Photoresponsive imaging members

Abstract: An imaging member comprised of an optional supporting substrate (1); a ground plane layer (3); a blocking layer (5); an optional adhesive layer (6); a photogenerator layer (7); and a charge-transport layer (9), wherein the blocking layer is comprised of a polyurethane of the formula: wherein A is a trivalent group; A′ is a bivalent group; R is alkylene, substituted alkylene, arylene, or substituted arylene; and x and y are number mole fractions of which the sum is equal to 1.0.

Description: This invention is generally directed to imaging members, and more specifically the present invention relates to the selection of certain polyurethanes which function as charge-blocking layers for photoresponsive imaging members, especially seamless organic imaging members. In one embodiment, the present invention relates to an imaging member as claimed in claim 1 comprised of a support substrate, a conductive ground plane, a charge-blocking layer comprised of an urethane polymer, an adhesive layer, a charge generating layer, and a charge-transport layer. In another embodiment of the present invention, there are provided seamless imaging members comprised of a hole-transport layer, a charge generating layer, an adhesive layer, a hole-blocking layer comprised of a urethane polymer, and a conductive support substrate. The aforementioned imaging members are useful in electrophotographic printing and imaging processes, and in particular, can be selected for the generation of latent images in electrostatic imaging systems. With further regard to the imaging members of the present invention, the primary function of the hole-blocking layer is to prevent dark injection of charge carriers from the ground plane or conductive substrate into the photogenerating layer, thus significantly reducing the dark decay characteristics of imaging members. Layered imaging members with blocking layers are known, especially those wherein the blocking layer is comprised of a metal oxide, or a siloxane, reference US-A-4,464,450. Illustrated in US-A-4,562, 132, are imaging members comprised of a support substrate, a hole-transport layer comprised of an aryl amine hole-transport compound dispersed in an inactive resinous binder, a charge generating layer comprised of a photogenerating pigment optionally dispersed in a resinous binder, and as a protective topcoating, a layer containing an electron-transport compound of the following formula dispersed in a resinous binder where X is cyano or alkoxycarbonyl groups, A and B are electron-withdrawing groups, m is a number from 0 to 2, n is 0 or 1, and W is an electron-withdrawing group of acyl (COR), alkoxycarbonyl (COOR), alkylaminocarbonyl (CONHR), or derivatives thereof. Moreover, illustrated in US-A-4 835 081 are inorganic photoresponsive imaging members having incorporated therein as protective overcoatings polycondensation polymers derived from the polycondensation of 2,2-bis(hydroxymethyl)-butyl 9-dicyanomethylenefluorene-4-carboxylate, and diisocyanate. Also disclosed in the copending application are layered photoresponsive imaging members comprised of a supporting substrate, a photoconductive layer, an arylamine hole-transport layer, and a protective overcoating layer comprised of the aforementioned polyurethane polymers. In addition, the polyurethane polymers of the copending application are useful as the top overcoating for positive-charging layered photoresponsive devices comprised of a supporting substrate, a hole-transport layer, and a photoconductive layer, and wherein the polymers are of the following formula wherein A is a trivalent linkage; B is a functional group such as an ester (-OCO-), a carbonate (-OCOO-) or a carbamate (-OCONH-); R is a bivalent group, and n represents a certain number of repeating units. The polyurethanes of the present invention are somewhat similar to the aforementioned polyurethane coatings. More specifically, the polyurethanes of the present invention contain therein certain highly flexible segments, thereby providing the desired flexibility characteristic useful for application in belt-type imaging devices. Furthermore, the presence of the soft flexible segments in the polyurethanes of the present invention greatly improves their solubilities in common coating solvents such as aromatic hydrocarbons, tetrahydrofuran, chlorinated hydrocarbons, and the like, thereby enabling the coating process to be accomplished in a variety of solvents by different coating techniques, such as