JPH0288246A - Printing head - Google Patents

Abstract

PURPOSE: To contrive to improve the print quality by modulating the frequency or amplitude, or both, of a liquid meniscus, which is arranged near a discharging means of a liquid from an orifice at a natural resonant frequency and amplitude with respect to the controlled phase relationship in relative to the phase position of the oscillation of the liquid meniscus above or below its equilibrium position. CONSTITUTION: Just after the discharge of an ink drop in an equilibrium mode, the ink meniscus at an orifice 17 naturally oscillates from its equilibrium position 9 and lasts to its 'dead time' To under the state that its amplitude dampens. A piezo material 22 such as a quartz, a barium titanate ore or a thin cyanite plate is installed in an ink cavity 14. The piezo material 22 is connected so as to be excitable with controlled electric signals in order to induce the oscillation of a controlled frequency and amplitude within the material 22. By means of the oscillation of the piezo material 22, an continuous oscillation, which is symmetrical to a certain ink meniscus, is obtained and then superposed to the 'natural oscillation' of the meniscus, resulting in substantially suppressing the natural oscillation of the meniscus and substantially extinguish the 'dead time' To, which is the cause of the limitation of the maximum action frequency Fmax of an ink jet printhead.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates generally to inkjet printing devices, and more particularly to devices that utilize an auxiliary ink pump device to improve operational performance. Such devices are devices that operate to maintain positive pressure within the ink cavity and ink channels of the inkjet pen to increase the maximum operating frequency of the inkjet pen.

[Prior art and problems]

In certain inkjet printing devices, such as thermal inkjet (TIJ) printers, the maximum achievable operating frequency, Fmax, is inherently limited by material factors.

That is, l) the ink in the ink delivery device, and 2) the ink meniscus (sa) in the orifice plate of the print head that remains for a certain period of time (To) after the ink droplet discharge is performed.
siscus) vibration.

One proposal for increasing Fmax and at the same time improving other operational aspects of thermal inkjet printheads is disclosed in Japanese Patent Application No. 63-2856 previously filed by the applicant.
It is disclosed in No. 14.

Thermal inkjet printers with such operating characteristics are currently known, e.g.
-Ackard Jarl, May 1985, Vol. 38, No. 5. Such printers use printhead devices that have resistive heating elements (resistors). This resistor then operates to receive adjacent dynamic pulses. The pulses cause the printhead operating frequency to exceed a certain limit by rapidly heating the heater resistor, vaporizing the ink in the adjacent ink reservoir and forcing it out of the orifice plate during an inkjet printing operation. As the temperature rises, the natural capillary action of the TIJ printer's ink delivery system may result in insufficient ink volume for the heater resistor, the adjacent ink cavity, and the ink reservoir connected to the ink channel leading to the cavity. There is a tendency not to supply it.

This "ink starvation phenomenon" becomes more and more significant as the viscosity of the ink increases.

In many applications, various types of paper, especially flat paper (pla
In order to improve the print quality on ink paper, it is necessary to increase the viscosity of the ink. Besides the aforementioned limitations due to such ink starvation phenomena, the natural oscillation of the ink meniscus at the orifice further constrains Pmax, and for some period of time immediately after the ink drop is ejected (To)
also remains. During this period of To, further ejection of ink drops is severely restricted.

[Purpose of the invention]

The present invention therefore aims to overcome the aforementioned drawbacks of inadequate natural capillary ink supply to an inkjet printhead during high frequency operation and to extend Fmax beyond current limits.

Another object is to provide a new and improved printhead operable such that meniscus oscillations of the ink in the orifice occur at a controlled frequency, a controlled amplitude, and a <RTIgt; This allows different amounts of ink droplets to be ejected from the same orifice by timing the ejection of the ink droplets with the height of the meniscus. That is, if jetting occurs when the meniscus level is low, a small ink drop will be ejected, and if jetting occurs when the meniscus level is high, a large ink droplet will be ejected.

