JP2001270102A - Liquid drop discharge head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid drop discharge head which can stably drive with a low voltage by reducing an air damper effect. SOLUTION: A partition wall 12 between electrodes for separating a gap space between a diaphragm 6 and electrodes 11 is provided immediately below a partition wall 5 between liquid chambers which separates liquid chambers 4. The number of the inter-electrode partition walls 12 is made smaller than the number of the inter-liquid chamber partition walls 5. The number of electrodes 11 included between adjacent inter-electrode partition walls 12 is set to be not smaller than 2 and smaller than 10. The electrodes 11 are disposed in a non parallel state to the diaphragm 6. A notch part is formed to an electrode forming part where the electrodes 11 are formed when the electrodes are disposed in the non parallel state. The inter-electrode partition wall 12 is a partition wall between recessed parts formed to a substrate where the electrodes 11 are set. Moreover, the inter-electrode partition wall 12 is joined to a substrate where the diaphragm 6 is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet discharge head.

[0002]

2. Description of the Related Art An ink jet head, which is a liquid drop discharge head used in an image recording apparatus such as a printer, a facsimile, a copying apparatus, or the like, is used as an ink jet recording apparatus. It has a communicating liquid chamber (also referred to as an ink flow path, a pressure chamber, a discharge chamber, a pressurized liquid chamber, etc.), a diaphragm forming a wall surface of the liquid chamber, and an electrode facing the diaphragm. An electrostatic inkjet head that discharges ink droplets from nozzles by deforming a diaphragm by electrostatic force generated by applying a voltage between the diaphragm and an electrode and changing the pressure / volume in a liquid chamber. It has been known.

In such an electrostatic type ink jet head, it is necessary to form a minute gap between the diaphragm and the electrode, and this gap is a portion for defining the amount of displacement of the actuator, and is used for controlling the temperature and humidity. When the gap length (the effective gap between the diaphragm and the electrode) changes due to deformation of the diaphragm due to environmental changes, the displacement characteristics of the diaphragm change.

Therefore, in order to uniformly displace the diaphragm without being affected by the environment such as temperature and humidity, the gap portion needs to be almost completely sealed from the outside air. Gas (inert gas such as air and nitrogen) exists in the gap, and when the actuator is driven at a high frequency and multiple nozzles are driven simultaneously, the gas is compressed due to the displacement of the diaphragm and the pressure increases. However, a so-called large air damper effect that displacement of the diaphragm is suppressed is generated.

Therefore, as described in Japanese Patent Application Laid-Open No. H11-34319, in order to reduce the air damper effect of the electrode forming portion, a gap other than the diaphragm portion is formed deeper than the diaphragm portion. The opening (notch) that communicates between the channels is formed in the column between the channels (the gap spacer that defines the gap length and also serves as the electrode spacing wall that separates the electrodes). It has been proposed that the provision of air enables the escape of air. Also, Japanese Patent Application Laid-Open No. 7-29908
The vibration chamber is also sealed in the official gazette, and the volume change amount is specified.
It is disclosed to keep it constant.

Further, in Japanese Patent Application Laid-Open No. 11-34319, the vibration chamber is sealed, and a gap other than immediately below the diaphragm is made wider than a gap immediately below the diaphragm, or an adjacent vibration chamber is communicated. It is disclosed that the capacity of the entire vibration chamber is increased and the rise in the pressure of the vibration chamber is reduced.

[0007]

However, as a result of trial production of the above-mentioned conventional electrostatic ink jet head, an air damper effect is reduced at a low driving frequency at which the diaphragm can be handled statically or quasi-statically. However, when the drive frequency was dynamically driven from several KHz to several + KHz, the air damper effect was not reduced even if the capacity was increased toward a place away from immediately below the diaphragm.

The inventors of the present invention have conducted various experiments and found that the effect of reducing the air damper effect is not obtained because the propagation frequency (sound speed) of the air pressure is taken into consideration when the driving frequency is 50 kHz. At this time, the pressure of the air is about 1.7 mm (= 1/50 KHz × １ ／ × 330 m / s).
ec), the pressure of the entire vibration chamber (gap space) does not rise because it only advances, and since the air itself travels only a small distance in a short time, only the pressure near the diaphragm increases. It was found that it was to do.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a droplet discharge head capable of stably driving at a low voltage with a reduced air damper effect.

