In electrophotography, a photoreceptor in the form of a plate, belt, or drum having an electrically insulating photoconductive element on an electrically conductive substrate is imaged by first uniformly electrostatically charging the surface of the photoconductive layer, and then exposing the charged surface to a pattern of light. The light exposure selectively dissipates the charge in the illuminated areas, thereby forming a pattern of charged and uncharged areas. A liquid or solid toner is then deposited in either the charged or uncharged areas to create a toned image on the surface of the photoconductive layer. The resulting visible toner image can be transferred to a suitable receiving surface such as paper. The imaging process can be repeated many times.

Both single layer and multilayer photoconductive elements have been used. In the single layer embodiment, a charge transport material and charge generating material are combined with a polymeric binder and then deposited on the electrically conductive substrate. In the multilayer embodiment, the charge transport material and charge generating material are in the form of separate layers, each of which can optionally be combined with a polymeric binder, deposited on the electrically conductive substrate. Two arrangements are possible. In one arrangement (the"dual layer"arrangement), the charge generating layer is deposited on the electrically conductive substrate and the charge transport layer is deposited on top of the charge generating layer. In an alternate arrangement (the"inverted dual layer'arrangement), the order of the charge transport layer and charge generating layer is reversed.

In both the single and multilayer photoconductive elements, the purpose of the charge generating material is to generate charge carriers (i. e., holes or electrons) upon exposure to light. The purpose of the charge transport material is to accept

these charge carriers and transport them through the charge transport layer in order to discharge a surface charge on the photoconductive element.

To produce high quality images, particularly after multiple cycles, it is desirable for the charge transport material to form a homogeneous solution with the polymeric binder and remain in solution. In addition, it is desirable to maximize the amount of charge which the charge transport material can accept (indicated by a parameter known as the acceptance voltage or"V."), and to minimize retention of that charge upon discharge (indicated by a parameter known as the residual voltage or"V").

Liquid toners generally produce superior images compared to dry toners.

Regardless of the toner used, a latent image is developed by the deposition of a dry or liquid toner on the photoconductor surface. The toner electrostatically adheres to the imaged areas of the photoconductor to form a developed image that is transferred to an imaging substrate. The optical density of the deposited toner, and of the image transferred to the imaging substrate, is a function of the potential difference, or "contrast,"between imaged and unimaged areas of the photoconductor. Thus, the degree of contrast depends on the difference between the surface charge potential initially applied to the photoconductor and the potential of the imaged areas after discharge.

To produce high contrast, and hence good optical density, the difference between the surface charge potential and the discharged potential in the imaged areas should be as high as possible. Unfortunately, the discharge process does not immediately reduce the surface charge potential to zero, but rather produces a residual electrostatic potential that limits the degree of contrast that can be achieved.

The existence of the residual potential can be explained by examining the mechanics of the discharge process, which has two components : an initial, rapid discharge phase and a subsequent, gradual discharge phase. In the rapid discharge phase, the imaging radiation generates charge carriers that quickly neutralize the surface charge in imaged areas to lower the surface potential. However, a portion of the charge carriers becomes trapped within the photoconductor bulk, resulting in the maintenance of a residual potential in the imaged areas. Over time, a gradual discharge phase occurs, in which the residual potential slowly drops to zero as the

trapped charge carriers are released by thermal excitation. Nevertheless, complete discharge may not occur until after the toner development stage of the electrophotographic cycle, and therefore may have no practical significance in achieving high contrast for toner deposition.

In addition to decreasing optical density, residual potential can also contribute to the appearance of undesirable"ghost"images in previously imaged areas of the photoconductor. A ghost image is any visible remnant of a previous image superimposed on a present image. The ghosting problem can result from a variety of mechanisms. One mechanism is the accumulation of trapped charge carriers in discharged areas over a series of imaging cycles that results in a"build-up"of residual electrostatic potential. The accumulation of trapped charge carriers leads to a higher residual potential in previously imaged areas of the photoconductor relative to previously unimaged areas. The accumulation of trapped charge carriers may also create space charge fields that decrease conductivity in the previously imaged areas.

The presence of higher residual potentials and/or space charge fields acts as a nonuniformity that decreases optical density upon development, and produces ghost images in areas in which differences in residual potential or conductivity exist.

Summary of the Invention One approach to minimizing residual potential is to increase the conductivity of the different layers of the photoconductor with electron transport agents. In a typical negatively charged dual layer construction this would involve addition of electron transport materials to layers of the photoconductor between the charge generation layer and the positively biased conductor. In a typical positively charged inverse dual layer system this would involve addition of electron transport materials to layers between the charge generation layer and the positively corona charged surface of the photoconductor.

