JP2003039657A - Piezoelectric actuator and ink jet print head comprising it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plurality of piezoelectric actuators arranged in array by cutting multilayer piezoelectric elements individually, and an ink jet print head comprising the piezoelectric actuators in which highly reliable, inexpensive multilayer piezoelectric elements are employed while suppressing variation of characteristics. SOLUTION: Active region of piezoelectric actuators located at the opposite ends of an array or piezoelectric actuators located in the vicinity thereof has a length shorter than that of the active region of remaining piezoelectric actuators.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator to which a weak displacement generated by an electric signal is applied. The present invention also relates to an inkjet printhead of a printer that ejects ink droplets by the pressure generated by a piezoelectric actuator to form an ink image on a recording medium.

[0002]

2. Description of the Related Art A general laminated piezoelectric element manufacturing process is as follows. A small amount of an organic binder, a plasticizer, and a dispersant are added to the pre-combustion powder of the piezoelectric ceramic and dispersed in a dispersion medium to form a slurry. This slurry is applied to a film forming device to form a thick film having a thickness of several tens of μm, and cut into an appropriate size to form a green sheet. Next, a metal paste for internal electrodes (silver-palladium alloy or the like) is printed and applied on one surface of the green sheet, several hundreds of these are stacked and thermocompression bonded by a press to form a green laminate. The green laminate is first heated to a temperature of about 400 ° C., and after undergoing a binder removal step of thermally decomposing all organic components contained therein, it is heated again to a temperature of 1000 ° C. or more to be sintered. This sintered body is a piezoelectric element containing a large number of metal electrodes inside, and after cutting and processing it to the desired size and shape, each internal electrode is an external electrode (metal film) provided on the side surface of the sintered body. To electrically connect to manufacture a laminated piezoelectric element.

Further, conventionally, there has been known an ink jet print head in which a piezoelectric actuator using this piezoelectric element presses ink and ejects the ink from a nozzle. A piezoelectric element used in such an ink jet print head generally has a structure in which a piezoelectric film is sandwiched between a lower electrode and an upper electrode, and it utilizes displacement of the piezoelectric film by applying a voltage to the electrodes. ing. In the piezoelectric actuator having such a structure, first, a laminated piezoelectric element having a length capable of forming a plurality of elements is adhered to a supporting substrate, and an electrode portion of the laminated piezoelectric element and a wiring pattern of the supporting substrate are electrically conductive with an adhesive. Etc. to electrically connect. After that, the laminated piezoelectric elements are individually cut with a dicing saw, a wire saw or the like to collectively form a plurality of piezoelectric actuators.

In an ink jet head using a piezoelectric actuator as a pressure generating means, when ink droplets are ejected from a plurality of nozzles and the ink is landed on a recording medium, in order to obtain a high quality image, it is ejected from each nozzle. It is desirable that the ink ejection speeds are the same. However, when an electric signal is applied to the piezoelectric actuator used in the inkjet print head, the resulting displacement amount of the piezoelectric actuator varies. This is because, in the process of manufacturing a laminated piezoelectric element, when heating and sintering at a temperature of 1000 ° C. or higher, silver, which is a material of the internal electrode, is diffused and the density distribution of the internal electrode becomes uneven depending on the place. Is.

The variation of the displacement amount is the variation of the ejection speed of the ink ejected from the nozzle. This variation in the amount of displacement is that the amount of displacement of the piezoelectric actuators located at both ends of the row and the amount of displacement of the piezoelectric actuators located in the vicinity thereof are different from those of the other piezoelectric actuators. Therefore, as disclosed in JP-A-5-246025,
A method of providing two or more dummy piezoelectric actuators at least one at each end of the piezoelectric actuators forming a row and a total of two or more dummy piezoelectric actuators is shown.

[0006]

However, providing the dummy piezoelectric actuators is disadvantageous in reducing the size of the piezoelectric actuators in a row in an ink jet head in which nozzles are arranged in rows. Using a piezoelectric actuator that does not actually contribute to printing is a waste of the piezoelectric element and increases the cost. Further, even in the method of using both ends which have large variations in displacement, the material is wasted and the cost of the laminated piezoelectric element is increased.

The present invention solves such a conventional problem, and an object thereof is to provide piezoelectric actuators located at both ends of a row, or piezoelectric actuators located at both ends of a row and piezoelectric elements in the vicinity thereof. Another object of the present invention is to provide a laminated piezoelectric element in which the length of the active region of the actuator is made substantially equal to the displacement amount of the other piezoelectric actuators. Another object of the present invention is to provide an inkjet printhead using a laminated piezoelectric element, which can reduce variations in ink ejection speed and can obtain high-quality image quality.

