JPH04345852A - Piezoelectric element for pulse-drop bonder - Google Patents

Abstract

PURPOSE:To provide the constitution of a piezoelectric element for maximally utilizing the piezoelectric characteristics of the piezoelectric electric element for an ink-jet printer head in a shape having the walls of a plurality of piezoelectric materials which will be shear deformed by applyed voltage, ink flow paths formed among the walls of said piezoelectric materials and a plurality of ink grooves operated as pressure chambers. CONSTITUTION:An electric field of 2.5kV/mm is applied in the thickness direction of a piezoelectric element 11 while flexible electrodes 42a, 42b are brought into contact with the top face of the cover plate 52 of a pulse-drop bonder and the underside of the piezoelectric element 11 and pushed lightly. The re- polarization treatment is conducted for 10min in an oven at 100 deg.C. The driving electrodes of a barium titanate group PTC thermistor material formed on the side faces of the grooves of the piezoelectric element 11 work as insulators in the re-polarization treatment, thus allowing excellent re-polarization treatment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element for a pulse droplet deposition device, and more specifically to a piezoelectric element for a pulse droplet inkjet printer head that utilizes shear deformation of a piezoelectric material.

0002

[Prior Art] Conventionally, the configuration and manufacturing method of a pulse droplet deposition device utilizing shear deformation of a piezoelectric element was disclosed in Japanese Patent Laid-Open No. 6
It is described in Publication No. 3-247051. An example of the configuration of the pulse droplet deposition device and the piezoelectric element is shown in FIG. This pulse droplet deposition device includes a droplet ejection nozzle plate 72 having a large number of ink ejection holes 71, and a droplet ejection nozzle plate 72 having a large number of ink ejection holes 71.
A large number of ink grooves 73 (pressure chambers) to which 2 are connected
and a shear deformation piezoelectric element 75 made of a piezoelectric material with drive electrodes formed on the side surfaces 74, and a liquid supply mechanism (not shown) for replenishing ink. In the above-mentioned pulse droplet deposition device, when an electric field is applied to the drive electrode, the piezoelectric material undergoes shear deformation, causing a change in the volume of the ink groove 72. As a result, the liquid pressure in the ink groove 72 changes, and ink is ejected from the ejection holes of the nozzle plate.

Conventionally, a conductive material such as nickel has been used as the drive electrode of the piezoelectric element, and it has been formed on the side surface of a groove formed in the piezoelectric element by techniques such as sputtering and plating.

0004

However, in the piezoelectric element that utilizes shear deformation of a piezoelectric material as described above, the polarization direction and the driving electric field direction are perpendicular to each other. Therefore, if the polarization state of the piezoelectric element deteriorates due to heat treatment or the like during the assembly process of the pulsed droplet deposition device, the polarization state cannot be restored by re-polarization treatment for piezoelectric elements that use conventional conductive materials for the electrodes. There wasn't. Furthermore, conventional conductive materials have insufficient corrosion resistance against increasingly diverse ink components. Furthermore, the adhesive strength between the piezoelectric material and the drive electrode film formed by sputtering or plating is not satisfactory.

The present invention has been made to solve the above-mentioned problems, and uses PTFE as a drive electrode of a piezoelectric element.
It is an object of the present invention to provide a piezoelectric element for a pulse droplet deposition device that can be repolarized by using a C thermistor material, has high corrosion resistance to ink, and has a drive electrode that has excellent adhesive strength with the piezoelectric element.

[0006]

[Means for Solving the Problem] In order to achieve this object, the piezoelectric element of the present invention has a structure having a plurality of ink grooves and a wall of piezoelectric material, and a side surface of the groove is made of a PTC thermistor material. A drive electrode is formed.

[0007]

[Operation] The piezoelectric element of the present invention having the above means is polarized in the height direction of the wall of the piezoelectric material (the depth direction of the groove). By applying an electric field between drive electrodes on both sides of the piezoelectric material wall, the piezoelectric material wall is sheared and deformed without any dimensional change in the height direction (thickness direction). In this case, the ink groove surrounded by the two piezoelectric walls causes a volume change. In other words, the ink grooves function as ink flow paths and pressure chambers to eject ink droplets.

[0008] Furthermore, a drive electrode formed of a PTC thermistor material has a property of being conductive at low temperatures and insulating at high temperatures, with the Curie temperature of the PTC thermistor material as a boundary. Therefore, during operation of a normal pulsed droplet deposition device, it operates as a drive electrode. At the time of repolarization, the PTC thermistor material acts as a mere insulator by setting the temperature condition at the time of polarization to be equal to or higher than the Curie temperature of the PTC thermistor material used.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a process of forming a film on the side surface 14 of a groove 12 formed in a piezoelectric element 11. The piezoelectric element 11 is made of lead zirconate titanate piezoelectric ceramic and has external dimensions of 6 x 25 x 1 mm. 6×25
Groove 1 with a width of 0.085 mm and a depth of 0.17 mm on the mm side
34 pieces of 2 are formed. The wall dimensions of the piezoelectric material are width 0.
085mm and height 0.17mm. The piezoelectric element 11
A sol-gel solution 16 of barium titanate PTC thermistor material prepared in a container 17 suspended by a wire 15
immerse it in water and pull it out at a constant speed. This method is called dip coating, and a thin film with a uniform thickness is formed. In this embodiment, the groove 12 of the piezoelectric element 11
The film was formed by masking the parts other than the sides. The formed film had a thickness of about 0.8 μm after drying. In this example, the film was formed by dip coating, but other methods such as multi-source sputtering may be used.

