JPH0557892A - Ink jet printing head - Google Patents

Abstract

PURPOSE:To efficiently emit ink by shortening the time from the start of driving to the generation of a stable surface tension wave and increasing amplitude by generating a surface wave tension corresponding to the undulation of the uneven part on a piezoelectric substrate. CONSTITUTION:Electrodes are provided to the surface and rear of a piezoelectric substrate 1 and a nozzle plate 2 having nozzles 3 is arranged in opposed relation to said substrate 1. An uneven part 41 is provided to the vibration surface coming into contact with ink of the substrate. A high frequency voltage source 28 selectively applying voltage changing at the cycle equal to the resonance frequency of the piezoelectric substrate 1 is mounted and surface tension wave vibration 31 is generated by the standing wave vibration 34 of a piezoelectric vibrator and ink mists 30 are emitted by the interference of two vibrations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head which makes ink droplets fly by utilizing the vibration of a piezoelectric substrate.

[0002]

2. Description of the Related Art In recent years, various searches have been made for an ink ejector using an ink mist flow.

The device disclosed in Japanese Patent Laid-Open No. 62-85948 is a precursor thereof. This is to atomize the liquid ink by ultrasonic vibration and at the same time to charge it, and to attach it to the recording medium by an electric field.

However, in the above-mentioned conventional example, since the same number of independent ultrasonic wave generating means as the recording elements are provided, there are problems that the apparatus becomes large and the resolution cannot be improved.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object thereof is to make it possible to control the discharge of fine liquid particles in an accurate direction and at the same time Elementized, high-density integration,
It is to propose a new inkjet printer that can be mounted.

[0006]

A piezoelectric substrate, a piezoelectric substrate, at least one pair of electrodes arranged on the front surface and the back surface of the piezoelectric substrate, and a nozzle facing the intersection area of the electrode pair are provided. A nozzle plate arranged parallel to the substrate,
Ink held in the gap between the piezoelectric substrate and the nozzle plate, driving means for selectively applying between the electrodes a voltage that changes at a cycle equal to the resonance frequency of the piezoelectric substrate, and vibration of the nozzle plate. It is composed of a mechanism.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, before describing the individual embodiments, the flight principle of ink mist provided by an ink jet print head according to the present invention will be described with reference to FIGS. FIG. 1 is a view of the ejection portion of one element of the inkjet print head as viewed from the top, and FIG. 2 is a view of the side.

In the figure, reference numeral 1 is a plate-shaped piezoelectric substrate having a thickness d formed flat. The piezoelectric substrate is polarized in advance so as to be displaced with respect to the electric field in the thickness direction.

A segment electrode 2 having a width Ws is formed on the lower surface of the piezoelectric substrate 1, and a common electrode 3 having the same width Wc is arranged on the other upper surface so as to face each other to form a pair. Mutual electrodes are rectangular Wc × as shown by diagonal lines in the figure
A vibrator having an intersecting region 32 having an area of Ws is formed.

Reference numeral 2 denotes a plate-shaped nozzle plate having a thickness dn, which is arranged in parallel with the piezoelectric substrate 1 at a distance g. Three
Is a nozzle having an inner diameter Nd opened in the nozzle plate and corresponds to the rectangular intersection region 32 of the electrodes.
The nozzle plate was made by electrolysis, and the cross section of the nozzle was shaped to open downward. A step 40 was provided on the upper surface of the nozzle plate. This reduces the thickness of the nozzle portion 3 as much as possible, and thins the ink meniscus formed in the nozzle,
In addition, the surface of the nozzle plate other than the nozzle portion is thickened to increase the rigidity of the nozzle plate. The thickness dn1 of the step portion is 10 μm, and the thickness dn2 of the nozzle plate is 30
μm. Since the gap g between the nozzle plate 2 and the piezoelectric substrate 1 was 10 μm, the thickness of the ink meniscus was about 20 μm.

Reference numeral 24 is an ink held by the surface tension between the nozzle plate 4 and the piezoelectric substrate 1. The ink 24 is guided to the intersection region 32, that is, directly below the nozzle 3 by the capillary force.

Reference numeral 41 denotes an uneven portion formed on the surface of the vibrator that contacts the ink. A photolithography method or the like may be used as a method of manufacturing the uneven portion, and a new material for the convex portion may be selectively deposited on the piezoelectric substrate, or a portion for the concave portion may be formed.

Now, the common electrode 4 is electrically grounded, and the segment electrode 5 is applied with a voltage varying with a period of T seconds. When the period T is close to the reciprocal of the frequency that is an integral multiple of the resonance frequency of the longitudinal vibration of the piezoelectric substrate 1 in the thickness direction, standing wave vibration occurs at the intersection 32 between the electrodes having open ends on both sides. Due to this vibration, the ink supplied onto the intersection 32 is excited, and the radiated sound pressure 33 in the upward direction in the drawing and the surface tension wave vibration 31 are generated on the ink surface. Due to the interference of these two vibrations, the mist 30 having a diameter of 1 μm to 50 μm was emitted almost vertically from an area slightly smaller than the nozzle opening area.

