Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-07-16
2003-05-20
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S110100, C430S111100
Reexamination Certificate
active
06566028
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a toner for developing electrostatic images or a toner for forming toner images in a toner-jet type image forming method, and a process for producing the toner. More particularly, this invention relates to a toner used preferably in a system where toner images formed by toner are heat-and-pressure fixed to printing sheets such as transfer mediums, and a process for producing such a toner.
2. Related Background Art
In electrostatic development, the system is so set up that toner particles charged electrostatically develop an electrostatic latent image formed on a photosensitive drum, by the aid of an electrostatic force acting in accordance with potential differences on the drum. Here, the toner particles are charged electrostatically by the friction between toner particles themselves or between toner particles and carrier particles. In order to cause this friction in a good efficiency and uniformly, it is important to make the toner retain a fluidity.
For such purpose, as methods commonly used to impart a fluidity to toners, a method is well known in which fluidity-providing agents such as inorganic fine particles as typified by silica, titania or alumina particles or organic fine particles comprised of polymeric compounds are externally added to toner particles surfaces. Also, the method of adding such fluidity-providing agent has many alternatives. For example, it is common to use a method in which the fluidity-providing agent is made to adhere to the surfaces of toner particles by the aid of electrostatic force, or van der Waals force, acting between toner particles and the fluidity-providing agent. This method of making the fluidity-providing agent adhere to the surfaces of toner particles is carried out using a stirrer or mixer.
In the above method, however, it is not easy to make the fluidity-providing agent adhere to the surfaces of toner particles in a uniformly dispersed state. Also, fluidity-providing agent particles not adhering to the toner particles may mutually form agglomerates, which are included in the toner in what is called a free state. It is difficult to avoid the presence of such free additives. In such a case, the fluidity of toner may decrease to cause, e.g., a decrease in quantity of triboelectricity, so that it may become impossible to attain a sufficient image density or inversely images with much fog may become formed. In addition, in conventional cases the fluidity-providing agent adheres to the surfaces of toner particles only by the aid of electrostatic force or van der Waals force as stated above. Hence, when continuous copying is made, the fluidity-providing agent may come off the surfaces of toner particles or become buried in toner particles increasingly, bringing about a problem that image quality attained at the initial stage of running can not be maintained at the latter half of continuous copying.
As a method of imparting the fluidity to toner without use of any fluidity-providing agent, a method is known in which, as disclosed in Japanese Patent Application Laid-open No. 7-181722, fine wax particles are made to stick to the surfaces of toner particles and are provided on their outer sides with polysiloxane layers obtained by polycondensation of an aminosilane alkoxide and an alkylalkoxysilane, and a method, as disclosed in Japanese Patent Application Laid-open No. 8-95284, a toner is obtained by polymerizing a monomer system to which an organosilane compound has been added. The toners obtainable by these methods, however, have smooth toner particle surfaces, and hence have had the problem of causing a lowering of transfer efficiency.
In addition, in the field of electrophotography, it has recently been more strongly required to form images with a higher image quality. Then, as a means for achieving a high image quality of images, toners used in developers may be made to have a sharp charge quantity distribution. When toners have a sharp charge quantity distribution, individual toner particles constituting the toner can be charged in a uniform quantity. Hence, images formed may have less fog or black spots around images and it becomes possible to reproduce toner images faithful to latent images formed on the photosensitive drum. In general, the charge quantity of toner particles is proportional to the particle diameter of toner particles. Accordingly, in order to make the toner have a sharp charge quantity distribution, it is thought to be effective to make the toner have a sharp particle size distribution. In order to impart electric charge to toner particles in a sufficient quantity, commonly employed is a method of adding what is called external additives such as inorganic fine particles as typified by silica, titania or alumina particles or organic fine particles comprised of polymeric compounds.
Since, however, it is common for such external additives to be made to stick mechanically to the surfaces of toner particles by means of a stirrer or mixer, the external additive may become released from toner particles or inversely become buried in toner particles. Such a phenomenon may occur especially when continuous printing is made. Then, this phenomenon may cause a change in the surface state of toner particles. Hence, when images are formed, it may become difficult to continuously maintain the charge quantity of toner kept at the running initial stage, and become difficult to maintain the initial sharp charge quantity distribution during the running. The external additives have had such problems.
Moreover, in recent years, with a surprising spread of personal computers, the demand for printers and copying machines employing electrophotographic systems shows a tendency of expanding from those for offices toward those for general users. With such a tendency, these printers and copying machines of electrophotographic systems are sought to be made small-sized as apparatus, to achieve energy saving for ecological requirement and to be made low-cost. As a method of settling these subjects, fixing temperature may be made lower. As a means for its achievement, it is attempted that binder resins constituting toners are made to have a lower molecular weight or a lower glass transition point (Tg), or waxes are incorporated into toner particles in a larger content.
Making binder resins have a lower molecular weight or have a lower glass transition point (Tg) can make melting temperature lower. However, such toners may concurrently have a poor storage stability to cause in-machine melt adhesion, or mutual melt adhesion of toner particles to have a low fluidity, especially in an environment of high temperature.
To solve such problems, methods are proposed in which silane compounds are used. For example, Japanese Patent Application Laid-open No. 7-98516 discloses a method in which a polyester resin and a metal alkoxide are kneaded and cross-linked. Also, Japanese Patent Application Laid-open No. 7-239573 discloses a method in which a vinyl type resin formed by covalent linkage of a vinyl monomer and a silane coupling agent having an unsaturated double bond and an alkoxysilyl group is used as a binder resin. In these methods, however, the binder resin is compositionally limited, or silane compounds are present even inside the toner particles. Thus, it has substantially been difficult to control fixing performance and storage stability which are performances conflicting with each other.
There are other methods. For example, Japanese Patent Application Laid-open No. 6-289647 discloses a method in which toner particles are coated with a curable silicone resin; Japanese Patent Application Laid-open No. 8-15894, a method in which a metal alkoxide is made to adhere to the surfaces of toner particles; and Japanese Patent Application Laid-open No. 9-179341, a method in which toner particles are provided with covering in the form of continuous thin films using a silane coupling agent. These methods are attempts to prepare base particles by the use of a resin having a relatively lo
Ayaki Yasukazu
Baba Yoshinobu
Ikeda Takeshi
Itabashi Hitoshi
Tazawa Yayoi
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