Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-09-04
2003-01-21
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Transfer
Reexamination Certificate
active
06510307
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transfer device for transferring an image on an image carrier to a recording material. More particularly, the present invention relates to improvements in a transfer device comprising a transferring member for transferring a recording material through a nip between the image carrier and the transferring member, an image-forming apparatus using the transferring member and method for producing the transferring member.
2. Description of the Related Art
By way of example, a conventional image-forming apparatus has been already provided in a form which operates in an electrophotographic process comprising the steps of forming an electrostatic latent image on an image carrier (which widely includes a latent image carrier such as photoreceptor drum, a combination of latent image carrier and intermediate transfer drum for intermediately transferring and retaining an image on the latent image carrier), developing the electrostatic latent image with a predetermined toner by a developing device, and then transferring the toner image formed on the image carrier onto a recording material via a transfer device.
As such a transfer device there has been known a non-contact type transfer device such as corotoron. This non-contact type transfer device is disadvantageous in that it causes troubles with generation of ozone. The recent trend is for more so-called contact type transfer device to be used which transfers a toner image on the image carrier to a recording material in a contact process while conveying the recording material through a nip between a transfer roll disposed in contact with or in the vicinity of the image carrier and the image carrier.
For this contact type transfer device, there has been often used a transfer roll comprising a metallic roll coated with a fluorinated rubber layer.
In order to effectively prevent troubles such as attachment of residual toners to this type of transfer roll, a cleaning device comprising a cleaning blade disposed in contact with the transfer roll is provided.
Such a cleaning blade may be made of an elastic material such as urethane rubber to prevent damage on the fluorinated layer which is a surface coat layer on the transfer roll.
In this type of transfer device, the frictional resistance of the cleaning blade with the surface of the transfer roll can be suppressed to a relatively small value due to the surface treatment of the transfer roll. However, this type transfer device is technically disadvantageous in that as the recording material runs, more external additives for toner are attached to the surface of the transfer roll, raising the coefficient of friction of the cleaning blade with the surface of the transfer roll and hence giving more rotary load to the transfer roll. Thus, the surface of the transfer roll cannot be cleaned at a low torque.
As a result, a high rotary torque is needed to rotate the transfer roll in a stable manner. This accordingly raises the cost of driving source to disadvantage.
In order to accurately control the density of an image transferred onto the recording material, a density control process which controls image density has been already proposed, e.g., by forming a density patch for density control on an image carrier, transferring the density patch to the surface of a transfer roll, and then detecting the density whereby the density corresponding to an image transferred to the recording material can be directly detected (see JP-A-7-168401 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”)).
However, the foregoing transfer device has a transfer roll comprising a surface rubber layer coated with a fluorinated layer and thus can hardly give specular reflection as a surface optical property. For example, even if a density patch is formed on the surface of the transfer roll, the density of the density patch can hardly be optically detected.
This density control process is also technically disadvantageous in that even if the density patch transferred to the transfer roll can be removed by the cleaning blade, residual toner gradually stains the surface of the transfer roll, the reflectance of the surface of the transfer roll is lowered, and hence the detection of density patch is inaccurate performed.
In particular, when the toner used comprises substantially spherical particles, it is more likely that the toner can pass through the cleaning blade to make the foregoing technical problems remarkable.
As a method for cleaning the surface of a hard and smooth transfer roll, there has been proposed that a metallic scraper is effective (as in JP-A-6-324583). However, there is no further specific disclosure relating to the transfer roll.
On the other hand, as a prior art of a transfer roll, there has been proposed a transfer roll comprising a first layer made of an elastic material and a second layer made of a resin having a higher resistance than that of the first layer (as in JP-A-3-202885). As the second layer (a surface layer), there has been disclosed one comprising a polycarbonate, polyester, nylon or the like as a base.
There is an apprehension that when the foregoing metallic scraper is applied to the transfer roll having such a constitution, the surface layer of the transfer roll is scratched or abraded in a short period of time to cause imperfect cleaning or defective detection of density patch.
In order to solve these technical problems, the present applicant proposed a transfer device provided with a transfer member (e.g., transfer roll) having a polyimide resin layer formed on the surface thereof (Japanese Patent Application No. 2000-278014).
In accordance with this type of transfer device, the constitution of a hard transfer roll having a metallic roll with a polyimide resin layer provided thereon makes it possible to eliminate the apprehension of scratching or abrasion even if the metallic scraper comes in contact with the transfer roll because the polyimide resin layer has a high mechanical strength.
In this transfer roll having a polyimide resin layer formed on the surface thereof, the polyimide resin layer is provided with some electrical conductivity to assure desired transferring properties. However, in view of manufacturing cost, the polyimide resin layer is thin. Thus, the resistance of the polyimide resin layer must be set to a somewhat high value to prevent the leakage of current between the metallic roll and the image carrier.
As a result, charge can be easily accumulated in the polyimide resin layer. Thus, there is an apprehension that when transfer is conducted in a high electric field as in printing on OHP sheet or cardboard or double-sided printing, a sufficient transfer electric field cannot be obtained, causing imperfect transfer.
Even if an epoxy resin layer having a high abrasion resistance is provided on the surface of the metallic roll instead of polyimide resin layer, there is an apprehension that the accumulation of charge causes imperfect transfer as in the case of polyimide resin layer because the epoxy resin layer has an extremely high resistance, although the cleaning properties of the metallic scraper may be kept good.
SUMMARY OF THE INVENTION
The present invention has been worked out to solve the foregoing technical problems. An object of the present invention is to provide a transfer device which can be cleaned at a low torque while maintaining good transferring properties and, when a method is employed which forms a process control image such as a density control patch on a transferring member, the transfer device can certainly accomplish the detection of process image, an image-forming apparatus using the transfer device, and method for producing the transferring member.
In other words, as shown in
FIGS. 1A and 1B
, according to the present invention, there is provided a transfer device for transferring an image on an image carrier
1
to a recording material
2
, the transfer device comprising a transferring member
4
adapted to nip and convey
Kawai Takeshi
Kitagawa Yusuke
Masubuchi Toshio
Matsumoto Koichi
Mitsuhashi Toshihiko
Fuji 'Xerox Co., Ltd.
Morgan & Lewis & Bockius, LLP
Ngo Hoang
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