JP2002291262A - Piezoelectric actuator and liquid eject head using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and high performance piezoelectric actuator with improved piezoelectric strain constant and a liquid eject head which can print at high speed using it with keeping its small size and high gradation. SOLUTION: In the piezoelectric actuator which comprises electrodes in both sides of a thin rectangular piezoelectric substrate 22, the ratio L/W of the length L and width W is set to between 20 and 200. By this configuration the piezoelectric strain constant is improved, and the liquid eject head can print at high speed with keeping its small size and high gradation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator and a liquid discharge head using the same, such as a medical micropump or an ink jet printer.

[0002]

2. Description of the Related Art Conventionally, as a liquid ejection head for intermittently ejecting a fine liquid, there is a micropump used for medication in a medical field or a printer in a familiar place. Hereinafter, an ejection head for an ink jet printer will be described as an example. Recently, an ink jet printer has rapidly become widespread as a means for easily realizing color printing at low cost. As this type of ink jet printer, there are two types, a bubble type and a piezoelectric type, depending on a method of ejecting ink. A bubble-type ink jet printer is provided with a heater in a pressurized chamber into which ink is introduced, and when a signal current is supplied to the heater, the ink is bumped and bubbles are generated. It is designed to inject. Then, a large number of pressurizing chambers of such a mechanism are connected in series to constitute a recording head.

[0003] On the other hand, a piezoelectric ink jet printer uses a piezoelectric actuator driven by a piezoelectric action. For example, Japanese Patent Application Laid-Open Nos. Hei 7-314672, Hei 11-198364, and
No. 177128 and Japanese Patent No. 312026. Specifically, one side wall of the ink pressurizing chamber as described above is configured as a vibrating plate, and the vibrating plate is vibrated by the piezoelectric actuator to pressurize the ink pressurizing chamber to jet ink from the jet port. It is supposed to. In this case as well, a plurality of pressurizing chambers of the above-described mechanism are connected in series to constitute an ejection head.

[0004] In a bubble type ink jet printer, the ink itself is required to have heat resistance in order to prevent a chemical change of the ink itself due to heat. It is difficult to vary the size of the ink particles to be performed, and therefore, in order to increase the gradation, it is troublesome to control the number of ink particles in a large range, that is, to expand the control range of the number of ink particles per unit area. Is necessary, the printing speed becomes slow,
There is a problem. In contrast, with a piezoelectric inkjet printer, quality control is easy because the ink can be used at room temperature, and the gradient is easily controlled by changing the drive voltage to control the size of one ink particle. For this reason, the piezoelectric ink jet printer tends to be used frequently.

[0005]

An important factor in determining the performance of the piezoelectric ink jet printer is the capability of the discharge head, and it is possible to intermittently eject fine liquid particles at high speed. That is the point. To this end, it is necessary to set the piezoelectric strain constant of the piezoelectric actuator provided for each ink pressurizing chamber as large as possible while maintaining the miniaturization of the apparatus. In today's demand for high-speed printing, it has become difficult to respond sufficiently with the conventional devices as described above, and it is necessary to return to the basics and improve the performance of the piezoelectric actuator alone. I was

[0006] The present invention focuses on the above problems,
It was created to solve this effectively. SUMMARY OF THE INVENTION It is an object of the present invention to provide a piezoelectric actuator capable of improving the piezoelectric distortion constant so as to be compact and capable of high-speed printing while maintaining a high gradation, and a liquid ejection head using the same.

[0007]

According to a first aspect of the present invention, there is provided a piezoelectric actuator in which electrodes are provided on both surfaces of a thin, substantially rectangular piezoelectric film. A piezoelectric actuator having a ratio L / W in a range of 20 to 200. The ratio L / W of the length L to the width W of the piezoelectric film is more desirably 40 or more. In this case, for example, as defined in claim 2, the length L is in a range of 1 to 12 mm. In addition, it is more preferably 4 mm or less. Further, for example, as defined in claim 3, the thickness T is 5 to 100 μm.
m.

