JP2015013370A - Droplet discharge head and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a droplet discharge head capable of easily lowering the viscosity of a liquid such as a thickened ink and of reducing the frequency of maintenance by suction or the consumption of the liquid, and to provide an image formation device.SOLUTION: A droplet discharge head is composed of a nozzle plate 1 having nozzles 2, pressure chambers 3, actuator substrates 4, piezoelectric elements 6, diaphragms 5, common liquid chambers 8, frame plates 7, supply ports 9, a driving IC 10, fluid resistance parts 12, sub-frame plates 13, various wirings and the like. The driving IC 10 applies to the piezoelectric element 6, a pulse waveform in which an intermediate potential higher than that used in a drive waveform at the time when the droplet is discharged is retained as a heating waveform before the start of droplet discharge from the nozzles 2, to heat the inside of the pressure chamber 3.

Description

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

  In image forming apparatuses such as printers, facsimiles, copiers, plotters, and multi-function machines, a liquid discharge apparatus that mounts a liquid droplet discharge head for discharging liquid droplets such as recording liquid and forms an image on a recording medium is provided. Is known. The droplet discharge device is also called a recording medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics (attached medium, recording medium, transfer paper, paper, etc.). Is used as a synonym regardless of the material.) Means a device that ejects droplets. In addition, “image formation” not only applies an image having a meaning such as a character or a figure to a recording medium, but also applies an image having no meaning such as a pattern to the recording medium. Meaning, recording, printing, printing, and printing are also used synonymously.

  As such a droplet discharge head, a piezoelectric material such as a piezoelectric element is used in a pressure chamber (also referred to as an ink flow path, a pressurized liquid chamber, a pressurized 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 this droplet discharge head, an intermittent discharge operation is performed in which a droplet is not discharged for a predetermined period after the droplet is discharged, and then the droplet is discharged again. In this intermittent nozzle that is not ejecting droplets, ink thickening may occur around the ink surface (hereinafter referred to as “meniscus surface”) due to drying. Due to this thickening, sufficient droplet ejection cannot be performed, which may affect image quality.

  In order to prevent such effects of ink thickening, there are already known methods such as stirring the ink in the pressure chamber by fine driving of the thin film piezoelectric body, and methods for forcibly discharging the thickened ink to the outside. (For example, refer to Patent Document 1). In Patent Document 1, the pressure chamber is agitated by fine driving of the thin film piezoelectric body, the thickened ink near the meniscus surface of the nozzle hole is drawn into the pressure chamber, and the operation of pushing out the ink in the pressure chamber to the nozzle hole side is repeated. . As a result, the ink viscosity in the vicinity of the nozzle and the pressure chamber is averaged to reduce the meniscus surface viscosity. Further, the meniscus surface is refreshed by discharging the thickened ink in the vicinity of the nozzle holes to the outside and moving the ink in the pressure chamber to the nozzle side every predetermined period.

  However, only by reducing the viscosity of the meniscus surface by such conventional stirring, the viscosity of the entire pressure chamber gradually increases, and even when the thin film piezoelectric body is driven to resume discharge, the discharge force is insufficient. Sufficient discharge cannot be performed. As a result, refreshing the meniscus surface during idle maintenance and empty ejection are frequently required, and it is necessary to discharge ink not only in the vicinity of the nozzle but also in the entire pressure chamber, which wastes ink. .

  On the other hand, it has been proposed to provide heating means in each pressure chamber of the droplet discharge head to adjust the temperature of ink in the droplet discharge head (see, for example, Patent Documents 2 and 3). In Patent Document 2, when a droplet is ejected from a nozzle hole, a driving waveform for ejecting the droplet is applied to the piezoelectric body. Then, when ink is not ejected, a driving waveform in which droplets are not ejected from the nozzle holes, and a heating driving waveform having a frequency twice or more the resonance frequency of the pressure chamber is applied to the piezoelectric body. The ink in the room is heated. However, Patent Document 2 is intended to maintain the ink temperature in the pressure chamber at a predetermined temperature by heating, and is not intended to eliminate local thickening due to drying of the meniscus surface.

  On the other hand, in Patent Document 3, for the purpose of eliminating local thickening in the vicinity of the nozzle hole, the piezoelectric body is driven to such an extent that droplets are not ejected from the nozzles during non-ejection, and pressure is applied immediately before droplet ejection. A method of heating ink from a chamber to a nozzle hole within a range in which the ink does not boil and is not discharged from the nozzle hole is disclosed. However, in this case, vibration of the piezoelectric body and heating by the heating means are required, which is troublesome, and since the heating means is provided for each nozzle, the number of parts and the number of wirings are increased. The configuration of the head is also complicated.

