Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2003-03-25
2004-12-07
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S267000, C399S270000, C399S282000, C430S122520
Reexamination Certificate
active
06829448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus and method, particularly to an image forming apparatus utilizing electrophotography such as a copying machine, a printer, a facsimile and a complex machine of those and its image forming method, more specifically, to an image forming apparatus having a hybrid developing apparatus which develops a latent image to which only charged toner is caused to jump from a developing roll holding the only charged toner on it using two components developer material, in which non-magnetic toner is charged by means of magnetic carrier.
2. Description of the Related Art
Heretofore, there are kinds of developing methods in an image forming apparatus utilizing electrophotography such as a copying machine, a printer, a facsimile and a complex machine of those. One is a two-components developer material method which uses toner and magnetic carrier; another is one-component developer material method which uses nonconductive toner or conductive toner, yet another is a hybrid developing method which develops a latent image to which only charged toner is caused to jump from a developing roll holding the only charged toner on it using two components developer material, in which non-magnetic toner is charged by means of magnetic carrier.
A two parts developer material method has advantages of such as excellent charging property of toner by carrier, long life of toner as well as uniformity of solid image. On the other hand, it has drawbacks of such as a large and complicated developing apparatus, generation of toner scattering or carrier accompanying as well as varying image quality depending on durability of carrier. A one-component developer material method has advantages of a compact developing apparatus as well as good dot reproducibility while it has drawbacks of the poor durability of a developing roll and a charge roller, which results in selective developing or high maintenance cost of supplies and material for developing apparatus. A hybrid developing method is a high rate image forming method which has good dot reproducibility and a long life, however it has heretofore such problems as generation of developing ghost or toner scattering.
Though a hybrid developing method has been developed as one of measures for a one-component non-contact developing, it has been recently developed as a high rate developing method for a developing method of superimposing multi-colors on one drum, in which a plurality of color images are sequentially formed on one latent image bearing body (a photosensitive body). Attention has been paid to this method as an art of quality color images because a color image with scarce color drift can be obtained by accurately overlapping different colored layers of toner on a latent image bearing body.
However, since developing apparatuses corresponding to a number of colors used should be disposed around the latent image bearing body in a developing method of superimposing multi-colors on one drum, the latent image bearing body becomes large in size so that this prevents from designing a compact image forming apparatus. Hence, attention has been paid to a tandem method in which a plurality of electro-photographic process units corresponding to colored toners used are aligned and colored images are formed synchronized with transferring of a transfer member so as to overlapping the colored images on the transfer member. However, this method has a drawback that the image forming apparatus becomes large because electro-photographic process units of kinds of colors should be aligned, though it has an advantage in having a rapid rate of printing. In order to improve measures for this problem, a compact tandem image forming apparatus has been proposed, which is provided with a small-sized image forming unit by narrowing a distance between latent image bearing bodies.
The compact tandem image forming apparatus thus designed has an advantage when it has a vertical developing apparatus in order to minimize a size in width direction of the image forming unit. That is, it is desirable regarding parts layout to dispose a developing apparatus in the upper part of the latent image bearing body. However, in case the developing apparatus is disposed in a vertical manner in a conventional two-components developer material method, flow of developer material, that is, the supply of developer material from a developer mixer to the part adjacent to a latent image bearing body is complicated so that down-sizing of the apparatus is limited, carrier adheres inevitably to the latent image bearing body and toner scatters unavoidably.
Though, as another method, a one-component developer material method in which carrier is not used is proposed, it has a drawback of enhancing color drift, which is the weak point of a tandem type, on account of the torque fluctuation of a latent image bearing body caused by contacting a developing roll to the latent image bearing body. Meanwhile, with a method in which a latent image bearing body is not touched, toner is charged by a charge roll and the toner thickness on the developing roll is restricted by an elastic doctor blade. Thus, additive for toner adheres to the charge roll so that the charging ability is decreased or toner adheres to the doctor blade so that toner thickness becomes uneven, which results in image defects.
Hence, as a measure for resolving the problems, the aforementioned hybrid developing method has attracted attention. Though the hybrid developing method has the problems with regard to generation of ghost and scattering of toner, the method has little torque fluctuation owing to non-contacting between the developing roll and the image bearing body as well as excellent dot reproducibility so that it provides a high-speed image forming apparatus capable of a long life.
A prior art regarding a hybrid developing method is disclosed in U.S. Pat. No. 3,866,574 which proposes a method wherein a non-magnetic toner thin layer is formed on a donor roll (developing roll) disposed untouchably toward a latent image bearing body and the toner is caused to jump to the latent image on the latent image bearing body by an alternative current electric field. While, U.S. Pat. No. 3,929,098 shows a developing apparatus which forms a toner layer by transferring the toner onto a donor roll using a magnetic roll.
However, although these arts enable toner to form a thin layer on a donor roll by means of two-components developer material, a strong alternative current electric field is necessary to separate toner from the donor when the electrostatic charge of the toner is high. The strong alternative current electric field disturbs the toner layer so that a problem concerning superimposing multi-colors arises. In this regard, so called a powder cloud developing method is disclosed in Japanese laid open patent publication, No. JP1991-113474 wherein auxiliary electrodes consisting of wires are provided between a donor roll and a latent image bearing body applying a weak alternative current electric field so as not to disturb the toner developed.
Theoretical aspect of the formation of toner layer on a developing roll using two-component developer material was reported by Toshiba Corporation in the Electrophotography Society Journal 19, 2 (1981) and the art is disclosed in Japanese laid-open patent publication JP1984-121077.
The aforementioned prior arts have a tendency of decreasing image consistency owing to selective developing as coarse particles of the high developing natured toner are apt to selectively jump to the latent image body and fine particles of the highly charged toner remains on the developing roll sleeve. Further, the control of charging toner is complicated so that a high surface potential and a big developing electrical field need to be applied. In this regard, if both toner consumption region and non-consumption region are generated on the developing roll, toner adhering state and toner potential vary on the surface of the developing roll. Th
Kamiyama Yuji
Nishimura Toshinori
Ozawa Yoshio
Sakata Shoichi
Dixit Mayankkumar
Kyocera Corporation
Lutzker Joel E.
Schulte Roth & Zabel LLP
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