Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-10-04
2001-02-27
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...
C430S137170, C427S216000
Reexamination Certificate
active
06194112
ABSTRACT:
REFERENCE TO COPENDING AND ISSUED PATENTS
Attention is directed to commonly owned and assigned U.S. Pat. No. 5,015,550, issued May 14, 1991, and U.S. Pat. No. 4,935,326, issued Jun. 19, 1990 to Creatura et al., respectively entitled “Electrophotographic coated carrier particles and methods thereof”, and “Electrophotographic carrier particles coated with polymer mixture” which patents disclose carrier and developer compositions, and a process for the preparation of carrier particles with substantially stable conductivity parameters which comprises (1) providing carrier cores and a polymer mixture, (2) dry mixing the cores and the polymer mixture, (3) heating the carrier core particles and polymer mixture, whereby the polymer mixture melts and fuses to the carrier core particles; and (4) thereafter cooling the resulting coated carrier particles.
The disclosure of the above mentioned patents are incorporated herein by reference in their entirety. The appropriate components and processes of those patent applications may be selected for the products and processes of the present invention in embodiments thereof.
BACKGROUND OF THE INVENTION
The present invention is generally directed to processes for the preparation of resin coated particulate materials, for example, carrier particles for use in two component xerographic developers. More specifically, the present invention relates to improved coating processes for the preparation of polymer coated carrier core particles.
Dry polymer coating processes for carrier particles are known in the art, reference for example, the aforementioned commonly owned U.S. Pat. Nos. 5,015,550, and 4,935,326.
The aforementioned references are incorporated in their entirety by reference herein.
In polymer particle coating processes of the prior art, various significant problems exist, for example difficulties in predicting or controlling, for example, the tribo and conductivity of the carrier. Some of the prior art coatings have a tendency to separate from the core in the form of chips or flakes. These flakes can have an adverse effect on the triboelectric charging properties of the developer. Another problem is fluctuations in the charge characteristics with changes in the relative humidity.
These and other disadvantages are avoided, or minimized with the coating processes of the present invention.
There remains a need for simple and economical coating processes for the preparation of resin coated carrier core particles wherein the resulting resin coated particles possess superior performance properties, such as tribo charging and durability, when used in, for example, two component developers.
The processes and products of the instant invention are useful in many applications, for example, including toner resins used for electrophotographic imaging processes, particularly color imaging, and for use, for example, in thermoplastic films and coating technologies.
SUMMARY OF THE INVENTION
Embodiments of the present invention, include:
A process comprising:
heating resin coated core particles for a time until the weight average molecular weight of the resin coating declines;
A resin coated carrier prepared by the process comprising:
heating resin coated core particles for a time until the weight average molecular weight of the resin coating decreases; and
A developer comprising the aforementioned resin coated carrier particles having coating resins with thermally diminished molecular weights, and toner particles.
These and other embodiments of the present invention are illustrated herein.
DETAILED DESCRIPTION OF THE INVENTION
The particle coating processes of the present invention may be used to process and prepare a variety of particulate and polymeric materials, including carrier core particles for used in liquid and dry developer marking applications in a cost efficient manner. An advantage of the present invention is that the processes affords control over the coating and surface properties of the resulting coated particulate products, and control over the triboelectric charging properties of the resulting coated core particles.
In embodiments, the present invention provides processes for the preparation of resin coated particles comprising:
heating resin coated core particles for a time so that or until the weight average molecular weight of the resin coating declines.
The weight average molecular weight decline or decrease can be, for example, from about 1 to about 90 percent, and preferably from about 2 to about 50 percent. The heating time or period can be, for example, from about 1 minutes to about 10 hours, and preferably from about 5 minutes to about 60 minutes, and can depend, for example, most importantly on the molecular weight and the charge properties desired of the resulting coated carrier particles, on the heating apparatus used, the scale of the process, heating temperature, the polymer or polymers selected, and the like parameters The resulting coated core particles can possess a resin coating with a substantially uniform thickness and excellent coating adhesion to the core, and the coated core particles possess improved or optimized triboelectric charge properties.
In an illustrative example, when the coating resin is a polymethylmethacrylate polymer and the core particles are steel, there is produced modified resin coated core particles where the triboelectric charge of the resulting coated core particles is in a range of from about 30 to about 45 microcoulombs per gram, whereas the triboelectric charge of the coated core particles before heating is a range of about 10 to about 60 microcoulombs per gram. The thickness of the resin coating of the resulting polymethylmethacrylate coated core particles can be, for example, from about 0.01 to about 0.5 microns, and preferably from about 0.01 to about 0.1 microns. The weight average molecular weight of the polymethylmethacrylate prior to heating can be from about 350,000 to about 450,000, and the molecular weight distribution or polydispersity can be about 4.0 to about 6.0 wherein the weight average molecular weight of the polymethylmethacrylate after heating can be from about 70,000 to about 140,000, and the molecular weight distribution can be from about 2.0 to about 4.0.
The modification and improvement of the coating properties and of the resulting resin coated core particles, while not desired to be limited by theory, is believed to result from either or both a molecular level change in the coating resin, such as molecular weight and or molecular weight distribution, and dependent and independent changes in the physical properties of the resin coating. In embodiments, the heating can be accomplished at from about 190° C. to about 270° C., more preferably from about 200° C. to about 260° C., and most preferably from about 210° C. to about 250° C. The preferences arise from experimental results which suggest that temperatures below the lower temperature limits may not effect the desired result or do so at a rate which is industrially inefficient, whereas temperatures above or outside the upper temperature limits appear to produce defective or less desirable coated products with, for example, unsatisfactory tribo properties, inadequate coating thicknesses, and or unsatisfactory coating core surface coverage. The defective resin coated core particles obtained at temperatures above the upper limits, while not desired to be limited by theory, are believed to result from, for example, uncontrolled or excessive resin decomposition, and mechanical and or evaporative losses of low molecular weight or low viscosity resin decomposition products.
Under the controlled heating regimes of the processes of the present invention, while not desired to be limited by theory, it is believed that the controlled heating liberates or drives off polar constituents from the resin coating composition. The polar constituents arising, for example, from commercially available Soken polymethylmethacrylate (MW
w
400,00), are believed to be a combination of volatile polymer degradation products, such as, methylmethac
Ahuja Suresh K.
Gill Robert A.
Maniar Deepak R.
Marcell Kevin
Mcgriff Richard B.
Goodrow John
Haack John L.
Xerox Corporation
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