dip coating, spray coating, and the like. More importantly, the incorporation of the flexible segments into the polyurethane structure renders the synthesis of higher molecular-weight polyurethanes feasible, thus affording mechanically strong and highly durable polyurethane blocking layers. The polyurethanes of the present invention also display good adhesion properties, thereby improving the adhesion of the photogenerating layer to the ground plane. In US-A-4 820 601, filed in 01.02.88 and published in 11.04.89, are illustrated imaging members with protective overcoatings comprised of the copolyurethanes selected as blocking layers for the same, or similar imaging members of the present invention. There are disclosed in US-A-4,474,865 improved photoresponsive imaging members with electron-transporting components containing specific dicyano fluoro ester moieties; 3,928,034, which illustrates the incorporation of electron transporting moieties chemically attached to polymers, reference columns 7 and 8; and 4,007,043; 4,063,947; 4,075,012; and 3,896,184. Also of interest are US-A-3,108,092; 3,451,969; 4,063,947; and 4,203,764; and NL-A-7606525. Of particular interest are US-A-and NL-A-7606525, which disclose imaging members with electron-transport compounds, reference column 3, line 57, to column 4, line 30, of the ′947 patent; US-A-3,907,650, which discloses hole-transport materials for an electron-blocking layer, reference column 3; 3,975,635, which discloses a xeroradiographic plate with a conductive backing member, an overlayer of selenium, and an intermediate layer of polyvinyl carbazole or an alloy of arsenic and selenium; 4,582,773 illustrating electrophotographic photoreceptors including a blocking layer formed from a doped microcrystalline semiconductor alloy; and US-A-4,013,623; 4,050,934, which disclose a dicyanomethylene group as the electrical active moiety for use in electron-transporting layers. Other patents of background interest are US-A-4,657,751, which mentions cuprous iodide as a conductive substrate film; 2,901,348; 3,713,821; 3,879,199; 3,888,665; 3,891,435; 3,972,717; 4,010,031; 4,082,551; 4,106,935; 4,391,888; and 4,415,639. While the above-described imaging members are suitable for their intended purposes, there continues to be a need for layered photoresponsive imaging members with functionally superior charge-blocking layers. More specifically, there continues to be a need for charge-blocking layers which can effectively block the dark injection of charge carriers from the ground plane into the photogenerating layer. Additionally, there continues to be a need for charge-blocking layers with excellent flexibility characteristics, thereby enabling their use in belt-type organic imaging members. Furthermore, there is a need for organic charge-blocking layer materials which are soluble in a variety of solvents thereby permitting improved coatability, and allowing economical spray and dip coating processes to be selected for the preparation thereof. Another need resides in the provision of charge-blocking layers with acceptable desirable adhesive properties enabling the layer to adhere to the ground plane or conductive substrate, thereby improving the overall layered lamination integrity of the imaging members. It is an object of the present invention to provide an improved photoresponsive imaging member. Accordingly the present invention provides photoresponsive imaging members having incorporated therein a charge-blocking layer containing a specific polyurethane as claimed in the appended claims. The polyurethanes which are the subject-matter of this invention are illustrated in the accompanying drawings. More specifically, in one embodiment of the present invention there are provided photoresponsive imaging members having incorporated therein a charge-blocking layer containing the polyurethane of the formula wherein A is a trivalent group such as dimethylene alkyl group, or triethylene amine; A′ is a bivalent group such as alkylene, arylene, polyether segments, and the derivatives thereof; R is alkylene, arylene, or derivatives thereof; and x and y are number mole fractions of which the sum thereof is equal to 1. More specifically, x and y are mole fractions of from 0.05 to about 0.95. Examples of polyurethanes selected to be contained in the charge-blocking layer include those as represented by the following Formulas I, II and III: wherein A is a trivalent group; R is a bivalent group such as alkylene, arylene, substituted alkylene or