Liquid discharge head, device that discharges liquid, and drive method of liquid discharge head

Abstract

To suppress a defect that a foreign matter such as charged mist or dust is attached onto a nozzle surface in a liquid discharge head of a nozzle plate vibration method.SOLUTION: A liquid discharge head 1 includes: a nozzle 2 discharging liquid; a pressure chamber 4 communicating with the nozzle; and a piezoelectric element 5 provided in a nozzle formation wall 110 of the pressure chamber. The liquid discharge head 1 applies a predetermined drive voltage across electrodes 51, 53 of the piezoelectric element and discharges liquid in the pressure chamber from the nozzle. When an alternate voltage including a positive voltage application period and a negative voltage application period is applied as the predetermined drive voltage, a direction of displacement of the piezoelectric element becomes opposite according to a polarity of the applied voltage.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a liquid ejection head, a device for ejecting liquid, and a method for driving a liquid ejection head.

[0002] Conventionally, a liquid ejection head is known that includes a nozzle for ejecting liquid, a pressure chamber connected to the nozzle, and a piezoelectric element provided in the nozzle-forming wall of the pressure chamber, and that applies a predetermined drive voltage between both electrodes of the piezoelectric element to eject the liquid in the pressure chamber from the nozzle.

[0003] Patent Document 1 discloses an inkjet head (liquid ejection head) that applies a predetermined drive signal (drive voltage) between both electrodes of a piezoelectric element provided in the nozzle-forming wall of a pressure chamber that communicates with the nozzle, thereby ejecting liquid from the pressure chamber through the nozzle. This inkjet head uses a drive signal that includes only a period in which a voltage in a fixed direction (positive voltage) is applied between both electrodes of the piezoelectric element (a drive signal that does not include a period in which a voltage in the opposite direction (negative voltage) is applied). In other words, by changing the voltage value applied between both electrodes of the piezoelectric element within the range of positive voltages, the piezoelectric element is displaced, changing the volume of the pressure chamber and ejecting liquid through the nozzle. Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the so-called nozzle plate vibration method in which a piezoelectric element is provided on the nozzle forming wall of a pressure chamber, there has traditionally been a problem in that foreign matter such as charged mist and dust is easily attracted to the nozzle surface where the nozzle opens (the ejection surface from which the liquid is ejected). [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides a liquid ejection head comprising a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and a piezoelectric element provided in the nozzle forming wall of the pressure chamber, wherein a predetermined drive voltage is applied between both electrodes of the piezoelectric element to eject the liquid in the pressure chamber from the nozzle, and wherein when an alternating voltage including a positive voltage application period and a negative voltage application period is applied as the predetermined drive voltage, the piezoelectric element undergoes displacement in opposite directions depending on the sign of the applied voltage. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress the problem of foreign matter such as electrically charged mist or dust adhering to the nozzle surface in a liquid ejection head of the so-called nozzle plate vibration type. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a nozzle plate vibration type liquid ejection head according to an embodiment. [Figure 2] FIG. 2 is a perspective view schematically showing a nozzle surface of the liquid ejection head. [Figure 3] 2 is an enlarged cross-sectional view of a portion surrounded by a dashed line indicated by the symbol X in FIG. 1. [Figure 4] FIG. 2 is a plan view schematically showing the internal structure of the liquid ejection head, and is a cross-sectional view taken along the line CC'. [Figure 5] FIG. 2 is a front view schematically showing the internal structure of the liquid ejection head, and is a cross-sectional view taken along the line AA'. [Figure 6] FIG. 2 is a side view schematically showing the internal structure of the liquid ejection head, and is a cross-sectional view taken along the line BB'. [Figure 7] 4 is a graph showing the static displacement amount versus the voltage applied to the piezoelectric element of the embodiment. [Figure 8] 4 is a graph showing an example of a waveform of a driving voltage in the embodiment. [Figure 9] 6(a) to 6(c) are graphs showing examples of drive voltages in a conventional configuration. [Figure 10]10 is a graph showing another example of a waveform of a driving voltage in the embodiment. [Figure 11] FIG. 2 is a block diagram showing an example of a drive voltage application section that applies a predetermined drive voltage from a drive waveform source to a first electrode (lower electrode) and a second electrode (upper electrode) of each piezoelectric element in each pressure chamber in an embodiment. [Figure 12] (a) is a graph showing an example of the waveform of the voltage output from the first drive waveform source. (b) is a graph showing the waveform of the voltage applied to the second electrode (upper electrode) of the piezoelectric element in the same example. (c) is a graph showing the waveform of the voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example. (d) is a graph showing the waveform of the voltage applied to the piezoelectric element in the same example (the voltage applied to the second electrode minus the voltage applied to the first electrode = drive voltage). [Figure 13] (a) is a graph showing another example of the waveform of the voltage output from the first drive waveform source. (b) is a graph showing the waveform of the voltage applied to the second electrode (upper electrode) of the piezoelectric element in the same example. (c) is a graph showing the waveform of the voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example. (d) is a graph showing the waveform of the voltage applied to the piezoelectric element in the same example (the voltage applied to the second electrode minus the voltage applied to the first electrode = drive voltage). [Figure 14] (a) is a graph showing yet another example of the waveform of the voltage output from the first drive waveform source. (b) is a graph showing the waveform of the voltage applied to the second electrode (upper electrode) of the piezoelectric element in the same example. (c) is a graph showing the waveform of the voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example. (d) is a graph showing the waveform of the voltage applied to the piezoelectric element in the same example (the voltage applied to the second electrode minus the voltage applied to the first electrode = drive voltage). [Figure 15](a) is a graph showing yet another example of the waveform of the voltage output from the first drive waveform source. (b) is a graph showing the waveform of the voltage applied to the second electrode (upper electrode) of the piezoelectric element in the same example. (c) is a graph showing the waveform of the voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example. (d) is a graph showing the waveform of the voltage applied to the piezoelectric element in the same example (the voltage applied to the second electrode minus the voltage applied to the first electrode = drive voltage). [Figure 16] FIG. 10 is a block diagram showing another example of a drive voltage application unit that applies a predetermined drive voltage from a drive waveform source to the first electrode (lower electrode) and second electrode (upper electrode) of each piezoelectric element in each pressure chamber in the embodiment. [Figure 17] FIG. 10 is a block diagram showing yet another example of a drive voltage application section that applies a predetermined drive voltage from a drive waveform source to the first electrode (lower electrode) and second electrode (upper electrode) of each piezoelectric element in each pressure chamber in the embodiment. [Figure 18] (a) is a graph showing the waveform of the voltage output from the first drive waveform source in the example of Figure 17. (b) is a graph showing the waveform of the voltage output from the third drive waveform source in the same example. (c) is a graph showing the waveform of the voltage applied to the second electrode (upper electrode) of the piezoelectric element in the same example. (d) is a graph showing the waveform of the voltage applied to the first electrode (lower electrode) of the piezoelectric element in the same example. (e) is a graph showing the waveform of the voltage applied to the piezoelectric element in the same example (voltage applied to the second electrode minus voltage applied to the first electrode = drive voltage). [Figure 19] FIG. 1 is a schematic diagram illustrating a printing apparatus according to an embodiment. [Figure 20] FIG. 2 is an explanatory plan view of an example of a head unit of the printing apparatus. [Figure 21] FIG. 10 is an explanatory plan view of the main parts of another printing device. [Figure 22] FIG. 2 is a side view illustrating the main parts of the printing apparatus of the present embodiment. [Figure 23] FIG. 2 is a plan view illustrating a main part of the liquid ejection unit according to the embodiment. [Figure 24] FIG. 2 is a front view illustrating the liquid ejection unit of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment in which the present invention is applied to a liquid ejection head provided in an apparatus for ejecting liquid will be described below. The present invention is not limited to the embodiments shown below, but may be modified, added, modified, deleted, or otherwise altered within the scope of what a person skilled in the art can conceive, and any embodiment is within the scope of the present invention as long as it achieves the functions and effects of the present invention.

