JPH10157163A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To print a high resolution image by superposing a pulse electrode on an individual electrode based on an image signal and flying thread-like ink from the tip of a needle electrode thereby flying the ink finely as compared with a case having no needle electrode to a recording medium in a stabilized direction. SOLUTION: A bias voltage is applied between a common electrode 8 and an individual electrode 2 at the time of starting print, and the tip at a needle electrode 3 projects slightly from the surface of an ink droplet. Consequently, thread-like ink flies from the tip of the needle electrode in response to a pulse electrode being superposed based on an image signal. Since the ink flies finely as compared with a case having no needle electrode 3 at a stabilized size, a high quality image can be printed. Furthermore, the needle electrode 3 can be kept in wet state entirely and constantly because it is oscillated and thereby the ink is fed stably while dealing with ink flight at single period.

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 printing an image by depositing ink droplets discharged from nozzle openings of a recording head on a recording medium.

[0002]

2. Description of the Related Art An ink jet recording apparatus of the type in which a small amount of ink droplets are ejected from a minute opening and an image is printed by a set of dots formed by depositing the ink droplets on a recording medium is used. In this configuration, ink is guided from a tank to an ink chamber connected to an opening, and kinetic energy is applied to the ink, whereby ink droplets are ejected from the opening and adhere to a recording medium to form dots.

One of the driving methods for applying kinetic energy to ink is to apply a voltage between an electrode provided in the vicinity of an opening and a common electrode with which a recording medium is in contact to discharge ink by electrostatic force (static method). Electro-suction system).

In this method, since the dot diameter on a recording medium can be controlled by pulse width modulation of an applied voltage, it has been attracting attention as a method for realizing a high-definition inkjet printer.

As an example of a recording head according to such a method, the technology described in Japanese Patent Application Laid-Open No. 49-1009038 discloses the shape of an opening of a recording head for discharging ink, the viscosity and surface tension of ink used. ing.

The technique described in Japanese Patent Application Laid-Open No. 56-28867 discloses that ink is caused to fly by a pulse voltage applied between a needle-like electrode and a counter electrode.

[0007]

In these systems, a high voltage of 2 to 3 kV is applied between an electrode or a needle electrode provided near an opening of a recording head and a common electrode to cause ink to fly by electrostatic force. Since the electric field concentrates on the opening and the vicinity of the needle electrode, the flying state changes depending on the amount of ink present at the place and the surface tension of the ink.

When a voltage is applied between a nozzle electrode and a common electrode as in the technique disclosed in Japanese Patent Application Laid-Open No. 49-1009038, a hemispherical ink droplet is formed at the tip of the nozzle. However, this is a state in which the viscosity and surface tension of the ink and the electrostatic force are balanced. At the moment when a large voltage is applied, the electrostatic force becomes larger than the surface tension of the ink and the thread-like ink flies from the tip of the hemispherical ink droplet. Is changed, the flying direction of the ink is determined by the start position of the change.

Normally, the ink changes from a portion closest to the counter electrode, but the shape may change from another position, and the ink may not fly to a desired position.

In the above-described technique, the flying direction of the ink is stabilized by defining the shape of the tip of the nozzle, but a sufficient effect has not yet been obtained.

As described in JP-A-56-28867, when a voltage is applied between the needle electrode and the common electrode to cause the ink to fly by electrostatic force, the ink is in contact with the needle. The ink will fly, but if the amount of protrusion of the needle from the opening surface is large, the ink will not reach the tip of the needle, so the ink will not fly, and if the amount of protrusion of the needle is small, thread-like ink will be formed. Instead, a large amount of ink flies onto the recording medium in contact with the common electrode.

In this configuration, the range of the optimum value of the amount of protrusion of the needle is
Since the viscosity of normal ink changes depending on the temperature, it is difficult to fly a stable amount of ink by changing the optimal protrusion amount of the needle depending on the viscosity. However, there is a problem that it is difficult to supply the ink sufficiently.

SUMMARY OF THE INVENTION It is an object of the present invention to form dots at desired positions by stabilizing the direction of ink ejection and to achieve high-definition images by stabilizing the amount of ink ejection. It is to provide a device.

It is still another object of the present invention to provide an ink jet recording apparatus capable of increasing the ink supply speed and causing the ink to fly at a high frequency.

[0015]

SUMMARY OF THE INVENTION A feature of the present invention is that a plurality of openings for discharging ink droplets, a common ink chamber adjacent to the openings, and a flow path connecting the openings to the common ink chamber. A recording head having an individual electrode and a needle electrode present at the center of the opening, a power supply for providing a common electrode at a position facing the recording head, and applying a potential difference between the common electrode and the individual electrode; An ink jet recording apparatus comprising: a power supply for applying a voltage to an individual electrode based on a signal; a power supply for applying a voltage between the individual electrode and a needle electrode; and means for vibrating the needle electrode. It is in.

