Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2000-11-02
2003-03-04
Dawson, Robert (Department: 1712)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031130, C106S031250, C106S031270, C106S287180, C106S287190, C106S001220, C523S161000, C523S200000, C523S205000, C523S212000, C427S216000, C427S220000, C428S402000, C428S403000
Reexamination Certificate
active
06527843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fine colored particles having good dispersibility and ink jet ink including the same.
2. Description of the Related Art
Dye ink has excellent transparency, high definition and good color development properties, and therefore dye ink is used as an ink for applications requiring high definition. However, dye ink has problems with regard to water resistance and light resistance. In order to solve these problems, inks using organic pigments or carbon black in place of the dye are produced.
However, for inks using organic pigments or carbon black, the organic pigments or carbon black are pulverized and dispersed mechanically with the help of a dispersant. Without pulverizing the organic pigments or the carbon black into fine particles and dispersing them stably in a medium, good transparency, high definition and good color development properties cannot be obtained, and in addition, problems with respect to, for example, secondary aggregation and storage stability may be caused. Furthermore, insufficient pulverization and dispersion may cause clogging of nozzles in ink jet ink applications.
On the other hand, mechanically making the particle size of the organic pigment or the carbon black very small requires a large amount of energy because then the surface energy becomes large. In addition, various efforts are required to prevent secondary aggregation and maintain the dispersion stability.
In order to solve these problems, the following methods were proposed as alternatives to the conventional method of pulverizing and dispersing the organic pigment or the carbon black with the help of a dispersant: using microcapsulated fine colored particles containing dye as ink (Japanese Laid-Open Patent Publication No. 62-95366); using colored emulsion polymerized particles as ink (Japanese Laid-Open Patent Publication No. 6-313141); obtaining lake pigment fine particles using a W/O emulsion (Japanese Patent Publication No. 7-47696); and making a colorant by adsorbing a dye onto porous ceramic fine particles (Japanese Laid-Open Patent Publication No. 9-71732).
However, the microcapsulated fine colored particles containing dye and the colored emulsion polymerized particles have a large particle size, and therefore have problems in the transparency and the definition degree and the color development properties. Furthermore, the concentration of a coloring material contained therein is low, so that the coloring ability is not sufficient.
The lake pigment fine particles prepared using a W/O emulsion employs emulsion, and therefore it is difficult to obtain particles as fine as several tens of nanometers with a high reproducibility, and the distribution of the particle size of the obtained particles is large. When the distribution of the particle size of the obtained particles is large, the saturation is deteriorated. Moreover, the production process is complicated.
To make a colorant by adsorbing a dye on porous ceramic fine particles, a particle aggregate produced by, for example, a sol-gel method is pulverized and used for the colorant. In this case, it is difficult to obtain a colorant comprising particles having a very small particle size and a narrow particle size distribution. Furthermore, the production process is complicated because it includes the steps of producing porous ceramic fine particles and then adsorbing a dye thereon.
Furthermore, when porous particles on which a dye is adsorbed are dispersed in a liquid medium to prepare ink, since the adsorption of the dye is only physical adsorption, the adsorbed dye may be desorbed again due to a change in the pH of the liquid medium or addition of a surfactant.
When it is adsorbed and used as ink, a surfactant may be added. In this case, the surfactant is adsorbed on the porous particles only physically, so that the surfactant may be desorbed due to a change in the pH of the liquid medium. The desorption of the surfactant impairs the function as ink.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve these problems. The inventors of the present invention found that when a hydrosol of fine particles comprising a metal oxide and a metal hydroxide having a nanometer particle size is reacted with a dye and an organic compound having an ionic group, fine colored particles having a nanometer size and a narrow particle size distribution that are coated with the organic compound can be obtained reliably and with a high reproducibility. Furthermore, such fine colored particles can be dispersed easily in either a nonpolar or a polar solvent and the dye is not eluded from the particles, so that a coloring liquid having good color properties, transparency and dispersion stability can be obtained. Thus, the inventors realized the present invention.
Thus, the present invention provides fine colored particles having excellent storage stability, transparency, high definition, color development properties, and coloring ability and thus has an excellent performance as a coloring material for ink jet ink.
The present invention relates to fine colored particles comprising a dye and a metal oxide, wherein the surface of the fine particles is coated with an organic compound having an ionic group (hereinafter, referred to as the fine colored particles of the present invention).
In a preferable embodiment, the metal oxide is a metal oxide hydrosol.
In a preferable embodiment, the surface of the fine particles and the ionic group interact electrically.
In a preferable embodiment, the organic compound having the ionic group is an ionic surfactant.
In a preferable embodiment, the electrical interaction is ionic bonding.
In a preferable embodiment, the surface of the fine particles is coated with the organic compound having the ionic group with the ionic group facing the surface of the particles, and further coated with a surfactant with its hydrophobic portion facing inward.
In a preferable embodiment, the CV value indicating a particle size distribution of the fine colored particles is 50% or less.
In a preferable embodiment, the CV value indicating a particle size distribution of the fine colored particles is 40% or less.
In a preferable embodiment, the CV value indicating a particle size distribution of the fine colored particles is 30% or less.
In a preferable embodiment, the metal oxide is selected from the group consisting of titanium oxide, aluminum oxide, zirconium oxide, iron oxide, tin oxide, zinc oxide, cerium oxide and mixtures of at least two of these oxides.
In a preferable embodiment, the dye is encapsulated in the metal oxide, or the dye is adsorbed on the surface of the metal oxide particles.
In a preferable embodiment, the average particle size of the fine colored particles is 1 nm to 500 nm.
In a more preferable embodiment, the average particle size of the fine colored particles is 3 nm to 250 nm.
In a preferable embodiment, the metal oxide is produced from a metal chloride, a metal hydroxide, a metal nitrate, a metal sulfate, or a metal acetate.
According to another aspect of the present invention, ink jet ink comprising the fine colored particles of the present invention and a liquid medium (hereinafter, referred to as an ink jet ink of the present invention).
In a preferable embodiment, the liquid medium used in the ink jet ink of the present invention is based on water or a hydrophilic organic solvent. The liquid medium is based on a hydrophobic organic solvent.
According to another aspect of the present invention, a first method for producing fine colored particles whose surface is coated with an organic compound having an ionic group includes (a) preparing an aqueous solution of at least one metal compound selected from the group consisting of a metal chloride, a metal hydroxide, a metal nitrate, a metal sulfate, and a metal acetate; (b) adjusting a pH of the aqueous solution of the metal compound so as to produce a hydrosol of fine particles comprising a metal oxide and a metal hydroxide; (c) adding an organic compound having an i
Matsui Hideo
Zaima Hiroaki
Dawson Robert
Kansai Research Institute, Inc.
Robertson Jeffrey B.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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