JP5200456B2 - Droplet discharge device - Google Patents

Description

  The present invention relates to a droplet discharge device, and more particularly to a droplet discharge device provided with a circulation path for circulating a liquid in the vicinity of a discharge nozzle.

  Conventionally, inkjet recording heads are moving in the direction of smaller nozzle diameters in order to reduce the size of ink drops that achieve high image quality and high density printing. In addition, in order to improve image quality on paper, there is an increasing demand for ejecting highly viscous ink.

  As the ink viscosity increases and the nozzle diameter decreases as described above, the ink drying speed near the nozzle increases, and frequent maintenance is required for printing.

  Therefore, in order to prevent drying of the nozzle (ink near the nozzle), an ink circulation path is installed in the very vicinity of the nozzle, and the ink is circulated so as to flow in a direction perpendicular to the nozzle arrangement at the time of non-printing or printing. Has been proposed (see, for example, Patent Document 1).

  Alternatively, the internal pressure of the common liquid chamber communicating with the ink circulation path in the vicinity of the nozzles is increased and decreased, and the ink meniscus surface formed near the ejection port is reciprocated between the substantial tip of the ejection port and the substantial front of the common liquid chamber. The structure to move is proposed (for example, refer patent document 2).

  In either configuration, in order to prevent drying of the nozzle part (ink near the nozzle), it is more effective to install the circulation path as close to the nozzle as possible. For example, the circulation path is installed on the back side of the nozzle plate. There is an example.

  However, if a circulation path is provided near the nozzle, a velocity component that causes ink to flow to the circulation path when ink droplets are discharged is generated. As a result, the presence of the circulation path affects the ink droplet ejection direction. Is a problem.

The above problem is that the circulation path exists in only one direction when viewed from the ejection direction with respect to the nozzle axis, so that the ink pressure escapes when ink droplets are ejected, and the symmetry of the ink velocity distribution collapses and the circulation path. The deviation in the direction affects the ejection direction of the ink droplets, causing a printing direction defect.
JP 2001-205814 A JP 2002-234175 A

  In view of the above-described points, it is an object of the present invention to provide a droplet discharge device that can prevent the nozzle from being dried with a simple structure.

The apparatus according to claim 1 includes a plurality of nozzles for ejecting droplets, the interior of the liquid varied pressure for ejecting droplets from a plurality of the nozzles, corresponding to a plurality of said each nozzle The pressure chamber, the first common flow path for supplying liquid to the pressure chamber, one end communicating with the pressure chamber, and the nozzle provided at a position overlapping the center of the other end , corresponding to each nozzle A substantially cylindrical communication path , a circulation path that is provided at the other end of the communication path, extends in a direction crossing the droplet discharge direction, and discharges liquid from the communication path, and corresponds to each nozzle. communicates respectively communicating the road, and a second common flow channel for recovering the liquid from each of said communication passage, said circulation passage between corresponding to a plurality of said nozzles, each of said viewed from the ejection direction wherein provided in different directions from the nozzle To.

In the invention of the above configuration, since the circulation path exists in a plurality of directions with respect to the nozzle axis, only the specific direction in which the circulation path exists is not the direction in which the fluid pressure escapes during discharge, and the symmetry of the velocity distribution is Image quality defects such as white streaks and density unevenness due to defective ejection direction on the print line can be prevented without collapsing in a specific direction. In addition, since the circulation paths between nozzles that discharge adjacent dots are different from each other when viewed from the discharge direction, adjacent dots do not shift in the discharge direction in the same direction, and discharge directions such as white streaks on the print line are defective. Occurrence can be prevented.

The droplet discharge head according to claim 2, wherein the circulation paths corresponding to any two of the plurality of nozzles that discharge droplets to adjacent landing points are viewed in the discharge direction. The flow path parameters are different from each other and are connected to the second common flow path .

