JP2842336B2 - Electrostatic inkjet 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 electrostatic ink jet recording apparatus, and more particularly, to an electrostatic ink jet recording apparatus which performs recording by electrostatically attaching toner particles to a recording medium.

[0002]

2. Description of the Related Art A conventional electrostatic ink jet recording apparatus is disclosed in Japanese Patent Application Laid-Open No. 1-26062. As shown in FIG. 5 , this is achieved by ejecting ink from the ink ejection port 58 using electrostatic attraction to form the recording paper P.
A plurality of recording electrodes 57 disposed inside the ink ejection opening 58, and the plurality of recording electrodes 57.
And a plurality of control electrodes 56 respectively arranged in a state insulated from the recording electrode 57 and a counter electrode 60 provided on the back surface of the recording paper P.

[0003] During ink ejection, an electrostatic field is first generated between the control electrode 56 and the recording electrode 57, thereby urging a stress that pushes the ink in the ink tank 52 toward the ink ejection port 58. Then, in addition to this stress,
An electrostatic field is generated between the ink and the counter electrode 60, and the ink is ejected by superimposing the electrostatic force.

More specifically, the control electrode 56 and the recording electrode 57 constitute a pair of parallel flat plates, and there is a liquid level of ink between the two electrodes. Therefore, when a potential difference is given between the control electrode 56 and the recording electrode 57 by giving a control voltage pulse to the control electrode 56, the ink moves to the ink ejection port 58 side due to the electric field between the two electrodes. This is due to the effect of stress acting on the interface between materials having different dielectric constants when the direction of the electric field is parallel to the interface. The ink is pushed out to the front surface of the ink ejection port 58 by this stress. When a voltage is applied between the recording electrode 57 and the counter electrode 60 from this state, ink is ejected from the ink ejection port 58 by an electrostatic field generated between the electrodes 57 and 60, and the ink is ejected from the counter electrode 60 side. To the recording medium 9.

[0005]

However, in the above conventional example, a potential difference is given between the control electrode and the recording electrode by giving a control voltage pulse to the control electrode, and the meniscus of the insulating ink is given by the electric field between the two electrodes. Is moved to the ink ejection port side, so that a stable ink meniscus cannot be formed, the responsiveness of the ink meniscus is poor, and the meniscus cannot follow during high-speed printing. Further, in the above-described conventional example, since the liquid ink itself is ejected, bleeding or dust occurs in printing, which causes a disadvantage that printing quality is deteriorated. Further, when a bias potential is applied to the counter electrode, there is a disadvantage that a spark is generated between the control electrode and the counter electrode for some reason, thereby damaging the head.

[0006]

An object of the present invention is to improve the disadvantages of the above-mentioned prior art, and in particular, to prevent the occurrence of voltage leakage when a high voltage pulse is applied to the ejection electrode, and to reduce the pulse voltage applied to the ejection electrode. It is another object of the present invention to provide an electrostatic ink jet recording apparatus which can reduce high voltage switching by reducing the number of recordings and realize high print quality recording comparable to electrophotographic recording.

[0007]

To achieve the above object, according to the first aspect of the present invention, there is provided an ink chamber for storing ink containing charged toner particles, and an opening communicating with the ink chamber and opening to the outside. An ink discharge section, a discharge electrode provided with a tip part of the ink discharge section somewhat protruding from the ink discharge section, an electrophoretic electrode disposed outside the ink chamber so as to surround the discharge electrode of the ink chamber, and a recording medium. And a counter electrode disposed to face the ink discharge unit with the interposition therebetween. In addition, a migration voltage source for applying a predetermined migration voltage to the migration electrode and an ejection voltage source for applying a pulse voltage to the ejection electrode are provided. Furthermore, a bias voltage source for applying a bias potential having a polarity opposite to the potential of the toner particles is connected to the counter electrode.
With continued to, the counter electrodes have a more high-resistance 1MΩ
To do .

For this reason, according to the present invention, only the charged toner particles are extracted from the tip of the ink meniscus by the high electric field formed between the discharge electrode and the counter electrode. That is, recording is performed by discharging in the direction of the recording medium. Further, since the potential difference between the discharge electrode and the counter electrode required for sufficient toner discharge is constant, the bias voltage having the opposite polarity to that of the toner particles is applied to the counter electrode, compared with the case where no bias is applied to the counter electrode. As a result, the pulse voltage applied to the ejection electrode is reduced. Furthermore, even if the potential difference between the discharge electrode and the counter electrode exceeds the dielectric strength of the space between the electrodes for some reason, the occurrence of sparks is prevented by the high resistance of the counter electrode itself.

