Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-07-25
2003-04-08
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C430S108400, C430S108100, C430S137110
Reexamination Certificate
active
06544706
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polymerized toner and a production process thereof, and more particularly to a polymerized tone of a core-shell structure, which is suitable for use in developing an electrostatic latent image formed by an electrophotographic process, electrostatic recording process or the like, and a production process thereof.
BACKGROUND ART
In an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus, an electrostatic latent image is formed on a photosensitive member has heretofore been developed with a developer. After the developer image formed by the development is transferred to a transfer medium such as paper as needed, the unfixed image is fixed by any of various methods such as heating, pressing and use of solvent vapor. As the developer, a toner is used either singly or in combination with carrier particles and/or a flowability improver. The toner means colored particles obtained by dispersing a colorant such as carbon black and other additives in a binder resin. Processes for producing toner are roughly divided into a grinding process and a suspension polymerization process.
In the grinding process, a thermoplastic resin, a colorant, a charge control agent, a parting agent and the like are melted and mixed into a resin composition, and the resin composition is ground and then classified, thereby producing a toner having a desired particle diameter. According to the grinding process, a toner having a measure of excellent properties can be produced. However, the grinding process involves important problems.
First, in the grinding process, there is a limit to the selection of materials for the toner. The resin composition formed by the melting and mixing must be such that can be ground and classified by economically usable apparatus. This requirement obliges the resin composition to become fully brittle. When the brittle resin composition is ground into particles, the colored particles formed tend to have a wide particle diameter distribution. In order to obtain a copy image having good resolution and gradation by an electrophotographic process, a toner having a narrow particle diameter distribution must be used. In the grinding process, therefore, the ground product must be classified after the grinding step of the resin composition to narrow the particle diameter distribution. Although the particle diameters of particles to be removed by classification vary according to the intended average particle diameter of the resulting toner, fine powder having a particle-diameter of 5 &mgr;m or smaller and coarse powder having a particle diameter of 20 &mgr;m or greater must be removed by classification, for example, when a toner having an average particle diameter of about 10 &mgr;m and a narrow particle diameter distribution is provided. Therefore, such classification results in a reduction in the yield of the toner.
Second, in the grinding process, it is difficult to uniformly disperse solid fine particles such as the colorant, charge control agent and parting agent in the thermoplastic resin. The unevenly dispersed state of the solid fine particles may form the cause that fog is increased, or image density is lowered. The uneven dispersion of these solid fine particles in the grinding process adversely affects the flowability, triboelectrification properties and the like of the resulting toner to a great extent to deteriorate properties of the toner, such as developing characteristics and durability. Accordingly, in the grinding process, it is necessary to take good care to uniformly disperse these solid fine particles. However, the dispersion by the melting and mixing has its limit.
Third, in order to improve the fixing ability of the resulting toner so as to meet high-speed copying and formation of full-color images, it is necessary to lower the glass transition temperature of the toner. When a thermoplastic resin having a low glass transition temperature is used, however, difficulty is encountered on the grinding of the resulting resin composition. Therefore, the glass transition temperature of the toner cannot be lowered to 60° C. or lower. It is hence difficult to provide a toner improved in fixing ability by the grinding process.
In order to overcome these problems in the grinding process, processes of producing a toner by suspension polymerization have been proposed in recent years. In the suspension polymerization process, (1) a monomer composition containing at least a polymerizable monomer and a colorant, with additives such as a charge control agent and a parting agent dissolved or uniformly dispersed therein as needed, is prepared, (2) the monomer composition is then poured into water or an aqueous dispersion medium composed principally of water, which contains a dispersion stabilizer, and the mixture is stirred until the average droplet diameter of droplets becomes constant, (3) a polymerization initiator is added to the dispersion and dispersed therein by means of a mixing device capable of mixing with high shearing force to form the monomer composition into fine droplets, and (4) the droplets are then polymerized to form colored polymer particles (i.e., polymerized toner).
According to the suspension polymerization process, the solid fine particles such as the colorant, charge control agent and parting agent are added to the polymerizable monomer, which is a low-viscosity liquid, to disperse them therein. Therefore, a satisfactory dispersing quality compared with the grinding process, in which such components are dispersed in the thermoplastic resin, can be ensured. According to the suspension polymerization process, a toner having a desired particle diameter and a narrow particle diameter distribution can be generally obtained at a yield as high as at least 90%, and so such a process has an economical advantage over the grinding process. Further, the glass transition temperature of the polymerized toner can be adjusted by selecting the kinds and combination of polymerizable monomers. As described above, the problems involved in the grinding process can be solved by the use of the suspension polymerization process. The polymerized toner can provide good copy images excellent in resolution and gradation and free of fog because it has a sharp particle diameter distribution and good electric properties, and moreover can be produced economically. However, the conventional polymerized toners have not come to fully meet the level of requirements for toners in recent years.
Copying machines, printers and the like of the electrophotographic system have been recently required to reduce demand power and to achieve the speeding-up of copying or printing. A step in which energy is particularly demanded in the electrophotographic system is a fixing step conducted after transferring a toner image from a photosensitive member to a transfer medium such as transfer paper. In the fixing step, the toner is fixed to the transfer medium by heating and melting it. Therefore, a heating roll heated to a temperature of at least 150° C. is used, and electric power is used as an energy source therefor. There is a demand for lowering the temperature of the heating roll from the viewpoint of energy saving. In order to lower the temperature of the heating roll, it is necessary to use a toner capable of fixing at a temperature lower than that heretofore used. Namely, it is necessary to lower the fixing temperature of the toner itself. Besides, the speeding-up of copying and printing has been strongly required with the advancement of the combination of image forming apparatus and the formation of personal computer network. In order to realize high-speed copying machines and high-speed printers, it is necessary to conduct fixing in a shorter time than before. When the fixing temperature of a toner can be lowered, it is also possible to shorten the fixing time by controlling the temperature of a heating roll. Therefore, the lowering of the fixing temperature of the toner also can meet the speeding-up of copyin
Dinsmore & Shohl LLP
Nippon Zeon Co. Ltd.
Rodee Christopher
LandOfFree
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