Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-02-28
2002-08-27
Rodee, Christoper (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S137170
Reexamination Certificate
active
06440628
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a toner for development of electrostatic images, comprising carbon black as a colorant, and more particularly to a toner for development of electrostatic images, which is excellent in various properties such as flowability, shelf stability, charging properties, environmental stability of image quality and durability of image quality, and is markedly improved in safety so as to inhibit an adverse influence on the human body and environment, and a production process thereof.
BACKGROUND ART
In an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus, a photosensitive member evenly and uniformly charged has heretofore been exposed to a light pattern to form an electrostatic latent image (electrostatic image), and the electrostatic latent image has been developed with a developer. More specifically, the developer is applied to the electrostatic latent image to form a developer image (visible image). As needed, the developer image is then transferred to a transfer medium such as paper, and fixed to the transfer medium by a method such as heating, pressing or use of solvent vapor.
A main component of developers is a toner for development of electrostatic images composed of colored fine particles comprising a binder resin and a colorant. The developers include two-component developers composed of a toner and carrier particles, and one-component developers composed substantially of a toner alone and making no use of any carrier particles. The one-component developers include magnetic one-component developers containing magnetic powder, and non-magnetic one-component developers containing no magnetic powder. In general developers, a flowability-imparting agent such as colloidal silica is often added independently in order to enhance the flowability of the toner.
Processes for producing a toner are roughly divided into a grinding process and a polymerization process. In the grinding process, a synthetic resin, a colorant and optional other additives are melted and mixed, the mixture is ground, and the ground product is then classified so as to obtain particles having a desired particle diameter, thereby obtaining colored particles (ground toner). In the polymerization process, a polymerizable monomer composition containing a colorant and a polymerizable monomer, in which various additives such as a charge control agent are uniformly dissolved or dispersed as needed, is prepared, the polymerizable monomer composition is dispersed in an aqueous dispersion medium containing a dispersion stabilizer by means of a mixing device to form fine droplets (oil droplets) of the polymerizable monomer composition, and the dispersion containing the fine droplets is then heated to subject the droplets to suspension polymerization, thereby obtaining colored polymer particles (polymerized toner) having a desired particle diameter. Polymerized toners include those produced by, for example, an emulsion polymerization process, dispersion polymerization process and the like in addition to that by the suspension polymerization process.
Images formed by an image forming apparatus such as an electrophotographic copying machine are required to improve their definition year by year. As a toner used in the image forming apparatus, a toner obtained by the grinding process has heretofore been mainly used. The grinding process tends to form colored particles having a wide particle diameter distribution. In order for the toner to exhibit satisfactory developing characteristics, therefore, the ground product must be classified to adjust the particles so as to have a particle diameter distribution limited to a certain extent. According to the polymerized toner on the other hand, a toner having even particle diameter can be provided without need of grinding and classification by controlling the droplet diameter and droplet diameter distribution of droplets of the polymerizable monomer composition in a polymerization step.
According to the suspension polymerization process among the polymerization processes, a toner scarcely containing residual ions caused by an emulsifying agent and the like can be provided in a spherical form near to a sphere. The spherical toner has excellent developing characteristics and permits the formation of high-quality images. The toner scarcely containing residual ions has good environmental stability and permits the provision of stable image quality even when environmental temperature and humidity vary. As a matter of fact, however, it is difficult to conduct the polymerization while uniformly dispersing the colorant in the polymerizable monomer composition and retaining the uniformly dispersed state. It is also difficult to conduct the polymerization while evenly controlling the droplet diameter of the droplets of the polymerizable monomer composition in the aqueous dispersion medium and stably dispersing the droplets in the dispersion medium.
For example, carbon black typical of the colorants is easy to aggregate, and so it is difficult to uniformly disperse the carbon black in a polymerizable monomer composition and retain the uniformly dispersed state. The carbon black tends to exert an adverse influence on the dispersion stability of droplets of the polymerizable monomer composition in the aqueous dispersion medium. As a result, it is difficult to provide a toner having a narrow particle diameter distribution.
On the other hand, there is also an increasing demand for prevention of environmental pollution by gasses and volatile components discharged from electrophotographic copying machines and printers with the enhancement of the demand for high image quality. For example, these image forming apparatus tend to generate ozone. Therefore, measures to change charging means and transferring means from corona discharge devices to charging rollers or belts and the like are taken to prevent the generation of ozone. In the polymerized toners, odor attributed to residual monomers, catalyst residue, solvents, etc. becomes a problem. Accordingly, measures to prevent the generation of odor and volatile components are taken by, for example, selecting the kind of a polymerization initiator.
However, sufficient measures have not been taken against a problem of environmental pollution caused by colorants. More specifically, carbon black generally used as a colorant contains a trace amount of polycyclic aromatic hydrocarbons such as benzo(a)pyrene which is known to be a carcinogen. Fears are entertained that these trace components contained in a toner will adversely affect the human body and environment by scattering of a developer from an image forming apparatus. Therefore, improvement in the safety of a toner containing carbon black becomes an important problem. In order to enhance the safety of the toner containing carbon black, it is considered that to reduce the content of polycyclic aromatic hydrocarbons in the toner as much as possible is effective.
Nevertheless, as a result of an investigation by the present inventors, it has been found that when carbon black containing a smaller amount of polycyclic aromatic hydrocarbons is used, it is difficult to obtain a toner capable of providing images excellent in image quality. In particular, when a toner is produced by the suspension polymerization process, the mere use of the carbon black containing a smaller amount of polycyclic aromatic hydrocarbons lower the dispersibility of the carbon black in a polymerizable monomer composition and the dispersion stability of droplets of the polymerizable monomer composition in an aqueous dispersion medium, resulting in difficulty to obtain a toner capable of providing high-definition images.
There have heretofore been made various proposals on improvement in the dispersibility of carbon black and reduction in volatile components in polymerized toners.
For example, (1) Japanese Patent Application Laid-Open No. 106250/1981 has proposed a process for producing a toner for development of electrostatic images, in which a po
Imai Katsuhiro
Watanabe Makoto
Dinsmore & Shohl LLP
Nippon Zeon Co. Ltd.
Rodee Christoper
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