Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-11-09
2002-08-20
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...
C430S109400, C430S111400, C430S137170
Reexamination Certificate
active
06436598
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polymerized toner and a production process thereof, and more particularly to a polymerized toner of a core-shell structure, which is suitable for use in developing an electrostatic latent image formed by an electrophotographic process, electrostatic recording process or the like, and a production process thereof.
BACKGROUND ART
In an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus, an electrostatic latent image formed on a photosensitive member has heretofore been developed with a developer. After the developer image formed by the development is transferred to a transfer medium such as paper as needed, the unfixed image is fixed by any of various methods such as heating, pressing and use of solvent vapor. As the developer, a toner is used either singly or in combination with carrier particles and/or a flowability improver. The toner means colored particles obtained by dispersing a colorant such as carbon black and other additives in a binder resin. Processes for producing a toner are roughly divided into a grinding process and a polymerization process.
In the grinding process, a thermoplastic resin, a colorant, a charge control agent, a parting agent and the like are melted and mixed into a resin composition, and the resin composition is ground and then classified, thereby producing a toner having a desired particle diameter. According to the grinding process, a toner having a measure of excellent properties can be produced. However, the grinding process involves important problems.
First, in the grinding process, there is a limit to the selection of materials for the toner for the purpose of ensuring a high toner yield. Second, in the grinding process, it is difficult to uniformly disperse solid fine particles such as the colorant, charge control agent and parting agent in the thermoplastic resin. Therefore, good flowability, triboelectrification properties and the like for the resulting toner cannot be achieved to deteriorate properties of the toner, such as developing characteristics and durability. Third, in order to improve the fixing ability of the resulting toner so as to meet high-speed copying and formation of full-color images, it is necessary to lower the glass transition temperature of the toner. When a thermoplastic resin having a low glass transition temperature is used, however, difficulty is encountered on the grinding of the resulting resin composition. Therefore, the glass transition temperature of the toner cannot be lowered to 60° C. or lower. It is hence difficult to provide a toner improved in fixing ability by the grinding process.
In order to overcome these problems in the grinding process, processes of producing a toner (polymerized toner) by suspension polymerization have been proposed in recent years. In the suspension polymerization process, solid fine particles such as a colorant, a charge control agent and a parting agent are added to a polymerizable monomer, which is a low-viscosity liquid, to disperse them therein. Therefore, a satisfactory, uniformly dispersing quality can be ensured compared with the grinding process. According to the suspension polymerization process, polymer particles (toner) having a desired particle diameter and a narrow particle diameter distribution can be generally obtained at a yield as high as at least 90%, and so such a process has an economical advantage over the grinding process. Further, the glass transition temperature of the polymerized toner can be adjusted by selecting the kinds and combination of polymerizable monomers. As described above, the problems involved in the grinding process can be solved by the use of the suspension polymerization process. However, the conventional polymerized toners have not come to fully meet the level of requirements for toners in recent years.
Copying machines, printers and the like of the electrophotographic system have been recently required to reduce demand power and 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 image 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 make a toner fixable at a temperature lower than that heretofore used. Namely, it is necessary to lower the fixing temperature of the toner itself. Besides, the speeding-up of copying and printing has been strongly required with the advancement of the combination of image forming apparatus and the formation of personal computer network. In order to realize high-speed copying machines and high-speed printers, it is necessary to conduct fixing in a shorter time than before. If the fixing temperature of a toner can be lowered, it is also possible to shorten the fixing time by controlling the temperature of a heating roll. Therefore, the lowering of the fixing temperature of the toner also can meet the speeding-up of copying and printing.
In order to meet requirements of energy saving, high-speed copying and the like from an image forming apparatus in the design of a toner, it is only necessary to lower a glass transition temperature of a binder resin (polymer component) 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 order to permit formation of bright images in color copying or color printing by the electrophotographic system, the mere melting and softening of toners 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. More specifically, in the color copying or color printing, development is generally conducted with color toners of 3 or 4 different colors to transfer the resulting toner image to a transfer medium at a time or by 3 or 4 installments, 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 fixing of such color toners, the respective color toners overlapped are required to be uniformly melted, and so 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, for example, methods in which the molecular weight of a 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, there is an adverse correlation between the means for coping with the lowering of the fixing temperature of a toner, the speeding-up of printing and the formation of color images, and the shelf stability (blocking resistance) of the toner. As means for solving this adverse correlation, various proposals have heretofore been made. Of these, there has been proposed a toner of a core-shell structure (also referred to as a capsule toner), in which individual colored polymer particles (core) having a low glass transition temperature are coated with a polymer having a high glass transition temperature. However, the conventional means have involved many problems to be solved.
For example, Japanese Patent Application Laid-Open No. 45558/1982 has propo
Honma Akira
Takasaki Takahiro
Dinsmore & Shohl LLP
Goodrow John
Nippon Zeon Co. Ltd.
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