Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
1994-09-29
2001-02-06
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S112000, C430S114000
Reexamination Certificate
active
06183931
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is generally directed to liquid developer compositions and, more specifically, the present invention relates to processes for the preparation of a liquid developer containing, for example, NORPAR® with supercritical fluid extraction. In embodiments, the present invention relates to processes for the preparation of liquid developers with high solids contents of, for example, about equal to or greater than 50 weight percent. The process of the present invention in embodiments comprises the extraction from the developer of the ink vehicle like NORPAR® by relatively mild supercritical extraction, and more specifically supercritical carbon dioxide solvent extraction to thereby concentrate the liquid ink solids of resin, pigment, and charge adjuvant or charge additive. The process of the present invention can be selected to fabricate liquid ink concentrates that can then be selected for electrographic, especially xerographic, systems wherein liquid hydrocarbons are recycled. Advantages of using high solids ink replenishment processes include avoiding the build up of excess liquid carrier by replenishing the developer housing with a percent solid ink that is equal to the percentage solid concentration of the image fixed to the paper, typically about 50 percent, and greater stability with respect to storage of the high solids ink versus a dilute suspension. The inks obtained with the process of the the present invention can be selected for a number of known imaging systems, such as xerographic imaging and printing processes, wherein latent images are rendered visible and which images possess excellent characteristics of image quality, solid area coverage and resolution.
Advantages, or problems solved with the processes of the present invention include the capability to consistently and uniformly achieve a liquid ink with a 50 or greater solids content without the potential for contamination by organic solvents used for extraction as, for example, is the situation with the processes as illustrated in U.S. Pat. No. 5,206,108 wherein hexane is used in combination with filtration or centrifugation to remove the aliphatic hydrocarbon vehicle in which the ink was generated. Alternative known means of liquid developer concentration include the use of a centrifuge, however, this operation is limited by the viscosity of the ink vehicle, the small particle size, and the similar densities of liquid and particle to typically less than about 30 percent solids. Various types of filter presses can achieve higher average solid concentrations, however, the inevitable nonuniformity of pressure applied throughout the filter cake results in a gradient of solids concentrations. Additionally, the compaction produced by a filter press may render the high solids ink more difficult to redisperse in the hydrocarbon vehicle for development in a printer.
Processes for the preparation of liquid inks by, for example, pressure filtration, or centrifugation are known. For example, U.S. Pat. No. 5,206,108 illustrates the use of hexane in combination with filtration or centrifugation to remove the aliphatic hydrocarbon vehicle in which the ink was generated, which process results in the contamination of the ink vehicle by organic solvents used for extraction. These contaminants possess a significant vapor pressure and are a health hazard that precludes their use in most environments. Alternative means of concentration include the use of a centrifuge, however, this operation is limited by the viscosity of the ink vehicle, the small ink particle size, and the similar densities of liquid and ink particle.
Various types of filter presses can achieve higher average solid concentrations, however, the nonuniformity of pressure applied throughout the filter cake results in a gradient of solids concentrations. Additionally, the compaction produced by a filter press may render the high solids ink more difficult to redisperse in the hydrocarbon vehicle for development in a copier or a printer.
Processes for the preparation of certain liquid electrostatic developers include mixing in a nonpolar liquid the thermoplastic resin, charging additive, and optional colorant and adjuvant in a manner that the resulting mixture contains, for example, from about 15 to about 30 percent by weight of solids; heating the mixture to a temperature of from about 70° C. to about 130° C. until a uniform dispersion is formed; adding an additional amount of nonpolar liquid sufficient to decrease the total solids concentration of the developer to about 10 to about 20 percent by weight; cooling the dispersion to about 10° C. to about 50° C.; adding the charge director compound to the dispersion; and diluting the dispersion.
In the initial mixture, the resin, colorant and charge adjuvant may be added separately to an appropriate vessel such as, for example, an attritor, heated ball mill, heated vibratory mill, such as a Sweco Mill manufactured by Sweco Company, Los Angeles, Calif., equipped with particulate media for dispersing and grinding, a Ross double planetary mixer manufactured by Charles Ross and Son, Hauppauge, N.Y., or a two roll heated mill, which usually requires no particulate media. Useful particulate media include materials like a spherical cylinder of stainless steel, carbon steel, alumina, ceramic, zirconia, silica and sillimanite. Carbon steel particulate media are particularly useful when colorants other than black are used. A typical diameter range for the particulate media is in the range of 0.04 to 0.5 inch (approximately 1.0 to approximately 13 millimeters). Other processes include extrusion, for example, U.S. Pat. No. 5,017,451 illustrates extrusion for melt mixing and a Microfluidizer® for particle size reduction. Also, in U.S. Pat. No. 5,387,489, the disclosure of which is totally incorporated herein by reference, there can be selected a piston homogenizer for particle size reduction.
When using an attritor, sufficient nonpolar liquid is added to provide a dispersion of from about 10 to about 50 percent solids. This mixture is then subjected to elevated temperatures during the initial mixing procedure to plasticize and soften the resin. The mixture is sufficiently heated to provide a uniform dispersion of all the solid materials of, for example, colorant, charge director, adjuvant and resin. However, the temperature at which this step is effected should not be high as to degrade the nonpolar liquid or decompose the resin or colorant if present. Accordingly, the mixture in embodiments is heated to a temperature of from about 70° C. to about 130° C., and preferably from about 75° C. to about 110° C. The mixture may be ground in a heated ball mill or heated attritor at this temperature for about 15 minutes to 5 hours, and preferably about 60 to about 180 minutes. After grinding at the above temperatures, an additional amount of nonpolar liquid may be added to the dispersion. The amount of nonpolar liquid to be added should be sufficient in embodiments to decrease the total solids concentration of the dispersion to about 10 to about 20 percent by weight.
The dispersion is then cooled to about 10° C. to about 50° C., and preferably to about 15° C. to about 30° C., while mixing is continued until the resin admixture solidifies or hardens. Upon cooling, the resin admixture precipitates out of the dispersant liquid. Cooling is accomplished by methods such as the use of a cooling fluid like water, glycols, such as ethylene gylcol, in a jacket surrounding the mixing vessel. Cooling is accomplished, for example, in the same vessel, such as an attritor, while simultaneously grinding with particulate media to prevent the formation of a gel or solid mass; without stirring to form a gel or solid mass, followed by shredding the gel or solid mass and grinding by means of particulate media; or with stirring to form a viscous mixture and grinding by means of particulate media. The resin precipitate is cold ground for about 1 to 36 hours, and preferably from about 2 to about 6 hours. Additional liquid may b
Dote Janis L.
Palazzo E. O.
Xerox Corporation
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