JPH10193592A - Liquid jet apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably supply ink, to realize the stable continuous jetting of ink and to enhance recording quality in a liquid jet apparatus utilizing an SAW streaming phenomenon. SOLUTION: An interdigital electrode 2 is provided on the propagation surface 1a of a propagation member 1 and an AC generator 3 is connected to the interdigital electrode 2. An almost triangular notch 7 is formed to the end part of the propagation member 1. The apex of a triangle is set to a jet position 8 to fix the jet position and a liquid surface can be stabilized by the capillary force of ink by a triangular shape. The wide angle θ of the notch 7 is set to 30 - below 180 deg. to reduce the effect of the wall surface bonding force of a fluid and a jet direction is stabilized. By this constitution, continuous jetting can be stably performed and printing quality can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid ejecting apparatus which uses a surface acoustic wave to fly ink.

[0002]

2. Description of the Related Art A so-called ink jet printer which ejects ink droplets and records a character or graphic corresponding to input information on a recording medium is excellent in that it can be quietly recorded directly on plain paper. This type of printer has a plurality of nozzles and ink pressurizing chambers corresponding to the nozzles,
Ink droplets are ejected from the nozzles by changing the ink liquid pressure in the ink pressurizing chamber in accordance with the recording information signal, and recording is performed on a recording medium such as a recording sheet facing the recording medium. As a means for pressurizing ink, a method using a piezoelectric element provided in an ink pressurizing chamber, a method for generating bubbles in an ink liquid by a micro heater, and the like are known. However, these printer heads require a number of nozzles to be arranged at a high density, and require extremely precise molding techniques. Also,
There is a problem that nozzle clogging is likely to occur due to drying of the ink or adhesion of dust, and the recording quality is degraded.

In order to solve such a problem, an ink jet system without a nozzle has been studied. One such example is Shiokawa et al., "Elucidation of SAW Streaming Phenomenon and Its Application", Journal of the Institute of Electronics and Communication Engineers, (US89-51).
As disclosed in SAW (Surface A)
A method utilizing a (Coustic Wave) streaming phenomenon has been considered. The SAW streaming phenomenon is a phenomenon in which a liquid is added onto a surface acoustic wave propagation surface, the surface acoustic wave is radiated into the liquid, and the excitation output thereof is increased, so that fine particles of the liquid fly.

Various studies have been made on an ink jet system utilizing the SAW streaming phenomenon. For example, Japanese Patent Application Laid-Open Nos. 4-14455 and 4-119854.
Gazette, JP-A-4-189145, JP-A-4-4-2
JP-A-39650, JP-A-4-259558, JP-A-4-263951, JP-A-4-294146
JP, JP-A-4-294147, JP-A-6-6-6
No. 4,173, and the like.

FIG. 5 is a conceptual diagram showing a first example of a conventional liquid ejecting apparatus. In the figure, 1 is a propagation body, 1a is a propagation surface,
2 is a comb-shaped interdigital electrode, 3 is an AC generator, 4 is a surface acoustic wave, 5 is ink, and 6 is an ink droplet. The propagation body 1 is formed of, for example, a flat-plate-shaped piezoelectric substrate, and a comb-shaped interdigital electrode 2 is provided on a propagation surface 1a that propagates a surface acoustic wave. An AC generator 3 is connected to the interdigital electrode 2. Further, the ink 5 is held at the end of the propagation body 1 orthogonal to the propagation direction of the surface acoustic wave 4. Such a configuration is described in, for example, Japanese Patent Application Laid-Open No. 4-189145.

When an AC voltage is applied to the interdigital electrode 2 by the AC generator 3, an alternating electric field is generated between the electrodes and a surface acoustic wave 4 is generated. The generated surface acoustic wave 4 propagates in a direction orthogonal to the comb-like portion of the interdigital electrode 2. The width of the surface acoustic wave 4 is the width of the comb-like portion of the interdigital electrode 2. The surface acoustic wave 4 propagates on the propagation surface 1a while substantially maintaining the wave width. The surface acoustic wave 4 propagates on the surface while rotating in a direction opposite to the traveling direction of the wave, and
When the surface acoustic wave 4 reaches the end, the surface acoustic wave 4 raises the ink in contact with the end of the propagation body 1 to the surface height of the propagation body 1 by the rotational force of the wave, and then ejects the ink. However, in order to raise the ink, it is necessary to stabilize the water level of the ink at an appropriate position. For example, the liquid level of the ink 5 is
Is desirably held so as to be continuous with the propagation surface 1a.

