JPS5831229B2 - droplet injection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a droplet ejecting device, for example, in a pulse jet type inkjet nozzle, the thickness of the piezoelectric element is reduced and the droplet ejecting efficiency is significantly improved. It relates to a droplet ejecting device.

First, an example of this type of device, which is related to the prior art and which is the object of improvement by the present invention, will be explained with reference to FIG. 1G.

In the figure, 1 is a nozzle part for jetting droplets;
2 and 4 are conduit portions that guide the liquid to the nozzle portion 1; 3 is a conduit portion that leads the liquid to the nozzle portion 1;
A diaphragm part formed in the middle of the conduit parts 2 and 4, 5 is a fluid diode, 6 is a common liquid reservoir, 7 is a
8 is a liquid supply tank; 10 is a liquid introduction pipe;
A drive circuit section, 11 is a main body, 12 is a base, 13 is a
It is a piezoelectric element.

Note that the common liquid reservoir 6 described above is for increasing droplet jetting efficiency and smoothing the supply of liquid, but does not contribute to the improvement of jetting efficiency in the present invention as described above. .

The sections from the nozzle section 1 to the common liquid reservoir 6 are formed as a groove section on one side of the main body 11, as shown in the sectional view 8 in FIG. In addition, a piezoelectric element 13 is bonded to the back side of the diaphragm part 3 (the top surface in the above cross-sectional view), and is connected to the first drive circuit part 10.

In the above configuration, the piezoelectric element 1 is filled with liquid between the nozzle part 1 and the supply tank 8, and the surface tension of the nozzle part 1 and the liquid pressure of the supply tank 8 are balanced.
When an electric pulse is applied to the piezoelectric element 3, the piezoelectric element 13 is suddenly distorted, and the volume of the diaphragm portion 3, or in other words, the diaphragm chamber as will be described later, changes to generate liquid pressure.

When this pressure wave of liquid pressure reaches the nozzle section 1, the surface tension of the nozzle section 1 is broken and the liquid is ejected from the nozzle in the form of particles.

Conventionally, in the droplet injection device as described above, it was easy to assume that if the strain force of the piezoelectric element was increased, the deformation of the diaphragm chamber would also be increased. The thickness of the piezoelectric element is determined by the thickness of the diaphragm, as described below, for the purpose of improving the effect of the sheath, adhesive wrapping around, and the thickness of the adhesive layer, as well as preventing discharge leakage between the front and back electrodes. The thickness of Jo,
It was about 2 to 3 times that of 4th grade).

However, in the case of such a conventional example, even if the area around the electrodes gets wet with some liquid, it is difficult to cause gaps between the electrodes, and it is difficult to be affected by the adhesive, and the droplet jetting characteristics between each nozzle are difficult to occur. This has the advantage of having small variations in the values.

However, on the other hand, since the piezoelectric element becomes thicker,
The drawback is that the voltage of the electric pulse that must be applied between the electrodes is high and the efficiency is poor.

In addition, the piezoelectric element was thick and therefore expensive.

The present invention eliminates the drawbacks of the prior art as described above, and provides a droplet ejecting device that generates liquid droplets in response to an electric signal and has high droplet ejection efficiency. Its purpose is to

The present invention is characterized by a nozzle section for jetting droplets while maintaining a controlled size and direction, a conduit section for guiding the liquid to the nozzle section, and a conduit section that connects a supply tank that stores the liquid to the middle of the nozzle section. In the droplet ejecting device, the liquid pressure drive unit causes a volume change in response to an applied electric signal and causes a droplet to be ejected from the nozzle unit. The resulting piezoelectric element is
The piezoelectric element is bonded to a diaphragm portion that forms a liquid partition, and the thickness of the piezoelectric element is 1.8 times or less than the thickness of the diaphragm.

More specifically, the present invention provides that when the same strain is applied to the piezoelectric element O, the thickness of the piezoelectric element at which the amount of volumetric deformation of the diaphragm chamber becomes maximum is equal to the diaphragm thickness; Considering that the thinner the diaphragm, the lower the voltage required to produce the same strain, this droplet ejecting device is designed to adhere a piezoelectric element that is thinner than 1.8 times the diaphragm thickness.