  The present invention has been made in view of the above circumstances, and the viscosity of a thickened liquid is complicated during intermittent operation of droplet discharge such as when the power is turned on or when printing is not performed for a long period of time. By enabling easy lowering without requiring a special configuration and effort, printing can be resumed smoothly, and maintenance frequency and liquid consumption can be reduced by suction. It is an object to provide a droplet discharge head and an image forming apparatus including the 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 pressure chamber communicating with the nozzle, a diaphragm provided on the pressure chamber, and a diaphragm. A thin film piezoelectric body that changes the volume in the pressure chamber by vibrating the diaphragm, and a drive control means that applies a drive waveform for discharging droplets to the thin film piezoelectric body. Before starting the discharge of droplets from the nozzle, a pulse waveform holding an intermediate potential higher than the intermediate potential used in the drive waveform for droplet discharge is applied to the thin film piezoelectric body as a heating waveform. Is heated.

  According to the present invention, the viscosity of the thickened liquid can be reduced without requiring a complicated configuration or trouble at the time of intermittent operation of the liquid droplet protrusion, such as when the power is turned on or when printing is not performed for a long period of time. It can be easily lowered. Therefore, it is possible to smoothly resume printing, reduce the frequency of maintenance by suction, and reduce the amount of liquid consumption, and an image including this droplet discharge head A forming apparatus can be provided.

It is sectional drawing which shows the structural example of the droplet discharge head which concerns on embodiment of this application. FIG. 2 is a plan view in which a frame is omitted from the droplet discharge head of FIG. 1. FIG. 2A is a cross-sectional view illustrating a configuration example of a piezoelectric body, and FIG. 2B is a plan view of a state in which a part of a first insulating protective film and a second insulating protective film are omitted. It is a graph which shows the voltage and application time of the heating waveform in Example 1. FIG. It is a graph which shows the voltage and application time of the heating waveform in Example 2. FIG. It is a graph which shows the voltage and application time of the heating waveform in Example 3. It is a graph which shows the voltage and application time of the heating waveform in Example 4. It is a graph which shows the change of the viscosity with time of the meniscus surface in Examples 1-4. It is a graph which shows the change of the viscosity with time of the meniscus surface in a comparative example. FIG. 10 is a schematic diagram illustrating a configuration of a main mechanism in an image forming apparatus according to a fifth embodiment. 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. A droplet discharge head according to an embodiment of the present application includes a nozzle that discharges droplets, a pressure chamber that communicates with the nozzle, a diaphragm provided on the pressure chamber, and a diaphragm provided on the diaphragm. A thin film piezoelectric body that changes the volume in the pressure chamber by being oscillated, and a drive control unit that applies a drive waveform for discharging droplets to the thin film piezoelectric body are configured. The drive control means applies, as a heating waveform, a pulse waveform that holds an intermediate potential higher than the intermediate potential used in the drive waveform for droplet ejection to the thin film piezoelectric body before the start of droplet ejection from the nozzle. Then, the pressure chamber is heated.

  By applying such a heating waveform, the charge / discharge current becomes higher than when droplet discharge is driven, the heat generation of the thin film piezoelectric body increases, and the entire droplet discharge head is heated. Therefore, even if the moisture in the liquid decreases and thickens due to drying during intermittent ejection, the liquid becomes viscous by heating due to the temperature dependence of the solvent of the liquid. Therefore, the viscosity of the dried portion in the vicinity of the meniscus surface can be lowered and the printing can be resumed smoothly by simply applying the heating waveform without requiring a complicated configuration or trouble. Further, it is possible to reduce the amount of liquid consumption by reducing the frequency of maintenance by suction.

  In addition, it is desirable that the heating waveform is a pulse waveform that is applied with a voltage width equal to or greater than the peak value of the drive waveform during droplet ejection. The peak value of the drive waveform refers to the voltage width from the intermediate potential to the lowest voltage at the time of pulling. As a result, the amount of charge / discharge current is further increased, the heat generation from the thin film piezoelectric body is further increased, the entire droplet discharge head is heated well, and the viscosity of the liquid in the droplet discharge head is reduced in a short time. It becomes possible.

  Further, it is desirable to apply a pulse waveform at the anti-resonance frequency of the meniscus surface of the nozzle as the heating waveform. As a result, it is possible to heat the liquid inside the pressure chamber without stirring, and it becomes easy to heat the entire pressure chamber, and it is possible to easily reduce the viscosity of the liquid in the droplet discharge head. Become.

  In addition, it is desirable that the heating waveform has a rise time and a fall time of the pulse waveform that are equal to or shorter than the rise time and the fall time of the drive waveform during liquid ejection. This increases the amount of charge / discharge current, increases the amount of heat generated from the thin film piezoelectric body, and enables heating in a short time.

