Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-06-11
2002-12-17
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C523S335000
Reexamination Certificate
active
06495302
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally directed to toner processes, and more specifically, to chemical processes which involve the aggregation and fusion of latex, colorant like pigment, or dye, and additive particles into toner particles, and wherein aggregation can be primarily controlled by utilizing a coagulant of polyaluminum chloride (PAC), and wherein there can be selected a latex comprised of, for example, submicron resin particles of, for example, about 0.1 to about 0.4 micron in volume average diameter, suspended in an aqueous phase of water, nonionic and anionic surfactants and optionally suspended in an anionic surfactant to which is added a colorant dispersion comprising, for example, submicron colorant particles of, for example, about 0.08 to about 0.3 micron in volume average diameter, anionic surfactant, or optionally a nonionic surfactant, or mixtures thereof, and optionally adding a wax dispersion comprised of submicron wax particles, for example about 0.1 to about 0.3 micron in volume average diameter, suspended in an aqueous phase of water and an anionic surfactant, and wherein the resultant blend is optionally stirred and heated to a temperature below the resin Tg, resulting in aggregates to which optionally is added a second latex, to which there is added an organic water soluble or water insoluble chelating agent wherein soluble refers, for example, to 100 percent soluble or dissolvable, and insoluble refers, for example, to less than about 50 percent soluble, and more specifically, zero percent solubility in, for example, water, adjusting the pH of the mixture with a base, and heating the mixture to a temperature above the resin Tg, followed by lowering the pH of the mixture with an acid to fuse the aggregates.
More specifically, the present invention is generally directed to the aggregation of latex, colorant like pigment, dye, or mixtures thereof, and optionally a wax in the presence of polyaluminum chloride (PAC) and optionally aluminum salts as a second coagulant, and wherein the coalescence or fusion of the aggregates is accomplished by first adding an organic chelating reagent followed by a reduction of the pH with an aqueous solution of, for example, nitric acid wherein the chelating agent prevents the formation of aluminum ions (Al
3
+) which could act as a coagulant thereby initiating further growth in particle size when the pH of the mixture is reduced to below about 3.5, and wherein there are generated toner compositions with, for example, a volume average diameter of from about 1 micron to about 25 microns, and more specifically, from about 2 microns to about 12 microns, and a narrow particle size distribution of, for example, from about 1.10 to about 1.33, and more specifically, a size distribution of about 1.11 to about 1.25, the size and size distribution being measured by a Coulter Counter without the need to resort to conventional pulverization and classification methods. Furthermore, the present invention in embodiments enables minimum washing, for example about 2 to about 4 washings to provide a suitable toner triboelectrical charge such as greater than about 20 &mgr;C/g at 20 percent RH. The toners generated can be selected for known electrophotographic imaging and printing processes, including digital color processes.
In embodiments of the present invention, an organic chelating component is primarily utilized to freeze or stabilize the aggregates particle size during coalescence in the presence of a base, for example sodium hydroxide. In polyaluminum chloride (PAC) processed wherein only a base is utilized as a freezing or stabilizing agent, upon reducing the pH of the mixture below about 3.5 there results the formation of aluminum ions (Al
3
+) which then will result in flocculation or further aggregation of the particles causing uncontrolled and undesirable processes. The present invention is directed toward overcoming this disadvantage by using organic chelation reagents which react with Al
3+
to form a stable complex which can withstand a low pH, for example a pH of about 2 to about 3.5 when the organic chelating reagent is, for example, 8-hydroxquinoline, salicylic acid, aluminum, 3,4-dihydrobenzoic acid, and the like, and yet more specifically, resulting in very stable complexes with metal salts, especially Al
3+
which are stable against acids and bases. Furthermore, when the toners generated are roll milled and aged over a period of, for example, about 2 to about 3 hours there results stable and negative toner charging with, for example, no or minimal wrong sign positively charged toner.
The toners generated with the processes of the present invention are especially useful for imaging processes, especially xerographic processes, which usually prefer a toner transfer efficiency. Also, the toners obtained with the processes illustrated herein can be selected for digital imaging systems, processes, and color processes wherein images with high resolution and excellent image uniformity results.
PRIOR ART
In xerographic systems, especially color systems, small sized toners of from about 2 to about 8 microns can be important to the achievement of high image quality for process color applications. It may also be important to have a low image pile height to eliminate, or minimize image feel and avoid paper curling after fusing. Paper curling can be particularly pronounced in xerographic color processes primarily because of the presence of relatively high toner coverage as a result of the application of three to four color toners. During the fusing step, moisture escapes from the paper due to high fusing temperatures of from about 120° C. to about 200° C. In the situation wherein with only one layer of toner is selected, such as in one-color black or highlight color xerographic applications, the amount of moisture driven off during fusing can be reabsorbed by the paper and the resulting print remains relatively flat with minimal paper curl. In process color where toner coverage is high, the relatively thick toner plastic covering on the paper can inhibit the paper from reabsorbing the moisture, and cause substantial paper curling. These and other imaging shortfalls and problems are avoided or minimized with the toners and processes of the present invention.
Also, it may be desirable to select certain toner particle sizes, such as from about 2 to about 10 microns, with a high colorant, especially pigment loading such as from about 4 to about 15 percent by weight of toner, so that the mass of toner necessary for attaining the desired optical density and color gamut can be significantly reduced to eliminate or minimize paper curl. Lower toner mass also ensures the achievement of image uniformity. However, higher pigment loadings, for example, of about 10 to about 20 percent by weight of toner may adversely affect the charging behavior of toners. For example, the charge levels may be too low for proper toner development or the charge distributions may be too wide and toners of wrong charge polarity may be present. Furthermore, higher pigment loading may also result in the sensitivity of charging behavior to charges in environmental conditions such as temperature and humidity. Toners prepared in accordance with the processes of the present invention minimize, or avoid these disadvantages.
There is illustrated in U.S. Pat. No. 4,996,127, the disclosure of which is totally incorporated herein by reference, a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. In U.S. Pat.
Hopper Michael A.
Hu Nan-Xing
Jiang Lu
Mychajlowskij Walter
Patel Raj D.
Palazzo E. D.
Rodee Christopher
Xerox Corporation
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