Photoconductive imaging members

Abstract: A photoconductive imaging member comprised of a hydroxygallium phthalocyanine photogenerator layer, a charge transport layer, a barrier layer, a photogenerator layer comprised of a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-10,21-dione, and thereover a charge transport layer.

Description: This invention is generally directed to imaging members, and, more specifically, the present invention is directed to improved multilayered imaging members with two photogenerating layers, one of which is sensitive to a wavelength of from 500 to 800 nanometers, such as BZP, reference U.S. Patent 4,587,189and one of which is sensitive to a wavelength of from 550 to 950 nanometers, reference for example U.S. Patent 5,482,811 especially Type V hydroxygallium phthalocyanine, and situated therebetween, and more specifically between the charge transport layer with the hydroxygallium phthalocyanine and the BZP layer, a suitable barrier layer of, for example, a polyester, such as MOR-ESTER 49,000® available from Norton International, and wherein there is enabled a number of advantages for the resulting imaging member, such as improving the BZP coating quality, and the photoconductive imaging member electricals of photosensitivity, and cycling stability. The photogenerating layers can be exposed to light of the appropriate wavelengths simultaneously, sequentially, or alternatively only one of the photogenerating layers can be exposed. The imaging members of the present invention in embodiments exhibit excellent cyclic stability, independent layer discharge, and substantially no adverse changes in performance over extended time periods. The aforementioned photoresponsive, or photoconductive imaging members can be negatively charged when the photogenerating layers are situated between the hole transport layers and the substrate. Processes of imaging, especially xerographic imaging and printing, including digital, are also encompassed by the present invention. More specifically, the layered photoconductive imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible with toner compositions of an appropriate charge polarity. The imaging members as indicated herein are in embodiments sensitive in the wavelength region of, for example, from 550 to 900 nanometers, and in particular, from 700 to 850 nanometers, thus diode lasers can be selected as the light source. Moreover, the imaging members of this invention are preferably useful in color xerographic applications where several color printings can be achieved in a single pass. US-A-5,587,262 discloses a photoconductive imaging member comprised of a substrate, a hydroxygallium phthalocyanine photogenerator layer, a charge transport layer, a photogenerator layer comprised of a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-6,11-dione and bisbenzimidazo- (2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-10,21-dione and as a top layer a charge transport layer. US-A-5,552,253 is concerned with a multiple layer photoreceptor comprising a substrate on which a first photoconductive stack and a second photoconductive stack is present. The first photoconductive stack consists of hydroxygallium phthalocyanine. The second photoconductive stack consists of benzimidazole perylene. The presence of a suitable hole-blocking layer capable of forming a barrier is disclosed in particular in column 4, lines 52 to 63. Thus, there remains a need for improving the color printing capability of xerographic processes, and in particular, to print more colors with a minimum number of passes, and therefore, improve the productivity of the printing process, and moreover, there is a need for improved photoconductive imaging members with excellent BZP coating qualities, and improved photoconductor electricals. This can be achieved with the imaging members of the present invention wherein there are sequentially arranged, for example, five layers. These imaging members can be referred to as a multilayered two-tier photoresponsive imaging member. The photodischarge behavior of two-tier imaging members can be selectively controlled by the wavelengths of exposure light and hence the member can be fully discharged, partially discharged or zero discharged. There can be two partially discharged areas depending, for example, on the location of the photodischarge, top tier discharge or bottom tier discharge. The fully discharged and zero discharged areas can be developed with appropriate toners to provide two different colors. Also, a flood exposure with a light effective on only the top tier can be selected to remove its partial charge to zero. The zero charge area can then be developed with another color toner. With two lasers of selected wavelengths, one effective on the top tier, the other on the bottom tier, and applying a further flood discharge on the top tier, three color printing in a single pass is achieved. It is the object of the present invention to provide improved layered photoresponsive imaging members with a sensitivity to visible light, and which members possess improved electricals and improved coating characteristics, especially for BZP, and wherein the charge transport molecules do not diffuse, or there is minimum diffusion thereof into the BZP layer, to provide improved layered photoresponsive imaging members with simultaneous photosensitivity to near infrared radiations, for example from 550 to 950 nanometers, and to light of a wavelength of from 500 to 800 nanometers, to provide photoconductive imaging members with two photogenerating layers, and two charge transport layers, and a barrier layer, to provide imaging members containing as one of the photogenerating pigments Type V hydroxygallium phthalocyanine, especially with XRPD peaks at, for example, Bragg angles (2 theta +/- 0.2°) of 7.4, 9.8, 12.4, 16.2, 17.6, 18.4, 21.9, 23.9, 25.0, 28.1, and the highest peak at 7.4 degrees. The X-ray powder diffraction