JP5776463B2 - Multilayer piezoelectric element, liquid discharge head, and image forming apparatus - Google Patents

Description

  The present invention relates to a multilayer piezoelectric element, a liquid discharge head, and an image forming apparatus.

  As an image forming apparatus such as a printer, a facsimile, a copying machine, a plotter, or a complex machine of these, for example, a liquid discharge recording type image forming using a recording head composed of a liquid discharge head (droplet discharge head) that discharges ink droplets. As an apparatus, an ink jet recording apparatus or the like is known.

  As the liquid ejection head, for example, a piezoelectric body as pressure generating means (actuator means) for generating pressure by pressurizing ink that is liquid in a liquid chamber, in particular, a laminated piezoelectric member in which piezoelectric layers and internal electrodes are alternately laminated An elastically deformable diaphragm member comprising a piezoelectric actuator in which a plurality of columnar piezoelectric elements (piezoelectric columns) are formed by grooving and forming a wall surface in a liquid chamber by displacement in the d33 or d31 direction of the laminated piezoelectric member A so-called piezoelectric head is known that discharges droplets by changing the volume and pressure of the liquid chamber.

  In a liquid discharge head using this multilayer piezoelectric element, in order to increase the density, it is necessary to perform fine groove processing by dicing or the like on the piezoelectric element, and the width of the piezoelectric column becomes narrow. .

  Here, as an internal electrode of the multilayer piezoelectric element, a silver palladium electrode is generally used in consideration of reliability.

  However, there is a problem in that voids are generated in the internal electrodes, and disconnection occurs in the internal electrodes of the individual piezoelectric columns when the voids are connected.

  Therefore, conventionally, it is known that by mixing alumina powder or the piezoelectric element material itself in the conductive paste used as the internal electrode, the internal electrode coverage after firing is improved and the internal electrode disconnection due to void generation is reduced. (Patent Document 1)

Japanese Patent No. 4396701

  However, in the configuration disclosed in Patent Document 1, by increasing the electrode coverage, there is a new problem that the restraining force increases with respect to the displacement as the piezoelectric element and the amount of displacement is reduced.

  The present invention has been made in view of the above points, and an object thereof is to reduce disconnection of internal electrodes without deteriorating the displacement characteristics of a piezoelectric element.

In order to solve the above problems, the multilayer piezoelectric element according to the present invention is
A laminated piezoelectric element in which piezoelectric layers and internal electrodes are alternately laminated,
The internal electrode contains a needle-shaped conductive filler extending in a uniaxial direction,
The conductive fillers are bonded to each other and formed in a mesh shape.

  According to the multilayer piezoelectric element according to the present invention, the disconnection of the internal electrode can be reduced without deteriorating the displacement characteristics of the piezoelectric element.

FIG. 3 is an external perspective view illustrating an example of a liquid discharge head according to the present invention. FIG. 2 is an explanatory cross-sectional view along a direction (liquid chamber longitudinal direction: line AA in FIG. 1) orthogonal to the nozzle arrangement direction of the head. It is sectional explanatory drawing which follows the nozzle arrangement | sequence direction (liquid chamber short direction: BB line of FIG. 1) of the head. It is typical explanatory drawing with which it uses for description of the internal electrode of an example of the laminated piezoelectric element which concerns on this invention. It is explanatory drawing with which it uses for description of the void in the internal electrode of a comparative example. It is explanatory drawing with which it uses for description of the disconnection of the internal electrode of a comparative example. FIG. 4 is a side explanatory view of a mechanism unit of an example of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. An example of a liquid discharge head according to the present invention will be described with reference to FIGS. 1 is an external perspective view of the head, FIG. 2 is a cross-sectional explanatory view along a direction perpendicular to the nozzle arrangement direction of the head (longitudinal direction of the liquid chamber: line AA in FIG. 1), and FIG. It is sectional explanatory drawing which follows the nozzle arrangement direction (liquid chamber short side direction: BB line of FIG. 1) of a head.

