Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
2000-08-14
2001-01-30
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C430S132000, C427S430100
Reexamination Certificate
active
06180310
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to dip coating and, more specifically, to a process for dip coating drums with a charge transport layer coating composition.
In the art of xerography, a xerographic plate containing a photoconductive insulating layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulator 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 electroscopic marking particles on the surface of the photoconductive insulating layer.
A photoconductive layer for use in xerography may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 in which a photosensitive member having at least two electrically operative layers is described. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer.
Various combinations of materials for charge generating layers and charge transport layers have been investigated. For example, the photosensitive member described in U.S. Pat. No. 4,265,990 utilizes a charge generating layer in contiguous contact with a charge transport layer comprising a polycarbonate resin and one or more of certain aromatic amine compound. Various generating layers comprising photoconductive layers exhibiting the capability of photogeneration of holes and injection of the holes into a charge transport layer have also been investigated. Typical photoconductive materials utilized in the generating layer include amorphous selenium, trigonal selenium, and selenium alloys such as selenium-tellurium, selenium-tellurium-arsenic, selenium-arsenic, and mixtures thereof. The charge generation layer may comprise a homogeneous photoconductive material or particulate photoconductive material dispersed in a binder. Other examples of homogeneous and binder charge generation layer are disclosed in U.S. Pat. No. 4,265,990. Additional examples of binder materials such as poly(hydroxyether) resins are taught in U.S. Pat. No. 4,439,507. The disclosures of the aforesaid U.S. Pat. No. 4,265,990 and U.S. Pat. No. 4,439,507 are incorporated herein in their entirety. Photosensitive members having at least two electrically operative layers as disclosed above in, for example, U.S. Pat. No. 4,265,990 provide excellent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely developed electroscopic marking particles. However, when the charge transport layer is applied by dip coating in extensively recirculated charge transport layer coating compositions, difficulties have been encountered due to the formation of coating non-uniformities such as axial or circumferential streaks appearing in the final charge transport layer. These streaks are undesirable because they may cause variations in the surface energy potential when an electrical charge is applied to the surface of the final charge transport layer which may cause printing defects in the final image, such as variations in light and dark final image print density. Also, stratification or segregation has been observed in the recirculated charge transport layer coating compositions which are believed to cause variations in viscosity control, coating thickness and electrical properties of the charge transport layer.
Variations in charge transport layer coating solution viscosity while coating, sudden and small charge transport layer coating solution flow rate changes, among other mechanisms, cause variations in coating material thickness. This thickness variation can be on any given drum or on different drums (batch-to-batch variations).
Thus, the characteristics of dip coating systems for forming a dip coated charge transport layer exhibit deficiencies which are undesirable for producing photoreceptors for high quality copiers, duplicators, printers, fax machines, multifunctional devices and the like.
INFORMATION DISCLOSURE STATEMENT
U.S. Pat. No. 5,149,612 issued to Langlois et al., on Sep. 22, 1992—Processes and apparatus for fabricating an electrophotographic imaging member in which a web coated with a charge generation layer is coated with a charge transport layer comprising a dopant, the improvement comprising detecting the change in dopant concentration required, determining the amount of highly doped charge transport composition and amount of undoped or lowly doped charge transport composition required to achieve the change in dopant concentration, feeding the determined amounts of highly doped charge transport composition and undoped or lowly doped charge transport composition into a mixing zone, rapidly mixing the amounts of highly doped charge transport composition and undoped or lowly doped charge transport composition to form a uniformly doped charge transport composition, and applying the uniformly doped charge transport composition to the charge generation layer.
U.S. Pat. No. 5,693,372 to Mistrater et al, issued Dec. 2, 1997—A process is disclosed for dip coating drums comprising providing a drum having an outer surface to be coated, an upper end and a lower end, providing at least one coating vessel having a bottom, an open top and a cylindrically shaped vertical interior wall having a diameter greater than the diameter of the drum, flowing liquid coating material from the bottom of the vessel to the top of the vessel, immersing the drum in the flowing liquid coating material while maintaining the axis of the drum in a vertical orientation, maintaining the outer surface of the drum in a concentric relationship with the vertical interior wall of the cylindrical coating vessel while the drum is immersed in the coating material, the outer surface of the drum being radially spaced from the vertical interior wall of the cylindrical coating vessel, maintaining laminar flow motion of the coating material as it passes between the outer surface of the drum and the vertical interior wall of the vessel, maintaining the radial spacing between the outer surface of the drum and the inner surface of the vessel between about 2 millimeters and about 9 millimeters, and withdrawing the drum from the coating vessel.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved coating process which overcomes the above-noted disadvantages.
It is another object of the present invention to provide an improved coating process which rapidly adjusts viscosity properties of a layer dip coating composition to more consistently achieve photoreceptors having high quality layers.
It is still another object of the present invention to provide an improved coating process which permits rapid viscosity adjustments to the charge transport coating composition while the photoreceptor fabrication process is in progress.
It is yet another object of the present invention to provide an improved coating process which prevents the formation of streaks during formation of charge transport layers during dip coating.
It is another object of the present invention to provide an improved coating process which reduces the number of unacceptable dip coated photoreceptor drums having streaked charge transport layers.
It is still another object of the present invention to provide an improved coating process which provides improved charge transfer layer coating thickness uniformity; provides improved coating solution homogeneity, and applied surface charge uniformity.
The foregoing objects and others are accomplished in accordance with this invention by providing a member comprising a process for
Haack John L.
Kondo Peter
Martin Roland
Xerox Corporation
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