Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-03-21
2004-09-14
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111350, C430S111410, C430S126200, C399S119000
Reexamination Certificate
active
06790575
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming method which utilizes an electrophotographic method or electrostatic printing method or the like applicable to copiers, printers, and fax machines and the like, an image forming apparatus, and a two-component developer applicable to image forming apparatus
2. Description of the Related Art
Generally, an electrophotographic method is recognized in the art as process utilizing a photoconductive substance. In the electrophotographic method, a latent electrostatic image is formed by various methods, on a latent electrostatic image carrier such as photoconductor. The latent electrostatic image is then developed with a toner, the toner is then transferred on to a paper or the like as necessary, fixed by heating or solvent vapor, to obtain copied images or printed images.
As means for developing latent electrostatic image formed on the latent electrostatic image carrier, wet developing processes and dry developing processes may be mentioned as examples.
The wet developing processes are processes in which a liquid developer is used. For dry developing processes, examples of methods include a method in which a toner containing colorant used as one-component developer dispersed in a binding resin, or a method in which a two-component developer containing a mixture of toner and a carrier.
Although each of these different means for developing a latent electrostatic image have various advantages and shortcomings, methods which utilize a two-component developer relatively have higher possibilities in responding to a higher-speed, longer-life requirements, compared to methods which utilize a single-component developer. Accordingly, dry developing processes utilizing the two-component developer are often employed presently and is widely used for primarily in medium- to high-speed copiers and printers.
Recently, a strong demand for higher definition and higher resolution in the copied or printed images has arose. In order to obtain such images having high definition and high resolution, in Japanese Patent Publication No. H6-82227/1994 (published), Japanese Patent Publication No. H7-60273/1995 (published), Japanese Patent Application Laid-Open No. H2-877/1990 (published), Japanese Patent Application Laid-Open No. H1-112253/1989 (published), Japanese Patent Application Laid-Open No. H2-284158/1990 (published), and Japanese Patent Application Laid-Open No. H7-295283/1995 (published), propose developers having small average particle diameter defined by the contained amount of the toner particles having particle diameter of 5 &mgr;m or less, and the distribution thereof.
In these publications, it is disclosed that, toner particles having diameter of 5 &mgr;m or less are mandatory components for forming high definition, high resolution images, and such toners containing small toner particles, when supplied smoothly during the development of latent images, contribute to generate faithful images of the latent images, that is, to generate images having outstanding reproducibility which do not protrude the contour of the latent images. On the other hand, there is a problem of an edge effect phenomenon in which the density around the center of an image becomes low compared to edge portions (i.e., corners) of the image. Such phenomenon appears more conspicuously as toner particles become smaller, for example 5 &mgr;m or less. However, it also discloses that such phenomenon may be suppressed by defining the No. % of the toner particles having an intermediate particle diameter of 5 &mgr;m or greater.
Moreover, as smaller the diameter of the particles become, it becomes more advantageous in terms of forming images of high resolution and high definition even if the content of toner particles having diameter of 5 &mgr;m or less in an entire toner is 17 No. %, this accounts for no more than a mere 3 vol. % when expressed as a vol. % age. In such level of quantity, it is very difficult to selectively place toner of a small particle diameter of 5 &mgr;m or less in the peripheral portions on a latent image. Furthermore, these toner particles are magnetic toner particles, containing 50 parts by mass or more of magnetic bodies relative to the binding resin. For that reason, magnetization in a magnetic field of 1 kiloersted (1 köe=approximately 79.6 kA·m) becomes great, exceeding 20 emu/g. Accordingly, the toner becomes difficult to develop due to the magnetic bias effect, and, particularly in cases where toner having a toner particle diameter of 5 &mgr;m or less is contained in the large quantity of 60 No. %, the toner becomes excessively charged (overcharged), and developing power further deteriorates. As a consequence, image density declines sharply, and this has constituted a problem. When the toner is difficult to develop, moreover, toner builds up on the carrier surface, a phenomenon called spent occurs, and the useful life of the developer is sharply reduced, which has also constituted a problem.
In order to prevent a spent phenomenon, conventionally, methods for coating the carrier surface with various resins have been proposed. However, although carriers coated in such a manner to exhibit outstanding charge characteristics, the threshold surface tension at the surface thereof is comparatively high, for such reason, the useful life thereof as a developer is not all that long, which has been a problem.
A carrier coated with an ethylene tetrafluoride copolymer is known. With this carrier, however, even though the problem of toner becoming spent does not readily occur due to the low surface tension, because the ethylene tetrafluoride copolymer is positioned on the most negative end in the frictional charge sequence, the carrier cannot be used when trying to electrify the toner to a negative polarity, which has been a problem.
Carriers have also been proposed as carriers of low surface tension which are coated with a coating layer containing a silicone resin. Examples include a carrier the surface whereof is coated with an unsaturated silicone resin and organo-silicone or silanol or the like mixed in a styrene-acrylic resin (U.S. Pat. No. 3,562,533, specification), a carrier the surface whereof is coated with a polyphenylene resin and an organo-silicone terpolymer resin (U.S. Pat. No. 3,847,127, specification), a carrier the surface whereof is coated with a styrene-acrylate-methacrylate resin and organo-silane, silanol, or siloxane or the like (U.S. Pat. No. 3,627,522, specification), a carrier the surface whereof is coated with a silicone resin (Japanese Patent Application Laid-Open No. S55-127567/1980 (published), and a carrier the surface whereof is coated with a resin-denatured silicone resin (Japanese Patent Application Laid-Open No. S55-157751/1980 (published). Thus, by using a carrier the surface whereof is coated with a silicone resin, resistance to becoming spent is improved, but, when the amount of toner having a particle diameter of 5 &mgr;m or less is great, the recent demand for longer useful life cannot be satisfied, which has been a problem.
Art wherein a small quantity of toner particles having a diameter of 5 &mgr;m or less is defined has been proposed, in Japanese Patent Application Laid-Open No. H4-124682/1992 (published) and Japanese Patent Application Laid-Open No. H10-91000/1998 (published), for single-component developing schemes. However, there is no provision concerning particle diameter distribution in a range wherein most of the toner particles that determine image quality exist, and the effectiveness of such art is limited to single-component developing schemes wherein single-component developers are used.
With the single-component developer schemes noted above, no use is made of a developer wherein carrier particles and toner particles are mixed, as in a two-component developer scheme wherein a two-component developer is used, but toner is held on a developing sleeve, either by electrical force produced by friction between the toner and the developing sleeve, or by magnetic force b
Higuchi Hiroto
Iwamoto Yasuaki
Kondo Maiko
Matsuda Hiroaki
Nakai Hiroshi
Goodrow John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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