JPH06238894A - Liquid-drop jetting device - Google Patents

Abstract

PURPOSE:To enable an effective stable deformation of walls of a piezoelectric material to be achieved momentarily through the application of driving voltage, and thus improve the reliability of stable jetting of liquid-drops by specifying the purity of an electrode material for driving electrodes formed on each side surface of walls of a piezoelectric material. CONSTITUTION:A piezoelectric material having a purity of 99% or higher is formed is driving electrodes on each side surface of walls of a piezoelectric material, whereby, when voltage is applied by taking the driving electrodes 25b, c as positive electrodes and driving electrodes 25a, d as negative electrodes, the walls 21b, c deform so that the volume of groove 22b increases and the volume of the grooves 22a, c decreases. When the applied voltage is removed therefrom, the walls b, c return to the original state, as a result that pressure is applied to the liquid that is filled in the groove 22b so as to jet liquid-drops. In order to, at this time, realize stable jetting of liquid-drops, the necessary time in a deformation of the walls 21 becomes of significant importance, and therefore such deformation is required to be done in a period of short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a liquid droplet ejecting apparatus, and more particularly to a driving electrode formed on a piezoelectric element used as an energy conversion element for ejecting liquid droplets. .

[0002]

2. Description of the Related Art Conventionally, various types of liquid droplet ejecting apparatuses using energy conversion elements have been developed and put into practical use for applications such as ink jet printers. As the energy conversion element used in the droplet ejection device, an electro-thermal conversion element such as a heating element or an electro-mechanical conversion element such as a piezoelectric material is used. In general, a liquid droplet ejecting apparatus using a piezoelectric material has an advantage that the selection range of the liquid that can be used is broader than that of a liquid ejecting apparatus that uses a heating element because there are few restrictions on the liquid to be used due to heat. However, compared with the integration degree of the electro-thermal conversion element to which the semiconductor manufacturing process can be applied, the integration degree using the piezoelectric element which is the electro-mechanical conversion element is low,
It involves various problems in terms of downsizing of the liquid droplet ejecting apparatus. In a liquid droplet ejecting apparatus that currently uses a piezoelectric body as an energy conversion element, a so-called unimorph piezoelectric element or bimorph piezoelectric element that mainly uses the lateral effect among the piezoelectric / electrostrictive effects of the piezoelectric body is used. The droplet ejecting device used is the mainstream.

Japanese Unexamined Patent Publication (Kokai) No. Sho 6-1987 discloses an invention of a liquid droplet ejecting apparatus for the purpose of highly integrating a piezoelectric element which is an energy conversion element.
3-247051, JP-A-63-252750 and JP-A-2-150355.

The above-mentioned patent discloses a piezoelectric material in which a plurality of grooves (channels) functioning as a liquid channel and a pressure chamber are formed in a piezoelectric material polarized in the thickness direction with a high degree of integration, and each groove (channel) is separated. By forming drive electrodes on the side surface of the wall, a shear mode deformation is generated among the piezoelectric / electrostrictive effects, a pressure change is generated in a groove (channel), and a desired droplet is provided on the front surface. The liquid droplet ejecting apparatus of the type that ejects from each of the nozzles, and realizes miniaturization thereof.

[0005]

However, in the liquid droplet ejecting apparatus having the structure disclosed in the above-mentioned patent, there is little detailed description about the drive electrodes formed on both side surfaces of the wall of the piezoelectric material, and in practice, the liquid droplet ejecting apparatus. There were many unclear points about the design of. Therefore, a large number of problems are involved in putting the droplet ejecting device having the stable droplet ejecting characteristics of the above method into practical use. The object of the present invention embodies various requirements for the drive electrodes formed on both sides of the wall of the piezoelectric material, in particular, the purity of the electrode material formed as the drive electrodes, in order to realize good droplet ejection. This is to realize a stable liquid droplet ejecting apparatus having the above configuration.

