Note: Descriptions are shown in the official language in which they were submitted.
)3
BACKGROUND OF THE INVENTION
-
This invention relates in general to xerography and
more specifically to a novel photosensitive device and a method
of use.
Vitreous and amorphous selenium is a photoconductive
material which has had wide use as a reusable photoconductor in
commercial xerography. However, its spectral response is limited
largely to the blue-green portion of the visible spectrum, i.e.
below 52 angstrom units.
Selenium also exists in a crystalline form known as
trigonal or hexagonal selenium. Trigonal selenium is well known
in the semiconductor art for use in the manufacture of selenium
rectifiers.
In the past, trigonal selenium was not normally used
in xerography as a photoconductive layer because of its relatively
high electrical conductivity in the dark, although in some
instances, trigonal selenium can be used in a binder configuration
in which the trigonal selenium particles are dispersed in the
matrix of another material such as an electrically active organic
material or a photoconductive material such as vitreous selenium.
It is also known that a thin layer of trigonal selenium
overcoated with a relatively thick layer of electrically active.
organic material, forms a useful composite photosensitive
member which exhibits improved spectral response and increased
sensitivity over conventional vitreous selenium-type photoreceptors.
This device and method are described in U.S. Patent 3,961,953.
It is known that when using trigonal selenium whether
it be dispersed in a binder or used as a generation material in
a composite photoconductive device that the trigonal selenium
exhibits a high dark decay and high dark decay after the
.
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photoreceptor has been cycled in a xerographic process. This
is referred to as fatigue dark decay. Also, after cycling the
photoreceptor in a xerographic process, the photoreceptor will
not accept as much charge as it did initially.
As mentioned, fatigue dark decay is defined as after
the member, i.e. photoreceptor, has been erased at least one
time during a xerographic cycle, then the member is recharged
and the dark decay is again examined. This dark decay is called
fatigued dark decay.
U.S. Patent 3,685,989 discloses a photoconductive
layer which comprises vitreous selenium or a selenium-arsenic
alloy which is doped with a small amount of sodium, lithium,
potassium, rubidium or cesium. This is done in this photoreceptor
in order to convert an essentially bipolar photoreceptor to
an essentially ambipolar photoreceptor.
As taught in the prior art, trigonal selenium used
as a photoconductive material in a xerographic process is not
predictable from knowing that vitreous or amorphous selenium
is a good photoconductive material. As taught in Keck, U.S.
2,739,079, trigonal selenium is quite conductive and would be
unsuitable as a generating material. Japanese Publication No.
16,198 of 1968 of Japanese (M. Hayashi) application 73,753 of
November 29, 1968, assigned to Matsushita Electric Industrial
Company also discloses that one should not use a highly
conductive photoconductive layer as a charge generation material
in a multi-layered device comprising a charge generation layer
and an overlayer of charge transport material. Therefore, since
Keck U.S. 2,739,079 teaches that trigonal selenium is highly
conductive, it was unobvious that trigonal selenium could be
used as a photoconductive material in a xerographic device merely
--3~
f~3
because vitreous or amorphous selenium was a good photoconductive
material for use in a xerographic device. Therefore, the
vitreous or amorphous selenium prior art is not analogous prior
art for use in teaching that trigonal selenium may act as
vitreous or amorphous selenium when used in xerographic devices.
U.S. 3,312,548 dicloses a xerographic plate having
a photoconductive insulating layer o~ a composition of selenium,
arsenic and doped with a halogen in a concentration of from about
10 to 10,000 parts per million.
Belgium Patent 763,540 issued ~ugust 26, 1971 (U.S.
application Serial No. 94,139, filed December 1, 1970, now
abandoned) discloses an electrophotographic member having at
least two electrically operative layers. The first layer
comprises a photoconductive layer which is capable of photo~
generating charge carriers and injecting the photogenerated
holes into a contiguous active layer. The active layer comprises
a transparent organic material which is substantially nonabsorbing
in the spectral region of intended use, but which is "active"
in that it allows injection of photogenerated holes from the
photoconductive layer, and allows these holes to be transported
through the active layer. The active polymers may be mixed with
inactive polymers or nonpolymeric material.
U.S. Patent 3,926,762 discloses a method of making
a photoconductive imaging deviGe which comprises directly
depositing a thin layer of trigonal selenium onto a supporting
conductive substrate.
U.S. 3,954,464 discloses a method of making a photo-
sensitive imaging device which comprises vacuum evaporating a
thin layer of vitreous selenium over a layer of electrically
active organic material which is contained on a supporting
.
V3
substrate, forming a relatively thin layer of electrically
insulating or electrically active organic material over the
trigonal selenium layer. This is followed by heating khe
device to an elevated temperature for a sufficient time to
convert the vitreous selenium to the crystalline trigonal
form.
U.S. Patent 3,961,953 discloses a method of making
a photosensitive imaging device which comprises vacuum evapora-
ting a thin layer of vitreous selenium onto a supporting
substrate, forming a relatively ~hicker layer of electrically
active organic material over the vitreous selenium layer.
This step if followed by heating the member to an elevated
temperature for a sufficient time to convert the vitreous
selenium into the crystalline trigonal form.
OBJECTS OF THE INVENTION
It is, therefore, an object of this invention to
provide a novel photosensitive device adapted for cyclic imaging
by the xerographic process which overcomes the above-noted
disadvantages.
It is a further object of this invention to provide
a process of doping trigonal selenium in order to control
dark decay.
It is a further object of this invention to utilize
this doped trigonal selenium in photosensitive devices in
order to improve cyclic charge acceptance and control and
improve dark decay both initially and after cycling the member
in a xerographic process.
SUMMARY OF THE INVENTION
The foregoing objects and others are accomplished in
accordance with this invention by providing a photosensitive
member, i.e. imaging member, which comprises a layer of
particulate photoconductive material dispersed in an organic
resinous binder. The particulate photoconductive material
comprises trigonal selenium doped with from about 0.01 to about
12.0~ by weight based on the weight of the trigonal selenium
of a material comprising sodium, lithium, potassium, rubidium
and cesium. The trigonal selenium doped with a dopant, i.e.
sodium, lithium, potassium, rubidium and cesium, prevents the
trigonal selenium when the trigonal selenium is being used
as a photoconductive material dispersed in a binder from
exhibiting unacceptable and undesirable amounts of dark decay
either initially, i.e. before charging and discharging of the
member, or fatigue dark decay, i.e. after the member has been
through a complete xerographic process, that is, charged and
erased and then recharged in the dark. The sensitivity and dark
decay of the trigonal selenium photoreceptor may be decreased or
increased, respectively, by washing the dopant in or out of the
trigonal selenium, e.g. see Fig. 5 and Fig. 6.
Typical applications of the invention include as
mentioned above a single photoconductive layer having trigonal
selenium in particulate form doped with sodium, lithium,
potassium, rubidium or cesium or mixtures thereof dispersed
in an organic resinous binder. This may be used as a
photosensitive device itself. ~nother typical application
of the invention includes a photosensitive member which has
at least two operative 'ayers. The first layer comprises a
layer of photoconductive material, i.e. trigonal selenium in
particulate form doped with sodium, lithium, potassium, rubidium
or cesium or mixtures thereof dispersed in an organic resinous
binder. This layer is capable of photogenerating charge
'
V ~
carriers and injecting these photogenerated charge carriers into
a contiguous or adjacent charge carrier transport layer. The
charge carrier transport layer may comprise a transparent organic
polymer or a nonpolymeric material which when dispersed in an
organic polymer results in the organic polymer becoming active,
i.e. capable of transporting charge carriers. The charge
carrier transport material should be substantially nonabsorbing
to visible light or radiation in the region of intended use,
but which is "active" in that it allows the injection of
photogenerated charge carriers e.g. holes, from the particulate
trigonal selenium layer and allows these charge carriers to
be transported through the active layer to selectively discharge
the surface charge on the free surface of the active layer.
It is not the intent of this invention to restrict the
choice of active materials to those which are transparent in the
entire visible region. For example, when used with a transparent
substrate, imagewise exposure may be accomplished through the
substrate without the light passing through the layer of active
material, i.e. charge transport layer. In this case, the active
layer need not be non-absorbing in the wavelength region of use.
Other applications where complete transparency is not required for
the active material in the visible region include the selective
recording of narrow-band radiation such as that emitted from lasers,
spectral pattern recognition, and possible functional color
xerography such as color coded form duplication.
Another embodiment of the instant invention may include
an imaging member having a first layer of electrically active
charge transport material contained on a supporting substrate, a
photoconductive layer of the instant invention overlying the active
layer and a second layer of electrically active charge transport
3;3
material overlying the photoconductive layer. Thls member i~
more fully described in U.S. Patent 3,953,207.
Another typical application of the invention in-
cludes a photosensitive member which may comprise a photo-
conductive insulating layer comprising a matrix material of
insulating organic resinous material and particulate trigonal
selenium doped with either sodium, lithium, potassium, rubidium
and cesium. Substantially all of the doped particulate trigonal
selenium in the layer is in substantially particle-to-particle
contact forming a multiplicity of interlocking trigonal
selenium paths through the thickness of the layer. The trigonal
selenium paths being present in a volume concentration,
based on the volume of the layer, of from about 1 to 25 percent.
