Patent Publication Number: US-9429859-B2

Title: Electrophotographic photosensitive member

Description:
INCORPORATION BY REFERENCE 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-201229, filed Sep. 27, 2013. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The present disclosure relates to electrophotographic photosensitive members. 
     Electrophotographic printers and multifunction peripherals each include an electrophotographic photosensitive member as an image bearing member. The electrophotographic photosensitive member includes a conductive substrate and a photosensitive layer disposed directly or indirectly on the conductive substrate. In one example, the photosensitive layer contains a charge generating material, a charge transport material, and an organic material, such as a resin, that binds these materials. Such an electrophotographic photosensitive member is called an electrophotographic organic photosensitive member. When a charge transport material and a charge generating material are contained in separate layers, the electrophotographic organic photosensitive member is referred to as a multi-layer photosensitive member. When a charge transport material and a charge generating material are both contained in the same layer, the electrophotographic organic photosensitive member is referred to as a single-layer photosensitive member. 
     In another example, the photosensitive member is an electrophotographic inorganic photosensitive member that contains an inorganic material (such as an amorphous silicon photosensitive member). Among the electrophotographic organic and inorganic photosensitive members, the electrophotographic organic photosensitive members allow easy film formation, which leads to easy manufacturing. In addition, the versatility of materials selectable for the electrophotographic organic photosensitive members ensures the applicability of the electrophotographic organic photosensitive members to many image forming apparatuses. 
     Examples of the charge transport material usable for a single- or multi-layer organic photosensitive member include a butadienylbenzene amine derivative. 
     SUMMARY 
     An electrophotographic photosensitive member according to the present disclosure includes a photosensitive layer that contains a charge generating material, a hole transport material, a binder resin, and a plasticizer. The photosensitive layer is a multi-layer or a single-layer. The hole transport material contains a triarylamine derivative represented by General Formula (1). The plasticizer contains at least one of a compound represented by General Formula (2a) and a compound represented by General Formula (2b). 
     
       
         
         
             
             
         
       
     
     In General Formula (1): Ar 1  represents an aryl group substituted with at least one substituent selected from the group consisting of an alkoxy group having 2 to 4 carbon atoms and an optionally substituted phenoxy group; and Ar 2  represents an aryl group optionally substituted with an alkyl group having 1 to 4 carbon atoms. 
     
       
         
         
             
             
         
       
     
     In General Formula (2a): R 1  to R 10  each independently represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms, a hydroxyl group, a cyano group, a nitro group, a trimethylsilyl group, or an amino group; or R 1  and R 6  are optionally bonded to each other to form an alkyl ring having 5 to 6 carbon atoms or a benzene ring. 
     
       
         
         
             
             
         
       
     
