Liquid ejection head, liquid ejection apparatus, and method for driving liquid ejection head

Abstract

A liquid ejection head includes a nozzle configured to eject a liquid; a pressure chamber communicating with the nozzle; and a piezoelectric element provided on a nozzle forming wall of the pressure chamber, such that the liquid in the pressure chamber is ejected from the nozzle by applying a predetermined drive voltage between two electrodes of the piezoelectric element, wherein when an alternating voltage including a positive voltage application period and a negative voltage application period is applied as the predetermined drive voltage, a direction in which the piezoelectric element is displaced becomes opposite in accordance with a sign of the applied voltage.

Description

LIQUID EJECTION HEAD, LIQUID EJECTION APPARATUS, AND METHOD FOR DRIVING LIQUID EJECTION HEAD

[0001] The present invention relates to a liquid ejection head, a liquid ejection apparatus, and a method of driving a liquid ejection head.

[0002] A liquid ejection head that is typically known in the related art includes a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and a piezoelectric element provided on a nozzle forming wall of the pressure chamber, such that the liquid in the pressure chamber is ejected from the nozzle by applying a predetermined drive voltage between two electrodes of the piezoelectric element.

[0003] Patent document 1 discloses an inkjet head (liquid ejection head) that applies a predetermined drive signal (drive voltage) between two electrodes of a piezoelectric element provided on a nozzle forming wall of a pressure chamber communicating with the nozzle such that a liquid in the pressure chamber is ejected through the nozzle. In this inkjet head, a drive signal that includes only an application period of a voltage (positive voltage) in a fixed direction is used between two electrodes of the piezoelectric element (a drive signal in which an application period of a voltage (negative voltage) in the opposite direction does not exist). That is, by changing the voltage value applied between the two electrodes of the piezoelectric element in a range of the positive voltage, the piezoelectric body is displaced to change the volume of the pressure chamber to eject the liquid from the nozzle.

[0004] Japanese Patent No. 6778121

[0005] However, in what is known as a nozzle plate vibration type liquid ejection head in which the piezoelectric element is provided on a nozzle forming wall of the pressure chamber, foreign matter such as charged mist or dust is likely to adhere to a nozzle surface (ejection surface from which liquid is ejected) on which the nozzle is opened.

[0006] In order to address the above described issue, a liquid ejection head according to one embodiment of the present disclosure includes a nozzle configured to eject a liquid; a pressure chamber communicating with the nozzle; and a piezoelectric element provided on a nozzle forming wall of the pressure chamber, such that the liquid in the pressure chamber is ejected from the nozzle by applying a predetermined drive voltage between two electrodes of the piezoelectric element, wherein when an alternating voltage including a positive voltage application period and a negative voltage application period is applied as the predetermined drive voltage, a direction in which the piezoelectric element is displaced becomes opposite in accordance with a sign of the applied voltage.

[0007] According to the embodiments of the present invention, in what is known as a nozzle plate vibration type liquid ejection head, it is possible to prevent foreign matter such as charged mist or dust from adhering to a nozzle surface.

[0008] FIG. 1 is a cross sectional view schematically illustrating a nozzle plate vibration type liquid ejection head according to an embodiment.FIG. 2 is a perspective view schematically illustrating a nozzle surface of the liquid ejection head.FIG. 3 is an enlarged sectional view of a portion surrounded by a broken line indicated by a symbol X in FIG. 1.FIG. 4 is a plan view schematically illustrating an internal structure of the liquid ejection head, and is a cross sectional view taken along a line C-C′.FIG. 5 is a front view schematically illustrating the internal structure of the liquid ejection head, and is a cross sectional view taken along a line A-A′.FIG. 6 is a side view schematically illustrating the internal structure of the liquid ejection head, and is a cross sectional view taken along a line B-B′.FIG. 7 is a graph illustrating a static displacement amount with respect to a voltage applied to the piezoelectric element according to the embodiment.FIG. 8 is a graph illustrating an example of a waveform of a drive voltage in the embodiment.FIG. 9A is a graph illustrating an example of a drive voltage in a related art configuration.FIG. 9B is a graph illustrating an example of a drive voltage in the related art configuration.FIG. 9C is a graph illustrating an example of a drive voltage in the related art configuration.FIG. 10 is a graph illustrating another example of the waveform of the drive voltage in the embodiment.FIG. 11 is a block diagram illustrating an example of a drive voltage application unit for applying a predetermined drive voltage from drive waveform sources to a first electrode (lower electrode) and a second electrode (upper electrode) of each piezoelectric element of each pressure chamber in the embodiment.FIG. 12 includes a graph (a) illustrating an example of a waveform of a voltage output from a first drive waveform source, a graph (b) illustrating a waveform of a voltage applied to a second electrode (upper electrode) of the piezoelectric element in the same example; a graph (c) illustrating the waveform of a voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example; and a graph (d) illustrating a waveform of a voltage applied to the piezoelectric element (a voltage obtained by subtracting an applied voltage of the first electrode from an applied voltage of the second electrode ＝ a drive voltage) in the same example.FIG. 13 includes a graph (a) illustrating another example of a waveform of a voltage output from a first drive waveform source; a graph (b) illustrating a waveform of a voltage applied to a second electrode (upper electrode) of the piezoelectric element in the same example; a graph (c) illustrating a waveform of a voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example; and a graph (d) illustrating a waveform of a voltage applied to the piezoelectric element (a voltage obtained by subtracting an applied voltage of the first electrode from an applied voltage of the second electrode ＝ a drive voltage) in the same example.FIG. 14 includes a graph (a) illustrating still another example of a waveform of a voltage output from a first drive waveform source; a graph (b) illustrating a waveform of a voltage applied to a second electrode (upper electrode) of the piezoelectric element in the same example; a graph (c) illustrating a waveform of a voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example; and a graph (d) illustrating a waveform of a voltage applied to the piezoelectric element (a voltage obtained by subtracting an applied voltage of the first electrode from an applied voltage of the second electrode ＝ a drive voltage) in the same example.FIG. 15 includes a graph (a) illustrating still another example of a waveform of a voltage output from a first drive waveform source; a graph (b) illustrating a waveform of a voltage applied to a second electrode (upper electrode) of the piezoelectric element in the same example; a graph (c) illustrating a waveform of a voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example; and a graph (d) illustrating a waveform of a voltage applied to the piezoelectric element (a voltage obtained by subtracting the voltage applied to the first electrode from the voltage applied to the second electrode ＝ a drive voltage) in the same example.FIG. 16 is a block diagram illustrating another example of a drive voltage applying section for applying a predetermined drive voltage from a drive waveform source to the first electrode (lower electrode) and the second electrode (upper electrode) of each piezoelectric element of each pressure chamber in the embodiment.FIG. 17 is a block diagram illustrating still another example of a drive voltage applying section for applying a predetermined drive voltage from a drive waveform source to the first electrode (lower electrode) and the second electrode (upper electrode) of each piezoelectric element of each pressure chamber in the embodiment.FIG. 18 includes a graph (a) illustrating a waveform of a voltage output from a first drive waveform source in the example of FIG. 17; a graph (b)illustrating a waveform of a voltage output from a third drive waveform source in the example; a graph (c) illustrating a waveform of a voltage applied to the second electrode (upper electrode) of the piezoelectric element in the same example; a graph (d) illustrating the waveform of a voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example; and a graph (e) illustrating a waveform of a voltage applied to the piezoelectric element (a voltage obtained by subtracting an applied voltage of the first electrode from an applied voltage of the second electrode ＝ a drive voltage) in the same example.FIG. 19 is a schematic explanatory view of a printing apparatus in an embodiment.FIG. 20 is a plan view of an example of a head unit of the printing apparatus.FIG. 21 is a plan view of a main part of another printing apparatus.FIG. 22 is a side view of a main part of a printing apparatus of the present example.FIG. 23 is a plan view of a main part of the liquid ejection unit of the present example.FIG. 24 is a front view of the liquid ejection unit of the present example.