In general, the advantages of the invention will
become apparent upon consideration of the following dis-
closure of the invention; especially when taken in conjunction
with the accompanying drawings wherein:
BRIEF DESCRIPTION OF THE DRA~INGS
Fig. 1 is a schematic illustration of one of the
members of the instant invention which comprises particulate
trigonal selenium dispersed in a resinous binder overlying
a substrate.
Fig. 2 is a schematic illustration of one of the
members of the instant invention wherein the particulate
trigonal selenium is geometrically dispersed within an
electrically insulating organic binder. This layer overlies
the substrate.
Fig. 3 is a schematic illustration of one of the
members of the instant invention illustrating a composite
-- 8 --
,
, ~ . .
photoreceptor comprising a charge carrier generation layer
overcoated with a charge carrier transport layer. The charge
carrier generation layer comprises doped trigonal selenium
dispersed in an organic resinous binder as the charge carrier
generation layer.
Fig. 4 is a schematic illustration of one embodiment
of a device of the instant invention. A composite photoreceptor
is disclosed comprising a charge carrier transport layer and
a charge carxier generation layer. The charge carrier generation
layer comprises sodium doped particulate trigonal selenium
geometrically dispersed n an insulating binder.
Fig. 5 illustrates rested dark decay and fatigue dark
decay of photoreceptors containing trigonal selenium both doped
and undoped as the photoconductive material.
Fig. 6 illustrates the photoinduced discharge curves
~PIDC) of the members illustrated in Fig. 5.
DETAILED ~ESCRIPTION OF T~E DRAWINGS
-
For a bet-ter understanding of the Figures, several terms
should be defined. The term "rested dark decay" when used in this
application means that it is the amount of voltage drop, i.e. surface
potential drop, of a member which has been rested and then charged
initially to an initial surface potential, measured in voltage,
and then allowed to remain in the dark. The drop in potential is
measured 0.06 seconds after charging, 0.22 seconds after charging,
and 0.66 seconds after charging. This "rested dark decay" means
that the photoreceptor has been rested in the dark for at least
30 minutes prior to testing i.e. cycling in a xerographic mode.
"Fatigue dark decay" means, for purpose of this
application, a drop in surface potential 0.06 seconds after
charging, then after 0.22 seconds and then after 0.66 seconds.
, . .. .
These measurements are made while the photoreceptor remains in
the dark. "Fatigue dark decay" further means that the photoreceptor
has been cycled at least one time through a xerographic cycle and
then discharged, i.e. erased, and then is being tested before the
photoreceptor has rested, preferably before 30 minutes has passed
after charging the photoreceptor. The process speed of the photo-
receptor is 30 inches per second.
Referring to Fig. 1, reference character 10 designates
an imaging member which comprises a supporting substrate 11 having
a binder layer 12 thereon. Substrate 11 is preferably comprised of
any suitable conductive material. Typical conductors comprise
aluminum, steel, nickel, brass or the like. The substrate may be
rigid or flexible and of any conventional thickness. Typical
substrates includes flexible belts of sleeves, sheets, webs,
plates, cylinders and drums. The substrate or support may also
comprise a composite structure such as a thin conductive coating
contained on a paper base; a plastic coated with a thin conductive
layer such as aluminum, nickel or copper iodine; or glass coated
with a thin conductive coating or chromium or tin oxide.
In addition, if desired, an electrically insulating
substrate may be used. In this instant, the charge may be placed
upon the insulating member by double corona charging techni~ues
well known or disclosed in the art. Other modifications using an
insulating substrate or no substrate at all include placing the
imaging member on a conductive backing member or plate in charging
the surface while in contact with said backing member. Subsequent
to imaging, the imaging member may then be stripped from the
conductive backing.
Binder layer 12 contains trigonal selenium particles
13 which have been doped with from about 0.01 to about 12.0% by
--10--
z~3
weight based on the weight of the trigonal selenium of any
one of the following materials or mixtures thereof, i.e. sodium,
lithium, potassium, rubidium and cesium. The doped trigonal
selenium particles are dispersed randomly without orientation
in binder 14-.
Binder material 14 may comprise any electrically
insulating resin such as those disclosedin Middleton et al
U.S. Patent 3,121,006. When using an electrically inactive
or insulating resin, it is essential that there be particle-to-
particle contact between the photoconductive particles. Thisnecessitates that the photoconductive material be present in
an amount of at least about 15% by volume of the binder layer
with no limit on the maximum amount of photoconductor in the
binder layer. If the matrix or binder comprises an active
material, the photoconductive material need only to comprise
about 1% or less by volume of the binder layer with no limita-
tion on the maximum amount of photoconductor in the binder layer.
Binder layer 12's thickness is not critical. Layer thicknesses
from about 0.05 to 40.0 microns have been found to be
satisfactory.
Binder material 14 may also comprise Saran ~, available
from Dow Chemical Company, which is a copolymer of polyvinyl
chloride and polyvinylidene chloride; polystyrene and poly-
vinyl buty~al polymers.
The trigonal selenium 13 used in binder layer 12 as
illustrated in Fig. 1 is doped wlth from about 0.01 to about
12.0~ by weight based on the weight of the trigonal selenium
of a material selected from the group consisting of sodium,
lithium, potassium, rubidium and cesium. The preferred doping ~ ;
material
X
: . - -: -
: .
: . ,. ;: i
. ,.,
633
is sodium. The most preferred amount o dopant is present in from
about 0.1 to abou~ 1.0~ by weight. This is the most preferred
amounts when using binders, such as PVX. ~owever, this amount
may vary if binders, such as electrically inactive binders, are
used. Preferably there may be an adhesive charge blocking layer
between the substrate and the charge generation layer, i.e.
doped trigonal selenium layer.
The preferred size of the doped particulate trigonal
selenium particles is from about 0.01 micron to about 10 microns
in diameter. The more preferred size of the doped particulate
trigonal selenium particles is from about 0.1 microns to about
0.5 microns in diameter.
The member 10 as shown in Fig. 1 may optionally
be overcoated with an electrically insulating organic resinous
lS material.
In another embodiment of the instant invention, the
structure of Fig. 1 is modified to insure that the doped
trigonal selenium particles are in the form of continuous
paths or particle-to-particle chains through the thickness of
binder layer 12. This embodiment it is illustrated by Fig. 2
which shows the doped trigonal selenium particles 13 in the
form of particle-to-particle chains. Layer 12 of Fig. 2 more
specifically may comprise doped trigonal selenium particles in
a multiplicity of interlocking photoconductive continuous paths
through the thickness of layer 14, the photoconductive paths
being present in a volume concentration based on the volume of
the layer, of from about 1-25%. A further alternative for layer
14 of Fig. 2 comprises doped trigonal selenium material in
substantially particle-to-particle contact in the layer in a
multiplicity of interlocking photoconductive paths through the
-12-
.
thickness of the member, the photoconductive paths being present
in a volume concentration, based on the volume of the layer,
of from about 1-25~.
Fig. 3 designates imaging member 30 in the form o~
an imaging member which comprises a supporting substrate 11 having
a binder layer 12 thereon, and a charge transport layer 15
positioned over binder layer 12. Substrate 11 may be of the
same material as described for use in Fig. 1. Binder layer 12
may be of the same configuration as and contain the same material
as binder layer 12 described in Fig. 1.
Active layer 15 may comprise any suitable transparent
organic polymer or nonpolymeric material capable of supporting
the injection of photogenerated holes and electrons from the doped
trigonal selenium binder layer and allowing the transport of these
holes or electrons through the organic layer to selectively
discharge the surface charge.
Polymers having this characteristic, i.e. capability of
transporting holes have been found to contain repeating units of
a polynuclear aromatic hydrocarbon which may also contain heteroatoms
such as for example, nitrogen, oxygen or sulphur. Typical polymers
include poly-N-vinyl carbazole (PVK), poly-l-vinyl pyrene (PVP),
poly-9-vinyl anthracene, polyacenaphthalene, poly-9-(4-pentenyl)-
carbaæole, poly-9-(5-hexyl)-carbazole, polyme~hylene pyrene,
poly-l-(pyrenyl)-butadiene and N-substituted polymeric acrylic
acid amides of pyrene. Also included are derivatives of such
polymers including alkyl, nitro, amino, halogen, and hydroxy
substituted polymers. Typical examples are poly-3-amino carbazole,
1,3-dibromo-poly-N-vinyl carbazole and 3,6-dibromo-poly-N-vinyl
carbazole in particular derivatives of the formula
-13-
33
LY~ ,X1
-CH-CH2- n
where X and Y are substituents and N is an integer. Also
included are structural isomers of these polymers, typical
examples include poly-N-vinyl carbazole, poly-2-vinyl carbazole
and poly-3-vinyl carba~ole. ~lso included are copolymers; typical
examples are N-vinyl carbazole/methyl acrylate copolymer
and l-vinyl pyrene/butadiene ABA, and AB block polymers.
