JP5831475B2 - Droplet discharge head, voltage control method, and image forming apparatus - Google Patents

Description

  The present invention relates to a droplet discharge head that discharges droplets from a hole such as a nozzle hole, a voltage control method for the droplet discharge head, and an image of a printer, a copying apparatus, a facsimile apparatus, or the like having the droplet discharge head. The present invention relates to a forming apparatus.

  As an image recording apparatus or an image forming apparatus such as a printer, a facsimile, a copying apparatus, or a plotter, an image recording apparatus or an image forming apparatus provided with a droplet discharge head that discharges droplets is known. As such a droplet discharge head, an electromechanical conversion of a piezoelectric element or the like in a pressurizing chamber (also referred to as an ink flow path, a pressurized liquid chamber, a pressure chamber, a discharge chamber, or a liquid chamber) communicating with the nozzle hole. There is a system in which droplets are ejected from nozzle holes by generating pressure fluctuations in the element. In this system, a plurality of systems have been put into practical use and commercialized. As an example, a thermal ink jet system that uses a pressure fluctuation to vaporize liquid by installing an electrothermal conversion element such as a heater in the pressurizing chamber, and a system that installs an electromechanical conversion element such as a piezoelectric element in the pressurizing chamber Is mentioned. Further, there may be mentioned a system that includes a vibration plate that forms the wall surface of the ink flow path and an energy generating means that includes an electrode facing the diaphragm, and pressurizes the droplets in the pressurizing chamber with the energy generated by the energy generating means. Two types of electromechanical transducers have been put into practical use: those using a piezoelectric actuator in a longitudinal vibration mode that extends and contracts in the axial direction of the piezoelectric element, and those using a piezoelectric actuator in a flexural vibration mode.

  Here, in an ink jet recording apparatus equipped with a droplet discharge head, in order to ensure stable discharge characteristics of the droplet of the droplet discharge head, the viscosity change of the droplet due to the drying and temperature of the droplet has been conventionally Measures have been taken (see, for example, Patent Documents 1 to 6). In Patent Document 1, as a measure for preventing the drying of droplets, a proposal is made to stir the liquid in the individual liquid chamber by applying a fine driving waveform to the nozzle to suppress the drying of the meniscus. Further, Patent Document 2 proposes applying an idle discharge waveform during suction as a maintenance operation after drying the droplets. As countermeasures against temperature characteristics, Patent Documents 3 to 6 propose that temperature control is provided and temperature control is performed with a temperature detection means and a heating signal, a preliminary waveform, or a fine drive waveform to ensure ejection stability. .

  And the application range of the droplet to discharge is wide, and the thing using the piezoelectric actuator of the bending vibration mode of an electromechanical conversion element attracts attention with respect to the request | requirement for future high definition. In the case of using an actuator in the flexural vibration mode, a uniform piezoelectric material layer is formed over the entire surface of the diaphragm by film formation technology. It is necessary to apply a voltage exceeding.

  However, even when the discharge characteristics are secured by applying a voltage exceeding the coercive electric field in this way, when the discharge is interrupted and restarted, the discharge characteristics can be maintained even when the droplet drying and the droplet viscosity are constant. It may change.

  The present invention has been made in view of the above circumstances, a droplet discharge head capable of stabilizing the discharge characteristics before and after interruption of droplet discharge, a voltage control method for the droplet discharge head, and the liquid An object of the present invention is to provide an image forming apparatus including a droplet discharge head.

In order to achieve the above object, a droplet discharge head according to the present application is provided with a nozzle for discharging droplets, a liquid chamber communicating with the nozzle, a diaphragm provided on the liquid chamber, and a diaphragm. An electromechanical transducer that generates pressure fluctuations in the liquid chamber by vibrating the diaphragm, and a voltage waveform exceeding the coercive electric field on the positive side is applied to the electromechanical transducer and the liquid droplets are ejected from the nozzle. And a voltage waveform that does not cause the liquid droplets to be discharged is applied to the electromechanical conversion element before the liquid droplet discharge starts, and has a portion that exceeds and falls below the positive coercive electric field. By applying a voltage waveform up to a negative bias within a range that does not exceed the negative coercive field with respect to the polarization direction, a negative bias is applied even when a voltage waveform that does not eject a droplet is ejected from the nozzle. and applying to

  According to the present invention, by stabilizing the polarization characteristics of the electromechanical conversion element before and after the discharge interruption, the droplet discharge head capable of stabilizing the discharge characteristics, the voltage control method of the droplet discharge head, and An image forming apparatus provided with this droplet discharge head can be provided.

It is sectional drawing which shows the basic structural example of a droplet discharge head. It is the model enlarged view of the fine domain structure of a PZT film, (a) shows the polarization direction of the PZT film domain before polarization treatment, (b) shows the polarization direction state of the PZT film domain after polarization treatment. Show. It is a graph which shows the polarization characteristic after the polarization process of a PZT film | membrane. It is sectional drawing which shows the structural example of the electromechanical conversion element used for the droplet discharge head which concerns on each Example of this application. The structure of the electromechanical conversion element containing the insulation protective film etc. which concern on each Example is shown, (a) is sectional drawing, (b) abbreviate | omitted a part of 1st insulation protective film and a 2nd insulation protective film FIG. It is explanatory drawing for demonstrating the behavior of a droplet discharge head before and after the droplet discharge interruption in a comparative example, and (a) is a graph showing the change of the droplet velocity Vj before and after the droplet discharge interruption, (B) is a graph which shows the polarization hysteresis at the time of a unipolar drive. 3 is a graph showing the voltage of a leveled voltage waveform and the application time in Example 1. It is a graph which shows the voltage and application time of a leveling voltage waveform in Example 2. 10 is a graph showing a voltage from reverse bias and application time in Example 3. 10 is a flowchart illustrating a voltage control procedure when a droplet is discharged according to a fourth exemplary embodiment. It is the schematic which shows the structure of the main mechanism part of Example 5 which concerns on the image forming apparatus of this application. It is a schematic plan view of the principal part of the main mechanism part of FIG.

  Hereinafter, embodiments of the droplet discharge head according to the present application will be described. First, a basic configuration example of a droplet discharge head will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a basic configuration of a droplet discharge head. FIG. 2 is a schematic diagram for explaining the polarization direction of the PZT film of the piezoelectric actuator. FIG. 3 is a graph showing the polarization characteristics after the polarization treatment of the PZT film.

[Basic configuration of droplet discharge head]
As shown in FIG. 1, a droplet discharge head 300 includes a nozzle plate 303 having nozzles 302 for discharging droplets, and a pressure chamber (an ink flow path, a pressure liquid chamber, a pressure chamber, a discharge chamber) that communicates with the nozzle 302. 301, also referred to as a chamber, a liquid chamber, or the like), a piezoelectric element 309 as an electromechanical transducer that pressurizes droplets in the pressurizing chamber 301, a pressure chamber substrate 304 provided with the pressurizing chamber 301, and pressurization A diaphragm (base) 305 provided between the chamber 301 and the piezoelectric element 309, a drive circuit member (not shown) for controlling driving of the piezoelectric element 309, and the like are configured.

[Basic configuration of electromechanical transducer (piezoelectric)]
First, the piezoelectric element 309 used in the droplet discharge head 300 will be described using a flexural vibration mode piezoelectric actuator. As an example of using the actuator of this flexural vibration mode, for example, a uniform piezoelectric material layer is formed by a film forming technique over the entire surface of the diaphragm, and this piezoelectric material layer is formed into a pressure generating chamber by a lithography method. A device in which a piezoelectric element is formed so as to be independent of each pressure generating chamber (pressurizing chamber 301) by dividing into corresponding shapes is known.

  In addition, as the piezoelectric element (electromechanical conversion element) 309 used for the actuator in the flexural vibration mode, for example, in the one shown in FIG. 1, the lower electrode 306 that is a common electrode and the electric electrode formed on the lower electrode 306 are used. A PZT film (piezoelectric layer) 307 serving as a mechanical conversion film and an upper electrode 308 that is an individual electrode formed on the PZT film 307 are configured. Further, an interlayer insulating film (not shown) is formed on the upper electrode 308 to insulate the lower electrode 306 and the upper electrode 308, and a contact hole (not shown) opened in the interlayer insulating film. ), And a wiring electrically connected to the upper electrode 308 is provided.

