Note: Descriptions are shown in the official language in which they were submitted.
--1--
HOLE TRAPPING LAYER COMPRISED OF NITROGEN CONTAINING
ELECTRON DONORS FOR USE IN OVERCOAT~D P~OTORECEPTORS
This invention is generally directed to an electro-
photographic imaging device and more specifically a device
which contains a trapping layer as well as a method of
imaging utilizing such a device.
The formation and development of images on the
imaging surfaces of photoconductive materials by electro-
static means is well known, one of the most widely used
processes being xerography, which is discussed in Carlson
U. S. Patent 2,297,691. Numerous types of photoreceptors
can be used in the electrophotographic process such photo-
receptors including organic materials, inorganic materials
and mixtures thereof. Photoreceptors are known wherein
the charge carrier generation and charge carrier transport
functions are accomplished by discrete contiguous layers.
Also known are photoreceptors which include an overcoating
layer of an electrically insulating polymeric material and
in conjunction with this overcoated type photoreceptor
there have been proposed a number of imaging methods. How-
ever, the art of electrophotography and more specifically
xerography, continues to advance and more stringent
demands need to be met by the copying apparatus in order
to increase performance standards to obtain higher quality
images and to act as protection for the photoreceptor as
well as to control the manner and the type of charges that
are transported and retained at various levels of the photo-
receptor device. In the present invention, there is des-
cribed in one embodiment an electrophotographic imaging
device employing an improved organic electrophotographic
imaging member which contains a trapping layer.
A method for utilizing an overcoated photoreceptor
device has been recently discovered and is described in
U.S. Patent No. 4,254,199, issued March 3, 1981, Simpei
Tutihasi. In the method described in this application,
there is utilized an imaging member comprislng a substrate,
~'
. -la-
a layer of a charge carrier injecting electrode material,
a layer of a charge carrier transport material, a layer of a
photoconductive charge carrier generating material and an
electrically insulating overcoating layer. In one embodi-
ment of operation, the member is charged a first time withelectrostatic charges of a first polarity, charged a second
time with electro-
--2--
static charges of a-polarity opposite to the first polarity in
order to substantially neutralize the charges residing on the
electrically insulating surface of the member and exposed to an
imagewise pattern of activating electromagnetic radiation
whereby an electrostatic latent image is formed. The electro-
static latent image may then be developed to form a visible
image which can be transferred to a receiving member. Subse-
quently, the imaging member may be reused to form additional
reproductions after the erasure and cleaning steps have been
accomplished. The actual operation of this member is best
il].ustrated by referring to the figures which are part o~ the
present application and more specifically, Figures 2A 2C.
The hole trapping layer discussed in greater detail
hereinafter, which is between the generating layer and insula-
ting layer, is of importance since if the holes, that is,positive charges, are not substantially retained at the inter-
face between the two above-mentioned layers, the efficiency
of the photoreceptor device is adversely affected when such
holes are allowed to freely migrate back to the generator
layer. If some of the holes are allowed to migrate, they
will travel towards the electrode layer and neutralize the
negative changes located between the hole injecting layer 14
and the transport layer 16, thus reducing the overall voltage
useful for the succeeding imaging process. This would adver-
sely affect the imaging system as well as lower the efficiencyof the device and render the cyclic characteristics of such
device unstable. The device is operative without the trap-
ping layer, however depending on the amount and the frequency
with which the holes travel throughout the system, the amount
of holes retained at the generator/insulator interface varies,
resulting in cyclic unstability. A trapping layer will assure
that substantially all the holes remain at the interface.
It is an object of an aspect of this invention to pro-
vide a photoreceptor device which overcomes the above-noted
disadvantages.
An object of an aspect of the present invention is to
, ~ provide an improved organic photoreceptor device and more
~' specifically a device containing a trapping layer.
-2a-
An object of an aspect of the present invention is
a method for the preparation of the trapping layer to be
used in the overcoated photoreceptor device.
An object of an aspect of the present invention is
the provision of a trapping layer which prevents charges
from migrating from the interface
3~8
between the generating layer and the overcoating insulating layer to the
injecting electrode so &S to improve image quality and reduce dark decay
and improve cyclability of the photoreceptor device.
