Patent Publication Number: US-5294508-A

Title: Electrophotographic photosensitive member with polyether polyols-polyisocyanate intermediate layer and apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an electrophotographic photosensitive member, particularly one having an improved intermediate layer disposed between an electroconductive support (hereinafter simply referred to as a &#34;support&#34;) and a photosensitive layer, and also an apparatus using such an improved electrophotographic photosensitive member. 
     For an electrophotographic photosensitive member of the Carlson type, it is generally important to ensure stability of a dark-part potential and a light-part potential in order to secure a constant image density on repetition of charging-exposure and provide images free from fog. 
     In order to ensure the potential stability, various proposals have been made, inclusive of, e.g., improvement in charge injection from the support to the photosensitive layer, improvement in adhesion between the support and the photosensitive layer, improvement in application characteristic of the photosensitive layer, and provision of an intermediate layer between the support and the photosensitive layer having a function of, e.g., covering defects on the support 
     There has been also proposed a photosensitive member having a photosensitive layer of a laminated structure functionally separated into a charge generation layer and a charge transport layer. The charge generation layer is generally formed in a very thin layer of, e.g., about 0.5 micron, so that the thickness of the charge generation layer is liable to be nonuniform due to defects, soiling, attachment or flaws on the surface of the support. Such a nonuniform thickness of the charge generation layer, however, results in a sensitivity irregularity of the photosensitive member, so that the charge generation layer is required to be as uniform as possible. 
     In view of the above circumstances, it has been proposed to dispose an intermediate layer between the charge generation layer and the support, functioning as a barrier layer and an adhesive layer and also covering defects on the support. 
     Hitherto, as resins constituting such intermediate layers between the photosensitive layer and the support, there have been known to use polyamide (Japanese Laid-Open Patent Application (JP-A) 48-47344, JP-A 52-25638), polyester (JP-A 52-20836, JP-A 54-206738), polyurethane (JP-A 53-89435, JP-A H2-115858), quarternary ammonium salt-containing acrylic polymer (JP-A 51-126148), and casein (JP-A 55-103556). 
     However, an intermediate layer composed of a material as described above changes its electric resistance corresponding to changes in environmental temperature and humidity, so that it has been difficult to ensure a stable potential characteristic over wide environmental conditions ranging from low temperature--low humidity to high temperature--high humidity by using an electrophotographic photosensitive member incorporating such an intermediate layer. 
     For example, when such a photosensitive member is repeatedly used under low temperature--low humidity conditions tending to increase the electric resistance of the intermediate layer, some charges remain in the intermediate layer to increase the light-part potential and the residual potential, thus resulting in fog in copied images. Further, in case where such a photosensitive member is used in an electrophotographic printer of the reversal development type, the resultant images are liable to be thin in density and fail to provide copies with a prescribed quality. 
     On the other hand, under high temperature--high humidity conditions, such an intermediate layer is liable to cause an inferior barrier function due to a lowering in electric resistance, thus resulting in an increase in carrier injection from the support side to cause a lowering in dark-part potential. As a result, under high temperature--high humidity conditions, copy images become thin. When such a photosensitive member is used in an electrophotographic printer of the reversal development type, the resultant images are liable to be accompanied with black spotty defects (black spots). Further, the above-mentioned photosensitive member of prior art having an intermediate layer comprising a cured layer of a polyurethane which is a reaction product between a polyether compound and a polyisocyanate compound, shows an effect of decreasing fog due to a lowering in electric resistance but is still accompanied with a problem that the resultant images are liable to be accompanied with black spotty defects (black spots). 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an electrophotographic photosensitive member capable of retaining a stable potential characteristic and thus stably forming images over wide environmental conditions ranging from low temperature--low humidity to high temperature--high humidity conditions. 
     Another object of the present invention is to provide an electrophotographic photosensitive member having an intermediate layer showing an excellent adhesion to the support and a good film characteristic and capable of forming good images free from defects under wide environmental conditions. 
     A further object of the present invention is to provide electrophotographic apparatus using such an improved photosensitive member. 
     According to the present invention, there is provided an electrophotographic photosensitive member, comprising: an electroconductive support, and an intermediate layer and a photosensitive layer disposed in this order on the support, wherein said intermediate layer comprises a reaction product of a mixture including a polyol compound [I], a polyol compound [II] having an OH equivalent different from that of the polyol compound [I] and a polyisocyanate compound; said polyol compound [I] is a polyether polyol compound having an OH equivalent of at least 500 and 2-60 OH groups per molecule; and said polyol compound [II] is a polyol compound having an OH equivalent of at most 300. 
     Thus, according to the electrophotographic photosensitive member of the present invention, by using an intermediate layer comprising a reaction product between the specific polyol compounds and polyisocyanate compound between the support and the photosensitive layer, it is possible to retain a stable potential characteristic and form good images over wide environmental conditions from low temperature--low humidity to high temperature--high humidity. 
     The OH equivalent used herein refers to a reciprocal (g/eq-OH) of a hydroxyl value measured according to JIS K0070 (test methods for acid value, saponification value, ester value, iodine value, hydroxyl value and non-saponified matter of chemical products). 
     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic sectional view of a transfer-type copying machine loaded with an electrophotographic photosensitive member according to the present invention. 
     FIG. 2 is a block diagram of a facsimile system using a printer incorporating an electrophotographic photosensitive member according to the present invention. 
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     The polyol compound [I] used in the present invention is a polyether polyol compound having an OH equivalent of at least 500 and 2-60 OH groups per molecule. Such a polyether polyol compound may for example be prepared through a process wherein one or more species of alkylene oxides each having 2-10  carbon atoms are polymerized or copolymerized together with an active hydrogen compound in the presence of a catalyst, and the product is treated for removal of the catalyst by an ordinary purification method, such as ion exchange, neutralization-filtration, or adsorption. A part of the polyether polyol compound can be substituted with another group. Examples of such a substituent may include halogen atoms, such as fluorine, chlorine and iodine, and aryl groups such as phenyl and naphthyl. 
     The active hydrogen compound may be a compound having two or more active hydrogen atoms, and examples thereof may include: polyhydric alcohols, such as ethylene glycol, propylene glycol, 1,4-butanediol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, and sucrose; amine compounds, such as monoethanolamine, ethylenediamine, diethylenetriamine, 2-ethylhexylamine, and hexamethylenediamine; and phenolic active hydrogen compounds, such as bisphenol A, bisphenol F, 1,1-bis(hydroxyphenyl)ethane, bisphenol AP, acetophenone, and hydroquinone. 
     Examples of the alkylene oxide having 2-10 carbon atoms may include: ethylene oxide, propylene oxide, butylene oxide, hexene oxide, cyclohexene oxide, and nonene oxide. 
     As the catalyst, basic catalysts such as sodium methoxide, sodium hydroxide, potassium hydroxide, lithium carbonate and triethylamine may generally be used, but a Lewis acid catalyst such as boron trifluoride can also be used. 
     Examples of the polyol compound [II] are shown in the following Table 1. 
     
