Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
1995-12-11
2002-01-22
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S272000
Reexamination Certificate
active
06341204
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a development apparatus, which is employed in an image forming apparatus such as a copying machine, printer, or the like employing the electrophotographic system or the electrostatic recording system, to develop an electrostatic image formed on an image bearing member.
In an image forming apparatus, for example, a copying machine, printer, facsimile, and the like, a latent image is formed on the image bearing member constituted of an electrophotographic photosensitive member, an electrostatic recording member of dielectric material, or the like, and then, the formed latent image is developed by a development apparatus, being visualized as a toner image.
As the development apparatus to be employed in the above image forming apparatus, various development apparatuses used with single component dry developer have been proposed or put to practical use. In any of these development apparatuses, it is extremely difficult to form a thin layer of the single component developer (toner) on the developer carrier member. In recent years, on the other hand, higher degrees of sharpness, resolution, and the like have been demanded, making it imperative to develop better methods for forming a thin layer of the toner, and to develop better apparatuses to be used with such methods. As a result, several solutions have been proposed.
According to one of the proposals, a development sleeve as the developer carrier member, the surface of which is blasted with regular particles to give it a relatively small degree of roughness, is used with a magnetic blade disposed to maintain a predetermined gap between itself and the development sleeve surface, and forms a thin layer of the triboelectrically charged toner on the development sleeve.
Even in the case of the development apparatus described above, when the toner with a smaller particle diameter and a lower melting point is simply employed to improve image quality and to quickly start up the apparatus, such toner is liable to be blocked adjacent to the magnetic blade due to the higher degree of flocculation of such toner, yielding images with nonuniformity, or images with fog, in a high humidity environment. In addition, in a low humidity environment, blotch, that is, a phenomenon in which the toner locally flocculates on the development sleeve due to charge-up, occurs to affect the images.
Japanese Laid-Open Patent Application No. 16736/1988 or the like discloses a countermeasure for the above phenomenon, in which an elastic blade composed of rubber, resin, or metal is placed in contact with the development sleeve, with a light contact pressure, so that the excessive amount of the toner adhering to the development sleeve surface is shaved off to regulate the toner layer thickness at the contact point, thereby forming a triboelectrically and uniformly charged thin layer of the toner, on the development sleeve. As a result, images of preferable quality, that is, images with no aberration or fog, can be produced.
According to another countermeasure, a roller composed of foamed polyurethane containing continuous cells, or a fur brush roller, is placed in contact with the development roller, on the upstream side of the contact point between the magnetic blade and development sleeve, relative to the rotational direction of the development sleeve. As such a roller is rotated, the toner adhering to the development sleeve is oscillated at the contact point between the two components, being rendered easily separable from the development sleeve, and at the same time, being triboelectrically charged. In addition, the other blocked adjacent to the magnetic blade as described above is loosened by the rotation of such a roller, recovering thereby preferable fluidity. As a result, high quality images with no blotch, no aberration, and no fog, can be produced as they are by the elastic blade system.
However, when the above two countermeasures (elastic blade system or contact roller system) are employed to continuously make tens to thousands of copies, the following problems occur toward the end of the continuous copying operation, or during toner replenishment.
[1] Elastic Blade System
As the copying operation continues, flocculated toner, coarse toner, dust, fuzz, and the like, which cannot pass the nip formed between the elastic blade and development sleeve, are accumulated in the nip. As a result, the sleeve surface areas correspondent to the accumulation of this foreign matter fail to be coated with the toner, effecting image aberration, in the form of white streaks, at the corresponding regions of the obtained image.
In particular, when the contact pressure between the elastic blade and development sleeve is relatively high, and at the same time, the melting point of the toner is low, the toner is fused to the blade as the copying operation continues. As a result, the toner is improperly regulated, being formed into a non-uniform layer, by the elastic blade, or the toner is given an insufficient amount of triboelectrical charge, by the elastic blade. Consequently, the produced images suffer from non-uniformity, fog, insufficient density, and the like. These phenomena stand out immediately after the toner is replenished, that is, when fresh toner, which has never been charged, is delivered to the adjacencies of the development roller.
[2] Contact Roller System
As a copying operation continues, the toner is gradually accumulated in the roller (foamed urethane roller containing continuous cells collects the toner through the continuous foams: fur brush roller collects the toner among the fiber strands). Consequently, in the case of the roller comprising a foamed material layer, it is hardened, or its cells are disintegrated as the frequency of its sliding contact with the sleeve increases, and in the case of the fur brush roller, it fatigues. As a result, the roller and the sleeve do not make proper contact, failing to shave the toner layer sufficiently and uniformly. In addition, the roller surface is also covered with the toner; therefore, the amount of the triboelectrical charge given in the nip between the roller and the sleeve is also reduced. Thus, the aforementioned blotches, non-uniform image density, fog, image density loss, and the like, occur. Further, when the contact pressure between the roller and sleeve is excessively increased by the hardening of the roller, the torque for driving the development sleeve may have to be excessively increased.
In addition to the problem related to the aformentioned endurance test in which tens of thousands of copies are made, the elastic blade system has another problem in that the thickness of the toner layer on the sleeve, and the amount of the toner charge, are delicately affected even by the slightest change in the amount of blade invasion to the sleeve, making it extremely difficult to set or stabilize the amount of blade invasion.
As means for solving the above problems, development apparatuses such as those disclosed in Japanese Laid-Open Patent Application No. 204562/1993 have been proposed. According to these proposals, foamed rubber containing independent cells is used as the material for the toner carrier member disposed near the magnetic blade, so that an appropriate amount of the toner is coated on the sleeve while stripping away the residual toner, and a preferable amount of charge is reliably given throughout the entire copying operation in which tens of thousands of copies are made.
Further, the sleeve is given a mirror-like peripheral surface; therefore, the amount of the toner coated on the sleeve can be reliably maintained at a predetermined level.
However, when development apparatuses with the above structure were subjected to an endurance test, in which microparticle toner with a particle diameter of no more than 6 &mgr;m was employed in order to improve the image quality, and one million copies were made in order to confirm the possible image stabilization, the following problems manifested.
Test 1
In this
Kobayashi Yoshiaki
Tomiki Satoshi
LandOfFree
Development apparatus employing toner supply roller... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Development apparatus employing toner supply roller..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Development apparatus employing toner supply roller... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2856633