Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-01-16
2004-03-16
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06705707
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink jet recording method and an ink jet recording device discharging ink by electrostatic force, and more particularly to an ink jet recording method and device controlling the formation of a meniscus around a leading edge of a projection when ink is discharged from the leading edge of the projection.
BACKGROUND OF THE INVENTION
In ink jet recording systems, processing such as a development stage is not required, and recording heads are small in size so that recording devices can be easily miniaturized. Accordingly, the ink jet recording systems have widely come in practice.
The conventional ink jet recording systems include a system using piezoelectric elements deformed depending on electric signals, a system using heating resistors generating heat depending on electric signals, and a system using electrostatic force according to electric signals.
All the above-mentioned ink jet recording systems have the problem that poor image drawing occurs by an increase in ink viscosity or solidification of ink caused by evaporation of solvent for ink from ink discharge portions Accordingly, ink jet recording devices are equipped with means for sealing ink discharge outlets when printing is not conducted, and means for cleaning the discharge outlets, if desired,
With respect to such a problem, JP-A-11-192732 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a method of discharging ink for every predetermined period from a recording head independently of image drawing for preventing clogging of ink, and JP-A-2000-127417 discloses a technique relating to a method for cleaning a discharge outlet. For solving such a problem, ink used in such ink jet recording systems contains an aqueous or organic solvent in a large amount, in which dye or pigment is contained as a coloring agent, and is low in viscosity and low in the concentration of the coloring agent.
In such ink jet recording systems, therefore, blurs of images occur so that it is difficult to form images of high image quality and high resolution. Further, the time is required for drying image formation areas so that it is difficult to improve the productivity.
On the other hand, for achieving an ink jet recording system giving reduced blurs of images, high drying speed, and high image quality and good productivity, Japanese Patent No. 3000672 and JP-A-2000-63723 disclose ink in which particles of coloring agent are dispersed in a solvent. For reducing the blurs of images and increasing the drying speed in the above-mentioned ink, it is effective to increase the coloring agent particle concentration and decrease the solvent concentration.
However, the application of the ink increased in the coloring agent particle concentration and decreased in the solvent concentration to the conventional ink jet recording systems results in clogging of the ink in a discharge portion. It is therefore difficult to draw good images. In particular, when minute droplets are discharged for obtaining images of high image quality and high resolution in the system using piezoelectric elements deformed depending on electric signals and the system using heating resistors generating heat depending on electric signals, it is necessary to decrease a nozzle diameter of the discharge portion, which is liable to cause clogging in the discharge portion.
Further, in the ink jet recording system in which ink is discharged by electrostatic force, a high-voltage pulse electric signal is necessary for discharging the ink increased in the coloring agent particle concentration and decreased in the solvent concentration. As a result, another problem arises that control units become extremely expensive.
On the other hand, as disclosed in International Patent Publication No. 501490/1998, a recording device is proposed in which ink in an ink discharge outlet of a recording head is kept in a state just before discharge, energy is given to the ink in the ink discharge outlet by an image signal through a meniscus formation unit (a unit for giving energy to ink such as a heater, an ultrasonic generator or a piezoelectric element) in response to an image signal, thereby destroying the balance of the ink which has been in a balanced state between electrostatic force and surface tension up to then to discharge an ink droplet from the ink discharge outlet, and the ink droplet is allowed to travel toward a recording medium while being accelerated by the electrostatic force to make a recording.
FIG.
5
(
a
)-(
1
) is a schematic cross sectional view showing a recording device based on such a principle, and
FIG. 5
(
a
)-(
2
) is a schematic plan view thereof. In the schematic plan view, a second bias electrode, an ink meniscus formation unit and an image receiving sheet are excluded for convenience' sake.
Referring to FIGS.
5
(
a
)-(
1
) and
5
(
a
)-(
2
), numeral
1
′ is a recording head, numeral
10
′ is an ink chamber, numeral
11
′ is a discharge outlet, numeral
13
is an ink meniscus formation unit, numeral
141
is a first bias electrode, and numeral
142
is a second bias electrode. Numeral
15
is a meniscus control unit for controlling the meniscus formation unit
13
, numeral
16
is a discharge control unit for controlling an electric signal applied across the first bias electrode
141
and the second bias electrode
142
, numeral
20
is an image receiving sheet fixed to an image receiving sheet fixing member (not shown) and moving in the direction indicated by the arrow, and numeral
9
is ink.
In the recording device, the discharge control unit
16
has previously applied a bias voltage Vb across the first bias electrode
141
and the second bias electrode
142
. The bias voltage Vb is such a voltage that the ink in the ink discharge outlet
11
′ of the recording head
1
′ is not discharged.
Then, energy is given to the ink in the ink discharge outlet
11
′ by the meniscus formation unit
13
in response to an image signal, thereby destroying the balance of the ink which has been in a balanced state between electrostatic force and surface tension up to then to discharge an ink droplet from the ink discharge outlet
11
′.
The discharged ink droplet is allowed to travel toward the image receiving sheet (recording medium)
20
while being accelerated by an electric field formed between the first bias electrode
141
and the second bias electrode
142
to make a record on the recording medium
20
.
FIGS.
5
(
b
)-
1
to
5
(
b
)-
5
show the principle of printing operation as described above.
An electrically heated transducer is used as the meniscus formation unit, and the ink in the discharge outlet is heated thereby to elevate the temperature thereof at the meniscus, thus forming an ink droplet. When the temperature is elevated, the surface tension is lowered below the critical surface tension. As a result, the ink is discharged from the discharge outlet. The ink droplet discharged is accelerated in the direction of the bias electrode
142
, and collides with the recording medium
20
.
The radius of the discharge outlet used herein is 20 &mgr;m.
FIG.
5
(
b
)-
1
is a cross sectional view showing the discharge outlet at a standstill position, and the ink is pressurized by the bias voltage. As a result, the ink meniscus expands, and the expansion of the ink meniscus allows the electric field to slightly concentrate. Bonding force by the ink pressure and the electric field is in a state of equilibrium with the surface tension.
FIG.
5
(
b
)-
2
shows a nozzle just after an energy supply pulse has been supplied to the meniscus formation unit (electrically heated transducer)
13
. Heat is transmitted to a surface of the ink, and the resulting increase in temperature causes a local decrease in the surface tension of the ink to somewhat develop the ink meniscus.
FIG.
5
(
b
)-
3
shows further development of the ink meniscus. The ink meniscus exhibits a substantially cylindrical form by a gradient of the surface tension fr
Fuji Photo Film Co. , Ltd.
Gordon Raquel Yvette
Sughrue & Mion, PLLC
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