Further, in the invention according to claim 2, the above-mentioned bi-directional
The ass voltage source has a function of selectively switching and connecting two different bias voltages having opposite polarities to the potential of the toner particles to the counter electrode . For this reason, in the present invention, the potential difference between the ejection electrode and the counter electrode is selectively set in two stages.

Further, according to the third aspect of the present invention, the discharge electrode is disposed on a lower surface portion in the ink discharge portion.
The configuration is adopted.

Accordingly, the above-mentioned object is to be achieved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
4 through FIG.

The electrostatic ink jet recording apparatus shown in FIGS. 1 and 2 has an ink chamber 2 for storing ink containing charged toner particles, and an ink discharge opening communicating with the ink chamber 2 and opening to the outside. (Discharge opening) 4, a discharge electrode 5 whose tip is somewhat protruded inside the ink discharge unit 4, and a discharge electrode 5 of the ink chamber 2 which is disposed outside the ink chamber 2 so as to surround the discharge electrode 5. And a counter electrode 10 disposed opposite to the ink discharge unit 4 with the recording medium P interposed therebetween. The migration electrode 8 is provided with a migration voltage source 11 for applying a predetermined migration voltage to the migration electrode 8. In addition, the ejection electrode 5 includes the ejection electrode 5.
And a discharge voltage source 12 for applying a pulse voltage to the power supply. Further, a bias voltage source 15 for applying a bias potential having a polarity opposite to the potential of the toner particles to the counter electrode 10 is connected to the counter electrode 10.

More specifically, in the present embodiment, the ink chamber 2 is provided with a slit-shaped discharge opening 4 at a part thereof, and the ink 1 is held inside.
The ink 1 is obtained by dispersing colored thermoplastic resin particles (toner) together with a charge control agent in a petroleum organic solvent (isoparaffin). The toner is positively charged to a positive polarity by a zeta potential. ing. The ink chamber 2 has an ink discharge port 13 and an ink supply port 14.
Is provided. The ink discharge port 13 and the ink supply port 14 are respectively connected to an ink tank (not shown) via a tube, and the ink 1 in the ink chamber 2 is 1 cm.
A negative pressure of about H ₂ O is applied, and forced ink circulation is energized.

The tip of the discharge electrode 5 is 8
It is provided so as to protrude outside by about 0 μm to 100 μm. An ink meniscus Me is formed between the protruding ejection electrode 2 and the ejection opening 4 due to the surface tension of the ink. Further, the discharge electrode 5 is provided on a lower surface portion in the discharge opening 4. The discharge electrode 5 is formed by electroforming a conductive material such as Cu or Ni, and has a width of 50.
It is about μm.

The counter electrode 10 is partially connected to a bias voltage source 15 for supplying a bias potential having a polarity opposite to the potential of the toner particles. The bias voltage source 15 has two different bias voltages Vb having opposite polarities to the potential of the toner particles.
1 and Vb2 are selectively switched and connected. The switching of the bias voltage is performed according to, for example, a print control code received from a higher-level device. Also,
The counter electrode 10 is formed in a roller shape by a conductive rubber member, and the roller itself has a resistance of about 1 MΩ or more,
Thus, a high resistance circuit is configured.

Next, the printing operation according to the present embodiment will be described.

During recording, a voltage having the same polarity as the zeta potential of the toner is applied to the migration electrode 8 by the migration voltage source 11,
The toner particles in the ink supplied from the ink supply port 14 are transported by electrophoresis to the vicinity of the ejection electrode 5. Subsequently, when a high-voltage pulse corresponding to the recording signal is applied to the ejection electrode 5 by the ejection voltage source 12, the electric field concentrates on the tip of the ejection electrode 5, that is, the tip of the ink meniscus Me. The charged toner group is pulled out from the tip of the ink meniscus Me, and becomes the toner group 3 and is discharged toward the counter electrode 10, that is, toward the recording paper.

FIG. 3B shows the potential states of the discharge electrode 5 and the counter electrode 10 required for discharging the toner group.

Regardless of the present embodiment, for example, the counter electrode 10
Is directly grounded, as shown in FIG. 3A, the toner group is discharged by setting the potential difference between the discharge electrode 5 and the counter electrode 10 to Vp1. However, in such a case, it becomes necessary to apply the high voltage Vp1 to the ejection electrode 5.