However, in this configuration, it is difficult to keep the water level of the ink 5 constant due to the vibration of the liquid surface after the ink droplet 6 flies. Therefore, there is a problem that stable continuous injection cannot be performed.

FIG. 6 is a conceptual diagram showing a second example of a conventional liquid ejecting apparatus. In the figure, the same parts as those in FIG. 21 is a slit. In this example, a slit 21 is formed on the propagation surface 1a in front of the surface acoustic wave 4 in the propagation direction and perpendicular to the propagation direction. The slits 21 are formed by facing the substrates so as to face each other, or by digging a groove in the center of the substrates. New ink is supplied to the slit 21 from below or from the lateral direction. Since the water level of the ink in the slit 21 is kept constant and stable by the capillary force, it is possible to perform more stable ejection than the configuration shown in FIG. However, this method has a drawback that it is difficult to align the left and right jetting positions and is susceptible to the reflected wave from the opposing surface.

FIG. 7 is a conceptual diagram showing a third example of a conventional liquid ejecting apparatus. In the figure, the same parts as those in FIG. 22 is a hole. In this example, instead of the slit 21 shown in FIG.
A hole 22 is formed on the top. The ink is supplied from the lower part of the hole 22 and the liquid level of the ink is held by capillary action. In this example, the ejection position of the ink droplet 6 is fixed, but it is extremely difficult to form the hole 22 on the piezoelectric substrate. Another drawback is that, depending on the hole diameter, the capillary force is too strong and a large power is required at the time of injection.

FIG. 8 is a conceptual diagram showing a fourth example of a conventional liquid ejecting apparatus. In the figure, the same parts as those in FIG. 23 is a notch.
In this example, a notch 23 is provided at the end of the propagation body 1. By arranging the cut portion 23 near the center of the surface acoustic wave propagating, the ejection position of the ink droplet 6 can be fixed. However, it is difficult to obtain a capillary force enough to stabilize the water level in such a small cut portion 23. Therefore, similarly to the example shown in FIG. 5, it is difficult to keep the water level of the ink 5 constant, and stable continuous ejection cannot be performed. There is also a disadvantage that the ink ejection position is not strictly fixed at one point.

As described above, in the conventional ink-jet system, it is difficult to continuously jet ink stably, and it is difficult to improve the print quality, or it is difficult to achieve the desired print quality, and a desired liquid ejecting apparatus can be easily obtained. I couldn't do that.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in a liquid ejecting apparatus utilizing the SAW streaming phenomenon, it is possible to supply ink stably and continuously eject ink stably. To achieve
The purpose is to improve the recording quality.

[0013]

According to a first aspect of the present invention, in a liquid ejecting apparatus, a surface acoustic wave generating means for generating a surface acoustic wave, and a surface acoustic wave generated by the surface acoustic wave generating means are propagated. Surface acoustic wave propagating means having a propagating surface to be caused, and liquid holding means for holding a liquid forward in the propagation direction of the surface acoustic wave generated by the surface acoustic wave generating means. A substantially triangular cut is formed at the end of the elastic wave in the propagation direction,
The wide angle of the cut is not less than 30 degrees and less than 180 degrees.

According to a second aspect of the present invention, in the liquid ejecting apparatus according to the first aspect, the cut is formed by combining at least two or more divided substrates. It is.

[0015]

FIG. 1 is a conceptual view showing a first embodiment of a liquid ejecting apparatus according to the present invention. FIG. 1 (A) is a perspective view, and FIG. 1 (B) is a plan view. . In the figure, the same parts as those in FIG. 7 is a cut, and 8 is an injection position. A substantially triangular cut 7 is formed at the end of the propagation body 1. The cut 5 is supplied with the ink 5 from an ink supply unit (not shown). Japanese Patent Application Laid-Open No. 4-189145 also discloses that triangular irregularities are provided. However, as described later, satisfactory recording cannot be performed simply by forming a triangular shape. In the present invention, by setting the wide angle θ of the cut 7 shown in FIG. 1B to 30 degrees or more and less than 180 degrees, the supply of ink is stabilized, and the recording quality is improved.

