Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2001-01-23
2003-04-29
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031890, C106S472000, C106S473000, C106S474000, C106S475000, C106S476000, C106S477000, C106S478000
Reexamination Certificate
active
06554891
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink composition containing a surface-modified pigment.
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 recording media. Various properties are required of inks used in such ink jet recording, and examples thereof include good storage stability, ejection stability, and rubbing/scratch resistance of prints.
An ink compositions is an aqueous solution which dissolves various water-soluble dyes. Further, inks in which pigments dispersed have also been provided. The ink composition comprising pigments dispersed in aqueous media are advantageously superior to ink compositions containing water-soluble dyes in waterfastness and lightfastness of printed images.
On the other hand, inks for ink jet recording are required to satisfy property requirements such that properties remain unchanged during storage for a long period of time, the storage stability is excellent (for example, the pigment can be stably kept in the state of dispersion for a long period of time), the ink does not clog fine nozzles, and prints yielded by the inks have excellent waterfastness and lightfastness. In particular, it is necessary for pigment-based inks to be realized high print density and high sharpness of prints and to free from nozzle clogging during printing or at the time of re-starting after interruption of printing. Japanese Patent Laid-Open Nos. 6074/1989 and 31881/1989 propose water-base pigment inks wherein carbon black has been dispersed with the aid of a surfactant or a polymeric dispersant. In these inks, however, increasing the content of a pigment as the colorant in the ink to enhance the print density of records has resulted in increased viscosity of the ink which disadvantageously deteriorates the anti-clogging properties. Further, a surfactant or a polymeric dispersant is necessary to improve the dispersion stability of the pigment. The addition of an excessive amount of the surfactant and the polymeric dispersant, however, is causative of the occurrence of bubbles or deteriorated antifoaming properties. For this reason, the use of such inks for ink jet recording often adversely affects printing stability.
In order to reduce drying of an ink using a dispersant and a pigment within fine nozzles, Japanese Patent Laid-Open No. 41396/1996 proposes a method wherein glycerin and propylene glycol are added in respective proper amounts. This method, however, is not satisfactory for meeting the requirement for anti-clogging properties in ink jet recording.
On the other hand, an attempt has been made to improve the dispersion stability of pigments in ink without using any dispersant. For example, Japanese Patent Laid-Open Nos. 3498/1996 and 120958/1998 propose inks using a surface-modified carbon black which has introduced surface active hydrogen or a salt thereof in a given amount or larger into the surface of carbon black. This carbon black can be dispersed without the aid of a surfactant or a polymeric dispersant. Further, Japanese Patent Laid-Open No. 110127/1998 describes a method for introducing sulfone groups into carbon black, and Japanese Patent Laid-Open No. 95941/1998 proposes an ink for ink jet recording, comprising the above surface-modified carbon black and a glycol ether.
SUMMARY OF THE INVENTION
The present inventors have now found that an ink composition, comprises a surface-modified pigment, a specific amount of glycerin and a specific amount of a glycol compound having a specific molecular weight can realize good printed images and, particularly when used in ink jet recording, has excellent anti-clogging properties and can realize images having high print density. 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 has excellent anti-clogging properties and can realize images having high print density, especially an ink composition which is best suited for use in ink jet recording.
Thus, according to the present invention, there is provided an ink composition comprising at least a colorant, glycerin, a glycol compound, and water, the colorant being a surface-modified pigment dispersible and/or dissolvable in water without any dispersant, the glycerin being contained in an amount of 3 to 30% by weight based on the ink composition, the glycol compound being contained in an amount of 1 to 20% by weight based on the ink composition and having a molecular weight of 130 to 3,000.
DETAILED DESCRIPTION OF THE INVENTION
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 at least a colorant, glycerin,; a glycol compound, and water.
a) Colorant
The ink composition according to the present invention contains a colorant. According to the present invention, the colorant is a pigment which has been rendered dispersible and/or dissolvable in water without a surfactant or a dispersant, such as a water-soluble resin, and is generally called “self-dispersible pigment.”
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 “colorant.” The pigment in this case, however, does not exclude a pigment which is in the state of dispersion.
The modification of the surface of the pigment to render the pigment “dispersible and/or dissolvable” may be carried out by directly bonding at least one hydrophilic functional group selected from the group consisting of, for example, carboxyl, carbonyl, hydroxyl, sulfone, and phosphoric acid groups and quaternary ammonium, or a salt thereof, onto the surface of the pigment. According to the present invention, the surface modification may be carried out by bonding at least one hydrophilic functional group, selected from the group consisting of carboxyl, carbonyl, hydroxyl, sulfone, and phosphoric acid groups and quaternary ammonium, or a salt thereof, onto the surface of the pigment through at least one group selected from the group consisting of alkyl, alkyl ether, and aryl groups.
More specifically, this surface-modified carbon black 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). The surface-modified carbon black may also be obtained by oxidizing the surface of a pigment with an oxidizing agent in water to introduce carboxyl or sulfone groups, or by bonding p-aminobenzoic acid or the like to the pigment to introduce carboxyl groups through a phenyl group. In the present invention, a single type or a plurality of types of functional groups may be grafted onto one pigment particle. The type of the functional group to be grafted and the degree of grafting may be suitably determined by taking into consideration the dispersion stability in the ink, the color density, the drying property at the front face of the ink jet head and the like.
According to the present invention, the surface-modified pigment is preferably one produ
Ito Hiroshi
Momose Masayuki
Bell Mark L.
Faison Veronica F.
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