EP1083048A1

EP1083048A1 - Ink jet recording head and manufacturing method thereof

Info

Publication number: EP1083048A1
Application number: EP99923867A
Authority: EP
Inventors: Takashi Nec Corporation OTA
Original assignee: NEC Corp
Current assignee: Fujifilm Business Innovation Corp
Priority date: 1998-06-02
Filing date: 1999-06-02
Publication date: 2001-03-14
Also published as: JP3248486B2; JPH11348276A; WO1999062712A1; AU4058699A; EP1083048A4

Abstract

A recording head includes a plurality of pressure chambers (2a, 2b, 2c) communicating with a nozzle and ink supply port and having vibration walls (3a, 3b, 3c), and a plurality of piezoelectric elements (7a, 7b, 7c) having external electrodes (8a, 9a) and respectively bonded to the plurality of vibration walls. The piezoelectric element has an active region (12a) in which distortion occurs by applying a voltage between the external electrodes and inactive regions (10a, 11a) in which no distortion occurs even if a voltage is applied, and the piezoelectric element is bonded to the pressure chamber through the active region and vibration wall and the inactive regions.

Description

1. Technical Field

The present invention relates to an ink jet recording head and method of manufacturing the same and, more particularly, to an ink jet recording head used in a printer, facsimile apparatus, or copying apparatus and a method of manufacturing the ink jet recording head.

2. Background Art

An ink jet recording head of this type is conventionally described in, e.g., Japanese Patent Laid-Open No. 9-174836.
Fig. 13 is a sectional view of a conventional ink jet recording head disclosed in Japanese Patent Laid-Open No. 9-174836.
In the conventional ink jet recording head, upper walls of pressure chambers 2a, 2b, and 2c which are filled with ink 1 are constructed from vibration plates 3a, 3b, and 3c. The vibration plates 3a, 3b, and 3c are bonded to piezoelectric elements 101a, 101b, and 101c, respectively. The piezoelectric elements 101a, 101b, and 101c are bonded and integrated to a base portion 102 on the surfaces opposite to the surfaces bonded to the vibration plates.
Fig. 14 is a sectional view taken along the line D - D in Fig. 13.
As shown in Fig. 14, the pressure chamber 2a communicates with a nozzle 4a. The pressure chamber 2a also communicates with an ink pool 6 through an ink supply port 5a. The piezoelectric element 101a is fixed to a constructing member of the pressure chamber 2a in inactive regions 201a and 202a indicating regions in which no distortion occurs inside even if a driving voltage is applied to the electrode. The element 101a is connected to the vibration plate 3a in an active region 203a indicating a region in which distortion occurs. Each of other pressure chambers 2b and 2c has the same arrangement.
A voltage is selectively applied to the piezoelectric element 101a in printing so that the generated displacement of the piezoelectric element 101a is transmitted to the pressure chamber 2a through the vibration plate 3a to compress the ink 1 in the pressure chamber 2a. Therefore, the ink droplet can be ejected from the nozzle.

3. Disclosure of Invention

[Problem to be Solved by the Invention]

In a conventional apparatus for compressing the pressure chamber by contraction/expansion operation of the piezoelectric element described above, the piezoelectric elements 101a, 101b, and 101c are integrated by the base portion 102. In this structure, although the piezoelectric elements 101a, 101b, and 101c are fixed to the pressure chambers 2a, 2b, and 2c through the inactive regions 201a and 202a, a so-called crosstalk occurs in which a displacement of a driven piezoelectric element is transmitted to an adjacent non-driven piezoelectric element through the base portion 102 and vibrates the adjacent non-driven piezoelectric element in the displacement direction, and the vibration of the non-driven piezoelectric element is transmitted to the corresponding pressure chamber. This crosstalk reduces the drop speed and diameter of an ejected ink droplet as the number of nozzles (the number of piezoelectric elements) which are simultaneously driven is large. In other words, the crosstalk varies the drop speed and diameter of the ink droplets ejected in accordance with the number of nozzles (the number of piezoelectric elements) which are simultaneously driven, thus causing ink droplet landing position deviation, printing density unevenness, and the like. As described above, the crosstalk causes printing quality degradation.

[Means of Solution to the Problem]

