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(11) | EP 0 903 233 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Ink jet head |
| (57) In an ink jet head provided with an ink-flowing path (4) in the form of a conduit
having a cross-section area; an ink-feeding port (8) through which ink is fed into
the ink-flowing path (4); and an ink-jetting port (3) through which the ink in the
ink-flowing path is jetted out; the cross-section area of the ink-flowing path (43)
neighboring the ink-feeding port (8) is smaller that the cross-section area of the
ink-flowing path (42) neighboring the ink-jetting port (3). |
BACKGROUND OF THE INVENTION
[0002] As one of an ink jetting style printing device of a drop on demand type, shear mode types disclosed in Japanese Tokkaisho 63-252750 and Japanese Tokkaihei Nos. 6-234212 through 234216 are known to be advantageous for downsizing and increasing of speed.
[0003] Fig. 1 is a perspective view showing a constitution of a shearing mode type ink jet head. In Fig. 1, numeral 1 represents a piezo-electric ceramic board, numeral 2 represents a nozzle plate, numeral 3 represents a nozzle, numeral 4 represents an ink-flowing path, numeral 5 represents a side wall, numeral 6 represents a cover plate, numeral 7 represents an ink feeding section (hereinafter, referred to as a manifold) and numeral 8 represents an ink feeding inlet.
[0004] On piezo-electric ceramic board 1, side wall 5, which is cut and processed by a diamond blade, is polarized in an arrowed direction wherein plural grooves (ink-flowing path) 4 is formed parallelly in which all of them has the same form for forming the size wall of groove 4. Depth of groove 4 becomes gradually shallow as becoming close to edge surface 12 on one end of the piezo-electric ceramic board. In the vicinity of edge surface 12, shallow groove 12 is formed. Inside plural grooves 4, metal electrodes 9 are formed by means of spattering at the upper half of both side surfaces. Inside shallow grooves 10, metal electrodes 11 are formed on each side surface and bottom surface. Each metal electrode 9 and metal electrode 11 are communicated.
[0005] Cover plate 6 is formed by means of a ceramic material or resin, in which ink feeding port 8 and manifold 7 are formed by means of grounding or cutting. A surface on which grooves 4 on piezo-electric ceramic board 1 is processed and a surface on which manifold 7 of cover plate 6 is processed are adhered by the use of epoxy-containing adhesive agent 16 (see Fig. 2). Upper surface of grooves 4 is covered by cover plate 6 for forming an ink-flowing path.
[0006] At the end of piezo-electric ceramic plate 1 and cover plate 6, nozzle plate 2 on which nozzle 3 is provided at a position corresponding to the position of each ink-flowing path 4 is adhered. Aforesaid nozzle plate is formed by polyalkylene terephthalate such as PET, polyimide, polyetherimide, polyetherketon, polyethersulfon, polycarbonate and plastic such as cellulose acetic acid.
[0007] On the surface opposite to a processed side of grooves 4 of piezo-electric ceramic board 1, board 13 on which pattern composed of the conductive layer is adhered by an epoxy-containing adhesive agent at the position corresponding to the position of each ink-flowing path 4. Conductive layer patter 14 and metal electrode 11 in shallow grooves 10 are connected by wire 15.
[0008] Figs. 2(a) and 2(b) explain operation theory of ink jetting. When jetting ink from ink-flowing path 4, positive driving voltage is impressed on metal electrodes 9a and 9b. Metal electrodes 9c and 9d are grounded. As shown in Fig. 2(b), driving electrical field is applied in an arrowed direction. Since the direction of aforesaid driving electrical field is perpendicular to the polarization direction of piezo-electric ceramic board, each side wall 5 is drastically deformed to the inside direction of ink-flowing path 4 due to piezo-electric shear stress. Due to aforesaid deformation, volume of aforesaid ink-flowing path 4 is reduced so that ink pressure is rapidly increased, occurring pressure wave. As a result, ink drops are jet from nozzles 3 communicating with ink-flowing path 4.
[0009] When the driving voltage is stopped, each side wall 5 returns to the position prior to deformation, volume of ink-flowing path 4 increase. From the ink feeding source (tank) not illustrated, ink is fed to ink-flowing path 4 through ink feeding port 8 and manifold 7 (see Fig. 3).
[0010] If higher jetting frequency is intended by the use of the above-mentioned conventional shearing mode type ink jet head, the above-mentioned pressure wave should be attenuated quickly so that waiting time for stable meniscus may be reduced. Namely, negative pressure wave occurred by rapid volume decrease of the ink-flowing path is basically reflected at a point where the depth of the grooves of the path starts to be shallow so that its amplitude is regulated. However, actually, the amplitude is more dynamic than the theory. Accordingly, it takes much time until attenuation. If ink is jetted quickly without waiting for the stabilization of the meniscus, problems such as that the size of ink drops are dispersed or jetting problem occurs due to involving air. Accordingly, there is a limitation in terms of increasing printing speed additionally.
SUMMARY OF THE INVENTION
[0011] The present invention was attained viewing the above-mentioned situations. An object thereof is to provide an ink jet head capable of jetting stably at high frequency.
[0012] The above-mentioned object of the present invention is attained by feeding ink from the ink feeding source, having an ink feeding port which distributes and fills ink to plural ink-flowing path, having an ink jet head which feeds ink to the ink-flowing path from the ink feeding port without using reservoir substantially, providing the above-mentioned ink-flowing path on the piezo-electric ceramic as grooves and a side communicating the ink feeding port is formed shallower compared with a side of ink jetting, the above-mentioned grooves are composed of a portion where depth is approximately constant, a portion where depth is gradually becomes shallow and a shallow portion in this order from the ink jetting side and providing a portion where vibration of the pressure wave is regulated on the above-mentioned grooves.
