Conductive polymer coatings

Abstract: A conductive polymer coating comprising an arylamine charge transport compound, an oxidized arylamine charge transport compound salt, and a polymer binder, wherein the oxidized arylamine charge transport compound salt has a counter anion selected from the group consisting of hexafluoroantimonate and hexafluoroarsenate.

Description: JP-A-60131544 discloses an electrophotographic toner comprising a para-substituted oxidized aryl amine compound with a hexafluoroantimonate counter ion, and a polymeric binder resin. US-A-5587224 relates to a conductive polymer coating comprising an arylamine, a photo acid catalyst comprising a hexafluoroantimonate salt and a polycarbonate as a polymeric binder. The coating is prepared by dissolving the compounds in methylene chloride, followed by a drying step. The aryl amine compound can further be para-substituted. US-A-3341464 discloses a coating composition comprising an aryl amine, silver hexafluoroarsenate as an oxidant and PMMA as a polymer binder. The aryl amine can further be para-substituted and the coating can be prepared by dissolving the compounds in acetone casting a film on a substrate and drying at 70° C. It was the object of this invention to overcome the deficiencies of the compositions as provided by the prior art. This object is achieved by the conductive polymer coatings according to claims 1 and 4 and the process for the preparation of a conductive polymer coating according to claim 7. Preferred embodiments are set forth in the subclaims. The present invention provides electrically and mechanically stable conductive polymer coatings comprising an arylamine charge transport compound, an oxidized arylamine charge transport compound salt, and a polymer binder. In embodiments, the oxidized arylamine charge transport compound salt comprises the oxidation product arising from the self-same arylamine charge transport compound. In other embodiments, the oxidized arylamine charge transport compound salt is formed from a compound other than the arylamine charge transport compound. The oxidized arylamine charge transport compound salt, in embodiments, can be formed in situ from the arylamine charge transport compound. Alternatively, the oxidized arylamine charge transport compound salt can be formed ex situ from the arylamine charge transport compound or from a different arylamine charge transport compound. The oxidized arylamine charge transport compound salt comprises an oxidized form of an arylamine charge transport compound and a counter ion, for example, hexafluoroantimonate and hexafluoroarsenate, which hexafluoro- salts are preferred counter anions. The arylamine charge transport molecules, either monomolecular or as incorporated into polymeric structures, are para-substituted arylamine charge transport compounds. Oxidation of the transport molecule can be accomplished by known chemical oxidizing reagents or can be an oxidation process accomplished, for example, chemically, photochemically, or electrochemically. Oxidizing compounds can be, for example, known chemical oxidants including ionic salts, Brønsted acids, halogens, Lewis acids, and mixtures thereof. Ionic salts include AgSbF 6 , AgAsF 6 , AgPF 6 , AgBF 4 , AgBr, Agl, AgF, AgCl, O 2 SbF 6 , O 2 AsF 6 , NOSbF 6 , NOAsF 6 , NO 2 SbF 6 , NO 2 AsF 6 , (CH 3 CH 2 )O + (CF 3 SO 3 )Al - , (CH 3 CH 2 )O + (CF 3 SO 3 )Ga - , (CH 3 CH 2 )O + (CF 3 SO 3 )B - , CH 3 (C=O) + (CF 3 SO 3 )Al - , and the like, and mixtures thereof. Brønsted acids include sulfonic acids, phosphoric acids, carboxylic acids, and the like, and mixtures thereof. Lewis acids include for example, AlCl 3 , GaCl 3 , SnCl 4 , BF 3 , FeCl 3 , AsF 3 , SnCl 4 , ZrCl 4 , ZnCl 2 , TiCl 4 , AuCl 3 , CuCl 2 , VCl 3 , InCl 3 , TaCl 5 , SbF 5, and the like, and mixtures thereof. The oxidant can be a sublimable material, such as, O 2 SbF 6 , O 2 SbF 6 , O 2 AsF 6 , NOSbF 6 , NOAsF 6 , Lewis acids, carboxylic acids, squaric acids, quinones, quinone dimethanes, carbon 60 cage and related fullerane compounds, and mixtures thereof. Photo-oxidants include, for example, diphenyliodonium salts and diarylsulfonium salts. The conductive coatings of the present invention have conductivities of 10 -12 to 1.0 S/cm, which conductivity is controlled by the concentrations of the oxidant and the charge transport units contained in the coatings. The conductive coatings of the present invention using, for example, the aforementioned oxidants exhibited excellent electrical stability compared to conductive coatings prepared with other oxidants and as illustrated herein. The conductive polymer coatings, in embodiments of the present invention, have electrical conductivities and mechanical stabilities that can be retained or maintained for an extended time, for example, from 8 to 10 weeks at a temperature of, for example, 85 to 100 °C and in a relative humidity of 50 to 100 percent. In embodiments, the coating compositions can additionally include optional additives such as an alkaline anti-corrosion additive, and a voltage stabilizing additive. Examples of alkaline anti-corrosion additive include, heterocyclic compounds with at least one nitrogen heteroatom, metallocene