substituted arylene group such as methylene, dimethylene, trimethylene, tetramethylene, phenylene, tolylene, and the like; R′ is an alkyl, or substituted alkyl substituent, an aryl or substituted aryl substituent; x and y represent number mole fractions of from about 0.05 to about 0.95, subject to the provision that the sum of x + y is equal to 1.0; and m and n are positive integers of from 1 to 20. Examples of alkyl substituents include those with from 1 to 25 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, dodecyl, and the like; while examples of aryl substituents are those with from 6 to 24 carbon atoms, such as phenyl and naphthyl. Specifically, examples of polyurethane polymers selected for the imaging members of the present invention include those represented by the formulae illustrated in Figures 1 to 10, wherein the substituents such as x and y are as defined herein. The polyurethanes of the present invention can be synthesized, reference Reaction Scheme 1 that follows, by the reaction of the dihydroxy-functionalized monomer (1a) and a diol (2) such as ethylene glycol, diethylene glycol, octanediol, and the like, with a slight excess of diisocyanate (3), in an inert reaction solvent medium at a temperature usually below 100°C, and preferably between 50°C to 85°C. In general, a suitable catalyst, such as tertiary amines, dibutyltin diacetate or dibutyltin dilaurate, can be employed to increase the rate of polymerization. wherein A, A′, x, y and R are as illustrated herein. Examples of suitable solvents for the above polymerization reaction include ethyl acetate, tetrahydrofuran, dioxane, dimethyl sulfoxide, dimethyl acetamide, and dimethylformamide. Also, the aforesaid reaction is generally accomplished in a period of from 2 to 24 hours depending on the nature of the reagents and reaction conditions. Examples of diisocyanates that may be selected for the preparation of the copolyurethanes include methane diisocyanate, 1,2-ethane diisocyanate, 1,3-propane diisocyanate, 1,6-hexane diisocyanate, 1,4-cyclohexane diisocyanate, 1,4-dimethylenecyclohexane diisocyanate, benzene diisocyanate, toluene diisocyanates, methylene bis(4-phenyl isocyanate), and the like. Specific examples of the dihydroxy-functionalized monomer (1a) selected for the preparation of the polyurethanes include 2,2-bis (hydroxymethyl)butyl 9-dicyanomethylenefluorene-4-carboxylate; 3,5-dihydroxyphenyl 9-dicyanomethylenefluorene-4-carboxylate; 2-[bis(2-hydroxyethyl)amino]ethyl 9-dicyanomethylenefluorene-4-carboxylate; 3-hydroxy-2-nitro-2-hydroxymethylpropyl 9-dicyanomethylenefluorene-4- carboxylate; 2,3-dihydroxypropyl 9-dicyanomethylenefluorene-4-carboxylate; 2-[bis(2-hydroxyethyl)amino]ethyl 9-dicyanomethylenefluorene-4-carboxylate; and 2,2-bis(hydroxymethyl)propyl 9-dicyanomethylenefluorene-4-carboxylate. The polyurethanes illustrated herein and synthesized, for example, in accordance with the processes specified can be characterized by various analytical techniques including spectroscopy, GPC, vapor pressure osmometry, and the like. Also, the polyurethane can be applied to the imaging members disclosed herein in a desired thickness. Generally, the thickness of this layer is from 0.01 to 2 µm, and preferably from 0.1 to 2 µm. The invention will now be illustrated with reference to specific preferred embodiments shown in the drawings, wherein Figures 1 through 10 are formulas representing the polyurethanes contained in the charge-blocking layer for the imaging members of the present invention; Figure 11 represents a cross-sectional view of a photoresponsive imaging member of the present invention; and Figure 12 represents a cross-sectional view of a preferred photoresponsive imaging member of the present invention. There is illustrated in Figure 11 a photoresponsive imaging member of the present invention comprised of an optional support substrate 1, such as of aluminum; a ground plane layer 3 of a thickness of from 0.1 to 150 µm of, for example, a copper iodide, or a carbon black dispersion in a suitable binder such as poly(vinyl fluoride), polyesters, and the like; a charge-blocking polyurethane layer 5 of the formulae illustrated herein of a thickness of from 0.001 to 25 µm, and preferably 0.1 to 3 µm; an optional adhesive layer 6 of a thickness of from 0.001 to 0.5 µm; a photogenerator layer 7 of a thickness of 0. 