Accordingly, one aspect the invention features an organic photoreceptor that includes a quaternary ammonium salt of a polystyrene sulfonate in at least one layer of the organic photoreceptor. Preferably, the quaternary ammonium salt of a polystyrene sulfonate has the formula :

where n is an integer from 200 to 5000 ; Ru ils an alkyl group (e. g., a C1 {26 alkyl group), a cycloalkyl group (e. g., a cyclohexyl group), an aryl group (e. g., a phenyl or naphthyl group), or an arylalkyl group (e. g., benzyl (CH2-phenyl)). Preferably, the quaternary ammonium salt of a polystyrene sulfonate is soluble in a solvent selected from the group consisting of water, an organic solvent, and a combination thereof, in an amount of at least 20% by weight. Suitable solvents include methanol, ethanol, l-methoxy-2-propanol, acetone, methyl ethyl ketone, chloroform, methylene chloride, tetrahydrofuran (THF), and mixtures thereof, such as a mixtures of 50 : 50 methanol : TET and of 50 : 50 1- methoxy-2-propanol : TIF.

Preferably, the quaternary ammonium salt of a polystyrene sulfonate is present in at least one of the layers in an amount from about 1 wt. % to about 50 wt. %. In one embodiment, the quaternary ammonium salt of a polystyrene sulfonate is present in the tie layer. In another embodiment, the quaternary ammonium salt of a polystyrene sulfonate is present in the barrier layer.

One more preferred quaternary ammonium salt of a polystyrene sulfonate is poly (tetrabutylammonium 4-styrenesulfonate). More preferably, tie layer is formed from a tie layer coating composition comprising from about 20 to about 35 wt. % poly (tetrabutylammonium 4-styrenesulfonate).

In a second aspect, the invention features an electrophotographic imaging apparatus that includes (a) a plurality of support rollers ; and (b) the above-described organic photoreceptor in the form of a flexible belt threaded around the support rollers. The apparatus preferably further includes a liquid toner dispenser.

In a third aspect, the invention features an electrophotographic imaging process that includes (a) applying an electrical charge to a surface of the above-

described organic photoreceptor ; (b) imagewise exposing the surface of the organic photoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of charged and uncharged areas on the surface ; (d) contacting the surface with a liquid toner that includes a dispersion of colorant particles in an organic liquid to create a toned image ; and (e) transferring the toned image to a substrate.

In a preferred embodiment, the organic photoreceptor is in the form of a flexible belt, e. g., a flexible belt threaded around a plurality of support rollers.

Preferably, at least one of the support rollers has a diameter no greater than about 40 mm.

The invention provides organic photoreceptors featuring a combination of good mechanical and electrostatic properties. These photoreceptors can be used successfully with liquid toners to produce high quality images even when subjected to significant mechanical stresses encountered when the photoreceptor is in the form of a flexible belt threaded around a plurality of small diameter rollers. The high quality of the images is maintained after repeated cycling.

Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.

Detailed Description The invention features organic photoreceptors that include charge transport compounds having the formula set forth in the Summary of the Invention, above. The electron transport compounds are quaternary ammonium salts of a polystyrene sulfonate. The organic photoreceptor may be in the form of a plate, drum, or belt, with flexible belts being preferred. The photoreceptor may include a conductive substrate and a photoconductive element in the form of a single layer that includes both the charge transport compound and charge generating compound in a polymeric binder. Preferably, however, the photoreceptor includes a conductive substrate and a photoconductive element that is a bilayer construction featuring a charge generating layer and a separate charge transport layer. The charge generating layer may be located intermediate the conductive substrate and the charge transport layer.

Alternatively, the photoconductive element may be an inverted construction in which

the charge transport layer is intermediate the conductive substrate and the charge generating layer.

The charge generating compound is a material which is capable of absorbing light to generate charge carriers, such as a dyestuff or pigment. Examples of suitable compounds are well-known and include metal-free phthalocyanine pigments (e. g., Progen 1 x-form metal-free phthalocyanine pigment from Zeneca, Inc.).

The binder is capable of dispersing or dissolving the charge transport compound (in the case of the charge transport layer) and the charge generating compound (in the case of the charge generating layer). Examples of suitable binders for both the charge generating layer and charge transport layer include styrenebutadiene copolymers, modified acrylic polymers, vinyl acetate polymers, styrene-alkyd resins, soya-alkyl resins, polyvinylchloride, polyvinylidene chloride, acrylonitrile, polycarbonate, polyacrylic and methacrylic esters, polystyrene, polyesters, and combinations thereof. Polycarbonate binders are particularly preferred. Examples of suitable polycarbonate binders include aryl polycarbonates such as poly (4, 4-dihydroxy-diphenyl-1, 1-cyclohexane) ("Polycarbonate Z") and poly (Bisphenol A carbonate-co-4, 4' (3, 3, 5-trimethyl cyclohexylidene) diphenol.