It is therefore a principal object of the present invention to prevent crosstalk in which vibrations based on the displacement of a driven piezoelectric element is transmitted to a non-driven pressure chamber and improve printing quality.
In order to achieve the above object, in the first invention of the present invention, a recording head comprises a pressure chamber unit communicating with a nozzle and ink supply port and including a plurality of pressure chambers each having one vibration wall on a surface in the same direction, and a plurality of piezoelectric elements each having two external electrodes and respectively bonded to the plurality of vibration walls. Each piezoelectric element is constructed from an active region in which distortion occurs inside when a voltage is applied to the external electrodes and an inactive region in which no distortion occurs inside when a voltage is applied to the external electrodes, the active region is bonded to the vibration wall of the pressure chamber, and the inactive region is bonded to only the pressure chamber. With this structure, each piezoelectric element is bonded to only the corresponding pressure chamber through the inactive region, and has no means for fixing a positional relationship between the piezoelectric elements. This can prevent that the displacement of a driven piezoelectric element is transmitted to a non-driven piezoelectric element and the non-driven piezoelectric element is vibrated in the displacement direction. Therefore, crosstalk in which vibrations caused by the displacement of the driven piezoelectric element are transmitted to a non-driven pressure chamber can be prevented.
In the second invention, the piezoelectric element further has the following arrangement in addition to the first invention. In the piezoelectric element, a plurality of piezoelectric material layers and a plurality of internal electrode layers are alternately stacked, and the internal electrodes are alternately staggered in a direction perpendicular to the stacking direction and alternately connected to two external electrodes formed on two side surfaces of the piezoelectric element in the staggering direction. The piezoelectric element is bonded to the vibration wall through the active region in which all the internal electrodes are stacked at a predetermined width, and to the pressure chamber through the inactive regions which are formed near the two external electrodes and in which the every second internal electrodes are stacked. With this structure, the vibration wall can sufficiently displace even if the width in the direction perpendicular to the stacking direction becomes narrow, thereby arranging the pressure chambers at a high density.
The third invention has the following arrangement in addition to the first invention. The piezoelectric element has a piezoelectric material, a non-piezoelectric material bonded on two sides of the piezoelectric material in a direction perpendicular to the array direction of the pressure chambers (i.e., in the horizontal direction of the plurality of pressure chambers), and two external electrodes formed on two surfaces opposing each other in the direction parallel to the array direction of the pressure chambers arranged at at least a part of the piezoelectric element. The piezoelectric element is bonded to the vibration wall through the piezoelectric material, and bonded to the pressure chamber through the non-piezoelectric materials formed on the two sides of the piezoelectric material. With this structure, the pressure chambers can be arranged at a high density, and an inexpensive single-layered piezoelectric element is used in place of an expensive stacked piezoelectric element, thereby obtaining the ink jet recording head at low cost.
The fourth and fifth inventions have the following arrangement in addition to the second and third inventions, respectively. The piezoelectric element has a notched portion in the inactive region between potions bonded to the vibration wall and bonded to the pressure chamber. With this structure, the displacement generated in the active region of the piezoelectric element is hardly constrained, thereby increasing electro-mechanical conversion efficiency (i.e., the pressure transmission efficiency for the ink in the pressure chamber).
The seventh invention is a method of manufacturing an ink jet recording head, comprising the first step of forming a piezoelectric element block having a length corresponding to a total length of the plurality of pressure chambers in an array direction of pressure chambers, and two external electrodes, an active region, and inactive regions, that are continuously formed throughout the length in the array direction, the second step of bonding the piezoelectric element block to the pressure chamber unit, and the third step of forming a plurality of piezoelectric elements respectively corresponding to the plurality of pressure chambers by cutting and separating the piezoelectric element block bonded to the pressure chamber unit. With this structure, the piezoelectric elements are separately formed after the piezoelectric element block and pressure chamber unit are bonded, thus improving the positioning precision of each pressure chamber and a corresponding piezoelectric element. 4. Brief Description of Drawings
Fig. 1 is a sectional view showing an ink jet recording head according to the first embodiment of the present invention;
Fig. 2 is a sectional view taken along the line A - A in Fig. 1;
Fig. 3 is a sectional view showing an ink jet recording head according to the second embodiment;
Fig. 4 is a sectional view taken along the line B - B in Fig. 3;
Fig. 5 is an exploded perspective view showing the first manufacturing method for the recording heads shown in Figs. 1 and 2;
Fig. 6A is a perspective view of a state wherein a pressure chamber unit and piezoelectric element block are bonded;
Fig. 6B is a perspective view of a state wherein the piezoelectric element block bonded to the pressure chamber is cut and separated;
Fig. 7A is a perspective view showing a method of manufacturing the piezoelectric element block according to second embodiment shown in Figs. 3 and 4 (the second manufacturing method);
Fig. 7B is a perspective view showing the method of manufacturing the piezoelectric element block according to the second embodiment shown in Figs. 3 and 4;
Fig. 7C is a perspective view showing the method of manufacturing the piezoelectric element block according to the second embodiment shown in Figs. 3 and 4;
Fig. 8 is a perspective view showing an ink jet recording head according to the third embodiment;
Fig. 9 is a sectional view taken along the line C - C in Fig. 8;
Fig. 10A is a perspective view showing a method of manufacturing the piezoelectric element block according to the third embodiment shown in Figs. 8 and 9 (the third manufacturing method);
Fig. 10B is a perspective view showing the method of manufacturing the piezoelectric element block according to the third embodiment shown in Figs. 8 and 9;
Fig. 11A is a perspective view showing the method of manufacturing the ink jet recording head according to the third embodiment shown in Figs. 8 and 9;
Fig. 11B is a perspective view showing the method of manufacturing the ink jet recording head according to the third embodiment shown in Figs. 8 and 9;
Fig. 12 is a perspective view showing an ink jet recording head according to the fourth embodiment;
Fig. 13 is a sectional view of a conventional ink jet recording head; and
Fig. 14 is a sectional view taken along the line D - D in Fig. 13.