Yet another objective is to increase the upper limit of usable ink viscosity. This is accomplished by utilizing the pumping action of a piezoelectric system to create a positive pressure above the natural capillary forces within the ink capillary cavities and ink capillary passages of the inkjet printhead.

[Summary of the invention]

To achieve the above objects and associated advantages of the present invention, the amplitude and frequency of the meniscus oscillations in the liquid ejection orifice eject ink through the orifice and the natural resonant frequency and amplitude with respect to the equilibrium position. A new and improved ink delivery system and method of operation for an inkjet printhead in a controlled configuration has been invented and developed. The frequency or amplitude or both of the ink meniscus at the orifice is modulated (controlled) into a controlled phase relationship related to the phase position of the meniscus oscillation above or below the equilibrium position.

In embodiments of the invention, a resistive heater element is aligned with the orifice plate, and an ink channel supplies ink to a chamber or ink reservoir between the resistive heater element and the orifice plate. .

In particular, the device of the present invention is selectively equipped with the following mechanisms. 1) a piezoelectric system mounted inside the ink cavity of the inkjet printhead; 2) an external piezoelectric system mounted directly on the orifice plate of the inkjet printhead; and 3) two piezoelectric systems, both mounted inside the ink cavity of the printhead. 4) Two (dual) piezoelectric systems, one inside the ink cavity of the printhead and the other external, directly on the orifice plate of the printhead. The foregoing ink delivery system includes: 1) producing vibrations of a controlled frequency Fm and a controlled amplitude I+m of the ink meniscus at the ink ejection orifice;
and enable variable and controlled ejection of ink drops from a single orifice, 2) extend the maximum operating frequency Fmax of the inkjet printhead, and 3) extend the range of usable ink viscosities. It can be used for.

The outline of the invention described above will become clearer from the detailed description along with the accompanying drawings.

〔Example〕

Referring now to FIG. 1, a single heater element (schematic representation of resistor H1 is shown) surrounded by barrier material 12 forming an ink channel 13 in close proximity to resistor 11. Barrier material 12 further forms an ink cavity region 14 outside the ink channel 13. Three-sided barrier layer structures of this type are generally known and are described, for example, in JP-A-63-307-957 previously filed by the applicant; Kaihei 1-
No. 118443.

FIG. 2 is a central cross-sectional view of the resistor of FIG. 1 with the internal printhead structure complete including the orifice plate.

FIG. 2 further illustrates ink cavity 14 formed between lower substrate 15 and outer orifice plate 16. FIG. Orifice 17 is located directly above resistor 11. Ink from the ink delivery system 18 is drawn into the area of the ink cavities 14 and ink channels 13 by capillary forces.

Served. An ink-shared printhead operating in this manner is considered to be operating in a "balanced mode." Immediately after the ejection of an ink drop in the equilibrium mode, the ink meniscus in the orifice 17 oscillates from the equilibrium position 9, as shown in FIG. 3A, and FIG. 3B,
Maximum expansion 20 and minimum expansion 21 as shown in Figure 3C.
and achieve.

Such "natural oscillations" are accompanied by attenuation of the amplitude as shown in FIG. I can't let you.

In accordance with the present invention, a piezoelectric material 22, such as quartz or barium titanate ore or alanite slats, is mounted within the ink cavity 14 as shown in FIG. 5 or in the orifice as shown in FIG. Externally disposed on the outer surface of plate 16.

Piezoelectric material 22 is connected to be excitable by a controlled electrical signal, which induces vibrations of controlled frequency and amplitude within material 22. This action, in turn, creates a positive ink pressure within the ink cavity 14 and ink channel 13, thereby performing the function of an ink pump.

The internal and external piezoelectric systems described above perform similar functions.

A variety of piezoelectric excitation circuits suitable for obtaining the piezoelectric excitation circuit signals disclosed herein are available, and the choice of circuit design for such an exciter is within the skill of those skilled in the art.

