JP2013000992A - Droplet discharge head, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a discharge performance of a liquid by preventing the voltage from being applied to conductive liquid in a pressurized liquid chamber even when a bias voltage is applied to a lower part electrode.SOLUTION: A vibrating plate 30 for boosting in the pressurized liquid chamber 12 is formed by depositing a silicon oxide film, polysilicon, a silicon oxide film, a p-doped polysilicon, and a silicon oxide film in the order on the surface of a silicon substrate. The p-doped polysilicon in the vibrating plate 30 is grounded (GND). A conductive layer 31 which corresponds to the p-doped polysilicon and is grounded is provided between the lower part electrode 51 and the pressurized liquid chamber 12 in the droplet discharge head. Therefore, when a method for driving by applying the bias voltage to the lower part electrode 51 is used, an electric field is generated between the lower part electrode 51 and the conductive layer 31, and the electric field is not generated between the lower part electrode and the pressurized liquid chamber.

Description

  The present invention relates to a droplet discharge head and an image forming apparatus.

  In general, a printer, a fax machine, a copier, a plotter, or an image forming apparatus that combines a plurality of these functions includes, for example, a liquid ejection head that ejects ink droplets, and ejects ink droplets while conveying a medium. 2. Related Art There is an ink jet recording apparatus that forms an image by adhering to a sheet. The medium here is also referred to as “paper”, but the material is not limited, and a recording medium, a recording medium, a transfer material, a recording paper, and the like are also used synonymously. The image forming apparatus means an apparatus for forming an image by discharging a liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics. The image formation is not only giving an image having a meaning such as a character or a figure to the medium but also giving an image having no meaning such as a pattern to the medium (simply ejecting a droplet). Also means. The ink is not limited to so-called ink, and is not particularly limited as long as it becomes liquid when ejected. For example, the ink is a generic term for liquids including DNA samples, resists, pattern materials, and the like. Use.

  An ink jet head in an ink jet recording apparatus, which is an example of an image forming apparatus, includes a nozzle that ejects ink droplets, a pressurizing liquid chamber that communicates with the nozzle, and an actuator unit that generates energy to pressurize the pressurizing liquid chamber. I have. The actuator means is driven to boost the pressure in the pressurized liquid chamber and eject ink droplets from the nozzles. Ink-on-demand systems, which eject ink droplets only when recording is required, are the mainstream. It is. Depending on the type of actuator means for ejecting ink droplets, it is roughly classified into methods such as a piezo method, a bubble method, and an electrostatic method.

  At present, an ink jet recording apparatus adopting a piezo method is mainly used. As this piezo-type actuator means, one using a flexural vibration mode piezoelectric actuator that vibrates in the thickness direction orthogonal to the axial direction of the piezoelectric element has been put into practical use. In the ink jet recording apparatus using the piezoelectric actuator in the flexural vibration mode, the piezoelectric element flexurally vibrates with respect to the vibration plate formed on a part of the inner wall of the pressurizing liquid chamber, thereby allowing the pressurizing liquid chamber to pass through the vibration plate. Change the internal pressure. Thereby, ink droplets in the pressurized liquid chamber are ejected from the nozzle holes.

  As an ink jet recording head using this flexural vibration mode piezoelectric actuator, one described in Patent Document 1 is known. In the ink jet recording head disclosed in Patent Document 1, a pressurized liquid chamber communicating with a nozzle hole is formed on a liquid chamber substrate stacked on a nozzle plate having nozzle holes, and a diaphragm is formed on a part of the inner wall of the pressurized liquid chamber. Is provided. That is, the diaphragm, the lower electrode, the piezoelectric element, and the upper electrode are laminated on a part of the inner wall of the pressurized liquid chamber formed by the nozzle plate. The piezoelectric element of the piezoelectric actuator unit that is provided on the diaphragm and applies displacement to the diaphragm is provided with two electrodes, an upper electrode and a lower electrode, and a drive signal that is an ejection signal is supplied to the upper electrode. The Then, a negative bias voltage is applied to the lower electrode. As a result, a drive waveform in a low voltage region in which a displacement amount larger than the displacement amount of the piezoelectric element in the drive waveform in the high voltage region can be obtained, and the discharge characteristics can be improved.

