Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-08-17
2002-05-21
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C430S111410, C430S137130
Reexamination Certificate
active
06391509
ABSTRACT:
The appropriate components of the above patents and copending applications may be selected for the present invention in embodiments thereof.
BACKGROUND OF THE INVENTION
This invention is generally directed to developer compositions, and more specifically, the present invention relates to developer compositions containing carriers. In embodiments of the present invention, the carrier particles can be comprised of a core, a polymer, or mixture of polymer coatings thereover, and which coating or coatings have incorporated therein a polymer, preferably a polyaniline, or a doped conductive polymer wherein the dopant can be a charge transfer agent., such as a sulfate, and wherein the resulting carriers are rendered conductive, for example a carrier conductivity of from about 10
−6
to about 10
−12
ohm-cm)
−1
. The carriers of the present invention may be mixed with a toner of resin, colorant, and optional toner additives to provide developers that can be selected for the development of images in electrostatographic, especially xerographic imaging systems, printing processes and digital systems.
More specifically, examples of conductive polymers that may be selected include polyacetylene, poly(p-phenylene), poly(p-phenylene sulfide), polyvinylenephenylene, poly(vinylene sulfide), polyaniline, polypyrrole, polythiophene and derivatives thereof, and a class of components with conjugated &pgr;-electron backbones, which when oxidized or reduced with charge transfer agents, or dopants in suitable amounts of, for example, from about 0.1 to about 20 weight percent, can convert an insulating polymer to a conductive polymer. The electrical conductivity of the conducting polymer is usually measured using a 4-point probe according to ASTM-257, and which conductivity can vary widely depending, for example, primarily on the oxidizing or reducing power of the dopant. Conductivities of about 1,100 (ohm-cm)
−1
have been reported for polyacetylene, 100 (ohm-cm)
−1
for polypyrrole and 10 (ohm-cm)
−1
for polythiophene with AsF
6
−
as the dopant ion. Using other doping agents such as BF
4
−
, I
2
, FeCl
4
−
, HCl, ClO
4
−
, conductivities of from about 500 to about 7,500 (ohm-cm)
−1
have been reported for polypyrrole, 1,000 (ohm-cm)
−1
for polythiophene, about 1,000 to about 10,000 (ohm-cm)
−1
for poly(3-alkylthiophene) and about 200 (ohm-cm)
−1
for polyaniline, however, many of the commercial polymer materials have conductivities between about 10
−12
and about 100 (ohm-cm)
−1
. Other doping agents include sulfuric acid, methanesulfonic acid, trifluoromethane sulfonic acid, benzenesulfonic acid, p-toluene sulfonic acid, p-ethylbenzene sulfonic acid, 1,3 benzenedisulfonic acid, 2-naphthalene sulfonic acid, 1,5 naphthalene sulfonic acid, and 2-anthraquinone sulfonic acid.
Advantages of the carriers of the present invention in embodiments include, for example, the selection of inherently conductive polymers as carrier coatings wherein the electrical conductivity thereof can be tailored to encompass the range from insulators to semiconductors to metals, and wherein the conductivity can increase linearly with the amount of conductive polymer in the blend. Compatibility of the conductive polymer with the host polymer coating is believed to be more superior than blends with inorganic fillers of conductive additives, or components present in the polymer carrier coating in amounts, for example, of from about 10 to about 70 percent, and preferably from about 20 to about 50 percent by weight of monomer or comonomer mixture. Superior compatibility is achieved with the present invention in embodiments, it is believed, because of the partial miscibility of the conductive polymeric component and the nonconductive polymer hosts, which serve to eliminate the sharp interface between the host polymer and an inorganic filler, which is typically the point of weakest mechanical integrity in the composite, and is the point where the material fractures on the surface of a carrier in a xerographic environment.
PRIOR ART
Developer compositions with coated carriers that contain conductive components like carbon black are known. Disadvantages associated with these prior art carriers may be that the carbon black can increase the brittleness of the polymer matrix, which causes the separation of the coating from the core, and thereby contaminates the toner and developer causing, for example, instabilities in the charging level of the developer as a function of factors, such as the developer age in the xerographic housing and the average toner area coverage of a printed page, or instabilities in the color gamut of the developer set. In addition, with carbon black it is difficult to tune, or preselect the carrier conductivity. These and other disadvantages are avoided, or minimized with the carriers of the present invention in embodiments thereof.
The conductivity of carbon blacks is generally independent of the type of carbon black used and, in composites, there is usually formed a filamentary network above a certain concentration, referred to as the “percolation” threshold. At concentrations of up to about 30 weight percent, conductivities of 10
−2
(ohm-cm)
−1
have been reported. The resistivity thereof, measured with a standard 4-pin method according to ASTM-257, is observed to increase with decreasing carbon black concentration.
Carrier particles for use in the development of electrostatic latent images are illustrated in many patents including, for example U.S. Pat. No. 3,590,000. These carrier particles may contain various cores, including steel, with a coating thereover of fluoropolymers, or terpolymers of styrene, methacrylate, and silane compounds. Recent efforts have focused on the attainment of coatings for carrier particles, for the purpose of improving development quality; and also to permit carrier particles that can be recycled, and which do not adversely effect the imaging member in any substantial manner. Some of the present commercial coatings can deteriorate, especially when selected for a continuous xerographic process where the entire coating may separate from the carrier core in the form of chips or flakes, and fail upon impact, or abrasive contact with machine parts and other carrier particles. These flakes or chips, which are not generally reclaimed from the developer mixture, have an adverse effect on the triboelectric charging characteristics of the carrier particles thereby providing images with lower resolution in comparison to those compositions wherein entire carrier coatings are retained on the surface of the core substrate. Further, another problem encountered with some prior art carrier coatings resides in fluctuating triboelectric charging characteristics, particularly with changes in relative humidity. The aforementioned modification in triboelectric charging characteristics provides developed images of lower quality, and with background deposits.
There is illustrated in U.S. Pat. No. 4,233,387, the disclosure of which is totally incorporated herein by reference, coated carrier components for electrostatographic developer mixtures comprised of finely divided toner particles clinging to the surface of the carrier particles. Specifically, there is disclosed in this patent coated carrier particles obtained by mixing carrier core particles of an average diameter of from between about 30 microns to about 1,000 microns, with from about 0.05 percent to about 3.0 percent by weight, based on the weight of the coated carrier particles, of thermoplastic resin particles. The resulting mixture is then dry blended until the thermoplastic resin particles adhere to the carrier core by mechanical impaction, and/or electrostatic attraction. Thereafter, the mixture is heated to a temperature of from about 320° F. to about 650° F. for a period of 20 minutes to about 120 minutes, enabling the thermoplastic resin particles to melt and fuse on the carrier core. While the developer and carrier particles pr
Drappel Stephan V.
Duggan Michael J.
Enright Thomas E.
Liebermann George
MacLeod Paula J.
Chapman Mark
Thompson Robert
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