  The liquid discharge head includes a flow path plate (flow path member, flow path substrate, liquid chamber substrate) 1 formed of a SUS substrate or the like, and a vibration plate member 2 that forms a vibration plate bonded to the lower surface of the flow path plate 1. And a nozzle plate 3 joined to the upper surface of the flow path plate 1. By these members, a plurality of liquid chambers (also referred to as a pressurized liquid chamber, a pressure chamber, a pressurizing chamber, a flow path, etc.) 6 as individual flow paths each communicating with a plurality of nozzles 4 that discharge droplets. A fluid resistance portion 7 that also serves as a supply path for supplying ink to the liquid chamber 6 and a liquid introduction portion 8 that communicates with the liquid chamber 6 through the fluid resistance portion 7 are formed, and the diaphragm member 2 is formed on the liquid introduction portion 8. Ink is supplied from a common liquid chamber 10 formed in a frame member 17 to be described later through the formed supply port 9.

  The flow path plate 1 forms openings such as the pressurized liquid chamber 6 and the fluid resistance portion 7 by etching the SUS substrate using an acidic etchant or machining such as punching (press). . The flow path plate 1 can be formed by etching a single crystal silicon substrate, for example.

  The diaphragm member 2 is formed of the first layer 2A and the second layer 2B, the first layer 2A forms a thin portion, and the first layer 2A and the second layer 2B form a thick portion. . And this diaphragm member 2 has each vibration field (diaphragm part) 2a formed in the 1st layer 2A which forms the wall surface corresponding to each liquid room 6, and in this vibration field 2a, An island-shaped convex portion 2b formed by the thick portion of the first layer 2A and the second layer 2B is provided on the outer surface (the side opposite to the liquid chamber 6), and a portion corresponding to the liquid chamber interval wall 30 is provided. Similarly, a thick portion 2c is provided.

  A piezoelectric actuator 11 including an electromechanical transducer as a driving means (actuator means, pressure generating means) for deforming the vibration region 2a is arranged on the opposite side of the diaphragm member 2 from the liquid chamber 6.

  The piezoelectric actuator 11 has a plurality of (here, two) laminated piezoelectric members 12 which are laminated piezoelectric elements according to the present invention, which are adhesively bonded onto a base member 13, and the piezoelectric member 12 has a half cut. A required number of columnar piezoelectric elements (hereinafter referred to as “piezoelectric columns”) 12A and 12B are formed in a comb shape at a predetermined interval with respect to one piezoelectric member 12 by groove processing by dicing.

  The piezoelectric columns 12A and 12B of the piezoelectric member 12 are the same, but the piezoelectric column that is driven by applying a driving waveform is the driving column 12A, and the piezoelectric column that is used as a mere support column without driving waveform is not driven. It is distinguished as a pillar 12B. That is, a so-called bi-pitch configuration is adopted.

  Then, the upper end surface (joint surface) of the drive column 12 </ b> A is joined and joined to the island-shaped convex portion 2 b of the diaphragm member 2. Further, the upper end surface of the non-driven column 12B is joined to the thick portion 2c of the diaphragm member 2 at a position corresponding to the liquid chamber interval wall 30.

  Here, the piezoelectric member 12 is formed by alternately laminating piezoelectric material layers (piezoelectric layers) 21 and internal electrodes 22A and 22B. The internal electrodes 22A and 22B are respectively end surfaces, that is, the diaphragm member 2 of the piezoelectric member 12. Is pulled out to a side surface (surface along the stacking direction) substantially perpendicular to the surface, connected to the individual external electrode 23 and the common external electrode 24 which are end surface electrodes formed on this side surface, and a voltage is applied between the external electrodes 23 and 24. This causes displacement in the stacking direction. In addition, the common external electrode 24 is drawn out to an end surface on the individual external electrode 23 side through an internal electrode (not shown) and to an end of the piezoelectric member 12 in the nozzle arrangement direction.