These and other objects of the present invention are accom-
5 plished by providing a trapping layer comprised of electron donating mol-
ecules. In a preferred embodiment, these materials are incorporated into
a layer comprised of adhesive polymers. The trapping layer of the photo-
responsive device is of substantial importance as mentioned hereinbefore,
its main function being to trap holes, that is, positive charges, thus the ma-
10 terial used in this layer must be capable of emitting electrons in order thatthe positive charges will be trapped, that is, remain in position at the inter-
face between the generating layer and the overcoating insulating layer. The
photoresponsive device may remain photosensitive without the trapping layer,
however, higher fields will be needed in order to render the device efficient,
15 the disadvantage of using higher fields being that it causes breakdown in
the system and more ozone is generated thus posing an environmental problem
in some situations. It is preferable to use lower voltages as the system is
more efficient and more stable and further with the hole trapping layer, the
dark decay of the system, that is leakage of charges, will improve signifi-
20 cantly so as to substantially eliminate such dark decay.
The hole trapping material can be any nitrogen containingelectron donating molecules which donate sufficient electrons so as to accom-
plish the above objectives while at the same time not adversely affecting
the imaging device and allowing cyclic stability of the photoreceptor device.
25 Generally, most organic electron donor materials can be used, that is, ma-
terials that will emit or readily give up electrons. In one embodiment of
the present invention, there is employed, as the nitrogen containing electron
donating molecules, aromatic amines selected from the group consisting
of those within the following formulas:
Z
Ar - N'
z
z
Ar - N
35~
--4--
and H
Ar - N'
H
wherein Z is Ar or R, R being an aliphatic radical or substituted aliphatic
radicals, and Ar is an aromatic radical or a substituted aromatic radical,
the substituents including for example alkyl, alkylene, halogen, and the like.
Examples of aliphatic materials include saturated as well as unsaturated
radicals such as alkyl, of from 1 to about 20 carbon atoms, alkylene of from
2 to about 24 carbon atoms. Illustrative examples of such radicals include
10 methane, ethane, propane, butane, isobutane, pentane, neopentane, heptane,
decane, tetradecane, eicosane, ethylene, propylene, butylene, alphabutylene,
pentylene, heptylene, decylene, pentadecylene, and the like. The substituted
alkyl or alkylene radicals include those mentioned above. Examples of hal-
ogen materials include chloride, bromide, iodide and fluoride. Illustrative
15 examples of aromatic radicals include those containing from about 6 to about
20 carbon atoms such as phenyl, napthyl anthryl and the like. Polymeric
nitrogen containing electron donating molecules are also useful trapping
layers within the scope of the present invention.
In one embodiment the aromatic substituted materials are of
20 the following formula:
Y~
wherein Y is an aliphatic radical, or a halogen, as defined herein.
Illustrative examples of specific materials which may be used
25 as the trapping layer of the present invention, it being noted that these ex-amples are not all inclusive, and other similar or equivalent materials can
be utilized, include triphenylamine, 2-methyl triphenylamine, 4-methyl tri-
phenylamine, tri-p-tolyamine, diphenylamine, p-bromoaniline, poly(2-vinyl
pyridine), polyvinylpyrrolidone, l-dimethylaminonapthylene, 2-amino anthra-
30 cene, nigrosine, induline, methylene blue, pheno safranine, congo red, indigoblue, capri blue, polyethyleneimine, l-amino-pyrene, 5,6-benzo quinoline, imino
dibenzyl, Nphenyl-l-naphthyl amine, and the like.
Although the hole trapping materials described are aromatic
type substances, certain aliphatic electron donor molecules particularly ali-
35 phatic amines wherein the aromatic nucleus is replaced by an aliphatic radicalin the above-mentioned formula can be used in the present invention in certain
instances as long as the particular aliphatic amine does not adversely affect
. `'` ~ ~ .
1~3'~39~
--5--
the objects of the invention and performs as an efficient
trapping layer so as to improve cyclability.
Generally, the hole trapping layer which is designated
by the numeral 21 in Figure 1, in one preferred embodiment, is
prepared by coating this layer on the surface of the generating
layer 18 followed by application of a laminated material con-
taining an adhesive layer and an insulating overcoat layer such
as Mylar. In another embodiment that is where the trapping
layer is not a discrete layer but is combined with the adhesive
materials, designated by 19 in Figure lA, the trapping mole-
cules are dispersed in an adhesive polymer and this layer is
then applied to the insulating film. In this way the hole
trapping layer can be effectively adhered to the generating
layer by lamination.
The thickness of the hole trapping layer can range
over a wide spectrum and also depends on the manner in which
the hole trapping layer is applied. For example, when a lami-
nation process is used, and the hole trapping layer is coated
on the generating layer, the thickness of the hole trapping
layer ranges from about 0.0005 to 1 micron and preferably
from about 0.05 to 0.2 microns, while when the hole trapping
layer is incorporated into an adhesive material, the trapping
layer ranges in thickness from about 1 to 15 microns and
preferably from 3 to about 8 microns. The thickness of the
adhesive layer when it is employed as a separate layer and
is not part of the hole trapping layer for example see
Figure 1, layer 22, ranges from about 1 to about 15 microns
and preferably from about 3 to about 8 microns.