     In General Formula (2b): R 11  to R 18  each independently represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms, a hydroxyl group, a cyano group, a nitro group, or an amino group; and R represents a single bond, —O— or —CH═CH—. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic cross-sectional view showing a structure of a multi-layer electrophotographic photosensitive member according to an embodiment of the present disclosure. 
         FIG. 1B  is a schematic cross-sectional view showing another structure of the multi-layer electrophotographic photosensitive member according to the embodiment of the present disclosure. 
         FIG. 1C  is a schematic cross-sectional view showing a yet another structure of the multi-layer electrophotographic photosensitive member according to the embodiment of the present disclosure. 
         FIG. 2A  is a schematic cross-sectional view showing a structure of a single-layer electrophotographic photosensitive member according to the embodiment of the present disclosure. 
         FIG. 2B  is a schematic cross-sectional view showing another structure of the single-layer electrophotographic photosensitive member according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the accompanying drawings, the following describes an electrophotographic photosensitive member according to an embodiment of the present disclosure. However, the present disclosure is not limited to the embodiment described below. 
     The electrophotographic photosensitive member of the present embodiment includes a conductive substrate and a photosensitive layer. The photosensitive layer is disposed over the conductive substrate. The electrophotographic photosensitive member may be either a multi-layer type or a single-layer type. The photosensitive layer contains a triarylamine derivative represented by General Formula (1). 
     With reference to  FIGS. 1A to 1C and 2A and 2B , the following describes in detail a multi-layer electrophotographic photosensitive member  10  and a single-layer electrophotographic photosensitive member  20  according to the present embodiment. 
     1. Multi-Layer Electrophotographic Photosensitive Member  10   
       FIGS. 1A to 1C  are schematic cross-sectional views showing different structures of the multi-layer electrophotographic photosensitive member  10  of the present embodiment. 
     (1) Basic Structure 
     As shown in  FIG. 1A , the multi-layer electrophotographic photosensitive member  10  includes a conductive substrate  11  and a photosensitive layer  12 . The photosensitive layer  12  is a multi-layer photosensitive layer that includes a charge generating layer  13  and a charge transport layer  14 . 
     The multi-layer electrophotographic photosensitive member  10  may be fabricated by forming the charge generating layer  13  on the conductive substrate  11 , and the charge transport layer  14  on the charge generating layer  13  by for example applying. The charge generating layer  13  contains a charge generating material. The charge transport layer  14  contains a charge transport material. 
     As shown in  FIG. 1B , the multi-layer electrophotographic photosensitive member  10  may have the charge transport layer  14  on the conductive substrate  11 , and the charge generating layer  13  on the charge transport layer  14 . Typically, in the multi-layer electrophotographic photosensitive member  10  shown in  FIG. 1B , the charge generating layer  13  is thinner than the charge transport layer  14 . Therefore, the charge generating layer  13  may wear or rupture over a prolonged use. In view of this, the multi-layer electrophotographic photosensitive member  10  preferably have the charge transport layer  14  on the charge generating layer  13  as shown in  FIG. 1A . 
     Preferably, in addition, an intermediate layer  15  may be provided between the conductive substrate  11  and the photosensitive layer  12  as shown in  FIG. 1C . 
     It is generally preferable that the charge transport layer  14  should be composed exclusively of a hole transport material. Yet, the charge transport layer  14  may contain both a hole transport material and an electron transport material. 
     (2) Conductive Substrate  11   
     The conductive substrate  11  may be formed from any of various conductive materials. Examples of the conductive substrate  11  include a conductive substrate formed from a metal (iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, or brass), a conductive substrate made from a plastic material on which any of the metals mentioned above is deposited or laminated, and a conductive glass substrate coated with aluminum iodide, anodized aluminum, tin oxide, or indium oxide. 
     That is, it is sufficient as long as the entire conductive substrate  11  is conductive or at least the surface of the conductive substrate  11  is conductive. In addition, the conductive substrate  11  preferably has a sufficient mechanical strength for use. 
     The conductive substrate  11  may be provided in the form of a sheet or a drum, depending on the structure of an image forming apparatus in which the conductive substrate  11  is to be used. 
     (3) Intermediate Layer  15   
     The multi-layer electrophotographic photosensitive member  10  may be provided with the intermediate layer  15  containing a predetermined resin and disposed on the conductive substrate  11  as shown in  FIG. 1C . 
     With the provision of the intermediate layer  15 , the multi-layer electrophotographic photosensitive member  10  can achieve an improved adhesion between the conductive substrate  11  and the photosensitive layer  12 . The intermediate layer  15  may contain a predetermined fine powder for scattering incident light. This can suppress occurrence of interference fringes. The presence of fine powder is also effective to suppress charge injection from the conductive substrate  11  to the photosensitive layer  12  during non-light exposure. Note that charge injection may cause fogging or black spots. The fine powder contained in the intermediate layer  15  is not particularly limited as long as the light-scattering and dispersibility are ensured. Examples of the fine powder include: white pigments (titanium oxide, zinc oxide, hydrozincite, zinc sulfide, white lead, and lithopone); inorganic pigments as extender (alumina, calcium carbonate, and barium sulphate); fluororesin particles; benzoguanamine resin particles; and styrene resin particles. The thickness of the intermediate layer  15  is preferably 0.1 μm or more and 50 μm or less. The provision of the intermediate layer  15  can further suppress charge injection from the conductive substrate  11  and thus prevents occurrence of local insulation breakdown. 
     (4) Charge Generating Layer  13   
     The charge generating material contained in the charge generating layer  13  of the multi-layer electrophotographic photosensitive member  10  is preferably one or more selected from the group consisting of metal-free phthalocyanine (t-type or X-type), titanyl phthalocyanine (α-type or Y-type), hydroxygallium phthalocyanine (V-type), and chlorogallium phthalocyanine (II-type). 
     Alternatively, the charge generating material contained in the charge generating layer  13  may be titanyl phthalocyanine having, from among CuKα characteristic X-ray (wavelength 1.542 Å) diffraction peaks at Bragg angles (2θ±0.2°), a maximum diffraction peak at least at 27.2°. The titanyl phthalocyanine may have in differential scanning calorimetry a single peak within a range of 270° C. to 400° C., in addition to the peaks resulting from evaporation of the absorbed water. Such titanyl phthalocyanine is effective to suppress the crystal form transition of the titanyl phthalocyanine from Y to α or from Y to β in an organic solvent contained in the application liquid for the photosensitive member and thus to improve the charge generating efficiency. 
     The content of the charge generating material is preferably 5 parts by mass or more and 1,000 parts by mass or less with respect to 100 parts by mass of the resin (base resin) contained in the charge generating layer  13 . Examples of the base resin usable for the charge generating layer  13  include polycarbonate resins, polyester resins, methacryl resins, acrylic resins, polyvinyl chloride resins, polystyrene resins, polyvinyl acetate resins, styrene-butadiene copolymer resins, vinylidene chloride-acrylonitrile copolymer resins, polyvinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, phenol-formaldehyde resins, styrene-alkyd resins, and N-vinylcarbazole resins. These resins described above may be used alone, or two or more of the resins may be used in combination. The thickness of the charge generating layer  13  is preferably 0.1 μm or more and 5 μm or less. 
     (5) Charge Transport Layer  14   
     The hole transport material contained in the charge transport layer  14  is a triarylamine derivative represented by General Formula (1). 
     
