Electrophotography – Image formation – Development
Reexamination Certificate
2002-10-31
2004-12-14
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Development
C492S056000
Reexamination Certificate
active
06832065
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in a roll used, for example, as a development roll in an electro-photographic apparatus such as a copying machine, a printer, a facsimile, etc.
2. Description of the Prior Art
Recently, a simplification of maintenance has been promoted in a field of an electro-photographic device, such as copying machine, a printer, a facsimile and so on, especially, a small electro-photographic device. In practice, a development device (hereinafter referred to as prior art) is used to develop an electrostatic latent image formed on an image bearing body such as a surface of photosensitive body, a photosensitive paper, a recording paper, etc., by using single component toner as disclosed in Japanese Patent Publication No. Sho 53 (1978)-3233.
FIG. 14
shows a conventional typical development apparatus. The development apparatus comprises a photosensitive drum
101
which includes a surface layer portion A and a substrate portion B.
The surface layer portion A acts as an image bearing body and the substrate portion B acts as a supporting member for the image bearing body.
The substrate portion B comprises a conductive elastic rubber
103
adhered on a surface of a metallic drum
102
and a flexible metallic foil
104
such as aluminum foil adhered on the rubber. The surface layer portion A comprises a photoconductive insulating layer
105
in which a metal such as selenium is formed by evaporating it on the metallic foil.
A development roll
106
is provided into press-contact with a surface of the photosensitive body
101
.
The development roll
106
has a metallic roll
107
and an elastic layer
108
composed of a compositive rubber and a urethane foam, etc, formed on a surface of the metallic roll.
Because a plasticizer and a low molecular substance which have been bred out from the elastic layer
108
of the development roll
106
contaminate the surface layer portion A of the photosensitive body
101
and adhesion (tacking) and filing of the toner occur on the elastic layer
108
of the development roll
106
, there has been also developed a development roll for preventing breed out of the plasticizer and low molecular substance and the adhesion and filming of the toner by coating a surface layer (not shown) of resin having a good mold-releasing property of toner on the surface of the elastic layer
108
of the development roll
106
.
A bias power source
109
is connected between the development roll
106
and the substrate portion B of the photosensitive drum
101
.
A hopper
111
for containing single component nonmagnetic toner
110
is provided at an upper portion of the development roll
106
in such a manner that a lower opening of the hopper is arranged with a predetermined space from the surface of the development roll
106
. A frictional charging member
112
is adhered to an inside of a right side wall of the hopper. A uniformized member
113
is provided in such a manner that a surface thereof is arranged in press-contact with the surface of the development roll
106
.
The uniformized member
113
comprise a metallic roll
114
, a rubber layer
115
adhered to a surface of the roll and a frictional charging member
116
coated on the rubber layer. The uniformized member is not rotated.
According to the development roll
106
, a thin layer of toner is carried onto the surface of the development roll
106
. The roll formed in such way is abutted with the photoconductive drum
101
to which electrostatic latent image is formed and then the toner is transferred from the development roll
106
to the photoconductive drum
101
in response to development electric field to visualize the electrostatic latent image recorded on the photoconductive drum
101
.
In the aforementioned development roll, it is necessary to control polarity of charge and charging amount of the toner by fictional charge due to contact between the toner and the surface of the development roll
106
.
The transfer of toner to the photoconductive drum
101
is performed in response to the development electric field and the polarity of toner charge by selecting an image portion of the electrostatic latent image or a non-image portion (naked portion) of the latent image. According to this apparatus, there is an advantageous effect that colorization is easy without using any magnetic material for the toner.
In the conventional development apparatus using single component of toner, some attempts are made to reduce hazards upon charging by lowering charging potential in order to lengthen life duration of the apparatus, especially the long life duration of the photosensitive body. Thus, there has been needed a system capable of developing with a reduced development potential.
From the viewpoint of higher image quality, it has been required to make as low as possible the saturated development potential and to sharpen the development &ggr; (gradation of a characteristic curve for image concentration level with respective to the electrostatic potential) to a possible extent. This enables to change from multi-values which provide a writing modulation pattern of image by using a great number of gradations, to binary values which provide the writing modulation pattern of image by using two gradations (i.e., perform change of gradation by operation of dots with the same concentration of dots), in order to change a gradient expression of image in digital to an area gradation.
Reducing resistance of the development roll to sharpen the developments &ggr; is a well-known. However, if the resistance of the development roll is reduced, a higher voltage, e.g., −250 V as the bias voltage is applied. Accordingly, there is a problem that a leak of electricity to the electrostatic latent image bearing body occurs. For this reason, in prior art, the leak of electricity to the electrostatic latent image bearing body has been prevented by adding conductivity-imparting agent such as carbon black to the elastic layer
108
of the development roll
106
thereby to make the resistance of the elastic layer
108
lower than that of the surface layer of the development roll
106
.
However, if the conductivity-imparting agent such as carbon black is highly charged in the elastic layer
108
, since the elastic layer is hardened, there are problems that (1) a sufficient nip cannot be obtained between the development roll
106
and the photoconductor drum
101
, thus resulting in a deterioration of image quality and (2) manufacturing facility is impaired, thus resulting in a difficulty in forming the elastic layer
108
into a shape of roll.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a roll for resolving the aforementioned problems in prior art. More specifically, it is an object of the present invention to provide a roll capable of carrying out reductions in hardness and resistance without any fear of leak to the latent image, and provide a development apparatus for using the roll.
To accomplish the above object, according to an aspect of the present invention, a roll is provided in which it comprises a core shaft, an elastic layer arranged around said core shaft and having a resistance, and a surface layer arranged around said elastic layer and having a resistance. The resistance of the surface layer is smaller than that of the elastic layer so that the entire volume resistance of the roll is less than a volume resistance of the elastic layer.
In one embodiment, the volume resistance of the elastic layer is less than 1.0×10
9
&OHgr;·cm. The entire volume resistance of the roll is also less than 1.0×10
7
&OHgr;·cm.
Further, an actual resistance of said surface layer is less than 1.0×10
8
&OHgr;, and a thickness of said surface layer is less than 30 &mgr;m.
According to the other aspect of the present invention, a development apparatus is provided, in which it comprises the roll as described above.
In one embodiment, the development apparatus has a photosensitive body having an image portion
Nakamura Makoto
Takano Yoshiyuki
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
Tran Hoan
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