Ink jet head allowing highly dense arrangement of nozzles

Abstract: An ink jet head includes an ink supply path (11), a pressure chamber (10), an orifice and an oscillator (7). By bending a portion of the wall surface of the pressure chamber (10) by oscillation of oscillator (7), ink is emitted. A portion of the wall surface of pressure chamber (10) is formed by an oscillating plate (4) of resin, and a unimorph including an elastic plate (5) and oscillator (7) provided on oscillating plate (4). Sidewalls (25) separating the inside of pressure chamber (10) are provided, and the dimension between the sidewalls is made shorter than the dimension of the unimorph.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an ink jet head used for an ink jet printer or the like, and more specifically, it relates to an ink jet head allowing highly dense arrangement of nozzles. Moreover it relates to a method of manufacturing such an ink jet head. Description of the Related Art An ink jet head of interest to the present invention is disclosed, for example, in Japanese Patent Laying-Open No. 6-64163. Fig. 10 is a perspective view of the ink jet head disclosed in this laid-open patent application. Referring to Fig. 10, there are a plurality of nozzle openings 101a, 101b, ... formed in a nozzle forming member 102. A pressure chamber forming member 103 is provided adjacent to nozzle forming member 102. An oscillating plate 104 is adhered to pressure chamber forming member 103. Electrodes are formed on both sides of oscillator 107. One electrode is connected to oscillating plate 104 and the other electrode is connected to a driving circuit by means of an anisotropic conductive film 108 or the like. Oscillating plate 104 also serves as a GND electrode. At a portion surrounded by nozzle forming member 102, pressure chamber forming member 103 and oscillating plate 104, there are formed a pressure chamber 110 and an ink outlet 111, filled with ink. When a voltage is applied between electrodes, a unimorph constituted by oscillating plate 104 and oscillator 107 is bent, pressing pressure chamber 110, so that ink drops are emitted from nozzle openings 101a, 101b, ... . In the figure, the reference character 112 represent a common ink pool, and 117 represents a flexible print circuit (FPC). The conventional ink jet head was structured as described above. However, as the oscillating plate is formed of a metal, it has a problem that reactive force is considerably large. A piezoelectric element is used for the oscillator. When a voltage is applied to the piezoelectric element by a signal from the driving circuit, the oscillating plate is displaced because of unimorph effect with the oscillating plate. That the oscillating plate has high rigidity means there is large reactive force preventing displacement of the oscillating plate. Therefore, displacement of the oscillating plate is suppressed, change in volume of the pressure chamber becomes smaller and the efficiency in emitting ink is degraded. Accordingly, it is necessary to enlarge the area of the oscillator or to apply a high voltage to the oscillator to obtain energy necessary for the emission. However, if the area of the oscillator is enlarged, degree of integration of nozzles becomes lower, the head becomes larger and hence the apparatus as a whole cannot be made compact. Further, if a high voltage is applied to the oscillator to ensure an amount of deformation of the oscillator, power consumed by the head is undesirably increased. Fig. 11a is a cross sectional view taken along the XI direction of the ink jet head shown in Fig. 10, and Fig. 11b is a side view of Fig. 11a. Referring to Figs. 11a and 11b, in the conventional head, the dimensions of an elastic plate 105 and oscillator 107 oscillating the sidewall of the pressure chamber are smaller than the dimension of the corresponding wall surface of the pressure chamber. The US-A-4,199,769 discloses a coincidence vector gate ink jet, in which a droplet is expressed from an outlet orifice by a coincident pressure produced by a pair of transducers at an outlet orifice. A pressure absorbing chamber is provided which permits a threshold pressure to be substantially increased to a level substantially above the minimum coincident pressure produced by the pair of transducers to express a droplet from the orifice. In the JP-A-5169654 a small sized ink jet recording head is described which is composed of a substrate on which a plurality of groovelike ink passages consisting of a nozzle, an ink feed route and a pressure chamber are provided. A part of piezoelectric element is bonded onto a diaphragm at a position above the ink passage and the pressure chamber. The JP-A-5177831 discloses a ink jet printing head in which a large number of individual ink passages are formed on a photosensitive glass substrate susceptible to anisotropic etching so as to extend from the rear end of the glass substrate to the front end thereof and a vibration plate is attached to the glass substrate on the side having the individual ink passages formed thereon so as to cover all of the ink passages and a common electrode is provided on the vibration plate and individual piezoelectric elements are fixed on the common electrode so as to be positioned above the individual ink passages and individual electrodes are provided on the individual piezoelectric elements. