JP2880008B2 - Ink jet recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus for recording characters, figures, etc. on a recording material by discharging ink from minute openings.

[0002]

2. Description of the Related Art In recent years, printers using an ink jet recording system have been actively used as terminal devices for personal computers and CAD. Among these ink jet recording methods, there is known a method of performing recording by generating bubbles, mist, and the like using an electrothermal conversion element. These are roughly classified into two types: one is a method in which ink is rapidly heated by a heating resistor element to generate bubbles, and the ink is ejected by using the force, and the other is a method in which ink is discharged between electrodes. Is a method in which a potential is applied to the conductive ink present in the ink to generate bubbles or mist due to heat generation or electrolysis of the ink itself, and recording is performed using the force. The latter is described, for example, in U.S. Pat. No. 3,179,042 (1965), JP-A-59-214659, JP-A-60-196356, and the like. Here, the operation will be described by taking JP-A-59-214659 as an example.

FIG. 4 shows the operation of the ink jet head disclosed in Japanese Patent Application Laid-Open No. Sho 59-214659. The ink ejection port 206 is formed in the nozzle substrate 201, and a pair of electrodes 202 and 203 facing in the radial direction are provided in the ink ejection port 206 slightly inside from the tip end thereof. The electrodes 202 and 203 are connected to a DC signal source 208.

Now, when the aqueous ink 204 is filled in the ink discharge port 206 (a) and a signal from the DC signal source 208 is applied, bubbles 205 are generated on the surfaces of the electrodes 202 and 203 by electrolysis (b). ). The bubble 205 grows further and pushes forward ink to the front (c), and the droplet 207
(D). By repeating this series of operations, ink is ejected and printing is performed.

In US Pat. No. 3,179,042 and Japanese Patent Application Laid-Open No. 60-196356, bubbles or mist are generated using Joule heat, and the construction and operation are almost the same.

[0006]

One of the biggest problems of the above-mentioned ink jet recording method is that ink ejection is unstable. This is caused by the fact that the generation of bubbles is not constant. In terms of phenomena, variations in the maximum volume achieved by bubbles, fluctuations in the locations where bubbles are generated, changes in the amount of ink discharged due to the generation of multiple bubbles, etc. Bending, satellite drops and dust are likely to occur. Therefore, how to generate bubbles stably has been a major problem of the prior art. Another issue is how to lower the drive voltage,
Another problem is that electrode consumption is minimized and power consumption is also reduced.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention provides an ink jet recording method in which a potential is applied to a conductive ink existing between electrodes to generate bubbles by the heat generation or electrolysis of the ink itself, and to perform recording using the force. It is an object of the present invention to provide an ink jet recording apparatus which stably generates air bubbles stably, provides uniform recording characteristics, and realizes low voltage driving.

[0008]

According to the present invention, in order to achieve the above object, a pair of electrodes are provided around both outer surfaces of an ink discharge port formed on an insulating nozzle plate and connected to a signal source. In addition, one side of the ink ejection port is communicated with the ink chamber, and a head drive signal having a repetitive waveform of a plurality of times is applied from a signal source to a single image signal within a predetermined time. Things.

[0009]

According to the present invention, the current density in the ink discharge port can be concentrated at the center of the central axis of the ink discharge port to stably generate bubbles at a low driving voltage, and the electrode consumption is reduced. can do.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is an enlarged schematic cross-sectional view of the vicinity of an ink discharge port of a recording head of an ink jet recording apparatus according to an embodiment of the present invention. 1
Reference numeral 01 denotes an ink chamber, which is composed of a case main body 102 and a thin nozzle plate 103 made of an insulating material (polyimide) for closing the front surface thereof. Reference numeral 104 denotes a ventilation hole for communicating the ink chamber 101 with the outside air. Reference numeral 105 denotes an ink ejection port formed in the nozzle plate 103. 106 and 107 are a pair of donut disk-shaped electrodes provided around the outside of the ink discharge port 105 on both surfaces of the nozzle plate 103. Electrodes 106,
Reference numeral 107 denotes copper plated with a platinum-based metal, which is connected to a signal source 108. In the ink chamber 101, a conductive ink 1 having a specific resistance of 1000 Ωcm or less is provided.
09 is accommodated. The ink 109 in the ink discharge port 105 is normally held at the outer edge of the outer electrode 106.

In such a configuration, when a signal voltage is applied from the signal source 108, a current flows between the electrodes 106 and 107 via the ink 109 in the ink discharge port 105. As shown in FIG. 2, the applied signal voltage has a repetitive waveform (sine wave) several to several tens of times within a certain time t for one image signal, during which one ink droplet 111 flies. Then, one dot is formed. By using such an AC signal form, the current density tends to concentrate at the center of the ink ejection port 105, and the driving voltage is reduced and the generation of bubbles is stabilized. The decrease in the drive voltage largely depends on the number of repetitions of the repetitive waveform. FIG. 3 shows the relationship. As the number of repetitions increases, the minimum drive voltage (threshold voltage) at which ink can be ejected sharply drops, and approaches a substantially constant value after about five times. Further, as the number of repetitions increases, the number of switching between the electrodes 106 and 107 increases, and the consumption of the electrodes due to the chemical reaction decreases. It should be noted that the same effect can be obtained not only with a sine wave but also with a rectangular wave, sawtooth wave or the like.

