Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-02-29
2001-01-09
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C430S126200, C430S137170
Reexamination Certificate
active
06171744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for electrophotography, electrostatic recording, electrostatic printing, etc., a method for producing it, and a method of image formation with it.
2. Description of the Related Art
Toner for electrophotograpy (this will be hereinafter referred to simply as “toner”) could be obtained by mixing, melting and kneading a binder resin, a colorant, and optionally a lubricant, an antistatic agent and other additives, cooling and solidifying the resulting mixture, grinding the solid, classifying the ground powder to prepare a toner matrix, followed by adding external additives such as a fluidizing agent, an antistatic agent, a cleaning promoter and the like to the toner matrix to thereby make them adhere to and fix on the surfaces of the toner matrix particles, and finally sieving the thus-processed toner particles to thereby remove coarse particles having been grown too large in the step of adding thereto the external additives.
In electrophotography with toner for image formation, the electrostatic latent image formed on a latent image carrier is developed with toner, then the toner image is once transferred onto an intermediate image receptor, and thereafter re-transferred onto an image-receiving object such as plain paper, plastic film or the like, and finally the toner image on the image-receiving object is fixed thereon under heat and/or pressure in a fixation unit generally equipped with a thermal fixing roll or belt system.
Therefore, the toner particles to be used in image formation through electrophotography have the capability of plastic deformation by heat and/or pressure. With the recent needs for power-saving and instant-on duplicators for rapid duplication, toner capable of melting at lower temperatures than usual is desired. However, toner that satisfies the requirement is often problematic in that it will fuse in the apparatus where it is produced.
Realizing high-quality images is especially desired these days, for which fine toner particles having a reduced particle size and having a narrowed particle size distribution are necessary. However, such fine toner particles will fuse more easily in the apparatus where they are produced. This is because re-structuring the apparatus for producing the intended fine toner particles will inevitably bring about the result that the particles produced therein fuse more easily. Concretely, for example, in the step of classifying toner particles, centrifugal classifiers heretofore used will have to be so modified that they enable high-revolution classification with an increased air flow. For their capabilities, however, the modified units for such high-revolution classification with an increased air flow being introduced thereinto are limited in producing the intended fine toner particles having a reduced particle size and having a narrowed particle size distribution, and will augment the fusion of the toner particles around rotors, etc.
In place of centrifugal classifiers, inertial classifiers where particles are classified by their inertial force are available on the market these days and are being used widely in the art. In the inertial classifier, particles having a large particle size are blown far away by their inertial force, while the others having a small particle size flow along a curved block, a Coanda block, owing to the specific capabilities of the classifier. Increasing the number of the edges for classification in the inertial classifier of that type enables multi-division classification. Even for small-sized particles, the inertial classifier could well classify them merely by moving the position of the edges without sacrificing its classification efficiency. Using the inertial classifier has made is possible to produce even fine toner having a reduced particle size and having a narrowed grain size distribution. In addition, only one inertial classifier enables multi-stage classification, for which, however, one centrifugal classifier must be repeatedly driven plural times. Having the advantages of reduced equipment cost and space with no reduction in the classification efficiency even for small-sized particles, inertial classifiers are being much used these days in the art.
However, inertial classifiers are still confronted with some problems. Concretely, in an inertial classifier, many toner particles fuse around the edges that define the classification point and around the ejector, and the fused toner particles will change the classification point. In that case, it becomes difficult to stably produce toner particles having the same quality (that is, having the same particle size distribution). Depending on the degree of toner fusion, the production condition must be re-settled, or the fused toner particles must be removed. This increases the cost for apparatus inspection, and greatly lowers the apparatus performance, as the apparatus must be dissembled and cleaned.
Also in the step of grinding toner raw material, the apparatus to be used must be modified so as to increase its grinding efficiency for the recent fine toner particles having a reduced particle size and having a narrowed particle size distribution. Concretely, in a jet-mill grinder, the air flow rate is increased; and for other mechanical grinders, the rotor revolution is increased. In particular, for grinding into fine toner particles having a narrowed particle size distribution, used is a grinding system equipped with a built-in pre-classifier for removing coarse particles or with an external closed circuit. In the grinding system of that type, however, toner particles fuse around the rotor in the built-in pre-classifier, and the fused particles will vary the classification point in the pre-classifiers. This is problematic as the toner particles ground could not have the intended particle size.
For increasing the grinding efficiency in producing fine toner particles having a reduced particle size, a method of varying the constituent monomers for the binder resin to be in toner, or a method of lowering the softening point or the glass transition point of the binder resin may be employed. These methods are effective for improving the grindability of toner particles, but are still problematic in that many toner particles fuse inside the grinder and the classifier used and even in the pipe line that connects the units, and the fused particles will soon come to have negative influences on the production condition within a short period of time. Moreover, it is known that the toner produced in the process where many particles fuse inside the production units contains an increased amount of coarse particles (having a large particle size of from 16 to 45 &mgr;m or so). The coarse toner particles will form image defects of grids and white spots on duplications. In addition, they will have not a few negative influences on the charging characteristics and the fixing characteristics of toner. Even though fine toner particles could get improved grindability in some degree according to the methods as above, they will much sacrifice their intrinsic properties for it.
Another method that may be employable for the intended purpose will be to add to toner a material capable of improving the grindability of toner material. For example, in Japanese Patent Laid-Open No. H04-257868, proposed is a technique of using an aromatic petroleum resin for improving both the grindability and the fixing capability of toner; and in Japanese Patent Laid-Open No. H07-278658, proposed is a technique of using a hydrogenated petroleum resin for improving both the grindability and the thermal stability of toner. The techniques proposed could improve the grindability of toner, but are still problematic in that they worsen the charging capability of toner.
For producing the intended, fine toner particles that can melt even at low temperatures and have a reduced particle size and a narrowed particle size distribution, the problem to be solved is that particles fuse inside the production equipment and
Igarashi Jun
Nakazawa Hiroshi
Fuji 'Xerox Co., Ltd.
Martin Roland
Oliff & Berridg,e PLC
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