JPH0250842A - Ink jet recording apparatus - Google Patents

Abstract

PURPOSE:To emit a desired ink droplet, to simplify constitution and to enhance the durability of an electrode part against abrasion by arranging two electrodes in a liquid chamber and giving potential difference between both electrodes. CONSTITUTION:A recording electrode 1, a common electrode 2 and one jet orifice 5 are provided to each liquid chamber and the ink jet orifice is arranged on the extension of each electrode. Now, when voltage is applied so that the potential of a recording electrode 1 becomes higher than that of the common electrode 2, a current flows from the recording electrode 1 to the common electrode 2 through ink. Small air bubbles 41 are generated on the recording electrode 1 by electrolysis at the initial period of the supply of a current. Since the electric resistance of a fluid is suddenly lowered by a temp. rise, a current rises and, at the same time, the small air bubbles 41 are unified to be grown into a united air bubble 42. An expanded air bubble 43 is generated on the basis of a current value slightly delayed from the max. current state and the ink is emitted from the ink jet orifice 5 in this expanded air bubble state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet recording device, and more particularly to a head for an on-demand type inkjet recording device.

Conventionally, as disclosed in Japanese Patent No. 60-500010, an electrode wire is disposed within a cylindrical insulating block, and ink droplets are ejected using electricity.
Another electrode is provided in the same liquid chamber, and 50 to 1
There is known a device that heats ink by applying a voltage of 500 V and concentrating current on dotted electrode portions. This principle is based on the fact that as the ink is heated, the electrical resistance of the ink decreases, and a ring-shaped electrostatic force acts straight from the edge of the electrode to the surface of the liquid, causing droplets to be ejected.

In other words, it applies the heating effect caused by energization and the effect of electrostatic force. In this conventional example, a conductive ink of about 10"60/(1) is used and a high driving voltage of 500 to 1500 µ is required, so in practice, the cost ratio of the drive circuit becomes high, which is a drawback. be.

Furthermore, since electrostatic force is used as the ejection force, there is a drawback that the efficiency is very low due to the arrangement of the electrodes.

Further, in the device described in U.S. Pat. No. 3,179,042, a liquid chamber tank is provided near the spatula 1, and the ink is heated in this tank to preheat the ink to have certain characteristics. Ink is sent to the head through
Here, by energizing the opposing electrodes, the ink between the electrodes is ionized or vaporized, generating a sudden force and ejecting the ink. This method requires additional equipment such as the provision of a preheating section, resulting in high costs, and, like the prior art described above, has the disadvantage of requiring a high voltage for the rolling voltage.

In addition, the present invention has been made in part in view of the above-mentioned circumstances.
In particular, by arranging two electrodes in the liquid chamber and applying a potential difference between the two electrodes, it is possible to eject the desired ink droplets.The simple configuration increases mass production efficiency and reduces costs. This was done for the purpose of improving the durability against abrasion of the electrode portion.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention includes a discharge port for discharging liquid, a liquid chamber communicating with the discharge port, a pair of electrodes provided in the liquid chamber, and a discharge port for discharging liquid. Voltage applying means for applying a voltage between the electrodes so as to apply a voltage to the liquid in the liquid chamber to cause bubbles to be generated in the liquid in the liquid chamber by electrolysis and to change the volume of the bubbles by the heat generated by the current supply. Furthermore, the area of one of the pair of electrodes in contact with the liquid is different from the area of the other electrode in contact with the liquid, and further, the area of contact with the liquid of the pair of electrodes is smaller. This is characterized in that one electrode has a higher potential than the other electrode. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a partially cutaway perspective view for explaining one embodiment of the present invention, and FIG. 2 is a cross-sectional view along line AA in FIG. 1, where 1 is a recording electrode, 2 is a common electrode, and 3 is the upper plate, 4 is the lower plate,
5 is an ink ejection port, 6 is an ink supply port, 7 is a partition wall, and 8 is a recording signal. A liquid chamber partitioned by the partition wall 7 communicates with one ink supply port to form a head. Each liquid chamber has a recording electrode], a common electrode 2, and one nozzle 5, and the ink nozzle 5 is disposed on an extension of each electrode.

As shown in FIG. 2, the recording electrode is made smaller than the common electrode 2, and current is concentrated on the recording electrode 1 to improve heat generation efficiency. The recording electrode 1 is manufactured by wiring in a line on a flat substrate, exposing only the necessary area, and applying a resist 9 to the remaining area, which enables high-density wiring. Further, although the recording electrode 1 and the common electrode 2 are arranged on the lower plate 4 which is the same substrate, one may be arranged on the upper plate 3 and the other on the lower plate 4.