       
         
         
             
             
         
       
     
     In General Formula (1): Ar 1  represents an aryl group substituted with at least one substituent selected from the group consisting of an alkoxy group having 2 to 4 carbon atoms and an optionally substituted phenoxy group; and Ar 2  represents an aryl group optionally substituted with an alkyl group having 1 to 4 carbon atoms. The triarylamine derivative represented by General Formula (1) used as the hole transport material has an arylamine group substituted with an alkoxy group having a predetermined number of carbon atoms or a phenoxy group. This favorably affects the electrical characteristics (in particular, for suppressing the residual potential) and suppresses crystallization. 
     The following is assumed to be the reason that the presence of the triarylamine derivative represented by General Formula (1) achieves the advantageous effect described above. 
     First of all, the triarylamine derivative represented by General Formula (1) has an arylamine group substituted with an alkoxy group having the predetermined number of carbon atoms or a phenoxy group. This can improve the solubility of the triarylamine derivative in a solvent. The improved solubility can contribute to effective suppression of crystallization or insufficient dispersion of the triarylamine derivative in the photosensitive layer during the formation of the photosensitive layer. 
     In addition, since the triarylamine derivative represented by General Formula (1) has an arylamine group substituted with an alkoxy group having the predetermined number of carbon atoms or a phenoxy group, the ionization potential can be reduced. This reduces the energy gap for charge transfer between the triarylamine derivative represented by General Formula (1) and the charge generating material (or another material). Consequently, the charge transport efficiency can be effectively improved. The use of the triarylamine derivative represented by General Formula (1) as the hole transport material contained in the charge transport layer is particularly effective for the multi-layer electrophotographic photosensitive member that includes the charge generating layer and the charge transport layer because migration of charges across the interface between the charge generating layer and the charge transport layer is effectively promoted. By the presence of an alkoxy group having the predetermined number of carbon atoms or a phenoxy group in an arylamine group, the triarylamine derivative represented by General Formula (1) can exhibit excellent electrical characteristics as the electrophotographic photosensitive member. 
     The content of the triarylamine derivative represented by General Formula (1) is preferably 30 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the resin (binder resin) contained in the charge transport layer  14 . The content of the triarylamine derivative represented by General Formula (1) within the range of 30 parts by mass to 100 parts by mass is preferred for further improving its dispersibility in the charge transport layer to achieve even more favorable electrical sensitivity. With the content less than 30 parts by mass, the triarylamine derivative represented by General Formula (1) falls short in its absolute quantity, which may result in insufficient electrical sensitivity. With the content exceeding 100 parts by mass, on the other hand, the triarylamine derivative represented by General Formula (1) may suffer from reduced dispersibility in the charge transport layer, which often causes crystallization. As a result, the charge transport efficiency may be reduced. 
     The content of the triarylamine derivative represented by General Formula (1) is more preferably 35 parts by mass or more and 95 parts by mass or less with respect to 100 parts by mass of the binder resin contained in the charge transport layer, and further more preferably 40 parts by mass or more and 90 parts by mass or less. 
     The following lists specific examples of the triarylamine derivative represented by General Formula (1), namely “HTM-1” to “HTM-9” respectively represented by Formulas (1-1) to (1-9). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The charge transport layer  14  may contain an additional hole transport material other than the triarylamine derivative represented by General Formula (1). The presence of the additional hole transport material serve to increase the total content of the hole transport materials without causing crystallization. 
     Examples of such an additional hole transport material include a nitrogen containing cyclic compound and a condensed polycyclic compound. Examples of the nitrogen containing cyclic compound and the condensed polycyclic compound include triarylamine-based compounds (excluding the triarylamine derivative represented by General Formula (1)), oxadiazole-based compounds (2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole), styryl-based compounds (9-(4-diethylaminostyryl)anthracene), carbazole-based compounds (polyvinyl carbazole), organic polysilane compounds, pyrazoline-based compounds (1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), hydrazine-based compounds, indole-based compounds, oxazole-based compounds, isoxazole-based compounds, thiazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, pyrazole-based compounds, and triazole-based compounds. These additional hole transport materials may be used alone, or two or more of the hole transport materials may be used in combination. 
     When an additional hole transport material is contained besides the triarylamine derivative represented by General Formula (1), the content of the additional hole transport material is preferably within the range of 1 part by mass to 100 parts by mass with respect to 100 parts by mass of the triarylamine derivative represented by General Formula (1). 
     The charge transport layer  14  may contain an electron transport material. Examples of the electron transport material include quinone derivatives, anthraquinone derivatives, malononitrile derivatives, thiopyran derivatives, trinitrothioxanthone derivatives, 3,4,5,7-tetranitro-9-fluorenone derivatives, dinitroanthracene derivatives, dinitroacridine derivatives, nitroanthraquinone derivatives, dinitroanthraquinone derivatives, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. The electron transport materials may be used alone, or two or more of the electron transport materials may be used in combination. 
     When the charge transport layer  14  contains the electron transport material described above, the content of the electron transport material is preferably within the range of 1 part by mass to 50 parts by mass with respect to 100 parts by mass of the triarylamine derivative represented by General Formula (1). 
     In the electrophotographic photosensitive member  10  according to the present embodiment, the charge transport layer  14  contains a plasticizer. The plasticizer contains at least one of a compound represented by General Formula (2a) and a compound represented by General Formula (2b). 
     
       
         
         
             
             
         
       
     
     In General Formula (2a), R 1  to R 10  each independently represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 12 carob atoms, a hydroxyl group, a cyano group, a nitro group, a trimethylsilyl group, or an amino group. Alternatively, R 1  and R 6  are optionally bonded to each other to form an alkyl ring having 5 to 6 carbon atoms or a benzene ring. 
     