Typical nonpolymeric materials include carbazole, N-ethylcarbazole,
N-phenylcarbazole, pyrene, tetraphene, l-acetylpyrene, 2,3-
benzochrysene, 6,7-benzopyrene, l-bromopyrene, l-ethylpyrene,
l-methylpyrene, perylene 2-phenylindole, tetracene, picene,
1,3,6,8-tetraphenylpyrene, chrysene, fluorene, fluorenone,
phenanthrene, triphenylene, 1,2,5,6-dibenzanthracene, 1,2,3,4-
dibenzanthracene, 2,3-benzopyrene, anthraquinone, dibenzothiophene,
and naphthalene and l-phenylnaphthalene. Due to the poor
mechanical properties of the nonpolymer materials they are
preferably used in conjunction with either an active polymeric
material or a nonac~ive polymeric binder. Typical examples
include suitable mixtures of carbazole in poly-N-vinyl carbazole
as an active polymer and carbazole in a nonactive binder. Such
nonactive binder materials include polycarbonates, acrylate poly-
mers, polyamides, polyesters, polyurethanes, and cellulose
polymers.
It should be understood that the use of any polymer
(a polymer being a large molecule built up by the repetition
)3
of small, simple chemical units), whose repeat unit contains the
appropriate aromatic hydrocarbon, such as carbazole, and which
supports hole lnjection and transport, may be used. It is not
the intent of the invention to restrict the type of polymer
which can be employed as the transport layer. Polyesters,
polysiloxanes, polyamides, polyurethanes and epoxies as well
as block, random or graft copolymers (containing the aromatic
repeat unit) are exemplary of the various types of polymers
which can be employed as the active material. In addition,
suitable mixtures of active polymers with inactive polymers or
nonpolymeric materials may be employed. One action of certain
nonactive material is to act as a plasticizer to improve the
mechanical properties of the active polymer layer. Typical
plasticizers include epoxy resins, polyester resins,
polycarbonate resins, l-phenyl napthalene and chlorinated
diphenyl.
The above transport layer 15 may comprise aromatic or
heterocyclic electron acceptor materials which have been found
to exhibit negative charge carrier transport properties as well
~0 as the requisite transparency characteristics~ Typical electron
acceptor materials included within the scope of the instant
invention include phthalic anhydride, tetrachlorophthalic
anhydride, benzil, mellitic anhydride, S-tricyanobenzene, picryl
chloride, 2,4-dinitrochlorobenzene, 2,4-dinitrobromobenzene,
4-nitrobiphenyl, 4,4-dinitrobiphenyl, 2,4,6-trinitroanisole,
trichlorotrinitrobenzene, trinitro-o-toulene, 4,6-dichloro-1,3-
dinitrobenzene, 4,6-dibromo-1,3-dinitrobenzene, P-dinitrobenze,
chloranil, bromanil, and mixtures thereof. It is further intended
to include within the scope of those materials suitable for use in
active transport layer 15, other reasonable structural or chemical
-15-
2~3
modifications of the above-described materials provided that the
modified compound exhibits the desired charge carrier transport
characteristics.
While any and all aromatic or heterocyclic electron
acceptors having the requisite transparency characteristic are
within the purview of the instant invention, particularly good
electron transport properties are found with aromatic or hetero-
cyclic compounds having more than one substituent of the strong
electron withdrawing substituents such as nitro(-N02), sulfonate
ion (-S03), carboxyl-(-COOH) and cyano-(CH) groupings. From
this class of materials, 2,4,7-trinitro-9-fluorenone (TNF),
2,4,5,7-tetranitrofluorenone, trinitroanthracene, dinitroacridene,
tetracyanopyrene, and dinitroanthraquinone are preferred materials
because of the availability and superior electron transport
properties.
It will be obvious to those skilled in the art that the
use of any polymer having the described aromatic or heterocyclic
electron acceptor moiety as an integral portion of the polymer
structuxe will function as an active transport material. It is
~ not the intent of the invention to restrict the type of polymer
which can be employed as the transport material, provided it has
an active electron acceptor moiety to provide the polymer with
electron transport characteristics. Polyesters, polysiloxanes,
polyamides, polyurethanes, and epoxies, as well as block, random
or graft copolymers containing the aromatic moiety are therefore
exemplary of the various types of polymers which could be employed.
In addition, electronically inactive polymers in which the active
electron acceptor or material is dispersed at high concentration
can be employed as hereina~ter described.
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z~
The active layer not only serves to transport holes
or electrons, but also protects the photoconductive layer from
abrasion or chemical attack and therefore extends the operating
life of the photoreceptor imaging member.
Electrically active layer or active layer when used
herein to define layer 15 of Figs. 3 and 4 means that the material
is capable of supporting the injection of photogenerated holes or
electrons from the generating material, i.e. layer 12 and is
capable of allowing the transport of these holes or electrons
through the active layer 15 in order to discharge a surface
charge on active layer 15.
The reason for the requirement that active layer, i.e.
charge transport layer 15, should be transparent is that most of
the incident radiation is utilized by the charge carrier generator
layer 12 for efficient photogeneration.
Charge transport layer 15 will exhibit negligible,
if any, discharge when exposed to a wavelength of light useful
in xerography, i.e., 4000 angstroms to 8000 angstroms. Therefore,
charge transport layer 15 is substantially transparent to
radiation in a region in which the photoconductor i5 to be used;
as mentioned, for any absorption of desired radiation by the
active material 15 will prevent this radiation from reaching the
photogeneration layer 12 where it is more effectively utilized.
Therefore, active layer 15 is a substantially nonphotoconductive
material which supports an injection of photogenerated holes from
the generation layer 12.
As mentioned, it is not the intent of this invention to
restrict the choice of active materials to those which are trans-
parent in the entire visible region. For example, when used with
a transparent substrate, imagewise exposure may be accomplished
-17-
! ~ -. ' ' .
z~)3
through the substrate without light passing through the layer
of active material. In this case, the active material need not
be non-absorbing in the wavelength region of use.
The active layer 15 which is employed in conjunction
with the generation layer 12 in the instant invention is a
material which is an insulator to the extent that electrostatic
charge placed on the active transport layer is not conducted
in the absence of illumination, i.e. rate sufficient to prevent
the formation and retention of an electrostatic latent image
thereon.
In general, the thickness of the active layer should
be from about 5-100 microns, but thicknesses outside this range
can also be used. The ratio of the thickness of the active layer
15 to the charge generation layer 12, should be maintained from
about 2:1 to 200:1 and in some instances as great as 400:1.
However, ratios outside this range can also be used.
In another embodiment of the instant invention, the
structure of Fig. 3 is modified to insure that the sodium doped
trigonal selenium particulate material is in the form of
continuous chain through the thickness of binder layer 12. This
embodiment is illustrated by Fig. 4 in which the basic structure
and materials are the same as those of Fig. 3, except the doped
trigonal selenium particulate material 13 is in the form of
continuous chains. The same as illustrated in Fig. 2 for the
particulate material 13.
In another embodiment, the various embodiments of this
invention, i.e. members, may be overcoated with electrically
insulating material. ~owever, it should be understood that when
using such overlayers, then instead of using an electrical
blocking layer between the substrate and the photoconductive or
-18-
f~2~3
charge generation layer there should be used a charge injecting
layer in place of this electrical blocking layer. There must
be charge injecting contact between the substrate and the photo-
conductive layer when using the electrically insulating overlayers.
In another embodiment o~ the present invention, a
photogenerating layer comprising a layer of material similar to
layer 12 illustrated in Fig. l and layer 12 illustrated in Fig. 2
may be sandwiched between an electron transporting material such
as TNF in an electrically inactive binder or a complex of PVK/TNF
(polyvinyl carbazole/2,4,7-trinitro-9-fluorenone) alone and a
layer of hole transport material. Therefore, when TNF alone
is used, it is preferably blended with an inactive polymeric
material in order to enhance the mechanical properties of the
layer. This con~iguration is suitable for use in xerographic
imaging with positive charging. If the position of the
transport layer are reversed, the device then becomes suitable
for use with negative charging. Therefore, in a broader
sense, this embodiment may comprise a three layered composite
photoreceptor device. The device may comprise a photogenerating
layer such as layer 12 in Figs. 1 and 2, i.e. doped trigonal
selenium dispersed randomly or geometrically in a binder,
sandwiched~between two electrically active layers. As mentioned
in one embodiment, the photoconductive layer is sandwiched or
laminated between a positive or hole transport layer on one side
and an electron or negative transport layer on the other side.
In another embodiment, both sides may be hole and
electron transporting, e.g. PVK/TNF complex on both sides (one
side thin enough to allow light ahsorption to the generation
layer).
--19--
Z~3
"Electrically active" when used herein means that the
material is capable of supporting the injection of photogenerated
charge carriers from the generating material and is capable of
allow;ng the transport of these charge carriers through the
active layer in order to discharge a surface charge on the active
layer.
"Electrically inactive" when used herein means that the
material is not capable of supporting the injection of photo-
generated charge carriers from the ~enerating material and is
not capable of allowing the transport of these charge carriers
through the material.
When the term "charge carrier" is used herein it refers
to both photogenerated holes and electrons.
In reference to Figs. 3 and 4, the active layer 15 may
comprise an activating compound useful as an additive to electri-
cally inactive polymeric materials making these materials
electrically active. The following compounds may be added to
the electrically inactive polymeric materials, i.e. materials
which are incapable of supporting the injection of photogenerated
holes from the generation material and incapable of allowing the
transport of these holes therethrough, in order to make the
electrically inactive polymeric material, electrically active
i.e. capable of supporting the injection of photogenerated holes
from the generation material and capable of allowing the transport
of these holes through the active layer in order to discharge
the surface charge on the active layer.