compounds, and mixtures thereof, for example, 2-(4-biphenylyl)-5,6-phenyl oxazole, 1,4-dichlorophthalazine, 1-phenyl pyrazole, di-pyridyl anthracenes, 1-phenyl-imidazole, 3-methyl-1-phenyl-pyrazole, 2,4,6-triphenyl-1,3,5-triazine, 2,6-di-t-butylpyridine, 4,7-diphenyl-1,10-phenanthroline, 2,6-bis(chloromethyl)pyridine, 2,5-diphenyl oxazole, 2,4,6-triphenoxy-1,3,5-triazine, 8-hydroxyquinoline aluminum, ferrocene, mixtures thereof, and the like. Many of the aforementioned heterocylic compounds are known electron transport materials. Examples of voltage stabilizing additives include substituted aromatic hydrocarbons of the formula Ar(X) n wherein Ar is an aryl group with, for example, from 6 to 24 carbon atoms, X is a substituent selected from the group consisting of -H, -F, -Br, -Cl, -I, -NO 2 , -SO 2 -R, wherein R is alkyl group with from 1 to 20 carbon atoms or an aryl group with from 6 to 24 carbon atoms, and n is an integer from 1 to 20, such as known aromatic hydrocarbon compounds, halogenated aromatic compounds, nitro aromatic compounds, sulfone aromatic compounds, cyano aromatic compounds, and mixtures thereof, for example, naphthalene, anthracene, phenanthrene, pyrene, 1,4-dichloronaphthalene, nitroanthracenes, 4,4'-dibromobiphenyl, 4-nitrobiphenyl, cyanobiphenyl, 2-nitroaniline, 9,10'-dibromoanthracene, benzophenone, diphenylsulfone, o-quinones, p-quinones, tetracyanoquinondimethane, 1,1'-biquinones, 9-dicyanomethylene fluorene, and mixtures thereof. Inert polymer binder materials include, but are not limited to solvent processable and melt processable thermoplastics and elastomeric thermoplastics such as polystyrenes, polycarbonates, polyesters, polyimides, polyurethanes, polysulfones, polyethersulfones, polyether ketones, polyamides and their copolymers and polymer blends. The polymer binder, in embodiments, can be an inert polymer, one or more, for example up to 5, charge transport polymer, and mixtures thereof, and selected in an amount of 30 to 80 weight percent of the total weight of the coating. When the polymer binder selected is a polymeric charge transport compound examples thereof include polyvinylcarbazoles, polythiophenes, polysilanes, polyanilines, poly(phenylene vinylenes), polyphenylenes, poly(phenylene sulfides), polyanilines, poly(phenylene sulfide phenylenamine), copolymers thereof containing triarylamine charge transport groups, and mixtures thereof. The arylamine charge transport compound is a para-substituted arylamine charge transport material, including polymers having para-substituted arylamine charge transport molecules molecularly doped therein, for example, in amounts of from 20 to 70 weight percent based on the total weight of the coating, and charge transport polymers containing para-substituted arylamine groups, that is, covalently bound arylamine groups in a main or pendant polymer chain, and mixtures thereof. The charge transport polymers include but are not limited to polyvinylcarbazoles, polythiophenes, polysilanes, polyanilines, poly(phenylene vinylenes), polyphenylenes, poly(phenylene sulfides), polyanilines, poly(phenylene sulfide phenylenamine), and polymers containing arylamine charge transport groups. The arylamine charge transport compound is a para-substituted arylamine charge transport material selected from the group of para-substituted arylamine charge transport compounds, molecularly doped polymers having para-substituted arylamine charge transport molecules, charge transport polymers containing para-substituted arylamine groups, and mixtures thereof. The arylamine charge transport compound can be of the alternative formulas: wherein Ar, Ar', and Ar" are independently selected from unsubstituted and substituted aromatic groups with from 6 to 30 carbon atoms, for example, phenyl, 3-methylphenyl, 4-methylphenyl, 3,4-dimethylphenyl, 4-ethylphenyl, 4-t-butylphenyl, 4-methoxyphenyl, 4-bromophenyl, 4-chlorophenyl, 3-iodophenyl, 4-flourophenyl, 4-phenylphenyl, 2-naphthyl, 1-naphthyl and mixtures thereof, and R 1 , R 2 , R 3 , R 1 ', R 2 ', and R 3 ' are independently selected from the group consisting of hydrogen, bromine, chlorine, fluorine, alkyl groups with from 1 to 24 carbon atoms, and alkoxy groups with from 1 to 24 carbon atoms, Z is selected from the atoms O, S, Se, or a substituent -CH 2 -, G is an alkaline group with 1 to 12 carbon atoms or a group selected from the partial formulas: wherein n' is an integer of from 1 to 12, and R and R' are alkyl groups with, for example, 1 to 12 carbon atoms. The arylamine charge transport compound can include the following arylamine compounds and mixtures thereof, a) aryldiamine compounds of the formula: wherein Ar is a substituted or unsubstituted aromatic group, for example, phenyl, 3-methylphenyl, 4-methylphenyl, 3,4-dimethylphenyl, 4-ethylphenyl, 4-t-butylphenyl, 4-methoxyphenyl, 4-bromophenyl, 4-chlorophenyl, 3-iodophenyl, 4-flourophenyl, 4-phenylphenyl, 2-naphthyl, 1-naphthyl and mixtures thereof, R 1 , R 2 and R 3 are independently selected from the group consisting of hydrogen, bromine, chlorine, fluorine, alkyl groups with from 1 to 24 carbon atoms, such as methyl, ethyl, butyl, isobutyl and alkoxy groups with from 1 to 24 carbon atoms, such as