Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2000-08-07
2002-03-12
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S137160, C430S108100, C430S109400, C430S110400
Reexamination Certificate
active
06355392
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of producing a toner by a dispersion polymerization process, the toner being useful for developing latent electrostatic images in electrophotography and electrostatic printing. More specifically, the invention relates to a method of producing small resin particles comprising coloring agents and other additives, whereby the particles produced are substantially free of contaminants, such as the dispersion solvent used in the polymerization process. The toners thus produced are useful for high-resolution color electrophotography and electrostatic printing.
BACKGROUND OF THE INVENTION
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process (disclosed in U.S. Pat. No. 2,297,691) involves placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic toner material. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image subsequently may be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Toners and developer compositions including colored particles are well known. Examples in the U.S. patent art include U.S. Pat. Nos. 5,352,521, 4,778,742, 5,470,687, 5,500,321, 5,102,761, 4,645,727, 5,437,953, 5,296,325 and 5,200,290. The traditional compositions typically contain toner particles consisting of a resin and colorants, wax or a polyolefin, charge control agents, flow agents and other additives. A typical toner formulation generally contains about 90-95 weight percent resin, about 2-10 weight percent colorant, 0-about 6 weight percent wax, 0-about 3 weight percent charge control agent, 0-about 3 weight percent flow agent and 0-about 1 weight percent other additives. The resins most frequently used are styrene-acrylic copolymers, styrene-butadiene copolymers and polyesters. The colorants usually are selected from black dyes and pigments, cyan dyes or pigments, magenta dyes or pigments, yellow dyes or pigments, and mixtures thereof.
Conventional color toners are produced by a milling process described, for example, in the afore-mentioned U.S. Pat. No. 5,102,761. In that process, a polyester resin is compounded with pigments, charge control agents (henceforth, abbreviated “CCA”) and occasionally, with wax, in a melt mixer. The resulting polymer mixture is mechanically crushed and then milled into small particles. The conventional toner particles typically have an irregular shape and a broad distribution in particle size. For optimum resolution of images and color, smaller particles perform better. Thus, for example, it is difficult to obtain resolutions better than about 600 dots/inch when the average particle size is larger than about 7 &mgr;m. For resolutions in the order of about 1200 dots/inch, particle sizes smaller than 5 &mgr;m are desirable. It is difficult to make particles smaller than about 7-10 &mgr;m by conventional processes because of the high energy cost of producing small particles as well as uniform narrow particle size distribution.
Improvements to cure such deficiencies have been attempted in the past. For example, the afore-mentioned U.S. Pat. Nos. 5,352,521, 5,470,687 and 5,500,321 disclose toner particles produced by dispersion polymerization processes. In the respective methods of those patents, monomers (typically styrenic and acrylate monomers) and additives such as pigments, CCA and wax are mixed together to form an initial dispersion. The initial dispersion is then further dispersed into an aqueous or a non-aqueous medium and the monomers are polymerized to form toner particles. The resultant toner particles, however, are deficient in uniform distribution of colorants, produce unacceptable transparency of the images formed, and have a high cost of production. Moreover, these processes are not useful to prepare polyester-based toner particles which, due to their superior compatibility with pigments, are preferred over particles based on styrenic or acrylic polymers.
Another example of improvement in the production of toner particles is provided in U.S. Pat. No. 6,001,524 which discloses small polyester toner particles produced by dispersion polymerization. In this method, polyester monomers together with a surfactant are dispersed into a non-aqueous medium and are polymerized to form small polyester particles. Dyes and CCA are then incorporated into the particles to form toner particles. One advantage of the dyed toner over the pigmented toner is that the former provides increased color fidelity as the dyes can be molecularly dispersed in the toner resins.
Dispersion polymerized toners represent a substantial improvement over milled toners in that the former can be made economically to have particle size smaller than 7 &mgr;m. However, the dispersion polymerized toners of the prior art nonetheless suffer from significant contamination problems. In the case of a condensation-type polymer resin such as a polyester resin, the dispersion polymerized particles are often contaminated with the dispersion medium. A condensation polymerization typically entails a significant volume reduction because the reaction proceeds with outward diffusion of reaction by-products from the reaction mixture. The volume reduction typically reaches about 50% of the monomer volume. The volume reduction, coupled with the fact that the condensation polymerization proceeds mostly in the surface region of the particles, often produces polyester particles with the dispersion solvent entrapped in the interior region of the particles or with capillary-like defects. The entrapped dispersion medium is difficult to eliminate from the particles by conventional purification processes. Images printed with toners containing a liquid contaminant often are “foggy” and are unacceptable for high-resolution printing.
There is continuing interest in, and need for the development of new and improved methods of producing toners for application in high-resolution color electrophotography.
Accordingly, an object of the present invention is to provide a method of producing high-resolution color toner which is free of afore-mentioned contaminants, using a novel dispersion polymerization of reactive oligomers (hereinafter also referred to as “macromer(s)”) to form resin particles characterized by small size and a narrow particle size distribution. The ability to control the size parameter of and contamination level within small resin particles by resort to the instant dispersion polymerization of functionalized macromers is an important aspect of the invention. Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.
SUMMARY OF INVENTION
One embodiment of the present invention is a process of preparing a functional oligomer (“macromer”) suitable for forming a particulate toner resin by a melt or solution polymerization process. The macromer may contain functional sites suitable for interacting with functionalized colorants selected from the group consisting of: hydroxyl moieties; alkoxyl moieties; sulfonic or derivatized sulfonic moieties; sulfinic or derivatized sulfinic moieties; carboxyl or derivatized carboxyl moieties; phosphonic or derivatized phosphonic moieties; phosphinic or derivatized phosphinic moieties; thiol moieties, amine moieties; alkyl amine moieties; quaternized amine moieties; and mixtures thereof.
Another embodiment of the present inve
Chapman Mark
MatSci Solutions, Inc.
Petraglia Susan P.
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