An organic photoreceptor according to the present invention preferably includes at least one additional layer as well, including one or more of the following : a barrier layer, a tie layer, a release layer, and the like. Preferably, in accordance with the present invention, an electron transport compound, as described above, is included in at least one layer of the organic photoreceptor. More preferable, it is included in at least one of a barrier layer, a tie layer, and a release layer. Even more preferably, it is included in the tie layer. When present, the electron transport material is included in a coating composition utilized to form the at least one layer, each as described in detail below, in an amount of about 1 wt. % to about 50 wt. % and, more preferably, from about 10 wt. % to about 40 wt. %.

Preferably, a release layer is typically applied over a barrier layer, if present, and must adhere well to the underlying layers, preferably without the need for adhesives. Additionally, the release layer must not significantly interfere with the charge transport characteristics of the photoreceptor. Conventional release layers are formed from a variety of well known materials including fluorinated polymers (such

as those described in U. S. Pat. Nos. 4, 996, 125 and 5, 723, 242, for example), siloxane polymers, silanes, silicone polymers (such as that described in U. S. Pat. No.

4, 600, 673, for example), polyethylene, and polypropylene, to name a few. Other suitable compositions for forming a release layer including a siloxane polymer with a low content of functional groups capable of crosslinking are described in U. S. Patent No. 5, 652, 078 (Jalbert et al.) and in copending U. S. Patent Application Ser. No.

09/504, 461, filed February 16, 2000 (Li et al.).

In one preferred embodiment, a release layer includes a composition including (a) from zero to about 30 parts by weight of a polymer having the formula

wherein R1, R2, R3, R6, R7, R10, R11, and R12 are each independently selected from an alkyl group, an alkenyl group, an aryl group, and an aralkyl group, such that at least one of R6 and IC is an alkenyl group, R4, R, RS, and R9 are each independently selected from an alkyl group, an aryl group, and an aralkyl group, 1, m, and n are each independently integers so long as the polymer contains greater than 3 mol% vinyl-containing siloxane groups ; (b) more than about 20 parts by weight of a polymer selected from the group of

wherein Rl3 R14, R15, R18, R19, R22, R23, and R24 are each independently selected from an alkyl group, an alkenyl group, an aryl group, and an aralkyl group, such that at least two of R13, R14, R15, R18, R19, R22, R23, and R24 alkenyl groups, R, R, R20, and Ruz are each independently selected from an alkyl group, an aryl group, and an aralkyl group,

p, q, and r are each independently integers so long as the polymer has less than 3 mol% vinyl-containing siloxane groups ; a (vinyl siloxy) (siloxy)- modified silica having a vinyl content of less than about 0. 6 vinyl equivalent/kg ; and a combination thereof ; and (c) greater than about 0 parts to about 20 parts by weight of a cross-linking agent of the formula wherein R36, R37, R38, R43, R44, and R45 are each independently selected from hydrogen, an alkyl group, an aryl group, and an aralkyl group, R39, R40, R41, and R42 are each independently selected from hydrogen, an alkyl group, and an aryl group, X is 0, or a divalent organic linking group, and s and t are independently integers so long as there are at least two functional groups capable of cross-linking per molecule.

Barrier layers included in photoreceptors are well known, and typically possess one or more of the following performance characteristics : (a) providing sufficient protection to the organic photoreceptor from damage due to corona- induced charge injection ; (b) substantially inert with respect to the organic photoconductive layer ; (c) exhibiting sufficient resiliency to withstand compressional and tensional forces exerted on the belt as it passes through the system when the photoreceptor is utilized in an endless belt form ; and (d) providing sufficient protection to limit or prevent a liquid toner from contacting the organic photoreceptor.

Preferably, the photoconductor element of the present invention further comprises a barrier layer between the photoconductor layer and the release layer.

The barrier layer protects the photoconductor layer from the toner carrier liquid and other compounds which might damage the photoconductor. The barrier layer also protects the photoconductive layer from damage that could occur from charging the

photoconductor element with a high voltage corona. The barrier layer, like the release layer, must not significantly interfere with the charge dissipation characteristics of the photoconductor element and must adhere well to the photoconductive layer and the release layer, preferably without the need for adhesives. The barrier layer may be any known barrier layer, such as a crosslinkable siloxanol-colloidal silica hybrid as disclosed in U. S. Patents 4, 439, 509 ; 4, 606, 934 ; 4, 595, 602 ; and 4, 923, 775 ; a coating formed from a dispersion of hydroxylated silsesquioxane and colloidal silica in an alcohol medium as disclosed by U. S. Patent 4, 565, 760 ; or a polymer resulting from a mixture of polyvinyl alcohol with methylvinylether/maleic anhydride copolymer. Preferably the barrier layer is a composite which includes silica and an organic polymer selected from the group consisting of polyacrylates, polyurethanes, polyvinyl acetals, sulfonate polyesters, and mixtures of polyvinyl alcohol with methylvinylether/maleic anhydride copolymer.

