JP2001001524A - Electrostatic ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic ink jet recording apparatus which can solve the problem in an electrostatic flocculation ink jet that a printing density is lowered because of diffusion of coloring material particles accompanying discharge signals or coloring material particles are not discharged. SOLUTION: The apparatus has a group 1 of a plurality of recording electrodes set along a nearly straight line, an upper plate 3 and a lower plate 4 holding the recording electrode group 1 therebetween, ink discharge openings 10 formed by the upper plate 3 and lower plate 4, and a plurality of guard electrodes 2 arranged via the recording electrode group 1 with separating the ink discharge openings 10. When recording electrodes of the recording electrode group 1 are selectively driven thereby discharging ink to print to a recording medium, an absolute value of a potential impressed to the guard electrodes 2 is controlled to be larger than an absolute value of a signal voltage impressed to the recording electrodes.

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 capable of obtaining a stable print density.

[0002]

2. Description of the Related Art Ink jet technology has been widely used as a low cost, high image quality and high speed printing technology in copiers, facsimile machines, printers and word processors as office automation and personal information recording devices. The principle of ink-jet recording is to use a heating element such as an electrothermal transducer, a piezo element such as an electromechanical transducer, There is an electrostatic type used as it is. Among them, the electrostatic type ink jet has a simple configuration of a recording head as compared with other types, and can perform gradation recording by controlling an electric signal applied to a recording electrode. Further, the amount of current consumed at the time of recording is remarkably small, and it can be said that this is a recording technology that is useful in the future as an energy-saving device. Further, by using an oil-based pigment ink, it is possible to perform printing with excellent water resistance, and it is particularly useful for office automation.

Here, the principle aspects of the electrostatic ink jet will be briefly described. As reported in JP-A-56-4467, when a recording voltage of several kV is applied between a recording electrode filled with ink and a counter electrode holding a recording medium, the recording voltage falls to a certain threshold. When it exceeds, the electrostatic force acting on the ink overcomes the surface tension of the ink, and the ink droplet is ejected from the recording electrode to the counter electrode and flies. For the construction of the head based on this principle, see, for example, U.S. Pat.
No. 467.

FIG. 6 is a perspective view of a conventional electrostatic ink jet head, and FIG. 7 is a cross-sectional view of the same electrostatic ink jet head, wherein 1 is a recording electrode, 3 is an upper plate, 4 is a lower plate, and 6 is Color material particles, 7 are aggregated ink droplets, 8 is a recording medium, and 9 is a counter electrode.

In the configuration of this example, a nozzle hole is not necessarily required for each recording electrode, and a so-called slit-type ink discharge port common to a plurality of recording electrodes can be used. A feature of such a configuration is that clogging due to drying of ink is reduced by not providing a nozzle. Therefore, this configuration is not only a so-called serial type head which has several hundred recording electrodes and scans in the width direction of the recording medium, but also a so-called full line type head which has recording electrodes for the width of the recording medium. It is also very effective.

[0006]

In this electrostatic ink jet, in order to operate each recording electrode independently, it is necessary to prevent charge leakage due to forming a closed loop with an adjacent electrode. For this purpose, an oily solvent having a high electric resistance is usually used as a solvent for the ink. In the example disclosed in JP-A-58-215353, specific resistance is about 10 ⁸ Ωcm, surface tension is 18 dyne / cm, and viscosity is 2 to 2.
An oil-based ink having ³⁰ cP and a specific gravity of 1.0 g / cm ³ is used. However, since the oily solvent has a lower surface tension than the aqueous solvent (surface strength of about 70 to 80 dyne / cm), when printing is performed, both the colorant particles and the solvent quickly penetrate into the fibers of the recording paper. In addition, there is a problem that print density is reduced, bleeding, and show-through is caused. This was due to the fact that the coloring material particles and the oil-based carrier liquid as the solvent flew at the same time.

On the other hand, as disclosed in JP-A-8-295023 and JP-A-9-193389, these problems are solved by discharging only the color material particles from the ink. An attempt was made. In these examples, the discharge principle is not necessarily clearly explained, but the electrostatic force is applied only to the color material particles,
Since only the color material particles fly, the above-described problem is solved because the carrier liquid is not contained in the discharged ink.