  FIG. 2 shows a schematic diagram of the fine domain structure of the PZT film. As shown in FIG. 2A, the polarization direction of the piezoelectric crystal of the PZT film is in a random state immediately before the pressure is applied. By repeating the voltage application to this, as shown in FIG. 2B, the piezoelectric crystal becomes an aggregate of domains in which the directions of polarization are aligned. For this reason, attempts have been made to align the direction of polarization before voltage application, and efforts have been made to stabilize the amount of displacement with respect to a predetermined drive voltage called an aging process or a poling (polarization process) process. It was. Specifically, a technique is applied in which a high voltage exceeding the drive pulse voltage is applied to the piezoelectric element. Further, a device has been devised in which a voltage is applied between the electrode and the charge supply means to generate a corona discharge, thereby supplying a charge and generating an electric field in the piezoelectric body. FIG. 3 shows the polarization characteristics after the polarization treatment.

  Here, the application range of the droplets to be ejected is wide, and attention is paid to the use of a piezoelectric actuator of a flexural vibration mode of an electromechanical transducer in response to a demand for higher definition in the future. As an actuator using a flexural vibration mode actuator, a uniform piezoelectric material layer is formed by a film forming technique over the entire surface of the diaphragm. In such an actuator, it is necessary to apply a voltage exceeding the coercive electric field as a driving voltage in order to earn displacement.

  The inventor diligently developed such a piezoelectric actuator and evaluated the stability of ejection characteristics. As a result, in a droplet discharge head that secures the discharge characteristics by applying a voltage that exceeds the coercive electric field, the discharge characteristics change even when the droplet drying and the viscosity of the droplets are constant. I found out. As a result of analyzing this phenomenon, it has been found that the ejection characteristics fluctuate because the polarization characteristics of the electromechanical transducer are interrupted. For this reason, the present inventors have invented the liquid discharge head of the present application that stabilizes the discharge characteristics by stabilizing the polarization characteristics of the electromechanical conversion element before and after interruption of droplet discharge.

  That is, the droplet discharge head of the present application includes a nozzle for discharging droplets, a liquid chamber communicating with the nozzle, a vibration plate provided on the liquid chamber, and a vibration plate provided on the vibration plate to vibrate the vibration plate. And an electromechanical conversion element that generates pressure fluctuations in the liquid chamber.

  In the liquid droplet ejection head as described above, when a liquid droplet is ejected, a voltage waveform exceeding the coercive electric field on the positive side is applied to the electromechanical conversion element to eject the liquid droplet from the nozzle. In addition, when the discharge of the droplet is interrupted and restarted, before starting the discharge of the droplet, a voltage waveform that has a portion that exceeds the positive coercive field and a portion that falls below the coercive field on the positive side and does not discharge the droplet, Applied to the electromechanical transducer. Hereinafter, this “voltage waveform that has a portion exceeding the positive coercive electric field and a portion below the coercive electric field and does not discharge the droplet” will be referred to as a “normalized voltage waveform”. In the present application, by applying the “leveling voltage waveform” before the start of ejection in this way, the polarization characteristics of the electromechanical transducer can be stabilized, and the ejection characteristics of the droplets can be improved. Printing can be maintained for a long time. Further, it is possible to reduce the cost of consumables by eliminating unnecessary discharge of droplets.

  In addition, the droplet discharge head of the present application discharges droplets from the nozzle by applying a voltage waveform up to a negative bias in a range not exceeding the negative coercive electric field with respect to the polarization direction of the electromechanical transducer, Even when the leveling voltage waveform is applied, the negative bias may be applied. As described above, by applying the reverse bias waveform to the polarization direction of the electromechanical conversion element and ejecting the liquid, and applying the leveling voltage waveform up to the reverse bias, the displacement efficiency as the actuator can be improved. At the same time, it is possible to improve the stabilization of the discharge characteristics.

  In addition, the droplet discharge head of the present application uses an electromechanical conversion element in a range from a negative bias in a range not exceeding the negative coercive electric field of the electromechanical conversion element to a maximum power supply voltage that can be applied as a leveling voltage waveform. You may comprise so that a voltage may be applied to. In this way, by applying a voltage waveform in the range from reverse bias to the maximum voltage on the positive side that can be applied within the range that does not exceed the negative coercive field of the electromechanical transducer, Polarization characteristics can be further stabilized.

  In addition, the droplet discharge head of the present application has a voltage waveform that makes the rising speed of the voltage displaced toward the discharge side of the liquid droplet of the leveled voltage waveform slower than the rising speed of the voltage of the discharge waveform at the time of discharging the droplet. You may comprise. With this configuration, it is possible to suppress current consumption in the leveling waveform.

  Further, the droplet discharge head of the present application has a voltage waveform that makes the voltage rising speed and falling speed of the leveling voltage waveform slower than the rising speed and falling speed of the discharge waveform voltage at the time of discharging the droplet, respectively. May be applied. With this configuration, it is possible to suppress the temperature rise by suppressing the head heat generation during the application of the voltage of the leveled voltage waveform, it is possible to perform the ejection operation without empty ejection, and it is possible to suppress wasteful consumption of the recording liquid. .

  Further, the droplet discharge head of the present application may be configured to apply a triangular waveform as the leveling voltage waveform, and can suppress a change in polarization characteristics caused by continuously applying a high electric field to the electromechanical transducer. .

  The voltage control method of the present application is a voltage control method for a droplet discharge head provided with an electromechanical transducer that generates a pressure fluctuation in a liquid chamber communicating with a nozzle by vibrating a diaphragm. There is an interruption time between the end of discharge and the start of discharge when applying the voltage waveform exceeding the positive coercive electric field to the electromechanical transducer of the head and discharging the droplet. In this case, a step of applying, to the electromechanical conversion element, a voltage waveform that has a portion that exceeds and falls below the positive coercive electric field and does not cause the droplets to be discharged is included. As described above, the maintenance time can be reduced by determining whether or not the smoothing waveform application is performed according to the state of the interruption time from the discharge end to the discharge start.

  Further, in the voltage control method of the present application, it is preferable to change the time for applying the voltage waveform that does not cause the droplets to be ejected, corresponding to the interruption time from the end of ejection of the droplets from the droplet ejection head to the start of ejection. As a result, the maintenance time can be optimized by changing the application time of the leveling waveform corresponding to the interruption time from the end of ejection to the start of printing.

  In addition, the voltage control method of the present application applies a voltage to the electromechanical conversion element up to a reverse bias, discharges a droplet, and at the end of voltage application, the positive side with respect to the polarization direction of the electromechanical conversion element After applying the bias, the voltage application to the electromechanical conversion element is preferably terminated. As a result, stable polarization characteristics can be ensured without polarization reversal of the electromechanical transducer.

  In addition, the image forming apparatus of the present application has the above-described droplet discharge head, and uses the voltage control method as described above to land the droplet discharged from the droplet discharge head on the deposition medium. Therefore, excellent image quality can be maintained by forming an image with a droplet discharge head having excellent droplet discharge characteristics.

  Embodiments of the droplet discharge head of the present application will be described below with reference to the drawings. Since the basic configuration of the droplet discharge head is as described above with reference to FIG. 1, description of the detailed configuration of the droplet discharge head is omitted. Below, the structural example of the electromechanical conversion element used with the droplet discharge head of each Example is demonstrated in detail with reference to FIG. 4, FIG. FIG. 4 is an enlarged cross-sectional view illustrating a configuration example of a main part of the electromechanical transducer. FIG. 5 shows a more detailed configuration example of an electromechanical transducer including an insulating protective film, etc., FIG. 5 (a) is a cross-sectional view, FIG. 5 (b) shows a part of the first insulating protective film, It is a top view in the state where the 2nd insulating protective film was omitted.