traces (XRPDs) were generated on a Philips X-Ray Powder Diffractometer Model 1710 using X-radiation of CuK-alpha wavelength (0.1542 nanometer). The diffractometer was equipped with a graphite monochrometer and pulse-height discrimination system. Two-theta is the Bragg angle commonly referred to in x-ray crystallographic measurements. I (counts) represents the intensity of the diffraction as a function of Bragg angle as measured with a proportional counter, and to provide multilayered two-tier photoresponsive, or photoconductive imaging members which can be selected for imaging processes including color xerography, such as xerocolography, and three color printing by selectively discharging the two-tier imaging member wherein, for example, three different surface potentials can be obtained after exposure to light, that is for example zero voltage when both tiers are discharged; partial voltage when one tier is discharged, or full voltage when neither tier is discharged. This object has been achieved by photoconductive imaging member according to the appended claims. More specifically, the photoconductive imaging members of the present invention are comprised of an optional supporting substrate, a photogenerating layer of hydroxygallium phthalocyanine, a charge transport layer, a barrier layer, a photogenerating layer of BZP perylene, which is preferably a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-10,21-dione, reference U.S. Patent 4,587,189; and as a top layer a second charge transport layer. In embodiments, it is preferred that the BZP layer possess an optical density of at least 2 to absorb about 99 percent or more of the 500 to 700 nanometers radiation, thus the lower tier (HOGaPc generator and bottom transport layer) will not be discharged by such a radiation or any monochromatic light with, for example, wavelengths within the range of 500 to 700 nanometers. The two-tier imaging member can be selected in color xerographic printing processes. More specifically, when selectively imaged with two laser lights of different wavelengths, color xerographic printing enables printing of three colors in a single pass process. After being charged to about -800 volts, the imaging member is selectively discharged by exposure to a suitable type of light. The top tier comprising BZP and top transport layer is discharged by about 680 nanometers of radiation. The bottom tier is discharged by about 830 nanometers of radiation. Thus, four resultant areas on the imaging member are created after passing an imaging station; and (a) the unexposed area retains the original surface potential, about -800 volts, (b) the area exposed with about 680 nanometers, which is discharged to about one-half of the original surface voltage, about -400 volts, (c) the area exposed with about 830 nanometers, which is also discharged to about one-half of the original surface voltage, that is about. -400 volts; and (d) the area exposed with both about 680 and about 830 nanometers which is fully discharged to about 0 (zero) volts. While only three potential levels are present on the imaging member at this stage immediately after exposure, there will be four distinctively different areas on the surface of the imaging member after xerographic development as indicated herein. After toning the area (a) with charge area development (CAD), the surface potential of (a) is changed to -400 volts by a positively charged black toner. Then, applying discharge area development step (DAD) and toning area (b), the surface potential is changed to -400 volts by negatively charged toners. As a result, the four areas are at equal potential (-400 volts) at this stage. By exposing the imaging member with a broad band exposure 500 to 700 nanometers, only area (c) is further discharged to 0 volts as the BZP layer is photoactive in this wavelength range. Area (a) is not discharged as the toners on it block this radiation. Area (b) is not discharged because the top BZP generator layer completely absorbs the radiation. By applying a (DAD) step, area (c) is now toned with another color toner. Area (b) remains untoned. Therefore, three color toners can be deposited in a single pass. According to the present invention, there is provided a photoconductive imaging member comprised of a hydroxygallium phthalocyanine photogenerator layer, a charge transport layer, a barrier layer, a photogenerator layer comprised of a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f)disoquinoline-10,21-dione, and thereover a charge transport layer. Preferably, the photogenerating layer components are dispersed in a resinous binder in an amount of from about 5 percent by weight to about 95 percent by weight. It is also preferred that the resinous binder is selected from the group consisting of polyesters, polyvinyl butyrals, polycarbonates, polystyrene-b-polyvinyl pyridine, and polyvinyl formals. Furthermore, it is preferable that the barrier layer is of a thickness of from 0.1 to 3 µm (micons). It is preferred that the barrier layer is a polyester. Preferably, the barrier layer is a 49,000® polyester with an Mw of about 69,000, and an Mn of about 37,000. The hole transport components in each transport layer are preferably present in an amount of from 25 weight percent to 60 weight percent. The present invention further provides a photoconductive imaging member comprised in the following sequence of a supporting substrate, a first hydroxygallium phthalocyanine photogenerator layer which absorbs light of a wavelength of from 550 to 950 nanometers, a first charge transport layer, a barrier layer, a second photogenerator layer comprised of a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a-1',2'-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-10,21-dione which absorbs light of a wavelength of from 500 to 800 nanometers, and thereover a second charge transport layer. It is preferred that the first photogenerator is situated between the