Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
1999-09-29
2001-04-10
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C430S132000, C430S058050
Reexamination Certificate
active
06214514
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to a process for fabricating electrophotographic imaging members, and, more specifically, to the formation of a charge transport layer
Typical electrophotographic imaging members comprise a photoconductive layer comprising a single layer or composite layers. One type of composite photoconductive layer used in xerography is illustrated, for example, in U.S. Pat. No. 4,265,990 which describes a photosensitive member having at least two electrically operative layers. The disclosure of this patent is incorporated herein in its entirety. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, where the two electrically operative layers are supported on a conductive layer the photogenerating layer is sandwiched between the contiguous charge transport layer and the supporting conductive layer, the outer surface of the charge transport layer is normally charged with a uniform electrostatic charge. The photosensitive member is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in illuminated areas of the photosensitive member while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electrostatic toner particles on the surface of the photosensitive member. The resulting visible toner image can be transferred to a suitable receiving material such as paper. This imaging process may be repeated many times with reusable photosensitive members.
As more advanced, complex, highly sophisticated, electrophotographic copiers, duplicators and printers were developed, greater demands were placed on the photoreceptor to meet stringent requirements for the production of high quality images. For example, the numerous layers found in many modern photoconductive imaging members must be uniform, free of defects, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a drum or belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a charge blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. This photoreceptor may also comprise additional layers such as an overcoating layer. Although excellent toner images may be obtained with multilayered photoreceptors, it has been found that the numerous layers limit the versatility of the multilayered photoreceptor. For example, when a thick, e.g., 29 micrometers, layer of a charge transport layer is formed in a single pass a raindrop pattern to form on the exposed imaging surface of the final dried photoreceptor. This raindrop phenomenon is a print defect caused by the coating thickness variations (high frequency) in photoreceptors having a relatively thick (e.g., 29 micrometers) charge transport layer. More specifically, the expression “raindrop”, as employed herein, is defined as a high frequency variation in the transport layer thickness. The period of variation is in the 0.1 cm to 2.5 cm range. The amplitude of variation is between 0.5 micrometer and 1.5 micrometers. The variation can also be defined on a per unit area basis. Raindrop can occur with the transport layer thickness variation is in the range of 0.5 to 1.5 microns per sq. cm. The morphological structure of raindrop is variable depends on where and how the device is coated. The structure can be periodic or random, symmetrical or oriented.
INFORMATION DISCLOSURE STATEMENT
U.S. Pat. No. 5,830,614 to Pai et al., issued Nov. 3, 1998—A charge transport dual layer is disclosed for use in a multilayer photoreceptor comprising a support layer, a charge generating layer and a charge transport dual layer including a first transport layer containing a charge-transporting polymer, and a second transport layer containing a charge-transporting polymer having a lower weight percent of charge transporting segments than the charge-transporting polymer in the first transport layer. This structure has greater resistance to corona effects and provides for a longer service life. The charge-transporting polymers preferably comprise polymeric arylamine compounds
While the above mentioned electrophotographic imaging members may be suitable for their intended purposes, there continues to be a need for improved imaging members, particularly for methods for fabricating multilayered electrophotographic imaging members in flexible belts
CROSS REFERENCE TO COPENDING APPLICATIONS
U.S. application Ser. No. 09/408,239 now U.S. Pat. No. 6,048,658 entitled “Process For Fabricating Electrophotographic Imaging Member” filed concurrently herewith in the names of K. J. Evans et al. now U.S. Pat. No. 6,048,658, issued Apr. 11, 2000. A process for fabricating electrophotographic imaging members is disclosed comprising providing a substrate with an exposed surface, simultaneously applying, from a coating die, two wet coatings to the surface, the wet coatings comprising a first coating in contact with the surface, the first coating comprising photoconductive particles dispersed in a solution of a film forming binder and a predetermined amount of solvent for the binder and a second coating in contact with the first coating, the second coating comprising a solution of a charge transporting small molecule and a film forming binder dissolved in a predetermined amount of solvent for the transport molecule and the binder, drying the two wet coatings to remove substantially all of the solvents to form a dry first coating having a thickness between about 0.1 micrometer and about 10 micrometers and dry second coating having a thickness between about 4 micrometers and 20 micrometers, applying at least a third coating in contact with the second coating, the third coating comprising a solution containing having a charge transporting small molecule, film forming binder and solvent substantially identical to charge transporting small molecule, film forming binder and solvent in the second coating, and drying the third coating to from a dry third coating having a thickness between about 13 micrometers and 20 micrometers.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved process for fabricating an electrophotographic imaging member.
It is another object of the present invention to provide an improved process for achieving coating uniformity in a charge transport layer.
It is still another object of the present invention to provide an improved process for eliminating raindrop defects in charge transport layers.
It is yet another object of the present invention to provide an improved process for reducing curl in electrophotographic imaging members.
The foregoing objects and others are accomplished in accordance with this invention by providing a process for fabricating electrophotographic imaging members comprising
providing an imaging member comprising a substrate coated with a charge generating layer having an exposed surface,
applying a first solution comprising a charge transporting small molecule and film forming binder to the exposed surface to form a first continuous charge transporting layer having a thickness greater than about 13 micrometers and less than about 20 micrometers after drying, and
applying at least a second solution having a composition substantially identical to the first solution to the exposed surface of the first charge transporting layer to form at least a second continuous charge transporting layer having a thickness greater than about 13 micrometers and less than about 20 micrometers.
In order to achieve the uniformity required to eliminate the raindrop defect, the first and second layer thicknesses and the coating solution must meet certain r
DeHollander David A.
Evans Kent J.
Roetker Michael S.
Haack John L.
Kondo Peter H.
Rodee Christopher
Xerox Corporation
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