[0009] The following describes embodiments of the present invention applied to a liquid ejection head provided in a liquid ejection apparatus serving as an apparatus for ejecting liquid.

[0010] The present invention is not limited to the embodiments described below, and may be modified within the scope of other embodiments, additions, alternations, deletions, and the like that can be conceived by those skilled in the art. Any aspect is included in the scope of the present invention as long as the operation and effect of the present invention are exhibited.

[0011] The liquid ejection head according to the present embodiment is a nozzle plate vibration type liquid ejection head that ejects liquid in the pressure chamber from a nozzle by varying the pressure of the pressure chamber with an actuator provided in the nozzle plate having a nozzle. The nozzle plate vibration type liquid ejection head has a feature that droplets can be ejected with a smaller force than a general unimorph type piezoelectric head (a head that ejects liquid by vibrating a surface facing a wall portion (nozzle communication wall) having a communication port communicating with a nozzle of a pressure chamber), and can achieve power saving of an actuator.

[0012] When the nozzle density is increased, a space for laying out wiring for applying a voltage is limited, and it is difficult to construct the wiring on the surface of the substrate. By constructing the wiring and the drive circuit in the substrate, it is possible to lay out the wiring even in a configuration in which the nozzle density is high. Generally, lead zirconate titanate (PZT) is widely used as a material of a piezoelectric body used as an actuator because of its high piezoelectric characteristics. However, when a piezoelectric film is formed on a substrate on which wiring and a drive circuit are formed, the drive circuit and the wiring in the substrate cannot withstand high temperature if PZT is used as a material of the piezoelectric body because the film formation and crystallization temperature of PZT is required to be 600℃ or higher. Therefore, in a configuration in which wiring and a drive circuit are constructed in a substrate, a piezoelectric material having a lower film forming temperature than PZT is required as the piezoelectric material, and a material having lower piezoelectric characteristics than PZT is necessarily selected. However, since the nozzle plate vibration type liquid ejection head described above has a feature that the liquid droplets can be ejected with a smaller force than that of a general unimorph type piezoelectric head, it is possible to satisfactorily eject the liquid even when a material having a lower piezoelectric property than PZT is selected. Therefore, even a piezoelectric material such as a non-lead material, which has a low film-forming / crystallization temperature but has a small power, can satisfactorily eject a liquid. This allows wiring and a drive circuit to be formed in the substrate, and thus, the density can be increased. Further, in the nozzle plate vibration type liquid ejection head, since the volume of the pressure chamber can be reduced, the head can be miniaturized.

[0013] FIG. 1 is a cross sectional view schematically illustrating a nozzle plate vibration type liquid ejection head according to the present embodiment. FIG. 2 is a perspective view schematically illustrating a nozzle surface of the liquid ejection head of the present embodiment. The liquid ejection head 1 includes a nozzle plate 110, a pressure chamber substrate 100, and a fluid resistance substrate 120. In addition, the liquid ejection head 1 includes a frame portion 140 and the like as described later.

[0014] The nozzle plate 110 is a thin film and has a plurality of nozzles 2 for ejecting liquid and piezoelectric elements 5 as an electromechanical transducer element which are annular actuators arranged around the respective nozzles 2. The pressure chamber substrate 100 includes a plurality of pressure chambers (also referred to as individual liquid chambers, pressurized liquid chambers, or the like) 4 which communicate with the plurality of nozzles 2. A nozzle 2 (a vibration film 103) is provided on one surface of each of the pressure chambers 4, and the fluid resistance substrate 120 and the opening 4a thereof are disposed on a side facing the one surface of a corresponding one of the pressure chambers 4. The frame portion 140 includes a common liquid chamber 3 that communicates with the plurality of pressure chambers 4 via the respective openings 4a. Electrical connection pads 55 for connecting to an external electrical component such as a power supply are provided at both ends of the liquid ejection head 1.

[0015] FIG. 3 is an enlarged sectional view of a portion surrounded by a broken line indicated by a reference symbol X in FIG. 1. The pressure chamber substrate 100 is a silicon on insulator (SOI) substrate, and includes a drive circuit 101 and a wiring portion 102 on a side on which the vibration film 103 is formed. The drive circuit 101 is a circuit including a transistor, a resistor, and the like. The wiring portion 102 includes a wiring portion for applying a drive voltage (drive waveform) to a first electrode 51 and a wiring portion for applying a drive voltage to the second electrode 53. The wiring portion 102 is electrically connected to the electrical connection pad 55 via a third contact 7c opened in the vibration film 103.

[0016] The nozzle plate 110 has a nozzle forming portion (film) 111 in which a plurality of nozzles 2 are formed and which covers the piezoelectric element 5, and a liquid repellent film 112 is formed on the nozzle surface of the nozzle forming portion 111. When the liquid is continuously ejected, mist generated simultaneously with the ejection adheres to the nozzle surface. When a large amount of mist adheres to the nozzle surface, the liquid ejected from the nozzle 2 may be affected by the liquid adhering to the nozzle surface and may be deviated from a desired landing position. By forming the liquid repellent film 112 on the nozzle surface, it is possible to prevent the adhesion of the liquid to the nozzle surface, and it is possible to prevent the liquid ejected from the nozzle 2 from being affected by the liquid adhering to the nozzle surface.

[0017] The piezoelectric element 5 of the nozzle plate 110 is provided with a first electrode 51 (also called a lower electrode), a piezoelectric film 52, and a second electrode 53 (also called an upper electrode). The piezoelectric element 5 is covered with a first insulating film 8a. The first insulating film 8a is provided with a hole-shaped fourth contact 7d for electrical connection to the first electrode 51 and a hole-shaped fifth contact 7e for electrical connection to the second electrode 53.

[0018] In addition, the first insulating film 8a is provided with a first lead wire 9a for electrically connecting the first electrode 51 of the piezoelectric element 5 to the wiring portion 102 of the pressure chamber substrate 100, and a second lead wire 9b for electrically connecting the second electrode 53 of the piezoelectric element 5 to the wiring portion 102 of the pressure chamber substrate 100.

[0019] The first lead wire 9a is electrically connected to the first electrode 51 via the fourth contact 7d, and is electrically connected to the wiring portion 102 via the first contact 7a. The second lead wire 9b is electrically connected to the second electrode 53 via the fifth contact 7e, and is electrically connected to the wiring portion 102 via the second contact 7b. The first lead wire 9a and the second lead wire 9b are covered with a second insulating film 8b. In this embodiment, the second insulating film 8b also covers the piezoelectric element 5, and functions to protect the piezoelectric element 5 by preventing moisture that has entered the resin-made nozzle forming portion 111 from entering the piezoelectric element 5.

[0020] Note that the first electrode 51 and the second electrode 53 may be provided with lead wiring portions, respectively, and may be directly connected to the wiring portion 102 in an electrode manner via a contact opened in the vibration film. In addition, an adhesion improving film for ensuring adhesion to the nozzle forming portion 111 may be formed on the second insulating film 8b.

[0021] The liquid filled in the liquid ejection head 1 enters the nozzles 2 and forms menisci in the nozzles. By applying a predetermined drive voltage to each of the electrodes 51 and 53 of the piezoelectric element 5, the piezoelectric film 52 is displaced (vibrated), and the vibration film 103 vibrates in the vertical (up-down) direction in FIG. 3. The vibration of the vibration film 103 causes a pressure change in the liquid in the pressure chamber, and the liquid is ejected from the nozzle 2.

[0022] In the liquid ejection head 1 of the present embodiment, a protective film 11 is formed on the inner peripheral surface of the nozzle 2, the inner peripheral surface of the pressure chamber 4, and the bottom surface of the common liquid chamber 3. The protective film 11 has lyophilicity with respect to the liquid ejected by the liquid ejection head 1 and serves as a surface layer that prevents erosion of the liquid. In the present embodiment, the liquid ejected by the liquid ejection head 1 is alkaline, and the pressure chamber substrate 100 and the vibration film 103 forming the pressure chamber 4 are made of silicon single crystal and silicon oxide. These materials are fragile to alkaline liquids and are dissolved and eroded in alkaline solutions. In order to prevent the adverse effects, the liquid-resistant protective film 11 for preventing the erosion of the liquid is formed, and thus it is possible to protect the pressure chamber substrate 100 and the vibration film 103 from the liquid.