[0006]

In order to achieve this object, in the droplet ejecting apparatus of the present invention, an electrode material having a purity of 99% or more is formed as a drive electrode on the side surface of the wall of the piezoelectric material.

[0007]

The operation of the drive electrode of the liquid droplet ejecting apparatus according to the present invention having the above structure will be described below. First, a voltage is applied according to a print pattern based on a signal input from the outside through drive electrodes formed on a part of both side surfaces of the wall of the piezoelectric material. At this time, paying attention to one wall, one side acts as a positive electrode and the other side acts as a negative electrode. In the droplet ejecting apparatus of the present invention, the drive electrodes of the electrode material having a purity of 99% or more formed on a part of both side surfaces of the wall of the piezoelectric material are instantaneous within a suitable time with respect to the drive signal corresponding to the external signal. At the same time, the wall of the piezoelectric material is deformed.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram of a droplet jetting apparatus of the present invention. The liquid droplet ejecting apparatus includes a plurality of grooves 22 that act as pressure chambers for ejecting ink droplets and ink droplets, and a plurality of driving electrodes 25 for applying a voltage to a part of both side surfaces. An actuator 2 formed of a wall 21 of a piezoelectric material, an ink introduction hole 16 adhered to the actuator 2, a cover plate 10 having an ink manifold 18, and a plurality of nozzles 12 adhered to the actuator 2 for ejecting ink droplets. Is formed from the nozzle plate 14. Here, the drive electrode 25 is made of various metals such as Al, Cr, Ni and Cu, and noble metals such as Au and Pt or alloys of various metals,
The electrode layer structure is composed of a single layer or a laminate of a plurality of layers.

Next, in order to explain the behavior when a voltage is applied, a schematic view of the state of the wall 21 and the groove 22 of the piezoelectric material when a drive voltage is not applied is shown in FIG. 2, and the piezoelectric material when a drive voltage is applied is shown. A schematic view of the state of the wall 21 and the groove 22 is shown in FIG. As shown in FIG. 2, when the voltage is not applied, the wall 21 of the piezoelectric material is
The a to e do not deform and the grooves 22a to 22d all have the same volume. Next, drive electrodes 25b and 25c
When a voltage is applied with a and d as negative electrodes, the walls 21b and c are deformed as shown in FIG. 3 to increase the volume of the groove 22b and decrease the volume of the grooves 22a and 22c. By removing the applied voltage from the state shown in FIG. 3, the walls 21b and 21c return to the state shown in FIG. 2, at which time pressure is applied to the liquid filling the groove 22b to eject droplets. At this time, in order to realize stable droplet ejection, the time required for the deformation of the wall 21 is important, and it is necessary to deform the wall 21 within a short time of several μsec or less.

Now, the following experiment was conducted in order to grasp the proper range of the thickness of the drive electrode. FIG. 4 shows a perspective view of the wall 21 of piezoelectric material and the drive electrode 25. In FIG. 4, the width dimension of the piezoelectric material wall 21 is represented by w, the height is represented by h, the length is represented by L, the thickness of the drive electrode 25 is represented by t, and the electrode depth in the wall height direction is represented by d.

First, w = 0.1 mm, h = 0.5 mm, L = for an experiment for grasping the minimum allowable value of the drive electrode thickness.
A wall of 8 mm piezoelectric ceramic material was prepared. The thickness t = 0.02, 0.
Nickel electrodes of 04, 0.08, 0.16, 0.32, and 0.64 μm were formed by a dry method such as a sputtering method or a vacuum evaporation method, and the specific resistance value of each electrode was measured. The result is shown in FIG. As is clear from FIG. 5, when the thickness t of the drive electrode is 0.04 μm or less, a large increase in specific resistance is seen. Since it is unlikely that the film quality of the nickel electrode itself deteriorated, this result is considered to be due to the loss of electrical continuity of the electrode film formed on the surface of the piezoelectric ceramic.