1 to 2 µm; and a charge-transport layer 9 of a thickness of from 5 to 50 µm containing a charge transport material 11 dispersed in an inactive resinous binder. Illustrated in Figure 12 is a photoresponsive imaging member of the present invention comprised of a polymeric substrate 15; a ground plane layer 17 comprised of copper iodide of a thickness of about 0.05 µm; a blocking layer 19 of a thickness of 0.3 µm comprised of the polyurethane of Figure 3 illustrated herein, and derived from the polycondensation of 2,2-bis(hydroxymethyl)butyl 9-dicyanomethylene-fluorene-4-carboxylate and t-butyl bis(2-hydroxyethyl)amine with toluene diisocyanates; an adhesive layer 20 comprised of a polyester, such as PE49000 available from Goodyear Chemical, phenoxy resins, silicon polymers, vinyl polymers, and the like of a thickness of 0.05 µm; a photogenerator layer 21 comprised of trigonal selenium of a thickness of 0.8 µm; and an aryl amine hole-transport layer 23 of thickness of 30 µm comprised of a diamine 24 such as N,N′-diphenyl-N,N′- bis(3-methyl phenyl) 1,1′-biphenyl-4,4′-diamine dispersed in an inactive resinous binder 25. With further reference to the photoresponsive imaging members illustrated herein, and particularly with reference to Figures 11 to 12, the support substrate layers may be comprised of any suitable material having the requisite mechanical properties. Thus, the substrate layers, usually of a thickness of from 50 to 5,000 µm, may be comprised of a layer of polymeric materials such as the commercially available 'Mylar' (trademark), polyesters, polyurethanes, polyamides, and the like. The substrate may be flexible or rigid, and may be of a number of many different configurations such as, for example, a plate, a cylindrical drum, a scroll, an endless flexible belt, and the like. Preferably, the substrate is in the form of an endless flexible belt or a rigid drum. The photoconductive or photogenerating layers of the imaging members of the present invention, reference for example the members of Figures 11 and 12, can be comprised of known photoconductive materials usually of a thickness of from 5 to 35 µm including, for example, amorphous selenium, amorphous selenium alloys, halogen-doped amorphous selenium, halogen-doped amorphous selenium alloys, trigonal selenium, selenide and carbonates with trigonal selenium, reference US-A-4,232,102 and 4,233,283; cadmium sulfide, cadmium selenide, cadmium telluride, cadmium sulfur selenide, cadmium sulfur telluride, cadmium seleno telluride, copper and chlorine-doped cadmium sulfide, and the like. Alloys of selenium included within the scope of the present invention are selenium tellurium alloys, selenium arsenic alloys, selenium tellurium arsenic alloys, and preferably such alloys containing selenium in an amount of from 70 to 99.5 percent by weight and an optional halogen material, such as chlorine, in an amount of from 50 to 200 parts per million. Also, this layer can be comprised of metal phthalocyanines, metal-free phthalocyanines, reference US-A-4,265,990; other known phthalocyanines, as disclosed in US-A-3,816,118; vanadyl phthalocyanine, squaraines, perylenes, and the like. Examples of known ground plane layers include inorganic materials such as, for example, aluminum, chromium, nickel, brass, copper iodide, and the like; conductive polymer materials such as aluminized Mylar; or carbon black impregnated polymer films. Various hole-transport layer compositions can be selected providing these substances are capable of transporting holes, this layer generally having a thickness in the range of from 5 to 50 µm, and preferably from 20 to 40 µm. Thus, the transport layer comprises aryl amine molecules of the formula dispersed in a highly insulating and transparent organic resinous material such as polycarbonates and the like as illustrated in, for example, the ′132 patent, wherein X is alkyl or halogen, preferably methyl or chlorine. The charge-transport layer is substantially nonabsorbing in the spectral region of intended use, that is, visible light, but is "active" in that it allows injection of photogenerated holes from the charge generating layer. Also, the resin becomes electrically active when it contains from about 10 to 75 weight percent of the substituted N,N,N′,N′-tetraphenylbenzidine corresponding to the foregoing formula. Compounds corresponding to this formula include, for example, N,N′-diphenyl-N,N′-bis-(alkylphenyl)benzidine, wherein the alkyl is methyl, ethyl, propyl, butyl, hexyl, N,N′-diphenyl-N,N′-bis(3-methylphenyl)benzidene; N,N′-diphenyl-N,N′-bis(3-methylphenyl)1,1′-biphenyl-4,4′-diamine; and the like. With halogen substitution, the compound is