JPH1034913A - Ink jet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording head capable of efficiently jetting small ink droplets. SOLUTION: A vibrating member 2 of a piezoelectric material is provided in a cylindrical nozzle 1, with an ink 3 supplied inside the nozzle 1. At the time, the ink 3 is supplied such that the liquid surface of the ink 3 becomes lower than the upper end of the vibrating member 2. An electric field is applied to the vibrating member 2 at a certain frequency for vibrating the same in the direction perpendicular to the wall surface of the nozzle so as to generate longitudinal waves toward the center of the cylinder under the liquid surface of the ink 3. The longitudinal waves can be propagated efficiently without spreading in the vicinity of the surface of the ink 3 so as to concentrate to the center of the nozzle 1 for jetting ink droplets from the ink surface. By attaching the droplets to a medium to be recorded, recording can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording head for flying ink by using vibration.

[0002]

2. Description of the Related Art Conventionally, there is a so-called on-demand type ink jet recording system in which ink droplets are ejected from nozzles as required to perform printing, and a piezo oscillator type and a thermal type are typical systems. The piezo vibrator type applies a pulse voltage to a piezoelectric element provided in the ink chamber, deforms the piezoelectric element, changes the ink liquid pressure in the ink chamber, and ejects ink droplets from nozzles to form dots on recording paper. It is to be recorded. Thermal type
The ink is heated by heating means provided in the ink chamber, and ink droplets are ejected from nozzles by bubbles generated thereby to record dots on recording paper.

[0003] In these ink-jet technologies, the resolution was conventionally about 300 dpi, but recently the resolution has been increased from 600 to 720 dpi. Along with this, it is necessary to reduce the diameter of a dot to be printed in accordance with the resolution in order to effectively exhibit the effect of increasing the resolution. As a method of reducing the dot diameter in the conventional method, there is a method of reducing the nozzle diameter. However, when the nozzle diameter is reduced, clogging of the nozzle due to dust and drying of the ink surface inside the nozzle, and change in the ink ejection direction due to adhesion of the residue on the nozzle circumference are likely to occur. As a result, defects occur in the image quality on the recording paper,
There is a problem that a nozzle diameter required for printing a dot diameter corresponding to the original resolution cannot be adopted.

On the other hand, an ink jet recording system using surface acoustic waves has recently been proposed. For example, Japanese Patent Application Laid-Open No. 54-10731 discloses a configuration in which a surface acoustic wave is formed by interdigital electrodes provided in a liquid chamber, ink is vibrated by the leaky Rayleigh wave, and ink droplets are ejected from a slit or a nozzle. Have been described. In Japanese Patent Application Laid-Open No. 62-66943, an interdigital electrode is formed concentrically at the bottom of the liquid chamber, a leaky Rayleigh wave is formed in a cone shape in the ink, and an ink surface is provided near the focal point of the wave. There has been proposed a device that concentrates vibration energy propagated in ink on the ink surface to eject ink droplets.

In these systems, the size of the formed ink droplet is not directly affected by the nozzle diameter, so that it is not necessary to make the ink discharge port small, and there is essentially no problem with the slit shape. . However, since the interdigital electrodes that generate surface acoustic waves are arranged in the ink, the electrode material and the components in the ink react due to high-frequency vibration, and the electrodes elute, and ink components adhere to the electrodes. Problems arise. Further, there is a problem that the leaky Rayleigh wave is attenuated when propagating in the ink, and the energy efficiency is low.

To solve these problems, a new ink jet recording method using surface acoustic waves has been proposed. The apparatus described in Japanese Patent Application Laid-Open No. 2-269958 is an example. FIG. 9 is a diagram illustrating the principle of a conventional ink jet recording system using surface acoustic waves. In the figure, 21 is a piezoelectric substrate surface, 22 is an interdigital electrode, 23 is a piezoelectric substrate, 24 is ink, 25 is a droplet, and 26 is a high frequency power supply. Interdigital electrodes 22 are formed on the surface 21 of the piezoelectric substrate 23. A high-frequency voltage is applied to the interdigital electrode 22 from a high-frequency power supply 26, and the ink 2
Put 4. Then, when the surface acoustic wave comes into contact with the ink 24, the vibration energy leaks into the ink 24 (generation of a leaky Rayleigh wave), whereby a part of the ink 24 flies as a droplet 25. In this method, the interdigital electrode 22 does not directly contact the ink 24, and it is not necessary to form a small nozzle, so that there is no reliability problem as in the above-described method.