The conceptual diagram is shown in FIG. Generally, a PZT-based piezoelectric ceramic material is used as the actuator material of the droplet ejection device of the present invention. The piezoelectric ceramic material is usually a polycrystalline sintered material, is composed of crystal grains 31 having an average grain size of about 1 to 5 μm, and has pores of the same size of several percent. That is, the surface on which the drive electrodes are formed has irregularities of about 2 μm. The electrode 25 formed on the surface having such unevenness
Has a considerable amount of electrical discontinuity as an electrode as shown in FIG. As the thickness of the formed electrode 25 becomes thinner, the discontinuity increases, and the result of the experiment is 0.0
It is considered that when the thickness becomes about 4 μm or less, the apparent specific resistance increases as a result. Therefore, the minimum allowable value of the drive electrode thickness is considered to be about 0.04 μm. An experiment was conducted using aluminum as the material of the drive electrode, and the same results as in the case of nickel were obtained.

On the other hand, considering the time required for the deformation of the wall of the piezoelectric material during driving, the piezoelectric material is electrically considered to be a capacitor in terms of circuit configuration. An electrical time constant τ related to the deformation time of the wall is represented by τ = C · R, where C is the capacitance of the piezoelectric material and R is the resistance of the drive electrode. As the thickness of the drive electrode becomes thin, not only the apparent specific resistance increases as is clear from the experimental results, but also the electrode cross-sectional area t × d decreases and the resistance value R itself increases, which is necessary for droplet ejection. This is not preferable because the margin for the permissible time constant is reduced and a large load is applied to the drive circuit design.

Therefore, in the liquid droplet ejecting apparatus of this embodiment, the thickness of the driving electrode is set to 0.04 μm or more. As a result, it was possible to obtain a droplet ejecting apparatus capable of realizing stable droplet ejection.

Next, w = 0.05 mm, h = 0.25 mm, for an experiment for grasping the maximum allowable value of the drive electrode thickness,
A wall of L = 8 mm of piezoelectric ceramic material was prepared. The thickness t = 0.5 on the side surface of the wall of the piezoelectric ceramic material,
Nickel electrodes of 1, 2, 5, 10 μm are formed by a dry method such as a sputtering method or a vacuum evaporation method, and the ratios t / w of the electrode thickness and the wall width dimension of the piezoelectric material are 1/100, 1/50, 1 respectively.
Samples were prepared such that they were / 25, 1/10, and 1/5. After the cover plate was adhered to this sample, a pulse voltage of 50 V was applied and the state of wall deformation was measured using a laser displacement meter. The measurement results are arranged by the volume change of the adjacent groove volume, and the electrode thickness is 0.5 μm (t / w
= 1/100), the result of plotting the data for each electrode thickness when the volume change is 100% is shown in FIG.
Shown in.

As is apparent from FIG. 7, the deformation efficiency is lowered in the sample in which the ratio t / w of the electrode thickness and the wall width dimension of the piezoelectric material is 1/5. This is because when an electrode material having a Young's modulus different from that of the piezoelectric material is formed as the driving electrode layer, the deformation of the wall of the piezoelectric material is not so much affected when the thickness of the electrode is thin, but the deformation is affected when the thickness is increased. This is because Further, as the electrode layer becomes thicker, naturally, the residual stress in the film and at the interface between the film and the piezoelectric material increases, which causes a problem that the film strength and the adhesion strength become weak. Therefore, the maximum allowable value of the drive electrode thickness is preferably 1/10 or less in the ratio r = t / w of the electrode thickness and the wall width dimension of the piezoelectric material.

An experiment was carried out when the material of the driving electrode was aluminum, and it was confirmed that the same tendency as in the case of nickel was exhibited.

Therefore, in the liquid droplet ejecting apparatus of this embodiment, the ratio of the thickness of the drive electrode to the wall width dimension of the piezoelectric material is 1 :.
It is configured to be 10 or more. As a result, it was possible to obtain a droplet ejecting apparatus capable of realizing stable droplet ejection.