methoxy, ethoxy, isobutoxy, and Z is selected from an atom O, S, Se, or a methylene substituent -CH 2 - ; b) aryltriamines compounds of the formula: wherein Ar and Ar' are independently selected from substituted and unsubstituted aromatic groups, R is selected from hydrogen, phenyl containing 6 to 20 carbon atoms and alkyl groups containing 1 to 12 carbon atoms, such as methyl, ethyl, butyl, isobutyl, and wherein i and j are integers from 1 to 2; c) aryltetraamines compounds of the formula: wherein Ar, Ar', and Ar'' are independently selected from substituted and unsubstituted aromatic groups with from 6 to 20 carbon atoms, p-Ar and p-Ar' are independently selected from para-substituted aromatic groups with from 6 to 20 carbon atoms, R is selected from hydrogen, phenyl with from 6 to about 20 carbon atoms and alkyl groups containing 1 to 12 carbon atoms, such as methyl, ethyl, butyl isobutyl, i, j, and k are integers 1 or 2, G is an alkaline group with 1 to 12 carbon atoms or a group selected from the partial formulas: wherein n' is an integer from 1 to 12, and R and R' are alkyl groups with 1 to 12 carbon atoms; d) arylpentaamines compounds of the formula: wherein Ar, Ar', Ar'', and Ar''' are independently selected from substituted and unsubstituted aromatic groups with from 6 to 20 carbon atoms, and i, j, k, and I are integers of 1 or 2; and e) arylhexaamines compounds of the formula: wherein Ar and Ar' are independently selected from substituted and unsubstituted aromatic groups with from 6 to 20 carbon atoms, p-Ar and p-Ar' are para-substituted aromatic groups with from 6 to 20 carbon atoms, i, j, and k are integers of 1 or 2, G is a alkaline group with 1 to 12 carbon atoms or an aromatic group selected from the formulas: wherein n' is an integer from 1 to 12, and R and R' are alkyl groups with 1 to 12 carbon atoms, such as methyl, ethyl, butyl, isobutyl. The arylamine charge transport compound can be para-substituted triarylamine compounds with at least one of the para-substituted molecular segments selected from the partial formulas: wherein R 1 is selected from the group consisting of bromine, chlorine, fluorine, alkyl groups with from 1 to 24 carbon atoms, such as methyl, ethyl, butyl, isobutyl, and alkoxy groups with from 1 to 24 carbon atoms, such as methoxy, ethoxy, butoxy, isobutoxy, R 2 and R 3 are independently selected from the group consisting of hydrogen, bromine, chlorine, fluorine, alkyl groups with from 1 to 24 carbon atoms, such as methyl, ethyl, butyl, isobutyl, , and alkoxy groups with from 1 to 24 carbon atoms, such as methoxy, ethoxy, butoxy, isobutoxy, and Z is an atom of O, S, Se, or a methylene substituent -CH 2 -. A preferred charge transport polymer, in embodiments, is selected from polymers that contain a para-substituted aryldiamine unit of the formula: wherein R 1 is selected from the group consisting of bromine, chlorine, fluorine, alkyl groups containing from 1 to 24 carbon atoms, such as methyl, ethyl, butyl, isobutyl, and alkoxy groups containing from 1 to 24 carbon atoms, such as methoxy, ethoxy, butoxy, isobutoxy R 2 and R 3 are independently selected from the group consisting of hydrogen, bromine, chlorine, fluorine, alkyl groups containing from 1 to 24 carbon atoms, such as methyl, ethyl, butyl, isobutyl, cyclohexyl, and alkoxy groups containing from 1 to 24 carbon atoms, such as methoxy, ethoxy, butoxy, isobutoxy, G is selected from the group consisting of alkaline groups of 1 to 12 carbon atoms and of the formulas: wherein n' is an integer from 1 to 12, and R and R' are alkyl groups with 1 to 12 carbon atoms, such as methyl, ethyl, butyl, isobutyl, cyclohexyl. A preferred para-substituted arylamine charge transport compound is of the formula: wherein the oxidized form of the para-substituted arylamine charge transport compound results from photo-oxidation with photo-oxidants such as diphenyliodonium salts and diarylsulfonium salts. The present invention provides conductive polymer coatings comprising a para-substituted arylamine charge transport compound, and an oxidization product of the para-substituted arylamine charge transport compound and an oxidizing agent or salt. The coating composition can further comprise optional additives, such as, an alkaline anti-corrosion compound, a voltage stabilizing compound, and a polymer binder. In embodiments, the coatings provided are useful in various charge transport and electron transport applications and devices, for example, as a thin film electrode or contact modification layer in electroluminescent devices to facilitate charge injection. The present invention provides a process for the preparation of a conductive polymer coating comprising: mixing an arylamine charge transport molecule, and oxidant, optional additives and a polymer binder in a solvent, preferably until complete solubilization of the polymer is achieved, to produce a coating mixture; depositing the conductive polymer coating solution mixture on a substrate, for example, by spin coating, flow coating, spray coating, dip coating, web coating and the like; and drying the coated substrate, for example, at from 25 to 150 °C. The preparative process is preferably accomplished by removing any precipitated