  In addition, an image forming apparatus according to an embodiment of the present application includes the above-described droplet discharge head, and is configured to land droplets discharged from the droplet discharge head on a deposition medium. Therefore, even during intermittent operation of droplet protrusion, such as when the power is turned on or when printing has not been performed for a long period of time, the viscosity of the thickened liquid can be easily adjusted without requiring a complicated configuration or labor. Can be lowered. Therefore, it is possible to obtain an image forming apparatus capable of smoothly restarting printing and maintaining excellent image quality even during intermittent operation. In addition, it is possible to reduce the amount of liquid consumption by reducing the frequency of maintenance by suction.

  Embodiments and comparative examples relating to the droplet discharge head of the present application will be described below with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a configuration example of a droplet discharge head according to an embodiment of the present application. FIG. 2 is a plan view of the liquid droplet ejection head of FIG. 1, with the subframe omitted. FIG. 3A is a cross-sectional view showing a configuration example of the piezoelectric element used in the embodiment, and FIG. 3B is a view of the piezoelectric element in a state where a part of the first insulating protective film and the second insulating protective film are omitted. It is a top view.

[Configuration of droplet discharge head]
As shown in FIG. 1, a droplet discharge head according to an embodiment of the present invention includes a nozzle plate 1 having a nozzle 2 for discharging droplets, a pressure chamber 3 in which the nozzle 2 communicates, and an actuator provided with the pressure chamber 3. The substrate 4, the piezoelectric element 6 as a thin film piezoelectric body that pressurizes the liquid in the pressure chamber 3, the diaphragm 5 provided between the piezoelectric element 6 and the pressure chamber 3, the common liquid chamber 8, and the common liquid chamber 8 are configured. A frame plate 7 that communicates with the ink tank (not shown), a supply port 9 that supplies liquid to the common liquid chamber 8, a driving IC 10 that controls driving of the piezoelectric element 6, and ink in the pressure chamber 3. Are provided with a fluid resistance 12 that also serves as a supply path for supplying gas, a subframe plate 13 that accommodates the piezoelectric element 6, various wirings (see FIG. 2), and the like.

(Configuration of nozzle plate 1 and nozzle 2)
The nozzle plate 1 is a substrate on which nozzles 2 for discharging droplets are arranged, and is formed from a resin, a metal material, or the like. As shown in FIG. 1, the nozzle 2 communicates with the pressure chamber 3, and discharges the liquid in the pressure chamber 3 to the outside as droplets. A plurality of nozzles 2 are arranged on both sides of the nozzle plate 1 in the short direction (left-right direction in FIG. 1) via the driving IC 10 in the longitudinal direction (front-rear direction in FIG. 1). That is, nozzle rows (not shown) made up of a plurality of nozzles 2 are arranged in two rows in the longitudinal direction of the nozzle plate 1.

  Further, the nozzle plate 1 is formed such that the longitudinal dimension is longer than the dimension of the actuator substrate 4. Thereby, at both ends in the longitudinal direction of the nozzle plate 1, as shown in FIG. 2, extending portions 1 a (only one is shown, the other is not shown) protruding from the end of the actuator substrate 4 are formed. Yes.

  On the extended portion 1a, as shown in FIG. 2, a wiring end portion 14a of an FPC (flexible wiring board) 14 for wiring connection is disposed. A plurality of wiring terminals 14b are arranged in parallel on the surface of the wiring end portion 14a. Further, a backing plate (not shown) is fixed to the back surface of the wiring end portion 14a, and the wiring end portion 14a of the FPC 14 is attached on the extending portion 1a.

(Configuration of actuator substrate 4)
The actuator substrate 4 is formed of a laminated body of glass or a thin metal plate, a silicon substrate, or the like. As a material for the actuator substrate 4, 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 examples, a single crystal substrate mainly having a (100) plane orientation was mainly used. Further, when the pressure chamber 3 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 the embodiment, it is 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.

(Configuration of pressure chamber 3)
A plurality of pressure chambers 3 are formed on the actuator substrate 4. As shown in FIG. 2, each pressure chamber 3 is formed in an elongated shape that is long in the short direction of the actuator substrate 4 (the left-right direction in FIG. 2). The pressure chambers 3 are arranged at equal pitches on both sides of the actuator substrate 4 in the short direction (left-right direction in FIG. 2) and in the longitudinal direction (up-down direction in FIG. 2) via the driving IC 10. And a plurality of rows of pressure chambers 3 are formed.

  As shown in FIG. 1, on both sides of the actuator substrate 4 in the short direction, individual flow paths 3 a that communicate with the pressure chamber 3 and supply liquid into the pressure chamber 3 are formed. As shown in FIG. 2, a plurality of the individual flow paths 3a are arranged in the longitudinal direction on both sides in the short direction of the actuator substrate 4 to form two rows of individual flow paths 3a.