Therefore, a detailed description of the specific excitation circuit design is omitted as it would be too complicated. However, piezoelectric excitation circuits are disclosed in many US patents, such as US Pat.
No. 7,927, No. 4,630,072, No. 4.498
, 089 and 4.521.786.

The vibration of the piezoelectric material 22 results in a constant, symmetrical, continuous vibration of the ink meniscus, as shown in FIG. 4B. Frequency Fm and amplitude shown in Figure 4B! - Such continuous, induced, symmetrical, controlled meniscus oscillations are superimposed on the "natural oscillations" shown in Figure 4A. The net result of the superposition of these two types of meniscus oscillations is a substantial suppression of the natural oscillations of the meniscus shown in FIG. This is the virtual disappearance of "dead time" (↑0).

Meniscus oscillation of induced meniscus oscillation! The timing of energizing the resistor 11 relative to - is important.

The resistor 11 is at the equilibrium position, that is, the point (
When energized by T), the inkjet print head will
It operates in "equilibrium mode" and a medium volume of ink droplets Veg are ejected. This ejected ink drop is equal to the amount it would be if no pulse was applied to the piezoelectric material, in "equilibrium mode"
The maximum achievable operating frequency Fmax of an inkjet printhead operating at is limited only by the frequency Fm of the induced meniscus oscillations. The resistor 11 is located at the maximum expansion position of the meniscus, that is, the point (
When energized at υ), the inkjet print head
The maximum amount of ink drops Vmax is ejected. When resistor 11 is fired at the position of minimum meniscus expansion, point (V) in FIG. 4B, the inkjet printhead operates in a "starvation mode" and a small volume of ink droplet Vain is ejected. By energizing resistor 11 at different points between rich and depleted modes, the amount of ink drops ejected is varied and controlled.

By having dual piezoelectric systems in the inkjet printhead that are independently controlled, the range of ejected ink drop volumes can be expanded, as shown in Figure 7. A piezoelectric exciter 22 connects the ink cavity 1
Fig. 4 shows the above system incorporated in 4.

FIG. 8 shows another system in which piezoelectric exciters 22 are incorporated both inside and outside the ink cavity 14, with the outside exciter being mounted on the orifice plate 16. The method of operation of these systems is the same in both FIGS. 7 and 8.

Each of the independently excited piezoelectric exciters 22 is energized by a control signal to induce oscillations, which in turn induce symmetrical meniscus oscillations as described above. When both piezoelectric exciters in an inkjet printhead are vibrated in phase with each other and with the same amplitude, the induced meniscus vibrations remain symmetrical as described above in accordance with FIG. 4B.

Inkjet printing, both piezoelectric exciters 2 in the head
2) may be vibrated with the same frequency and amplitude but different phases from each other; or 2) may be vibrated with the same amplitude and different frequencies and different phases from each other.
A combination of frequency, amplitude and phase shift can be selected to induce asymmetric meniscus oscillations as shown in Figures A and 9B.

If the induced asymmetric meniscus oscillation is shifted in the positive direction as shown in Figure 9A, the maximum IVmax of the ejected ink droplet will be smaller than in the symmetric case because the meniscus expansion is further magnified in the asymmetric case. It can be further increased. A critical condition is reached when the asymmetric positive meniscus expansion becomes large enough that actual drop ejection begins to occur. Large positive asymmetric expansion of the meniscus is facilitated by proper selection of ink viscosity and ink surface energy.

Alternatively, as shown in FIG. 9B, if the asymmetric meniscus oscillation is shifted in the negative direction, the minimum amount of ink drops Va+in ejected can be even smaller than in the symmetrical case. A critical condition is reached when the asymmetric negative meniscus expansion becomes large enough that the printhead begins to blow air through orifice ports in the printhead orifice plate.

