JPH07178902A - Inkjet head and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] To provide an ink jet head having excellent image forming quality by uniformly ejecting ink droplets in a nozzle row. [Structure] The displacement of the laminated piezoelectric conversion element 11 in the direction indicated by the piezoelectric strain constant d ₃₁ is used for ejecting ink droplets, and the laminated piezoelectric conversion element 11 is connected to a plurality of ink chambers 19 and arranged in rows. In the inkjet head, the length of the active portion 17 of the laminated piezoelectric conversion element 11 is changed within the laminated piezoelectric conversion element array 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-demand type ink jet head in which a laminated piezoelectric conversion element is used as pressure generating means and ink is ejected from a nozzle by a drive voltage applied to the pressure generating means.

[0002]

2. Description of the Related Art A piezoelectric conversion element made of a piezoelectric material has a function as a conversion element of electric energy and mechanical energy, and is therefore applied to fields such as actuators. In recent years, the piezoelectric conversion element is of a laminated type and is used as an actuator of an inkjet head, whereby a significant reduction in drive voltage has been obtained. An ink jet head using a laminated piezoelectric conversion element is disclosed in Japanese Unexamined Patent Publication No. 3-264360 and is small in size by ejecting ink droplets by using displacement in a direction perpendicular to the electric field of the laminated piezoelectric conversion element. The inkjet head that can be driven at a low voltage and is easy to manufacture is shown in FIG.

[0003]

However, the above-mentioned prior art has the following problems.

FIG. 13 and FIG. 14 are schematic views showing the displacement state of the laminated piezoelectric conversion element when ink is ejected from a conventional ink jet head. 11 is a laminated piezoelectric conversion element, 12 is a mounting plate, 19 is an ink chamber, 23 is a pressure plate, 26 is an ink chamber side wall, 27 is an ink droplet ejection nozzle, 28 is a nozzle plate, and 29 is an ink chamber forming member. . The thickness of each piezoelectric material layer of the laminated piezoelectric conversion element 11, the piezoelectric strain constant of the piezoelectric material, and the active portion length are all uniform in the element array. The laminated piezoelectric conversion element 11 is displaced about the mounting plate 12 as a fulcrum when a driving voltage is applied, and generates ink droplet ejection pressure. However, the rigidity of the mounting plate 12 or the member forming the ink chamber is insufficient, so that the plate deforms as shown in each drawing. Therefore, although the displacement amount of each element itself is uniform in the element array, the change in the volume of the ink chamber becomes smaller in a part of the element array than in the other, and the ink droplet ejection amount becomes different. Due to the difference in the ink droplet ejection amount in the nozzle row, a high-density portion and a low-density portion are formed in the formed image, making it difficult to obtain a high-quality image.

As another problem, the internal electrodes between the piezoelectric material layers of the laminated piezoelectric conversion element are partially disconnected, so that the active portion in the element is reduced and the displacement amount varies in the element array. The disconnection of the internal electrodes increases as the density of the device increases, so that the manufacturing yield further decreases if a fine image is to be obtained.

Therefore, the present invention is intended to solve such a problem, and an object of the present invention is to provide an ink jet head having an excellent image forming quality by uniformly ejecting ink droplets in a nozzle array. It is in.

[0007]

The ink jet head of the present invention is intended to solve such a problem. In the direction indicated by the piezoelectric strain constant d ₃₁ of a laminated piezoelectric conversion element in which piezoelectric materials and electrodes are alternately laminated. In an inkjet head in which the displacement is used for ejecting ink droplets and the laminated piezoelectric conversion elements are connected to a plurality of ink chambers and arranged in rows, the length of the active portion of the laminated piezoelectric conversion elements is set to the laminated piezoelectric element. It is characterized in that it is changed in the conversion element array, and in particular, the length of the active portion of the laminated piezoelectric conversion element is shortened on both sides of the laminated piezoelectric conversion element array.