  In the invention with the above configuration, since the flow channel parameters (flow channel length, opening area, height, width, etc.) of nozzles that discharge adjacent dots are different, adjacent dots are discharged in the same direction. It is possible to prevent the occurrence of white streaks on the print line without causing a direction shift.

According to a third aspect of the present invention, the flow path parameter is one or more of the length, opening area, height, and width of the circulation path.

  Since the present invention has the above-described configuration, it has been possible to provide a droplet discharge device that can prevent the nozzle from being dried with a simple structure and can suppress image defects due to the displacement of the droplet landing position.

<Overview of image forming apparatus>
1 to 3 show a droplet discharge device according to a first embodiment of the present invention.

  1 is a perspective view showing a structure of a droplet discharge device according to a first embodiment of the present invention, FIG. 2 is a top view, and FIG. 3 is a cross-sectional view.

  As shown in FIGS. 1 and 3, the droplet discharge device 10 introduces ink supplied from the supply common flow path 12 into the pressure chamber 15, and pressurizes the pressure chamber 15 with the piezoelectric element 13, thereby connecting the ink to the communication path. 14 is pressure-fed and ejected from the nozzle 16 as ink droplets.

  A circulation path 18 is provided in the vicinity of the nozzle 16 of the communication path 14 in a direction (horizontal direction in the figure) orthogonal to the ejection direction (vertical direction in the figure), and communicates with the circulation common flow path 20 so that the ink that is not ejected. Return to the circulation common flow path 20. The ink in the circulation common flow path 20 is discharged or collected again as droplets while circulating in the common flow path.

  As shown in FIG. 2, each circulation path 18 communicates between the vicinity of the nozzle 16 and the circulation common flow path 20 at different angles / shapes as viewed from the discharge direction. That is, the direction in which the liquid flows in the path from the communication path 14 to the circulation common flow path 20 via the circulation path 18 is different between the adjacent nozzles 16. Since the above relationship is established between the arbitrary nozzles 16, the direction of the circulation path 18 with respect to the nozzles 16 is randomized. This is the same relationship not only between the physically adjacent nozzles 16 but also between the nozzles 16 that eject ink droplets that form adjacent landing points (dots).

  That is, as shown in FIG. 4, when the ejection heads 11 provided with a plurality of nozzles 16 are arranged side by side in the conveyance width direction of the paper P, dots 30A to 30C that form the print line 22 on the paper P are considered. . Since the nozzles 16A for printing the dots 30A and the nozzles 16B for printing the dots 30B are adjacent to each other, the circulation paths 18 are arranged in different directions as described above.

  Further, the nozzle 16B and the nozzle 16C for printing the dot 30C are provided in separate ejection heads 11 and are not physically adjacent to each other, but the dots 30B and 30C are adjacent on the print line 22. Therefore, the circulation paths 18 are also arranged in different directions as described above.

<Circular angle and discharge direction>
Conventionally, as shown in FIGS. 14 and 15, in a method in which an ink circulation path 118 is installed in the immediate vicinity of the nozzle 116 and circulated during non-printing or printing, the circulation path 118 provided to prevent the nozzle 116 from drying. It is more effective to install the nozzle as close to the nozzle 116 as possible, and an example is that it is installed on the back side of the nozzle plate 117.

  However, if the circulation path 118 is located near the nozzle 116 as shown in FIG. 15A, a velocity component 119 that flows to the circulation path 118 is generated as shown in FIG. It has an influence. That is, since the liquid flow around the meniscus of the nozzle 116 is directed toward the open circulation path 118, the liquid pressure in the nozzle 116 loses symmetry with respect to the discharge direction, and the discharge direction is shifted in the opposite direction to the circulation path 118. .

    If the direction of the circulation path 118 is always a constant direction with respect to the nozzles 116, the landing points of the ink droplets are all shifted in the same direction, so printing failure does not occur in principle. However, since the density is increased to improve the image quality, the parameters such as the direction and length of the circulation path 118 cannot be made uniform in terms of manufacturing and configuration.

