Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-06-22
2002-09-24
Chapman, Mark (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S137150, C523S335000, C524S458000, C524S492000, C526S081000
Reexamination Certificate
active
06455219
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a novel process for incorporating silica particles into latex particles, which latex particles find particular utility in the manufacture of toner particles for use in xerographic applications.
2. Description of Related Art
Good flow properties are usually desired and often are critical for toners, and materials such as fumed silicas are known to be added to the surface of toner particles to improve flow, and may also improve charge stability of the toner and carrier mixture.
In general, it is known to include silica, also referred to as silicon dioxide, in toner particles as surface additives as discussed above. The silica imparts several advantageous properties to the toner, including, for example, toner flow, tribo enhancement, admix control, improved development and transfer stability and higher toner blocking temperature.
Most desirably, the silica improves and controls the toner flow properties of the toner. Toner cohesivity can have detrimental effects on toner handling and dispensing. Toners with excessively high cohesion can exhibit “bridging” which prevents fresh toner from being added to the developer mixing system. Conversely, toners with very low cohesion can result in difficulty in controlling toner dispense rates and toner concentration, and can result in excessive dirt in the machine. In addition, in certain applications, toner particles are first developed from a magnetic brush to donor rolls. Toner flow must be such that the electric development fields are sufficient to overcome the toner adhesion to the donor rolls and enable adequate image development to the photoreceptor. Following development to the photoreceptor, the toner particles must also be able to be transferred from the photoreceptor to the substrate.
Therefore, it is necessary to have a toner that minimizes both cohesion of particles to one another, and adhesion of particles to surfaces such as the donor rolls and the photoreceptor. Minimizing the toner cohesion and adhesion will provide high and stable development and high and uniform transfer, allowing reliable image formation.
As a method of making toner particles, a method employing the use of emulsion polymerization to form the toner resin binder is known. Emulsion polymerization comprises forming an emulsion of a surfactant and monomer in water, then polymerizing the monomer in the presence of a water soluble initiator. Emulsion polymerization is a well known industrial process. In forming toner compositions for use with reprographic or xerographic print devices, emulsion aggregation processes are known. For example, emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797. Also of interest may be U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935 (spherical toners).
In addition, the following U.S. patents relate to emulsion aggregation processes of forming toner compositions, the disclosures of which are incorporated herein by reference in their entireties:
U.S. Pat. No. 5,945,245 describes a surfactant free process for the preparation of toner comprising heating a mixture of an emulsion latex, a colorant, and an organic complexing agent.
U.S. Pat. No. 5,977,210 describes a process for the preparation of ink compositions comprising the emulsion polymerization of monomer, water, surfactant, and initiator with stirring and heating to provide a latex; mixing therewith a pigment dispersion of pigment particles, water, and cationic surfactant; blending the mixture; thereafter stirring the mixture; and subsequently adding additional anionic surfactant to stabilize the aggregate particles.
In such methods, one manner of incorporating the silica additive in the toner is to add the silica in the form of a pre-aggregated silica gel following the completion of the emulsion polymerization step of forming the toner binder resin. However, this method of incorporating the silica requires additional process steps in forming the pre-aggregated silica and requires additional processing time in emulsifying the silica gel into the binder. Also, it is a difficult process to scale-up in terms of viscosity, mixing, homogenization and pH control. In addition, when the toner particles having silica incorporated by such methods are heated in the aggregation and coalescing steps, a large number of coarse particles are produced, which can degrade print quality.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to develop a novel method of incorporating silica into the toner to derive the beneficial properties therefrom while eliminating the above-discussed problems associated with current methods of incorporating silica.
These and other objects of the present invention are achieved by the present invention, which in embodiments relates to a process for making silica-containing latex particles, comprising polymerizing monomer in an emulsion comprising the monomer, water, silica particles, and optionally at least one surfactant, by adding at least one free radical initiator to the emulsion to form the silica-containing latex particles.
In further embodiments, the invention relates to an emulsion polymerization process for making silica-containing latex particles, comprising: forming an aqueous monomer emulsion by adding at least one monomer to an aqueous composition comprising a surfactant and silica particles in water to form a mixture, and emulsifying the mixture; charging a portion of the aqueous monomer emulsion to a reactor; adding an aqueous solution containing a free radical initiator to the reactor to produce a seed latex; and subsequently adding a remaining portion of the aqueous monomer emulsion to the reactor to obtain the silica-containing latex particles.
The silica-containing latex particles made by the present invention are ideally suited for use in toner particles, for example by adding a colorant therein and aggregating and coalescing the particles.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention in embodiments is directed to processes for the preparation of silica-containing latexes and which latexes can be selected for emulsion/aggregation/coalescence processes for forming toner illustrated in the patents mentioned hereinafter. Preferably, the emulsion polymerization process comprises an in situ seeded, monomer emulsion fed semicontinuous polymerization to produce the latex.
In embodiments, the present invention is directed to a process for making silica-containing latex particles, comprising polymerizing monomer in an emulsion comprising the monomer, water, silica particles, and optionally at least one surfactant, by adding at least one free radical initiator to the emulsion to form the silica-containing latex particles.
While any suitable emulsion process may be used in the present invention, most preferably a seed polymerization method is utilized. That is, the polymerization of the monomer of the emulsion is preferably conducted by first forming a seed latex from a portion of the emulsion and at least one free radical initiator, and subsequently adding a remaining portion of the emulsion, optionally with additional free radical initiator, to the seed latex. The use of a seed latex significantly reduces batch-to-batch variations in the emulsion polymerization process. Also, in situ seed formation at the beginning of a reaction is simplified since no additional reactor is needed to formulate the seed latexes.
In a preferred embodiment of the invention, the silica-containing latex particles are made by first forming an aqueous monomer emulsion by adding at least one monomer to an aqueous composition comprising a surfactant and silica particles in water to form a mixture, and then emulsifying the mixture. Next, a porti
Boils-Boissier Danielle C.
Chen Allan K.
Duque Rosa M.
Gerroir Paul J.
Helbrecht Arthur
Chapman Mark
Oliff & Berridg,e PLC
Palazzo Eugene O.
Xerox Corporation
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