In one preferred embodiment of the present invention,
the photoresponsive device is comprised of a hole trapping
layer 21 sandwiched in between a generator layer 18, an ad-
hesive layer 22 and/or an overcoating insulating layer 20,
the remaining portions of the photoreceptor device being
comprised of a substrate, a hole injecting electrode layer
thereover comprised of carbon black dispersed in a polymer,
11~23~
-5a-
a charge transport layer comprised of an electrically
inactive organic polymer having dispersed therein an electric-
ally active material, the combination of which is substantial-
ly nonabsorbing to visible electromagnetic radiation but
allows the injection of photogenerated holes from a charge
generating layer in contact with the hole transport layer
which layer is overcoated with the charge generating
material 18 previously described.
-5a-
According to one aspect of this invention there is
provided a layered photosensitive imaging member which com-
prises from the bottom up: ~a) a bottom support substrate;
(b) a hole in~ecting electrode material capable of inject-
ing holes into a layer on its surface, this layer being com-
prised of materials selected from the group consisting of
carbon black, or graphite, dispersed in a polymer or gold;
(c) a hole transport layer in operative contact with the
layer of hole injecting material, which transport layer com
prises a combination of a highly insulating organic polymer
having dispersed therein small molecules of an electrically
active material, the combination of which is substantially
nonabsorbing to visible light but allows injection of photo-
generated holes from a charge generator in contact with the
hole transport layer and electrically induced holes from the
layer of injecting electrode material; (d) a layer of photo-
charge generating material on and in operative contact with
the charge transport layer; (e) a hole trapping layer com-
prised of nitrogen-containing electron donating molecules
selected from the group consisting of those molecules
embraced within the following formulas:
Z
- Ar-N
z
z
Ar-N
H
and
H
Ar-N
H
wherein Z is Ar or R, R being an aliphatic radical or a sub-
stituted aliphatic radical and Ar is an aromatic radical or
a substituted aromatic radical; and (f) a layer of insulating
organic polymer overlaying the layer of photo-charge genera-
~) ting material.
-5b-
In accordance with another aspect of this invention
there is provided an electrophotographic imaging method
comprising providing an imaging member of the type herein-
before described, charging the imaging member with negative
electrostatic charges, charging the imaging member with
positive electrostatic charges in order to substantially
neutralize the negative charge residing on the surface
of the imaging member and exposing the imaging member to
an imagewise pattern of electromagnetic radiation to which
the charye carrier generating material is responsive whereby
there is formed an electrostatic latent image within the
imagin~ member.
BRIEF DESCRIPTION OF THE DRAWINGS
"J
`` 1~3239~3
For a better understanding of the present invention and further
features thereof, reference is made to the following detailed description of
various preferred embodiments wherein:
Eigures 1 and lA are partially schematic crosssectional view
5 of a photoreceptor device containing a trapping layer which may be utilized
in the method of the present invention;
Figures 2A to 2C illustrate the various method steps employed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Illustrated in Figure 1 is a photoreceptor generally designated
10 10 comprising a substrate 12, a layer of charge injecting electrode material
14, a layer of charge carrier transport material 16, a layer of photoconductive
charge carrier generating material 18, a layer of trapping material 21, a layer
of adhesive material 22, and a layer of electrically insulating polymeric mater-ial 20, it being noted that the layer of adhesive material 22 can be coated
15 on the electrically insulating polymeric material in one embodiment. Figure
lA illustrates a similar type of photoreceptor with the exception that the
layer of trapping material is represented by 19, this layer being comprised
of a combination of trapping and adhesive materials.
Substrate 12 may be opaque or substantially transparent and
20 may comprise any suitable material having the requisite mechanical proper-
ties. The substrate may comprise a layer of non-conducting material such
as an inorganic or organic polymeric material; a layer of an organic or inor-
ganic material having a conductive surface layer arranged thereon or a con-
ductive material such as, for example, aluminum, brass or the like. The sub-
25 strate may be flexible or rigid and may have any of many different config-
urations such as, for example, a plate, a cylindrical drum, a scroll, an endlessflexible belt, and the like. Preferably, the substrate is in the form of an end-less flexible belt.
The thickness of this layer can vary but generally is from about
30 3 to 100 mils and preferably from about 3 to 10 mils although thicknesses of
over 100 mils and less than 3 mils can be used.
Charge carrier injecting electrode layer 14 must be capable of
injecting charge carriers or holes into the transport layer 16 under the influence
of an electrical field. The charge carrier injecting electrode layer may be
35 sufficiently laterally conductive to also function as the ground electrode for
the photoreceptor and in such a situation a separate additional conductive
.