substate and the charge transport layer, and the second photogenerator layer is situated betweeen said barrier layer and said second charge transport layer, and wherein the barrier layer is comprised of a blocking layer component. Preferably, the supporting substrate is comprised of a conductive substrate comprised of a metal. It is further preferred that the conductive substrate is aluminum, aluminized MYLAR®, or titanized MYLAR®. It is also preferred that each photogenerator layer has a thickness of from 0.05 to 10 µm (microns). Preferably, each transport layer has a thickness of from 5 to 30 µm (microns). The barrier layer is preferably of a thickness of from 0.1 to 3 µm (microns). Embodiments of the present invention include a method of imaging which comprises generating an electrostatic latent image on the imaging member comprised in the following order of a supporting substrate, a hydroxygallium phthalocyanine photogenerator layer, a first charge transport layer, a barrier layer, a photogenerator layer comprised of a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-10,21-dione, and as a top layer a second charge transport layer; developing the latent image; and transferring the developed electrostatic image to a suitable substrate; and wherein the imaging member is first exposed to light of a wavelength of from 500 to 800 nanometers, and then is exposed to light of a wavelength of from 550 to 950 nanometers; and a method of imaging which comprises generating an electrostatic latent image on an imaging member comprised of a supporting substrate, a hydroxygallium phthalocyanine photogenerator layer, a first charge transport layer, a polyester barrier layer, a photogenerator layer comprised of a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-10,21-dione, and as a top layer a second charge transport layer, developing the latent image; and transferring the developed electrostatic image to a suitable substrate; and wherein the imaging member is simultaneously exposed to light of a wavelength of from 500 to 800 nanometers; and a wavelength of from 550 to 950 nanometers. According to the present invention, there is provided a method of imaging which comprises generating an electrostatic latent image on the imaging member of the present invention, developing the latent image, and transferring the developed electrostatic image to a suitable substrate; and wherein the imaging member is first exposed to light of a wavelength of from 500 to 800 nanometers, and then is exposed to light of a wavelength of from 550 to 950 nanometers. Preferably, the wavelengths are 680 and 830 nanometers, respectively. The imaging member is preferably simultanously exposed to light of a wavelength of from 500 to 800 nanometers, and a wavelength of from 550 to 950 nanometers. Of importance with respect to the present invention is the selection of a suitable barrier layer, examples of which include polyesters, such as VITAL® PE100 and PE200 available from Goodyear Chemicals, and especially MOR-ESTER 49,000® available from Norton International. The barrier layer can be coated on to the first charge transport layer from a tetrahydrofuran and/or dichloromethane solution with a thickness ranging from 0.1 to 3.0 µm (microns). The main function of the barrier layer is to prevent the diffusion of transport molecules from the first transport layer into the top BZP layer, which otherwise results in charge leakage and cross talk. Cross talk refers, for example, to the undesirable discharge of one generator layer when the second generator layer is exposed to laser light. For example, if a two-tier imaging member is charged to -800V, ideally a 400V (50 percent) discharge with no cross talk is expected from each tier when they are sequentially exposed to light. However, in a non-ideal situation, the first tier might be photodischarged to, for example, -400V followed by a voltage drop of 200V, due to charge leakage, followed by the photodischarge of the second tier to zero volt. In this situation, the imaging member can possess a 25 percent cross talk. Cross talks of, for example, less than 3 percent are acceptable and will not, it is believed, adversely affect developability. The incorporation of the barrier layer significantly improves the discharge split of the two-tier imaging member and reduced cross talk from 17 to 21 percent to 2 to 4 percent. The hydroxygallium photogenerating layer, which is preferably comprised of hydroxygallium phthalocyanine Type V, is in embodiments comprised of, for example, about 50 weight percent of the Type V and about 50 weight percent of a resin binder like polystyrene/polyvinylpyridine; and the BZP layer is in embodiments comprised of, for example, about 80 weight percent of BZP dispersed in a resin binder like polyvinylbutyral. The photoconductive imaging member with two photogenerating layers and two charge transport layers can be prepared by a number of methods, such as the coating of the layers, and more specifically as illustrated herein. Thus, the photoresponsive imaging members of the present invention can in embodiments be prepared by a number of known methods, the process parameters and the order of coating of the layers being dependent, for example, on the member desired. The photogenerating and charge transport layers of the imaging members can be coated as solutions or dispersions onto a selective substrate by the use of a spray coater, dip coater, extrusion coater, roller coater, wire-bar coater, slot coater and doctor blade coater, gravure coater, and dried at from 40 to 200°C for from 10 minutes to several hours under stationary conditions or in an air flow. The coating can be accomplished to provide a final coating thickness of from 0.01 to 30 µm (microns) after drying. The fabrication conditions for a given photoconductive layer can be tailored to achieve optimum performance and cost in the final members. Imaging members of the present invention are