Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
1993-12-21
2002-03-26
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
C430S058750, C430S059600, C430S066000, C430S132000
Reexamination Certificate
active
06361913
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to electrophotographic imaging members and, more specifically, to layered photoreceptor structures with overcoatings containing hydrogen bonded materials and processes for making and using the photoreceptors.
Electrophotographic imaging members, i.e. photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The 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.
A latent image is formed on the photoreceptor by first uniformly depositing an electric charge over the surface of the photoconductive layer by one of any suitable means well known in the art. The photoconductive layer functions as a charge storage capacitor with charge on its free surface and an equal charge of opposite polarity (the counter charge) on the conductive substrate. A light image is then projected onto the photoconductive layer. On those portions of the photoconductive layer that are exposed to light, the electric charge is conducted through the layer reducing the surface charge. The portions of the surface of the photoconductor not exposed to light retain their surface charge. The quantity of electric charge at any particular area of the photoconductive surface is inversely related to the illumination incident thereon, thus forming an electrostatic latent image.
The photodischarge of the photoconductive layer requires that the layer photogenerate conductive charge and transport this charge through the layer thereby neutralizing the charge on the surface. Two types of photoreceptor structures have been employed: multilayer structures wherein separate layers perform the functions of charge generation and charge transport, respectively, and single layer photoconductors which perform both functions. These layers are formed on an electrically conductive substrate and may include an optional charge blocking and an adhesive layer between the conductive layer and the photoconducting layer or layers. Additionally, the substrate may comprise a non-conducting mechanical support with a conductive surface. Other layers for providing special functions such as incoherent reflection of laser light, dot patterns for pictorial imaging or subbing layers to provide chemical sealing and/or a smooth coating surface may be optionally be employed.
One common type of photoreceptor is a multilayered device that comprises a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. The charge transport layer can contain an active aromatic diamine molecule, which enables charge transport, dissolved or molecularly dispersed in a film forming binder. This type of charge transport layer is described, for example in U.S. Pat. No. 4,265,990. The disclosures of this patent is incorporated herein in its entirety. Other charge transport molecules disclosed in the prior art include a variety of electron donor, aromatic amines, oxadiazoles, oxazoles, hydrazones and stilbenes for hole transport and electron acceptor molecules for electron transport. Another type of charge transport layer has been developed which utilizes a charge transporting polymer wherein the charge transporting moiety is incorporated in the polymer as a group pendant from the backbone of the polymer backbone or as a moiety in the backbone of the polymer. These types of charge transport polymers include materials such as poly(N-vinylcarbazole), polysilylenes, and others including those described, for example, in U.S. Pat. Nos. 4,618,551, 4,806,443, 4,935,487, and 4,956,440. The disclosures of these patents are incorporated herein in their entirety. Other charge transporting materials include polymeric arylamine compounds and related polymers described in U.S. Pat. Nos. 4,801,517, 4,806,444, 4,818,650, 4,806,443, 5,030,532, copending application Ser. No. 07/797,753, now U.S. Pat. No. 5,283,143, entitled “ELECTROPHOTOGRAPHIC IMAGING MEMBER CONTAINING ARYLAMINE TERPOLYMERS WITH CF3 SUBSTITUTED MOIETIES”, to Yanus et al, filed Nov. 25, 1991 and copending application Ser. No. 08/148,818, now U.S. Pat. No. 5,356,943, to Yanus et al, entitled “ELECTROPHOTOGRAPHIC IMAGING MEMBERS CONTAINING POLYARYLAMINE POLYESTERS”, mailed by Express Mail on Nov. 8, 1993, the disclosures of which are also incorporated herein by reference in their entirety.
One of the design criteria for the selection of the photosensitive pigment for a charge generator layer and the charge transporting molecule or polymer for a transport layer is that, when light photons photogenerate holes in the pigment, the holes be efficiently injected into the charge transporting moiety in the transport layer. More specifically, the injection efficiency from the pigment to the transport layer should be high. A second design criterion is that the injected holes be transported across the charge transport layer in a short time; shorter than the time duration between the exposure and development stations in an imaging device. The transit time across the transport layer is determined by the charge carrier mobility in the transport layer. The charge carrier mobility is the velocity per unit field and has dimensions of cm2/volt sec. The charge carrier mobility is a function of the structure of the charge transporting moiety, the concentration of the charge transporting moiety in the transport layer and the electrically “inactive” binder polymer in which the charge transport molecule is dispersed (if the transport layer consists of charge transporting molecules dispersed in a binder). It is believed that the injection efficiency can be maximized by choosing a transporting moiety whose ionization potential is lower than that of the pigment (assuming the charge transporting carriers are holes). However, low ionization potential molecules may have other deficiencies, one of which is their instability in an atmosphere of corona effluents. A copy quality defect resulting from the chemical interaction of the surface of the transport layer with corona effluents is referred to as “parking deletion” and is described in detail below.
Photoreceptors are cycled many thousands of times in automatic copiers, duplicators and printers. This cycling causes degradation of the imaging properties of photoreceptors, particularly multilayered organic photoconductors which utilize organic film forming polymers and small molecule low ionization donor material in the charge transport layers. Such wear is accelerated when the photoreceptor is utilized in systems employing abrasive development systems such as single component development systems. Wear is an even greater problem where a drum is utilized which has such a small diameter that it must rotate many, many times merely to form images for each conventional size 8.5 inch by 11 inch document. Wear of the photoreceptor can be compensated by increasing the thickness of the charge transport layer. However, large increases in thickness of the charge transport layer can render the photoreceptor inoperable at high imaging process speeds because of the inadequate (very long) transit times of common charge transport layer materials. Also, large decreases in thickness due to wear can cause dramatic changes in electrical characteristics in only a few thousand cycles that cannot be readily compensated by even sophisticated computerized control apparatus.
When the electrophotographic imaging member is utilized in liquid ink development systems, leaching of small molecules from the charge transport layer into the liquid development can occur. Loss of the small molecule material due to leaching causes undesirable deterioration in electrical properties of the photoreceptor. Also, undesirable crystallization of the small molecule in the charge transport layer can adversely affect the electrical imaging characteristics of the photoreceptor.
Reprographic machines utilizing multilayered organic photoconductors also employ corotrons or scorotrons to charge the pho
Pai Damodar M.
Yanus John F.
Dote Janis L.
Thompson Robert
Xerox Corporation
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