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an ink jet head which allows higher degree of integration of nozzles. Another object of the present invention is to provide an ink jet head which can be made compact. A still another object of the present invention is to provide an ink jet head allowing reduced power consumption. The above described objects of the present invention can be attained by the ink jet head in accordance with the features of the appended claim 1. The dimension of the bending portion provided by the unimorph is made larger than the dimension of the wall surface of the pressure chamber corresponding to the unimorph, whereby the dimension of the oscillator constituting the unimorph is made close to the channel pitch corresponding to the dimension between wall surfaces of the pressure chamber. Accordingly, highly dense arrangement of nozzles becomes possible. The ink jet head further includes an electrode forming a connecting terminal provided on the oscillator. The oscillator is adhered to the elastic plate by means of a first adhesive layer, and adhered to the connecting terminal by means of a second adhesive layer. The second adhesive layer is thicker than the first adhesive layer. The thickness of the adhesive layer in contact with the oscillator is made thinner on the side of the oscillating plate than on the side of the connecting terminal. Therefore, the problem that the adhesive layer on the side opposite to the oscillating plate binds the oscillator and prevents deformation of the oscillating plate, can be prevented. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1a to 1c are perspective view and cross sections, respectively, of an ink jet head in accordance with the present invention. Fig. 2a is a side view of the ink jet head in accordance with the present invention, and Fig. 2b is a partial enlargement of Fig. 2a. Fig. 3 is a perspective view of another embodiment of the ink jet head in accordance with the present invention. Fig. 4a is a side view of the aforementioned another embodiment of the ink jet head in accordance with the present invention, and Fig. 4b is a partial enlargement of Fig. 4a. Fig. 5 shows an oscillating plate and a pattern of electrodes formed on the oscillating plate. Fig. 6 shows an oscillator (PZT) plate in cut state. Fig. 7 shows a pattern of FPC bearing rear electrodes of the oscillator. Fig. 8a shows nozzles of the ink jet head in accordance with the present invention, and Fig. 8b is a cross section taken along the line A-A' of Fig. 8a. Figs. 9a to 9f are cross sections showing the steps of assembling the ink jet head in accordance with the present invention. Fig. 10 is a perspective view of a conventional ink jet head. Figs. 11a and 11b are cross sections of a conventional ink jet head. DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Referring to Figs. 1a to 1c, a plurality of nozzle openings 1a, 1b, ... are formed in nozzle forming member 2. Pressure chamber forming member 3 is provided adjacent to nozzle forming member 2. An oscillating plate 4 formed of resin is provided adjacent to pressure chamber forming member. Referring to Fig. 2a, an elastic plate 5 which also serves as an electrode, is provided adjacent to oscillating plate 4. An oscillator 7 formed of a piezoelectric element is provided adjacent to oscillating plate 4. Electrodes 6a, 6b are arranged on both surfaces of oscillator 7. One electrode 6a conducts electricity by contacting with the elastic plate 5 which also serves as an electrode, and the other electrode 6b conducts electricity by contacting with a connecting terminal 9 with an anisotropic conductive film 8 or the like interposed. In a portion surrounded by nozzle forming member 2, pressure chamber forming member 3 and oscillating plate 4, pressure chamber 10 and ink outlet 11 are formed, filled with ink. Ink outlet 11 is further communicated with common ink pool 12. Head substrate 13 is constituted by nozzle forming member 2 and pressure chamber forming member 3. When a voltage is applied between electrodes 6a and 6b, a contracting force in the planar direction acts on oscillator 7, a unimorph constituted by oscillator 7 and elastic plate 5 is bent, pressing oscillating plate 4, so that volume of pressure chamber 10 is changed and ink drops are emitted from nozzle openings 1. Nozzle forming member 2 and pressure chamber forming member 3 are formed, for example, of stainless parts, bonded by diffusion bonding, for example, and assembled as head substrate 13. In the present embodiment, elastic plate 5 electrically in contact with oscillator 7 and oscillating plate 4, and a signal line connected thereto are formed integrally on an FPC (Flexible Print Circuit) 14, so as to facilitate assembly. However, it is also possible to fabricate these separately and then assemble the separately provided parts. Referring to Fig. 2, oscillating plate 4 is fixed on head substrate 13 by means of an epoxy resin adhesive, for example. Oscillator 7 is formed of a sheet of a piezoelectric element, on both surfaces of which metal films 6a and 6b as electrodes are formed. The thinner the sheet, the