JPH0557891A - Ink jet printing head - Google Patents

Abstract

PURPOSE:To obtain a density gradation image by selectively atomizing ink by the resonance of a piezoelectric substrate. CONSTITUTION:A nozzle plate 2 having nozzles 3 is arranged so as to be opposed to the crossing region of the electrodes 4, 5 provided on a piezoelectric substrate 1 and vibrated by a first vibration mechanism as shown by an arrow 31. A high frequency voltage source 28 being a second vibration mechanism selectively applying voltage changing at the cycle equal to the resonance frequency of the piezoelectric substrate 1 across the electrodes 4, 5 is provided and standing wave vibration 34 is generated in the piezoelectric substrate 1. Surface tension wave vibration 310 is generated in ink by two vibration mechanisms and a meniscus 29 is vibrated as shown by an arrow 320. Ink mists 30 are emitted by the interference of three 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]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the individual embodiments, the principle of flight of ink mist provided by an ink jet print head according to the present invention will be described with reference to FIG. 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
An intersection 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.

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.

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 in the thickness direction of the piezoelectric substrate 1, the standing wave vibration 34 is generated at the intersection 32 between the electrodes whose both ends are open ends.

At the same time, the nozzle plate 21 is vibrated in the direction of arrow 31 by another vibrating mechanism (not shown).

The ink supplied to the intersection 32 is excited by the above two vibrations, and the sound pressure 3 radiated upward in the drawing is increased.
3, the surface tension wave vibration 310 occurs on the ink surface, and the meniscus 29 also vibrates as indicated by the arrow 320.

Due to the interference of these three vibrations, the mist 30 having a diameter of 1 μm to 50 μm was emitted from the area slightly smaller than the nozzle opening area, almost vertically.

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-mentioned piezoelectric materials, or a laminate of the above-mentioned piezoelectric materials in a film form. It is possible.

The piezoelectric substrate 1 was provided with a groove 23 having a width of 100 μm and a depth of 70% of that of the piezoelectric substrate. The upper part of the groove is a vibrating part 7 for exciting ink, and the lower part is a nozzle plate exciting part 8 for exciting the nozzle plate 2. The above two excitation parts are driven independently, but this groove 2
The vibration is separated by 3.

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 numerals 9 and 10 denote excitation electrodes provided on both surfaces of the nozzle plate excitation portion 8. Of these, 9 was fixed at 0V.

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 15 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 connected together with the segment electrode group in the portion 25 through the anisotropic conductive film, and the other end is connected to the common electrode group 34 in the portion 26 through the anisotropic conductive film similarly. 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, the tab substrate 11 and the tape substrate 13 are mounted on the piezoelectric substrate 1 on which the segment electrode 5, the common electrode 4, the nozzle plate excitation electrodes 9, 10, the common electrode group 34, and the groove 23 are formed. The piezoelectric substrate 1 was adhered to the support substrate 6, and the nozzle plate 2 was heated and pressure-bonded to the nozzle plate excitation portion 8 with an epoxy adhesive to form the piezoelectric substrate 1.

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.
m ³ to 3.0 g / cm ³ , surface tension of 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. In addition, when a similar signal is applied between the nozzle plate excitation electrodes 9 and 10, the nozzle plate excitation portion vibrates and the nozzle plate adhered thereto vibrates. Both of these vibrations allowed the ink to fly as droplets.

FIG. 5 shows the temporal correlation between the waveform of the driving voltage applied to the segment electrode 5 and the nozzle plate exciting electrode 10 of this embodiment and the meniscus vibration. a) is 3 in FIG.
2 shows the displacement of meniscus vibration, b) shows the drive potential of the electrode 10 for exciting the nozzle plate, and c) shows the drive potential of the arbitrary segment electrode 5. The horizontal axis is the time axis. The meniscus vibration a) is generated by the vibration of the nozzle plate induced by the periodic intermittent wave of the nozzle plate excitation electrode signal b). This vibration is attenuated by repeating the vibration at the natural frequency determined by the fluid system and the solid vibration system near the nozzle. In this example, this natural period was about 120 μsec. Since the printing cycle Tp is set to 1 msec, it is almost attenuated at the next printing timing. With such meniscus vibration, the maximum point of arrow C is reached in about 30 μsec after driving. At this time, the maximum acceleration is applied to the meniscus in the direction in which the ink is ejected. By applying a recording signal to the segment electrode as in C) in synchronization with this C point,
We were able to atomize and fly the ink most efficiently.

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

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

[0035]

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 an ejection 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 a drive signal 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 Supporting Substrate 7 Ink Excitation Part 8 Nozzle Plate Excitation Part 9 Nozzle Plate Excitation Electrode a 10 Nozzle Plate Excitation Electrode b 11 TAB Substrate 12 Driver IC 13 Tape Substrate 14 Connector 15 Tube 16 Packing 17 Inkjet head 18 Paper 23 Groove 24 Ink

Claims (2)

[Claims] 1. A piezoelectric substrate, at least one pair of electrodes arranged on a front surface and a back surface of the piezoelectric substrate, and a nozzle facing each other in an intersecting region of the electrode pair, the parallel to the piezoelectric substrate. Driving means for selectively applying a voltage that changes at a cycle equal to the resonance frequency of the piezoelectric substrate between the nozzle plate, the ink held in the gap between the piezoelectric substrate and the nozzle plate, and the electrodes. And an inkjet print head vibration mechanism. 2. The ink jet print head according to claim 1, wherein the vibration mechanism of the nozzle plate is a piezoelectric vibrator directly attached to the nozzle plate.