[0023] The pressure chamber 4 and the nozzle 2 are formed by dry etching. Since the gas for dry etching contains fluorine, a surface film containing fluorine is formed on the inner wall surface of the pressure chamber 4 and the inner peripheral surface of the nozzle 2 after etching, and the inner wall surface of the pressure chamber 4 and the inner peripheral surface of the nozzle have liquid repellency. If the inner peripheral surface of the pressure chamber 4 has liquid repellency, the liquid does not spread on the inner peripheral surface of the pressure chamber 4 when the liquid is filled, and thus the pressure chamber 4 is not filled with the liquid well, and air bubbles may be generated in a corner portion of the pressure chamber 4.

[0024] In the present embodiment, since the protective film 11 having lyophilicity is formed on the inner peripheral surface of the pressure chamber 4 and the inner peripheral surface of the nozzle 2, it is possible to improve the wettability of the liquid with respect to the inner peripheral surfaces of the pressure chamber 4 and the nozzle 2. The protective film 11 may be more lyophilic to the liquid than the film formation surface (the lower layer surface of the protective film 11) of the pressure chamber 4 or the nozzle 2 on which the protective film 11 is formed. When the liquid solvent is aqueous, the protective film 11 is highly hydrophilic, and when the liquid solvent is oily, the protective film 11 is highly lyophilic, whereby the protective film 11 can be formed to be highly lyophilic.

[0025] In this way, by forming the protective film 11 having lyophilicity with respect to the liquid filled in the pressure chamber 4 on the inner peripheral surfaces of the nozzle 2 and the pressure chamber 4, the liquid easily wets and spreads on the inner peripheral surfaces of the pressure chamber 4 and the nozzle 2 when the liquid is filled. As a result, the filling property of the liquid can be improved, and the pressure chamber 4 and the nozzle 2 can be filled with the liquid in a favorable manner without pressurization or suction when the liquid is filled. Therefore, it is possible to prevent the occurrence of a crack in the vibration film 103 when the liquid is filled.

[0026] Since the solvent of the liquid of the present embodiment is aqueous, by forming the protective film 11 which does not contain at least fluorine on the inner peripheral surfaces of the pressure chambers 4 and the nozzles 2, it is possible to improve the lyophilicity compared to a surface film which contains fluorine and is formed by dry etching. In addition, since this film is in direct contact with various liquids, it is desirable that the film is made of a material having liquid resistance, for example, a metal oxide which forms a passive state. As a method for further improving the lyophilicity, silicon dioxide (SiO2) can be mixed with the metal oxide forming the passive state at the molecular level. The SiO2of the protective film 11 has an OH group having hydrophilicity by substitution of O on the surfaces. This can further impart hydrophilicity to the protective film 11. Examples of the metal of the metal oxide include tantalum (Ta), niobium (Nb), titanium (Ti), zirconium (Zr), hafnium (Hf), and tungsten (W), which are highly compatible with oxidation numbers. In particular, Zr and Hf having a valence similar to that of SiO2, or Ta having a valence close to that of Zr and Hf are particularly desirable.

[0027] Further, for example, the protective film 11 may have a two-layer structure of a liquid-resistant film and a lyophilic film. In this case, after the liquid-resistant film is formed on the inner peripheral surfaces of the nozzles 2 and the pressure chambers 4, the lyophilic film is formed on the liquid-resistant film.

[0028] In this embodiment, a lyophilic protective film 11 is also formed on the surface opposite to the film-forming surface of the vibration film 103 of the pressure chamber substrate 100 that constitutes the bottom surface of the common liquid chamber 3, but the protective film 11 on this surface may be configured to only have liquid resistance. However, it is necessary to provide a process of forming the protective film 11 on the bottom surface of the common liquid chamber 3 separately from a process of forming a lyophilic protective film on the inner peripheral surface of the nozzle or the wall surface of the pressure chamber, and thus there is a concern that the number of manufacturing processes increases. In addition, by forming the protective film 11 on the bottom surface of the common liquid chamber 3, the liquid easily spreads on the bottom surface of the common liquid chamber 3, and thus the filling property of the liquid is also improved. Therefore, it is preferable to form the lyophilic protective film 11 also on the surface of the pressure chamber substrate 100 that constitutes the bottom surface of the common liquid chamber 3, opposite to the surface on which the vibration film 103 is formed.

[0029] The material of the vibration film 103 may be any material having at least insulating properties, such as SiO2, SiN, metal oxides, and resins. However, in order to increase the displacement, a material having a low Young modulus is desirable, and in consideration of the difference in the coefficient of linear expansion from the pressure chamber substrate 100, SiO2(silica dioxide) having a relatively small difference in the coefficient of linear expansion is most desirable as the material of the vibration film 103.

[0030] The first electrode layer 151 and the second electrode layer 153 are preferably made of a metal having a low electrical resistance and low reactivity, such as Ir or Mo. As the piezoelectric material forming the piezoelectric layer 152, in a case where the drive circuit 101 and the wiring portion 102 are built in the pressure chamber substrate 100 in order to improve the density as in the present embodiment, a piezoelectric material having a film forming temperature of 450℃ or lower is desirable in order not to destroy them. Examples of the piezoelectric material having a film forming temperature of 450℃ or lower include AlN and ScAlN having a higher piezoelectric constant than AlN.

[0031] Further, by using ScAlN as the piezoelectric material, the following advantages can be obtained. That is, although the piezoelectric characteristics can be improved by aligning the crystal orientation of the piezoelectric film 52, it is necessary to provide an orientation control layer between the vibration film 103 and the first electrode 51 for the orientation control. When the piezoelectric material of the piezoelectric film 52 is ScAlN, the lattice constant of the first electrode 51 made of Mo can be made close to that of ScAlN by using ScAlN also as the orientation control layer. As a result, the crystal orientation of the piezoelectric film 52 is aligned, and the piezoelectric characteristics can be improved.

[0032] FIG. 4 is a plan view schematically illustrating the internal structure of the liquid ejection head 1 according to the present embodiment, which is a cross sectional view taken along a line C-C′. FIG. 5 is a front view schematically illustrating the internal structure of the liquid ejection head 1 according to the present embodiment, which is a cross sectional view taken along a line A-A′. FIG. 6 is a side view schematically illustrating the internal structure of the liquid ejection head 1 according to the present embodiment, which is a cross sectional view taken along a line B-B′.

[0033] As illustrated in FIGS. 5 and 6, the liquid ejection head 1 according to the present embodiment is configured by arranging the nozzle plate 110, a pressure chamber substrate 100, a fluid resistance substrate 120, and a frame portion 140 in this order.

[0034] The pressure chamber substrate 100 has a pressure chamber array 40 in which the plurality of pressure chambers 4 are arranged. The openings 4a of the fluid resistance substrate 120 are opened on the upper surface (surface on the common liquid chamber 3 side) of the pressure chamber array 40, and the common liquid chamber 3 formed in the frame portion 140 is disposed so as to face the openings 4a of each fluid resistance substrate 120. In the present embodiment, as an example, the size of the pressure chamber 4 is 220 μm, and the widths of the partition walls that partition the pressure chambers 4 are 30 μm, and as a result, the center-to-center spacing L2 (see FIG. 6) between two adjacent pressure chambers 4 is 250 μm.

[0035] The liquid stored in an external liquid storage portion is supplied to the liquid ejection head 1 via a liquid supply port 33 of the frame portion 140. The liquid supplied from the liquid supply port 33 is supplied to the common liquid chamber 3, and is supplied from the common liquid chamber 3 to each of the pressure chambers 4 via the openings 4a of the fluid resistance substrate 120. A liquid ejection port 36 communicates with the common liquid chamber 3. The liquid in the common liquid chamber 3 that is not supplied to the pressure chambers 4 via the openings 4a of the fluid resistance substrate 120 is returned to an external ink storage unit from the liquid ejection port 36 via an external pump or the like.