[Configuration of electromechanical transducer]
As shown in FIG. 4, the electromechanical transducer 400 according to the embodiment of the present application includes an actuator substrate 401, a film formation diaphragm 402, a first electrode 403, an electromechanical transducer film 404, and a second electrode 405. It is configured. As shown in FIG. 5, the electromechanical transducer 400 according to the embodiment of the present application further includes a first insulating protective film 406 as a protective film, a third electrode 408 and a fourth electrode 409 (lead wiring), and a first 2 has an element structure including an insulating protective film 407 and the like. The electromechanical conversion element 400 is driven by driving means (not shown) such as a driving IC in which the first electrode 403 and the second electrode 405 are connected to each other through wiring.

  As shown in FIG. 5, the first insulating protective film 406 has a contact hole portion 410, and the first electrode 403 and the third electrode 408, and the second electrode 405 and the fourth electrode 409 are electrically connected. It has become. At this time, the first electrode 403 and the third electrode 408 are used as the common electrode wiring 411, the second electrode 405 and the fourth electrode 409 are used as the individual electrode wiring 412, and these are protected on the upper surfaces of the common electrode 411 and the individual electrode wiring 412. A second insulating protective film 407 is formed. The second insulating protective film 407 is partially opened (opening portion O) to form an electrode PAD. The electrode prepared for the common electrode wiring 411 is referred to as a common electrode PAD 413, and the electrode manufactured for the individual electrode wiring 412 is referred to as an individual electrode PAD 414. A polarization process is performed between the common electrode wiring 411 and the individual electrode wiring 412 by voltage application or corona charging.

[Material and construction method of electromechanical transducer]
Below, the material and construction method of each structure of the electromechanical conversion element 400 are demonstrated concretely.

(Actuator board)
As a material of the actuator substrate 401, it is preferable to use a silicon single crystal substrate, and it is usually preferable to have a thickness of 100 μm to 600 μm. Although there are three types of plane orientations (100), (110), and (111), (100) and (111) are generally widely used in the semiconductor industry. In the present embodiment, a single crystal substrate mainly having a (100) plane orientation is mainly used. Further, when the pressurizing chamber 301 as shown in FIG. 1 is manufactured, the silicon single crystal substrate is processed using etching. As an etching method in this case, it is common to use anisotropic etching.

Anisotropic etching utilizes the property that the etching rate differs with respect to the plane orientation of the crystal structure. For example, in anisotropic etching immersed in an alkaline solution such as potassium hydroxide KOH, the (111) plane has an etching rate of about 1/400 compared to the (100) plane. Therefore, while a structure having an inclination of about 54 ° can be produced in the plane orientation (100), a deep groove can be provided in the plane orientation (110), so that the arrangement density can be increased while maintaining rigidity. I know you can. Therefore, in this embodiment, it is also possible to use a single crystal substrate having a (110) plane orientation. However, in this case, silicon dioxide SiO ₂ (which is also a mask material) may be etched, so that this point is utilized with attention being paid to this point.

(Film formation diaphragm)
As shown in FIG. 1, in response to the force generated by the PZT film 307, the vibration plate (base) 305 is deformed and displaced, and droplets in the pressurizing chamber 301 are ejected. Therefore, it is preferable that the film-forming diaphragm 402 of the embodiment of the present invention shown in FIG. 4 has a predetermined strength. Examples of the material of the film formation vibration plate 402 include silicon Si, silicon dioxide SiO ₂ , and silicon nitride Si ₃ N ₄ , and a material in which the vibration plate 305 is manufactured by a CVD method (Chemical Vapor Deposition). .

It is preferable to select a material close to the linear expansion coefficient of the first electrode 403 as the lower electrode and the electromechanical conversion film 404 for the film formation diaphragm 402. In particular, for the electromechanical conversion film 404, PZT (Pb (Zr, Ti) O, zirconate-lead titanate) is generally used as a material. Therefore, a material having a linear expansion coefficient of 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ as a linear expansion coefficient close to 8 × 10 ⁻⁶ (1 / K) is preferable, and further 7 × A material having a linear expansion coefficient of 10 ^{−6 to} 9 × 10 ⁻⁶ is more preferable.

Specific materials for the film formation diaphragm 402 include aluminum oxide Al ₂ O ₃ , zirconium oxide ZrO ₂ , iridium oxide IrO ₂ , ruthenium oxide RUO ₂ , tantalum oxide Ta ₂ O 5, hafnium oxide HfO ₂ , osmium oxide OsO _4. , Rhenium oxide ReO ₂ , rhodium oxide Rh ₂ O ₃ , palladium oxide PdO, and compounds thereof. The film-forming diaphragm 402 can be manufactured using a spin coater by using a sputtering method or a Sol-gel method. The film thickness of the film formation diaphragm 402 is preferably 0.1 μm to 10 μm, and more preferably 0.5 μm to 3 μm. If it is smaller than this range, it becomes difficult to process the pressurizing chamber 301 as shown in FIG. 1, and if it is larger than this range, the film-forming diaphragm 402 is difficult to deform and displace, and the discharge of the droplet becomes unstable. Therefore, it is not preferable.

(First electrode)
The first electrode 403 is preferably made of metal or a metal and an oxide. Here, in both cases, an adhesion layer (not shown) is interposed between the film formation diaphragm 402 and the metal film for the first electrode 403 so as to suppress both peeling and the like. The details of the metal electrode film and oxide electrode film of the first electrode 403 including the adhesion layer will be described below.

"Adhesion layer"
After titanium Ti is sputter-deposited as an adhesion film, the titanium film is thermally oxidized in an oxygen O ₂ atmosphere at 650 ° C. to 800 ° C. for 1 minute to 30 minutes using an RTA (rapid thermal annealing) apparatus. A titanium oxide film (TiO ₂ film) is formed. In order to produce the titanium oxide film, reactive sputtering may be used, but a thermal oxidation method at a high temperature of the titanium film is desirable. This is because the production by reactive sputtering requires a special sputtering chamber configuration because the silicon substrate needs to be heated at a high temperature. Furthermore, the crystallinity of the titanium oxide film is better in the oxidation by the RTA apparatus than in the oxidation by a general furnace. This is because, according to oxidation in a normal heating furnace, a titanium film that is easily oxidized forms several crystal structures at a low temperature, and thus it is necessary to break it once. Therefore, oxidation by an RTA apparatus having a high temperature rising rate is advantageous for forming a good crystal. Moreover, as materials other than Ti, materials such as tantalum Ta, iridium Ir, ruthenium Ru, and the like are also preferable.

  The film thickness of the adhesion film is preferably 10 nm to 50 nm, and more preferably 15 nm to 30 nm. Below this range, there is concern about the adhesion, and above this range, the crystal quality of the electrode film produced on the adhesion film is affected, which is not preferable.

"Metal electrode film"
Conventionally, platinum Pt having high heat resistance and low reactivity has been used as the metal material of the metal electrode film, but it may not be said that it has sufficient barrier properties against lead Pb. Examples include platinum group elements such as Ir and platinum-rhodium alloys, and alloy films thereof. In addition, when platinum is used, it is preferable that the previous adhesive layer is laminated first because the adhesiveness with the film-forming diaphragm 402 (particularly SiO ₂ ) which is the base is poor.

  As a method for producing the metal electrode film, vacuum film formation such as sputtering or vacuum deposition is generally used. As a film thickness, 80 nm-200 nm are preferable, and 100 nm-150 nm are more preferable. When the thickness is smaller than this range, it is not preferable because a sufficient current cannot be supplied as a common electrode and a problem occurs when droplets are discharged. In addition, when the material is thicker than this range, the cost increases when using an expensive material of the platinum group element, and when the material is made of platinum, the surface is increased when the film thickness is increased. Roughness increases. Further, it is not preferable because the oxide electrode film or PZT formed thereon has an influence on the surface roughness and crystal orientation, and causes a problem that a sufficient displacement cannot be obtained for droplet discharge.