At this time, since the surface tension wave 31 occurs corresponding to the undulations of the uneven portion, the time from the start of driving to the generation of a stable surface tension wave is short and the amplitude thereof is large, so that the fog is efficiently generated. It can be discharged as a liquid.

FIGS. 3 and 4 show a typical embodiment of the present invention constructed as an ink jet printer head for a line printer based on such a principle. 3 is a side view of the inkjet print head,
FIG. 4 is a view seen from the upper surface of the nozzle side.

In FIG. 3, reference numeral 1 is a narrow piezoelectric substrate having a length exceeding the effective printing area, and this piezoelectric substrate was formed of a zirconate titanate (PZT) type piezoelectric ceramic having a thickness of 1 mm.

In addition to the materials used in this example, piezoelectric ceramics such as ZnO, LiNbO3, quartz, LiTaO3, B, etc.
It is also possible to use a piezoelectric single crystal such as i12GeO20 or Si12GeO20, a polymer piezoelectric material such as polyvinylidene fluoride (PVDF), a mixture of the above piezoelectric materials, or a laminate of the above piezoelectric materials in a film form. It is possible.

A common electrode 4 is formed on the ink excitation portion 7 of the piezoelectric substrate by photolithography. The electrode width Wc of the common electrode 4 was set to about 100 μm.
The common electrode was fixed at 0V. A segment electrode 5 is also formed on the lower end of the piezoelectric substrate 1 by the photolithography method. Electrode width Ws of segment electrode 5
Was about 100 μm, and the inter-electrode pitch Pt was 170 μm.

For both the common electrode and the segment electrode, both surfaces of the piezoelectric substrate are lap-polished, and then a chromium thin film of 10 n is formed.
Then, a gold thin film having a thickness of 1 μm was formed thereon.

Reference numeral 2 is a nozzle plate, and reference numeral 3 is a plurality of nozzles formed in the nozzle plate. The nozzle corresponds to the intersection of each common electrode and segment electrode. The nozzle plate 4 was a nickel plate having a thickness of 30 μm. The nozzle inner diameter Nd was 30 μm.

Reference numeral 33 denotes a hole 15 provided corresponding to the nozzle while maintaining the gap between the nozzle plate 2 and the piezoelectric substrate 1.
Is a step for forming a flow path for guiding the ink to the ejection portion. By setting the thickness of the step to be 15 μm, the gap between the nozzle plate and the piezoelectric substrate 1 could be maintained at 10 μm.

Reference numeral 11 is a TAB substrate on which a driver IC 12 for driving each element of the ink excitation unit is mounted. One end of the TAB substrate is electrically collectively connected to the segment electrode group at the portion 25 via the anisotropic conductive film, and the other end is connected to the common electrode group 34 at the portion 26 via the anisotropic conductive film as well. There is. The output switch circuit of the driver 16 is composed of a complementary MOS circuit, and has a three-state output type of a high voltage output state, a low voltage output state, and a high impedance state.

The common electrode group 34 supplies electric power, control signals, recording signals, etc. to the driver IC 12.

Reference numeral 13 is a film-shaped circuit board connected to the common electrode group and the nozzle plate exciting electrodes 9 and 10, and the other end is connected to the connector 14.

Reference numeral 6 is a support substrate for fixing the above-mentioned components. It also serves as an ink supply path. A tube 15 is pressed into the upper part of the support substrate via a packing 16, and ink is supplied through this tube. The support substrate was formed by molding aluminum.

When assembling the above ink jet,
First, segment electrode 5, common electrode 4, common electrode group 3
4. The tab substrate 11 and the tape substrate 13 are mounted on the piezoelectric substrate 1 having the grooves 23 formed therein. The piezoelectric substrate 1 was adhered to the support substrate 6, and the nozzle plate 2 was heated and pressure-bonded with an epoxy adhesive to be adhered.

The ink 24 is guided to the ejection portion in the arrow B direction by the capillary force. The ink used was prepared by dissolving and dispersing 3 wt% and 5 wt% of diethylene glycol in pure water. The viscosity of the ink was 1.5 cps. Further, flight experiments with several kinds of ink showed that the viscosity at 25 ° C. was 0.5 cps to 8 cps and the specific gravity was 0.5 g / c.
m3 to 3.0 g / cm3, surface tension 10 dynes /
Good printing could be obtained from cm to 100 dynes / cm.

Now, a predetermined voltage and control signal are applied to the driver IC.
When a rectangular voltage of 1.5 MHz is applied to any segment electrode 2 given to No. 12, the piezoelectric substrate between the segment electrode and the common electrode resonates. This vibration allowed the ink to fly as droplets.

Next, the shape of the uneven portion of the present invention will be described. FIG. 5 and FIG. 6 are conceptual views of the uneven portion viewed from above.
In FIG. 5, the convex portions 43 are formed in a lattice shape. With such a structure, surface waves can also be generated in a lattice shape.