  Further, FPCs 15 which are flexible wiring boards as wiring members are provided on both side surfaces of the base member 13 in the direction orthogonal to the nozzle arrangement direction. The individual external electrode 23 of the driving column 12A of the piezoelectric member 12 and the common external electrode for extraction (not shown) and the wiring electrode of the FPC 15 are joined by solder bonding, and a driving circuit (driver) for supplying a driving signal to the driving column 12A is supplied to the FPC 15 IC) is mounted.

  The nozzle plate 3 is formed from a nickel (Ni) metal plate, and is manufactured by an electroforming method (electroforming). In this nozzle plate 3, nozzles 4 having a diameter of 10 to 35 μm are formed corresponding to the respective liquid chambers 6 and bonded to the flow path plate 1 with an adhesive. A water repellent layer is provided on the droplet discharge side surface (surface in the discharge direction: discharge surface or surface opposite to the liquid chamber 6 side) of the nozzle plate 3.

  Further, a frame member 17 formed by injection molding with an epoxy resin or polyphenylene sulfite is joined to the outer peripheral side of the piezoelectric actuator 11 composed of the piezoelectric member 12, the base member 13, the FPC 15, and the like. The frame member 17 is formed with the above-described common liquid chamber 10 and further has a supply port for supplying ink to the common liquid chamber 10 from the outside. The supply port 19 is further provided with a sub-tank and an ink cartridge (not shown). Connected to an ink supply source.

  In this head, the piezoelectric pillars 12A and 12B are diced at an interval of 300 dpi. It is arranged in two rows facing each other, and the individual liquid chambers 6 and the nozzles 4 are arranged in a staggered arrangement with two rows at intervals of 150 dpi, so that a resolution of 300 dpi can be obtained in one scan. Yes.

  In the liquid discharge head configured as described above, for example, the drive column 12A contracts by lowering the voltage applied to the drive column 12A from the reference potential, and the vibration region 2a forming the liquid chamber wall surface of the diaphragm member 2 is lowered. As the volume of the individual liquid chamber 6 expands, the ink flows into the individual liquid chamber 6, and then the voltage applied to the drive column 12A is increased to extend the drive column 12A in the stacking direction. By deforming the vibration region 2 a in the direction of the nozzle 4 and contracting the volume of the liquid chamber 6, the ink in the liquid chamber 6 is pressurized and ink droplets are ejected (jetted) from the nozzle 4.

  Then, by returning the voltage applied to the drive column 12A to the reference potential, the vibration region 2a of the diaphragm member 2 is restored to the initial position, and the liquid chamber 6 expands to generate a negative pressure. Ink is filled into the liquid chamber 6 from the chamber 10. Therefore, after the vibration of the meniscus surface of the nozzle 4 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (pulling-pushing), and it is also possible to perform striking or pushing depending on the direction to which the driving waveform is given.

  Next, an example of the multilayer piezoelectric element according to the present invention will be described with reference to FIG. FIG. 4 is a schematic explanatory diagram for explaining the internal electrodes of the piezoelectric element.

  As described above, the piezoelectric member 12 that is a multilayer piezoelectric element is obtained by alternately laminating piezoelectric layers 21 and internal electrodes 22A and 22B (hereinafter referred to as “internal electrodes 22” when not distinguished).

  Here, the internal electrode 22 uses a baking type conductive paste, and contains a needle-shaped conductive filler 101 (see FIG. 4) extending in a uniaxial direction in addition to silver and palladium powder.

  The content ratio of the needle-shaped conductive filler extending in the uniaxial direction to the silver or palladium powder is preferably in the range of 5 to 60 wt%, more preferably 10 to 30 wt%.

  Further, as the needle-shaped conductive filler extending in the uniaxial direction, a needle-shaped filler having a ceramic filler as a core material and subjected to metal plating can be used. Thereby, the shrinkage | contraction at the time of baking can be reduced.

  For example, a ceramic filler having a diameter of 0.1 to 0.5 μm and a length of 10 to 20 μm and subjected to silver electroless plating can be used.

