Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2001-06-29
2004-05-04
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031750, C106S031890
Reexamination Certificate
active
06730155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aqueous ink composition and a set of color ink compositions suitable for ink-jet printing.
2. Discussion of Background
Ink-jet printing can perform image formation by ejecting an ink liquid from a nozzle. Ink-jet printers have been rapidly spreading in recent years to output numerous documents and images prepared using a computer. Such a wide spread of ink-jet printers is ascribed to the following advantages of the ink-jet printing: printing can be performed on a sheet of plain paper, formation of color images is very easy, and noise development and consumption of electric power can be reduced. Owing to the recent progress of the ink-jet recording technique, high quality ink images equivalent to photographic images can be obtained. At the same time, however, requirements for the ink-jet printing have been diversified, namely, durability of the printed ink images in terms of water resistance and light resistance, and ink-ejection stability in the course of high speed printing.
In the ink-jet recording, a variety of water-soluble dyes are commonly used as coloring agents for the ink composition. However, the use of water-soluble dyes produces some problems. Namely, the light resistance of printed ink images is poor because the water-soluble dyes have low light resistance. Further, the water resistance of printed images is also poor, which results from the use of the water-soluble dyes.
To improve the fastness of the printed ink images, some aqueous ink compositions are proposed, each employing a pigment of which light resistance and water resistance are superior to those of the water-soluble dyes. Although the pigment-containing ink composition can provide ink images with high fastness properties, the pigments capable of exhibiting a desirable hue and saturation are fewer in number than dyes. As a result, it becomes difficult for the pigment-containing ink composition to produce color ink images with a satisfactory hue and a wide range of color reproduction. In addition, when such color images are printed on a transparent sheet for an over head projector (OHP), the projected images are lacking in sharpness because of low transparency of the recorded images.
Further, most of the color-pigment containing ink compositions which have already been put to practical use are used with paper specially designed for ink-jet printing. The application of the color-pigment containing ink compositions is limited, for example, to the application particularly requiring high light resistance and water resistance of the printed images. No color-pigment containing ink composition can cope with the formation of high quality images on a sheet of plain paper at high speed.
The pigment-containing ink composition for use with ink-jet printing is required to ensure good dispersion stability and storage stability in order to prevent clogging of a nozzle from which the ink is to be ejected. For this purpose, the pigment is finely dispersed so that the average particle diameter of the pigment particles may reach at least 0.2 &mgr;m or less and the maximum particle diameter may be about 0.6 &mgr;m in the particle size distribution. Further, in an on-demand type ink-jet printer, an aqueous ink composition remaining in a nozzle is dried if ink ejection from the nozzle is stopped for a long time. In this case, evaporation of the water content from the ink composition will impair the dispersed condition of the pigment in the ink composition, and consequently, the pigment particles will tend to aggregate and adhere to the inner surface of the nozzle. Even after the evaporation of water content inside of the nozzle, the pigment particles are expected to show good dispersion properties when the nozzle is subsequently replenished with the ink composition. Such properties of the pigment will be hereinafter referred to as “re-dispersibility.” The re-dispersibility of the pigment is a very significant factor to ensure stable ink-ejection performance. On the contrary, the factor of re-dispersibility has been less considered in the conventional pigment dispersion technique although this factor is connected with the reliability of ink-jet printing.
The prior art related to the present invention is found, for example, in Japanese Laid-Open Patent Application Nos. 6-107991 and 8-209048.
An ink composition disclosed in Japanese Laid-Open Patent Application 6-107991 comprises a pigment, water-soluble resin dispersant, and a surfactant of polyoxyalkylether phosphate. This ink composition is aimed to ensure stable ink-ejection performance in the course of continuous printing by controlling the wetting of the inner surface of the nozzle by the ink. However, the viscosity of the ink composition tends to increase as a whole because of the use of the polymeric dispersant. Such tendency will often hinder the ink-ejection performance and retard the response to high frequencies that is considered essential for high-speed printing. In addition, the presence of the resin dispersant promotes aggregation and thickening of the ink composition during long-term storage. Japanese Laid-Open Patent Application 6-107991 does not suggest the ink-ejection stability after water evaporation from the ink composition remaining in the nozzle and the re-dispersibility of the pigment.
Japanese Laid-Open Patent Application 8-209048 discloses an ink composition for ink-jet recording of a thermal jet system (bubble-jet system). The ink composition comprises a disperse dye or pigment, and a water-soluble polymer and/or a surfactant, with the surfactant having a hydrophilic-lipophilic balance (HLB) of 10 or more, such as polyoxyethylene alkyl ether or polyoxyethylene alkylphenyl ether having an anionic dissociation group of phosphoric acid or carboxylic acid at the end of an ethylene oxide moiety. In this application, the above-mentioned surfactant is used to obtain fine dispersion, ensure the storage stability, and prevent the dispersant extremely heated by heating elements from adhering to the surface of the heating elements. There is no description about the ink-ejection stability and the re-dispersibility of the pigment after evaporation of water content from the ink composition in the nozzle. The HLB of the surfactant specified in Japanese Laid-Open Patent Application 8-209048 is rather wide, so that there is a possibility of the problem occurring when the selected surfactant is used in combination with any pigment illustrated in the specification. Namely, it is supposed that the ink-ejection stability may become unsatisfactory and the pigment particles may tend to adhere to the inner surface of a nozzle if the ink is allowed to stand in the nozzle without being ejected therefrom for a long time, and the water content evaporates from the ink remaining in the nozzle. In other words, the above-mentioned re-dispersibility of the pigment is poor.
Furthermore, with respect to the physical properties of the ink composition disclosed in Japanese Laid-Open Patent Application 8-209048, the surface tension of the ink composition is specified as in the range of 35 to 55 mN/m. The above specified surface tension results in slow ink permeation, so that this conventional ink composition cannot cope with the image formation on plain paper at high speed, which is one of the objects aimed by the present invention. It is impossible to forecast the phenomena to impair the ink reliability, that is, a decrease in dispersion stability and re-dispersibility of the pigment, and poor ink-ejection stability after water evaporation, which would be caused if the surface tension is controlled to less than 35 mN/m by the addition of a penetrating agent to achieve high-speed printing on plain paper. As a matter of course, Japanese Laid-Open Patent Application 8-209048 suggests no method for solving the above-mentioned problems of reliability.
With respect to yellow pigment ink compositions, monoazo pigments such as C.I. Pigment Yellow 74 and C.I. Pigment Yellow 154 as disclosed in Japanese Laid-
Arita Hitoshi
Bannai Akiko
Gotoh Akihiko
Kaneko Tetsuya
Koyano Masayuki
Faison Veronica F.
Klemanski Helene
Ricoh & Company, Ltd.
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