particles arising from, for example, the reaction of the oxidant and the arylamine charge transport molecule in the coating mixture, and thereafter dissolving a polymer binder and optional additives in the coating solution to provide a coating solution that is free of particulate matter. The coatings can have a thickness of, for example, from 0.01 cm to 0.5 cm, and conductivities of from 10 -12 to 100.0 S/cm and which conductivity is highly stable over a broad relative humidity range of from 0 to 100 percent. The improved conductivity stability is maintained, for example, from 60 to 90 days, at substantially higher temperatures, and at higher humidity values compared to control materials and as illustrated herein. The improved conductivity and humidity stability performance represent a stability improvements, for example, from 4 to 8 fold. In alternative embodiments, the preparative process can be accomplished by mixing the components of the composition in an extruder for achieving uniform mixing and dispersion followed by a coating step as illustrated herein. Parts and percentages are by weight unless otherwise indicated. In the following examples the following four representative charge transport molecules were used: N,N'-diphenyl-N,N'-di-(m-tolyl)-(1,1'-biphenyl)-4,4'-diamine, hereinafter referred to as m-TPD; N,N'-diphenyl-N,N'-di(p-tolyl)-(1,1'-biphenyl)-4,4'-diamine, hereinafter referred to as p-TPD; N, N'-di-p-tolyl-N,N'-p-ethylphenyl-1,1'-biphenyl-4,4'-diamine, hereinafter referred to p-DE-TPD; and N, N, N', N'-tetra-p-tolyl-(1,1'-biphenyl)-4,4'-diamine, hereinafter referred to as TM-TPD. Both m-TPD and p-TPD are commercially available from H.W. Sands Corp. as Catalogue Nos. ST16/1 and ST16/3, respectively. The synthesis of TM-TPD is given in Example I. p-DE-TPD was also analogously prepared according to the procedure given in Example 1. Silver trifluoroacetate (AgTFA), iodine (I 2 ), bis(p-t-butylphenyl)iodonium hexafluoroarsenate, hereinafter referred to as photoacid, silver hexafluoroantimonate (AgSbF 6 ), nitrosonium hexafluoroantimonate (NOSbF 6 ) were used as oxidants. The synthesis of the photoacid is disclosed, for example, in the U.S. Patent No. 5,587,224, while the other oxidants are commercially available. Polymer binders include MAKROLON® a polyester commercially available from Bayer Corp. and PCZ-200 a polycarbonate derived from bisphenol Z, and is commercially available from Mitsubishi Chemical Corp. EXAMPLE I Preparation of N, N, N', N'-tetra-p-tolyl-biphenyldiamine (TM-TPD): Synthesis of 4'-methyacetanilide: Into three neck round bottom flask (5 L) equipped with a mechanical stirrer, a condenser, and an addition funnel, were added p-toluidine (995 g, 9.3 mol) and hexanes (1.6 L). Acetic anhydride (960 mL, 10.2 mol) was added dropwise for 2 h enough to reflux, then refluxed for 1 h and cooled to room temperature to give a brown solid. This was collected by suction filtration, transferred into a beaker, and washed with water (2 L) for 30 min. The filtration and washing procedures were repeated. The wet white crystals were air dried for 7 days to provide N-(4-methylphenyl)acetamide (1,343 g, 97% yield). Melting point: 150-152 °C. ( lit. 153 °C, Merck index, 11 , 67; ). Synthesis of N,N-Di-p-tolylamine: To a round bottom flask (3L) equipped with a condenser a Dean-Stark trap, a mechanical stirrer, and an argon-outlet with a thermometer, was added 4'-methylacetanilide (448 g, 3.0 mol), 4-iodotoluene (746 g, 3.4 mol, from Aldrich), potassium carbonate (830 g, 6.0 mol), copper sulfate (20 g), and toluene (50 mL). The reaction mixture was heated at 210 °C for 24 hours in an oil bath. The resulting solution was decanted to a round bottom flask (5 L) and the remaining solid was washed with hot ethanol (3 x 500). To the combined mixtures were added potassium hydroxide (340 g) and water (400 mL) and then refluxed for 24 h. To resulting solution was added concentrated HCl (400 mL) dropwise followed by toluene (1,000 mL). The mixture was refluxed for 10 min. The hot organic layer (top) was separated, washed with a hot water (500 mL x 2), and concentrated under reduced pressure. The resulting solid was recrystallized from the mixture of toluene (100 mL) and hexanes (700 mL). The obtained wet crystals were ground with a mortar and pestle, filtered, washed with hexanes (100 mL), and dried in air for 24 hours to give brown crystals (360 g, 6 mol). The filtrate was concentrated under reduced pressure and recrystallized from the mixture of toluene (20 mL) and hexanes (150 mL) to give a brown solid (120 g, second crop). The combined solid was distilled at 165 oC and 1 Torr to give a white solid (445 g) while the forerun first portion (15 g, distilled at 65-80 °C and 1 Torr) was discarded. The white solid was recrystallized from hexanes (500 mL) to give a white solid (422 g, 71% yield). Melting point: 80-82 °C (lit. 79° ∞ C, TCl catalog ) 1 H-NMR (CDCl 3 ): 7.04 (d, 4H), 6.93 (d, 4H), 5.45 (s, br, 1H), 2.33 (s, 6H ) ppm. Note that when iodotoluenes from Oakwood Product Inc., or Charkit Chemical Inc., were used, the above reaction was very slow. Three portions of CuSO 4 (50 g) was added every 10 hours and the reaction was completed in 40 hours (over 95% conversion of 4'-methylacetanilide). During work-up after hydrolysis, suction filtration was required to remove copper residues. Synthesis of N, N, N', N'-tetra-p-tolyl-(1,1'-biphenyl)-4,4'-diamine (TM-TPD): To a round bottom flask (5 L) equipped with a condenser a Dean-Stark trap, a mechanical stirrer, and an argon-outlet with a thermometer, was added 4,4'-diiodobiphenyl (DIB, 406 g, 1.0 mol), N,N-di-p-tolylamine (417 g, 2.1 mol), potassium hydroxide (448 g, 8.0 mol), and toluene (300 mL). After adding 1,10-phenanthroline (9.0 g) and CuCl (1.5 g) at 130 oC, the mixture was vigorously refluxed at 137 °C. After adding another portion of CuCl (3.5g), a very exothermic reaction occurred. The reaction mixture was further heated at 130 °C for 4 hours. To the reaction mixture, was added water (400 mL), toluene (400 mL), and acetic acid (400 mL). The resulting solution was washed with water (2 L) by gentle swirling in a 6 L separatory funnel and the top layer was separated and collected. The aqueous layer was suction-filtered and residue was washed with toluene (300 mL) and top layer was separated. After combining organic layers, the washing process was repeated once again. The dark organic solution was concentrated under reduced pressure and the resulting solution was chilled in freezer for 1 hour to yield a brown solid. After filtering, the brown solid was washed with acetone (3 x 400 mL) and dried in oven at 45 °C and 10 Torr. To a round bottom flask (2 L) equipped with a condenser, a mechanical stirrer, an argon-outlet with a thermometer, and heating mantle was charged the crude product (350 g) and a neutral alumina (200 g) and toluene (1 L). The mixture was heated at 90 °C for 2.5 hour. The resulting yellow solution was filtered through a preheated Buchner funnel. The residue on alumina was extracted with hot toluene (350 mL x 2) and the organic layers combined. After concentrating the combined yellow solution in vacuo, the resulting pale yellow solid (350 g) and acetone (400 g) were heated at 60 °C and stirred at 23 °C for 15 hour under argon to give a pale yellow solid. After filtering, washing with acetone (200 mL x 3), and drying under reduced pressure for 16 hours, a pure TM-TPD (306 g, 56% yield) was obtained. Melting point: 217-219 °C; 1 H-NMR (CDCl 3 ): 7.39 (d, 4H), 7.07-7.00 (m, 20H), 2.31 (s, 12H) ppm. EXAMPLE II This example describes the preparation of coating solution with different compositions. Preparation of coating solution using AgSbF 6 as the oxidant with filtration: m-TPD (32.0 g) and methylene chloride (544 g) were magnetically stirred in a 500 mL bottle until complete solubilization of m-TPD. AgSbF 6 , in an amount of 1.6 g, 0.5 weight percent with respect to m-TPD as then added. The resulting solution was stirred for 16 hours and the resulting solution was allowed to stand for at least two hours to settle the silver precipitate and used as the stock solution. Alternatively, the silver precipitate can be removed by filtration. Into a 2 ounce bottle was added a portion of the stock solution (72.0 g) and MAKROLON 5705 (7.5 g) and the mixture was shaken for 5 hour to dissolve the MAKROLON and to give a coating solution with the following solid weight percents: MAKROLON (65%), m-TPD (35%) and AgSbF 6 in an amount of 5 weight percent with respect to m-TPD. The same stock solution was used to formulate another coating solution as follow: Into a 2 ounce bottle was added a portion of the stock solution (72.0 g), MAKROLON 5705 (7.5 g) and 2-(4-biphenylyl)-5-phenyloxazole (0.12 g) as a anticorrosion additive, and the mixture was shaken for 5 hour to dissolve the MAKROLON and to give a coating solution with the following solid weight percents: MAKROLON (65%), m-TPD (35%), AgSbF 6 in an amount of 5 weight percent with respect to m-TPD, and 2-(4-biphenylyl)-5-phenyloxazole in an amount of 3 weight percent with respect m-TPD. m-TPD (16.0 g) and chlorobenzene (229 g) were magnetically stirred in a 250 mL bottle until complete solubilization of m-TPD. AgSbF 6 in an amount of 0.8 g, 0.5 weight percent with respect to m-TPD, was added. The resulting solution was stirred 16 hours. The resulting solution was allowed to stand for at least two hours to settle the silver precipitate and used as the stock solution. Into a 2 ounce bottle was added portion of the stock solution (61.5 g) and PCZ 200 ( polycarbonate Z, 7.5 g), and the mixture was shaken for 5 hours to dissolve the MAKROLON and to give a coating solution with the following solid weight percents: PCZ 200 (65%), m-TPD (35%) and AgSbF 6 in an amount of 5% with respect to m-TPD. Coating solutions using other charge transport molecules, polymer binders, solvents, and/or anticorrossion additives at different weight percents were similarly prepared. Preparation of coating solution using AgSbF 6 as the oxidant without removing silver: a mixture of m-TPD (4.0 g), MAKROLON (7.44 g), AgSbF 6 (0.08 g) and methylene chloride (68 g) in an amber bottle was roll milled until complete solubilization of the polymer to give a coating solution with the following solid weight percents: Makrolon (65%), m-TPD (35%) and AgSbF 6 in an amount of 2 weight percent with respect to m-TPD. Preparation of coating