Further, by changing the area of the external electrode formed on the outermost piezoelectric element material layer of the laminated piezoelectric conversion element in the laminated piezoelectric conversion element array, the active portion of the outermost piezoelectric material layer is formed. It is characterized in that the length is changed, and in particular, the area of the external electrode of the laminated piezoelectric conversion element is reduced on both sides of the laminated piezoelectric conversion element row, and the maximum thickness of the laminated piezoelectric conversion element is increased. The piezoelectric strain constant of the piezoelectric material of the outer layer is different from the piezoelectric strain constant of the piezoelectric material of the other layer, or the thickness of the piezoelectric material of the outermost layer of the laminated piezoelectric conversion element is different from the thickness of the piezoelectric material of the other layer. It is characterized by

Furthermore, in the ink jet head manufacturing method of the present invention, the displacement in the direction indicated by the piezoelectric strain constant d ₃₁ of the laminated piezoelectric conversion element formed by alternately laminating the piezoelectric material and the electrode is used to eject the ink droplets. The laminated piezoelectric conversion element is connected to a plurality of ink chambers and arranged in a row, and the area of the external electrode formed on the outermost piezoelectric material layer of the laminated piezoelectric conversion element is defined by the inside of the laminated piezoelectric conversion element array. By changing
In the method of manufacturing an inkjet head in which the length of the active portion of the outermost piezoelectric material layer is changed, the electrode area is corrected after the formation of the external electrode of the laminated piezoelectric conversion element.

In the conventional head using the laminated piezoelectric conversion element, the ejection efficiency of the ink droplets is different due to the rigidity of the supporting portion and the action portion of the laminated piezoelectric conversion element, and the ejected ink amount is different between both ends of the element array. Many were less near the center. In this embodiment, by correcting the displacement amount of the laminated pressure conversion element in the element array, it is possible to make the ejected ink droplet amount substantially uniform in the laminated piezoelectric conversion element array.

The calculated displacement amount L of the unit layer is represented by the following equation, and the displacement amount of each layer of the piezoelectric material sandwiched between the internal electrodes can be calculated.

[0012]

[Equation 1]

Here, d ₃₁ is a piezoelectric strain constant in the direction perpendicular to the electric field and is a value determined by the piezoelectric material. a
Indicates the length of the active portion, which is determined by the overlapping length of the internal electrodes facing each other. t is the thickness of the piezoelectric material sandwiched between the internal electrodes, and indicates the thickness of the stack. V indicates an applied voltage.

From this equation, as a method of correcting the displacement amount, the effect can be obtained by first changing the length of the active portion at the central portion and the end portion of the element array. In order to make the calculated displacement amount L in the d ₃₁ direction larger in the central portion than in the end portion of the stacked piezoelectric transducer element array, it is sufficient to make the portion on the central portion side larger than the active portion length a of the end portion side element. . Since the active portion length a is the overlapping length of the upper and lower internal electrodes, the displacement amount can be corrected by making the central electrode length on the central side longer than the internal electrode length on the end side. Since the laminated piezoelectric conversion element is manufactured by alternately printing and sintering the piezoelectric material and the electrode material, the above-described correction can be performed only by changing the printed shape of the electrode at the time of manufacturing.

As another method, the laminated thickness t on the central portion side is made smaller than the laminated thickness t of the element on the end portion side of the element row, or the central portion is more than the piezoelectric strain constant d ₃₁ of the piezoelectric material on the end portion side. A method such as enlarging the one on the side can be considered. However, 2 described later
The two methods are difficult to manufacture and are not suitable for mass production, and it is most effective to correct the displacement amount by the length of the active part.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a perspective view of a laminated piezoelectric conversion element array showing a first embodiment of the present invention. 11a, 11b in the figure
Is a laminated piezoelectric conversion element (hereinafter referred to as a piezoelectric element),
12 is a mounting plate, 13 is an internal electrode, 14 is an external electrode,
Reference numeral 15 is a piezoelectric material layer, 16 is a laminated piezoelectric conversion element array (hereinafter referred to as an element array), and 17 is a hatched portion, each laminated pressure conversion element is an active portion (hereinafter referred to as an active portion) that expands and contracts according to a voltage from each electrode. It is called).

FIG. 2 is an exploded perspective view showing the structure of the internal electrodes of the laminated piezoelectric conversion element according to the first embodiment of the present invention. The figure shows a state before processing into each piezoelectric element.

In this embodiment, as shown in FIG. 1, the active parts 17 of the piezoelectric elements 11a at both ends of the piezoelectric element array 16 are made the shortest, and the active parts are gradually lengthened toward the central part of the piezoelectric element array 16. The length of the active portion of the element 11b located in the central portion of the piezoelectric element array 16 and having the smallest ink droplet ejection amount is set to the maximum. As shown in FIG. 2, by stacking the piezoelectric material layer 15 and the internal electrode 13, the active portion shown in FIG. 1 is obtained.

