Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-06-04
2001-03-13
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S138000, C399S297000
Reexamination Certificate
active
06200718
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polymerized toner, and more particularly to a polymerized toner suitable for use in developing an electrostatic image formed by an electrophotographic process, electrostatic recording process or the like, a production process thereof, an image forming process comprising using such a polymerized toner, and an image forming apparatus containing the polymerized toner.
BACKGROUND ART
In the electrophotographic process or electrostatic recording process, there are 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 as developers for making electrostatic images (electrostatic latent images) visible. The one-component developers include magnetic one-component developers containing magnetic powder, and non-magnetic one-component developers containing no magnetic powder. In the non-magnetic one-component developers, a flowability improver such as colloidal silica is often added independently in order to enhance the flowability of the toner. As the toner, there are generally used colored particles obtained by dispersing a colorant such as carbon black and other additives in a binder resin and granulating the dispersion.
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 a toner. In the polymerization process, a polymerizable monomer composition is prepared by uniformly dissolving or dispersing a colorant, a polymerization initiator and optional various additives such as a crosslinking agent and a charge control agent in a polymerizable monomer, the polymerizable monomer composition is dispersed in an aqueous dispersion medium containing a dispersion stabilizer by means of a stirrer to form minute droplets of the polymerizable monomer composition, and the dispersion containing the minute droplets is then heated to subject the droplets to suspension polymerization, thereby obtaining colored polymer particles (polymerized toner) having a desired particle diameter.
In either developer, an electrostatic latent image is actually developed with the toner. In an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus, an electrostatic latent image is generally formed on a photosensitive member evenly charged by exposure to a light pattern, and a 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 transfer paper, 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 to the transfer medium under heat.
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. However, the classification itself is complicated, and its yield is poor, and so the percent yield of the toner is reduced to a great extent. Therefore, the polymerized toner easy to control its particle diameter without conducting complicated production steps such as classification has come to attract attention in recent years. According to the suspension polymerization process, a polymerized toner having desired particle diameter and particle diameter distribution can be obtained without need of grinding and classification. However, the conventional polymerized toners have involved a problem that they cannot fully meet requirements in recent years, such as the speeding-up of copying, the formation of full-color images and energy saving.
In recent years, copying machines, printers and the like of the electrophotographic system have been required not only to reduce demand power, but also 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 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. The use of the toner capable of fixing at a temperature lower than that heretofore used permits lowering the temperature of the heating roll, and on the other hand shortening the fixing time when the temperature of the heating roll is not very lowered. Therefore, such a toner can meet the speeding-up of copying and printing.
In order to meet the requirements, such as energy saving and the speeding-up of copying, from the image forming apparatus in the design of a toner, it is only necessary to lower the glass transition temperature of a binder resin making up the toner. When a toner is made up of a binder resin having a low glass transition temperature, however, the toner becomes poor in the so-called shelf stability because particles themselves of the toner tend to undergo blocking during storage or shipment, or in a toner box of an image forming apparatus, to aggregate.
In recent years, there has been a demand for formation of bright images in color copying or color printing by the electrophotographic system. For example, in the full-color copying, the mere melting and softening of toners in a fixing step to fusion-bond the toners to a transfer medium are not enough, but it is necessary to uniformly melt and mix the toners of different colors to mix their colors. In particular, since color images have come to be often used in OHP (overhead projector) sheets for presentations in various meetings or conferences, toner images fixed to such OHP sheets have been required to have excellent permeability through OHP. In order to meet the excellent permeability through OHP, it is necessary for the toners to uniformly melt on a transparent OHP sheet made of a synthetic resin. Therefore, the melt viscosity of each toner at about the fixing temperature thereof must be designed low compared with the conventional toners. Means for lowering the melt viscosity of the toner include a method in which the molecular weight or glass transition temperature of a binder resin used is lowered compared with the binder resins for the conventional toners. In either method, however, the toner becomes poor in shelf stability because the toner tends to undergo blocking.
As a method for obtaining a polymerized toner having excellent fixing ability, it has heretofore been proposed in, for example, Japanese Patent Application Laid-Open No. 136065/1991 to subject a polymerizable monomer containing a colorant and a charge control agent to suspension polymerization in the presence of a macromonomer. The macromonomer is a relatively long-ch
Takasaki Takahiro
Yanagida Noboru
Armstrong Westerman Hattori McLeland & Naughton LLP
Goodrow John
Nippon Zeon Co. Ltd.
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