One of the preferred embodiments of this invention
comprise active layer 15 of Figures 3 and 4 as an electrically
active layers which comprises an electrically inactive resinous
-20-
. . : ,.; :
,
Z~3
material made electrically active by the addition of certain
activating compounds added thereto which comprise:
(1) N,N'-diphenyl-N,N'-bis(phenylmethyl)-[l,l'-
biphenyl~-4,4'-diamine with the following formula:
(
\
~CH2 CH2
~ ~
It was found that N,N'-diphenyl-N,N'-bis(phenylmethyl)-
~l,l'-biphenyl]-4,4'-diamine dispersed in an organic binder
transports charge very efficiently without any trapping when
this layer is used contiguous a generation layer, i.e. photo-
conductive layer, and subjected to charge light discharge cycles
in an electrophotographic mode. There is no buildup of the
residual potential over many thousands of cycles.
Furthermore, when N,N'-diphenyl-N,N'-bis(phenylmethyl)-
[l,l'-biphenyl]-4,4'-diamine dispersed in a binder is used as a
transport layer contiguous a charge generation layer, i.e. photo-
conductive layer, there is no interfacial trapping of the
charge photogenerated in and injected from the generating layer.
No deterioration in charge transport was observed when these
transport layers containing N,N~-diphenyl-N,N~-bis(phenylmethyl)
~l,l'-biphenyl]-4,4'-diamine dispersed in a binder subjected
to ultraviolet radiation.
(2) Another activating compound useful as an additive
-21-
2~3
to the electrically inactive polymeric material making it
electrically active is:
~)S C~
wherein Rl is selected from the group consisting of hydrogen,
(ortho) CH3, (meta) CH3 or (para) C~3, and R2 is selected from
the group consisting of (ortho) CH3, (meta) CH3 and (para) CH3.
The preferred materials are N,N'-diphenyl-N,N'-bis-
(2-methylphenyl)-~2,2'-dimethyl-1,1'-biphenyl]-4,4'-diamine;
N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[2,2'-dimethyl-1,1'-
biphenyl]-4,4'-diamine; N,N'-diphenyl-N,N'-bis(4-methylphenyl)-
[2,2'-dimethyl-1,1'-biphenyl]-4,4'-diamine; ~,N,N',N'-tetra(2-
methylphenyl)-[2,2'-dimethyl-1,1'-biphenyl]-4,4'-diamine; N,N'-
bis(2-methylphenyl)-N,N'-bis(3-methylphenyl)-[2,2'~dimethyl-
1,1'-biphenyl]-4,4'-diamine; N,N'-bis(2-methylphenyl)-N,N'-
bis(4-methylphenyl)-2,2'-dimethyl-1,1'-biphenyl]-4,4'-diamine;
N,N'-bis(3-methylphenyl)-N,N'-bis(2-methylphenyl)-2,2'-dimethyl-
1,1'-biphenyl]-4,4'-diamine; N,N,N',N'-tetra(3-methylphenyl)-
[2,2'-dimethyl-1,1'-biphenyl]-4,4'-diamine; N,N' bis(3-methyl-
phenyl)-N,N'-bis(4-methylphenyl)-~2,2'-dimethyl-1,1'-bipheny].]-
4,4'-diamine; N,N'-bis(4-methylphenyl)-N,N'-bis(2-methylphenyl)-
[2,2'-dimethyl-1,1'-biphenyl]-4,4'-diamine; N,N'-bis(4-
methylphenyl)-N,N'-bis(3-methylphenyl)-[2,2'-dimethyl-1,1'-
biphenyl[-4,4'-diamine and N,N,N',N'-tetra(4~methylphenyl)-
[2,2'-dimethyl-1,1'-biphenyl]-4,4'-diamine.
-22-
: .
The most prefexred materials are;
N,N,N',N'-Tetraphenyl-[2,2'-dimethyl-1,1'-biphenyl]-
4,4'-diamine;
_N - N_~
N,N,N',N'-Tetra-(3-methylphenyl)-[2,2'-dimethyl-1,1'-
biphenyl]-4,4'-diamine:
H3C CH3
~ f H3
(~ ~ N
H3C CH3
N,N'-Diphenyl-N,N'~bis(3-methylphenyl)-2,2'-dimethyl-
1,1'-biphenyl[4,4'-diamine:
,~ r~
(~ 3
N._ ~ ~9 N~
H3C CH3
-23-
The electrically active layer, i.e., the photogenerated hole
transport layer 15, is substantially nonabsorbing to visible
light or radiation in the region of intended use, but is "active"
in that is allows the injection of photogenerated holes from the
photoconductive layer, i.e. charge generation layer, and allows
these photogenerated holes to be transported through the electrically
active charge transport layer to selectively discharge a surface
charge on the surface of the active layer or at the interface
between the substrate and the transport layer.
It was found that, unlike the prior art, when the
N,N,N',N'-tetraaryl-bitolyldiamines of the instant invention were
dispersed in an organic binder this layer transports charge very
efficiently without any trapping of charges when this layer is
used contiguous to a generator layer and subjected to charge/light
discharge cycles in an electrophotographic mode. There is no
buildup of the residual potential over many thousands of cycles.
(3) Another activating compound which may be added to
the electrically inactive polymeric material in order to make the
material electrically active is as follows:
~0
X ~ ~ X
wherein X is selected from the group consisting of (or~ho) CH3,
(meta) CH3, tPara) CH3, (ortho) Cl, (meta) C1 and (para) C1. The
chemical name of the above formula is N,N'-diphenyl-N,N'-bis-
(alkylphenyl)-[l,l'-biphenyl]-4,4'-diamine wherein the alkyl is
-24-
~:. ., , ; . . .. . .
selected from the group consisting of 2-methyl, 3-methyl and 4-
methyl or the compound may be N,N'-diphenyl-N,N'-bis(halo phenyl)-
[l,l'-biphenyl]-4,4'-diamino wherein the halo is selected from the
group consisting of 2-chloro, 3-chloro and 4-chloro.
Furthermore, when the substituted ~J,N,N',N'-tetraphenyl-
[l,l'-biphenyl]-4,4'-diamines of the instant invention dispersed
in a binder are used as transport layers contiguous a charge
generation layer, there is no interfacial trapping of the charge
photogenerated in and injected from the generating layer. When
subjected to ultraviolet radiation, no deterioration in charge
transport was observed in these transport layers containing
the substituted N,N,N',N'-tetraphenyl-ll,l'-biphenyl]-4,4'-
diamines of the instant invention.
Furthermore, the transport layers comprising substituted
N,N,N',N'-tetraphenyl-[l,l'-biphenyl]-4,4'-diamines of the instant
invention dispersed in a binder were found to have sufficiently
high (Tg) even at high loadings, thereby eliminating the problems
associated with low (Tg) as discussed above.
(4) Another activating compound which may be added
~ to the electrically inactive polymeric material to make it
electrically active is bis-(4-diethylamino-2-methylphenyl)phenyl-
methane which has the formula:
CH3 CH3
~ I ~
(C2H5)2~ C2H5)2
~J
In all of the above charge transport layers, the
-25-
- : ... .
~ r' ~ , .
activating compound which m~kes the electrically inactive
polymeric material eleetrically active should be present in
amounts of from about 15 to about 75 percent by weight,
preferably ~rom about 25 to 50 percent by weight.
Active layer 15 may comprise any transport electrically
inactive resinous material sueh as those described in
Middleton et al, U.S. Patent 3,121,006.
The preferred electrically inactive resinous mater-
ials are polycarbonate resins. The preferred polycarbonate
resins have a molecular weight (Mw) from about 20,000 to about
100,000, more preferably from about 50,000 to about 100,000.
The materials most preferred as the electrically
inactive resinous material is poly(4,4'-isopropylidene-
diphenylene carbonate) with a molecular weight (Mw) of from
about 35,000 to about 40,000, available as Lexan~ 145 from
General Electric Company; poly(4,4'-isopropylidene-diphenylene
carbonate) with a molecular weight (Mw) of from about 40,000
to about 45,000, available as Lexan~ 141 from the General
Electric Company; a polycarbonate resin having a molecular
weight (Mw) of from about 50,000 to about 100,000, available
as Makrolon~ from Farbenfabricken Bayer A.G. and a polycar-
bonate resin having a moleeular weight (Mw~ of from about
20,000 to about 50,000, available as Merlon~ from Mobay Chemical
Company.
Alternatively, as mentioned, active layer 15 may
comprise a photogenerated electron transport material.
Fig. 5 (sample 13 shows the rested dark deeay and
the fatigue dark decay of a photoreceptor containing trigonal
selenium undoped as the photoconductive material dispersed in
an electrically active binder as the generator layer which is
- 26 -
X ,
~,~Z~LZ~)3
overcoated wi~h a transport layer. This member was made by the
process as set forth in Example IX. The negative corona charge
density was about 1.2 x 10 3 C/m2 and the thickness of the member
was about 25 microns. The member was rested in the dark for 15
hours prior to charging. Then the member was charged to a maximum
of 1280 volts initially measured 0.06 seconds charging. After 0.22
seconds, while the photoreceptor remained in the dark, its rested
dark decay was 60 volts, i.e. the surface potential had dropped to
1220 volts. After 0.66 seconds the surface potential was 1140
volts indicating a dark decay of 140 volts.