[0036] Next, the piezoelectric element 5, which is a feature of the present embodiment, will be described. In the nozzle plate vibration type liquid ejection head, the electrodes 51 and 53 of the piezoelectric element 5, the wiring portion 102 for a drive voltage, and the like are arranged in the vicinity of the nozzle surface where the nozzles 2 are opened. Therefore, an electrostatic force generated by applying a voltage to the piezoelectric element 5 by a drive voltage or the like acts outward from the nozzle surface, and the electrostatic force attracts surrounding foreign matter such as charged mist and dust onto the nozzle surface. As a result, such foreign matter may adhere to the nozzle surface, which may cause problems such as deterioration of ejection reliability and accumulation of damage to various elements including the piezoelectric element due to long-term voltage application.

[0037] Normally, a drive signal including only an application period of a voltage in a certain direction (either positive or negative voltage) is applied between two electrodes of the piezoelectric element, and the piezoelectric element is displaced only in one direction to perform a liquid ejection operation. In this case, in order to generate a large displacement by the piezoelectric element, the maximum value (maximum value of the absolute value) of the voltage (either positive or negative voltage) applied as the drive voltage must be increased. Therefore, the larger the maximum displacement of the piezoelectric element is, the larger the maximum voltage value applied to the electrodes of the piezoelectric element and the wiring for the drive voltage becomes. This increases the electrostatic force that attracts foreign matter to the nozzle surface, which increases the adhesion of foreign matter.

[0038] In this embodiment, therefore, the piezoelectric element 5 is displaced in accordance with the sign of the voltage applied between the electrodes 51 and 53 and, specifically, in the opposite direction. An alternating voltage including a positive voltage application period and a negative voltage application period is used as a drive voltage applied between the electrodes 51 and 53 and of the piezoelectric element 5.

[0039] According to this configuration, the piezoelectric element 5 can be displaced in two directions opposite to each other in accordance with positive and negative voltages of the drive voltages. Therefore, the maximum displacement of the piezoelectric element 5 is the sum of the maximum displacement in the positive direction when a positive voltage is applied and the maximum displacement in the negative direction when a negative voltage is applied. In this case, the maximum value (maximum value of the absolute value) of the positive voltage during the application of the positive voltage and the maximum value (maximum value of the absolute value) of the negative voltage during the application of the negative voltage are both smaller than the maximum value (maximum value of the absolute value) of the voltage in the above described configuration in which only one of the positive and negative voltages is applied. As a result, according to the present embodiment, it is possible to reduce the electrostatic force which attracts the foreign matter onto the nozzle surface, and it is possible to prevent the adhesion of the foreign matter.

[0040] FIG. 7 is a graph illustrating a static displacement amount with respect to the voltage applied to the piezoelectric element 5 of the present embodiment. In FIG. 7, the applied voltage is represented by a potential of the second electrode (upper electrode) 53 with respect to a potential of the first electrode (lower electrode) 51. The positive and negative signs of the displacement are as follows: the displacement in the direction of contracting the pressure chamber 4 is positive, the applied voltage for displacing the piezoelectric element 5 in the positive direction is positive (a positive voltage), and the applied voltage for displacing the piezoelectric element 5 in the negative direction is negative (a negative voltage).

[0041] As illustrated in FIG. 7, the piezoelectric element 5 of the present embodiment is characterized in that the direction of displacement is opposite in accordance with a sign of a voltage applied between the first electrode (lower electrode) 51 and the second electrode (upper electrode) 53, and the displacement is substantially linear with respect to the voltage within a voltage range used for driving. As the piezoelectric element 5 exhibiting such characteristics, for example, a piezoelectric element using aluminum nitride (AlN) or aluminum scandium nitride (ScAlN) as the piezoelectric film 52 is preferable, and a piezoelectric element using ScAlN having a higher piezoelectric constant than AlN is more preferable.

[0042] Other candidate materials include piezoelectric materials of group IIb-VIbcompounds such as CdS, CdSe, ZnO, ZnTe, and CdTe, and group IIIb-Vbcompounds such as GaAs, GaSb, InS, and InSb. Most of the group IIb-VIbcompounds and group IIIb-Vbcompounds have a zincblende or wurtzite crystal structure. In the present embodiment, a piezoelectric material having a wurtzite crystal structure can be suitably used. The wurtzite crystal belongs to a hexagonal crystal system, and the crystal has a polar axis that is a c-axis. In the wurtzite crystal, only d31, d33, and d15are piezoelectric constants due to the symmetry. When an electric field is applied to the crystal in the c-axis direction, displacement in the c-axis direction can be generated, and at this time, strain is also generated in a direction perpendicular to the c-axis direction. By utilizing this strain, a unimorph structure in which the piezoelectric film and the vibration film are laminated is formed, thereby causing deformation of the vibration film to eject liquid.

[0043] FIG. 8 is a graph illustrating an example of the waveform of the drive voltage in the present embodiment. As the drive voltage of the present embodiment, an alternating voltage including a positive voltage application period and a negative voltage application period is used. The range of the drive voltage is a range in which the displacement of the piezoelectric element 5 is substantially linear with respect to the voltage. The following gives a specific description.

[0044] The range of the drive voltage is from －Vmax to Vmax, where Vmax is the absolute value of the voltage applied to the piezoelectric element. In the example of the waveform of FIG. 8, ｜V1｜ ＞ ｜V2｜, and thus Vmax ＝ ｜V1｜ ＝ V1. As illustrated in FIG. 7, the displacement δ of the piezoelectric element 5 is linear in the range from －V1 to ＋V1, that is, δ(－V1) and －δ(V1) are approximately equal. That is, the displacement of the piezoelectric element 5 is substantially linear with respect to the voltage.

[0045] As in the present embodiment, when the piezoelectric element 5 configured to be displaced in an opposite direction in accordance with a sign of the voltage applied between the first and second electrodes 51 and 53 is used, the advantage is that the absolute value of the drive voltage can be lowered.

[0046] More specifically, when ΔV1 represents the voltage change for obtaining the amount of displacement necessary to obtain a desired liquid ejection speed, in the case of the above configuration where only positive or negative voltage is applied, for example, a drive voltage with a waveform as illustrated in any of FIGS. 9A to 9C will be used. FIG. 9A is an example of a drive waveform (pull-pull waveform) for expanding the pressure chamber 4 (filling the pressure chamber 4 with liquid) after contracting the pressure chamber 4 (after ejection), FIG. 9B is an example of a drive waveform (pull-push waveform) for contracting the pressure chamber 4 after expanding the pressure chamber 4, and FIG. 9C is an example of a pull-push waveform when the drive voltage is only a positive voltage.

[0047] In the case of the above described configuration in which only one of the positive and negative voltages is applied, as illustrated in FIGS. 9A to 9C, in order to obtain the voltage change ΔV1 for obtaining the amount of displacement necessary to obtain a desired liquid ejection speed, a maximum value ｜V1’｜ of the drive voltage corresponding to ΔV1 is required. However, in general, depending on the conditions such as the withstand voltage of the piezoelectric element 5 and the driving capability of other elements, it is sometimes desired to reduce the maximum value ｜V1’｜ of the drive voltage.

[0048] According to the present embodiment, in the case of obtaining the voltage change ΔV1 for obtaining the amount of displacement necessary to obtain a desired liquid ejection speed, for example, as illustrated in FIG. 10, the maximum value (absolute value) of the positive voltage can be set to ＋V1 / 2, and the maximum value (absolute values) of the negative voltage can be set to －V1 / 2. In this case, the maximum value (absolute value) of the drive voltage can be reduced to half of the above described configuration in which only one of the positive and negative voltages is applied. Even when the V1 of the maximum value (absolute values) of the positive voltage and the V2 of the maximum value (absolute values) of the negative voltage are different as in the waveform of the drive voltage of the present embodiment illustrated in FIG. 8, the maximum value of the drive voltage (the absolute value of the V1 in the example of FIG. 8) can be lowered compared to the above described configuration in which only one of the positive and negative voltages is applied.

