Patent Application
20080070136
An electrophotographic photoreceptor was fabricated in the following manner. A coating solution for an undercoat layer comprising 100 parts of a zirconium compound (ORGATICS™ ZC540), 10 parts of a silane compound (A110™, manufactured by Nippon Unicar Co., Ltd), 400 parts of an isopropanol solution, and 200 parts of butanol was prepared. The coating solution was applied onto a cylindrical aluminum (Al) substrate subjected to a honing treatment by dip coating, and dried by heating at 150° C. for 10 minutes to form an undercoat layer having a film thickness of 0.1 micrometer.
A 0.5 micron thick charge generating layer was subsequently dip coated on top of the undercoat layer from a dispersion of Type V hydroxygallium phthalocyanine (12 parts), alkylhydroxy gallium phthalocyanine (3 parts), and a vinyl chloride/vinyl acetate copolymer, VMCH™ (Mn=27,000, about 86 weight percent of vinyl chloride, about 13 weight percent of vinyl acetate, and about 1 weight percent of maleic acid), available from Dow Chemical (10 parts), in 475 parts of n-butylacetate.
Subsequently, a 20 μm thick charge transport layer (CTL) was dip coated on top of the charge generating layer from a solution of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (82.3 parts), 2.1 parts of 2,6-di-tert-butyl-4-methylphenol (BHT), available from Aldrich, and a polycarbonate, PCZ-400, poly(4,4′-dihydroxy-diphenyl-1-1-cyclohexane), Mw=40,000, available from Mitsubishi Gas Chemical Company, Ltd. (123.5 parts), in a mixture of 546 parts of tetrahydrofuran (THF) and 234 parts of monochlorobenzene. The CTL was dried at 115° C. for 60 minutes.
An overcoat formulation was prepared as follows: a mixture of a resole-type phenol-formaldehyde resin (5.04 parts), a phenolic charge transport component of N,N′-bis(3-hydroxyphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (3 parts), and a catalyst of p-toluenesulfonic acid pyridine complex (0.3 part) was dissolved in a solvent of 1-methoxy-2-propanol (5.4 parts). After filtering with a 0.45 μm PTFE filter, the solution was applied onto the photoreceptor surface, and more specifically, onto the charge transport layer, using a cup coating technique, followed by thermal curing at 150° C. for 35 minutes to form an overcoat layer having a film thickness of 3 μm. The resulted overcoat resin layer contained about 30 to about 35 weight percent of the charge transport component, and the remainder about 65 to about 70 weight percent of resin.
A Comparative Example photoreceptor or photoconductor was prepared by repeating the above process except that the overcoat layer was omitted.
The electrical performance characteristics of the above prepared photoreceptors, such as electrophotographic sensitivity and short term cycling stability, were tested in a scanner. The scanner was known in the industry and equipped with means to rotate the photoconductor drum while it was electrically charged and discharged. The charge on the photoconductor sample was monitored by electrostatic probes placed at precise positions around the circumference of the photoconductor or photoreceptor. The photoreceptor devices were charged to a negative potential of 500 volts. As the devices rotated, the initial charging potentials were measured by voltage probe 1. The photoconductor samples were then exposed to monochromatic radiation of known intensity, and the surface potential measured by voltage probes 2 and 3. Finally, the samples were exposed to an erase lamp of appropriate intensity and wavelength, and any residual potential was measured by voltage probe 4. The process was repeated under the control of the scanner's computer, and the data was stored in the computer. The PIDC (photoinduced discharge curve) was obtained by plotting the potentials at voltage probes 2 and 3 as a function of the light energy. The photoreceptor having the overcoat layer showed comparable PIDC characteristics as the control or Comparative Example device.
The electrical cycling performance of the photoreceptor was performed using an in house fixture similar to a xerographic system. The photoreceptor device with the overcoat showed stable cycling of over 170,000 cycles in a humid environment (28° C., 80 percent RH).
The wear resistance for the above photoconductors was measured using an in house testing fixture comprising a BCR (bias-charging roller) charging unit, an exposure unit, a toner developer unit, and a cleaning unit. The photoreceptors were set to rotate at about 88 RPM for 50,000 cycles. The thickness of the photoreceptor was measured at the beginning and at the end of the testing. The wear rate was estimated based on the thickness loss expressed in nanometers per kilocycle. The above photoreceptor with the overcoat offered a wear rate of about 21 nanometers/kc, as compared to the higher wear rate of about 85 nanometers/kc for the control.
The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.