                                           TABLE 1                                 
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Polyol compounds [I]                                                      
         Alkylene oxide                                                   
Active   Number of carbon atoms                                           
                     Substituent                                          
hydrogen *1, *2      and rate of                                          
                            Polymer form                                  
                                    OH                                    
No.                                                                       
   compound                                                               
         2 3  4 6  9 substitution                                         
                            BK *3                                         
                                RM *4                                     
                                    equivalent                            
                                          Nf *9                           
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1  TMP *5                                                                 
         20                                                               
           80                   ∘                             
                                    1200  3                               
2  &#34;     50                                                               
           50                       1500  3                               
3  &#34;     50                                                               
           50               ∘                                 
                                    2000  3                               
4  &#34;     50                                                               
           30 20                ∘                             
                                    3000  3                               
5  BG *6 20                                                               
           70 10                ∘                             
                                     500  2                               
6  &#34;       100                      1800  2                               
7  1,4-BDO *7                                                             
         30                                                               
           60 40                ∘                             
                                    2200  2                               
8  &#34;     20                                                               
           50 30            ∘                                 
                                    1200  2                               
9  glycerin                                                               
         30                                                               
           70               ∘                                 
                                     600  3                               
10 &#34;     80                                                               
           10   10          ∘                                 
                                    4000  3                               
11 &#34;     80                                                               
           10      10           ∘                             
                                    5000  3                               
12 &#34;     90   10            ∘                                 
                                     700  3                               
13 No.2/No.5 = 1/1 (wt./wt.) mixture                                      
                                     750  2.5                             
14 glycerin                                                               
         60                                                               
           30   10              ∘                             
                                    2700  3                               
15 &#34;       80 20     chlorine 5%                                          
                            ∘                                 
                                    1500  3                               
16 PTEL *8                                                                
         30                                                               
           70        chlorine 2%                                          
                                ∘                             
                                    1200  4                               
17 &#34;     40                                                               
           60                   ∘                             
                                     650  4                               
18 sorbitol                                                               
         20                                                               
           8         phenyl 2%  ∘                             
                                    1600  6                               
19 &#34;     40                                                               
           60                   ∘                             
                                    2000  6                               
20 &#34;     40                                                               
           50      10           ∘                             
                                    2800  6                               
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     NOTES OF TABLE 1 
     *1: Number of carbon atoms 
     2: ethylene oxide 
     3: propylene oxide 
     4: butylene oxide 
     6: cyclohexene oxide 
     9: nonene oxide 
     *2: Numerals denote weight % values of the added alkylene oxides 
     *3: block polymer 
     *4: random polymer 
     *5: trimethylolpropane 
     *6: ethylene glycol 
     *7 : 1,4-butanediol 
     *8: pentaerythritol 
     *9: Nf=number of functional groups 
     The polyol compound [II] used in the present invention is a polyol compound having an OH equivalent of at most 300 and having at least two hydroxyl groups. Examples thereof may include: polyhydric alcohols, such as ethylene glycol, propylene glycol, 1,4-butanediol, glycerin, trimethylolpropane, sorbitol, pentaerythritol and sucrose; and phenolic active hydrogen compounds, such as bisphenol A, bisphenol F, 1,1-bi(4-hydroxyphenyl)methane, bisphenol AP, bisphenol Z and hydroquinone. It is also possible to use a polyol compound [II] obtained through a process like the above-mentioned process for production of the polyol compound [I] wherein one or more species of alkylene oxides each having 2-10 carbon atoms are polymerized or copolymerized together with a polyol compound having at least two hydroxyl groups as described above in the presence of a basic or acid catalyst as described above, and the product is treated for removal of the catalyst by an ordinary purification method, such as ion exchange, neutralization-filtration or adsorption. 
     
