Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-05-15
2002-06-04
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S836000, C524S779000, C526S317100, C526S319000
Reexamination Certificate
active
06399701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a surfactant-free semi-continuous emulsion polymerization process for making submicron sized particles containing poly(methyl methacrylate) (PMMA), and to a method of preparing carrier particles coated with a coating containing the submicron sized particles. The aforementioned coated carrier particles are especially useful, in conjunction with toner particles, in forming developer compositions to be used in imaging processes, especially xerographic processes.
2. Description of Related Art
Various methods are known for directly preparing resin particles from monomers, including dispersion polymerization, encapsulation, emulsion polymerization, and emulsion-aggregation.
U.S. Pat. No. 5,902,853 describes a process for the preparation of resin particles comprising adding a mixture of at least one free radical reactive monomer continuously to a heated aqueous solution of a water soluble free radical initiator and a water soluble salt to form latex emulsion particles and aggregates thereof, wherein the rate of continuous addition of the monomer is greater than the rate at which monomer is consumed by polymerization. By this process, monomer polymerization and particle aggregation can be achieved simultaneously under controlled monomer excess feed or “flood” feed conditions to provide monodisperse resin particles and resin particle aggregates thereof with a volume average diameter size range of, for example, from about 1 to about 10 micrometers. The composition and processes are described to enable emulsifier free emulsion polymerization processes achieving monodisperse resin particles or resin particle aggregates within an average diameter size range of, for example, from about 1 to about 3 micrometers and geometric particle size distributions below about 1.05, for example, of from about 1.01 to about 1.02. The resin particles and particle aggregates which are described to be suitable for use in dry and liquid developers and toner for printing applications.
U.S. Pat. No. 5,455,315 describes an in situ process for the preparation of resin particles comprising preparing a seed particle latex by aqueous emulsion polymerization of a first mixture comprised of at least one monomer, an optional chain transfer agent, and a water soluble free radical initiator, wherein the reaction of the free radical initiator and monomer produces oligomeric radicals which provide in situ stabilization to the resulting first generation seed particles; optionally diluting the first seed particle latex with water; heating and starve feed adding to the first generation seed particles a second mixture comprised of at least one monomer, an organic soluble free radical initiator, an optional chain transfer agent, an optional water soluble free radical initiator, and an optional surfactant to form a third mixture comprised of second generation seed particles; heating and starve feed adding to the second generation seed particles additional said second mixture to form a fourth mixture comprised of third generation seed particles; heating and starve feed adding to the third generation seed particles additional said second mixture to form a fifth mixture comprised of fourth generation seed particles; and heating and starve feed adding to the fourth generation seed particles additional said second mixture to form a sixth mixture comprised of fifth generation seed particles.
U.S. Pat. No. 5,679,724 describes submicron particles for ink jet inks. In particular, the patent describes an ink for ink jet printing to include an emulsifiable polymer resin and a pigment, and made by (a) combining (1) an emulsion of an emulsifiable polymer resin in an anionic medium with (2) a pigment and a cationic surfactant, and (b) aggregating particles in the mixture of step (a) to a desired particle size, thereby producing a solution of aggregated particles. The particles can optionally be coalesced to alter the particle size of the particles.
U.S. Pat. Nos. 5,219,943 and 4,935,469 both disclose processes for producing monodispersed fine particles of a vinyl polymer comprising polymerizing monomers containing at least one vinyl monomer, and a methacrylic ester in the presence of a surface active agent, a persulfate polymerization initiator, and a divalent metal as an electrolyte. Monodispersed vinyl polymer fine particles having a particle size of one micrometer or greater with a very narrow size distribution can be obtained.
The aforementioned U.S. Pat. Nos. 5,219,943 and 4,935,469 are typical in describing known emulsion polymerization processes. In these processes, surface active agents (also known as surfactants or emulsifiers) are used to stabilize the emulsion during emulsion polymerization. The presence of surfactants is usually important for stabilizing the emulsion polymerization process. Generally, the surfactants include both ionic and nonionic surfactants. However, the same surfactants that contribute advantage in the emulsion polymerization step can be detrimental to the functional properties or processing of the final particles.
As a result, surfactants used in emulsion aggregation emulsion polymerization processes should be removed from the particle by washing. However, the removal of these surfactants from the emulsion aggregation particles is very tedious and resource consuming.
What is still desired is an efficient manner of producing submicron sized poly(methyl methacrylate) particles which find particular utility as components of a coating for carrier particles of a two-component developer.
SUMMARY OF THE INVENTION
The present invention is directed to a method for preparing small sized poly(methyl methacrylate) (PMMA) polymer and copolymer particles by a surfactant-free semi-continuous emulsion polymerization process.
In the process, submicron sized particles comprised of poly(methyl methacrylate) are prepared by (i) preparing an aqueous phase containing a free radical initiator in water by heating and stirring, (ii) preparing a monomer composition comprising at least 80% by weight methyl methacrylate, (iii) adding the monomer composition to the aqueous phase to initiate emulsion polymerization of the monomer composition, the adding being done at a rate such that from 0.05% to 5% by weight of the total weight of the monomer composition is added per minute, (iv) continuing heating and stirring following completion of the adding of the monomer composition for an amount of time, and (v) drying and recovering the submicron sized particles comprised of poly(methyl methacrylate), wherein the process is conducted in the absence of any surfactants.
The present invention is further directed to a process of making coated carrier particles by a powder coating process, in which the coating contains the small sized poly(methyl methacrylate) (PMMA) polymer and copolymer particles made by the surfactant-free semi-continuous emulsion polymerization process.
In this process, the submicron sized particles comprised of poly(methyl methacrylate) are first prepared as above. Then, following preparation of the submicron sized particles comprised of poly(methyl methacrylate), the coated carrier particles are prepared by (i) mixing a carrier core with a coating composition comprising the submicron sized particles comprised of poly(methyl methacrylate) for a time until the coating composition adheres to the carrier core, and (ii) heating the mixture for a time sufficient to melt and fuse the coating composition to the carrier core, thereby obtaining the coated carrier particle.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention is particularly drawn to the formation of small sized particles, i.e., submicron sized particles having an average size of less than 1 &mgr;m, comprised of PMMA polymer or PMMA copolymers. For PMMA copolymers, the methyl methacrylate (MMA) monomer should comprise at least 80%, preferably at least 90%, more preferably at least 95%, and most preferably at least 99%, by weight of the monomer composition used to form the copolymer. As
Enright Thomas E.
Henderson Kenneth Derek
Kelly Bernard A.
Liebermann George
Paine Anthony James
Palazzo Eugene O.
Zalukaewa Tatyana
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