larger strain can be obtained with lower voltage, and hence the smaller becomes the power consumption. Oscillator 7 is in contact with elastic plate 5 on one surface, and in contact with connecting terminal 9 on the other surface. Connecting terminal 9 is integral with FPC, and it is connected to the driving circuit. Fig. 2b is an enlarged view of connecting portion between elastic plate 5 and oscillator 7. Referring to Fig. 2b, a conductive adhesive or an epoxy resin 16, for example, Amicon A-316® manufactured by Grace Company, is used for the bonding between oscillator 7 and elastic plate 5. Though not conductive, epoxy resin layer is sufficiently thin, and therefore it is electrically connected to the electrode (elastic plate 5) of FPC 14, as well as to oscillator 7 at ups and downs of electrode 6a. Another electrode 6b of the PZT is in contact with electrode 9 of FPC 17 by means of anisotropic conductive film 8, such as 3370C® manufactured by Three Bond Company. Anisotropic conductive film 8 is thicker as an adhesive layer as compared with epoxy resin (epoxy resin layer is at most 5 µm, while anisotropic conductive film is about 35 µm in thickness), and therefore it does not strongly bind movement of PZT 7. Therefore, it does not suppress deformation when PZT 7 and oscillating plate 4 deform toward the pressure chamber. In this case, by fixing only the periphery of electrode 9 by anisotropic conductive film 8, deformation is less suppressed. Fig. 1b is a cross sectional view taken along the direction Ib of the ink jet head shown in Fig. 1a, and Fig. 1c is a side view of Fig. 1b. Referring to Figs. 1b and 1c, one wall surface of the pressure chamber includes an oscillating plate 4, an elastic plate 5 formed on oscillating plate 4, and an oscillator 7 formed on elastic plate 5, of which dimensions are larger than the dimension of the corresponding wall surface of the pressure chamber. As a result, the size of the oscillator can be selected close to the channel pitch. As a result, highly dense arrangement of nozzles becomes possible. Normal oscillation of the oscillator is ensured even if the channel pitch is made smaller, since oscillation at the sidewall portion of the channel is facilitated by employing a less elastic member as the oscillating plate. In the head as a whole, nozzles are arranged lengthwise and widthwise as shown in Figs. 8a and 8b. Fig. 6 shows oscillators in the whole head in accordance with the embodiment shown in Fig. 1. Oscillators corresponding to respective nozzles are arranged like a lattice. The oscillators are cut out by using a dicing saw or the like, from a PZT of a slightly larger size. The method of assembly will be described with reference to Figs. 9a, 9b, 9c, 9d and 9e. These oscillators are cut out from a large PZT plate 18/7 and bonded directly. This method of assembly is employed for the following reasons. Namely, rather than adhering a PZT one by one on each corresponding channel, it is preferable that the PZT plate 18/7 cut out and kept in the cut out state should be adhered as it is are to reduce the number of manufacturing steps and to reduce manufacturing cost. Further, since the size of the PZT plate is made larger than necessary, the PZT plate can be conveniently processed on a jig even when the size and position of the PZT plate mounted on the jig is unsatisfactory. The PZT plate 18/7 is fixed on a jig 22 by means of a double sided adhesive tape 19 which can be separated when heated (Fig. 9a), and the oscillators 7 are cut from the PZT plate to a prescribed size by a dicing saw in accordance with a reference of the jig (Fig. 9b). At this time, respective oscillators 7 cut out from PZT plate 18 are already located at positions corresponding to the electrode on the side of the oscillating plate 4. On a sheet having low elasticity, the oscillator plate 4 such as an FPC having a pattern of bodies having high modulus of elasticity is adhered (Fig. 9c), and a nozzle body is further adhered (Fig. 9d). Here such adhesion is controlled in accordance with reference holes, based on the reference holes of jig 22. Thus the steps of assembly can be simplified and adhesion with high precision becomes possible. Thereafter, the tape 19 is heated and separated (Fig. 9e). Thus the oscillators 7 cut from the PZT plate 18 can be adhered on electrode 5 of oscillating plate 4 all at once. Thereafter, FPC 17 having rear connecting electrode 9 is mounted with anisotropic conductive film 8 interposed (Fig. 9f). The electrodes 5 on the side of the oscillating plate of FPC 14 have rows in the Y direction connected commonly (Fig. 5). Electrodes 9 of another FPC 17 have columns in X direction connected in common (Fig. 7). By combining these and performing matrix-wise driving, the number of FPC wires and the number of drivers can be reduced, and hence the cost can be reduced. Further, at this time, the electrodes 5 on the side of the oscillating plate 4 are processed to have a pattern common to the oscillators 7 in the longitudinal direction, and the electrodes 9 on the opposite sides are processed to have a pattern common to the oscillators 7 in the shorter side direction. By such patterning, the portion of contact between the PZT and the opposite electrodes can be reduced, and