3~?8
--7--
layer is not necessary.
Numerous materials can be used as the charge inject-
ing electrode layer including those materials (such as for
example, gold graphite, carbon black or graphite dispersed
in various polymer resins and the like) which effectively
inject holes that is positive charges into the transport
layer. These materials are capable of injecting holes under
the influence of an electrical field. In a preferred embodi-
ment, carbon black or graphite dispersed in varous polymers
is used as the injecting electrode, this charge injecting
electrode being prepared as described in U. S. Patent No.
4,251,612, issued February 17, 1981. J.Y.C. Chu and S.
Tutihasi, inventors, which in one method involves solution
casting of a mixture of carbon black or graphite dispersed
in an adhesive polymer solution onto a support substrate
such as Mylar or aluminized Mylar. The hole injecting
electrode which is preferably carbon black or graphite dis-
persed in a polymer also functions as a permanent adhesive
between the substrate and the organic transport layer. Thus,
the injecting layer does not have a tendency to peel off,
that is to be separated from the transport and support layer
so that the quality of the image is not adversely effected
after repetitive usage. Gold, silver and other such
materials when used as the injecting electrode, perform satis-
factorily, however, they do not adhere as well as carbon orgraphite dispersed in a polymer. One other advantage of
using carbon black and graphite in polymers are that these
materials are rather inexpensive when compared to gold, for
example, are more readily available and function in some
instances more effectively than gold.
Illustrative examples of polymers that can be used
as the material within which the carbon black or graphite is
dispersed include, for example, polyesters such as PE-100 com-
mercially available from Goodyear Chemical Company. Other
polyester materials that are useful include those materials
classified as polymeric esterification products of a dicar-
boxylic acid and a diol comprising a diphenol. Typical
* trade mark
--8--
diphenols include 2,2-bis(4-beta hydroxy ethoxy phenyl)-
propane, 2,2-bis(4-hydroxy isopropoxy phenyl)propane, 2,2-bis
(4-beta hydroxy ethoxy phenyl)pentane, 2,2-bis(4-beta hydroxy
ethoxy phenyl) butane and the like, while typical dicarboxylic
acids include oxalic acid, malonic acid, succinic acid, adipic
acid, phthalic acid, terephthalic acid, maleic acid, fumaric
acid and the like. Any polyester or other polymeric materials
may be used providing they do not adversely affect the system
and allow a uniform dispersion of the carbon black or graphite
therein.
The hole injectin~ layer has a thickness in the range
of from about 1 to about 20 microns or more with the prefer-
red range being rrom about 4 microns to about 10 microns.
The maximum thickness is generally determined by the mechani-
cal properties desired. The charge carrier injecting materialsand charge carrier transport materials require a particular
work function relationship in order that hole injection from
the former into the latter can be effectively accomplished.
Normally the hole injecting materials have a relatively high
work function.
The ratio of polymer to carbon black or graphite
ranges from about 0.5 to 1 to 2 to 1 with a preferred ratio
of about 6 to 5.
The charge carrier transport layer 16 can be any
number of numerous suitable materials which are capable of
transporting holes, this layer generally having a thickness
in the range of from about 5 to about S0 microns and prefer-
ably from about 20 to about 40 microns. In a preferred
embodiment this transport layer comprises molecules of the
formula:
~\ /~ '
~ ~ N ~ N ~
3~3
-8a-
dispersed in a highly insulating and transparent organic
polymeric material wherein X is selected from the group con-
sisting of (ortho) CH3, ~meta) CH3, (para) CH3, ~ortho) Cl,
(meta) Cl, (para) Cl. This charge transport layer, which
is described in detail in Canadian Patent No. 1,104,866,
issued July 14, 1981, M. Stolka, is substantially non-absorb-
ing in the spectral region of intended use, i.e., visible
light, but is "active" in that it allows injection of photo-
generated holes from the charge generator layer and elec-
trically induced holes from the injecting electrode. Thehighly insulating polymer, which has a resistivity of at
least 1012 ohm-cm to prevent undue dark decay, is a material
which is not necessarily capable of supporting the injection
of holes from the injecting or generator layer and is not
capable of allowing the transport of these holes through the
material. However, the polymer becomes electrically
active when it contains from about 10 to 75 weight percent of
the substituted N,N,N',N'-tetraphenyl-[l,l'-biphenyU 4-4'-diamines correspondingto the foregoing formula. Compounds corresponding to this formula include,
for example, N,N'diphenyl-N,N~bis(alkyl-phenyl~[l,l-biphenyl]-4,4-diamine
wherein the aLcyl is selected from the group consisting of methyl such as 2-
5 methyl, 3-methyl and 4-methyl, ethyl, propyl, butyl, hexyl and the like. In
the case of chloro substitution, the compound is named N,N'diphenyl-N,N'-
bis (halo phenyl~[l,l'biphenyl]-4,4'-diamine wherein the halogen atom is 2-
chloro, 3-chloro or 4-chloro.