Also, for example, as defined in claim 4,
The piezoelectric film may be of a single-layer type. Further, for example, as defined in claim 5, the piezoelectric film and the electrodes on both sides of the piezoelectric film are of a stacked type in which a plurality of the piezoelectric films are alternately stacked.

According to a sixth aspect of the present invention, there is provided a discharge liquid chamber arranged at a predetermined pitch, a discharge liquid supply port provided in each of the discharge liquid chambers for supplying a discharge liquid thereto,
An ejection nozzle hole provided on one side wall for partitioning each of the discharge liquid chambers, a diaphragm provided to partition another side wall of each of the discharge liquid chambers, and a diaphragm provided on each of the vibration plates. A liquid discharge head comprising: the piezoelectric actuator according to any one of 1 to 5. The invention defined in claim 7 is a case where the discharge liquid is ink, and is a liquid discharge head for an ink jet printer.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a piezoelectric actuator according to the present invention and a liquid discharge head using the same, particularly a discharge head for an ink jet printer, will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic sectional view showing an inkjet discharge head using the piezoelectric actuator of the present invention, and FIG. 2 is an enlarged perspective view showing a part of the piezoelectric actuator in FIG. As shown in the figure, the inkjet discharge head 2 has an ink chamber 4 as a large number of elongated discharge liquid chambers (hereinafter also referred to as ink chambers) having a substantially rectangular cross section. The number of the ink chambers 4 depends on the size of the recording head 2 and is, for example, several tens to several hundreds.
The ink chamber 4 has a predetermined pitch P1, for example,
The ink chambers 4 are arranged at a pitch of １００100 μm, the adjacent ink chambers 4 are partitioned by partition walls 6, and the bottom is partitioned by bottom partition walls 8.

The ceiling of each ink chamber 4 has a diaphragm 10 having a relatively small thickness, for example, about 5 to 10 μm.
The diaphragm 10 of each ink chamber 4 can vibrate uniquely, as described later. The diaphragm 10, the partition walls 6 and the bottom partition wall 8 are formed by integral sintering using, for example, ZrO ₂ (zirconium oxide). A nozzle base 12 made of, for example, a relatively thick stainless steel plate is provided below the bottom partition wall 8, and a nozzle plate 14 made of, for example, a thin stainless steel plate is sequentially joined to the lower portion of the nozzle base 12. The nozzle base 12 may be directly joined to each partition 6 without providing the bottom partition wall 8, and a part of the nozzle base 12 may be used instead of the bottom partition wall 8.

An ink supply port 16 is formed in the nozzle base 12 so as to correspond to each of the ink chambers 4, and supplies ink to each of the ink chambers 4 as needed through an ink flow path (not shown). It is possible to do. Also,
A fine jet nozzle hole 18 having a diameter of, for example, about 10 to 30 μm is formed through the bottom partition wall 8, the nozzle base 12, and the nozzle plate 14 that partition the ink chambers 4. These injection nozzle holes 18
Are provided so as to correspond to each ink chamber 4 one by one. As described later, the vibration plate 10 is vibrated to
By pressurizing the inside, ink droplets can be ejected from the ejection nozzle holes 18.

The piezoelectric actuators 20 of the present invention are provided one above the other on each of the vibration plates 10 so as to correspond to each other. More specifically, the piezoelectric actuator 20 has a substantially rectangular piezoelectric film 22 formed by firing, for example, a titanic acid / lead zirconate ceramic material. An upper electrode 24 made of a silver or chromium-gold composite film is joined, and a lower electrode 26 made of, for example, a platinum or titanium-platinum composite film is joined to the lower surface side. The thickness of each of the upper electrode 24 and the lower electrode 26 is about 0.1 to 8 μm, and the lower electrode 26 may be provided as a single wide electrode in common with each piezoelectric actuator 20. Good. In this case, the width of the piezoelectric actuator 20 is
The width is set within a range of about 60 to 95% of the width of the ink chamber 4.