  For example, in the configuration as shown in FIG. 16, a symmetrical arrangement is indispensable in units of nozzle rows or units of a certain amount of nozzle area. Therefore, the direction of the circulation path 118 relative to the nozzles 116 is also symmetric with respect to the symmetry line 120. The difference in the displaced ejection direction also becomes large at the symmetrical position, and streaks occur.

<First Embodiment>
FIG. 5 shows an example of direction setting in the circulation path of the droplet discharge device according to the first embodiment of the present invention.

  As shown in FIGS. 5A and 5C, in the first embodiment of the present invention, the method of randomizing the direction of the circulation path 18 is performed by the plate 17 (see FIG. 3) constituting the circulation path 18 and the circulation path 18. The angle at which the circulation path 18 extends is randomly patterned in a radial direction of a circle 19 having the radius of the circulation path 18 with the nozzle 16 as the center, on the flow path plate that connects the common flow path 20 for circulation with the center. Is possible.

  As a result, the ink droplets are ejected in the direction (straight line 15) symmetrical with the direction 18D of the circulation path 18 around the nozzle 16, and land on the print line center 22A shown in FIG.

  However, when the angular difference between the circulation paths 18 between the nozzles 16 that draw the adjacent dots 30 is large, the directions of the two circulation paths 18 are symmetrical with respect to the printing direction (paper P conveyance width direction). When opened, the difference in ejection angle, that is, the printing deviation of the dots 30 is maximized.

  As shown in FIG. 5B, if the above-mentioned deviation is too large, such as an angle difference of 90 degrees, a line where ink droplets do not land on the print line 22 is formed in the paper P feed direction. A white line 24 is generated by forming a blank section.

  Therefore, the angle difference of the circulation path 18 between the nozzles 16 that draw the adjacent dots 30 changes gradually without changing greatly, or may be randomly arranged with a small change rate as described later. desirable.

  The rate of change of the direction 18D of the circulation path 18 includes the position of the circulation path 18, the circulation amount, the flow path parameter ratio between the circulation path 18 and the communication path 14, the drive waveform, the distance from the droplet discharge device 10 to the paper P, Although it varies depending on the printing resolution, when the landing position deviation due to the circulation path 18 occurs on the paper P by 15 μm or more, the angle of the direction 18D of the circulation path 18 between the adjacent dots 30 is within 60 °, preferably 30 °. Within is good. As shown in FIG. 17, in the ejector in which the landing position deviation of 15 μm occurs due to the installation of the circulation path 18, if the angle of the direction 18D of the circulation path 18 between adjacent dots 30 is 30 degrees or less, the result of the sensory evaluation The occurrence of white stripes 24 is at a level that cannot be visually confirmed.

  In addition, density cycle fluctuations of 0.27 cycle / mm or less or 2.7 cycle / mm or more are difficult to recognize as a stripe pattern due to human visual characteristics with respect to the stripe pattern. That is, when the fluctuation width of the density at an image density of about 0.2 to 0.3 that is generally conspicuous is sufficiently small (about 10%), the spatial frequency is lower than about 0.27 (line / mm), or When it is higher than about 2.7 (line / mm), it is known that the density fluctuation is difficult to be recognized by the human eye (refer to Japanese Patent Laid-Open No. 6-19222). The angle of the circulation path 18 with respect to the nozzles 16 is gradually changed, and the frequency of the angle change of the circulation path 18 in the image arrangement is 0.27 cycle / mm or less, or 2.7 cycle / mm or more.

  FIG. 6 shows an example of direction setting in the circulation path of the droplet discharge device according to the first embodiment of the present invention.

  As shown in FIG. 6A, in the first embodiment of the present invention, as a method of randomizing the deviation of the ink droplet ejection direction, the direction of the circulation path 18 is set to a predetermined angle while the rate of change in angle remains small. Arrange randomly within the range.

