Vmax (1) (In the above formula (1), the peak voltage V ₀ is a voltage value at which the first-order differential coefficient based on the displacement voltage obtained from the displacement-voltage curve becomes the maximum value. .) A piezoelectric element comprising a piezoelectric layer, a first electrode provided on one side of the piezoelectric layer, and a second electrode provided on the opposite side of the piezoelectric layer;
An actuator characterized in that the piezoelectric element is driven under the condition that the relationship between the minimum voltage Vmin and the maximum voltage Vmax applied to the piezoelectric element and the peak voltage V ₀ satisfies the following expression (1). .
Vmin <V ₀ <Vmax (1) (In the above formula (1), the peak voltage V ₀ is a voltage value at which the first-order differential coefficient based on the displacement voltage obtained from the displacement-voltage curve becomes the maximum value. .)

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