JPH11334069A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of image quality. SOLUTION: The ink jet head comprises a plurality of ink chambers each containing ink, and a nozzle plate 15 arranged with a plurality of orifices 16 for ejecting ink drop. A counterbore is formed in the outer surface of the nozzle plate 15 around each orifice 16 and a water repellent part is formed on the outside of the inner circumferential edge of the counterbore. When an ink drop is ejected from the orifice 16, the ink drop is formed to break the central part of meniscus. Consequently, even if ink adheres to the inner circumferential edge of the counterbore, it is not attracted to an ink drop being ejected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head.

[0002]

2. Description of the Related Art Conventionally, in recording an image such as a character or a pattern on a medium such as paper, an ink jet recording apparatus capable of recording at a high speed without generating noise and requiring no special fixing process. Is used. In the ink jet recording apparatus, ink droplets are ejected toward the medium by an ink jet head. As a method of ejecting the ink droplets, an electrostatic method is used. And a piezoelectric method using a piezoelectric element such as a piezo element.

In an ink jet head which discharges ink droplets by a piezoelectric method, a plurality of ink chambers are formed, and a nozzle plate is attached so as to close one end of each ink chamber. An orifice is formed in the nozzle plate for discharging the ink in each of the ink chambers as ink droplets. Then, when the wall is deformed by applying a voltage to the piezoelectric element constituting the wall of the ink chamber, pressure is applied to the ink in the ink chamber, and ink droplets are ejected from the orifice.

[0004]

However, in the above-described conventional ink jet head, the trajectory of the ejected ink droplet is bent, or after the ink droplet is ejected,
Ink droplets (hereinafter referred to as “satellite”) are ejected, or ink droplets are ejected erroneously (crosstalk) due to deformation or vibration of a wall when ink droplets are ejected from an adjacent ink chamber, Ink clogging may occur.

[0005] As a result, the dots formed on the medium due to the attachment of the ink droplets become irregular (uneven) or the shape of the dots is distorted, thereby deteriorating the image quality. FIG. 2 is a first diagram showing the ejection state of ink droplets in a conventional inkjet head, FIG. 3 is a diagram showing the ejection process of ink droplets in a conventional inkjet head, and FIG. 4 is an ejection state of ink droplets in a conventional inkjet head. FIG. 5 is a diagram showing dots formed on a medium by a conventional inkjet head.

In the figure, 40 is an ink chamber, 41 is a wall,
43 is a nozzle plate and 50 is an orifice. Then, in order to stably eject the ink droplets 45 from the orifice 50 and to prevent the ink 44 from adhering to the outer surface S1 of the nozzle plate 43, the outer surface S1 is subjected to a water repellent treatment. . If the ink 44 does not adhere to the edge of the orifice 50, the ink droplet 4
The trajectory No. 5 is normal without bending as shown by type A in FIG. However, the outer surface S of the nozzle plate 43
When the ink 44 adheres to the surface of the orifice 50, the ink 44 adheres to the inner edge of the orifice 50. As a result, the ink 44 and the ejected ink droplet 4
5 attracts, the trajectory of the ink droplet 45 after being ejected bends toward the side where the ink 44 adheres, as shown by types B and C. As a result, the dots formed on the medium (not shown) become irregular or the shape of the dots is lost, and the image quality is reduced.

As shown in FIGS. 3 (a) and 3 (b), the ink 46 in the ink chamber 40 passes through the orifice 50 by being pressurized, swells, and then moves to (c). Follow the tail as shown. Then, when separated as shown in (d), the ink is ejected as ink droplets 45 as shown in (e) and FIG. 4, and at this time, the tail portion is applied to a plurality of satellites 47. And follows the ink droplet 45. As a result, a large dot d1 is formed on the medium by the ink droplet 45 and a small dot d2 is formed by the satellite 47.

In this case, since the ink jet head performs printing while being moved with respect to the medium, the satellites 47 sequentially arrive after the ink droplets 45 reach the medium. As a result, as shown in FIG. 5, the dots d1 and d2 are slightly shifted from each other on the medium, thereby deteriorating the image quality. In the ink jet head configured to eject the ink droplets 45 by the piezoelectric method, the wall 41 of the ink chamber 40 is deformed when a voltage is applied to a piezoelectric element (not shown) so that the ink droplets 45 are ejected. Because it is
When the ink droplet 45 is ejected from the adjacent ink chamber 40, the ink droplet 45 is erroneously ejected due to deformation, vibration, or the like of the wall 41. As a result, an extra dot d2 is formed on the medium, and the image quality deteriorates.