By doing this, a large change in the volume of the diaphragm chamber can be achieved with a low piezoelectric pulse, greatly improving the droplet jetting efficiency, and making it possible to create a highly productive drive circuit. It is something.

Next, embodiments of the present invention will be described with reference to FIGS. 2 to 6.

2 is a model cross-sectional view of the diaphragm part 3, that is, the diaphragm chamber described above, 3A is a thin-walled diaphragm, 3B is a diaphragm chamber, and 11A is a diaphragm chamber. 12A and 13A are cross-sectional views of the main body, the base, and the piezoelectric element, respectively.

Note that the diaphragm portion 3 and the piezoelectric element 13A form a liquid pressure 1 driving portion.

The diaphragm chamber 3B is formed by chemically etching a Si (silicon) plate to form a thin-walled diaphragm 3A as shown in the figure.The diaphragm chamber 3B is mounted on a Pyrex glass base 12A. 11A is bonded by an electrostatic adhesion method called anodic bonding, and then the main body 11A is bonded.
A piezoelectric element 13A is bonded onto the diaphragm chamber 3B.

In the configuration shown in FIG. 2, when piezoelectricity is applied to the piezoelectric element 131 and compressive strain is generated in the piezoelectric element 13A in the direction of the arrow shown in the figure, the diaphragm portion 3 is deformed as shown by the dotted line due to the bimetallic effect. This occurs, and the volume of the diaphragm chamber 3B becomes smaller.

Therefore, the pressure in the diaphragm chamber 3B increases rapidly, and the pressure wave causes the liquid to break the surface tension and eject from the tip of the nozzle part 1, and droplets are ejected.

Now, as shown in the figure, the thickness of the diaphragm 3A is hD, the thickness of the piezoelectric element 13A is hps, and the center deflection of the diaphragm 3A is δ.

Therefore, FIG. 3 shows the relationship between the central deflection δ of the diaphragm 3A when a certain strain is applied to the piezoelectric element 13A, and the thickness hP of the piezoelectric element 13A.

FIG. 3 shows that the center deflection δ of the diaphragm 3A becomes the largest when h, /hD21, that is, the thickness hP of the piezoelectric element 13A becomes equal to the thickness hD of the diaphragm 3A.

As shown in the same figure, the thickness of the piezoelectric element 13A is
As P becomes thicker, the central deflection δ of the diaphragm 3A becomes smaller, and when the plate thickness hP is doubled, the central deflection δ becomes about 80% of its maximum value δ.

Therefore, the thickness hp of the piezoelectric element 13A is approximately the same as the thickness hD of the diaphragm 3A, 0.5<hp/hD.
<2)? It has been found that rubbing is advantageous in terms of structural mechanics.

Next, when applying the same strain to the piezoelectric element 13A, the voltage applied to the piezoelectric element 13A is
PO is proportional.

Therefore, when the results shown in FIG. 3 above are shown for the case where the same voltage is applied to the piezoelectric element, the result is shown in FIG. 4G.

In addition, in this FIG. 4, the vertical axis is the diaphragm chamber 3B.
The volume change of hP/hD-1 is set as 1.

From this Figure 4, it can be seen that the above-mentioned structural mechanics
Compared to when hP/hD=1, the volume change AV is about half when hP/hD is 1.8, and if the piezoelectric element is thicker than that, the efficiency is very low and it may not be suitable for practical use. understood.

Therefore, taking all of these points into consideration, if the thickness of the piezoelectric element is made thinner than 1.8 times the thickness of the diaphragm, electric pulses can be effectively converted into changes in the volume of the diaphragm chamber.
A droplet ejecting device having efficient droplet ejecting characteristics can be obtained.

This means that even if the voltage of the electric pulse is low, good droplet ejection characteristics can be obtained, the single drive circuit is also inexpensive, and even higher reliability can be expected.

As mentioned above, it has been found that the thinner the piezoelectric element is, the more efficient droplet jetting can be obtained.However, on the other hand, as the piezoelectric element becomes thinner, the distortion of the piezoelectric element increases, and There is a limit because the stress acting on the adhesive layer also increases.

In addition, as described in the conventional example, when the piezoelectric element becomes thinner, it becomes more susceptible to the influence of the adhesive and the adhesive layer.

Furthermore, as the piezoelectric element becomes thinner, variations in the thickness of the diaphragm will directly affect the droplet jetting characteristics.