  That is, the direction 18D of the circulation path 18 is randomly arranged as shown in FIG. 6A, but the direction 18D itself falls within a narrow angle range (for example, within ± 45 degrees). As a result, the landing point deviation of the dots 30 forming the print line 22 varies randomly within a predetermined variation range, so that the occurrence of white stripes 24 can be suppressed.

  In this method, the generation of a low frequency density cycle can be considered. However, this may be dealt with by changing the droplet speed of the ink droplets by adjusting the driving waveform and randomizing the landing positions.

Second Embodiment
FIG. 7 shows an example of direction setting in the circulation path of the droplet discharge device according to the second embodiment of the present invention.

  As shown in FIG. 7, in the second embodiment of the present invention, the method of randomizing the ink droplet ejection direction deviation is not by changing the direction of the circulation path 18 but by randomly changing the flow path parameter of the circulation path 18. Realized.

  That is, by randomly patterning the flow channel length, the flow channel opening area (height, width), and the like, which are the flow channel parameters of the circulation channel 18, the direction 18D of each circulation channel 18 remains the length of the straight line 21 as it is. That is, the landing position deviation length of the ink droplets ejected from the nozzles 16 can be varied randomly. Thereby, the landing point deviation of the dots 30 forming the print line 22 is the same only in the direction, and the deviation amount varies randomly within a predetermined fluctuation range, so that the occurrence of the white stripe 24 can be suppressed.

  The second embodiment may be used in combination with the first embodiment. That is, the effect can be obtained by changing the direction D of the circulation path 18 at random within a predetermined range and further changing the flow path parameter of the circulation path 18 at random.

<Third Embodiment>
8, 9, and 10 show examples of direction setting in the circulation path of the droplet discharge device according to the third embodiment of the present invention.

  As shown in FIGS. 8, 9, and 10, in the third embodiment of the present invention, the circulation path 18 is provided at a position where the extension direction of the circulation path 18 does not enter the surface of the nozzle 16.

  The ink flow in the vicinity of the nozzle 16 due to the liquid circulation is in a tangential direction of a circle (inner shape of the communication path 14) centering on the axis of the nozzle 16, that is, the ink flow to the circulation path 18 at the time of ejection is By designing so as not to have a component vector directly in the direction of the circulation path 18, the ink flow in the communication path 14 by the circulation path 18 becomes a vortex centered on the nozzle 16 axis, and the nozzle 16 axis radial direction By reducing the change in the asymmetry of the flow velocity to the nozzle, it is possible to prevent a discharge direction defect during ink droplet discharge.

  Although the configuration in which one circulation path 18 is provided for the nozzle 16 as shown in FIG. 10 is effective, more preferably, two or more circulation paths 18 are provided at positions symmetrical to the axis of the nozzle 16. As a result, symmetry can also be maintained in terms of shape, so that the ink flow generated in the communication path 14 can also have symmetry. In order to realize the configuration of the circulation path 18, the left and right sides in the drawing are conventionally used for the tributary side used as the circulation common flow path 20 for adjacent rows, for example, the central communication path 14 in FIG. 9. The above-described configuration can be realized by communicating with the circulation common flow path 20 and connecting the circulation path 18 to both.

  By adopting this configuration, as shown in FIG. 10, a dead water area and a slow water area are less likely to be generated in the vicinity of the back surface of the nozzle 16 compared to a configuration in which only one circulation path 18 is provided (the entire interior of the communication path 14). (Circulating flow can occur).

  Further, by arranging in the tangential direction of the inner periphery of the communication path 14, the ink flow from the communication path 14 to the circulation path 18 becomes a vortex along the inner periphery of the communication path 14 symmetrical to the central axis of the nozzle 16, and the conventional radial direction. It is possible to reduce the flow unevenness at the time of ejection due to the ink flow generation.

  As an example of a manufacturing method of the discharge device according to the present embodiment, it can be manufactured by stacking plates (conventional method). That is, by adding at least one laminated plate related to the circulation path 18, for example, as shown in FIG. 9, if one circulation path plate 17A connected to the communication path 14 is added, the discharge having the structure of FIG. Can with equipment. Further, as shown in FIG. 9, the common flow path may be divided into upper and lower portions by a partition plate 17B, the piezoelectric element 13 side may be the supply common flow path 12, and the nozzle 16 side may be the circulation common flow path 20.