The organic polymer and silica are preferably present in the barrier layer at a silica to polymer weight ratio ranging from 9 : 1 to about 1 : 1. Barrier layers of this type are disclosed in U. S. Patent No. 6, 001, 522 (Woo et al.). Another preferred barrier layer can be a composite material of an organic polymer with a silanol. The silanol has the formula Y, Si (OH) b wherein : Y includes, for example, alkyl or alkoxy groups having from 1 to 6 carbon atoms ; alkoxyalkyl groups in which the alkoxy portion contains from 1 to 2 carbon atoms and the alkyl portion contains from 1 to 6 carbon atoms ; halogenated alkyl groups having from 1 to 6 carbon atoms and from 1 to 2 halogen substituents ; aminoalkyl groups having from 1 to 6 carbon atoms and one amino group attached to either the 2, 3, 4, 5 or 6 carbon atom ; a vinyl group ; a phenyl group which may contain 1 to 2 halogen substituents ; a cycloalkyl group having from 5 to 6 carbon atoms and which may contain 1 to 2 substituents ; and hydrogen, a is a number ranging from 0-2, b is a number ranging from 2-4, and a plus b equals 4.

The organic polymer is preferably selected from the group consisting of

polyacrylates, polyurethanes, polyvinyl acetals, sulfonate polyesters, and mixtures of polyvinyl alcohol with methylvinylether/maleic anhydride copolymer.

Yet another preferred barrier layer is preferably formed from a barrier layer coating composition that can include a cellulose resin, a methylvinyl ether/maleic anhydride copolymer, a polyamide, a crosslinking agent, and a combination thereof.

Preferred barrier layer coating compositions are described in copending U. S. Patent Application Ser. No. 09/504, 456 (filed February 16, 2000) (Ackley et al.).

For example, in one preferred barrier layer, the cellulose resin is a selected from the group consisting of a modified cellulose, an unmodified cellulose, and a combination thereof. More preferably, the cellulose resin is selected from the group of methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, a cellulose ester, and a combination thereof. A preferred crosslinking agent is a bis aldehyde, preferably an aliphatic dialdehyde and, even more preferably, the cross-linking agent is glyoxyl, such as that commercially available under the trade designation GLYOXAL 40, from Aldrich Chemical, Milwaukee, WI.

Preferably, the resin and the copolymer are present in a barrier coating composition in a ratio of about 0. 4 : 1. 0 to about 1. 0 : 0. 4 and, more preferably, the ratio of the resin to the copolymer is about 1 : 1 Preferably, the barrier layer coating composition includes the cellulosic resin in an amount from about 0. 2% solids by weight to about 15. 0% solids by weight, more preferably, in an amount of 0. 6% solids by weight to about 2. 5% solids by weight, and, even more preferably, in an amount of 0. 75% solids by weight.

Preferably, the barrier layer coating composition includes the copolymer in an amount of about 1. 2% solids by weight to about 0. 3% solids by weight, more preferably, about 0. 9% solids by weight to about 0. 6% solids by weight, and, even more preferably, about 0. 75% solids by weight.

The barrier layer coating composition preferably includes a ratio of the cellulosic resin to the copolymer of about 0. 4 : 1. 0 to about 1. 0 : 0. 4, more preferably, the ratio of the cellulosic resin to the copolymer is about 1 : 1. Thus, in one preferred embodiment, the barrier layer coating composition includes the cellulosic resin in an amount of about 0. 75% solids by weight of the cellulose resin and the copolymer in an amount of about 0. 75% solids by weight of the copolymer.

The crosslinking agent is preferably a bis aldehyde and, more preferably, the cross-linking agent is glyoxal. Preferably, the barrier layer coating composition includes the cross-linking agent in an amount from about 1. 0% solids by weight to about 10. 0% solids by weight, and, more preferably, from about 1. 0% solids by weight to about 7. 5% solids by weight of the sum amount of the resin and the copolymer in the barrier layer coating composition.

The barrier layer typically has a thickness of about 0. 2 micrometers to about 1. 0 micrometers and, more preferably, from about 0. 4 micrometers to about 0. 8 micrometers.

The barrier coating composition may also include at least one optional component, such as surfactants, plasticizers, anti-static agents, wetting agents, anti- foaming agents, conductive additives, and fillers, to name a few. One preferred optional component is a surfactant, preferably a nonionic surfactant, such as that commercially available under the trade designation TRITON X-100, from Aldrich Chemical, Milwaukee, WI.