  In addition, the actuator substrate 4 is formed with a fluid resistance 12 that communicates with the pressure chamber 3 and the individual flow path 3 a and supplies a liquid from the individual flow path 3 a to the pressure chamber 3. The fluid resistance 12 has a small cross-sectional area and is configured to limit the flow rate of the liquid flowing from the individual flow path 3a to the pressure chamber 3. When the actuator substrate 4 is formed of a silicon single crystal substrate or the like, as described above, the pressure chamber 3, the individual flow path 3a, the fluid resistance 12 and the like can be formed by etching.

  Further, as shown in FIG. 1, the nozzle plate 1 is joined to one side of the actuator substrate 4 (the lower side in FIG. 1), and the open ends of the pressure chamber 3, the individual flow path 3a, and the fluid resistance 12 are The nozzle plate 1 is closed. A thin film-like diaphragm 5 is disposed on the other surface side of the actuator substrate 4 (upper side in FIG. 1), and the other end side of the pressure chamber 3 is closed by the diaphragm 5.

(Configuration of diaphragm 5)
The vibration plate (film formation vibration plate) 5 receives a force generated by the piezoelectric element 6 and is deformed and displaced to change the volume of the pressure chamber 3, thereby discharging a droplet from the nozzle 2. Therefore, it is preferable that the diaphragm 5 of the first embodiment shown in FIG. 3 has a predetermined strength. Examples of the material of the diaphragm 5 include silicon Si, silicon dioxide SiO ₂ , and silicon nitride Si ₃ N ₄ , and those prepared using the diaphragm 5 by a CVD method (Chemical Vapor Deposition).

It is preferable to select a material close to the linear expansion coefficient of the first electrode 601 and the electromechanical conversion film 602 (see FIG. 3) as a lower electrode, which will be described later, for the diaphragm 5. In particular, the electromechanical conversion film 602 generally uses PZT (Pb (Zr, Ti) O, zirconate-lead titanate) as a material. From this, the material of the diaphragm 5 had a linear expansion coefficient of 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ as a linear expansion coefficient close to 8 × 10 ⁻⁶ (1 / K). A material is preferable, and a material having a linear expansion coefficient of 7 × 10 ^{−6 to} 9 × 10 ⁻⁶ is more preferable.

Specific materials for the diaphragm 5 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 , oxide Examples thereof include rhenium ReO ₂ , rhodium oxide Rh ₂ O ₃ , palladium oxide PdO, and compounds thereof. The diaphragm 5 can be produced with a spin coater using a sputtering method or a Sol-gel method. The film thickness of the diaphragm 5 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 will be difficult to process the pressure chamber 3 on the actuator substrate 4, and if it is larger than this range, the vibration plate 5 will be difficult to deform and displace, and the ejection of droplets will become unstable.

  Further, by opening the diaphragm 5, as shown in FIG. 1, the plurality of individual flow paths 3a corresponding to the plurality of pressure chambers 3 and the common liquid chamber 8 communicate with each other.

(Configuration of piezoelectric element 6)
As shown in FIG. 1, the piezoelectric element 6 is provided on the surface of the diaphragm 5 opposite to the side on which the pressure chamber 3 is provided. The piezoelectric element 6 expands and contracts when an AC voltage is applied to vibrate the vibration plate 5, and the vibration of the vibration plate 5 changes the volume of the pressure chamber 3 to apply pressure. The diaphragm 5 and the piezoelectric element 6 constitute a piezoelectric actuator. Further, as shown in FIG. 2, a plurality of piezoelectric elements 6 are arranged on both sides in the short direction of the diaphragm 5 in a straight line in the longitudinal direction to form two rows of piezoelectric elements 6. Yes.

  Hereinafter, as a specific example of the piezoelectric element 6, the configuration of an electromechanical conversion element will be described with reference to FIG. 3. As shown in FIG. 3A, the piezoelectric element 6 is formed on the upper surfaces of the actuator substrate 4 and the diaphragm (film-forming vibrator) 5 described above, and includes a first electrode 601, an electromechanical conversion film 602, and a second electrode. 603, an element configuration including a first insulating protective film 604 as a protective film, a third electrode 606 and a fourth electrode 607 (lead-out wiring), a second insulating protective film 605, and the like. The driving of the piezoelectric element 6 is performed by a driving IC 10 (see FIG. 1) in which the first electrode 601 and the second electrode 603 are connected to each other through wiring.