Other electrically active small molecules which can be dispersed
10 in the electrically inactive polymer to form a layer which will transport holes
include triphenylmethane, bis-(4-diethylamino-2-methylphenyl) phenylmethane;
4',4"-bis(diethylamino)-2,2"-dimethyltriphenyl methane; bis-4(-diethylamino
phenyl) phenylmethane; and 4,4'-bis(diethylamino~2,2'-dimethyltriphenylmeth-
ane.
lS Transport layer 16 may comprise any electrically inactive binder
polymeric material such as those described by Middleton et al, in U.S. Patent
B 3,121,006,~eer-pe~e~ herein by-refere~ce~ The polymeric binder contains
from 10 to 75 weight percent of the active material corresponding to the for-
egoing formula and preferably from about 35 to about 50 weight percent of
20 this material. Typical organic polymeric materials useful as the binder include
polycarbonates, acrylate polymers, vinyl polymers, cellulose polymers, poly-
esters, polysiloxanes, polyamides, polyurethanes and epoxies as well as block,
random or alternating copolymers thereof. Preferred electrically inactive
binder materials are polycarbonates having a molecular weight (Mw) of from
25 about 20,000 to about 100,000 with a molecular weight in the range of from
about 50,000 to about 100,000 being particularly preferred.
Photoconductive charge carrier generating layer 18 generally
may comprise any photoconductive charge carrier generating material known
for use in electrophotography provided it is electronically compatible with
30 the chflrge carrier transport layer and the charge carriers can travel in both
directions across the interface between the two layers. Particularly preferred
photoconductive charge carrier generating materials include materials such
as phthalocyanines like metal free, for example, the X-form of phthalocyanine,
or metal phthalocyanines including vanadyl phthalocyanine. These materials
35 can be used alone or as a dispersion in a polymeric binder. Layer 18 is typi-cally from about 0.5 to about 10 microns or more in thickness. Generally,
3~3
--10--
it is desired to provide this layer in a thickness which is sufficient to absorbat least 90 percent (or more) of the incident radiation which is directed upon
it in the imagewise exposure step.
Electrically insulating overcoating layer 20 typically has a bulk
resistivity of from about 1012 to about 5 x 1014 ohm-cm and typically is from
about S to about 25 microns in thickness. Generally, this layer provides a
protective function in that the charge carrier generating layer is kept from
being contacted by toner and ozone which is generated during the imaging
cycles. The overcoating layer also must prevent charges from penetrating
through it into charge carrier generating layer 18 or from being injected into
it by the latter. Preferably, therefore, layer 20 comprises materials having
higher bulk resistivities. Generally, the minimum thickness of the layer in
any instance is determined by the functions the layer must provide whereas
the maximum thickness is determined by mechanical considerations and the
resolution capability desired for the photoreceptor. Typical suitable materials
include Mylar (a polyethylene terephthalate film commercially available from
E. I. duPont de Nemours), polyethylenes, polycarbonates, polystyrenes, poly-
esters, polyurethanes and the like. The particular material selected in any
instance should not be one which will dissolve or react with the materials used
in layers 16 and 18.
The formation of the electrically insulating layer 20 over the
previous layer may be carried out by lamination or solution coating, where
layer 20 constitutes a preformed mechanically tough film, it is typically nec-
essary to provide sufficient adhesive material in order to provide an integral
25 structure which is desirable for use in a repetitive imaging method. The e-
lectrical properties of any such adhesive interlayer should be similar to those
of the overcoating. Alternatively, they may be similar to the binder material
of the charge carrier generating layer 18 where a binder materifll is present
in that layer. Mechanically, the adhesive interlayer should provide an adhesive
30 state that firmly binds the layers together without any air gaps or the like
which could disturb image definition.