By individually applying a voltage signal between the upper electrode 24 and the lower electrode 26 of each piezoelectric actuator 20 configured as described above, the piezoelectric actuator 20 expands and contracts by a piezoelectric action. As a result, the vibration plate 10 is distorted and vibrates, and the ink in the ink chamber 4 is ejected from the ejection nozzle hole 18 as an ink droplet by the pressure fluctuation. The ink jet head 2 is mounted on a head base (not shown),
Ink is ejected while scanning a recording medium such as recording paper. Here, the upper and lower electrodes 2 of the piezoelectric film 22 in FIG.
Displacement △ L and the piezoelectric strain constant d ₃₁ of length L direction upon application of a voltage V between 4,26 is defined as the following equation (1). ΔL / L = d ₃₁ V / T (1) When the electric field V / T is kept constant, the displacement ΔL is proportional to the piezoelectric strain constant d ₃₁ and the length L of the piezoelectric film. The piezoelectric strain constant d ₃₁ and the length L of the piezoelectric film is in a direction to minimize the as large as possible is desired. According to the equation (1), the displacement ΔL is irrelevant to the element width W. However, in the present invention, the displacement ΔL, that is, the piezoelectric strain constant d
₃₁ greatly depends on the element width W. Therefore, in order to operate at a high yield a high piezoelectric strain constant d ₃₁ in a smaller voltage efficiency, length L, a width W of the piezoelectric film 22
And the relationship between the thickness T and the thickness T are very important, and are set as described below in the present invention.

That is, first, the ratio L / W of the length L to the width W of the piezoelectric film 22 is set in the range of 20 to 200.
The thickness T of the piezoelectric film 22 is preferably 5 to 100 μm.
It is better to set it within the range of m. Further, the length L of the piezoelectric film 22 is preferably set within a range of 1 to 12 mm. Hereinafter, the reason will be described with reference to data. Figure 3 is the ratio L / W and the piezoelectric strain when the thickness is a graph showing the relationship between the ratio L / W and the piezoelectric strain constant d ₃₁ when the 5 [mu] m, 4 is the thickness of the piezoelectric film of 10μm piezoelectric film graph showing the relationship between the constant d _31, FIG. 5 is a graph showing the relationship between the ratio L / W and the piezoelectric strain constant d ₃₁ when the 30μm thickness of the piezoelectric film. FIG. 6 shows the ratio L / L when the length of the piezoelectric film is 12 mm.
W and is a graph showing the relationship between the piezoelectric strain constant d _31.
Incidentally, the piezoelectric strain constant d ₃₁ is given generally by the following formula (2). _{d 31 = (ε O · ε} T 33 · S E 11) 1/2 · k 31 ... (2) where epsilon _O is the dielectric constant in vacuum, epsilon ^T ₃₃ is the dielectric constant of the ^material, _{S E 11} is elastic _{compliance, k 31} is the electromechanical coupling coefficient.

[0016] First, as small voltage above in order to obtain a large displacement by the formula (1), the absolute value of piezoelectric strain constant d ₃₁ can be said to be better larger. For example, it can be said that the piezoelectric strain constant _{d 31} is desirable if the 200 × ^{10 -12} m / V or more. To obtain and large ink jetting pressure is smaller in the present embodiment, a stable region than the variation is small, approximately 340 × absolute value of piezoelectric strain constant d ₃₁ is
It was set to be 10 ⁻¹² m / V or more. In this regard, referring to FIGS. 3 to 5, the thickness T of the piezoelectric film 22 is 5
Be varied to 30 .mu.m, if the ratio L / W is substantially 20 or more, the absolute value of piezoelectric strain constant _{d 31} is substantially 340 × ^{10 -12}
m / V or more, which proves that the above condition is satisfied. Moreover, in this case, the length L of the piezoelectric film 22 is set to 1 to
It can be seen that the above condition is satisfied even when changed within the range of 12 mm. Also, this piezoelectric strain constant d ₃₁ is
The increase is saturated when the ratio L / W is about 100 to 120, and the length L of the piezoelectric film 22 has a reasonable dimension due to the demand for miniaturization of the ejection head.
The upper limit of / W is about 200.

