Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-06-28
2003-07-29
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C406S031000, C406S150000, C406S150000, C406S150000, C406S150000, C406S150000, C406S150000, C406S150000, C406S150000, C406S150000, C210S767000, C210S787000, C347S100000
Reexamination Certificate
active
06599356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a pigment dispersed liquid, to the pigment dispersed liquid obtained by this method, and to pigment ink in which this pigment dispersed liquid is used. The pigment dispersed liquid of the present invention and the pigment ink in which this pigment dispersed liquid is used can be advantageous for ink-jet printer inks that are discharged from a recording head by subjecting the ink to discharge energy by utilizing mechanical energy (produced with a piezoelectric device or the like) or thermal energy (produced with a heating element). Also, the pigment dispersed liquid of the present invention and the pigment ink in which this pigment dispersed liquid is used can be employed in various applications, such as ink for fountain pens, ball-point pens, felt-tip pens and other writing implements, industrial coating liquids, and paints that are used for airbrushes, and so forth.
2. Description of the Related Art
Dyes have been mainly used as the colorant for ink-jet printer inks, but in recent years the use of pigments has been investigated because of its better durability. When a pigment is used as a colorant, the recording product has superior water resistance, light fastness, and other aspects of durability, as compared to when a dye is used.
Unlike dyes, pigments do not dissolve in water, so when they are used as a colorant for water-based inks, a resin or other such dispersant is adsorbed to the pigment surface and the pigment particles are dispersed in water for use. It is difficult, though, to keep a pigment in a stable dispersed state within an aqueous medium, and the adsorbed dispersant may come off the pigment surface, which can lead to a situation in which the colorant is dispersed in the form of particles and the pigment particles agglomerate together and precipitate. Moreover, when the particles are relatively large in diameter (300 nm or more), the state in which the particles of the colorant are dispersed may cause detrimental effects such as settling of the pigment due to the weight of the pigment particles themselves.
In some cases, other than the colorant and water, various solvents, surfactants, and so forth were also added to an ink-jet printer ink or a bubble-jet printer ink. It was difficult to maintain a stable dispersed state with a conventional method in which a resin or other such dispersant was used to disperse pigment particles in an aqueous medium. Also, when a resin-dispersed pigment ink was used in continuous printing, the resin would adhere and remain around the nozzles of the ink jet head or the like, and this built-up resin would deflect the ink trajectory, or the resin would dry and solidify within the nozzles as the water evaporated, and this would sometimes lead to poor discharge.
In view of this, various techniques have been proposed for obtaining self-dispersing pigments by imparting water dispersibility to the pigment itself. For instance, in Japanese Laid-Open Patent Applications H10-195360, H10-330665, and elsewhere, it has been proposed to used a self-dispersing carbon black pigment in which carboxyl groups, carbonyl groups, sulfone groups, hydroxyl groups, or other such hydrophilic groups are bonded, either directly or via polyvalent groups, to the surface of the carbon black; in Japanese Laid-Open Patent Applications H8-3498, H10-195331, H10-237349, and elsewhere it has been proposed that dispersibility can be improved by oxidizing the surface of the carbon black; and in Japanese Laid-Open Patent Applications H8-283598, H1-10110, H10-110111, and elsewhere, it has been proposed to use a surface-treated pigment in which sulfone groups have been introduced at the surface of an organic pigment.
Also, Japanese Laid-Open Patent Application H11-49974 discusses the preparation of an organic pigment block that is positively charged on the surface by using an organic pigment block in which sulfone groups have been introduced and treating it with monovalent metal ions; also a water-based ink composition with excellent storage stability, which contains water, a dispersant, and pigment microparticles prepared from this organic pigment block with a positively charged surface is discussed.
Various ink properties are required of ink used in an ink-jet printer, but it is especially important to ensure the storage stability of the ink itself and the discharge stability during ink-jet recording (preventing clogging, deflection, and so forth). Excellent quality is also required of the print on the recording paper (such as a printed image with high print density and little bleeding). Specifically, it is desirable for an ink-jet printer ink to simultaneously satisfy the above-mentioned ink properties, discharge characteristics, and high print quality. Because the self-dispersing surface-treated pigment has dispersion groups that work through chemical bonding on its surface, it has excellent storage stability, making it easy to ensure the various requirements of an ink-jet printer ink as discussed above are met.
Today, however, an ink-jet printer must be capable of printing very fine printed images at high speed, and extremely fine ink dots have to be discharged at a higher frequency than in the past. Therefore, the ink that is used is also subject to more stringent requirements in order to achieve stable printing characteristics. In particular, with a pigment ink, which unlike a dye consists of particles dispersed in the ink, achieving both stable discharge characteristics and good storage stability has become quite difficult even with a self-dispersing pigment ink whose basic characteristics are excellent.
It is therefore hoped that a pigment ink for ink-jet printers will be developed, which can be used for today's ink-jet printers with fine nozzles, to achieve high image quality, and which can secure storage stability and the required printing characteristics.
DISCLOSURE OF THE INVENTION
Concerning the manufacture of ink containing a self-dispersing surface-treated pigment as described above, the inventors conducted diligent research into the conditions for satisfying the above-mentioned storage stability (particularly, the storage stability under the condition when the ink is left aside at high temperatures), and discharge stability (prevention of clogging, ink deflection, and so forth), whereupon they discovered that it is important to optimize the refining treatment of a pigment or pigment dispersed liquid upon dispersing a surface-treated pigment in an aqueous solvent. Particularly, they discovered that it is very important to conduct, under optimal conditions, membrane process, such as precision filtration, ultrafiltration, dialysis filtration, reverse osmosis, or electrodialysis, of the pigment dispersed liquid, or to conduct centrifugal sedimentation filtration by repeating centrifugal sedimentation and dispersion of the pigment. The present invention is based on this finding.
Accordingly, this invention is a method for manufacturing a pigment dispersed liquid, comprising at least: Step A of introducing a hydrophilic dispersibility-imparting group directly and/or via another atomic group to the surface of pigment particles; Step B of dispersing the pigment obtained in Step A in an aqueous medium; and Step C of conducting refining treatment of the dispersed liquid obtained in Step B.
According to a preferred embodiment of this invention, the pigment in which a hydrophilic, dispersibility-imparting group has been introduced directly and/or via another atomic group in Step A is a carbon black pigment and/or an organic pigment.
According to a preferred embodiment of this invention, the pigment in which a hydrophilic, dispersibility-imparting group has been introduced directly and/or via another atomic group in Step A is one or more pigments selected from the group consisting of C.I. pigment yellow, C.I. pigment red, C.I. pigment violet, C.I. pigment blue, C.I. pigment orange, C.I. pigment green, and C.I. pigment brown.
According to a preferred
Hara Kazuhiko
Hayashi Hiroko
Komatsu Hidehiko
Ota Hitoshi
Green Anthony J.
Seiko Epson Corporation
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