                                           TABLE 2                                 
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Polyol compounds [II]                                                     
Active   Alkylene oxide                                                   
hydrogen Number of carbon atoms *1, *2                                    
                        Polymer form                                      
                                 OH                                       
compound 2  3  4  6  9  block                                             
                            random                                        
                                 equivalent                               
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A glycerin                                                                
         80 20              ∘                                 
                                 200                                      
B &#34;      50 50          ∘                                     
                                 250                                      
C &#34;                               30                                      
D EG *3  100                     150                                      
E &#34;      60 40              ∘                                 
                                 200                                      
F bisphenol A                                                             
         50 50              ∘                                 
                                 300                                      
G &#34;      100                     250                                      
H TMP *4 80    20       ∘                                     
                                 200                                      
I &#34;      60    40           ∘                                 
                                 290                                      
J PTEL *5                                                                 
         40       60        ∘                                 
                                 250                                      
K &#34;      90 10          ∘                                     
                                 200                                      
L sorbitol                                                                
         80 10       10     ∘                                 
                                 300                                      
M &#34;      80 20              ∘                                 
                                 200                                      
N PG *5     100                  300                                      
O B/M = 50/50 (wt./wt.) mixture  222                                      
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     Notes of Table 2 
     *1: Number of carbon atoms 
     2: ethylene oxide 
     3: propylene oxide 
     4: butylene oxide 
     6: cyclohexene oxide 
     9: nonene oxide 
     *2: Numerals denote weight % values of the added alkylene oxides 
     *3: ethylene glycol 
     *4: trimethylolpropane 
     *5: pentaerythritol 
     *6: propylene glycol 
     Examples of the polyisocyanate compound to be used in the present invention may include: 2,4-toluene diisocyanate, 2-6-toluene diisocyanate (trade name: &#34;TDI-100&#34;), 4,4&#39;-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate and mixtures and adducts thereof. 
     The polyisocyanate compound can also be used in a blocked isocyanate form (terminal-protected isocyanate). The blocking agent may for example be methyl ethyl ketoxime, phenol, caprolactam, ethyl acetoacetate, methanol or sodium hydrogenesulfite. 
     The blocking may be effected by adding such a blocking agent to the polyisocyanate compound and performing the reaction at 30°-90° C. for 0.5-2  hours. 
     The intermediate layer comprising a reaction product of the polyol compounds and polyisocyanate compound may be formed by applying a mixture including the polyol compounds and polyisocyanate compound and then subjecting the resultant layer to curing under heating, or by synthesizing a polymer of the polyol compounds and polyisocyanate compound in advance and then applying a solution of the polymer in an appropriate solvent, followed by drying. 
     It is also possible to form a polyoxyalkylene segment-containing polyisocyanate compound by reaction of at least one of the polyol compounds with the polyisocyanate compound, such a polyoxyalkylene segment-containing polyisocyanate compound is a blocked form by reacting the terminals thereof with a blocking agent, or a compound by adding a polyol such as a polyoxyalkylene polyol to the terminal of such a polyisocyanate compound, and applying a paint containing compounds, followed by curing under heating to form an intermediate layer. 
     For the reaction between the polyol compound and the polyisocyanate compound, it is possible to use a catalyst for accelerated reaction. The catalyst used for this purpose may for example include: amine catalysts, such as triethylamine, dimethylethanolamine, and triethylenediamine; and metal salt catalysts, such as zinc octylate, tin octylate and dibutyltin dilaurate. 
     The polyol compounds and the polyisocyanate compound may preferably be reacted in a functional group molar ratio (NCO group/OH group) of 1.0-2.0 between the NCO and OH groups. 
     Further, the polyol compound [I] and the polyol compound [II] may preferably be used in a weight ratio ([I]/[II]) of 0.05-50, particularly 0.2-20. 
     The intermediate layer of the photosensitive member according to the present invention may be composed of a single layer comprising a reaction product between the above-mentioned polyol compounds and polyisocyanate compound, but can also assume a laminated structure including plural layers, at least one of which comprises the above-mentioned reaction product. In case where the intermediate layer is composed of plural layers, another layer not comprising the above-mentioned reaction product may comprise a resin material, such as polyamide, polyester or phenolic resin. 
     The intermediate layer used in the present invention can further contain, e.g., another resin, additive or electroconductive substance, according to necessity. 
     Examples of such an electroconductive substance may include: powder or short fiber of metals such as aluminum, copper, nickel, and silver; electroconductive metal oxides, such as antimony oxides, indium oxide and tin oxide; carbon film, carbon black and graphite powder; and electroconductive obtained by coating with such an electroconductive substance. 
     The thickness of the intermediate layer according to the present invention may be determined in view of electrophotographic characteristics and influence of defects on the support and may generally be set within the range of 0.1-50 microns, more suitably 0.5-30 microns. 
     The intermediate layer may be formed by an appropriate coating method, such as dip coating, spray coating or roller coating. 
     In the present invention, the photosensitive layer may be either of a single layer-type or of a laminated layer-type functionally separated into a charge generation layer and a charge transport layer. 
     A charge generation layer of the laminated layer-type photosensitive layer may for example be prepared by dispersing a charge-generating substance, such as azo pigment, quinone pigment, quinocyanine pigment, perylene pigment, indigo pigment, azulenium salt pigment or phthalocyanine pigment into a solution containing a resin such as polyvinyl butyral, polystyrene, polyvinyl acetate, acrylic resin, polyvinylpyrrolidone, ethyl cellulose or cellulose acetate butyrate to form a coating liquid, and applying the coating liquid onto the above-mentioned intermediate layer. The charge generation layer may have a thickness of at most 5 microns, preferably 0.05-2 microns 
     A charge transport layer may be formed on such a charge generation layer by dissolving a charge transporting substance of, e.g., a polycyclic aromatic compound having a structure of biphenylene, anthracene, pyrene, phenanthrene, etc., in its main chain or side chain, a nitrogen-containing cyclic compound such as indole, carbazole, oxadiazole or pyrazoline, triarylamine compound, hydrazone compound, or styryl compound into a solution of a film-forming resin to form a coating liquid, and applying the coating liquid. The film-forming resin may for example include polyester, polycarbonate, polymethacrylate and polystyrene. 
     The charge transport layer may ordinarily have a thickness of 5-40 microns, preferably 10-30 microns. 
     The laminated layer-type photosensitive layer can also assume a structure wherein the charge generation layer is disposed on the charge transport layer. 
     A single layer-type photosensitive layer may be formed as a layer containing both the charge generating substance and the charge transporting substance together in a resin. 
     In the present invention, it is also possible to constitute the photosensitive layer as a layer of an organic photoconductive polymer, such as poylvinylcarbazole or polyvinylanthracene, a vapor-deposition layer of a charge generation substance as described above, a vapor-deposited selenium layer, a vapor-deposited selenium-tellurium layer, or an amorphous silicon layer. 
     On the other hand, the support used in the present invention may be any one as far as it has an electroconductivity, inclusive of, e.g., a metal, such as aluminum, copper, chromium, nickel, zinc or stainless steel formed into a cylinder or sheet; a plastic film or paper laminated with a foil of a metal such as aluminum or copper, a plastic film provided thereon with a vapor-deposited layer of, e.g., aluminum, indium oxide or tin oxide, or a plastic film or paper coated with an electroconductive layer of an electroconductive substance alone or dispersed in an appropriate binder resin. 
     The electrophotographic photosensitive member according to the present invention may be applicable to an electrophotographic apparatus in general, inclusive of a copying machine, a laser printer, an LED printer and a liquid crystal shutter-type printer, and further widely applicable to apparatus, such as a display, a recording apparatus, a mini-scale printing, a plate production apparatus and a facsimile apparatus utilizing electrophotography in an applied form. 
     FIG. 1 shows a schematic structural view of an ordinary transfer-type electrophotographic apparatus using an electrophotosensitive member of the invention. Referring to FIG. 1, a photosensitive drum (i.e., photosensitive member) 11 as an image-carrying member is rotated about an axis 11a at a prescribed peripheral speed in the direction of the arrow shown inside of the photosensitive drum 11. The surface of the photosensitive drum is uniformly charged by means of a charger 12 to have a prescribed positive or negative potential. The photosensitive drum 11 is exposed to light-image L (as by slit exposure or laser beam-scanning exposure) by using an image exposure means (not shown), whereby an electrostatic latent image corresponding to an exposure image is successively formed on the surface of the photosensitive drum 11. The electrostatic latent image is developed by a developing means 14 to form a toner image. The toner image is successively transferred to a transfer material P which is supplied from a supply part (not shown) to a position between the photosensitive drum 11 and a transfer charger 15 in synchronism with the rotating speed of the photosensitive drum 11, by means of the transfer charger 15. The transfer material P with the toner image thereon is separated from the photosensitive drum 11 to be conveyed to a fixing device 18, followed by image fixing to print out the transfer material P as a copy outside the electrophotographic apparatus. Residual toner particles on the surface of the photosensitive drum 11 after the transfer are removed by means of a cleaner 16 to provide a cleaned surface, and residual charge on the surface of the photosensitive drum 11 is erased by a pre-exposure means 17 to prepare for the next cycle. As the charger 12 for charging the photosensitive drum 11 uniformly, a corona charger is widely used in general. As the transfer charger 15, such a corona charger is also widely used in general. 
     According to the present invention, in the electrophotographic apparatus, it is possible to provide an apparatus unit which includes plural means inclusive of or selected from the photosensitive member (photosensitive drum), the charger, the developing means, the cleaner, etc. so as to be attached to or released from the apparatus body, as desired. The device unit may, for example, be composed of the photosensitive member and the cleaner to prepare a single unit capable of being attached to or released from the body of the electrophotographic apparatus by using a guiding means such as a rail in the body. The apparatus unit can be further accompanied with the charger and/or the developing means to prepare a single unit. 
     In a case where the electrophotographic apparatus is used as a copying machine or a printer, exposure light-image L may be given by reading data on reflection light or transmitted light from an original or, converting the data on the original into a signal and then effecting a laser beam scanning, a drive of LED array or a drive of a liquid crystal shutter array. 
     In a case where the electrophotographic apparatus according to the present invention is used as a printer of a facsimile machine, exposure light-image L is given by exposure for printing received data. FIG. 2 shows a block diagram of an embodiment for explaining this case. Referring to FIG. 2, a controller 21 controls an image-reading part 20 and a printer 29. The whole controller 21 is controlled by a CPU (central processing unit) 27. Read data from the image-reading part is transmitted to a partner station through a transmitting circuit 23, and on the other hand, the received data from the partner station is sent to the printer 29 through a receiving circuit 22. An image memory memorizes prescribed image data. A printer controller 28 controls the printer 29, and a reference numeral 24 denotes a telephone handset. 
     The image received through a line 25 (the image data sent through the circuit from a connected remote terminal) is demodulated by means of the receiving circuit 22 and successively stored in an image memory 26 after a restoring-signal processing of the image data. When image for at least one page is stored in the image memory 26, image recording of the page is effected. The CPU 27 reads out the image data for one page from the image memory 26 and sends the image data for one page subjected to the restoring-signal processing to the printer controller 28. The printer controller 28 receives the image data for one page from the CPU 27 and controls the printer 29 in order to effect image-data recording. Further, the CPU 27 is caused to receive image for a subsequent page during the recording by the printer 29. As described above, the receiving and recording of the image are performed. 
     Hereinbelow, the present invention will be explained based on Examples wherein &#34;part(s)&#34; means &#34;part(s) by weight&#34;. 
     EXAMPLE 1 
     Polyol compounds [I] and [II] are selected from those listed in Tables 1 and 2, respectively, and a paint for an intermediate layer having the following composition was prepared by mixing. 
     
