Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2000-02-29
2001-09-18
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031650, C106S031880, C106S031330
Reexamination Certificate
active
06290764
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink employed for an ink jet printing apparatus, and particularly to an ink for an electrostatic ink jet printing which is used in an electrostatic ink jet printing apparatus cohering and discharging color material particles in the ink due to an electrostatic force so as to apply a printing to a recording medium.
BACKGROUND INFORMATION
An increased attention is recently paid to a non-impact printing technique in view that a generation of a sound at a recording time is significantly as small as can be ignored.
In particular, an ink jet method which can print on a plain paper at a high speed by using a comparatively simple mechanism is a significantly useful printing technique, various kinds of techniques have been suggested, and a technique which is suitable for a high speed printing, a high resolution and a full color printing has been eagerly going to be researched. Among them, there is representatively a multi nozzle type which prints a plurality of dots in parallel, for example, a bubble jet method which discharges an ink drop due to a pressure of a steam generated by a heat of a heat generating body and a piezoelectric method which discharges an ink drop due to a mechanical pressure pulse generated by a piezoelectric element.
However, there is a problem that the conventional ink jet printer is not suitable for improving a resolution. That is, in the bubble jet method which employs the pressure of the steam, it is hard to generate an ink drop having a diameter smaller than 20 &mgr;m, and in the piezoelectric method which employs the pressure generated by the piezoelectric element, it is hard to produce a head having a high resolution due to a problem on a processing technology since the recording head has a complex structure.
Further, the ink employed in the conventional ink jet method has a lot of technical problems.
In this case, as characteristics required in the ink for the ink jet, firstly, an even image having a high density without a bleeding and a photographic fog can be obtained on a paper, secondly, a weather resistance of the image is good, thirdly, a drying property of the ink is good on the paper, and fourthly, no clogging is generated and a discharge stability and a discharge response are excellent.
In order to obtain these characteristics, there has been proposed various kinds of electrostatic ink jet methods which apply a voltage on an electrode array formed in a thin film and employ an electrostatic force so as to discharge the ink.
Here, a description will be given of a technique disclosed in Japanese Patent National Publication of translated version 7-502218, as the conventional electrostatic type ink jet method.
The conventional electrostatic ink jet technique in accordance with the publication is structured such as to apply a voltage having the same polarity as that of a charged color material particle to an electrode at a front end of a slit so as to form an aggregate of the color material particles and discharge the aggregate of the color material particles from a front end of a printing electrode.
Then, in accordance with the technique, since the color material particles are discharged in a cohered state, an ink having a little solvent is formed on the paper as a dot, so that a printing having a high density and a less bleeding can be realized. Further, since the solvent is reduced, the ink is quickly dried on the printing medium. Further, since a pigment is employed for the color material particles of the ink as is different from the other ink jet methods which employ a dye ink, it is possible to obtain an image having an improved weather resistance.
Further, in the conventional electrostatic type ink jet technique, since the printing head is structured such as to be formed in a slit shape which does not require independent nozzles at every dots, it is effective for preventing and repairing a clogging which causes a great problem for putting the ink jet head to a practical use, so that the discharge stability is always good and a reliability can be maintained.
Further, the conventional electrostatic ink jet technique can easily form a printing dot having a diameter about 10 to 20 &mgr;m in accordance with a length of a printing signal pulse, and can also form a large printing dot having a diameter equal to or more than 100 &mgr;m. Accordingly, since it is possible to achieve a multi value area gradation as well as a high resolution, it can be said to be an ink jet method which is most suitable for obtaining a high resolution and a full color.
Hereinafter, a description will be given of a structure and an ink discharge process of an electrostatic type ink jet head, and a characteristic of an ink for the electrostatic type ink jet. In this case, hereinafter, the ink for the electrostatic type ink jet is simply referred to as an ink.
FIG. 1
is a schematic view which shows a structure of an electrostatic type ink jet head,
FIG. 2
is a schematic view which shows a structure of an inner portion of the electrostatic type ink jet head shown in
FIG. 1
,
FIG. 3
is a side cross sectional view of the electrostatic type ink jet head shown in
FIG. 1
, and
FIGS. 4
to
7
are schematic views which show a discharge motion of an ink performed by the electrostatic type ink jet head shown in
FIG. 1
in a subsequent manner.
As illustrated, a printing head has a lower casing
7
and an upper casing
8
which are bonded to each other so as to be integrally formed. A slit hole
2
is formed at a front end of the printing head, and a plurality of printing electrodes
1
which are driven by a printing electrode driver so as to discharge an ink drop are provided in such a manner as to extend inward from the slit hole
2
.
A front end of the printing electrode
1
s formed in a convex shape and is placed so as o protrude from the slit hole
2
corresponding to discharge hole at a degree of 50 to 200 &mgr;m so that the printing electrode
1
can concentrate an electric field to the ink existing near the front end of the printing electrode
1
and a stable discharge can be performed by stably forming a meniscus.
Further, the printing electrode
1
is constituted by a lead wire
3
for applying a signal voltage, and a tab wiring substrate
4
which is integrally formed with a pad (not shown) for being electrically connected to the printing electrode driver.
An ink tank
6
in which an ink is charged is formed within the printing head by an opposing space between the lower casing
7
and the upper casing
8
so as to be communicated with the slit hole
2
. A migration electrode
5
is provided on an inner surface of the ink tank
6
for applying an electrophoresis in a direction of the slit hole
2
to the color material particle within the ink tank
6
and increasing a density of the color material near the slit hole
2
.
Here, the tab wiring substrate
4
and the migration electrode
5
mentioned above are bonded to the lower casing
7
. Further, the pad is bonded to an FPC wiring substrate (not shown). In this case, a matrix circuit, a driver IC and the like are mounted on the FPC wiring substrate.
As shown in
FIG. 4
, in this electrostatic type ink jet head, in a state that the ink is charged within the ink tank
6
and within a slit-like ink flow passage, the ink forms a meniscus
9
within a periphery of the slit hole
2
due to a surface tension. Then, since a back pressure about ±100 Pa is applied to the ink within the ink tank
6
, the meniscus
9
is formed in a state of gently protruding from the ink discharge hole.
In this case, a printing paper
10
corresponding to a printing medium for the ink is arranged in a direction of discharging the ink, and an opposing electrode
11
which discharges the ink toward the printing paper
10
due to an electrostatic force is arranged on a back surface of the printing paper
10
. In this case, in the case that a color material particle
12
is charged in a positive potential, a negative voltage about −1 kV is applied to the opposing electrode
11
a
Faison Veronica F.
Klemanski Helene
Matsushita Electric - Industrial Co., Ltd.
Stevens Davis Miller & Mosher LLP
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