       
         
         
             
             
         
       
     
     In General Formula (2b), R 11  to R 18  each independently represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 12 carbon atoms, a hydroxyl group, a cyano group, a nitro group, or an amino group. In addition, R represents a single bond, —O— or —CH═CH—. 
     The following lists specific examples of the compound represented by General Formula (2a), namely “ADD-1” to “ADD-8” respectively represented by Formulas (2a-1) to (2a-8). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The following lists specific examples of the compound represented by General Formula (2b), namely “ADD-9” to “ADD-11” respectively represented by Formulas (2b-1) to (2b-3). 
     
       
         
         
             
             
         
       
     
     In the case where R 1  and R 6  in General Formula (2a) are optionally bonded to each other to form an alkyl ring, a carbon atom in the alkyl ring may be substituted with an alkyl group as shown in General Formula (2a-11). 
     
       
         
         
             
             
         
       
     
     In General Formula (2a-11), R 19  and R 20  each independently represent an alkyl group having 1 to 3 carbon atoms. 
     Specific examples of the compound represented by General Formula (2a-11) include a compound represented by Formula (2a-10). 
     
       
         
         
             
             
         
       
     
     The binder resin used for the charge transport layer  14  preferably contains at least one of a polycarbonate resin having a skeleton represented by General Formula (3a) and a polycarbonate resin having a skeleton represented by General Formula (3b). 
     
       
         
         
             
             
         
       
     
     In General Formula (3a), R 1  represents a methyl group or a hydrogen atom. 
     
       
         
         
             
             
         
       
     
     In General Formula (3b), R 2  represents a methyl group or a hydrogen atom. 
     The following lists specific examples of the polycarbonate resin represented by General Formula (3a) or (3b), namely “Resin-1”, “Resin-2”, and “Resin-3” respectively represented by Formulas (3a-1), (3a-2), and (3b-1). 
     
       
         
         
             
             
         
       
     
     Alternatively, the binder resin used for the charge transport layer  14  preferably contains at least one of a polyarylate resin having a skeleton represented by General Formula (3c) and a polyarylate resin having a skeleton represented by General Formula (3d). 
     
       
         
         
             
             
         
       
     
     In General Formulas (3c) and (3d), R 3  represents a methyl group or a hydrogen atom. In addition, R 4  and R 5  each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. In addition, p+q=1 and 0.1≦p≦0.9 are both satisfied. 
     The following is a specific example of the polyarylate resin represented by General Formula (3c), namely “Resin-4” represented by Formula (3c-1). 
     
       
         
         
             
             
         
       
     
