Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-09-25
2003-05-13
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108500, C430S137170
Reexamination Certificate
active
06562535
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a toner for development of electrostatic images for developing electrostatic latent images formed on a photosensitive member by an electrophotographic process, electrostatic recording process or the like, and more particularly to a toner for development of electrostatic images, which is sharp in particle diameter distribution, excellent in flowability and shelf stability, small in dependence of charge level on environment and little in deterioration of image quality by continuous printing.
BACKGROUND ART
In an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus, an electrostatic latent image (electrostatic image) is formed on a photosensitive member uniformly and evenly charged by exposure to a light pattern of the image, and a developer is applied to the exposed region or unexposed region on the photosensitive member to conduct development. The developer image formed on the photosensitive member is generally transferred to a transfer medium such as paper or OHP film, and the unfixed image is then fixed to the transfer medium by a method such as heating, pressing or use of solvent vapor. As the developer, is used a toner composed of colored particles comprising a binder resin in which a colorant and various kinds of additives such as a charge control agent and a parting agent have been dispersed.
As toners for development of electrostatic images, ground toners obtained by melting and mixing a colorant and a charge control agent, and optionally various kinds of additives such as a parting agent in a thermoplastic resin to prepare a resin composition and then grinding and classifying the resin composition have heretofore been used mainly. In recent years, polymerized toners easy to control their particle diameter and permitting omitting complicated production steps such as grinding and classification have come to attract attention. In any toner, a charge control agent is generally contained in order to make the toner have charge properties.
In general, a polymerized toner is produced by pouring a polymerizable monomer composition containing a polymerizable monomer, a colorant, a charge control agent and the like in an aqueous dispersion medium containing a dispersion stabilizer to disperse it in the aqueous medium by means of a mixer having high shearing force, thereby forming fine droplets of the monomer composition, and then subjecting the dispersion containing the fine droplets to suspension polymerization. A polymer formed by the polymerization of the polymerizable monomer becomes a binder resin, and the additives such as the colorant are dispersed therein. In the polymerization process of such a polymerized toner, it is extremely important from the viewpoint of properties of the resulting toner to uniformly disperse the additives such as the colorant and charge control agent in the polymerizable monomer, and to stably form the fine droplets of the monomer composition in the aqueous dispersion medium.
However, the colorant such as carbon black is generally high in hydrophilicity and hence difficult to uniformly disperse in the polymerizable monomer. When the dispersion of the colorant is insufficient, the colorant becomes unevenly distributed on the surfaces of the droplets of the monomer composition due to its high hydrophilicity, and the droplet diameter distribution of the droplets also becomes broad. As a result, the flowability and developing ability of the resulting polymerized toner are deteriorated, and classification is required to lower the yield of the polymerized toner.
Further, since many of charge control agents such as nigrosine dyes which have heretofore been generally used are high in hydrophilicity like the colorant, they have involved such problems that the dispersibility of other components such as the colorant is inhibited, the stability of the droplets of the monomer composition in the aqueous dispersion medium is inhibited, and the blocking resistance of the resulting polymerized toner is adversely affected to lower the shelf stability thereof, in addition to its poor dispersibility.
In order to solve such problems, there is adopted a method in which in a process of forming droplets of a monomer composition in an aqueous dispersion medium, a suspension formed is vigorously stirred by means of a mixing device having high shearing force, or the like to finely disperse the droplets. However, it is difficult to sufficiently enhance the uniformly dispersing ability of the additives and the stability of the droplets by such process for forming the droplets. In addition, a toner to be produced is colored with a charge control agent itself such as a nigrosine dye or metallized dye. Therefore, such a charge control agent cannot be used as a charge control agent for color toners.
Various proposals have been made as to charge control agents used in place of the charge control agents such as nigrosine dyes. For example, Japanese Patent Application Laid-Open No. 175456/1991 discloses a production process of a polymerized toner, in which a colorant is dispersed in a polymerizable monomer in the presence of a copolymer of a styrene monomer and a quaternary ammonium salt group-containing acrylic ester, and the resultant dispersion is then subjected to suspension polymerization, and describes the resultant polymerized toner as being sharp in particle diameter distribution and also excellent in moisture absorption resistance. The quaternary ammonium salt group-containing copolymer is a charge control agent having positively charging ability. In addition, Japanese Patent Application Laid-Open Nos. 217464/1989, 15858/1991 and 243954/1991 disclose a polymerized toner containing a charge control agent having negatively charging ability composed of a sulfonic group-containing copolymer.
When such a charge control resin having positively or negatively charging ability is used, the charge properties of the resulting toner is good in an initial stage of printing, and an image having high image quality free of fog is provided therefrom. In addition, the charge control resin is colorless and hence can be applied to color toners. However, the toner containing such a charge control agent does not have sufficiently stable charge properties, and so image density becomes thin in an early stage when conducting continuous printing. In addition, the toner containing the charge control resin has high dependence of image quality on environment, and it is hence difficult to retain sufficiently high quality under a high-temperature and high-humidity environment. Its tendency becomes strong in the case of continuous printing in particular. Further, when the charge control resin having negatively charging ability is used, flying-off of the resulting toner tends to occur by continuous printing.
Japanese Patent Application Laid-Open No. 195166/1992 has proposed a toner making combined use of a negatively charged charge control agent composed of a polymer comprising an acrylamide monomer having a sulfonic group-containing hydrocarbon group, and a charge control aid having a charge controlling action of an opposite polarity thereto and composed of a quaternary ammonium salt compound. According to this publication, it has been reported that when the negatively charged charge control agent and the charge control aid composed of the quaternary ammonium salt compound are used in combination, the charge distribution of the resulting toner becomes sharp when it is used as a magnetic two-component developer. The toners specifically shown in this publication are free of fogging and flying-off of toner and achieve image quality high in image density in printing up to 1,000 sheets, and is sharp in charge distribution even after printing of 10,000 sheets. However, the image quality after the printing of 10,000 sheets is greatly lowered compared with the image quality at the time printing was conducted on 1,000 sheets. In recent developing apparatus that conduct printing on paper as many as 20 sheets per minute
Kishimoto Takuji
Masuo Kojiro
Niwa Kazu
Yokoyama Shuichi
Dinsmore & Shohl LLP
Goodrow John
Nippon Zeon Co. Ltd.
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