Further, since the diameter of the orifice 50 is very small, generally about 30 [μm], and the ink 46 is locally exposed to the outside air, the ink 46 can easily be formed unless the ink jet recording apparatus is used for a long time. It will dry. Therefore, the orifice 50 is closed and ink clogging occurs. As a result, if ink clogging occurs in the orifice 50, printing becomes impossible, and if ink clogging occurs in some orifices 50, some dots will not be formed on the medium. I will.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the conventional ink jet head and to provide an ink jet head in which the image quality does not deteriorate.

[0011]

For this purpose, in the ink jet head of the present invention, a plurality of ink chambers each containing ink and a plurality of ink chambers corresponding to the respective ink chambers are provided.
A nozzle plate formed with a plurality of orifices for discharging ink droplets. A counterbore is formed around the orifice on the outer surface of the nozzle plate, and a water-repellent portion is formed outside the inner peripheral edge of the counterbore.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of a main part of a nozzle plate of an ink jet head according to a first embodiment of the present invention, FIG. 6 is a perspective view of the ink jet head according to the first embodiment of the present invention, and FIG. FIG. 8 is a side view of the ink jet head according to the first embodiment, FIG. 8 is a perspective view of a nozzle plate of the ink jet head according to the first embodiment of the present invention, and FIG. 9 is an enlarged orifice according to the first embodiment of the present invention. FIG.

As shown in FIG. 1, in an ink jet head that discharges ink droplets by a piezoelectric method, a plurality of ink chambers 13 are formed in a piezoelectric element 11, and ink is stored in each of the ink chambers 13. Is done. A nozzle plate 15 is attached to the piezoelectric element 11 so as to close one end of the ink chamber 13, and a manifold 14 communicating with an ink tank (not shown) is attached to the other end of the ink chamber 13. A plurality of orifices 16 for ejecting ink droplets are formed in the nozzle plate 15 so as to correspond to the respective ink chambers 13.

When a voltage is applied to the piezoelectric element 11 to deform it, a wall (not shown) forming the ink chamber 13 is deformed, pressure is applied to the ink in the ink chamber 13, and ink droplets are ejected from the orifice 16. Is done. And
The ink in the ink tank is supplied to the ink chamber 13 via the manifold 14. In addition, the ink-jet head is set at 30 [cm / s] with respect to a medium not shown.
It is moved at a moderate speed and prints images such as characters and patterns on a medium.

The orifice 16 has a diameter of about 30 [μm], and is formed by arranging several tens of orifices in one ink jet head. Further, since the piezoelectric element 11 is repeatedly deformed at a period of about 2 / 10,000 seconds, 5,000 or more ink droplets are ejected from each orifice 16 toward the medium per second. In addition, the medium is 1 to 1 from the nozzle plate 15.
2 [mm] apart.

When the ejected ink droplet reaches the medium, it forms a dot having a diameter of about 100 μm on the medium. As a result, the image is printed on the medium.
By the way, since the image is formed by the set of dots, the shorter the distance between the dots and the greater the number of dots forming the image, the more inconspicuous the dots and the higher the image quality.

As described above, in the ink jet head which ejects ink droplets by the piezoelectric method,
Since the ink is not heated, the ink does not deteriorate due to heat. Further, since the deformation of the piezoelectric element 11 can be controlled by adjusting the voltage applied to the piezoelectric element 11, the pressure applied to the ink can be arbitrarily adjusted, and the diameter of the ejected ink droplet can be reduced. Can be controlled.

Therefore, it is possible to easily perform gradation printing by adjusting the size and density of the dots formed on the medium. By the way, the outer surface S11 of the nozzle plate 15
In FIG. 8, a circular counterbore 17 having a constant depth is formed around each orifice 16 as shown in FIGS. The counterbore 17 has a bottom surface 17a as a plane,
It is desirable that the diameter is about several tens [μm] and the depth is about 5 to 15 [μm]. Also, as shown in FIG. 1, the orifice 16 is tapered so that the diameter decreases toward the outer surface S11 of the nozzle plate 15.

A water-repellent portion is formed outside the inner peripheral edge of the spot facing 17. That is, in the nozzle plate 15, the outer surface S1 excluding the inner peripheral surface 16a of the orifice 16 and the bottom surface 17a and the wall surface 17b of the counterbore 17
1 is subjected to a water-repellent treatment. As the water-repellent treatment, a fluorine resin coating or the like is employed. On the other hand, the inner peripheral surface 16a, the bottom surface 17a, and the wall surface 17b are subjected to a hydrophilic treatment. As the hydrophilic treatment, machining, surface roughening by chemicals, or the like is employed.