     In addition, the charge transport layer  14  may contain an additional binder resin. Examples of such an additional binder resin include thermoplastic resins (for example, polycarbonate resins other than those described above, polyester resins, polyarylate resins, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, acrylic copolymers, styrene-acrylic acid copolymers, polyethylene, ethylene-vinyl acetate copolymers, chlorinated polyethylene, polyvinyl chloride, polypropylene, ionomer, vinyl chloride-vinyl acetate copolymers, alkyd resins, polyamide, polyurethane, polysulfone, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, and polyether resins), thermosetting resins (for example, silicone resins, epoxy resins, phenolic resins, urea resins, and melamine resins), and photocurable resins (for example, epoxy acrylate, and urethane-acrylate). These additional binder resins may be used alone, or two or more of the binder resins may be used by mixing or copolymerization. The thickness of the charge transport layer  14  is preferably within a range of 5 μm to 50 μm or less. 
     The charge transport layer  14  may contain an electron transport material in addition to the hole transport material. Examples of the electron transport material include quinone derivatives, anthraquinone derivatives, malononitrile derivatives, thiopyran derivatives, trinitrothioxanthone derivatives, 3,4,5,7-tetranitro-9-fluorenone derivatives, dinitroanthracene derivatives, dinitroacridine derivatives, nitroanthraquinone derivatives, dinitroanthraquinone derivatives, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. The electron transport materials may be used alone, or two or more of the electron transport materials may be used in combination. When the charge transport layer  14  contains the electron transport material described above, the content of the electron transport material is preferably within the range of 1 part by mass to 50 parts by mass with respect to 100 parts by mass of the triarylamine derivative represented by General Formula (1). 
     [Method for Manufacturing Multi-Layer Electrophotographic Photosensitive Member  10 ] 
     The multi-layer electrophotographic photosensitive member  10  may be manufactured through the following procedures, for example. First, an application liquid for forming a charge generating layer is prepared mixing in a solvent the charge generating material, the base resin, and one or more additives as needed. The resultant application liquid is applied to a conductive substrate (aluminum element tube) by dip coating, spray coating, bead coating, blade coating, or roller coating, for example. Thereafter, the application liquid is subjected to hot-air drying at 100° C. for 40 minutes, for example. As a result, the charge generating layer  13  having a predetermined thickness is formed. 
     The solvent used for preparing the application liquid can be selected from various organic solvents. Examples of the solvent include alcohols (such as methanol, ethanol, isopropanol, and butanol), aliphatic hydrocarbons (such as n-hexane, octane, and cyclohexane), aromatic hydrocarbons (such as benzene, toluene, and xylene), halogenated hydrocarbons (such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, and chlorobenzene), ethers (such as dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, and 1,4-dioxane), ketones (such as acetone, methyl ethyl ketone, and cyclohexane), esters (such as ethyl acetate, and methyl acetate), dimethyl formaldehyde, dimethyl formamide, and dimethyl sulfoxide. These solvents may be used alone, or two or more of the solvents may be used by mixing. 
     Next, an application liquid for forming a charge transport layer is prepared by dispersing, in the solvent described above, the triarylamine derivative represented by General Formula (1), the binder resin described above, and one or more additives as needed. Thereafter, the resultant application liquid is applied to the charge generating layer  13  having been formed, followed by drying. The method for preparing, applying, and drying the application liquid may be the same as that employed for forming the charge generating layer  13 . 
     Note that the electrophotographic photosensitive member according to the present disclosure is preferably the multi-layer electrophotographic photosensitive member  10  for the following reason. When the electrophotographic photosensitive member according to the present disclosure is the multi-layer electrophotographic photosensitive member  10 , the triarylamine derivative represented by General Formula (1) used as the hole transport material can effectively exhibit its excellent electrical characteristics. In the case of a multi-layer electrophotographic photosensitive member, charges need to be transferred across the interface between the charge generating layer and the charge transport layer, which may decrease the charge transport efficiency. Yet, the present disclosure involves the use of the triarylamine derivative represented by General Formula (1) as the hole transport material. This serves to lower the ionization potential such that charges can stably migrate across the interface between these layers. 
     2. Single-Layer Electrophotographic Photosensitive Member  20   
     The electrophotographic photosensitive member according to the present disclosure may be the single-layer electrophotographic photosensitive member  20 . 
     For example, the single-layer electrophotographic photosensitive member  20  according to the present disclosure includes a conductive substrate  21  and a photosensitive layer  22  composed of a single layer as shown in  FIG. 2A . The photosensitive layer  22  is disposed over the conductive substrate  21 . 
     The single-layer electrophotographic photosensitive member  20  may be additionally provided with an intermediate layer  23  between the conductive substrate  21  and the photosensitive layer  22  as shown in  FIG. 2B , on condition that the characteristics of the photosensitive member are not inhibited. 
     The conductive substrate and the organic material usable for the single-layer electrophotographic photosensitive member  20  may be the same as those described above for the multi-layer electrophotographic photosensitive member  10 . The content of the triarylamine derivative represented by General Formula (1) is preferably 20 parts by mass or more and 120 parts by mass or less with respect to 100 parts by mass of the binder resin contained in the photosensitive layer  22 . In the single-layer electrophotographic photosensitive member  20 , in addition, the photosensitive layer  22  contains the hole transport material and the electron transport material. The content of the electron transport material is preferably 10 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the binder resin contained in the photosensitive layer  22 . The content of the charge generating material is preferably 0.2 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the binder resin contained in the photosensitive layer  22 . The thickness of the photosensitive layer  22  is preferably 5 μm or more and 100 μm or less. 
     EXAMPLES 
     The following describes Examples of the present disclosure. The present disclosure is not limited to the scope of Examples below. 
     Example 1 
     1. Manufacture of Electrophotographic Photosensitive Member 
     (1) Forming Intermediate Layer 
     First, a surface-treated titanium oxide (“SMT-A” manufactured by TAYCA CORPORATION, number-average primary particle diameter: 10 nm) was prepared. More specifically, a titanium oxide was subjected to a surface treatment with alumina and silica by using a bead mill, followed by another surface treatment using methyl hydrogen polysiloxane during wet dispersion. Then, 2 parts by mass of the resultant titanium oxide and 1 part by mass of a four-component copolymer polyamide resin of polyamide 6, polyamide 12, polyamide 66, and polyamide 610 (“Amilan (registered trademark) CM8000” manufactured by Toray Industries, Inc.) were put into a solvent containing 10 parts by mass of methanol, 1 part by mass of butanol, and 1 part by mass of toluene, followed by mixing for 5 hours to disperse these materials. The resultant mixture was filtered by using a 5-μm filter to prepare an application liquid for forming an intermediate layer. 
     Next, into the application liquid prepared in the above manner, an aluminum conductive substrate (support substrate) having the shape of a drum (diameter: 30 mm and length: 246 mm) was dipped at a rate of 5 mm/sec with one end thereof held up. As a result, the application liquid was applied to the surface of the aluminum conductive substrate. Then, the application liquid was hardened at 130° C. for 30 minutes to form a 2-μm-thick intermediate layer. 
     (2) Forming Charge Generating Layer 
     Next, with the use of a bead mill, the following were mixed and dispersed for 2 hours: 1.5 parts by mass of the titanyl phthalocyanine represented by Formula (4) as a charge generating material (CGM-1); 1 part by mass of a polyvinyl acetal resin (“S-LEC (registered trademark) BX-5” manufactured by Sekisui Chemical Co., Ltd.) as a binder resin; and a mixture solvent of 40 parts by mass of propylene glycol monomethyl ether and 40 parts by mass of tetrahydrofuran. As a result, an application liquid for forming a charge generating layer was prepared. The resultant application liquid was filtered by using a 3-μm filter. Thereafter, the filtered application liquid was applied by dip coating to the intermediate layer formed in the above-described manner, followed by drying for 5 minutes at 50° C. Through the above procedures, a 0.3-μm-thick charge generating layer was formed. 
                         