FIG. 2 is a diagram showing the piezoelectric element 11 after heat treatment. The coated barium titanate PTC thermistor material is heat treated at 500 to 1000°C. The barium titanate-based PTC thermistor material is completely crystallized by heat treatment, and a diffusion reaction progresses at the interface with the piezoelectric ceramic material, resulting in strong adhesion. The thickness of the film after heat treatment was approximately 0.5 μm. The piezoelectric element 11 shown in FIG.
A drive electrode 24 made of TC thermistor material is formed. Since this PTC thermistor material is a ceramic material, it has excellent ink resistance.

FIG. 3 shows the temperature and resistivity characteristics of the barium titanate PTC thermistor material used in this example. It can be seen that it exhibits a specific resistance of several Ω-cm or less from room temperature to about 50° C., and functions as a conductive material. The Curie temperature of this material is approximately 80℃, and above this temperature, it is 1010Ω.
It can be seen that it exhibits a specific resistance of about -cm and functions as an insulating material. It is well known that the Curie temperature of barium titanate-based PTC thermistor materials can be controlled by techniques such as adding trace amounts of additives or replacing cations.

FIG. 4 shows the process of polarizing the piezoelectric element 11. A piezoelectric element 11 having a drive electrode 24 made of a barium titanate PTC thermistor material formed on the side surface of the groove 12 is sandwiched between flexible electrodes 42a and 42b and placed in an oil bath (not shown) filled with insulating silicone oil. It was then placed in a container and polarized by applying an electric field of 2.5 kV/mm at 100° C. for 10 minutes. When the flexible electrode 42a is used as an anode and the flexible electrode 42b is used as a cathode, the polarization direction 43 is downward in the thickness direction.

FIG. 5 shows an example of the configuration of a pulse droplet deposition device using the piezoelectric element described above. The piezoelectric element 11 is bonded to the cover plate 52 via a flexible adhesive layer 51. Ink ejection holes 5 are provided on the longitudinal front surface of the groove 12 of the piezoelectric element 11.
Glue the nozzle plate 54 with 3. After that, the back cover 55 and the back plate 56 are bonded together.

Next, to explain the operation of this pulsed droplet deposition device, this pulsed droplet deposition device applies a voltage to the drive electrode 24 made of barium titanate PTC thermistor material formed on the side surface of the groove 12 of the piezoelectric element 11. This causes a shear deformation of the wall 13 of piezoelectric material. The portion formed by the groove 12 and the cover plate 52 operates as an ink flow path and an ink chamber, and causes a volume change due to shear deformation of the piezoelectric material wall 13 described above. Ink droplets are ejected from the ink ejection holes 53 due to the generation of pressure due to the change in volume.

FIG. 6 shows how the piezoelectric element is repolarized. When the piezoelectric element 11 is incorporated into a pulsed droplet deposition device, it undergoes various bonding steps. Generally, piezoelectric ceramics used in such piezoelectric elements often have a Curie temperature of about 300°C. The bonding process is often accompanied by heat treatment. Polarized piezoelectric ceramics completely lose their ferroelectricity above the Curie temperature, but even when exposed to temperatures of 100 to 200°C, the polarization state deteriorates. Therefore, in order to make full use of the piezoelectric properties of the piezoelectric ceramics used, it becomes necessary to repolarize the piezoelectric ceramics after the assembly process. However, when using the internal shear mode of the deformation mode of the piezoelectric material as in the piezoelectric element of this example, the polarization direction and the driving electric field application direction are perpendicular to each other. Couldn't polarize. However, since the piezoelectric element of this embodiment uses a barium titanate-based PTC thermistor material as the drive electrode, the repolarization process can be easily performed. The flexible electrodes 42a and 42b are brought into contact with the upper surface of the cover plate 52 and the lower surface of the piezoelectric element 11 of the pulse droplet deposition apparatus shown in FIG.
An electric field of kV/mm was applied. This repolarization treatment was performed in an oven at 100° C. for 10 minutes. In the repolarization process described above, the drive electrode 24 made of barium titanate PTC thermistor material formed on the side surface of the groove 12 of the piezoelectric element 11 acts as an insulator, and a good repolarization process can be achieved. Therefore, we were able to realize a pulsed droplet deposition device that takes full advantage of the piezoelectric properties of the piezoelectric ceramic material used.

[0016]

[Effects of the Invention] As is clear from the above explanation, the piezoelectric element for a pulse droplet deposition device that utilizes shear deformation of a piezoelectric material according to the present invention has a drive electrode made of a PTC thermistor material. The present invention provides a piezoelectric element for a pulse droplet deposition device that can be repolarized, can make maximum use of piezoelectric properties, has a drive electrode that has excellent adhesive strength with the piezoelectric material, and has excellent ink resistance.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the film forming process of this example.

FIG. 2 is a schematic diagram showing a piezoelectric element in which a drive electrode made of PTC thermistor material is formed on the side surface of a groove according to this embodiment.

FIG. 3 is a diagram showing the relationship between specific resistance and temperature of the PTC thermistor material used in this example.

FIG. 4 is a schematic diagram showing the polarization process of the piezoelectric element of this example.

FIG. 5 is a schematic diagram showing a configuration example of a pulse droplet deposition device using the piezoelectric element of this embodiment.

FIG. 6 is a schematic diagram showing the process of repolarizing the piezoelectric element after assembly in this embodiment.

FIG. 7 is a schematic diagram showing a configuration example of a pulse droplet deposition device using a conventional piezoelectric element.

[Explanation of symbols]

11 Piezoelectric element 12 Ink groove 13 Piezoelectric material wall 14 Side of groove

Claims (1)

[Claims] 1. A piezoelectric element for a pulse droplet deposition device, which has a plurality of ink grooves and a wall made of piezoelectric material, and a drive electrode for applying an electric field to the side surface of the ink groove. A piezoelectric element for a pulse droplet deposition device, characterized in that the element is made of a PTC thermistor material.