Here, an example of an ink jet head using the piezoelectric element of this embodiment as an actuator will be shown. FIG. 3 is a perspective view showing the outline of an inkjet head, and FIG. 4 is a sectional view of a piezoelectric element. The piezoelectric element 11 is the mounting plate 1
2 are arranged in a row on the mounting plate 12, and the mounting plate 12 further includes the fixing plate 2.
It is fixed at 0. The tip of the piezoelectric element 11 is fixed via a pressure plate 23 to an ink chamber 19 defined by an ink chamber side wall 26, and the ink chamber communicates with a nozzle 27 provided on a nozzle plate 28 and an ink tank (not shown). To do.

FIG. 4 is a sectional view of the piezoelectric element of this embodiment. The internal electrode 13a is the tip of the piezoelectric element 11 and the external electrode 14
The internal electrode 13b is electrically connected to the external electrode 14b at the end surface of the piezoelectric element 11 on the mounting plate side. External electrode 1
4a, 14b is directly mounted, or is mounted on the mounting plate 12 using a conductive paste or the like, and a drive voltage is applied.

When a voltage is applied to the piezoelectric element 11, the piezoelectric element 11 contracts with the mounting plate 12 as a fulcrum (indicated by an arrow 25 in FIG. 4), and the pressure plate 23 is pulled at the tip of the piezoelectric element 11 to cause the ink. The volume of the chamber 19 is increased. Ink is sucked and filled into the ink chamber 19 from an ink tank (not shown) connected thereto. It is necessary to gradually apply the voltage so that the behavior of the ink in the ink chamber 19 does not change. Then, when the applied voltage is rapidly released, the volume of the ink chamber 19 returns to its original state, and a part of the ink volume previously filled is ejected from the nozzle as an ink droplet.

5 and 6 are schematic views showing the displacement state of the piezoelectric element of the ink jet head. 5 shows a case where the mounting plate is deformed by the displacement of the piezoelectric element, and FIG. 6 shows a case where the ink chamber forming member is deformed by the displacement of the piezoelectric element. In reality, both members are deformed at the same time. In the figure, 11 is a piezoelectric element, 12 is a mounting plate, 19 is an ink chamber, 23 is a pressure plate, 26 is an ink chamber side wall, 27 is a nozzle, 28 is a nozzle plate, and 29 is an ink chamber forming plate.

Since the mounting plate and each member forming the ink chamber do not have sufficient rigidity, they are deformed as shown in the figure. When a uniform displacement amount is shown in all the element rows as in the conventional case, the volume change of the ink chamber in the central portion of the element rows becomes small. Therefore, the amount of ink droplets ejected from the nozzle in the central portion of the element array is smaller than that at the end portion of the element array. Therefore, in this embodiment, as shown in the figure, the active portion in the central portion of the element array was lengthened to increase the displacement amount, and the volume change of the obtained ink chamber could be made substantially uniform.

Next, a method of manufacturing the laminated piezoelectric conversion element of the present invention will be described in detail.

FIG. 7 is a diagram showing a procedure for alternately stacking piezoelectric materials and internal electrodes. As shown in FIG. 7 (a),
First, the piezoelectric green sheet 32 corresponding to the piezoelectric material layer is formed. Next, as shown in FIG. 7B, the electrode paste 33 for the internal electrodes is printed on the green sheet 32. Next, as shown in FIG. 7C, the green sheet 32 is laminated on the electrode paste 33, and as shown in FIG.
An electrode paste 34 that forms a pair with the electrode paste 33 and serves as a counter electrode is printed. By repeating the lamination of the green sheets 32 and the printing of the electrode pastes 33 and 34 as described above, a laminated body 35 as a prototype of the piezoelectric substrate as shown in FIG. 7E is obtained.

Next, after the laminated body 35 of the green sheet and the electrode paste is thermocompression bonded, it is sintered at a high temperature of about 1000 ° C., and finally the external electrodes are formed to form the piezoelectric element of the present invention. A strange substrate can be created. As the external electrode, a thin film electrode is formed by sputtering, vacuum evaporation, electroless plating, or the like, or a thick film electrode is formed by a conductive adhesive. The piezoelectric material was appropriately selected from lead zirconate titanate and the like.