         ______________________________________                                    
Polyol compound [I] (No. 1)                                               
                      13.3    wt. part(s)                                 
Polyol compound [II] (D)                                                  
                      3.3     wt. part(s)                                 
Hexamethylene diisocyanate (HMDI)                                         
                      3.4     wt. part(s)                                 
Dibutyltin dilaurate (DBTL)                                               
                      0.02    wt. part(s)                                 
Methyl ethyl ketone (MEK)                                                 
                      80      wt. part(s)                                 
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     The paint was applied onto an aluminum cylinder (OC (outer diameter)=30 mm, L (length)=360 mm) by dipping and then dried and cured at 150° C. for 30 min. to form a 3.0 micron-thick intermediate layer. 
     Separately, 4 parts of a disazo pigment represented by the following formula: ##STR1## 2 parts of of a butyral resin (butyral degree: 68%, Mw (weight-average molecular weight): 24000) and 34 parts of cyclohexanone were dispersed for 8 hours by means of a sand mill containing 1 mm-dia. glass beads and diluted with 60 parts of tetrahydrofuran (THF) to prepare a coating liquid. The thus prepared coating liquid was applied by dipping onto the above prepared intermediate layer and dried at 80° C. for 15 min. form a 0.2 micron-thick charge generation layer. 
     Then, 10 parts of a hydrazone compound of the formula: ##STR2## 
     10 parts of a bisphenol Z-type polycarbonate (Mw=30000), 10 parts of dichloromethane and 50 parts of monochlorobenzene were dissolved in mixture to form a coating liquid for a charge transport layer. The coating liquid was applied onto the above-formed charge generation layer by dipping and dried for 60 min. at 110° C. to form a 20 micron-thick charge transport layer. 
     The thus-prepared electrophotographic photosensitive member was incorporated in a copying apparatus, and the electrophotographic performances thereof were evaluated by a process wherein steps of charging-exposure-development-transfer-cleaning were repeated at a cycle of 0.8 sec under low temperaturelow humidity conditions (15° C-15%RH). The results are summarized in Table 3 appearing hereinafter. 
     As is shown in Table 3, the photosensitive member showed a large difference between the dark-part potential (V D ) and light-part potential (V L ), thus providing a sufficient contrast. Further, as a result of 1000 sheets of successive image formation, images could be formed in a very stable state without causing an increase in light-part potential (V L ). 
     EXAMPLES 2-4 
     Electrophotographic photosensitive members were prepared in the same manner as in Example 1 except that the following compositions were respectively used for preparing the intermediate layers. 
     EXAMPLE 2 
     