5. Best Mode of Carrying Out the Invention

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment

Fig. 1 is a sectional view showing an ink jet recording head according to the first embodiment of the present invention, and Fig. 2 is a sectional view taken along the line A - A in Fig. 1.
Referring to Fig. 1, pressure chambers 2a, 2b, and 2c filled with ink 1 are formed such that a plate-like deformable vibration plate 3 (this vibration plate having projections 3a, 3b, and 3c) are bonded to a plate-like substrate member in which a plurality of recess portions-each having the same shape are aligned at a predetermined interval. As shown in Fig. 2, the pressure chamber 2a communicates with a nozzle 4a for ejecting an ink droplet toward a printing medium and an ink pool 6 for supplying the ink 1 through an ink supply port 5a. Note that, although not illustrated, other pressure chambers 2b and 2c communicate with nozzles 4b and 4c and the ink pool 6 for supplying the ink 1 through ink supply ports 5b and 5c, respectively.
Piezoelectric elements 7a, 7b, and 7c which correspond to the pressure chambers 2a, 2b, and 2c, respectively, and are completely separated from each other are bonded to the vibration plate 3.
The piezoelectric element 7a is a so-called stacked piezoelectric element. As shown in Fig. 2, the piezoelectric element 7a has a plurality of internal electrodes a and a plurality of internal electrodes b which are alternately connected to two external electrodes 8a and 9a, respectively. When a voltage is applied to the external electrodes 8a and 9a, an electric field is applied to an active region 12a serving as an overlap region of the internal electrodes respectively connected to the external electrodes 8a and 9a while sandwiching piezoelectric ceramic layers c between them to cause distortion.
In other regions in the piezoelectric element 7a, i.e., in each of inactive regions 10a and 11a, only the internal electrodes a or b which are stacked while sandwiching the piezoelectric ceramic layer c between them and connected to one of the external electrodes are present. Therefore, even when the voltage is applied to the external electrodes 8a and 9a, no electric field is applied in the inactive regions 10a and 11a. In this structure, therefore, no distortion occurs in the inactive regions 10a and 11a. The piezoelectric element 7a is bonded to portions fixed to a substrate member of the vibration plate 3, i.e., portions on the lower surfaces of the corresponding inactive regions 10a and 11a. The piezoelectric element 7a is also connected to a projection 3a of the vibration plate 3 corresponding to the pressure chamber 2a on a lower surface of the active region 12a.
Note that, each of other piezoelectric elements 7b and 7c has the same arrangement as the piezoelectric element 7a.
In this case, when the voltage is selectively applied to the external electrodes of the piezoelectric element in printing, the piezoelectric element displaces in the stacking direction of the internal electrodes. Since the generated displacement of the piezoelectric element is transmitted to the pressure chamber through the vibration plate 3 to compress the ink in the pressure chamber, the ink droplets can be ejected from the nozzle.
In the first embodiment of the present invention, each of the piezoelectric elements 7a, 7b, and 7c is bonded to two portions fixed to the substrate member of the corresponding vibration plate 3, i.e., two portions on the lower surfaces of corresponding inactive regions 10a and 10b interposing the corresponding active region 12a. Also, the piezoelectric elements 7a, 7b, and 7c are completely separated. This can prevent the non-driven piezoelectric element from directly receiving the displacement of the driven piezoelectric element, applying the pressure to its pressure chamber, and vibrating in the displacement direction. In addition, the force caused by the generated displacement of the driven piezoelectric element is applied to the substrate member in the curving direction so that the substrate member vibrates. However, this vibration in the curving direction generates little pressure in the pressure chamber corresponding to the non-driven piezoelectric element, thereby occurring no crosstalk.
As described above, in the first embodiment, so-called crosstalk in which vibrations caused by the displacement of the driven piezoelectric element are transmitted to the non-driven piezoelectric element can be prevented. Hence, the drop speed and diameter of the ejected ink droplet are not varied by the number of nozzles (i.e., the number of piezoelectric elements) which are simultaneously driven, thereby ejecting the stable ink droplet. As a result, the ink jet recording head with good printing quality can be obtained. Second Embodiment