However, in this configuration, since the parallel interdigital electrodes are used as the electrodes, the surface acoustic waves propagate in directions other than the propagation direction, resulting in poor energy efficiency and crosstalk. The direction and size of the droplet flying from the surface are extremely unstable compared to the above-described conventional example. In order to increase the directivity of propagation of the surface acoustic wave, the width d of the interdigital electrode needs to be at least 10 times or more the wavelength λ. The diameter of the droplet is the width d of the interdigital electrode.
Depends on the wavelength λ
Need to be shorter. However, shortening the wavelength λ increases the oscillation frequency, and requires an expensive power supply. Therefore, there is a problem that the oscillation frequency cannot be unnecessarily increased.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an ink jet recording head capable of efficiently ejecting small-diameter ink droplets without requiring a fine nozzle. It is the purpose.

[0009]

According to a first aspect of the present invention, in an ink jet recording head, a liquid ink and a longitudinal wave are generated from a plurality of directions near the surface of the liquid ink to propagate and concentrate the liquid droplets. It has vibration generating means for discharging, and the end of the vibration generating means on the side of the liquid ink discharge direction is flush with the surface of the liquid ink or protrudes from the surface of the liquid ink in the ink discharge direction. It is a feature.

According to a second aspect of the present invention, there is provided an ink jet recording head, comprising: a cylindrical nozzle holding liquid ink inside; and vibration generating means formed in the cylindrical nozzle. The end of the liquid ink in the ejection direction side is flush with the surface of the liquid ink or protrudes from the surface of the liquid ink in the ink ejection direction. A longitudinal wave is generated in the liquid ink by vibrating in a direction.

According to a third aspect of the present invention, in the ink jet recording head according to the first or second aspect, the vibration generating means is constituted by a piezoelectric cylindrical member or a plurality of piezoelectric members. It is assumed that.

According to a fourth aspect of the present invention, in the ink jet recording head according to the first or second aspect, the electrode of the vibration generating means is provided on a portion of the vibration generating means protruding from the surface of the liquid ink. It is characterized by having.

According to a fifth aspect of the present invention, in the ink jet recording head according to the second aspect, the set of the vibration generating means and the nozzle is arranged in a line.

According to a sixth aspect of the present invention, in the ink jet recording head according to the second aspect, a set of the nozzles and the vibration generating means is arranged in a matrix, and the nozzles and the vibration generating means arranged in each row or column are arranged. A set of means is arranged at different positions in the column or row direction.

[0015]

FIG. 1 is a cross-sectional view showing a first embodiment of an ink jet recording head according to the present invention, and FIG.
FIG. In the figure, 1 is a nozzle, 2 is a vibration member, and 3 is ink. FIG. 2 is a diagram of FIG. 1 viewed from the direction A. The nozzle 1 has a cylindrical shape, and the ink 3 is supplied inside thereof. At this time, the ink 3 is supplied such that the liquid level of the ink 3 supplied to the nozzle 1 is lower than the upper end of the vibrating member 2 on the ink ejection port side.

The vibrating member 2 is made of a material that generates mechanical strain due to an electric field. For example, a piezoelectric material such as barium titanate, lithium niobate, lead zirconate titanate, or zinc oxide is used. The vibration member 2 is deformed so as to contract or expand in a direction perpendicular to the surface of the nozzle 1. Here, the vibrating member 2 uses an integral cylindrical piezoelectric material, and is arranged on the circumference of the nozzle 1. Not limited to this,
A plurality of arc-shaped vibrating members which are divided into several members may be arranged on the entire circumference of the nozzle 1 or may be intermittently arranged on the circumference of the nozzle 1. In addition, the cross-sectional shape of the nozzle 1 is not limited to a circle, but may be various shapes such as a regular n-gon, and the vibration member may be arranged so that longitudinal waves generated by the vibration member are concentrated at one point. .

Further, since the end of the vibration member 2 on the ink discharge side protrudes from the liquid surface of the ink 3, for example, an electrode can be connected to the protruding portion. In such a configuration, since the electrode and the ink 3 do not contact each other, damage to the electrode is reduced, and high reliability can be maintained.

In the example shown in FIG. 1, the vibrating member 2 is arranged outside the nozzle. However, even if the vibrating member 2 is arranged inside the nozzle or the nozzle itself is the vibrating member 2. The same is true.

Here, the bottom of the nozzle 1 is connected to an ink supply mechanism (not shown) for supplying the ink 3 or an ink chamber (not shown) for temporarily storing the supplied ink via another nozzle or directly. Is done.

FIG. 3 is a plan view for explaining the operation principle of the ink jet recording head according to the first embodiment of the present invention, and FIG. 4 is a sectional view of the same. When an electric field is applied to the vibration member 2 and vibrates at a frequency perpendicular to the wall surface of the nozzle 1 as shown in FIG. 3, a longitudinal wave is generated below the liquid surface of the ink 3 toward the center of the cylinder. This longitudinal wave is nozzle 1
Vibration energy given from the wall surface of the nozzle 1 is concentrated on the center of the cylinder because the center is concentrically collected from the entire wall surface. Therefore, when sufficient vibration intensity is given at a certain frequency, droplets are ejected from the surface of the ink near the center of the cylindrical nozzle 1 as shown in FIG. Recording can be performed by attaching the droplets to a recording medium.