(3) Forming Charge Transport Layer
 
     An ultrasonic disperser was charged with 45 parts by mass of the triarylamine derivative represented by Formula (1-1) as a hole transport material (HTM-1), 0.5 parts by mass of IRGANOX 1010 as an additive, 2 parts by mass of the electron transport material represented by Formula (5) (ETM-1), 10 parts by mass of a plasticizer represented by Formula (2a-1) (ADD-1), 100 parts by mass of a polycarbonate resin represented by Formula (3a-1) as a binder resin (Resin-1, viscosity average molecular weight: 50,500), and a mixture solvent of 350 parts by mass of tetrahydrofuran and 350 parts by mass of toluene, followed by mixing. Thereafter, the mixture was dispersed for 10 minutes to prepare an application liquid for forming a charge transport layer. 
     
       
         
         
             
             
         
       
     
     The resultant application liquid was applied to the charge generating layer in the same manner as the application liquid for forming a charge generating layer, followed by drying at 120° C. for 40 minutes. Through the above procedures, a 20-μm-thick charge generating layer was formed to complete the electrophotographic photosensitive member. 
     2. Evaluations 
     (1) Evaluations of Electrophotographic Photosensitive Members 
     &lt;Evaluations of Electrical Characteristics&gt; 
     With the use of an electrical characteristics tester (manufactured by Gentec Inc.), each electrophotographic photosensitive member was measured for its charge ability (surface potential V 0 ) and sensitivity (potential V L  upon expiry of 50 msec started immediately after the exposure) in the environment of 10° C. and 20% RH under the following conditions. 
     &lt;Conditions for Charge Ability Measurement&gt; 
     Rotational speed: 31 rpm 
     Electric current flowing into drum: −10 μA 
     &lt;Conditions for Sensitivity Measurement&gt; 
     Charge amount: 600 V 
     Wavelength of light exposure: 780 nm 
     Amount of light exposure: 0.26 μJ/cm 2    
     Table 1 shows the evaluation results. 
     &lt;Evaluations of Crystallization&gt; 
     Each electrophotographic photosensitive member prepared was evaluated for occurrence of crystallization at the surface. 
     More specifically, the surface of each electrophotographic photosensitive member was observed under an optical microscope for the presence of crystallization. Table 1 shows the evaluation results. In Table 1, “Good” indicates that no crystallization was observed. 
     &lt;Evaluation of Oil Resistance&gt; 
     Each electrophotographic photosensitive member was evaluated for its oil resistance in the following manner. A human hand was used to apply a sufficient amount of oil components to the entire surface of the electrophotographic photosensitive member. The resultant electrophotographic photosensitive member was then allowed to stand for 48 hours. Thereafter, the electrophotographic photosensitive member was mounted to a printer (“C711dn” manufactured by Oki Data Corporation) and a gray image was formed by the printer. The resultant image was visually observed for the presence of any image defect resulting from a crack and evaluated according to the following criteria. Table 1 shows the evaluation results. 
     (Very Good): The number of cracks observed in an image region corresponding to one drum rotation is 0. 
     (Good): The number of cracks observed in an image region corresponding to one drum rotation is 1 or more and 10 or less. 
     (Acceptable): The number of cracks observed in an image region corresponding to one drum rotation is 11 or more and 20 or less. 
     (Poor): The number of cracks observed in an image region corresponding to one drum rotation is 21 or more. 
     Example 2 
     An electrophotographic photosensitive member of Example 2 was prepared and evaluated in the same manner as Example 1, except that HTM-2 represented by Formula (1-2) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 3 
     An electrophotographic photosensitive member of Example 3 was prepared and evaluated in the same manner as Example 1, except that HTM-3 represented by Formula (1-3) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 4 
     An electrophotographic photosensitive member of Example 4 was prepared and evaluated in the same manner as Example 1, except that HTM-4 represented by Formula (1-4) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 5 
     An electrophotographic photosensitive member of Example 5 was prepared and evaluated in the same manner as Example 1, except that HTM-5 represented by Formula (1-5) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 6 
     An electrophotographic photosensitive member of Example 6 was prepared and evaluated in the same manner as Example 1, except that HTM-6 represented by Formula (1-6) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 7 
     An electrophotographic photosensitive member of Example 7 was prepared and evaluated in the same manner as Example 1, except that HTM-7 represented by Formula (1-7) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 8 
     An electrophotographic photosensitive member of Example 8 was prepared and evaluated in the same manner as Example 1, except that HTM-8 represented by Formula (1-8) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 9 
     An electrophotographic photosensitive member of Example 9 was prepared and evaluated in the same manner as Example 1, except that HTM-9 represented by Formula (1-9) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 10 
     An electrophotographic photosensitive member of Example 10 was prepared and evaluated in the same manner as Example 4, except that Resin-2 (viscosity average molecular weight: 50,500) represented by Formula (3a-2) was used as the binder resin instead of Resin-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 11 
     An electrophotographic photosensitive member of Example 11 was prepared and evaluated in the same manner as Example 4, except that Resin-3 (viscosity average molecular weight: 50,500) represented by Formula (3b-1) was used as the binder resin instead of Resin-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 12 
     An electrophotographic photosensitive member of Example 12 was prepared and evaluated in the same manner as Example 4, except that Resin-4 (viscosity average molecular weight: 50,500) represented by Formula (3c-1) was used as the binder resin instead of Resin-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 13 