"Oxide electrode film"
As a material for the oxide electrode film, strontium / ruthenium oxide SrRuO ₃ is preferably used. In addition to the materials on the left, Srx (A) (1-x) Ruy (1-y), A = Ba, Ca, B = Co, Ni, x, y = 0 to 0.5 Preferably mentioned. The film forming method is produced by sputtering. The film quality of the SrRuO ₃ thin film changes depending on the sputtering conditions. Therefore, in order to place the SrRuO ₃ film (also referred to as SRO film formation) in the (111) orientation in accordance with the platinum Pt (111) of the first electrode 403 with particular emphasis on the crystal orientation, It is preferable to form a film by heating the substrate at 500 ° C. or higher.

  For example, as SRO film formation conditions, there is a method of performing thermal oxidation at a crystallization temperature (650 ° C.) by RTA treatment after film formation at room temperature. In this case, the SRO film is sufficiently crystallized, and a sufficient value can be obtained as a specific resistance as an electrode. However, as the crystal orientation of the film, (110) is likely to be preferentially oriented, and the PZT film formed thereon is also likely to be (110) oriented.

  Regarding SRO crystallinity produced on Pt (111), the lattice constants of Pt and SRO are close to each other. Therefore, in the usual θ-2θ measurement, the 2θ positions of SRO (111) and Pt (111) are overlapped and discriminated. Is difficult. With respect to Pt, diffraction lines cancel each other at a position where 2θ tilted by Psi = 35 ° is about 32 ° due to the disappearance rule, and no diffraction intensity is observed. Therefore, it is possible to confirm whether the SRO is preferentially oriented to (111) by tilting the Psi direction by about 35 ° and judging from the peak intensity where 2θ is about 32 °. Data when 2θ = 32 ° is fixed and Psi is shaken is shown below.

  When Psi = 0 °, almost no diffraction intensity is observed with SRO (110), but near Psi = 35 °, diffraction intensity is observed. I was able to confirm. In addition, regarding the SRO produced by the room temperature film formation + RTA process described above, the diffraction intensity of SRO (110) can be seen when Psi = 0 °.

  Although details will be described later, when the amount of displacement after being driven is estimated to be deteriorated compared to the initial displacement when continuously operating as a piezoelectric actuator, the orientation of PZT has a great influence. (110) is insufficient in suppressing displacement deterioration. Further, when the surface roughness of the SRO film is observed, it affects the film formation temperature, and the surface roughness is very small from room temperature to 300 ° C. and becomes 2 nm or less. As for the roughness, the surface roughness (average roughness) measured by AFM is used as an index. The surface roughness is very flat but the crystallinity is not sufficient. Sufficient characteristics can be obtained for the initial displacement as a PZT piezoelectric actuator and the displacement deterioration after continuous driving. Absent.

  The surface roughness is preferably 4 nm to 15 nm, and more preferably 6 nm to 10 nm. Exceeding this range is not preferable because the dielectric strength of PZT formed thereafter is very poor and leaks easily. Therefore, in order to obtain crystallinity and surface roughness as described above, film formation is performed at a film formation temperature of 500 to 700 ° C., preferably 520 to 600 ° C.

Regarding the composition ratio of Sr and Ru after film formation, Sr / Ru is preferably 0.82 or more and 1.22 or less. If it is out of this range, the specific resistance increases, and sufficient conductivity as an electrode cannot be obtained. Furthermore, the film thickness of the SRO film is preferably 40 nm to 150 nm, and more preferably 50 nm to 80 nm. If the thickness is smaller than this range, sufficient characteristics cannot be obtained for initial displacement and displacement deterioration after continuous driving, and it is difficult to obtain a function as a stop etching layer for suppressing PZT overetching. Therefore, it is not preferable. On the other hand, exceeding this range is not preferable because the dielectric strength of PZT formed thereafter is poor and leaks easily. The specific resistance is preferably 5 × 10 ⁻³ Ω · cm or less, and more preferably 1 × 10 ⁻³ Ω · cm or less. If it is larger than this range, sufficient contact resistance cannot be obtained at the interface with the fifth electrode (not shown) as the common electrode wiring 411, and sufficient current cannot be supplied as the common electrode wiring 411. This is not preferable because a problem occurs when droplets are ejected.

(Electromechanical conversion membrane)
As a material of the electromechanical conversion film 404, PZT was mainly used. PZT is a solid solution of lead zirconate (PbTiO ₃ ) and titanic acid (PbTiO ₃ ), and the characteristics differ depending on the ratio. In general, a composition exhibiting excellent piezoelectric characteristics has a ratio of PbZrO ₃ and PbTiO ₃ of 53:47. The chemical formula indicates Pb (Zr0.53, Ti0.47) O ₃ , generally PZT (53/47).

Examples of composite oxides other than PZT include barium titanate BaTiO _{3. In} this case, a barium titanate precursor solution is prepared by dissolving barium alkoxide and a titanium alkoxide compound in a common solvent. It is also possible.

These materials are described by the general formula ABO ₃ , and correspond to composite oxides containing A = Pb, Ba, Sr, B = Ti, Zr, Sn, Ni, Zn, Mg, and Nb as main components. Specific descriptions thereof include (Pb1-x, Ba) (Zr, Ti) O ₃ , (Pb1-x, Sr) (Zr, Ti) O ₃ , which partially replaces Pb at the A site with Ba or Sr. This is the case. Such substitution is possible with a divalent element, and the effect thereof has an effect of reducing characteristic deterioration due to evaporation of lead during heat treatment.

  As a method for manufacturing the electromechanical conversion film 404, it can be manufactured by a spin coater using a sputtering method or a Sol-gel method. In that case, since patterning is required, a desired pattern is obtained by photolithography etching or the like.

When PZT is produced by the Sol-gel method, a PZT precursor solution can be produced by using lead acetate PbO, zirconium alkoxide, and titanium alkoxide compound as starting materials and dissolving them in methoxyethanol as a common solvent to obtain a uniform solution. Since metal alkoxide compounds are easily hydrolyzed by moisture in the atmosphere, acetylacetone C ₅ H ₈ O ₂ , acetic acid C ₂ H ₄ O ₂ , diethanolamine C ₄ H ₁₁ NO _2, etc. are used as stabilizers in the precursor solution. An appropriate amount of stabilizer may be added.

  When a PZT film is obtained on the entire surface of the base substrate, it is obtained by forming a coating film by a solution coating method such as spin coating and performing heat treatments such as solvent drying, thermal decomposition, and crystallization. The transformation from the coating film to the crystallized film is accompanied by volume shrinkage. Therefore, in order to obtain a crack-free film, it is necessary to adjust the precursor concentration so that a film thickness of 100 nm or less can be obtained in one step.

  The thickness of the electromechanical conversion film 404 is preferably 0.5 μm to 5 μm, and more preferably 1 μm to 2 μm. If it is smaller than this range, it will not be possible to generate a sufficient displacement, and if it is larger than this range, many layers will be stacked, which is not preferable because the number of steps increases and the process time becomes longer.

  Further, the relative dielectric constant is preferably 600 or more and 2,000 or less, and more preferably 1,200 or more and 1,600 or less. If this value is not satisfied, sufficient displacement characteristics cannot be obtained. If the value is larger than this value, polarization processing is not performed sufficiently, and there is a problem that sufficient characteristics cannot be obtained for displacement degradation after continuous driving. It is not preferable.

(Second electrode)
The second electrode 405 is preferably made of a metal or an oxide and a metal. Details of the oxide electrode film and the metal electrode film are described below.

"Oxide electrode film"
The material or the like of the oxide electrode film is as described for the oxide electrode film used in the first electrode 403. The film thickness of the SRO film is preferably 20 nm to 80 nm, and more preferably 40 nm to 60 nm. If the film thickness is smaller than this range, sufficient characteristics cannot be obtained for the initial displacement and displacement deterioration characteristics, and if it exceeds this range, the dielectric strength of the PZT formed thereafter is poor and it is liable to leak.

