Electrophotographic photosensitive member, and electrophotograhic apparatus, device unit, and facsimile machine employing the same

Abstract: An electrophotographic photosensitive member has an electroconductive support, and a photosensitive layer formed thereon. The photosensitive layer contains a compound represented by the formula (1).

Description: The present invention relates to an electrophotographic photosensitive member, particularly to an electrophotographic photosensitive member having a photosensitive layer which does not cause image deterioration on repeated image formation and exhibits excellent durability. The present invention relates also to an electrophotographic apparatus, a device unit, and a facsimile machine employing the above electrophotographic photosensitive member. Related Background Art Many kinds of electrophotographic photosensitive members employing an organic compound as the photoconducting substance have been developed and practically used so far. Such electrophotographic photosensitive members employing an organic photoconductive substance are expected to be further improved in electrophotographic properties such as sensitivity and photoresponsiveness because of the flexibility in material design thereof, and are advantageous in ease of film formation, high productivity, and relatively low cost. However, such types of photosensitive members generally have serious disadvantages of low durability. The durability includes electrophotographic durability such as of sensitivity, residual potential, chargeability, blurring of images, etc. and mechanical durability such as resistance to abrasion and scratching of the surface of the photosensitive member by rubbing. It is already known that the lowering of the durability of the electrophotographic properties results mainly from the deterioration of the organic photoconductive substance in the photosensitive layer caused by ozone, NOx, or the like generated by the corona charger. The deterioration of the organic photoconductive substance leads to crushed images and undecipherable images, namely blurring of images. The deterioration was found to be more remarkable with organic photoconductive substances having a lower oxidation potential since the deterioration results from a kind of oxidation. From the viewpoint of the electrophotographic properties, polishing of the surface of the photosensitive member to provide incessantly a fresh surface is effective for obtaining high-quality images. On the other hand, from the viewpoint of the mechanical durability, less abrasion is desired and therefore a slipping agent is dispersed on the surface of the photosensitive member, which retards the rapid removal of the deteriorated charge-transporting substance and tends to cause actually blurring of images. To solve such problems, for example, Japanese Patent Application Laid-Open No. Sho-63-30850 discloses use of a compound having an oxidation potential of not less than 0.6 V as the charge-transporting substance contained in the surface layer of the photosensitive member. Recently, as the result of elongation of the life of the photosensitive member, the problem has come to be noticed that, when the photosensitive member is left standing in a copying machine for a long time after continuous use, the chargeability of a photosensitive member becomes apparently lowered at the portion of the photosensitive member kept in proximity to the corona-discharging charger, namely so-called a dormant memory phenomenon, giving blank areas in stripe (white bands in positive development, and black bands in reversal development) in the image. This dormant memory phenomenon is especially remarkable when the employed charge-transporting substance has an oxidation potential of 0.6 V or higher. The occurrence of the aforementioned blurring of images is caused by ozone or NOx generated by corona discharge. In the case where the employed charge-transporting substance has an oxidation potential of less than 0.6 V, the charge-transporting substance itself is oxidized by the ozone or NOx at the surface of the photosensitive member to have lower resistance, being liable to cause blurring of images. On the other hand, in the case where the employed charge-transporting substance has an oxidation potential of not less than 0.6 V, the charge-transporting substance is relatively resistant to oxidation, and therefore the ozone or NOx is considered to penetrate deeply into the photosensitive layer to oxidize the charge-generating substance to lower the resistance thereof, whereby hole injection from the support is promoted, resulting in lower apparent potential and causing dormant memory phenomenon. Although this lowering of the apparent potential is considered to occur during the use of the photosensive member, the lowering occurs uniformly throughout the surface of the photosensitive member, so that the blank of images caused by local potential drop is not observed. When the photosensitive member is left standing after the continuous operation, local potential drop occurs in the vicinity of the charger where the concentrations of ozone and NOx are extremely high, giving the blank of images