When the nozzle plate 15 itself is formed of a material having water repellency, the water repellent treatment is not required. When the nozzle plate 15 itself is formed of a material having hydrophilicity, the hydrophilic treatment is not performed. Not required. Next, the operation of the ink jet head having the above configuration will be described.
FIG. 10 is a first diagram illustrating the state of the ink according to the first embodiment of the present invention, FIG. 11 is a second diagram illustrating the state of the ink according to the first embodiment of the present invention, and FIG. FIG. 13 is a third diagram illustrating the state of the ink according to the first embodiment of the present invention, and FIG. 13 is a fourth diagram illustrating the state of the ink according to the first embodiment of the present invention.

In the drawing, reference numeral 15 denotes a nozzle plate;
Is an orifice, 17 is a counterbore, 61 is ink, 62 is an ink drop, and m is a meniscus. When the ink droplet 62 is not ejected from the orifice 16, as shown in FIG. 10, the ink 61 is filled in the orifice 16 and the counterbore 17, forms an ink film in the counterbore 17, and does not flow out. A slightly concave meniscus m is formed. This is because the inside of an ink tank (not shown) communicating with the manifold 14 (FIG. 7) has a slight negative pressure, the ink 61 has a high viscosity, and the counterbore 17
This is because the diameter of the ink 61 is about several tens [μm] and is small, so that the effect of the surface tension of the ink 61 is increased.

When the ink droplet 62 is ejected from the orifice 16, as shown in FIGS. 11 to 13, the shape of the meniscus m changes, and the ink droplet 62 is moved to the center of the counterbore 17, that is, the meniscus m. Is formed so as to break the central part of. At this time, even if the ink 61 adheres to the inner peripheral edge of the spot facing 17, the ejected ink droplet 62 is formed so as to break the central portion of the meniscus m away from the inner peripheral edge of the spot facing 17. In addition, the ink 61 attached to the inner peripheral edge and the ejected ink droplet 62 do not attract each other. Therefore, the ink droplet 62 after being ejected is
Does not bend, so that the dots formed on a medium (not shown) do not become irregular or the shape of the dots does not collapse. As a result, the image quality does not deteriorate.

When the ink droplet 62 is ejected, a part of the ink 61 in the counterbore 17 is pulled with the swelling of the ink 61, but the amount of the pulled ink 61 is extremely small and the amount of movement is small. Therefore, the ink 61 is pulled back by the ink film formed in the spot facing 17, and the ink 61 does not trail and move forward. Therefore, since a plurality of satellites are not formed when the ink droplet 62 is ejected, a small dot is not formed on the medium. As a result, the image quality does not deteriorate. In this case, the size of the spot facing 17 is set such that the ink 61 drawn along with the swelling of the ink 61 can be sufficiently pulled back.

In the ink jet head which discharges the ink droplets 62 by the piezoelectric method, the ink 61 may expand due to deformation or vibration of the wall when the ink droplets 62 are discharged from the adjacent ink chamber 13. However, since the amount of the ink 61 to be swollen is extremely small and the momentum is small, the ink 61 is pulled back by the ink film formed in the spot facing 17. Therefore, no extra dots are formed on the medium, and the image quality is not degraded.

Further, even when the ink jet recording apparatus is not used for a long time, the ink 61 is not easily dried because the spot facing 17 is filled with a relatively large amount of the ink 61. Therefore, the orifice 16 is not blocked, and ink clogging does not occur. As a result, the dots can be reliably formed on the medium, so that the image quality does not deteriorate.

When the ink jet recording apparatus is not used for a long time, it is possible to surely prevent clogging of the ink by attaching a lid or the like covering the nozzle plate 15. By the way, after the ink droplet 62 is ejected from the orifice 16, the meniscus m
Vibrate, and eventually attenuate, and finally form a concave surface again as shown in FIG. 10, during which the meniscus m continues to vibrate.

FIG. 14 is a fifth diagram showing the state of the ink according to the first embodiment of the present invention. In the figure, 1
6 is an orifice, 17 is a counterbore, and m is a meniscus. As shown in the figure, when the next ink droplet 62 (FIG. 13) is ejected from the orifice 16 while the vibration of the meniscus m continues, the ink droplet 62 is formed by breaking the unstable ink film. Therefore, the trajectory of the ink droplet 62 is bent or a plurality of satellites are formed.

