Roll or roller – Concentric layered annulus – Specific composition
Reexamination Certificate
2000-03-27
2001-09-04
Hughes, S. Thomas (Department: 3726)
Roll or roller
Concentric layered annulus
Specific composition
C399S176000
Reexamination Certificate
active
06283904
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a conductive roll, such as a charge roll. This invention is suitable for use in, for example, a copying machine, or printer in which an electrophotographic process is employed.
2. Description of the Related Art
There is known a conductive roll having, for example, a conductive layer of an elastic material, a resistance adjusting layer and a protective layer which are formed on the outer periphery of a shaft in the order mentioned. The conductive layer is generally intended for, for example, imparting electric conductivity to the roll, enabling the roll to make intimate contact with a photosensitive drum and preventing any resonance noise from being made between the roll and the photosensitive drum upon application of an AC voltage. The resistance adjusting layer is generally intended for, for example, adjusting the electric resistance of the whole roll and improving its resistance to leak. The protective layer is generally intended for, for example, preventing the adherence of any toner to the roll surface and the contamination of the photosensitive drum by bleeding or blooming from the inside of the roll. An electron conductive agent, such as carbon black, or an ion conductive agent, such as a conjugated system polymer, has so far properly been employed, if necessary, in the resistance adjusting layer for imparting electric conductivity to it, or adjusting its electric resistance.
SUMMARY OF THE INVENTION
The electric resistance which is determined by an ion conductive agent depends on its electron traverse speed. The electron traverse speed is high at a high temperature and a high humidity (while bringing about a low resistance), and low at a low temperature and a low humidity (while bringing about a high resistance). It has, therefore, been a drawback of a resistance adjusting layer containing an ion conductive agent that its electric resistance varies greatly according to its environment, thereby causing a variation in the density of an image produced.
On the other hand, it has been a drawback of a resistance adjusting layer containing an electron conductive agent that its electric resistance depends on its working history, or the conditions of its extrusion molding, such as the extruding temperature, thereby bringing about an image density lacking stability.
In order to solve these problems, the present inventors have paid attention to a number of points as stated below. An electron conductive agent, such as carbon black, has an enlarged or reduced distance between its particles according to an increase or decrease in volume of its matrix which depends on temperature. Therefore, it tends to show a high electric resistance at a high temperature and a high humidity and a low electric resistance at a low temperature and a low humidity, as opposed to an ion conductive agent.
It has, however, been found that the dependence of a resistance adjusting layer upon its environment as stated above can be controlled effectively if it contains both an electron conductive agent and an ion conductive agent in appropriate proportions. It has also been found that, if such is the case, the dependence of its electric resistance upon its working history can be effectively controlled, too.
It has further been found that the incorporation of insulating particles conforming to certain conditions in a resistance adjusting layer makes it possible to prevent the cohesion of its electron conductive agent and control the dependence of its electric resistance upon its working history still more effectively. It has also been found that the incorporation of insulating particles makes it possible to prevent any increase or enlargement of picture defects (e.g. due to defects of a drum in a copying machine) and give a greatly improved surface to the resistance adjusting layer.
Thus, this invention resides in a conductive roll comprising a conductive layer of an elastic material, a resistance adjusting layer and a protective layer which are formed on the outer periphery of a shaft in the order mentioned, wherein the resistance adjusting layer is formed from a composition containing 10 to 150 parts by weight of an electron conductive agent, not more than two parts by weight of an ion conductive agent and 20 to 80 parts by weight of an insulating filler, relative to 100 parts by weight of nitrile rubber, or nitrile rubber hydride as a base material.
According to this invention, the resistance adjusting layer contains both an electron conductive agent and an ion conductive agent in optimum proportions. Therefore, the resistance adjusting layer shows a stable electric resistance in an environment having from a low temperature of, say, 10° C. and a low humidity of, say, 10% to a high temperature of, say, 30° C. and a high humidity of, say, 90%. Thus, the dependence of its electric resistance upon its environment can be greatly lowered. Moreover, the resistance adjusting layer has an effectively controlled dependence of its electric resistance upon its working history.
Any proportion of the electron conductive agent below 10 parts by weight is undesirable, since no sufficient effect can be obtained from its incorporation. Any proportion thereof exceeding 150 parts by weight is also undesirable, since the resistance adjusting layer becomes less easy to process and the electron conductive agent becomes lower in dispersibility. Any proportion of the ion conductive agent exceeding two parts by weight is also undesirable, since it separates in an environment having a high temperature and a high humidity.
According to this invention, the resistance adjusting layer contains also an insulating filler in a certain range of parts by weight. It makes the cohesion of the electron conductive agent, such as carbon black, less likely to occur, and makes it possible to prevent effectively any drop in electric resistance of the resistance adjusting layer. Therefore, it is possible to prevent effectively any trouble caused by electric shortcircuiting, such as enlarged picture defects, when the photosensitive drum has a chipped or broken portion. Moreover, the filler gives a smooth surface to the resistance adjusting layer, and thereby makes it possible to prevent the contamination of the roll surface.
Referring to the proportion of the insulating filler, its range which is effective for preventing the cohesion of the electron conductive agent does not necessarily coincide with its range which is effective for giving a smooth surface to the resistance adjusting layer. Its proportion as employed for defining this invention is, therefore, defined by a broader range covering from the lowermost proportion in one of the two ranges to the uppermost proportion of the other range, thus including a proportion which is effective for at least one of those two purposes.
The above and other advantages of the invention will become more apparent in the following description and the accompanying drawings.
REFERENCES:
patent: 5312662 (1994-05-01), Ohta et al.
patent: 5567494 (1996-10-01), Ageishi et al.
patent: 5604031 (1997-02-01), Yamamoto et al.
patent: 5822658 (1998-10-01), Tanaka et al.
patent: 6190295 (2001-02-01), Kawano et al.
patent: 4426627 A1 (1995-02-01), None
patent: 19709627 A1 (1998-09-01), None
patent: 7-134472 (1995-05-01), None
patent: 8-73660 (1996-03-01), None
Imamura Wataru
Itoh Masahiko
Itoh Tetsuya
Butler Marc W.
Hughes S. Thomas
Jacobson & Holman PLLC
Tokai Rubber Industries Ltd.
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