FIG. 6 shows the unevenness formed in a strip shape. The surface wave generation efficiency is lower than that of the above-mentioned lattice-like material, but the shape is simple and therefore easy to form. Moreover, since ink is supplied by the capillary force through the concave portion 44, the ink is less likely to run out.

FIG. 7 is an enlarged sectional view showing another example of the uneven portion. The pitch p and the depth d1 of the unevenness have optimum values depending on the particle size of the generated ink mist and the driving frequency, but generally the pitch is 3 μm to 50 μ, and the depth d1 is 1 μm.
Good results were obtained in the range of m to 10μ.

In FIG. 7, the surface of the concave portion 44 is replaced by the convex portion 4
Compared with No. 3, if the ink used is made easier to wet, the ink 24 collects only in the recesses 44, so that the tension in the ink that becomes a resistance at the time of atomization ejection can be reduced, and the ejection efficiency can be improved. I was able to do it. Such a structure can be easily formed by applying a water-repellent coating material to a flat vibrating substrate in advance and then forming a recess by chemical etching.

FIG. 8 is also an enlarged sectional view of the uneven portion. Recess 4
If the surface of No. 4 is made harder to be wetted by the ink to be used as compared with the convex portion 43, the ink 24 is thickly accumulated in the convex portion 43. It was possible to reduce the size and improve the ejection efficiency. In such a structure, after the unevenness is formed, the water-repellent coating is applied to
It can be easily formed by polishing the surface No. 3 thinly.

FIG. 9 shows another example of the uneven portion.
It is a figure which shows the distribution of the pitch p of the unevenness of FIG. In the examples up to now, it has been explained that the shape pitches of the uneven portions are all the same. However, in some cases, it is better to intentionally vary the pitch so that the particle size distribution of the ejected mist ink has a width, which is good for printing an image that requires gradation expression. May bring. In order to form the unevenness of the distribution as shown in FIG. 9, it is possible to easily form it by preparing hard abrasive grains close to this distribution in advance and strongly hitting the piezoelectric substrate surface.

With the above structure, it is possible to perform stable printing with a driving power of 0.03 W per element and a driving voltage of 25 V.

In this embodiment, the structure in which the ink is ejected from the common electrode side has been explained, but the ink can be ejected from the segment electrode side.

[0037]

According to the present invention, ink can be selectively ejected with a simple structure having only a single piezoelectric substrate and electrodes and nozzle plates provided thereon.
Therefore, there is an effect that the device can be made high-definition, miniaturized, and inexpensive.

[Brief description of drawings]

FIG. 1 is a top view of a discharge unit of an inkjet print head according to the present invention.

FIG. 2 is a side view of the ejection unit of the inkjet print head according to the present invention.

FIG. 3 is a side view of one embodiment of an inkjet printhead.

FIG. 4 is a front view of an embodiment of an inkjet printhead.

FIG. 5 is a diagram illustrating an example of the shape of the uneven portion of the inkjet print head according to the present invention.

FIG. 6 is a diagram illustrating an example of another shape of the uneven portion of the inkjet print head according to the present invention.

FIG. 7 is a diagram illustrating an example of another shape of the uneven portion of the inkjet print head according to the present invention.

FIG. 8 is a diagram illustrating another example of the shape of the uneven portion of the inkjet print head according to the present invention.

FIG. 9 is a diagram illustrating an example of another shape of the uneven portion of the inkjet print head according to the present invention.

[Explanation of symbols]

 1 Piezoelectric Substrate 2 Nozzle Plate 3 Nozzle 4 Common Electrode 5 Segment Electrode 6 Support Substrate 7 Ink Excitation Section 11 TAB Substrate 12 Driver IC 13 Tape Substrate 14 Connector 15 Tube 16 Packing 17 Inkjet Head 18 Paper 23 Groove 24 Ink 41 Concavo-convex Section

Claims (7)

[Claims] 1. A piezoelectric substrate, at least one pair of electrodes arranged on the front surface and the back surface of the piezoelectric substrate, and a voltage between the electrodes which changes at a cycle equal to the resonance frequency of the piezoelectric substrate is selectively applied. A vibrator configured with a driving unit that applies a voltage to the piezoelectric substrate; a nozzle plate disposed in parallel with the piezoelectric substrate, the nozzle plate being provided with nozzles that face each other in an intersecting region of the electrode pair; and the piezoelectric substrate and the nozzle plate. An ink jet print head comprising: an ink held in a gap; and an uneven portion on a surface of the vibrator that contacts the ink. 2. The ink jet print head according to claim 1, wherein the uneven portion has a lattice shape. 3. The ink jet print head according to claim 1, wherein the uneven portion has a strip shape. 4. The inkjet print head according to claim 1, wherein the concave surface and the convex surface of the uneven portion have different wettability with respect to the ink. 5. The ink jet print head according to claim 4, wherein the concave and convex concave surfaces have a lower wettability with respect to the ink than the convex surfaces. 6. The inkjet print head according to claim 4, wherein the concave and convex concave surfaces have higher wettability with respect to the ink than the convex surfaces. 7. The ink jet print head according to claim 1, wherein the intervals of the irregularities have a normal distribution.