1. Field of the Invention
The present invention relates to an inkjet head adapted for use in an inkjet printer, which ejects ink droplets and records by printing various images on a target-recording medium.
2. Description of the Related Art
Hitherto, an inkjet recording device is well known, which records by printing characters and images on a target recording medium by using an inkjet head having a plurality of nozzles, which eject ink.
As shown in
One end section of each channel 5 is longitudinally extended to one edge face of the piezoelectric ceramic plate 1 while the other end section of the channel 5 does not extend to the other edge face of the plate, so that the channel depth becomes gradually shallower toward the other end section.
Moreover, electrodes 4 for applying a driving electric field are formed on the open-side faces of both sidewalls 21 for each channel 5 so as to extend along the longitudinal direction.
Furthermore, an ink chamber plate 2 constituting a common ink chamber 6, which communicating with the shallower end section of each channel 5 is connected to the piezoelectric ceramic plate 1 on the open sides of the channels 5 so as to form a head tip 26. A nozzle plate 3 is connected to the end face of a composite body consisting of the piezoelectric ceramic plate 1 and the ink chamber plate 2, where the channels 5 open up from the composite body and nozzle holes 11 are formed at positions of the nozzle plate 3 facing respective channels 5. The nozzle plate 3 and the head tip 26 are fixed by a head cap 12, and the electrodes 4 formed on the head tip 26 and a driving circuit board 14 are connected by a flexible board 19.
Moreover, an ink flow-channel member 40 to supply ink to the common ink chamber 6 is fixed to the ink chamber plate 2, an ink inlet port 41 for introducing ink is formed at the center of the flow-channel member 40, and a pressure relief unit 70 for absorbing any fluctuation in pressure during the printing operation is connected to the ink inlet port 41. Furthermore, since a filter 7 is fixed to the flow-channel member 40 so as to prevent foreign materials from flowing into and plugging the nozzle holes 11 and since the filter 7 partitions the flow-channel of the flow-channel member 40, the flow channel of the flow-channel member 40 is separated into an ink reservoir A 10 located on the upstream side of the nozzle holes 11 and an ink reservoir B 43 located on the downstream side of the nozzle holes 11. These parts and elements are eventually fixedly mounted on the base 13 made of an aluminum material.
In an inkjet head configured in this manner, when ink is filled in each of the channels 5 through the pressure release unit 70 and the flow-channel member 40 and when a predetermined driving electric field is applied to a predetermined channel 5 through the electrodes 4, the volume in a predetermined channel 5 changes due to the deformation of the sidewalls 21, resulting in ink in the predetermined channel 5 being ejected from the corresponding nozzle hole 11.
Nevertheless, in the case of the conventional inkjet head, air bubbles are trapped and stagnated in the ink reservoir A 10 which is located on the upstream side of the filter. For example, as shown in
Specifically, for instance, when using ink such as water-based ink, etc. where the permeation of air bubbles is worse, it becomes easy to generate air bubbles and shortages in the supply of ink increase. Moreover, air bubbles remaining in such an ink reservoir A 10 are generally removed by performing a so-called cleaning operation, namely, sucking from the side of the nozzle holes 11 or pressurizing from the ink supply side. However, even if this cleaning operation is performed, there is a problem such that air bubbles stagnating in the ink reservoir A 10, that is, the upstream side of the filter 7, are difficult to be practically removed without passing through the filter 7.
Furthermore, specifically, in the case where droplet size of ink is large and the number of the nozzle openings is large, that is, when the amount of ink ejected per unit time is large, the amount of remaining air bubbles which exists in the ink reservoir becomes large, so that there is a problem that the area of the ink flow-channel becomes essentially narrow and the shortage in the supply of ink increases. It might be considered that the flow rate of ink is accelerated by making the flow-channel of the ink reservoir narrow. However, there is a problem that the size of the filter becomes smaller in practice and this becomes a reason for the shortage in the supply of ink to the common ink chamber.
Moreover, even when using such a technique, it is impossible to completely remove air bubbles remaining at the upstream side of the filter 7 in the ink reservoir A 10 by performing the above-mentioned cleaning operation.
By taking into account the above-mentioned facts, it is an object of the present invention to provide an inkjet head and an inkjet recording device which can prevent air bubbles in ink from remaining in an ink reservoir and inside of a head tip with certainty, and which can relatively easily remove air bubbles.