[0049] Here, for example, if the waveform is a waveform that starts from V1 as in the drive waveform illustrated in FIG. 9C, it is necessary to apply the voltage V1 in advance during a non-drive period (a period during which the drive voltage is not applied to the piezoelectric element 5) before the drive waveform is applied. In this case, in the nozzle plate vibration type liquid ejection head as in the present embodiment, the electrostatic force generated by the application of voltage to the electrodes 51 and 53 of the piezoelectric element 5 or to the wiring portion 102 for the drive voltage acts in the direction outward from the nozzle surface even during the non-drive period. Therefore, there is a concern that surrounding foreign matter such as charged mist or dust is attracted and attached onto the nozzle surface by electrostatic force.

[0050] Therefore, the drive waveform of the present embodiment is preferably a waveform starting from the 0 V as illustrated in FIG. 8. In this case, since the voltage applied during the non-drive period can be made 0 V, the electrostatic force that is generated by the application of voltage to the electrodes 51 and 53 of the piezoelectric element 5 and the drive voltage wiring portions 102 does not act outward from the nozzle surface during the non-drive period. Therefore, it is possible to prevent surrounding foreign matter such as charged mist or dust from being attracted and from adhering onto the nozzle surface by electrostatic force.

[0051] Next, an example of control for applying a drive voltage to the piezoelectric element 5 in the present embodiment will be described. FIG. 11 is a block diagram illustrating an example of a drive voltage application unit 520 that applies a predetermined drive voltage from drive waveform sources 521 and 522 to a first electrode (lower electrode) 51 and a second electrode (upper electrode) 53 of each of the piezoelectric elements 5-1, 5-2, 5-3, ..., and 5-N of the pressure chambers 4. In the present example, a second drive waveform source 522 is grounded and is maintained at 0 V.

[0052] In FIG. 12, (a) to (d) are graphs illustrating examples of voltage waveforms in the respective components. Note that (a) of FIG. 12 is a graph illustrating a waveform of the voltage output from a first drive waveform source 521, (b) of FIG. 12 is a graph illustrating a waveform of the voltage applied to the second electrode (upper electrode) 53 of the piezoelectric element 5, (c) of FIG. 12 is a graph illustrating a waveform of the voltage applied to the first electrode (lower electrode) 51 of the piezoelectric element 5, and (d) of FIG. 12 is a graph illustrating a waveform of the voltage applied to the piezoelectric element 5 (voltage obtained by subtracting the voltage applied to the first electrode 51 from the voltage applied to the second electrode 53 ＝ drive voltage).

[0053] In FIG. 12, a period (1) indicates a period in which the first drive waveform source 521 is selected in the waveform selection units 525 and 526, and a period (2) indicates a period in which the second drive waveform source 522 is selected in the waveform selection units 525 and 526. By selecting the drive waveform sources 521 and 522 at an appropriate timings in the waveform selection units 525 and 526 of each of the piezoelectric elements 5-1 to 5-N, it is possible to select whether or not to eject the liquid for each of the piezoelectric elements 5-1 to 5-N.

[0054] With the configuration of the present example, as illustrated in (d) of FIG. 12, a drive voltage composed of an alternating voltage including a positive voltage application period and a negative voltage application period can be applied between the electrodes 51 and 53 and of each of the piezoelectric elements 5-1 to 5-N.

[0055] In FIG. 13, (a) to (d) are graphs illustrating other examples of the voltage waveforms in respective components. The present example illustrated in (a) to (d) in FIGS. 13 is different from the example of (a) to (d) in FIG. 12 in that the first drive waveform source 521 is configured to output only a positive voltage. In the present example, as illustrated in (c) of FIG. 13, the voltage of the first drive waveform source 521 is also input to the first electrode (lower electrode) 51 of the piezoelectric element 5 to change the voltage.

[0056] According to the present example, even when the first drive waveform source 521 is configured to output only a positive voltage, as illustrated in (d) of FIG. 13, a drive voltage composed of an alternating voltage including a positive voltage application period and a negative voltage application period can be applied between the electrodes 51 and 53 and of each of the piezoelectric elements 5-1 to 5-N. As in the present example, the first drive waveform source 521 is configured to output only a positive voltage, and thus it is possible to reduce the cost of various elements (circuit components) such as an amplifier.

[0057] In FIG. 14, (a) to (d) are graphs illustrating still other examples of the voltage waveforms in respective components. In the present example illustrated in (a) to (d) of FIG. 14, the first drive waveform source 521 outputs only a positive voltage, as in the example illustrated in (a) to (d) of FIG. 13. However, in the non-drive period (non-ejection period), as illustrated in (a) to (d) of FIG. 13, the voltage of the first drive waveform source 521 is input to both the first electrodes (lower electrodes) 51 and the second electrodes (upper electrodes) 53 of the piezoelectric element 5, whereby the drive voltage applied to the piezoelectric element 5 is set to 0 V as illustrated in (d) of FIG. 13. Such a control example may be adopted.

[0058] In FIG. 15, (a) to (d) are graphs illustrating still other examples of the voltage waveforms in respective components. The present example illustrated in (a) to (d) of FIG. 15 is different from the above described example, and is a configuration in which a constant voltage source that outputs only a constant positive voltage is used as the first drive waveform source 521. In the present example, the waveform of the voltage applied to each of the first electrode (lower electrode) 51 and the second electrode (upper electrode) 53 of the piezoelectric element 5 is controlled by the switching operation of the waveform selection units 525 and 526. In the present example, although the rise time / fall time of the waveform is fixed by the time constant determined by the capacitance and the electric resistance value of the piezoelectric element 5 and other elements, it is possible to reduce the cost of the first drive waveform source 521.

[0059] FIG. 16 is a block diagram illustrating another example of the drive voltage application unit 520 that applies a predetermined drive voltage from the drive waveform sources 521 and 522 to the first electrode (lower electrode) 51 and the second electrode (upper electrode) 53 of each of the piezoelectric elements 5-1 to 5-N of each of the pressure chambers 4. In the present example, the second drive waveform source 522 is omitted, and the waveform selection units 525 and 526 selects the floating state in the period (2). Such an example may be adopted.

[0060] FIG. 17 is a block diagram illustrating still another example of the drive voltage application unit 520 that applies a predetermined drive voltage to the first electrode (lower electrode) 51 and the second electrode (upper electrode) 53 of each of the piezoelectric elements 5-1 to 5-N of each pressure chamber 4. In the present example, three drive waveform sources 521 to 523 are used.

[0061] In FIGS. 18, (a) to (e) are graphs illustrating examples of voltage waveforms in respective components in the example of FIG. 17. (a) of FIG. 18 is a graph illustrating the waveform of the voltage output from the first drive waveform source 521, and (b) of FIG. 18 is a graph illustrating the waveform of the voltage output from the third drive waveform source 523. The second drive waveform source 522 is grounded and maintained at 0 V. (c) of FIG. 18 is a graph illustrating the waveform of the voltage applied to the second electrode (upper electrode) 53 of the piezoelectric element 5, (d) of FIG. 18 is a graph illustrating the waveform of the voltage applied to the first electrode (lower electrode) 51 of the piezoelectric element 5, and (e) of FIG. 18 is a graph illustrating the waveform of the voltage (＝ drive voltage) applied to the piezoelectric element 5.

[0062] In the present example, the voltage waveform of the first drive waveform source 521 and the voltage waveform of the third drive waveform source 523 are waveforms with mutually inverted polarities. In the present example, although the configuration is complicated, the advantage is that the output voltage value (absolute value) of each drive waveform source 521 or 523 can be reduced to half compared to the above described example.