[0009] The liquid ejection head in this embodiment is a nozzle plate vibration type liquid ejection head that ejects liquid in a pressure chamber from the nozzle by varying the pressure in the pressure chamber using an actuator provided in a nozzle plate having nozzles. The nozzle plate vibration type has the advantage that droplets can be ejected with less force than a typical unimorph type piezo head (which ejects liquid by vibrating the surface facing a wall portion (nozzle communication wall) having a communication port that communicates with the nozzle of the pressure chamber), and this can reduce the power consumption of the actuator.

[0010] Increasing nozzle density limits the space available for laying out the wiring required for voltage application, making wiring construction on the substrate surface difficult. By building wiring and drive circuits within the substrate, wiring can be laid out even in configurations with high nozzle density. Lead zirconate titanate (PZT) is commonly used as the piezoelectric material for actuators due to its high piezoelectric properties. However, when forming a piezoelectric film on a substrate containing wiring and drive circuits, PZT requires a deposition and crystallization temperature of 600°C or higher. Therefore, using PZT as the piezoelectric material would prevent the drive circuits and their wiring within the substrate from withstanding such high temperatures. Therefore, in configurations where wiring and drive circuits are built within the substrate, a piezoelectric material with a lower deposition temperature than PZT is required, forcing the selection of a material with lower piezoelectric properties than PZT. However, the nozzle plate vibration method described above has the advantage of ejecting droplets with less force than a typical unimorph piezo head, so it is possible to achieve good liquid ejection even with a material with lower piezoelectric properties than PZT. Therefore, even lead-free piezoelectric materials, which have low film formation and crystallization temperatures but low power, can eject liquid effectively. This allows wiring and drive circuits to be built inside the substrate, enabling higher density. Furthermore, the nozzle plate vibration method allows the volume of the pressure chamber to be reduced, making it possible to miniaturize the head.

[0011] FIG. 1 is a cross-sectional view that schematically shows a nozzle plate vibration type liquid ejection head according to this embodiment. FIG. 2 is a perspective view schematically showing the nozzle surface of the liquid ejection head of this embodiment. The liquid ejection head 1 comprises a nozzle plate 110, a pressure chamber substrate 100, and a fluid resistance substrate 120. In addition, the liquid ejection head 1 also comprises a frame portion 140 and the like, as will be described later.

[0012] The nozzle plate 110 is thin-film shaped and has a plurality of nozzles 2 that eject liquid, and piezoelectric elements 5 that function as electromechanical conversion elements that are annular actuators and are arranged around the nozzles 2. The pressure chamber substrate 100 has a plurality of pressure chambers (also referred to as individual liquid chambers or pressurized liquid chambers) 4 that respectively communicate with the plurality of nozzles 2. The nozzles 2 (vibration membranes 103) are located on one side of each pressure chamber 4, and the fluid resistance substrate 120 and its openings 4a are located on the side opposite this surface. The frame portion 140 has a common liquid chamber 3 that communicates with the plurality of pressure chambers 4 via the openings 4a. Electrical connection pads 55 are provided on both ends of the liquid ejection head 1 for connection to electrical components such as an external power source.

[0013] FIG. 3 is an enlarged cross-sectional view of a portion surrounded by a broken line indicated by the symbol X in FIG. The pressure chamber substrate 100 is an SOI (Silicon on Insulator) substrate, and has a drive circuit 101 and a wiring section 102 on the side where the vibrating membrane 103 is formed. The drive circuit 101 is a circuit including transistors, resistors, etc. The wiring section 102 has a wiring section for applying a drive voltage (drive waveform) to the first electrode 51, and a wiring section for applying a drive voltage to the second electrode 53. In addition, the wiring section 102 is electrically connected to an electrical connection pad 55 via a third contact 7c opened in the vibrating membrane 103.

[0014] The nozzle plate 110 has a nozzle forming section (film) 111 formed with a plurality of nozzles 2 and covering the piezoelectric elements 5, and a liquid-repellent film 112 is formed on the nozzle surface of this nozzle forming section 111. When liquid is continuously ejected, mist generated simultaneously with the ejection adheres to the nozzle surface. If a large amount of this mist adheres to the nozzle surface, the liquid ejected from the nozzles 2 may be affected by the liquid adhering to the nozzle surface and may deviate from the desired landing position. By forming the liquid-repellent film 112 on the nozzle surface, it is possible to prevent the liquid from adhering to the nozzle surface, and it is also possible to prevent the liquid ejected from the nozzles 2 from being affected by the liquid adhering to the nozzle surface.

[0015] The piezoelectric element 5 of the nozzle plate 110 has a first electrode 51 (also referred to as a lower electrode), a piezoelectric film 52, and a second electrode 53 (also referred to as an upper electrode). The piezoelectric element 5 is covered with a first insulating film 8a. The first insulating film 8a has formed therein 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.

[0016] In addition, the first insulating film 8a is formed with a first lead-out wiring 9a that electrically connects the first electrode 51 of the piezoelectric element 5 and the wiring portion 102 of the pressure chamber substrate 100, and a second lead-out wiring 9b that electrically connects the second electrode 53 of the piezoelectric element 5 and the wiring portion 102 of the pressure chamber substrate 100.

[0017] The first extraction wiring 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 extraction wiring 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 extraction wiring 9a and the second extraction wiring 9b are covered with a second insulating film 8b. In this embodiment, the second insulating film 8b also covers the piezoelectric element 5 and has the function of preventing moisture that has entered the nozzle forming portion 111 made of resin from entering the piezoelectric element 5, thereby protecting the piezoelectric element 5.

[0018] It is also possible to provide lead wiring portions for the first electrode 51 and the second electrode 53, respectively, and connect them directly to the wiring portion 102 in an electrode manner via contacts opened in the vibration membrane. Also, an adhesion improving film for ensuring adhesion with the nozzle forming portion 111 may be formed on the second insulating film 8b.

[0019] The liquid filling the liquid ejection head 1 enters the nozzle 2 and forms a meniscus inside the nozzle. 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 (vibrates), and the vibrating film 103 vibrates in the vertical direction in Figure 3. The vibration of the vibrating film 103 causes a pressure change in the liquid inside the pressure chamber, and the liquid is ejected from the nozzle 2.