In order to solves the aforementioned problems, the present invention provides an inkjet head, which includes a plurality of channels juxtaposed in parallel to be communicated with nozzles, a common ink chamber which supplies ink to each of the channels, an ink flow-channel provided for being communicated with the common ink chamber, and a filter element provided in the ink channel configured by the common ink chamber and the ink flow-channel, wherein a fluid routing channel that communicates with the atmosphere from an area on the upstream-side of the nozzles without passing through the filter element and nozzles is provided in the region composed of the filter element consisting of the ink flow-channel and the filter element having a mesh filter therein and wherein the aforementioned fluid routing channel communicating with the atmosphere has a function to maintain a vacuum pressure in the ink channel configured by the aforementioned nozzles and the ink flow-channel.
As will be understood from the above explanation, since the present invention provides a fluid routing channel, which communicates with the atmosphere, not through a filter element and a nozzle from the area of an upstream side of the nozzle in the region composed of the ink flow-channel and the filter element such as the mesh filter, etc., air bubbles remaining at the upstream side of the filter element can be removed, and, moreover, since it has a function which maintains a vacuum pressure in the ink channel configured by the nozzle and the ink supply channel, stable printing can be performed.
Hereinafter, the present invention will be described in detail referring to preferred embodiments of the present invention.
As shown in the drawing figures, an inkjet head 15 of the first embodiment has a head tip 26, a flow-channel 9 as an ink flow-channel, which is provided on one face side thereof, a circuit board 14 on which a driving circuit, etc. is mounted in order to drive the head tip 26, and a pressure relief unit 20 to relieve a pressure change in the head tip 26, and each of these components is fixedly mounted on the base 13. As shown in
Next, details of the area surrounding the head tip 26 which becomes a source for generating pressure for ejection will be explained. On the piezoelectric ceramic plate 1 constituting the piezoelectric ceramic plate head tip 26, a plurality of channels 5 are juxtaposed in parallel to be communicated with the nozzle holes 11 and each channel 5 is separated and isolated by sidewalls 21. One end section extending in the longitudinal direction of each channel 5 is arranged to come to one edge face of the piezoelectric ceramic plate 1, the other opposite end section does not reach the other edge face of the ceramic plate 1 and thus, the depth of each channel 5 becomes gradually shallower. Moreover, electrodes 4 for applying a driving electric field are formed along the longitudinal direction of the open sides of the channel 5 at the sidewalls 21 on both sides in the width direction of each channel 5.
Respective channels 5 formed in the piezoelectric ceramic plate 1, for instance, are formed by using a disc-like die cutter and the part where the depth becomes gradually shallower is formed according to the shape of the die cutter. Moreover, the electrodes 4 formed in respective channels 5 are formed by, for example, evaporation from a well-known angle of inclination. One end of the flexible board 19 is connected to the electrodes 4 provided on the open sides of both sidewalls 21 of thusly formed channels 5, and the electrodes 4 are electrically connected to the driving circuit by connecting another end of the flexible board 19 to the driving circuit on the circuit board 14 which is not shown in the drawing figures.
Moreover, an ink chamber plate 2 is connected to the open side of the respective channels 5 of the piezoelectric ceramic plate 1. In the ink chamber plate 2, a common ink chamber 6 formed so as to pierce or extend through the plate 2 in its thickness direction is provided for covering all over the area of the juxtaposed channels 5.
The ink chamber plate 2 may be made of a ceramic plate and a metal plate and so on. However, when taking into consideration the deformation after joining with the piezoelectric ceramic plate 1, a ceramic plate which has a similar thermal expansion coefficient to that of the plate 1 is preferably employed.
A nozzle plate 3 is connected to the end face where the channels 5 open up from the composite body consisting of the piezoelectric ceramic plate 1 and the ink chamber plate 2, and nozzle holes 11 are formed at respective positions of the nozzle plate 3 facing the respective channels 5.
In this embodiment, the nozzle plate 3 is made larger than the area of the end face where the channels 5 open up from the composite body consisting of the piezoelectric ceramic plate 1 and the ink chamber plate 2. This nozzle plate 3 is one obtained by forming the nozzle holes 11 in a polyimide film by the use of, for example, an excimer laser device. Moreover, although it is not shown in the drawing figures, a water-repellant membrane having water-repellency is provided to coat the face of the nozzle plate 3 which confronts a printed target so as to prevent adhesion of ink.
Moreover, a head cap 12 holding the nozzle plate 3 is connected to the outer face of the end face side where each channel 5 opens up from the composite body formed by this piezoelectric ceramic plate 1 and the ink chamber plate 2. This head cap 12 is connected to the outside of the end face of the composite body of the nozzle plate 3 for stably holding the nozzle plate 3 in position.
In the head tip 26 having the described configuration, a face of the piezoelectric ceramic plate 1 opposite to the face thereof confronting the ink chamber plate 2 is securely connected to the base 13.
