Electrophotography – Image formation – Development
Reexamination Certificate
2000-03-15
2001-11-20
Braun, Fred L. (Department: 2852)
Electrophotography
Image formation
Development
C399S249000
Reexamination Certificate
active
06321053
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a liquid developing apparatus, more in detail to the liquid developing apparatus in which spread of a surplus developer concentrated on both ends of a photosensitive element is prevented, an efficiency of squeezing is elevated, and the surplus developer is removed.
(b) Description of the Related Art
In some of the conventional liquid developing apparatuses, a surplus developer is removed, and adhesion of toner on a photosensitive element, a developing roller and a squeezing roller is prevented in addition to acceleration of development by applying a bias voltage to a developing element and a squeezing element.
JP-A-9(1997)-15981 describes a surplus developer removing apparatus which employs a squeezing roller including a porous elastic member and a conductive surface layer made by a material having a low surface energy and high air-permeability formed thereon. In the surplus developer removing apparatus, adhesion of toner and lowering of a function of removing the surplus developer are prevented by applying, to the squeezing roller, a voltage between several hundreds to several thousands Volts having the same polarity as that of the toner.
JP-A-6(1994)-19266 describes a liquid developing apparatus which includes a first developing electrode for applying a bias voltage having the same polarity as that of all electrostatic latent image and a second developing electrode for applying a bias voltage having the reverse polarity. In the apparatus, by making the electrodes a dish-like shape, a longer and effective developing time can be secured, a development fogging is suppressed after removing the toner on the non-image portion, and the adhesion of the toner on the developing electrodes is prevented.
JP-A-56(1981)-81870 describes a roller to which a bias voltage having a polarity reverse to that of toner is applied is disposed between a developing part and a transcribing part and near a photosensitive element to remove a surplus developer in an image-forming process.
JP-A-10(1998)-274885 describes a liquid developing apparatus in which a bias voltage is applied between a developing roller and a cleaning roller not in contact with the developing roller to remove remaining toner on the developing roller.
It is also described in a publication that first and second squeezing rollers are used in a conventional liquid developing apparatus, as shown in FIG.
1
. When a photosensitive element on which a developer is applied by a developing roller (not shown) moves from left to right in FIG.
1
and passes the first squeezing roller
11
, the developer is squeezed from the edges of the first squeezing roller
11
, and the surplus developer is likely to be left on the both edges of the sensitive element.
The second squeezing roller
12
having a pair of removing elements
13
on the both ends thereof is mounted immediately after the squeezing roller
11
to rotate in the direction reverse to the moving direction of the photosensitive element, thereby removing the surplus toner on the belt-like photosensitive element.
Another apparatus is proposed in which air nozzles are disposed on both sides of the moving photosensitive element and near the squeezing roller to remove the developer by preventing the flow-out of the surplus developer.
However, the conventional liquid developing apparatuses have the following problems.
Since the developer supplied to the photosensitive element by means of the developing roller spreads in the direction of the roller axis when a pressure is applied to the developer by the squeezing roller, the surplus developer is likely washed away and spreads towards the both ends of the photosensitive element to be concentrated thereon. When the conventional liquid developing apparatus is applied to a so-called one-pass type color printer, a surplus developer having a first color spreading to the both ends of the photosensitive element remains to be mixed with a developer having a second color, thereby lowering the reproducibility of the colors to deteriorate chroma.
In order to solve the problem, the removal of the surplus developer remaining on the both edges of the photosensitive element may be conducted by employing the secondary squeezing roller
12
as shown in FIG.
1
. However, the toner adhered to the secondary squeezing roller
12
and the abrasion thereof gradually reduce the ability of removing the developer, and a stain on the image ends is generated by the developer remaining on the both edges of the photosensitive element.
In order to remove the surplus carrier by the air nozzles, an air pump having a larger capacity is required because an amount of the surplus developer is large to increase an amount of air-flow required therefor. The employment of the air pump having the larger capacity may be a cause of pollution and a noise generated by carrier components of the developer evaporated in the apparatus.
A number of proposals have been conventionally presented as described above in which the surplus carrier is removed and the adhesion of the toner is prevented by applying the bias voltage, and the squeezing efficiency of the squeezing roller is improved by removing the surplus carrier from the developing roller, the squeezing roller and the photosensitive element. However, the conventional techniques do not pay attention to the pollution of the image edges.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a liquid developing apparatus in which spread of a surplus developer concentrated on both edges of a photosensitive element is prevented.
The present invention provides a liquid developing apparatus including: a photosensitive element having an electrostatic latent image thereon; a developing roller for supplying a developer to the photosensitive element; a squeezing roller for squeezing the photosensitive element; and a regulatory roller located upstream the squeezing roller and opposing to the photosensitive element, the regulatory roller including a pair of annular projections projecting therefrom in a radial direction in vicinity of both ends of the regulatory roller for maintaining the developer on the photosensitive element between the annular projections.
In accordance with the liquid developing apparatus of the present invention, an amount of the developer spreading beyond the annular projections is extremely small, and if necessary, the surplus developer may be discharged through a gap between the developing roller and the regulatory roller. Accordingly, most of the developer uniformly exists on the photosensitive element, and even if a small amount of the developer spreads beyond the annular projections, at least part of the developer may be returned to the photosensitive element between the annular projections.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.
REFERENCES:
patent: 3601092 (1971-08-01), Satomi
patent: 4127082 (1978-11-01), Kawabata
patent: 5481342 (1996-01-01), Arearo et al.
patent: 5713068 (1998-01-01), Teschendorf et al.
patent: 5893012 (1999-04-01), Schubert et al.
patent: 6049684 (2000-04-01), Nishikawa et al.
patent: 56-81870 (1981-07-01), None
patent: 56-155965 (1981-12-01), None
patent: 63-75778 (1988-04-01), None
patent: 2-123383 (1990-05-01), None
patent: 5-289528 (1993-11-01), None
patent: 6-19266 (1994-01-01), None
patent: 9-15981 (1997-01-01), None
patent: 10-274885 (1998-10-01), None
Japanese Office Action issued Jan. 18, 2000 in a related application and English translation of relevant portions.
Braun Fred L.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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