The charge carrier injecting electrode material which comprises
layer 14 is a hole injecting material such as graphite, gold, and carbon or graph-
ite dispersed in a polymer and the initial charging step is carried out with
35 negative polarity. More specifically, there is represented in Figure 2A the
condition of the photoreceptor after it has been electrically charged nega-
tively a first time in the absence of illumination by any suitable electrostaticcharging apparatus such as a corotron. The negative charges reside on the
surface of electrically insulating layer 20. As a consequence of the charging,
an electrical field is established across the photoreceptor and as a consequence5 of the electrical field, holes are injected from the charge carrier injecting
electrode layer into the charge carrier transport layer. The holes injected
into the charge carrier transport layer are transported through the layer, enterinto the charge carrier generating layer 18 and travel through the latter until
they reach the interface between the charge carrier generating layer 18 and
10 the hole trapping layer where they become trapped. The charges are thus
substantially trapped at the interface, and establish an electrical field acrossthe electrically insulating layer 20, therefore, where negative charging is
carried out in the first charging step, charge carrier injecting layer 14 and
charge carrier transport layer 16 must comprise materials which will allow
15 injection of holes from the former into the latter and charge transport layer16 comprises materials which will predominantly transport holes. The charge
carrier transport layer 16 and the charge carrier generating layer 18 must
comprise materials which will allow injection of holes from the former into
the latter and allow the holes to travel to the interface between layer 18 and
20 hole trapping layer 19 or 21. Generally, the electrical field established by the
first charging is in the range of from 10 volts/micron to about 100 volts/micron.
Subsequently, the member is charged a second time in the ab-
sence of illumination with a polarity opposite to that employed in the first
charging step for the purpose of substantially neutralizing the charges residing25 on the surface of the member. The second charging of the member in this
embodiment is effected with positive polarity. Subsequent to the second
charging step, the surface of the photoreceptor should be substantially free
of electrical charges. The substantially neutralized surface is created by
selecting a charging voltage based on the dielectric thickness ratio of the
overcoating layer 20, plus the hole trapping layer 19, or 21 and 22 to the totalof the charge carrier transport and charge carrier generating layers 16 and
18 respectively. By substantially neutralized is meant that the voltage across
the photoreceptor member upon illumination of the photoreceptor may be
brought to substantially zero.
In Figure 2B, there is illustrated the condition of the photore-
ceptor after the second charging step, wherein no charges are shown on the
~3Z;398
--12--
surface of the member. The positive charges residing at the interface of
layers 18 and 19 in Fig. lA or layers 18 and 21 in Fig. 1 as a result of the first
charging step remain substantially trapped at that interface at the conclusion
of the second charging step. However, there is now a uniform layer of neg-
5 ative charges located at the interface between layers 14 and 16. The netresult of the second charging step is to establish a uniform electrical field
across the charge carrier transport and charge carrier generating layers. In
order to obtain this result, it is important that the negative charges be located
at the interface between the charge carrier injecting layer 14 and charge
10 carrier transport layer 16 and prevented from entering into the transport layer.
For this reason, it is preferred to utilize a charge carrier transport material
which will transport only one species of charge carrier, holes in this situation.
Where a charge carrier transport material capable of transporting both species
of charge carriers is employed, in layer 16, the charge carrier injecting ma-
15 terial would have to be selective so that the latter would be unable to injectelectrons into layer 16 thus placing constraints on the selections of materials.
The member is then exposed to an imagewise pattern of electro-
magnetic radiation (Figure 2C) to which the charge carrier generating ma-
terial comprising layer 18 is responsive. Exposure of this member is accom-
20 plished through the electrically insulating overcoating. As a result of theimagewise exposure an electrostatic latent image is formed in the photore-
ceptor as the hole electron pairs are generated in the light struck areas of
the charge carrier generating layer. The light generated holes are injected
into the charge carrier transport layer and travel through it to be neutralized
25 by the negative charges located at the interface between layers 14 and 16
whereas the light generated electrons neutralize the positive charges trapped
at the interface between layers 18 and 19 or 21. In the areas of the member
which did not receive any illumination, the positive charges remain in their
original position, thus there continues to be an electrical field across the
30 charge carrier transport and charge carrier generating layers in the areas
which do not receive any illumination whereas the electrical field across the
same layers in the areas which did receive illumination is discharged to some
low level.
The electrostatic latent image formed in the member may be
35 developed to form a visible image by any of the well known xerographic de-
velopment techniques, for example, cascade, magnetic brush, liquid devel-
~3~8
--13--
opment and the like. The visible image is typically transferred to a receivermember by any conventional transfer technique and affixed thereto. While
it is preferably to develop the electrostatic latent image with marking ma-
terial the image may be used in a host of other ways such as, for example,
5 I'reading" the latent image with an electrostatic scanning system.
When the photoreceptor is to be reused to make additional repro-
ductions as is the case in a recyclible xerographic apparatus any residual charge
remaining on the photoreceptor after the visible image has been transferred
to a receiver member typically is removed therefrom prior to each repetition
10 of the cycle as is any residual toner material remaining after the transfer
step. Generally, the residual charge can be removed from the photoreceptor
by ionizing the air above the electrically insulating overcoating of the photo-
receptor while the photoconductive carrier generating layer is uniformly illumi-nated and grounded. For example, charge removal can be effected by A.C.