[0013] Namely, the present inventors thought that considerable part of negative pressure wave is transferred to the manifold through the ink-flowing path since the ink is retained on a large volume basis by the manifold covering each ink-flowing path and that time necessary for the stabilization of the meniscus takes longer since the meniscus is vibrated in a form in which vibrations having several kinds of amplitudes are synthesized. Accordingly, in order to surely regulate the amplitude inside the ink-flowing path, grooves are provided on shallow portions for feeding ink without passing the manifold substantially.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
Fig. 1 is a perspective view showing a constitution of a shearing mode type ink jet head.
Figs. 2(a) and 2(b) are drawings explaining the operation theory of ink jetting by aforesaid shearing mode type ink jet head.
Fig. 3 is a drawing showing feeding of an ink onto a conventional shearing mode type ink jet head.
Fig. 4 is a side cross sectional view showing one example of an embodiment including an ink-flowing path related to the ink jet head of the present invention and the ink feeding section.
Fig. 5 is a side cross sectional view showing another example of an embodiment including the ink-flowing path and the ink feeding section.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] Hereinafter, the present invention will be explained referring to embodiments. However, the embodiments of the present invention will not be limited thereto.
[0016] Fig. 4 is a side cross sectional view showing one example of an embodiment related to an ink-flowing path and an ink feeding section of an ink jet head of the present invention. In Fig. 4, a groove having a portion 41 in which depth is generally constant, portion 42 in which depth becomes shallow gradually and shallow portion 43 and ink feeding inlet 8 prepared for plural ink-flowing paths for shallow portion 43 path 4, formed with cover plate 6, located in shallow portion 43 are communicated. If ink feeding inlet 8 is communicated with a shallow portion, transfer of negative pressure wave can be ignored. Therefore, the width of the path may be constant or varied as shown in Fig. 4.
[0017] In addition, it is preferable to regulate the vibration of the pressure wave by varying the material or the surface physical properties of an ink contact surface of a cover plate or providing a floating portion by cutting the cover plate in the vicinity of a position which corresponds to the portion in which depth becomes shallow gradually.
[0018] Fig. 5 shows another example of the embodiment related to an ink flow path and an ink feeding section. In this example, the ink flow path becomes gradually shallow from an ink jetting side to a shallow groove. The ink feeding inlet is provided in the vicinity of a shallow groove of the ink-flowing path which becomes gradually shallow.
[0019] Comparison was made using the following two types of ink jet heads. Namely, a conventional ink jet head having a manifold in which the size of ink feeding inlet is 2.0 mm, the depth is 2.0 mm and the length of the aperture section to the ink-flowing path is 14 mm, a portion of the ink-flowing path in which the depth is approximately constant having depth of 420 µm, width of 105 µm and length of 7.0 mm and 64 pieces of nozzles and a new type ink jet head having an ink inlet port covering the entire ink-flowing path in which the ink-flowing path is similar to the conventional type as shown in Fig. 4. Ink having the following composition was jet onto gelatin-coated paper for ink jetting at driving voltage of 20 V and frequency of 6 kHz as an ink drop of 50 pl for the following evaluation to be compared on printing quality. The form and the position of dot were observed with a CCD image picture device for evaluating targeting accuracy, whether or not there exists satellite droplet and dot quality.
〈〈Ink composition - viscosity = 7.0 cps, surface tension = 35 dyn/cm〉〉
[0020]
| Yellow dye [Diwa-IJ-Yellow-214-H (DIRECT YELLOW 86) produced by Diwa KK] | 5 wt parts |
| Surfactant [Surphynol 465 produced by Nisshin Chemical Industry] | 0.2 wt parts |
| Triethanolamine | 0.05 wt parts |
| Urea | 0.05 wt parts |
| Diethylene glycol | 30 wt parts |
| Triethylene glycol monobuthylether | 5 wt parts |
〈〈Evaluation results〉〉
[0021]
| Conventional | Invention | |
| (Evaluation on targeting accuracy) | ||
| Dispersion on the central value of the nozzle row direction | σ = 5 µm | σ = 3 µm |
| Dispersion on the central value perpendicular to the nozzle row | σ = 15 µm | σ = 8 µm |
| (whether or not there is a satellite) | ||
| Ratio of dot on which a satellite occurs | 30/100 | 2/100 |
| (Evaluation on dot) | ||
| Ratio of complete round dot | 75/100 | 100/100 |
| (The others are ellipses) | ||
1. An ink jet head, comprising:
an ink-flowing path in the form of a conduit having a cross-section area;
an ink-feeding port through which ink is fed into the ink-flowing path; and
an ink-jetting port through which the ink in the ink-flowing path is jetted out;
wherein the cross-section area of the ink-flowing path neighboring the ink-feeding
port is smaller that the cross-section area of the ink-flowing path neighboring the
ink-jetting port.
2. The ink jet head of claim 1, wherein the ink jet head comprises a plurality of the
ink-flowing paths and the ink is distributed so as to be fed into the plurality of
the ink-flowing paths through the ink-feeding port.
3. The ink jet head of claim 1, wherein the ink-feeding port is communicated with a section
having the smaller cross-section area.
4. The ink jet head of claim 1, wherein the ink-flowing path is provided with a section
to refrain oscillation of pressure wave.
5. The ink jet head of claim 1, wherein the ink-flowing path comprises a first section,
a second section and a third section in the order from the ink-jetting port to the
ink-feeding port so that the ink-feeding port is communicated with the third section,
and wherein the cross-section area of the first section is kept almost constant, the
cross-section area of the second section is made to become gradually smaller and the
cross-section area of the third section is smaller than that of the first section.
6. The ink jet head of claim 1, wherein the ink-flowing path comprises a groove provided
to a piezo-electric ceramic board.