Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-11-28
2002-04-30
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S058500, C430S058550, C430S058800, C430S125320, C430S133000
Reexamination Certificate
active
06379853
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates in general to electrophotography, and more specifically, to electrophotographic imaging members comprising two charge transport layers, processes for fabricating such members, and use of such members to limit toner consumption due to excess toner deposition.
2. Description of Related Art
Electrophotographic imaging members (i.e. photoreceptors) are well known. Typical electrophotographic imaging members are commonly used in electrophotographic (xerographic) processes in either a flexible belt or a rigid drum configuration. These electrophotographic imaging members comprise a photoconductive layer comprising a single layer or composite layers. One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990, which describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive or charge generating layer that is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, where the two electrically operative layers are supported on a conductive layer, the charge generating layer is sandwiched between a contiguous charge transport layer and the supporting conductive layer. Alternatively, the charge transport layer may be sandwiched between the supporting electrode and a charge generating layer. Photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member that thereafter transfers the image to a member such as paper.
One problem with prior art photoreceptors relates to photoinduced discharge curve (PIDC) characteristics of the photoreceptors. The expression “photoinduced discharged curve” (PIDC), as employed herein, is defined as a relationship between the potential as a function of exposure and a measure of the sensitivity of the device. It generally represents the supply efficiency (number carriers injected from the generator layer into the transport layer per incident photon) as a function of the field across the device. More specifically, when the V
low
, voltage at a high light exposure, is below a predetermined value, the imaging system consumes toner too rapidly, resulting in early failure of the imaging system. This is due to excess deposition of toner in the image areas to form very dense layers. V
low
, is related to V
residual
. The combination of electrical bias and V
low
results in overtoning during electrostatic latent image development to form toner images that are too dense, i.e., the electrical development field is too large. “V
low
”, as employed herein, is defined as the surface potential of a PIDC at a high intensity light exposure of, e.g., about 2.5-15 ergs/cm
2
. “V
residual
”, as employed herein, is defined as the surface potential of a PIDC at a given light exposure (e.g., about 25-300 ergs/cm
2
), that is significantly higher (e.g., about 10 times higher) than the exposure leading to V
low
. Cyclic stability is important and V
residual
and V
low
can increase with cycling due to persistently trapped charges. V
low
approaches V
residual
in an infinite amount of time. Thus, it is desirable to raise V
low
in a controlled fashion to a desirable value, which can be maintained under repeated use, and preferably without significantly altering the initial and low exposure photosensitivity. In other words, a more tunable photoreceptor is desirable.
Tunable photoreceptors, due to their tunable photosensitivity characteristics, have the advantage of being applicable to many different xerographic machines, including printers, copiers, duplicators, facsimile machines, multifunctional machines, and the like. With dual photoconductive components in a charge generating layer, a high sensitivity pigment such as hydroxygallium phthalocyanine and a low sensitivity pigment such as alkylhydroxygallium phthalocyanine, the initial photosensitivity can be adjusted within a range corresponding to the loading ratio of each component. However, it is often difficult to match both high field and low field photoinduced discharge curves (V
low
PIDC) by merely adjusting the charge generating layer composition. V
low
is related to charge generation and transport and can be adjusted by photogeneration and charge transport efficiencies. V
low
, is a critical parameter to toner consumption and is difficult to adjust by merely varying the composition of a charge generation layer. For example, a multilayered photoreceptor comprising a charge generating layer of chlorogallium phthalocyanine dispersed in a film forming binder and a charge transport layer comprising an arylamine charge transport material in a film forming binder has a low V
low
, and attempts to raise V
low
by lowering the photogeneration efficiency by changing the charge generating layer composition are not sufficient because they may also change the initial photosensitivity to some undesirable value.
U.S. Pat. No. 6,068,960 discloses a photoreceptor fabrication method including depositing a charge generating layer, depositing a first charge transport layer having a first charge carrier mobility value and depositing a second charge transport layer having a second charge carrier mobility value that is different from the first charge carrier mobility value. These steps can occur in any order and the difference in the first charge carrier mobility value and the second charge carrier mobility value is accomplished by including a first binder and a first charge transport material in a first charge transport layer and a second binder and a second charge transport material in a second charge transport layer. The first binder is selected to have a lower solubility limit for the first charge transport material than the solubility limit of the second binder for the second charge transport material. Or alternatively, a first polymeric compound composed of a first charge transport moiety covalently bonded to a first binder moiety is selected for a first transport layer and a second polymeric compound composed of a second charge transport moiety covalently bonded to a second binder moiety in a second transport layer, and selecting the proportion of the first charge transport moiety in the first polymeric compound to be less than the proportion of the second charge transport moiety in the second polymeric compound.
U.S. patent application Ser. No. 09/152,972, now U.S. Pat. No. 6,127,077 entitled “Photoreceptors With Delayed Discharge” filed Sep. 14, 1998, discloses a photoreceptor having a substrate, including: (a) a charge generating layer; (b) a first charge transport layer having a first charge carrier mobility value; and (c) a second charge transport layer having a second charge carrier mobility value. The first charge transport layer is closer to the charge generating layer than the second charge transport layer and the second charge transport layer is contiguous to the first charge transport layer. Also, the second charge carrier mobility value is higher than the first charge carrier mobility value.
The entire disclosures of each of the above cited patents and patent applications are incorporated herein by reference in their entireties.
While the above mentioned treatment techniques may be suitable for their intended purposes, there continues to be a need for an improved photoreceptor in which V
low
can be flexibly raised without significant changes to the other parts of PIDC, especially the initial and low exposure photosensitivities.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved photoreceptor having a V
low
that can be flexibly raised to some desirable value without subst
Chen Cindy C.
Dinh Kenny-Tuan T.
Hammond Harold F.
Lin Liang-bih
Nealey Richard H.
Rodee Christopher
Xerox Corporation
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