Another preferred optional component is silica particles. The silica particles preferably are colloidal silica having average diameter from 5 to 200 nm. As used herein,"colloidal silica"refers to a dispersion of silicon dioxide particles in which the silica particles can range in size from about 5 to about 30 nm. One suitable colloidal silica is commercially available under the trade designation SNOTEX O, from Nissan Chemical Industries, Ltd., Tarrytown, NJ. Preferably, the colloidal silica is present in a barrier layer coating composition in an amount of less than about 20%, more preferably, less than about 15%, and even more preferably from about 12% to about 6% of total solids by weight of the sum of the resin and the copolymer in the barrier layer coating composition.

Suitable conductive additives include conductive pigments, conductive polymers, doped conductive polymer compositions, photoconductive organic molecules, and conductive pigments (or conductive particles) are preferred. The amount of conductive pigment is preferably less than 35% and, more preferably, less than about 20% by weight of the barrier layer.

Preferably, a barrier coating composition is applied to an organic photoconductor using any conventional coating technique, such as air doctor coating,

blade coating, air knife coating, squeeze coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, spray coating, dip coating, bar coating, extrusion coating, die coating, for example.

Optionally, an organic photoreceptor in accordance with the present invention can have a structure including an organic photoconductor, a barrier layer (as described above), a tie layer, and a release layer. In one embodiment, the tie layer can be positioned between the barrier layer and the release layer to enhance adhesion of the release layer to the barrier layer in the organic photoreceptor. In another embodiment, the tie layer can be positioned between the charge generating layer and the barrier layer to enhance adhesion of the barrier layer to the organic photoconductor. One with ordinary skill in the art will readily appreciate that an organic photoreceptor according to the present invention may possess a variety of layered configurations, such as the presence of a tie layer between the release layer and the barrier layer as well as the presence of a tie layer between the charge generating layer and the barrier layer.

Preferably, a tie layer is formed from a tie layer coating composition comprising an organic polymer. The term"organic polymer"refers to a material that is formed from a carbon chain or ring structure containing hydrogen and, optionally, heteroatoms such as sulfur, oxygen, nitrogen, and a combination thereof Preferably, an organic polymer suitable for use in the present invention include those selected from the group of polyetheramines, polyvinyl acetals, polyamides, methylvinyl ether/maleic anhydride copolymer, and combinations thereof Preferably, an organic polymer is present in a tie layer coating composition in an amount of less than about 30% solids in the tie layer coating composition.

One preferred type of organic polymer for use in a tie layer in accordance with the present invention is a polyetheramine having aromatic ether/amine repeating units in its backbone and pendant hydroxyl moieties. Namely, a suitable polyetheramine is preferably formed by reacting diglycidyl ethers of dihydric aromatic compounds (e. g., the diglycidyl ether of bisphenol-A, hydroquinone, or resorcinol) with amines, preferably having no more than two amine hydrogens per molecule (e. g., piperazine or ethanolamine), as is described in U. S. Pat. No. 5, 275, 853 (Silvis et al.). Preferred polyetheramines are commercially available under the trade

designations BLOX 205 and XU 19040, both from The Dow Chemical Company, Midland, MI.

Another preferred type of organic polymer for use in a tie layer in accordance with the present invention is a polyamide, preferably, a soluble polyamide as is known in the art. For example, suitable polyamide materials are commercially available under the trade designations ULTRAMID, from BASF Corporation, Mount Olive, NJ ; and AMa,LAN, from Toray Ltd., Japan. Preferably, the polyamide is included in a tie layer coating composition in an amount of less than about 10%, more preferably, less than about 7. 5%, and even more preferably, less than about 5% by weight.

Yet another preferred type of organic polymer for use in a tie layer in accordance with the present invention is a mixture of a polyvinyl acetal, preferably polyvinyl butyral, with a methylvinyl ether/maleic anhydride copolymer, in which the ratio of polyvinyl acetal to methylvinyl ether/maleic anhydride copolymer is preferably from about 5 : 1 to about 15 : 1 and, more preferably, about 12 : 1. Preferably, the mixture of a polyvinyl acetal with methylvinyl ether/maleic anhydride copolymer is included in a tie layer coating composition in an amount of less than about 10%, more preferably, less than about 7. 5%, and even more preferably, less than about 5% by weight. Optionally, a coupling agent can be included and is preferably selected from the group of glycidoxy-propyltrimethoxysilane, vinyltrimethyoxysilane, chloromethyltrimethoxysilane, methyltrimethoxysilane, and 3- aminopropyltriethoxysilane. If present, the coupling agent is typically present in an amount less than about 5% by weight of the tie layer coating composition.

