JP3289050B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic photoreceptor, an electrophotographic photoreceptor using an inorganic photoconductor such as selenium, cadmium sulfide or zinc oxide is known. Recently, an organic photoconductor using an organic photoconductor such as poly-N-vinylcarbazole or polyvinylanthracene has been developed in place of the inorganic photoconductor. Electrophotographic photoreceptors using an organic photoconductor include a single-layer type in which a photosensitive layer in which a charge generating substance and a charge transporting substance are dispersed in a binder resin is provided on a conductive support; There is a function-separated type in which a charge generation layer in which a charge generation material is dispersed in a binder resin and a charge transport layer in which a charge transport material is dispersed in a binder resin are laminated thereon.

As the single-layer type electrophotographic photoreceptor, JP-A-61-7840, JP-A-61-48861, and JP-A-61-48861 have been disclosed.
However, all of them have a high binder resin concentration at a carrier generation site (a region that almost absorbs exposure for potential decay) and have a low carrier generation efficiency. A high-sensitivity photoreceptor has not yet been obtained.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic photosensitive member having extremely high sensitivity and a small residual potential.

[0005]

According to the present invention, in an electrophotographic photosensitive member having a photosensitive layer containing at least a charge generating substance and a charge transporting substance on a conductive support, the photosensitive layer is A photosensitive layer in which at least two or more layers are laminated, and wherein the concentration of the charge generating substance with respect to the binder resin in each layer of the photosensitive layer is closer to the farthest away from the exposure incident side for forming an image. And an electrophotographic photosensitive member having, on a conductive support, a photosensitive layer containing at least both a charge generating substance and a charge transporting substance At
The photosensitive layer is a single layer, and a binder tree in the photosensitive layer
An electrophotographic photoreceptor characterized in that the charge generation substance concentration with respect to fat is continuously increased from the farthest side of the exposure incidence side for forming an image toward the side closer thereto, and Of the photosensitive layers in the electrophotographic photosensitive member,
Total solid content of the part closest to the exposure entrance side for image formation
An electrophotographic photoreceptor characterized by having a binder resin concentration of 40% by weight or less with respect to

In an organic electrophotographic photoreceptor, high sensitivity is an important point. In order to increase the sensitivity of the photoreceptor, two methods of increasing the quantum efficiency or increasing the mobility are conceivable. The present inventors have focused on the former, and have studied repeatedly. As a result, it has been clarified that in the carrier generation process of the organic electrophotographic photoreceptor, the initial stage of the carrier generation is caused by an electron transfer reaction between the charge generation material and the charge transport material. That is, it has been found that the contact between the charge generation material and the charge transport material plays an important role in the carrier generation and injection process, and that the carrier generation efficiency increases as the contact amount between the charge generation material and the charge transport material increases. That is, it has been found that one of the conditions for increasing the sensitivity is to make the structure (form) such that the contact amount between the charge generating substance and the charge transporting substance becomes large when the photoreceptor is formed.

In a conventional photoreceptor, a binder resin is contained in the photoreceptor layer in order to improve the adhesiveness of the photoreceptor layer, or to reduce the abrasion of the photoreceptor when repeatedly used. This is common sense and an effective means. On the other hand, according to the study by the present inventors, it has been clarified that the binder resin, which is the above-mentioned effective means, inhibits the contact between the charge generating substance and the charge transporting substance. That is, since the binder resin was present in the charge generation layer, the contact area between the charge generation material and the charge transport material was small, and it was found that the electron transfer reaction was not efficiently performed.

In order to carry out the electron transfer reaction efficiently, it is sufficient that the photosensitive layer does not contain a binder resin. In that case, however, the adhesiveness between the photosensitive layer and the lower layer also deteriorates, or There is still a problem that the fatigue of the photoconductor during repeated use is increased.
Therefore, as a result of studying a method for improving the electron transfer reaction efficiency (to increase the sensitivity) while improving the above problems, as a result of the so-called single-layer type electrophotographic photoreceptor, the photosensitive layer is formed of two or more layers. With the configuration, the charge generation substance concentration in the photosensitive layer is configured to be sequentially increased from the farthest side of the exposure incident side for forming an image toward the closer side, or the photosensitive layer is configured as a single layer, It has been found that the charge generation substance concentration in the photosensitive layer can be achieved by continuously increasing (giving a concentration gradient) from the farthest side of the exposure incidence side to the side closer to the exposure side for forming an image. . Furthermore, they have found that this can be achieved by setting the binder resin concentration at the portion closest to the exposure incidence side for image formation in the photosensitive layer to be 40% by weight or less, and completed the present invention.

