Electrophotography – Image formation – Development
Reexamination Certificate
2001-12-18
2003-12-23
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Image formation
Development
C399S286000
Reexamination Certificate
active
06668148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a developing apparatus for making latent electrostatic images visible in an electrophotographic apparatus or electrostatic recording apparatus, and to an image forming apparatus capable of obtaining high-quality images using the developing apparatus.
2. Description of the Related Art
Conventionally, developing apparatus utilizing a single-component toner supplies developer to the surface of a developer bearing member (herein after also referred to as a toner carrier, developer roller, etc.) by an elastic roller of sponge or the like which rotates, electrically charges the developer and causes it to adhere, restricts the thickness of the developer layer by a blade or roller-shaped layer thickness regulating member, forms a uniform thin layer of developer on the surface of the developer bearing member, causes it to adhere to a latent electrostatic image formed on a latent image carrier, develops that, and turns it into a visible image.
At such time, there have been the following problems with the layer thickness regulating member.
Conventionally, for the surface member of the layer thickness regulating member, in view of the fact that the electrostatic charging characteristics of the developer are affected by the frictional electrostatic charging characteristics of the various members, when a negatively charged developer is used, a positively charged material has sometimes been used for the purpose of increasing the developer charge or conversely decreasing the oppositely charged developer.
In particular, because nylon materials exhibit very strong positive charging qualities, they have been frequently used for the purpose of improving the charging characteristics of developers. Examples include nylon and polyether copolymers (Japanese Patent Application Laid-Open No. H9-50185/1997), nylons having specific mechanical properties (Japanese Patent Application Laid-Open No. H8-328381/1996), and nylons formed on urethane rubber (Japanese Patent Application Laid-Open No. H8-248769/1996). Developer bearing members are generally classified in two types, hard and soft types according to the shape of the photo-sensitive member (drum or belt) and developing method (contact or non-contact), and layer thickness regulating member are needed which accord therewith.
However, nylon materials exhibit poor releasability, leading to problems such as that the developer strongly adheres to the surface of the layer thickness regulating member, so-called toner sticking occurs, the charging characteristics of the developer changes over time, and the phenomenon of streaks or irregularities occurring in the thin developer layer arises.
Also, when the coefficient of friction (&mgr;) of the layer thickness regulating member is large, toner aggregates or foreign matter is sandwiched between parts of the layer thickness regulating member and developer roller that are in contact, and streaks occur in the thin toner layer, making it difficult to obtain a uniform stable thin layer.
Meanwhile, as a method of maintaining long life of a developing apparatus (hereinafter also referred to as a developing unit), as affected by toner sticking, developing apparatuses have been proposed (cf. Japanese Utility Model Application Laid-Open No. S63-364/1988 (published), for example) wherein, a thin layer roller driven to turn in the same direction as the developer roller by a drive source is made to contact the developer roller.
Here, the turning speed of the developer roller is set to a prescribed speed that satisfies the developing conditions, and the turning speed of the thin layer roller is set so that the thin layer roller turns at a very low speed.
In this developing apparatus, the thin layer roller that makes the toner adhering to the surface of the developer roller a thin layer contacts the developer roller at only one place, and the place where the thin layer roller contacts the developer roller (toner carrier) changes due to the turning of the thin layer roller, wherefore, as compared to the developer blade, it is difficult for toner sticking to occur on the thin layer roller, and useful life extension was expected.
However, in the above-described developing apparatuses wherein a thin layer roller is used, there was a problem, as described below, caused by toner aggregates that were generated inside the developing apparatuses.
That is, whereas the supply roller functioning as the toner supply member is generally made of a sponge material, when the sliding contact between the developer roller and the supply roller is repeated as the developing apparatus is used, portions of the sponge configuring the supply roller are torn away and circulate as minute foreign matter together with the toner inside the developing apparatus. When the developing apparatus is used over an extended period, toner adheres to the minute pieces of sponge torn away as described in the foregoing when toner is rubbed between the developer roller and the supply roller or between the developer roller and the thin layer roller, and toner fuses with toner at the site of that sliding contact, whereupon toner aggregates are generated.
These toner aggregates that are generated follow along the normal flow of toner and reach the vicinity of sliding contact between the developer roller and thin layer roller. The thin layer roller turns in the same direction as the developer roller, and renders the toner adhering to the surface of the developer roller into a thin layer. However, the turning speed of the developer roller is set at a prescribed speed which satisfies the developing conditions, whereas the turning speed of the thin layer roller is set so that the thin layer roller turns at a very low speed.
For that reason, toner aggregates that have gotten into the wedge-shaped portion at the entrance to the sliding contact region between the developer roller and the thin layer roller either are returned back to the interior of the developing apparatus without entering that sliding contact region, or enter into that sliding contact region. The toner aggregates that have entered the sliding contact region are used in the developing of the latent electrostatic images, causing anomalous images to be generated, or remain in the sliding contact region and adhere strongly to the surface of the thin layer roller, creating portions where no thin layer will be formed and causing white streaks in the images.
Furthermore, when the developing apparatus continues to be used with the toner aggregates present in the sliding contact region between the developer roller and the thin layer roller, the surfaces of the developer roller and thin layer roller where the toner aggregates make contact will deteriorate, and it will become impossible to obtain the desired thin toner film on the developer roller. For that reason, it is necessary to enhance the thin layer roller toner releasability, and prevent the aggregates from adhering to the thin layer roller surface.
In addition to the aggregates, moreover, toner also melts and adheres in a thin film form to the thin layer roller surface in what is called toner filming, and there has been hoped that thin layer roller surface toner releasability can be further improved.
As means for eliminating the difficulties described in the foregoing, the method of deploying a fluorine resin excelling in toner releasability to the thin layer roller surface is adopted. In addition to coating on the fluorine resin coating material by an ordinary method such as spraying or roll coating, this can be accomplished by mounting a fluorine resin tube to the thin layer roller surface.
However, although fluorine resins are very outstanding in terms of releasability and the difficulties noted earlier are eliminated, positioned, in triboelectric series, on the extreme negatively charged side, wherefore difficulties arise in that, especially when using a negatively charged toner, the toner charge amount is low, or, for that reason, a thin toner layer is not formed uniformly, or, w
Hirano Yasuo
Morohoshi Naoya
Cooper & Dunham LLP
Lee Susan S. Y.
Ricoh & Company, Ltd.
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