Therefore, while the vibration of the meniscus m continues, it is necessary to prevent the next ink droplet 62 from being ejected, so that the printing throughput is reduced accordingly. Therefore, a second embodiment of the present invention will be described in which the attenuation time of the vibration of the meniscus m can be shortened. In addition, about what has the same structure as 1st Embodiment, the description is abbreviate | omitted by attaching the same code | symbol.

FIG. 15 is a sectional view of a nozzle plate of an ink jet head according to a second embodiment of the present invention. In this case, for example, the meniscus m
Is retracted, the meniscus m contacts the inner peripheral edge 16b of the orifice 16, and the counterbore 17 is set shallow so that the meniscus m forms a two-step arc. In the present embodiment, the depth of the spot facing 17 is set to about 5 [μm].

Next, the operation of the ink jet head having the above configuration will be described. FIG. 16 is a first diagram showing the state of the ink according to the second embodiment of the present invention, FIG. 17 is a second diagram showing the state of the ink according to the second embodiment of the present invention, and FIG. FIG. 19 is a third diagram showing the state of ink in the second embodiment of the present invention, and FIG. 19 is an explanatory diagram of meniscus vibration in the second embodiment of the present invention. In FIG. 19, the horizontal axis represents time, and the vertical axis represents amplitude and drive voltage.

In the figure, 16 is an orifice, 17 is a counterbore, 61 is ink, and m is a meniscus. At the time of non-printing, as shown in FIG. 16, the ink 61 is filled in the orifice 16 and the counterbore 17, and the meniscus m draws a two-step arc. At the time of printing, pressure is applied to the ink 61 in the ink chamber 13 (FIG. 7), and an ink droplet 62 (FIG. 13) is formed so as to break the center of the meniscus m. Discharged from 16. The meniscus m immediately thereafter forms a convex surface as shown by a solid line in FIG. Thereafter, the inside of the ink chamber 13 becomes negative pressure with the ejection of the ink droplet 62, so that the ink 61 in the counterbore 17 is drawn rightward in FIG. 17, and the meniscus m is shown by a broken line in FIG. Such a concave surface is formed. And meniscus m
Tries to vibrate by alternately repeating the convex surface as shown by the solid line and the concave surface as shown by the broken line. In the state of the broken line, the meniscus m contacts the inner peripheral edge 16b of the orifice 16, so that Energy is absorbed, and vibration is stopped in the spot facing 17. As a result, as shown in FIG. 18, the meniscus m vibrates in the orifice 16 by alternately repeating a convex surface shown by a broken line and a concave surface shown by a solid line.

In this case, the vibration of the meniscus m in the orifice 16 is generated for a small amount of the ink 61 due to the small length of the vibration chord. Therefore, the vibration of the meniscus m has a small amplitude and a short cycle,
Decays in a very short time. Then, since the decay time of the vibration of the meniscus m can be extremely shortened, the next ink droplet 62 can be ejected earlier by that amount. As a result, the print throughput can be increased. In the present embodiment, the amplitude is set to about 5 to 10 [μm].

In FIG. 19, line L1 corresponds to FIG.
The vibration waveform of the meniscus m when the deep counterbore 17 is formed as shown in FIG. 4, and the line L2 is the vibration waveform of the meniscus m when the shallow counterbore 17 is formed as shown in FIG. At a point G where the line L2 branches from the line L1, the meniscus m contacts the inner peripheral edge 16b of the orifice 16.

In general, when the liquid surface is vibrated, it is necessary to consider not only the primary mode vibration but also the higher mode vibration. However, in the ink jet recording apparatus, the viscosity of the ink 61 used is Is relatively high and the vibration occurs in a very small area such as the orifice 16, so it is sufficient to consider only the first-order mode vibration. Therefore, higher order mode vibrations are ignored.

It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0036]

As described above in detail, according to the present invention, in an ink jet head, a plurality of ink chambers each containing ink and ink droplets are ejected in correspondence with each ink chamber. Nozzle plate having a plurality of orifices formed therein.