A further preferred type of organic polymer for use in a tie layer in accordance with the present invention is a mixture of a polyvinyl acetal, preferably polyvinyl butyral, and a cross-linking agent, preferably, a bis aldehyde, more preferably, an aliphatic dialdehyde, and, even more preferably, glyoxal, such as that commercially available under the trade designation GLYOXAL 40, from Aldrich Chemical, Milwaukee, WI. Preferably, the mixture of a polyvinyl acetal with a cross- linking agent is included in a tie layer coating composition in an amount of less than about 10%, more preferably, less than about 7. 5%, and even more preferably, less than about 5% by weight.

Preferably, a tie layer coating composition also includes silica, preferably colloidal silica. Preferred colloidal silica compositions are commercially available under the trade designations SNOTEX O, from Nissan Chemical Industries, Ltd., Tarrytown, NY, and CABOSIL TS-720 from Cabot Corp., Tuscola, IL. The tie layer coating composition preferably includes colloidal silica in an amount of about 0 to about 12% by weight.

In accordance with the present invention, a tie layer coating composition is applied to at least one surface on the organic photoconductor, such as on the surface of the charge generating layer, the surface of the barrier layer, or both. Regardless of the surface on which the tie layer coating composition is applied, the resulting tie layer preferably has a thickness of about 0. 05 micrometer to about 0. 7 micrometer.

The electron transport compounds, and photoreceptors including these compounds, are suitable for use in an imaging process with either dry or liquid toner development. Liquid toner development is generally preferred because it offers the advantages of providing higher resolution images and requiring lower energy for image fixing compared to dry toners. Examples of useful liquid toners are well- known. They typically include a colorant, a resin binder, a charge director, and a carrier liquid. A preferred resin to pigment ratio is 2 : 1 to 10 : 1, more preferably 4 : 1 to 8 : 1. Typically, the colorant, resin, and the charge director form the toner particles.

Organic photoreceptors according to the invention are particularly useful in a compact imaging apparatus where the photoreceptor is wound around several small diameter rollers (i. e., having diameters no greater than about 40 mm). A number of apparatus designs may be employed, including for example, the apparatus designs disclosed in U. S. 5, 650, 253 and U. S. 5, 659, 851.

The invention will now be described further by way of the following examples.

Examples Preparation of poly (tetrabutylammonium 4 styrenaulfonate) AMBERLITE IR120 (plus), a commercially available poly (sodium 4- styrenesulfonate) (70, 000 MWt.) from Aldrich Chemical Company, Milwaukee, WI,

and an aqueous 40 wt. % solution of tetrabutylammonium hydroxide was obtained from Aldrich Chemical Company and used without further purification.

A column prepared with 300 grams of AMBERLITE IR120 (plus) resin was washed with 600 ml of water. To this column was added a solution of 30 grams (145 meq of S03Na) of poly (sodium 4-styrenesulfonate) in 195 ml of water. The column was eluted with water. The first fraction collected was acidic to pH<l.

Approximately 900 ml of water was collected until the pH of the eluant became neutral. To the eluant collected from the ion exchange chromatography was added 94. 4 gram (145. 5 mmol, 1 eq) of a solution of 40 wt. % tetrabutylammonium hydroxide in water. The pH of the resulting aqueous solution was approximately 6.

This solution was concentrated in vacuo (aspirator) at 45°C for several hours to give 65. 2 grams of product. Assuming complete recovery this represents 61. 9 grams of product with 3. 3 grams of water (5. 06 wt. % water). To this material was added 350 grams of l-methoxy-2-propanol and allowed to mix overnight to give a solution that is 14. 91 wt. % poly (tetrabutylammonium 4-styrenesulfonate) in 1-methoxy-2- propanol with 0. 795 wt. % water. ICP analysis of this solution indicated 0. 01 wt. % residual Na that corresponds to a 99. 4 % conversion.

Orsanic Photoreceptor Preparation The following construction was utilized in evaluating the performance of the electron transport compound (herein, ETM), prepared as described above.

Silicone Release Layer Tie Layer Barrier Layer Charge Generation Layer (CGL) Charge Transport Layer (CTL) PET Sub-layer Aluminum Ground Plane PET Support An inverted dual layer organic photoconductor (herein,"OPC") was prepared utilizing compound (2) as described inU. S. Pat. App. Ser. No. 09/172, 379, filed October 14, 1998, entitled"Organophotoreceptors for Electrophotography Featuring Novel Charge Transport Compounds" (Mott et al.) was used as the substrate, that included a polyester layer, an aluminum layer, a PET layer (formed from a resin commercially available under the trade designation VITEL PE 2200, from Bostik Chemicals, Middleton, MA, at a 4. 4% solids in a 2 : 1 MEK : toluene mixture, coated at a thickness of 0. 2 micrometers using a slot die coater with a web speed of 3. 048 meters/min., dried in 4 oven zones of 110°C, 120°C, 140°C, and 150°C), a charge transport layer, and a charge generating layer. A barrier layer coating composition was then coated over the charge generating layer at a thickness ranging from 0. 2-0. 8 micrometers. The web was run at 10 feet (3. 048 m) per minute, through 20 feet (6. 096 m) of oven.