As shown in Fig. 5, the fatigue dark decay was obtained
by charging the member initially to a maximum of 1100 volts measured
0.06 seconds after charging. This is 180 volts less than the
member was capable of being charged initially in the rested dark
decay test. After the member remained in the dark for 0.22 seconds,
it discharged to 920 volts which represents a fatigued dark decay
of 180 volts. After 0.66 seconds the member discharged to 770
volts, indicating a fatigue dark decay of 330 volts.
It is convenient to express this fatigue dark decay as
a percentage of the ratio of the surface potential change between
0.22 seconds and 0.66 seconds and the surface potential at 0.22
seconds after charging, e.g. in sample 1, 8% and 16~ for the rested
and fatigued dark decay, respectively.
As can be seen from Fig. 5 the volts of charge on the
surface of the member initially, i.e. after 15 hours dark rest,
is almost the same as the volts of charge on the surface of the
member after a xerographic cycle for the doped members. However,
there is a measurable difference in these surface potential values
for the undoped trigonal selenium. In other words, the drop between
-27-
i
:, .
)3
the rested and the fatigued dark decay is high in the undoped
and low in the doped.
In Fig. 5 (sample 1), i.e. undoped trigonal selenium,
shows 180, 300 and 370 volts difference, respectively, in the
surface potential at 0.06, 0.22 and 0.66 seconds after charging
of the rested, i.e. the member had not been xerographically cycled
in at least 15 hours, versus the fatigued member, i.e. the member
had been xerographically cycled and discharged (erased) in at least
a 30 minute period. However, the doped samples, i.e. Fig. 5
(samples 2-8), showed almost no differences within the experimental
measurement error.
From Fig. 5 (samples 1-8), it is shown by doping
trigonal selenium with sodium for use as a photoconductive
material in a photoreceptor that (1) the surface potential after
fatigue of the undoped trigonal selenium containing photoreceptor
was less than the surface potential of the doped fatigued
trigonal selenium containing photoreceptor. That is, the
fatigued doped members accepted more charge, almost as much
charge as these members accepted when rested, as compared to the
fatigued undoped member which accepted much less charge. The
surface potential of the undoped member becomes much less, much
faster, than the surface potential of the doped members. (2) Also
both the rested and fatigued dark decay are more in the undoped
member after 0.06 seconds, 0.22 seconds and 0.66 seconds in the
dark as compared to the rested and fatigued dark decay in the doped
members.
Referring now to Fig. 6, which shows the photo-induced
discharge curves (PIDC) of members containing doped and undoped
trigonal selenium as the photoconductive material, these PIDC's
show surface potential versus the exposure at the photoreceptor
-28-
. . . . . .
in ErgS/cm2. The PIDC of each sample was taken at two different
times, i.e. 0.06 seconds after exposing and 0.5 seconds after
exposing. The exposure station is loca~ed 0.16 seconds after
charging for a photoreceptor process speed of 30 inches per
second. The PIDC's of sample 1 of Fig. 5 are shown as the
bottom two PIDC's on the graph. The next two PIDC's up the graph
are for sample 3 from Fig. 5. The next two PIDC's are for sample
4 from Fig. 5. The next two PIDC's are for sample 6. The next
PIDC is for sample 7 and the top PIDC is for sample 8.
The square points represent PIDC points (0.5 seconds
after exposing) and the round points represent PIDC points (0.06
seconds after exposing).
Upon examining Fig. 6, it is clear that the PIDC's of
number 1, i.e. sample #1 from Fig. 5 (photoreceptor containing
undoped trigonal selenium), are unstable since the 0.06 seconds
after exposing, PIDC, and the 0.5 seconds after exposing, PIDC,
have changed with time. However, the PIDC's for number 3 (sample
#3, Fig. 5) photoreceptor containing doped trigonal selenium,
number 4 (sample #4, Fig. 5) photoreceptor containing doped
trigonal selenium as well as number 6, 7, and 8 are stable. That
is, the PIDC's vary only slightly with time between 0.06 seconds
after exposing and 0.5 seconds after exposing. In fact, in number
7 and 8 the PIDC's show no variance since the PIDC for 0.06 seconds
after exposing and the PIDC for 0.5 seconds after exposing were about
the same. These curves are superimposed on each other. There-
fore, by doping the trigonal selenium contained in the photo-
receptors, the dark decay is removed from the photoreceptors or at
the least controlled resulting in the stablization of the PIDC's
of these doped members. Most importantly, in the doped members
the PIDC's do not change as a function of time. However, in the
-29-
33
undoped members the PIDC ' s do change as a function of time. This
greatly affects image quality. For example, if a machine were to
use a photoreceptor in belt form and the photoreceptor being used
was undoped trigonal selenium and the member was flash exposed, then
the belt would normally move into the development zone. The leading
edge of the latent image on the belt would go into the develop-
ment ~one before the trailing edge of the image. The PIDC
at the leading edge of the photoreceptor will be different from
the PIDC at the trailing edge, since the PIDC of this undoped
member changes as a func-~ion of time. Therefore, the latent
image when developed would be unacceptable. The PIDC would
unacceptably vary from one end of the image to the other.
However, this effect will vary as a function of the photoreceptor
process speed, i.e. the greater the speed, the greater the effect.
Therefore, this would not happen when using a photoreceptor
containing doped trigonal selenium as the photoconductive
material, since the PIDC's of these members do not change as
a function of time. The latter situation leads to good print
characteristics.
As can be seen from the PIDC's of all the samples, i.e.
Fig. 6, all the sensitivities of the samples are a function of
Na doping level. In addition, the dark decay is also a function
of Na doping level, i.e. Fig. 5. Hence, depending on the Na
doping level the PIDC's are stable and do not change with time.
However, as mentioned, in the undoped member even though the
sensitivity is acceptable the members, i.e. sample #1, PIDC is
unstable and changes with time. Furthermore, the dark decay is
unacceptable.
One preferred embodiment involves exposing the
particulate trigonal selenium to sodium. A preferred method
involves washing the trigonal selenium with sodium hydroxide.
-30-
The trigonal selenium may be washed with water then with the
sodium solution. The amount of sodium on the external surface
of each particle of trigonal selenium may be varied by varying
the sodium hydroxide concentration. This procedure may also vary
the amount of sodium on the internal surface of the trigonal selenium
particles. The excess sodium, e.g. sodium hydroxide, is removed
and depending on the amount of sodium left, this varies the
electrical properties of the trigonal selenium. Preferred
amounts of sodium range from about 0.01 percent by weight to
1.0 percent by weight sodium based on the total weight of
trigonal selenium present. However, 0.01 to 12.0~ by weight
may be used. In addition to sodium hydroxide, sodium carbonate
(Na2C03), sodium bicarbonate (NaHC03) and sodium acetate
(NaC2H302) and sodium selenite (Na2SeO3) may be used to introduce
the sodium into the solution. In addition, other sodium salts
may be used. Similarly, the hydroxides and the salts of lithium,
potassium, rubidium and cesium may be used.
Preferably, the particulate trigonal selenium should
be in the size range from about 0.01 micron to about 10 microns
~ in diameter with the most preferred size being about 0.1 micron
to 0.5 micron in diameter. This size is important in the sense
that these particles of trigonal selenium have a high surface
to volume ratio. A relatively large amount of sodium may be
placed on the surface of these relatively small particles. This
~5 will control the surface component of dark decay. However, it
is preferable that these particles also contain small cracks
and crevasses. It is preferred that the dopants, e.g. sodium,
- lithium, potassium, rubidium and cesium, be deposited in these
cracks or crevasses. This helps control the bulk dark decay of
the trigonal selenium particles. That is, getting the dopants
-31-
`:
Z`~3
into these cracks and crevasses helps control and relieve bulk
charge trapping. Therefore, both the external and internal
surface of the particles of trigonal selenium are being doped.
Another possible explanation for doping the internal surface,
i.e cracks and crevasses, of the particles o~ trigonal selenium
particles is that all of the light does not stop at the surface
of the particles but goes into the inside or inner portion of
the particle and excites the material, i.e. trigonal selenium,
at that point. When the dopants are located in the cracks
and crevasses then these dopants help relieve the dark discharge.
That is, the dopants help with bulk discharge of each particle
of trigonal selenium. As mentioned, it is believed that both
the surfacc and the internal portion o~ particles of trigonal
selenium are helped by the dopants being on both the surface
and in the cracks and crevasses of the particles.
The salts, such as ~aOH, NaHCO3, NaCO3 and CH3COONa,
and Na2SeO3 may also serve to neutralize any residual selenious
acid (H2SeO3) left from the preparation formed by Se reacting
with water.
The following examples further specifically define
the present invention with respect to a method of making the
doped trigonal selenium containing photoconductive members.
The percentages are by weight unless otherwise indicated.
The examples below are intended to illustrate various
preferred embodiments of the instant invention.
