JPS6046257A - Inkjet recorder - Google Patents

Abstract

PURPOSE:To prevent the lowering of the dot positioning accuracy and the deterioration in the flying direction due to ink sag by adding an opposed electrode arranged on the back of a recoding paper and a high voltage power source for applying a potential between an orifice for injecting ink drops and the opposed electrode to more than double the ink drop flying speed. CONSTITUTION:A bimorph made up of a piezo-electric element 5 and a flexible upper plate 4 deflects so as to reduce the capacity of an injection chamber 1 by applying a voltage to the piezo-electric element 5 to generate a pressure wave inside, which causes an ink drop 6 to jet toward a recording paper 7 from an orifice 2. The ink drop 6 is charged negatively instantly leaving an inkjet head, accelerated by an electrostatic field generated between the inkjet head and the opposed electrode 8, reaching the recording paper 7 gaining a sufficient speed exceeding 10m/sec and forms a dot on the recording paper. This can reduce the lowering of and variation in the dot positioning accuracy due to an air flow and further, can prevent the deterioration in the flying directivity of the ink drop due to an ink sag.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention reduces the volume of the ejection chamber by applying electric pulses to a piezoelectric element, and improves the flight characteristics of inkjet printers that eject ink droplets at the appropriate time. The present invention relates to an inkjet recording apparatus that performs the following.

First, we will explain the conventional drop-on-demand inkjet head. FIG. 1 is a sectional view showing a basic embodiment of the present invention. One end of the ejection chamber 1 is exposed to the atmosphere following an ink droplet ejection orifice 2, and the other end communicates with an ink supply hole 3. Ink passes through the ink supply hole 3 to an ink tank (6 not shown).
is supplied to the injection chamber 1.

A piezoelectric element 5 is attached to a flexible upper plate 4 constituting a part of the wall of the injection chamber 1, forming a No.XI immorph. By applying electricity to the piezoelectric element 5, the upper plate 4 bends in the direction of reducing the volume of the ejection chamber l, generating a pressure wave 21IE inside, and this pressure wave causes the ejection to move from the orifice 2 toward the recording paper 7. Ink W4
6 is injected.

An fC recording device using this pour-on-demand inkjet head has the following features: (1) Since ink can be generated during JM, ink changes over time are good.

(2) The configuration is simple as no ink recovery device is required. Therefore, a low-cost recording device can be realized.

(3) Low noise, (4) Can be recorded on plain paper, and (5) Can be easily converted to color by changing the ink.

(6) Multi-nozzle configuration is easy and high speed is possible.

Although it has excellent features such as, its disadvantage is that its ink droplet ejection capacity is small. This has resulted in disadvantages such as the ink droplet flying speed being generally KtJs and the ink droplet flying characteristics tending to deteriorate. For example, in continuous inkjet heads, the ink droplet flight speed is 10 to 20 m/s, whereas in continuous inkjet heads, it is usually 3 to 4 m/s.
Small as S. When the flying speed of the ink droplets is low as described above, there is a major problem in that the dots are susceptible to the influence of air currents while flying, resulting in poor dot positioning accuracy and deterioration of print quality. This problem has a greater effect on recording devices with higher resolution and higher speed recording devices with faster head movement speeds.

Furthermore, since the ink droplet ejection capacity is small, there is a problem that ink droplets adhere to the tip of the nozzle, and the adhering ink droplets drag the ink droplets and the flying direction of the ink is shifted. This phenomenon is
The problem often persists until the nozzle tip is cleaned by a cleaning mechanism (not shown) provided in the recording apparatus. One way to increase the ejection capacity of ink droplets is to make the piezoelectric element itself larger to increase its ejection capacity, but in reality, the trend is to make heads smaller, more integrated, and have multiple nozzles, and piezoelectric elements There is also a demand for miniaturization for themselves. Furthermore, miniaturization of the head is effective in improving the droplet generation frequency, and increasing the size of the piezoelectric element can be said to be an extremely unrealistic solution. In this way, conventional inkjet, drop-on-demand, and inkjet recording devices
The ink drop ejection capacity is generally small, and this problem will be solved in the future.
This becomes an increasingly serious problem as heads become smaller and more integrated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a drop-on-demand type inkjet recording apparatus that has a high ink droplet ejection capacity and a high ink droplet flying speed in order to eliminate the above-mentioned drawbacks.

According to the present invention, a counter electrode disposed on the back side of the recording paper, a high-voltage power supply that applies a potential between the ink droplet ejection orifice and the counter electrode are added to the droplet, drop-on-demand type inkjet head described above. An inkjet recording device is obtained.

Hereinafter, the present invention will be explained according to examples.

FIG. 3 is a sectional view of an embodiment of an inkjet recording apparatus according to the present invention. Ejection chamber l, orifice for ink ejection 2. ink supply hole 3, flexible upper plate 4,
The piezoelectric element 5 and recording paper 6 are the same as the conventional drop-on-demand history inkjet head of FIG.

The counter electrode 8 is arranged on the back surface of the recording paper 7 when viewed from the inkjet head side, and the high voltage DC power supply 9 applies a high voltage between the inkjet head and the counter electrode 8. In this example, we will use inkjet.

It is assumed that the parts of the board are metal. If the members of the inkjet head are non-conductive, it is necessary to attach electrodes to the parts that come into contact with the ink. The principle of ink droplet discharge is as follows.