  In an ink jet recording head, normally, the surface of the nozzle plate is grounded so that dust and paper powder do not adhere to the surface by electrostatic force. When a bias voltage is applied to the lower electrode as in the ink jet recording head of Patent Document 2, an electric field is generated between the nozzle plate and the lower electrode. For this reason, an electrostatic force is applied to the ink in the pressurized liquid chamber interposed between the nozzle plate and the lower electrode. As a result, when the type of ink is, for example, conductive ink, there is a problem that the ink aggregates in the pressurized liquid chamber, and the aggregated ink closes the nozzle holes and deteriorates the ink ejection characteristics.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to improve the liquid discharge characteristics without applying a voltage to the conductive liquid in the pressurized liquid chamber even when a bias voltage is applied to the lower electrode. An object of the present invention is to provide a droplet discharge head and an image forming apparatus that can be formed.

In order to achieve the above object, the invention of claim 1 is characterized in that a nozzle plate having a nozzle hole for discharging a conductive liquid and grounded, and an additive layer laminated on the nozzle plate and communicated with the nozzle hole. A liquid chamber substrate that forms a pressure liquid chamber; and a piezoelectric actuator portion that pressurizes the pressure liquid chamber via a vibration plate formed on a part of an inner wall of the pressure liquid chamber. Is a droplet discharge head having a lower electrode to which a bias voltage is applied, an upper electrode to which a driving voltage is applied, and a piezoelectric layer that is displaced based on the driving voltage applied to the upper electrode. A conductive layer is provided between the pressurized liquid chamber and the conductive layer, and the conductive layer is grounded.
According to a second aspect of the present invention, in the liquid droplet ejection head according to the first aspect, the conductive layer is formed from a conductive semiconductor material to which impurities are added, or includes a metal oxide. It is characterized by.
Further, the invention of claim 3 is characterized in that an image is formed on a recording material by discharging the recording liquid from the droplet discharge head according to claim 1 or 2.

  In the present invention, the lower electrode of the piezoelectric actuator section is separated from the pressurized liquid chamber via the diaphragm. When a bias voltage is applied to the lower electrode, an electric field is generated between the conductive liquid in the pressurized liquid chamber in contact with the grounded nozzle plate and the lower electrode. However, since a conductive layer is provided between the lower electrode and the pressurized liquid chamber and this conductive layer is grounded, an electric field is generated between the conductive layer and the lower voltage. Thereby, an electric field is not generated between the conductive liquid in the pressurized liquid chamber and the lower electrode. Therefore, the property of the conductive liquid does not change, and the liquid ejection characteristics by applying the bias voltage are improved.

  As described above, according to the present invention, even when a bias voltage is applied to the lower electrode, no voltage is applied to the conductive liquid in the pressurized liquid chamber, and the effect that the liquid discharge characteristics can be improved can be obtained.

1 is a perspective view illustrating a configuration of an ink jet recording apparatus according to an embodiment. It is a side view of the mechanism part of the inkjet recording device of this embodiment. It is sectional drawing of the droplet discharge head of this embodiment. It is a partial top view of the actuator part of the droplet discharge head of this embodiment. It is process sectional drawing which shows the manufacturing process of the droplet discharge head of this embodiment. It is process sectional drawing which shows the manufacturing process of the droplet discharge head of this embodiment. It is a partial top view which shows the structure which drops the conductive layer in GND in the droplet discharge head of this embodiment. It is a characteristic view which shows the drive waveform and bias voltage which are applied to a piezoelectric element. It is sectional drawing of another droplet discharge head of this embodiment.