  As shown in FIG. 3B, the first insulating protective film 604 has a contact hole portion 608, and the first electrode 601 and the third electrode 606, and the second electrode 603 and the fourth electrode 607 are respectively It has a conductive configuration. At this time, the first electrode 601 and the third electrode 606 are used as the common electrode wiring 609, and the second electrode 603 and the fourth electrode 607 are used as the individual electrode wiring 610. A second insulating protective film 605 is formed on the upper surfaces of the common electrode wiring 609 and the individual electrode wiring 610 to protect them. The second insulating protective film 605 is partially opened (opening portion O) to form an electrode PAD. What is produced for the common electrode wiring 609 is the common electrode PAD 611, and what is produced for the individual electrode wiring 610 is the individual electrode PAD 612. A polarization process is performed between the common electrode wiring 609 and the individual electrode wiring 610 by voltage application or corona charging.

<First electrode 601>
The first electrode 601 is preferably made of a metal or a metal and an oxide. Here, in both cases, an adhesive layer (not shown) is interposed between the diaphragm 5 and the metal film for the first electrode 601 so as to suppress both peeling and the like. The details of the metal electrode film and oxide electrode film of the first electrode 601 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. Further, when platinum is used, it is preferable that the previous adhesive layer is laminated first because the adhesiveness to the diaphragm 5 (particularly SiO ₂ ) as a 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. For this reason, in order to place the (r) orientation of the SrRuO ₃ film (also referred to as SRO film formation) in accordance with the platinum Pt (111) of the first electrode 601 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 609, and sufficient current cannot be supplied as the common electrode wiring 609. This is not preferable because a problem occurs when droplets are ejected.

<Electromechanical conversion film 602>
As a material for the electromechanical conversion film 602, 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 602, 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 602 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 laminated.

  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 603>
The second electrode 603 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 and the like of the oxide electrode film are as described for the oxide electrode film used in the first electrode 601. 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 601. The film thickness is preferably 30 nm to 200 nm, and more preferably 50 nm to 120 nm. When the film thickness is smaller than this range, it is not preferable because a sufficient current cannot be supplied as the individual electrode wiring 610 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 insulating protective film 604>
The first insulating protective film 604 needs to be made of 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 piezoelectric element 6 due to the film formation / etching process. is there. An organic material is not preferable because the film thickness needs to be increased in order to obtain sufficient protection performance. When the first insulating protective film 604 is a thick film, the vibration displacement of the diaphragm 5 is remarkably hindered, resulting in a droplet discharge head having a low discharge performance.

  In order to obtain high protection performance with a thin film of the first insulating protective film 604, it is preferable to use an oxide, nitride, or carbide film, but an electrode material, 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 604 include a vapor deposition method and an ALD method (Chemical Vapor Deposition), but the ALD method is preferable in that a wide range of materials can be used.

Preferred materials for the first insulating protective film 604 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 first insulating protective film 604 needs to be thin enough to ensure the protection performance of the piezoelectric element 6 and at the same time, as thin as possible so as not to inhibit the displacement of the diaphragm 5. is there. A preferable film thickness of the first insulating protective film 604 is in a 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 piezoelectric element 6 as a protective layer is insufficient, and the performance of the piezoelectric element 6 is deteriorated as described above.

Further, the first insulating protective film 604 may have a two-layer structure. 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 603 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 604, 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 601 as the lower electrode and the individual electrode wiring 610. 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.

<Third electrode 606 and fourth electrode 607>
The material of the third electrode 606 and the fourth electrode 607 is preferably a metal electrode material made of Ag (silver) alloy, copper Cu, aluminum Al, gold Au, platinum Pt, or iridium Ir. As a method for manufacturing the third electrode 606 and the fourth electrode 607, 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 606 and the fourth electrode 607 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. Further, when the common electrode wiring 609 and the individual electrode wiring 610 are used, the contact resistance at the contact hole portion 608 (10 μm × 10 μm) is preferably 10Ω or less as the common electrode wiring 609 and 1Ω as the individual electrode wiring 610. The following is preferred. Further, the common electrode wiring 609 is more preferably 5Ω or less, and the individual electrode wiring 610 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 605>
The second insulating protective film 605 is a passivation layer that functions as a protective layer for the individual electrode wiring 610 and the common electrode wiring 609. As shown in FIG. 3, the upper surface of the individual electrode wiring 610 and the common electrode wiring 609 is covered with a second insulating protective film 605 except for the leading portion of the individual electrode wiring 610 and the leading portion of the common electrode wiring 609 (not shown). Cover. 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 the material of the second insulating protective film 605, 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.

  The thickness of the second insulating protective film 605 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 605 preferably has a structure having an opening O on the piezoelectric element 6 and the surrounding diaphragm 5 (see FIG. 3A). This is the same reason that the pressure chamber region of the first insulating protective film 604 is thinned. As a result, a highly efficient and highly reliable droplet discharge head can be obtained.

The opening O can be formed by using a photolithography method and dry etching because the piezoelectric element 6 is protected by the first insulating protective film 604 and the second insulating protective film 605. 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.

