Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2000-03-13
2003-10-14
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S110200, C430S137180
Reexamination Certificate
active
06632579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner which is useful for electrophotography and the like, and to a method for manufacturing the toner.
2. Discussion of the Background
Currently, with the rapid digitalization in electrophotography, there is a steadily increasing need for a developer which can reproduce images having good image qualities. In addition, full color copiers and printers for the production of color images are in rapid increasing demand, because of the increase in demand for the preparation of color documents which are used for various presentations and for the reproduction of digital color images prepared by computers, digital cameras and scanners. Further, since computers are widely used in small offices and in home offices, attempts to miniaturize these image forming apparatuses and to reduce the costs thereof have been made. Furthermore, in order to save materials and avoid environmental pollution, recycling of these apparatuses and their supplies has been attempted. However, with the current state of the art, high-functional toners, which can produce good images, generally have poor reliability and, therefore, good images cannot be continuously produced over a long period of time.
The toners which are used in electrophotography are generally manufactured by the following method in which (1) a melted resin is mixed with additives such as a colorant, a charge controlling agent and the like, to disperse the additives in the resin; (2) the mixture is cooled; (3) the mixture is pulverized using high-speed air; and (4) the pulverized mixture is classified to obtain a toner having a proper particle diameter distribution.
In general, although the colorant is finely dispersed in the resin, the charge controlling agent is dispersed in the resin with relatively large particle diameter in comparison to the colorant. In addition, since the charge controlling agent is generally poorly compatibile with the resin, the charge controlling agent tends to easily separate from the resin upon pulverization. Therefore, the charge controlling agent often adheres to and contaminates the inside of the pulverizer. Further, the free charge controlling agent tends to transfer to the surface of the resultant toner, which results in a toner which does not have uniform charge properties. When the thus manufactured toner is used for a long time in an electrophotographic image forming apparatuses such as a copier or printer, the charge controlling agent easily releases from the toner and contaminates the developing units and other units of the apparatuses and carriers of the developers in the developing units; thereby resulting in deterioration of image quality.
The charge properties of a toner largely depend on the materials of the surface part of the toner. In other words, the charge controlling agent, which is dispersed inside the toner, has little affect on the charge properties of the toner. In addition, charge controlling agents are generally expensive. Therefore, a need exists for charge controlling agents which are preferably included on only the surface part of toners.
In attempting to solve these problems and in order to fulfill the need, Japanese Laid-Open Patent Publication No. 55-28032 discloses a magnetic toner in which fine particles consisting of a charge controlling agent are contacted with the surface of the toner at a high temperature, while a flow of air is supplied to fix the charge controlling agent to the toner surface. However, since the treatment is performed at a high temperature, a problem which occurs is that toner particles adhere to each other, resulting in formation of aggregates of the toner particles, and in addition a problem occurs in that the resultant toner has uneven charge properties, because the charge controlling agent cannot uniformly cover the surface of the toner. In addition, the fine particles cannot be entirely fixed on the surface of the toner and, therefore, the charge controlling agent is easily released from the toner by mechanical external forces.
Japanese Laid-Open Patent Publication No. 63-244056 discloses a toner which is manufactured by impacting colored particles with charge controlling particles and then passing the colored particles through a narrow space to fix the charge controlling particles thereon. However, a problem of the resultant toner is that the toner has uneven charge properties, because the covering of the charge controlling particles on the surface of each toner particle is not uniform and in addition the charge controlling particles fixed on the toner are easily released from the toner when the toner is mechanically mixed with a carrier, or rubbed with toner charging blades or toner layer regulating blades in developing units of image forming apparatuses.
In order to obtain images having good image qualities such as high resolution, attempts have been made to improve toners by preparing toners of relatively small average particle diameter and/or a narrow particle diameter distribution. However, toner particles manufactured by pulverization have irregular shapes, and when the toner particles are mixed with carriers and stirred in developing units, and/or rubbed with toner layer regulating blades or charging blades, the toner is further pulverized, thereby resulting in superfine toner particles and deterioration of image qualities. In addition, since the toner particles have an irregular shape, the toner exhibits poor fluidity and, therefore, the toner needs a large amount of a fluidizing agent. Another problem which occurs is that the filling factor of a toner bottle is relatively small, resulting in difficulties with miniaturization of toner bottles and image forming apparatuses.
Further image transfer processes for forming full color images in which full color images, which are formed on a photoconductor, are transferred to a transfer medium or a paper sheet are becoming more and more complex. Since the toner, which is manufactured by pulverization and, therefore, has an irregular shape, has poor transferability, a problem which tends to occur in that a portion of the transferred image is omitted, and when attempting to solve this problem, another problem occurs is that toner consumption increases.
Therefore, the need has increased for a toner which can produce images having good image qualities with small toner consumption, which results in decreases of running costs, by improving the transferability of the toner.
When a toner has good transferability, a toner cleaning device is not necessary for an image forming apparatus because almost all the toner images which form on a photoconductor or on an intermediate transfer medium are transferred to a transfer sheet and, therefore, miniaturization and cost reduction of image forming apparatus are possible and further the apparatus have an advantage in that disposal of waste toner is not needed.
In attempting to improve these drawbacks of toners having an irregular shape, a variety of methods have been proposed for manufacturing spherical toners.
For example, a particulate toner has been proposed which is manufactured by a suspension polymerization method in which oil drops, which include a monomer and toner property forming agents such as a colorant and which are dispersed in water are polymerized to form the particulate toner. The resultant toner is spherical and, therefore, the toner represents an improvement over the toner which has an irregular shape to some extent. However, it is difficult by the suspension polymerization method to obtain a toner having good transferability and cleaning properties by controlling its shape, for example, so as to have an intermediate shape between a spherical shape and an irregular shape.
In suspension polymerization, the conversion rate of monomer to polymer is preferably maximized and, therefore, it takes a long time to prepare the polymer. In addition, after the polymerization process and the following separation of the toner from water, the water and monomers which remain in the
Dote Janis L.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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