First, the configuration of an ink jet recording apparatus equipped with an ink jet recording head which is an example of a liquid droplet ejection head according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a configuration of an ink jet recording apparatus according to the present embodiment, and FIG. 2 is a side view of a mechanism portion of the ink jet recording apparatus according to the present embodiment.
An ink jet recording apparatus 100 according to this embodiment shown in FIGS. 1 and 2 includes a carriage 101 that can move in the main scanning direction inside the apparatus main body, a droplet discharge head 1 mounted on the carriage 101, and a droplet discharge head 1. A paper feed cassette (or paper feed tray) capable of storing a number of recording sheets 30 from the front side is housed in the lower part of the apparatus main body. (It may also be) 104 is detachably mounted. Further, it has a manual feed tray 105 that is opened to manually feed the recording paper 30, takes in the recording paper 30 fed from the paper feed cassette 104 or the manual feed tray 105, and prints a required image by the printing mechanism unit 103. After recording, the paper is discharged to a paper discharge tray 106 mounted on the rear side.

  The print mechanism 103 holds a carriage 101 slidably in the main scanning direction by a main guide rod 107 and a sub guide rod 108 which are guide members horizontally mounted on left and right side plates (not shown). (Y), cyan (C), magenta (M), and black (Bk) droplet ejection heads 1 that eject ink droplets of each color are arranged in a sub-scanning direction in which a plurality of ink ejection ports (nozzles) are orthogonal to the main scanning direction. And are mounted with the ink droplet ejection direction facing downward. In addition, each ink cartridge 102 for supplying ink of each color to the droplet discharge head 1 is replaceably mounted on the carriage 101.

  The ink cartridge 102 is provided with an air opening communicating with the atmosphere at the upper side, and a supply port for supplying ink to the droplet discharge head 1 at the lower side, and has a porous body filled with ink inside. The ink supplied to the droplet discharge head 1 is maintained at a slight negative pressure by the capillary force of the material. Further, although the droplet discharge head is used for each color as the droplet discharge head 1, one droplet discharge head having nozzles for discharging ink droplets of each color may be used.

  Here, the carriage 101 is slidably fitted to the main guide rod 107 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the secondary guide rod 108 on the front side (upstream side in the paper conveyance direction). doing. In order to move and scan the carriage 101 in the main scanning direction, a timing belt 112 is stretched between a driving pulley 110 and a driven pulley 111 that are rotationally driven by a main scanning motor 109a. The carriage 101 is reciprocally scanned by forward and reverse rotations of the main scanning motor 109.

  On the other hand, in order to convey the recording paper 30 set in the paper feeding cassette 104 to the lower side of the droplet discharge head 1, a paper feeding roller 113 and a friction pad 114 for separating and feeding the recording paper 30 from the paper feeding cassette 104, A guide member 115 that guides the recording paper 30, a conveyance roller 116 that reverses and conveys the fed recording paper 30, a conveyance roller 117 that is pressed against the circumferential surface of the conveyance roller 116, and a recording sheet from the conveyance roller 116 And a tip roller 118 that defines 30 feed angles. The conveyance roller 116 is rotationally driven via a gear train by the sub-scanning motor 109b.

  In addition, a printing receiving member 119 that is a paper guide member is provided to guide the recording paper 30 fed from the transport roller 116 corresponding to the movement range of the carriage 101 in the main scanning direction on the lower side of the droplet discharge head 1. ing. A conveyance roller 120 and a spur 121 that are rotationally driven to send out the recording paper 30 in the paper discharge direction are provided on the downstream side of the printing receiving member 119 in the paper conveyance direction, and the recording paper 30 is sent out to the paper discharge tray 106. A paper discharge roller 123, a spur 124, and guide members 125 and 126 that form a paper discharge path are disposed.

  During recording by the recording apparatus 100, the droplet discharge head 1 is driven according to the image signal while moving the carriage 101, thereby discharging ink onto the stopped recording paper 30 to record one line, Thereafter, after the recording paper 30 is conveyed by a predetermined amount, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the recording paper 30 reaches the recording area, the recording operation is terminated and the recording paper 30 is discharged.

  A recovery device 127 for recovering the ejection failure of the droplet ejection head 1 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 101. Each of the recovery devices 127 includes a cap unit, a suction unit, and a cleaning unit (not shown). During printing standby, the carriage 101 is moved to the recovery device 127 side, and the droplet discharge head 1 is capped by the capping unit to keep the discharge port portion in a wet state, thereby preventing discharge failure due to ink drying. Further, by ejecting ink that is not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.

