Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-01-24
2002-05-07
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C399S038000
Reexamination Certificate
active
06383699
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an imaging member or photoreceptor which includes a blocking layer doped with quaternary ammonium salts containing long chain alkyl groups or polymeric structures to assist the transporting of photogenerated electrons.
An example of a photoreceptor that has been used as a drum or belt in electrophographic imaging systems includes a substrate, a conductive layer, a charge blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. For electrophotographic imaging systems which use uniform negative polarity charging prior to imagewise exposure it is the charge blocking layer that conducts off negative charge while preventing positive charge leakage. To avoid poor charge acceptance and high dark decay, the blocking layer must effectively block hole injection. To avoid high charge buildup at the charge blocking layer which results in low density in prints or printout defects (dark spots) in the background area under Discharge Area Development (DAD) scheme, the blocking layer must allow the passage of electrons. Conventional materials used in the charge blocking layer include: gamma-aminopropyltriethoxysilane, phenolic binder-titanium dioxide, polyvinylchloride-polyacrylonitrile emulsion, zirconium/siliane/partly hydrolyzed polyvinyl butyral, and nylon-terpolymer.
In organic photoreceptors, insulating polymers are commonly used as blocking layers. However, until now polymers with high enough electron transporting properties have not been developed. While insulating polymers can efficiently block hole injection from the underlying ground plane, their thickness is limited because they are ineffecient at transporting photoinjected electrons from the charge generation layer to the substrate layer. To limit its resistivity an insulating polymer charge blocking layer must be thin. The use of a thin charge blocking layer results in the problem of incomplete coverage of the underlying substrate due to inadequate wetting on localized unclean substrate surface areas. This leads to charge leakage. In particular, thin blocking layers are more susceptible to the formation of pinholes which allow positive charges to leak through the charge blocking layer and result in print defects including charge deficient spots (CDSs) and Bias Charge Roll (BCR) leakage breakdown. Further, thin charge blocking layers are more susceptible to contaminants which cause positive charges to pass through the charge blocking layer, thus resulting in charge deficient spots and creating copy print-out defects.
One approach to solve the problems associated with using insulating polymers in the charge blocking layer is to use a thick layer (i.e. 2 to 20 microns) of dispersed TiO
2
(an n-type semiconductor). Such a dispersed TiO
2
blocking layer can transport photogenerated electrons and eliminate the possibilities of pin holes arising from incomplete coverage of the substrate underlying the blocking layer. However, in order to coat the thick dispersed TiO
2
blocking layer, a dispersion of high solids content (≧30%) is required. In addition, a high loading of TiO
2
(≧70 weight % of total solid) is required in order to transport electrons efficiently at this thickness. The high solid content and high TiO
2
loadings very often cause pigment sedimentation and limit the dispersion pot life. Such requirements greatly limit the available binders and solvents for this application.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved electrophotographic imaging members which overcome the above noted shortcomings of the prior art and to provide an improved electrophotographic imaging member having a blocking layer that has a uniform thickness.
It is a further object of the present invention to provide improved electrophotographic imaging members in which the blocking layer can be applied as a layer having a thickness of over 2 microns.
The present invention provides an improved electrophotographic imaging member having a hole blocking layer which suppresses the development of charge deficient spots associated with copy print-out defects.
Preferably, the present invention provides an improved electrophotographic imaging member having a hole blocking layer which suppresses the development of Bias Charge Roll (BCR) leakage breakdwon.
The resulting electrophotographic imaging member exhibits high quality imaging and printing characteristics.
Moreover, the blocking layer in the electrophotographic imaging member has a lower loading of TiO
2
than prior art blocking layers.
The electrophotographic imaging member in the present invention has a blocking layer formed from a dispersion of lower solids content than prior art blocking layers.
This invention pertains to an electrographic photosensitive material comprising a blocking layer, charge transport layer, an electroconductive substrate layer and a charge generation layer, where the blocking layer comprises TiO
2
with an average particle size less than about 50 nm and a quaternary ammonium salt, and where the quaternary ammonium salt is uniformly distributed in the blocking layer and is less than about 5 wt % of the blocking layer.
This invention also pertains to an electrographic photosensitive material comprising a blocking layer, where the blocking layer comprises TiO
2
with an average particle size of about 10 nm to about 300 nm, and a quaternary ammonium salt, and where the quaternary ammonium salt is greater than about 0.08 wt % and less than about 1 wt % of the blocking layer.
This invention encompasses the above-described electrographic photosensitive materials, where the TiO
2
comprises less than about 70 wt % of the total solids content of the blocking layer.
This invention includes the above-described electrographic photosensitive materials, where the quaternary ammonium salt is greater than about 0.08 wt % and less than about 0.1 wt % of the blocking layer.
In another aspect, this invention features the above-described electrographic photosensitive materials, where the quaternary ammonium salt is selected from the group consisting of salts containing long chain alkyl groups and salts containing polymeric structures.
Also within the scope of this invention are the above-described electrographic photosensitive materials, where the TiO
2
is rutile-type TiO
2
.
In a further aspect, this invention includes the above-described electrographic photosensitive materials, where the blocking layer is in direct contact with the substrate layer.
This invention encompasses the above-described electrographic photosensitive materials, where the blocking layer further comprises a phenolic resin binder.
This invention also encompasses the above-described electrographic photosensitive materials, where the quaternary ammonium salt is Calgon 261-LV
In an embodiment, this invention features the above-described electrographic photosensitive materials, where the quaternary ammonium salt is a methyltrialkyl (C
8
-C
10
)-ammonium halide.
This invention features the above-described electrographic photosensitive materials, where the methyltrialkyl (C
8
-C
1
)-ammonium halide is present in the blocking layer at a concentration of between about 400 and about 1000 ppm.
This invention further pertains to an image forming apparatus for forming images on a recording medium comprising an imaging light having a wavelength and an organic photoreceptor having a blocking layer, an electroconductive substrate layer, and a charge generation layer, where the blocking layer comprises TiO
2
particles and a quaternary ammonium salt and where the quaternary ammonium salt is uniformly distributed in the blocking layer and is less than about 5 wt % of the blocking layer.
This invention includes the above described image forming apparatus, where the TiO
2
in the blocking layer has a particle size smaller than about 10% of the wavelength of the imaging light.
This invention relates to the above described image forming apparatuses, where the quaternary ammonium salt is selected from the group
Limburg William W.
Yuh Huoy-Jen
Goodrow John
Lahive & Cockfield LLP
Xerox Corporation
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