         ______________________________________                                    
Polyol compound [I] (No. 3)                                               
                      11.9     part(s)                                    
Polyol compound [II] (E)                                                  
                      5.1      part(s)                                    
TDI                   3.0      part(s)                                    
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     EXAMPLE 3 
     
         ______________________________________                                    
Polyol compound [I] (No. 4)                                               
                      7.3      part(s)                                    
Polyol Compound [II] (F)                                                  
                      7.3      part(s)                                    
HMDI in a blocked form with methyl                                        
                      5.4      part(s)                                    
ethyl ketoxime (MEKO)                                                     
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     EXAMPLE 4 
     
         ______________________________________                                    
Polyol compound [I] (No. 9)                                               
                      14.3     part(s)                                    
Polyol compound [II] (K)                                                  
                      1.6      part(s)                                    
4,4&#39;-diphenylmethane  4.1      part(s)                                    
diisocyanate (MDI)                                                        
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     The above-prepared photosensitive members were evaluated in the same manner as in Example 1. As a result, the respective photosensitive members showed a large difference between dark-part potential (V D ) and light-part potential (V L ), thus providing a sufficient potential contrast. Further, as a result of 1000 sheets of successive image formation, the respective photosensitive members provided images in a very stable state while causing almost no increase in light-part potential (V L ). 
     The results are also summarized in Table 3. 
     EXAMPLE 5 
     
         ______________________________________                                    
Polyol compound [I] (No. 5)                                               
                      31.5     parts                                      
Polyol compound [II] (D)                                                  
                      7.9      parts                                      
TDI                   10.6     parts                                      
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     The above ingredients were reacted under stirring for 3 hours at 90° C. to form a reaction product (polymer). 
     