  Further, when a discharge failure occurs, the discharge port (nozzle) of the droplet discharge head 1 is sealed with a capping unit, and bubbles and the like are sucked out from the discharge port with the suction unit through the tube, and adhere to the discharge port surface. The discharged ink, dust, etc. are removed by the cleaning means, and the ejection failure is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

  As described above, since the ink jet recording apparatus 100 includes the ink jet recording head having the actuator unit, stable ink droplet ejection characteristics can be obtained and the image quality can be improved.

  FIG. 3 is a cross-sectional view of the droplet discharge head of this embodiment. FIG. 4 is a partial plan view of the actuator portion of the droplet discharge head of this embodiment. The droplet discharge head 1 shown in FIG. 1 mainly has a laminated structure in which a nozzle substrate 10, a liquid chamber substrate 20, a vibration plate 30, and a protective substrate 40 are stacked. Nozzle holes 11 are formed in the nozzle substrate 10 by pressing and polishing a SUS substrate having a thickness of 30 to 50 [μm]. The nozzle hole 11 communicates with the pressurized liquid chamber of the liquid chamber substrate. A silicon substrate is used for the liquid chamber substrate 20, and groove portions serving as ink flow paths such as the pressurized liquid chamber 12 and the fluid resistance portion 13 are formed. The diaphragm 30 is provided with an actuator unit such as a piezoelectric layer, an upper electrode, and a lower electrode. The vibration plate 30 is formed by sequentially forming a silicon oxide film, polysilicon, silicon oxide film, p-doped polysilicon, and silicon oxide film on the surface of the silicon substrate. The p-doped polysilicon in the diaphragm 30 corresponds to the conductive layer 31 of the present embodiment, and the conductive layer 31 is grounded (GND). On the diaphragm 30, an actuator portion composed of a multilayer structure of a platinum film serving as the lower electrode 51, a piezoelectric layer (PZT) 52, and a platinum film serving as the upper electrode 53 was formed by etching silicon. It is formed in a region facing the pressurized liquid chamber 12.

  The protective substrate 40 includes a wiring member 54 electrically connected to the lower electrode 51 and the upper electrode 53. The protective substrate 40 forms a piezoelectric element protective space. Columns are formed to increase the rigidity of the space and the flow path partition wall so as to prevent the protection and displacement of the liquid and to support the entire liquid chamber. Further, the lower electrode 51, the interlayer insulating film 55 disposed between the upper electrode 53 and the wiring member 54, and the passivation film 56 covers the upper surface and the side surface of the actuator portion as moisture resistance for protecting the wiring member 54. Has been placed. The lower electrode pad portion 57 is provided so as to be electrically connected to the wiring member 54 electrically connected to the lower electrode 51, and the upper electrode pad portion 58 is electrically connected to the upper electrode 53. 54 to be electrically connected.

  In the above embodiment, p-doped polysilicon is used as the material used for the conductive layer 31 shown in FIG. 3, but any conductive material that does not melt during piezo firing may be used. For example, it is not limited to p-doped or n-doped polysilicon, but the same effect can be obtained even with a semiconductor material having conductivity. Moreover, not only a semiconductor but metal oxides, such as SRO, LNO, ZnO, and SnO, may be used. Even if it is a metal, as long as it does not melt | dissolve at the time of baking of piezo like Pt and Ir, substitution is possible.

Next, the manufacturing method of the droplet discharge head of this embodiment will be described with reference to FIGS. 5 and 6 which are process cross-sectional views showing the manufacturing process.
First, as shown in FIG. 5A, a <100> silicon substrate 201 having a thickness of 400 [μm] is heat-treated to form a silicon oxide film 202 on the surface by 0.6 [μm]. The diaphragm layer 202 is formed by laminating 0.5 [μm] polysilicon and 0.3 [μm] silicon oxide film, and the conductive layer 203 containing 0.5 [μm] p-doped polysilicon. A diaphragm layer 204 of a silicon oxide film of 0.3 [μm] is laminated. Thereafter, as shown in FIG. 5B, a platinum (Pt) layer 205 to be a lower electrode of the piezoelectric element is formed by sputtering to a thickness of 0.2 [μm] and patterned. Further, as shown in FIG. 5C, the piezoelectric layer 206 is formed by 2 [μm] by the sol-gel method, and the platinum (Pt) layer 207 to be the upper electrode is formed by 0.1 [μm]. . Thereafter, the upper electrode and the piezoelectric layer are patterned by a lithoetch method.

