1. Field of the Invention
The present invention relates to an ink jet print head for ejecting ink by the deformation of a piezoelectric ceramic element by application of a voltage, and a method of producing the same.
2. Description of the Related Art
Conventionally, there has been provided an ink jet print head which uses a piezoelectric ceramic element. An example is a drop-on-demand type ink jet print head with ink filled channels (ink channels) wherein the volume in the ink channels changes with deformation of the piezoelectric ceramic element. When the volume reduces, this device ejects ink in an ink channel from a nozzle as a liquid droplet. When the volume increases, ink from an ink introduction port is introduced to the channel. By causing an ink droplet to be ejected from an ink channel as required by incoming print data, a desired character or image is formed on, for example, paper opposing the ink jet print head.
This type of ink jet print head is described in Japanese Patent Application Kokai Nos. SHO63-247051, SHO63-252750, and HEI2-150355.
Conventionally, this type of ink jet print head is used, for example, in ink jet printers. A first example of a conventional ink jet print head wherein a piezoelectric ceramic element 76 is provided to a sidewall 74 of a housing 72 forming an ink chamber 70 will be explained while referring to FIG. 1.
In order to produce the piezoelectric ceramic element 76, a piezoelectric ceramic sheet is first formed from piezoelectric ceramic powder using such techniques as tape casting processes or extrusion processes. The piezoelectric ceramic sheet is cut to a predetermined size and is sintered at a predetermined temperature to obtain a piezoelectric ceramic sinter. Grinding processes are performed to smooth the surface of the piezoelectric ceramic sinter to a uniform flatness. The piezoelectric ceramic sinter is then polarized. Thus, the piezoelectric ceramic element 76 is obtained. Electrodes 77 are formed to both surfaces 90 of the piezoelectric ceramic element 76. A drive circuit 79 is connected to the electrodes 77.
Thus produced piezoelectric ceramic element 76 deforms when the drive circuit 79 applies a drive voltage to the electrode 77. As indicated by the single-dot chain line, the sidewall 74 deforms with deformation of the piezoelectric ceramic element 76, reducing the volume of the ink chamber 70 and thereby ejecting the ejection liquid, ink in this example, filling the ink chamber 70 from the nozzle 82 as an ink droplet 80. Afterward, when application of the drive voltage stops, the piezoelectric ceramic element 76 reverts to its shape prior to deformation, increasing the volume of the ink chamber 70 so that ink flows from the ink supply channel 84 into the ink chamber 70. A plurality of these ink chambers 70 are provided in an array when the device is used in an ink jet printer.
A second conventional example of a conventional ink jet print head 1 as described in Japanese Patent Application Kokai No. HEI2-150355 includes a piezoelectric ceramic plate 2; a cover plate 3; a nozzle plate 31; and a substrate 41 as shown in FIG. 2. To produce this ink jet print head 1, a piezoelectric ceramic element is first formed in the same way as described in the first conventional example. A plurality of grooves 8 are cut into the piezoelectric ceramic element using, for example, a thin, disk-shaped diamond blade, to form the piezoelectric ceramic plate 2. The grooves 8 are cut parallel to each other and to equal depths so as to become gradually shallower in progressing toward the end 15 of the piezoelectric ceramic plate 2. The depth of each groove 8 decreases thus becoming a shallow groove 16 near the end 15. The sidewalls 11, which form the side surfaces of the grooves 8, are polarized in the direction labeled by the arrow 5 in FIGS. 3a and 3b. A metal electrode 13 is formed by sputtering along the upper half of both side surfaces of each groove 8. A metal electrode 9 is formed by sputtering on the side and bottom surfaces of the inner surface of the shallow groove 16. Thus the metal electrode 9 formed in the shallow groove 16 connects the two metal electrodes 13 formed to side surfaces of the groove 8.
The cover plate 3 is formed from, for example, a ceramic material or a resin material. An ink introduction port 21 and a manifold 22 are cut or ground into the cover plate 3. An epoxy-type adhesive 4, for example, is used to bond the surface of the cover plate 3 containing the manifold 22 to the surface of the piezoelectric ceramic plate 2 containing the grooves 8. As a result, the cover plate 3 covers the grooves 8 thereby forming in the ink jet print head 1 a plurality of ink channels 12 having a mutual interval in the horizontal direction. As shown in FIG. 3a, the ink channels 12 are long and narrow in rectangular cross section. All the ink channels are filled with ink.