"Metal electrode film"
The material of the metal electrode film is as described for the metal electrode film used in the first electrode 403. The film thickness is preferably 30 nm to 200 nm, and more preferably 50 nm to 120 nm. When the film thickness is thinner than this range, it is not preferable because a sufficient current cannot be supplied as the individual electrode wiring 412 and a problem occurs when droplets are discharged. Furthermore, when the film thickness is larger than this range, the use of an expensive platinum group element material increases the cost. For this reason, the surface roughness increases when the film thickness is increased by using platinum as a material, and when the sixth electrode (not shown) is produced through the insulating protective film, a process such as film peeling is performed. This is not preferable because defects are likely to occur.

(First insulation protective film)
The first insulating protective film 406 needs to be a dense inorganic material because it is necessary to select a material that prevents moisture in the atmosphere from passing through while preventing damage to the electromechanical conversion element due to the film formation / etching process. There is. An organic material is not preferable because the film thickness needs to be increased in order to obtain sufficient protection performance. If the first insulating protective film 406 is a thick film, the vibration displacement of the film formation diaphragm 402 is remarkably hindered, resulting in a droplet discharge head having a low discharge performance.

  In order to obtain a high protection performance with the first insulating protective film 406 as a thin film, it is preferable to use an oxide, a nitride, or a carbonized film, but an electrode material, a piezoelectric material, It is necessary to select a material having high adhesion to the diaphragm material. In addition, it is necessary to select a film forming method that does not damage the electromechanical transducer. That is, a plasma CVD method in which a reactive gas is turned into plasma and deposited on a substrate, or a sputtering method in which a film is formed by causing plasma to collide with a target material and flying is not preferable. Examples of a preferable film formation method for the first insulating protective film 406 include a vapor deposition method and an ALD method (Chemical Vapor Deposition), but the ALD method is preferable in terms of a wide range of materials that can be used.

Preferred materials for the first insulating protective film 406 include oxides used for ceramic materials such as aluminum oxide Al ₂ O ₃ , zinc oxide ZrO ₂ , yttrium oxide Y ₂ O ₃ , tantalum oxide Ta ₂ O ₃ , titanium oxide TiO _{2, and the} like. An example is a membrane. In particular, by using the ALD method, a thin film having a very high film density is produced and damage in the process is to be suppressed.

  The film thickness of the first insulating protective film 406 needs to be a sufficiently thin film that can ensure the protection performance of the electromechanical transducer 400, and at the same time, as much as possible so as not to inhibit the displacement of the film formation diaphragm 402. It needs to be thin. A preferable film thickness of the first insulating protective film 406 is in the range of 20 nm to 100 nm. When the thickness is larger than 100 nm, the displacement of the vibration plate is reduced, and a droplet discharge head with low discharge efficiency is obtained, which is not preferable. On the other hand, when the thickness is less than 20 nm, the function of the electromechanical conversion element 400 as a protective layer is insufficient, and the performance of the electromechanical conversion element 400 is deteriorated as described above.

Further, the first insulating protective film 406 may be configured in two layers. In this case, in order to increase the thickness of the second insulating protective film, a configuration in which the second insulating protective film is opened in the vicinity of the second electrode 405 so as not to significantly disturb the vibration displacement of the diaphragm can be cited. . At this time, any oxide, nitride, carbide, or a composite compound thereof can be used as the second insulating protective film. Among these, silicon dioxide SiO ₂ generally used in semiconductor devices can be used.

  Arbitrary methods can be used for forming the first insulating protective film 406, and a CVD method and a sputtering method can be exemplified. Among these, it is preferable to use a CVD method capable of forming an isotropic film in consideration of the step coverage of the pattern forming portion such as the electrode forming portion. The film thickness of the second insulating protective film needs to be a film thickness that does not cause dielectric breakdown by the voltage applied to the first electrode 403 as the lower electrode and the individual electrode wiring 412. That is, it is necessary to set the electric field strength applied to the insulating protective film within a range not causing dielectric breakdown. Further, in consideration of the surface property of the base of the second insulating protective film, pinholes, etc., the film thickness is required to be 200 nm or more, and more preferably 500 nm or more.

(3rd electrode and 4th electrode)
The material of the third electrode 408 and the fourth electrode 409 is preferably a metal electrode material made of any of Ag (silver) alloy, copper Cu, aluminum Al, gold Au, platinum Pt, and iridium Ir. As a manufacturing method of the third electrode 408 and the fourth electrode 409, a sputtering method and a spin coating method are used, and then a desired pattern is obtained by photolithography etching or the like.

  The film thickness of the third electrode 408 and the fourth electrode 409 is preferably 0.1 μm to 20 μm, and more preferably 0.2 μm to 10 μm. If it is smaller than this range, the resistance becomes large and it becomes impossible to pass a sufficient current through the electrode, and the head ejection becomes unstable, which is not preferable. If it is larger than this range, the process time becomes longer, which is not preferable. When the common electrode wiring 411 and the individual electrode wiring 412 are used, the contact resistance in the contact hole portion 410 (10 μm × 10 μm) is preferably 10Ω or less for the common electrode wiring 411 and 1Ω for the individual electrode wiring 412. The following is preferred. Further, the common electrode wiring 411 is more preferably 5Ω or less, and the individual electrode wiring 412 is more preferably 0.5Ω or less. Exceeding this range is not preferable because a sufficient current cannot be supplied and a problem occurs when droplets are ejected.

(Second insulating protective film)
The second insulating protective film 407 is a passivation layer that functions as a protective layer for the individual electrode wiring 412 and the common electrode wiring 411. As shown in FIG. 5, the upper surfaces of the individual electrode wiring 412 and the common electrode wiring 411 are covered except for the leading portion of the individual electrode wiring 412 and the leading portion of the common electrode wiring 411 (not shown). Thus, inexpensive Al or an alloy material containing Al as a main component can be used as the electrode material. As a result, a low-cost and highly reliable droplet discharge head can be obtained.

As a material of the second insulating protective film 407, any inorganic material or organic material can be used, but it is necessary to use a material with low moisture permeability. Examples of the inorganic material include oxides, nitrides, and carbides, and examples of the organic material include polyimide, acrylic resin, and urethane resin. However, in the case of an organic material, it is necessary to form a thick film, which is not suitable for patterning described later. Therefore, it is preferable to use an inorganic material that can exhibit a wiring protection function with a thin film. In particular, it is preferable to use silicon nitride Si ₃ N ₄ on the Al wiring because it is a technology that has been proven in semiconductor devices.

  Further, the thickness of the second insulating protective film 407 is preferably 200 nm or more, and more preferably 500 nm or more. A thin film thickness is not preferable because a sufficient passivation function cannot be exhibited, disconnection due to corrosion of the wiring material occurs, and the reliability of the droplet discharge head is lowered.

  The second insulating protective film 407 preferably has a structure having an opening O on the electromechanical conversion element 400 and on the film formation diaphragm 402 around it. This is the same reason that the pressure chamber region of the first insulating protective film 406 is thinned. As a result, a highly efficient and highly reliable droplet discharge head can be obtained.

The opening O can be formed by photolithography and dry etching because the electromechanical conversion element 400 is protected by the first and second insulating protective films 406 and 407. Further, the area of the PAD part is preferably 50 × 50 μm ² or more, and more preferably 100 × 300 μm ² or more. If it is less than this value, it is not preferable because sufficient polarization treatment cannot be performed, and there is a problem that sufficient characteristics cannot be obtained for displacement deterioration after continuous driving.

[Production example of droplet discharge head]
Next, a procedure for manufacturing a droplet discharge head including the electromechanical conversion element 400 used in each example and comparative example will be specifically described below.

  A thermal oxide film (film thickness of 1 micron) was formed on a 6-inch silicon wafer, and a titanium film (film thickness of 30 nm) was formed by a sputtering apparatus as an adhesion film as the first electrode 403. Thereafter, thermal oxidation was performed at 750 ° C. using an RTA apparatus, and subsequently a platinum film (film thickness: 100 nm) as a metal film and an SrRuO film (film thickness: 60 nm) as an oxide film were formed by sputtering. The substrate heating temperature during sputtering film formation was 550 ° C., and film formation was performed under these conditions.