Fig. 3 is a sectional view showing an ink jet recording head according to the second embodiment of the present invention, and Fig. 4 is a sectional view taken along the line B - B in Fig. 3.
Unlike the first embodiment described above, in the second embodiment, notched portions are formed in inactive regions formed on two sides of an active region of each of piezoelectric elements 13a, 13b, and 13c.
As shown in Fig. 4, in the piezoelectric element 13a, notched portions 17a and 18a are respectively formed in inactive regions 14a and 15a formed on two sides of an active region 16a. Each surface of the notched portions 17a and 18a on the side of the active region 16a positions apart from the active region 16a at a predetermined interval. Therefore, the every second stacked electrodes are exposed on inner surfaces of the notched portions 17a and 18a.
A non-stacked portion d in which internal electrodes a and b are not stacked and which occupies 20% or more of the thickness of the piezoelectric element 13a is formed on that side of the piezoelectric element 13a which opposes the side to which a vibration plate 3 is bonded. The notched portions 17a and 18a preferably have a depth to almost ensure the thickness of the non-stacked portion d. That is, the notched portions 17a and 18a preferably have a depth nearly equal to the thickness of the stacked portion in which the internal electrodes a and b are stacked. Assume that stacked portions corresponding to the notched portions 17a and 18a are left. In this case, even if internal electrodes are stacked in these stacked portions, the inactive regions 14a and 15a undesirably limit the displacement of the active region 16a. Since the stacked portions corresponding to the notched portions 17a and 18a are omitted, the cost can be reduced as compared with a piezoelectric element whose total thickness is increased by adding the thickness of the stacked portions. The corners of the notched portions 17a and 18a preferably have curved surfaces with appropriate curvature to avoid stress concentration.
Intermediate electrodes 19a and 20a are formed on the most part of the inner surfaces of the notched portions 17a and 18a by plating or sputtering and connect the plurality of internal electrodes in the inactive regions 14a and 15a, respectively. External electrodes 21a and 22a are formed on the two end faces of the piezoelectric element 13a by plating or sputtering in the same manner as the intermediate electrodes 19a and 20a. The internal electrodes in the active region 16a of the piezoelectric element 13a are alternately connected to the intermediate electrodes 19a and 20a, and further connected to external electrodes 21a and 22a through the internal electrodes in the inactive regions 14a and 15a. Therefore, when a voltage is applied to the external electrodes 21a and 22a, the voltage is applied to the internal electrodes in the active region 16a of the piezoelectric element 13a through the internal electrodes of the inactive regions 15a and 16a and the intermediate electrodes 19a and 20a, thereby applying an electric field to the active region 16a. In this case, however, no electric field is applied in the inactive regions 14a and 15a.
The piezoelectric element 13a is fixed to the vibration plate 3 on the lower surfaces of the corresponding inactive regions 14a and 15a which are separated from the active region 16a by the notched portions 17a and 18a. The fixed portions are portions fixed by a substrate member constructing a pressure chamber.
On the other hand, the active region 16a of the piezoelectric element is connected to a projection 3a of the vibration plate 3 corresponding to a pressure chamber 2a.
Note that, each of other piezoelectric elements 13b and 13c has the same arrangement as the piezoelectric element 13a.
In the second embodiment of the present invention, not only the same effect as in the first embodiment described above but also the following effect can be obtained. Since the notched portions are formed in the inactive regions near the active region of the piezoelectric element, the inactive region hardly constrains the displacement generated in the active region of the piezoelectric element, thereby improving electro-mechanical conversion efficiency (i.e., the pressure transmission efficiency for ink in the pressure chamber). More specifically, the piezoelectric element is different from that in the conventional apparatus in which the active region and the inactive regions formed on the two sides of the active region are integrated each other. Accordingly, unlike the conventional apparatus, the inactive region does not constrain the displacement generated from the active region, thereby improving the pressure transmission efficiency for the ink in the pressure chamber.