[0008]

SUMMARY OF THE INVENTION The above-described object is to stack the piezoelectric material amount and the conductive material amount alternately, and cut the laminated piezoelectric element composed of the active region and the inactive region individually to form a row. In the plurality of arranged piezoelectric actuators, the lengths of the active areas of the piezoelectric actuators located at both ends of the row or the piezoelectric actuators located at both ends of the row and the piezoelectric actuators in the vicinity thereof are calculated as the lengths of the active areas of the remaining piezoelectric actuators. It is achieved by making it smaller than

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a structural explanatory perspective view of a main part of an ink jet print head using a piezoelectric actuator using a d31 type laminated piezoelectric element. Reference numeral 2 shown in FIG. 1 is an orifice plate having a plurality of nozzles 1 formed therein.
The processing accuracy of the opening shape of the nozzle 1 has a great influence on the ink ejection characteristics of the inkjet print head. The manufacturing method of the orifice plate 2 is required to have high processing accuracy in order to suppress variations in nozzle accuracy among a plurality of nozzles 1. Therefore, the orifice plate 2 is formed by nickel electroforming, stainless steel precision pressing, laser machining, or the like. This orifice plate 2
The chamber plate 4 in which the pressure chamber 3 is formed, and the restrictor plate 6 in which the restrictor 5 that connects the ink supply path 10 and the pressure chamber 3 and controls the ink inflow into the pressure chamber 3 are formed are positioned. To join.

Further, a diaphragm plate 9 having a vibrating plate 7 for efficiently transmitting the pressure of the piezoelectric actuator 13 to the pressure chamber and a filter portion 8 for removing dust and the like in the ink flowing into the restrictor 5 from the common ink passage 10. The housing 11 having the common ink passage 10 is similarly positioned and joined. Chamber plate 4, restrictor plate 6, diaphragm plate 9
Is made by etching of stainless steel or electroforming of nickel. An ink introducing pipe 19 for guiding the ink from the external ink tank to the common ink passage 10 is joined to the housing 11 made of metal or resin.

Next, the order of manufacturing the piezoelectric actuator 13 of the present invention will be described. First, a plurality of laminated piezoelectric element rods are arranged and bonded and fixed on the end face of the support substrate 16 in the direction perpendicular to the thickness direction. Next, the electrode portion of the laminated piezoelectric element rod and the wiring pattern of the supporting substrate are electrically connected with a conductive adhesive or the like. Then, the laminated piezoelectric element rod is divided by cutting using a dicing saw, a wire saw, or the like. At this time, each of the divided laminated piezoelectric elements 14 corresponds to each pressure chamber. Further, the support substrate 16 has an individual electrode 17 and a common electrode 1 for sending an electric signal independent of an external drive circuit to each laminated piezoelectric element 14.
8 is formed. The piezoelectric element 14 is distorted by applying a selective electric signal from the external drive circuit to the piezoelectric element 14. Since the piezoelectric element 14 is bonded onto the highly rigid support substrate 16, the piezoelectric element 14 is preferentially displaced to increase the pressure in the pressure chamber 3.

Finally, the piezoelectric actuator 1 comprising a plurality of laminated piezoelectric elements 14 and a supporting substrate 16 for fixing them.
3 is positioned and joined to the adhesive assembly of the housing and plates described above with an adhesive 12.

FIG. 2 is a partial sectional view of an ink jet print head for explaining an embodiment of the present invention. The piezoelectric actuator 13 includes a support substrate 16 and a laminated piezoelectric element 14. The support substrate 16 is a fixing member that fixes the laminated piezoelectric element 14. The laminated piezoelectric element 14 is bonded to the vibration plate 7 via the adhesive 12. The vibrating plate 7 and the chamber plate 4 form a pressure chamber 3. The pressure in the pressure chamber 3 changes rapidly due to the deformation of the vibrating plate 7. An individual electrode 17 and a common electrode 18 are formed on the support substrate 16 and are electrically connected to the laminated piezoelectric element 14 by a conductive bonding member 15. By applying a selective electric signal from the external drive circuit to the laminated piezoelectric element 14, the laminated piezoelectric element 14 is displaced in the direction toward the nozzle 1. Due to this displacement, the vibrating plate 7 is deformed via the adhesive 12, and the ink filled in the pressure chamber 3 is pressurized, so that the nozzle 1
The ink is ejected as an ink droplet. The ink jet print head described in this embodiment is used in an apparatus that discharges ink from the nozzle 1 and forms an ink image on a recording medium based on such a principle.