     An electrophotographic photosensitive member of Example 13 was prepared and evaluated in the same manner as Example 4, except that ADD-2 represented by Formula (2a-2) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 14 
     An electrophotographic photosensitive member of Example 14 was prepared and evaluated in the same manner as Example 4, except that ADD-3 represented by Formula (2a-3) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 15 
     An electrophotographic photosensitive member of Example 15 was prepared and evaluated in the same manner as Example 4, except that ADD-4 represented by Formula (2a-4) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 16 
     An electrophotographic photosensitive member of Example 16 was prepared and evaluated in the same manner as Example 4, except that ADD-5 represented by Formula (2a-5) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 17 
     An electrophotographic photosensitive member of Example 17 was prepared and evaluated in the same manner as Example 4, except that ADD-6 represented by Formula (2a-6) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 18 
     An electrophotographic photosensitive member of Example 18 was prepared and evaluated in the same manner as Example 4, except that ADD-7 represented by Formula (2a-7) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 19 
     An electrophotographic photosensitive member of Example 19 was prepared and evaluated in the same manner as Example 4, except that ADD-8 represented by Formula (2a-8) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 20 
     An electrophotographic photosensitive member of Example 20 was prepared and evaluated in the same manner as Example 4, except that ADD-9 represented by Formula (2b-1) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 21 
     An electrophotographic photosensitive member of Example 21 was prepared and evaluated in the same manner as Example 4, except that ADD-10 represented by Formula (2b-2) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 22 
     An electrophotographic photosensitive member of Example 22 was prepared and evaluated in the same manner as Example 4, except that ADD-11 represented by Formula (2b-3) was used as the plasticizer instead of ADD-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Example 23 
     An electrophotographic photosensitive member of Example 23 was prepared and evaluated in the same manner as Example 1, except that the content of the plasticizer was changed to 20 parts by mass. Table 1 shows the evaluation results. 
     Example 24 
     An electrophotographic photosensitive member of Example 24 was prepared and evaluated in the same manner as Example 1, except that the content of the plasticizer was changed to 30 parts by mass. Table 1 shows the evaluation results. 
     Comparative Example 1 
     An electrophotographic photosensitive member of Comparative Example 1 was prepared and evaluated in the same manner as Example 1, except that HTM-10 represented by Formula (11-1) was used as the hole transport material instead of HTM-1. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Comparative Example 2 
     An electrophotographic photosensitive member of Comparative Example 2 was prepared and evaluated in the same manner as Comparative Example 1, except that HTM-11 represented by Formula (11-2) was used as the hole transport material instead of HTM-10. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Comparative Example 3 
     An electrophotographic photosensitive member of Comparative Example 3 was prepared and evaluated in the same manner as Comparative Example 1, except that HTM-12 represented by Formula (11-3) was used as the hole transport material instead of HTM-10. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Comparative Example 4 
     An electrophotographic photosensitive member of Comparative Example 4 was prepared and evaluated in the same manner as Comparative Example 1, except that HTM-13 represented by Formula (11-4) was used as the hole transport material instead of HTM-10. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Comparative Example 5 
     An electrophotographic photosensitive member of Comparative Example 5 was prepared and evaluated in the same manner as Comparative Example 1, except that HTM-14 represented by Formula (11-5) was used as the hole transport material, instead of HTM-10. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Comparative Example 6 
     An electrophotographic photosensitive member of Comparative Example 6 was prepared and evaluated in the same manner as Comparative Example 1, except that HTM-15 represented by Formula (11-6) was used as the hole transport material instead of HTM-10. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Comparative Example 7 
     An electrophotographic photosensitive member of Comparative Example 7 was prepared and evaluated in the same manner as Comparative Example 1, except that HTM-16 represented by Formula (11-7) was used as the hole transport material instead of HTM-10. Table 1 shows the evaluation results. 
     
       
         
         
             
             
         
       
     
     Comparative Example 8 
     An electrophotographic photosensitive member of Comparative Example 8 was prepared and evaluated in the same manner as Example 1, except that no plasticizer was added. Table 1 shows the evaluation results. 
     Comparative Example 9 
     An electrophotographic photosensitive member of Comparative Example 9 was prepared and evaluated in the same manner as Comparative Example 5, except that no plasticizer was added. Table 1 shows the evaluation results. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                   
                 Electrical 
                   
                   
               
               
                   
                 CTL 
                 characteristics 
                 Appearance 
                 Oil resistance 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 HTM 
                 Resin 
                 ADD 
                 ADD content 
                 Vo/V 
                 V L /V 
                 of drum 
                 evaluations 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 HTM-1 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 694 
                 57 
                 Good 
                 Very good 
               
               
                 Example 2 
                 HTM-2 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 671 
                 60 
                 Good 
                 Very good 
               