First Manufacturing Method

A method of manufacturing the ink jet recording head in the present invention will be described next.
Fig. 5 is an exploded perspective view showing the method of manufacturing the recording heads shown in Figs. 1 and 2.
First, a first pressure chamber plate 23 having spaces serving as perspective pressure chambers is bonded to a nozzle plate 4 having nozzles 4a, 4b, and 4c. An ink supply port plate 5 in which ink supply ports 5a, 5b, and 5c, and portions serving as the perspective pressure chambers are aligned at predetermined intervals is then bonded to the first pressure chamber plate 23. A second pressure chamber plate 24 having spaces serving as the perspective pressure chambers is then bonded to the ink supply port plate 5. Subsequently, a vibration plate 3 (vibration plate module) having projections 3a, 3b, and 3c is bonded to the second pressure chamber plate 24, and a piezoelectric element block 7 having two external electrodes 8 and 9 is bonded on the vibration plate module 3.
All the internal electrodes and piezoelectric ceramic layers are alternately stacked in the central portion between a pair of side surfaces at a predetermined width in the piezoelectric block 7. Near each side surface, the internal electrodes and piezoelectric ceramic layers are stacked such that adjacent every second internal electrodes sandwich two piezoelectric ceramic layers. These internal electrodes and piezoelectric ceramic layers are sintered and integrated, and the two external electrodes 8 and 9 extending from the two side surfaces to the upper surface of the piezoelectric element block are formed.
The nozzle plate 4 is manufactured by forming the nozzles 4a, 4b, and 4c in a stainless steel plate or the like by pressing. Alternately, the nozzle plate 4 having the nozzles 4a, 4b, and 4c and made of nickel or the like is formed by electroforming.
The first pressure chamber plate 23, ink supply port plate 5, and second pressure chamber plate 24 are formed from stainless steel plates or the like by pressing, or from photosensitive dry films by photolithography.
In the vibration plate 3, peripherals of the projections 3a, 3b and 3c have shapes thinner than other portions of the vibration plate 3. The vibration plate 3 is made of nickel by electroforming, or of the stainless steel plate or the like by half etching.
In each bonding, the stainless steel plates are to be bonded by heating and diffusion or using an adhesive, and the dry films can be bonded to each other by heat fusing.
Note that, the piezoelectric element block 7 and vibration plate 3 are bonded by using an adhesive.
A pressure chamber unit 25 constructed from the nozzle plate 4, first pressure chamber plate 23, ink supply port plate 5, second pressure chamber plate 24, and vibration plate 3, and the piezoelectric element block 7 are bonded in this manner.
Fig. 6A is a perspective view of a state wherein a pressure chamber unit and piezoelectric element block are bonded.
The piezoelectric element block 7 is worked from the state shown in Fig. 6A such that the vibration plate 3 is cut exceeding the bonding surface of the pressure chamber unit 25 to a predetermined depth. At this time, the cut position is determined using the external shape of the pressure chamber unit 25 as reference such that each piezoelectric element is accurately positioned to and formed on a corresponding pressure chamber. The piezoelectric element block 7 is cut in accordance with the determined cutting position, and piezoelectric elements 7a, 7b, and 7c are separated and formed, as shown in Fig. 6B. The piezoelectric element block 7 can be cut by a dicing saw or wire saw.
According to the first manufacturing method of the present invention, after the piezoelectric element block and pressure chamber unit 25 are bonded, each piezoelectric element is positioned to a corresponding pressure chamber, and the piezoelectric elements are separated from each other, thereby improving the positioning precision of each pressure chamber and a corresponding piezoelectric element. Therefore, the ink jet recording head having a little variation in characteristics can be obtained.

Second Manufacturing Method

The second manufacturing method for the ink jet recording head will be described next.
The second manufacturing method of the present invention is basically the same as the first manufacturing method described above except for a piezoelectric element block 13 is bonded to a pressure chamber unit 25 after notches are formed in the piezoelectric element 13.
Figs. 7A to 7C are views for explaining a method of manufacturing the piezoelectric element block 13, and show the second manufacturing method.
Referring to Fig. 7A, the piezoelectric element block 13 having the same arrangement as the piezoelectric element block shown in the first embodiment is prepared. In the upper portion shown in Fig. 7A, the piezoelectric element block 13 of the second embodiment shown in Figs. 3 and 4 is formed such that a non-stacked portion d in which no internal electrodes are stacked occupies 20% or more of the thickness in the stacking direction.
On the lower surface of the piezoelectric element block 13 opposite to the side to which the non-stacked portion d is formed, inactive regions in which the internal electrodes and piezoelectric ceramic layers are alternately stacked such that adjacent every second internal electrodes sandwich two piezoelectric ceramic layers are formed, as described above. Notched portions 17 and 18 are respectively formed in the inactive regions by a dicing saw or wire saw (Fig. 7B). The notched portions 17 and 18 are arranged apart from each other at a predetermined distance in the widthwise direction of the active region and formed at a uniform depth throughout the length of the block. The notch is formed to have a depth to ensure the thickness of the aforementioned non-stacked portion d, i.e., to have the depth nearly equal to the thickness of the stacked portion (i.e., the portion in which the internal electrodes are stacked).
Intermediate electrodes 19 and 20 are then formed on the inner surfaces of the notched portions 17 and 18, and external electrodes 21 and 22 are formed on the two sides of the piezoelectric element block 13 by plating or sputtering (Fig. 7C). At this time, the non-formation region of the external electrodes and intermediate electrodes are masked by a resist, and the masking members are removed after forming electrode films.
The piezoelectric element block 13 shown in Fig. 7C is manufactured in this manner and bonded to the pressure chamber unit 25. The piezoelectric element block 13 is then positioned with respect to the pressure chambers in the same manner as the first manufacturing method, and cut and separated.
According to the second manufacturing method of the present invention, since the notched portions are formed in the inactive regions near the active region of the piezoelectric element, the ink jet recording head excellent in electro-mechanical conversion efficiency (i.e., the pressure transmission efficiency for ink in the pressure chamber) can be obtained. In addition, the pressure chambers and piezoelectric elements can be easily and precisely positioned in manufacturing the ink jet recording head.