A barrier layer located on the OPC was utilized in all examples herein and was formed from a barrier layer coating composition as described in U. S. Patent Application Ser. No. 09/504, 456 (Ackley et al.) filed February 16, 2000. Namely, a 3% stock solution of methyl cellulose, commercially available under the trade

designation METHOCEL A15LV, from Dow Chemical, Midland, MI, was made in water. The water was heated to about 90°C. The methyl cellulose powder was then added under agitation. The solution was then cooled to about 4°C using an ice bath, and agitated using an air mixer for about 20 minutes at 4°C. The solution was then allowed to sit and reach ambient temperature.

A 3% stock solution of methylvinylether/maleic anhydride copolymer, commercially available under the trade designation GANTREZ AN-169, from ISP Chemical, Wayne, NJ, was made in water. The water was brought up to about 90°C, then the copolymer was added under agitation. The solution was agitated at 90°C until the solution became clear. This took about 40 minutes.

A ratio of 1 : 1, by weight, of each stock solution was combined in an empty container. A nonionic surfactant, commercially available under the trade designation TRITON X100, from Aldrich Chemical, Milwaukee, WI, was then added in an amount of 0. 2 g/lOOg of water. The solution was then diluted with methanol. A dialdehyde cross-linker, commercially available under the trade designation GLYOXAL 40, from Aldrich Chemical, Milwaukee, WI, was then added in an amount of 5% by weight.

The barrier layer coating composition described above was at a thickness of 0. 2 micrometers using a slot die coater with a web speed of 3. 048 meters/min., dried in 4 oven zones set at 110°C, 120°C, 140°C, and 150°C to dry the barrier layer coating composition, forming the barrier layer.

A release layer coating composition was prepared, as generally described in copending U. S. Patent App. Ser. No. 09/504, 461, filed February 16, 2000, Li et al.

In accordance with the teachings therein, the following coating composition was prepared utilizing the following components : CAB-O-SIL TS-720 is a hydrophobic treated silica commercially available from the Cab-O-Sil division of Cabot Corp., Tuscola, IL.

FBA is a 70 : 30 mixture by weight of diethylfumarate and benzyl alcohol.

SE-33 is a high molecular weight, linear polydimethyl-vinylsiloxane gum having 0. 1-0. 4 mol% pendant vinyl groups, substantially free of terminal vinyl groups and commercially available from GE Silicones, Waterford, NY.

SYL-OFF 4000 is a platinum-based catalyst commercially available from Dow

Coming, Midland, MI.

SYL-OFF 7678 is a polysiloxane cross-linking agent having about 50% methylhydrosiloxane groups and about 50% dimethylsiloxane groups commercially available from Dow Coming, Midland, MI.

VDT-954 is a trimethylsiloxy terminated poly (vinylmethylsiloxane) polymer containing 11-13 mol% vinylmethylsiloxane and having a viscosity of 300, 000- 500, 000 cSt believed to have a molecular weight of about 230, 000 and is commercially available from Gelest Inc., Tullytown, PA.

DMS-V52 is a vinyl terminated polydimethylsiloxane having a vinyl eq/Kg of 0. 013-0. 016 commercially available from Gelest Inc., Tullytown, PA.

A release coating composition was prepared as two parts, part A, and part B.

The two parts A and B were mixed just prior to coating to make the fully reactive system.

Part A : In a glass jar was added 26. 26 parts of a 10% solids solution of SE 33 in heptane and 2. 45 parts of a 30% solids solution of VDT-954 in heptane. To this mixture was then added 3. 92 parts of a 30% solids solution of DMS-V52 in heptane.

To this mixture was then added 42. 13 parts of heptane and 15 parts of methyl ethyl ketone. To this mixture was then added 0. 525 parts of FBA and 0. 1575 parts of SYL-OFF 4000. To the well mixed solution was then added 0. 02625 parts of CAB-O-SIL TS-720.

Part B : In another jar, 0. 50 parts of SYL-OFF 7678 and 9. 5 parts of heptane were added.

Parts A and B were mixed just prior to coating. To construct an organic- photoreceptor (OPR) belt, the release coating composition was coated and subsequently cured at 150°C for 1. 5 min on top of the inverted dual layer photoreceptor with a barrier layer and a tie layer, each as described above. The coating thickness of the release layer was 0. 65 micrometer.