[0063] Next, an example of a liquid ejection apparatus according to the present invention will be described with reference to FIGS. 19 and 20. FIG. 19 is a schematic explanatory view of a printing apparatus which is an ink jet recording apparatus which is an image forming apparatus as an apparatus which ejects liquid in the present embodiment. FIG. 20 is a plan view illustrating an example of a head unit of the printing apparatus of the embodiment.

[0064] A printing apparatus 500 which is an apparatus for ejecting a liquid includes a carrying-in unit 501 configured to carry in a continuous body 510, and a guiding-transporting unit 503 configured to guide and transport the continuous body 510 carried in from the carrying-in unit 501 to a printing unit 505. The printing apparatus 500 also includes the printing unit 505 configured to perform printing for forming an image by ejecting liquid onto the continuous body 510, a drying unit 507 configured to dry the continuous body 510, a carrying-out unit 509 configured to carry out the continuous body 510, and the like.

[0065] The continuous body 510 is fed from an original winding roller 511 of the carrying-in unit 501, guided and transported by respective rollers of the carrying-in unit 501, the guiding-transporting unit 503, the drying unit 507, and the carrying-out unit 509, and wound by a winding roller 591 of the carrying-out unit 509. In the printing unit 505, the continuous body 510 is transported on a transport guide member 559 so as to face a head unit 550, and an image is printed on the continuous body 510 by the liquid ejected from the head unit 550.

[0066] In the printing apparatus 500 according to the embodiment, the head unit 550 includes two head modules 100A and 100B according to the embodiment described above in a common base member 552.

[0067] When the alignment direction of the liquid ejection heads 1 in the direction orthogonal to the transport direction of head modules 100A and 100B is the head arrangement direction, the same color liquid is ejected in head rows 1A1 and 1A2 of head module 100A. Similarly, head rows 1B1 and 1B2 of head module 100A, head rows 1C1 and 1C2 of head module 100B, and head rows 1D1 and 1D2 of head module 100B are paired to eject liquid of the required colors, respectively.

[0068] Next, another example of a printing apparatus as an apparatus for ejecting liquid according to the invention will be described with reference to FIGS. 21 and 22. FIG. 21 is a plan view of a main part of the printing apparatus of the present example. FIG. 22 is a side view of the main part of the printing apparatus of the present example.

[0069] The printing apparatus 500 of the present example is a serial type apparatus, in which a carriage 403 moves back and forth in the main scanning direction by a main scanning movement mechanism 493. The main scanning movement mechanism 493 includes a guide member 401, a main scanning motor 405, a timing belt 408, and the like. The guide member 401 is bridged between the left and right side plates 491A and 491B and movably holds the carriage 403. The carriage 403 is then moved back and forth in the main scanning direction by the main scanning motor 405 via the timing belt 408 that is bridged between a driving pulley 406 and a driven pulley 407.

[0070] The carriage 403 is provided with a liquid ejection unit 440 in which the liquid ejection head 1 according to the present invention and a head tank 441 are integrated. The liquid ejection head 1 ejects, for example, liquids of respective colors of yellow (Y), cyan (C), magenta (M), and black (K). The liquid ejection head 1 includes nozzle rows including a plurality of nozzles arranged in the sub-scanning direction orthogonal to the main-scanning direction, with the ejection direction facing downward. The liquid ejection head 1 is connected to a liquid circulation device, and liquid of a required color is supplied and circulated.

[0071] The printing apparatus 500 includes a transport mechanism 495 for transporting a sheet 410. The transport mechanism 495 includes a transport belt 412 as a transporting unit and a sub-scanning motor 416 for driving the transport belt 412. The transport belt 412 absorbs the sheet 410 and transports it in a position facing the liquid ejection head 1. The transport belt 412 is an endless belt, and is stretched between a transport roller 413 and a tension roller 414. The adsorption can be performed by electrostatic adsorption, air suction, or the like. The transport roller 413 is rotated by the sub-scanning motor 416 via a timing belt 417 and a timing pulley 418, so that the transport belt 412 is moved in the sub-scanning direction.

[0072] Further, a maintenance-recovery mechanism 420 for maintaining and recovering the liquid ejection heads 1 is disposed on one side of the carriage 403 in the main scanning direction and on a side of the transport belt 412. The maintenance-recovery mechanism 420 includes, for example, a cap member 421 for capping the nozzle surface of the liquid ejection head 1, and a wiper member 422 for wiping the nozzle surface. The main scanning movement mechanism 493, the maintenance-recovery mechanism 420, and the transport mechanism 495 are attached to a housing including side plates 491A and 491B and a back plate 491C.

[0073] In the printing apparatus 500 configured as described above, the sheet 410 is fed onto the transport belt 412 and adsorbed thereon, and the sheet 410 is transported in the sub-scanning direction by the circulation movement of the transport belt 412. Therefore, the liquid ejection head 1 is driven in accordance with an image signal while the carriage 403 is moved in the main scanning direction, and thereby liquid is ejected onto the sheet 410 that is stopped to form an image.

[0074] Next, another example of the liquid ejection unit according to the present invention will be described with reference to FIG. 23. FIG. 23 is a plan view of a main part of the liquid ejection unit of the present example.

[0075] The liquid ejection unit 440 includes a housing portion including the side plates 491A and 491B, and the back plate 491C, the main scanning movement mechanism 493, the carriage 403, and the liquid ejection head 1, among the members forming the liquid ejection apparatus.

[0076] The maintenance-recovery mechanism 420 may be further attached to, for example, the side 491B of the liquid ejection unit 440.

[0077] Next, still another example of the liquid ejection unit according to the invention will be described with reference to FIG. 24. FIG. 24 is a front view of the liquid ejection unit of the present example.

[0078] The liquid ejection unit 440 includes the liquid ejection head 1 to which a flow path component 444 is attached, and a tube 456 connected to the flow path component 444.

[0079] The flow path component 444 is disposed inside the cover 442. The head tank 441 may be included instead of the flow path component 444. A connector 443 for electrical connection to the liquid ejection head 1 is provided on the upper portion of the flow path component 444.

[0080] In the present invention, the liquid to be ejected is not particularly limited as long as it has a viscosity or surface tension that allows ejection from the head, but it is preferable that the viscosity is 30 mPa・s or less at normal temperature under normal pressure or by heating or cooling. More specifically, the liquid may be a solution, suspension, emulsion, or the like containing a solvent such as water or an organic solvent, a coloring agent such as a dye or a pigment, a function-imparting material such as a polymerizable compound, a resin, or a surfactant, a biocompatible material such as DNA, amino acid, protein, or calcium, or an edible material such as a natural pigment. These can be used in applications such as an inkjet ink, a surface treatment liquid, a liquid for forming a constituent element of an electronic element or a light-emitting element or an electronic circuit resist pattern, and a three dimensionally modelling material liquid.

[0081] The liquid to be ejected may be a metal material such as solder or a material that is fixed at normal temperature such as wax ink, which is heated and melted and ejected from the nozzles. Further, the liquid to be ejected may be a liquid such as UV ink having a high viscosity at normal temperature, which is heated to reduce the viscosity and ejected from the nozzles. In this case, by providing a heating unit such as a heater in the frame portion 140 or the pressure chamber substrate 100, the ejection material in the pressure chamber 4 can be brought into a molten state or a state of low viscosity, and the liquid can be favorably ejected from the nozzles. In this case, as the electrostrictive material of the piezoelectric body, it is preferable to use aluminum nitride (AlN) containing at least one material of scandium, yttrium, titanium, magnesium, hafnium, zirconium, tin, chromium, and boron. Specifically, part of aluminum in aluminum nitride is replaced with at least one of the above materials. Thus, at least one of the above materials can be contained in aluminum nitride. As the piezoelectric material, by substituting a part of aluminum of aluminum nitride with at least one of the materials described above, the piezoelectric performance can be enhanced. The electrostrictive material of the piezoelectric body is not limited to aluminum nitride, and any electrostrictive material having high heat resistance that does not change the displacement amount even in a high-temperature environment may be used.