<Fourth embodiment>
FIGS. 11 to 13 show examples of direction setting in the circulation path of the droplet discharge device according to the fourth embodiment of the present invention.

  As shown in FIG. 11, in the fourth embodiment of the present invention, the circulation path 18 is provided at a position where the extension direction of the circulation path 18 does not enter the surface of the nozzle 16, and one of the plurality of circulation paths 18 is connected. A circulation path 18A for supplying ink to the vicinity of the nozzle 16 in the passage 14 is used, and the other is a circulation path 18B for discharging ink from the communication path 14 to the circulation common flow path 20.

  With the above-described structure, the ink flow in the vicinity of the nozzle 16 due to the liquid circulation is tangential to a circle (inner shape of the communication path 14) centering on the nozzle 16 axis, that is, the circulation path 18B during discharge. The ink flow into the communication path 14B can be designed to have no component vector in the direction of the direct circulation path 18B, and the ink flow in the communication path 14 by the circulation path 18A is centered on the nozzle 16 axis. By reducing the change in asymmetry of the flow velocity in the radial direction of the nozzle 16 in the vortex shape, it is possible to prevent ejection direction defects during ink droplet ejection.

  By installing a plurality of circulation paths 18 at different positions in the discharge direction, that is, at different positions (heights) in the length direction of the communication path 14, the circulation paths 18 (A) to 18 (18) as shown in FIG. The ink flow (arrow in the figure) is not generated as it is to B), and it can be made the ink flow toward the circulation path 18 (B) after making a round in the communication path 14 near the nozzle 16.

  Further, by arranging in the tangential direction of the inner periphery of the communication path 14, the ink flow from the communication path 14 to the circulation path 18 becomes a vortex along the inner periphery of the communication path 14 symmetrical to the central axis of the nozzle 16, and the conventional radial direction. It is possible to reduce the flow unevenness at the time of ejection due to the ink flow generation.

  As an example of a manufacturing method of the discharge device according to this embodiment, it can be manufactured by stacking plates (conventional method). That is, by adding one laminating plate for the circulation path 18 and one for the collection side, for example, as shown in FIG. 12, a supply path plate 17A and a circulation path plate 17B connected to the communication path 14 are added. A discharge device having the structure of FIG. 11 can be obtained. Further, the supply common flow path 12 and the circulation common flow path 20 may be arranged side by side. Further, the same supply common channel 12 as the common channel on the ink supply side may be used on the inflow side of the circulation path 18A.

  Alternatively, as shown in FIG. 13, the circulation paths 18A and 18B may be provided in substantially the same direction when viewed from the discharge direction. Also in this case, by installing a plurality of circulation paths 18A and 18B at different positions (heights) in the length direction of the communication path 14, a dead water area and a slow water area are unlikely to occur near the back surface of the nozzle 16, and ink droplet ejection is performed. It can be set as the structure which prevents the discharge direction defect at the time.

<Effect>
Since this invention was set as the said structure, it has the following outstanding effects.

  That is, in the droplet discharge device 10 provided with the circulation path 18 in the vicinity of the nozzle 16 to prevent the nozzle 16 from drying, the liquid pressure escapes to the circulation path 18 when ink droplets are ejected, and the ejection direction of the ink droplets ejected from the nozzle 16 For the problem that affects the discharge direction, the direction of the circulation path 18 as viewed from the discharge direction is made random for each nozzle, or the flow path parameter of the circulation path 18 is made random, thereby randomizing the influence on the discharge direction and landing. The deviation of the point can be made inconspicuous.