According to such a configuration, in a printable state, an appropriate bias voltage is applied between the common electrode and the individual electrodes, and in this state, the ink swells hemispherically outside the opening. In.

The needle electrode is set at a position where the tip of the needle electrode comes out of the hemispherical ink surface, and is vibrated by a vibrator. Apply pulse voltage.

In this case, there are a case where the voltage applied to the individual electrode and the needle electrode is the same and a case where the needle electrode is set to a slightly higher potential depending on the properties such as the viscosity of the ink. Since the ejection amount of the ink changes in accordance with the time during which is applied, it is possible to form dots with gradation on the recording medium.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 8 shows the overall appearance of the ink jet recording apparatus. Reference numeral 7 denotes a recording medium such as paper.
Reference numeral 0 denotes an ink tank, 11 denotes a recording head, 12 denotes a recording head support member, 13 denotes a recording medium transport roll, 15 denotes a motor, and 16 denotes a recording medium guide.

The recording head 11 has a large number of openings (ink ejection ports) arranged at appropriate intervals, and is supported by a recording head support member 12 with the openings oriented in the horizontal direction. The recording media 7 are arranged so that the arrangement direction intersects the transport direction of the recording medium 7.

The recording medium 7 guided by a recording medium guide 16 is conveyed by a recording medium conveying roll 13 connected to a motor 15.

A common electrode (not shown) is provided below the recording medium transport roll 13, and a voltage (bias voltage) is applied between the common electrode and an individual electrode existing in the opening of the recording head 11. I have.

The recording head 11 moves from the ink tanks 10 to 1
The ink is guided to an opening formed in a size of 00 to 200 μm, and a pulse voltage based on an image signal is applied to an individual electrode present in the opening while being superimposed on the bias, and applied. Ink is ejected from the opening to execute printing.

In an ink jet recording apparatus capable of performing color printing, the recording head 11 includes cyan, magenta,
An opening group for four colors of yellow and / or black is formed.

An electric pulse for energizing a driving member for ejecting ink droplets from each opening is given in accordance with print data given from a host device such as a personal computer, and a control device (not shown) in the ink jet recording apparatus.
Generated by

This control device is composed mainly of a microcomputer, controls the generation of electric pulses in accordance with print data supplied from a host device to generate ink droplets from the recording head 11, and rotates the motor 15 for recording. It has a function of driving the medium transport roll 13.

Next, a method of ejecting ink will be described in detail below.

FIG. 1 is a sectional view of a recording head of an ink jet recording apparatus used in the present invention.

Reference numeral 1 is a plate, 2 is an individual electrode, 3
Is a needle electrode, 4 is a common ink chamber, 5 is a partition, and 6 is a vibrator. The ink enters the common ink chamber 4 from the ink tank, and is guided to the openings formed in the numerous individual electrodes 2 ahead. . Note that the openings need not necessarily be individual electrodes.

Then, the individual electrodes 2 described in this embodiment
Has a diameter of about 100 to 300 μm.

An individual electrode 2 is provided in a flow path connecting the common ink chamber and the opening, and a needle electrode 3 is provided at the center of the individual electrode 2. The diameter of the needle electrode is 40 to 100 μm.
m, and the needle tip is preferably formed at an acute angle.

FIG. 2 is a sectional view taken along the line aa ′ in FIG. 1. A distribution line connected to the individual electrode 2 is formed on the surface of the plate 1.

The needle electrodes 3 are connected to the partition walls 5 so as to be able to individually apply signal voltage pulses.

The partition 5 is configured to vibrate by a vibrator 6, and the vibrator 6 is preferably a laminated piezo element.

The stacked piezo element is obtained by stacking piezo elements in the thickness direction and applying a voltage in the stacking direction of the individual piezo elements to obtain a large displacement in the stacking direction. Will be described later together with the description of the ink discharge process.

When ink is ejected from the opening, a voltage is applied between the individual electrode 2 and the common electrode, and the amount of ink flying is determined by the application time. Images can be printed,
The process of flying the ink will be described in more detail with reference to FIG.

FIG. 6A shows a state during non-printing, in which no voltage is applied, and FIG. 6B shows a state in which an appropriate bias voltage is applied between the individual electrode 2 and the common electrode. In the applied state, the ink forms a curved surface from the opening and swells outward, and the magnitude of this bias voltage is about 2 kV when the distance between the two electrodes is 1 mm.