EX~MP~ I
Preparation of undoped trigonal_selenium - Into a
500 milliliter Erlenmeyer flask fitted with a magnetic stirrer
is placed 100 gms. of reagent grade sodium hydroxide (NaOH)
dissolved in 100 milliliters of deionized water. When the
solution is complete, then 23.7 gms. of X-grade amorphous
selenium beads available from Canadian Copper Refineries are
added. The solution is stirred at 85C for fi~e hours. Then
deionized water is added to bring the total volume up to 300
milliliters. The solution is stirred for one minute. The heat
is then removed and the solution allowed to digest at least for
18 hours.
The above solution is then filtered through a coarse
fritted glass funnel into a vacuum glass containing 3700
milliliters of deionized water. The water should be swirling.
The total volume is 4 liters. The solution is stirred for
five minutes. Then 10 milliliters of 30 percent reagent grade
hydrogen peroxide (H2O2) is added dropwise to the solution
over a period of two minutes. The solution is stirred for
an additional 30 minutes. Trigonal selenium is then
precipitated out of the solution resulting in the proper size
of particulate trigonal selenium being formed. The precipitated
trigonal selenium, i.e. solids, may be allowed to settle out. Then
decant the supernatent and replace this with deionized water.
This washing procedure is repeated until the resistivity of the
supernatent equals that of the deionized water. Then the
trigonal selenium (undoped) is filtered out on a ~o~ 2 filter
paper. The undoped trigonal selenium is dried at 60C
in a forced air oven for 18 hours. The sodium content of
the final undoped trigonal selenium powder is 20 ppm (parts per
million) other metal impurities are less than 20 ppm. The
yield is 80 percent.
EXAMPLE II
Th`e preparation of undoped trigonal selen m - Into
a 500 millil~ter Erlenmeyer flask fitted with a magnetic stirrer
.
and a dropping funnel is placed 100 gms. of reagent grade sodium
hydroxide (NaOH) and dissolved in 100 milliliters of deionized
water. When the solution is complete, 23.7 gms. of X-grade
amorphous selenium beads available from CCR (Canadian Copper
Refineries) is added. Then the solu-tion is heated to 85C and
stirred for five hours. Then deionized water is added to bring
the total volume of the solution up to 300 milliliters. The
solution is stirred for one minute. The heat is removed and the
solution is allowed to digest at least 18 hours. The above
solution is filtered through a coarse fritted glass funnel into
a flask containing deionized water. The water should be swirling
during the addition. The quantity of the water is such that upon
precipitation, the final volume of slurry is 4 liters. The
solution is stirred for five minutes. Stoichiometric amounts
of either one of the following acids may be added: either 208
milliliters of 12 normal (N) HC1, 150 milliliters of 16 normal (N)
HNO3 or 70 milliliters of 36 normal (N) H2SO4 or 133 ml of 17.4
(N) CH3COOH or 155 gm of H2SeO3. These are diluted to the desired
concentrations which is usually 1.2 normal (N). Then these
solutions are added to the polyselenide solution as rapidly
as possible. A procedure that may be used to dilute the acid
to 2 liters [1.2 normal (N)] and add to 2 liters of polyselenide
solution. After the addition, the solution is stirred for
1/2 hour. The particulate size is as desired.
A particular procedure which may be followed is
to allow the solids, i.e. precipitated trigonal selenium,
to settle out. Then decant the supernatent and replace it
with deionized water. This washing procedure is repeated
until the resistivity of the supernatent equals that of the
-34-
)3
deionized water. Then the trigonal selenium is filtered
on a No. 2 filter paper. The selenium is dried at 60C
in a forced air oven for 18 hours. The sodium content of the
undoped final trigonal selenium powder is 20 ppm. The other
me~al impurities are less than 20 ppm. The yield is 95 percent.
EX~MPLE III
P'reparation of so'dium doped 'tr'igonal selenium -_
Trigonal selenium made by either Example I or Example II
may be used. The trigonal selenium must be thoroughly washed
and before filtering, decant as much of the supernatent
as possible. Then refill the solution to a volume of four
liters with a 0.6 normal (N) solution of sodium hydroxide (NaOH).
Alternatively, 0.6 N, Na2CO3, NaHCO3, CH3COONa, Na2SeO3 may
be used. This solution should be swirled for 1/2 hour. Tlle solids
should be allowed to settle out and remain in contact with the
sodium hydroxide (NaOH) or Na2CO3, NaHCO3, CH3COONa, Na2SeO3
solution for 18 hours. The solution is decanted and the supernatent
is retained. The doped trigonal selenium is filtered on a No. 2
filter paper. The retained supernatent is used to rinse the
beaker and funnel. The doped trigonal selenium is dried at 60C
in a forced air oven for 18 hours. The sodium levels average
approximately 1.0 percent by weight based on the total
weight of the trigonal selenium. All other metal impurities
are less than 30 ppm.
'EXAMPLE IV
Prepara'tion of' a member cont'ain'.in'~ 'undoped tr'igonal
selenium d'i'sp-ers'ed' in an' electrical'ly ac'tive' r'esih'ous binder - A
five mil aluminized Myla ~ substrate is rinsed with CH2C12 methylene
chloride. The aluminized Myla ~ substrate is allowed to dry at
ambient temperatures. In a glove box with the humidity less than
-35-
20 percent and the temperature at 82F, a layer of l/2 percent
DuPont 49,000 adhesive, a polyester available from DuPont, in
CHC13 (chloroform~ and trichloroethane 4 to 1 volume is coated
onto the substrate with a Bird applicator. The wet thickness
of the layer is l/2 mil. This layer is allowed to dry for one
minute in the glove box and ten minutes in a 100C oven.
Alternatively, the aluminized Myla ~ may be coated with a layer
of l/2~ Monsanto B72A (polyvinylbutyrol~ in ethanol with a Bird
applicator. The wet thickness is 1/2 mil. The layer is allowed
to dry in a glove box for 1 minute and lO minutes in 100C oven.
A generator layer containing 20~ by volume undoped
trigonal selenium is prepared as follows:
Into a 2 ounce amber bottle is added 0.8 grams
purified PVK and 14 ml. of l:l THF/toluene. Added to this
solution is 100 grams of l/8 inch stainless steel shot and
0.8 grams undoped trigonal selenium. The above mixture is
placed on a ball mill for 72 hours. Then the solution is
coated on the above interface layer with a Bird applicator.
The wet thickness is ]/2 mil~ Then this member is annealed at
100C in a vacuum for 13 hours. The dry thickness is 2 microns.
EXAMPLE V
Preparation of a member contain~ing undoped trigonal
selenium dispersed i_ an active binder - A five mil aluminized
Myla ~ substrate is rinsed with CH2C12 methylene chloride. The
aluminized Myla ~ substrate is allowed to dry at ambient tempera-
ture. In a glove box with the humidity less than 20 percent and
the temperature at ~2F, a layer of one percent Hytre ~, a polyester
blocked polymer available from DuPont, in CHC13 (chloroform~ is
coated onto the substrate with a l/2 mil Bird applicator. The
; -36-
:
33
wet thickness of the layer is 1/2 mil. This layer is allowed
to dry for one minute in the glove box and five minutes in a
100C oven. Then this is coated with a second layer of 1 percent
PVK in benzene with a Bixd applicator. A 1/2 mil wet layer is
applied. This layer is allowed to dry for one minute in the
glove box and 5 minutes in a 100C oven.
A layer containing 25 percent by volume based on the
total volume of the member of undoped trigonal selenium is prepared
as follows: In a two ounce amber bottle is placed 0.328 grams of
PVK, 0.0109 grams of TNF and 14 ml of benzene. 100 grams of
stainless steel shot is added and 0.44 grams o~ undoped trigonal
selenium as prepared in Example I or Example II is added. The
above solution is placed on a paint shaker for one hour. Then
7 ml of benzene is added. The solution is placed on a roller
mill for 1 minute. The solution is then coated on the above-
prepared aluminized Myla ~ substrate by making 3 passes with a 1/2
mil Bird applicator on the above-prepared aluminumed Myla ~
substrate. The solution is allowed to dry for 1 minute between
each pass. Then this member is annealed at 100C in a vacuum
~0 for 18 hours. The dried thickness is 2 microns.
' EXAMP'LE VI
Pr'epa'ra'tion of a me'mber 'conta'ining doped trigonal
selenium `dispersed in an electri_ally ~ac'tive' re's no'us binder -
A five mil aluminized Myla ~ substrate is rinsed with methylene
chloride (CH2C12). The aluminized Myla ~ is allowed to dry at
ambient temperature. In a glove box with humidity less than
20 percent and the temperatuxe at 82F r a layer of 1/2 percent
DuPont 49,000 adhesive in CHC13 (chloroform~ and trichloroethane
4 to 1 volume, is coated onto the aluminized Myla ~ with a
Bird applicator to a wet thickness of 1/2 mil. The coating is
-37-
dried for 1 minute in the glove box and 10 minutes in a 100C
oven. Alternatively, the aluminized Myla ~ may be coated with a
layer of 1/2 percent Monsanto B72A (polyvinylbutyral) in ethanol
with a Bird applicator. The wet thickness is 1/2 mil. The layer
is allowed to dry in a glove box for 1 minute and lO minutes in
100C oven.