[0020] Furthermore, in the liquid ejection head 1 of this embodiment, a protective film 11 is formed on the inner circumferential surfaces of the nozzles 2, the inner circumferential surfaces of the pressure chambers 4, and the bottom surface of the common liquid chamber 3 as a surface layer that is lyophilic to the liquid ejected by the liquid ejection head 1 and prevents erosion of the liquid. In this embodiment, the liquid ejected by the liquid ejection head 1 is alkaline, and the pressure chamber substrate 100 and vibration membrane 103 that form the pressure chambers 4 are made of single crystal silicon and silicon oxide. These materials are vulnerable to alkaline liquids and are eluted and eroded by alkaline solutions. To prevent this, a liquid-resistant protective film 11 that prevents erosion of the liquid is formed, thereby protecting the pressure chamber substrate 100 and vibration membrane 103 from the liquid.

[0021] Furthermore, the pressure chambers 4 and nozzles 2 are formed by dry etching. Because the dry etching gas contains fluorine, a fluorine-containing surface film is formed on the inner wall surfaces of the pressure chambers 4 and the inner circumferential surface of the nozzle 2 after etching, making the inner wall surfaces of the pressure chambers 4 and the inner circumferential surface of the nozzle 2 liquid-repellent. If the inner circumferential surface of the pressure chamber 4 is liquid-repellent, the liquid will not wet and spread over the inner circumferential surface of the pressure chamber 4 when filling it, which may prevent the pressure chamber 4 from being filled properly with liquid and may result in air bubbles forming in the corners of the pressure chamber 4, etc.

[0022] In this embodiment, the protective film 11 having lyophilic properties is formed on the inner peripheral surface of the pressure chamber 4 and the inner peripheral surface of the nozzle 2, thereby improving the wettability of the liquid to the inner peripheral surfaces of the pressure chamber 4 and the nozzle 2. The protective film 11 only needs to have a higher lyophilicity to the liquid than the film formation surface (the surface below the protective film 11) of the pressure chamber 4 or the nozzle 2 on which the protective film 11 is formed. If the solvent of the liquid is aqueous, a highly hydrophilic protective film is used, and if the solvent of the liquid is oil-based, a highly lyophilic protective film is used, thereby forming a highly lyophilic protective film.

[0023] In this way, by forming the protective film 11, which has lyophilicity to the liquid filling the pressure chamber 4, on the inner circumferential surfaces of the nozzle 2 and the pressure chamber 4, the liquid easily spreads over the inner circumferential surfaces of the pressure chamber 4 and the nozzle 2 when filling the pressure chamber 4. As a result, the liquid filling property can be improved, and the pressure chamber 4 and the nozzle 2 can be filled with the liquid well without applying pressure or suction when filling the liquid. Therefore, it is possible to prevent cracks from occurring in the vibration membrane 103 when filling the liquid.

[0024] Because the solvent for the liquid in this embodiment is aqueous, forming a protective film 11 that does not contain at least fluorine on the inner circumferential surfaces of the pressure chamber 4 and the nozzle 2 improves lyophilicity compared to a fluorine-containing surface film formed by dry etching. Furthermore, because this film comes into direct contact with various liquids, it is desirable to use a liquid-resistant material, such as a metal oxide that forms a passivation state. To further improve lyophilicity, a material in which silicon dioxide (SiO2) is mixed with the passivation metal oxide at the molecular level can be used. The SiO2 of the protective film 11 has its surface substituted with OH groups that have hydrophilic properties. This further enhances hydrophilicity of the protective film 11. Examples of metals that can be used in the above metal oxides include tantalum (Ta), niobium (Nb), titanium (Ti), zirconium (Zr), hafnium (Hf), and tungsten (W), which have high oxidation state compatibility. Zr and Hf, which have valences similar to those of SiO2, and Ta, which has a valence close to or slightly different from those, are particularly desirable.

[0025] Furthermore, for example, the protective film 11 may have a two-layer structure of a liquid-resistant film and a liquid-philic film. In this case, after a liquid-resistant film is formed on the inner circumferential surfaces of the nozzle 2 and the pressure chamber 4, a liquid-philic film is formed on the liquid-resistant film.

[0026] In this embodiment, a lyophilic protective film 11 is also formed on the surface of the pressure chamber substrate 100 opposite the film-forming surface of the vibration membrane 103, which constitutes the bottom surface of the common liquid chamber 3. However, the protective film 11 on this surface may be liquid-resistant only. However, the process of forming the protective film 11 on the bottom surface of the common liquid chamber 3 must be performed separately from the process of forming the lyophilic protective film on the inner circumferential surface of the nozzle and the wall surfaces of the pressure chamber, which may increase the number of manufacturing steps. Furthermore, by forming the protective film 11 on the bottom surface of the common liquid chamber 3, the liquid can more easily wet and spread across the bottom surface of the common liquid chamber 3, thereby improving the liquid filling performance. For this reason, it is preferable to form a lyophilic protective film 11 on the surface of the pressure chamber substrate 100 opposite the film-forming surface of the vibration membrane 103, which constitutes the bottom surface of the common liquid chamber 3.

[0027] The material of the vibrating membrane 103 may be any material that is at least insulating, such as SiO2, SiN, metal oxide, resin, etc. However, to increase the displacement, a material with a low Young's modulus is desirable, and considering the difference in linear expansion coefficient with the pressure chamber substrate 100, SiO2 (silicon dioxide) is the most desirable material for the vibrating membrane 103, as this difference is relatively small.

[0028] The first electrode layer 151 and the second electrode layer 153 are preferably made of a metal with low electrical resistance and low reactivity, such as Ir or Mo. When the drive circuit 101 and wiring section 102 are built into the pressure chamber substrate 100 to improve density, as in this embodiment, the piezoelectric material that makes up the piezoelectric layer 152 is preferably a piezoelectric material whose film formation temperature is 450°C or less to prevent them from being damaged. Examples of piezoelectric materials whose film formation temperature is 450°C or less include AlN and ScAlN, which has a higher piezoelectric constant than AlN.

[0029] Furthermore, using ScAlN as the piezoelectric material offers the following advantage. Although the piezoelectric properties can be improved by aligning the crystal orientation of piezoelectric film 52, an orientation control layer must be provided between vibrating film 103 and first electrode 51 to control the orientation. When the piezoelectric material of piezoelectric film 52 is ScAlN, using ScAlN as the orientation control layer also makes it possible to bring the lattice constant of first electrode 51, which is made of Mo, closer to that of ScAlN. As a result, the crystal orientation of piezoelectric film 52 is aligned, enabling improved piezoelectric properties.

[0030] FIG. 4 is a plan view schematically showing the internal structure of the liquid ejection head 1 in this embodiment, and is a cross-sectional view taken along the line CC'. FIG. 5 is a front view schematically showing the internal structure of the liquid ejection head 1 in this embodiment, and is a cross-sectional view taken along the line AA'. FIG. 6 is a side view, and a cross-sectional view taken along the line BB', that schematically shows the internal structure of the liquid ejection head 1 in this embodiment.

[0031] As shown in FIGS. 5 and 6, the liquid ejection head 1 of this embodiment is configured by arranging a nozzle plate 110, a pressure chamber substrate 100, a fluid resistance substrate 120, and a frame portion 140 in this order.

[0032] The pressure chamber substrate 100 has a pressure chamber array 40, which is an area where a plurality of pressure chambers 4 are arranged. Openings 4a of the fluid resistance substrate 120 are formed on the upper surface (the surface on the common liquid chamber 3 side) of the pressure chamber array 40, and the common liquid chambers 3 formed in the frame portion 140 are arranged so as to face the openings 4a of the fluid resistance substrates 120. In this embodiment, as an example, the dimension of the pressure chambers 4 is 220 μm, and the width of the partition walls that separate the pressure chambers 4 is 30 μm, and as a result, the center-to-center distance L2 (see FIG. 6) between two adjacent pressure chambers 4 is 250 μm.

