Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1997-09-11
2001-12-11
RoDee, Christopher D. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S110100, C430S137170
Reexamination Certificate
active
06329115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for use in electrophotography, which is capable of producing high quality images with high resolution, and the method of producing such a toner.
2. Discussion of Background
In recent years, in line with the image formation by digital system of the electrophotographic process, a developer is required to reproduce high quality images. In addition, there are many chances of outputting digital images by use of a computer, digital camera, and scanner, and full-color copying machines and printers for producing hard copy of a full-color image have been widely utilized. Further, with respect to the computer for home or office use, many trials have been made to make such equipment compact, drop the manufacturing cost, and minimize waste products so as to increase the recyclability.
The toner for image formation in the electrophotographic process is conventionally prepared by pulverizing a mass comprising a resin and a colorant in a stream at high revolution, and separating the particles with desired particles size by classification. According to the above-mentioned conventional method, the particle diameter of the toner particles is controlled to be as small as possible, and the particle size distribution thereof is controlled to be as narrow as possible for improving the quality of the obtained toner image. However, the shape of the toner particles prepared by the above-mentioned pulverizing method is amorphous. Therefore, the toner particles thus obtained by the pulverizing method tend to be easily broken to pieces by the application of stress thereto. To be more specific, when such conventional toner particles are employed for a two-component developer, the toner particles are easily broken while stirring with a carrier in a developing unit. In the case of a one-component developer, the toner particles are also easily broken when coming in contact with a toner-layer-thickness regulator or a triboelectric charging blade. The thus generated finely-divided pieces of toner particles will lower the image quality of obtained toner images.
Further, the fluidity of the toner particles thus prepared by the pulverizing method is poor because they are amorphous in shape, so that a large quantity of fluidity-imparting agent is required. In addition, because of the amorphous shape, the packing of toner particles in a toner bottle is lowered, thereby preventing the equipment from being made compact.
For the formation of a full-color image, a full-color toner image formed on the surface of a photoconductor is transferred to an intermediate image transfer member and a sheet of paper. As mentioned above, the image transfer step becomes very complicated when a full-color toner is employed. In addition, the transfer performance of the toner particles prepared by the pulverizing method is poor. Therefore, the amount of toner required to form a toner image is necessarily increased, otherwise the toner image will not be transferred perfectly.
There is an increasing demand for the decrease of consumption of toner particles and the formation of high quality image with no partial omission, and further the reduction of running cost by increasing the image transfer efficiency. If the image transfer efficiency is remarkably high, it is not necessary to provide a cleaning unit for removing the toner particles remaining on the photoconductor or the intermediate image transfer member. This is capable of making the equipment compact, reducing the cost, and making use of the toner efficiently.
On the other hand, toner particles can be prepared by the suspension polymerization. To be more specific, an oily droplet comprising a monomer and a colorant is subjected to polymerization in water. By this method, the obtained toner particles are spherical. Therefore, the drawbacks caused by the amorphous shape of the toner particles obtained by the pulverizing method can be eliminated to some extent.
However, the suspension polymerization method has the shortcoming that it is difficult to prepare the toner particles in an intermediate shape between the spherical shape and the amorphous shape, which is considered to satisfy the image transfer performance and the cleaning properties at the same time.
Further, in order to increase the conversion from a monomer to a polymer in the course of suspension polymerization, it takes so much time to complete the polymerization.
In addition, when the wet polymerized particles are dried after separated from water, it is necessary to remove not only a water component but also a monomer component remaining in the porimerized particles. The removal of the monomer remaining in the polymerized particles is considerably difficult. This is because the toner particles obtained by polymerization tend to fuse and adhere to each other at a temperature lower than 100° C., so that the temperature for drying the particles is limited. Thus, the toner particles are dried at low temperature under reduced pressure. However, it takes so much time to dry the particles, thereby increasing the manufacturing cost.
Further, if the toner particles are not completely dried in the course of the above-mentioned drying step, the toner particles tend to adhere to each other while stored at high temperature. This will cause the blocking phenomenon. Or the monomer remaining in the toner particles tend to ooze out to the surface of the particles during the storage at high temperature, so that the charging properties of toner are unfavorably changed. As a result, it is impossible to produce high quality toner images.
When the toner particles are prepared by the suspension polymerization, the area of interface is large, so that large quantities of dispersants such as a surfactant, inorganic finely-divided particles, and a water-soluble polymeric protective colloid are essential in the polymerization. The above-mentioned dispersants are apt to leave on the toner particles thus obtained by polymerization. Under the circumstances of high temperature, such remaining dispersant components will have an adverse effect on the triboelectric charging characteristics which are determined by the surface of the toner particles.
To solve the above-mentioned problem, it is conventionally proposed to sufficiently wash the obtained toner particles for the removal of the dispersant therefrom. However, in this case, a large amount of wash water is necessary, and the facility for drain necessarily increases the manufacturing cost of toner.
The suspension polymerization is regarded as one of bulk polymerization from a microscopic viewpoint. Therefore, controlling is difficult so as to obtain polymers having low molecular weights and classified in a narrow molecular weight distribution. This becomes a serious problem when a full-color toner is prepared by the above-mentioned suspension polymerization method. To be more specific, the quality of a full-color toner image is determined by the smoothness and transparency of the image. If the molecular weight of a resin component for use in the full-color toner is excessively high, the full-color image cannot be fixed with satisfactory smoothness and transparency by the application of the same energy as required to fix a resin with a low molecular weight. For example, a low-molecular weight polyester with excellent fixing properties cannot be obtained by condensation polymerization in water, so that such a resin cannot be applied to the above-mentioned conventional suspension polymerization method.
Furthermore, it is difficult to finely disperse a colorant such as a pigment in a monomer without a dispersant. Although the colored performance of the obtained toner particles is improved by using a dispersant, the dispersant has an adverse effect on the charging characteristics of the obtained toner. In addition, when the hydrophilic nature of the employed pigment is strong, the pigment tends to shift to the interfaces of the particles in the course of polymerization, so that unsatisfactory color development
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
Rodee Christopher D.
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