On the other hand, when the bias potential Vb (<0) is applied to the opposing electrode 10 as in this embodiment, FIG.
As shown in (b), by applying a voltage Vp2 lower than Vp1 to the discharge electrode 5, the toner group can be discharged. Here, Vp2−Vb = Vp1. Thus, by applying the bias potential to the counter electrode 10, the pulse voltage applied to the ejection electrode 5 can be reduced.

The discharged toner group 3 adheres to the recording medium P, and a print image is formed on the recording medium P by repeating the above recording operation. Thereafter, the toner adhered to the recording medium P is heated by a heater (not shown) and is thermally fixed.

On the other hand, after the recording operation, only the toner particles in the ink are consumed, and the toner concentration in the vicinity of the discharge electrode 5 decreases. Therefore, it is necessary to replenish the toner particles in the vicinity of the discharge electrode 5 in order to continue stable discharge. There is. In the present embodiment, the charged toner in the ink supplied from the ink supply port 14 is electrophoresed by an electric field generated between the migrating electrode 8 and the discharge electrode 5, and is conveyed to the vicinity of the discharge electrode 5. The surplus ink 1 is discharged from the ink discharge port 13.

As described above, according to the present embodiment, the high electric field formed between the ejection electrode 5 and the counter electrode 10
Only the charged toner particles are drawn out from the tip of the ink meniscus Me, and are discharged as a toner group in the direction of the counter electrode 10, that is, in the direction of the recording medium P, so that recording is performed. P, which can prevent print bleeding or the like which is noticeable in the conventional ink jet printing in which the liquid ink is directly jetted. High printing quality can be realized.

Here, in the above printing operation, if the counter electrode 10 is a perfect conductor, if the distance between the ejection electrode 5 and the counter electrode 10 is less than a certain value, the electrodes 5, 10
Sparks are generated between the electrodes, and the heat generated at the time of the sparks may melt the metal portions of the discharge electrode 5 and the counter electrode 10 and cause a problem that the function as a head is lost.

On the other hand, when the opposing electrode 10 itself has a resistance as in the present embodiment, the potential difference between the discharge electrode 5 and the opposing electrode 10 due to some reason causes a difference in the space between the electrodes 5 and 10. Even if the dielectric strength is exceeded, the counter electrode 1
The generation of spark is prevented by the resistance of the electrode 0 itself, and the discharge electrode 5 and the counter electrode 10 can be protected from destruction by the spark.

Next, switching control between normal printing and draft printing in the above printing operation will be described with reference to FIG. Draft printing refers to a printing operation performed at a lower printing density than usual, and generally employs a method of thinning out ejection dots or a method of reducing the amount of toner particles per ejection dot.

The opposite electrode 10 has, for example, two different bias potentials Vb1 (<0), opposite in polarity to the potential of the toner particles, according to a print control code or the like input from a host device.
Vb2 (<0) is selectively applied. When the normal printing is selected, the bias potential Vb2 is applied to the counter electrode 10. Here, Vp2−Vb2 = Vp1. In this case, a necessary and sufficient amount of toner particles is ejected due to the potential difference between the ejection electrode 5 and the counter electrode 10, and normal dark printing can be performed.

On the other hand, when draft printing is selected,
A bias potential Vb1 whose absolute value is lower than the normal bias potential Vb2 is applied to the counter electrode 10. In this case, since the potential difference between the discharge electrode 5 and the counter electrode 10 is smaller than usual, a sufficient amount of toner particles required for printing is not discharged, and as a result, draft printing is performed.

As described above, according to the present embodiment, only the charged toner particles are extracted from the tip of the ink meniscus Me by the high electric field formed between the ejection electrode 5 and the counter electrode 10, and this is extracted. Counter electrode 1 as toner group
Since the recording is performed by discharging in the direction of 0, that is, in the direction of the recording medium P, only the toner particles in the ink 1 can be adhered to the recording medium P. Therefore, in the conventional inkjet printing in which the liquid ink is directly ejected, It is possible to prevent noticeable printing bleeding and the like, thereby realizing high printing quality comparable to that of the electrophotographic method, even though the ink jet method is used.

By applying a bias potential to the counter electrode 10, the pulse voltage applied to the discharge electrode 5 can be reduced, and the switching of the applied voltage pulse can be performed at high speed, thereby performing high-speed printing. be able to.

Further, since the counter electrode 10 is a high resistance circuit, the potential difference between the discharge electrode 5 and the counter electrode 10 may exceed the dielectric strength of the space between the electrodes 5 and 10 for some reason. Also, generation of a spark is prevented by the resistance of the opposing electrode 10 itself, and the discharge electrode 5 and the opposing electrode 10 can be protected from destruction by the spark.