useful in various electrostatographic imaging and printing systems, particularly those conventionally known as xerographic processes. Specifically, the imaging members of the present invention are useful in xerographic imaging processes wherein the Type V hydroxygallium phthalocyanine pigment absorbs light of a wavelength of from 550 to 950 nanometers, and preferably from 700 to 850 nanometers; and wherein the second BZP layer absorbs light of a wavelength of from 500 to 800 nanometers, and preferably from 600 to 750 nanometers. In these processes, electrostatic latent images are initially formed on the imaging member followed by development, and thereafter, transferring the image to a suitable substrate. Moreover, the imaging members of the present invention can be selected for electronic printing processes with gallium arsenide diode lasers, light emitting diode (LED) arrays which typically function at wavelengths of from 660 to 830 nanometers. In embodiments, the photoconductive imaging member comprised in sequence of a conductive supporting substrate, a hydroxygallium phthalocyanine photogenerating layer thereover, a first transport layer, a blocking layer, a BZP photogenerating layer thereover, and a second top transport layer, can be initially charged with red light, about 670 nanometers, IR, about 830 nanometers, and subsequently charged with red light at 670 nanometers, and IR at 830 nanometers, and which subsequent charges are applied to a portion of the member not initially charged. The negatively charged photoresponsive imaging member of the present invention in embodiments is comprised, in the following sequence, of a supporting substrate, a barrier layer comprised of, for example, MOR-ESTER 49,000® , a photogenerator layer comprised of Type V hydroxygallium phthalocyanine, optionally dispersed in an inactive polymer binder, a first hole transport layer thereover comprised of N,N'-diphenyl-N,N'-bis(3-methyl phenyl)-1,1'-biphenyl-4,4'-diamine dispersed in a polycarbonate binder, a barrier layer thereover, thereover a photogenerating layer of BZP, and a top layer of N,N'-diphenyl-N,N'-bis(3-methyl phenyl)-1,1'-biphenyl-4,4'-diamine dispersed in a polycarbonate binder. Embodiments of the present invention also include a photoconductive imaging member comprised of a hydroxygallium phthalocyanine photogenerator layer, a charge transport layer, a barrier layer, a photogenerator layer comprised of a mixture of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-10,21-dione, and thereover a charge transport layer. Examples of substrate layers selected for the imaging members of the present invention can be opaque or substantially transparent, and may comprise any suitable material having the requisite mechanical properties. Thus, the substrate may comprise a layer of insulating material including inorganic or organic polymeric materials, such as MYLAR® a commercially available polymer, MYLAR® containing titanium, a layer of an organic or inorganic material having a semiconductive surface layer, such as indium tin oxide, or aluminum arranged thereon, or a conductive material inclusive of aluminum, chromium, nickel or brass. The substrate may be flexible, seamless, or rigid, and many have a number of many different configurations, such as for example a plate, a cylindrical drum, a scroll, and an endless flexible belt. In one embodiment, the substrate is in the form of a seamless flexible belt. In some situations, it may be desirable to coat on the back of the substrate, particularly when the substrate is a flexible organic polymeric material, an anticurl layer, such as for example polycarbonate materials commercially available as MAKROLON® . The thickness of the substrate layer depends on many factors, including economical considerations, thus this layer may be of substantial thickness, for example over 3,000 µm (microns), or of minimum thickness providing there are no adverse effects on the system. In one embodiment, the thickness of this layer is from 75 to 300 µm (microns). Generally, the thickness of each of the photogenerator layers depends on a number of factors, including the thicknesses of the other layers and the amount of photogenerator material contained in these layers. Accordingly, each layer can be of a thickness of, for example, from 0.05 to 10 µm (microns9, and more specifically, from 0.25 to 1 µm (micron) when, for example, each of the photogenerator compositions is present in an amount of from 30 to 75 percent by volume. The maximum thickness of the layers in an embodiment is dependent primarily upon factors, such as photosensitivity, electrical properties and mechanical considerations. The photogenerating layer binder resin, present in various suitable amounts, for example from 1 to 20, and more specifically from 1 to 10 weight percent, may be selected from a number of known polymers such as poly(vinyl butyral), poly(vinyl carbazole), polyesters, polycarbonates, poly(vinyl chloride), polyacrylates and methacrylates, copolymers of vinyl chloride and vinyl acetate, phenoxy resins, polyurethanes, poly(vinyl alcohol), polyacrylonitrile and polystyrene. In embodiments of the present invention, it is desirable to select a coating solvent that does not disturb or adversely effect the other previously coated layers of the device. Examples of solvents that can be selected for use as coating solvents for the photogenerator layers are ketones, alcohols, aromatic hydrocarbons, halogenated aliphatic hydrocarbons, ethers, amines, amides, esters, and the like. Specific examples are cyclohexanone, acetone, methyl ethyl ketone, methanol, ethanol, butanol, amyl alcohol, toluene, xylene, chlorobenzene, carbon tetrachloride, chloroform, methylene chloride, trichloroethylene, tetrahydrofuran, dioxane, diethyl ether, dimethyl formamide, dimethyl acetamide, butyl acetate, ethyl acetate and methoxyethyl acetate. The coating of the photogenerator layers in embodiments of the