Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-05-18
2002-10-08
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S137210, C430S110300, C430S110400
Reexamination Certificate
active
06461783
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to toner compositions and a dispersion comminution method of producing toners for developing latent electrostatic images in electrophotography, electrostatic recording and electrostatic printing. More specifically, this invention relates in a preferred embodiment to a dispersion comminution method of forming suitably sized resin particles which incorporate a coloring agent and other suitable components therein 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 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 0 to about 6 weight percent wax, from 0 to about 3 weight percent charge control agent, about 0.25-1 weight percent flow agent and from 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 in 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.
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 generally have a smooth surface texture and tend to lack a fast triboelectric charging characteristics which is important in mono-component electrophotography development systems.
Another desirable property in a particulate toner composition is a narrow particle size distribution. It is generally believed that a narrow size distribution leads to a more uniform charge distribution in the toner composition which, in turn. leads to a better line resolution in a printed image as well as reduction in spotty background. The conventional milling method of producing toner particles is generally inefficient in producing particles with a narrow size distribution and therefore has to employ a classification step to remove particles that are too small or too large from the toner composition.
Narrowness of the size distribution may be expressed by the 80% span (the span). The span is defined as the ratio of the size range in which middle 80% by volume of the particles occupy to the median size. A more detailed description of the definition of the span is in a later section on the characterization methods used in the present invention. A smaller value of the span therefore means a narrower size distribution. The span value of a typical toner composition which is commercially available after afore-mentioned classification step is about 1.2. A method of toner particle formation yielding particles with the span value less than 1.2 without a classification process is highly desirable.
There is continuing interest in the development of new and improved methods of producing toners for application in high-resolution electrop
Kim Chul-Hwan
Kim Jong-kwan
Lim Seung-Wook
Yoon Hyun-Nam
DPI Solutions, Inc.
Ferrell Michael W.
Rodee Christopher
LandOfFree
Micro-serrated color toner particles and method of making same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Micro-serrated color toner particles and method of making same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Micro-serrated color toner particles and method of making same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2948542