  Then, on the green sheet forming the piezoelectric layer 21, in addition to silver and palladium powder, screen printing is performed with a conductive paste containing a needle-shaped conductive filler extending in a uniaxial direction, this process is repeated, and firing is performed. A laminated piezoelectric member 12 was manufactured.

  Here, silver and palladium powder have a lower melting point than the needle-shaped conductive filler, and the needle-shaped conductive filler is coated with the melted silver and palladium at the time of firing, and the needle-shaped conductive filler is bonded to each other with cooling. Is done.

  As a result, as shown in FIG. 4, uniaxially extending needle-shaped conductive filler 101 is formed in a network structure as internal electrode 22, and a state in which silver palladium (metal bonding portion) 102 is bonded to each other is formed. Is obtained.

  The characteristics of the laminated piezoelectric member 12 were evaluated by changing the addition amount of the needle-shaped conductive filler 101 in the material of the internal electrode 22 and performing groove processing at a pitch equivalent to 600 dpi.

  In this case, the internal electrode coverage changed according to the amount of the needle-shaped conductive filler 101 extending in the uniaxial direction, and the generation state of the void 103 (see FIG. 4) was also changed.

  When the content ratio of the needle-shaped conductive filler 101 with respect to silver and palladium powder was 5 wt%, an increase in size due to the bonding between the voids 103 was confirmed, and disconnection of the internal electrode was recognized. The internal electrode coverage at this time was about 50%.

  In addition, when the content ratio was 10 to 30 wt%, it was confirmed that the internal electrode coverage was 70 to 80%, the internal electrode was disconnected, and the displacement characteristics of the piezoelectric element were not deteriorated.

  On the other hand, when the content ratio was 60 wt%, the internal electrode coverage was 95%, and disconnection was eliminated, but it was confirmed that the displacement characteristics of the piezoelectric element were deteriorated.

  As described above, the needle-shaped conductive filler extending in the uniaxial direction is contained in the internal electrode and formed into a mesh shape, thereby preventing the internal electrode from being disconnected due to the connection of voids and reducing the internal electrode coverage. As a result, the restraining force against the displacement by the internal electrode is reduced, and the displacement characteristics are not deteriorated.

  In the above embodiment, the needle-shaped conductive filler extending in the uniaxial direction is subjected to silver electroless plating and the conductive filler is used. However, even with a conductive filler subjected to metal coating such as Ni electroless plating, Similar effects can be obtained.

  Further, as a needle-shaped conductive filler extending in a uniaxial direction, a chain-like nickel filler having a diameter of about 0.05 to 0.2 μm and a length of 10 to 30 μm, or coated with silver or the like The thing etc. which were made can also be used.

  Here, the chain nickel filler means a needle-shaped conductive filler in which individual nanoparticles are connected in a daisy chain and extend in a uniaxial direction when producing nickel nanoparticles.

  Here, for comparison, an internal electrode containing no needle-shaped conductive filler will be described with reference to FIGS.

  When no needle-shaped conductive filler is contained, a large number of voids 103 are generated in the internal electrode 22 as shown in FIG. 5, and particularly in a high-density head in which high-density piezoelectric columns 12A and 12B are arranged, The width of the electric pole (arrangement direction) is narrowed, and the disconnection of the internal electrode 22 is more likely to occur.

  Specifically, if a piezoelectric column having a width of 20 μm is formed, assuming that the region A in FIG. 5 is formed as a piezoelectric column, the void 103 continues in the direction of the width of the piezoelectric column at a position indicated by a circle 104 in FIG. And it turns out that the internal electrode is torn up and down in FIG. This position corresponds to the ◯ position in FIG. 6 where the piezoelectric column in the A region is extracted, and the portion on the left side of this position is disconnected from the external common electrode 24, and a voltage cannot be applied.

  An ink tank integrated head can also be configured by integrating a tank for supplying ink to the liquid discharge head of each of the above embodiments.

  Next, an example of the image forming apparatus according to the present invention including the liquid discharge head according to the present invention will be described with reference to FIGS. 11 is an explanatory side view of the mechanism of the apparatus, and FIG. 12 is an explanatory plan view of the main part of the mechanism.