  Next, as shown in FIG. 5D, an interlayer insulating film 208 is formed by 0.3 [μm] by plasma CVD, and a via hole 209 for making wiring contact is formed by lithoetch. The interlayer insulating film 208 patterns a conductive portion 210 between a wiring member and an upper electrode to be formed next, a conductive portion 211 to a bypass wiring member, and a through portion 212 that becomes an ink supply hole. Further, as shown in FIG. 5E, an extraction electrode 213 is formed from an aluminum material. Since the lead electrode 213 receives stress due to vibration of the diaphragm driven by the piezoelectric body, the lead electrode 213 is made of a soft aluminum material and has a thickness of about 1 [μm] so as not to be disconnected by vibration.

  Next, as shown in FIG. 5F, a silicon nitride film 214 of 2 [μm] is formed by plasma CVD as a passivation film for protecting the aluminum wiring and patterned. After that, as shown in FIG. 6A, the ink supply port of the diaphragm and the portion 215 that becomes the common liquid chamber are etched in advance. Further, gold is laminated by plating to form the upper electrode pad portion 216 and the lower electrode pad portion 217 at the same time. By forming the upper electrode pad portion 216 and the lower electrode pad portion 217 with gold, electrical connection with a driver IC (not shown) is connected by low-temperature wire bonding. Also, gold has a low resistance value, and has a great effect of lowering the resistance values of the upper electrode and the lower electrode. Further, the lower electrode pad portion 217 may be formed separately from the upper electrode pad portion 216, and copper, aluminum, or the like may be used as a material for the pad portion. In that case, the upper electrode pad part 216 that is not protected from the outside may require a protective layer that protects against corrosion.

  Thereafter, as shown in FIG. 6 (b), a protective substrate 218 in which a column is separately formed on a glass substrate by blasting is bonded to the liquid chamber substrate side, and the liquid chamber substrate is protected as shown in FIG. 6 (c). The surface opposite to the substrate bonding surface is polished to a desired thickness. The protective substrate 218 may be a silicon substrate obtained by processing a recess by a lithoetch method, or may be a silicon substrate processed by wet etching using an alkaline etching solution such as TMAH or KOH. Further, it may be a molded part such as a resin mold or a metal injection mold. In addition, when the driver circuit is integrally formed on the actuator substrate, an oxide film formed by a pyro-oxidation method is formed by a LOCOS oxidation method, and a driver circuit is formed on the same substrate by selecting an oxide film formation region. You can also Thereafter, as shown in FIG. 6C, concave portions to be the pressure liquid chamber 220, the fluid resistance portion 221 and the ink supply portion 222 are formed on the opposite surface of the liquid chamber substrate 219 which is a silicon substrate by ICP dry etching. Finally, as shown in FIG. 6 (d), a nozzle substrate 224 in which nozzle holes 223 are formed by pressing and polishing separately on a 30 to 50 [μm] thick SUS substrate is used as the flow path of the liquid chamber substrate 219. The droplet discharge head is completed by connecting the aluminum wiring connected to the partition forming surface and the upper and lower electrodes of the piezoelectric element to the drive circuit.

