Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-05-12
2001-03-27
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S058050, C430S058400, C430S059600, C430S132000, C430S058750
Reexamination Certificate
active
06207334
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to electrophotographic imaging members and, more specifically, to layered photoreceptor structures with improved combination of overcoat layer and charge transport layer and processes for making and using the imaging members.
Electrophotographic imaging members, i.e. photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The it photoconductive layer is an insulator in the dark so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated.
Many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers, is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, 3 to 10 revolutions are required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can require up to 1 million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the micro corona generated by the BCR during charging, damages the photoreceptor, resulting in rapid wear of the imaging surface, e.g., the exposed surface of the charge transport layer. For example wear rates can be as high as about 16&mgr; per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems. One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, e.g. the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, avoidance of perturbation of underlying layers during coating. Although various hole transporting small molecules can be used in overcoating layers, one of the toughest overcoatings discovered comprises cross linked polyamide (e.g. Luckamide) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine. This tough overcoat is described in U.S. Pat. No. 5,368,967, the entire disclosure thereof being incorporated herein by reference.
Durable photoreceptor overcoatings containing cross linked polyamide (e.g. Luckamide) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine (DHTBD) [Luckamide-DHTBD] have been prepared using oxalic acid and trioxane to improve photoreceptor life by at least a factor of 3 to 4. Such improvement in the bias charging roll (BCR) wear resistance involved crosslinking of Luckamide under heat treatment, e.g. 110° C.-120° C. for 30 minutes. However, adhesion of this overcoat to certain photoreceptor charge transport layers, containing certain polycarbonates (e.g., Z-type 300) and charge transport materials [e.g., bis-N,N-(3,4-dimethylphenyl)-N-(4-biphenyl )amine and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine] is greatly reduced under such drying conditions. On the other hand, under drying conditions of below about 110° C., the overcoat adhesion to the charge transport layer was good, but the overcoat had a high rate of wear. Thus, there was an unacceptably small drying conditions window for is the overcoat to achieve the targets of both adhesion and wear rate. Another shortcoming of the prior art is the very low charge carrier mobilities in the overcoat. If the charge carrier mobility is low, the charge carriers (created during the exposure step) that have transited through the transport layer might still be in transit in the overcoat by the time the exposed region of the photoreceptor arrives at the development subsystem. This results in higher Photoinduced discharge Characteristic (PIDC) tail voltages. PIDC is the plot of the potential versus the exposure. PIDC tail is the voltage remaining on the photoreceptor at higher exposure levels. Maximum discharge is observed if the photogenerated carriers (created during the exposure step) transit the transport layer and the overcoat layer. To the extent the carriers are still in transit, lower discharge results for a given exposure. Therefore, in order to achieve maximum discharge with lower mobility material in the overcoat, the overcoat thickness has to be small. Small thickness limits the wear life of the overcoating. In order to increase life, it is necessary to reduce wear rates and increase the overcoat thickness. Thicker overcoats require higher mobilities in order to accomplish maximum discharge for a given exposure.
INFORMATION DISCLOSURE STATEMENT
U.S. Pat. No. 5,702,854 to Schank et al., issued Dec. 30, 1998—An electrophotographic imaging member is disclosed including a supporting substrate coated with at least a charge generating layer, a charge transport layer and an overcoating layer, said overcoating layer comprising a dihydroxy arylamine dissolved or molecularly dispersed in a crosslinked polyamide matrix. The overcoating layer is formed by crosslinking a crosslinkable coating composition including a polyamide containing methoxy methyl groups attached to amide nitrogen atoms, a crosslinking catalyst and a dihydroxy amine, and heating the coating to crosslink the polyamide. The electrophotographic imaging member may be imaged in a process involving uniformly charging the imaging member, exposing the imaging member with activating radiation in image configuration to form an electrostatic latent image, developing the latent image with toner particles to form a toner image, and transferring the toner image to a receiving member.
U.S. Pat. No. 5,681,679 issued to Schank, et al. on Oct. 28, 1997—A flexible electrophotographic imaging member is disclosed including a supporting substrate and a resilient combination of at least one photoconductive layer and an overcoating layer, the at least one photoconductive layer comprising a hole transporting arylamine siloxane polymer and the overcoating comprising a crosslinked polyamide doped with a dihydroxy amine. This imaging member may be utilized in an imaging process including forming an electrostatic latent image on the imaging member, depositing toner particles on the imaging member in conformance with the latent image to form a toner image, and transferring the toner image to a receiving member.
U.S. Pat. No. 6,004,709, issued to Renfer et al, on Dec. 21, 1999—An allyloxypolyamide composition is disclosed, the allyloxypolyamide being represented by a specific formula. The allyloxypolyamide may be synthesized by reacting an alcohol soluble polyamide with formaldehyde and an allylalcohol. The allyloxypolyamide may be cross linked by a process selected from the group consisting of
(a) heating an allyloxypolyamide in the presence of a free radical catalyst, and
(b) hydrosilation of the double bond of the allyloxy group of the allyloxypolyamide with a silicon hydride reactant having at least 2 reactive sites.
A preferred article comprises
a substrate,
at least one photoconductive layer, and
an overcoat layer comprising
a hole transporting hydroxy arylamine compound having at least two
hydroxy functional groups, and
a cross linked allyloxypolyamide film forming binder.
A stabilizer may be added to the overcoat.
U.S. Pat. No. 5,976,744 issued to Fuller et al. on Nov. 2, 1999—An electrophotographic imaging member is disclosed including
a supporting substrate coated with
at least one photoconductive layer, and
an overcoating layer, the overcoating layer including a
a hydroxy functionalized aromatic diamine and
a hydroxy functionalized triarylamine dissolved or molecularly dispersed in
a crosslinked acrylated polyamide matrix, the hydroxy functionalized triarylamine being a compound different from the
DeFeo Paul J.
Dinh Kenny-tuan T.
Fuller Timothy J.
Nolley Robert W.
Nolley Vivian D.
Martin Roland
Nolley Vivian D.
Oliff & Berridg,e PLC
Xerox Corporation
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