(Wiring configuration)
The wiring is formed on the surface of the diaphragm 5 opposite to the surface on which the pressure chamber 3 is provided. As this wiring, as shown in FIG. 2, a Com wiring 15 extending in the longitudinal direction along the both lateral edges of the diaphragm 5 is formed by etching or the like. A plurality of piezoelectric elements 6 are connected to the Com wiring 15.
ing.

As shown in FIG. 2, an input terminal 15 a that branches from the Com wiring 15 is formed at the longitudinal end of the diaphragm 5. In addition, a pair of Vcom wirings 16 is formed near the center of the end of the diaphragm 5. Further, the Vcom wiring 16 is formed with a plurality of input terminals 16 a branched from the Vcom wiring 16. A plurality of input terminals 17 positioned between the input terminals 16 a of the pair of Vcom wires 16 are further formed at the end of the diaphragm 5. These input terminals 15a, 16a,
Reference numeral 17 denotes a bonding connection (wire bonding) to a plurality of wiring terminals 14b provided on the wiring end portion 14a of the FPC 14 by bonding wires (not shown).

(Configuration of subframe plate 13)
As shown in FIG. 1, the subframe plate 13 is bonded or fixed on the diaphragm 5. The sub-frame plate 13 is formed with a plurality of vibration allowing recesses 13a for accommodating the respective piezoelectric elements 6 in the rows of the piezoelectric elements 6 formed in two rows in the short direction. The plurality of vibration allowing recesses 13a are formed in substantially the same shape as the pressure chambers 3 that are long in the lateral direction, and are provided so as to coincide with the positions of the pressure chambers 3 in the vertical direction and to overlap each other.

  As shown in FIG. 1, the subframe plate 13 has an arrangement space 13 b elongated in the longitudinal direction at the center in the lateral direction. In this arrangement space 13b, a driving IC (driver integrated circuit) 10 fixed on the diaphragm 5 is arranged as a control device (control unit, control circuit). The driving IC 10 is sealed with the underfill agent 11 so that the back surface side does not come into contact with other components.

  The driving IC 10 is wired to one end of each piezoelectric element 6 and further connected to input terminals 16a and 17 so as to drive and control the piezoelectric element 6 on the diaphragm 5 (see FIG. 2). ).

(Configuration of frame plate 7)
As shown in FIG. 1, the frame plate 7 is bonded or fixed onto the subframe plate 13. On both sides of the subframe plate 13 and the frame plate 7 in the short direction, the subframe plate 13 and the frame plate 7 are straddled as shown in FIG. 1 outside the row of the piezoelectric elements 6 arranged in two rows. As described above, a pair of common liquid chambers 8 is formed. The pair of common liquid chambers 8 are elongated in the longitudinal direction along the arrangement direction of the rows of individual flow paths 3a arranged in the longitudinal direction. In the frame plate 7, supply ports 9 that communicate with the respective common liquid chambers 8 are formed in portions corresponding to the respective rows of the piezoelectric elements 6, as shown in FIG. 1. Each supply port 9 is provided in the frame plate 7 so as to be positioned at, for example, the approximate center in the extending direction (longitudinal direction) of each row of the piezoelectric elements 6 or the end side.

[Production example of droplet discharge head]
Next, a procedure for manufacturing a droplet discharge head 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 as an adhesion film as the first electrode 601 by a sputtering apparatus. 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 602, 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, dried at 120 ° C., and then thermally decomposed at 500 ° C. 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 603, and a Pt film (film thickness: 125 nm) was formed as a metal film by sputtering. Thereafter, a photoresist (TSMR8800) manufactured by Tokyo Ohka Co., Ltd. was formed by spin coating, a resist pattern was formed by ordinary photolithography, and then a pattern was prepared using an ICP etching apparatus (manufactured by Samco).

Next, as the first insulating protective film 604, 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, a contact hole portion 608 is formed by etching. Next, AL was sputtered as the third electrode 606 and the fourth electrode 607, and was patterned by etching. Further, as the second insulating protective film 605, Si ₃ N ₄ was formed to a thickness of 500 nm by plasma CVD, and the piezoelectric element 6 was manufactured. At this time, 25 areas of 30 mm × 10 mm square in a 6 inch wafer were arranged.

  The sub-frame plate 13 (see FIG. 1) provided with an opening for forming a part of the common liquid chamber 8 (see FIG. 1) was adhesively bonded to the actuator substrate 4 thus formed. As the subframe plate 13, a silicon wafer was used to form a thermal oxide film. In Example 1, 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 4.

  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 4. Moreover, the pressure chamber 3 of the silicon wafer was processed, and head assembly such as nozzle bonding was performed. Thus, a droplet discharge head as shown in FIG. 1 was produced.

