Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
1999-09-10
2001-05-15
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C427S374100, C264S171250, C264S237000
Reexamination Certificate
active
06232028
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photoconductors generally and more particularly to organic photoconductors and a treatment therefor.
BACKGROUND OF THE INVENTION
Various types of organic photoconductors are known. Most organic photoconductors are susceptible to attack by organic solvents of the type used in liquid toner electrophotography and are therefore unsuitable for such applications. These photoconductors include those which dissolve in the solvents and others which are caused to crack as the result of exposure thereto when they are under stress, especially when under tension.
It is known in the art to provide protective coatings for organic photoconductors. Examples of these coatings are given in U.S. Pat. Nos. 4,891,290 and 4,894,304.
U.S. Pat. No. 4,497,566 describes a system in which an organic photoconductor is heated to relieve tension in the photoconductor and then cooled immediately prior to its use in an imaging system. In the method described in this patent the photoconductor as a whole is in tension during the entire process with the tension being taken up by the backing layer after the heat treatment. This solution is impractical since it requires that the heat treatment be performed in situ as part of the imaging process itself.
U.S. Pat. No. 5,376,491, the disclosure of which is incorporated herein by reference, describes two methods of treatment for organic photoconductors which are susceptible to cracking used with liquid toner under mechanical stress. One of these methods involves the chemical treatment of the photoconductor to soften the photoconductive layer thereof and a second method which induces a compressive stress in the photoconductive layer. In use, the photoconductive layer, when the photoconductor is wrapped about a drum, remains in compressing and does not crack.
The other methodology for heat treatment of the photoconductor is to subject the photoconductor to tension, heat treat the photoconductor such that stress is relieved in the photoconductive layer, allowing the photoconductor to cool and then removing the stress, prior to utilizing the photoconductor in an imaging process.
R. C. U. YU, “Heat Shrinkage of Photoreceptor Belt onto a Drum” Xerox Disclosure Journal, Vol. 20, No. 2, Mar. 1, 1995-Apr. 30, 1995, describes a system whereby a photoreceptor is heat shrunk onto a drum, for later use.
SUMMARY OF THE INVENTION
The present invention provides an improved photoconductor which is resistant to cracking in a stressed environment wherein organic solvents of the type used in liquid toner electrophotography are present.
In the present invention a photoconductor comprising a base layer and a photoconductive layer is formed into a curved configuration with the photoconductive layer facing outward. In this position, without applying any stress on the photoconductor, the photoconductive layer is subjected to a heat treatment which relives the stress in the photoconductor. After relieving the stress, the photoconductor is either cooled or allowed to cool while it is still in the curved position to a temperature below a stress relief temperature thereof.
As a result of this treatment, when the photoconductor is flattened, or when it is bent with a radius of curvature larger than that at which the photoconductive layer was stress relieved and cooled, there will be a built-in compression in the layer which will enable it to better resist cracking.
In a preferred embodiment of the invention, the base layer is not stress relieved, i.e., the temperature to which it is heated in heat treatment is below its stress relief temperature. Preferably, the radius of the bend in the photoconductor at which the stress relief and, more importantly, the cooling takes place is smaller than the radius of a drum on which it is mounted.
There is thus provided, in accordance with a preferred embodiment of the invention a method of processing a photoconductor comprising:
providing a photoconductor, preferably an organic photoconductor, having a base layer and a photoconductive layer;
bending the photoconductor with the photoconductive layer facing outward without subjecting the photoconductor to substantial external stress other than by virtue of said bending;
heat treating the bent photoconductor, preferably to a temperature above a stress relief temperature of the photoconductive layer such that stress in the photoconductive layer is relieved; and
cooling the bent photoconductor.
There is further provided, in accordance with a preferred embodiment of the invention, a method of processing a photoconductor comprising:
providing a long photoconductor sheet having a base layer and a photoconductive layer;
serially supplying contiguous portions of the photoconductor sheet in a bent configuration with the photoconductive layer facing outward at a heating station at which the bent photoconductor is heat treated; and
cooling the bent photoconductor.
In one preferred embodiment of the invention the photoconductor is heated to a temperature at which stress in the base layer is not relieved. Alternatively the photoconductor is heated to a temperature at which stress in the base layer is relieved.
In a preferred embodiment of the invention cooling the bent photoconductor comprises allowing the bent photoconductive layer to cool by convection. In one preferred embodiment of the invention, cooling the photoconductive layer comprises contacting the photoconductive layer with a cooling fluid which may comprise a gas.
In a preferred embodiment of the invention, the photoconductive layer is allowed to cool to a temperature below a stress relief temperature of the photoconductive layer in the bent condition. Preferably, the stress relief temperature of the photoconductive layer is the glass transition temperature of a charge transport layer comprised therein and wherein the photoconductive layer is heated above the glass transition temperature in the bent condition and then allowed to cool to below that temperature while it is still bent.
Preferably, the photoconductive layer comprises a charge transport layer having a glass transition temperature.
In a preferred embodiment of the invention, the photoconductor is heated by contacting it with hot water. In an alternative preferred embodiment of the invention the photoconductor is heated by contacting it with steam. Preferably, the photoconductive layer is heated to a temperature of over 80° C., more preferably above 90° C. and below 95° C. most preferably about 92° C. Alternatively it can be heated to a temperature below 80° C. or above 95° C. It should be understood that for higher temperatures, the amount of time during which the photoconductor must be treated for crack avoidance is reduced. In a particular example, eight minutes of treatment are required at 80° C. and only one minute is required at 90° C.
Preferably, the photoconductive layer is allowed to cool to a temperature of 40° C. prior to removing the bend therefrom.
Preferably the bend has a radius substantially smaller than that of the drum on which the photoconductor is to be mounted. Preferably the radius is above about 5 mm, more preferably between about 7-30 mm and most preferably about 7 or 8 mm to 11 or 12 mm.
In a preferred embodiment of the invention the photoconductor is in the form of a continuous sheet which is first fed to a heating station, in a curved configuration, at which station it is heated and then fed to a cooling station, at which cooling station it is cooled, still in a curved configuration. In a preferred embodiment of the invention the photoconductor is unbacked by any support at the heating and cooling stations.
There is further provided, in accordance with a preferred embodiment of the invention, an organic photoconductor treated in accordance with the above treatment method.
There is further provided, in accordance with a preferred embodiment of the invention, a method of imaging comprising: placing an organic photoconductor, treated in accordance with the above treatment method, on a drum; forming an electrostatic image o
Landa Benzion
Rosen Yosef Yossi
Tzori Gilad
Chapman Mark
Fenster & Company Patent Attorneys Ltd.
Indigo N.V.
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