Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-02-09
2002-10-22
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S472000, C423S449400
Reexamination Certificate
active
06468342
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aqueous pigment dispersion, and more particularly concerns an aqueous pigment dispersion containing carbon black having improved long-term aqueous dispersing property as a colorant and a preparation method thereof as well as an aqueous dispersion capable of increasing a writing or printing density and a preparation method thereof.
BACKGROUND OF THE INVENTION
Conventionally, aqueous dye ink containing a black dye has been mainly used as a recording solution used for writing tools and ink-jet printers. In recent years, in order to improve picture quality and durability of a recorded object, aqueous pigment ink using a pigment such as carbon black has received much attention.
For example, Japanese Patent Laid-Open Publication No. 6074/1989 and Japanese Patent Laid-Open Publication No. 31881/1989 have disclosed aqueous pigment ink in which carbon black is dispersed by using a surfactant and a polymer dispersant.
However, in this type of ink, when content of the colorant in ink is increased in order to raise printing density of a recorded object, the problem arises of which ink viscosity rapidly increases at the same time. Moreover, in order to stably disperse carbon black, it is necessary to add excessive amounts of a surfactant and a polymer dispersant; however, these may cause generation of bubbles and degradation in antifoaming property, resulting in degradation of printing stability, especially in the case of the application of ink-jet recording ink.
In order to solve the above-mentioned problems, Japanese Patent Laid-Open Publication No. 3498/1996 and Japanese Patent Laid-Open Publication No. 120958/1998 have disclosed an aqueous pigment dispersion in which carbon black is wet-oxidized by using hypohalite so that a group containing certain amount of active hydrogen (for example, a carboxyl group or a hydroxyl group) or a salt thereof is introduced onto a surface of carbon black, thereby allowing the surface modified carbon black itself to spontaneously disperse without the need of a surfactant and a polymer dispersant.
On the other hand, with respect to a refining method for macromolecule chromophore (MMC) for forming a pigment for ink-jet ink, Japanese Patent Laid-Open Publication No. 222573/1999 has disclosed a method in which: an aqueous solution of MMC is prepared, a liquid having desired counter ion is added to the solution, this is membrane-filtered, and the liquid addition and the filtration are repeated so that crust formation and corrugation are reduced, thereby making it possible to improve reliability of ink, such as long-term ink stability.
SUMMARY OF THE INVENTION
The first objective of the present invention is to further improve the above-mentioned surface modified carbon black in its initial dispersing property to water and in its long-term dispersing property, and consequently to provide an aqueous pigment dispersion that is less susceptible to aggregation of carbon black particles and has superior dispersion stability. The second objective of the present invention is to provide an aqueous pigment dispersion that provides superior printing density when used as ink-jet ink.
In general, surface modified carbon black, obtained by wet-oxidizing carbon black by using hypohalite, contains a great amount of alkali metal cation and halogen ion, in particular, chlorine ion. This is because upon oxidizing carbon black, hypohalite generates an alkali metal cation and halogen ion.
The inventors of the present invention have found that amounts and kinds of alkali metal cation and halogen ion give influences on the surface modified carbon black in its dispersing stability to water and in its printing density and the like when used as ink-jet ink. Then, they have further found that it is possible to greatly improve the surface modified carbon black in its dispersing stability to water by limiting concentration of alkali metal cation and halogen ion contained in the aqueous pigment dispersion, and also to greatly improve its printing density as ink jet ink by specifying kinds of the alkali metal cation; thus, the present invention has been accomplished.
The present invention provides an aqueous pigment dispersion containing surface modified carbon black that is obtained by wet-oxidizing carbon black by using hypohalous acid and/or a salt thereof, and alkali metal cation, and the aqueous pigment dispersion is characterized in that concentration of the alkali metal cation is not more than 2% by weight.
Moreover, the present invention provides an aqueous pigment dispersion containing surface modified carbon black that is obtained by wet-oxidizing carbon black by using hypohalous acid and/or a salt thereof, alkali metal cation and halogen ion, and the aqueous pigment dispersion is characterized in that concentration of the alkali metal cation is not more than 2% by weight and concentration of the halogen ion is not more than 1000 ppm.
With respect to the alkali metal cation, potassium ion and rubidium ion are preferably used.
An aqueous pigment dispersion of the present invention is preferably prepared by using a method that has the steps of: finely dispersing carbon black into water; oxidizing the carbon black by using hypohalous acid and/or a salt thereof; and adjusting concentration of alkali metal cation in the solution to not more than 2% by weight. This method may also include the step of adjusting concentration of halogen ion to not more than 1000 ppm, and may further include the step of substituting alkali metal ion in the solution by potassium ion.
DETAILED DESCRIPTION OF THE INVENTION
An aqueous pigment dispersion of the present invention contains surface modified carbon black that is obtained by wet-oxidizing carbon black by using hypohalous acid and/or a salt thereof, and in the aqueous pigment dispersion, alkali metal cation and halogen ion generated upon wet-oxidizing carbon black are removed to not more than certain amount.
Here, the alkali metal cation refer to lithium ion (Li
+
), sodium ion (Na
+
), potassium ion (K
+
), rubidium ion (Rb
+
), cesium ion (Cs
+
) and the like. Concentration of alkali metal cation in the aqueous pigment dispersion may be measured by using, for example, an atomic absorption analysis method.
In this case, halogen ion refers to chlorine ion (Cl
−
), bromine ion (Br
−
), iodine ion (I
−
) and the like. Amount of halogen ion in the aqueous pigment dispersion may be measured by using, for example, an ion electrode.
With respect to carbon black as raw materials, coloring carbon black generally available in the market may be used. More specifically, when classified based upon pH, any of acidic carbon black, neutral carbon black and basic carbon black may be used, and when classified based upon a manufacturing method, any of furnace-type carbon black, channel-type carbon black, acetylene-type carbon black and thermal-type carbon black may be used.
Specific examples of carbon black used in the present invention include: #900, MA600 and MA77 (made by Mitsubishi Kagaku K.K.), Color Black FW18, Color Black S170, Special Black 4A and Printex 30 (made by Degussa Corp.), Monarch 880, Regal 250R, Regal 400R and Regal 660R (made by Cabot Corp.), Raven 1040, Raven 1255 and Conductex SC ULTRA (made by Columbian Chemicals Co.). Here, these are only examples of preferable carbon black, and the present invention is not intended to be limited by these.
In the present invention, such carbon black as raw materials is wet-oxidized in water by using hypohalous acid and/or a salt thereof. Specific examples of the hypohalous acid and/or a salt thereof include: sodium hypochlorite and lithium hypochlorite, sodium hypobromite, and lithium hypobromite; and sodium hypochlorite is particularly preferable from the viewpoint of reactivity and costs.
The oxidizing reaction is carried out as follows: Carbon black and hypohalite (for example, sodium hypochlorite) having an effective halogen concentration of 5 to 15% by weight are loaded into an appropriate amount of water,
Itoh Sohko
Matsui Makiko
Murai Nobuyuki
Yagyu Tatsuya
Green Anthony J.
Orient Chemical Industries Ltd.
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