<Comparative example>
In the comparative example, discharge evaluation was performed using the droplet discharge head manufactured as described above. When the evaluation was interrupted once and then discharged again, the droplet velocity (hereinafter referred to as “Vj”) was about It decreased by 4%. Thereafter, it was confirmed that Vj returned to normal as the discharge was repeated. The viscosity from the meniscus surface at this time (residual vibration measurement by laser Doppler) was observed. As a result, it was confirmed that the viscosity of the meniscus surface was as shown in FIG. 9 at the end of discharge after continuous drive, when discharge was stopped, when discharge was started again, and at the time of continuous discharge. Therefore, the decrease in Vj is considered to be due to the effect of the liquid being thickened by drying the meniscus surface (volatilization of water from the meniscus surface) during the interruption of ejection.

<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, a heating waveform as shown in FIG. 4 was applied when the liquid droplet was ejected from the liquid droplet ejection head, suspended for one hour, and restarting the ejection. As the heating waveform, the intermediate potential was made higher than the intermediate potential at the time of driving, and the peak value of the pulse was made higher than the peak value at the time of driving.

  As an example, the time interval T of the heating waveform is 3 us for the droplet discharge head in which the resonance period of the pressure chamber 3 is 5 us (μsec). The profile of the entire heating waveform at this time is shown below. The fall (Tf) time and rise (Tr) time of the heating waveform were 1 us. The intermediate potential of the heating waveform was set to 20 V higher than the intermediate potential of 15 V during driving, and the peak value was set to 20 V compared to 18 V during driving (see FIG. 4). By applying such a heating waveform for 30 seconds, the entire droplet discharge head was heated, and the viscosity of the ink in the pressure chamber 3 decreased. When Vj was measured by applying a drive waveform after the heating waveform, it was confirmed that the Vj reduction rate could be reduced to 2% or less.

<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, the heating waveform as shown in FIG. 5 was applied when the liquid ejection from the liquid droplet ejection head was interrupted for 1 hour and the ejection was resumed. In this heating waveform, the intermediate potential is set to 20 V, the peak value is set to 18 V, which is the same as that of the driving waveform, and the resonance period of the pressure chamber 3 is 5 us. The same experiment as 1 was performed. At this time, a result equivalent to that in Example 1 (Vj reduction rate was reduced to 2% or less, and the same in the following examples) was obtained with a waveform application time of 20 sec.

<Example 3>
Next, the droplet discharge control of the third embodiment using the droplet discharge head will be described with reference to FIG. In Example 3, as shown in FIG. 6, the conditions were the same as those in Example 2 except that Tr and Tf of the heating waveform were changed from 1 us to 0.8 us. Under these conditions, the same experiment as in Examples 1 and 2 was performed, and the same effects as in the other examples could be obtained.

<Example 4>
Next, the droplet discharge control of the fourth embodiment using the droplet discharge head will be described with reference to FIG. In Example 4, as shown in FIG. 7, the conditions were the same as those in Example 4 except that the peak value of the heating waveform was changed from 18 V to 20 V under the same conditions as in Example 3. Under these conditions, the same experiment as in Examples 1 and 2 was performed, and the same effects as in the other examples could be obtained.

  Table 1 below shows the application time of the heating waveform required to obtain the same result as in Example 1 for each of the above Examples. Table 1 also shows the charge / discharge currents and the heat generation amounts of Examples 2 to 4 when the charge / discharge current and the heat generation amount of Example 1 are set to be “1”, respectively. The charge / discharge current was calculated from the heating waveform applied as described above in each example based on the electrostatic capacitance of the piezoelectric element 6, and the calorific value was calculated from that.

  In addition, as a confirmation experiment, a change in the viscosity of the meniscus surface with the heating waveform in each example was measured. As a measurement method, in each Example, the heating waveform was applied as described above, and the meniscus vibration on the nozzle surface was measured using a laser Doppler interferometer, whereby the viscosity was calculated from the vibration behavior. The measurement results are shown in FIG. As shown in FIG. 8, when the heating waveform in Example 1 was applied for 30 seconds and the viscosity of the heating waveform in Examples 2 to 4 was used as a reference, the time to reach this reference viscosity was measured. The heating waveform application time shown in FIG.

  As described above, in the liquid droplet ejection heads of the first to fourth embodiments, the pulse that is held at an intermediate potential higher than the intermediate potential used in the drive waveform at the time of droplet ejection before resuming ejection during the intermittent operation. A waveform is applied to heat the ink in the pressure chamber. Since such an ink has the property that the viscosity is lowered by heating due to the temperature dependence of the solvent, the ink viscosity is lowered by heating the ink in the pressure chamber by heat generated by the charge / discharge current. . Therefore, even when the power is turned on or when printing is not performed for a long period of time, even if the meniscus surface is dried and the moisture in the ink is reduced and thickened, the heating waveform as in each embodiment is applied. As a result, not only the ink in the pressurizing chamber but also the viscosity of the dried and thickened portion near the meniscus surface can be lowered more efficiently. As a result, printing can be resumed smoothly, and the frequency of maintenance due to suction and the amount of liquid consumption can be reduced.