A generator layer containing 20 percent by volume doped
trigonal selenium is prepared as follows: I~to a 2 ounce amber
bottle is added 0.8 grams purified PVK and 14 ml of 1:1 THF/
toluene. Added to this solution is 100 grams of 1/8 inch stain-
less steel shot and 0.8 grams doped trigonal selenium as prepared
in Example III. The above mixture is placed on a ball mill for
72 hours. Then the solution is coated on the above interface
layer with a Bird applicator. The wet thickness is 1/2 mil.
Then this member is annealed at 100C in a vacuum for 18 hours~
The dry thickness is 2 microns.
EX~MPLE VII
Prepar'ation of a s'o'dium'doped'trigonal`selenium member
where-in` the'dope'd trig~nal selenium i-s dispersed 'in 'an electrically
active resinous bi~der - A ~ive mil aluminized Myla ~ substrate
is rinsed with methylene chloride (CH2C12). The aluminized Myla
is allowed to dry at ambient temperature. In a glove box with
humidity less than 20 percent and the temperature at 82F, a layer
of one percent Hytre ~, a polyester blocked polymer available
from DuPont, in CHC13 (chloroform) is coated onto the aluminized
Myla ~ with a Bird applicator to a dry thickness of 1/2 mil.
The coating is dried for one minute in the glove box and five
minutes in a 100C oven. A second coating is applied to the member
which is one percent PVK in benzene ~C6H6~ with a Bird applicator
resulting in a dry thickness of lJ2 mil. This layer is allowed
-38-
f~3
to dry for one minute in the glove box and 5 minutes in a 100C
oven.
A 25 percent by volume doped trigonal selenium containing
member is prepared by placing into a two ounce amber bottle
0.328 gm. of P~K, 0.0109 gm. of ~NF and 14 milliliters of
benzene (C6H6). Added to this is one hundred gms. of stainless
steel shot and 0.44 gms. of doped trigonal selenium as prepared
in Example III. The above solution is placed on a paint shaker
for one hour. Then 7 milliliters of benzene (C6H6) is added. This
10 solution is placed on a roller mill for one minute. Then the
solution is coated by making three passes with a Bird applicator.
The solution is allowed to dry for one minute between each pass.
The member is annealed at 100C in a vacuum oven for 18 hours.
The dried layer is about two microns thick.
E'XAMPLE VIII
Prepar _ion of'N,N'-dipheny'l-N,N''-bis('3-me't lphenyl)
[l,l'-biphenyl]-4,4'-diamine - In a 500 milliliter, round bottom,
3-necked flask fitted with a mechanical stirrer and blanketed with
Argon, is placed 360 gms. (1 mole) of N,N'-biphenylbenzidene,
20 550 gms. (2.5 moles) of m-iodotoluene, 550 gms. (4 moles)
potassium carbonate (anhydrous) and 50 gms. of copper bronze
catalysts and 1,500 milliliters of dimethylsulfoxide (anhydrous).
The heterogeneous mixture is refluxed for 6 days. The mixture
is allowed to cool. 2000 milliliters of benzene is added. The
25 dark slurry is then filtered. The filtrate is extracted 4 times
with water. Then the filtrate is dried with magnesium sulfate
and filtered. The benzene is taken off under reduced pressure.
The black produce is column chromatographed using ~oelm neutral
alumina. ~olorless crystals of the'product are obtained by
-39-
)3
recrystallizin~ the product from n-octane. The melting point
is 167-169C. The yield is 360 gms. (65 percent~.
E AMPL~ IX
A co~posite~photoconductive member is prepared which
s comprises a genera~or lay~r which is overcoated with a transport
layer - ~ five mil aluminized Myla ~ substrate is rinsed with
CH2C12. This substrate is allowed to dry at ambient temperature.
In a glove box with humidity less than 20 percent and the
temperature at 82F the aluminized Myla ~ substrate is coated
with a layer of 1/2 percent Dupont 49,000 adhesive in CHC13 and
trichloroethane at 4:1 volume with a Bird applicator. The wet
thickness is 1/2 mil. The layer is allowed to dry for 1 minute
in a glove box and 10 minutes in 100C oven. Alternatively, the
aluminized Myla ~ may be coated with a layer of 1/2 percent
Monsanto B72A (polyvinylbutyral) in ethanol with a Bird
applicator. The wet thickness is 1/2 mil. The layer is allowed
to dry in a glove box for 1 minute and 10 minutes in 100C oven.
A generator layer containing 20% by vol~me undoped
trigonal selenium is prepared as follows: Into a 2 ounce amber
bottle is added 0.8 grams purified PVK and 14 ml of 1:1 THF/
toluene. Added to this solution is 100 grams of 1/8 inch
stainless steel shot and 0.8 grams undoped trigonal selenium as
prepared in Example I or IIo The above mixture is placed on
a ball mill ~or 72 hours. Then the solution is coated on the above
interface layer with a Bird applicator. The wet thickness is
1/2 mil. Then this member is annealed at 100C in a vacuum
for 18 hours. The dry thickness is 2 microns.
; The above generator layer is overcoated with a charge
transport layer which i5 prepared as follows: A transport layer
containing 50 percent by weight Makrolon~, a polycarbonate resin
-40-
. . .
having a molecular weight (Mw) of from about 50,000 to about
100,000, available from Larbensabricken Bayer A.G., is mixed with
50 percent by weight N,N'-diphenyl-N,N'-bis(3-methylphenyl)-
[l,l'-biphenyl]-4,4'-diamine as prepared in Example VIII. This
solution is mixed in 15 percent by weight methylene chloride. All
of these components are placed into an amber bottle and dissolved.
The mixture is coated to a dr~ 25 micron thickness layer on top of
the generator layer using a Bird applicator. ~he humidity is equal
to or less than 15 percent. The solution is annealed at 70C
in a vacuum for 18 hours. The member is tested the same as the
members as shown in Fig. 5 and Fig. 6. The rested dark decay
and the fatigue dark decay o~ this photoreceptor containing
undoped trigonal selenium as a photoconductive material dispersed
in an electrically insulating resinous binder as a generating
material overcoated with a charge transport material is tested
as follows. The member is rested in the dark for 15 hours prior
to charging. Then the member is charged to a maximum of 1280
volts initially measured at 0.06 seconds after charging. After
0.22 seconds while the photoreceptor remains in the dark, its
rested dark decay is 60 volts, i.e. the surface potential dropped
to 1220 volts. After 0.66 seconds the surface potential is 1140
volts indicating a dark decay of 140 volts.
The fatigued dark decay is obtained by charging the
member initially to a maximum of 1100 volts measured at 0.06
secGnds after charging. This is 180 volts less than the member
was capable of being initially in the rested dark decay test.
After the member is retained in the dark for 0.22 seconds, it
discharges to 920 volts, which represents a fatigued dark decay
of 180 volts. After 0.66 seconds, the member discharges to 770
volts indicating a fatigued dark decay of 330 volts.
-41-
.
13
EXAMPLE X
A composite photoconductive member is prep~ared which
comprises a generation layer which is overcoated with a transport
layer - The generation layer comprises undoped trigonal selenium
dispersed in a resinous binder.
A five mil aluminized Myla ~ substrate is rinsed
with methylene chloride. This substrate is allowed to dry
at ambient temperature. In a glove box with the humidity less
than 20 percent and the temperature at 82F, the aluminized Myla ~
substate is coated with a layer of one percent Hytrel~ in chloroform
with a Bird applicator. The wet thickness of this layer is 1/2
mil. The layer is allowed to dry for one minute in a glove box
and five minutes in 100C oven. This layer is coated with a
second layer of one percent PVK in benzene with the sird applicator.
The wet thickness of this layer is 1/2 mil. This layer is allowed
to dry for one minute in the glove box and 5 minutes in a 100C
oven.
A generation layer containing 25 percent by volume
undoped trigonal selenium is prepared as follows. Into a 2 ounce
amber bottle is added 0.328 gm~ PVK, 0.0109 gm. TNF and 14
milliliter of benzene. Added to this solution is 100 gms. of
stainless steel shot and 0.44 gm. undoped trigonal selenium.
The above mixture is placed on a paint shaker for one hour. Then
7 milliliters of benzene is added. Then the solution is placed
on a roller mill for one minute. Then the solution is coated
by making three passes with the slurry with a Bird applicator.
One minute is allowed between passes in order for the solution to
dry. The solution is annealed at 100C in ~acuum for 18 hours.
The dry thickness of the layer is 2 microns.
-42-
The above generator layer is overcoated with a charge
transport layer which is prepared as follows. A transport layer
containing 50 percen~ by weight o Makrolon~, a polycarbona~e resin
having a molecular weight (Mw) of from about 50,000 to about
lO0,000, available from Larbensabricken Bayer A. G., is mixed
with 50 percent by weight of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-
[l~l'-biphenyl~-4~4'-diamine as prepared in Example VIII. This
solution is mixed in 15 percent by weight methylene chloride.
All of these components are placed into an amber bottle and
dissolved. The mixture is coated to a dry 25 micron thickness
layer on top of the generator layer using a Bird Applicator.
The humidity is equal to or less than 15 percent. The solution
is annealed at 70C in a vacuum for 18 hours. The member is
tested as in Fig. 5 and Fig. 6.
EXAMPLE XI
-
Preparation of a multilayered -imaging member c mprising
a generation layer over'coated with a' transpor't'layer - A five mil
aluminized Myla ~ substrate is rinsed with methylene chloride.