remarkably. JP-A-63-159856 discloses a specific electrophotographic positive charge sensitive body and its image forming process wherein the electrophotographic sensitive body contains the compound shown by the following formula: wherein R 1 and R 2 are each hydrogen atom, alkyl or aryl group, R is hydrogen or halogen atom, nitro, amino, alkyl, alkoxy, aryl, or aralkyl group, (n) is 0, 1 or 2, when (n) = 2, R may be the same or the different with each other. FR-A-2602064 discloses an electrophotosensitive member comprising a photosensitive layer which contains a charge transporting material having an oxidation potential of not less than 0,6 V and a lubricant on the surface of the member. SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic photosensitive member which is capable of giving images of high quality without blurring nor blank of images. Another object of the present invention is to provide an electrophotographic photosensitive member which is capable of giving stably high-quality images without accumulation of the residual potential even when repeatedly used. A further object of the present invention is to provide an electrophotographic apparatus, a device unit, and a facsimile machine employing the photosensitive member. The present invention provides an electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer formed thereon, the photosensitive layer containing a compound selected from compounds represented by the formulas (1) and (2): The present invention further provides an electrophotographic apparatus, a device unit, and a facsimile machine employing the photosensitive member defined above. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates roughly the constitution of an electrophotographic apparatus employing the photosensitive member of the present invention. Fig. 2 illustrates an example of a block diagram of a facsimile system employing the photosensitive member of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT The electrophotographic photosensitive member of the present invention comprises a photosensitive layer containing the compound selected from compounds represented by the formulas (1) and (2): The amount to be added of the compound of the formulas (1) or (2) in the present invention is preferably in the range of from 0.2 to 30 %, more preferably from 0.4 to 15 % by weight, based on the weight of the layer to which the compound is added. With the amount of addition of less than 0.2 % by weight, the prevention of the deterioration may be insufficient, while with the amount of the addition of more than 30 % by weight, the sensitivity or the residual potential is liable to be adversely affected. The compound of the formulas (1) or (2) may be used individually or in combination thereof, and further may be used combinedly with an additive such as an antioxidant, a UV absorber, and a plasticizer. The photosensitive layer employed in the electrophotographic photosensitive member of the present invention may be of a monolayer type which contains a charge-generating substance and a charge-transporting substance one and the same layer, or may be of a lamination type which comprises a charge-generating layer containing a charge-generating substance and a charge-transporting layer containing a charge-transporting substance. The charge-generating substance may be any substance which has charge-generating ability, including the substances below: (1) Azo type pigments including monoazo, bisazo, and trisazo type pigments, (2) Phthalocyanine pigments including metal phthalocyanine and non-metal phthalocyanine, (3) Indigo type pigments including indigo and thioindigo, (4) Perylene type pigments including perylenic anhydride and perylenimide, (5) Polycyclic quinones type pigments including anthraquinone and pyrene quinone, (6) Squarilium dyes, (7) Pyrylium salts and thiopyrylium salts, (8) Triphenylmethane dyes, (9) Inorganic substances such as selenium and amorphous silicon. These charge-generating substances may be used individually or in combination of two or more thereof. The charge-transporting substance is selected from hydrazone type compounds, stilbene type compounds, carbazole type compounds, pyrazoline type compounds, oxazole type compounds, thiazole type compounds, triarylmethane type compounds, polyarylalkanes, and the like. These may be used individually or in combination of two or more thereof. The higher the oxidation potential of the charge-transporting substance, the higher is the durability thereof. The improvement of the durability is more remarkable with the substances having the oxidation potential of 0.6 V or higher, particularly 0.7 V or higher. In a lamination type of photosensitive layer, the charge-generating layer may be formed by dispersing the aforementioned charge-generating substance together with a suitable solvent in a binder regin and applying the dispersion on an electroconductive support and drying, or otherwise may be formed by depositing the substance in a thin film on an electroconductive support according to a dry process such as sputtering, and CVD. The aforementioned binder resins include polycarbonates, polyesters, polyarylates, butyral resins, polystyrenes, polyvinylacetals, diallyl