According to the contents disclosed in Japanese Patent Application Laid-Open No. 9-193389, the use of ink having a specific resistance of 10 ¹⁰ Ωcm or more results in extremely high print density,
Particularly favorable effects can be obtained with respect to the sharpness of the contour.
As described above, it is understood that the dispersibility of the color material particles in the ink needs to be deteriorated in order to make the color material particles and the solvent move to some extent independently. This is because if the dispersibility of the color material particles is good, the color material particles cannot be distinguished from the solvent, and only the color material particles cannot be discharged.

According to JP-A-8-295023,
By applying a voltage of the same polarity as the charging polarity of the color material particles to the recording electrode, the color material particles migrate and aggregate at the tip of the recording electrode due to electrostatic repulsion, and only the color material particles are discharged. I have. However, in practice, Japanese Patent Application Laid-Open
As shown in Japanese Patent No. 52920, when a signal voltage is applied to the recording electrode, a potential gradient is formed between the recording electrode and the counter electrode, so that the coloring material particles also migrate toward the recording electrode tip. However, at the same time, a potential gradient is formed in the opposite direction, so that the coloring material particles migrate in the opposite direction. This is because the action of the force is due to the electrostatic repulsion between the color material particles and the recording electrode, and the recording electrode exerts a force to keep the color material particles away. This is shown in FIG. FIG. 8 is a view for explaining the diffusion of the conventional color material particles, and is a schematic view of the recording electrode and the ink meniscus as viewed from above. The recording electrode and the ink meniscus move away from the selected electrode and diffuse to the unselected electrode. It is shown.

As described above, in actuality, when the signal voltage is applied to the recording electrode, the color material particles perform the coagulation discharge and simultaneously diffuse to the opposite side of the ink discharge port. Then, due to the diffusion, the concentration of the color material particles at the ink discharge port becomes extremely low, and a problem has been found that cohesive discharge no longer occurs. In such a case, the print density is extremely reduced, and in the extreme case, the discharge of the color material particles does not occur. Such a problem becomes more serious as the length of the ink ejection port becomes longer, and becomes particularly serious in a so-called full line head in which the ink ejection port has a length in the width direction of the recording medium. This is because the larger the space in which the color material particles can diffuse, the more likely the diffusion occurs.

According to the present invention, there is provided an electrostatic printer capable of solving the above-described problems in the electrostatic coagulation type ink jet, such as a decrease in print density due to diffusion of color material particles accompanying a discharge signal, or non-discharge of color material particles. It is an object of the present invention to provide a type ink jet recording apparatus.

[0012]

According to the present invention, a plurality of recording electrode groups provided substantially along a straight line, an upper plate and a lower plate sandwiching these recording electrode groups up and down, and an upper plate and a lower plate. The recording medium includes an ink ejection port to be formed, and a plurality of guard electrodes that divide the ink ejection port and are arranged to sandwich the recording electrode group. The recording medium is ejected by selectively driving the recording electrode group. An electrostatic ink jet recording apparatus that performs printing on the guard electrode, wherein the control is performed such that the absolute value of the potential applied to the guard electrode has a time that is greater than the absolute value of the signal voltage applied to the recording electrode group. Features.

With this configuration, there is provided an electrostatic ink jet recording apparatus which can solve the problem in the electrostatic coagulation type ink jet, that is, the reduction of the printing density due to the diffusion of the color material particles accompanying the ejection signal or the non-ejection of the color material particles. Can be provided.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 comprises a plurality of recording electrode groups provided along a substantially straight line, an upper plate and a lower plate sandwiching these recording electrode groups up and down, an upper plate and a lower plate. And a plurality of guard electrodes which divide the ink discharge ports and are arranged so as to sandwich the recording electrode group, and selectively drive the recording electrode group to discharge ink to perform recording. An electrostatic ink jet recording apparatus for performing printing on a medium, wherein the control is performed so that the absolute value of the potential applied to the guard electrode is longer than the absolute value of the signal voltage applied to the recording electrode group.

According to a second aspect of the present invention, the ink discharge port is
The recording electrodes are arranged so as to be shifted from each other in a direction intersecting a substantially straight line provided with the recording electrode group.

According to a third aspect of the present invention, the guard electrode has the same shape as the recording electrode group.

According to a fourth aspect of the present invention, another guard electrode is disposed near at least one of the upper plate and the lower plate.

