Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1997-12-29
2002-09-10
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108300, C430S109300, C430S110300, C430S137170
Reexamination Certificate
active
06447968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic toner for developing electrostatic latent images in image forming processes such as electrophotography and electrostatic printing. It also relates to a process for producing such a magnetic toner, and an image forming method making use of the magnetic toner.
2. Related Background Art
A number of methods are conventionally known as electrophotography, as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publication Nos. 42-23910 (U.S. Pat. No. 3,666,363) and 43-24748 (U.S. Pat. No. 4,071,361) and so forth. In general, copies or prints are obtained by forming an electrostatic latent image on a photosensitive member by utilizing a photoconductive material and by various means, subsequently developing the latent image by the use of a toner to form a toner image, and transferring the toner image to a transfer-receiving medium such as paper if necessary, followed by fixing by the action of heat, pressure or heat-and-pressure. The toner not transferred and remaining on the photosensitive member is removed by a various method to cleaning the photosensitive member surface, and the above steps are repeated.
As developing methods by which electrostatic latent images are developed by the use of toners, the magnetic brush development as disclosed in U.S. Pat. No. 2,874,063, the cascade development as disclosed in U.S. Pat. No. 2,618,552, the powder cloud development as disclosed in U.S. Pat. No. 2,221,776, the fur brush development and the liquid development are known in the art. In these developing methods, the magnetic brush development, the cascade development and the liquid development, which employ developers mainly composed of a toner and a carrier, are put into practical use. These methods are all superior methods which can relatively stably obtain good images, but on the other hand have problems inherent in the two component type developers, such that the carrier may: deteriorate and the mixing ratio between the toner and the carrier may change.
To eliminate such problems, developing methods employing one component type developers comprised of a toner only are proposed in variety. In particular, methods employing one component type developers having toner particles having magnetic properties are available.
U.S. Pat. No. 3,909,258 discloses a developing method employing a magnetic toner having an electrical conductivity. This is a method in which a conductive magnetic toner is supported on a cylindrical conductive sleeve having a magnet in its inside and the toner is brought into contact with electrostatic latent images to carry out development. In this development, in the developing zone, a conducting path is formed between the surface of an electrostatic latent image bearing member and the surface of the sleeve by conductive magnetic toner particles, and electric charges are brought from the sleeve to the conductive magnetic toner particles through the conducting path, where the conductive magnetic toner particles adhere to image areas of electrostatic latent images by the Coulomb force acting between the conductive magnetic toner particles and the images areas. Thus the electrostatic latent images are developed. This development carried out using a conductive magnetic toner is a method having avoided the problems inherent in the conventional two component type development. On the other hand, since the magnetic toner is conductive, there is the problem that it is difficult to electrostatically transfer the developed images from the electrostatic latent image bearing member to a final transfer-receiving medium such as plain paper.
As a developing method employing a high-resistivity magnetic toner that enables electrostatic transfer, there is a developing method utilizing dielectric polarization of magnetic toner particles. Such a method, however, has the problems that the development speed is substantially low and the density of developed images is not well attained.
As other developing methods employing a high-resistivity, insulating magnetic toner, methods are known in which magnetic toner particles are triboelectrically charged by the mutual friction between magnetic toner particles or by the friction between magnetic toner particles and a developing sleeve or the like and electrostatic latent images are developed using the magnetic toner having triboelectric charges. Such methods, however, have the problems that the triboelectric charging tends to be insufficient because of a small number of contact times between the magnetic toner particles and the friction member and the magnetic toner particles charged tend to agglomerate on the sleeve because of the Coulomb force increasing between the magnetic toner particles and the sleeve.
Japanese Patent Application Laid-Open No. 55-18656 (corresponding to U.S. Pat. Nos. 4,395,476 and 4,473,627) discloses novel jumping development that has eliminated the above problems. This is a method in which a magnetic toner is very thinly coated on a developing sleeve, and the toner thus coated is triboelectrically charged. Subsequently, the magnetic toner layer thus formed on the developing sleeve is made close to electrostatic latent images to develop the electrostatic latent images. According to this method, since the magnetic toner is very thinly coated on the developing sleeve, the opportunities of contact between the developing sleeve and the magnetic toner increase to enable sufficient triboelectric charging, and also since the magnetic toner is supported by magnetic force and the magnet and the magnetic toner are relatively moved, the magnetic toner particles are released from their mutual agglomeration and can be sufficiently brought into friction with the sleeve, whereby good images can be obtained.
In the insulating magnetic toner particles used in the above developing method, a finely divided magnetic material is mixed and dispersed in a considerable quantity and the magnetic material is partly laid bare to the surfaces of magnetic toner particles, and hence the properties of the magnetic material affect the fluidity and triboelectric chargeability of the magnetic toner, to consequently affect various performances such as developing performance and running performance required in magnetic toners.
Stated in detail, in the jumping development making use of a magnetic toner containing a conventional magnetic material, as a result of repetition of a developing step (e.g., copying) over a long period of time, the fluidity of the developer containing the magnetic toner may lower to make it impossible to achieve sufficient triboelectric charging, so that the charging tends to become non-uniform, and fog tends to occur in an environment of low temperature and low humidity, tending to cause problems on images. In the case when the binder resin and magnetic material that constitute magnetic toner particles have a weak adhesion, the magnetic material may come off the surfaces of magnetic toner particles as a result of the repetition of the developing step, so that a decrease in density of the toner images may occur.
In the case when the magnetic material is not uniformly dispersed in the magnetic toner particles, the magnetic toner particles containing the magnetic material in a large quantity and having small particle. diameters may accumulate on the developing sleeve to sometimes cause a decrease in image density and an uneven light and shade called sleeve ghost.
In the past, with regard to magnetic iron oxides contained in magnetic toners, Japanese Patent Application Laid-Open Nos. 62-279352 and 62-278131 (corresponding to U.S. Pat. Nos. 4,820,603 and 4,975,214, respectively) disclose a magnetic toner containing magnetic iron oxide particles incorporated with silicon element. In such magnetic iron oxide particles, the silicon element is intentionally brought into presence inside the magnetic iron oxide particles, but there is room for further improvement in the fluidity of the magnetic toner containing the magnetic iron oxide particles.
Japanese Pate
Dote Janis L.
Fitzpatrick ,Cella, Harper & Scinto
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