present invention can be accomplished with spray, dip or wire-bar methods such that the final dry thickness of the photogenerator layer is, for example, from 0.01 to 30 µm (microns) and preferably from 0.1 to 15 µm (microns) after being dried at, for example, 40°C to 150°C for 5 to 90 minutes. Illustrative examples of polymeric binder materials that can be selected for the photogenerator pigments are as indicated herein, and include those polymers as disclosed in U.S. Patent 3,121,006. As adhesives usually in contact with the supporting substrate, there can be selected various known substances inclusive of polyesters, polyamides, poly(vinyl butyral), poly(vinyl alcohol), polyurethane and polyacrylonitrile. This layer is of a thickness of from 0.001 to 1 µm (micron). Optionally, this layer may contain effective suitable amounts, for example from 1 to 10 weight percent, conductive and nonconductive particles, such as zinc oxide, titanium dioxide, silicon nitride and carbon black to provide, for example, in embodiments of the present invention further desirable electrical and optical properties. Aryl amines selected for the hole transporting layers, which generally is of a thickness of from 5 to 75 µm (microns), and preferably of a thickness of from 10 to 40 µm (microns), include molecules of the following formula dispersed in a highly insulating and transparent polymer binder, wherein X is an alkyl group, a halogen, or mixtures thereof, especially those substituents selected from the group consisting of Cl and CH 3 . Examples of specific aryl amines are N,N'-diphenyl-N,N'-bis(alkylphenyl)-1,1-biphenyl-4,4'-diamine wherein alkyl is selected from the group consisting of methyl, ethyl, propyl, butyl and hexyl; and N,N'-diphenyl-N,N'-bis(halophenyl)-1,1'-biphenyl-4,4'-diamine wherein the halo substituent is preferably a chloro substituent. Other known charge transport layer molecules can be selected, reference for example U.S. Patents 4,921,773 and 4,464,450. Examples of the highly insulating and transparent polymer binder material for the transport layers include components, such as those described in U.S. Patent 3,121,006. Specific examples of polymer binder materials include polycarbonates, acrylate polymers, vinyl polymers, cellulose polymers, polyesters, polysiloxanes, polyamides, polyurethanes and epoxies as well as block, random or alternating copolymers thereof. Preferred electrically inactive binders are comprised of polycarbonate resins having a molecular weight of from 20,000 to 100,000 with a molecular weight of from 50,000 to 100,000 being particularly preferred. Generally, the transport layer contains from 10 to 75 percent by weight of the charge transport material, and preferably from 35 percent to 50 percent of this material. Also, included within the scope of the present invention are methods of imaging and printing with the photoresponsive devices illustrated herein. These methods generally involve the formation of an electrostatic latent image on the imaging member, followed by developing the image with a toner composition comprised, for example, of thermoplastic resin, colorant, such as pigment, charge additive, and surface additives, reference U.S. Patents 4,560,635; 4,298,697 and 4,338,390, subsequently transferring the image to a suitable substrate, and permanently affixing the image thereto. In those environments wherein the device is to be used in a printing mode, the imaging method involves the same steps with the exception that the exposure step can be accomplished with a laser device or image bar. Parts and percentages are by weight unless otherwise indicated. All XRPDs were determined as indicated herein. EXAMPLE I Alkoxy-bridged Gallium Phthalocyanine Dimer Synthesis Using Gallium Methoxide Obtained From Gallium Chloride and Sodium Methoxide In Situ: To a 1 liter round bottomed flask were added 25 grams of GaCl 3 and 300 milliliters of toluene, and the mixture was stirred for 10 minutes to form a solution. Then, 98 milliliters of a 25 weight percent sodium methoxide solution (in methanol) were added while cooling the flask with an ice bath to keep the contents below 40°C. Subsequently, 250 milliliters of ethylene glycol and 72.8 grams of o-phthalodinitrile were added. The methanol and toluene were quickly distilled off over 30 minutes while heating from 70°C to 135°C, and then the phthalocyanine synthesis was performed by heating at 195°C for 4.5 hours. The alkoxy-bridged gallium phthalocyanine dimer was isolated by filtration at 120°C. The product was then washed with 400 milliliters DMF at 100°C for 1 hour and filtered. The product was then washed with 600 milliliters of deionized water at 60°C for 1 hour and filtered. The product was then washed with 600 milliliters of methanol at 25°C for 1 hour and filtered. The product was dried at 60°C under vacuum for 18 hours. The alkoxy-bridged gallium phthalocyanine dimer, 1,2-di(oxogallium phthalocyaninyl) ethane, was isolated as a dark blue solid in 77 percent yield. The dimer product was characterized by elemental analysis, infrared spectroscopy, 1 H NMR spectroscopy and X-ray powder diffraction. Elemental analysis showed the presence of only 0.10 percent of chlorine. Infrared spectroscopy: major peaks at 573, 611, 636, 731, 756, 775, 874, 897, 962, 999, 1069, 1088, 1125, 1165, 1289, 1337, 1424, 1466, 1503, 1611, 2569, 2607, 2648, 2864, 2950, and 3045 cm -1 ; 1 H NMR spectroscopy (TFA-d/CDCl 3 solution, 1:1 v/v, tetramethylsilane reference): peaks at 4.00 (4H), 8.54 (16H), and 9.62 (16H); X-ray powder diffraction pattern: peaks at Bragg angles (2 theta ± 0.2°) of 6.7, 8.9, 12.8, 13.9, 15.7, 16.6, 21.2, 25.3, 25.9, and 28.3 with the highest peak at 6.7 degrees. EXAMPLE II Hydrolysis of Alkoxy-bridged Gallium Phthalocyanine to Hydroxygallium Phthalocyanine (Type I): The hydrolysis of alkoxy-bridged gallium phthalocyanine synthesized in Example I to hydroxygallium phthalocyanine was performed as follows. Sulfuric