To prepare a green sheet, first, the piezoelectric material is pre-sintered and then powdered, and an organic binder, plasticizer, dispersant,
A green sheet was prepared by mixing with a solvent to form a slurry, and then adhering the slurry to a roller, transferring it to a uniform thickness with a blade, punching it into a certain size and drying it. The electrode paste was appropriately selected or mixed from silver, palladium, platinum, etc., and mixed with a solvent and a binder before use.

Next, a second embodiment of the present invention will be described with reference to FIGS.

As shown in FIGS. 8 and 9, the active portions 17 are linearly aligned at the central portion of the piezoelectric element array, and the active portions 17 are changed in the direction of the free ends of the piezoelectric elements. According to this embodiment, the same effect as that of the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 10 is a perspective view of the piezoelectric element of this embodiment as seen from the mounting plate side. When a piezoelectric element is processed, a phenomenon in which the amount of displacement differs from element to element due to partial disconnection of internal electrodes or the like occurs. As described above, variations in the amount of displacement adversely affect printing.

Whether the element is good or bad is judged by confirming the displacement amount in the state of the element 11, but it is impossible to change the length of the internal electrode as a method of changing the displacement amount according to the result. Therefore, in this embodiment, the displacement amount of each element is corrected by changing the length of the external electrode 14 as shown in FIG. The electrode of the element 11 is 3 by a laser trimmer or the like.
The cutting was performed at the position of 0, and the length of the active portion of the outermost piezoelectric material layer 15a was corrected according to the displacement amount of each element. Here, the case where the displacement amount of the element 11c is the smallest is taken as an example, and the element 11c
The external electrodes 14 of other elements are corrected according to the displacement amount of c. Therefore, the element 11c has no correction portion. This embodiment makes it possible to make the displacement amount substantially uniform even if there is a defective element in the element array.

Conventionally, if the displacement amount of one element in an element array is insufficient from the standard, the element array becomes defective and the manufacturing yield is poor. However, according to the present embodiment, the displacement amount can be made substantially uniform by reducing the active portion of the outermost piezoelectric material layer of the other device in accordance with the device exhibiting the minimum displacement amount in the element array. The row can be used as a non-defective product, the manufacturing yield can be improved, and the cost can be reduced.

Further, the efficiency of displacement amount correction can be improved by the following embodiments.

In the structure of the conventional piezoelectric element, the thickness and material of the piezoelectric material are uniform, and the correction range is limited in the outermost layer electrode length. Therefore, in order to improve the correction efficiency, the displacement amount of the outermost piezoelectric material layer is increased, and the influence of the displacement amount of the outermost piezoelectric material layer on the displacement amounts of all the elements is increased.

The fourth and fifth embodiments of the present invention will be shown below. In the fourth example, the outermost piezoelectric material layer was made thinner than the other layers by the mathematical formula 1 than the other layers. FIG. 11 is a sectional view of the element of this example. As shown in the figure, by further reducing the thickness of the outermost piezoelectric material layer 15b and correcting the external electrode 14 in the same manner as in the third embodiment, a further effect was obtained.

In the same manner as the fifth embodiment, it is also possible to increase only the piezoelectric strain constant of the outermost piezoelectric material layer in the fourth embodiment.
The same effect as that of the above example was obtained.

In both the fourth and fifth embodiments, the contribution of the active portion length of the outermost layer piezoelectric material to the displacement of the entire element can be increased, and the variation in displacement amount can be corrected in a wider range. Became. According to this example, a better manufacturing yield could be obtained.

Further, as described below, the ink ejection amount in the element array shown in the first embodiment can be corrected only by correcting the external electrodes. FIG. 12 is a plan view of the piezoelectric element array of the sixth embodiment as viewed from the mounting plate side. The shaded area is the external electrode 14 that drives the outermost piezoelectric material. The active portion of the piezoelectric material layer driven by the internal electrodes is shown by the shaded portion 18. In this example, the displacement amount was corrected by changing the length of the active portion of the outermost piezoelectric material layer at the central portion and the end portion of the element array 16. When the external electrode 14 was formed by sputtering, patterning was performed using a mechanical mask to change the length of the external electrode 14 in the element array. This can simplify the process. It is also possible to perform patterning by lift-off or photolithography after forming the external electrode 14.

After that, by confirming the displacement amount of the element and further correcting the variation in the displacement amount, it becomes possible to manufacture an ink jet head in which the ejection amount of ink droplets in the element array is more uniform.