[0010]

In order to solve the above-mentioned problems, in a droplet discharge head according to the present invention, an electrode for separating a gap space formed between a diaphragm and an electrode immediately below a liquid chamber spacing wall. It has a spacing wall, and the number of the electrode spacing walls is different from the number of the liquid chamber spacing walls.

Here, it is preferable that the number of electrodes included between adjacent electrode spacing walls is 2 or more and less than 10.
Preferably, the electrodes are arranged in a non-parallel state with respect to the diaphragm. When the electrodes are arranged in a non-parallel state, it is preferable to provide a notch in the electrode forming portion on which the electrode is formed.

Preferably, the electrode spacing wall is a recessed spacing wall formed on a substrate on which electrodes are provided. Further, it is preferable that the electrode spacing wall is joined to a substrate provided with a diaphragm.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of the electrostatic ink jet head according to the first embodiment of the present invention along a liquid chamber long side direction. FIG. 2 is a schematic cross-sectional view of the same head along a liquid chamber short side direction. .

This electrostatic ink jet head is formed by joining a diaphragm substrate 1 and an electrode substrate 2. Diaphragm board 1
A nozzle 3 for discharging liquid droplets, a liquid chamber 4 communicating with the nozzle 3 and separated by a liquid chamber spacing wall 5, a diaphragm 6 forming a bottom of the liquid chamber 4, and a liquid chamber 4. A common liquid chamber 8 for supplying ink to the liquid chamber 6 and a fluid resistance portion 7 communicating the liquid chamber 6 and the common liquid chamber 8 are formed.

Further, a concave portion 10 is formed in the electrode substrate 2,
An electrode 11 is formed on the bottom surface of the concave portion 10 so as to oppose the diaphragm 6 with a predetermined gap, and the diaphragm 6 and the electrode 11 constitute an actuator section that deforms and displaces the diaphragm 6 by electrostatic force. . Although not shown, an insulating film such as an oxide film or a nitride film is formed on the surface of the electrode 11 to prevent damage due to contact with the diaphragm 6.

Here, the concave portion 10 of the electrode substrate 2 forming the gap space between the diaphragm 6 and the electrode 11 is formed corresponding to at least two liquid chambers 4 so that the concave portion 10 (Electrode spacing wall) 12 separates the gap space between two electrodes 11. That is, the number of the electrode spacing walls 12 is made different from the number of the liquid chamber spacing walls 5 and is reduced. Therefore, a space (referred to as a “vibration chamber 14”) in which the diaphragm 6 formed between the electrode spacing walls 12, 12 or between the electrode spacing wall 12 and the outer peripheral partition 13 is deformed.
Called. ) Is less than the number of liquid chambers 4.

The electrode spacing wall 12 and the outer peripheral partition 13 are joined to the diaphragm substrate 1. The electrode spacing wall 12 also functions as a gap spacer for defining a gap length between the diaphragm 6 and the electrode 11. Here, the electrode substrate 2
The vibration chamber 14 and the gap spacer, and the joint between the diaphragm substrate 1 and the electrode substrate 2 are formed by the electrode spacing wall 12 which is the spacing wall of the recess 10 by forming the recess 10 in the recess 10. May be interposed between the diaphragm substrate 1 and the electrode substrate 2.

The opening of the vibration chamber 14 is sealed with a sealant 15 in order to prevent foreign substances such as moisture and dust from entering, so that the vibration chamber 14 is a closed space.

In the ink jet head configured as described above, by applying a driving waveform between the diaphragm 6 and the electrode 11, an electrostatic force (electrostatic attraction) is generated between the diaphragm 6 and the electrode 11. As a result, the diaphragm 6 is deformed and displaced toward the electrode 11. As a result, the internal volume of the liquid chamber 4 is expanded and the internal pressure is reduced.
Then, the liquid chamber 4 is filled with ink.

Next, when the voltage application to the electrode 11 is stopped,
The electrostatic force stops working, and the diaphragm 6 is restored by its own elasticity. With this operation, the internal pressure of the liquid chamber 4 increases, and ink droplets are ejected from the nozzles 3. When a voltage is applied to the electrode again, the diaphragm 6 is drawn into the electrode 11 again by the electrostatic attraction force.

As described above, the displacement of the vibration plate 6 compresses the air in the closed space (vibration chamber 14) and increases the pressure. Therefore, the vibration plate 6 is pushed back by the pressure of the vibration chamber 14, The displacement is smaller than the displacement of the diaphragm 6 calculated by the calculation when there is no air. Here, the pressure increase ΔP is represented by the equation (1).