acid (94 to 96 percent, 125 grams) was heated to 40°C in a 125 milliliter Erlenmeyer flask, and then 5 grams of the chlorogallium phthalocyanine were added. Addition of the solid was completed in approximately 15 minutes, during which time the temperature of the solution increased to about 48°C. The acid solution was then stirred for 2 hours at 40°C, after which it was added in a dropwise fashion to a mixture comprised of concentrated (30 percent) ammonium hydroxide (265 milliliters) and deionized water (435 milliliters), which had been cooled to a temperature below 5°C. The addition of the dissolved phthalocyanine was completed in approximately 30 minutes, during which time the temperature of the solution increased to about 40°C. The reprecipitated phthalocyanine was then removed from the cooling bath and allowed to stir at room temperature for 1 hour. The resulting phthalocyanine was then filtered through a porcelain funnel fitted with a Whatman 934-AH grade glass fiber filter. The resulting blue solid was redispersed in fresh deionized water by stirring at room temperature for 1 hour and filtered as before. This process was repeated at least three times until the conductivity of the filtrate was <20 µS. The filter cake was oven dried overnight at 50°C to give 4.75 grams (95 percent) of Type I HOGaPc, identified by infrared spectroscopy and X-ray powder diffraction, XRPD. The X-ray powder diffraction traces (XRPDs) were generated on a Philips X-Ray Powder Diffractometer Model 1710 using X-radiation of CuK-alpha wavelength (0.1542 nanometers). The diffractometer was equipped with a graphite monochrometer and pulse-height discrimination system. Two-theta is the Bragg angle commonly referred to in x-ray crystallographic measurements. I (counts) represents the intensity of the diffraction as a function of Bragg angle as measured with a proportional counter. Infrared spectroscopy: major peaks at 507, 573, 629, 729, 756, 772, 874, 898, 956, 984, 1092, 1121, 1165, 1188, 1290, 1339, 1424, 1468, 1503, 1588, 1611, 1757, 1835, 1951, 2099, 2207, 2280, 2384, 2425, 2570, 2608, 2652, 2780, 2819, 2853, 2907, 2951, 3049 and 3479 (broad) cm -1 ; X-ray diffraction pattern: peaks at Bragg angles of 6.8, 13.0, 16.5, 21.0, 26.3 and 29.5 with the highest peak at 6.8 degrees (2 theta +/- 0.2°). EXAMPLE III Conversion of Type I Hydroxygallium Phthalocyanine to Type V: The Type I hydroxygallium phthalocyanine pigment obtained in Example II was converted to Type V HOGaPc as follows. The Type I hydroxygallium phthalocyanine pigment (3.0 grams) was added to 25 milliliters of N,N-dimethylformamide in a 60 milliliter glass bottle containing 60 grams of glass beads (0.25 inch in diameter). The bottle was sealed and placed on a ball mill overnight (18 hours). The solid was isolated by filtration through a porcelain funnel fitted with a Whatman GF/F grade glass fiber filter, and washed in the filter using several 25 milliliter portions of acetone. The filtered wet cake was oven dried overnight at 50°C to provide 2.8 grams of Type V HOGaPc which was identified by infrared spectroscopy and X-ray powder diffraction. Infrared spectroscopy: major peaks at 507, 571, 631, 733, 756, 773, 897, 965, 1067, 1084, 1121, 1146, 1165, 1291, 1337, 1425, 1468, 1503, 1588, 1609, 1757, 1848, 1925, 2099, 2205, 2276, 2384, 2425, 2572, 2613, 2653, 2780, 2861, 2909, 2956, 3057 and 3499 (broad) cm -1 ; X-ray diffraction pattern: peaks at Bragg angles of 7.4, 9.8, 12.4, 12.9, 16.2, 18.4, 21.9, 23.9, 25.0 and 28.1 with the highest peak at 7.4 degrees (2 theta +/- 0.2°). EXAMPLE IV Fabrication and Testing of Two-Tier Imaging Member Without Barrier Layer: A two-tier imaging member was prepared by sequentially coating the four layers: 1) HOGaPC generator of Example III, 2) charge transport, 3) BZP generator, and 4) charge transport all contained on a supporting substrate of a titanized MYLAR® , which was precoated with a thin 0.025 µm (micron) silane blocking layer and a thin 0.1 µm (micron) polyester adhesive layer. The first photogenerating layer was hydroxygallium phthalocyanine as prepared above. The BZP for the second photogenerating layer was as illustrated in U.S. Patent 4,587,189, and more specifically, was comprised of a mixture of about 50/50 weight percent of bisbenzimidazo(2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-10,21-dione. The dispersion of Type V hydroxygallium phthalocyanine (HOGaPC) was prepared by milling 0.125 gram of the HOGaPC, prepared as described in Example III, from a precursor pigment, which was prepared as described in Example I, and 0.125 gram of polystyrene-b-polyvinylpyridine in 9.0 grams of chlorobenzene in a 30 milliliter glass bottle containing 70 grams of 1/8 inch stainless steel balls. The bottle was put on a Norton roller mill running at 300 rpm for 20 hours. The dispersion was coated on the titanized MYLAR® substrate using 1 mil film applicator to form a photogenerator layer. The formed photogenerating layer HOGaPc was dried at 135°C for 20 minutes to a final thickness of about 0.3 µm (micron). A hole transporting layer solution was prepared by dissolving 2.64 grams of N,N'-diphenyl-N,N-bis(3-methyl phenyl)-1,1'-biphenyl-4,4'-diamine, and 3.5 grams of polycarbonate in 40 grams of dichloromethane. The solution was coated onto the HOGaPc generator layer using a 6 mil film applicator. The charge transporting layer thus obtained was dried at from 100°C to 135°C for 20 minutes to provide a final thickness of about 15 µm (microns). Thereafter, the BZP generator layer was coated thereover as illustrated above. The BZP dispersion was prepared by milling 0.40 gram of BZP pigment mixture, 0.1 gram of polycarbonate, and 8.00 grams of tetrahydrofuran in a 30 milliliter bottle containing 70 grams of 0.32 cm (1/8 inch) stainless steel balls. The milling time was for 5 days. The BZP dispersion was diluted and coated with a 2 mil applicator and the coated device was dried at from 100°C to 