In addition, since two different bias potentials having opposite polarities to the potential of the toner particles are switched and connected to the counter electrode 10, the discharge electrode 5 and the counter electrode 10 are connected.
The potential difference between the two can be set in two stages, so that normal printing and draft printing can be selectively performed.

Here, in the present embodiment, the meniscus forming portion 7 is constituted by the ejection opening 4 and the ejection electrode 5.
Further, the meniscus forming section 7 may be separately formed by a wire or the like. Also, the counter electrode 10 may be a high resistance circuit using a metal flat plate and a resistor inserted between the metal flat plate and the bias voltage source 15 without depending on the present embodiment.

[0035]

The present invention is constructed and functions as described above. According to this, only the toner particles charged from the tip of the ink meniscus by the high electric field formed between the ejection electrode and the counter electrode are provided. The recording is performed by ejecting the toner as a toner group in the direction of the counter electrode, that is, in the direction of the recording medium, so that only the toner particles in the ink can be adhered to the recording medium, thereby directly ejecting the liquid ink. It is possible to prevent bleeding or the like of the printing that has been remarkably appeared in the conventional inkjet printing, thereby,
Despite the ink jet method, it is possible to realize high printing quality comparable to the electrophotographic method.

Further, by applying a bias potential having a polarity opposite to that of the charged toner to the counter electrode, the pulse voltage applied to the discharge electrode can be reduced, and the switching of the applied voltage pulse can be performed at high speed. High-speed printing can be performed.

Further, since the counter electrode is a high resistance circuit,
Even if the potential difference between the discharge electrode and the counter electrode for some reason exceeds the dielectric strength of the space between the electrodes, sparks are prevented by the resistance of the counter electrode itself, and the discharge electrode and the counter electrode are connected. Can protect against destruction by sparks.

In particular, in the second aspect of the invention, since two different bias potentials having opposite polarities to the potential of the toner particles are switched and connected to the counter electrode, the potential difference between the discharge electrode and the counter electrode is set in two stages. Can be set,
It is possible to provide an unprecedented excellent electrostatic ink jet recording apparatus capable of selectively performing normal printing and draft printing.

[Brief description of the drawings]

FIG. 1 is a partially cutaway plan view showing an embodiment of the present invention.

FIG. 2 is a partially cutaway side view showing one embodiment of the present invention.

FIG. 3 is a diagram showing a voltage applied to an ejection electrode when the toner group is ejected. FIG. 3A is a comparative example, and FIG.
(B) shows the applied voltage in the present embodiment.

FIG. 4 is a diagram illustrating control for switching between a normal print mode and a draft print mode in the embodiment shown in FIG. 1;

FIG. 5 is a perspective view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink 2 Ink chamber 3 Toner group 4 Discharge opening (ink discharge part) 5 Discharge electrode Me Ink meniscus 7 Meniscus formation part 8 Migration electrode P Recording medium 10 Counter electrode 11 Migration voltage source 12 Discharge voltage source 13 Ink discharge port 14 Ink Supply port 15 Bias voltage source

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Hagiwara 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Hitoshi Minemoto 5-7-1 Shiba, Minato-ku, Tokyo Japan Electric Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/06

Claims (3)

(57) [Claims] 1. An ink chamber for containing ink containing charged toner particles, an ink discharge section communicating with the ink chamber and opening to the outside, and a tip end of the ink discharge section protrudes somewhat into the ink discharge section. A discharge electrode provided outside the ink chamber so as to surround the discharge electrode of the ink chamber, and a counter electrode disposed opposite to the ink discharge section with a recording medium interposed therebetween. with the door, and electrophoresis voltage source for applying a predetermined migration voltage to the electrophoresis electrode, the ink jet recording apparatus comprising a discharge voltage source for applying a pulse voltage to the ejection electrode, before Symbol toner to the counter electrode Connect a bias voltage source that applies a bias potential of the opposite polarity to the potential of the particles,
An electrostatic ink jet recording apparatus, wherein the counter electrode has a high resistance of 1 MΩ or more . 2. The bias voltage source has a function of selectively switching and connecting two different bias voltages having polarities opposite to the potential of the toner particles to the counter electrode. The electrostatic ink jet recording apparatus according to claim 1, wherein: 3. The electrostatic ink jet recording apparatus according to claim 1, wherein the ejection electrode is provided on a lower surface portion in the ink ejection section.