[0082] The “liquid ejection unit” is a unit in which functional components and mechanisms are integrated with the liquid ejection head, and includes an assembly of components related to the ejection of liquid. For example, the “liquid ejection unit” includes a combination of the liquid ejection head and at least one of the head tank, the carriage, the supply mechanism, the maintenance and recovery mechanism, the main scanning movement mechanism, and the liquid circulation device.

[0083] Here, the integration includes, for example, a liquid ejection head and functional components or mechanisms that are fixed to each other by fastening, gluing, or engaging, or one component is held movable with respect to the other component. The liquid ejection head, functional components, and mechanism may also be configured to be detachable from each other.

[0084] For example, as a liquid ejection unit, there is a liquid ejection unit in which a liquid ejection head and a head tank are integrated. In addition, there is a liquid ejection head and a head tank which are connected to each other by a tube or the like and are integrated with each other. Here, a unit including a filter may be added between the head tank and the liquid ejection head of the liquid ejection unit.

[0085] Further, as the liquid ejection unit, there is a liquid ejection unit in which the liquid ejection head and the carriage are integrated.

[0086] In addition, as the liquid ejection unit, there is a liquid ejection unit in which the liquid ejection head is movably held by a guide member forming a part of the scanning movement mechanism, such that the liquid ejection head and the scanning movement mechanism are integrated. In addition, there is a liquid ejection unit in which the liquid ejection head, the carriage, and the main scanning movement mechanism are integrated.

[0087] In addition, as the liquid ejection unit, there is a liquid ejection unit in which a cap member which is a part of the maintenance and recovery mechanism is fixed to a carriage to which the liquid ejection head is attached, such that the liquid ejection head, the carriage, and the maintenance and recovery mechanism are integrated.

[0088] In addition, as the liquid ejection unit, there is a liquid ejection unit in which a tube is connected to a liquid ejection head to which a head tank or a flow path component is attached, such that the liquid ejection head and a supply mechanism are integrated. The liquid in the liquid storage source is supplied to the liquid ejection head via the tube.

[0089] The main scanning moving mechanism includes a single guide member. The supply mechanism includes a single tube and a single loading unit.

[0090] Here, the “liquid ejection unit” is described in combination with the liquid ejection head, but the “liquid ejection unit” includes a head module including the liquid ejection head described above or a head unit integrated with the functional components and mechanisms described above.

[0091] The “liquid ejection apparatus” includes an apparatus which includes a liquid ejection head, a liquid ejection unit, a head module, a head unit, and the like and which ejects liquid by driving the liquid ejection head. The liquid ejection apparatus includes not only an apparatus capable of ejecting liquid to an object to which liquid can adhere but also an apparatus for ejecting liquid into air or liquid.

[0092] The “liquid ejection apparatus” may include a unit for feeding, transporting, and ejecting a material to which liquid can adhere, a pre-processing apparatus, a post-processing apparatus, and the like.

[0093] For example, as the “liquid ejection apparatus”, there are an image forming apparatus which is an apparatus that forms an image on a sheet by ejecting ink, and a solid model forming apparatus (three-dimensional model forming apparatus) which ejects a liquid for forming a model onto a powder layer formed by layering powder in order to form a solid model (three-dimensional model).

[0094] The “liquid ejection apparatus” is not limited to an apparatus in which a significant image such as a character or a figure is visualized by the ejected liquid. For example, the printing apparatus may form a pattern or the like that has no meaning, or may form a three dimensional image.

[0095] The “object to which the liquid can adhere” means an object to which the liquid can adhere at least temporarily, and means an object to which the liquid adheres and is fixed, an object to which the liquid adheres and permeates, or the like. Specific examples of the medium include a recording medium such as paper, recording paper, recording sheet, a film, or cloth, an electronic component such as an electronic substrate or a piezoelectric element, and a medium such as a powder layer, an organ model, or an inspection cell. Unless otherwise specified, the medium includes all media to which a liquid adheres.

[0096] The material of the “object to which liquid can adhere” may be any material to which liquid can adhere even temporarily, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, or ceramics.

[0097] The “liquid ejection apparatus” may be an apparatus in which a liquid ejection head and an object to which liquid can adhere are relatively moved, but is not limited thereto. Specific examples of the liquid ejection apparatus include a serial type apparatus in which a liquid ejection head is moved, a line type apparatus in which a liquid ejection head is not moved, and the like.

[0098] In addition, as the “liquid ejection apparatus”, there is a treatment liquid applying apparatus which ejects a treatment liquid onto a sheet in order to apply the treatment liquid onto the surface of the sheet for the purpose of reforming the surface of the sheet. There is also a spray granulation apparatus that sprays a composition liquid in which a raw material is dispersed in a solution through a nozzle to granulate fine particles of the raw material.

[0099] In the present application, the terms “image formation”, “recording”, “printing”, “imprinting”, “printing”, “shaping”, and the like are used synonymously.

[0100] The above descriptions are merely examples, and each of the following aspects provides a unique effect.First Aspect

[0101] According to a first aspect, a liquid ejection head 1 is provided. The liquid ejection head 1 includes a nozzle 2 for ejecting liquid, a pressure chamber 4 communicating with the nozzle, and a piezoelectric element 5 provided on a nozzle forming wall (for example, the nozzle plate 110) of the pressure chamber, such that the liquid in the pressure chamber is ejected from the nozzle by applying a predetermined drive voltage between two electrodes (for example, a first electrode 51 and a second electrode 53) of the piezoelectric element, wherein when an alternating voltage including a positive voltage application period and a negative voltage application period is applied as the predetermined drive voltage, a direction in which the piezoelectric element is displaced becomes opposite in accordance with a sign of the applied voltage.

[0102] In what is known as a nozzle plate vibration type liquid ejection head in which the piezoelectric element is provided on a nozzle forming wall of the pressure chamber, the electrodes of the piezoelectric element, a wiring for a drive voltage, and the like are disposed in the vicinity of a nozzle surface (an ejection surface from which liquid is ejected) on which the nozzle is opened. Therefore, electrostatic force generated by applying a voltage to the piezoelectric element acts outward from the nozzle surface, and there is a risk that the electrostatic force will attract surrounding foreign matter such as charged mist or dust onto the nozzle surface. As a result, such foreign matter adheres to the nozzle surface, and problems such as deterioration of ejection reliability and accumulation of damage to various elements including the piezoelectric element due to long-term voltage application may occur.

[0103] In particular, in the related art nozzle plate vibration type liquid ejection head, a drive signal including only an application period of a voltage in a certain direction (positive voltage) is normally applied between two electrodes of the piezoelectric element, and the piezoelectric element is displaced only in one direction (direction corresponding to the positive voltage) to perform a liquid ejection operation. In this case, in order to generate a large displacement by the piezoelectric element, the maximum value (maximum value of the absolute value) of the positive voltage applied as the drive signal must be increased. Therefore, the larger the maximum displacement of the piezoelectric element is, the larger the maximum voltage value applied to the electrodes of the piezoelectric element and the wiring for the drive voltage becomes. As a result, the electrostatic force that attracts the foreign matter onto the nozzle surface increases, and the adhesion of the foreign matter increases.

[0104] In this aspect, the piezoelectric element configured to be displaced in an opposite direction in accordance with a sign of a voltage applied between the electrodes of the piezoelectric element is used. As a predetermined drive voltage applied between the electrodes of the piezoelectric element, an alternating voltage including a positive voltage application period and a negative voltage application period is used. According to this configuration, the piezoelectric element can be displaced in two opposite directions in accordance with the positive and negative voltages of the drive voltages, and therefore the maximum displacement amount of the piezoelectric element is the sum of the maximum displacement amount in the positive direction when the positive voltage is applied and the maximum displacement amount in the negative direction when the negative voltage is applied. Therefore, when the same maximum displacement amount as that in the related art configuration is to be obtained, the maximum value (maximum value of the absolute value) of the positive voltage at the time of applying the positive voltage and the maximum value (maximum value of the absolute value) of the negative voltage at the time of applying the negative voltage are smaller than the maximum value (maximum value of the absolute value) of the positive voltage in the related art configuration in which only the positive voltage is applied. As a result, it is possible to reduce the electrostatic force which attracts the foreign matter onto the nozzle surface, and it is possible to prevent the adhesion of the foreign matter.Second Aspect

[0105] A second aspect is characterized in that, in the first aspect, the piezoelectric element is configured such that δ(Vmax) and δ(－Vmax) are substantially equal to each other, where Vmax is a maximum value of an absolute value of the predetermined drive voltage, δ(Vmax) is a displacement amount when the positive voltage having the maximum value is applied, and δ(－Vmax) is a displacement amount when the negative voltage having the maximum value is applied.