With the above arrangement, it is possible to prevent a decrease in print density due to diffusion of color material particles accompanying a discharge signal or non-discharge of color material particles.

(Embodiment 1) FIG. 1 is a perspective view of an electrostatic ink jet head according to Embodiment 1 of the present invention, and FIG.
FIG. 3 is a diagram for explaining how the same color material particles are prevented from being diffused, and FIG. 3 is a diagram showing signal voltage waveforms applied to the recording electrode group and the guard electrode.

According to the first aspect of the present invention, as shown in FIG. 1, a plurality of recording electrode groups 1 provided substantially along a straight line,
An upper plate 3 and a lower plate 4 which sandwich the recording electrode group 1 up and down, and an ink discharge port 10 formed by the upper plate 3 and the lower plate 4
And a plurality of guard electrodes 2 arranged to separate the ink discharge ports 10 and sandwich the recording electrode group 1, and the absolute value of the potential applied to the guard electrode 2 is equal to the absolute value of the signal voltage applied to the recording electrodes of the recording electrode group 1. Control is performed so as to have a time T2 that is larger than the value.

With this configuration, a certain time interval T2 (FIG. 3) is set in the ink ejection port separated by the guard electrode 2.
, There is a potential gradient from the guard electrode 2 toward the recording electrode group 1, so that even if a recording signal voltage is applied to any of the recording electrodes in the recording electrode group 1 sandwiched by the guard electrodes 2, the guard electrode 2 Due to the potential gradient between the recording material and the recording electrode group 1, there is an effect that the color material particles 6 are not diffused and the pigment concentration at the ink discharge port 10 is not reduced. For example, when the color material particles 6 are positively charged, the potential of the guard electrode 2 is changed to the recording electrode group 1 in the time interval T2.
Is set higher than the signal voltage given to When a recording signal is applied to the recording electrode group 1 at the time interval T1, the coloring material particles 6 receive an electrostatic repulsion and diffuse in four directions around the recording electrode group 1, but after the time interval T1, recording is performed. Since the potential of the electrode group 1 is lower than that of the guard electrode 2, as shown in FIG. 2, the coloring material particles 6 receive a force that returns in the direction of the recording electrode, thereby preventing diffusion. Time interval T
The same effect can be obtained by setting the absolute value of the potential of the guard electrode 2 higher than that of the recording electrode not only in the period 2 but also in the period of the time interval T1.

Further, the potential difference between the guard electrode 2 and the recording electrode group 1 is (interval between both electrodes (μm)) × (1 V / μm) ×
(Ink dielectric constant) is preferably set to a value not exceeding. By setting in this range, no discharge occurs between the recording electrode and the guard electrode 2.

The first embodiment will be described more specifically.
In FIG. 1, a total of 256 signal electrodes are arranged substantially in a line in a straight line. The electrodes were formed on the basis of polyimide and formed of nickel by plating. The recording electrode of recording electrode group 1 has a resolution of 150 dpi (15 inches per inch).
0). The recording electrodes were formed with a width of 60 μm, a thickness of 40 μm, and a pitch of 169 μm. The ink discharge port 10 is formed by an upper plate 3 and a lower plate 4, and the upper plate 3 and the lower plate 4 are each formed by using an acrylic resin, and are processed by die molding and injection molding. The lower plate 4 is provided with partition walls having a thickness of 50 μm every 32 electrodes so that all the recording electrodes are divided into 8 groups of 32 electrodes.

Each barrier was provided with a gold film by gold sputtering, and was electrically connected to a DC power supply. A pulse signal voltage of 200 V and a DC voltage of 100 V were applied to the recording electrode and the guard electrode 2 with waveforms as shown in FIG. When printing was performed by applying a DC voltage of -1 kV to a counter electrode (not shown), diffusion of color material particles in a substantially linear direction around a recording electrode to which a printing signal was applied was prevented, and stable printing density was obtained. was gotten. When a similar experiment was performed without applying a gold film to the barrier and forming no electrode, the coloring material particles diffused in a substantially linear direction around the recording electrode to which the print signal was given, and when printing was performed continuously, the coloring material particles were dispersed. The density decreased remarkably, and printing could not be continued.

