Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2002-07-26
2004-06-01
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06742881
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention related to an ink container containing an absorbent member for holding the ink to be supplied to an ink jet head employed by an ink jet printer, or the like. In particular, it relates to an ink container improved to make it possible to satisfactorily use pigment-based ink.
An ink container for supplying an inkjet head with ink is structured so that the ink holding force of an ink holding member disposed in the ink container is used for generating the ink supplying pressure necessary for the ink ejection characteristic of an inkjet head, or that the pressure generated by the pressure head difference between the position of the ink surface in the ink container and the position of the ejection orifice of an inkjet head is used as the pressure for supplying ink through an ink supplying tube.
In recent years, a personal computer has come to be widely used, and with the widespread usage of a personal computer, a printer has come to be widely used. There is a call for reducing printer size, and therefore, a large number of printers employ an ink container having the former of the above described structures, in which the ink holding force of the ink holding member is utilized. As for the material for the ink holding member placed in an ink container, generally, foamed polyurethane or PP fibers are employed in consideration of ink holding member cost, and of the state of contact between the ink holding member and ink. Numerous microscopic holes or microscopic gaps in these materials generate capillary force, which functions as ink holding force. In consideration of color development, ejection stability, countermeasure for the problem that while an ink container is left unused for a long period of time, the ink in the portion of the ink absorbent member adjacent to the ink outlet dries and solidifies, and the like, dyestuff-based ink has long been used as the ink to be filled into an ink holding member structured as described above.
In recent years, even a print produced by an inkjet has begun be required to match a print produced by a laser beam printer (LBP) in terms of print density, color development, and/or resistance to ambient elements. In particular, it is desired that black ink is improved in terms of the optical density of a print produced by recording letters on ordinary recording paper.
When using an ink employing dyestuff as coloring agent, it is difficult to improve the above described optical density, because of the characteristics of dyestuff. Further, an ink employing dyestuff as coloring agent has not been improved enough to be satisfactory in terms of waterproofing and light-proofing. Thus, in order to solve the above described problems of dyestuff-based ink, it has been proposed to use recording paper dedicated for inkjet recording, more specifically, ordinary recording paper provided with an ink catching layer (coated paper). However, such recording paper is most costly than ordinary recording paper. Therefore, there has been demand for a method for improving image quality while using inexpensive ordinary recording paper.
There are some methods for effecting a high level of image quality on the surface of recording paper, in which ink density is improved by ejecting ink processing agent at the same time as ink is ejected. However, employment of any of such methods increases the size of a recording apparatus itself, and also, the cost of the ink processing agent adds to the overall cost. Thus, usage of a recording apparatus employing such a method has been limited to special jobs.
Thus, it has been proposed to use pigment as the coloring agent for ink. When pigment is used as the coloring agent for ink, it is relatively easy to increase the optical density because of the pigment properties. Further, pigment is superior in waterproofness to dyestuff. Therefore, the number of opportunities for using pigment as the coloring agent for black ink for a recording apparatus used mainly for outputting documents or the like, has been increasing.
Further, recently, the choice of coloring agent seems to be shifting from dyestuff to pigment, even in the field of color ink.
In the case of pigment-based ink, there are problems which will be described next: When the ink in an ink container is such ink that contains pigment as a coloring agent, and liquid medium in which the pigment is dispersed, and the ink container is left undisturbed for a long period of time, pigment settles, because pigment is greater in molecular weight than dyestuff or the like, being therefore affected by gravity. As a result, the coloring agent concentration within the ink container becomes nonuniform. Here, settle means the phenomenon that microscopic particles are caused to sink by gravity. Provided that microscopic particles do not agglomerate, the rate at which microscopic particles settle is determined by the relation between the speed at which the particles settle in the gravity direction, and which can be obtained by Stokes equation given below, and the Brownian movement of the particles.
Stokes′ equation:
Vs=
2
a
(&rgr;−&rgr;0)
g/
9
(1)
Vs: setting speed
a: particle radius
&rgr;: particle concentration
&rgr;0: solvent
g: gravitational acceleration
: solvent viscosity
Brownian movement:
X
=(
Rtt
/3
&pgr;NA&rgr;a
) (2)
X: average distance particles move in time t
R: gas constant
T: absolute temperature
NA: Avogadro s number
: solvent viscosity
a: particle radius
The microscopic particles settle when the setting speed obtained by the Stokes equation given above overwhelms the dispersion resulting from the Brownian movement.
Further, an ink container is provided with an air vent for connecting the internal space of the ink container to the atmospheric air; allowing the evaporative components in the ink in the ink container to evaporate through the air vent. Therefore, as time goes by, the coloring agent concentration increases, adding to the nonuniformity of the coloring agent concentration in the ink container. In particular, when an air vent is in a surface other than the surface opposing the surface in which the ink outlet is present, the increase in the coloring agent concentration in the adjacencies of the ink outlet caused by the coloring agent settlement and ink component evaporation are more apparent.
In the case of an ink container in which pigment-based ink is directly held in a pouch-like internal container, without being absorbed in an absorbent member or the like, and in which negative pressure is generated using a leaf spring or the like, the pigment in the pouch-like internal container can be easily stirred by utilizing the scanning movement of the carriage resulting from a recording operation. Therefore, the above described pigment settlement does not become a serious problem.
However, in the case of an ink container, the entire internal space of which is filled with absorbent material such as foamed polyurethane, PP fibers, or the like, the ink holding force of the absorbent material substantially suppresses the pigment dispersion. Therefore, the pigment distribution in the absorbent material becomes nonuniform while the ink container is left undisturbed. In the case of this type of an ink container, once the pigment distribution becomes nonuniform, it is virtually impossible to instantly re-disperse the coloring agent. For example, if an ink container is left unused, being mounted in an inkjet recording apparatus, for a long period of time, the pigment settles. As a result, the pigment concentration in the ink in the adjacencies of the ink outlet portion located in the bottom wall of the ink container in terms of the gravity direction increases, whereas the pigment concentration in the ink in the top portion of the ink container decreases. If a recording operation is carried out in this condition, a recording head ejects ink with higher pigment concentration in the initial period of the ink consumption, whereas it ejects ink with lower pigment concentration during the latter h
Iwanaga Shuzo
Kotaki Yasuo
Udagawa Kenta
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