Note: Descriptions are shown in the official language in which they were submitted.
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IMAGING MEMBER
Back~round of the Invention
This invention relates in general to xerography and more
specifically to a novel photosensitive device.
s In the art of more or less conventional xerography, a xero-
graphic plate containing a photoconductive insulating layer is imaged by
first uniformly electrostatically charging its surface. The plate is then
exposed to a pattern of activating electromagnetic radiation, such as light,
which selectively dissipates charge in the illuminated areas of the
photoconductive insulator resulting in a latent electrostatic image corres-
ponding to the pattern of light-struck and nonlight-struck areas. The latent
electrostatic image may then be developed to form a visible image by
depositing finely divided electroscopic marking particles on the surface of
the photoconductive insulating layer.
In recent years, interest has been shown in flexible electro
photographic plates for use in high speed office copying machines. Some of
these plates are multilayered devices comprising, a conductive substrate,
an adhesive blocking interface layer and a photoresponsive layer thereon.
The photoresponsive region of the plate may be a single photoconductive
material, e.g. selenium or this region may be composed of separate layers
of a charge generation layer and a charge transport layer. The charge
generation layer can be any photoresponsive material. This material can be
conveniently dispersed in a polymeric matrix material. The charge
transport layer may comprise an organic charge transport molecule
dissolved or dispersed in a polymeric matrix material. During the imaging
process, photons of light generate charge in imagewise fashion in the
charge generation layer. These charges are injected into and transported
across the charge transport layer to discharge in imagewise fashion the
uniformly charged surface of the transport laye-r. The s~harge transport
layer is substantially nonabsorbing in the spectral region of intended use,
i.e. visible light, but is "active" in that it allows (1) injection of
photogenerated charge from the charge generation layer and (2) efficient
transport of these charges to the surface of the transport layer to
discharge the surface charge thereon.
It is essential that intimate adhering contact be maintained
between the conductive substrate and the charge generation layer. If
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partial delamination occurs, then effective charge injection
will not occur.
Difficulty has been experienced with different-
variant forms of this kind of layered photoreceptor in main-
S taining integrity between the conductive layer and thecharge generation layer or the charge transport layer. The
art is constantly searching for means to effectively bond
the charge generation layer or the transport layer to the
conductive substrate.
Another problem experienced with attempts to employ
proprietary adhesives, e.g. DuPont's 49000 polyester adhe-
sive, is that components of the layers to be bonded migrate
into and through the adhesive layer and even into the next
adjacent layers. This causes charge trapping which ulti-
mately results in an intolerable increase in residual poten-
tial. By solving these problems, greater assurance of high
quality copy can be obtained.
Various aspects of the invention are as follows:
In an imaging member for electrophotography compri-
sing a conductive substrate having thereon a photoconductivelayer selected from the group consisting of selenium and
selenium alloys, the improvement consisting of positioning
between said conductive substrate and the photocollductive
layer, a layer consisting essentially of an acetal of poly
~Ivinyl alcohol).
In an imaging member for electrophotography com-
prising a conductive substrate having thereon a composite
photoconductive layer comprising of a charge generation
layer and a contiguous charge transport layer, the improve-
ment consisting of positioning between said conductive sub-
strate and the composite layer, a layer consisting essen-
tially of an acetal of poly (vinyl alcohol).
In a more specific embodiment, the imaging member
is a flexible member having a conductive substrate, an ad-
hesive interface layer of an acetal of polyvinyl alcohol,
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a charge generation layer and, contiguous therewith, a
charge transport layer. Among the outstanding advantages
of this interfacial composition is that it exhibits out-
standing tensile strength, modulus of elasticity, adhesive
properties and electrical characteristics which far exceed
the properties of prior art interfacial layers.
The advantages of the instant invention will
become apparent upon consideration of the following dis-
closure of the invention, especially when taken in conjunc-
tion with the accompanying drawing wherein: the Figurerepresents one embodiment of a xerographic member as con-
templated for use in the instant invention.
In the drawing, reference character 10 illustrates
by a cross-sectional view an improved photoreceptor device
of the instant invention. Reference character 11 designates
a support member which can be an insulating material, for
example, polyethylene terephthalate, which is overcoated
with a conductive material 12, such as aluminum. This
combination of 11 and 12 is obviously merely for purposes
of illustration.