A tie layer was utilized in all examples herein and was positioned between the barrier layer and the release layer. The tie layer was formed from a tie layer coating composition including 3. 1% poly (hydroxy amino ether) commercially available under the trade designation XUR, from Dow Chemical, Midland MI, 58. 1% tetrahydrofuran, and 38. 8% 1-methoxy2-propanol, as described in U. S. Patent

Application Ser. No. 09/504, 456 (Ackley et al.) filed February 16, 2000. The electron transport compound prepared above was added to the tie layer composition in an amount of 0% (Comparative Examples A and B, below), 20% (Examples 1 and 3, below), or 35% (Examples 2 and 4, below) by weight. The tie layer coating composition was coated on a substrate including a barrier layer with a 4 mil shim and a 5 micron filter at a web speed of 3. 048 m/min.

The coating compositions described above were applied using a conventional slot die coater.

Each of the layer coating compositions described above were sequentially coated on the OPC that was then passed through 4 oven zones set at 90°C, 100°C, 110°C, and 120°C to dry each of the coating compositions prior to coating the next coating composition. An inverted dual layer organic photoconducter having, in order, a barrier layer, a tie layer, and a release layer formed thereon is referred to as an organic photoreceptor (OPR).

Testins of the OPR : Electrostatic measurements were obtained from the following sequence of test subroutines : 1) PRODSTART : This test was designed to evaluate the electrostatic cycling of a new, fresh belt. The belt was completely charged for three cycles (drum rotations) ; discharged with the laser at 780nm, 600dpi on the forth cycle ; completely charged for the next three cycles ; discharged with only the erase lamp at 720nm on the eighth cycle ; and, finally, completely charged for the last three cycles.

2) LONGRUN : The belt was electrostatically cycled, according to the following sequence for each belt-drum revolution, for 4, 000 drum revolutions : the belt was charged by the corona, the laser was cycled on and off to discharge a portion of the belt, and, finally, the erase lamp discharged the whole belt in preparation for the next cycle. The laser was cycled so that the first 16. 7 cm of the belt was never exposed, the following 8 cm section was exposed, then 4 cm was unexposed, the next 8 cm section was exposed, and finally the last 12. 5 cm was unexposed. This pattern was repeated for 4, 000 drum revolutions and the data was collected during the first cycle and then after each 200th drum revolution.

3) After the 4, 000th cycle (long run test), the PRODSTART (now called PRODEND) test was run again. The results of the testing are shown in the table below.

Table 1 Ex ETM Temp V acc (V)1 Vres (V)2 # V acc (V) # V res (V) ut. % A 0 71 693-694 128-169 1 41 1 20 74 768-780 127-169 12 42 2 35 73 765-761 108-137-4 29 ach Example was subjected to 4000 charge-discharge cycles. For each Example, the first value in the column labeled"V acc (V)"represents the initial charge, or charge acceptance, at cycle 1 and the second value in that column represents the initial charge at cycle 4000. Similarly, for each Example, the first value in the column labeled"Vres (V)"represents the discharged voltage at cycle 1 while the second value in that same column represents the discharged voltage at cycle 4000.

The residual potential after discharge is the"V res"value in Table 1. The values in the table in the column labeled" V res"indicate the charge in the discharge voltage from cycle 1 to 4, 000. A positive value indicates that the discharge voltage increases from cycle 1 to 4, 000. Ideally, a value as close to zero as possible is desired for A V res.

As shown in Table 1, an increase in discharge voltage is about 41, as shown with Comparative Example A (having no electron transport compound according to the present invention). The discharge voltage remained about the same in Example 1 (having 20 wt. % of an electron transport compound) but reduced to 29 volts in Example 2 (having 35 wt. % of an electron transport material).

The data in Table 2, below, show contrast values that are the difference between the acceptance voltage (V acc) and the discharge voltage (V res). Ideally, a high value is desired.

Table 2 Ex. ETM Temp. Contrast Contrast wt. e Cycle 1 Cycle 4K Contrast A 0 71 565 525-40 1 20 74 641 611-30 2 35 73 657 624-33

The data in Table 2 shows the contrast potential for the Examples at cycle 1 and cycle 4, 000. The column labeled"0 contrast"indicates the change in contrast potential between cycle 1 and 4, 000. A negative number indicates the contrast is decreasing. Ideally, this value should be as close to zero as possible.

With no electron transport material added, Comparative Example A showed a change in contrast potential of-40 volts. The change in contrast potential improves to-30 volts and-33 volts, with the addition of 20 wt. % (Example 1) and 35 wt. % (Example 2) electron transport compound, respectively.

All patents, patent applications, and publications disclosed herein are incorporated by reference in their entirety, as if individually incorporated. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. The invention is not limited to the details shown and described, for variations obvious to one skilled in the art will be included within the invention defined by the claims