135°C for 20 minutes. The optical density of the BZP layer was greater than 2.0. Finally, a transport layer comprised of a second diamine hole transport layer identified above was coated on top of the BZP layer and dried as illustrated before. The resulting device was comprised of four sequentially deposited layers, bottom HOGaPc generator layer/bottom charge transport layer/top BZP generator layer/top charge transport layer, and all contained on a titanized MYLAR® conductive substrate. The xerographic electrical properties of the imaging member can be determined by known means, including as indicated herein electrostatically charging the surfaces thereof with a corona discharge source until the surface potentials, as measured by a capacitively coupled probe attached to an electrometer, attained an initial value V o of about -800 volts. After resting for 0.5 second in the dark, the charged members attained a surface potential of V ddp , dark development potential. Each member was then exposed to light from a filtered Xenon lamp with a XBO 150 watt bulb, thereby inducing a photodischarge which resulted in a reduction of surface potential to a V bg value, background potential. The percent of photodischarge was calculated as 100 x (V ddp -V bg )A/ ddp . The desired wavelength and energy of the exposed light was determined by the type of filters placed in front of the lamp. The monochromatic light photosensitivity was determined using a narrow band-pass filter. When exposing the charged imaging member with 680 nanometers of light at an intensity of 30 ergs/cm 2 , a photodischarge of 54 percent and a cross talk of 17 percent were obtained. Cross talk in a two-tier imaging member reduces developability and is undesirable discharge of a charge generating layer when the second generator layer is exposed to the laser light. When exposing the charged imaging member with the 830 nanometers of light at an intensity of 10 ergs/cm 2 , a photodischarge of 73 percent and a cross talk of 21 percent were observed. The imaging member was fully discharged when it was exposed to both 680 and 830 nanometers of light. The charged imaging members showed a significant amount of aging after six months. The cross talks measured (as above) at 680 nanometers and 830 nanometers increased, respectively, to 36 percent and 33 percent. These results indicate that the photodischarge behavior of the two charge imaging members are not independent and that there is a cross talk between them. EXAMPLE V Fabrication and Testing of Two-Tier Imaging Member With Barrier Layer: A two-tier imaging member was prepared by sequentially coating the five layers: 1) HOGaPC generator, 2) charge transport, 3) barrier layer, 4) BZP generator, and 5) charge transport all contained on a supporting substrate of a titanized MYLAR® , which was precoated with a thin 0.025 µm (micron) silane blocking layer and a thin 0.1 micron polyester adhesive layer. The first and second photogenerating layers were, respectively, hydroxygallium phthalocyanine and BZP as prepared above. A hole transporting layer solution was prepared by dissolving 2.28 grams of N,N'-diphenyl-N,N-bis(3-methyl phenyl)-1,1'-biphenyl-4,4'-diamine, and 4.23 grams of polycarbonate in 40 grams of dichloromethane. The solution was coated onto the HOGaPc generator layer using a 6 mil film applicator. The charge transporting layer thus obtained was dried at from 100°C to 135°C for 20 minutes to provide a final thickness of about 15 µm (microns). A barrier layer was prepared by dissolving 0.2 gram of MOR-ESTER 49,000® polyester in 10 grams of dichloromethane. The solution was then coated onto the first charge transporting layer. The barrier layer thus obtained was dried at 100°C for 20 minutes to provide a final thickness of about 0.8 µm (micron). Thereafter, the BZP generator layer was coated thereover as illustrated above. The optical density of the BZP layer was greater than about 2.0, for example about 2.5. Finally, the amine transport layer was prepared and coated on top of the BZP layer and dried as illustrated before. The resulting device was comprised of five sequentially deposited layers, bottom HOGaPc Type V generated from Example III, photogenerator layer/first charge transport layer/barrier layer/top BZP generator layer/second charge transport layer, and all contained on a titanized MYLAR® supporting conductive substrate. The xerographic electrical properties of the imaging member were determined by repeating the process of Example IV. When exposing the charged imaging member with the 680 nanometers of light at an intensity of 30 ergs/cm 2 , a photodischarge of 48 percent and a cross talk of 2 percent were obtained. When exposing the charged imaging member with the 830 nanometers of light at an intensity of 10 ergs/cm 2 , a photodischarge of 46 percent and a cross talk of 4 percent were observed. The two-tier imaging member with the barrier layer tested showed no sign of aging, and the cross talk and discharge characteristics were maintained; in contrast with the imaging member prepared without the barrier layer which evidenced substantial increase in cross talk with aging. These results indicated that by incorporating a barrier layer, the photodischarge behavior of the two-tier imaging member significantly improved, and compared with Example IV independent photodischarge from each tier with substantial decrease in cross talk was achieved. Furthermore, the barrier layer prevented the degradation of the two-tier imaging member with time. EXAMPLE VI Stability of Two-Tier Imaging Member with Barrier Layer: The electrical stability of the two-tier imaging member of Example V was monitored by repeating the charging and discharging steps 10,000 times. In the first cycle, the member was charged to V ddp , about -800 volts, it was exposed to 670 nanometers light to have the top tier partially discharged to V2 (about -450 volts) due to light absorption by BZP, and then