         ______________________________________                                    
The above reaction product                                                
                      10       parts                                      
MEK                   60       parts                                      
Dichloromethane       30       parts                                      
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     A coating liquid was prepared by mixing the above ingredients, and an electrophotographic photosensitive member was prepared in the same manner as in Example 1 except that the coating liquid for preparing the intermediate layer. 
     The thus-prepared photosensitive member was evaluated in the same manner as in Example 1. As a result, the photosensitive member showed a large difference between dark-part potential (V D ) and lightpart potential (V L ), thus providing a sufficient potential contrast. Further, as a result of 1000 sheets of successive image formation, the photosensitive member provided images in a very stable state while causing almost no increase in light-part potential (V L ). 
     The results are also shown in Table 3. 
     COMPARATIVE EXAMPLES 1 AND 2 
     Electrophotographic photosensitive members were prepared in the same manner as in Example 1 except that the following compositions were respectively used for preparing the intermediate layers. 
     COMPARATIVE EXAMPLE 1 
     
         ______________________________________                                    
Alcohol-soluble copolymer nylon                                           
                        5       part(s)                                   
(&#34;Amilan CM-8000&#34;, mfd. by Toray K.K.)                                    
Methanol                95      part(s)                                   
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     COMPARATIVE EXAMPLE 2 
     
         ______________________________________                                    
Polyester polyol        14      part(s)                                   
(&#34;Nippolan 125&#34;, mfd. by Nihon                                            
Polyurethane Kogyo K.K.)                                                  
DBTL                    0.02    part(s)                                   
MEK                     80      part(s)                                   
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     The photosensitive members were evaluated in the same manner as in Example 1. As a result, both photosensitive members showed an increase in light-part potential (V L ), thus resulting in images accompanied with fog after 1000 sheets of successive copying. 
     The results are also summarized in Table 3 below. 
     Separately, the intermediate layers were formed according to the above-described methods of Examples 1-5 and Comparative Examples 1 and 2, and the adhesion strengths thereof were evaluated by a square matrix pattern (or checker pattern) peeling test according to JIS K5400 (General test method for paints). 
     As a result, the intermediate layers according to Examples 1-5 were all free from peeling, thus showing good adhesion to the aluminum substrate. On the other hand, the intermediate layers of Comparative Examples 1 and 2 showed peeling rates of 25% and 29%, respectively. 
     
                       TABLE 3                                                     
______________________________________                                    
                   After 1000 sheets                                      
Initial stage      of successive copying                                  
Dark-part    Light-part                                                   
                       Light-part                                         
potential    potential potential Image                                    
V.sub.D (-V) V.sub.L (-V)                                                 
                       V.sub.L (-V)                                       
                                 evaluation                               
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Example                                                                   
1      670       185       200     Good                                   
2      680       190       205     Good                                   
3      665       180       185     Good                                   
4      675       185       195     Good                                   
5      680       200       210     Good                                   
Comp.                                                                     
Example                                                                   
1      665       190       325     Fog occurred                           
2      670       200       360     Fog occurred                           
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     EXAMPLE 6 
     
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Resol-type phenolic resin                                                 
                     25 parts                                             
Electroconductive titanium oxide                                          
                     50 parts                                             
powder (coated with tin oxide                                             
containing 10% of antimonyl                                               
oxide)                                                                    
Methyl cellosolve    20 parts                                             
Methanol              5 parts                                             
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     The above-ingredients were subjected to 2 hours of mixing and dispersion in a sand mill containing 1 mm-dia. glass beads to prepare a paint for a first intermediate layer. 
     The paint was applied onto an aluminum cylinder (OD=30 mm, L=260 mm) by dipping and then dried and cured at 150° C. for 20 min. to form a 20 micron-thick first intermediate layer. 
     
         ______________________________________                                    
Polyol compound [I] (No. 13)                                              
                      7.7      part(s)                                    
Polyol compound [II] (G)                                                  
                      5.1      part(s)                                    
TDI in a blocked form with MEKO                                           
                      7.2      part(s)                                    
DBTL                  0.02     part(s)                                    
MEK                   80       part(s)                                    
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     The above ingredients were dissolved in mixture to form a paint for a second intermediate layer, which was then applied by dipping onto the first intermediate layer and dried and cured at 150° C. for 20 min. to form a 0.6 micron-thick second intermediate layer. 
     Then, 3 parts of a disazo pigments of the formula: ##STR3## 2 parts of polyvinyl benzal (benzal degree=80%, Mw=11000) and 35 parts of cyclohexanone were subjected to 12 hours of mixing and dispersion by a sand mill containing 1 mm-dia glass beads and further dispersed after adding 60 parts of methyl ethyl ketone (MEK) to form a coating liquid for a charge generation layer. The coating liquid was applied by dipping onto the above second intermediate layer and dried at 80° C. for 20 min. to form a 0.2 micron-thick charge generation layer. 
     Then, 10 parts of a styryl compound of the formula: ##STR4## 10 parts of a bisphenol Z-type polycarbonate (Mw=30000), 15 parts of dichloromethane and 45 parts of monochlorobenzene were dissolved in mixture to form a coating liquid for a charge transport layer. The coating liquid was applied onto the above-formed charge generation layer by dipping and dried for 60 min. at 120° C. to form a 18 micron-thick charge transport layer. 
     The thus-prepared electrophotographic photosensitive member was incorporated in a laser printer of the reversal development type, and the electrophotographic performances thereof were evaluated by a process wherein steps of charging-exposuredevelopment-transfer-cleaning were repeated at a cycle of 1.5 sec under normal temperature - normal humidity conditions (23° C.-50% RH) and high temperature-high humidity conditions (30° C-85%RH). The results are summarized in Table 4 appearing hereinafter. 
     As is shown in Table 4, the photosensitive member showed a large difference between the dark-part potential (V D ) and light-part potential (V L ), thus providing a sufficient contrast. Further, also under the high temperature--high humidity conditions, the dark-part potential was stable and good images free from black spots or fog could be formed. 
     EXAMPLES 7-10 
     Electrophotographic photosensitive members were prepared in the same manner as in Example 6 except that the following compositions were respectively used for preparing the second intermediate layers. 
     EXAMPLE 7 
     