FIG. 6 (c) shows the case where a voltage higher than that of FIG. 6 (b) is applied, and shows the moment when the thread-like ink is ejected from a part of the hemispherical ink. 0.4 to 2.8 kV.

FIG. 6D shows a state in which the ink is flying toward a recording medium (not shown) after a lapse of time as compared with FIG. 6C. The thickness depends on the magnitude of the applied voltage, and fine dots can be formed on the recording medium when the ink is flying in a thread shape.

When a voltage higher than that shown in FIG. 6D is applied, a large amount of ink may be ejected from the entire opening to contaminate the recording medium or the inside of the printing apparatus. Is applied between the individual electrode and the common electrode to form fine dots by flying the thread-like ink.

FIG. 5 shows the energy of the ink droplet in the processes of FIGS. 6 (a) to 6 (d).

In the state (a), no voltage is applied, and the potential energy is set to zero.

In the state (b), the ink droplet forms a curved surface and swells outward from the opening, and the electrostatic force acting on the ink and the surface tension are balanced.

When the voltage applied between the individual electrode 2 and the common electrode is further increased, the ink grows hemispherically,
In the state (c), the ink flies in a thread form from a part of the hemisphere. This moment is when the state moves away from the state with the highest potential energy to the state with the lowest potential energy.

Here, the state where the potential energy is the largest is a state of the limit where the surface tension acting on the ink and the electrostatic force are balanced. If the limit is exceeded, a change in the shape of a part of the spherical surface occurs (the protrusion is formed). Formed), the direction in which the surface tension acts changes, and the shape of the ink further changes accordingly, the electrostatic force becomes larger than the surface tension, and the ink becomes a string and flies in the direction of the common electrode.

Finally, the state (d) is a state where the potential energy is stable.

As described above, the state shown in FIG. 6C is a limit state where the surface tension acting on the ink and the electrostatic force are balanced, and the shape of the ink is hemispherical.

Normally, from this state, a projection is formed on the hemispherical ink surface at a position farthest from the opening, that is, on a spherical surface at a position closest to the opposing electrode, and the ink is formed in a thread form toward the opposing electrode. To fly.

FIG. 7A shows a normal ink flying state. However, since the state of FIG. 6C is an unstable state, a projection is necessarily formed on the spherical surface closest to the counter electrode. It is not always formed.

If the projection is formed at a position other than the position closest to the counter electrode, the thread-like ink flies off the desired position as shown in FIG. 7 (b), deteriorating the image quality. Occurs.

In order not to cause such a problem,
It is effective to arrange the needle-like member at the center of the opening so that the thread-like ink flies from the ink surface closest to the counter electrode.

FIG. 3 shows an example of a method of installing the needle-like members. A bias voltage B is applied between the common electrode 8 and the individual electrodes 2.

Further, a pulse voltage is applied to the individual electrode 2 by the control device 9 based on the image signal, and the needle electrode 3 can superimpose a potential on the individual electrode 2 and is installed at the center of the opening. You.

The shape of the ink droplet when the bias voltage is applied slightly differs depending on the presence or absence of the needle electrode 3, and the voltage at which the ink starts flying also changes.

The potential superposed on the needle electrode with respect to the individual electrode is 0 to 100 V, and depends on the viscosity and electric resistance of the ink used.

Next, the details of the needle electrode 3 will be described. If the amount by which the needle electrode 3 protrudes from the opening surface is too small, the purpose of installing the needle electrode 3 cannot be attained. Does not fly, because ink is not supplied to the needle tip.

Therefore, there is an appropriate value for the amount by which the needle electrode 3 protrudes from the opening surface, and it is set to about the radius of the opening. This appropriate value depends on the diameter of the opening, the viscosity of the ink used, the surface tension, and the like.

At the start of printing, a bias voltage is applied between the common electrode 8 and the individual electrode 2 so that the tip of the needle electrode 3 slightly protrudes from the surface of the ink droplet and is superimposed based on the image signal. The thread-like ink flies from the tip of the needle electrode in response to the applied pulse voltage.

In this case, since the ink flies finer and more stably than when the needle electrode 3 is not present,
High quality images can be printed.

Further, since the needle electrode 3 is vibrated, the entire needle electrode can be kept in a wet state at all times, so that stable ink supply can be performed, and it is possible to cope with ink flying in a short cycle. .

In the technique disclosed in Japanese Patent Application Laid-Open No. 56-28867, only a voltage is applied between the needle electrode and the common electrode, so that a hemispherical ink droplet is not formed, and the flow of ink toward the tip of the needle electrode is reduced. It is weak and it is difficult to fly ink in a short period even when the needle is vibrated. In addition, the installation range and the vibration range of the needle electrode are narrowed, and it is difficult to stably fly the ink. However, according to the present invention, these problems can be solved.