further discharged by 825 nanometers of light (absorbed by HOGaPc in the bottom tier) to V3 (at about -80 volts). The variations in V ddp , V2 and V3 and represented as ΔV ddp , ΔV2, ΔV3 provided an indication of the stability of the imaging member. In 10,000 cycles, the changes ΔV ddp , ΔV2, ΔV3 were only 23, 20 and 27 volts indicating excellent electrical stability. The stability test was repeated again with charging, and discharging the bottom tier, and then the top tier using lights of 825 nanometers, and 670 nanometers, respectively. The variations of ΔVddp, ΔV2 and ΔV3 were measured to be 16, 18 and 13 volts, and an excellent stability was observed. Whether the top or bottom tier of imaging member was the first to be discharged, the stability of the member was maintained for extended imaging cycles, for example 300,000 cycles. EXAMPLE VII Adhesive Strength of Two-Tier Imaging Member With Barrier Layer The adhesion of the multilayer imaging member was determined by peel strength measurements using an INSTRON® Tensile Tester. The procedure used was the standard test method for peel strength of adhesive bonds and identified as method ASTM D903 (American Society for Testing of Materials). The average load per unit width required to separate progressively one layer from the other over the adhered surfaces at a separation angle of 180° was determined. It was expressed in units of grams/centimeter. The samples used were 15 centimeters (length) x 2.5 centimeters (width) and mounted on an aluminum backing plate. One end of the sample with the aluminum plate was held in the upper jaw of the INSTRON while the other end of the sample was peeled and held on the lower jaw of the INSTRON. During the test, the upper jaw was fixed while the lower jaw with the peeled sample was lowered at a speed of 30 centimeters/minute. The testing machine was retained in an environmentally controlled room at a temperature of 50°C and a relative humidity of 23 percent. A two-tier imaging member of Example V with a barrier layer of MOR-ESTER 49,000® polyester and a thickness of 0.8 µm (micron) had a peel strength of 162 grams/centimeter. By comparison, a two-tier imaging member of Example IV with no barrier layer had a much lower peel strength of 67 grams/centimeter.

Claims: A photoconductive imaging member comprising a first hydroxygallium phthalocyanine photogenerator layer, a first charge transport layer, a barrier layer to prevent diffusion of transport molecules from the first charge transport layer into a second photogenerator layer, a second photogenerator layer comprising a mixture of bisbenzimidazo(2,1-a-1',2'-b)-anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo-2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-10,21-dione, and thereover a second charge transport layer. A photoconductive imaging member according to claim 1 comprising in the following sequence a supporting substrate, a first hydroxygallium phthalocyanine photogenerator layer which absorbs light of a wavelength of from 550 to 950 nm, a first charge transport layer, a barrier layer to prevent diffusion of transport molecules from the first charge transport layer into a second photogenerator layer, a second photogenerator layer comprising a mixture of bisbenzimidazo (2,1-a-1',2'-b)anthra(2,1,9-def:6,5,10-d'e'f)diisoquinoline-6,11-dione and bisbenzimidazo(2,1-a:2',1'-a)anthra(2,1,9-def:6,5,10-d'e'f')diisoquinoline-10,21-dione which absorbs light of a wavelength of from 500 to 800 nm, and thereover a second charge transport layer. The imaging member in accordance with claim 1 wherein the photogenerating layer components are dispersed in a resinous binder in an amount of from 5 percent by weight to 95 percent by weight. The imaging member in accordance with claim 2 wherein said charge transport layers comprise aryl amine molecules. The imaging member in accordance with claim 4 wherein the aryl amines are of the formula wherein X is selected from the group consisting of alkyl and halogen, and wherein the aryl amine is dispersed in a highly insulating and transparent resinous binder. The imaging member in accordance with claim 5 wherein alkyl contains from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms. A method of imaging which comprises generating an electrostatic latent image on the imaging member of claim 1, developing the latent image, and transferring the developed electrostatic image to a suitable substrate; and wherein the imaging member is first exposed to light of a wavelength of from 500 to 800 nm, and then is exposed to light of a wavelength of from 550 to 950 nm. The imaging member in accordance with claim 1 or 2 wherein the hydroxygallium phthalocyanine is Type V hydroxygallium phthalocyanine. The imaging member in accordance with claim 8 wherein the Type V hydroxygallium phthalocyanine is prepared by hydrolyzing a gallium phthalocyanine precursor pigment by dissolving said hydroxygallium phthalocyanine in a strong acid and then reprecipitating the resulting dissolved pigment in a basic aqueous media; removing any ionic species formed by washing with water; concentrating the resulting aqueous slurry comprised of water and hydroxygallium phthalocyanine to a wet cake; removing water from said wet cake by drying; and subjecting said resulting dry pigment to mixing with the addition of a second solvent to cause the formation of said hydroxygallium phthalocyanine. The imaging member in accordance with claim 9 wherein the Type V hydroxygallium phthalocyanine has major peaks, as measured with an X-ray diffractometer, at Bragg angles (2 theta+/-0.2°) 7.4, 9.8, 12.4, 16.2, 17.6, 18.4, 21.9, 23.9, 25.0, 28.1 degrees, and the highest peak at 7.4 degrees.

Inventors: ALLEN GEOFFREY C, ESTEGHAMATIAN MOHAMMAD, HOR AH-MEE, MURTI DASARAO K, ALLEN, GEOFFREY C., ESTEGHAMATIAN, MOHAMMAD, HOR, AH-MEE, MURTI, DASARAO K.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1998
Main classification: G03G5
IPC codes: G03G5