15 corona discharge in the presence of illumination from a light source or pre-
ferably a grounded conductive brush could be brought into contact with the
surface of the photoreceptor in the presence of such illumination. This latter
mode also will remove any residual toner particles remaining on the surface
of the photoreceptor.
Examples of adhesive materials layer 22 or as part of layer 19
include polyesters such as those commercially available from E. 1. duPont
E~ Co. (re~3~ Polyester 49000), polyurethanes and the like).
The invention will now be described in detail with respectto specific preferred embodiments thereof, it being understood that these
Examples are intended to be illlustrative only and the invention is not intended25 to be limited to the materials, conditions, process parameters, etc., recitedherein. All parts and percentages are by weight unless otherwise indicated.
EXAMPLE I
A photoreceptor was fabricated using an approximately 5 mil
thick Mylar substrate. A charge injecting composition was formed by pre-
30 paring a 12 percent solution of PE-100 polyester resin available from Goodyear
Chemicals in chloroform, adding to it approximately about 10 percent by weight
of carbon black and ball milling the mixture for about 24 hours with steel shot.An approximately 4-6 micron thick layer of the composition was deposited on
the Mylar substrate and the sample was then dried to remove residual solvents.
f ~-;,
.,
239~3
--14--
An approximately 25 micron thick charge carrier transport layer made up
of ~,N'-diphenyl-N,N'-bis (3-methylphenyl~[l,l~biphenyl]-4-4' diamine in a
polycarbonate binder (1:1 ratio) was formed on the carbon black layer by solventcoating from a methylene chloride solution using a draw bar coating technique.
5 The member was then dried in a vacuum oven at a temperature of about 70C
for about 24 hours.
A charge carrier generating layer comprised of a dispersion of
5 percent DuPont 49000 polyester and a 2.3 percent X-metal free phthalo-
cyanine in methylene chloride was applied as an overcoat to the transport
B layer followed by drying. A 1 percent alcoholic solution of ~igrosine was
applied on the surface of the charge carrier generating layer followed by
drying to form the hole trapping layer and finally an approximately 0.5 mil
thick layer of Mylar film having a polyester adhesive preapplied thereto was
laminated to the hole trapping layer.
The photoreceptor was charged at a first time with a potential
of -400 volts and then charged a second time with a potential of +800 volts.
The photoreceptor was then uniformly illuminated with white light. Electrical
measurements show that the field across the photoreceptor was discharged
to substantially zero potential. The process was repeated successfully for
20 more than two thousand times thus indicating that the photoreceptor is suit-
able for use according to the method of the present invention.
When the hole trapping layer was used in the photoreceptor
device, excellent cyclic stability was obtained thus allowing the production
of continuous images of high quality in a commercial cowing machine in excess
25 of five thousand copies. Therefore images of high quality were immediately
obtained and there was no waiting period as compared with when no trapping
layer is used, the cyclic stability is not maximized and there is a waiting period
prior to achieving the cyclic stability desired in order that improved images
of high quality can be produced.
EXAMPLE Il
A photoreceptor was fabricated by coating an approximately
7 mil thick Mylar substrate with an approximately 8 micron layer of the con-
ductive hole injecting composition as described in Example I by the same
technique. An approximately 27 micron thick hole transport layer and 3 micron
35 thick charge carrier generating layer of the same compositions as used in theprevious example were deposited successively over the conductive hole in
.
.~ :
1~32~8
jecting layer by solvent coating according to the procedures described in Ex-
ample I.
The hole trapping material was incorporated into the laminating
adhesive layer by mixing 0.5 percent by weight of Nigrosine with a solution
of DuPont 46923 adhesive polyester. The resulting solution was coated on
a 0.5 mi] transparent Mylar film to form an approximately 4 micron thick
trapping adhesive layer. Finally the Mylar film was laminated over the charge
carrier generating layer. This photoreceptor was charged a first time wlth
a potential of -480 volts and then charged a second time with a potential of
~1160 volts and subsequently the photoreceptor was then uniformly illuminated
with white light. Electrical measurements show that the field across the
photoreceptor was discharged to substantially zero potential, thus indicating
that the photoreceptor was suitable for use according to the present invention.
When the hole trapping layer was used in the photoreceptor
device, excellent cyclic stability was obtained thus allowing the production
of continuous images of high quality in a commercial copying machine in excess
of five thousand copies. Therefore images of high quality were immediately
obtained and there was no waiting period as compared with when no trapping
layer is used, the cyclic stability is not maximized, and there is a waiting
period prior to achieving the cyclic stability desired in order that improved
images of high quality can be produced.
