Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-04-01
2004-04-13
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S110200, C430S137110, C430S137170
Reexamination Certificate
active
06720122
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a toner for development of electrostatic images for developing electrostatic latent images formed on a photosensitive body by an electrophotographic process, electrostatic recording process or the like and a production process thereof, and more particularly to a toner for development of electrostatic images, which is excellent in fixing ability, shelf stability and flowability and capable of forming high-quality images, and a production process thereof.
BACKGROUND ART
In an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus, exposure to a light pattern is conducted on a photosensitive member uniformly and evenly charged to form an electrostatic latent image (electrostatic 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 sheet, and 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 for development of electrostatic images composed of colored particles comprising a binder resin in which a colorant and other additives (for example, a charge control agent, a parting agent, etc.) have been dispersed.
As toners for development of electrostatic images, ground toners obtained by melting and mixing a colorant and other additives 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 which are easy to control their particle diameter and permit omitting complicated steps such as grinding and classification and providing high-quality images have come to be widely used.
In general, a polymerized toner is produced by pouring a polymerizable monomer composition containing a polymerizable monomer, a colorant, a charge control agent, a parting 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 with a polymerization initiator. A polymer formed by the polymerization of the polymerizable monomer becomes a binder resin, and the colorant and other additives are dispersed therein.
The toner for development of electrostatic images has been required to permit forming a high-definition and high-density image having excellent image quality, undergo no deterioration of image quality even by changes in environments such as temperature and humidity and make it possible to conduct continuous printing or copying. In addition to these requirements, the toner for development of electrostatic images has been recently required to permit contributing to energy saving and coping with the speeding-up of printing or copying and the formation of full-color images. Therefore, the toner for development of electrostatic images has been required to improve its fixing properties such as lowering of fixing temperature without impairing the shelf stability (blocking resistance) while retaining the achievement of high image quality.
Specifically, in image forming apparatus such as copying machines, printers and the like of the electrophotographic system, in which the toner for development of electrostatic images is used, it has been recently attempted to reduce demand power. A step in which energy is particularly consumed in the electrophotographic system is a fixing step for fixing a developer image (toner image) after transferring the developer image on a photosensitive member to a transfer medium such as paper. In the fixing step, a fixing roll or fixing belt heated to a high temperature of at least 150° C. is used to fix the toner image to the transfer medium, and electricity is used as an energy source therefor. There is a demand for lowering this fixing temperature from the viewpoint of energy saving.
There has recently been a demand for the speeding-up of copying and printing. In particular, the speeding-up of copying and printing has been more and more required with the advancement of the combination of image forming apparatus and the formation of personal computer network. Therefore, it is necessary to shorten the fixing time in a high-speed printer or copying machine.
As a method for meeting such requirements from the image forming apparatus in the design of a toner for development of electrostatic images, there is a method in which a glass transition temperature of a binder resin is lowered. When the glass transition temperature of the binder resin is lowed, however, the resulting toner becomes poor in the so-called shelf stability because particles of the toner undergo blocking during storage of the toner or in a toner box of an image forming apparatus, to aggregate.
More recently, color-printing and color-copying techniques have been developed. In order to conduct color printing or color copying, an electrostatic latent image on a photosensitive member is developed with color toners of 3 or 4 different colors to transfer the resulting toner image to a transfer medium at a time or successively, and the toner image is then fixed. Therefore, the thickness of the toner layer to be fixed becomes thicker compared with a black-and-white image. In order to develop a desired color tone by color mixing, the respective color toners overlapped are required to be uniformly melted upon fixing of such color toners.
Therefore, the melt viscosity of each toner at about the fixing temperature thereof must be designed low compared with the conventional toners so as to become easy to melt. Means for lowering the melt viscosity of the toner include, for example, methods in which the molecular weight of a binder resin used is made lower compared with the resins for the conventional toners, and in which the glass transition temperature thereof is lowered. In any of these methods, however, the toner becomes poor in shelf stability because the toner tends to undergo blocking.
As described above, when the methods for improving a toner so as to cope with the energy saving, the speeding-up of printing and copying and the formation of color images are adopted, the shelf stability of the toner is deteriorated. More specifically, there is an adverse correlation between these methods and the shelf stability.
In order to provide a toner for development of electrostatic images having good low-temperature fixing ability, there has heretofore been proposed a method in which a low-softening point substance having parting property, such as paraffin wax, is caused to exist in a toner to lower the softening point of the toner (Japanese Patent Application Laid-Open Nos. 173067/1988 and 161144/1994). However, such a toner is difficult to achieve high image quality and balance the low-temperature fixing ability with the shelf stability at a high level.
Specifically, Japanese Patent Application Laid-Open No. 173067/1988 has proposed a production process of a polymerized toner, comprising the steps of adding polyolefin wax into a monomer mixture containing a polymerized monomer and a colorant, heating the resultant mixture to a temperature higher than a polymerization temperature to dissolve the polyolefin wax in the polymerizable monomer and then cooling the mixture down to a temperature equal to the polymerization temperature to deposit the polyolefin wax. According to this production process, however, the polyolefin wax is dissolved in the polymerizable monomer at the high temperature, and a polymerization initiator is then poured therein at the polymerization temperature, so that the control of the polymerization reaction is difficult to fail to easily obtain a uniform toner.
Japanese Patent Application Laid-Open No. 161144/1994 has proposed a toner in which a small amount of paraffin
Armstrong Kratz Quintos Hanson & Brooks, LLP
Dote Janis L.
Zeon Corp.
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