The nozzle plate 31 provided with nozzles 32 is adhered to the end of the piezoelectric ceramic plate 2 and the cover plate 3. The nozzles 32 are positioned so that the positions of each nozzle 32 will correspond to the position of its respective ink channel 12. The nozzle plate 31 is formed from a plastic such as polyalkylene terephthalate (for example, polyethylene terephthalate), polyimide, polyether imide, polyether ketone, polyether sulfone, polycarbonate, or cellulose acetate.
The substrate 41 is attached by, for example, an epoxy adhesive to the non-grooved side of the piezoelectric ceramic plate 2. A conductor layer 42 is formed to the substrate 41 in a pattern corresponding to positions of the ink channels 12. An individual conductor wire 43 is connected by wire bonding between each metal electrode 9 in each shallow groove 16 and its corresponding conductor layer pattern 42.
An explanation of the construction of a control portion for driving the ink jet print head of FIG. 2 will be provided while referring to the block diagram of the control portion in FIG. 4. The conductor layer pattern 42 formed in the substrate 41 are individually connected to an LSI chip 51. A clock line 52, a data line 53, a voltage line 54, and a ground line 55 are also connected to the LSI chip 51. Based on the clock pulse consecutively supplied from the clock line 52, the LSI chip 51 determines when ink should be ejected from which nozzles 32 according to data from the data line 53. A voltage V from the voltage line 54 is applied to the conductor layer pattern 42 in continuity with the metal electrode 13 within the driven ink channel 12. A 0 V voltage from the ground line 55 is applied to conductor layer patterns 42 not in continuity with driven ink channels.
An explanation will be provided on the operation of the ink jet print head 1 while referring to FIGS. 3a and 3b. Now assume that the LSI chip 51 determines to eject ink from ink channel 12b in the ink jet print head 1 according to incoming data. The LSI chip therefore applies a positive drive voltage V to metal electrodes 13e and 13f and grounds metal electrodes 13d and 13g. As shown in FIG. 3b, drive electric fields are generated in the sidewalls 11b and 11c in directions indicated by arrows 14b and 14c respectively. Because the drive electric field directions 14b and 14c are orthogonal to the direction of polarization 5, a piezoelectric thickness shear effect causes the sidewalls 11b and 11c to rapidly deform, in this case, in the inward direction of the ink channel 12b. This deformation reduces the volume of the ink channel 12b, rapidly increases the pressure in the ink, generates a pressure wave, and ejects an ink droplet from the nozzle 32 (see FIG. 2) communicating with the ink channel 12b.
When application of the drive voltage V stops, because the sidewalls 11b and 11c gradually regain their predeformation shape (see FIG. 3a), the ink pressure within the ink channel 12b gradually decreases. When this happens, ink is supplied to the ink channel 12b from the ink supply port 21 (see FIG. 2) through the manifold 22 (see FIG. 2).
An explanation of the construction of an ink jet printer in which the ink jet print head 1 of FIG. 2 is employed will be provided while referring to FIG. 5. The above-described ink jet print head 1 and an ink reservoir 61 are both mounted on a carriage 62. The print head 1 and the ink reservoir 61 are connected so as to connect the inner portion of the ink reservoir 61 with the ink introduction port 21 (see FIG. 2) of the ink jet print head 1. When ink within the ink reservoir 61 is exhausted, the ink reservoir 61 is detached from the carriage 62, and replaced with a new one. The carriage 62 returnably moves along the slider 63. The ink jet print head 1 prints characters on a recording paper 66 supported on a platen 64. Paper feed rollers 65a and 65b move the recording paper 66 in a direction orthogonal to the direction in which the carriage 62 is moved. Because of this, the ink jet print head 1 can print characters anywhere on the surface of the recording paper 66.
