Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
1999-12-09
2002-05-14
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S137100
Reexamination Certificate
active
06387583
ABSTRACT:
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 (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. Some U.S. patents in this regard are 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 normally contain toner particles consisting of 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, about 0.25-1 weight percent flow agent and 0-about 1 weight percent other additives. Major resins are styrene-acrylic copolymers, styrene-butadiene copolymers and polyesters. The colorants usually are selected from cyan dyes or pigments, magenta dyes or pigments, yellow dyes or pigments, and mixtures thereof.
One of the main advantages of selecting organic dyes instead of pigments for color toner compositions resides in the provisions of increased color fidelity as the dyes can be molecularly dispersed in the toner resins. To obtain a homogeneous dispersion, it is generally necessary to build into these molecules certain substituents for enhancing their compatibility with the toner resin. Unless the dye molecules are substantially fully compatible with the toner resins, they have a tendency to aggregate with time, especially when subjected to heat, pressure and humidity thereby resulting in a loss of color fidelity. Additionally, the low molecular weight of the dye molecules causes a high lability or mobility of the dye molecules in the toner resin resulting in undesirable bleeding of the dyes.
An attempt for improvement is to incorporate a dye into preformed resin particles by dispersing the particles in a dye solution and diffusing the dye into the central portion of each resin particle. For example, U.S. Pat. No. 5,565,298 discloses a method of producing toner particles comprising of a copolymer of styrene and n-butylmethacrylate formed by a suspension polymerization method and dyed by dispersing in a bath comprising of a dye and methanol as solvent. However, the method has several deficiencies that make it unsuitable for producing high-resolution toner particles. The dyeing has to be carried out below the glass transition temperature of the resin and it therefore takes a long dyeing time. Particles also tend to coagulate in the course of dyeing resulting in a large average particle size and a broad size distribution. Incorporating a sufficient amount of dyes for vivid color image is difficult due to a limited solubility of dyes in polymer resins. Dyes tend to migrate out of the particle during storage and evaporate during the fixing stage of electrophotography process, severely interfering with operation of electrophotography equipment.
There is continuing interest in 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 has a superior combination of properties for electrophotographic imaging systems by dispersing resin particles and a dye in a bath and effecting the dye molecules to be absorbed in the central portion of each resin particle while substantially maintaining the size and size distribution of the resin particles.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.
SUMMARY OF INVENTION
There is provided in accordance with the present invention a process of preparing a toner for developing latent electrostatic images comprising: dispersing a particulate polymer resin with functional sites suitable for interacting with a functionalized dye in a liquid organic medium; the polymer being substantially insoluble in the organic medium; providing a functionalized dye to the organic medium wherein the functionalized dye has functional sites adapted for interacting with the functional sites on the particulate polymer resin; maintaining the organic medium containing the particulate resin at an elevated temperature for a time sufficient to dye the resin and separating the organic medium from the particulate polymer resin. The functionalized dye is thus applied to the resin particles and the particle size of the particulate polymer resin is substantially unchanged during the dyeing process recited above.
The particulate polymer resin is most preferably a polyester resin. The polyester resin may have functional sites suitable for interacting with a functionalized dye selected from the group consisting of: hydroxyl moieties; alkoxyl moieties; sulfonic or derivatized sulfonic moieties; sulfonic or derivatized sulfonic 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. In typical embodiments the particulate polymer resin has a volume average particle size of from about 1 to about 15 microns. Generally at least about 80 weight percent of the particles of the particular polymer resin are within from about 0.5 to about 1.5 times the volume average particle size of the particulate polymer resin. In other embodiments the particulate polymer resin has a volume average particle size from about 2 to about 10 microns and sometimes from about 2 to about 4 microns while an average particle size of from about 5 to about 8 microns is preferred in some embodiments.
In some cases the polyester resin is prepared by way of dispersion polymerization.
Any suitable dye may be used in the practice of the present invention so long as it can be bound to the particulate polymer resin. Preferred dyes include basic dyes, acid dyes, or reactive dyes. The weight ratio to dye to particulate polymer resin is generally from about 1:100 to about 10:100 or from about 1 to about 10 percent by weight.
The solubility parameter value of the organic medium is smaller than the solubility parameter value of the particulate polymer resin by at least about 1. More preferably the solubility parameter of the organic medium is smaller than the solubility parameter value of the particulate polymer resin by at least about 2. Particularly preferred are paraffin containing organic media.
A dyeing aid, typically a surfactant, is preferably included in the inventive process. Most preferred are non-ionic surfactants as detailed further herein. Especially useful non-ionic surfactants include the residue of an ethylene oxide moiety or a propylene oxide moiety.
The surfactant may be present in an amount of from about 0.2 to about 2 times the amount of non-polar solvent present in the organic medium, that is from about 5 to about 200 percent by weight of the non-polar solvent, whereas from about 10 to about 50 percent is more typical with
Ferrell Michael W.
MatSci Solutions, Inc.
Rodee Christopher
LandOfFree
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