FIG. 5 is an explanatory view of the traveling direction of the longitudinal wave in the first embodiment of the ink jet recording head according to the present invention. FIG. 6 is a diagram showing the longitudinal wave when the vibration member 2 is below the ink level. It is explanatory drawing of a traveling direction. As shown in FIG. 5, when the vibration member 2 protrudes from the liquid surface of the ink 3 in the liquid ink ejection direction, the longitudinal wave near the liquid surface of the ink 3 proceeds toward the center of the cylinder without being shaken up and down. To do
Vibration energy is well concentrated at the center of the cylinder. On the other hand, as shown in FIG. 6, when the vibration member 2 does not protrude from the liquid surface of the ink 3 in the ink ejection direction, the progress of the longitudinal wave is slightly curved in the ejection direction near the liquid surface of the liquid ink 3. Therefore, it is difficult for the vibration energy to sufficiently concentrate on the center of the cylinder.

Therefore, by setting the liquid surface such that one end of the vibration member 2 protrudes from the liquid surface of the ink 3 in the direction of ejecting the liquid ink, longitudinal waves generated in the ink 3 can be stably formed. The vicinity of the surface of the ink 3 is directed toward the center of the cylinder, and the vibration energy emitted from the vibration member 2 is efficiently concentrated near the surface of the ink 3 at the center of the cylinder,
It can be used for discharging the ink 3.

As a specific example, 15 MHz
, A droplet having a diameter of about 50 μm was generated. Also, when the vibrating member 2 is divided into a plurality of arc-shaped vibrating members, the ink 3 can be ejected from the center of the cylindrical nozzle 1 by adjusting the phases to be vibrated.

FIG. 7 is a sectional view showing a second embodiment of the ink jet recording head of the present invention. Reference numerals in the figure are the same as those in FIG. In the above-described first embodiment, an example is described in which the depth of the ink 3 at the nozzle 1 is small, but the present invention is not limited to this. The example shown in FIG. 7 shows a case where the nozzle 1 is long and the depth of the ink 3 is deep, and FIG. 7 shows only the vicinity of the tip of the nozzle 1. In a lower part (not shown), ink is supplied directly or indirectly to an ink supply mechanism (not shown).

Even with such a configuration, by supplying the ink 3 so that the liquid level of the ink 3 is lower than the end of the vibration member 2 on the ink ejection side, the ink level can be reduced as shown in FIG.
As shown in the figure, the longitudinal wave generated in the vibration member 2 travels near the surface of the ink 3. Therefore, at the center of the cylindrical nozzle 1, in the vicinity of the surface of the ink 3, the vibration energy from the vibration member 2 can be efficiently concentrated, and the ink droplet can be ejected.

Although FIG. 7 shows the case where the nozzle 1 is long, the length of the nozzle 1 is short but the depth of the lower communicating portion is deep and the depth of the ink 3 from the liquid level is deep. It is the same even if there is.

FIG. 8 is a configuration diagram showing a third embodiment of the ink jet recording head of the present invention. In the figure, 11
Denotes a substrate, 12 denotes an ink chamber, and 13 denotes an ink supply tube.
In each of the above examples, only one nozzle is shown, but a plurality of nozzles may be arranged. The third embodiment shown in FIG. 8 shows an example in which the nozzles 1 of the first embodiment shown in FIGS. 1 and 2 are arranged in a matrix.

The substrate 11 is provided with openings in the form of a matrix. This opening can be formed by, for example, a laser. At this time, a process using a CO ₂ laser having a high throughput is preferable when cost is important, and an excimer laser is preferable when heat damage or cracks are considered. To further reduce the cost, drilling or punching can be used.

In the example shown in FIG.
The other nozzles are slightly shifted in the horizontal direction so that other nozzles are not arranged in a direction orthogonal to the arrangement direction. By performing printing while relatively moving the printing head and the printing medium having such an arrangement in the vertical direction, printing with a printing density higher than the horizontal arrangement interval of the nozzles 1 can be performed.

Each nozzle 1 is provided with a vibration member 2. As shown in FIG. 8A, vertical leads A1 to A5 and horizontal leads B1 to B6 are provided to supply electric energy to the vibration member 2. Here, by selecting one of the leads A1 to 5 and one of the other leads B1 to B6 and supplying electric energy, the vibration member 2 corresponding to one nozzle 1 selectively operates. , Can be excited. By controlling the selection operation, the operation timing, and the relative movement with respect to the recording medium according to the image data, it is possible to record an image on the recording medium.
Note that FIG. 8A is a schematic view, and in fact, at points corresponding to the intersections of the leads A1 to A5 and the leads B1 to B6 in FIG. I have.