N,N′-diphenyl-N,N′-bis(halophenyl)benzidene. Other electrically active small molecules which can be dispersed in the electrically inactive resin to form a layer which will transport holes include triphenylamine, bis-(4-diethylamino-2-methylphenyl)phenyl methane, and bis-(4-diethylaminophenyl)phenylmethane. Several advantages are associated with the imaging members of the present invention inclusive of enabling the generation of images with excellent resolution, and no background deposits for an extended number of imaging cycles exceeding, for example 200,000; and moreover, the members, especially seamless photoresponsive members with the carbon black impregnated transparent ground planes, can be irradiated from behind the ground plane, thus providing certain enabling architectural advantages such as permitting the incorporation of an erase lamp inside the photoreceptor loops. Furthermore, the addition of a charge-blocking layer in combination with the polyurethane blocking layer improves the acceptance potential while effectively reducing the dark conductivity of the imaging members, thus enabling the members to achieve acceptable desirable contrast potentials easily with relatively low or no background deposits. The presence of the blocking layer also enhances the resistance of the imaging members to environmental changes, such as changes in humidity and temperature. These changes generally have an adverse effect on the electrical performance of photoresponsive imaging members, giving rise to high dark conductivity and high residual potentials. These undesired electrical effects usually result in poor copy quality such as faint images with high backgrounds. Also, the sensitivity of the imaging member to humidity and temperature would render the copy quality dependent on the environmental conditions. With further respect to the present invention, there are envisioned imaging and printing processes wherein, for example, an electrostatic latent image is generated on the imaging members illustrated herein subsequently rendering the image visible with a developer composition comprised of a toner with resin particles such as styrene polymers, pigment particles such as carbon black, charge-enhancing additives such as cetyl pyridinium chloride, external additives such as colloidal silicas and metal salts, and metal salts of fatty acids inclusive of zinc stearate, reference for example US-A-4,298,672; 4,338,390; 4,560,635; 3,590,000; 3,900,588, and 3,983,045; thereafter transferring the developed image to a suitable substrate such as paper; and permanently affixing the image thereto by, for example, heat or other similar processes. The invention will now be described in detail with respect to specific preferred embodiments thereof, it being understood that these examples are intended to be illustrative only and the invention is not intended to be limited to the materials, conditions, and process parameters recited herein. All percentages and parts are by weight unless otherwise indicated. EXAMPLE I Synthesis of 2,2-bis(hydroxymethyl)butyl 9-dicyanomethylenefluorene-4-carboxylate (a): A mixture of 2.1 kilograms of trimethylolpropane, 173 grams of fluorenone-4-carboxylic acid, and 8 milliliters of sulfuric acid was mechanically stirred and heated in a 5-liter flask at 100°C for 5 hours. The mixture was cooled to about 80°C, and 1 liter of methanol was added. Thereafter, the resulting solution was poured slowly into 17 liters of 3 percent aqueous sodium bicarbonate solution with constant stirring, and the crude product resulting was filtered, washed several times with water, and dried. Purification by recrystallization from ethyl acetate afforded 187 grams of pure 2,2-bis(hydroxymethylbutyl) fluorenone-4-carboxylate, m.p., 134 to 135.5°C. A solution of 240 grams of the ester as obtained above, 93 grams of malononitrile, and 5 milliliters of piperidine in 2.3 liters of absolute methanol was heated under reflux in a nitrogen atmosphere for 5 hours. After the reaction, the mixture was cooled to about 50°C, and the solid product was filtered. The product obtained of Formula (a) was washed twice with methanol, dried in vacuo at 100°C to afford 229 grams of pure (a), m.p., 208 to 209°C. EXAMPLE II Synthesis of 3,5-dihydroxyphenyl 9-dicyanomethylenefluorene-4-carboxylate (b): A solution of 30.0 grams of phloroglucinol and 70 milliliters of pyridine in 300 milliliters of dichloromethane was stirred at room temperature under a nitrogen atmosphere. Thereafter, a solution of 8.0 grams of (4-chloroformyl-9-fluorenylidene)malononitrile in 400 milliliters of dichloromethane was added thereto over a period of 1 hour. After addition, the reaction mixture was further stirred for another hour. The mixture was washed three times with dilute aqueous HCl solution, twice with dilute aqueous NaHCO₃ solution, and once with water. The solution was dried, filtered, and evaporated under reduced pressure to give the crude product. Recrystallization from methanol afforded 6.1 grams of (b), m.p., 255.5 to 257°C. EXAMPLE III Synthesis of 2-[bis(2-hydroxyethyl)amino]ethyl 9-dicyanomethylene fluorene-4-carboxylate (c): A solution of 100.0 grams of triethanolamine and 58 milliliters of dry pyridine in 350 milliliters of dry dichloromethane was stirred at room temperature under a nitrogen atmosphere. Thereafter, a solution of 8.0 grams of (4-chloroformyl-9-fluorenylidene)malononitrile in 400 milliliters of dry dichloromethane was added over a period of 1 hour. After addition, the reaction mixture was further stirred for another hour. The reaction mixture was washed several times with water to remove the excess amines and the corresponding hydrochloride salts, dried with anhydrous magnesium sulfate, and filtered. Evaporation of the filtrate provided 5 grams of crude product. Purification by recrystallization from isopropanol afforded 4.5 grams of pure (c), m.p., 155.5 to 156.5°C. Other hydroxy carboxylates can be prepared in a manner similar to Examples I and III. EXAMPLE IV Synthesis of Copolyurethane (Figure 1, x = 0.5; y = 0.5): A mixture of 0.030 mole of diol monomer (a), 0.030 mole of diethylene glycol, 0.063 mole of toluene diisocyanates (mixture of 2,4- and 2,6-diisocyanates), and 0.05 gram of dibutyltin dilaurate was dissolved in 100 milliliters of dried dimethyl sulfoxide. The mixture was heated under an inert atmosphere at 70 to 75°C for 4 hours, after which 5 milliliters of ethanol were added. Thereafter, the reaction mixture was heated for another hour before cooling down to room temperature. This mixture was then poured slowly into 3 liters of swirling methanol to precipitate the resultant polyurethane. The polyurethane product was filtered and washed twice with 500 milliliters of methanol. The yield of the above copolyurethane with the formula as represented by Figure 1 was 86 percent after drying in vacuo at 65°C for 24 hours; DP (degree of polymerization) was 103; Tg 121°C (midpoint); IR (KBr) 1,729; 2,221 cm⁻¹. EXAMPLE V Synthesis of Copolyurethane (Figure 1, x = 0.6; y = 0.4): The copolyurethane of Figure 1 above was prepared according to the procedure of Example IV with the exceptions that 0.036 mole of diol monomer (a), 0.024 mole of diethylene glycol, and 0.063 mole of toluene diisocyanates were employed; and the reaction was conducted for 6 hours. The yield was 88 percent; DP 112; and Tg 134°C; IR (KBr) 1,730; 2,221 cm⁻¹. EXAMPLE VI Synthesis of Copolyurethane (Figure 3, x = 0.5; y = 0.5): A mixture of 0.150 mole of diol monomer (a), 0.150 mole of t-butyl bis(2-hydroxyethylamine), and 0.316 mole of tolylene diisocyanates, and 0.2 gram of dibutyltin dilaurate in 700 milliliters of dried dimethylsulfoxide was heated under a nitrogen atmosphere at 70 to 75°C for 10 hours. Subsequently, 10 milliliters of absolute ethanol was added and the reaction was continued at the same temperature for another hour. After cooling down to room temperature, the reaction mixture was poured into 5 liters of methanol to precipitate the above polyurethane product. The precipitate was filtered, washed with methanol, and dried in vacuo at 60°C for 24 hours. The yield of the above copolyurethane was 91 percent; DP 121; and Tg 134°C; IR (KBr) 1,730; 2,222 cm⁻¹. EXAMPLE VII Synthesis of Copolyurethane (Figure 4, x = 0.5; y = 0.5): The synthesis of the above copolyurethane was accomplished in accordance with the procedure of Example VI with a mixture of 0.030 mole of diol monomer (a), 0.030 mole of 1,8-octanediol, 0.063 mole of toluene diisocyanates, and 0.05 gram of dibutyltin dilaurate. The yield of the above copolyurethane was 84 percent; DP 99; Tg 118°C; IR (KBr) 1,730; 2,222 cm⁻¹. EXAMPLE VIII Synthesis of Copolyurethane (Figure 6, x = 0.6; y = 0.4): The synthesis of the above copolyurethane was accomplished in accordance with the procedure of Example IV with monomer (c), 1,5-pentanediol and toluene diisocyanates except that the reaction was conducted in dry dimethylformamide. The yield of the above copolyurethane was 92 percent; DP 103; Tg 107°C; IR (KBr) 1,730; 2,222 cm⁻¹. EXAMPLE IX Synthesis