The substrate is allowed to dry at ambient temperature. In a
glove box with the humidity less than 20 percent and the temperature
at 82F, the substrate is coated with a layer of l/2 percent DuPont
49,000 adhesive in a 4:1 by volume chloroform and trichloroethane
with a Bird applicator to a wet thickness of 1/2 mil. The layer
is allowed to dry in a glove box for one minute and in a 100C
oven for lO minutes. Alternatively, the aluminized Myla ~ may
be coated with a layer of l/2 percent ~onsanto B72~ (polyvinyl~
butyral) in ethynal with a Bird applicator. The wet thickness is
l/2 mil. The layer is allowed to dry in a glove box for l
minute and 10 minutes in a 100C oven.
A charge generation layer containing 20 percent by volume
-43-
,, ; , :
Z~33
of sodium doped trigonal selenium is prepared as follows. ~ 2
ounce amber bottle is provided and 0.8 gram purified ~VK, and 14
ml of 1:1 THF/toluene is added to the bottle. To this solution
is added 100 gms. of 1/2 inch stainless steel shot and 0.8 gm.
sodium doped trigonal selenium as prepared in Example III.
This solution is placed on a ball mill for 72 hours.
Then the solution is coated on the above interface layer with a
sird applicator. The wet thickness is 1/2 mil. Then this member
is annealed at 100C in a vacuum for 18 hours. A dry thickness
is formed which is 2 microns thick.
A charge transport layer is formed on the above charged
generating layer. The charge transport layer comprises a 50-50
by weight solution of ~akrolo ~, a polycarbonate resin having a
molecular weight (Mw) of from about 50,000 to about 100,000
~5 available from Larbenfabricken Bayer A. G., and N,N'-diphenyl-
N,N'-bis(3-methylphenyl)-[1,1'-biphenyl~-4,4'-diamine as prepared
in Example VIII. This solution is placed into 15 percent by
weight methylene chloride. All of these ingredients are placed
in an amber bottle and dissolved. The components are coated
with a Bird applicator to form a dry coating of 25 microns
on top of the charge generation layer. The humidity is equal
to or less than 15 percent. The solution is annealed at 70C
in a vacuum for 18 hours.
The member is tested as in Fig. 5 and Fig. 6, sample 6.
The rested dark decay and fatigue dark decay in the photoconductive
which contains doped trigonal selenium is tested. In order to
illustrate the rested dark decay, the member is charged to a
maximum of 1260 volts initially measured at 0.06 seconds after
charging and after 0.22 seconds it discharges to 1200 volts,
representing a rested dark decay of 60 volts. After 0.66 seconds it
-44-
2~3
discharges to 1190 volts, representing a rested dark decay of
70 volts. The fatigue dark decay is shown by initially charging
the member to a maximum of 1300 volts measured at 0.06 seconds
after charging and after 0.22 seconds in the dark, the member
discharges to 1210 voltsr representing a fatigue dark decay of
90 volts. After 0.66 seconds the member discharges to 1190
volts, representing a fatigue dark decay of 110 volts.
EXAMPLE XII
Fabrication of undoped; trigonal seleni-um binder layer -
A trigonal selenium binder layer containing 30 percent by volume
trigonal selenium is prepared as follows: Into a 2 ounce clear
glass bottle is added 1 ounce (vol.) 1/8 inch stainless steel shot,
7.5 grams Flexclad~ cubes, a polyester available from Goodyear,
11.5 grams trigonal selenium as prepared in Example I or II, and
21.0 ml chloroform. The jar is placed on a paint shaker for 1
hour. The slurry is then placed in a vacuum desiccator and a
vaccum pulled to remove air bubbles in the slurry. The slurry is
coated on a 5 mil aluminum substrate with a multiple clearance bar.
The wet thickness is 10 mil. The la~er is dried for 2 hours at
~ 60C and heated to 150C for 20 minutes.
The plate is tested electrically b~ charging the plate
to a field of 20 volts/micron and discharging it at a wavelength
of 5800 angstrom units at 8 x 1012 photons/cm2 second. The plate
exhibits satisfactory discharge at the above fields and is capable
of use in forming visible images.
The member is also tested as illustrated in Figs. 5 and
6. However, this member is charged with positive corona. The
undoped trigonal selenium containing member has a high dark
discharge and an unstable PIDC as compared to members containing
doped trigonal selenium as the photoconductive material.
-45-
33
EXAMPLE XIII
Fabrication of doped trigonal selenium binder layer -
A trigonal selenium binder layer containing 30 percent by volume
doped trigonal selenium as prepared in Example III is prepared
as follows: Into a 2 ounce clear glass bottle is added 1 ounce
(vol.) 1/8 inch stainless steel shot, 7.5 grams Flexcla ~ polyester
cubes available from Goodyear, 11.5 grams doped trigonal selenium
prepared as in Example III and 21.0 ml chloroform. The jar is
placed on a paint shaker for 1 hour. The slurry is then placed
in a vacuum desiccator and a vacuum is pulled to remove air
bubbles in the slurry. The slurry is coated on a 5 mil aluminum
substrate with a multiple clearance bar. The wet thickness is
10 mil. The layer is dried for 2 hours at 60~C and heated to
150C for 20 minutes.
The plate is tested electrically by charging the plate
to a field of 30 volts/micron and discharging it at a wavelength
of 5800 angstrom units at 8 x 1012 photons/cm2 second. The plate
exhibits satisfactory discharge at the above fields and is
capable of use in forming visible images.
The member is also tested as illustrated in Figs~ 5 and
6. However, this member is charged with positive corona. The
doped trigonal selenium containing member has a low dark
discharge as compared to the member as prepared in Example
XII, i.e. undoped trigonal selenium, and has a stable PIDC as
compared to the member as prepared in Example XII.
EXAMPLE XIV
Fabrication of undoped_trigonal selenium contained
in a geometrically controlled ph t_receptor - A photoreceptor
with geometricall~ controlled photoconductive material, i.e.
undoped trigonal selenium, contained therein is prepared as follows:
-46-
2~3
The member contains 8 percent by volume undoped
trigonal selenium. Into a 4 ounce clear glass bottle is added
2 ounces (vol.) 1/8 inch stainless steel shot, 4.5 grams o~
undoped trigonal selenium as prepared in Examples I or II and
18.75 ml of a 1:1 isopropyl alcohol/isobutylalcohol~ This is
placed on a ball mill for 6 hours at lS0 RPM. To this slurry is
added 14.4 grams of spray dried Flexcla ~, a polyester available
from Goodyear, and 30 ml of a 1:1 isopropylalcohol/isobutyl-
alcohol. This is ball milled for 18 hours at 150 RPM.
The slurry is filtered through a 100 mesh screen, then
allowed to stand for 10 minutes to remove air bubbles. The slurry
is coated on a 5 mil aluminum substrate with a 10 mil multiple
clearance bar. This layer is dried for 3 hours at 50C. It is
then fused for 20 minutes at 175C.
The trigonal selenium is in substantially particle-to-
particle contact in said member in a multiplicity of interlocking
paths or chains through the thickness of the layer. The undoped
trigonal selenium paths or chains are present in a volume
concentration, as mentioned, as 8 percent based on the volume of
the layer.
The member is tested as illustrated in Figs. 5 and 6.
However, this member is charged with positive corona.
The undoped trigonal selenium containing member has a high
dark discharge and an unstable PIDC as compared to members
containing doped trigonal selenium as the photoconductive material.
~XAMPLE ~V
Fabricatio'n of dcp~ed trigonal selenium ontained in
a geomet-rical'l controlled ph'otorec'ept'or - A phbtoreceptor with
- --Y - -- .
geometrically controlled photoconductive material, i.e. doped
trigonal selenium, contained therein is prepared as follows:
47-
The member contains 8 percent by volume doped
trigonal selenium. Into a 4 ounce clear glass bottle is added
2 ounces (vol.) 1/8 inch stainless steel shot, 4.5 grams of doped
trigonal selenium as prepared in Examples III and 18.75 ml o~ a
1:1 isopropylalcohol/isobutylalcohol. This is placed on a ball
mill for 6 hours at 150 RPM. To this slurry is added 14.4 grams
of spray dried Flexcla ~, a polyester available from Goodyear,
and 30 mil of a 1:1 isopropylalcohol/isobutylalcohol. ThiS is
ball milled from 18 hours at 150 RPM.
The slurry is filtered through a 100 mesh screen, then
allowed to stand for 10 minutes to remove air bubbles. The slurry
is coated on a 5 mil aluminum substrate with a 10 mil multiple
clearance bar. This layer is dried for 3 hours at 50C. It is
then fused for 20 minutes at 175C.
The trigonal selenium is in substantailly particle-to-
particle contact in said member in a multiplicity of interlocking
paths or chains through the thickness of the layer. The doped
trigonal selenium paths or chains are present in a volume
concentration, as mentioned, as 8 percent based on the volume
of the layer.
The member is tested as illustrated in Figs. 5 and 6.
However, this member is charged with positive corona. The doped
trigonal selenium containing member has a low dark discharge
and a stable PIDC as compared to members containing undoped
trigonal selenium as the photoconductive material.
-48-