FIG. 4 shows a power supply arrangement different from that shown in FIG. 3, in which a negative bias voltage is applied to the common electrode 8 in the printing state.

The image signal is sent to the control unit 9 based on the image signal.
The method of superimposing the voltage when the ink flies is the same as that described with reference to FIG.

In FIGS. 3 and 4, the voltage application method is set such that the potential on the ink side is more positive than the common electrode, but the polarity depends on the charging polarity of the colorant contained in the ink. Therefore, the potential on the ink side may be set to be more negative than the common electrode.

[0066]

According to the present invention, an appropriate bias voltage is applied between the common electrode and the individual electrode to make the ink bulge out of the opening in a hemispherical shape, and the ink is swollen based on the image signal. The pulse voltage is superimposed on the individual electrode so that the thread-like ink flies from the tip of the needle electrode, so that the ink flies toward the recording medium in a thinner and more stable direction than when no needle electrode is present. Therefore, there is an effect that a high-definition image can be printed.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view showing an embodiment of an ink jet recording head according to the present invention.

FIG. 2 is a transverse cross-sectional view of the inkjet recording head shown in FIG.

FIG. 3 is a diagram showing an example of a power supply wiring in the ink jet recording head shown in FIG.

FIG. 4 is a diagram showing an example of power supply wiring in the ink jet recording head shown in FIG.

FIG. 5 is a diagram illustrating an energy state in a process of discharging ink.

FIG. 6 is a diagram illustrating a process of discharging ink.

FIG. 7 is a diagram illustrating an ink ejection state.

FIG. 8 is an external view of an inkjet recording apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Plate, 2 ... Individual electrode, 3 ... Needle electrode, 4 ... Common ink chamber, 5 ... Partition wall, 6 ... Vibrator, 7 ... Recording medium, 8 ... Common electrode, 9 ... Control device, 10 ... Ink tank, 11 ... Recording head, 12 ... Recording head support member, 13 ... Recording medium transport roll, 15 ... Motor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshinobu Fukano 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Akira Shimada 7-1 Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Akira Sasaki 1-1-1, Higashitagacho, Hitachi City, Ibaraki Pref.Hitachi, Ltd.Electrical Equipment Division Taga Headquarters (72) Inventor Tetsuro Akasaki Ibaraki 1-1-1, Higashitaga-cho, Hitachi City, Hitachi, Ltd.Electrical Equipment Business Division, Hitachi, Ltd. Inside the Taga Headquarters (72) Inventor Takuo Kawaguchi 1-1-1, Higashi Taga-cho, Hitachi City, Hitachi City, Ibaraki Prefecture, Japan Inside the department

Claims (7)

[Claims] A plurality of openings for discharging ink droplets, a common ink chamber for temporarily storing ink to be ejected from the openings, and individual electrodes existing in a flow path connecting the common ink chamber and the individual openings. A recording head having an ink supply passage connecting the common ink chamber from the ink tank, a common electrode provided at a position facing the recording head, and applying a voltage between the individual electrode and the common electrode to form ink. An ink jet recording apparatus for performing printing by flying, wherein a needle electrode electrically connected to an individual electrode is provided at the center of an opening, and a vibration member for vibrating the needle electrode is provided. . 2. The ink jet recording apparatus according to claim 1, wherein a needle electrode provided at the center of the opening is set to a higher potential than an individual electrode. 3. The ink jet recording apparatus according to claim 1, wherein the potential of the individual electrode is increased at the start of printing, a voltage is applied between the common electrode and the individual electrode, and the ink is discharged based on the image signal. An ink jet recording apparatus which controls so that a voltage pulse is superimposed on a corresponding individual electrode when discharging. 4. An ink jet recording apparatus according to claim 1, wherein the potential of the common electrode is increased at the start of printing, a voltage is applied between the common electrode and the individual electrodes, and the ink is discharged based on the image signal. An ink jet recording apparatus, which controls so that a voltage pulse is applied to a corresponding individual electrode at the time of ejection. 5. The ink jet recording apparatus according to claim 1, wherein the needle electrode is projected from the opening surface to a length corresponding to a radius of the opening. 6. An ink jet recording apparatus according to claim 1, wherein the control is performed so as to vibrate the needle electrode simultaneously with the start of printing. 7. The ink jet recording apparatus according to claim 1, wherein the amount of ink flying is controlled by changing the pulse width of a voltage applied to the individual electrode.