[0033] Liquid stored in an external liquid storage unit is supplied to the liquid ejection head 1 via a liquid supply port 33 in the frame unit 140. The liquid supplied from this liquid supply port 33 is supplied to the common liquid chamber 3, and from the common liquid chamber 3 to each pressure chamber 4 via the openings 4a in each fluid resistance substrate 120. A liquid outlet 36 is also connected to the common liquid chamber 3. Of the liquid in the common liquid chamber 3, the liquid that is not supplied to each pressure chamber 4 via the openings 4a in the fluid resistance substrate 120 is returned from the liquid outlet 36 to an external ink storage unit via an external pump or the like.

[0034] Next, the piezoelectric element 5, which is a characteristic feature of this embodiment, will be described. In the nozzle plate vibration method, the electrodes 51 and 53 of the piezoelectric element 5 and the wiring portion 102 for the drive voltage are located near the nozzle surface where the nozzle 2 is open. As a result, electrostatic force generated by the application of voltage to the piezoelectric element 5, such as a drive voltage, acts outward from the nozzle surface, and this electrostatic force attracts surrounding foreign matter such as charged mist and dust onto the nozzle surface. As a result, problems occur in which such foreign matter adheres to the nozzle surface, which can lead to problems such as a deterioration in ejection reliability and accumulation of damage to various elements, including the piezoelectric element, due to the application of voltage for long periods of time.

[0035] Typically, a drive signal that only includes a period during which a voltage (either positive or negative) in a certain direction is applied between the electrodes of a piezoelectric element, displacing the piezoelectric element in only one direction to eject liquid. In this case, in order to generate a larger displacement in the piezoelectric element, the maximum value (maximum absolute value) of the voltage (either positive or negative voltage) applied as the drive voltage must be increased. Therefore, the greater the maximum displacement of the piezoelectric element, the greater the maximum voltage value applied to the electrodes of the piezoelectric element and the wiring for the drive voltage. This increases the electrostatic force that attracts foreign particles onto the nozzle surface, increasing the problem of foreign particles adhering to the nozzle.

[0036] Therefore, in this embodiment, the piezoelectric element 5 is displaced in accordance with the sign of the voltage applied between the electrodes 51 and 53, specifically, the direction of displacement is reversed. The drive voltage applied between the electrodes 51 and 53 of this piezoelectric element 5 is an alternating voltage that includes a period in which a positive voltage is applied and a period in which a negative voltage is applied.

[0037] With this configuration, the piezoelectric element 5 can be displaced in two opposite directions by the positive and negative voltages in the drive voltage. 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, both the maximum value (maximum absolute value) of the positive voltage when a positive voltage is applied and the maximum value (maximum absolute value) of the negative voltage when a negative voltage is applied are smaller than the maximum value (maximum absolute value) of the voltage in the configuration described above in which only positive or negative voltages are applied. Therefore, with this embodiment, it is possible to reduce the electrostatic force that attracts foreign matter onto the nozzle surface, thereby preventing the problem of foreign matter adhering.

[0038] FIG. 7 is a graph showing the static displacement amount versus the voltage applied to the piezoelectric element 5 of this embodiment. 7, the applied voltage is shown as the potential of the second electrode (upper electrode) 53 relative to the potential of the first electrode (lower electrode) 51. The positive and negative signs for the displacement are such that a displacement in the direction that contracts the pressure chamber 4 is positive, an applied voltage that displaces the piezoelectric element 5 in the positive direction is positive voltage, and an applied voltage that displaces the piezoelectric element 5 in the negative direction is negative voltage.

[0039] 7, the piezoelectric element 5 of this embodiment is characterized in that the direction of displacement is reversed depending on the sign of the voltage applied between the first electrode (lower electrode) 51 and the second electrode (upper electrode) 53, and that the displacement is approximately linear with respect to the voltage within the range of voltage used for driving. A piezoelectric element 5 exhibiting such characteristics preferably uses, for example, aluminum nitride (AlN) or scandium aluminum nitride (ScAlN) as the piezoelectric film 52, and more preferably uses ScAlN, which has a higher piezoelectric constant than AlN.

[0040] Other candidate materials are CdS, CdSe, ZnO, ZnTe, CdTe, etc. b -VI b Intergroup compounds, such as GaAs, GaSb, InS, and InSb b -V b Examples of piezoelectric materials include intergroup compounds. b -VI b Group III and b -V b Many of the group compounds have a zinc blende or wurtzite crystal structure. In this embodiment, a piezoelectric material having a wurtzite crystal structure can be suitably used. Wurtzite crystals belong to the hexagonal system, and the c-axis of the crystal has polarity as the polar axis. Due to their symmetry, wurtzite crystals have a piezoelectric constant of d 31 , d 33 , d 15 By applying an electric field in the c-axis direction of the crystal, displacement in the c-axis direction can be generated, but in this case, distortion also occurs in the direction perpendicular to this. By utilizing this distortion and creating a unimorph structure in which a piezoelectric film and a vibration film are stacked, deformation of the vibration film can be generated, allowing liquid to be ejected.

[0041] FIG. 8 is a graph showing an example of a waveform of a driving voltage in this embodiment. In this embodiment, an alternating voltage including a period in which a positive voltage is applied and a period in which a negative voltage is applied is used as the driving voltage. The driving voltage range is a range in which the displacement of the piezoelectric element 5 is approximately linear with respect to the voltage. This will be explained in detail below.

[0042] The range of the drive voltage refers to the range from -Vmax to Vmax, where Vmax is the absolute value of the voltage applied to the piezoelectric element. In the example waveform of FIG. 8, |V1|>|V2|, so Vmax = |V1|=V1. In the piezoelectric element 5 of this embodiment, as shown in FIG. 7, the displacement δ is linear in the range from -V1 to +V1, meaning that δ(-V1) and -δ(V1) are approximately equal. In other words, the displacement of the piezoelectric element 5 is approximately linear with respect to the voltage.

[0043] As in this embodiment, when using a piezoelectric element 5 in which the direction of displacement reverses depending on the sign of the voltage applied between the first electrode 51 and the second electrode 53, the absolute value of the drive voltage can be reduced, which is an advantage.

[0044] More specifically, when the voltage change amount required to obtain the displacement required to obtain a desired liquid ejection speed is ΔV1, in the above-described configuration in which only positive or negative voltages are applied, a drive voltage having a waveform such as that shown in any of Figures 9(a) to 9(c) is used. Note that Figure 9(a) is an example of a drive waveform (push-pull waveform) that expands (fills the pressure chamber 4 with liquid) after contracting (after ejection), Figure 9(b) is an example of a drive waveform (pull-push waveform) that contracts the pressure chamber 4 after expanding, and Figure 9(c) is an example of a pull-push waveform when the drive voltage is only a positive voltage.

[0045] 9(a) to 9(c), in the above-described configuration in which only positive or negative voltages are applied, a maximum value |V1'| of the drive voltage corresponding to ΔV1 is required to obtain a voltage change amount ΔV1 necessary to obtain the amount of displacement required to obtain a desired liquid ejection speed. However, in general, depending on conditions such as the withstand voltage of the piezoelectric element 5 and the drive capabilities of other elements, there are cases in which it is desired to reduce the maximum value |V1'| of the drive voltage.