  Next, a solution adjusted to Pb: Zr: Ti = 114: 53: 47 was prepared as the electromechanical conversion film 404, and a film was formed by spin coating. For the synthesis of a specific precursor coating solution, lead acetate trihydrate, isopropoxide titanium and isopropoxide zirconium were used as starting materials. Crystal water of lead acetate was dissolved in methoxyethanol and then dehydrated. The lead amount is excessive with respect to the stoichiometric composition. This is to prevent crystallinity deterioration due to so-called lead loss during heat treatment.

  Isopropoxide titanium and isopropoxide zirconium were dissolved in methoxyethanol, the alcohol exchange reaction and the esterification reaction were advanced, and the PZT precursor solution was synthesized by mixing with the methoxyethanol solution in which the lead acetate was dissolved. The PZT concentration was 0.5 mol / L. Using this PZT precursor solution, a film was formed by spin coating, and after film formation, 120 ° C. drying → 500 ° C. thermal decomposition was performed. After thermal decomposition treatment of the third layer, crystallization heat treatment (temperature: 750 ° C.) was performed by RTA (rapid heat treatment). At this time, the film thickness of PZT was 240 nm. This process was performed a total of 8 times (24 layers) to obtain a PZT film thickness of about 2 μm.

  Next, an SrRuO film (film thickness: 40 nm) was formed as an oxide film as the second electrode 405, and a Pt film (film thickness: 125 nm) was formed as a metal film by sputtering. Thereafter, a photoresist made by Tokyo Ohka Co., Ltd. (TSMR8800) is formed by spin coating, a resist pattern is formed by ordinary photolithography, and then a pattern as shown in FIG. 5 is used by using an ICP etching apparatus (manufactured by Samco). Was made.

Next, as the first insulating protective film 406, an AL ₂ O ₃ film having a thickness of 50 nm was formed using an ALD method. At this time, film formation was advanced by alternately laminating TMA (Sigma Aldrich Co.) for AL as a raw material and O ₃ generated by an ozone generator for O. Thereafter, as shown in FIG. 5, a contact hole portion 410 is formed by etching. Thereafter, AL was sputtered as the third electrode 408 and the fourth electrode 409, and was patterned by etching. Further, as the second insulating protective film 407, Si ₃ N ₄ was deposited to a thickness of 500 nm by plasma CVD, and the electromechanical conversion element 400 was produced. At this time, 25 areas of 30 mm × 10 mm square in a 6 inch wafer were arranged.

  A subframe (not shown) provided with an opening for forming a part of the common liquid chamber (see pressurizing chamber 301 in FIG. 1) was adhesively bonded to the actuator substrate 401 thus formed. This subframe uses a silicon wafer to form a thermal oxide film. In this embodiment, aluminum is formed by sputtering, but electrodes such as gold and platinum can also be used. Further, Au stud bumps (not shown) were formed on the individual electrodes on the actuator substrate 401.

  Thereafter, polarization treatment was performed by corona charging treatment. For the corona charging treatment, a tungsten wire having a diameter of 50 μm was used. A voltage of 7 kV was applied to the corona wire and a voltage of 2 kv was applied to the guard electrode on the subframe, and the treatment was performed for 30 seconds. Then, DrIC was mounted on the actuator substrate 401. Moreover, the liquid chamber processing of the silicon wafer was performed, and head assembly such as nozzle bonding was performed.

<Comparative example>
In the comparative example, the liquid ejection head manufactured as described above was driven without the “leveling voltage waveform”, and the ejection was interrupted and then ejected again. As a result, the liquid droplet velocity (hereinafter referred to as “Vj”) was obtained. Decreased by about 4%. Thereafter, as the discharge was repeated, it was confirmed that Vj returned to normal as shown in FIG. Looking at the polarization characteristics (PE hysteresis) at that time, it was confirmed that the state was as shown in FIG. 6B at the end of discharge, at the start of discharge, and at the time of continuous discharge. The “normalized voltage waveform” refers to a voltage waveform that has a portion that exceeds and falls below the coercive electric field on the positive side, and that does not discharge droplets.

  As described above, it has been found that Vj is stabilized by repeating continuous discharge. However, when idle discharge is performed, droplets are consumed, and thus cannot be performed every time.

  In addition, as a method for stabilizing the polarization characteristics after interruption, a case where a fine driving waveform that does not discharge droplets was applied was also verified. As the fine drive waveform, a pulse waveform of voltage waveform: 1 to 4v was applied. However, Vj drop at the start of discharge and change in polarization characteristics could not be suppressed.

<Example 1>
Next, the droplet discharge control of the first embodiment using the above-described droplet discharge head will be described with reference to FIG. In Example 1, after the droplets were ejected from the droplet ejection head, one hour was interrupted, and when restarting the ejection, a “normalized voltage waveform” that stabilizes the polarization characteristics was applied. As the leveling voltage waveform, as shown in FIG. 7, 0 v-15 v is applied as the potential difference of the voltage waveform, the falling time for displacement to the pull-in side is set to 1 μs, and the holding time is set as a condition for not performing the idle ejection. 1.5 μs. Then, the rise time displaced to the discharge side is set to 4 μs, that is, the rise speed is set to be slower than that during the normal discharge, thereby preventing the idle discharge. It was confirmed that by applying this waveform at 100 kHz for 10 sec, the polarization characteristics were stabilized, and the Vj reduction rate after the interruption could be reduced to 2% or less. Here, “the drawing side” refers to the pressure chamber direction in which the droplet is not discharged, and “displaces the voltage toward the drawing side” refers to applying a voltage that draws the droplet into the pressure chamber. “Discharge side” refers to the external direction in which droplets are ejected, and voltage “displaces to the ejection side” refers to application of a voltage for ejecting droplets.

  In the first embodiment, the rise time is 4 μs. However, the present application is not limited to this, and can be adjusted within a range where ejection is not performed. Further, the polarization characteristics can be controlled even under idle discharge conditions. However, since the amount of droplets to be discarded increases, it is desirable that the idle discharge conditions be not used.

<Example 2>
Next, the droplet discharge control of the second embodiment using the droplet discharge head will be described with reference to FIG. In Example 2, after discharge of a droplet from the droplet discharge head, it was interrupted for 1 hour, and when restarting discharge, a “running voltage waveform” that stabilizes the polarization characteristics was applied. As for the leveling voltage waveform, as shown in FIG. 8, 0v-15v is applied as the potential difference of the voltage waveform, the fall time for displacement to the pull-in side is set to 4 μs, and the discharge voltage is displaced to the discharge side, as shown in FIG. A triangular waveform with a rise time of 4 μs was applied at 125 kHz for 10 seconds. As a result, it was confirmed that the Vj decrease rate after interruption can be reduced to 2% or less.

  In addition, by using this voltage waveform, the falling speed and rising speed are made slower than the discharge waveform during normal discharge, so that no idle discharge occurs and head heat generation during application of the `` normalized voltage waveform '' can be prevented. it can. In addition, by applying a triangular wave, the time during which a high electric field is applied to the electromechanical transducer 400 can be shortened, and long-term polarization characteristic deterioration due to a leveled voltage waveform can be suppressed.

<Example 3>
Next, the droplet discharge control of the third embodiment using the droplet discharge head will be described with reference to FIG. In the third embodiment, as a droplet ejection waveform, as shown in FIG. 9, a voltage in the positive direction from the reverse bias is applied to the polarization direction of the electromechanical transducer 400. That is, the voltage waveform is applied to the negative bias in the range not exceeding the negative coercive electric field with respect to the polarization direction of the electromechanical transducer 400. Thereby, since the displacement efficiency is improved, the discharge characteristics can be improved.

  As a method of applying the reverse bias, a predetermined voltage, 5v in this case, is applied to the common electrode wiring 411 side of the electromechanical transducer 400, and a rectangular wave of 2v to 17v is applied to the individual electrode wiring 412. As a result, a voltage of −3v to 12v is substantially applied to the electromechanical transducer 400. By applying the maximum applied voltage on the positive side from the negative bias voltage within the range in which the leveling voltage waveform does not exceed the negative side coercive field with respect to this ejection waveform, within the drive voltage range, Polarization characteristics can be stabilized.

