CA1132398A - Hole trapping layer comprised of nitrogen containing electron donors for use in overcoated photoreceptors - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Disclosed is a novel hole trapping layer and the use of this layer in an overcoated photoresponsive device, this trapping layer being comprised in one embodiment of nitrogen containing electron donating molecules containing aromatic amines selected from the group consisting of those within the following formula:

and wherein Z is Ar or R, R being an aliphatic radical or a substituted aliphatic radical, and Ar is an aromatic radical or a substituted aromatic radical.
This hole trapping layer can be used in an overcoated photoreceptor device comprised of a substrate, overcoated with an injecting electrode layer which in turn is overcoated with a transport layer, followed by a generating layer overcoated with the trapping layer and finally an overcoating of an insulating organic polymer. Polymeric nitrogen containing electron donat-ing molecules are also useful trapping layers.

Description

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-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~

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~

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 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 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 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 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 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 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~

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.

Claims (23)

WHAT IS CLAIMED IS:

1. A layered photosensitive imaging member which comprises from the bottom up:
(a) a bottom support substrate;
(b) a hole injecting electrode material capable of injecting holes into a layer on its surface, this layer being comprised 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 injectingmaterial, which transport layer comprises 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 photogenerated 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 comprised of nitrogen-containing electron donating molecules selected from the group consisting of those molecules embraced within the following formulas:

and wherein Z is Ar or R, R being an aliphatic radical or a substituted 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 generating material.

2. A layered photosensitive imaging member in accordance with Claim wherein the material used as the hole trapping layer is nigrosine.

3- The material in accordance with Claim 1 wherein the hole trapping material is methylene blue.

4. A photosensitive imaging device in accordance with Claim 1 wherein the hole trapping material is 5,6-benzoquinoline or triphenylamine.

5. An imaging member in accordance with Claim 1 wherein the trapping layer is dispersed in an adhesive polyester.

6. An imaging member in accordance with Claim 1 wherein the injecting material is carbon black dispersed in a polyester.

7- An imaging member in accordance with Claim 1 wherein the hole injecting material is graphite dispersed in a polyester.

8- An imaging member in accordance with Claim 1 wherein the hole trappingmaterial is Induline 3B HCl.

9 An imaging member in accordance with Claim 1 wherein the hole trappingmaterial is diphenyl amine.

10. An imaging member in accordance with Claim 1 wherein the hole trapping layer is p-bromoaniline.

11. An imaging member in accordance with Claim 1 wherein the hole trapping layer contains as an additional material an adhesive material.

12. An imaging member in accordance with Claim 1 wherein the electrically active material dispersed in the insulating organic polymer is a nitrogen containing compound of the formula:

wherein X is selected from the group consisting of (ortho) CH3, (meta) CH3, (para) CH3, (ortho) Cl, (meta) Cl, (para) Cl.

13. An imaging member in accordance with Claim 12 wherein the hole transport layer contains from about 10 to 75% of the nitrogen containing composition.

14. An imaging member in accordance with Claim 13 wherein the transport layer active material is N,N'-diphenyl-N,N'-bis-(3-methyl phenyl){l,l'-biphenyl]-4,4'-diamine.

15. An imaging member in accordance with Claim 1 wherein the generating layer is selected from the group consisting of metal free phthalocyanines and metal phthalo-cyanines.

16. An imaging member in accordance with Claim 15 wherein the metal free phthalocyanine is X-metal free phthalocyanine.

17. An imaging merrier in accordance with Claim 15 wherein the metal phtkalocyanine is vanadyl phthalocyanine.

18. An electrophotographic imaging method comprising providing an imaging member of Claim 1, charging the imaging member with negative electrostatic charges, charging the imaging member with positive electro-static 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 charge carrier generating material is responsive whereby there is formed an electrostatic latent image within the imaging member.

19. A method in accordance with Claim 18 and further including the step of forming a visible image by contacting the surface of the imaging member with electroscopic marking materials.

20. An imaging method in accordance with Claim 18 wherein the trapping material is dispersed in a polymer.

21. A layered photosensitive imaging member in accordance with Claiml wherein the thickness of the hole trapping layer ranges from about 0.0005 microns to about 1 micron.

22. A layered photosensitive imaging member in accordance with Claim 1 wherein the thickness of the hole trapping layer ranges from about 1 micron to about 15 microns,

23. A layered photosensitive imaging member in accordance with Claim 1 wherein the hole trapping layer has a thickness of from about 3 microns to about 8 microns and the substrate is the non-conducting material, polyethylene terephthalate, or the conductive material aluminum.