Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-11-28
2002-03-12
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C428S402000
Reexamination Certificate
active
06355391
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a micro-powder resin. In particular, the invention relates to a novel carrier coating for xerographic carriers which uses a sub-micron sized powder recovered from a latex emulsion as the base resin in the carrier coating. The coating resins find particular utility as a coating for xerographic carriers.
2. Description of Related Art
The electrostatographic process, and particularly the xerographic process, is well known. This process involves 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 importance with respect to the aforementioned developer compositions is the appropriate triboelectric charging values associated therewith, as it is these values that 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 consist of a roughly spherical core, often referred to as the “carrier core,” which may be made from a variety of materials. The core is typically coated with a resin. This resin may be made from a polymer or copolymer. The resin may have conductive material or charge enhancing additives incorporated into it to provide the carrier particles with more desirable and consistent triboelectric properties. The resin may be in the form of a powder, which may be used to coat the carrier particle. Often the powder or resin is referred to as the “carrier coating” or “coating.”
Prior art methods of incorporating conductive material into carrier coating include the use of electrostatic attraction, mechanical impaction, in situ polymerization, dry-blending, thermal fusion and others. These prior art methods of incorporating conductive material into carrier coatings often result in only minimal amounts of conductive material being incorporated into the coating or produces conductive carrier coatings too large for effective and efficient use in some of the smaller carriers. Other prior art conductive coating resins use dry-blending processes and other mixing to incorporate the carbon black or other conductive material into the polymer. However, in order to avoid transfer of carbon black from conductive polymers so obtained, the amount of carbon black that can be blended is severely limited, e.g., to 10% by weight or less. This in turn severely limits the conductivity achievable by the resultant conductive polymer.
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 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 of the present commercial 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.
Further, another 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” is used to refer to hot and humid conditions, while the term “C Zone” is used to refer 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 1.0 in order to obtain good development in high humidity.
A carrier coating commonly used is #MP-116 PMMA available from Souken Chemical in Japan. This powder typically has a diameter of 0.4 to 0.5 micrometers and is a made from polymethyl methacrylate. However, it is required to use high amounts of #MP-116 PMMA to coat 30 to 50 micrometer carrier cores to achieve surface area coverage on the carrier of 85% to 95%. Use of such high amounts of carrier coating often results in lower carrier yields due to fused aggregates. Fused aggregates must 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.
Various coated carrier particles for use in electrostatographic developers are known in the art. 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 fluoro-polymers and ter-polymers of styrene, methacrylate, and silane compounds.
There is illustrated in U.S. Pat. No. 4,233,387 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 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, the conductivity values of the resulting particles are not constant in all instances, for example, when a change in carrier coating weight is accomplished to achieve a modification of the triboelectric charging characteristics. Further in regard to U.S. Pat. No. 4,233,387, only specific triboelectric charging values can be generated, when certain conductivity values or characteristics are contemplated.
U.S. Pat. No. 4,937,166, incorporated by reference herein in its entirety, describes a carrier composition comprised of a core with a coating thereover comprised of a mixture of first and second polymers that are not in close proximity thereto in the triboelectric series. The core is described to be iron, ferrites, steel or nickel. The first and second polymers are selected from the group consisting of polystyrene and tetrafluoroethylene; polyethylene and tetrafluoroethylene; polyethylene and polyvinyl chloride; polyvinyl acetate and tetrafluoroethylene; polyvinyl acetate and polyvinyl chloride; polyvinyl acetate and pol
Hoffend Thomas R.
Maniar Deepak R.
McStravick Mary L.
Skorokhod Vladislav
Van Dusen John Gregory
Goodrow John
Oliff & Berridg,e PLC
Palazzo Eugene O.
Xerox Corporation
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