This type of ink jet print head 1 produces a spray of small ink droplets each time an ink droplet is ejected. A portion of this spray becomes attached to the nozzle plate 31. Left alone, ink will accumulate gradually on the surface of the nozzle plate 31, preventing ejection of ink droplets. A moderate period after printing of characters is completed, or after printing is completed, the carriage 62 is moved to the left side of the printer into a non-printing area. A wiper 68, formed from, for example, resin or cotton fibers, is provided to a support member 69 fixed in the non-printing area. The wiper 68 engages or contacts the surface of the nozzle plate 31 as the print head moves left. This sweeping movement causes the wiper 68 to remove ink spray attached to the nozzle plate 31. The wiper 68 is replaced when a large amount of ink accumulates thereon.
The wiper 68 can also be provided to a movable member, and caused to wipe the surface of the nozzle plate 31 of the ink jet print head 1 several times after the print head 1 is moved to the non-printing area.
A third conventional example of a conventional ink jet print head 1 also described in Japanese Patent Application Kokai No. HEI2-150355 is shown in cross section in FIG. 6. Components similar to those described in the second conventional example will be accompanied by the same numbering to omit superfluous explanation. The ink jet print head 1 of this example is substantially the same as that of the above-described second example except that the manifold 22 is not formed in the cover plate 3. In this example, the piezoelectric ceramic plate 2 is formed with through-holes 23, and a base plate 60 formed with a manifold 22 is provided between the piezoelectric ceramic plate 2 and the substrate 41. To produce this ink jet print head, grooves 8, which form the ink channels 12, and shallow channels 16 are formed in the piezoelectric ceramic plate 2. A through hole 23 is then formed in the bottom of each groove 8. A manifold 22 is formed in the base plate 60 running perpendicular to the grooves 8. An ink introduction port 21 is formed in the cover plate 3. The cover plate 3 is adhered to the grooved side of the piezoelectric ceramic plate 2. Then, the side of the base plate 60 with the manifold 22 formed therein is adhered to the side of the piezoelectric ceramic plate 2 with the through holes 23 formed therein. At this time, because the through holes 23 confront the manifold 22, the manifold 22 is brought into communication with the plurality of grooves 8. Further, the nozzle plate 31 is adhered to the piezoelectric ceramic plate 2, the cover plate 3, and the base plate 60. The substrate 41 is adhered to the side of the base plate 60 opposite that with the manifold 22 formed therein.
A fourth conventional example of a conventional ink jet print head 1 as described in European Patent Application Publication No. 0 516 284 A2 will be described below with reference to FIG. 7. Components similar to those described in the second conventional example will be accompanied by the same numbering to omit superfluous explanation. The ink jet print head 1 of this example is substantially the same as that of the second example except that the nozzle plate 31 is omitted from the ink jet print head 1. That is, the ink jet print head 1 of this example is constructed from a piezoelectric ceramic plate 2; the cover plate 3; and the substrate 41. The piezoelectric ceramic plate 2 of this example is formed with not only the grooves 8 and the shallow grooves 16 but also small grooves 7. The small grooves 8 have cross-sectional area smaller than the cross-sectional area of the grooves 8. The small grooves 7 are cut into the piezoelectric ceramic plate 2 in fluid communication with the grooves 8.
An epoxy-type adhesive, for example, is used to bond the surface of the cover plate 3 to the surface of the piezoelectric ceramic plate 2 containing the grooves 8. As a result, the cover plate 3 covers the grooves 8 thereby forming in the ink jet print head 1 a plurality of ink channels having a mutual interval in the horizontal direction. Also the small grooves 7 are covered, forming a plurality of nozzles with positions corresponding precisely to the positions of the channels.
It is noted that similarly as in the second conventional example, the substrate 41 is adhered to the piezoelectric ceramic plate 2 in the same manner as in FIG. 2.
Conventional ink jet print heads, however, have various problems. For example, there has been a problem with the piezoelectric ceramic element 76 of the first conventional example of FIG. 1 in that, as shown in FIG. 8, the cutting and grinding processes for forming the piezoelectric ceramic element 76 generate microcracks 91 in the cut and ground surfaces 90 of the piezoelectric ceramic element 76. Because the piezoelectric ceramic element 76 deforms upon application of a voltage, the microcracks can progress into a break.
