Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-09-05
2002-04-02
Dote, Janis L. (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
06365313
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a toner for development of electrostatic images, and more particularly to a toner for development of electrostatic images, which is excellent in stability to positive charging, flowability and shelf stability and moreover little in variation of charge level by changes in environments such as temperature and humidity or continuous printing, and can retain high image quality in monochromatic or color images, and a production process thereof.
BACKGROUND ART
In general, in an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus, an electrostatic latent image is formed on a photosensitive member uniformly and evenly charged by exposure to a light pattern, and a developer (toner) is applied to the electrostatic latent image to form a toner image (visible image). The toner image is transferred to a transfer medium such as paper or OHP film, and the unfixed toner image is then fixed to the transfer medium by a method such as heating, pressing or use of solvent vapor. In the fixing step, the toner is often fusion-bonded to the transfer medium by passing the transfer medium, to which the toner image has been transferred, through between a heating roll (fixing roll) and a press roll to press-bond the toner under heat.
Processes for producing a toner are roughly divided into a grinding process and a polymerization process. In recent years, polymerized toners easy to control their particle diameter without conducting complicated production steps such as classification have come to attract attention. According to the polymerization process, a polymerized toner having desired particle diameter and particle diameter distribution can be obtained without need of grinding and classification.
By the way, developers for making an electrostatic latent image on a photosensitive member visible by electrostatic attraction force include a negatively charged developer and a positively charged developer and are used properly depending on a development system or the kind of the photosensitive member. In order to control the charging properties of a developer, various kinds of charge control agents are generally used. A positive charge development system making use of a positively charged developer is preferred because it generally generates ozone in a smaller amount upon charging of a photosensitive member compared with a negative charge development system making use of a negatively charged developer, and is hence safe for users and gives them no unpleasant feeling. In addition, the positive charge development system is expected to permit the formation of images having high resolution by its combination with a polymerized toner having a small and even particle diameter.
As positively charged toners, there have heretofore been known those containing a Nigrosine dye as a charge control agent. However, the Nigrosine dye is black and adversely affects the coloring of color toners.
Japanese Patent Application Laid-Open No. 123852/1984 discloses a process for producing a toner, in which a monomer system containing a polymerizable monomer and a cationic polymer is suspended in a dispersion medium containing an anionic dispersing agent to polymerize it. Although the polymerized toner obtained by this process is excellent in blocking resistance because the cationic polymer collects on the surface of the toner to form a shell, however, it has involved a drawback that sufficient charge capacity cannot be achieved when it is used in a non-magnetic one-component development system in which an electric charge is applied to a toner by triboelectrification through a sleeve or blade, so that fogging occurs.
Japanese Patent Application Laid-Open No. 15858/1991 discloses a polymerized toner obtained by subjecting a polymerizable monomer system containing at least a polar substance and a parting agent to suspension polymerization, in which a copolymer having a weight average molecular weight of 2,000 to 15,000 and composed of styrene and/or a-methylstyrene and 2-acrylamide-2-methylpropanesulfonic acid is used as the polar substance to provide the polymerized toner as a toner having stable charge property. However, the polymerized toner obtained by using the above-described copolymer as the polar substance has insufficient flowability, and so an image formed therefrom is blurred or deteriorated in image quality. The polymerized toner tends to undergo blocking and hence has poor shelf stability.
Japanese Patent Application Laid-Open No. 175456/1991 discloses a process for producing a toner for development of electrostatic images, in which a colorant is dispersed in a polymerizable monomer in the presence of a quaternary ammonium salt group-containing copolymer represented by a specific formula, and the resultant dispersion is subjected to suspension polymerization in a suspension medium containing an inorganic dispersing agent. This publication describes the fact that the weight average molecular weight of the quaternary ammonium salt group-containing copolymer is preferably within a range of 2,000 to 20,000. The publication also shows experimental examples where calcium tertiary phosphate was used as the inorganic dispersing agent to produce a polymerized toner. However, the polymerized toners obtained by using the quaternary ammonium salt group-containing copolymer are insufficient in flowability and shelf stability and moreover high in environmental dependence of image quality and also insufficient in durability of image quality.
As described above, it has been extremely difficult to obtain a polymerized toner which is excellent in stability to positive charging, environmental stability of charge level, flowability, shelf stability, etc., low in environmental dependence of image quality of images formed from such a toner, and suitable for use as a color toner.
DISCLOSURE OF THE INVENTION
It is an object of the present Invention to provide a toner for development of electrostatic images, which is excellent In stability to positive charging, flowability and shelf stability and moreover little in variation of charge level by changes in environments such as temperature and humidity or continuous printing, and can retain high image quality in monochromatic or color images, and a production process thereof.
Another object of the present invention is to provide a toner for development of electrostatic Images, which is excellent in stability of droplets of a polymerizable monomer composition In an aqueous medium upon polymerization, low in environmental dependence of image quality of images formed from such a toner and excellent in durability, and a production process thereof.
A further object of the present invention is to provide a toner for development of electrostatic images, which has the property of being positively charged and can be provided as a color toner, and a production process thereof.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art. As a result, it has been found that in a process for producing a toner for development of electrostatic images by subjecting a polymerizable monomer composition containing at least a colorant, a polymerizable monomer and a charge control agent to suspension polymerization in an aqueous medium containing a dispersing agent, a cationic inorganic dispersing agent is used as the dispersing agent, and a specific quaternary ammonium salt group-containing copolymer is used as the charge control agent, thereby obtaining a polymerized toner excellent in such various properties as described above.
According to the present invention, there is thus provided a toner for development of electrostatic images, obtained by subjecting a polymerizable monomer composition containing at least a colorant, a polymerizable monomer and a charge control agent to suspension polymerization in an aqueous medium containing a dispersing agent, wherein
(a) the dispersing agent is a cationic inorganic dispersing agent; and
Kishimoto Takuji
Masuo Kojiro
Dinsmore & Shohl LLP
Dote Janis L.
Nippon Zeon Co. Ltd.
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