Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Patent
1997-12-18
1999-09-14
Goodrow, John
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
430137, 430138, G03G 9093
Patent
active
059521449
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for producing a toner for development of electrostatic latent images, and more particularly to a process for producing a toner for development of electrostatic latent images formed by electrophotography, electrostatic recording, etc.
BACKGROUND ART
Electric latent images formed by an electrophotographic apparatus, electrostatic recording apparatus or the like have heretofore been first developed with a toner. After the toner image thus formed is then transferred to a transfer medium such as paper as needed, the unfixed toner image is fixed by any of various methods such as heating, pressing and use of solvent vapor.
In general, a toner has heretofore been produced by melting and mixing a colorant, a charge control agent, an offset preventing agent and the like in a thermoplastic resin, uniformly dispersing them in the thermoplastic resin to prepare a composition, grinding the composition and then classifying the ground product. According to this production process (i.e., grinding process), a toner having a measure of excellent properties can be produced. However, there is a limit to the selection of materials for the toner. For example, the composition formed by the above melting and mixing must be such that can be ground and classified by economically usable apparatus. This requirement obliges the composition obtained by the melting and mixing to become fully brittle. For this reason, the toner obtained by such a grinding process involves the following disadvantage. When the above composition is ground into particles, the particles formed tend to have a wide particle diameter distribution. When it is intended to obtain a copy image having good resolution and gradation, therefore, fine powder having a particle diameter of 5 .mu.m or smaller and coarse powder having a particle diameter of 20 .mu.m or greater must be removed from the ground product by classification, so that the yield of the toner becomes very low.
Besides, in the grinding process, it is difficult to uniformly disperse solid fine particles such as the colorant, charge control agent and offset preventing 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 and influences 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.
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, a monomer composition with a polymerizable monomer, a colorant, a charge control agent, an offset preventing agent, a polymerization initiator and the like dissolved or dispersed uniformly is poured into water or an aqueous dispersion medium composed principally of water, which contains a dispersion stabilizer, and dispersed therein by means of a mixing device capable of mixing with high shearing force to form fine droplets of the polymerizable monomer composition, and the droplets are then polymerized, thereby forming toner particles (i.e., polymerized toner).
According to the suspension polymerization process, the colorant, charge control agent, offset preventing agent and the like are added to the 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 resin, can be ensured. According to the suspension polymerization process, toner particles having the desired particle diameters can be generally obtained at a yield of at least 90%, and so such a process has an economical advantage over
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Hasegawa Jun
Ogawa Tokudai
Sakai Jun
Watanabe Makoto
Yamada Fumio
Goodrow John
Nippon Zeon Co. Ltd.
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