phthalate resins, acrylic resins, methacrylic resins, vinyl acetate resins, phenol resins, silicone resins, polysulfones, styrene-butadiene copolymers, alkid resins, epoxy resins, urea resins, and vinyl chloride-vinyl acetate copolymers, but is not limited thereto. These resins may be used individually or in combination of two or more thereof. The resin contained in the charge-generating layer is in an amount of not more than 80 % by weight, more preferably not more than 40 % by weight based on the total weight of the charge-generating layer. The charge-generating layer has a film thickness preferably not more than 5 µm, more preferably in the range of from 0.01 to 2 µm. The charge-generating layer may further contain a sensitizer. The charge-transporting layer may be formed by dissolving the aforementioned charge-transporting substance in a suitable binder resin with the aid of a suitable solvent, and applying to a charge-generating layer and drying the resulting solution. The binder resin includes the resins mentioned above for the charge-generating resin and additionally includes photoelectric polymers such as polyvinylcarbazole and polyvinylanthracene. The blending ratio of the charge-transporting substance to the binder resin is preferably in the range of from 10 to 500 parts by weight of the charge-transporting substance to 100 parts by weight of the binder resin. The charge-transporting layer has a thickness preferably in the range of from 5 to 40 µm, more preferably from 10 to 30 µm. In the present invention, a compound represented by the formulas (1) or (2) may be contained in any layers of a charge-generating layer, a charge-transporting layer, and a protecting layer as mentioned below as well as a single type of a photosensitive layer. When the photosensitive layer on which the charge-transporting layer is laminated, the compound represented by the formulas (1) or (2) may be contained preferably in at least one of the charge-transporting layer or the protecting layer, more preferably in the charge-transporting layer. The charge-transporting layer may be laminated on the charge-generating layer, or conversely the charge-generating layer may be laminated on the charge-transporting layer, in the present invention. In the case where the photosensitive layer is of a monolayer type, it may be formed by dispersing and dissolving the charge-generating substance and the charge-transporting substance in the aforementioned binder resin and applying and drying the resulting liquid. The film thickness is preferably in the range of from 5 to 40 µm, more preferably from 10 to 30 µm. The present invention is particularly suitably employed in the cases where the durability of the photosensitive member is improved by use of a charge-transporting substance having a relatively high oxidation potential (e.g., 0.6 V or higher), or where the durability is improved by applying a lubricant, or additionally a dispersing agent for dispersing the lubricant uniformly on the surface layer to reduce the abrasion of the photosensitive member. The lubricant suitably used in the present invention includes powdery fluoro-resins, powdery polyolefin resins, powdery silicone resins, powdery fluorinated carbon, and the like. Powdery fluoro-resins are preferred in view of lubricity and releasability. The powdery fluoro-resins include tetrafluoroethylene resins, chlorotrifluoroethylene resins, tetrafluoroethylene-hexafluoropropylene resins, vinyl fluoride resins, vinylidene fluoride resins, difluorochloroethylene resins and copolymers comprising polymer components of these resins. The powdery polyolefins includes polyethylenes, polypropylenes, and copolymers comprising components of these polymers. The amount of addition of such a lubricant is preferably in the range of from 1 to 100 %, more preferably from 1.5 to 30 % by weight based on the binder resin in the layer to which the lubricant is added. A subbing layer, which has a barrier function and an adhesion function, may be provided between the electroconductive support and the photosensitive layer in the present invention. The material for the subbing layer includes polyvinyl alcohol, polyethylene oxide, ethylcellulose, methylcellulose, casein, polyamides, glue and gelatin. The material is dissolved in a suitable solvent and applyed on the electroconductive support. The thickness of the resulting layer is preferably not more than 5 µm, more preferably in the range of from 0.2 to 3.0 µm. Further, a protecting layer, which is made of a simple resin layer or a resin layer containing an electroconductive substance dispersed therein, may be provided on the photosensitive layer in the present invention for the purpose of protecting the photosensitive layer from various external mechanical and electrical forces. The protecting layer is included in the photosensitive layer in the present invention. The above-described layers are formed on the electroconductive support by use of a suitable organic solvent according to a coating method such as immersion coating, spray coating, spinner coating, roller coating, Meyer bar coating, and blade coating. The electroconductive support in the present invention