Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-05-31
2001-07-24
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S096000
Reexamination Certificate
active
06265124
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed toward photoconductors and compositions used to form photoconductors. More particularly, the invention is related to charge generation compositions and charge generation layers comprising a polymeric hindered phenol selected from the group consisting of butylated reaction products of p-cresol and dicyclopentadiene. The invention is also directed towards methods of improving electrical characteristics and fatigue properties of photoconductors.
BACKGROUND OF THE INVENTION
In electrophotography, a latent image is created on the surface of an imaging member such as a photoconducting material by first uniformly charging the surface and then selectively exposing areas of the surface to light. A difference in electrostatic charge density is created between those areas on the surface which are exposed to light and those areas on the surface which are not exposed to light. The latent electrostatic image is developed into a visible image by electrostatic toners. The toners are selectively attracted to either the exposed or unexposed portions of the photoconductor surface, depending on the relative electrostatic charges on the photoconductor surface, the development electrode and the toner.
Typically, a dual layer electrophotographic photoconductor comprises a substrate such as a metal ground plane member on which a charge generation layer (CGL) and a charge transport layer (CTL) are coated. The charge transport layer contains a charge transport material which comprises a hole transport material or an electron transport material. For simplicity, the following discussions herein are directed to use of a charge transport layer which comprises a hole transport material as the charge transport compound. One skilled in the art will appreciate that if the charge transport layer contains an electron transport material rather than a hole transport material, the charge placed on a photoconductor surface will be opposite that described herein.
When the charge transport layer containing a hole transport material is formed on the charge generation layer, a negative charge is typically placed on the photoconductor surface. Conversely, when the charge generation layer is formed on the charge transport layer, a positive charge is typically placed on the photoconductor surface Conventionally, the charge generation layer comprises the charge generation compound or molecule, for example a squaraine pigment, a phthalocyanine, or an azo compound, alone or in combination with a binder. The charge transport layer typically comprises a polymeric binder containing the charge transport compound or molecule. The charge generation compounds within the charge generation layer are sensitive to image-forming radiation and photogenerate electron-hole pairs therein as a result of absorbing such radiation. The charge transport layer is usually non-absorbent of the image-forming radiation and the charge transport compounds serve to transport holes to the surface of a negatively charged photoconductor. Photoconductors of this type are disclosed in the Adley et al U.S. Pat. No. 5,130,215 and the Balthis et al U.S. Pat. No. 5,545,499.
Cottman, U.S. Pat. No. 4,446,264, discloses compounds which are prepared by reacting maleic anhydride, maleic acid or their esters with thiols, and which exhibit a synergistic effect when combined with a phenolic antioxidant for the stabilization of polymers, rubbers and lubricants. Cottman discloses suitable phenolic antioxidants include the butylated reaction product of p-cresol and dicyclopentadiene.
Nguyen, U.S. Pat. No. 5,320,923, discloses an organic positive-charging photoconductor for laser printers having a conductive substrate, a hydroxy-containing binder, a phthlaocyanine pigment and a reactive stabilizer containing silicon. Nguyen teaches the binder may comprise phenolic resins or phenoxy resins.
Levin, et al., U.S. Pat. No. 5,972,549, disclose photoconductors comprising a substrate, and a charge transport layer comprising binder and a charge transport compound comprising at least one of the hydrazone, aromatic amine, or substitute aromatic amine, and a charge generation layer comprising binder, phthalocyanine charge generating compound, and a hindered hydroxylated aromatic compound. Levin, et al. teach that the hindered hydroxylated aromatic compound reduces electrical fatigue on cycling without adversely affecting the electrical performance of the photoconductor.
Inorganic photoconductive materials such as selenium, zinc oxide, and cadmium sulfide tend to show low loss of charge in the dark, however, photoconductors comprising such materials are often difficult and/or expensive to produce. Additionally, environmental disposal issues often arise when inorganic compounds are utilized. Organic photoconductive materials are generally less expensive and are less likely to cause environmental concerns. However, photoconductors comprising organic charge generation molecules may exhibit blurring of images caused by deterioration due to ozone and/or nitrogen oxides generated by corona discharge. Thus, it is desirable for photoconductors to comprise antioxidants which may mitigate damages caused from gases such as ozone or nitrogen oxides. Additionally, it is desirable to develop methods of improving the electrical properties and the fatigue characteristics of photoconductors.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide improved photoconductors and charge generation layer compositions.
It is another object of this invention to provide photoconductors having improved electrical characteristics and fatigue properties.
It is another object of this invention to provide charge generation layer compositions comprising antioxidants.
It is another object of this invention to provide binder blends which form stable dispersions.
It is yet another object of this invention to provide photoconductors which exhibit increased sensitivity without requiring an increase in the amount of charge generation molecules.
In accordance with one aspect of the invention there are provided photoconductors comprising a substrate and a charge generation layer comprising a charge generation molecule and a first binder selected from the group consisting of butylated reaction products of p-cresol and dicyclopentadiene.
In accordance with another aspect of the invention there are provided methods of improving an electrical characteristic of a photoconductor, comprising the step of forming a photoconductor comprising a substrate and a charge generation layer comprising a binder blend. The binder blend comprises a first binder selected from the group consisting of butylated reaction products of p-cresol and dicyclopentadiene and a second binder.
In accordance with yet another aspect of the invention there are provided methods of improving fatigue properties of a photoconductor comprising an organic charge generation molecule, the method comprising the step of forming a photoconductor comprising a substrate and a charge generation layer comprising an organic charge generation molecule and a polymeric hindered phenol selected from the group consisting of butylated reaction products of p-cresol and dicyclopentadiene.
In accordance with one aspect of the invention there are provided charge generation compositions comprising charge generation molecule, solvent and binder blend. The binder blend comprises a polymeric hindered phenol selected from the group consisting of butylated reaction products of p-cresol and dicyclopentadiene.
In accordance with another aspect of the invention there are provided photoconductors comprising a charge generation layer comprising a polymeric hindered phenol selected from the group consisting of butylated reaction products of p-cresol and dicyclopentadiene, wherein the photoconductor exhibits a voltage of no greater than about 200 volts 25 milliseconds after exposure to laser energy of 0.30 &mgr;J/cm
2
.
Additional embodiments and advantages of the photoconductors, charge generation layers, charge gener
Bellino Mark Thomas
Luo Weimei
Brady John A.
Goodrow John
Lexmark International Inc.
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