Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-08-15
2004-05-11
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S110100, C430S110300, C399S333000, C399S330000, C399S331000, C399S329000, C399S328000
Reexamination Certificate
active
06733944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming process in which an electrostatic latent image formed by an electrophotographic process, an electrostatic recording process or a similar process is developed with a developer.
2. Description of the Related Art
Methods of making image data visible through an electrostatic latent image, such as electrophotography, are currently used in various fields. In electrophotography, an electrostatic latent image is formed on the surface of a photoreceptor through charging and exposing steps, and the latent image is developed with a developer containing a toner, followed by transferring and fixing steps to make the developed image visible.
The developers used for the development can be divided into two-component developers composed of a toner and a carrier, and single-component developers only made of a magnetic toner or a non-magnetic toner. In order to prepare toner particles for producing a developer, a kneading and pulverizing process is ordinarily used in which a thermoplastic resin is melted and kneaded with a pigment, a charging modifier and a releasing agent such as wax, and the resultant mixture is cooled, pulverized into fine particles and then classified. To the toner particles produced by the kneading and pulverizing process are added, at the surfaces thereof, inorganic or organic fine particles, as necessary, for improving fluidity and cleanability.
The shape of the toner particles produced by the conventional kneading and pulverizing process is irregular and the surface composition thereof is not uniform. The shape and the surface composition of the toner particles vary depending on pulverability of the materials used and conditions of a pulverizing step. It is difficult to control the shape and the surface composition of the toner particles. Particularly if a material that is easily pulverizable is used to produce the toner particles, there are problems in that the particles produced are too minute or have altered shapes owing to a mechanical force such as a shear force generated in a developing device.
When a two-component developer is used, the above described incidences cause the finely-pulverized toner particles to firmly adhere to a carrier, whereby chargeability of the developer is accelerated to deteriorate. When a single-component developer is used, the above-described incidences provide a broader distribution in particle size. Therefore, toners become likely to scatter or developability is lowered due to a change in the shape of the toner particles, whereby image quality is frequently deteriorated.
In a case where the shape of the toner particles is irregular, the fluidity of the toner is insufficient even if an auxiliary for fluidizing toners is added to the toner. Consequently, while the toner is used, there arise problems in that, owing to a mechanical force such as a shear force, minute particles of the auxiliary fall into cavities of the toner particles, whereby the fluidity of the toner decreases with the passage of time, and developability, transferability and cleanability are impaired. If such a toner is the toner collected once or twice after cleaning and then returned to a developing device to be re-used, the quality of the image formed with the toner is further deteriorated. In order to prevent such incidences from occurring, it is conceivable to increase the amount of the auxiliary to be added. In this case, however, problems arise in that black spots may appear on the photoreceptor and the auxiliary may be scattered.
If a releasing agent such as wax is added inside the toner particle, the releasing agent frequently appears at the surface of the produced toner particles depending on the combination of a releasing agent and a thermoplastic resin. Particularly in the case where a resin that has elasticity due to a high molecular weight component and hence is slightly difficult to pulverize is combined with a brittle wax such as polyethylene, polyethylene frequently appears at the surface of the produced toner. The thus produced toner has poor releasing performance at the time of fixing and poor cleanability of non-transferred toner present on a photoreceptor. However, polyethylene appearing at the particle surface is released from the surface by a shear force generated in a developing device. As a result, polyethylene is easily transferred to a developing roll, a photoreceptor, a carrier and the like. Contamination caused by transferring degrades reliability as a developer.
Under these circumstances, attempts have been made in recent years to solve the above-described problems by controlling the shape and the surface composition of toner particles, and methods of producing toners in a wet manner have been intensely studied. For example, Japanese Patent Application Laid-Open (JP-A) Nos. 63-282749 and 6-250439 propose an emulsion polymerization aggregating process in which a dispersion of resin particles is prepared by emulsion polymerization while another dispersion is prepared in which a colorant is dispersed in an aqueous medium (solvent). Thereafter, the two solutions are mixed and heated to form aggregated particles whose particle size corresponds to a toner particle size, followed by further raising the temperature to effect coalescence of the aggregated particles, to finally produce a toner.
In recent years, high image quality has been increasingly demanded. Particularly in forming color images, trends are currently toward toner particles having a smaller and uniform size in order to achieve detail depiction. Generally, if a toner having a broad particle size distribution is used to form an image, toner particles belonging to a region of finer sizes in the distribution seriously cause contamination at a developing roll, a charging roll, a charging blade, a photoreceptor and a carrier, and also cause troublesome toner scattering. Accordingly, it is difficult to simultaneously achieve high image quality and high reliability. Further, the toner having a broad particle size distribution cannot yield high reliability in a system that has a cleaning function or a toner re-cycling function.
The toner having a finer particle size is likely to produce troubles particularly in a transferring step, to thus degrade high image quality. This is presumably attributed to the fact that an adhesive force of a toner to a photoreceptor, for example, a non-electrostatically adhesive force such as van der Waals force increases. In order to solve such a problem, it is necessary to adequately control an adhesive force between a toner and a photoreceptor, for example, by controlling the shape and the surface state of the toner particles.
As described above, it is very difficult to produce a toner having a very small and uniform particle size by employing a conventional kneading and pulverizing process. In principle, the smaller the particle size, the more the shape is distorted. Hence, it is impossible to avoid the above-described incidences from occurring in a transferring step. From the foregoing, an emulsion polymerization aggregating process has intensely been studied among wet toner-producing processes, since the process makes it possible to readily produce a toner having a very small and uniform particle size.
However, if toner particles are produced by employing an emulsion polymerization aggregating process, reaction usually progresses toward a goal, by applying heat, to make toner particles having irregular shapes to have a more smooth and spherical shape, that is, to make the particles to have a smaller surface area. Therefore, in principle, as the toner particles have a smaller particle size, the spherical degree thereof is higher (the surface area thereof is smaller); while as the toner particles have a larger particle size, the irregular degree of the shape is higher (the surface area thereof is larger). Moreover, in order to achieve all performances including transferability, transferring efficiency, cleanability and durability required of a toner, it is nec
Ishiyama Takao
Kadokura Yasuo
Kamada Hiroshi
Sato Shuji
Suwabe Masaaki
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
Rodee Christopher
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