Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-05-18
2003-04-08
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...
C430S110300, C430S110400, C430S137100
Reexamination Certificate
active
06544705
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to toner compositions and a dispersion dyeing method of producing toners for developing latent electrostatic images in electrophotography, electrostatic recording and electrostatic printing. More specifically, this invention relates in preferred embodiments to micro-serrated dyed color toner compositions and a co-solvent-mediated dispersion dyeing method of suitably sized resin particles to form toner particles for high-resolution electrophotography, electrostatic recording 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 (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. Electrostatic images formed on an electrophotographic photoconductor and an electrostatic recording medium are generally developed by using (i) a mono-component toner composition comprising a binder resin, a coloring agent such as a dye or pigment and a charge control agent thereto when necessary or (ii) a two-component type developer composition comprising a toner composition blended with solid carrier particles. 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, from about 0 to about 6 weight percent wax, from about 0 to about 3 weight percent charge control agent, about 0.25-1 weight percent flow agent and from about 0 to 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-butyl methacrylate 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.
A dispersion dyeing process for particulate resin is disclosed in a co-pending patent application, Ser. No. 09/457,543. The invention provides a method of producing high-resolution color toner 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. The polymer resin contains functional groups in its molecular structure for interacting with a functionalized dye in order to effect a deep dyeing as welt as to bind to enhance dye fastness. The bath comprises an organic solvent which is immiscible with the polymer resin and a non-ionic surfactant. The surfactant not only prevents the resin particles from coalescing but provides a solubility of the dye so that dyeing can be effected. There are, however, several disadvantages associated with the invention. Dyes usable for the invention are limited to the ones that have solubility in the surfactants. Furthermore, the functionalized dyes generally are not soluble in the organic solvents used in the invention and have a very limited solubility in the surfactants. The dyeing process therefore is slow and has to be carried out at an elevated temperature which is typically about 40° C. above the glass transition temperature of the resin. As a result, the toner particles produced by the process tend to have a spherical shape and a smooth surface texture. Consequently, the toner composition of the invention tends to have a slow triboelectric charging characteristic and is not advantageous for use in a mono-component electrophotographic development system.
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 comprising an organic solvent, a surfactant and a dye-mediating co-solvent and expeditiously 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 as well as desirable surface properties.
Another object of the present invention is to provide a method of producing high-resolution toner of which toner particles are substantially spherical and have micro-serrated surface texture.
Yet another object of the present invention is to provide a high-resolution color toner composition of which particles are spherical in shape with a diameter in the range of about 1 to 10 microns, have a narrow size distribution and have a micro-serrated surface texture.
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 color toner composition including dyed resin particles having a volume average diam
Choi Eui-Jun
Kim Chul-Hwan
Kim Seok-Jin
Park Tae-Ho
Yoon Hyun-Nam
DPI Solutions, Inc.
Ferrell Michael W.
Rodee Christopher
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