Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-01-07
2004-06-08
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S137150, C430S111400
Reexamination Certificate
active
06746809
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a toner for development of electrostatic images and a production process thereof, and more particularly to a toner for development of electrostatic images, which is extremely low in the content of residual polymerizable monomers and excellent in environmental safety and moreover flowability, and a production process thereof.
BACKGROUND ART
In an electrophotographic process, electrostatic recording process, electrostatic printing process or the like, a toner for development of electrostatic images (hereinafter referred to as “toner” merely) is used as a developer for developing an electrostatic latent image formed on a photosensitive member into a visible image. The toner is composed of colored resin particles containing at least a binder resin and a colorant, and additionally containing various kinds of additives such as a charge control agent and a parting agent as needed.
Processes for producing the toner are roughly divided into a grinding process and a polymerization process. The grinding process is a process of producing a toner (ground toner) by melting and kneading individual components such as a binder resin and a colorant, and then grinding and classifying the kneaded product. The polymerization process is a process of producing polymer particles (polymerized toner particles) by subjecting a polymerizable monomer composition containing a polymerizable monomer and a colorant, and optionally various kinds of additives such as a charge control agent and a parting agent to suspension polymerization. The colored polymer particles containing the colorant may be used as core particles to form a polymer layer (shell) on the surfaces thereof, thereby providing polymer particles of a core.shell structure. In the polymerization process, a suspension polymerization process is generally used. However, any other polymerization process such as an emulsion polymerization process may be adopted if desired. In the polymerized toner, the polymer component formed by the polymerization of the polymerizable monomer becomes a binder resin.
In any technique of the grinding process and the polymerization process, it is difficult to completely react the polymerizable monomer in the polymerization step for forming the binder resin. Therefore, it is unavoidable that an unreacted polymerizable monomer remains in the toner. When a toner in which a polymerizable monomer remains in a comparatively great amount is used in an image forming apparatus such as an electrophotographic copying machine or laser printer, the remaining polymerizable monomer is vaporized out of the toner by heating upon fixing of an image formed, or the like to worsen a working environment or emit unpleasant odor. The toner in which the polymerizable monomer remains in a comparatively great amount tends to undergo blocking during its storage or in a toner box of an image forming apparatus, thereby impairing the flowability of the toner. Further, when the toner in which the polymerizable monomer remains in a comparatively great amount is used, such disadvantages that an offset phenomenon occurs upon the fixing of an image formed, and filming on individual members in the image forming apparatus tends to occur.
In the grinding process, the residual polymerizable monomers can be removed from the binder resin formed with relative ease in advance in a post-treatment after the polymerization. Therefore, there is no possibility that the amount of the polymerizable monomer removed may be adversely affected by the additive components such as the colorant, or that the toner may aggregate in the removal step of the unreacted polymerizable monomer, since the binder resin can be melted and kneaded with the additives such as the colorant, charge control agent and parting agent after removing the residual polymerizable monomers from the binder resin, and the resulting mixture is ground, whereby a toner can be provided. However, any toner substantially spherical and sharp in particle diameter distribution can not be obtained by the grinding process.
On the other hand, in the case of the polymerized toner, the residual polymerizable monomers must be removed from the polymer particles containing the additives such as the colorant, charge control agent and parting agent. It is difficult to reduce the residual polymerizable monomers because the residual polymerizable monomers is easy to be adsorbed on these additives. In addition, when a removal method such as drying of the resulting polymerized toner under reduced pressure is adopted for the purpose of reducing the amount of the residual polymerizable monomers, disadvantages such as aggregation tends to occur.
According to the polymerization process, a toner substantially spherical and sharp in particle diameter distribution can be provided, thereby forming a high-quality image. In recent years, there has been a strong demand for meeting requirements such as provision of high definition images, energy saving, speeding-up of printing (including copying and recording), miniaturization of apparatus, formation of full-color images and the like. In order to meet these requirements, it is required to design a polymerized toner so as to make the average particle diameter of the resulting polymerized toner smaller than that of a generally used toner or make the fixing temperature thereof lower than before. When it is intended to meet these requirements against the polymerized toner, however, it is more and more difficult to reduce the amount of the residual polymerizable monomers while avoiding the disadvantages such as aggregation.
In the polymerization process, a polymerized toner is recovered from a suspension (slurry) containing the polymer particles formed through post-treatments such as dewatering, washing and drying. As processes for reducing the content of the residual polymerizable monomers in the resulting polymerized toner, have heretofore been known, for example, (1) a process of treating a polymerized toner after a drying step, (2) a process of treating a polymerized toner after a dewatering step and before a drying step, and (3) a process of treating a polymerized toner in a slurry before a dewatering step.
As the process (1), Japanese Patent Application Laid-Open No. 92736/1995 has proposed a process in which a dried polymerized toner is heated and subjected to a deaerating treatment under reduced pressure. This publication shows in the experimental results thereof that the amount of the polymerizable monomer remaining in the polymerized toner is reduced to 150 ppm. However, the heat treatment of the dried polymerized toner involves a problem that toner particles show a tendency to aggregate to one another. In the case of a toner (hereinafter referred to as “low-temperature fixing toner”) the fixing temperature of which has been designed low so as to be suitable for use in high-speed printing or the like, the tendency becomes a great problem. The reason for it is that in the low-temperature fixing toner, those having a low glass transition temperature, melting point or the like are used as toner components including a binder resin component for the purpose of realizing fixing at a comparatively low temperature thereof, and so these components are softened to become liable to aggregate when the polymerized toner is heated. Accordingly, this process is an unpractical process for low-temperature fixing toners designed so as to lower the fixing temperature.
As the process (2), Japanese Patent Application Laid-Open No. 207122/1998 has proposed a process in which polymer particles containing a colorant are dried under reduced pressure while pouring a gas into the polymer particles. However, this process is difficult to remove the polymerizable monomer adsorbed on the colorant and the like though the amount of the residual polymerizable monomers can be reduced to about 100 ppm. Further, in this process, the polymer particles in a wet state are dried under reduced pressure while heating them. Therefore, when the process is applied to a low-temperatu
Fujino Takeo
Sato Kazuhiro
Chapman Mark A.
Nippon Zeon Co. Ltd.
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