[0017] Thus, the above results, setting the ratio L / W of length L and width W of the piezoelectric film 22 in the range of 20 to 200 is necessary from the viewpoint of enhancing the piezoelectric strain constant _{d 31} It turns out that it is. In this case, the length L of the piezoelectric film 22 is
It can also be seen that it is better to set at least within the range of 1 to 12 mm. Also, FIG. 6 is a graph showing the dependency on the thickness of the piezoelectric film of the piezoelectric strain constant d _31. Here, the thickness T of the piezoelectric film 22 is variously changed from 5 to 1000 μm (= 1 mm). The length L of the piezoelectric film 22 is 12 mm
Is set to a constant.

As is clear from this graph, the ratio L / W
Is not less than 20, the thickness T of the piezoelectric film 22 is 1000
If the [mu] m (= 1 mm), the absolute value of piezoelectric strain constant _{d 31} is lower to about 310-320. On the other hand, when the thickness T is 5 to 100 μm, the piezoelectric strain constant d _{3 at} a ratio L / W of 20 or more, preferably 40 or more.
The absolute value of ₁ is about 340 or more, which indicates that very good characteristics can be obtained. In this case, the thickness T is 100 μ
At m, the piezoelectric strain constant is rather low, and it is found that the thickness T is preferably in the range of 5 to 30 μm, and the characteristics are particularly good.

By setting the dimensions and the dimensional ratio of the piezoelectric film as described above, the piezoelectric distortion constant can be greatly improved, and the ink ejection pressure can be controlled over a wide range. Even with a high-density nozzle array, high-speed printing can be performed while maintaining a high gradation.

In the above embodiment, a so-called single-layer piezoelectric actuator in which electrodes 24 and 26 are provided on both surfaces of a single piezoelectric film 22 has been described as an example. However, the present invention is not limited to this. As shown in FIG. 7, the present invention can of course be applied to a so-called laminated piezoelectric actuator in which a plurality of piezoelectric films and electrodes having the above-described dimensions are alternately stacked. In the example of FIG. 7, four layers of 25 μm piezoelectric films are stacked on each other to make the total thickness 100 μm, and the electrodes can be alternately taken out to the side surfaces. An electrode 36 for applying a negative voltage is provided on the upper surface, the lower surface, and the right side surface of the surface of the laminate, and an electrode 34 for applying a positive voltage is provided on the other side surface. In such a laminated piezoelectric actuator, the thickness of the entire piezoelectric film is the same as that of the above-described single-layer piezoelectric actuator, but the driving voltage is set to be the same by reducing the thickness of each piezoelectric film. This can increase the electric field applied to the piezoelectric film. On the other hand, if the driving electric field is set to be the same, the driving voltage can be reduced. Then, when the characteristics of the laminated piezoelectric actuator of this example were evaluated, the same results as in the case of a single layer of 100 μm shown in FIG. 6 could be obtained.

FIG. 8 is a sectional view showing an embodiment of a liquid ejection head for an ink jet printer using another piezoelectric actuator 40 according to the present invention. The same reference numerals are given to the same structures as those in FIG. In this example, the piezoelectric film 42 is formed vertically with respect to the ink chamber 4 as shown in the figure. Although not shown, the upper end of the piezoelectric film 42 is fixed to a member of an actuator. Therefore, the displacement of the piezoelectric film 42 generated in the longitudinal direction when a voltage is applied is directly transmitted to the vibration plate 10 through the tip protrusion 44, and the inside of the ink chamber 4 is pressurized to thereby eject the ejection nozzle hole 1.
8 is designed to eject ink droplets. Here, the piezoelectric film 42 may be a single layer type or a laminated type, and in the case of a laminated type, the driving voltage can be suppressed low similarly to the above example. When the characteristics of this vertical example were evaluated, it was possible to obtain substantially the same effect as the above-described structure in which the piezoelectric film was placed sideways.

