Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
1998-09-18
2002-06-25
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S069000, C430S059100, C428S472200
Reexamination Certificate
active
06410197
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to methods for treating a conductive aluminum substrate and to aluminum substrates treated according to the present methods. The present invention is also directed to methods of forming photoconductors wherein the photoconductor aluminum substrate is treated in accordance with the aforementioned methods, and to photoconductors formed by such methods.
BACKGROUND OF THE INVENTION
Typically, photoconductors comprise a conductive substrate which is conventionally formed of aluminum. It is advantageous to anodize the surface of the conductive aluminum substrate in order to improve the toughness and handling ability of the substrate and to suppress specular reflections such as Moire patterns. In a typical anodization process, the raw aluminum substrate or core is first cleaned and deoxidized, and then a porous alumina/hydrated aluminum oxide layer is formed by electrolytic oxidation of the aluminum in an electrochemical cell. The alumina layer is highly porous as it generally comprises hexagonal columns separated by deep pores.
The porous alumina layer is usually sealed, i.e., the pores of the alumina are filled or closed, in order to improve the electrophotographic properties of the anodized substrate. Several different sealing processes are commonly used. One sealing process, referred to as the water sealing process, involves immersion of the porous alumina layer in boiling water to convert the alumina to a hydrated alumina phase. This conversion is accompanied by a volume increase which seals or plugs the pores. In another sealing process, a metallic salt, for example a salt of a heavy metal such as cobalt or nickel, is contacted with the alumina layer. The metal deposits, typically as a hydroxide, within the pores of the alumina layer to provide a sealing effect. However, the use of heavy metals such as cobalt or nickel is disadvantageous in that high waste disposal costs are incurred. Additionally, alumina surface layers sealed by either the water sealing or metal salt sealing processes exhibit less than optimal adhesion to overlying layers when the aluminum substrates are employed in photoconductors. Poor adhesion of photoconductive layers to an aluminum substrate can result in catastrophic delamination during printer operation and therefore an undesirably shortened useful life for the photoconductor.
In the past, barrier layers and/or sublayers have been employed between a photoconductor substrate and an adjacent charge generation layer or charge transport layer. However, the use of such layers is disadvantageous in that the barrier or sublayer must be applied by dip coating or another controlled process and therefore significantly increases both the production time and costs for the photoconductor.
Accordingly, a need exists for methods for more easily preparing aluminum substrates, for example for use in photoconductors and for photoconductor substrates, which exhibit improved adhesion to overlying photoconductive layers.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide methods for treating conductive aluminum substrates. It is a more specific object of the present invention to provide methods for treating conductive aluminum substrates which are suitable for use in photoconductors. It is a further object of the invention to provide methods for treating aluminum photoconductor substrates to provide the substrates with good toughness and handling ability while overcoming disadvantages of prior art methods. It is a related object to provide conductive aluminum substrates which exhibit good adhesion to overlying layers when the substrates are employed as photoconductor substrates, while maintaining good performance of the photoconductors.
These and additional objects and advantages are provided by the methods, substrates and photoconductors of the present invention. According to the present invention, the methods for treating a conductive aluminum substrate comprise anodizing a surface of an aluminum substrate to form a porous alumina surface layer, contacting the alumina surface layer with a liquid dispersion or solution of a polymer or at least one polymer-forming component, under conditions sufficient for the polymer to seal pores of the alumina surface layer, and removing excess polymer from the alumina surface layer. Preferably, the excess polymer is removed from the alumina surface layer by rinsing. Optionally, the surface of the treated alumina layer may be dried. The polymer seals the pores of the alumina surface layer to allow good electrophotographic properties when the layer is employed as a photoconductor substrate and allows good adhesion of the substrate to overlying photoconductive layers, for example overlying charge generation layers and/or charge transport layers used to form photoconductors. Additionally, photoconductors which include conductive aluminum substrates treated according to the present methods exhibit good electrical characteristics and print quality and improved durability owing to the good adhesion of the photoconductive layers to the aluminum substrate.
These and additional objects and advantages provided by the methods, substrates and photoconductors of the present invention will be more fully understood in view of the following detailed description.
DETAILED DESCRIPTION
According to the present methods, the surface of a conductive aluminum substrate is anodized to form a porous alumina surface layer. Preferably, the surface is cleaned and deoxidized prior to the anodization. The alumina surface layer is then contacted with a liquid dispersion or solution of a polymer or at least one polymer-forming component under conditions sufficient for polymer to seal pores of the alumina surface layer. Excess polymer is then removed from the alumina surface layer, for example by rinsing the layer before the polymer dries thereon.
The conductive aluminum substrate is described herein as suitable for use as a substrate of a photoconductor. However, it will be apparent to those skilled in the art that the conductive aluminum substrate as disclosed herein may be employed in various other devices and embodiments. Typically, a photoconductor substrate is in the form of a drum, and comprises a thin surface layer of aluminum which functions as an electrical ground plane. The aluminum may be deposited on the drum by any suitable method, including, for example, by vacuum evaporation. Both aluminum and aluminum alloys may be employed. Various aluminum alloys are suitable for preparing photoconductive drum substrates, one example of which comprises the alloy 3003. The aluminum substrate will have a thickness adequate to provide the required mechanical stability for the photoconductor. Typically, drum substrates have a thickness of from about 0.75 mm to about 1 mm, although greater or smaller thicknesses are equally within the scope of this invention.
Processes for anodization of a surface of an aluminum substrate to form a porous alumina surface layer are known in the art and may be employed in the present methods. Preferably, the aluminum is first cleaned and deoxidized before anodization. To anodize the surface of the aluminum layer, the aluminum is subjected to electrolytic oxidation in an electrochemical cell. The electrolyte typically comprises an acidic component, for example an inorganic acid such as sulfuric acid, although many other acids may be employed in place of sulfuric acid in accordance with techniques known in the art. The alumina grows as hexagonal columns separated by deep pores resulting in an alumina layer which is highly porous. The anodization may be conducted to form an alumina layer of any desired thickness. When the aluminum substrate is to be employed as a photoconductor substrate, an alumina surface layer of up to about 10 microns, preferably up to about 5 microns, is preferred. Suitable cell operating conditions, including specific electrolyte composition and concentration, bath temperature, current density and duration, will be apparent t
Bellino Mark Thomas
Neely Jennifer Kaye
Randolph Catherine Mailhe
Srinivasan Kasturi Rangan
Brady John A.
Dote Janis L.
Lexmark International Inc.
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