On the other hand, the flow-channel 9 is connected to one side of this ink chamber plate 2.
Herein, the structure of the flow-channel 9 and the internal structure of the flow-channel 9 in which ink actually flows will be explained in detail by referring to
Moreover, in the flow-channel 9, a filter 7 is provided in the part which is facing the common ink chamber 6 extending in the juxtaposed direction of respective channels 5 as a filter element having holes with a diameter of 8 micrometers, for instance, to remove dust and other foreign material mixed in with the ink, and the ink reservoir A 10 located at the upstream side and the ink reservoir B 43 located at the downstream side are formed partitioning the inner wall of the flow-channel 9 by the filter 7.
Then, in the inkjet head 15 of this embodiment, for instance, ink coming from the ink tank fills up the ink reservoir 54 of the pressure relief unit 20 during the initial filling, and ink is introduced into the flow-channel 9 while passing through the flow-channel joint 50 and the ink inlet port 22. Since air bubbles 27a and 27b mixed in with the ink have a large resistance for passing through the filter 7, they remain in the ink reservoir A 10. Moreover, when the introduction of ink continues further, ink flows into the ink reservoir B 43 and the air bubbles 27a and 27b respectively are delivered to the bubble exhausting holes 8a and 8b. Ink passing through the ink reservoir B 43 passes inside of the head tip 26 and flows into the nozzle holes 11. Air bubbles 27a and 27b pass through the bubble exhausting holes 8a and 8b together with ink, pass through the bubble returns 51a and 51b and the bubble-removal channel 53, and then they are exhausted into the atmosphere together with ink through the tube 25, resulting in no air bubbles at all being present in the ink reservoir A 10. The path along which air bubbles flow from the ink flow-channel 9 through the tube 25 into the atmosphere constitutes an atmosphere-communication channel.
As explained above, in the inkjet head of this embodiment 15, air bubbles in the area of the ink reservoir A 10 are exhausted into the atmosphere together with ink passing through the bubble-removal joint 28 and the tube 25 after passing the bubble exhausting holes 8a and 8b, the bubble returns 51a and 51b, and the bubble-removal channel 53, so that air bubbles are certainly prevented from remaining in the ink reservoir A 10. Therefore, shortages in the supply of ink to the common ink chamber 6 and each channel 5 can be surely prevented, which would be caused by a reduction in the ink-storage capacity of the ink reservoir A 10, which reduction might be in turn caused by any residual bubbles.
Moreover, in this embodiment, since the bubble-removal joint 28 exhibits such a function that ink and bubbles are exhausted to the atmosphere during cleaning by the apply of a pressure, and a vacuum pressure created in the ink routing channel connecting the ink tank 80 with the inkjet head 15 is maintained during the printing operation, an ordinary printing operation can be stably performed.
Thus, since the air bubbles can surely be prevented from being left in the ink reservoir A 10, any failure in printing operation and so on can be surely prevented.
Of course, according to the inkjet head 15 of this embodiment, even in the case where the amount of ink ejected per unit time is large and ink such as water based ink, etc. is used, where the permeation of air bubbles is worse, shortages in the supply of ink to both the common ink chamber 6 and each channel 5 can be surely prevented, and the ejection stability of ink and the reliability thereof can be improved.
The reason why air bubbles which did not pass through the filter 7 could pass the vacuum pressure retaining filter 29 is that the vacuum pressure retaining filter 29 has markedly larger holes than the filter 7 and has a smaller flow through resistance. However, the vacuum pressure retaining filter 29 can sufficiently keep roughly 50 mm H2O which is a vacuum pressure inside the ink routing channel created in the ink tank and the inkjet head 15 by the surface tension of ink when the mesh is filled with ink. Moreover, the vacuum pressure retaining filter 29 used in the present invention has a hole diameter of 25 micrometers, but it is not necessary to be limited to this embodiment, and there is no problem if an appropriate hole diameter is selected according to the respective purpose.
According to such an inkjet type recording device, characters and images can be recorded by printing on the target recording medium by transferring the target recording medium S and scanning the inkjet head 50 in a direction perpendicular to the transfer direction thereof.