Air blowing can be modified by proper selection of ink viscosity and ink surface energy.

The pumping action of the additional piezoelectric system described above allows inkjet printheads to work with even lower viscosity (less than about 3 cps) and higher surface tension inks (more than about 55 dynes per cm), as well as the currently used inks. It also becomes possible to use inks with lower viscosity and even higher viscosity.

In general, higher viscosity inks penetrate the surface of the paper more slowly, thereby increasing print quality on a variety of papers, especially xerographic or bond papers. Printheads using higher viscosity inks therefore print more reliably on wider, flat paper.

By being able to use inks that have both high viscosity and low surface tension, the drying time on flat paper is also faster.

The availability of lower surface tension and higher viscosity inks offers many advantages over current technology. Standard ink technology, which uses soluble dyes in normal aqueous solutions, can be significantly improved. It will be expanded to allow use of a wider range of solutions.

For example, in combination with water to obtain the desired solvent properties,
This expanded range of solvents allows the use of higher molecular mass glycols, ethers, ketones, etc., making dyes that are currently unacceptable due to solubility or reactivity with the ink solution It can be used in the novel printhead disclosed herein. Such additional dyes can enhance the contrast, color, tone and print quality of the print on the print media. In addition to improving the printing performance specific to highly viscous inks, mixing other solvents and dyes may also improve water fixability, reliability, tack fixation, light fixation, and storage stability.

Additionally, additional color dyes may be used, with concomitant improvements in color gamut and bleed properties.

Reducing surface tension requirements and increasing viscosity tolerances allows the printhead to be used with "non-standard" inkjet inks (eg, non-aqueous, dye-based).

For example, pigment-based, microemulsion or encapsulated inks could be used. Such a new coloring system would provide higher water fixability, improved tack fixation, better color gamut, reliability, and light fixability and tack fixation.

Many variations are possible to the embodiments described above without departing from the scope of the invention. For example, the present invention is not limited to the particular printhead configuration shown in cross-section, but is also applicable to known [side-shooter J "front shake" and "edge-shooter" configurations, as well as heater resistor This can be implemented using printheads with a variety of configurations, including offset centerlines and orifice centers. Furthermore, the structure of the ink delivery channels and ink reservoir cavities can also be varied according to the design constraints applicable to a variety of thermal inkjet printheads, and the configuration of the hydraulic tuning and crosstalk reduction mechanisms can be varied. could also be included.

〔Effect of the invention〕

As is clear from the above description, in the present invention, by providing an additional excitation means in the print head, the upper limit operating frequency becomes higher, and the amount of ink a and droplets ejected from the orifice can be controlled. , it is also possible to use ink with higher viscosity, and print quality can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing an example of a configuration in which a resistive element is arranged in an ink supply channel, and FIG. 2 is a thermal inkjet
3A, 3B, and 3C are cross-sectional views showing three states of meniscus vibration in the orifice opening; FIG. 4A is a view showing natural meniscus vibration; 4B is a diagram showing meniscus vibration induced by the present invention, FIGS. 5 to 8 are cross-sectional schematic diagrams of a print head according to the present invention, and FIGS. 9A and 9
Figure B shows the induced meniscus oscillations being shifted from the meniscus equilibrium position by an amount controlled by the timing of the pressure pulses generated by the piezoelectric pump of the printhead.

Claims (2)

[Claims] (1) means for discharging fluid from said orifice at a natural resonant frequency and amplitude with respect to the equilibrium position of the fluid meniscus in the orifice; and a phase position of vibration of said fluid meniscus located close to said means and above or below said equilibrium position; and means for controlling the frequency or amplitude, or both, of the fluid meniscus in a controlled phase relationship related to the fluid meniscus. 2. The print of claim 1, wherein the control means includes a piezoelectric crystal disposed in close proximity to the fluid to generate a pressure wave operative to modulate the fluid meniscus relative to the equilibrium position in the orifice. head.