(Embodiment 2) FIG. 4 is a perspective view of an electrostatic ink jet head according to Embodiment 2 of the present invention. The invention according to claim 2 is characterized in that the ink discharge ports 10 are arranged so as to be shifted from each other in a direction intersecting a substantially straight line provided with the recording electrode group 1. Even when the recording electrode density is such that the guard electrode 2 cannot be inserted between the recording electrodes, the recording electrode group 1
Are shifted from each other, the guard electrode 2 can be arranged. By displacing the recording electrode groups 1, both ends of each recording electrode group 1 are free spaces. Therefore, no matter how large the electrode density is, there is no need to insert the guard electrode 2 between the recording electrode groups 1, so that the guard electrodes 2 can be arranged at both ends of the recording electrode group 1 regardless of the electrode density. it can. Further, with such a configuration, the distance between the recording electrode group 1 and the guard electrode 2 can be increased, so that the difference between the potentials to be applied to both electrodes can be increased.

Embodiment 2 will be described more specifically. In FIG. 4, 128 recording electrodes of recording electrode group 1 were arranged at an electrode density of 600 dpi. Ink outlet 10 is 32
Divided into four groups, one for each ink ejection port 1
0 was formed so as to be shifted substantially perpendicular to the straight line. (32 in FIG. 4)
It is shown in groups of three instead of books. 3) Since the recording electrode groups 1 of each group were not arranged in a horizontal line, the guard electrodes 2 could be arranged even in a high-density array of about 600 dpi (pitch of 40 μm). The distance between the recording electrode group 1 and the guard electrode 2 is set to 100 to make the voltage difference between the guard electrode 2 and the recording electrode group 1 large.
It was set to μm. The upper plate 3, the lower plate 4, and the ink flow path were formed by molding acrylic resin. The guard electrode 2
The end portion of each ink discharge port 10 was formed by vapor deposition of gold. The recording electrode and the guard electrode 2 have waveforms as shown in FIG.
A V pulse signal voltage and a DC voltage of 420 V were applied. A DC voltage of -1 kV is applied to a counter electrode (not shown),
When printing was performed, diffusion of the coloring material particles in a substantially linear direction around the recording electrode to which the printing signal was applied was prevented, and a stable printing density was obtained.

At a recording electrode density of 300 dpi, a head having 256 recording electrodes and four pairs of guard electrodes was prototyped. In this case, all the recording electrodes were divided into four groups by 64 recording electrode groups 1, and both ends of each recording electrode group 1 were used as guard electrodes 2. That is, four sets of 66 recording electrodes formed on a substrate were prepared, and they were arranged so as to be shifted from each other. Two electrodes at both ends of each recording electrode group 1 were used as guard electrodes 2. The guard electrode 2 can be replaced with the same electrode as the signal electrode. When 32 signal electrode groups were formed, 34 signal electrodes were formed in advance, and the guard electrodes 2 were used at both ends, whereby the effect of the guard electrode 2 could be obtained at low cost. .

The ink flow path was molded from resin to form an ink discharge port 10 having a width of 34 recording electrodes. A 200 V pulse signal voltage and a 200 V DC voltage biased by 100 V were applied to the recording electrode and the guard electrode 2, respectively. When a DC voltage of -1.5 kV was applied to the counter electrode (not shown) and printing was performed, diffusion of the coloring material particles in a substantially linear direction around the recording electrode to which the print signal was applied was prevented, and stable printing was performed. The print density was obtained.

FIG. 5 is a perspective view of an electrostatic ink jet head according to another embodiment of the present invention. As shown in FIG. 5, by providing the auxiliary electrode 5 for preventing the diffusion of the coloring material particles separately from the guard electrode 2, the diffusion of the coloring material particles could be prevented three-dimensionally. The auxiliary electrode 5 was made of a copper plate and arranged inside the upper plate 3. 100 for the recording electrode
A 200 V DC signal was applied to the V-biased 200 V pulse signal voltage, guard electrode 2 and auxiliary electrode 5. When a DC voltage of -1.5 kV was applied to the counter electrode (not shown) and printing was performed, the color material particles diffused in a substantially linear direction around the recording electrode to which the print signal was given, and the upper plate 3 and the lower plate 3 were printed. Diffusion in the direction of the plate 4 was also prevented at the same time, and a stable print density was obtained.