Next, an experiment was conducted on the relative density of the metal film formed as the drive electrode. It is clear that when the relative density theoretically decreases, the number of vacancies increases and the apparent resistivity increases. However, as for the resistance value, it is possible to satisfy the allowable resistance value by increasing the thickness of the drive electrode, so that it does not cause a big problem. The problem here is the problem of deterioration of the corrosion resistance of the drive electrode film due to the decrease in relative density. In the liquid droplet ejecting apparatus as in the present invention, the drive electrode 25 is a liquid (mainly ink) filled in the groove 22.
Will be exposed to. Therefore, a so-called electrolytic corrosion phenomenon occurs. In this case, it is conceivable that when the relative density decreases, the number of open pores (connection pores) increases in the electrode layer, the surface area in contact with the liquid increases, and the corrosion resistance deteriorates. In an actual liquid jet device, it is possible to form a protective film on the surface of the drive electrode to improve corrosion resistance, but sufficient coverage can be achieved even if the protective film is formed on the electrode layer with low relative density. The problem is that you can't.

FIG. 8 shows about 1 using the relative density as a parameter.
Corrosion resistance of a sample with a nickel electrode having a thickness of μm to saline solution, and corrosion resistance of a sample of the same sample with a silicon dioxide film having a thickness of about 1 μm formed on the electrode as a protective film to a saline solution having a relative density of 90%. The corrosion resistance of each was set as 100%, and the corrosion resistance at each relative density was shown. As an evaluation item of corrosion resistance, the corrosion rate was measured for the sample having only the electrode layer, and the number of defects generated per unit area was measured for the sample having the protective film. As is clear from FIG. 8, the experimental results show that the corrosion resistance rapidly deteriorates in the electrode film having a relative density of 65% regardless of the presence or absence of the protective film. Therefore, it was found that the minimum required relative density of the metal material forming the drive electrode film is 70%.

Therefore, in the liquid droplet ejecting apparatus of this embodiment, the relative density of the metal material forming the drive electrode film is 70%.
It is configured as described above. As a result, it was possible to obtain a droplet ejecting apparatus capable of realizing stable droplet ejection.

Next, an experiment was conducted on the purity of the metal material forming the drive electrode. When the purity decreases, the number of ions as impurities increases in the electrode film. In the droplet ejecting apparatus of the present invention, it is a necessary condition to deform the wall of the piezoelectric material within a short time, and in this case, a large instantaneous current will flow through the drive electrode. If the drive electrode has a thickness distribution or has electrical discontinuity, current concentration may occur further when an instantaneous current flows, and there is a risk that impurity ions move and migrate. In addition, a partial disconnection of the electrode film may sometimes occur.

As an experiment, 0.04 μm thick aluminum was formed as an electrode on the surface of the piezoelectric ceramic material. At this time, the purity of aluminum is 99.99.
Samples of 9, 99.99, 99.9, 99, and 95% were prepared and tested. The experimental condition is a current of 1 A of 30 mi.
A current was applied for n, and the change of the electrode surface before and after that was observed with a microscope. The samples with a purity of 99% or more showed almost no change before and after energization, but with the samples with a purity of 95%, an increase in discontinuity points of the electrode film was observed. In the measurement of electric resistance before and after energization, there was almost no change in the resistance value when the purity was 99% or more, but about 15% before and after energization when the purity was 95%.
% Resistance increase was measured. As is apparent from the results of this experiment, it is considered preferable that the purity of the metallic material of the drive electrode used in the droplet ejecting apparatus of the present invention is at least 99% or more. 99 other metals such as nickel
In the case of a purity of not more than%, the same change as above was observed although the degree of difference was observed.

Therefore, in the liquid droplet ejecting apparatus of this embodiment, the drive electrode is made of a metal material having a purity of 99% or more. As a result, it was possible to obtain a droplet ejecting apparatus capable of realizing stable droplet ejection.