FIG. 3 is a perspective view of the structure of the laminated piezoelectric element 14. By applying a selective electric signal from the external drive circuit to the laminated piezoelectric element 14, the laminated piezoelectric element 14
Generates a displacement in the direction toward the nozzle 1, and this displacement amount δ is obtained by the following equation. δ = d31 · L · E / t where d31 is the piezoelectric constant determined by the piezoelectric material, L is the length 23 of the active portion where the internal electrode 21 of the common electrode and the internal electrode 22 of the individual electrode intersect, and E is the electric Applied voltage of signal, t
Is the interlayer distance 24 of the internal electrodes.

Using the laminated piezoelectric element described above, a laminated piezoelectric element having a length capable of forming a plurality of elements is adhered to a supporting substrate, and the electrode portion of the laminated piezoelectric element and the wiring pattern of the supporting substrate are electrically conductive. An electrical connection is made with an adhesive, the laminated piezoelectric elements are individually cut, and a plurality of piezoelectric actuators are formed in a row so as to be arranged in a row. Is applied to the piezoelectric actuator,
The result of measuring the displacement amount of the obtained piezoelectric actuator is shown in FIG. In the figure, the piezoelectric actuator No. 1 and No. 128 are located at both ends in the row. From this figure, it can be seen that the displacement amounts of the piezoelectric actuators located at both ends in the row and in the vicinity thereof are larger than the other displacements.

Next, in an ink jet print head using the piezoelectric actuator as a pressure generating means, a constant voltage is applied to the piezoelectric actuator from an external drive circuit to measure the ink ejection speed when ink is ejected from the nozzle 1. The results obtained are shown in FIG. In this figure, nozzle No. And the piezoelectric actuator No. 1 of FIG. Correspond to each nozzle, and the nozzle No. 1 and No. 128
Are located at the ends of the row. From this figure, it can be seen that the ink ejection speeds of the nozzles at both ends in the row are faster than the others. Further, comparing FIG. 4 and FIG. 5, there is a correlation between the displacement amount of the actuator and the ink ejection speed. A high ink ejection speed has a large displacement amount of the actuator, and a slow ink ejection speed has a small displacement amount. In other words, it can be said that the variation in the ink ejection speed is the variation in the displacement of the piezoelectric actuator. In order to suppress the variation in the ink ejection speed that deteriorates the print quality, the variation in the displacement of the piezoelectric actuator is suppressed. This is to reduce the displacement of the piezoelectric actuator and the piezoelectric actuator in the vicinity thereof, and to make the displacement the same as the others.

In order to reduce the displacement amount of the piezoelectric actuator, since the displacement amount δ and the length L of the active portion are in a proportional relationship from the above equation, in the present invention, the internal electrode 21 of the common electrode and the internal electrode of the individual electrode are The length of the active part 2 where the electrodes 22 intersect each other 2
3 was reduced. In order to reduce the length 23 of both ends and the active part in the vicinity thereof in the laminated piezoelectric element, when applying and printing the internal electrode metal paste on one surface of the green sheet in the manufacturing process of the laminated piezoelectric element, This is because it suffices to apply and print the metal paste for the internal electrodes in the vicinity thereof in a thinner manner than the other ones, and it is easy to carry out collectively in the manufacturing process and is easy. In FIG. 4, the displacement amount of the piezoelectric actuators No1 to No4 is about 5 to 6% larger than the displacement of the central portion.
In order to make this equal to the central portion, if the applied area of the internal electrode metal paste is made thinner than the central portion by about 5 to 6% and the active portion length 23 is made smaller, the displacement amount at the central portion becomes substantially equal, and the piezoelectric actuator The variation in the amount of displacement is reduced.

Further, in FIG. 4, the displacement amount of the piezoelectric actuator gradually changes from both ends toward the center. Therefore, when the active portion length 23 is gradually reduced from both ends toward the center, the displacement amount at the center portion becomes substantially equal to
Variations in the displacement of the piezoelectric actuator can be reduced.

Further, in FIG. 4, the range in which the displacement of the piezoelectric actuator is large is the entire length (nozzles No. 1 to N).
o. 128) within about 1/3 (nozzle No. 1 to N
o. 42, nozzle No. 86 to No. 128). When the length 23 of the active region is reduced within this range, the displacement amount of the central portion becomes substantially equal to that of the displacement amount of the piezoelectric actuator.