[0106] According to this aspect, the displacement amount of the piezoelectric element can be changed in a substantially linear manner over the entire range of the applied drive voltages.Third Aspect

[0107] A third aspect is characterized in that, in the second aspect, the piezoelectric element is made of aluminum nitride or aluminum scandium nitride.

[0108] According to this aspect, when the same maximum displacement amount as that of the related art configuration is to be obtained, the maximum value (maximum value of the absolute value) of the positive voltage at the time of applying the positive voltage and the maximum value (maximum value of the absolute value) of the negative voltage at the time of applying the negative voltage can be reduced to half of the maximum value (maximum value of the absolute value) of the positive voltage in the related art configuration in which only the positive voltage is applied.Fourth Aspect

[0109] A fourth aspect is characterized in that, in any one of the first to third aspects, the two electrodes of the piezoelectric element are electrodes provided independently on a per piezoelectric element basis.

[0110] According to this aspect, a drive voltage that changes potentials of the two electrodes of each piezoelectric element can be used. This makes it possible to reduce the absolute value of the drive voltage.Fifth Aspect

[0111] A fifth aspect is a liquid ejection apparatus, including:

[0112] the liquid ejection head according to any one of the first to fourth aspects; and

[0113] a drive voltage application unit 520 configured to apply the predetermined drive voltage between the two electrodes of the piezoelectric element of the liquid ejection head.

[0114] According to this aspect, in the liquid ejection apparatus using what is known as a nozzle plate vibration type liquid ejection head, it is possible to prevent foreign matter such as charged mist or dust from adhering to the nozzle surface.Sixth Aspect

[0115] A sixth aspect is characterized in that, in the fifth aspect, no voltage is applied between two electrodes of the piezoelectric element during a non-drive period of the drive voltage application unit.

[0116] According to this aspect, since it is possible to prevent the generation of electrostatic force due to the voltage applied between two electrodes of the piezoelectric element during the non-drive period, it is possible to prevent foreign matter such as charged mist or dust from adhering to the nozzle surface.Seventh Aspect

[0117] A seventh aspect is characterized in that, in the fifth or sixth aspect, the drive voltage application unit applies an alternating voltage, as the predetermined drive voltage, the alternating voltage including voltage application periods in the order of a positive voltage application period, a negative voltage application period, and the positive voltage application period.

[0118] According to this aspect, the pressure chamber can be contracted and expanded by utilizing resonance, so that a large displacement of the piezoelectric element can be obtained with a small drive voltage.Eighth Aspect

[0119] An eighth aspect is the liquid ejection head according to any one of the fifth to seventh aspects, wherein the drive voltage application unit applies the predetermined drive voltage by varying the voltage applied to the two electrodes of the piezoelectric element.

[0120] This makes it possible to reduce the absolute value of the drive voltage.Ninth Aspect

[0121] A ninth aspect of the present invention is a method for driving a liquid ejection head, the liquid ejection head including a nozzle configured to eject a liquid; a pressure chamber communicating with the nozzle; and a piezoelectric element provided on a nozzle forming wall of the pressure chamber such that the liquid in the pressure chamber is ejected from the nozzle by applying a predetermined drive voltage between two electrodes of the piezoelectric element, the method including:

[0122] applying an alternating voltage, as the predetermined drive voltage, the alternating voltage including a positive voltage application period and a negative voltage application period, using, as the piezoelectric element, a piezoelectric element in which a direction of displacement becomes opposite in accordance with a sign of the voltage applied between the two electrodes.

[0123] According to this aspect, when what is known as a nozzle plate vibration type liquid ejection head is driven, it is possible to prevent foreign matter such as charged mist or dust from adhering to the nozzle surface.

[0124] The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2024-009284 filed on January 25, 2024. The entire contents of these applications are incorporated herein by reference.

[0125] 1 liquid ejection head 2 nozzle 3 common liquid chamber 4 pressure chamber 4a opening 5 piezoelectric element 11 protective film 33 liquid supply port 36 liquid ejection port 40 pressure chamber array 51 first electrode 52 piezoelectric film 53 second electrode 55 electrical connection pad 100 pressure chamber substrate 100A,100B head module 101 drive circuit 102 wiring portion 103 vibrating membrane 110 nozzle plate 111 nozzle forming portion 112 liquid repellent film 112 120 fluid resistance substrate 140 frame portion 151 first electrode layer 152 piezoelectric layer 153 second electrode layer 440 liquid ejection unit 500 printing apparatus 520 drive voltage application unit 521 first drive waveform source 522 second drive waveform source 523 third drive waveform source 525 waveform selection unit 526 waveform selection unit 550 head unit

Claims

1. A liquid ejection head comprising: a nozzle configured to eject a liquid; a pressure chamber communicating with the nozzle; and a piezoelectric element provided on a nozzle forming wall of the pressure chamber, such that the liquid in the pressure chamber is ejected from the nozzle by applying a predetermined drive voltage between two electrodes of the piezoelectric element, wherein when an alternating voltage including a positive voltage application period and a negative voltage application period is applied as the predetermined drive voltage, a direction in which the piezoelectric element is displaced becomes opposite in accordance with a sign of the applied voltage.

2. The liquid ejection head according to claim 1, wherein the piezoelectric element is configured such that δ(Vmax) and δ(－Vmax) are substantially equal to each other, when Vmax is a maximum value of an absolute value of the predetermined drive voltage, δ(Vmax) is a displacement amount when the positive voltage having the maximum value is applied, and δ(－Vmax) is a displacement amount when the negative voltage having the maximum value is applied.

3. The liquid ejection head according to claim 2, wherein the piezoelectric element is made of aluminum nitride or aluminum scandium nitride.

4. The liquid ejection head according to any one of claims 1 to 3, wherein the two electrodes of the piezoelectric element are electrodes provided independently on a per piezoelectric element basis.

5. A liquid ejection apparatus comprising: the liquid ejection head of any one of claims 1 to 3; and a drive voltage application unit configured to apply the predetermined drive voltage between the two electrodes of the piezoelectric element of the liquid ejection head.

6. The liquid ejection apparatus according to claim 5, wherein the drive voltage application unit does not apply a voltage between the two electrodes of the piezoelectric element in a non-drive period of the piezoelectric element.

7. The liquid ejection apparatus according to claim 5, wherein the drive voltage application unit applies an alternating voltage as the predetermined drive voltage, the alternating voltage including voltage application periods in an order of the positive voltage application period, the negative voltage application period, and the positive voltage application period.

8. The liquid ejection apparatus according to claim 5, wherein the drive voltage application unit applies the predetermined drive voltage by varying the voltage applied to the two electrodes of the piezoelectric element.

9. A method for driving a liquid ejection head, the liquid ejection head including a nozzle configured to eject a liquid; a pressure chamber communicating with the nozzle; and a piezoelectric element provided on a nozzle forming wall of the pressure chamber such that the liquid in the pressure chamber is ejected from the nozzle by applying a predetermined drive voltage between two electrodes of the piezoelectric element, the method comprising: applying an alternating voltage, as the predetermined drive voltage, the alternating voltage including a positive voltage application period and a negative voltage application period, using, as the piezoelectric element, a piezoelectric element in which a direction of displacement becomes opposite in accordance with a sign of the voltage applied between the two electrodes.

Images