Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-11-20
2003-01-07
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S031280, C106S410000, C106S413000, C106S414000, C106S453000, C106S460000, C106S472000, C106S476000, C106S494000, C106S495000, C106S496000, C106S497000, C106S498000, C106S499000, C106S506000, C008S550000, C008S618000
Reexamination Certificate
active
06503317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to aqueous based pigment dispersions and ink compositions containing same wherein the pigment is dispersed in a dispersant dye in the absence of surfactants or resins.
2. Description of Related Art
Aqueous based pigment dispersions are used in a variety of industrial applications such as the manufacture of printing ink, paint, pulp and paper, coatings, and textiles to provide coloration. Inks and coatings typically contain clear extenders which generally consist of resins and additives which are suitable for the specific application. The resins and additives employed cause the pigment to adhere to the surface of the substrate being colored. Since dispersed pigments typically have fine particle sizes, one only needs to provide minimal agitation to establish coloration. Therefore, the use of dispersed pigments are convenient for color formulators.
The more common employed pigment dispersants include styrene/acrylic copolymers, acrylic polymers, polyvinyl pyrrolidone resins, octylphenol ethoxylates, acetylenics, phosphate esters, and sulfonates. There are other commercially available pigment dispersants some of these are described in the
Directory on Emulsifiers and Detergents
, Volume 1: Emulsifiers and Detergents, MC Publishing Co., Glen Rock, N.J. The choice of dispersant or class of dispersants for an aqueous pigment dispersion will depend on the end-use intended for the aqueous pigment dispersion. The pigment employed is typically hydrophobic and therefore insoluble in water. However, the dispersant may have both hydrophobic and hydrophilic properties. In an aqueous based dispersions, the hydrophobic portion of the dispersant attaches to the pigment while the hydrophilic portion resides in the aqueous phase of the dispersion. The hydrophobic portion (hydrophile) of the dispersant can be anionic, nonionic or cationic. Anionic or nonionic hydrophiles are more commonly used in the printing, ink, paint, textile and pulp and paper industries. For example, various printing ink applications, especially film printing applications, typically require the use of styrene/acrylic resin pigment dispersants. On the other hand, in textile applications non-ionic surfactant pigment dispersants are used.
The use of styrene/acrylic resins and surfactants presents a number of drawbacks when aqueous pigment dispersions are used, for example, in ink jet printing and pulp and paper applications. When used in pulp and paper applications, such use can lead to foaming which, consequently can cause defects in the paper, e.g. mottling. Foaming itself has a negative effect on pulp and paper production. In thermal cure ink jet applications, the use of resins and surfactants can clog the ink jet printing head as these components sometimes break up to form water-insoluble fragments which adhere to the interior nozzle of the print head. In addition, high surface tensions are normally required for ink jet inks in order to achieve reduced dot gain in the printed product. Due to their nature, however, surfactants tend to lower the surface tension of inks. Color gamut is another key parameter employed to measure inking systems, however, many surfactants, such as lignosulfonates, are darkly colored and therefore can detract from the colorization by the pigment.
As the aforementioned problems clearly illustrate, the use of surfactants and resins introduce a number of drawbacks related to the use of conventional aqueous pigment dispersions in industrial printing applications. Therefore, finding a dispersant that addresses these problems has become an important industry objective. Industrial initiatives presently ongoing are aimed at developing aqueous pigment dispersions for paper and pulp and ink jet printing applications that overcome these drawbacks. In the meantime, the paper and pulp and ink jet printing industries employ dyes or dye based pigments for coloration. Dyes will continue to be heavily used as colorants in these industries until the problems associated with pigmented systems have been resolved.
Improving the lightfastness of printed materials continues to be a primary objective for the large format printing market (i.e. billboards and posters). Likewise, paper mills seek to adopt pigment colorants for the improved lightfastness they offer. Doing so would offer manufacturing advantages such as eliminating the need for filtration systems to remove the excess dye from manufacturing waste streams. Moreover, the lightfastness of dye based materials is limited and improvements in this area have been slow in coming. The pulpand paper industry also uses low-end pigments such as OT Yellow and C.I. Pigment Yellow 14 for various applications. These pigments, however, only offer slightly improved lightfastness properties.
The general specification for pigments suitable for use in industrial applications include the obvious requirements of daylight resistance, alkali, acid, and heat resistance and the wettablity of the pigment by the vehicle selected. Pigments to be dispersed in aqueous vehicles are chosen for their flow characteristics, gloss level and printability. Dispersion stability is also important. Additional physical and economic requirements for the pigment is that it have low oil absorption, high color strength and be economically priced.
Dyes are fundamentally different from pigments as they are normally pure organic or metallo organic complexes which are generally soluble in the medium they color. For instance, water soluble dyes are often used in aqueous based applications. The color or tinting strength of a pigment or dye is a measure of its ability to impart color to a system. Dye color is produced by selective absorption. No discrete particles are present, no scatter occurs and the system is transparent. By contrast, pigment color is primarily related to its chemical composition, particle size and distribution. The actual color strength, in the case of a pigmented printing ink will depend upon film thickness and the concentration of the pigment. Dyes, once dissolved, are generally present as single molecules, while pigments are deaggregated to primary particles or crystals and dispersed into a medium, a process that typically requires high energy to effect suitable coloration. Primary pigment particles are composed of many thousands of molecules packed into a concentrated area having a dimension of 50 to 500 nanometers. These primary particles can be amorphous or crystalline. Dye based inks are widely used on paper for bread wrappers, bags, etc. where no lightfastness requirement is demanded. Because of their almost Newtonian behavior, low viscosity inks of high color strength may be formulated enabling clean printing to be obtained. The migration tendencies of dyes do not encourage their use on plastic films or in contact with a wide range of products. Due perhaps to their differences, the use of dyes and pigments have generally been mutually exclusive to one another. An exception is the use of dyes to form dye based pigment like materials (e.g. laked pigments such as FD&C Red No. 6, C.I. Pigment Red 81 and C.I. Pigment Violet 3). The lightfastness of a dye may be improved, for example, by using a high acid value phenolic type resin in place of, or in combination with, tannic acid, reducing the amount of resin required; a technique known as “laking”. Laking can affect the shade or coloration of the dye considerably. The lightfastness of dye based ink formulations is substantially less by comparison than that of pigment based ink formulations.
U.S. Pat. No. 3,477,866 discloses the use dyes to form dye based pigments formed from the salts of acid dyes dispersed in water using conventional surfactants and resins. U.S. Pat. No. 4,162,348 discloses the use of anionic surfactants to disperse a pigment and a dye. The two dispersions are then combined to form a single colorant. U.S. Pat. No. 4,468,230 relates to dispersions of anionic acid dyes having limited solubility using conventional surfactants. U.S. Pat. No
Ortalano Darren Mark
Vissing Christopher Joseph
Green Anthony J.
Persley Sidney
Sun Chemical Corporation
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