Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-11-27
2002-04-23
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
Reexamination Certificate
active
06376147
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a method for producing a liquid toner or developer composition, more particularly a liquid toner or developer composition comprising metallic particles. The invention also relates to liquid toner or developer compositions made by such a process, and the use of such liquid toner or developer compositions in electrostatographic imaging processes.
2. Description of Related Art
A latent electrostatic image can be developed with toner particles dispersed in an insulating non-polar liquid. Such dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a beam of radiant energy. Other methods are also known for forming latent electrostatic images such as, for example, providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. After the latent image has been formed, it is developed by colored toner particles dispersed in a non-polar liquid. The image may then be transferred to a substrate or receiver sheet, such as paper or transparency.
Insufficient particle charge can result in poor image quality and also can result in poor transfer of the liquid developer or solids thereof to paper or other final substrates. Poor transfer can, for example, result in poor solid area coverage if, for example, insufficient toner is transferred to the final substrate, and can also cause image defects such as smears and hollowed fine features. Conversely, overcharging the toner particles can result in low reflective optical density images or poor color richness or chroma since only a few very highly charged particles can discharge all the charge on the dielectric receptor, causing too little toner to be deposited.
Useful liquid toners comprise thermoplastic resin toner particles and a dispersant non-polar liquid. Generally, a suitable colorant, such as a dye or pigment, is present in the toner particles. The colored toner particles are dispersed in a non-polar liquid that generally has a high volume resistivity, such as in excess of 10
9
&OHgr;-cm, a low dielectric constant, for example below 3.0, and a high vapor pressure. Generally, the toner particles have an average particle size (by area) or diameter of less than 7 microns as measured with a Horiba CAPA 700 Particle Sizer.
Various methods are known in the art for producing liquid toners and developers. The conventional process for producing such liquid toners involves a two-step batch process, wherein the first step involves a hot step where the non-polar liquid and molten resin are melt mixed with pigment and other additives, and the second step involves a cold step where the molten contents are cooled to cause solidification and formation of particles in the non-polar liquid.
For example, one process of making such liquid toners is described in U.S. Pat. No. 4,760,009, the entire disclosure of which is incorporated herein by reference, which describes such a two step process. According to the patent, the process comprises a first step of dispersing a thermoplastic resin, a non-polar liquid having a Kauri-butanol value of less than 30, and optionally a colorant at an elevated temperature in a vessel by means of moving particulate media. The temperature in the vessel is maintained at a temperature sufficient to plasticize and liquefy the resin and below that at which the non-polar liquid boils and the resin and/or colorant decomposes. In a second step, the dispersion is cooled to permit precipitation of the resin out of the dispersant. The particulate media is maintained in continuous movement during and subsequent to the cooling. Both steps are carried out in a suitable vessel, such as an attritor, a heated ball mill, or a heated vibratory mill, equipped with particulate media for dispersing and grinding. The result is described as toner particles having an average by area particle size of less than 10 &mgr;m and a plurality of fibers. Following the second step, the dispersion of toner particles can be separated from the particulate media.
The patent describes that useful thermoplastic resins or polymers that are able to form fibers and that can be used in the production method include ethylene vinyl acetate copolymers, copolymers of ethylene and an &agr;,&bgr;-ethylenically unsaturated acid, copolymers of ethylene/acrylic or methacrylic acid/alkyl (C1 to C5) ester of methacrylic or acrylic acid, polyethylene, isotactic polypropylene (crystalline), ethylene ethyl acrylate series, and ethylene vinyl acetate resins.
Other methods for forming liquid toners, which are generally variants of the above process, are described, for example, in U.S. Pat. Nos. 5,604,075, 5,688,624, 5,783,349 and 5,866,292, the entire disclosures of which are incorporated herein by reference. For example, U.S. Pat. No. 5,604,075 describes a process for the preparation of liquid developers with reduced fines, which comprises heating a liquid developer comprised of thermoplastic resin, pigment, charge adjuvant, liquid hydrocarbon, and optional charge director. The heating is accomplished at about 5° C. below the melting point of the thermoplastic resin, which heating enables the fines comprised of the developer components, and of a size diameter of from about 0.1 to about 0.4 micron, to be reduced.
SUMMARY OF THE INVENTION
Despite the various liquid toners and developers that are available, and the known methods for making such liquid toners and developers, there remains a need in the art for improved liquid toners and developers that provide high print quality, and for methods for producing such liquid toners and developers. This need is particularly evident for liquid toners and developers having a broader spectrum of available custom colors, including metallic colors.
In particular, there is a large market for metallic-colored inks and printing. However, it has been very difficult in the past to provide liquid toners and developers that can provide high quality prints with metallic colors. Accordingly, the present invention provides new and improved liquid toners and developers, that include metallic colorants, and which provide high quality printed images.
More particularly, in embodiments, the present invention provides a liquid toner comprising:
a carrier liquid, and
toner particles including a thermoplastic resin and a metallic colorant dispersed in said thermoplastic resin,
said toner particles being dispersed in said carrier liquid.
In other embodiments, the present invention provides methods for producing such a liquid toner composition, as well as methods for developing an image using such a liquid toner composition.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
According to the present invention, a liquid toner or developer composition is provided that includes any of a wide variety of metallic colorants. These liquid toner and developer compositions provide high quality printed images, while exhibiting good properties in terms of image development, transfer of the developed image to a substrate such as paper, and fusing of the image to the substrate.
The liquid toner and developer compositions can be made according to any of the various known techniques, including those in the above-described patents, as will be apparent to those skilled in the art. For example, the liquid toner and developer compositions can be made by the conventional processes including the steps of (1) preparing a colorant/resin mixture, and (2) cold grinding the colorant/resin mixture with addition of a suitable non-polar liquid, to prepare the final liquid toner or developer composition. In embodiments of the present invention, the liquid toner can be dry ground between the above steps (1) and (2) to reduce the particle size of the colorant/resin mixture prior to the cold grinding step, if desired. In other embodiments of the present invention, the liquid toner can be
Bonsignore Frank J.
Gibson George A.
Chapman Mark
Oliff & Berridg,e PLC
Palazzo Eugene O.
Xerox Corporation
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