Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2002-02-06
2004-04-13
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C523S335000
Reexamination Certificate
active
06720123
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing a toner for developing electrostatic image to be used for copying machines and printers of electrophotographic system. More particularly, it relates to a process for producing a toner for developing electrostatic image which facilitates controlling of the shape of toner particles in the step of aging agglomerate particles of primary polymer particles.
BACKGROUND OF THE INVENTION
Toners for developing electrostatic image having conventionally been commonly used in the electrophotography have been produced by melt-kneading a mixture comprising a varying binder such as styrene/acrylate series copolymer or a polyester containing therein a colorant such as carbon black or a pigment and, if necessary, a charge control agent and a magnetic material using an extruder, and pulverizing and classifying the kneaded product. However, the conventional toners obtained by the melt-kneading/pulverizing method have the limit as to controlling of toner particle size, and it is difficult to produce a toner of substantially 10 &mgr;m or less, particularly 8 &mgr;m or less, in average particle size with a good yield and thus the conventional toners cannot be said to be sufficient for providing a high resolution which will be required in the electrophotography in the future.
In addition, in order to obtain low temperature fixing properties, it has been proposed to blend a wax having a low melting point with a toner upon kneading but, in the kneading/pulverizing method, the maximum blending content of the wax is about 5% which fails to provide a toner having enough low temperature fixing properties. Also, in the case of producing toner by mechanically pulverizing the flakes obtained from the melt-kneaded product, there results a toner with a broad particle size distribution and only in a poor yield. This tendency is serious particularly in the case of obtaining a toner with a small particle size.
On the other hand, in recent years, it has been known, as a process substituting for the melt-kneading/pulverizing method, to produce a polymerization toner by the emulsion polymerization agglomeration process or the suspension polymerization process. These processes permit to control dispersion of the raw materials as is different from the melt-kneading/pulverizing process. In particular, the emulsion polymerization agglomeration process permits to control particle size, particle size distribution and shape of the toner particles.
In the case of producing a toner by the emulsion polymerization process, a pigment, a charge control agent, etc. are added to the resin-emulsified dispersion obtained by the polymerization and containing primary particles of the resin of 0.05 &mgr;m to 0.5 &mgr;m in particle size and, further, an electrolyte or the like is added thereto to agglomerate the primary particles to form agglomerate particles of 3 to 9 &mgr;m in particle size. Then, the agglomerate particles are aged at an elevated temperature of the glass transition temperature (Tg) of the primary particles or higher than that to first fuse particles at the surface and then particles in the inside of each agglomerate particle to each other, followed by washing and drying the slurry containing the toner particles to obtain toner particles as a product. Shape of the toner particles exerting an important influence on the properties of the toner is controlled in the aging step at an elevated temperature.
Japanese Patent Laid-Open No. 2000-131882 proposes to change the concentration of at least either of an agglomerating agent and a stabilizing agent upon thermobonding which corresponds to the aging step. To be specific, the concentration is decreased by about 6% through the addition of distilled water upon thermobonding. Also, it is described in U.S. Pat. No. 5,849,456 to add a surfactant in the step of fusing the particles.
However, in these processes, the scope of resins to which these processes can be applied is small and, with agglomerate particles having a higher glass transition temperature (Tg), the primary particles are so difficult to deform that it is difficult to fuse the particles to each other. Therefore, toner particles obtained by the process are difficult to control their shape and, in addition, they have a weak strength and tends to form fine powder, which exerts detrimental influences upon image quality.
SUMMARY OF THE INVENTION
The subject of the present invention is to provide a process for producing a toner for developing electrostatic image, which facilitates to control shape of toner particles in the step of aging agglomerate particles of primary polymer particles.
As a result of intensive investigations to solve the above-described problem, the inventors have found that agglomerate particles can easily be deformed and controlling of the shape of toner particles can easily be effected by largely reducing the concentration of solid content in the toner-aging step in comparison with the concentration in the agglomerate step through addition of water or the like, thus having achieved the invention.
That is, a gist of the invention lies in the process for producing a toner for developing electrostatic image involving the agglomerate stop wherein a dispersion liquid containing at least primary polymer particles and colorant particles is stirred in a stirring tank to agglomerate the particles to thereby obtain agglomerate of the particles and the aging step wherein the resultant agglomerate of the particles is kept at a temperature higher than the glass transition temperature (Tg) of the primary polymer particles by 10° C. or more for a predetermined period of time to thereby fuse the particles, which process is characterized in that the concentration of solid content (C1) in the agglomerate step is 10 to 40% by weight, and that the concentration of the solid content (C2) in the aging step is in the range of 0.3C1≦C2≦0.8C1.
Another gist of the invention lies in the process of the above-described toner for developing electrostatic image, wherein water is mixed upon or after the completion of the agglomerate step.
A further gist of the invention lies in the process for producing the above-described toner for developing electrostatic image, wherein the agglomerate step and the aging step are conducted in the same stirring tank.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The toner of the invention contains as its constituents primary polymer particles, colorant particles and, if necessary, wax, a charge control agent and other additives. The toner of the invention is commonly produced by the emulsion polymerization-agglomeration process. In the emulsion polymerization-agglomeration process, the primary polymer particles obtained by the emulsion polymerization, at least primary colorant particles, and primary particles of charge control agent optionally added are co-agglomerated to form an agglomerate of the particles, followed by adhering or fixing thereto particulate resin to produce a toner.
Next, the primary polymer particles to be used in the invention are described below.
The primary polymer particles may contain a wax. In the case where the primary polymer particles contain the wax, the particles are obtained preferably by the process of seed emulsion polymerization of a monomer mixture using the particulate wax as seed, though not being particularly limited.
In conducting the emulsion polymerization, the polymerization is allowed to proceed by adding successively a monomer having a Brønsted acid group (hereinafter sometimes referred to merely as “acid group”) or a monomer having a Brønsted base group (hereinafter sometimes referred to merely as “base group”) and a monomer having neither of the Brønsted acid group and the Brønsted base group (hereinafter sometimes referred to as “other monomer”). In this case, the monomers may be separately added, or a plurality of the monomers may previously be mixed with each other to add. Further, it is also possible to change the monome
Hoshino Toyomasa
Mitsuhashi Kazuo
Tokunaga Tomohiko
Xu Yuqing
Mitsubishi Chemical Corporation
Oblon, Spivak, McClelland, Maier & Neustadt, P.C
Rodee Christopher
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