may be in such a structure as shown below: (1) Metal such as aluminum, aluminum alloys, stainless steel, and copper, (2) A non-electroconductive support such as glass, a resin, or paper, or an electroconductive support mentioned in the above item (1) on which a film of a metal such as aluminum, palladium, rhodium, gold, and platinum is formed by dispersion, vapor-deposition, or lamination, and (3) A non-electroconductive support such as glass, a resin, or paper, or an electroconductive support mentioned in the above item (1) on which a layer of an electroconductive polymer, a layer of electroconductive compound such as tin oxide, and indium oxide, or a layer of a resin containing such electroconductive compound dispersed therein is formed by vapor-deposition, or coating. The electroconductive support may be in a shape of a drum, a sheet, or a belt, but is not limited thereto. The electrophotographic photosensitive member of the present invention is not only applicable to electrophotographic copying machines but also applicable widely in electrophotographic fields including laser printers, CRT printers, facsimile machines, electrophotographic engraving systems, and the like. Fig. 1 illustrates roughly an example of the constitution of an electrophotographic apparatus employing the photosensitive member of the present invention. In Fig. 1, a drum type photosensitive member 1 serves as an image carrier, being driven to rotate around the axis 1a in the arrow direction at a predetermined peripheral speed. The photosensitive member 1 is charged positively or negatively at the peripheral face uniformly during the rotation by an electrostatic charging means 2, and then exposed to image-exposure light L (e.g. slit exposure, laser beam-scanning exposure, etc.) at the exposure portion 3 with an image-exposure means (not shown in the drawing), whereby electrostatic latent images are sequentially formed on the peripheral surface of the photosensitive member in accordance with the exposed image. Thus formed electrostatic latent image is developed with a toner by a developing means 4. The toner-developed images are sequentially transferred by a transfer means 5 onto a surface of a transfer-receiving material P which is fed between the photosensitive member 1 and the transfer means 5 synchronously with the rotation of the photosensitive member 1 from a transfer-receiving material feeder not shown in the drawing. The transfer-receiving material P having received the transferred image is separated from the photosensitive member surface, and introduced to an image fixing means 8 for fixiation of the image and sent out of the copying machine as a duplicate copy. The surface of the photosensitive member 1, after the image transfer, is cleaned with a cleaning means 6 to remove any remaining un-transferred toner, and is treated for charge elimination with a pre-exposure means 7 for repeated use for image formation. The generally employed charging means 2 for uniformly charging the photosensitive member 1 is a corona charging apparatus. The generally employed transfer means 5 is also a corona charging means. In the electrophotographic apparatus, two or more of the constitutional elements of the above described photosensitive member, the developing means, the cleaning means, etc. may be integrated into one device unit, which may be made demountable from the main body of the apparatus. For example, at least one of the charging means, the developing means, and the cleaning means is combined with the photosensitive member 1 into one device unit which is demountable from the main body of the apparatus by aid of a guiding means such as a rail in the main body of the apparatus. An electrostatic charging means and/or a developing means may be combined with the aforementioned device unit. When the electrophotographic apparatus is used as a copying machine or a printer, the light L for optical image exposure may be projected onto the photosensitive member as reflected light or transmitted light from an original copy, or otherwise the information read out by a sensor from an original is signalized, and according to the signalized information light is projected onto a photosensitive member, by scanning with a laser beam, driving an LED array, or driving a liquid crystal shutter array. When the electrophotographic apparatus is used as a printer of a facsimile machine, the optical image exposure light L is for printing the received data. Fig. 2 is a block diagram of an example of this case. A controller 11 controls the image-reading part 10 and a printer 19. The entire of the controller 11 is controlled by a CPU 17. Readout data from the image reading part 10 is transmitted through a transmitting circuit 13 to the other communication station. Data received from the other communication station is transmitted through a receiving circuit 12 to a printer 19. The image data is stored in image memory 16. A printer controller 18 controls a printer 19. The numeral 14 denotes a telephone set. The image received through a circuit 15, namely image information from a remote terminal connected through the circuit, is demodulated by the receiving circuit 12, treated for decoding