  Here, in the discharge waveform for applying the voltage up to the reverse bias, the leveling voltage waveform, and the like, the voltage is always turned to the positive side, and then the voltage is turned off (terminated). In Example 3, the common electrode side is first dropped to 0 v at the end, and then the individual electrode side is set to 0 v. When the voltage waveform is turned off as it is after applying a reverse bias, the state in which charges in the direction opposite to the polarization direction of the electromechanical transducer 400 are accumulated is maintained. As a result, it has been found that the polarization characteristics change in the long term, causing a change in Vj.

<Example 4>
Next, the droplet discharge control of the fourth embodiment using the droplet discharge head will be described with reference to FIG. In the fourth embodiment, regarding the application of the leveling voltage waveform, whether the leveling voltage waveform is applied for each head, each nozzle row, or each nozzle in the interruption time after the ejection waveform is applied to the electromechanical transducer 400. It is configured to determine whether or not to control the application time. That is, when the interruption time becomes equal to or longer than the predetermined time, it indicates that the discharge sequence is started after the leveling voltage waveform is applied. Further, the setting time is set so that the application time of the leveling voltage waveform becomes longer as the interruption time becomes longer. This is because the polarization characteristic change of the electromechanical transducer 400 increases as the interruption time increases.

  Hereinafter, the procedure of droplet discharge control according to the fourth embodiment will be described in detail with reference to the flowchart of FIG. First, in step S1, droplets are ejected from the droplet ejection head and printed. Next, when the droplet ejection is interrupted and the ejection is resumed, it is determined in step S2 whether or not the interruption time is a predetermined time or more. If the interruption time is less than the predetermined time, it is determined that application of the leveling voltage waveform is unnecessary, and droplet discharge (printing) is performed in step S3. On the other hand, if the interruption time is equal to or longer than the predetermined time, next, the interruption time is determined in step S4, and at the same time, in step S5, referring to the data table in which the condition of the leveling voltage waveform is set, The application time of the leveling voltage waveform corresponding to the interruption time is acquired. That is, the longer the intermediate time, the longer the application time of the leveling voltage waveform. According to this application time, a voltage waveform is applied for each head (or for each nozzle row and for each nozzle) in step S6. Next, in step S7, it is determined whether or not idle ejection is necessary. If necessary, idle ejection is performed in step S8, and droplet ejection (printing) is performed in step S9. If idle ejection is unnecessary, droplet ejection (printing) is performed in step S9 without performing idle ejection.

  By the control as described above, when the interruption time is short, the maintenance sequence by applying the leveling voltage waveform can be shortened, and the productivity of the droplet discharge head can be improved.

<Example 5>
Next, in Example 5, an example of an image forming apparatus including the droplet discharge head of the present application will be described with reference to FIGS. 11 and 12. FIG. 11 is a schematic view showing the configuration of the main mechanism of the image forming apparatus, and FIG. 12 is a schematic plan view of the main part of the main mechanism.

[Configuration of Image Forming Apparatus]
As shown in FIGS. 11 and 12, the image forming apparatus 100 according to the present embodiment is a serial type image forming apparatus, and as shown in FIG. 12, guide members horizontally mounted on left and right side plates (not shown). The guide rod 101 and the guide rail 102 hold the carriage 103 slidably in the main scanning direction. In this holding state, the main scanning motor 104 moves and scans the carriage 103 in the direction indicated by the arrow (main scanning direction) via the timing belt 105 spanned between the driving pulley 106A and the driven pulley 106B.

  In this carriage 103, for example, droplet discharge heads 107k, 107c, 107c, 107c of the present embodiment that discharge recording liquid droplets of each color of black (K), cyan (C), magenta (M), and yellow (Y). The recording head 107 constituted by 107m and 107y is arranged in the direction along the main scanning direction, and is mounted with the droplet discharge direction facing downward. Here, although the independent droplet discharge heads 107k, 107c, 107m, and 107y are used, the present application is not limited to this. For example, a configuration using one or a plurality of heads having a plurality of nozzle rows for discharging recording liquid droplets of each color may be employed. Further, the number of colors and the arrangement order are not limited to this. The carriage 103 is also equipped with a sub tank 108 for each color for supplying droplets of each color to the recording head 107. As shown in FIG. 11, the sub tank 108 is supplied with recording liquid from a main tank (ink cartridge, not shown) via a recording liquid supply tube 109.

  On the other hand, as shown in FIG. 11, the main body of the image forming apparatus 100 includes a paper feed cassette 110 including a paper stacking section (pressure plate) 111 on which recording media (hereinafter referred to as “paper”) 112 are stacked, and this paper feed. A paper feeding unit for feeding paper 112 from the cassette 110. The paper feeding unit includes a half-moon roller (hereinafter referred to as “paper feeding roller”) 113 that separates and feeds paper 112 from the paper stacking unit 111 one by one, and a material having a large friction coefficient facing the paper feeding roller 113. And a separation pad 114 made of The separation pad 114 is urged toward the paper feed roller 113 by urging means (not shown).

  A transport unit is provided for transporting the paper 112 fed from the paper feed unit below the recording head 107. As the conveyance unit, a conveyance belt 121, a counter roller 122, a conveyance guide 123, a pressure roller 125A, a tip pressure roller 125B, and a charging roller 126 are provided.

  The transport belt 121 is for electrostatically attracting and transporting the paper 112 fed from the paper feed unit. The counter roller 122 is for conveying the paper 112 fed from the paper supply unit via the guide 115 with the conveyance belt 121 interposed therebetween. The conveyance guide 123 is for causing the paper 112 fed substantially vertically upward by the counter roller 122 and the conveyance belt 121 to change the direction by approximately 90 ° and to follow the conveyance belt 121. The pressure roller 125 </ b> A and the tip pressure roller 125 </ b> B are urged toward the transport belt 121 by the pressing member 124. The charging roller 126 is a charging unit for charging the surface of the conveyance belt 121.

  Here, the conveyance belt 121 is an endless belt, and is stretched between the conveyance roller 127 and the tension roller 128. The conveyance roller 127 is configured to rotate in the belt conveyance direction (sub-scanning direction) by being rotated from the sub-scanning motor 131 via the timing belt 132 and the timing roller 133. Note that a guide member 129 is disposed on the back surface side of the conveyor belt 121 in correspondence with an image forming area formed by the recording head 107. The charging roller 126 is arranged so as to contact the surface layer of the conveyor belt 121 and rotate following the rotation of the conveyor belt 121, and applies 2.5N to both ends of the shaft as a pressing force.

  The image forming apparatus 100 further includes a paper discharge roller 152 and a paper discharge unit as a paper discharge unit for discharging the paper 112 recorded by the recording head 107 as a separation unit for separating the paper 112 from the conveyance belt 121. A roller 153 and a paper discharge tray 154 for stocking the paper 112 to be discharged are provided. A double-sided paper feeding unit 155 is detachably attached to the back of the image forming apparatus 100. The double-sided paper feeding unit 155 takes in and reverses the paper 112 returned by the reverse rotation of the transport belt 121 and feeds it again between the counter roller 122 and the transport belt 121.

As shown in FIG. 12, the image forming apparatus 100 further includes a maintenance / recovery mechanism 156 for maintaining and recovering the nozzle state of the recording head 107 in the non-printing area on one side of the carriage 103 in the scanning direction. It is arranged. The maintenance / recovery mechanism 156 discharges the thickened recording liquid by a plurality of caps 157 for capping each nozzle surface of the recording head 107, a wiper blade 158 as a blade member for wiping the nozzle surface, and the like. And a blank discharge receptacle 159 for receiving droplets when performing blank discharge for discharging droplets that do not contribute to recording.
Hereinafter, in the image forming apparatus 100 configured as described above, the sheets 112 are separated and fed one by one from the sheet feeding unit, and the sheet 112 fed substantially vertically upward is guided by the guide 115. Thereafter, the paper 112 is sandwiched between the transport belt 121 and the counter roller 122 and transported, and further, the leading end is guided by the transport guide 123 and pressed against the transport belt 121 by the front end pressure roller 125B, and the transport direction is approximately 90 °. To be converted.