The length of the triangular cut 7 is not particularly limited as long as it can hold the ink and stabilize the water level, and the end is open even if it is closed as long as the ink supply is not hindered. Although it does not matter, it is more advantageous in processing that the end portion is open. In addition, when the end is in an open state, it is possible to communicate with a wide ink pool or the like as shown in FIG. 5 and to use the ink pool as a buffer to supply ink therefrom. Furthermore, in the open state, there is no influence of reflected waves and the like, and stable ejection is possible.

In such a configuration, the AC generator 3
When an AC voltage is applied to the comb-shaped interdigital electrode 2 to generate a surface acoustic wave 4, the surface acoustic wave 4 propagates on the propagation surface 1 a toward the slit 7. When it reaches the ejection position 8 which is the end of the triangular cut 7 on the side of the comb-shaped interdigital electrode 2, it contacts the ink 5. Therefore, the ink droplet 6 flies at the ejection position 8. Since the ejection position 8 is a vertex of a triangle, the ink 6 flies from one point, and the direction in which the ink droplet 6 flies is good. Further, since the width decreases toward the ejection position 8, the capillary force gradually increases toward the ejection position 8, and the liquid level of the ink 5 can be stably maintained by the capillary force. Therefore, since the ink droplets 6 can fly stably even during continuous ejection, the print quality can be improved as compared with the related art.

In order to increase the capillary force and improve the stability of the water level, it is desirable to reduce the wide angle θ of the cut 7 as much as possible. However, when the capillary force is too strong, not only does the ink eject a large amount of energy to eject ink, but also drops cannot be formed when the viscosity of the ink is high. Further, even when the drop can be ejected, the wide angle θ of the cut 7 is 3 °.
If the angle is less than 0 degrees, the effect of the fluid wall adhesion (Coanda effect) is large, and the direction of the continuously ejected drop is pulled in the direction of the wall surface of the cut 7, making it impossible to obtain a stable directionality.

FIG. 2 is a graph showing the relationship between the wide angle of the cut and the solid angle at the time of ink ejection, and FIG. 3 is a schematic diagram for explaining an example of the relationship between the wide angle of the cut and the solid angle at the time of ink ejection. is there. Here, the relationship between the wide angle and the solid angle in pure water, ink 1 and ink 2 was compared. The viscosities of pure water, ink 1 and ink 2 have a relationship of pure water <ink 1 <ink 2. Here, as shown in FIG. 3, the solid angle φ is a solid angle of a cone having a spread range of the ink attached on the recording medium as a bottom surface and a jetting position 8 as a vertex. I have.

A region where the wide angle θ is 30 degrees or less (the hatched region in FIG. 2) even with pure water having the lowest viscosity.
In this case, as shown in FIG. 3A, the ink is dispersed at the same solid angle φ as the wide angle θ due to the Coanda effect. The wall adhesion of the liquid increases as the viscosity increases. Therefore, when the ink ejection speed is the same, the angle at which the ink adheres to the wall surface (the hatched area in FIG. 2) increases as the viscosity of the ink increases,
It is necessary to provide a wide angle θ. When the angle between the liquid ejection direction (on the wide angle bisector) and the wall surface of the cut 7 exceeds a certain value, the constraint of the wall adhesion force is gradually released, and the solid angle of the injection is reduced as shown in FIG. Narrowing, 60 for pure water
The solid angle becomes less than 5 degrees near the degree. This state is shown in FIG.
This is shown in FIG. Note that the wide angle θ of the cut 7 is 15
When the temperature is less than the degree, the capillarity is too restrained to eject the liquid.

As described above, it is necessary to select a wide angle according to the viscosity of the ink so that the solid angle at the time of ink ejection becomes small. At this time, wide angle θ should be at least 30 degrees or more.
If it is not set, it is difficult to continuously eject ink with good directionality. If the wide angle θ is 180 degrees as shown in FIG. 5, it is difficult to keep the water level of the ink 5 constant as described above. Further, since the injection position 8 does not become one point as in the above-described vertex of the triangle, the injection position 8 varies. Therefore, the wide angle θ needs to be less than 180 degrees.

