Roll or roller – Concentric layered annulus – Specific composition
Reexamination Certificate
1999-04-15
2001-09-25
Echols, P. W. (Department: 3726)
Roll or roller
Concentric layered annulus
Specific composition
C399S176000
Reexamination Certificate
active
06293895
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transfer roller.
2. Description of the Related Art
With conventional electrophotographic printers, a charging device uniformly charges the surface of a photoconductive drum and then an LED head illuminates the charged surface to form an electrostatic latent image. The electrostatic latent is developed by a developing device into a toner image. Then, the toner image is transferred by a transfer device to a print medium. A fixing device subsequently fixes the toner image on the print medium.
FIG. 7
is a perspective view of a transfer device of a conventional electrophotographic printer.
A transfer roller
11
is in pressure contact with a photoconductive drum
12
. The transfer roller
11
rotates in a direction shown by arrow A and the photoconductive drum
12
rotates in a direction shown by arrow B. The transfer roller
11
receives a transfer voltage or positive high voltage +E. The photoconductive drum
12
carries a toner image
13
formed thereon. When a print medium
14
passes between the transfer roller
11
and the photoconductive drum
12
, a transfer current flows from the transfer roller
11
to the photoconductive drum
12
, thereby causing the toner image
13
to be deposited on the print medium
14
.
The transfer roller
11
has a uniform surface resistance, so that a uniform transfer current flows through any areas in contact with the photoconductive drum
12
. The transfer roller
11
is urged by a constant pressure F against the photoconductive drum
12
, thereby creating an appropriate longitudinal contact area between the transfer roller
11
and the photoconductive drum
12
. This ensures that the print medium
14
travels straightforwardly in a direction shown by arrow C as the transfer roller
11
and the photoconductive drum
12
rotate.
The transfer roller
11
includes a metal shaft with a rubber material deposited thereon. The rubber material is formed by kneading, for example, a semiconductive urethane rubber, silicone rubber, or the like. The rubber material is foamed, vulcanized into a sponge-like material by adding a vulcanizing agent, and finally formed into a specific shape and dimensions. An electrically conductive material is added to the rubber material, thereby making the rubber material electrically semiconductive.
The conventional transfer roller
11
suffers from the following problems. Some rubber materials react with the material of the photoconductive drum
12
when they are left in an environment of high temperature and high humidity for a long time, so that the rubber material welds with the photoconductive drum, or the vulcanizing agent, semiconductive material, or the like is deposited to the photoconductive drum. As a result, the photoconductive drum is contaminated, causing lines to appear in the printed image. This decreases the print quality.
In order to solve this problem, the length of time during which vulcanization is performed is extended so that less vulcanizing agent is added to the rubber material, or the surface of the transfer roller
11
is coated with an inert material. However, such treatments not only are insufficient in preventing drum contamination but also lose some degrees of freedom in designing the characteristics of transfer roller
11
such as electrical resistance and mechanical hardness.
SUMMARY OF THE INVENTION
The present invention was made to solve the aforementioned problems of the conventional transfer rollers.
An object of the invention is to provide a transfer roller which prevents drum contamination so as to maintain the quality of printed images.
Another object of the invention is to provide a transfer roller, which still maintains the degrees of freedom in designing the characteristics of the transfer roller.
A transfer roller is used in an electrophotographic printer. The transfer roller rotates in contact with a rotating photoconductive drum with a print medium travelling therebetween. The transfer roller has a metal shaft around which a rubber roller is formed. The rubber roller is sponge-like and electrically semiconductive. The rubber roller is covered with a resin tube which has a lower layer formed on the rubber roller and an upper layer formed on the lower layer. One of the upper and lower layers has a higher sealing effect than the other of the upper and lower layers, and the other of the upper and lower layers has a higher stability of electrical resistance than the one of the upper and lower layer.
An organic ion electrically conductive material is added to the upper layer for stable electrical resistance while carbon black is added to the lower layer for increased sealing effect.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
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Ando Hirokazu
Furuya Satoru
Koyama Tatsuya
Butler Marc W.
Echols P. W.
Oki Data Corporation
Rabin & Berdo P.C.
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