of the image information in CPU 17, and successively stored in the image memory 16. When at least one page of image information has been stored in the image memory 16, the images are recorded in such a manner that the CPU 17 reads out the one page of image information, and sends out the decoded one page of information to the printer controller 18, which controls the printer 19 on receiving the one page of information from CPU 17 to record the image information. During recording by the printer 19, the CPU 17 receives the subsequent page of information. Images are received and recorded in the manner as described above. The present invention is described in more detail by reference to Examples. In Examples, the oxidation potential was shown by the peak position of the current-potential curve which was obtained by sweeping the potential of the working electrode by means of a potential sweeper by use of a saturated calomel electrode as the reference electrode, and 0.1N (n-Bu) 4 N + ClO 4 in acetonitrile as the electrolyte solution. More specifically, the sample was dissolved in the 0.1N (n-BU) 4 N + ClO 4 in acetonitrile as the electrolyte at a concentration of form 5 to 10 mmol%. Then a potential was applied to this sample solution and the potential was raised linearly from a low potential. The change of the current was measured to obtain a current-potential curve. The potential value at the first inflection point in the current-potential curve was taken as the oxidation potential of the present invention. The unit "part" is based on weight hereinafter. Example 1 An aluminum cylinder of 80 mm diameter and 360 mm long was employed as the electroconductive support. Onto this support, 5 % solution of a polyamide resin (Amylan CM-8000®, made by Toray Industries, Inc.) in methanol was applied by immersion coating to form a subbing layer of 0.5 µm thick. 10 Parts of a disazo pigment represented by the formula below as the charge-generating substance: 6 parts of a polyvinylbutyral resin (Eslec BX-1®, made by Sekisui Chemical Co., Ltd.), and 50 parts of cyclohexanone were dispersed by means of a sand mill employing glass beads. This dispersion was diluted with 100 parts of tetrahydrofuran. The diluted dispersion was applied on the above subbing layer to form a charge-generating layer of 0.2 µm thick. Then, 10 parts of the stilbene compound (oxidation potential: 0.81 V) represented by the formula below: and 10 parts of a polycarbonate resin (Panlite L-1250®, made by Teijin Kasei K.K.) were dissolved in a mixture of 50 parts of dichloromethane and 10 parts of monochlorobenzene. To this solution, the liquid dispersion was added which had been separately prepared by dispersing 1 part of a tetrafluoroethylene resin (Lubron L-2®, made by Daikin Industries, Ltd.) and 0.1 part of a dispersing agent (Arron GF-300®, made by Toagosei Chemical Industry Co., Ltd.) in 10 parts of monochlorobenzene. Further thereto, 0.1 part of 2,3-dimethylquinoxaline was added. This solution was applied onto the above charge-generating layer by immersion coating to form a charge-transporting layer of 19 µm thick. The resulting electrophotographic photosensitive member was set in an electrophotographic copying machine (NP-3825, made by Canon K.K.), and the properties of the electrophotographic photosensitive member were measured as below. Firstly, the conditions for latent image formation were determined to achieve the dark area potential (V D ) of -650 V and the light area potential (V L ) of -150 V. The quantity of image exposure therefor was defined as the initial sensitivity. After 5000 sheets of copying was practiced continuously, the values of V D and V L were measured, and the fall of V D and the rise of V L were determined. Thereafter, the photosensitive member was left standing in the copying machine. The portion of the photosensitive member left standing directly below the corona charger is marked. After left standing for 10 hours, the photosensitive member was subjected to measurement of the surface potentials at the portion of the member which had been left directly below the corona charger and at the portion which had been left not directly below the corona charger, and the difference of the two potentials (ΔV D ) was derived. The quality of the image after 5000 sheets of copying was evaluated visually. The results are shown in the Table. Example 2 A photosensitive member was prepared and evaluated in the same manner as in Example 1 except that the amount of the 2,3-dimethylquinoxaline was changed to 0.5 part. The results are shown in the Table. Comparative Example 1 A photosensitive member was prepared and evaluated in the same manner as in Example 1 except that the 2,3-dimethylquinoxaline was not used. The results are shown in the Table. Comparative Example 2 A photosensitive member was prepared and evaluated in the same manner as in Example 2 except that 4,4'-dipyridyl was used instead of the 2,3-dimethylquinoxaline. The results are shown in the Table. As described above, the present invention provides an electrophotographic photosensitive member which gives images of high quality stably even after repeated use without blurring or blank of the images.