of Copolyurethane (Figure 8, x = 0.7; y = 0.3): The synthesis of the above copolyurethane was accomplished in accordance with the procedure of Example V with 0.042 mole of diol monomer (b), 0.018 mole of t-butyl bis(2-hydroxyethyl)amine, 0.063 mole of 1,4-benzenediisocyanate, and 0.05 gram of dibutyltin dilaurate. The reaction was conducted in dried tetrahydrofuran, and the yield of the above copolyurethane was 87 percent; DP 89; Tg 138°C; IR (KBr) 1,730; 2,222 cm⁻¹. EXAMPLE X Two substantially identical photoresponsive imaging devices were fabricated as follows. The first member was comprised of a six-layer structure with a configuration as illustrated in Figure 11, and the second a five-layer structure without the polyurethane blocking layer to serve as a control device. The conductive ground planes comprised of commercially available cuprous iodide were fabricated as follows: a saturated solution of cuprous iodide in butyronitrile was prepared by agitating 2.3 grams of ultra pure cuprous iodide in 100 milliliters of butyronitrile for 4 to 16 hours, followed by filtering through a filter of 0.4 µm porosity. The clear filtrate was coated by drawbar technique onto a 'Mylar' substrate using a 150 µm bar gap. Subsequently, the ground plane coating was dried in an air convection oven at 100°C for 10 minutes. The dry thickness of the coating was about 0.5 µm. The upper four layers, reference Figure 11, were coated from appropriate solutions using the above described known drawbar technique. Except for the top transport layer, each coating was dried for one hour before the subsequent layer was coated. The blocking layer of a thickness of 0.25 µm was prepared from a solution of 0.15 gram of the copolyurethane of Figure 1 in 10 milliliters of tetrahydrofuran, and was coated at a thickness of about 0.2 µm using 12 µm bar gap. Overcoated on top of the blocking layer was a 0.06 µm thick adhesive layer which was obtained from a solution of 0.12 gram of Reillen 4200 poly(vinyl pyridine) in 20 milliliters of isobutanol and 2 milliliters of isopropanol. The photogenerating layer of trigonal selenium, about 1 µm in thickness, was obtained by coating a dispersion of 28.5 parts of trigonal selenium, 16 parts of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-benzidine, 55.5 parts of poly(vinyl carbazole) in a mixture of tetrahydrofuran and toluene. The top transport layer of a thickness of 25 µm was prepared from a solution of 40 parts of N,N′-diphenyl-N,N′-bis(3-methylphenyl)benzidine and 60 parts of 'Makrolon' (trademark) polycarbonate in methylene chloride. The transport layer coating was dried at 50°C for 30 minutes, and then at 110°C for another 10 minutes. The two members, one with the polyurethane blocking layer, and one without, were tested electrically by negatively charging with a corotron, and discharging by exposure to a tungsten white light. The acceptance potentials of these imaging devices after charging, and their residual potentials after exposure to white light were recorded. The surface potential was measured using a wire loop probe contained in a shielded cylinder and placed directly above the surface of the imaging device. The cylinder was grounded, and the loop was capacitively coupled to the surface potential of imaging device. The following table summarizes the electrical performance of these devices, and indicates the effective blockage of charge injection by the blocking layer: EXAMPLE XI A photoresponsive imaging device comprising a five-layer structure with a conductive substrate as a ground plane was fabricated by essentially repeating the procedure of Example X. The conductive substrate was a 75 µm thick carbon black impregnated thermoplastic sheet available commercially from E.I. Dupont De Nemours, Inc. The thermoplastic was poly(vinyl fluoride) with a loading of carbon black dispersion of about 25 percent. The resistivity of this ground plane was 10⁴ ohms/square. A blocking layer of thickness of about 0.8 µm was coated on the ground plane in accordance with the procedure of Example X, except that the copolyurethane of Figure 2 was selected in place of the copolyurethane of Figure 1. On top of the blocking layer was coated in succession a photogenerating layer, and a transport layer which were identical to those of Example X. A control imaging device without the blocking layer was also fabricated by repeating the aforementioned process. The members (devices) were then electrically tested in a cyclic scanner for over 200 cycles. The scanner was