[0046] According to this embodiment, when obtaining the voltage change amount ΔV1 required to obtain the displacement amount necessary to obtain the desired liquid ejection speed, for example, as shown in FIG. 10, the maximum value (absolute value) of the positive voltage can be set to +V1 / 2 and the maximum value (absolute value) 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 that in the above-mentioned configuration in which only positive or negative voltages are applied. As shown in the drive voltage waveform of this embodiment in FIG. 8, even if the maximum value (absolute value) of the positive voltage, V1, and the maximum value (absolute value) of the negative voltage, V2, are different, the maximum value of the drive voltage (the absolute value of V1 in the example of FIG. 8) can be reduced compared to the above-mentioned configuration in which only positive or negative voltages are applied.

[0047] 9(c), it becomes necessary to apply voltage V1 in advance during the non-drive period (the period when no drive voltage is applied to the piezoelectric element 5) before applying the drive waveform. In this case, with a nozzle plate vibration method like that of this embodiment, electrostatic force generated by applying voltage to the electrodes 51 and 53 of the piezoelectric element 5 and the wiring portion 102 for the drive voltage acts outside the nozzle surface even during the non-drive period. This raises concerns that surrounding foreign matter such as charged mist and dust may be attracted to and adhere to the nozzle surface by electrostatic force.

[0048] Therefore, the drive waveform in this embodiment is preferably a waveform that starts at 0 V, as shown in Fig. 8. In this case, the applied voltage during the non-drive period can be set to 0 V, so that the electrostatic force generated by applying a voltage to the electrodes 51, 53 of the piezoelectric element 5 or the wiring portion 102 for the drive voltage does not act outside the nozzle surface during the non-drive period. This prevents the problem of surrounding foreign matter such as charged mist or dust being attracted to and adhering to the nozzle surface by electrostatic force.

[0049] Next, an example of control for applying the drive voltage to the piezoelectric element 5 in this embodiment will be described. 11 is a block diagram showing an example of a drive voltage application unit 520 that applies a predetermined drive voltage from drive waveform sources 521 and 522 to the first electrode (lower electrode) 51 and the second electrode (upper electrode) 53 of each piezoelectric element 5-1, 5-2, 5-3, ..., 5-N of each pressure chamber 4. In this example, the second drive waveform source 522 is earthed and maintained at 0 V.

[0050] 12(a) to 12(d) are graphs showing examples of voltage waveforms at various points. Note that Figure 12(a) is a graph showing the waveform of the voltage output from the first drive waveform source 521, Figure 12(b) is a graph showing the waveform of the voltage applied to the second electrode (upper electrode) 53 of the piezoelectric element 5, Figure 12(c) is a graph showing the waveform of the voltage applied to the first electrode (lower electrode) 51 of the piezoelectric element 5, and Figure 12(d) is a graph showing the waveform of the voltage applied to the piezoelectric element 5 (the voltage obtained by subtracting the voltage applied to the first electrode 51 from the voltage applied to the second electrode 53 = drive voltage).

[0051] 12, period (1) indicates the period during which the first drive waveform source 521 is selected by the waveform selection units 525, 526, and period (2) indicates the period during which the second drive waveform source 522 is selected by the waveform selection units 525, 526. By selecting the drive waveform sources 521, 522 at appropriate timing in the waveform selection units 525, 526 of each of the piezoelectric elements 5-1 to 5-N, it is possible to select whether or not to eject liquid for each of the piezoelectric elements 5-1 to 5-N.

[0052] With the configuration of this example, as shown in FIG. 12(d), a driving voltage consisting of an alternating voltage including a period in which a positive voltage is applied and a period in which a negative voltage is applied can be applied between the electrodes 51, 53 of each of the piezoelectric elements 5-1 to 5-N.

[0053] 13(a) to 13(d) are graphs showing other examples of voltage waveforms at various points. 12(a) to (d), the present example shown in Figures 13(a) to (d) is configured such that the first drive waveform source 521 outputs only a positive voltage. In this example, as shown in Figure 13(c), the voltage of the first drive waveform source 521 is also input to the first electrode (lower electrode) 51 of the piezoelectric element 5, thereby changing the voltage.

[0054] According to this example, even if the first drive waveform source 521 is configured to output only positive voltages, it is possible to apply a drive voltage consisting of an alternating voltage including a positive voltage application period and a negative voltage application period between the electrodes 51, 53 of each of the piezoelectric elements 5-1 to 5-N, as shown in Fig. 13(d). Since the first drive waveform source 521 is configured to output only positive voltages, as in this example, it is possible to reduce the prices of various elements (circuit components) such as amplifiers.

[0055] 14(a) to 14(d) are graphs showing still other examples of voltage waveforms at various points. 14(a) to (d), similarly to the example of FIGS. 13(a) to (d), the first drive waveform source 521 is configured to output only positive voltages. However, during non-drive periods (non-ejection periods), as shown in FIGS. 13(b) and (c), the voltage of the first drive waveform source 521 is input to both the first electrode (lower electrode) 51 and the second electrode (upper electrode) 53 of the piezoelectric element 5, thereby setting the drive voltage applied to the piezoelectric element 5 to 0 V, as shown in FIG. 13(d). Such a control example may also be used.

[0056] 15(a) to 15(d) are graphs showing still other examples of voltage waveforms at various points. 15(a) to 15(d), unlike the above-described examples, a configuration is used in which a constant voltage source that outputs only a constant positive voltage is used as first drive waveform source 521. In this example, the waveforms of the voltages applied to first electrode (lower electrode) 51 and second electrode (upper electrode) 53 of piezoelectric element 5 are controlled by switching operations of waveform selection units 525 and 526. In this example, the rise time and fall time of the waveform are fixed by a time constant determined by the capacitance and electrical resistance values of piezoelectric element 5 and other elements, but it is possible to reduce the cost of first drive waveform source 521.

[0057] FIG. 16 is a block diagram showing another example of a drive voltage application unit 520 that applies a predetermined drive voltage from drive waveform sources 521, 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 in each pressure chamber 4. In this example, the second drive waveform source 522 is omitted, and the waveform selection sections 525 and 526 select the floating state during the period (2).

[0058] 17 is a block diagram showing yet another example of the drive voltage application section 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 in each pressure chamber 4. In this example, three drive waveform sources 521 to 523 are used.

[0059] 18(a) to 18(e) are graphs showing examples of voltage waveforms at various points in the example of FIG. 18(a) is a graph showing the waveform of the voltage output from first drive waveform source 521, and FIG. 18(b) is a graph showing the waveform of the voltage output from third drive waveform source 523. Second drive waveform source 522 is earthed and maintained at 0 V. FIG. 18(c) is a graph showing the waveform of the voltage applied to second electrode (upper electrode) 53 of piezoelectric element 5, FIG. 18(d) is a graph showing the waveform of the voltage applied to first electrode (lower electrode) 51 of piezoelectric element 5, and FIG. 18(e) is a graph showing the waveform of the voltage (= drive voltage) applied to piezoelectric element 5.