  Next, a configuration in which the conductive layer in the droplet discharge head of this embodiment is dropped to GND will be described. FIG. 7 is a partial plan view showing a configuration in which the conductive layer in the droplet discharge head of this embodiment is dropped to GND. In the figure, the same reference numerals as those in FIG. 4 denote the same components. The droplet discharge head of this embodiment has a conductive layer electrically separated from the lower electrode. Then, as shown in FIG. 7, a conductive layer pad portion 62 that is connected to the conductive layer 60 is disposed near the lower electrode pad portion 61 of the actuator as a configuration in which the conductive layer 60 is dropped to GND. The pad portion 62 is electrically connected to the GND of the IC chip. The method of dropping the conductive layer to GND is not limited to this method, and a method of electrically connecting the nozzle plate dropped to GND and the conductive layer may be used.

  Next, an example of a method for driving the droplet discharge head according to the present embodiment will be described. FIG. 8 is a characteristic diagram showing a drive waveform and a bias voltage applied to the piezoelectric element. The drive waveform shown in the figure is applied to the upper electrode, and a bias voltage of 5 [V] is applied to the lower electrode. As a result, in addition to the configuration of the droplet discharge head of the present embodiment, driving with the driving method can improve the discharge performance without causing ink aggregation. With respect to the drive waveform applied to the upper electrode, by changing the switching timing, three types of waveforms for large droplets, medium droplets, and small droplets are applied to the piezoelectric element as shown in FIG. Ink droplets are ejected. The drive waveform applied to the upper electrode is not limited to this example, and the effect of the present invention can be expected as long as the drive waveform can stably eject ink.

  In this embodiment, an electrically isolated conductive layer is provided between the lower electrode and the pressurized liquid chamber, and the conductive layer is dropped to GND, so that electrostatic force is generated in the ink even when a bias voltage is applied to the lower electrode. This prevents the phenomenon of aggregation. For this reason, a similar effect can be expected if the head has a structure having an electrode layer between the pressure generating means and the pressurized liquid chamber. For example, in the above embodiment as shown in FIG. 3, the structure has a column for supporting the entire individual liquid chamber, but as shown in FIGS. The same effect can be expected even with the droplet discharge head 2 that does not have a column that supports the above.

  As described above, according to the embodiment, as shown in FIG. 3, the conductive layer 31 dropped to GND is provided between the lower electrode 51 and the pressurized liquid chamber 12 in the droplet discharge head. Even when a method of driving by applying a bias voltage to the lower electrode 51 is used, no electric field is generated between the lower electrode and the pressurized liquid chamber. As a result, ink droplets can be ejected without agglomerating ink in the pressurized liquid chamber. Thereby, ink ejection characteristics can be improved.

DESCRIPTION OF SYMBOLS 1 Droplet discharge head 2 Droplet discharge head 10 Nozzle board | substrate 11 Nozzle hole 12 Pressurized liquid chamber 13 Fluid resistance part 20 Liquid chamber board | substrate 30 Diaphragm 31 Conductive layer 40 Protective substrate 51 Lower electrode 52 Piezoelectric layer 53 Upper electrode 54 Wiring Member 55 Interlayer insulating film 56 Passivation film 57 Lower electrode pad portion 58 Upper electrode pad portion 59 Through hole 60 Conductive layer 61 Lower electrode pad portion 62 Conductive layer pad portion 100 Inkjet recording apparatus

JP 2006-321200 A

Claims (3)

A nozzle plate having a nozzle hole for discharging a conductive liquid and grounded; a liquid chamber substrate stacked on the nozzle plate to form a pressurized liquid chamber communicating with the nozzle hole; and the pressurized liquid A piezoelectric actuator section that pressurizes the pressurized liquid chamber through a diaphragm formed on a part of the inner wall of the chamber, and the piezoelectric actuator section is applied with a lower electrode to which a bias voltage is applied and a drive voltage is applied. A droplet discharge head having an upper electrode and a piezoelectric layer that is displaced based on an applied drive voltage.
A droplet discharge head, wherein a conductive layer is provided between the lower electrode and the pressurized liquid chamber, and the conductive layer is grounded. The droplet discharge head according to claim 1,
The droplet discharge head, wherein the conductive layer is formed of a conductive semiconductor material to which an impurity is added, or includes a metal or a metal oxide.   An image forming apparatus, comprising: a recording liquid ejected from the liquid droplet ejection head according to claim 1 to form an image on a recording material.

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