(Embodiment 3) The invention according to a third aspect is characterized in that the guard electrode 2 has the same shape as the recording electrodes of the recording electrode group 1, and the recording electrodes are directly connected to the guard electrodes 2. By doing so, there is no need to insert a metal to be the guard electrode 2 or to form a metal film, which has an effect that the guard electrode 2 can be formed at low cost. In this case, in each of the recording electrode groups 1, two more recording electrodes are formed on the substrate, and the two electrodes at both ends are used as guard electrodes 2. Of course, the number of guard electrodes 2 does not need to be two, so that the card electrodes 2 can be formed two by two. In this case, four more recording electrodes are formed, and two at each end are used. It can be a guard electrode.

In this embodiment, how a color material particle moves when a signal voltage is applied to a recording electrode will be described for a case where the color material particle is positively charged. When the signal as shown in FIG. 3 is used, the potential of the guard electrode 2 is always higher than the potential of the recording electrode group 1 during the time interval T2. 6 moves. Then, next, when a signal voltage is applied to the selected recording electrode at the time interval T1, the aggregated ink is ejected from the selected recording electrode. At this time,
In the signal voltage V1 of the selected recording electrode and the voltage V2 of the guard electrode 2, if V1> V2, diffusion from the selected recording electrode occurs in all directions. If V1 <V2, repulsion from the guard electrode 2 occurs. No diffusion by force. Also in the former case, the diffusion is prevented again at the time interval T2 when the time interval T1 ends, which is effective. The signal applied to the guard electrode 2 does not need to be a DC voltage as shown in FIG. 3, and any signal may be provided if a period in which the potential of the guard electrode 2 is higher than the potential of the recording electrode is provided in the time interval T2. A signal waveform can be used.

(Embodiment 4) The invention according to a fourth aspect is characterized in that another guard electrode 2 is provided in the vicinity of the upper plate 3 and the lower plate 4 or at least one of them. Then, by adding such an auxiliary electrode,
This has the effect that diffusion of the colorant particles can be prevented three-dimensionally. The guard electrode 2 arranged along a substantially straight line has an effect of preventing the diffusion of the coloring material particles in a substantially straight line direction, but cannot prevent the diffusion in a direction intersecting the substantially straight line. Therefore, by providing another auxiliary electrode in a direction intersecting the substantially straight line and performing the same signal voltage control as that of the guard electrode 2, it is possible to three-dimensionally prevent the color material particles from diffusing.

[0033]

As described above, according to the present invention, the diffusion of the coloring material particles is prevented, and a stable printing density can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view of an electrostatic inkjet head according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a state in which diffusion of color material particles is prevented according to the first embodiment of the present invention.

FIG. 3 is a diagram showing signal voltage waveforms applied to recording electrode groups and guard electrodes according to the first to fourth embodiments of the present invention.

FIG. 4 is a perspective view of an electrostatic inkjet head according to a second embodiment of the present invention.

FIG. 5 is a perspective view of an electrostatic inkjet head according to another embodiment of the present invention.

FIG. 6 is a perspective view of a conventional electrostatic ink jet head.

FIG. 7 is a sectional view of a conventional electrostatic ink jet head.

FIG. 8 is a diagram illustrating diffusion of conventional color material particles.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording electrode group 2 Guard electrode 3 Upper plate 4 Lower plate 5 Auxiliary electrode 6 Color material particle 10 Ink ejection port

Claims (4)

[Claims] A plurality of recording electrode groups provided along a substantially straight line, an upper plate and a lower plate sandwiching these recording electrode groups up and down, an ink discharge port formed by the upper plate and the lower plate, An electrostatic ink jet that includes a plurality of guard electrodes that divide the ink ejection port and is disposed so as to sandwich the recording electrode group, and selectively drives the recording electrode group to eject ink to print on a recording medium; A recording apparatus, wherein the control is performed such that the absolute value of the potential applied to the guard electrode is longer than the absolute value of the signal voltage applied to the recording electrode group. apparatus. 2. The electrostatic ink jet recording according to claim 1, wherein the ink discharge ports are arranged so as to be mutually shifted in a direction intersecting a substantially straight line provided with the recording electrode group. apparatus. 3. The electrostatic ink jet recording apparatus according to claim 2, wherein said guard electrode has the same shape as said recording electrode group. 4. The electrostatic ink jet recording apparatus according to claim 1, wherein another guard electrode is arranged near at least one of the upper plate and the lower plate.