  This image forming apparatus is a serial type image forming apparatus, and a carriage 233 is slidably held in the main scanning direction by main and slave guide rods 231 and 232 which are guide members horizontally mounted on the left and right side plates 221A and 221B. The main scanning motor that does not perform moving scanning in the direction indicated by the arrow (carriage main scanning direction) via the timing belt.

  The carriage 233 is supplied with ink supplied to the same head as the liquid discharge head according to the present invention for discharging ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). A recording head 234 with an integrated tank is arranged in a sub-scanning direction orthogonal to the main scanning direction with a nozzle row composed of a plurality of nozzles, and is mounted with the ink droplet ejection direction facing downward.

  Each of the recording heads 234 has two nozzle rows, and one nozzle row of one recording head 234a has a black (K) droplet, the other nozzle row has a cyan (C) droplet, and the other nozzle row has the other nozzle row. One nozzle row of the recording head 234b discharges magenta (M) droplets, and the other nozzle row discharges yellow (Y) droplets. Here, a configuration in which droplets of four colors are ejected in a two-head configuration is used, but it is also possible to arrange four nozzle rows per head and eject each of the four colors with one head.

  Further, the ink of each color is replenished and supplied from the ink cartridge 210 of each color to the tank 235 of the recording head 234 via the supply tube 236 of each color.

  On the other hand, as a paper feeding unit for feeding the paper 242 stacked on the paper stacking unit (pressure plate) 241 of the paper feed tray 202, a half-moon roller (feeding) that separates and feeds the paper 242 one by one from the paper stacking unit 241. A separation pad 244 made of a material having a large coefficient of friction is provided opposite to the sheet roller 243 and the sheet feeding roller 243, and the separation pad 244 is urged toward the sheet feeding roller 243 side.

  A guide 245 for guiding the paper 242, a counter roller 246, a conveyance guide member 247, and a tip pressure roller 249 are used to feed the paper 242 fed from the paper feeding unit to the lower side of the recording head 234. And a holding belt 251 which is a conveying means for electrostatically attracting the fed paper 242 and conveying it at a position facing the recording head 234.

  The conveyor belt 251 is an endless belt, and is configured to wrap around the conveyor roller 252 and the tension roller 253 so as to circulate in the belt conveyance direction (sub-scanning direction). In addition, a charging roller 256 that is a charging unit for charging the surface of the transport belt 251 is provided. The charging roller 256 is disposed so as to come into contact with the surface layer of the conveyor belt 251 and to rotate following the rotation of the conveyor belt 251. The transport belt 251 rotates in the belt transport direction when the transport roller 252 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 242 recorded by the recording head 234, a separation claw 261 for separating the paper 242 from the transport belt 251, a paper discharge roller 262, and a paper discharge roller 263 are provided. A paper discharge tray 203 is provided below the paper discharge roller 262.

  A double-sided unit 271 is detachably attached to the back surface of the apparatus main body. The duplex unit 271 takes in the paper 242 returned by the reverse rotation of the transport belt 251, reverses it, and feeds it again between the counter roller 246 and the transport belt 251. The upper surface of the duplex unit 271 is a manual feed tray 272.

  Further, a maintenance / recovery mechanism 281 that is a head maintenance / recovery device according to the present invention includes a recovery means for maintaining and recovering the nozzle state of the recording head 234 in the non-printing area on one side of the carriage 233 in the scanning direction. Is arranged. The maintenance / recovery mechanism 281 includes cap members (hereinafter referred to as “caps”) 282a and 282b (hereinafter referred to as “caps 282” when not distinguished) for capping each nozzle surface of the recording head 234, and nozzle surfaces. A wiper blade 283 that is a blade member for wiping the ink, and an empty discharge receiver 284 that receives liquid droplets for discharging the liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. ing.