[0060] In this example, the voltage waveform of first drive waveform source 521 and the voltage waveform of third drive waveform source 523 are waveforms with mutually inverted polarities. Although the configuration is also complex in this example, there is an advantage in that the output voltage value (absolute value) of each of drive waveform sources 521 and 523 can be reduced by half compared to the above example.

[0061] Next, an example of a liquid ejection device according to the present invention will be described with reference to FIGS. FIG. 19 is a schematic explanatory diagram of a printing apparatus that is an inkjet recording apparatus, which is an image forming apparatus serving as a device that ejects liquid in this embodiment. FIG. 20 is an explanatory plan view of an example of a head unit of a printing device according to this embodiment.

[0062] A printing apparatus 500, which is an apparatus for ejecting this liquid, includes a carry-in means 501 that carries in a continuum 510, and a guide / conveyance means 503 that guides and conveys the continuum 510 carried in from the carry-in means 501 to a printing means 505. The printing apparatus 500 also includes a printing means 505 that ejects a liquid onto the continuum 510 to form an image, a drying means 507 that dries the continuum 510, and an ejection means 509 that ejects the continuum 510.

[0063] The continuous web 510 is sent out from a main winding roller 511 of the carry-in means 501, guided and conveyed by the rollers of the carry-in means 501, the guide and conveying means 503, the drying means 507, and the conveying means 509, and wound up by a winding roller 591 of the conveying means 509. In the printing means 505, the continuous web 510 is conveyed on a conveying guide member 559 opposite the head unit 550, and an image is printed by liquid ejected from the head unit 550.

[0064] In the printing device 500 of this embodiment, the head unit 550 includes the two head modules 100A and 100B according to this embodiment described above, mounted on a common base member 552.

[0065] When the direction in which the liquid ejection heads 1 of the head modules 100A and 100B are lined up in a direction perpendicular to the transport direction is defined as the head arrangement direction, the head arrays 1A1 and 1A2 of the head module 100A eject liquid of the same color. Similarly, the head arrays 1B1 and 1B2 of the head module 100A are paired, the head arrays 1C1 and 1C2 of the head module 100B are paired, and the head arrays 1D1 and 1D2 are paired, and each ejects liquid of the required color.

[0066] Next, another example of a printing apparatus as a liquid ejecting apparatus according to the present invention will be described with reference to FIGS. FIG. 21 is an explanatory plan view of the main parts of the printing apparatus of this example. FIG. 22 is an explanatory side view of the main part of the printing apparatus of this example.

[0067] The printing apparatus 500 of this example is a serial type apparatus, and a carriage 403 is moved 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, etc. The guide member 401 is hung between left and right side plates 491A and 491B to movably hold the carriage 403. The main scanning motor 405 then moves the carriage 403 back and forth in the main scanning direction via a timing belt 408 hung between a drive pulley 406 and a driven pulley 407.

[0068] This carriage 403 is equipped with a liquid ejection unit 440 that integrates the liquid ejection head 1 according to the present invention and a head tank 441. The liquid ejection head 1 ejects liquid of each color, for example, yellow (Y), cyan (C), magenta (M), and black (K). The liquid ejection head 1 is mounted with a nozzle row consisting of multiple nozzles arranged in a sub-scanning direction perpendicular to the main scanning direction, and the ejection direction facing downward. The liquid ejection head 1 is connected to a liquid circulation device, which circulates and supplies liquid of the required color.

[0069] The printing apparatus 500 is equipped with a transport mechanism 495 for transporting paper 410. The transport mechanism 495 includes a transport belt 412, which is a transport means, and a sub-scanning motor 416 for driving the transport belt 412. The transport belt 412 attracts the paper 410 and transports it at a position facing the liquid ejection head 1. The transport belt 412 is an endless belt that is stretched between a transport roller 413 and a tension roller 414. The attraction can be achieved by electrostatic attraction or air suction. The transport belt 412 moves in a circular motion in the sub-scanning direction as the transport roller 413 is rotationally driven by the sub-scanning motor 416 via a timing belt 417 and a timing pulley 418.

[0070] Furthermore, a maintenance and recovery mechanism 420 that maintains and recovers the liquid ejection head 1 is disposed on one side of the carriage 403 in the main scanning direction, beside the conveyor belt 412. The maintenance and recovery mechanism 420 is composed of, for example, a cap member 421 that caps the nozzle surface of the liquid ejection head 1, a wiper member 422 that wipes the nozzle surface, and the like. The main scanning movement mechanism 493, the maintenance and recovery mechanism 420, and the conveyor mechanism 495 are attached to a housing that includes side plates 491A and 491B and a back plate 491C.

[0071] In the printing device 500 configured in this manner, the paper 410 is fed onto the conveyor belt 412 and adsorbed thereon, and the paper 410 is conveyed in the sub-scanning direction by the circular movement of the conveyor belt 412. Then, by driving the liquid ejection head 1 in accordance with an image signal while moving the carriage 403 in the main scanning direction, liquid is ejected onto the stationary paper 410 to form an image.

[0072] Next, another example of the liquid discharge unit according to the present invention will be described with reference to FIG. FIG. 23 is a plan view illustrating the main parts of the liquid discharge unit of this example.

[0073] This liquid ejection unit 440 is composed of the components that make up the device for ejecting the liquid, including a housing portion consisting of side plates 491A, 491B and a back plate 491C, a main scanning movement mechanism 493, a carriage 403, and a liquid ejection head 1.

[0074] It is also possible to configure a liquid discharge unit in which the above-described maintenance and recovery mechanism 420 is further attached to, for example, the side plate 491B of this liquid discharge unit 440.

[0075] Next, still another example of the liquid discharge unit according to the present invention will be described with reference to FIG. FIG. 24 is an explanatory front view of the liquid discharge unit of this example.

[0076] This liquid discharge unit 440 is composed of a liquid discharge head 1 to which a flow path part 444 is attached, and a tube 456 connected to the flow path part 444 .

[0077] The flow path part 444 is disposed inside the cover 442. A head tank 441 may be included instead of the flow path part 444. A connector 443 for electrically connecting with the liquid ejection head 1 is provided on the upper part of the flow path part 444.

[0078] In the present application, the liquid to be ejected may have a viscosity and surface tension that allows it to be ejected from the head, and is not particularly limited. However, it is preferable that the viscosity of the liquid be 30 mPa·s or less at room temperature and normal pressure, or upon heating or cooling. More specifically, the liquid may be a solution, suspension, emulsion, or the like containing a solvent such as water or an organic solvent, a colorant such as a dye or a pigment, a functionalizing material such as a polymerizable compound, a resin, or a surfactant, a biocompatible material such as DNA, amino acids, proteins, or calcium, or an edible material such as a natural colorant. These liquids can be used, for example, in inkjet inks, surface treatment solutions, liquids for forming components of electronic devices or light-emitting elements, liquids for forming electronic circuit resist patterns, and material liquids for 3D modeling.

