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
2002-01-29
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...
C430S137150, C430S138000
Reexamination Certificate
active
06342328
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a toner for development of electrostatic images for developing electrostatic latent image s formed by an electrophotographic process, electrostatic recording process or the like, 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 (electrostatic 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 toner image thus transferred 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.
A toner for development of electrostatic images is generally composed of colored resin particles (colored polymer particles) comprising a binder resin and a colorant. Processes for producing the toner for development of electrostatic images are roughly divided into a grinding process and a polymerization process. In the grinding process, a colorant, a charge control agent, a parting agent and the like are melted and mixed in a thermoplastic resin to prepare a resin composition, the resin composition is then ground and classified, thereby producing a toner (ground toner) composed of colored resin particles. In the polymerization process, a monomer composition containing a polymerizable monomer, a colorant, a charge control agent, a parting agent and the like, which are uniformly dissolved or dispersed therein, is poured into water or an aqueous dispersion medium composed mainly of water, which contains a dispersion stabilizer, and the mixture is stirred until droplets become stable. A polymerization initiator is added to the mixture, and the monomer composition is dispersed by means of a mixer having high shearing force to form the monomer composition into fine droplets. The droplets are polymerized to form a toner (polymerized toner) composed of colored polymer particles. According to the polymerization process, a polymerized toner having a desired particle diameter and a sharp particle diameter distribution can be obtained without conducting grinding and classification.
In copying machines, printers and the like of an electrophotographic system, it has recently been attempted to reduce demand power. A step in which energy is particularly demanded in the electrophotographic system is the so-called fixing step conducted after transferring a toner from a photosensitive member to a transfer medium. A heating roll heated to a temperature of at least 150° C. is generally used for fixing, 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.
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 such high-speed copying machines and high-speed printers, it is necessary to conduct fixing in a shorter time.
In order to meet such requirements from the image forming apparatus in the design of a toner, it is only necessary to lower a glass transition temperature of a binder resin. When the glass transition temperature of the binder resin is lowered, however, the resulting toner becomes poor in the so-called shelf stability because particles themselves of the toner undergo blocking during storage or in a toner box to aggregate.
On the other hand, in the case of color toners used in the electrophotographic system, 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 addition, 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 shelf stability of a toner and the means for coping with the lowering of the fixing temperature of the toner, the speeding-up of printing and the formation of color images. As means for solving this adverse correlation, it has heretofore been proposed to solve the problem of shelf stability by taking measures to additives, or covering colored polymer particles having a low glass transition temperature with a polymer having a high glass transition temperature to form a toner (capsule toner) of a core-shell structure.
However, with respect to the additives, importance is attached to the role of imparting various functions such as charge properties and parting ability, and so it has been difficult to well balance the shelf stability of a toner with the fixing ability and the like thereof by such additives. Description is given taking, for example, a charge control agent as an example.
In order to cause a toner to adhere to an electrostatic latent image on a photosensitive member by electrostatic attraction force to make the latent image visible, it is necessary to control the charge property of the toner. A negatively or positively charged toner is used according to the kinds of a developing system and a photosensitive member. In order to control the charge property of the toner, a charge control agent is generally used. However, the charge control agents heretofore used have involved various problems.
More specifically, metal complex compounds have heretofore been mainly used as charge control agents for imparting negatively charge property to a toner. However, the kinds of metals thereof are heavy metals such as chromium, manganese and cobalt, and so the metal complex compound have involved a problem of safety.
Japanese Patent Application Laid-Open No. 262055/1987 has proposed a process for producing colored fine particles having an average particle diameter of 1 to 5 &mgr;m comprising a pigment, a zinc alkylsalicylate complex and a binder resin, said process comprising subjecting the pigment, the zinc alkylsalicylate complex and a monomer for forming the binder resin to suspension polymerization in the presence of a water-insoluble inorganic salt and then decomposing the water-insoluble inorganic salt to dissolve it in water. However, the suspension polymerization of the monomer composition containing the metal complex compound has involved problems that the dispersion stability of droplets is lowered, and the droplet diameter thereof is made small.
In order to solve the problem of safety in the metal complex compounds, Japanese Patent Application Laid-Open Nos. 184762/1988, 167565/1990, 15858/1991 and 243954/1991 have proposed that a copolymer of a styrene monomer and a sulfonic group-containing acrylamide is used as a charge control agent. When a copolymer having a copolymerization ratio of styrene and/or a-methylstyrene to 2-acrylamido-2-methylpropanesulfonic acid of 98:2 to 80:20 and a weight average molecular weight of 2,000 to 15,000, which is specifically shown in these publications, is used as a charge control agent, however, the dispersibility of a
Masuo Kojiro
Niwa Kazu
Sato Kazuhiro
Takasaki Takahiro
Dinsmore & Shohl LLP
Goodrow John
Nippon Zeon Co. Ltd.
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