Polymerization processes

Details Polymerization processes Polymerization processes

2001-07-02

2002-09-10

Goodrow, John (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Electric or magnetic imagery, e.g., xerography,...

Process of making developer composition

C430S137170

Reexamination Certificate

active

06447974

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to semicontinuous emulsion polymerization process and to a method for preparing toner particles wherein, for example, the latex selected is formed by emulsion polymerization in the presence of an anionic surfactant. The aforementioned toners are especially useful for imaging processes, especially xerographic processes, which processes usually prefer high toner transfer efficiency, such as those processes with a compact machine design or those that are designed to provide high quality colored images with excellent image resolution and acceptable signal-to-noise ratio, and excellent image uniformity.
Embodiments of the present invention relate to a semicontinuous emulsion polymerization process for the preparation of toner compositions, and wherein the latex selected for such processes can be generated in the absence of a nonionic surfactant, and more specifically, wherein there is selected an anionic surfactant partitioning process, that is for example, wherein a part of the anionic surfactant is added at one stage of the process and the remaining part of the surfactant is added at a second stage in the process thereby permitting, for example, excellent latex particle sizes of from about 150 to about 300 nanometers without increasing or decreasing the total amount of surfactant utilized. For example, when too much initial stage surfactant partitioning, for example more than about 20 percent of the total anionic surfactant to be used in the process, is selected there may result small particle sizes of less than about 150 nanometers resulting in high viscosity for the toner aggregated slurry of more than 300 cps at temperatures between 35° C. to 45° C. measured at a shear-rate 100 s
−1
which can result in a longer toner aggregation cycle time, for example 2 to 3 hours or a process with significant reactor fouling, poor toner particle size distribution (GSD>1.25 by volume), coarse toner particles and the like. When too little initial stage surfactant is added, for example, less than 1 percent of the total anionic surfactant to be used in the process, there may result too large a particle size of more than 300 nanometers causing low viscosity in the toner process, for example a toner aggregated slurry viscosity of less than 50 cps at temperatures between 35° C. to 450° C. measured at shear rate 100 s
−1
which may cause poor toner particle size distribution, toner fines and poor particle size control. Although these disadvantages are noted, the processes of the present invention can encompass such disadvantages depending, for example, on the particle sizes desired, viscosity desired, and other characteristics.
More specifically, in embodiments the present invention relates to anionic surfactant partitioning methods to achieve, for example, optimum polymer latex size of, for example, about 150 to about 300 nanometers, and more specifically, from about 175 to about 225 nanometers particle diameter size without using any nonionic surfactant, and wherein the anionic surfactant selected is added, for example, in an amount of from about 1 to about 20 percent by weight to the aqueous phase in the reactor and the remainder of the anionic surfactant is used to generate the monomer emulsion.
PRIOR ART
It is known to form toners by aggregating a colorant with a latex polymer. In U.S. Pat. No. 5,853,943, the disclosure of which is totally incorporated herein by reference, there is illustrated a semicontinuous emulsion polymerization process for preparing a latex by first forming a seed polymer.
In known emulsion polymerization processes, surfactant emulsifiers are used to stabilize the emulsion during emulsion polymerization. Generally, the surfactants used include both ionic and nonionic surfactants. However, these surfactants which can be an advantage for emulsion polymerization can be detrimental to the functional properties or processing of the final toners. In particular, the presence of certain surfactants, particularly nonionic surfactants, can contribute to undesirable final toner characteristics, such as sensitivity to relative humidity, low tribo charge, high dielectric loss, aging and poor toner flow.
A number of emulsion aggregation processes possess disadvantages in that, for example, the toner tribo charge depends primarily on environmental changes. Thus, for example, toner tribo charge degradation can be observed with these processes in an environment of high temperature and high humidity (>30° C. and >80 percent relative humidity). The tribo charge of the emulsion aggregation toner particles at high relative humidity can generally be controlled by avoiding the presence of surfactants, particularly nonionic surfactants, on the particle surface. Another disadvantage of a number of prior art emulsion processes is that the adhesive properties between the resulting toner particles and the substrate is poor at high relative humidity in view of the presence of nonionic surfactants on the toner particles. Thus, surfactants used in emulsion aggregation emulsion polymerization processes should be removed from the toner particles by washing to obtain stable triboelectric properties. However, nonionic surfactants are known to form hydrogen-bonded complexes with carboxylic acids and are thus difficult to remove from the surface of, for example, acrylic acid-containing particles. In addition, often the removal of these surfactants, particularly nonionic surfactants, from the emulsion aggregation particles is tedious and resource consuming, since surfactant removal is an equilibrium process and requires acceleration to be cost effective.
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. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 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; 5,501,935; 5,919,595; 5,916,725; 5,902,710; 5,863,698 and 5,858,601.
SUMMARY OF THE INVENTION
Aspects of the present invention relate to a process for the preparation of a latex polymer comprising
(i) preparing or providing an aqueous phase containing an anionic surfactant;
(ii) preparing or providing a monomer emulsion in water which emulsion contains an anionic surfactant;
(iii) adding about 50 percent or less of the monomer emulsion to the aqueous phase to thereby initiate seed polymerization and to form a seed polymer, the aqueous phase further containing a free radical initiator; and
(iv) adding the remaining amount of the monomer emulsion to (iii) and heating to complete an emulsion polymerization and wherein there is generated the polymer; a process wherein the process is free of nonionic surfactant; a process wherein the anionic surfactant is a diphenyloxide disulfonate; a process wherein the free radical initiator is added to the aqueous phase before, during or simultaneously with the monomer emulsion; a process wherein the free radical initiator is contained in the monomer emulsion when it is added to the aqueous phase; a process wherein the free radical initiator is added over a period of from about 5 to about 24 minutes; a process wherein the free radical initiator contained in the aqueous phase during the seed polymerization is present in an amount of from about 5 to about 100 percent by weight; a process wherein the free radical initiator is a persulfate initiator; a process wherein the monomer emulsion further comprises a chain transfer agent; a process wherein the surfactant in (i) is present in an amount present in an amount of from about 0.1 to about 3 percent of the total amount used in forming the latex, and the portion of the monomer emulsion added in (iii) is selected in an amount of about 0.5 to about 3 percent by weight o

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