As shown in the drawing figures, an inkjet head 15 of the second embodiment has a head tip 26, a flow-channel 30 which is provided on one face side thereof, a circuit board 14 on which a driving circuit, etc. is mounted to drive the head tip 26, and a pressure relaxation unit 60 to relieve the pressure change in the head tip 26, and each of these components is fixed on the base 13. In this pressure relaxation unit 60, a deformable film connected to the pressure relaxation unit 60 body to form a concave shaped ink reservoir and a flow-channel joint 61 to transfer ink collected in this ink reservoir to the flow-channel 30 are provided (
Next, the details of the area surrounding the head tip 26 to be a pressure source for ejection will be explained. On the piezoelectric ceramic plate 34 constituting the head tip 26 a plurality of channels 5 are lined up in parallel to communicate with the nozzle holes 11, and each channel 5 is separated by the sidewalls 21. One end section along the longitudinal direction of each channel 5 is provided at one edge face of the piezoelectric ceramic plate 34, the other end section of the channel is not reaching the other edge face of the plate, and the depth of the channel becomes gradually shallower. Moreover, electrodes 4 for applying a driving electric field are formed along the longitudinal direction of the open sides of the channels 5 at the sidewalls 21 of both sides along the width direction of respective channels 5.
Each channel 5 formed on the piezoelectric ceramic plate 34 is formed by using a disc-like die cutter and the part where the depth becomes gradually shallower is formed according to the shape of the die cutter. Moreover, the electrodes 4 formed in respective channels 5 are formed by, for example, evaporation from a well-known angle of inclination. One end of the flexible board 19 is connected to the electrodes 4 provided on the open sides of both sidewalls 21 of such a channel 5, and the electrodes 4 are electrically connected to the driving circuit by connecting the other end of the flexible board 19 to the driving circuit on the circuit board 14 which is not shown in the drawing figures.
Moreover, an ink chamber plate 35 is connected to the open side of the channels of the piezoelectric ceramic plate 34. In the ink chamber plate 35, a common ink chamber 6 formed passing through the thickness direction is provided covering the whole area of the juxtaposed channels 5 and, in addition, air bubble holes 32a and 32b which are separated by the common ink chamber 6 are provided and slits 33a and 33b are formed to exhaust air bubbles at the bubble holes 32a and 32b.
Although the ink chamber plate 35 can be made of a ceramic plate and a metal plate and so on, a ceramic plate which has a similar thermal expansion coefficient to that of the piezoelectric plate 34 is preferably used by considering the deformation after joining with the piezoelectric ceramic plate 34.
A nozzle plate 3 is connected to the end face where the channels 5 open up from the composite body formed with the piezoelectric ceramic plate 34 and the ink chamber plate 35, and nozzle holes 11 are formed at positions of the nozzle plate 3 facing respective channels 5.
This nozzle plate 3 is one in which the nozzle holes 11 are formed in a polyimide film by using, for instance, an excimer laser device. Moreover, although it is not shown in drawing figures, a water-repellant film having water-repellency is provided at the face of the nozzle plate 3 which is facing a target of printing operation, in order to prevent adhesion of ink.
Moreover, the head cap 12 holding the nozzle plate 3 is connected to the outer face of the end face side where each channel 5 opens up from the composite body formed by this piezoelectric ceramic plate 34 and the ink chamber plate 35. This head cap 12 is connected to the outside of the end face of the composite body of the nozzle plate 3 for stably holding the nozzle plate 3.
In the head tip 26 having the described configuration, a face which is on the opposite side of the ink chamber plate 35 of the piezoelectric ceramic plate 34 is connected and fixed to the base 13. On the other hand, the flow-channel 30 is connected to one side of this ink chamber plate 35.
Herein, the structure of the flow-channel 30 (ink flow-channel) and the internal structure of the flow-channel 30 in which ink actually flows will be explained in detail. In the flow-channel 30, an ink inlet port 63 is provided at the center and actual ink flows using a system for supplying ink through the flow-channel joint 61 and the ink inlet port 63.
Moreover, in the flow-channel 30, the filter 7 (a filter element) having holes with a diameter of 8 micrometers is provided at the part which is facing the common ink chamber 6 extending in the juxtaposing direction of respective channels 5, for instance, to remove dust and foreign material mixed in with the ink, and the ink reservoir A 64 located at the upstream side and the ink reservoir B 65 located at the downstream side are formed partitioning the inner wall of the flow-channel 30 by the filter 7. Flow-channel openings 31a and 31b are formed on both sides of the ink reservoir A 64 and these flow-channel openings 31a and 31b are located at the positions communicating with the bubble holes 32a and 32b, respectively, which are provided on the aforementioned ink chamber plate 35. That is, the flow-channel openings 31a and 31b formed on both sides of the ink reservoir A 64 are connected to a fine hole 36 with a diameter of 0.1 mm, which opens to the same surface as the nozzle holes 11 formed in the nozzle plate 3, through the bubble holes 32a and 32b and slits 33a and 33b and form a channel communicating with the atmosphere. This fine hole 36 also has the function to maintain a vacuum pressure in the ink flow-channel, and the size has to be decided so as to be an appropriate size for use in an inkjet head 15. Moreover, in this embodiment, the slits 33a and 33b are formed in the ink chamber plate 35, however, a slit may be formed in the piezoelectric ceramic plate 34, and there is no problem if another component having a flow through channel is connected to the fine hole 36 and not through the piezoelectric ceramic plate 34 and the ink chamber plate 35. In this embodiment, flow-channel openings 31a and 31b are provided at both ends relative to the ink inlet port 63 located at the center of the flow-channel 30, however, there is no problem if an ink inlet hole is provided at one end of the flow-channel 30 and a flow-channel opening is provided at another end, and the position and number are not limited.