binding of the movement of the oscillating plate 4 can be suppressed. (Second Embodiment) Another embodiment of the present invention will be described with reference to Figs. 3 and 4. Fig. 3 and Figs. 4a and 4b show another embodiment of the present invention. Pressure chamber forming member 3 is formed of a plastic material, such as polyether sulfone. Oscillating plate 4 is also formed of the same material. If the surfaces of these are melt by means of a solvent, such as a methyl ethyl ketone if these are both formed of polyether sulfone, the surfaces are brought into pressure contact. Since adhesive is not used, undesirable influence such as flowing of adhesive into the pressure chamber can be avoided, and highly strong adhesion is realized. An electrode 5 serving also as an elastic plate and a signal line connecting electrode 5 to an electrode 21 on the side of the FPC oscillating plate are formed on oscillating plate 4 by sputtering or vapor deposition. Alternatively, a method may be used in which an electrode material such as copper foil is deposited on the oscillating plate and an electrode pattern is formed by etching. The signal line on oscillating plate 4 is connected to FPC 14 by anisotropic conductive film 20 or the like. On electrode 5 serving also as an elastic plate, electrode 6a of oscillator 7 is adhered, and the other electrode 6b of the oscillator is connected to FPC 17 by anisotropic conductive film 8. Here, by forming an electrode by sputtering or vapor deposition on an oscillating plate, it becomes possible to process the oscillating plate and the electrode without using any adhesive, a process for providing each electrode becomes unnecessary, and hence dimensional precision can be improved. When the electrodes are formed collectively by etching, it becomes unnecessary to position each material for providing electrode one by one. Therefore, the manufacturing steps can be simplified and dimension precision can be improved. Further, since the nozzle body and the oscillating plate are bonded by melting the surfaces using a solvent, highly strong bonding becomes possible. Further, since the problem of flowing of the adhesive to the nozzle constituting portion can be avoided, stable dimensional precision can be obtained. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: An ink jet head in which oscillation is caused in a pressure chamber (10) communicated with a nozzle (1) by partially bending a wall surface of said pressure chamber (10) thereby to emit ink, comprising: an oscillating plate (4) formed of a resin provided on at least a portion of the wall surface of said pressure chamber; and a unimorph including an elastic plate (5) and an oscillator (7) provided on said oscillating plate; wherein the dimensions of said elastic plate (5) and said oscillator (7) are larger than the dimensions of said portion of the wall surface of said pressure chamber (10); and an electrode forming a connecting terminal (9) provided on said oscillator, characterized in that said oscillator (7) is adhered to said elastic plate (5) by a first adhesive layer (16), and adhered to said connecting terminal (9) by a second adhesive layer (8), said second adhesive layer being thicker than said first adhesive layer. The ink jet head according to claim 1, wherein said first adhesive layer (16) is a conductive adhesive or an epoxy resin. The ink jet head according to claim 1, wherein said second adhesive layer is an anisotropic conductive film (8). The ink jet head according to claim 1, including a plurality of said pressure chambers provided as a matrix in row and column directions, wherein said elastic plates (5) operate as electrodes and are connected commonly in said row direction, and wherein said electrodes forming connecting terminals (9) which are formed on the side of said oscillators (7) opposite to said elastic plates (5) are connected commonly in said column direction. A method of manufacturing an ink jet head according to claim 1 in which an oscillation is caused in a pressure chamber (10) communicated with a nozzle (1) by partially bending a wall surface of said pressure chamber (10) and to emit ink thereby, comprising the steps of: adhering a PZT plate (18/7) on a jig (22) with a separable sheet (19) interposed; cutting said PZT plate (18/7) to a prescribed dimension to form oscillators (7); adhering an oscillating plate (4) on a side of said cut oscillators (7) not provided with said separable sheet (19); and removing said separable sheet (19) and thereafter forming a rear electrode (9) on that portion from which the sheet (19) is removed. The method of manufacturing an ink jet head according to claim 5, further comprising the step of: forming an elastic plate operating as an electrode (5) on said oscillating plate (4) by sputtering before said adhering. The method of manufacturing an ink jet head according to claim 5, further comprising the steps of: forming an elastic plate operating as an electrode (5) on said oscillating plate (4) by vapor depositions before said adhering.

Inventors: KOYAMA KAZUYA, TSURUI KOHJI, YOSHIMURA HISASHI, KOYAMA, KAZUYA, TSURUI, KOHJI, YOSHIMURA, HISASHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1996
Main classification: B41J2
IPC codes: B41J2