Therefore, as described above, in the present invention, when the piezoelectric element 13A is made thin, the thickness of the diaphragm 3A is made uniform and without variation, and a uniform bonding technique is required.

Regarding this structure, FIG. 5 shows one embodiment thereof.

In addition, in the figure, 14 is an Au layer, and 15 is an Au-Si layer.
It is a eutectic layer.

As previously mentioned, the reason why Si is used for the diaphragm 3A is because it allows for easy diaphragm processing with high precision.Specifically, it can be achieved by ultrasonic processing or chemical etching It is.

For example, if Si is etched at an appropriate temperature of about 60 to 80°C with an alkaline etching solution prepared by adding an inhibitor such as alcohol to a KOH solution, an etching rate of about 0.5 μm/min can be obtained, and an etching rate of about 1 μm/min can be obtained. It is possible to process the diaphragm portion 3 with high processing accuracy.

On the other hand, the Au layer 14 on the surface of the piezoelectric element 13A is metalized by vapor deposition, sputtering, etc., and if the upper surface of the diaphragm 3A is set as a Si surface, the thickness of the Au layer 14 is 340 to 400.
At about ℃, the Au-8i eutectic lid O becomes uniform Au-8.
An i-eutectic layer 15 is obtained.

Of course, in this case, the piezoelectric element 13A is at or above the Curie point, and repolarization is required.

However, in this way, a highly efficient, highly productive, and reliable droplet ejecting device can be realized with no variation and high yield.

Furthermore, as the piezoelectric element becomes thinner, discharge leakage between the electrodes becomes more likely to occur as described in the conventional example.
”-c, the front electrodes 16, 1B.

This problem can be solved by providing one or both of the back electrodes 17, 19, and 21 inward from the end of the piezoelectric element to increase the distance between the edges.

Taking all of the above into consideration, according to the present invention,
A droplet jetting device with good droplet jetting efficiency and high productivity can be obtained, and it can be said that this development has excellent practical effects.

[Brief explanation of the drawing]

In Fig. 1, A is a cross-sectional view of the conventional inverted version with a supply tank added, the opening is a schematic front view thereof, C is a schematic side cross-sectional view of the same with a drive circuit added, and Fig. 2 is a cross-sectional view of the conventional inverted structure with the addition of a supply tank. A schematic cross-sectional view of a diaphragm portion according to an embodiment, corresponding to the cross section taken along the line B-B in FIG. 1, and FIG. 3 is a graph showing the relationship between the plate thickness of the piezoelectric element and the diaphragm and the deflection in the diaphragm portion. , FIG. 4 is a relationship curve diagram between each plate thickness and the amount of volume change in the diaphragm portion, and FIG.
6a""-c in FIG. 6 are main part configuration diagrams also according to one embodiment. 1... Nozzle part, 2, 4.7... Conduit part, 3... Diaphragm part, 3A...
Diaphragm, 3B...Diaphragm chamber, 5.
...Fluid diode, 6 ... Common liquid reservoir, 8 ... Supply tank, 10 ... Drive circuit section, 11A ... Main body, 12A・・・・・・
Base, 13A...Piezoelectric element, hP...
・Thickness of piezoelectric element, hD...Thickness of diaphragm.

Claims (1)

[Scope of Claims] 1. A nozzle section for jetting droplets while maintaining a controlled size and direction, a conduit section for guiding the liquid to the nozzle section, and a conduit section midway between the supply tank containing the liquid and the nozzle section. In a droplet ejecting device, the liquid pressure drive section is coupled to a liquid pressure drive section that causes a volume change in response to an applied electric signal and ejects a droplet from the nozzle section. The resulting piezoelectric element is configured to be adhered to a diaphragm part that forms a partition wall of liquid, and the thickness of the piezoelectric element is 1.8 times or less the thickness of the diaphragm in the diaphragm part. A droplet injection device featuring: 2. A droplet injection device according to claim 1, wherein the diaphragm portion is formed by chemically etching a Si plate. 3. A droplet injection device according to claim 2, wherein the diaphragm is bonded to the piezoelectric element by metallizing the bonding surface thereof using a eutectic reaction. 4. The droplet ejecting device according to claim 1, wherein at least one electrode on the front and back sides of the piezoelectric element is provided apart from the end of the piezoelectric element.