Also, piezoelectric ceramic particles 94 can drop out of the cut and ground surface 90 in the piezoelectric ceramic element 76, as indicated by the broken line in FIG. 8, increasing the roughness of the surface 90. This prevents forming a continuous metal electrode 77 or forming the metal electrode to a uniform thickness. When the metal electrode 77 is formed in this way, the amount that a piezoelectric ceramic element 76 deforms by application of a voltage varies with the piezoelectric ceramic element 76 so that the volume of ink droplets ejected from each nozzle 82 also varies. This degrades quality of printed characters.
Because in the second through fourth conventional example the sidewall 11 which deforms to eject ink is formed in the same way as in the first conventional example, that is, by cutting and the like of the piezoelectric ceramic element, as shown in FIG. 8, microcracks 91 are generated in the side surface of the sidewall 11 (the cut surface 90). Because application of a voltage deforms the sidewall surface 11 by piezoelectric thickness shear effect, when microcracks are generated, there is a great possibility that the deformation will promote the cracks into a break.
For the same reason as described above in the first conventional example, a rough sidewall 11 surface (which is the cut surface 90) prevents forming a continuous or uniformly thick metal electrode 13. Such variation causes each sidewall 11 to deform to a different extent so that ink droplets ejected from each nozzle 32 contain different volumes. Quality of printed characters suffers accordingly.
Especially, in the ink jet print head of the fourth conventional example as shown in FIG. 7, the small grooves 7, which form the nozzles in the piezoelectric ceramic plate 2', are formed also by cutting processes. For this reason, as shown in FIG. 8, microcracks are generated in the bottom and side surfaces (the cut surfaces) of the small grooves 7. Piezoelectric ceramic particles 94 can fall from the bottom walls and sidewalls 90 of the small grooves, as indicated by the broken line in FIG. 8. This worsens the roughness of the surfaces. As a result, when ejecting ink droplets, the flow of ink passing through the nozzle is disrupted, affecting the direction of the ink droplet. Ink spray is easily generated in this situation, degrading quality of printed characters.
There has been another problem in ink jet print heads constructed as per the second and third conventional examples of FIGS. 2 and 6. Because the nozzle plate 31 formed with nozzles 32 is adhered to the cover plate 3 and the piezoelectric ceramic plate 2, the relative positions of the nozzles to the channels 8 is determined by where the nozzles 32 are formed in the nozzle plate 32 and where the nozzle plate is adhered to the tip of the piezoelectric ceramic plate 2 and the cover plate 3. Therefore, the nozzles 32 are sometimes imprecisely aligned with the ink channels 8. Also, when the nozzle plate 31 is adhered, excess adhesive runs into the inner surface of the nozzles 32, disrupting the linear ejection of ink or clogging the nozzles.
There has been a further problem in the ink jet print head of the second conventional example shown in FIG. 2 in that because both the ink introduction port 21, for introducing ink from an ink supply source (ink reservoir 61), and the manifold 22, which supplies the introduced ink to the plurality of ink channels, are formed in the cover plate 3, the shape of, and controlling cutting processes for forming, the cover plate 3 becomes complex. Because the direction of the cutting operation is changed to form the grooves 8 and the shallow grooves 16 in the piezoelectric ceramic plate 2, the process control becomes complex. Therefore, production of the cover plate 3 and the piezoelectric ceramic plate 2 is time consuming and not well suited for mass production.
In a conventional ink jet print head of the third example shown in FIG. 6, the ink introduction port 21 is formed in the flat cover plate 3. Grooves 8, shallow grooves 16, and the through holes 23 are formed in the piezoelectric ceramic plate 2. The manifold 22 is formed in the base plate 60. For this reason, the form of the cover plate 3 becomes simpler and the speed at which the cover plate 3 can be formed increases. However, because the through hole 23 is formed in the bottom of the groove 8 of the piezoelectric ceramic plate 2, the shape of the piezoelectric ceramic plate 2 becomes more complex than that of the second conventional example, and cutting processes become time consuming. Also, because the base plate 60 is required for forming the manifold 22, the number of components increases and production costs increase. Therefore, the device is poorly suited to mass production.