Roll or roller – Single annular member – per se – Specific nonmetallic composition
Reexamination Certificate
2001-12-13
2003-11-18
Rosenbaum, I Cuda (Department: 3726)
Roll or roller
Single annular member, per se
Specific nonmetallic composition
C492S056000
Reexamination Certificate
active
06648807
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a conductive rubber roller used in an image-forming apparatus, such as electrophotographic copying machines, electrophotographic printers, and electrostatic recording apparatus, wherein the conductive rubber roller is disposed in contact with an electrophotographic photosensitive member.
In the image-forming apparatus, such as electrophotographic copying machines, electrophotographic printers, and electrostatic recording apparatus, a toner used as a developer is made to adhere to an electrostatic latent image formed by exposing an electrophotographic photosensitive member, which has been electrostatically, uniformly charged, and then the toner (toner image) is transferred to a transfer medium such as paper to form an image. Also, methods for charging the electrophotographic photosensitive member include a noncontact charging method utilizing corona discharge and a contact charging method making use of a conductive roller. Transfer methods also similarly include a noncontact corona transfer method and a contact roller transfer method.
In the conductive roller, a conductive rubber material having an electrical resistance of from 1×10
5
to 1×10
11
&OHgr;·cm as volume resistivity is used. Such a conductive rubber material is compounded with a conductive filler such as carbon black in order to achieve the intended conductivity. In the conductive rubber material thus obtained, however, its electrical resistance is influenced by changes in the applied voltage, and hence an applied-voltage control unit must be provided when used as a charging member. Also, such a conductive rubber material may have non-uniform resistance value depending on how the conductive filler stands dispersed in the rubber material, and it has been difficult to obtain rubber materials having stable electrical resistance.
As a means for solving such a problem, a method is known in which a conductive rubber which is a polymer having a low electrical resistance is used for a rubber component used as a charging member to attain a stated electrical resistance. The conductivity of such a conductive rubber material does not rely on a conductive filler, such as carbon black. Hence, it has a small variation in electrical resistance depending on material lots or a small dependence on the applied voltage, and is a material, which is very easy to handle. It, however, has a disadvantage that it has a great difference in electrical resistance between a low-temperature, low-humidity environment and a high-temperature, high-humidity environment, in other words, a high environmental dependence.
Because of an advantage of a relatively small variation of electrical resistance, conductive rubbers, such as an acrylonitrile butadiene rubber and an epichlorohydrin rubber are used as materials for conductive rollers. Of these materials, the acrylonitrile butadiene rubber has a low resistivity of from 1×10
9
to 10
10
&OHgr;·cm and is inexpensive. Accordingly, it is in wide use as a material for conductive rollers, in particular, as a material for transfer rollers.
However, for reasons of making machinery compact and achieving cost reduction, power sources for applying electric charges to transfer rollers are also made compact, and have come to be of a type to which a great voltage cannot be applied. Accordingly, the rubber materials are also demanded to be those having a volume resistivity of from 1×10
8
&OHgr;·cm to 1×10
9
&OHgr;·cm, which is lower by about one figure than ever, and also those having a low environmental dependence.
An acrylonitrile butadiene rubber is commonly used in an acrylonitrile content ranging between 15% by weight and 50% by weight. However, in the case when the acrylonitrile content is in such a proportion, the electrical resistance is not so greatly variable, and the electrical resistance can only be regulated by a small amount.
As a method of regulating its electrical resistance, carbon black may be added. The addition of carbon black, however, is not preferable because it tends to cause a variation in electrical resistance.
Methods are also proposed in which an acrylonitrile butadiene rubber is blended with an epichlorohydrin rubber, which is also conductive-rubber. The epichlorohydrin rubber includes a homopolymer of epichiorohydrin and its copolymer with ethylene oxide. The product obtained by copolymerization with ethylene oxide has a lower electrical resistance because ethylene oxide is in a higher content in its composition. In proposals using a blend with an epichiorohydrin rubber, a blend proportion of the epichlorohydrin rubber is 25 parts or more based on 100 parts of the total weight, which is so high as to result in a great environmental dependence (Japanese Patent Application Laid-Open No. 8-292640) or, since a blend having a low ethylene oxide content of 40 mol % or less, i.e., one having a high electrical resistance is used, the electrical resistance can be regulated to be in a narrow range (Japanese Patent Application Laid-Open No. 11-65269), either of which is not preferable in the sense that the electrical resistance should be regulated to be at a low-resistance side, which is lower by about one figure.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a conductive rubber roller which can solve the above problems, having a low environment dependence of electrical resistance and a small scattering of electrical resistance.
To achieve the above object, the present invention provides a conductive rubber roller comprising a conductive support and a rubber layer;
the rubber layer comprising a component (A), an epichlorohydrin rubber containing 40 mol % or more of ethylene oxide and a component (B), an acrylonitrile butadiene rubber component having an acrylonitrile content of 20% by weight or less.
the component (A) being in a proportion of 5 or more to less than 25 in weight ratio, based on the total weight of the components (A) and (B).
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have taken note of the fact that the electrical resistance of an epichlorohydrin rubber changes depending on an ethylene oxide content in the epichlorohydrin rubber and the electrical resistance decreases with an increase in the ethylene oxide content. They have considered that, an acrylonitrile butadiene rubber having a small environmental dependence should be blended with a small quantity of an epichlorohydrin rubber, in particular, one having a large ethylene oxide content, i.e., one having a low electrical resistance, whereby the resultant blend could be made to have a low electrical resistance while keeping small the environmental dependence of acrylonitrile butadiene rubber.
The conductive rubber roller of the present invention is described below in detail.
The conductive rubber roller of the present invention consists basically of a conductive support and a rubber layer.
As the conductive support used, any support may be used as long as it is electrically conductive and can withstand the load applied to the roller, such as rotation. Commonly used is a roller comprised of a metal such as iron or stainless steel, or any of these which has been plated.
Rubber components used in the present invention are an acrylonitrile butadiene rubber and an epichlorohydrin rubber. The acrylonitrile butadiene rubber and the epichlorohydrin rubber are highly compatible with each other, and become uniformly mixed when blended. As a result, the blended mix can be a rubber material having a small variation in electrical resistance.
The component (B), acrylonitrile butadiene rubber, is one having an acrylonitrile content of 20% by weight or less, and may preferably be one having an acrylonitrile content of 18% or less, and preferably 10% by weight or more as the lower limit. If the acrylonitrile butadiene rubber has an acrylonitrile content more than 20% by weight, it may have a high environmental dependence. If on the other hand the acrylonitrile butadiene rubber has an acrylonitri
Hashimoto Masayuki
Okuda Mitsuru
Takahashi Masayuki
Canon Kasei Kabushiki Kaisha
Cuda Rosenbaum I
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