Then, in the inkjet head 15 of this embodiment, for instance, ink coming from the ink tank (not shown in the figure) fills up the ink reservoir 62 of the pressure relief unit 60 during the initial filling, and ink is introduced into the flow-channel 30 passing through the flow-channel joint 61 and the ink inlet port 63. Since bubbles 37a and 37b mixed in with the ink have a large resistance for passing through the filter 7, they remain in the ink reservoir A 64. Moreover, when the introduction of ink further continues, ink flows into the ink reservoir B 65 and air bubbles 37a and 37b respectively move to the flow-channel openings 31a and 31B. Ink passing through the ink reservoir B 65 passes inside of the head tip 26 and flows into the nozzle holes 11. Air bubbles 37a and 37b together with ink pass through the flow-channel openings 31a and 31b and pass the bubble holes 32a and 32b and the slits 33a and 33b, and then they are exhausted into the atmosphere together with ink, resulting in no air bubbles at all existing in the ink reservoir A 64.
As explained above, in the inkjet head 15 of this embodiment, air bubbles in the area of the ink reservoir A 64 are exhausted together with ink into the atmosphere, passing through the flow-channel openings 31a and 31b, the bubble holes 32a and 32b, the slits 33a and 33b, and fine hole 36, so that air bubbles can be prevented with certainty from being left in the ink reservoir A 64. The path along which air bubbles flow from the ink flow-channel 30 through the fine hole 36 into the atmosphere constitutes an atmosphere-communication channel. Therefore, shortages in the supply of ink to the common ink chamber 6 and each channel 5 can be surely prevented, which would otherwise be caused by a change in the storage capacity of the ink reservoir A 64 due to the presence remaining of air bubbles.
Moreover, in this embodiment, since there is a function where the ink and the bubbles are exhausted into the atmosphere during cleaning by vacuuming and presurizing and since a vacuum pressure created in the ink flow-channel connecting the ink tank 80 with the inkjet head 15 is maintained by a meniscus formed by the fine hole 36 during the printing operation, an ordinary printing operation can be stably performed.
In this embodiment, since the fine hole 36 is formed on the same surface as the nozzle plate 3, an inkjet can be made smaller and a lower cost can be achieved.
Thus, since the bubbles can surely be prevented from staying in the ink reservoir A 64, printing problems, etc. can surely be prevented.
Of course, according to the inkjet head of this embodiment, even in the case when the amount of ink ejected per unit time is large and ink such as water based ink, etc. is used, where the permeation of bubbles is worse, shortages in the supply of ink to the common ink chamber 6 and to each of the channels 5 can be surely prevented, and the ejection stability of ink and the reliability can be improved.
Number | Date | Country | Kind |
---|---|---|---|
2005-182850 | Jun 2005 | JP | national |
2005-367821 | Dec 2005 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
4187512 | Matsunaga et al. | Feb 1980 | A |
4340895 | Kikuchi | Jul 1982 | A |
4575738 | Sheufelt et al. | Mar 1986 | A |
5489925 | Brooks et al. | Feb 1996 | A |
5847734 | Pawlowski, Jr. | Dec 1998 | A |
5936650 | Ouchida et al. | Aug 1999 | A |
6036305 | Nagasaki et al. | Mar 2000 | A |
6634738 | Shinada et al. | Oct 2003 | B1 |
20010013884 | Crystal et al. | Aug 2001 | A1 |
20020057320 | Kaga et al. | May 2002 | A1 |
20030048337 | Jones et al. | Mar 2003 | A1 |
20030234845 | Tominaga et al. | Dec 2003 | A1 |
20040196341 | Ogura et al. | Oct 2004 | A1 |
Number | Date | Country |
---|---|---|
0383558 | Feb 1990 | EP |
1574341 | Sep 2005 | EP |
2004249571 | Sep 2004 | JP |
Number | Date | Country | |
---|---|---|---|
20070008384 A1 | Jan 2007 | US |