In each nozzle 1, after the ink is jetted, it is necessary to supply the jetted ink to prepare for the next jet. Therefore, in this example, as shown in FIG.
To store the ink, and to supply the ink to the ink chamber 12 at a constant pressure from an ink tank (not shown) via the ink supply pipe 13. Accordingly, the positions of the ink surfaces in the nozzles 1 are always kept constant, and the dots to be recorded can be aligned while keeping the distance to the recording medium constant, so that high-quality recording can be performed.

In FIG. 8, the lower part of the nozzle 1 is formed shallow and connected to the ink chamber 12 in accordance with the first embodiment shown in FIG. It is also possible to set to 12. In this case, ink 3
Is a modification of the second embodiment in which the depth is deep.
Needless to say, the nozzle 1 in the second embodiment may be arranged in a matrix by lengthening the portion of the nozzle 1.

FIG. 8 shows the arrangement of the matrix. However, the present invention is not limited to this, and a configuration of only one line is also possible.
In FIG. 8, the individual nozzles are shown as cylindrical, but
For example, it is formed as a common slit for multiple nozzles,
A configuration in which, for example, an arc-shaped vibrating member is arranged on one side or both sides of the position corresponding to the nozzle and ink droplets fly from the center of the arc is also possible.

[0034]

As is apparent from the above description, according to the present invention, the ink is supplied such that the liquid level of the ink is located at the liquid bottom side from the ink discharge side end of the vibrating member, and the ink is supplied. Vibration energy is applied to the vicinity of the liquid surface, and the vibration energy is propagated and concentrated in a direction substantially parallel to the liquid surface of the ink. Therefore, small droplets can be ejected accurately in a direction perpendicular to the surface of the liquid ink. At the same time, the vibration energy can be efficiently concentrated on the minute area near the liquid surface of the ink. It is also possible to adopt a configuration in which the ink does not come into contact with the electrode of the vibrating member. In this case, there is an effect that the electrode is less damaged and high reliability can be maintained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of an ink jet recording head of the present invention.

FIG. 2 is a plan view showing a first embodiment of the ink jet recording head of the present invention.

FIG. 3 is a plan view for explaining the operation principle of the inkjet recording head according to the first embodiment of the present invention.

FIG. 4 is a cross-sectional view for explaining the operation principle of the inkjet recording head according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of a traveling direction of a longitudinal wave in the first embodiment of the ink jet recording head of the present invention.

FIG. 6 is an explanatory diagram of a traveling direction of a longitudinal wave when the vibration member 2 is below a liquid level of ink.

FIG. 7 is a sectional view showing a second embodiment of the ink jet recording head of the present invention.

FIG. 8 is a configuration diagram showing a third embodiment of the ink jet recording head of the present invention.

FIG. 9 is a diagram illustrating the principle of a conventional ink jet recording system using surface acoustic waves.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Nozzle, 2 ... Vibration member, 3 ... Ink, 11 ... Substrate,
12 ... ink chamber, 13 ... ink supply tube.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyuki Shiratsuki 430 Sakai, Nakai-cho, Ashigara-gun, Kanagawa Green Tech Nakai Fuji Xerox Co., Ltd.

Claims (6)

[Claims] 1. A liquid ink, and a vibration generating means for generating longitudinal waves from a plurality of directions near the surface of the liquid ink to cause the waves to propagate and concentrate, thereby discharging droplets. An ink jet recording head, wherein an end on the ejection direction side is at the same height as the surface of the liquid ink or protrudes from the surface of the liquid ink in the ink ejection direction. 2. A liquid ejection apparatus comprising: a cylindrical nozzle having liquid ink held therein; and a vibration generating means formed in the cylindrical nozzle, wherein the end of the vibration generating means on the liquid ink ejection direction side has The liquid ink projects at the same height as the surface of the liquid ink or in the direction of ink ejection from the surface of the liquid ink, and vibrates the vibration generating means in a plane direction substantially parallel to the surface of the liquid ink, thereby generating a longitudinal wave on the liquid ink. An ink jet recording head characterized by generating: 3. The ink jet recording head according to claim 1, wherein said vibration generating means is constituted by a piezoelectric cylindrical member or a plurality of piezoelectric members. 4. The ink jet recording head according to claim 1, wherein an electrode of said vibration generating means is provided on a portion of said vibration generating means protruding from a surface of said liquid ink. 5. The ink jet recording head according to claim 2, wherein a set of said vibration generating means and said nozzle is arranged in a line. 6. A set of the nozzles and the vibration generating means are arranged in a matrix, and a set of the nozzles and the vibration generating means arranged in each row or column are arranged at different positions in the column or row direction. The ink jet recording head according to claim 2, wherein