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Aluminized polyethylene terephthalate is an effective material which is
used in place of a fully metallic substrate. Layer 11 can be any one of a
number of insulating or dielectric support materials and 12 can be any
number of conductive materials. The substrate can be polyethylene,
polypropylene, polycarbonate, ceramic, etc. The advantage of using a
material such as polyethylene terephthalate is that it is flexible and
extremely strong.
Thus, the support may comprise other materials such as
metallized paper, plastic sheets covered with a thin coating of aluminum or
copper iodide or glass coated with a thin conductive layer of chromium or
tin oxide. It is preferred to use a dielectric belt coated with aluminum
with its inherent coating of aluminum oxide. The conductive layer 12 is
overcoated with the interfacial layer 13 which comprises an acetal of
polyvinyl alcohol.
Typical acetals of polyvinyl alcohol include the following:
poly(vinyl formal), poly(vinyl acetal) and poly(vinyl butyral). The preferred
acetal is poly(vinyl butyral). The molecular weight range of the poly(vinyl
butyral) is preferably from about 30,000-270,000. The molecular weight
range of the poly(vinyl formal) and poly(vinyl acetal) is preferably from
about 10,000 to 40,000. The interface layer can be deposited in a thickness
range of about 100 Angstroms to 5000 Angstroms. It is preferred that this
thickness be about 500 Angstroms. This material is conveniently coated
from alcohol solutions such as isopropanol or mixtures of ethanol and
isopropanol, etc.
Coated on top of interfacial layer 13 is the photoresponsive
material of choice. In the ~igure shown herein, the photoreceptor is a
combination of layer 14 and layer 15. In this type of photoreceptor, the
arrangement provides for a layer 14 which is known as a charge generation
layer and layer 15 which is known as a charge transport layer. It is to be
understood, however, that the present invention is not limited to this type
of photoreceptor since it can be a single layer of photoreceptor such as
selenium or a selenium alloy. As illustrated, layer 14 can comprise a
particulate charge generation material such as amorphous or trigonal
selenium or phthalocyanine dispersed in a binder material such as poly-N-
vinyl carbazole. And layer 15 cfln be formed of an organic charge transfer
compound dissolved in an organic matrix material. A photoreceptor of this
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type will be found described in U.S. Patent 4,115,116, issued September 19,
1978.
The interfacial layer may be made by any convenient technique.
For example, the selected acetal may be dissolved in a solvent and the
5 solution coated onto the supporting substrate. The solvent is then allowed
to evaporate leaving a dried coating on the supporting substrate. Residuals
of the solvent are then driven off by drying at an efficient temperature.
Typical coating techniques which are suitable for forming the interfacial
layer include spray coating, draw coating, dip coating or flow coating.
A preferred application of the instant invention includes the use
A f the instant interface with an aluminized Mylar substrate. The thickness
of the Mylar is about 3 mil and the thickness of the aluminum overcoat is
200 Angstroms. A coating of about 500 Angstroms of polyvinyl butyral B-
72A, obtainable from Monsanto Company, is applied to the surface from a
0.5% solution in isopropanol. This layer was applied using a draw bar
technique and residual isopropanol was removed by heating the system at a
temperature between 90 C and 110 C for 5 minutes. On top of this layer
of pol~(vinyl butyral) is deposited a 1 micron layer of vitreous selenium by a
conventional vacuum deposition technique. A charge transport layer is
deposited over the vitreous selenium layer by applying a solution of N,N'-
diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl~-4,4'-diamine in a bis-
phenol-~ polycarbonate (Lexan~ 145) obtained from General Electric
Company and having a molecular weight of from about 25,000 to about
40,000 using methylene chloride as a solvent. This layer is applied to the
vitreous selenium layer using a Bird film applicator. The coating is then
vacuum dried at 40C for about 18 hours to form a 22 micron thick dry
layer of charge transport material. The above member is then heated to
about 125 C for about 16 hours which is sufficient to convert the vitreous
selenium to the crystalline trigonal form.
This device was examined and subjected to conventional Carlson
xerography imaging cycles totaling about 20,000 cycles. The residual
remained at 40 volts and showed no signs of cycle up which would have
indicated a pro~ressive increase in the residual voltage on discharge of the
photoreceptor. The overall mechanical integrity of the structure was
excellent revealing no evidence of delamination between the conductive
layer and the polyvinyl butyral or between the generator layer and the
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polyvinyl butyral.
The invention has been described in detail with particular
reference to a preferred embodiment, but it will be understood that
variations and modifications can be effected within the spirit and scope of
5 the invention as described hereinabove and as defined in the appended
claims.