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Polyol compound [I] (No. 10)                                              
                     2.3      part(s)                                     
Polyol compound [II] (O)                                                  
                     9.0      part(s)                                     
HMDI in a phenol-blocked form                                             
                     8.7      part(s)                                     
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     EXAMPLE 8 
     
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Polyol compound [I] (No. 17)                                              
                     10.5     part(s)                                     
Polyol compound [II] (L)                                                  
                     2.6      part(s)                                     
MDI in an MEKO-blocked form                                               
                     6.9      part(s)                                     
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     EXAMPLE 9 
     
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Polyol compound [I] (No. 19)                                              
                     13.1     part(s)                                     
Polyol compound [II] (C)                                                  
                     0.7      part(s)                                     
TDI in an MEKO-blocked form                                               
                     6.2      part(s)                                     
DBTL                 0.02     part(s)                                     
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     EXAMPLE 10 
     
         ______________________________________                                    
Polyol compound [I] (No. 7)                                               
                     5.1      part(s)                                     
Polyol compound [II] (M)                                                  
                     7.5      part(s)                                     
HMDI in a trimerized form                                                 
                     7.4      part(s)                                     
(isocyanurate)                                                            
Tin octylate         0.02     part(s)                                     
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     The above-prepared photosensitive members were evaluated in the same manner as in Example 6. As a result, each photosensitive member maintained a stable dark-part potential (V D ) even under high temperature--high humidity conditions and could provide good images free from occurrence of black spots or fog. 
     The results are summarized in Table 4. 
     COMPARATIVE EXAMPLES 3-5 
     Eleectrophotographic photosensitive members were prepared in the same manner as in Example 6 except that the following compositions were respectively used for preparing the second intermediate layers. 
     COMPARATIVE EXAMPLE 3 
     
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N-methoxylated 6-nylon                                                    
                     5         part(s)                                    
(Mw = 50000, methoxymethyl-                                               
substitution rate = 28%)                                                  
Methanol             95        part(s)                                    
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     COMPARATIVE EXAMPLE 4 
     
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Poly(oxypropylene)triol                                                   
                     15        part(s)                                    
(hydroxy value = 170 mgKOH/g)                                             
TDI                  5         part(s)                                    
DBTL                 0.02      part(s)                                    
MEK                  80        part(s)                                    
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     COMPARATIVE EXAMPLE 5 
     
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Polyol compound [I] (No. 13)                                              
                     15.5      part(s)                                    
TDI in an MEKO-blocked form                                               
                     4.5       part(s)                                    
DBTL                 0.02      part(s)                                    
MEK                  80        part(s)                                    
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     The photosensitive members were evaluated in the same manner as in Example 6. As a result, the photosensitive member according to Comparative Examples 3 showed a decrease in chargeability to lower the darkpart potential (V D ) under the high temperature--high humidity conditions and also provided images accompanied with black spots and fog. On the other hand, the photosensitive members according to Comparative Examples 4 and 5 did not show a decrease in chargeability under the high temperature--high humidity conditions, but the resultant images were accompanied with black spots. 
     The results are summarized in Table 4. 
     
                       TABLE 4                                                     
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       Enrivonmental conditions                                           
       23° C., 50% RH                                              
                   30° C., 85% RH                                  
       V.sub.D (-V)                                                       
              V.sub.L (-V)                                                
                       V.sub.D (-V)                                       
                                Image                                     
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Example                                                                   
6        615      155      610    Good                                    
7        620      165      610    Good                                    
8        630      160      625    Good                                    
9        625      155      605    Good                                    
10       635      170      620    Good                                    
Comparative                                                               
Example                                                                   
3        635      165      560    Black spots and                         
                                  fog occurred                            
4        630      165      610    Black spots                             
                                  occurred                                
5        620      170      600    Black spots                             
                                  occurred                                
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     EXAMPLE 11 
     