Next, an experiment was conducted on an allowable value range for the average film thickness of the distribution of the thickness of the drive electrode layer to be formed.
In the droplet ejecting apparatus of the present invention, it is a necessary condition to deform the wall of the piezoelectric material within a short time, and in this case, a large instantaneous current will flow through the drive electrode. If the driving electrode has a thickness distribution or has electrical discontinuity, current concentration may occur further when an instantaneous current flows, and there is a risk that impurity ions in the electrode material may move or migrate. In addition, a partial disconnection of the electrode film may sometimes occur.

As an experiment, aluminum having an average thickness of 0.2 μm was formed as an electrode on the surface of a piezoelectric ceramic material, and samples having film thickness distributions of ± 25%, ± 50% and ± 70% were prepared. In the experiment conducted using these samples, a current of 1 A was applied for 30 min, and before and after that, changes in the electrode surface were observed using a microscope. Thickness distribution ± 5
For 0% or less, almost no change was observed before and after energization, but in the sample with a film thickness distribution of ± 70%, an increase in discontinuity of the electrode film was observed. Also, when the electric resistance was measured before and after energization, there was almost no change in the resistance value when the film thickness distribution was ± 50% or less, but when the film thickness distribution was ± 70%, the resistance value increased by about 10% before and after energization. It was measured.

The reason for explaining this result is that the fact that the thickness distribution is ± 70% when the electrode is formed has a drawback in the method and conditions for forming the electrode, and the film quality is different between the thick part and the thin part. It is thought that there is a difference in that. Therefore, forming an electrode using an electrode forming method / condition that produces a film thickness distribution of ± 50% or more with respect to the average film thickness is used as a method of forming the drive electrode of the droplet ejecting apparatus of the present invention. It is thought that it cannot be done. That is, the film thickness distribution with respect to the average film thickness of the electrode layer is preferably at least ± 50% or less. However, depending on the method of forming the electrode, the film thickness of the edge part of the formed electrode may continuously decrease, but the thinned part is effective as an electrode against the deformation of the wall of the piezoelectric material. Is considered to be non-functional and therefore need not be included in the above range.

Therefore, the droplet jetting apparatus of this embodiment is constructed so that the film thickness distribution with respect to the average film thickness of the electrode layer is ± 50% or less. As a result, it was possible to obtain a droplet ejecting apparatus capable of realizing stable droplet ejection.

An experiment was conducted to grasp the range of the allowable width with respect to the set value of the electrode depth in the height direction of the wall of the piezoelectric material of the electrode to be formed next. 9 to 12 show the state of the electrode depth of the drive electrode 25 formed on the side surface of the wall 21 of the piezoelectric material. Considering the case where the set value of the electrode depth d is d = 0.5 · h with respect to the height h of the wall 21 of the piezoelectric material as shown in FIG.
There are three possible variations in electrode depth, as shown in FIGS. FIG. 10 shows the case where the electrode depth d is shallower than the set value (d <0.5 · h), and FIG. 11 is the case where the electrode depth d is deeper than the set value (d> 0.5 · h). 1
2 represents the case where the left and right electrode depths are different.

As an experimental sample, w = 0.1 mm, h
= 0.5 mm, L = 8 mm, the wall of the piezoelectric ceramic material was prepared. An aluminum electrode having a thickness t = 0.64 μm is formed on the side surface of the wall of the piezoelectric ceramic material by a sputtering method,
The electrode depth d = by being formed by a dry method such as a vacuum deposition method
Based on a 250 μm sample, d = 150, 175, 2
00, 225, 275, 300, 325, 350 μm samples (corresponding to FIGS. 10 and 11) and d = (225, 2
75), (200,300), (175,325),
Samples (150, 350) (corresponding to FIG. 12) were prepared. In FIG. 13, the maximum displacement and the volume change of the groove volume at that time were measured by applying a drive voltage to the above sample, and the data of the sample of each electrode depth when the data of the sample of d = 250 is set to 100 is shown in%. did. As for the maximum displacement and the volume change of the groove volume, the sample to which the cover plate 10 is bonded as shown in FIG. 14 is obliquely cut, a driving voltage of 50 V is applied, the wall is deformed, and the displacement amount is measured using a laser displacement meter. Then, the measurement was performed while stepwise scanning every 10 μm in the wall height direction. The maximum value of the displacement amount of the obtained data was defined as the maximum displacement, and the volume change was defined as the integrated value of the obtained displacement distribution.