, FIG. 4 is a diagram for explaining the operation when a recording signal is applied to the recording electrode 1- in the above embodiment,
This figure shows the state of bubbles generated on the recording electrode 1, and the fifth
The figure shows voltage and current waveforms when a voltage Vp is applied between the recording electrode and the common electrode 2. Now, when a voltage is applied so that the potential of the recording electrode 1 is higher than the potential of the common electrode 2, a current flows from the recording electrode 1 to the common electrode 2. The conductivity of the ink used is 10"1 to 10-28
It has relatively good conductivity as indicated by /. To explain the generation of bubbles over time using FIGS. 4 and 5, at the initial stage of energization ((1) in FIG. 5), chlorine, oxygen, etc. contained in the ink are deposited on the recording electrode 1 by electrolysis. Small bubbles 41 are generated (FIG. 4(a)). Hydrogen bubbles are generated on the common electrode 2 as well as on the recording electrode 1, but the bubbles grow faster on the recording electrode 1 because the surface area is larger. Fifth
From the state shown in FIG. 5 (1) to FIG. 5 (2), the electric current increases because the electrical resistance of the fluid rapidly decreases due to the temperature rise. At the same time, the small bubbles 41 merge, and the combined bubbles 42
(Fig. 4(b)). Maximum current (Figure 5 (2)
) An expanding bubble 43 is generated at a current value slightly delayed from the state (FIG. 5 (3)) (FIG. 4 (C)).

Ink is ejected from the ink ejection port 5 in this expanded bubble state. In FIG. 5(4), even though Vp is applied, current cannot flow because the surface of the recording electrode 1 is covered with air bubbles. Therefore, the bubble is rapidly cooled by the liquid around the bubble, turning into a contracted bubble 44 (FIG. 4(d)), and then disappearing (FIG. 4(e)).

FIG. 6 shows current waveforms when the potential difference between the recording electrode 1 and the common electrode 2 is changed. In FIG. 6(a), the recording electrode 1 is made higher than the common electrode 2. In FIG. The case of so-called positive polarization is shown,
FIG. 6(b) shows a so-called negative electrode configuration in which the recording electrode 1 is lower than the common electrode 2.

When the positive electrode is used, the above-mentioned Figures 4 (a) to (e) are repeated, but when the negative electrode is used, the generated bubbles are hydrogen, so
The electric breakdown voltage is 1 / compared to oxygen and chlorine generated at the anode.
]-, has a very small breakdown voltage of 99 times and 115.5 times, so the current increases rapidly as shown in the figure, causing discharge.

Furthermore, the state of wear of the electrodes is also affected by voltage application. FIG. 7 is a graph showing the temporal characteristics of electrode wear when the initial electrode amount of the electrode on the substrate 4 is defined as H and the amount of wear is defined as h, as shown in FIG. Electrodeization, (2
) indicates the amount of wear due to negative polarization. From FIG. 7, it can be seen that electrode wear is less when the potential of the recording electrode is higher than that of the common electrode. The arrangement relationship between the electrodes and the ink jet ports is not limited to the above-described embodiment, but they may also be arranged in a direction perpendicular to the direction of the electrodes, as shown in FIG.

As is clear from the above explanation, according to the present invention, by applying electricity between two electrodes, rapid heat is applied to the bubbles caused by electrolysis, causing the bubbles to rapidly expand, and liquid can be produced with a simple configuration. It can spray the liquid inside the room. Further, by using a positive electrode, it is possible to prevent discharge phenomena, prevent wear of the electrode, and improve durability.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view for explaining one embodiment of the present invention, FIG. 2 is a sectional view taken along line AA in FIG. 1, and FIG.
FIG. 4 is a sectional view showing another embodiment. FIG. 5 is an explanatory diagram of the operation of the present invention, and FIGS. 6 to 8 are
FIG. 2 is a diagram for explaining the present invention in detail. DESCRIPTION OF SYMBOLS 1 - Recording electrode, 2... Common electrode, 5... Ink jetting port, 6... Ink supply port, 8... Recording signal.

Claims (1)

[Scope of Claims] 1. A discharge port for discharging liquid, a liquid chamber communicating with the discharge port, a pair of electrodes provided in the liquid chamber, and between the pair of electrodes, an inkjet comprising: a voltage applying means for applying a voltage so as to apply a current to the liquid in the liquid chamber to cause bubbles to be generated by electrolysis in the liquid in the liquid chamber, and to change the volume of the bubbles by heat generated by the current supply; Recording device. 2. The inkjet recording apparatus according to claim 1, wherein one of the pair of electrodes has an area in contact with the liquid that is different from an area in contact with the liquid of the other electrode. 3. The inkjet recording apparatus according to claim 2, wherein the one of the pair of electrodes that has a smaller area in contact with the liquid has a higher potential than the other electrode.