Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-10-19
2003-02-25
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S031600, C106S031750, C106S031770, C106S031800, C106S031850, C106S031860, C106S031890, C106S031900, C106S410000, C106S412000, C106S472000, C106S473000, C106S474000, C106S476000, C106S494000, C106S495000, C106S496000, C106S497000, C106S498000, C106S499000, C347S100000
Reexamination Certificate
active
06524383
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for manufacturing a pigment dispersion, to the pigment dispersion obtained by this method, and to a pigment ink in which this pigment dispersion is used. The pigment dispersion of the present invention and the pigment ink in which this pigment dispersion is used can be used to advantage for ink jet printer inks that are discharged from a recording head by subjecting the ink to discharge energy utilizing mechanical energy (produced with a piezoelectric device or the like) or thermal energy (produced with a heating element). Also, the pigment dispersion of the present invention and the pigment ink in which this pigment dispersion is used can be used in various applications, such as inks 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.
BACKGROUND ART
In the past, 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 the better durability of pigments. 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.
Meanwhile, 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 with 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, such as when the pigment particles agglomerate together and precipitate or, when the particles are relatively large in diameter, the weight of the pigment particles themselves causes them to precipitate naturally.
Because various solvents, surfactants, and so forth are also generally present in an ink jet printer ink along with the colorant and water, 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 around the nozzles of the ink jet head, and this built-up resin would deflect the ink trajectory, or resin would dry and solidify within the nozzles as the water evaporated, and this would 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 a self-dispersing carbon black 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 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 carbon black; and in Japanese Laid-Open Patent Applications H8-283598, H10-110110, H10-110111, and elsewhere it has been proposed 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 sulfqne groups have been introduced and treating it with monovalent metal ions, and also discusses 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.
Further, Japanese Laid-Open Patent Application 2000-53902 proposes an ink in which the colorant consists of pigment particles (giant molecule chromophores) having water-solubilizing functional groups and a polymer on their surface, which is accomplished by interposing benzene rings introduced into carbon black.
Various ink properties are required of a ink used in an ink jet printer, but it is especially important to ensure the storage stability of the ink itself and 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 above-mentioned 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 characteristics required of an ink jet printer ink as discussed above.
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. Therefore, the ink that is used is also subject to much more stringent requirements in order to achieve stable printing characteristics. In particular, unlike a dye, with a pigment ink having 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. Also, since the colorant is still a dispersion system even with a self-dispersing pigment, the problem of settling that occurs when the particles are large in diameter remains unsolved.
It is therefore an object of the present invention to provide a self-dispersing pigment dispersion with which stable printing characteristics can be obtained even with today's high-quality, high-speed ink jet printers, and with which storage stability and high print quality can be ensured and natural precipitation of the pigment can be kept to a minimum.
DISCLOSURE OF THE INVENTION
The inventors conducted diligent research into the conditions for satisfying the above-mentioned printing characteristics, storage stability, and precipitation characteristics required of an ink jet printer ink in the manufacture of pigment dispersions that make use of these self-dispersing pigments, whereupon they discovered that it is of the utmost importance to add a suitable wetting agent ahead of time and perform the dispersion treatment in this mixed state in the step of dispersing in an aqueous medium a self-dispersing pigment that has been surface treated. The present invention is based on this finding.
Therefore, the method of the present invention for manufacturing a pigment dispersion comprises the steps of surface-treating a self-dispersing type of pigment, in which at least a hydrophilic, dispersibility-imparting group is introduced to the pigment surface directly and/or via a polyvalent group, and dispersing the self-dispersing pigment obtained in the surface treatment step in an aqueous medium, wherein this method for manufacturing a pigment dispersion is characterized in that the dispersion step is a step in which at least the self-dispersing pigment, a wetting agent, and water are dispersed in the form of a liquid mixture.
In a preferred embodiment of the present invention, a surface tension of the mixture in the dispersion step is no more than 40 mN/m.
In a preferred embodiment of the present invention, a pigment concentration of the mixture in the dispersion step is no more than 50 wt %.
In a preferred embodiment of the present invention, the wetting agent in the dispersion step is one or more substances selected from the group consisting of acetylene glycols, acetylene alcohols, glycol ethers, and alkylene glycols.
In a preferred emb
Hara Kazuhiko
Komatsu Hidehiko
Nakamura Hiroto
Ohta Hitoshi
Yatake Masahiro
Green Anthony J.
Seiko Epson Corporation
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