[0079] The liquid to be ejected may be a metallic material such as solder or a material that is fixed at room temperature, such as wax ink, which is heated and melted before being ejected from the nozzle. Alternatively, the liquid to be ejected may be a liquid that is highly viscous at room temperature, such as UV ink, which is heated and reduced in viscosity before being ejected from the nozzle. In this case, by providing a heating means such as a heater on the frame portion 140 or the pressure chamber substrate 100, the material in the pressure chamber 4 can be melted or reduced in viscosity, allowing for smooth ejection of the liquid from the nozzle. In this case, aluminum nitride (AlN) containing at least one of scandium, yttrium, titanium, magnesium, hafnium, zirconium, tin, chromium, and boron is preferably used as the electrostrictive material for the piezoelectric element. Specifically, a portion of the aluminum in the aluminum nitride is replaced with at least one of the above materials. This allows the aluminum nitride to contain at least one of the above materials. By replacing a portion of the aluminum in the aluminum nitride as a piezoelectric material with at least one of the above materials, the piezoelectric performance can be improved. The electrostrictive material of the piezoelectric body is not limited to aluminum nitride, but may be any electrostrictive material having high heat resistance and whose displacement does not change even in a high temperature environment.

[0080] A "liquid ejection unit" is a liquid ejection head integrated with functional parts and mechanisms, and includes a collection of parts related to ejecting liquid. For example, a "liquid ejection unit" includes a liquid ejection head combined with at least one of the following components: a head tank, a carriage, a supply mechanism, a maintenance and recovery mechanism, a main scanning movement mechanism, and a liquid circulation device.

[0081] Here, "integrated" includes, for example, a liquid ejection head and a functional part or mechanism that are fixed to each other by fastening, bonding, engaging, etc., or one that is held movably relative to the other. The liquid ejection head, functional part, or mechanism may also be configured to be detachable from each other.

[0082] For example, some liquid ejection units have a liquid ejection head and a head tank integrated together, while others have a liquid ejection head and a head tank integrated together by being connected to each other by a tube, etc. Here, a unit including a filter can be added between the head tank and the liquid ejection head of these liquid ejection units.

[0083] Furthermore, there is a liquid ejection unit in which the liquid ejection head and the carriage are integrated.

[0084] In some liquid ejection units, the liquid ejection head is movably held by a guide member that constitutes part of the scanning movement mechanism, and the liquid ejection head and the scanning movement mechanism are integrated together. In other liquid ejection units, the liquid ejection head, the carriage, and the main scanning movement mechanism are integrated together.

[0085] Furthermore, there is a liquid ejection unit in which a cap member, which is part of the maintenance and recovery mechanism, is fixed to a carriage on which a liquid ejection head is attached, thereby integrating the liquid ejection head, carriage, and maintenance and recovery mechanism.

[0086] In some liquid ejection units, a tube is connected to a liquid ejection head equipped with a head tank or flow path components, integrating the liquid ejection head with a supply mechanism. Liquid is supplied from a liquid storage source to the liquid ejection head via this tube.

[0087] The main scanning movement mechanism includes the guide member alone, and the supply mechanism includes the tube alone and the loading unit alone.

[0088] Here, the "liquid ejection unit" is described in combination with a liquid ejection head, but the "liquid ejection unit" also includes a head module or head unit that includes the liquid ejection head described above, and that integrates the functional components and mechanisms described above.

[0089] "Liquid ejection devices" include devices that are equipped with a liquid ejection head, a liquid ejection unit, a head module, a head unit, etc., and that eject liquid by driving the liquid ejection head. Liquid ejection devices include not only devices that can eject liquid onto objects to which the liquid can adhere, but also devices that eject liquid into air or liquid.

[0090] This "liquid ejecting device" can also include means for feeding, transporting, and discharging items onto which liquid can be attached, as well as pre-processing devices and post-processing devices.

[0091] For example, examples of "liquid ejecting devices" include image forming devices that eject ink to form images on paper, and three-dimensional modeling devices (three-dimensional modeling devices) that eject modeling liquid onto a powder layer formed from layers of powder in order to create a three-dimensional object (a three-dimensional model).

[0092] Furthermore, the term "liquid ejection device" is not limited to devices that use ejected liquid to visualize meaningful images such as letters and figures. For example, it also includes devices that form patterns that have no meaning in themselves, and devices that create three-dimensional images.

[0093] The above-mentioned "object onto which a liquid can adhere" means an object onto which a liquid can adhere at least temporarily, an object onto which the liquid can adhere and stick, an object onto which the liquid can penetrate, etc. Specific examples include media such as paper, recording paper, film, cloth, electronic substrates, electronic components such as piezoelectric elements, powder layers, organ models, and test cells, and unless otherwise specified, all objects onto which a liquid can adhere are included.

[0094] The material of the "substance to which a liquid can adhere" may be any material to which a liquid can adhere, even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, or ceramics.

[0095] Furthermore, the "liquid ejection device" may be a device in which a liquid ejection head and an object onto which liquid can be attached move relatively, but is not limited to this. Specific examples include a serial type device in which a liquid ejection head moves, and a line type device in which a liquid ejection head does not move.

[0096] Other examples of "liquid ejecting devices" include treatment liquid application devices that eject treatment liquid onto paper to apply the treatment liquid to the surface of the paper for purposes such as modifying the surface of the paper, and spray granulation devices that spray a composition liquid in which raw materials are dispersed through a nozzle to granulate the raw material particles.

[0097] In the present application, the terms image formation, recording, printing, copying, printing, modeling, etc. are all synonymous.

[0098] The above description is merely an example, and each of the following aspects provides unique effects. [First aspect] The first aspect is a liquid ejection head 1 comprising a nozzle 2 for ejecting liquid, a pressure chamber 4 communicating with the nozzle, and a piezoelectric element 5 provided in a nozzle forming wall of the pressure chamber (e.g., a nozzle plate 110), and which applies a predetermined drive voltage between both electrodes (e.g., a first electrode 51 and a second electrode 53) of the piezoelectric element to eject the liquid in the pressure chamber from the nozzle, characterized in that when an alternating voltage including a positive voltage application period and a negative voltage application period is applied as the predetermined drive voltage, the piezoelectric element undergoes displacement in opposite directions depending on the sign of the applied voltage. In the so-called nozzle plate vibration method, in which a piezoelectric element is provided on the nozzle-forming wall of a pressure chamber, the electrodes of the piezoelectric element and wiring for the drive voltage are located near the nozzle surface where the nozzle opens (the ejection surface from which liquid is ejected). As a result, electrostatic force generated by applying voltage to the piezoelectric element acts outward from the nozzle surface, which can attract surrounding foreign matter such as charged mist or dust onto the nozzle surface. As a result, such foreign matter can adhere to the nozzle surface, causing problems such as a deterioration in ejection reliability and accumulation of damage to various elements, including the piezoelectric element, due to long-term voltage application. In particular, in conventional liquid ejection heads using a nozzle plate vibration method, a drive signal that only includes a period during which a voltage in a fixed direction (positive voltage) is applied between the electrodes of a piezoelectric element is typically applied, displacing the piezoelectric element in only one direction (the direction corresponding to the positive voltage) to eject liquid. In this case, in order to generate a larger displacement in the piezoelectric element, the maximum value (maximum absolute value) of the positive voltage applied as the drive signal must be increased. Therefore, the greater the maximum displacement of the piezoelectric element, the greater the maximum voltage value applied to the electrodes of the piezoelectric element and the wiring for the drive voltage. This increases the electrostatic force that attracts foreign particles onto the nozzle surface, increasing the problem of foreign particle adhesion. In this embodiment, a piezoelectric element is used in which the direction of displacement is reversed depending on the sign of the voltage applied between its two electrodes. The predetermined drive voltage applied between the electrodes of this piezoelectric element is an alternating voltage including a period in which a positive voltage is applied and a period in which a negative voltage is applied. With this configuration, the piezoelectric element can be displaced in two opposite directions depending on the positive and negative drive voltages. Therefore, the maximum displacement of the piezoelectric element 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. Therefore, when attempting to obtain the same maximum displacement as in the conventional case, both the maximum positive voltage (maximum absolute value) when a positive voltage is applied and the maximum negative voltage (maximum absolute value) when a negative voltage is applied are smaller than the maximum positive voltage (maximum absolute value) in the conventional case in which only a positive voltage is applied. As a result, it is possible to reduce the electrostatic force that attracts foreign particles onto the nozzle surface, thereby preventing the problem of foreign particle adhesion.