As is apparent from FIG. 13, the influence of the electrode depth on the maximum displacement tends to be smaller than the influence on the volume change. From the experimental results, when the electrode depth d is ± 30% with respect to the set value, the maximum displacement and volume change are within the range of about 5%. Considering the droplet jetting stability in the droplet jetting apparatus of the present invention and the droplet jetting stability between the droplet jetting apparatuses, it is necessary to generate a stable pressure, and to realize this, the maximum of the wall of the piezoelectric material is required. It is desirable that the displacement and the volume change be realized within 5%, and for that purpose, it is considered necessary that the accuracy of the electrode depth is within ± 30% of the set value.

Therefore, the droplet ejecting apparatus of this embodiment is constructed so that the accuracy of the electrode depth is within ± 30% of the set value. As a result, it was possible to obtain a droplet ejecting apparatus capable of realizing stable droplet ejection.

[0033]

As is apparent from the above description, in the droplet ejecting apparatus of the present invention, the drive electrode formed on the side surface of the wall of the piezoelectric material is composed of the electrode material layer having a purity of 99% or more. By applying the driving voltage, efficient and stable deformation of the wall of the piezoelectric material can be instantaneously realized, and stable droplet ejection can be reliably performed for a long time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a droplet ejection device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state of walls and grooves of the liquid droplet ejecting apparatus of this embodiment.

FIG. 3 is a cross-sectional view showing a state of walls and grooves when a voltage is applied to the liquid droplet ejecting apparatus of this embodiment.

FIG. 4 is a perspective view of a wall of a piezoelectric material and a drive electrode of the liquid droplet ejecting apparatus of this embodiment.

FIG. 5 is a diagram showing the relationship between drive electrode thickness and specific resistance.

FIG. 6 is a conceptual diagram of electrodes formed on the wall of the piezoelectric material of the liquid droplet ejecting apparatus of this embodiment.

FIG. 7 is a relationship diagram between the drive electrode thickness and the deformation efficiency.

FIG. 8 is a diagram showing a relationship between drive electrode relative density and corrosion resistance.

FIG. 9 is a diagram showing drive electrodes formed on both side surfaces of a wall of a piezoelectric material of the liquid droplet ejecting apparatus of this embodiment.

FIG. 10 is a diagram showing drive electrodes formed on both side surfaces of a wall of a piezoelectric material of the liquid droplet ejecting apparatus of this embodiment.

FIG. 11 is a diagram showing drive electrodes formed on both side surfaces of a wall of a piezoelectric material of the liquid droplet ejecting apparatus of this embodiment.

FIG. 12 is a diagram showing drive electrodes formed on both side surfaces of a wall of a piezoelectric material of the liquid droplet ejecting apparatus of this embodiment.

FIG. 13 is a relational diagram of drive electrode depth, maximum displacement amount, and volume change.

FIG. 14 is a schematic view of a method of measuring the displacement amount of the wall of the piezoelectric material.

[Explanation of symbols]

 2 Piezoelectric element (actuator) 21 Wall of piezoelectric material 22 Groove 25 Drive electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C23C 4/12

Claims (1)

[Claims] 1. A droplet ejecting apparatus using a piezoelectric element that is an electro-mechanical conversion element as an energy generator for ejecting a droplet, wherein the piezoelectric element is used as a liquid flow path and a pressure chamber in a piezoelectric material. In a liquid droplet ejecting apparatus composed of a plurality of acting grooves and a piezoelectric material wall provided with drive electrodes on both side surfaces, the electrode material of the drive electrode formed on the side surface of the piezoelectric material A droplet ejecting device having a purity of at least 99% or more.