[0022]

(Equation 1)

In the equation (1), P ₀ is the initial pressure of the vibration chamber 14, V is the initial volume of the vibration chamber 14, and ΔV is the volume change due to the displacement of the diaphragm 6 (referred to as an air damper effect). . In order to reduce the air damper effect, reduce the pressure rise ΔP inside the vibration chamber, and achieve a lower driving voltage and improved responsiveness, it is effective to increase the initial capacity of the vibration chamber 14. It is understood that.

Therefore, in the ink jet head of this embodiment, as described above, the concave portion 1 of the electrode substrate 2 is provided.
The number 0 is one corresponding to at least two liquid chambers 4 to secure a space for two liquid chambers as the vibration chamber 14 corresponding to one liquid chamber 4. Therefore, the initial capacity of the vibration chamber 14 is increased as compared with the case where the electrode spacing wall is provided between the electrodes, so that the pressure rise is correspondingly reduced and the damper effect can be reduced.

Here, the number of the liquid chamber spacing walls 5 and the electrode spacing walls 1
The relationship between the numbers 2 and the number of liquid chambers 4 included in one vibration chamber 14 was examined in detail. Here, using a head having a nozzle pitch of 150 dpi, the short side width of the diaphragm 6 = 130 μm and the long side length of the diaphragm 6 = 1000 μm
m, thickness of the liquid chamber spacing wall 5 = 39 μm, gap length = 0.
25 μm, liquid chamber 4 formed directly above one vibration chamber 14
, The number of actuators to be simultaneously driven is n, the thickness of the diaphragm 6 is h, the maximum displacement of the diaphragm 6 not driven is δh, and the maximum displacement of the liquid chamber spacing wall 5 is δH. . Table 1 shows the results.

[0026]

[Table 1]

As can be seen from the table, when the thickness h of the vibration plate 6 is 3 μm, the number of the liquid chambers 4 (the number of the vibration plates 6) disposed immediately above one vibration chamber 14 is ten. When the nine diaphragms 6 are driven, the displacement of the remaining one diaphragm 6 that is not driven is 0.07 μm.

Further, when the thickness h of the vibration plate 6 is 2.5 μm, the number of the liquid chambers 4 disposed immediately above one vibration chamber 14 is set to 10, and the nine vibration plates 6 are driven. The maximum displacement δh of the remaining one vibrating plate 6 is 0.12 μm
m. This corresponds to about half of the gap (gap length) between the diaphragm 6 and the electrode 11, and the liquid chamber 4 that is not driven
Unnecessary pressure may be applied to the nozzle and affect the injection.

Therefore, the number of the liquid chambers 4 corresponding to one vibration chamber 14, that is, the number of the electrodes 11 separated by the electrode spacing wall 12.
Is preferably less than 10. Specifically, the number of liquid chambers corresponding to one vibration chamber may be determined according to the volume of the vibration chamber, the rigidity of the vibration plate, the thickness of the liquid chamber separation wall, the strength of the electrode separation wall, and the like. I just need.

Next, an ink jet head according to a second embodiment of the present invention will be described with reference to FIG. In this embodiment, an electrode forming portion 16 having a substantially right-angled triangular cross section for arranging the electrode 11 in the recess 10 of the electrode substrate 2 is formed by rising, and the electrode 11 is formed in the electrode forming portion 16. Thus, the diaphragm 6 and the electrode 11 are opposed to each other in a non-parallel state in the transverse direction of the diaphragm. The gap formed between the non-parallel diaphragm 6 and the electrode 11 is called a non-parallel gap.

By thus arranging the diaphragm 6 and the electrode 11 to face each other in a non-parallel state, the diaphragm 6
Since the displacement starts from a point where the gap between them is short, the gap length between the diaphragm 6 and the electrode 11 gradually decreases. Therefore, the driving voltage for displacing the diaphragm 6 can be reduced.

The electrode forming portion 16 formed in the concave portion 10 of the electrode substrate 2 can be formed by excavating the electrode forming portion 16 by etching or the like when forming the concave portion 10.

Further, by forming the thickness of the protective film formed on the surface of the electrode 11 so as to fill the narrowest portion between the electrode forming portion 16 and the diaphragm substrate 1, the protective film and the diaphragm substrate 1 are joined. And can function as a support member serving as an electrode spacing wall formed immediately below the liquid chamber spacing wall 5.