solution using NOSbF 6 as the oxidant: Into a 500 mL flask equipped with a condenser, a magnetic stirrer and a drying tube were added m-TPD (40.0 g) and methylene chloride (425 g). The mixture was stirred until m-TPD was dissolved and NOSbF 6 (2.0 g) was then added. The resulting solution was stirred overnight and transferred into a 500 mL narrow neck bottle to give a stock solution. Into a 4 ounce bottle was added portion of the stock solution (93.4 g) and MAKROLON 3108 (15 g) and the mixture was shaken for 19 hours to dissolve the MAKROLON and to give a coating solution with the following solid weight percents: MAKROLON (65%), m-TPD (35%) and AgSbF 6 in an amount of 5 weight percent with respect to m-TPD. A portion of this solution (93.4 g) and MAKROLON 3108 (15.0 g) were shaken Preparation of coating solution using a photoacid as the oxidant: Into a 2 ounce bottle was added m-TPD (4.0 g), MAKROLON 3108 (7.44 g), photoacid (0.08 g, 2 weight percent with respect to m-TPD, dioctyl phthalate (0.074 g, as a plasticizer), and methylene chloride (68 g). The mixture was shaken for 20 hours to give a coating solution with the following solid weight percents: m-TPD (35%), MAKROLON 3108 (65%), photoacid (2%), dioctyl phthalate (in an amount of 1 weight percent with respect to MAKROLON). Into a 2 ounce bottle was added m-TPD (4.0 g), MAKROLON 3108 (7.44 g), photoacid (0.08 g, 2 weight percent with respect to m-TPD), polyester PE 200 from DuPont (0.074 g, as the voltage stabilizer), and methylene chloride (68 g). The mixture was shaken for 20 hours to give a coating solution with the following solid weight percents: m-TPD (35%), MAKROLON 3108 (65%), photoacid (2%), and PE 200 (in an amount of 1 weight percent with respect to MAKROLON). Into a 2 ounce bottle was added m-TPD (4.0 g), MAKROLON 3108 (7.44 g), photoacid (0.08 g, 2 weight percent with respect to m-TPD), polysiloxane fluid (0.074 g, as a low surface energy additive), and methylene chloride (68 g). The mixture was shaken for 20 hours to give a coating solution with the following solid weight percents: m-TPD (35%), MAKROLON 3108 (65%), photoacid (2%), polysiloxane fluid (in an amount of 1 weight percent with respect to MAKROLON). EXAMPLE III Coating Deposition : MYLAR (75 microns) substrates with titanium coatings of about 200 to 300 Angstroms were from ICI Inc. Substrates were overcoated with a silane blocking layer (200 to 500 Angstroms derived from 2-aminoisopropyltriethoxylsilane) and then an adhesive layer (200 to 500 Angstroms) of 49K polyester (from DuPont). The resulting substrates were used for depositing the conductive coatings using a Gardner mechanical driven film applicator which is enclosed in a plexiglass box. A substrate was placed on the vacuum plate of the Gardner coater and a size 0.004 Bird film applicator was placed on top of the substrate then coated with a conductive polymer layer using a coating solution prepared as described in Example II. The resulting coating was air dried for 1 hour and then dried in a forced air oven at 125 °C for 30 min to give a coating with a thickness of about 20-25 microns. In the case of photoacid coatings, UV exposure for 99 seconds was needed to induce the conductivity in the coatings. Time Constant Measurements: An Electrodag electrode was painted on the sample for charge relaxation time measurement which involved applying a pulsed voltage to the sample between electrodes. It is generally known to those of ordinary skill in the art that the charge relaxation time constant is inversely proportional to the conductivity. Table 1 shows a series of m-TPD/MAKROLON (35/65) coatings and various oxidants and additives. All the coatings were deposited from methylene chloride. The weight percents of the oxidant and additives with respect to the charge transport molecule are also given. All the samples were stress tested in an environmental chamber of 85 % relative humidity (RH) and 50 °C. The time constants of the samples were measured at different time intervals to determine the electrical stability of the coatings. As shown in Table 1, the charge relaxation time constants for samples 1 through 8 increase at least by a factor of 3 with respect to their respective initial values after 1 week of stress test. This indicates that the coatings have less than I week of stability and become at least 3 time less conductive. Sample 9 using AgAsF 6 shows 1 week of stability, but becomes 5 time more insulative after 2 weeks. Samples 10 through 13 using AgSbF 6 or NOSbF 6 as the oxidant show only small change in the charge relaxation time constant indicating very high stability in the conductivity. The stability of the AgSbF 6 based coatings is highly reproducible as exemplified by the data for samples 11 a and 12a which were coated from coating solutions that had been aged two-months. The improved stability seen for coatings resulting from AgAsF 6 , AgSbF 6 and NOSbF 6 was unexpected and not believed to have been previously reported. Comparative stability of m-TPD/MAKROLON (35/65) coatings. Sample NO. Oxidant (wt%) & additive (wt%) Charge relaxation time constant (millisecond) As coated 1 wk 2 wk 3 wk 4 wk 5 wk 6 wk 7 wk 8wk 1 TTA·SbCl 6 (5%) 0.43 4.50 - - - - - - - 