Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2001-06-20
2003-07-01
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031280, C106S031600, C347S100000
Reexamination Certificate
active
06585815
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ink set, an ink-jet printing method, a recording unit, an ink cartridge and an ink-jet printing apparatus.
2. Related Background Art
In the course of the increasing popularity of ink-jet printers and other similar devices as we observe today, they are required to print high quality images than ever. It is well known that one of the major factors that determine the printing quality is the ink dots formed on the printing medium or the optical density (to be also referred to as OD hereinafter) of the ink dots. In the operation of printing black characters, the higher the OD value of the dots formed by means of black ink on the printing medium, the better the contrast to the base color of the printing medium and the quality of the image formed of ink dots. Similarly, the image formed of ink dots by using ink of some other color, which may be cyan, magenta or yellow, is better when the OD value of the dots is high.
The amount of the coloring material of ink that is left on the surface of the printing medium without permeating the latter is one of the various factors that affect the quality of the dots formed by ink on the printing medium. From this point of view, ink is normally ejected from the printing head at a rate as high as possible. A simple and easy way for increasing the amount of ink applied to a same area of the printing medium is to repeat the scanning operation of the printing head for a number of times so as to eject ink repeatedly onto the same area. This technique is currently very popular.
Another technique for increasing the amount of the coloring material of ink remaining on the surface of the printing medium is to apply a treatment liquid that makes the coloring material undissolvable onto the printing medium with ink in order to raise the amount of the coloring material left on the surface of the printing medium and improve the optical density of the dot image formed on the printing medium.
The applicant of the present patent application proposed a printing apparatus and a printing method realized on the basis of this technique in Japanese Patent Application Laid-Open No. 8-281930. According to the cited patent document, when printing a black image, treatment liquid is ejected onto the printing medium to make it show a predetermined pixel pattern along with the black ink that is ejected to the image area. The treatment liquid is cationic and hence shows the polarity opposite to that of the black ink that is anionic so that it makes black ink undissolvable and raises the density of the formed image. Additionally, the image density is raised further and the color tone is prevented from shifting if ink of some other color is ejected simultaneously to show the predetermined pattern.
The invention of the above cited patent document further provides the advantages that no printing head dedicated to the treatment liquid is required and the water resistance of the formed image is improved by the treatment liquid by using a printing apparatus having a simple configuration and that it can effectively prevent the phenomenon of feathering and that of bleeding from taking place.
The European patent application EP 831135 A1 discloses a similar technique. According to this patent document, pale magenta or cyan ink is ejected onto the dots of black ink with a low density to turn the black ink undissolvable by means of an ingredient of the low pale ink.
Generally, ink is selected from the viewpoint of ink ejection performance, printing characteristics including fixability and printing quality including blurring of printed images, optical reflection density and chromogenic property. Meanwhile, it is well known that there are two types of ink in terms of the coloring material contained therein. They are dye ink and pigment ink.
Pigment ink is advantageous to dye ink from the viewpoint of water-resistance and light-resistance and adapted to print characters clearly to realize high quality printing. On the other hand, pigment ink takes more time than dye ink for fixation on a printing medium and is not satisfactory in terms of abrasion resistance of the image after fixation if compared with dye ink. Additionally, each ink dot of pigment ink formed on a printing medium by a single ink ejecting operation of a nozzle is relatively small if compared with that of dye ink. The pigment contained in pigment ink can be reliably and stably dispersed in ink by means of the electric repulsion of a polymeric dispersant that outdoes the intermolecular force applied to the pigment particles of ink that are apt to aggregate. Therefore, it is preferable to add a polymeric dispersant to pigment ink at a rate that depends on the pigment content of pigment ink. Further, it is also proposed to prepare pigment ink containing a self-dispersion type pigment.
On the other hand, in the field of ink-jet printing technology, methods of applying ink and treatment liquid that reacts with the applied ink have been proposed in order to improve the quality of printed characters and images (e.g., in terms of the water resistance and the optical density (OD) of the image formed on a printing medium) by causing the applied ink and the treatment liquid to favorably react each other on the printing medium. Some of such methods have already found practical applications.
SUMMARY OF THE INVENTION
As a result of researches conducted by the inventors of the present invention for dissolving the problems specific to pigment ink, while exploiting the advantages thereof, they obtained the following findings.
When a pigment ink where the pigment is dispersed by a polymeric dispersant is applied onto a plain paper by means of an ink-jet recording method, the pigment particles contained in the ink aggregate due to the penetration into the paper and evaporation of the solvent of ink, which is typically water. Now, in terms of the behavior of the ink on the paper, the more the amount of the polymeric dispersant is contained in the ink, the stronger the aggregational force of the ink is, which shows that the aggregational force is stronger when the polymeric dispersant is contained in the ink at a higher rate. As a result, the ink dot formed on the recording medium with the ink containing a polymeric dispersant at a higher rate tends to have a smaller diameter than that formed with the ink containing it at a lower rate, provided that a predetermined volume of ink is ejected from an in-jet head, and keep a distorted profile produced as a result of the collision of the ink with the surface of the sheet of paper. Therefore, in order to obtain ink dots showing a sufficient recording density and having a dot diameter necessary for forming an image without generating white stripes, it is necessary to increase the volume of ink ejected from the ink-jet head. However, the fixation of the ink to the printing medium may take longer time and the scratch resistance of the recorded image may be reduced because of the strong aggregational force of the pigment particles around which the polymeric dispersant are absorbed.
The use of a penetrant may be conceivable to improve the ink permeability of the printing medium in order to increase the ink dot diameter and improve the fixation of the ink to the printing medium. However, the use of a penetrant can be accompanied by a problem of a degraded ink dot profile (a degraded circumferential profile of each ink dot, due to a phenomenon typically referred to as feathering) and that of permeation of ink to the rear surface of the paper (so-called back-through) that are undesirable for producing high quality recorded images. Additionally, even if the ink dot diameter is relatively increased, the OD (optical density) of the ink dot may not be raised because the coloring material of the ink can penetrate into the printing medium.
Meanwhile, ink containing a self-dispersible pigment has been proposed. With such ink, the dot diameter can be increased because the self-dispersible pigment contained in ink has aggregational force w
Fujimoto Yasunori
Koitabashi Noribumi
Tsuboi Hitoshi
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