Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-04-13
2002-05-21
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C399S260000, C399S276000
Reexamination Certificate
active
06391511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a developing apparatus, an apparatus unit and an image forming method by which an electrostatic latent image formed on an electrostatic latent image bearing member used in electrophotography, electrostatic recording or magnetic recording is developed to render it visible by the use of a developer carried and transported on a developer carrying member.
2. Related Background Art
A number of methods are conventionally known as electrophotography. In general, copies are obtained by forming an electrostatic latent image on an electrostatic latent image bearing member (photosensitive member) by utilizing a photoconductive material and by various means, subsequently developing the electrostatic latent image by the use of a developer having a toner, to make it visible to form a toner image, transferring the toner image to a transfer medium such as paper as occasion calls, and then fixing the toner image to the transfer medium by the action of heat, pressure or the like.
Development systems in electrophotography are chiefly grouped into one-component type development and two-component type development. In recent years, electrophotographic apparatus are demanded to be made light-weight and small-sized. Accordingly, since the part of a developing apparatus or assembly must be made small, a developing apparatus employing a one-component type development carried out using one-component type developers are used in many cases.
More specifically, such one-component type development systems require no carrier particles such as glass beads or iron powder required in two-component type development systems, and hence can make developing assemblies themselves small-sized and light-weight. Also, since in the two-component type development systems the concentration of toner in the two-component type developer must be kept constant, a device for detecting toner concentration so as to supply the toner in the desired quantity is required, thus, in the case of the two-component type development systems, this also tends to make developing assemblies have larger size and weight. On the other hand, in the one-component type development systems, such a device is not required, and hence the developing assemblies can also be made small-sized and light-weight.
Known as the one-component type development system making use of one-component type developers is, e.g., a system in which an electrostatic latent image is formed on a photosensitive drum serving as a latent image bearing member, positive or negative electric charges are imparted to a toner serving as a one-component type developer, by the friction between a developing sleeve as a developer carrying member and the toner and/or the friction between a developer layer-thickness regulating member for regulating toner coat quantity on the developing sleeve and the toner, then, by this developing sleeve thin coated with the toner on its surface, the toner standing positively or negatively charged is transported to a developing zone at which the photosensitive drum and the developing sleeve face each other, and in the developing zone the toner is caused to fly and adhere to the electrostatic latent image formed on the surface of the photosensitive drum, to perform development to make the electrostatic latent image visible as a toner image.
The one-component type developers used in such one-component type development system include a one-component type magnetic developer containing a magnetic material for making the one-component type developer carried on the developer carrying member chiefly by the action of magnetic force, and a one-component type non-magnetic developer containing no magnetic material. In the latter case, the one-component type non-magnetic developer is carried on the developer carrying member chiefly by the action of electrostatic force. The one-component type developers also include, from their charge polarities, those having a negatively chargeable toner and those having a positively chargeable toner. Then, when, e.g., development is performed on an OPC (organic photoconductor) photosensitive member holding on its surface a negatively charged electrostatic latent image, a developer having a positively chargeable toner is used when what is called regular development is performed, and a developer having a negatively chargeable toner is used when what is called reverse development is performed. Negatively charging OPC photosensitive members are widely used because they have stable performance and are available at a low price. Thus, in printers and digital copying machines, the developer having a negatively chargeable toner is used in many cases since the reverse development is performed. In analog copying machines which performs regular development, the developer having a positively chargeable toner is used in many cases since the regular development is performed.
As the developer carrying member having the function to carry and transport such a developer on the surface when the development is performed, a member is used which is produced by molding, e.g., a metal, an alloy or compound thereof into a cylinder and treating its surface by electrolysis, blasting or filing so as to have a stated surface roughness. When, however, the developer carrying member made of such a material is used and the developer layer is regulated by the developer layer-thickness regulating member into a thin layer and formed on the developer carrying member surface, the developer present on the developer carrying member surface and in the vicinity thereof comes to have a very high electric charge, so that it is strongly attracted to the developer carrying member surface by the action of mirror force. This makes the toner particles have no opportunity of their friction with the developer carrying member, and hence the developer comes to have no preferable electric charges (a phenomenon called “charge-up”). Under such a condition, no satisfactory development and transfer can be performed, resulting in images with much uneven image density and many black spots around line images. Moreover, the toner attracted to the surface of the developer carrying member by such mirror force may trigger spot-like images, what is called blotches which may occur on and adhere to the developer carrying member, or may cause melt-adhesion of toner.
In recent years, developers (toners) are sought to be fixable at a lower temperature for the purpose of energy saving. In such a case, too, it is desired to form highly minute images. In order to realize the fixing of toner at a low temperature, there is, e.g., a tendency that when toners are produced the Tg (glass transition temperature) of the developer is set a little lower or a low-molecular weight component or a low-melting substance such as wax is added to a binder resin in a little larger quantity. When, however, such a toner is used in image formation, the developer tends to melt-adhere to the surface of the developer carrying member because of temperature rise or physical action of the body of an apparatus, consequently tending to cause a decrease in image density, images with white lines and blotchy images.
Japanese Patent Application Laid-open No. 1-112253 and No. 2-284158 disclose a proposal of using toners having small particle diameters so that image quality can be made higher and images can be made more highly minute. Such toners having small particle diameters, however, have a larger surface area per unit weight, and hence tend to have a larger electric charge on the surface, where the toner may stick or adhere to the surface of the developer carrying member because of the phenomenon of what is called “charge-up”, so that the toner fed afresh onto the developer carrying member can be charged with difficulty. In such a case, the toner tends to have a nonuniform charge quantity. This tends to cause sleeve ghost on images, and the resultant images tend to be formed as nonuniform images such as images with lines and fogged images in solid black images and
Fujishima Kenji
Goseki Yasuhide
Okamoto Naoki
Otake Satoshi
Saiki Kazunori
Canon Kabushiki Kaisha
Chapman Mark
Fitzpatrick ,Cella, Harper & Scinto
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