2 TTA·SbF 6 (5%) 0.36 2.20 - - - - - - - 3 TTA·AsF 6 (5%) 0.60 3.67 - - - - - - - 4 photoacid (2%) 0.20 0.66 8.46 - - - - - - 5 AgTFA (5%) 0.16 4.5 - - - - - - - 6 AgTFA (4%)/I 2 (0.5 eqv. with respect to AgTFA 0.41 1.17 2.70 3.56 - - - - - 7 AgBF 4 (5%) 2.11 >100 - - - - - - - 8 AgPF 6 (5%) 0.45 5.91 - - - - - - - 9 AgAsF 6 (5%) 0.21 0.22 1.49 - - - - - - 10 AgSbF 6 (5%) 0.27 0.25 0.37 0.45 0.50 0.56 0.70 0.78 0.80 11 AgSbF 6 (5%)/2-(4-biphenylyl)-5-phenyl oxazole (1%) 0.25 0.34 0.23 0.31 0.43 0.51 0.77 0.68 0.95 11a Same as 11 but from a two-month aged coating solution 0.21 0.23 0.31 0.43 0.51 0.68 0.71 0.84 0.88 12 AgSbF 6 (5%)/2,5-di-t-butylpyridine (3%) 0.36 0.50 0.66 0.66 0.63 0.78 0.69 0.82 0.89 12a Same as 12 but from a two month aged coating solution 0.47 0.49 0.54 0.64 0.50 0.51 0.75 0.83 0.85 13 AgSbF 6 (4%)/AgTFA (2%) 0.26 0.18 0.25 0.29 0.33 0.49 0.50 0.59 1.17 14 NOSbF 6 0.16 0.11 0.13 0.17 0.23 0.24 0.20 0.25 0.23 All coatings were deposited from methylene chloride. Where time constant values are not indicated, tests were discontinued for lack of stability. EXAMPLE IV As shown in Table 2, samples 16 and 16a having TM-TPD as the charge transport molecules show improved stability over the m-TPD based sample 15 by a factor of about 2. This example illustrates that coatings resulting from para-substituted charge transport molecule such as TM-TPD show improved stability over non-para-substituted charge transport molecule such as m-TPD. It can be determined from samples 17, 18, 19 and 20 that the order of the stability of the coatings is TM-TPD > p-DE-TPD > p-TPD > m-TPD, indicating that the completely para-substituted compounds, for example, TM-TPD and p-DE-TPD, provide the most stable coatings, followed by those based the 50% para-substituted p-TPD. Coatings, such as sample 17, derived from the non-para-substituted m-TPD are least stable. Samples 21, 22 and 23 contain a mixture of m-TPD and TM-TPD as the charge transport molecules. It can be seen, that sample 21 which has the highest TM-TPD percentage is the most stable of the three samples; while sample 23 which has the lowest TM-TPD percentage is the least stable. Comparative stability of coatings having different charge transport molecules Sample NO. Charge transport molecule(35%)/MAKROLON (65%)/oxidant (2%) AgSbF 6 (2%) Charge relaxation time constant (millisecond) As coated 1 wk 2 wk 3 wk 4 wk 5 wk 6 wk 7 wk 8wk 15 m-TPD/AgSbF 6 0.41 0.37 0.39 0.48 0.57 0.78 0.98 1.56 1.78 16 TM-TPD/AgSbF 6 (coating dry at 100 °C) 0.14 0.16 0.17 0.19 0.18 0.18 0.26 0.25 0.28 16a TM-TPD/AgSbF 6 (coating dry at 125°C) 0.19 0.22 0.22 0.26 0.25 0.24 0.29 0.31 0.27 17 m-TPD/photoacid 0.29 1.60 2.50 - - - - - - 18 p-TPO/photoacid 0.20 0.54 0.77 1.45 1.88 3.94 - - - 19 p-DE-TPD/photoacid 0.13 0.40 0.41 0.49 0.53 0.69 1.24 1.34 1.78 20 TM-TPD/photoacid (dried at 100 °C) 0.20 0.15 0.26 0.30 0.34 0.42 0.58 0.66 0.87 20a TM-TPD/photoacid (dried at 125 °C) 0.22 0.23 0.31 0.31 0.35 0.44 0.53 0.58 0.72 21 m-TPD/TM-TPD (10/25)/photoacid 0.21 0.23 0.26 0.66 0.40 0.56 0.87 0.95 1.34 22 m-TPD/TM-TPD (20/15) 0.33 0.37 0.52 0.98 0.91 1.23 1.78 2.78 3.25 23 m-TPD/TM-TPD (30/5) 0.50 0.66 1.02 1.24 2.48 - - - - All coatings were deposited from methylene chloride. EXAMPLE V This example further illustrate that para-substituted charge transport molecules show improved stability over non-para-substituted ones. As shown in Table 3, samples based m-TPD with PCZ 200, samples 24 through 28, had very poor electrical stabilities on the order of less than about one week. In contrast, TM-TPD based samples resulting from different coating solvents, samples 29 through 35, are very stable under stress condition over about 8 weeks. Comparative stability of coatings. Sample NO. Charge transport molecule(35%)/PCZ(65%)/p hotoacid (2%)//solvent Charge relaxation time constant (millisecond) As coated 1 wk 2 wk 3 wk 4 wk 5 wk 6 wk 7 wk 8wk 24 m-TPD//metheylene chloride 0.44 4.07 - - - - - - - 25 m-TPD//toluene 0.58 70 - - - - - - - - 26 m-TPD//THF 0.54 6.91 - - - - - - - 27 m-TPD//chlorobenzene 0.44 14.9 - - - - - - - 28 m-TPD//THF:chlorobenzene (3:1) 0.45 13.0 - - - - - - - 29 TM-TPD//methylene chloride 0.36 0.30 0.31 0.38 0.39 0.41 0.29 0.58 0.62 30 TM-TPD//THF 0.48 0.38 0.43 0.53 0.56 0.62 0.84 0.92 0.99 31 TM-TPD//toluene 0.50 0.52 0.52 0.70 0.77 0.75 0.91 0.89 0.93 32 TM-TPD//1,1,2-trichloroethane 0.34 0.31 0.34 0.43 0.45 0.54 0.60 0.63 0.74 33 TM-TPD//chlorobenzene 0.35 0.33 0.32 0.38 0.42 0.47 0.50 0.61 0.71 34 TM-TPD// THF:chlorobenzene (3:1) 0.28 0.34 0.29 0.26 0.29 0.24 0.22 0.21 0.22 35 TM-TPD/PE200 (3%)//THF:chlorobenzene (3:1) 0.35 0.62 0.61 0.70 0.60 0.55 0.45 0.49 0.51