<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. 10 and 11. FIG. 10 is a schematic view showing the configuration of the main mechanism of the image forming apparatus, and FIG. 11 is a schematic plan view of the main part of the main mechanism.

[Configuration of Image Forming Apparatus]
As shown in FIGS. 10 and 11, the image forming apparatus 100 according to the embodiment is a serial type image forming apparatus. As shown in FIG. 11, the image forming apparatus 100 is a guide member horizontally mounted on left and right side plates (not shown). A guide rod 101 and a 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.

  For example, a droplet discharge head 107k similar to the embodiment of the present application for discharging droplets of recording liquids of each color of black (K), cyan (C), magenta (M), and yellow (Y) is applied to the carriage 103. , 107c, 107m, and 107y are arranged in a direction along the main scanning direction, and are 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. 10, the sub tank 108 is replenished 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. 10, the main body of the image forming apparatus 100 includes a paper feed cassette 110 including a paper stacking unit (pressure plate) 111 on which an adherent medium (hereinafter referred to as “paper”) 112 is 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. 11, the image forming apparatus 100 further includes a maintenance / recovery mechanism 156 for maintaining and recovering the state of the nozzles 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.

  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.

  Accordingly, by driving the recording head 107 in accordance with the image signal while moving the carriage 103 in the forward and backward directions, droplets are ejected onto the stopped paper 112 and landed on the paper 112 to make one line. Minutes are recorded, and after the paper 112 is conveyed by 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 when the power is turned on or when printing is not performed for a long period of time, the heating waveform as described in the first to fourth embodiments is applied. Thereby, the viscosity of the recording liquid thickened by the drying of the meniscus surface can be lowered, and the liquid droplets can be smoothly discharged from the liquid droplet discharge heads 107k, 107c, 107m, and 107y. Further, operations such as nozzle suction and idle discharge can be reduced.

  As described above, the image forming apparatus 100 according to the fifth embodiment of the present application includes the liquid ejection head according to the present application, and applies the heating waveform to reduce the ink viscosity when restarting after the droplet ejection is interrupted. Therefore, printing can be resumed smoothly, and printing with excellent image quality can be continued. Further, the maintenance frequency by nozzle suction and the consumption amount of the recording liquid can be reduced, and the 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, the present invention is applied to an image forming apparatus such as a facsimile, a copying apparatus, a plotter, and a multi-function machine. Can be applied. Further, the present invention can be applied to an image forming apparatus that uses a fixing processing liquid as 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. The present invention can solve the problems of the present invention as long as the liquid viscosity can be satisfactorily lowered when the droplet discharge is interrupted and restarted. In each of the above embodiments, the droplet discharge head for discharging a recording liquid such as ink 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.

DESCRIPTION OF SYMBOLS 1 Nozzle plate 2 Nozzle 3 Pressure chamber 5 Vibrating plate 6 Piezoelectric element (thin film piezoelectric body)
10 Drive IC (drive control means)
100 Image forming apparatus 107k, 107c, 107m, 107y Droplet discharge head 112 Paper (attached medium)

Japanese Patent Laid-Open No. 9-29996 Japanese Patent No. 4645947 Japanese Patent Laid-Open No. 10-286947

Claims (5)

A nozzle for discharging droplets;
A pressure chamber communicating with the nozzle;
A diaphragm provided on the pressure chamber;
A thin film piezoelectric body provided on the diaphragm and changing the volume in the pressure chamber by vibrating the diaphragm;
Drive control means for applying a drive waveform for discharging the droplets to the thin film piezoelectric body,
The drive control means has a pulse waveform in which an intermediate potential higher than the intermediate potential used in the drive waveform for discharging the droplet is held in the thin film piezoelectric body before the start of discharging the droplet from the nozzle. Is applied as a heating waveform to heat the pressure chamber.   The heating waveform is a pulse waveform which is a peak value of the driving waveform at the time of discharging the droplet and is applied with a voltage width equal to or greater than a voltage width from the intermediate potential to the lowest voltage at the time of drawing. The droplet discharge head according to claim 1.   The droplet discharge head according to claim 1, wherein a pulse waveform is applied as the heating waveform at an anti-resonance frequency on the meniscus surface of the nozzle.   4. The heating waveform according to claim 1, wherein a rise time and a fall time of the pulse waveform are equal to or less than a rise time and a fall time of the drive waveform when the droplet is discharged. The droplet discharge head according to Item.   An image forming apparatus comprising the liquid droplet ejection head according to claim 1, wherein the liquid droplets ejected from the liquid droplet ejection head are landed on an adherend medium.