Third Embodiment

The third embodiment of the present invention will be described below.
Fig. 8 is a perspective view showing an ink jet recordings head according to the third embodiment of the present invention, and Fig. 9 is a sectional view taken along the line C - C in Fig. 8.
Unlike the second embodiment shown in Figs. 3 and 4, in the third embodiment, piezoelectric elements 26a, 26b, and 26c are single-layered piezoelectric elements on which a pair of external electrodes opposing each other are formed in the array direction of pressure chambers (i.e., in the direction of the piezoelectric element 26a → piezoelectric element 26b → piezoelectric element 26c in Fig. 8 (i.e., in the horizontal direction in Fig. 8)).
More specifically, the piezoelectric element 26a in this embodiment is a single-layered piezoelectric element, and non-piezoelectric material portions 27 which do not deform when applying an electric field are bonded on two sides of a piezoelectric material portion 28, as shown in Fig. 9. The piezoelectric material portion 28 serves as an active region, and the non-piezoelectric material portions serve as inactive regions. A depth of notched portions 17 and 18 is determined depending on the displacement limitation of the active region by the inactive regions and a decrease in rigidity of the notched portions. In the same manner as the second embodiment, the corners of the notched portions 17 and 18 preferably have curved surfaces with appropriate curvature to avoid a stress concentration.
External electrodes 29a and 30a which respectively cover a pair of surfaces opposing each other in the array direction of the pressure chambers are formed on the piezoelectric element 26a by plating or sputtering so as to cover at least a part or the whole of the piezoelectric material portion 28. Pad portions 31a and 32a are formed on the upper surface of the piezoelectric element 26a to connect the external electrodes 29a and 30a to a driving circuit (not shown).
With this structure, even if a voltage is applied to the external electrodes 29a and 30a, the non-piezoelectric material portions 27 do not deform. The piezoelectric material portion 28 deforms when the voltage is applied to the external electrodes 29a and 30a to apply the pressure to a pressure chamber 2a.
In the same manner as the second embodiment shown in Figs. 3 and 4, the piezoelectric element 26a is fixed to a vibration plate 3 on the lower surfaces of the corresponding inactive regions which are separated from the active region by the notched portions 17 and 18. The fixed portions are portions fixed by a substrate member constructing a pressure chamber.
On the other hand, an active region 16a is connected to a projection 3a corresponding to the pressure chamber 2a.
Each of other piezoelectric elements 26b and 26c has the same arrangement as the piezoelectric element 26a.
In the third embodiment of the present invention, similar to the second embodiment, since no crosstalk occurs, the good printing quality can be obtained, and electro-mechanical conversion efficiency can be improved. In addition, since no expensive stacked piezoelectric element is used, the ink jet recording head can be realized at low cost.

Third Manufacturing Method

The third manufacturing method of the present invention which is a method of manufacturing the recording head shown in Fig. 9 will be described next.
Figs. 10A and 10B are perspective views showing the method of manufacturing the piezoelectric element block according to the third embodiment, and Figs. 11A and 11B are perspective views showing the method of manufacturing the ink jet recording head according to the third embodiment.
Referring to Fig. 10A, a piezoelectric element block 26 formed by bonding non-piezoelectric material portions 27 to a pair of side surfaces of a piezoelectric material portion 28, respectively, is prepared. Notched portions 17 and 18 are respectively formed in inactive regions comprised of the non-piezoelectric material portions 27 on the lower surface of the piezoelectric element block 26 by a dicing saw or wire saw. The notched portions 17 and 18 are arranged apart from the active region at a predetermined distance and formed at a uniform depth throughout the length of the block.
Photosensitive resin layers 33 which are used to form patterns as masks when forming external electrodes are formed on the upper and entire side surfaces of the piezoelectric element block 26 and the entire inner surfaces of the notched portions 17 and 18 (Fig. 10B).
The piezoelectric element block 26 on which the photosensitive resin layers 33 are formed is then bonded to a pressure chamber unit 25.
The photosensitive resin layers 33 are positioned with respect to the pressure chambers and exposed such that portions at which the pad portions of the external electrodes are formed are removed after cutting the block, and unexposed portions are removed (Fig. 11A).
Subsequently, the piezoelectric element block is positioned with respect to the pressure chambers and, in the same manner in the first and second manufacturing methods, cut and separated by a dicing saw or the like (Fig. 11B).
After that, the external electrodes are formed by plating or sputtering at the portions which are not covered by the photosensitive resin layers 33. After forming the electrode films, the photosensitive resin layers 33 are removed.
According to the third manufacturing method of the present invention, the single-layered piezoelectric elements each having a pair of electrodes opposing each other in the array direction of the pressure chambers are bonded to the pressure chambers, respectively, thereby arranging the pressure chambers at a high density. In addition, not only electro-mechanical conversion efficiency can be improved, but also the ink jet recording head can be easily manufactured at low cost because no expensive stacked piezoelectric element is used.

Fourth Embodiment

The fourth embodiment of the present invention will be described below.
Fig. 12 is a perspective view showing an ink jet recording head according to the fourth embodiment of the present invention.
The fourth embodiment is similar to the third embodiment described above in that piezoelectric elements 34a, 34b, and 34c are single-layered piezoelectric elements on which a pair of external electrodes opposing each other are formed in an array direction of pressure chambers, except that no notched portions are formed.
The piezoelectric element 34a in this embodiment is a single-layered piezoelectric element, as described aboye, and non-piezoelectric material portions which do not deform when applying an electric field are bonded on two sides of a piezoelectric material portion, similar to the third embodiment. The piezoelectric material portion therefore serves as an active region, and the non-piezoelectric material portions serve as inactive regions.