Claims: An electrophotographic photosensitive member comprising an electroconductive support, and a photosensitive layer formed thereon, the photosensitive layer containing a compound selected from compounds represented by the formulas (1) and (2): An electrophotographic photosensitive member according to claim 1, wherein said compound is a compound represented by the formula (1) below: An electrophotographic photosensitive member according to claim 1, wherein said compound is a compound represented by the formula (2): An electrophotographic photosensitive member according to claim 1, wherein the amount of said compound is 0.2 to 30 % by weight based on the total weight of the layer to which said compound is added. An electrophotographic photosensitive member according to claim 4, wherein the amount of said compound is 0.4 to 15 % by weight based on the total weight of the layer to which said compound is added. An electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer comprises a charge-generating layer and a charge-transporting layer. An electrophotographic photosensitive member according to claim 6, comprising an electroconductive support, a charge-generating layer and a charge-transporting-layer in the order named. An electrophotographic photosensitive member according to claim 6, comprising an electroconductive support, a charge-transporting layer and a charge-generating layer in the order named. An electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer is a single layer. An electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer has a protecting layer. An electrophotographic photosensitive member according to claim 6, wherein said charge-transporting layer contains a compound selected from compounds represented by formulas (1) and (2). An electrophotographic photosensitive member according to claim 6, wherein said charge-generating layer contains a compound selected from compounds represented by formulas (1) and (2). An electrophotographic photosensitive member according to claim 7, wherein said charge-transporting layer contains a compound selected from compounds represented by formulas (1) and (2). An electrophotographic photosensitive member according to claim 10, wherein said protecting layer contains a compound selected from compounds represented by formulas (1) and (2). An electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer comprises a charge-transporting substance having the oxidation potential of not less than 0.6 V. An electrophotographic photosensitive member according to claim 1, wherein a surface layer of the photosensitive layer contains a lubricant. An electrophotographic photosensitive member according to claim 16, wherein said lubricant is selected from the group consisting of powdery fluoro-resins, powdery polyolefin resins, powdery silicone resins and powdery fluorinated carbon. An electrophotographic photosensitive member according to claim 17, wherein said lubricant is powdery fluoro-resins. An electrophotographic photosensitive member according to claim 1, further comprising a subbing layer. An electrophotographic apparatus comprising an electrophotographic photosensitive member, an image forming means for forming a latent image, a developing means for developing the formed latent image, and a transferring means for transferring a developed image to a transfer-receiving material, said electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer formed thereon, the photosensitive layer contains a compound according to claim 1. A device unit comprising an electrophotographic photosensitive member and at least one means selected from the group consisting of a charging means, a developing means and a cleaning means, said electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer formed thereon, said photosensitive layer contains a compound according to claim 1, said unit holding integrally the electrophotographic photosensitive member, and at least one means selected from the group consisting of the charging means, the developing means and the cleaning means, and being removable from the main body of an electrophotographic apparatus. A facsimile machine comprising an electrophotographic apparatus and a means for receiving image information from a remote terminal, said electrophotographic apparatus comprising an electrophotographic photosensitive member, said electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer formed thereon, said photosensitive layer containing a compound according to claim 1.

Inventors: GOTO KOJI, SUMINO FUMIO, YOSHIDA AKIRA, GOTO, KOJI, SUMINO, FUMIO, YOSHIDA, AKIRA, Goto, Koji, c/o Canon Kabushiki Kaisha, Sumino, Fumio, c/o Canon Kabushiki Kaisha, Yoshida, Akira, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G03G5
IPC codes: G03G5