Next, an ink jet head according to a third embodiment of the present invention will be described with reference to FIG. This embodiment is different from the third embodiment in that the electrode forming portion 16 is different from that of the third embodiment.
The notch 18 is formed at one or a plurality of locations.

That is, even if the number of the electrode spacing walls 12 is reduced, if the electrode forming portion 16 having the inclined surface is provided to provide the electrodes 11 in a non-parallel state, a substantial gap between the diaphragm 6 and the electrode forming portion 16 is reduced. There is a possibility that the electrode chamber 16 becomes narrower and the electrode forming portion 16 functions as an electrode spacing wall, so that the effective volume of the vibration chamber 14 becomes the same as that of each of the electrodes 11. Therefore, the notch 18 is provided in the electrode forming part 16 so that the vibration chamber 14 is not substantially divided for each electrode 11. Thereby, even when a non-parallel gap is formed, the volume of the vibration chamber can be increased and the air damper effect can be reduced.

When the electrode 11 facing the diaphragm 6 is removed, the electrostatic force is reduced. Therefore, a portion of the electrode forming portion 16 where the electrode 11 is not formed (for example, a portion not facing the diaphragm 6 in the longitudinal direction of the diaphragm). ) Is preferably formed with the notch 18.

In each of the above embodiments, an example is described in which the present invention is applied to an ink jet head for discharging ink droplets. However, the present invention can be similarly applied to a head for discharging another liquid such as a liquid resist.

[0038]

As described above, according to the droplet discharge head of the present invention, the electrode spacing wall that separates the electrodes is provided immediately below the liquid chamber, and the number of the electrode spacing wall and the liquid chamber spacing wall is reduced. Since they are different, the air damper effect can be reduced, and the reliability is improved.

Here, by setting the number of electrodes included between adjacent electrode spacing walls to be two or more and less than ten, unnecessary pressure is not applied to the non-driven diaphragm, and the ejection characteristics are stabilized.

Further, by arranging the diaphragm and the electrodes in a non-parallel state, low voltage driving can be achieved. In this case, by providing the cutout portion in the electrode forming portion for forming the electrode, it is possible to reduce the effective space reduction, reduce the air damper effect, and improve the reliability.

Further, the electrode spacing wall is formed as a recessed spacing wall formed on the substrate on which the electrodes are provided, thereby simplifying the structure. Further, the electrode spacing wall is joined to the substrate provided with the vibration plate to separately support the member. Is unnecessary and the configuration is simplified.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional explanatory view along a long side direction of a liquid chamber of an electrostatic inkjet head according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional explanatory view along a liquid chamber short side direction of the head.

FIG. 3 is a schematic cross-sectional explanatory view along a liquid chamber short side direction of an electrostatic inkjet head according to a second embodiment of the present invention.

FIG. 4 is an explanatory perspective view of a main part of an electrostatic inkjet head according to a third embodiment of the invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... diaphragm board, 2 ... electrode board, 3 ... nozzle, 4 ... liquid chamber, 5 ... liquid chamber spacing wall, 6 ... diaphragm, 10 ... recess, 11 ...
Electrodes, 12: electrode spacing wall, 14: vibration chamber, 18: notch.

Claims (6)

[Claims] 1. A diaphragm forming a wall surface of a liquid chamber communicating with a nozzle for discharging droplets, an electrode opposed to the diaphragm, and the diaphragm being deformed and displaced by electrostatic force from the nozzle. In a droplet discharge head that discharges droplets, an electrode spacing wall that separates a gap space formed between the vibration plate and the electrode immediately below a liquid chamber spacing wall that separates the liquid chamber,
A droplet discharge head characterized in that the number of electrode spacing walls and the number of liquid chamber spacing walls are different. 2. The droplet discharge head according to claim 1, wherein the number of electrodes included between adjacent electrode spacing walls is two or more and less than ten. 3. The droplet discharge head according to claim 1, wherein the electrodes are arranged in a non-parallel state with respect to the vibration plate. 4. The droplet discharge head according to claim 3, wherein a cutout portion is provided in an electrode forming portion on which the electrode is formed. 5. The droplet discharge head according to claim 1, wherein the electrode interval wall is a recess interval wall formed on a substrate on which the electrode is provided. 6. The droplet discharge head according to claim 1, wherein the electrode spacing wall is joined to a substrate provided with the vibration plate.