               
                 Example 3 
                 HTM-3 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 699 
                 60 
                 Good 
                 Very good 
               
               
                 Example 4 
                 HTM-4 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 689 
                 58 
                 Good 
                 Very good 
               
               
                 Example 5 
                 HTM-5 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 701 
                 55 
                 Good 
                 Very good 
               
               
                 Example 6 
                 HTM-6 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 702 
                 65 
                 Good 
                 Very good 
               
               
                 Example 7 
                 HTM-7 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 707 
                 67 
                 Good 
                 Very good 
               
               
                 Example 8 
                 HTM-8 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 721 
                 58 
                 Good 
                 Very good 
               
               
                 Example 9 
                 HTM-9 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 696 
                 55 
                 Good 
                 Very good 
               
               
                 Example 10 
                 HTM-4 
                 Resin-2 
                 ADD-1 
                 10 parts 
                 702 
                 65 
                 Good 
                 Very good 
               
               
                 Example 11 
                 HTM-4 
                 Resin-3 
                 ADD-1 
                 10 parts 
                 700 
                 66 
                 Good 
                 Very good 
               
               
                 Example 12 
                 HTM-4 
                 Resin-4 
                 ADD-1 
                 10 parts 
                 701 
                 80 
                 Good 
                 Very good 
               
               
                 Example 13 
                 HTM-4 
                 Resin-1 
                 ADD-2 
                 10 parts 
                 698 
                 65 
                 Good 
                 Very good 
               
               
                 Example 14 
                 HTM-4 
                 Resin-1 
                 ADD-3 
                 10 parts 
                 678 
                 58 
                 Good 
                 Very good 
               
               
                 Example 15 
                 HTM-4 
                 Resin-1 
                 ADD-4 
                 10 parts 
                 702 
                 62 
                 Good 
                 Good 
               
               
                 Example 16 
                 HTM-4 
                 Resin-1 
                 ADD-5 
                 10 parts 
                 693 
                 65 
                 Good 
                 Good 
               
               
                 Example 17 
                 HTM-4 
                 Resin-1 
                 ADD-6 
                 10 parts 
                 693 
                 68 
                 Good 
                 Good 
               
               
                 Example 18 
                 HTM-4 
                 Resin-1 
                 ADD-7 
                 10 parts 
                 689 
                 64 
                 Good 
                 Very good 
               
               
                 Example 19 
                 HTM-4 
                 Resin-1 
                 ADD-8 
                 10 parts 
                 701 
                 63 
                 Good 
                 Very good 
               
               
                 Example 20 
                 HTM-4 
                 Resin-1 
                 ADD-9 
                 10 parts 
                 682 
                 66 
                 Good 
                 Very good 
               
               
                 Example 21 
                 HTM-4 
                 Resin-1 
                 ADD-10 
                 10 parts 
                 687 
                 64 
                 Good 
                 Good 
               
               
                 Example 22 
                 HTM-4 
                 Resin-1 
                 ADD-11 
                 10 parts 
                 692 
                 63 
                 Good 
                 Good 
               
               
                 Example 23 
                 HTM-1 
                 Resin-1 
                 ADD-1 
                 20 parts 
                 710 
                 57 
                 Good 
                 Very good 
               
               
                 Example 24 
                 HTM-1 
                 Resin-1 
                 ADD-1 
                 30 parts 
                 702 
                 58 
                 Good 
                 Very good 
               
               
                 Comparative 
                 HTM-10 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 703 
                 232 
                 Crystalized 
                 — 
               
               
                 example 1 
               
               
                 Comparative 
                 HTM-11 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 680 
                 211 
                 Crystalized 
                 — 
               
               
                 example 2 
               
               
                 Comparative 
                 HTM-12 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 693 
                 254 
                 Crystalized 
                 — 
               
               
                 example 3 
               
               
                 Comparative 
                 HTM-13 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 690 
                 75 
                 Good 
                 Acceptable 
               
               
                 example 4 
               
               
                 Comparative 
                 HTM-14 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 685 
                 73 
                 Good 
                 Acceptable 
               
               
                 example 5 
               
               
                 Comparative 
                 HTM-15 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 693 
                 279 
                 Heavily 
                 — 
               
               
                 example 6 
                   
                   
                   
                   
                   
                   
                 Crystalized 
               
               
                 Comparative 
                 HTM-16 
                 Resin-1 
                 ADD-1 
                 10 parts 
                 699 
                 85 
                 Good 
                 Acceptable 
               
               
                 example 7 
               
               
                 Comparative 
                 HTM-1 
                 Resin-1 
                 None 
                 10 parts 
                 702 
                 57 
                 Good 
                 Acceptable 
               
               
                 example 8 
               
               
                 Comparative 
                 HTM-14 
                 Resin-1 
                 None 
                 10 parts 
                 710 
                 69 
                 Good 
                 Poor 
               
               
                 example 9 
               
               
                   
               
            
           
         
       
     
     The respective electrophotographic photosensitive members of Examples according to the present disclosure all contained a predetermined triarylamine derivative as the hole transport material in addition to a predetermined plasticizer. As the results shown in Table 1 clarify, each electrophotographic photosensitive member according to the present disclosure achieved to suppress crystallization and exhibited excellent charge generating efficiency, excellent electrical characteristics, and improved oil resistance.