Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2001-01-08
2002-08-27
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031650, C106S031860, C106S031890
Reexamination Certificate
active
06440203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink composition which can yield high-quality printed images on recording media.
2. Background Art
Ink jet recording is a recording method wherein droplets of ink are ejected through fine nozzles to form letters or figures on the surface of recording media. Various properties are required of inks used in such ink jet recording, and examples thereof include good dispersion stability, ejection stability, and rubbing/scratch resistance of prints.
Inks comprising various water-soluble dyes dissolved in aqueous media have generally been used. Further, inks comprising pigments dispersed in aqueous media have also been provided. Inks comprising pigments dispersed in aqueous media are advantageously superior to inks using water-soluble dyes in waterfastness and lightfastness of printed images.
Inks for ink jet recording are required to satisfy property requirements such that, for example, properties remain unchanged during storage for a long period of time, the ink does not clog fine nozzles, prints have high density and high sharpness, and prints yielded by the inks have good storage stability, for example, in terms of waterfastness and lightfastness. In particular, in the case of pigment-based inks, storage stability (that is, stable dispersion of the pigment for a long period of time) and freedom from nozzle clogging during printing or at the time of re-starting after interruption of printing are required.
On the other hand, a method has been proposed wherein the penetration of an ink composition is enhanced to shorten the drying time of printed images and, in addition, to form large pixels (for example, dots) using a small amount of ink. For example, the use of a color ink containing a surfactant or a solvent capable of penetrating recording media and a salt, which can impart a capability of penetrating recording media to ink, has been proposed (Japanese Patent Laid-Open No. 106735/1994).
The penetrating pigment-based ink is advantageous in that the ink component can effectively penetrate recording media, but on the other hand, in some cases, the color development is somewhat poor when this ink is printed on plain paper. Enhancing the content of the pigment in the ink is considered effective for improving the color development. Enhancing the content of the pigment, however, often enhances the viscosity of ink, and thus is often unfavorable for the ejection stability of ink. Ink using a self-dispersible pigment can prevent an increase in viscosity even when the content of the pigment in the ink is increased. Further, this ink has excellent color development. In some cases, however, this ink is somewhat poor in fixation on recording media. The addition of a resin emulsion or a water-soluble resin has been proposed as means for improving the fixation of ink. In general, however, the addition of the resin emulsion or the water-soluble resin is likely to enhance the viscosity of the ink.
SUMMARY OF THE INVENTION
The present inventors have now found that an ink composition containing a first colorant and a second colorant can realize good printed images. The present inventors have particularly found that this ink composition, when used in an ink jet recording method, can exhibit excellent color development, can be stably ejected, does not cause nozzle clogging, can realize stable printing, and can realize images having excellent fixation. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide an ink composition which can realize good images, especially an ink composition which, when used in an ink jet recording method, exhibits excellent color development and fixation and can realize good image quality.
According to a first aspect of the present invention, there is provided an ink composition comprising: a first colorant; a second colorant; a penetrating agent; water; and a water-soluble organic solvent,
said first colorant being a pigment which is dispersible and/or dissolvable in water without any dispersant, said second colorant being a pigment dispersion comprising a pigment and a dispersant for dispersing the pigment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Ink Composition
The ink composition according to the present invention is used in recording methods using ink compositions, for example, ink jet recording, recording method using writing utensils, such as pens, and other various printing methods. Particularly preferably, the ink composition according to the present invention is used in the ink jet recording method.
The ink composition according to the present invention comprises a first colorant, a second colorant, a penetrating agent, water, and a water-soluble organic solvent.
First Colorant
According to the present invention, the first colorant is a pigment which has been rendered dispersible and/or dissolvable in water without any dispersant, and is generally called “self-dispersible pigment.” This pigment has been rendered dispersible and/or dissolvable in water without any dispersant by treating a pigment on its surface so as to bond at least one functional group selected from the group consisting of carbonyl, carboxyl, hydroxyl, and sulfone groups, or a salt thereof, onto the surface of the pigment. More specifically, this surface-treated pigment may be prepared by grafting a functional group or a molecule containing a functional group onto the surface of carbon black by physical treatment, such as vacuum plasma, or chemical treatment (for example, oxidation with hypochlorous acid, sulfonic acid or the like). According to the present invention, a single type or a plurality of types of functional groups may be grafted on one carbon black particle. The type and the degree of grafting of the functional group(s) may be properly determined by taking into consideration, for example, dispersion stability in ink, color density, and drying properties at the front end of an ink jet head.
In the present invention, when the pigment is stably present in water without any dispersant, this state is expressed as the state of “dispersion and/or dissolution.” Not infrequently, it is difficult to clearly distinguish the state of dissolution of a material from the state of dispersion of the material. In the present invention, any pigment can be used so far as the pigment can stably exist in water without any dispersant, independently of whether the pigment is in a dispersion form or a solution form. Therefore, in the present specification, a pigment, which can stably exist in water without any dispersant, is sometimes referred to as a “first colorant.” The pigment in this case, however, does not exclude a pigment which is in the state of dispersion.
Preferred pigments usable in the present invention may be produced, for example, by a method described in Japanese Patent Laid-Open No. 3498/1996. Carbon black treated by the method described in this publication has a high surface active hydrogen content of 1.5 to 2.5 mmol/g. As a result, the dispersibility of the treated carbon black in water is very high. Commercially available products may also be used as the above pigment, and preferred examples thereof include Microjet CW 1 manufactured by Orient Chemical Industries, Ltd.
For the pigment used in the first colorant, inorganic and organic pigments may be used without particular limitation so far as, as described above, they can be rendered dispersible and/or dissolvable in water without the aid of any dispersant. Inorganic pigments usable herein include, in addition to titanium oxide and iron oxide, carbon blacks produced by known processes, such as contact, furnace, and thermal processes. Organic pigments usable herein include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments), polycyclic pigments (for example, phthalocyanine, perylene, perinone, anthraquinone, quinacridone, dioxazine, thioindigo, isoindolinone, and quinophthalone pigments), dye-type chelate pigments (for exampl
Klemanski Helene
Ladas & Parry
Seiko Epson Corporation
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