A counterbore is formed around the orifice on the outer surface of the nozzle plate, and a water-repellent portion is formed outside the inner peripheral edge of the counterbore. In this case, when the ink droplet is ejected from the orifice,
An ink droplet is formed so as to break the center of the meniscus. At this time, even if ink adheres to the inner peripheral edge of the spot facing, the ejected ink droplets are formed so as to break the center of the meniscus away from the inner peripheral edge of the spot facing, so that the ink adhering to the inner peripheral edge is formed. Is not attracted to the ejected ink droplets. Therefore, since the trajectory of the ink droplet after being ejected does not bend, the dots formed on the medium do not become irregular and the shape of the dot does not collapse. As a result, the image quality does not deteriorate.

Further, when the ink droplet is ejected, a part of the ink in the counterbore is pulled as the ink swells.
Since the amount of ink drawn is very small and the momentum is small, the ink is drawn back by the ink film formed in the counterbore and the ink does not trail and move forward. Therefore, since a plurality of satellites are not formed when the ink droplet is ejected, a small dot is not formed on the medium. As a result, the image quality does not deteriorate.

In an ink jet head which discharges ink droplets by a piezoelectric method, deformation of a wall when ink droplets are discharged from an adjacent ink chamber,
Although the ink tends to swell due to vibration or the like, the amount of the ink is extremely small and the momentum is small, so that the ink is pulled back by the ink film formed in the counterbore. Therefore,
Since no extra dots are formed on the medium, the image quality does not deteriorate.

Furthermore, even when the ink jet recording apparatus is not used for a long time, the ink is not easily dried because the spot facing is filled with a relatively large amount of ink. Therefore, the orifice is not blocked, and ink clogging does not occur. As a result, the dots can be reliably formed on the medium, so that the image quality does not deteriorate.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a nozzle plate of an inkjet head according to a first embodiment of the present invention.

FIG. 2 is a first diagram illustrating an ejection state of ink droplets in a conventional inkjet head.

FIG. 3 is a view showing a process of ejecting ink droplets in a conventional inkjet head.

FIG. 4 is a second diagram illustrating the ejection state of ink droplets in a conventional inkjet head.

FIG. 5 is a diagram showing dots formed on a medium by a conventional inkjet head.

FIG. 6 is a perspective view of the inkjet head according to the first embodiment of the present invention.

FIG. 7 is a side view of the inkjet head according to the first embodiment of the invention.

FIG. 8 is a perspective view of a nozzle plate of the inkjet head according to the first embodiment of the present invention.

FIG. 9 is an enlarged view of an orifice according to the first embodiment of the present invention.

FIG. 10 is a first diagram illustrating a state of ink according to the first embodiment of the present invention.

FIG. 11 is a second diagram illustrating the state of the ink according to the first embodiment of the present invention.

FIG. 12 is a third diagram illustrating the state of the ink according to the first embodiment of the invention.

FIG. 13 is a fourth diagram illustrating the state of the ink according to the first embodiment of the invention.

FIG. 14 is a fifth diagram illustrating the state of the ink according to the first embodiment of the invention.

FIG. 15 is a sectional view of a nozzle plate of an inkjet head according to a second embodiment of the present invention.

FIG. 16 is a first diagram illustrating a state of ink according to a second embodiment of the present invention.

FIG. 17 is a second diagram illustrating a state of ink in the second embodiment of the present invention.

FIG. 18 is a third diagram illustrating the state of the ink according to the second embodiment of the invention.

FIG. 19 is an explanatory diagram of a meniscus vibration according to the second embodiment of the present invention.

[Explanation of symbols]

 13 Ink chamber 15 Nozzle plate 16 Orifice 16b Inner peripheral edge 17 Counterbore 61 Ink 62 Ink droplet S11 Outer surface m Meniscus

Continuing from the front page (72) Inventor Toshiyuki Asaka 4-11-11 Shibaura, Minato-ku, Tokyo Inside offshore company data

Claims (4)

[Claims] (A) a plurality of ink chambers each containing ink; and (b) a nozzle plate formed with a plurality of orifices for ejecting ink droplets corresponding to the respective ink chambers. And (c) a counterbore is formed around each of the orifices on the outer surface of the nozzle plate, and a water-repellent portion is formed outside an inner peripheral edge of the counterbore. 2. The water-repellent portion is formed by performing a water-repellent treatment on an outer surface of the nozzle plate.
2. The inkjet head according to item 1. 3. The ink jet head according to claim 1, wherein the orifice is tapered so that the diameter decreases toward the outer surface of the nozzle plate. 4. The ink jet head according to claim 1, wherein a depth of the counterbore is set to such a degree that a meniscus contacts an inner peripheral edge of the orifice during non-printing.