Fourth Manufacturing Method

The fourth manufacturing method of the present invention which is a method for manufacturing the recording head shown in Fig. 12 according to the fourth embodiment will be described next.
In the fourth manufacturing method, similar to the third manufacturing method, a piezoelectric element block which is formed to bond each non-piezoelectric material portion to one of a pair of side surfaces of a piezoelectric material portion is prepared.
In this manufacturing method, photosensitive resin layers 33 which are used to form patterns as masks when forming external electrodes are formed on the upper and entire side surfaces of the piezoelectric element block in which no notched portion is formed. The piezoelectric element block in which the photosensitive resin layers 33 are formed is then bonded to a pressure chamber unit 25.
The photosensitive resin layers 33 are positioned with respect to the pressure chambers and exposed such that portions at which the pad portions of the external electrodes are formed are removed after cutting the block, and unexposed portions are removed.
Subsequently, the piezoelectric element block is positioned with respect to the pressure chambers and, in the same manner in the first, second, and third manufacturing methods, cut and separated by a dicing saw or the like.
After that, the external electrodes are formed by plating or sputtering at the portions which are not covered by the photosensitive resin layers 33. After forming the electrode films, the photosensitive resin layers 33 are removed.
According to the fourth manufacturing method of the present invention, since the processes for forming notched portions in the piezoelectric element and for forming the photosensitive resin layers in the notched portions are not required, the ink jet recording head can be easily manufactured at low cost.
Note that, a positional relationship between a pressure chamber in a pressure chamber unit, a nozzle, and an ink supply port is not limited to this, if the pressure chambers are aligned and a vibration plate is formed on a single surface.
As has been described above, according to the present invention, a piezoelectric element has an active region in which distortion occurs inside when a voltage is applied between external electrodes and an inactive region in which no distortion occurs inside when the voltage is applied between the external electrodes, and is bonded to a corresponding pressure chamber through the active region and a vibration wall and to the corresponding pressure chamber through the inactive region. With this structure, the displacement of the driven piezoelectric element is not transmitted to the non-driven piezoelectric element, and the non-driven piezoelectric element is not vibrated in the displacement direction, thereby preventing crosstalk in which the vibration caused by the displacement by the driven piezoelectric element is transmitted to the non-driven pressure chamber. As a result, printing quality can be improved.
Also, since a notched portion is formed in each inactive region between portions bonded to the vibration plate of the piezoelectric element and bonded to the pressure chamber, the inactive region does not constrain the displacement of the active region of the piezoelectric element. Therefore, the pressure transmission efficiency for the ink in the pressure chamber can be improved.
In addition, in the manufacturing method of the present invention, after the piezoelectric element block and the pressure chamber unit are bonded, each piezoelectric element is positioned to the corresponding pressure chamber, and the piezoelectric elements are separated from each other, thereby improving the positioning precision of each pressure chamber and a corresponding piezoelectric element. As a result, the recording head having a little variation in characteristics of each pressure chamber can be obtained. Further, the recording head capable of the high density, minimizing, having a plurality of nozzles, performing at a high-density, compact, multi-nozzle, high-speed, low-power, low-cost recording head can be provided.

Claims

An ink jet recording head characterized by comprising:

a pressure chamber unit (25) communicating with a nozzle (4a) and ink supply port (5a) and including a plurality of pressure chambers (2a, 2b, 2c) respectively having vibration walls (3a, 3b, 3c); and

a plurality of piezoelectric elements (7a, 7b, 7c) each having two external electrodes (8a, 9a) and respectively bonded to the plurality of vibration walls,
wherein each of said plurality of piezoelectric elements has an active region (12a) in which distortion occurs inside if a voltage is applied to the two external electrodes and an inactive region (10a, 11a) in which no distortion occurs inside if a voltage is applied to the two external electrodes, and is bonded to the corresponding pressure chamber through the active region and vibration wail and to the corresponding pressure chamber through the inactive region.
An ink jet recording head according to claim 1, characterized in that

piezoelectric material layers (c) and internal electrodes (a, b) are alternately stacked in each of said piezoelectric elements on the side of the vibration wall of the pressure chamber,

the internal electrode comprises a first electrode (a) having one end connected to one of the two external electrodes and a second electrode (b) having one end is connected to the other of the two external electrodes, and the first and second electrodes are stacked on each other at a predetermined interval through the piezoelectric material layer so as to overlap each other in the active region, and

the inactive region of each of said piezoelectric elements comprises first and second inactive regions formed in a direction perpendicular to the stacking direction while interposing the active region therebetween, and one and the other external electrodes are formed near the first and second inactive regions, respectively.
An ink jet recording head according to claim 1, characterized in that