[0022]

As described above, according to the piezoelectric actuator of the present invention and the liquid ejection head such as a medical micropump or ink jet printer using the same, the following excellent operational effects can be exhibited. it can. By setting each dimension and size ratio of the piezoelectric film within a predetermined range, the piezoelectric distortion constant can be greatly improved, and therefore, in the case of an ink jet printer, the ejection pressure of ink can be controlled over a wide range. Therefore, high-speed printing can be performed while maintaining a high gradation even with a small and high-density ejection nozzle arrangement.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an inkjet discharge head using a piezoelectric actuator of the present invention.

FIG. 2 is an enlarged perspective view showing a part of a piezoelectric actuator in FIG.

[3] The thickness of the piezoelectric film is a graph showing the relationship between the ratio L / W and the piezoelectric strain constant d ₃₁ when the 5 [mu] m.

[4] The thickness of the piezoelectric film is a graph showing the relationship between the ratio L / W and the piezoelectric strain constant d ₃₁ when the 10 [mu] m.

[5] The thickness of the piezoelectric film is a graph showing the relationship between the ratio L / W and the piezoelectric strain constant d ₃₁ when the 30 [mu] m.

[6] The length of the piezoelectric film is a graph showing the relationship between the ratio L / W and the piezoelectric strain constant d ₃₁ when the 12 mm.

FIG. 7 is a perspective view showing a laminated portion of a piezoelectric film of a laminated piezoelectric actuator according to another embodiment of the present invention.

FIG. 8 is a sectional view of a discharge head portion showing still another embodiment of the piezoelectric actuator of the present invention.

[Explanation of symbols]

 2 Ink jet recording head 4 Ink chamber 10 Vibration plate 18 Injection nozzle 20, 40 Piezoelectric actuator 22, 42 Piezoelectric film 24 Upper electrode (electrode) 26 Lower electrode (electrode) 34 One side electrode of stacked type 36 The other of stacked type Electrode 44 Protruding tip of piezoelectric film L Length of piezoelectric film T Thickness of piezoelectric film W Width of piezoelectric film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F04B 17/06 B41J 3/04 103A 53/00 F04B 21/00 N 23/00 H01L 41/08 C H01L 41 / 09 S 41/083 U (72) Inventor Toru Abe 5200 Mikajiri, Kumagaya-shi, Saitama F-term in Advanced Electronics Research Laboratory, Hitachi Metals, Ltd. 2C057 AF37 AF55 AG12 AG39 AG44 AG48 BA04 BA14 3H069 AA04 BB01 CC10 DD11 DD44 DD48 EE01 EE41 3H071 AA05 BB01 CC11 CC17 CC31 CC47 DD04 DD42 DD84 DD89 EE11 EE12 3H075 AA07 BB04 BB21 CC30 CC32 CC36 DA05 DB02

Claims (7)

[Claims] 1. A piezoelectric actuator comprising electrodes provided on both surfaces of a thin, substantially rectangular piezoelectric film, wherein the ratio L / W of the length L to the width W of the piezoelectric film is in the range of 20 to 200. A piezoelectric actuator characterized by the above-mentioned. 2. The piezoelectric actuator according to claim 1, wherein the length L is in a range of 1 to 12 mm. 3. The piezoelectric actuator according to claim 1, wherein the thickness T is in a range of 5 to 100 μm. 4. The piezoelectric actuator according to claim 1, wherein the piezoelectric film is of a single-layer type. 5. The piezoelectric actuator according to claim 1, wherein the piezoelectric film and the electrodes on both sides of the piezoelectric film are of a stacked type in which a plurality of the piezoelectric films are alternately stacked. 6. A plurality of discharge liquid chambers arranged at a predetermined pitch, a discharge liquid supply port provided in each of the discharge liquid chambers for supplying a discharge liquid thereto, and dividing each of the discharge liquid chambers. 6. An ejection nozzle hole provided on one side wall to be formed, a diaphragm provided so as to partition the other side wall of each of the liquid discharge chambers, and a diaphragm provided on each of the diaphragms. A liquid discharge head comprising: the described piezoelectric actuator. 7. A liquid discharge head for an ink jet printer, wherein the discharge liquid is ink.