equipped with a single wire corotron set to deposit 9x10⁻⁸ coulombs/cm² of charge on the imaging surface. The imaging devices were wrapped around an aluminum drum with a circumference of 765 mm, and rotated at a speed of 12 rpm, giving a surface speed of 150 mm per second. The devices were discharged with a tungsten white light source. The device with a blocking layer exhibited stable acceptance for over 200 cycles, and the residual potential remained at 30 to 50 volts. The acceptance potential of the control device was considerably lower and unstable after 200 cycles of charging and discharging, reference the following table. EXAMPLE XII A photoresponsive imaging member similar to Example X was prepared by repeating the procedure of this Example with a 'Mylar' substrate, an eight-µm thick conductive layer comprising 15 percent of carbon black (Black Pearls 2000 available from Cabot Corporation) in polyester PE-49000 (from Dupont), a blocking layer of the copolyurethane of Figure 3, an adhesive layer, a photogenerating layer, and a transport layer identical to those of Example X. The solution for the conductive layer was prepared by dispersing by agitation 0.94 gram of carbon black in a solution of 5.32 grams of polyester PE-49000 in 325 milliliters of methylene chloride. The device was electrically tested by repeating the procedure of Examples X and XI, and substantially similar results were obtained. EXAMPLE XIII A photoresponsive imaging member similar to that of Example XII was prepared by repeating the procedure of this Example with the exception that a ball grained aluminum plate was employed as the conductive layer instead of the carbon black impregnated polyester film. Electrical testing of the device was accomplished by repeating the procedure of Example X. Substantially similar results were obtained. EXAMPLE XIV A photoresponsive imaging member similar to that of Example X was prepared by repeating the procedure of this Example with the exception that a polypyrrole conductive coating was used instead of cuprous iodide. The polypyrrole conductive layer was prepared by coating a 5 percent solution of ICP-117 polypyrrole dispersion (from Polaroid Corporation) using a drawbar with a 50 µm gap opening. The coating was dried as before at 100°C for 10 minutes. Electrical testing was accomplished in accordance with the procedure of Example X, and substantially similar results were obtained.

Claims: A photoconductive imaging member comprising: an optional support substrate (1); a ground plane layer (3); a charge-blocking layer (5); an optional adhesive layer (6); a charge generating layer (7), and a charge-transport layer (9), in this order, wherein the charge-blocking layer comprises a polyurethane of the formula: wherein A is a trivalent group; A′ is a bivalent group; R is alkylene, substituted alkylene, arylene, or substituted arylene; and x and y are number mole fractions of which the sum is equal to 1.0. An imaging member in accordance with claim 1 wherein the photogenerator layer includes selenium or a selenium alloy. An imaging member in accordance with claim 1 or 2, wherein the trivalent group A contains from 4 to 20 carbon atoms. An imaging member in accordance with any preceding claim, wherein A is 2,2-dimethylene butyl, 2,2-dimethylene propyl, 2,2-dimethylene ethyl, or triethylene amine. An imaging member in accordance with any preceding claim, wherein the blocking layer is of a thickness of from 0.01 to 2 µm. An imaging member in accordance with any preceding claim, wherein R is an arylene group of from 6 to 24 carbon atoms. An imaging member in accordance with any of claims 1 to 5, wherein R is a alkylene group of from 1 to 20 carbon atoms. An imaging member in accordance with any preceding claim, wherein the bivalent group A′ contains heteroatoms of nitrogen, oxygen or sulfur. An imaging member in accordance with claim 8, wherein A′ is -CH₂CH₂OCH₂CH₂-; -CH₂CH₂OCH₂CH₂OCH₂CH₂-; -CH₂CH₂N(t-C₄H₉)CH₂CH₂-; or -CH₂CH₂SCH₂CH₂- An imaging member in accordance with any preceding claim, wherein the charge generating layer is comprised of a photogenerating pigment optionally dispersed in a resinous binder, and the charge transport layer is comprised of an aryl amine hole-transport material dispersed in a resinous binder.

Inventors: ONG BENG S, SPIEWAK JOHN W, THORNTON CONSTANCE J, YUH HUOY-JEN, ONG, BENG S., SPIEWAK, JOHN W., THORNTON, CONSTANCE J., YUH, HUOY-JEN
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1989
Main classification: G03G5
IPC codes: G03G5