  At this time, a positive voltage and a negative output are alternately applied to the charging roller 126 from an AC bias supply unit (not shown) by a control circuit (not shown), that is, an alternating voltage is applied. This voltage is a charging voltage pattern in which the conveyor belt 121 alternates, that is, a positive and a negative are alternately charged in a strip shape with a predetermined width in the sub-scanning direction that is the circumferential direction. When the sheet 112 is fed onto the conveyance belt 121 charged with the plus and minus alternately, the sheet 112 is attracted to the conveyance belt 121 by electrostatic force, and the sheet 112 is moved in the sub-scanning direction by the circumferential movement of the conveyance belt 121. To be transported.

  Therefore, by driving the recording head 107 according to the image signal while moving the carriage 103 in the forward and backward directions, droplets are ejected onto the stopped paper 112 to record one line. After carrying a predetermined amount, the next line is recorded. When the recording end signal or the signal that the rear end of the paper 112 reaches the recording area is received, the recording operation is finished, and the paper 112 is discharged onto the paper discharge tray 154.

  In the case of double-sided printing, when recording on the front surface (first printed surface) of the paper 112 is completed, the transported belt 121 is rotated in the reverse direction so that the recorded paper 112 is stored in the double-sided paper feed unit 155. And the paper 112 is reversed (the back side becomes the print side). The reversed paper 112 is fed again between the counter roller 122 and the transport belt 121, and the timing is controlled. After the paper 112 is transported onto the transport belt 121 and recorded on the back surface as described above, The paper is discharged to a paper discharge tray 154.

  During printing (recording) standby, the carriage 103 is moved to the maintenance / recovery mechanism 156 side, the nozzle surface of the recording head 107 is capped by the cap 157, and the nozzles are kept in a wet state. Prevents ejection failures due to drying. In the state where the recording head 107 is capped with the cap 157, the recording liquid is sucked from the nozzle (referred to as “nozzle suction” or “head suction”), and a recovery operation is performed to discharge the thickened recording liquid and bubbles. By this recovery operation, wiping is performed by the wiper blade 158 in order to clean and remove the droplets adhering to the nozzle surface of the recording head 107. In addition, an empty discharge operation is performed to discharge droplets not related to recording before starting recording or during recording. Thereby, the stable ejection performance of the recording head 107 is maintained. Further, when resuming printing, by using the voltage control method as described above, droplets are ejected from the droplet ejection heads 107k, 107c, 107m, and 107y, thereby suppressing wasteful ejection and the like. Thus, printing can be continued while maintaining good discharge characteristics.

  As described above, the image forming apparatus 100 according to the fifth embodiment of the present application includes the liquid discharge head according to the present application and applies the voltage control method according to the present application. It becomes possible to stabilize and excellent printing can be continued. Further, wasteful consumption of the recording liquid can be suppressed and cost can be improved. In the fifth embodiment, the present application is described as an example in which the present application is applied to an image forming apparatus having a printer configuration. However, the present invention is not limited to this. For example, an image forming apparatus such as a facsimile, a copying apparatus, a plotter, and a multifunction machine including these. Can be applied to. Further, the present invention can also be applied to an image forming apparatus using a fixing processing liquid that is a liquid other than the recording liquid.

  Examples 1 to 5 described above are examples, and the present application is not limited to these examples. Any configuration that can stabilize the ejection characteristics before and after the interruption of droplet ejection can solve the problems of the present application. In each of the above embodiments, the droplet discharge head that discharges the recording liquid is shown as the droplet discharge head according to the present application. However, the droplet discharge head is not limited to this. The present invention may be applied to a liquid droplet ejection head that ejects a liquid other than the recording liquid, for example, a liquid resist for patterning, a liquid droplet ejection head that ejects a gene analysis sample, and the like.

100 Image forming apparatus 107, 107k, 107c, 107m, 107y Droplet discharge head 301 Pressurizing chamber (liquid chamber)
400 Electromechanical transducer 401 Actuator substrate 402 Film formation diaphragm (vibration plate)

Japanese Patent Laid-Open No. 2003-34148 JP 2007-136989 A Japanese Patent No. 4218083 Japanese Patent No. 4857575 JP 2012-2104018 A JP 2012-196881A

Claims (9)

A nozzle for discharging droplets;
A liquid chamber communicating with the nozzle;
A diaphragm provided on the liquid chamber;
An electromechanical transducer that is provided on the diaphragm and generates pressure fluctuations in the liquid chamber by vibrating the diaphragm; and
A voltage waveform exceeding a positive coercive electric field is applied to the electromechanical conversion element to discharge the droplet from the nozzle, and before the start of discharging the liquid droplet, it falls below a portion exceeding the positive coercive electric field. A voltage waveform that does not cause the droplets to be ejected is applied to the electromechanical transducer ,
By applying a voltage waveform up to a negative bias in a range not exceeding a negative coercive electric field with respect to the polarization direction of the electromechanical transducer, the liquid droplets are discharged from the nozzle and the liquid droplets are not discharged. A droplet discharge head characterized by applying a negative bias even when a voltage waveform is applied . As the voltage waveform that does not discharge the droplet, a voltage is applied to the electromechanical transducer in a range from a negative bias in a range not exceeding a negative coercive field of the electromechanical transducer to a maximum positive power supply voltage that can be applied. The droplet discharge head according to claim 1 , wherein the droplet discharge head is applied. A voltage waveform in which the rising speed of the voltage that is displaced toward the droplet discharge side of the voltage waveform that does not discharge the droplet is slower than the rising speed of the voltage of the discharge waveform when the droplet is discharged. droplet discharge head according to claim 1 or 2, characterized in that. A voltage waveform that makes the rising speed and falling speed of the voltage waveform that does not discharge the droplets slower than the rising speed and falling speed of the voltage of the discharge waveform when discharging the droplet, respectively. applying the liquid droplet ejection head according to any one of claims 1 to 3, characterized in that. As the voltage waveform that does not eject the liquid droplet, the liquid droplet ejection head according to any one of claims 1 to 4, wherein applying a triangular waveform. A voltage control method for a droplet discharge head including an electromechanical conversion element that generates pressure fluctuations in a liquid chamber communicating with a nozzle by vibrating a diaphragm,
Applying a voltage waveform exceeding the coercive electric field on the positive side to the electromechanical conversion element of the droplet discharge head, and discharging the droplet;
When there is an interruption time between the end of discharge and the start of discharge when discharging is started, before the discharge, there are a portion that exceeds the positive coercive electric field and a portion that is below the coercive field. Applying a voltage waveform that is not discharged to the electromechanical transducer,
In the step of discharging the droplet, the droplet is discharged from the nozzle by applying a voltage waveform up to a negative bias within a range not exceeding a negative coercive electric field with respect to the polarization direction of the electromechanical transducer. ,
A voltage control method comprising applying a voltage waveform up to a negative bias with respect to a polarization direction of the electromechanical transducer in the step of applying a voltage waveform that does not cause the droplet to be ejected . In response to the interruption time until the start discharged from the discharge end of the droplet from the liquid droplet ejection head, in claim 6, characterized in that to change the time for applying a voltage waveform that does not eject the droplets The voltage control method as described. A voltage is applied to the electromechanical conversion element up to a reverse bias, and the droplet is ejected.At the end of voltage application, after applying a positive bias with respect to the polarization direction of the electromechanical conversion element, The voltage control method according to claim 6 or 7 , wherein the voltage application to the electromechanical conversion element is terminated. A droplet discharge head according to any one of claims 1 to 5 , wherein the droplet discharged from the droplet discharge head using the voltage control method according to claims 6 to 8 is a deposition medium. An image forming apparatus characterized by being landed on top.