  Alternatively, by providing a plurality of circulation paths 18 for one nozzle 16 and disposing the nozzle 16 on the extended line, more preferably by arranging the circulation path 18 in the circumferential tangential direction of the communication path 14. Since the flow of ink toward the circulation path 18 is a spiral flow along the circumference, the influence of the ink flow in the radial direction of the communication path 14 is prevented, thereby suppressing the influence on the ejection direction and shifting the landing point. Can be suppressed.

<Others>
As mentioned above, although the Example of this invention was described, it cannot be overemphasized that this invention is not limited to said Example at all, and can implement in a various aspect in the range which does not deviate from the summary of this invention.

  That is, in this embodiment, an inkjet recording head that discharges high-viscosity ink droplets is given as an example of a droplet discharge device. However, the present invention is not limited to this, and any device that discharges droplets can be used. It can also be applied to other devices.

1 is a perspective view showing a droplet discharge device according to a first embodiment of the present invention. 1 is a perspective view showing a droplet discharge device according to a first embodiment of the present invention. It is sectional drawing which shows the droplet discharge apparatus which concerns on 1st Embodiment of this invention. It is a conceptual diagram which shows the droplet discharge head which concerns on 1st Embodiment of this invention. It is a conceptual diagram which shows the effect of the droplet discharge apparatus which concerns on 1st Embodiment of this invention. It is a conceptual diagram which shows the effect of the droplet discharge apparatus which concerns on 1st Embodiment of this invention. It is a conceptual diagram which shows the effect of the droplet discharge apparatus which concerns on 2nd Embodiment of this invention. It is the perspective view and top view which show the droplet discharge apparatus which concerns on 3rd Embodiment of this invention. It is sectional drawing which shows the droplet discharge apparatus which concerns on 3rd Embodiment of this invention. It is a top view which shows the modification of the droplet discharge apparatus which concerns on 3rd Embodiment of this invention. It is the perspective view and top view which show the droplet discharge apparatus which concerns on 4th Embodiment of this invention. It is sectional drawing which shows the droplet discharge apparatus which concerns on 4th Embodiment of this invention. It is a top view which shows the modification of the droplet discharge apparatus which concerns on 4th Embodiment of this invention. It is the perspective view, top view, and sectional drawing which show the conventional droplet discharge device. It is sectional drawing which shows the conventional droplet discharge apparatus. It is a top view which shows the conventional droplet discharge apparatus. It is a table | surface which shows the relationship between the angle which the adjacent circulation paths of a droplet discharge apparatus make, and white stripe generation | occurrence | production.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Droplet discharge device 11 Discharge head 12 Supply common flow path 13 Piezoelectric element 14 Communication path 15 Pressure chamber 16 Nozzle 17 Plate 18 Circulation path 20 Circulation common flow path 22 Print line 24 White stripe 30 Dot P Paper

Claims (3)

A plurality of nozzles for discharging droplets;
The interior of the liquid varying pressure from a plurality of the nozzles for ejecting liquid droplets, a pressure chamber corresponding to each of a plurality of said nozzles,
A first common flow path for supplying liquid to the pressure chamber;
A substantially cylindrical communication path corresponding to each nozzle , wherein one end communicates with the pressure chamber, and the nozzle is provided at a position overlapping the center of the other end;
A circulation path corresponding to each nozzle , which is provided at the other end of the communication path and extends in a direction intersecting the droplet discharge direction and discharges the liquid from the communication path ;
A second common flow path that communicates with each of the circulation paths and collects liquid from each of the communication paths; and
The liquid droplet ejection apparatus according to claim 1, wherein the circulation paths corresponding to the plurality of nozzles are provided in different directions from the nozzles when viewed from the ejection direction . Among the plurality of nozzles, the circulation paths corresponding to any two nozzles that discharge droplets to adjacent landing points extend in different directions when viewed in the discharge direction, and flow path parameters 2. The droplet discharge device according to claim 1 , wherein are different from each other and connected to the second common flow path . The droplet discharge device according to claim 2, wherein the flow path parameter is one or more of a length, an opening area, a height, and a width of the circulation path .

Images