By applying a voltage to the voltage element 5, the bimorph made up of the piezoelectric element 5 and the flexible upper plate 4 is deflected in a direction that reduces the volume of the injection chamber 1, and a pressure wave is generated inside. Ink droplets 6 are ejected from the orifice 2 toward the recording paper 7 by the waves. The ink droplet 6 is negatively charged at the moment it leaves the inkjet, tohe, do, and is accelerated by the electrostatic field generated between the inkjet head and the counter electrode 80, achieving a sufficient speed of 10 m/s or more and recording. It reaches the paper 7 and forms a dot on the recording paper.

In the inkjet recording apparatus of the present invention, the ejection of ink droplets is left to the conventional on-demand method, and after ejection is accelerated by the electrostatic field between the inkjet and the counter electrode 8.

Now, in the same way, a recording device using electrostatic acceleration
According to Japanese Patent Publication No. 36-13768, both ink drop discharge and acceleration are realized by electrostatic acceleration. Therefore, it has the following disadvantages compared to the present invention.

(1) Ink discharge relies only on electrostatic acceleration, so the voltage of the high-voltage DC power supply is high (requires about three times that of the present invention) (2) Ink discharge relies on electrostatic acceleration Therefore, it is difficult to generate ink droplets, and the ink often becomes string-like.

(3) Since the ink discharge relies on electrostatic acceleration, the initial velocity of the ink droplet is Om/S, and the velocity when it reaches the paper surface is relatively low by 41.

(4) In order to increase the electrostatic field, the cap between the nozzle and the recording paper must be made as small as 0.3 to 0.5 mm. For this reason, contact accidents between the nozzle and the paper are likely to occur.

(5) In order to control the discharge of ink (c droplets), it is necessary to turn on and off a high-voltage DC voltage for each nozzle according to print data, but it is difficult to control such a high-voltage DC voltage.

Now, in the present invention, the smaller the gap between the inkjet head and the recording paper 7, the lower the voltage of the high voltage DC power supply 9 can be. It is preferable to adjust it to .0. Gear like this.

Another advantage of the present invention is that it allows a relatively large drop.

In this embodiment, it is assumed that the counter electrode is cylindrical and also serves as a platen, but it may be rod-shaped or of other shapes.

The voltage of the high-voltage DC power supply is
In the case of No. 1, the voltage must be higher than the voltage at which the ink droplets start flying only by electrostatic attraction without applying any voltage to the piezoelectric element 5, but in the case of the present invention, the appropriate voltage is 1 or less. Ta.

3 According to the present invention, it is not necessary to discharge ink droplets using electrostatic attraction, so a relatively small electrostatic field is sufficient, and since there is no need to control this electrostatic field, control becomes very easy. .

Since the high-voltage DC power supply 9 flows only as much current as the ink droplets are charged, its current capacity is small, and a small one is sufficient.

With the inkjet recording apparatus according to the present invention, conventional three to three
The upper limit of ink droplet flight speed was 4 m/s, but it was easily reduced to 1
By exceeding 0 m/s, we were able to significantly reduce the deterioration and variation in door 1 positioning accuracy due to air flow, and also to prevent deterioration of the flight direction of ink droplets due to ink dripping, achieving high-quality recording. .

As mentioned above, according to the present invention, by simply adding a high-voltage 1α current power supply with a small current capacity to the conventional inkjet recording device of the drop-on-demand type,
The conventional ink droplet flight speed has been improved to over 2@ at once,
Door 1 seen in conventional mud, pour-on-demand recording equipment
An inkjet recording device can be obtained that prevents deterioration in positioning accuracy and deterioration in flight directionality due to ink dripping. Further, in the inkjet recording device according to the present invention, the piezoelectric element is
Since it is only necessary to discharge ink droplets, the negative charge of the piezoelectric element is reduced, and it has the advantage that it is possible to reduce the size of the piezoelectric element, and by extension, to achieve miniaturization and integration of the inkjet, tohe, and do itself. There is.

In the embodiments, a single nozzle has been described, but it goes without saying that this can also be applied to a multi-nozzle, and even in the case of a multi-nozzle,
Since the counter electrode and the high-voltage direct current source can coexist between each nozzle, there is no need to newly install one, and it also has the advantage of not increasing the cost of the device.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the configuration of a conventional drop-on-demand inkjet head, Figure 2 (a) is a diagram of the ink discharge state under normal conditions, and Figure 2 (b) is ink discharge when there is ink dripping at the nozzle tip. The state diagram, FIG. 3, is a cross-sectional view of the structure of an embodiment of the present invention. In the figure, l...Ejection chamber, 2...Ink droplet ejection orifice,
3... Ink supply hole, 4... Flexible upper plate,
5... Piezoelectric element, 6... Ink droplet, 7... Recording paper, 8... Counter electrode, 9... High voltage DC power supply. Representative Patent Attorney Shino Uchihara 1

Claims (1)

[Claims] An ink ejection chamber, an ink supply hole connected to the ink ejection chamber, an ink droplet ejection orifice connected to the ink ejection chamber at one end and open to the atmosphere at the other end, and a part of the wall of the ink ejection chamber. A flexible upper plate, a piezoelectric element affixed to the upper plate, a piezoelectric element drive circuit that applies electric pulses to the piezoelectric element, and a recording sheet disposed opposite the ink droplet ejection orifice. An inkjet recording apparatus comprising: a counter electrode disposed on the back side of the recording paper; and a high-voltage power source that applies a potential between the ink droplet ejection orifice and the counter electrode.