  Further, in the non-printing area on the other side in the scanning direction of the carriage 233, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to the recording in order to discharge the recording liquid thickened during the recording. A discharge receiver 288 is disposed, and the idle discharge receiver 288 is provided with an opening 289 along the nozzle row direction of the recording head 234 and the like.

  In this image forming apparatus configured as described above, the sheets 242 are separated and fed one by one from the sheet feeding tray 202, and the sheet 242 fed substantially vertically upward is guided by the guide 245, and is conveyed to the conveyor belt 251 and the counter. It is sandwiched between the rollers 246 and conveyed, and further, the leading end is guided by the conveying guide 237 and pressed against the conveying belt 251 by the leading end pressing roller 249, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately applied to the charging roller 256, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 251 alternates, that is, in the sub-scanning direction that is the circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 242 is fed onto the conveyance belt 251 charged alternately with plus and minus, the sheet 242 is attracted to the conveyance belt 251, and the sheet 242 is conveyed in the sub scanning direction by the circumferential movement of the conveyance belt 251.

  Therefore, by driving the recording head 234 according to the image signal while moving the carriage 233, ink droplets are ejected onto the stopped paper 242 to record one line, and after the paper 242 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 242 has reached the recording area, the recording operation is finished and the paper 242 is discharged onto the paper discharge tray 203.

  As described above, since the image forming apparatus includes the liquid discharge head according to the present invention as a recording head, a high-quality image can be stably formed.

  In the present application, the “paper” is not limited to paper, but includes OHP, cloth, glass, a substrate, etc., and means a material to which ink droplets or other liquids can be attached. , Recording media, recording paper, recording paper, and the like. In addition, image formation, recording, printing, printing, and printing are all synonymous.

  The “image forming apparatus” means an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. “Formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply causing a droplet to land on the medium). ) Also means.

  The “ink” is not limited to an ink unless otherwise specified, but includes any liquid that can form an image, such as a recording liquid, a fixing processing liquid, or a liquid. Used generically, for example, includes DNA samples, resists, pattern materials, resins, and the like.

  In addition, the “image” is not limited to a planar image, and includes an image given to a three-dimensionally formed image and an image formed by three-dimensionally modeling a solid itself.

  Further, the image forming apparatus includes both a serial type image forming apparatus and a line type image forming apparatus, unless otherwise limited.

DESCRIPTION OF SYMBOLS 1 Flow path plate 2 Vibrating plate member 3 Nozzle plate 4 Nozzle 5 Nozzle communication path 6 Pressurized liquid chamber (individual liquid chamber, individual liquid chamber)
DESCRIPTION OF SYMBOLS 10 Common liquid chamber 12 Piezoelectric member 12A, 12B Piezoelectric column 15 FPC (wiring member)
21 Piezoelectric layers 22A and 22B Internal electrodes 23 Individual external electrodes 24 Common external electrodes 101 Needle-shaped conductive fillers 102 Metal joints 233 Carriages 234a and 234b Recording heads

Claims (8)

A laminated piezoelectric element in which piezoelectric layers and internal electrodes are alternately laminated,
The internal electrode contains a needle-shaped conductive filler extending in a uniaxial direction,
The laminated piezoelectric element, wherein the conductive fillers are bonded to each other and formed in a mesh shape.   The multilayer piezoelectric element according to claim 1, wherein the conductive filler is formed by performing metal plating on a needle-shaped filler having a ceramic as a core. The conductive filler is laminated piezoelectric element according to claim 1, characterized in that the two Kkerufira. The conductive filler is laminated piezoelectric element according to claim 3, characterized in that it is formed by performing silver plating on the surface of the front yn Kkerufira.   The multilayer piezoelectric element according to claim 1, further comprising a metal material different from the needle-shaped conductive filler.   6. The multilayer piezoelectric element according to claim 5, wherein the metal material has a melting point lower than that of the needle-shaped conductive filler, and the conductive fillers are bonded to each other by the metal material.   A liquid ejection head comprising the multilayer piezoelectric element according to claim 1.   An image forming apparatus comprising the liquid discharge head according to claim 7.

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