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Polyol compound [I] (No. 11)                                              
                     15.6      part(s)                                    
Polyol compound [II] (M)                                                  
                     1.7       part(s)                                    
TDI in MEKO-blocked form                                                  
                     2.7       part(s)                                    
Electroconductive titanium                                                
                     20        part(s)                                    
oxide powder (coated with tin                                             
oxide containing 8% of antimony                                           
oxide)                                                                    
Rutile-type titanium oxide powder                                         
                     20        part(s)                                    
DBTL                 0.02      part(s)                                    
MEK                  40        part(s)                                    
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     The above-ingredients were subjected to 3 hours of mixing and dispersion in a sand mill containing 1 mm-dia. glass beads to prepare a paint for a first intermediate layer. 
     The paint was applied onto an aluminum cylinder (OD=60 mm, L=260 mm) by dipping and then dried and cured at 150° C. for 20 min. to form a 15 micron-thick first intermediate layer. 
     Then, the paint for the second intermediate layer prepared in Example 6 was applied by dipping onto the above first intermediate layer, and dried and cured at 150° C. for 20 min. to form a 0.6 micron-thick second intermediate layer. 
     Then, 4 parts of a disazo pigment of the formula: ##STR5## 2 parts of polyvinyl butyral (butyral degree=71%, Mw =18000) and 34 parts of cyclohexanone were subjected to 6 hours of mixing and dispersion by a sand mill containing 1 mm-dia. glass beads and further dispersed after adding 60 parts of methyl ethyl ketone (MEK) to form a coating liquid for a charge generation layer. The coating liquid was applied by dipping onto the above second intermediate layer and dried at 80° C. for 15 min to form a 0.3 micron-thick charge generation layer. 
     Then, the coating liquid for a charge transport layer used in Example 6 was applied by dipping onto the charge generation layer and dried at 120° C. for 60 min to form a 22 micron-thick charge transport layer. 
     The thus-prepared electrophotographic photosensitive member was incorporated in a copying apparatus, and the electrophotographic performances thereof were evaluated by a process wherein steps of charging-exposure-development-transfer-cleaning were repeated at a cycle of 0.6 sec under low temperaturelow humidity conditions (10° C.-10%RH). The results are summarized in Table 5 appearing hereinafter. 
     As is shown in Table 5, the photosensitive member showed a large difference between the dark-part potential (V D ) and light-part potential (V L ), thus providing a sufficient contrast. Further, as a result of 1000 sheets of successive image formation, images could be formed in a very stable state without causing an increase in light-part potential (V L ). 
     EXAMPLE 12 
     
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Alcohol-soluble copolymer nylon                                           
                      3 parts                                             
(&#34;Amilan CM-8000&#34;, mfd. by                                                
Toray K.K.)                                                               
N-methoxymethylated 6-nylon                                               
                      3 parts                                             
(Mw = 150000, methoxymethyl                                               
substitution rate = 30%)                                                  
Methanol              94 parts                                            
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     An electrophotographic photosensitive member was prepared in the same manner as in Example 1 except that a coating liquid prepared from the above ingredients was used for forming the second intermediate layer. 
     EXAMPLE 13 
     An electrophotographic photosensitive member was prepared in the same manner as in Example 11 except that the second insulating layer was omitted to form on the support a laminated structure composed of the first intermediate layer, the charge generation layer and the charge transport layer. 
     The above-prepared photosensitive members of Examples 12 and 13 were evaluated in the same manner as in Example 11. As a result, each photosensitive member showed a large difference between the dark-part potential (V D ) and light-part potential (V L ), thus providing a sufficient potential contrast. Further, as a result of 1000 sheets of successive image formation, the photosensitive members provided images in a very stable state while causing almost no increase in light-part potential (V L ). 
     The results are summarized in Table 5. 
     COMPARATIVE EXAMPLES 6 AND 7 
     
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Resol-type phenolic resin                                                 
                      20 parts                                            
Electroconductive titanium                                                
                      20 parts                                            
oxide powder (coated with tin                                             
oxide containing 8% of antimony                                           
oxide)                                                                    
Rutile-type titanium oxide powder                                         
                      20 parts                                            
Methyl cellosolve     25 parts                                            
Methanol              15 parts                                            
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     A paint for the first intermediate layer was prepared from the above ingredients otherwise in the same manner as in Example 11. 
     Electrophotographic photosensitive members of Comparative Examples 6 and 7 were prepared in the same manner as in Examples 12 and 13, respectively, except that the above-prepared paint was used for forming the first intermediate layer. 
     The photosensitive members were evaluated in the same manner as in Example 11. As a result, the photosensitive member of Comparative Example 6 caused an increase in light-part potential (V L ) after 1000 sheets of successive image formation, thus providing images accompanied with fog. 
     On the other hand, the photosensitive member of Comparative Example 7 having the charge generation layer and charge transport layer directly formed on the first intermediate layer showed only a low dark-part potential (V D ) due to insufficient barrier characteristic causing a large charge injection from the support side. As a result, it failed to provide a potential contrast necessary for image formation. 
     The results are summarized in Table 5. 
     
                                           TABLE 5                                 
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Resin components for                                                      
intermediate layers                                                       
                 Initial stage                                            
                           After 1000 sheets                              
1st        2nd   V.sub.D (-V)                                             
                      V.sub.L (-V)                                        
                           V.sub.L (-V)                                   
                                Image                                     
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Example                                                                   
11   Polyether                                                            
           Polyether                                                      
                 715  170  175  Good                                      
     urethane                                                             
           urethane                                                       
12   Polyether                                                            
           nylon 725  150  165  Good                                      
     urethane                                                             
13   Polyether                                                            
           none  730  155  165  Good                                      
     urethane                                                             
Comp.                                                                     
Example                                                                   
6    phenolic                                                             
           nylon 705  165  295  Fog occurred                              
     resin                                                                
7    phenolic                                                             
           none  385  180  (evaluation impossible)                        
     resin                                                                
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