[0042]

According to the present invention, the length of the active portion of the piezoelectric element is corrected according to the variation in the ink droplet amount in the element array, so that a uniform ink droplet weight is obtained and a high quality image is obtained. It is possible. In addition, the length of the external electrode is changed according to the amount of displacement of each element, and a high quality image is obtained by correcting the active portion length of the outermost piezoelectric material layer,
Since the yield can be improved, the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view showing a laminated piezoelectric conversion element array according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing the configuration of internal electrodes of the laminated piezoelectric conversion element according to the first embodiment of the present invention.

FIG. 3 is a perspective view of an inkjet head using the laminated piezoelectric conversion element array according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a laminated piezoelectric conversion element according to a first embodiment of the present invention.

FIG. 5 is a schematic view showing the deformation of the mounting plate due to the displacement of the laminated piezoelectric conversion element array according to the first embodiment of the present invention.

FIG. 6 is a schematic view showing deformation of a member forming an ink chamber due to displacement of the laminated piezoelectric conversion element array according to the first embodiment of the present invention.

FIG. 7 is a perspective view showing a method of manufacturing a laminated piezoelectric conversion element of the present invention.

FIG. 8 is a perspective view showing a laminated piezoelectric conversion element array according to a second embodiment of the present invention.

FIG. 9 is an exploded perspective view showing the configuration of internal electrodes according to the second embodiment of the present invention.

FIG. 10 is a perspective view showing a laminated piezoelectric conversion element array according to a third embodiment of the present invention.

FIG. 11 is a sectional view showing a laminated piezoelectric conversion element according to a fourth embodiment of the present invention.

FIG. 12 is a plan view showing a laminated piezoelectric conversion element array according to a sixth embodiment of the present invention.

FIG. 13 is a schematic diagram showing deformation of a mounting plate due to displacement of a conventional stacked piezoelectric transducer element array.

FIG. 14 is a schematic view showing deformation of a member forming an ink chamber due to displacement of a conventional stacked piezoelectric conversion element array.

[Explanation of symbols]

 Reference Signs List 11 laminated piezoelectric conversion element 12 mounting plate 13 internal electrode 14 external electrode 15 piezoelectric material layer 16 laminated piezoelectric conversion element array 17 laminated piezoelectric conversion element active portion

Claims (7)

[Claims] 1. A plurality of nozzle openings for ejecting ink,
A pressure chamber communicating with each of the nozzle openings and a piezoelectric strain constant d ₃₁ arranged in a line on one wall surface of the pressure chamber to pressurize the pressure chamber.
In an ink jet head provided with a laminated piezoelectric conversion element having a displacement in the direction shown by, the length of the active portion of the laminated piezoelectric conversion element arranged in a row is within the laminated piezoelectric conversion element row. An inkjet head that is different. 2. The ink jet head according to claim 1, wherein the length of the active portion of the laminated piezoelectric conversion element is shortened on both sides of the laminated piezoelectric conversion element row. 3. The active portion of the outermost piezoelectric material layer is formed by changing the area of an external electrode formed on the outermost piezoelectric element material layer of the laminated piezoelectric conversion element in the laminated piezoelectric conversion element array. The ink jet head according to claim 1, wherein the length is changed. 4. The ink jet head according to claim 3, wherein the area of the external electrode of the laminated piezoelectric conversion element is reduced on both sides of the laminated piezoelectric conversion element row. 5. The ink jet head according to claim 3, wherein the piezoelectric strain constant of the piezoelectric material of the outermost layer of the laminated piezoelectric conversion element is different from the piezoelectric strain constant of the piezoelectric material of the other layers. 6. The ink jet head according to claim 3, wherein the thickness of the piezoelectric material of the outermost layer of the laminated piezoelectric conversion element is different from the thickness of the piezoelectric material of the other layers. 7. A displacement of a laminated piezoelectric conversion element formed by alternately laminating a piezoelectric material and electrodes in a direction indicated by a piezoelectric strain constant d ₃₁ is used for ejecting ink droplets, and the laminated piezoelectric conversion element has a plurality of inks. The outermost layer piezoelectric material is arranged in a row so as to be connected to the chamber and the area of the external electrode formed on the outermost piezoelectric material layer of the laminated piezoelectric conversion element is changed in the laminated piezoelectric conversion element row. In the method of manufacturing an inkjet head in which the length of the active portion of the layer is changed, the electrode area is corrected after the external electrodes of the laminated piezoelectric conversion element are formed.