Claims: A conductive polymer coating comprising an arylamine charge transport compound, an oxidized arylamine charge transport compound salt, and a polymer binder, wherein the oxidized arylamine charge transport compound salt has a counter anion selected from the group consisting of hexafluoroantimonate and hexafluoroarsenate, wherein the arylamine charge transport compound is a para-substituted arylamine charge transport material, wherein the oxidized arylamine charge transport compound salt comprises an oxidation product of said arylamine charge transport compound and an oxidizing compound, wherein the oxidizing compound is selected from the group comprising ionic salts, and wherein the ionic salt is selected from the group of: AgSbF 6 , AgAsF 6 , AgPF 6 , AgBF 4 , AgBr, Agl, AgF, AgCl, O 2 SbF 6 , O 2 AsF 6 , NOSbF 6 , NOAsF 6 , NO 2 SbF 6 , NO 2 AsF 6 , (CH 3 CH 2 )O + (CF 3 SO 3 )Al - , (CH 3 CH 2 )O + (CF 3 SO 3 )Ga - , (CH 3 CH 2 )O + (CF 3 SO 3 )B - , CH 3 (C=O) + (CF 3 SO 3 )Al - and mixtures thereof. The conductive polymer coating in accordance with claim 1 wherein the arylamine charge transport compound is selected from the group consisting of those represented by the formulas: and wherein Ar, Ar', and Ar'' are independently selected from unsubstituted and substituted aromatic groups with from 6 to 30 carbon atoms, and R 1 , R 2 , R 3 , R 1 ', R 2 ', and R 3 ' are independently selected from the group consisting of hydrogen, bromine, chlorine, fluorine, alkyl groups with from 1 to 24 carbon atoms, and alkoxy groups with from 1 to 24 carbon atoms, Z is selected from the an atom O, S, Se, or substituent -CH 2 -, G is an alkaline group with 1 to 12 carbon atoms or a group selected from the partial formulas: wherein n' is an integer from 1 to 12, and R and R' are alkyl groups with 1 to 12 carbon atoms. The conductive polymer coating in accordance with claim 1 wherein the arylamine charge transport is selected from the formulas, and mixtures thereof: a) aryldiamine compounds of the formula: and wherein Ar is a substituted or unsubstituted aromatic group, R 1 , R 2 and R 3 are independently selected from the group consisting of hydrogen, bromine, chlorine, fluorine, alkyl groups with from 1 to 24 carbon atoms, and alkoxy groups with from 1 to 24 carbon atoms, and Z is selected from an atom O, S, Se, or methylene substituent -CH 2 - ; b) aryltriamines compounds of the formula: wherein Ar and Ar' are independently selected from substituted and unsubstituted aromatic groups, R is selected from hydrogen, phenyl and alkyl groups containing 1 to 12 carbon atoms, and wherein i and j are integers of 1 to 2; c) aryltetraamines compounds of the formula: wherein Ar, Ar', and Ar" are independently selected from substituted and unsubstituted aromatic groups, p-Ar and p-Ar' are independently selected from para-substituted aromatic groups, R is selected from hydrogen, phenyl and alkyl groups containing 1 to 12 carbon atoms, i, j, and k are integers 1 or 2, G is an alkaline group with 1 to 12 carbon atoms or a group selected from the partial formulas: wherein n' is an integer from 1 to 12, and R and R' are alkyl groups with 1 to 12 carbon atoms; d) arylpentaamines compounds of the formula: wherein Ar, Ar', Ar", and Ar''' are independently selected from substituted and unsubstituted aromatic groups, and i, j, k, and l are integers of 1 or 2; and e) arylhexaamines compounds of the formulas: wherein Ar and Ar' are independently selected from substituted and unsubstituted aromatic groups, p-Ar and p-Ar' are para-substituted aromatic groups, i, j, and k are integers of 1 or 2, G is a alkaline group with 1 to 12 carbon atoms or an aromatic group of the formulas: wherein n' is an integer from 1 to 12, and R and R' are alkyl groups with 1 to 12 carbon atoms. A conductive polymer coating comprising a para-substituted arylamine charge transport compound, and an oxidization product of the para-substituted arylamine charge transport compound and an oxidizing compound, wherein the oxidizing compound is selected from the group comprising ionic salts, and wherein the ionic salt is selected from the group of: AgSbF 6 , AgAsF 6 , AgPF 6 , AgBF 4, AgBr, AgI, AgF, AgCl, O 2 SbF 6 , O 2 AsF 6 , NOSbF 6 , NOAsF 6 , NO 2 SbF 6 , NO 2 AsF 6 , (CH 3 CH 2 )O + (CF 3 SO 3 )Al - , (CH 3 CH 2 )O + (CF 3 SO 3 )Ga - , (CH 3 CH 2 )O + (CF 3 SO 3 )B - , CH 3 (C=O) + (CF 3 SO 3 )Al - and mixtures thereof. The electroluminescent device comprised of a conductive polymer coating of claim 4, wherein said coating is a thin film electrode or a contact modification layer, and wherein the coating facilitates charge injection. A process for the preparation of a conductive polymer coating according to claim 1 comprising: mixing a para-substituted arylamine charge transport molecule, and an oxidizing agent, optional additives and a polymer binder in a solvent to produce a coating mixture; depositing the conductive polymer coating solution mixture on a substrate; and drying the coated substrate; wherein the oxidizing compound is selected from the group comprising ionic salts, and wherein the ionic salt is selected from the group of: AgSbF 6 , AgAsF 6 , AgPF 6 , AgBF 4, AgBr, AgI, AgF, AgCl, O 2 SbF 6 , O 2 AsF 6 , NOSbF 6 , NOAsF 6 , NO 2 SbF 6 , NO 2 AsF 6 , (CH 3 CH 2 )O + (CF 3 SO 3 )Al - , (CH 3 CH 2 )O + (CF 3 SO 3 )Ga - , (CH 3 CH 2 )O + (CF 3 SO 3 )B - , CH 3 (C=O) + (CF 3 SO 3 )Al - and mixtures thereof. A printing machine comprising an imaging member comprising a conductive coating in accordance with claim 1.

Inventors: EWING JOAN R, HSICH BING R, VANLAEKEN ANITA C, EWING, JOAN R., HSICH, BING R., VANLAEKEN, ANITA C.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1998
Main classification: H01B1
IPC codes: C09D7, H01B1, G03G5, G03G15, C09D5