Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-12-06
2003-09-02
Goodrow, John 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...
C430S108100, C430S108700, C430S111400, C430S126200
Reexamination Certificate
active
06613491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic toner and an electrophotographic developer that are used for developing an electrostatic latent image in an electrophotographic process and an electrostatic recording process, and a process for forming an image.
2. Description of Related Art
In the electrophotographic process, an electrostatic latent image formed on a latent image holding member (photoreceptor) is developed with a toner containing a colorant, and the resulting toner image is transferred to a transfer material and then fixed with a heat roll to obtain an image. The latent image holding member is separately subjected to cleaning for the formation of another electrostatic latent image. A dry developer used in the electrophotographic process is roughly classified to a one-component developer employing solely a toner composed of a binder resin and a colorant and other materials, and a two-component developer formed by mixing the toner and a carrier. The one-component developer can be classified to a magnetic one-component developer using magnetic powder, which is fed to a latent image holding member by magnetic power for development, and a non-magnetic one-component developer using no magnetic powder, which is fed to a latent image holding member by application of charge with a charging roll for development. In the market of electrophotography in the last half of eighties, miniaturization and high performance are strongly demanded for digitalization, and particularly for a full color image, high image quality equivalent to sophisticated printing and silver halide photography is demanded.
Digital processing is essential for realizing high image quality, and the effect of the digital processing includes complicated image processing that can be carried out at high speed. According to the effect, characters and photographic images can be separately controlled, and reproducibility of qualities of them is greatly improved in comparison to the analog technology. In particular, it is important for photographic images that gradation correction and color correction become possible, and it is advantageous in gradation characteristics, fineness, sharpness, color reproducibility and graininess in comparison to the analog technology. It is necessary that an image as an image output must be produced strictly reflecting a latent image produced by an optical system, and therefore reduction in the particle diameter of toners is accelerated to aim for highly faithful reproducibility. However, it is difficult only by the reduction of the particle diameter of the toner that high image quality is stably obtained, and improvements of the fundamental characteristics in development, transferring and fixing characteristics are becoming important.
In particular, a color image is formed by superimposing toners of three or four colors. Therefore, when one of the toners exhibits such characteristics that are different from the initial characteristics or different from the characteristics of the toners of other colors from the standpoint of development, transfer and fixing, it suffers deterioration in image quality, such as reduction in color reproducibility, deterioration of graininess and formation color unevenness. It is important how to conduct stable control of the characteristics of the respective toners in order to maintain the stable image of high quality in the initial stage even when the time lapses. It has been reported that the toner is agitated in a developing device, which easily brings about change of microstructure on the toner surface, and the transfer property is largely changed (JP-A-10-312089).
It has been proposed to improve flowability, charging property and transfer property of a toner that the shape of the toner is approximated to a spherical shape (JP-A-62-184469). However, when the toner has a spherical shape, the following problems are liable to occur. A developing device is equipped with a feeding amount controlling plate for controlling the feeding amount of the developer to a constant amount, and the feeding amount can be controlled by changing the space between a magnetic roll and the feeding amount controlling plate. However, the flowability of the developer is increased by using the spherical toner, and the tapped bulk density thereof is increased. As a result, the developer is trapped at the part for controlling the feeding, and such a phenomenon occurs that the feeding amount becomes unstable. Although the feeding amount can be improved by controlling the surface roughness of the magnetic roll and decreasing the distance between the controlling plate and the magnetic roll, the packing phenomenon caused by trapping the developer is further intensified, and the stress applied to the toner is also increased corresponding to the phenomenon. Consequently, such a problem has been confirmed that the toner easily suffers change of the microstructure of the toner surface, particularly burying or separation of an external additive, whereby the developing characteristics and the transfer characteristics are greatly changed from those in the initial stage.
In order to solve the problem, it has been reported that the packing property is suppressed by combining a spherical toner and a non-spherical toner, so as to attain high image quality (JP-A-6-308759). However, although it is effective to suppress the packing property, the non-spherical toner is liable to remain as transfer residue, and a high transfer efficiency cannot be attained. Furthermore, in the case where development and recovering are simultaneously carried out, the proportion of the non-spherical toner is increased because of recovering the non-spherical toner as transfer residue to cause a problem where the transfer efficiency is further reduced.
It has been proposed in order to improve developing property, transfer property and cleaning property of a spherical toner that two kinds of inorganic fine particles having different average particle diameters, i.e., an average particle diameter of 5 nm or more but less than 20 nm and an average particle diameter of 20 nm or more but 40 nm or less, are used in combination and are added in a particular amount (JP-A-3-100661). While this exerts high developing property, transfer property and cleaning property in the initial stage, the stress applied to the toner cannot be relieved with the lapse of time, and burying or separation of an external additive easily occurs to change the developing property and the transfer property to a large extent from the initial stage.
On the other hand, there have been reports that the use of inorganic fine particles having a large particle diameter is effective to suppress burying of an external additive on a toner (JP-A-7-28276, JP-A-9-319134 and JP-A-10-312089). However, all the inorganic fine particles in the reports have a large specific gravity, and separation of the external additive is unavoidable due to the agitation stress when the size of the external additive is increased. Furthermore, because the inorganic fine particles do not have a complete spherical shape, it is difficult that the standing of the external additive cannot be controlled to a constant state when the inorganic fine particles are attached to the surface of the toner. Consequently, the techniques are insufficient because the miniature surface protrusions functioning as a spacer are fluctuated, and stress is concentrated selectively at the protrusions, whereby burying or separation of the external additive is accelerated.
A technique has been disclosed that organic fine particles having a diameter of from 50 to 200 nm are added to a toner in order to effectively exert the spacer function (JP-A-6-266152). The spacer function can be effectively exerted by using the organic fine particle in the initial stage. However, although the organic fine particles suffer less burying or separation upon stress with the lapse of time, it is difficult that the high spacer function is stably attained since the organic f
Eguchi Atsuhiko
Inoue Satoshi
Kataoka Rieko
Kiyono Fusako
Ohishi Kaori
Fuji 'Xerox Co., Ltd.
Goodrow John L
Oliff & Berridg,e PLC
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