Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-06-20
2004-07-20
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111100, C430S111350, C430S137130
Reexamination Certificate
active
06764799
ABSTRACT:
BACKGROUND
The present invention relates to carrier compositions, and more specifically, coated carriers that are substantially free or free of conductive components like conductive carbon blacks. Examples of utility for the aforementioned carriers include their incorporation into copying and printing machines, such as xerographic machines, multifunctional devices, color systems, and the like, and wherein the coated carriers can be economically generated, for example, the blending of a carrier core and micropowder coating.
REFERENCES
The electrostatographic process, and particularly the xerographic process, is known. This process involves, for example, the formation of an electrostatic latent image on a photoreceptor, followed by development of the image with a developer, and subsequent transfer of the image to a suitable substrate. Numerous different types of xerographic imaging processes are known wherein, for example, insulative developer particles or conductive developer particles are selected depending on the development systems used. Moreover, of interest with respect to the aforementioned developer compositions is the appropriate triboelectric charging values associated therewith, as it is these values that may enable continued formation of developed images of high quality and excellent resolution. In two component developer compositions, carrier particles are used in charging the toner particles.
Carrier particles in part are comprised, for example, of a roughly spherical core, often referred to as the “carrier core”, which may be generated from a variety of materials, or purchased. The core is typically coated with a resin, such as a polymer or copolymer, and which resin may contain a conductive component, such as certain carbon blacks, to, for example, provide carrier particles with more desirable and consistent triboelectric properties. Including conductive components in the carrier coating may be disadvantageous in some instances, for example, it can be difficult and costly to blend the core and conductive component, and also the conductive component may not fully serve its purposes. For example, processes of incorporating conductive material into carrier coating include the use of electrostatic attraction, mechanical impaction, in situ polymerization, dry blending, thermal fusion and others, and which processes often result in only minimal amounts of conductive material being incorporated into the coating or there is generated conductive carrier coatings too large for effective and efficient use especially with smaller sized carriers. Additionally, dry blending processes and other mixing to incorporate the carbon black or other conductive material into the polymer coating can be selected, however, to avoid, or minimize transfer of the carbon black from the polymer coating the amount of carbon black that may be blended may be limited, for example, to 20 percent by weight or less, which limits the conductivity achievable by the resultant conductive polymer. Also, the carbon black from the carrier coating polymer can contaminate the toner resulting in charges in both charging performance and color of the toner, such as for example, a light colored toner, such as yellow.
In addition to the problems associated with loading conductive materials into coating resins, recent efforts to advance carrier particle science have focused on the attainment of conductive coatings for carrier particles to improve development quality, and provide particles that can be recycled and that do not adversely affect the imaging member in any substantial manner. Many coatings can deteriorate rapidly, 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 causing failure upon impact or abrasive contact with machine parts and other carrier particles. These flakes or chips, which cannot generally be 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 the carrier coatings are retained on the surface of the core substrate.
A further problem encountered with some prior art carrier coatings resides in fluctuating triboelectric charging characteristics, particularly with changes in relative humidity. High relative humidity hinders image density in the xerographic process, may cause background deposits, leads to developer instability, and may result in an overall degeneration of print quality. In the science of xerography, the term “A Zone” refers, for example, to hot and humid conditions, the term “C Zone” refers, for example, to cold and dry conditions. Triboelectric charges are usually lower in the “A Zone” than in the “C Zone.” It is desirable to have the measured triboelectric charges (
tc
) for a particular carrier in the A Zone and the C Zone, when entered into a ratio of A zone
tc
/C zone
tc
to be close to about 1 to obtain development in high humidity.
A carrier coating commonly used is a polymethyl methacrylate (#MP-116 PMMA) available from Soken Chemical of Japan. This powder typically has a diameter of about 0.4 to 0.5 micrometer and it can be generated from polymethyl methacrylate. Usually high amounts of PMMA are selected for the coating of a 30 to 50 micrometer carrier core and to achieve surface area coverage on the carrier of about 85 percent to 95 percent. The use of such high amounts of carrier coating often results in lower carrier yields because, for example, of the formation of fused aggregates. Fused aggregates usually need to be broken up or removed by screening. Crushing or breaking up of the aggregates may result in weak or “chipped off” areas on the carrier surface potentially causing poor coating quality. Screen separation may result in a lower yield as aggregates are removed from the final product.
The above disadvantages and problems can be avoided or minimized with the coated carriers of the present invention in embodiments thereof. More specifically, there is a need to enable the effective, economical incorporation of carrier polymers, especially at certain coating weights, onto carrier cores to permit conductive carriers without the use of an additional conductive components while providing for and maintaining desirable xerographic qualities such as high coating efficiency, proper performance in both the A Zone and the C Zone, and stable charging characteristics.
Carrier particles for use in the development of electrostatic latent images are described in many patents including, for example, U.S. Pat. No. 3,590,000. These carrier particles may consist of various cores, including steel, with a coating thereover of fluoropolymers and terpolymers of styrene, methacrylate, and silane compounds.
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 450° F. for a period of about 20 minutes to about 60 minutes, enabling the thermoplastic resin particles to melt and fuse on the carrier core. While the developer and carrier particles prepared in accordance with the process of this patent, the disclosure of which is incorporated herein by reference in its entirety, are suitable for their intended purposes, t
Hawkins Michael S.
Maniar Deepak R.
McStravick Mary L.
Skorokhod Vladislav
VanDusen John G.
Palazzo E. O.
Rodee Christopher
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