In FIG. 6, the laminated piezoelectric element was used and adhered to a support substrate, the laminated piezoelectric element was cut into individual pieces, and a plurality of piezoelectric actuators were collectively formed so as to be arranged in one row. , Showing a piezoelectric actuator. The active portion lengths 231 and 232 of the piezoelectric actuators located at the ends of the rows and the piezoelectric actuators in the vicinity thereof are set to other active portion lengths 2
Less than 3n (active portion length 231 ≦ 232 ≦ ... <23
n). With this configuration, the displacement amounts of the piezoelectric actuators located at both ends of the row, or the piezoelectric actuators located at both ends of the row and the piezoelectric actuators in the vicinity thereof can be made substantially equal to the displacement amounts of the other piezoelectric actuators. In addition, the piezoelectric actuator using the laminated piezoelectric element reduces the variation in the ejection speed of the ink ejected from the nozzles in the row, and the ink jet print head can obtain a high quality image.

In the present embodiment, the d31 type laminated piezoelectric element is used, but the same effect can be obtained in laminated piezoelectric elements using other plane orientations.

[0023]

According to the present invention, in a plurality of piezoelectric actuators which are formed by cutting the laminated piezoelectric element individually and arranging them in rows, a metal paste for an internal electrode is formed in a manufacturing process step of the laminated piezoelectric element. By partially changing the coating / printing width of (1), it is possible to provide a laminated piezoelectric element having stable characteristics and reducing variations in individual displacement amounts. Further, by configuring an inkjet printhead using the above-mentioned laminated piezoelectric element, it is possible to provide an inkjet printhead which is small in size, excellent in ink ejection characteristics, and inexpensive.

[Brief description of drawings]

FIG. 1 is a structural explanatory perspective view of a main part of an inkjet printhead using a piezoelectric actuator.

FIG. 2 is a partial cross-sectional view of an inkjet printhead using a piezoelectric actuator.

FIG. 3 is a perspective view showing the structure of a main part of a laminated piezoelectric element.

FIG. 4 is a graph showing the position and displacement of a piezoelectric actuator according to the conventional technique.

FIG. 5 is a graph showing a nozzle position and an ink droplet ejection speed in the related art.

FIG. 6 is a structural explanatory perspective view of a main part of the piezoelectric actuator of the present invention.

[Explanation of Codes] 1 ... Nozzle, 2 ... Orifice plate, 3 ... Pressure chamber, 4
... chamber plate, 5 ... restrictor, 6 ... restrictor plate, 7 ... diaphragm, 8 ... filter part, 9 ... diaphragm plate, 10 ... common ink passage, 11 ... housing, 12 ... adhesive, 13 ... piezoelectric actuator, 1
4 ... Multilayer piezoelectric element, 15 ... Conductive bonding member, 16 ... Support substrate, 17 ... Individual electrode, 18 ... Common electrode, 19 ... Ink introduction pipe, 20 ... External electrode, 21 ... Common electrode side internal voltage, 22 ... Internal voltage of individual electrodes, 23,231,2
32 to 23n ... Length of active part, 24 ... Distance between layers.

Continued front page    F-term (reference) 2C057 AF21 AG12 AG47 AP02 AP25                       BA04 BA14

Claims (4)

[Claims] 1. A plurality of piezoelectric actuators, wherein a piezoelectric material amount and a conductive material amount are alternately laminated, and a laminated piezoelectric element composed of an active region and an inactive region is individually cut and arranged in a row. , The lengths of the active regions of the piezoelectric actuators located at both ends of the row or the piezoelectric actuators located at both ends of the row and the piezoelectric actuators in the vicinity are smaller than the lengths of the active areas of the remaining piezoelectric actuators. Piezoelectric actuator. 2. The piezoelectric actuator according to claim 1, wherein in the laminated piezoelectric element, the length of the active region is gradually reduced from both ends of the row toward the center. 3. The laminated piezoelectric element according to claim 1, wherein the range of reducing the length of the active region is within about 1/3 of the entire length of the laminated piezoelectric element from both ends of the laminated piezoelectric element. The piezoelectric actuator according to 1 or 2. 4. Pressure chambers for storing ink, pressure generating means for generating pressure fluctuations in the pressure chambers by applying electric signals individually communicating with these pressure chambers, and at least a part of the wall surface of the pressure chambers. A diaphragm that is connected to the pressure generating means with an adhesive, a restrictor that is a flow path that supplies ink to the pressure chamber, and a common ink passage that supplies ink to the restrictor, An ink jet print head having a nozzle for ejecting ink droplets from the pressure chamber, wherein the nozzle is arranged in one row or a plurality of rows, wherein the piezoelectric actuator according to claim 1, 2 or 3 is used as the pressure generating means. Inkjet print head that is characterized by