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
2003-03-11
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, C524S223000, C428S402000
Reexamination Certificate
active
06531255
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to particulate resin compositions suitable for production of high-resolution toners for developing latent electrostatic images in electrophotography, electrostatic recording and electrostatic printing. More specifically, this invention relates in preferred embodiments to a dispersion comminution method of forming suitably sized resin particles which may be converted to a particulate toner composition for high-resolution electrophotography, electrostatic recording and electrostatic printing by incorporating a coloring agent and other suitable components therein.
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 over coating treatment.
Also well known are techniques to develop such electrostatic images. Developer is a vehicle in which are dispersed charged colored toner particles. The photoreceptor bearing the electrostatic latent image is contacted with the developer. The contact causes the charged toner particles in the developer to migrate to the charged areas of the photoreceptor to develop the latent image. Then, the photoreceptor is developed with the charged colored particles adhering to the latent image in image configuration. The developed image is then typically transferred to a suitable substrate, such as paper or transparency material, and optionally may be fixed to the substrate by heat, pressure or other suitable means.
Toners and developer compositions including colored particles are well known. In this regard, see 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 disclosures of which are hereby incorporated by reference. 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.
Conventional color toner particles are produced by a milling process described, for example, in the aforementioned U.S. Pat. No. 5,102,761. In that process, a polyacrylate resin is compounded with pigments, charge control agents (“CCA”) and occasionally 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 more than about 7 &mgr;m. For resolutions in the order of about 1200 dots/inch, particle sizes smaller than 5 &mgr;m are typically needed. 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.
Many previous attempts to produce small toner particles with the size smaller than 7 &mgr;m have been made. For example, the aforementioned U.S. Pat. Nos. 5,352,521, 5,470,687 and 5,500,321 disclose toner particles produced by dispersion polymerization. In such a method, monomers (typically styrenic and acrylate monomers) and additives such as pigments, CCA and wax are mixed together to form a dispersion. This is then further dispersed into an aqueous or a non-aqueous medium and the monomers are polymerized to form toner particles. This method has the advantage over other methods that spherical toner particles with a small diameter can be prepared by a single process. However, the polymerization involves a substantial volume contraction and it results in entrapment of the dispersion medium inside the toner particles. Furthermore, the polymerization is difficult to be brought to completion and a substantial portion of the monomers remains in the toner particles. The residual monomers and the entrapped dispersion solvent are difficult to separate from the particles. Also, the polarity of the polymerizing materials changes drastically in the course of the polymerization and the additives tend to exude from the particle bulk and tend to concentrate on the surface thereof. Further, agents employed, such as dispersion-stabilizing agent and surface active agent, which cause the charging characteristics and preservability of the toner particles to deteriorate, remain on the surface of the toner particles, and those agents are extremely difficult to remove from the toner particles. Some methods have included the suggestion of dispersing polymer/solvent droplets in a water medium and shearing the mixture. However, water tends to get into the interstices between particles and agglomerate them. Once agglomeration occurs, it is very difficult to drive off the water without damaging or otherwise altering the physical properties of the particles, especially with respect to polymers having relatively low softening points, that is below about 100° C.
A co-pending application, U.S. patent application Ser. No. 09/571,772 discloses a method of producing toner particles by comminuting resin particles comprising a colorant and a charge control agent in a solvent which does not dissolve the resin. However, applicability of the method is somewhat limited to toner resins with a relatively low molecular weight and the method generally requires a moderately high temperature and a vigorous shearing for effective comminution of toner particles. Furthermore, the toner particles produced by the method typically have a smooth surface texture and tend to lack fast triboclectric charging characteristics which is important in mono-component electrophotography development systems.
Co-pending U.S. patent application Ser. No. 09/860,959 entitled MICRO-SERRATED COLOR TONER PARTICLES AND METHOD OF MAKING SAME, discloses an improved method of producing toner particles by an improved dispersion comminution method of producing high-resolution color toner which has a superior combination of properties for electrophotographic imaging systems. The process includes forming spherical toner particles with a small diameter distribution by way of dispersing a polymer resin compounded with a colorant, a vaporizable plasticizer component and other additives in a dispersion medium including a surfactant under shearing conditions. The method may be carried out at a substantially low temperature compared to the method disclosed aforementioned U.S. patent application Ser. No. 09/571,772 and allows a resin with a high molecular weight to be used for preparing a toner composition. Furthermore,
Kim Chul-Hwan
Lim Seung-Wook
Park Tae-Ho
Yoon Hyun-Nam
DPI Solutions, Inc.
Ferrell Michael W.
Rodee Christopher
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