Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-12-20
2002-05-14
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031860, C106S031280, C106S031650, C106S031520
Reexamination Certificate
active
06387168
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to inks, particularly, inks used in printing of an ink-jet system, and ink-jet printing processes. The present invention also relates to ink containers, ink sets and ink-jet printing apparatus. The present invention is applicable to all apparatus by which printing can be performed on various kinds of printing media such as paper, cloth, leather, nonwoven fabric and OHP paper, for example, business machines and instruments such as printers, copying machines and facsimiles, to which an ink-jet system is applied.
2. Related Background Art
An ink-jet system is a system having various merits of low noise, low running cost, high-speed printing, easy miniaturization of apparatus, easy formation of color images, etc. and hence widely used in printers, copying machines and the like. In such a printer or the like, inks used are generally selected from the viewpoints of ejection properties, printing properties such as fixing ability, print quality such as feathering or bleeding of printed images, optical reflection density and coloring ability, etc.
It is widely known that inks are roughly divided into two kinds of inks of dye inks and pigment inks according to a coloring material contained therein. Of these, the pigment inks have merits of, for example, being excellent in water fastness and light fastness compared with the dye inks, and permitting the achievement of clear character quality. A pigment contained in a pigment ink is generally stably dispersed in the ink using a dispersing agent such as a polymeric dispersant. A specific action thereof is as follows. Namely, pigment particles are adsorbed on the polymeric dispersant to conquer intermolecular force acting between the pigment particles, which brings on aggregation of the pigment particles, making good use of mainly electrical repulsion force and the like of the polymeric dispersant, thereby stably dispersing the pigment particles in the ink. Accordingly, it is necessary to add the polymeric dispersant to the ink according to the amount of the pigment. When printing is conducted on plain paper with such an ink by means of an ink-jet system, pigment particles aggregate due to the penetration of a solvent such as water in the ink into the paper and evaporation thereof into the air. At this time, as behavior on the paper, the cohesion of the pigment particles becomes stronger as the amount of the polymeric dispersant increases. Therefore, the diameter of an ink dot formed on the printing medium by the ink having a certain volume ejected from an ink-jet head becomes small, and as the shape thereof, a distorted shape formed upon impact on the paper almost remains as it is. It is hence necessary to control the volume of the ink ejected from the ink-jet head larger in order to provide ink dots having an optical density sufficient to form an image and a dot diameter required for printing free of occurrence of white stripes and the like. However, this requirement may have incurred the slowdown of fixing of the ink to the printing medium or deteriorated the rub-off resistance of the printed image in cooperation with the lowering of penetrability of the ink due to strong cohesion of the pigment particles on which the polymeric dispersant has been adsorbed.
It is also considered that a penetrant is contained in an ink in order to improve the penetrability of the ink into printing media so as to enlarge the diameter of an ink dot and enhance the fixing ability of the ink. However, in some cases, this method may cause phenomena unfavorable for intending the formation of a high-quality printed image, such as deterioration of dot shape (deterioration of peripheral shape of dot such as so-called feathering) and penetration of the ink into the back surface of the paper (so-called strike-through). Besides, since a coloring material penetrates into the interior of the printing medium, the optical density (OD) of ink dots may not become very high in many cases even when the dot diameter is relatively enlarged.
Further, inks using a self-dispersing pigment have been proposed. According to these inks, the diameter of a dot can be enlarged probably because the cohesion of the pigment on paper is weak compared with the inks containing a pigment dispersed by the above-described dispersing agent. However, it is not yet sufficient.
As described above, inks and printing processes, which satisfy various factors controlling the quality of a printed image, for example, the fixing ability of the inks, enlargement of ink dot diameter, evenness of density within an ink dot, high optical density of ink dot itself, etc., at a high level, and also stability as inks, particularly ejection stability as ink-jet inks, are yet in a fair way to research aimed at still more improvement.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ink that the ink droplet applied to the printing medium moderately spreads in the lateral directions of a printing medium and is prevented from penetrating in the thickness direction of the printing medium, and consequently can provide a dot that is high and even in optical density of image within the dot and has an excellent external shape in that feathering is scarcely observed.
Another object of the present invention is to provide an ink-jet printing process which can form a high-quality image having a high optical density of image while reducing the amount of an ink applied to a printing medium.
A further object of the present invention is to provide an ink-jet printing apparatus capable of stably printing a high-quality image, and an ink container and an ink set used in this process.
A still further object of the present invention is to provide an ink for forming images and an image forming process, which can provide an optical density of image and image quality that can satisfy properties finally required of an ink forming a dot or an ink forming a pixel (including an overlapped dot portion by a dot matrix such as 3×3 or 4×4).
The above objects can be achieved by the present invention described below.
In an aspect of the present invention, there is thus provided an ink comprising a first pigment, a second pigment and a dispersant, both of the pigment being dispersed in an aqueous medium, wherein the first pigment is a self-dispersing pigment having an anionic group or a cationic group, the group being bonded directly or through an atomic group to a surface of the pigment, the second pigment is a pigment dispersible in an aqueous medium with the dispersant, and the dispersant is an ionic polymeric dispersant having a same polarity as that of the group bonded to the surface of the pigment or a nonionic polymeric dispersant.
In another aspect of the present invention, there is provided an ink used in an image printing process comprising the steps of ejecting an ink from an orifice by means of an ink-jet system; applying the ink to a printing medium; and forming an element of an image, the ink comprising a first pigment, a second pigment and a dispersant, both of the pigment being dispersed in an aqueous medium, wherein the first pigment is a self-dispersing pigment having an anionic group or a cationic group, the group being bonded directly or through an atomic group to a surface of the pigment, the second pigment is a pigment dispersible in an aqueous medium with the dispersant, and the dispersant is an ionic polymeric dispersant having a same polarity as that of the group bonded to the surface of the pigment or a nonionic polymeric dispersant.
In an aspect of the present invention, there is also provided an ink-jet printing process comprising the steps of ejecting an ink toward a printing medium by means of an ink-jet system; and forming an image on the printing medium, wherein the ink comprises a first pigment, a second pigment and a dispersant, both of the pigment being dispersed in an aqueous medium, wherein the first pigment is a self-dispersing pigment having an anionic group or a cationic group, the grou
Koitabashi Noribumi
Sugama Sadayuki
Takizawa Yoshihisa
Tsuboi Hitoshi
Canon Kabushiki Kaisha
Faison Veronica F.
Fitzpatrick ,Cella, Harper & Scinto
Koslow C. Melissa
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