FIG. 4 is a conceptual diagram showing a second embodiment of the liquid ejecting apparatus according to the present invention. In the figure, the same parts as those in FIG. 9a and 9b are separation substrates. In the second embodiment, the separation substrate 9a
And 9b are abutted against the propagator 1 to form a triangular cut 7. Generally, a substrate made of a ferroelectric material is frequently used as the propagation body 1, and among them, a single crystal substrate such as LiNbO3 is most suitable. However, when such a substrate is used, it is very difficult to form the tip of the cut 7 at an acute angle. As shown in FIG. 4, by employing a configuration in which two or more different substrates that are linearly processed are abutted, the processing is greatly facilitated. The separation substrates 9a and 9b are preferably made of the same material as the propagation body 1, but are not particularly limited as long as the propagation speed of the sound wave is higher than that of the ink.

In the first and second embodiments, a lens for converging the surface acoustic wave 4 may be provided on the propagation surface 1a of the propagation body 1 between the interdigital electrode 2 and the injection position 8. . If the focal position of this lens is set to the injection position 8, the surface acoustic waves 4
Can be concentrated at the ejection position 8, and the ink droplet 6 can be ejected efficiently. Further, the surface acoustic wave 4 focused by the lens has a sharp change in the intensity distribution of the excitation power near the focal point, so that a drop having a small particle diameter can be emitted. Therefore, minute ink droplets can be formed, and the printing quality can be improved. The lens may be formed, for example, by forming an unpolarized portion of a ferroelectric into a lens shape and forming a propagation surface of the lens as an unpolarized portion.

Further, when the focal position of the lens and the ejection position 8 are different, a waveguide may be provided between the focal position and the ejection position 8. When the waveguide is provided, the traveling direction of the surface acoustic wave 4 can be changed, and the degree of freedom of the positional relationship between the interdigital electrode 2 and the cut 7 can be increased.

[0025]

As is apparent from the above description, according to the present invention, a triangular cut is provided at the end of the surface acoustic wave propagation surface, and the wide angle is adjusted within a range of 30 degrees or more and less than 180 degrees. This makes it possible to fix the ink ejection position to one of the apexes of the cut portion, and at the cut apex portion, water is pulled up by an appropriate capillary force, thereby enabling stable continuous ejection. As described above, the supply of the ink can be stabilized, and the ejection characteristics of the ink can be stabilized, so that the recording quality can be improved. Further, by changing the wide angle of the triangular cut within the above range, it is also possible to control the ink supply and the ejection characteristics according to the viscosity of the ink to be used.

Furthermore, by forming a triangular cut with another substrate abutted, the sharpness of the cut end can be increased, the ink ejection characteristics can be stabilized, and the recording quality can be improved. effective.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a first embodiment of a liquid ejecting apparatus according to the present invention.

FIG. 2 is a graph showing a relationship between a wide angle of cut and a solid angle at the time of ink ejection.

FIG. 3 is a schematic diagram illustrating an example of a relationship between a wide angle of cut and a solid angle at the time of ink ejection.

FIG. 4 is a conceptual diagram illustrating a liquid ejecting apparatus according to a second embodiment of the present invention.

FIG. 5 is a conceptual diagram showing a first example of a conventional liquid ejecting apparatus.

FIG. 6 is a conceptual diagram showing a second example of a conventional liquid ejecting apparatus.

FIG. 7 is a conceptual diagram showing a third example of a conventional liquid ejecting apparatus.

FIG. 8 is a conceptual diagram showing a fourth example of a conventional liquid ejecting apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Propagation body, 1a ... Propagation surface, 2 ... Comb-shaped interdigital electrode, 3 ...
AC generator, 4 surface acoustic wave, 5 ink, 6 ink drop, 7 cut, 8 ejection position, 9a, 9b separation substrate.

Claims (2)

[Claims] A surface acoustic wave generating means for generating a surface acoustic wave; a surface acoustic wave propagating means having a propagation surface for propagating the surface acoustic wave generated by the surface acoustic wave generating means;
The liquid crystal display has liquid holding means for holding a liquid in a propagation direction of the surface acoustic wave generated by the surface acoustic wave generation means. The surface acoustic wave propagation means has a substantially triangular cut at an end in the surface acoustic wave propagation direction. Wherein the wide angle of the cut is not less than 30 degrees and less than 180 degrees. 2. The liquid ejecting apparatus according to claim 1, wherein the cut is formed by combining at least two or more divided substrates.