JPH0516362A - Liquid discharge device - Google Patents

Abstract

PURPOSE:To enable high-speed repetitive operation to be performed by a method wherein a pair of electrodes are arranged on an inner surface of a liquid passage near a liquid discharge opening of an ink jet printer or the like, liquid is gasified by discharge energy between a pair of the electrodes, and a liquid drop is discharged by pressure at that time. CONSTITUTION:A discharge head 1 of the title liquid discharge device is constructed by a passage 2 and tank 3 connected thereto, of which an inside is filled by liquid. A positive electrode 5 and a negative electrode 6 are formed as a pair of electrodes in the passage 2 near a discharge opening 4. Then, the liquid is gasified by heating by discharge energy when voltage is applied between both electrodes 5, 6 to discharge between both electrodes, and a bubble 7 is generated. A liquid drop 8 is discharged from the discharge opening 4 by pressure of the bubble 7. Since an energy supply part for discharging the liquid can be structured finely, simply thereby, a fine and highly integrated multi-nozzle discharge device can be easily realized and besides, repetitive operation at a high speed is enabled to be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid ejecting apparatus which can be used in a micro-quantity dispensing machine or an ink jet printer.

[0002]

2. Description of the Related Art A conventional liquid ejecting apparatus is a method for directly applying a mechanical force from the outside of a liquid flow path or a fine electric heater inside the liquid flow path as a means for generating a force for ejecting liquid fine particles. There was a method of arranging and heating this to generate bubbles inside the liquid flow path to exert an indirect force. A specific example of the former is shown in FIG. The ejection head 1 has a flow path 2 and a tank 3 continuous with the flow path 2, and the inside thereof is filled with a liquid. The tip of the flow path 2 is opened to the outside and serves as a discharge port 4. The thickness of a part of the discharge head 1 that is in contact with the flow path 2 is reduced, and the piezoelectric element 12 is bonded thereto. The reason for reducing the thickness of a part is to effectively apply the force generated by the bending motion of the piezoelectric element 12 to the liquid.
As in (b), a voltage is applied to the piezoelectric element 12 to deform a part of the flow path 2 inward, so that the droplet 8 is ejected from the ejection port 4. On the other hand, FIG. 4 shows a method of ejecting droplets by the latter electric heater. Similar to the previous example, the discharge head 1 is composed of the flow path 2 and the tank 3 communicating with the flow path 2, and the electric heater 13 is formed in the flow path 2 near the discharge port 4. By heating the electric heater 13 by applying an electric current, bubbles 7 are generated inside the flow path 2 and droplets 8 are ejected from the ejection port 4 as shown in FIG. 4B. In comparison with the former, the latter is more compact and can be miniaturized, and at the same time is easier to manufacture. In recent years, therefore, many inkjet printers using this method have been manufactured and used.

[0003]

In the above-mentioned prior art, heating with an electric heater is used as a bubble generating method for discharging droplets. For this reason, it is necessary to construct an electric heater having a certain area in the flow path, which has been a bottleneck for high integration of a multi-nozzle head having a plurality of ejection ports. In addition, since the generation of bubbles is induced by heating the electric heater and conducting this heat to the liquid, it is necessary to input extra energy, and at the same time when repeatedly discharging, there is a delay in heating or the electric heater. It has drawbacks in that thermal control is complicated, such as the time required for cooling in the vicinity, and high-speed repeatability is difficult.

An object of the present invention is to provide a highly integrated multi-nozzle liquid ejecting apparatus which has a plurality of ejecting ports and can operate at high speed at low cost.

[0005]

The above object is to arrange a pair of electrodes on the inner surface of a liquid flow path, apply a voltage between the electrodes to cause discharge, and generate a bubble in the liquid flow path by the discharge energy. This is achieved by ejecting a liquid drop by the pressure generated.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, the basic principle of the embodiment of the present invention is shown in FIG.
This will be described with reference to (a) and (b). The ejection head 1 is composed of a flow path 2 and a tank 3 continuous with the flow path 2, and the inside thereof is filled with a liquid. Inside the flow path 2 near the discharge port 4, a positive electrode 5 and a negative electrode 6 are formed as a pair of electrodes. In such a structure, when a voltage is applied between the positive electrode 5 and the negative electrode 6 as shown in FIG. 1B, a discharge is generated between the electrodes, and the discharge energy causes the liquid to be heated and vaporized to generate bubbles 7
To occur. As a result, the droplet 8 is ejected from the ejection port 4. The volume of liquid to be discharged in such a configuration
Factors that must be taken into consideration for controlling the discharge speed include electric resistance, insulation resistance, viscosity, specific heat of liquid, distance between electrodes, applied voltage, discharge time, and flow passage cross-sectional area. In the case of using water as the fluid, in the case of experimenting with a prototype head having a flow path cross-sectional area of 1600 square micrometers and a distance between electrodes of 20 micrometers, a discharge voltage of 60 V results in about 0.2.
It is possible to eject micro cubic centimeter droplets. As an application example, there is an inkjet printer head. In this case, a special ink is used as the liquid to be ejected, but especially by adjusting the electrical properties so that stable discharge is generated, high speed up to 15 kHz It can be driven repeatedly. FIG. 2 shows a multi-nozzle head in an embodiment that makes use of the high integration characteristic of the liquid ejection principle of the present invention. As shown in FIG. 2 (a), a nozzle substrate 9 in which a plurality of grooves corresponding to discharge ports and flow paths are formed on a glass plate, and a positive electrode 5 and a negative electrode 6 made of tungsten are provided on a substrate made of alumina at an interval of 20 micrometers Then, a plurality of patterned electrode substrates 10 are bonded and integrated to form a multi-nozzle head as shown in FIG. At this time, the surfaces of the positive electrode 5 and the negative electrode 6 are provided with the discharge part 14 so that the discharge generation site is near the discharge port 4.
Also, the portions other than the power feeding portion 15 are covered with the insulating film 11.
SiO2 is used as an insulating film to ensure heat resistance and corrosion resistance
I used a membrane.

[0007]

According to the present invention, since the energy supply unit for discharging liquid can be made fine and simple in structure, a fine and highly integrated multi-nozzle discharging device can be easily realized. Further, since the energy supply is direct, the energy conversion efficiency is good and high-speed repetitive operation becomes possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure and operation principle of a liquid ejection device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing the structure of a multi-nozzle head according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the structure and operation principle of a conventional liquid ejection device.

FIG. 4 is a cross-sectional view showing the structure and operation principle of a conventional liquid ejection device.

[Explanation of symbols]

 1 Discharge Head 2 Flow Path 3 Tank 4 Discharge Port 5 Positive Electrode 6 Negative Electrode 7 Bubble 8 Droplet 9 Nozzle Substrate 10 Electrode Substrate 11 Insulating Film 12 Piezoelectric Element 13 Electric Motor 14 Discharge Section 15 Power Supply Section

Claims (1)

Claim: What is claimed is: 1. A pair of electrodes are opposed or juxtaposed to the inner surface of the liquid flow path near the liquid discharge port, and a voltage is applied between the pair of electrodes to discharge the liquid. A liquid ejecting device characterized in that a liquid drop is ejected by a pressure generated when the ink is turned into bubbles.