[0099] [Second mode] The second aspect is characterized in that, in the first aspect, when the maximum absolute value of the specified driving voltage is Vmax, the displacement amount when the positive voltage having this maximum value is applied is δ(Vmax), and the displacement amount when the negative voltage having this maximum value is applied is δ(-Vmax), δ(Vmax) and δ(-Vmax) are approximately equal. This allows the displacement of the piezoelectric element to be changed almost linearly over the entire range of the applied drive voltage.

[0100] [Third aspect] A third aspect is the second aspect, characterized in that the piezoelectric element is aluminum nitride or aluminum scandium nitride. According to this aspect, when attempting to obtain the same maximum displacement amount as conventionally, the maximum value of the positive voltage (maximum absolute value) when a positive voltage is applied and the maximum value of the negative voltage (maximum absolute value) when a negative voltage is applied can be reduced by half compared to the maximum value of the positive voltage (maximum absolute value) in the conventional case where only a positive voltage is applied.

[0101] [Fourth aspect] A fourth aspect is characterized in that in any one of the first to third aspects, both electrodes of the piezoelectric element are individual electrodes for each piezoelectric element. This allows the use of a drive voltage that changes the potential of both electrodes of each piezoelectric element, thereby making it possible to reduce the absolute value of the drive voltage.

[0102] [Fifth mode] The fifth aspect is a device for ejecting liquid, characterized in that it comprises a liquid ejection head according to any one of the first to fourth aspects, and a drive voltage application unit 520 that applies a predetermined drive voltage between both electrodes of a piezoelectric element of the liquid ejection head. According to this aspect, in a liquid ejection device that uses a liquid ejection head of the so-called nozzle plate vibration type, it is possible to suppress the problem of foreign matter such as electrically charged mist or dust adhering to the nozzle surface.

[0103] [Sixth aspect] A sixth aspect is the fifth aspect, characterized in that no voltage is applied between both electrodes of the piezoelectric element during the non-driving period of the drive voltage application section. This makes it possible to suppress the generation of electrostatic force due to the voltage applied between the two electrodes of the piezoelectric element during the non-driving period, thereby suppressing the problem of foreign matter such as charged mist or dust adhering to the nozzle surface.

[0104] [Seventh aspect] A seventh aspect is the fifth or sixth aspect, characterized in that the drive voltage application unit applies, as the predetermined drive voltage, an alternating voltage including voltage application periods in the order of a positive voltage application period, a negative voltage application period, and a positive voltage application period. According to this, 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 driving voltage.

[0105] [Eighth aspect] The eighth aspect is a liquid ejection device according to any one of the fifth to seventh aspects, characterized in that the drive voltage application unit applies the predetermined drive voltage by varying the voltage applied to both electrodes of the piezoelectric element. This makes it possible to reduce the absolute value of the drive voltage.

[0106] [Ninth aspect] A ninth aspect is a method for driving a liquid ejection head comprising a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and a piezoelectric element provided in a nozzle forming wall of the pressure chamber, and applying a predetermined drive voltage between both electrodes of the piezoelectric element to eject the liquid in the pressure chamber from the nozzle, characterized in that the piezoelectric element is one in which the direction of displacement is reversed depending on the sign of the voltage applied between the two electrodes, and an alternating voltage including a period in which a positive voltage is applied and a period in which a negative voltage is applied is applied between the two electrodes of the piezoelectric element as the predetermined drive voltage. According to this aspect, when driving a liquid ejection head of the so-called nozzle plate vibration type, it is possible to suppress the problem of foreign matter such as electrically charged mist or dust adhering to the nozzle surface. [Explanation of symbols]

[0107] 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 outlet 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 section 103: Vibration membrane 110: Nozzle plate 111: Nozzle forming section 112: Liquid repellent film 120: Fluid resistance board 140: Frame section 151: First electrode layer 152: Piezoelectric layer 153:Second electrode layer 440: Liquid dispensing unit 500:Printing device 520: Drive voltage application unit 521: First drive waveform source 522: Second drive waveform source 523: Third drive waveform source 525: Waveform selection section 526: Waveform selection section 550: Head unit [Prior art documents] [Patent documents]

[0108] [Patent Document 1] Patent No. 6778121

Claims

1. a nozzle for discharging a liquid; a pressure chamber communicating with the nozzle; a piezoelectric element provided on a nozzle forming wall of the pressure chamber, a liquid ejection head that applies a predetermined drive voltage between both electrodes of the piezoelectric element to eject the liquid in the pressure chamber from the nozzle, A liquid ejection head characterized in that when an alternating voltage including a positive voltage application period and a negative voltage application period is applied as the specified drive voltage, the piezoelectric element has a displacement whose direction is reversed depending on the sign of the applied voltage.

2. 2. The liquid ejection head according to claim 1, The liquid ejection head is characterized in that, when the maximum absolute value of the specified drive voltage is Vmax, the amount of displacement when the positive voltage having this maximum value is applied is δ(Vmax), and the amount of displacement when the negative voltage having this maximum value is applied is δ(-Vmax), δ(Vmax) and δ(-Vmax) are approximately equal.

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

4. 4. The liquid ejection head according to claim 1, A liquid ejection head characterized in that both electrodes of the piezoelectric element are individual electrodes for each piezoelectric element.

5. A liquid ejection head according to any one of claims 1 to 3, a drive voltage application unit that applies a predetermined drive voltage between both electrodes of the piezoelectric element of the liquid ejection head.

6. 6. The liquid ejection device according to claim 5, The liquid ejection device is characterized in that the drive voltage application section does not apply a voltage between both electrodes of the piezoelectric element during a non-driving period of the piezoelectric element.

7. 6. The liquid ejection device according to claim 5, A liquid ejection device, characterized in that the drive voltage application unit applies, as the predetermined drive voltage, an alternating voltage including voltage application periods in the order of a positive voltage application period, a negative voltage application period, and a positive voltage application period.

8. 6. The liquid ejection device according to claim 5, The liquid ejection device is characterized in that the drive voltage application section applies the predetermined drive voltage by varying the voltage applied to both electrodes of the piezoelectric element.

9. A method for driving a liquid ejection head, comprising: 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, the method applying a predetermined drive voltage between both electrodes of the piezoelectric element to eject liquid in the pressure chamber from the nozzle, The piezoelectric element is one whose displacement direction is reversed depending on the sign of the voltage applied between the two electrodes, A method for driving a liquid ejection head, comprising applying an alternating voltage including a period during which a positive voltage is applied and a period during which a negative voltage is applied as the predetermined drive voltage between both electrodes of the piezoelectric element.

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