each of said piezoelectric elements comprises a piezoelectric material (28) formed on the side of a vibration wall of a pressure chamber and indicating the active region and non-piezoelectric materials (27) formed so as to bond to the two side surfaces of the piezoelectric material formed on the pressure chamber, the two external electrodes are formed on two surfaces perpendicular to the two side surfaces of the piezoelectric material, and

each of said piezoelectric elements is bonded to the vibration wall through the piezoelectric material and bonded to the pressure chamber through the non-piezoelectric materials formed on the two side surfaces of the piezoelectric material.
An ink jet recording head according to claim 2, characterized in that

each of said piezoelectric elements has a notched portion (17a, 18a) in the inactive region between portions bonded to the vibration wall and bonded to the pressure chamber.
An ink jet recording head according to claim 3, characterized in that

each of said piezoelectric elements has a notched portion (17a, 18a) in the inactive region between portions bonded to the vibration wall and bonded to the pressure chamber.
An ink jet recording head according to claim 2, characterized in that

each of said piezoelectric elements has a non-stacked portion (d) which is formed on a portion where the internal electrodes are stacked and occupy 20% or more of the thickness of the entire stacked layer, and in which no internal electrode is stacked, and a notched portion (17, 18) formed by notching, at a predetermined width, the stacked portion of the inactive region between portions bonded to the vibration wall and bonded to the pressure chamber, and an intermediate electrode (19a, 20a) connecting between an external electrode and internal electrode is formed in the notched portion.
A method of manufacturing an ink jet recording head characterized in that

a pressure chamber unit (25) communicating with a nozzle (4a) and ink supply port (5a) and including a plurality of pressure chambers (2a, 2b, 2c) respectively having vibration walls (3a, 3b, 3c), and a plurality of piezoelectric elements (7a, 7b, 7c) each having two external electrodes (8a, 9a) and respectively bonded to the plurality of vibration walls are formed, each of the plurality of piezoelectric elements has an active region (12a) in which distortion occurs inside if a voltage is applied to the external electrodes and inactive regions (10a, 11a) in which no distortion occurs inside if a voltage is applied to the external electrodes, and is bonded to a corresponding pressure chamber through the active region and vibration wall and to the corresponding pressure chamber through the inactive region, and

said method comprises

the first step of forming a piezoelectric element block (7) having a length corresponding to a total length of the plurality of pressure chambers, and the two external electrodes, the active region, and the inactive regions, that are continuously formed throughout the length,

the second step of bonding the piezoelectric element block to the pressure chamber unit, and

the third step of forming the plurality of piezoelectric elements respectively corresponding to the plurality of pressure chambers by cutting the piezoelectric element block bonded to the pressure chamber unit to separate from each other.
A method of manufacturing the ink jet recording head according to claim 7, characterized in that:

each of the piezoelectric elements comprises a piezoelectric material (28) formed on a pressure chamber and indicating the active region, and non-piezoelectric materials (27) formed so as to bonded to two side surfaces of the piezoelectric material on the pressure chamber and indicating inactive regions, and the two external electrodes are arranged on two surfaces perpendicular to the two side surfaces of the piezoelectric material; and

the first step comprises the fourth step of forming a piezoelectric element block (26) by bonding the piezoelectric material and a pair of non-piezoelectric materials each having a length equal to that of the piezoelectric material so as to have a length corresponding to the total length of the plurality of pressure chambers.
A method of manufacturing the ink jet recording head according to claim 7, characterized in that

the first step comprises the step of forming a notched portion, throughout the length of the piezoelectric element block, in the inactive region between portions bonded to the vibration wall of the piezoelectric element block having the length corresponding to the total length of the plurality of pressure chambers and bonded to the pressure chamber of the piezoelectric element block.
A method of manufacturing the ink jet recording head according to claim 8, characterized in that

the first step comprises the step of forming a notched portion, throughout the length of the piezoelectric element block, in the inactive region between portions bonded to the vibration wall of the piezoelectric element block having the length corresponding to the total length of the plurality of pressure chambers and bonded to the pressure chamber of the piezoelectric element block.
A method of manufacturing the ink jet recording head according to claim 8, characterized in that:

the two external electrodes have pad portions (31a, 32a) formed to extend on an upper surface of each of the piezoelectric elements, and

said method comprises the fifth step of forming a photosensitive resin layer (33) on an upper and entire side surfaces of the piezoelectric element block having a width corresponding to a total width of a plurality of pressure chambers,

the sixth step of bonding the piezoelectric element block on which the photosensitive resin layer is formed to the pressure chamber unit,

the seventh step of positioning the piezoelectric element block with respect to the pressure chamber, exposing the photosensitive resin layer, and removing a portion of the photosensitive resin layer in which the pad portion of the external electrode is formed,

the eighth step of cutting the piezoelectric element block bonded to the pressure chamber unit to form a plurality of piezoelectric elements respectively corresponding to the plurality of pressure chambers, and

the ninth step of forming external electrodes each having the pad portion on cut surfaces and the portion (36) removed in the eighth step of each of the piezoelectric elements.