Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2000-08-09
2002-04-02
Rodee, Christopher (Department: 1753)
Electrophotography
Image formation
Photoconductive member
C430S069000, C399S164000
Reexamination Certificate
active
06366752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates in general to electrophotographic imaging systems and, more specifically to imaging systems wherein component parts thereof include spherical silicone additives to reduce photoreceptor drag and wear.
2. Description of Related Art
Conventional electrophotographic and electrostatographic imaging systems include photosensitive members, i.e., photoreceptors, that are commonly used in electrophotographic or electrostatographic (Xerographic) processes in either a flexible belt or a rigid drum configuration. The flexible belt can be either seamless or seamed. Photoreceptors generally comprise a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer acts as an insulator in the dark so that electric charges are retained on its surface. When exposed to light the charge dissipates.
A latent image is generally formed on the photoreceptor by first uniformly depositing an electric charge over the surface of the photoconductive layer using one of several methods well known in the art. The photoconductive layer acts as a charge storage capacitor with a 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 the portions of the photoconductive layer that are exposed to light, the electric charge conducts through the layer and reduces the surface charge. The portions of the surface of the photoconductor that are not exposed to light retain their surface charge. The quantity of electric charge at any particular point on 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 a conductive charge and generate and transport this charge through the layer thereby neutralizing the charge on the surface. Two types of photoreceptor structures have been commonly used: multilayer structures wherein separate layers perform the functions of charge generation and charge transport, respectively, and single layer photoconductors that perform both functions. These layers are formed on an electrically conductive substrate and may include an optional charge blocking 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 employed.
As more advanced, higher speed electrophotographic copiers, duplicators and printers have been developed, degradation of image quality has been encountered during extended cycling. During extended cycling, a photoreceptor's imaging properties degrade as a result of the photoreceptor's continuous exposure to abrasion, chemical attack, heat and light. Degradation due to cycling is particularly common among multilayered organic photoconductors that use organic film forming polymers and small molecule, low ionization donor material in the charge transport layers. Such wear is further accelerated when the photoreceptor is used in systems that employ abrasive development systems such as single component development systems. Wear is an even greater problem where a drum is used that has such a small diameter that it must rotate many times merely to form a single image for conventional 8.5 inch by 11 inch sized documents. Wear of the photoreceptor can be compensated for by increasing the thickness of the charge transport layer. However, a large increase in charge transport layer thickness can make a photoreceptor inoperable at high imaging process speeds because of the very long transit times of common charge transport layer materials. Also, large decreases in the thickness due to wear can cause dramatic changes in electrical characteristics in only a few thousand cycles that cannot be readily compensated for even with sophisticated computerized control apparatus.
In many of today's high volume, high precision electrophotographic imaging systems, extended cycling causes adherent spots to form on the photoreceptor's surface. To prevent imaging defects that can occur as a result of these adherent spots, many modem electrophotographic systems include a spots blade. The function of a spots blade is to remove adherent spots from the surface of the photoreceptor. Conventional cleaning blades work in a similar manner; however, the primary function of a cleaning blade is to remove toner from the photoreceptor's surfaces.
Spots blades are generally oriented either in a doctor mode or a wiper mode. Unfortunately, because intimate contact between the spots blade and the photoreceptor's surface is necessary in order to remove the adherent spots, the spots blade often imparts drag to the system that results in higher torque requirements for driving the photoreceptor.
In addition to the frictional wear encountered at the photoreceptor's outermost layer, another problem encountered when one or more photoconductive layers are applied to a flexible supporting substrate is curling of the photoconductive member. To counteract the curling tendency, imaging engineers have applied coatings to the side of the supporting substrate opposite the photoconductive layers. These coatings, or layers formed by the coatings, are generally referred to as anti-curl layers, backing layers, or anti-curl backing layers. However, difficulties with these anti-curl layers have been encountered. For example, photoreceptor curl can occur in as few as 1,500 imaging cycles under the stressful conditions of high temperature and humidity. Moreover, engineers have found that during the cycling of the photoconductive member, relatively rapid wear of the anti-curl coating causes the photoconductive imaging member to curl. In some tests the anti-curl coating became completely removed in 150,000 to 200,000 cycles. This wear problem becomes even more pronounced when photoconductive members in the form of belts or webs are supported in part by backer bars or stationary guide surfaces that cause the anti-curl layer to wear away very rapidly, producing debris that scatters and deposits on critical machine components, such as lenses, corona charging devices and the like, thereby adversely affecting machine performance.
Also, the anti-curl coatings occasionally separate from the substrate during extended cycling and render the photoconductive imaging member unacceptable for forming quality images. It has also been found that when long webs of a flexible photoconductor having an anti-curl coating on one side of a supporting substrate and a photoconductive layer on the opposite side of the substrate are rolled into large rolls, dimples and creases form on the photoconductive layer that result in print defects in the final developed images. Furthermore, when the webs are formed into belts, segments of the outer surface of the anti-curl layer in contact with each other during shipping or storage at elevated temperatures also cause creases and dimples to form that are seen as undesirable aberrations in the final printed images. Expensive and elaborate packaging is necessary to prevent the anti-curl coating from contacting itself. Additional difficulties have been encountered in continuous coating machines during the winter manufacturing of coated photoconductive imaging members because of occasional seizing that prevents transport of the coated web through the machine for downstream coating.
Numerous attempts have been made to reduce frictional damage to electrophotographic imaging system photoreceptors. Unfortunately, each solution often leads to additional problems. Moreover, since most of the solutions are aimed at reducing friction between the photoreceptor's outermost
Oliff & Berridg,e PLC
Rodee Christopher
Xerox Corporation
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