In addition to this effect, the current is applied to the electrode 10
6 and 107 have the shape of a donut disk, so that they wrap around the ink ejection port 105 from the periphery along the central axis of the ink ejection port 105. Therefore, the ink ejection port 105
The current density on the cross section of the ink ejection port 105 in the direction perpendicular to the central axis of the curve has a gradient in the radial direction and becomes uniform in the circumferential direction. As a result, bubbles 1 generated by Joule heat
10 is generated and grown more stably so as to have its center on the central axis of the ink discharge port 105, and extrudes the ink 109a on the front surface of the bubble 110 to the outside to fly as a droplet 111, thereby achieving stable recording. Can be performed.

If the diameter of the circular openings of the electrodes 106 and 107 is larger than the diameter of the ink
5, the gradient of the current density in the radial direction becomes large, and the bubble 110 can be formed more stably at the center. In the opposite case, although the stability is slightly reduced, the value of the current density itself is increased, and the generation of the bubbles 110 can be performed at a lower voltage. As for the thickness of the electrodes 106 and 107, the thickness of the outer electrode 106 particularly affects the characteristics. In the electrode 106, the only portion that contacts the ink 109a is the inner wall portion of the circular opening.
, The current density increases as the thickness increases, and bubbles 110 are easily generated.

The stability of ink ejection is also affected by the degree of wetting of the surface of the electrode 106. Therefore, a water-repellent film such as ethylene tetrafluoride may be coated on the surface of the electrode 106 in order to secure the stability of ink ejection.

As described above, according to the above embodiment, a pair of electrodes 106 and 107 are provided around the outer surfaces of the ink discharge ports 105 formed in the nozzle plate 103 and connected to the signal source 108, respectively. From 108, a drive voltage having a repetitive waveform (sine wave) of 5 times or more is applied to one image signal within a certain time t,
5 is connected to the ink chamber 101, so that when a signal voltage is applied between the electrodes 106 and 107, the current density in the ink ejection port 105 is reduced by the center axis of the ink ejection port 105. It is possible to generate bubbles stably by concentrating on the parts,
Consumption can be suppressed and the driving voltage can be reduced.

In the above embodiment, the ink ejection port 10
5 shows the case of one mono-nozzle head, but in the case of a multi-nozzle having a plurality of ink ejection ports,
A similar effect can be obtained by dividing one of 6, 107 into one and dividing the other.

In the above embodiment, the ink ejection port 10
5 shows a configuration in which one side of the ink discharge port communicates directly with the ink chamber 101. However, a type in which one side of the ink discharge port communicates with the ink chamber via a pipe or the above-described JP-A-59-21 is used.
It is needless to say that the present invention can be applied to a recording head of a type having a pair of electrodes inside an ink ejection port disclosed in Japanese Patent No. 4659 or the like.

[0018]

As described above, according to the present invention, a pair of electrodes are provided around the outer surfaces of both sides of the ink discharge port formed in the insulating nozzle plate, and a plurality of repetitions are performed for one image signal within a predetermined time. By connecting to a head drive signal source having a waveform and connecting one side of the ink discharge port to the ink chamber, when a signal voltage is applied between the electrodes, the current density in the ink discharge port is reduced by the ink. The stable generation of air bubbles can be secured by concentrating on the center of the central axis in the discharge port,
Stable recording characteristics can be obtained, the consumption of the electrodes can be controlled, the driving voltage can be reduced, and the effect is great.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a recording head of an ink jet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of a head drive signal in the device.

FIG. 3 is a diagram showing a repetition frequency characteristic of the head drive signal.

FIG. 4 is a schematic view showing the principle of a conventional ink jet recording apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Ink chamber 102 Case main body 103 Nozzle plate 104 Vent hole 105 Ink ejection port 106, 107 Electrode 108 Signal source 109 Ink 110 Bubble 111 Droplet

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/05

Claims (1)

(57) [Claims] An electric potential is applied to the conductive ink existing between the electrodes.
The heat generated by the ink itself or the
Inkjet that generates bubbles and uses the force to record
In Tsu DOO recording method, an ink ejection port formed on an insulating nozzle plate, and a pair of electrodes arranged on the outside ambient of the ink discharge port be in both sides of the nozzle plate, the pair of electrodes An ink-jet head that is connected and has a head drive signal source having a waveform that is repeated a plurality of times within a certain period of time for one image signal, and an ink chamber that communicates with the ink ejection port and stores ink having a specific resistance of 1000 Ωcm or less. Recording device.