EXAMPLE m
The procedure of Example I was repeated with the exception
that Induline 3B HCl was used in place of the Nigrosine and substantially
resolution resulted and improved cyclability was achieved. Also the photo-
receptor was charged in accordance with the potentials of Example I with
substantially similar results thus indicating that the photoreceptor is suitablefor use according to the methods of the present invention.
EXAMPLE IV
The procedure of Example II was repeated with the exception
that the trapping material used was methylene blue in place of the Nigrosine
and substantially similar results were obtained, that is images of high quality
and excellent resolution resulted and improved cyclability was achieved. Also
the photoreceptor was charged in accordance with the potentials of Example
I with substantially similar results thus indicating that the photoreceptor is
suitable for use according to the methods of the present invention.
239~
--16--
EXAMPLE V
The procedure of Example II ~as repeated with the exception
that Induline 3B HCl was used in place of the Nigrosine and substantially
similar results were obtained, that is images of high quality and excellent
5 resolution resulted and improved cyclability was achieved. Also the photo-
receptor was charged in accordance with the potentials of Example I with
substantially similar results thus indicating that the photoreceptor is suitablefor use according to the methods of the present invention.
EXAMPLE VI
The procedure of Example Il WRS repeated with the exception that
diphenylamine (9.2 weight percent) was used in place of the Nigrosine and
substantially similar results were obtained, that is images of high quality and
excellent resolution resulted and improved cyclability was achieved. Also
the photoreceptor was charged in accordance with the potentials of Example
15 I with substantially similar results thus indicating that the photoreceptor is
suitable for use according to the methods of the present invention.
EXAMPLE VII
The procedure of Example II was repeated with the exception
that ~bromoaniline (9.2 weight percent) was used in place of the Nigrosine
20 and substantially similar results were obtained, that is images of high quality
and excellent resolution resulted and improved cyclability was achieved. Also
the photoreceptor was charged in accordance with the potentials of Example
I with substantially similar results thus indicating that the photoreceptor is
suitable for use according to the methods of the present invention.
EXAMPLE VIII
The procedure of Example II was repeated with the exception
that polyvinylpyrrolidone (9.2 weight percent) was used in place of the Nigro-
sine and substantially similar results were obtained, that is images of high
quality and excellent resolution resulted and improved cyclability was achieved.30 Also the photoreceptor was charged in accordance with the potentials of Ex-
ample I with substantially similar results thus indicating that the photoreceptor
is suitable for use according to the methods of the present invention.
EXAMPLE IX
The procedure of Example II was repeated with the exception
35 that phenazine was used in place of the Nigrosine and substantially similar
results were obtained, that is images of high quality and excellent resolution
~ ~3'~ 8
resulted and improved cyclability was achieved. Also the photoreceptor was c
charged in accordance with the potentials of Example I with substantially
similar results thus indicating that the photoreceptor is suitable for use ac-
cording to the methods of the present invenffon.
EXAMPLE X
The procedure of Example II was repeated with the exception
that triphenylamine (9 weight percent ) was used in place of the Nigrosine
and substantially similar results were obtained, that is images of high quality
and excellent resolution resulted and improved cyclability was achieved. Also
the photoreceptor was charged in accordance with the potentials of Example
I with substantially sirnilar results thus indicating that the photoreceptor is
suitable for use according to the methods of the present invention.
EXAMPLE XI
The procedure of Example II was repeated with the exception
that in place of the Induline 3B HCl there was used a polyethyleneamine
(9 weight percent) in place of the Nigrosine and substantially similar results
were obtained, that is images of high quality and excellent resolution resulted
and improved cyclability was achieved. Also the photoreceptor was charged
in accordance with the potentials of Example I with substanffally similar re-
sults thus indicating that the photoreceptor is suitable for use according to
the methods of the present invention.
EXAMPLE XII
The procedure of Example II was repeated with the exception
that 5,6-benzo quinoline, a tertiary amine was used in place of the Induline
3B HCl and substantially similar results were obtained, that is images of
high quality and excellent resolution resulted and improved cyclability was
achieved. Also the photoreceptor was charged in accordance with the poten-
tials of Example I with substantially similar results thus indicating that the
photoreceptor is suitable for use according to the methods of the present
invention.
Although the invention has been described with respect to spe-
cific preferred embodiments, it is not intended to be limited thereto, but
rather those skilled in the art will recognize that variations and modificationsmay be made therein which are within the spirit of the invention and the scope
3S of the claims.