Here, the exposure incident side for forming an image will be described. For example, when exposure is performed from the photoconductor surface side as usual, the exposure incidence side for image formation is the front side, and when exposure is performed from the support side, the exposure incidence side for image formation is The side means the support side.

Next, a method for sequentially changing the charge transport substance concentration in the photosensitive layer will be described. 1) Stepwise change method Two or more types of photosensitive layer coating liquids having different charge-generating substance concentrations are successively overcoated. At this time, a coating liquid for a photosensitive layer is used in which the charge generating substance concentration is sequentially higher from the farthest side of the exposure incident side for forming an image to the side closer to it. 2) Method of Continuously Changing Using two or more kinds of coating liquids for photosensitive layers in which the concentration of the charge generating substance is changed, successive coating is performed while the lower layer is wet. Also in this case, a coating solution for a photosensitive layer is used in which the charge sending substance concentration is sequentially higher from the farthest side of the exposure incident side for forming an image to the side closer to the side. In any of the cases 1) and 2), the photosensitive resin binder resin of the photosensitive layer from the farthest side of the exposure incident side for forming an image toward the side closer to the farthest side.
It is important that the charge-generating substance concentration that is higher. In particular, it is important that the binder resin concentration is 40% by weight or less based on the total solid content of the portion closest to the exposure incidence side for image formation. Preferably, the concentration of the charge generating substance is 5% by weight or more, and the concentration of the charge transporting substance is 50% by weight or more. More preferably, the structure of the photosensitive layer closest to the exposure incident side for image formation is Is limited to the charge generating substance and the charge transporting substance.

Here, in the case of a photoreceptor in which the photosensitive layer is the uppermost layer, if the concentration of the charge generating substance in the outermost photosensitive layer is too high, problems such as film shaving in repeated use occur. In this case, a binder resin may be used within a range where there is no problem in electrical characteristics. Alternatively, it is an effective means to make the structure such that the binder resin concentration on the front surface side of the photosensitive layer becomes high and to perform the exposure from the back surface side. Further, providing a protective layer on the photosensitive layer is also an effective means.

Next, the present invention will be described in more detail with reference to the drawings. The figure shows a configuration example in the case of exposing from the photoconductor surface side. FIG. 1 is a cross-sectional view illustrating a configuration example of a photoconductor of the present invention. A photosensitive layer 15 having a multilayer structure is provided on a conductive support 11. FIG. 2 is a cross-sectional view showing another configuration example of the photoreceptor of the present invention. A single-layer photosensitive layer 15 is provided on a conductive support 11. FIG. 3 is a sectional view showing another configuration example of the photoconductor of the present invention, in which a protective layer 17 is provided on the photosensitive layer 15. FIG. 4 is a cross-sectional view showing still another configuration example of the photoconductor of the present invention, in which an intermediate layer 19 is provided between the conductive support 11 and the photosensitive layer 15. When the photosensitive layer is a multilayer (FIGS. 1, 3, and 4), the photosensitive layer is
1, 15-2, and 15-3. The charge generation substance concentration is 15-1>15-2> when the exposure is performed from the front side.
15-3. When the photosensitive layer is a single layer (FIG. 2),
When exposure is performed from the front side, the concentration of the charge generating substance in the photosensitive layer increases from the support side toward the front side. When the exposure is performed from the support side, the concentration of the charge generating substance may be reversed in each configuration.

The conductive support 11 includes a volume resistor 10.
Those exhibiting conductivity of ¹⁰ Ω or less, for example, metals such as aluminum, nickel, chromium, nichrome, copper, silver, gold, platinum, oxides such as tin oxide, indium oxide, etc. Coated with plastic, paper or the like, or a plate of aluminum, aluminum alloy, nickel, stainless steel, etc. I. , I .; I. After forming into a tube by a method such as extrusion, drawing, or the like, a tube or the like that has been surface-treated by cutting, superfinishing, polishing, or the like can be used.

Next, the photosensitive layer 15 will be described. The photosensitive layer 15 has a multilayer structure (at least two or more layers) having different charge generating substance concentrations or a layer in which the charge generating substance concentration is continuously changed, and is a layer containing a charge generating substance and a charge transporting substance as main components. If necessary, a binder resin may be used. As the binder resin, polyamide,
Polyurethane, epoxy resin, polyketone, polyvinylketone, polystyrene, poly-N-vinylcarbazole, polycarbonate (bisphenol A type, bisphenol Z type), polyester, methacrylic resin, acrylic resin, polyethylene, polyvinyl chloride, polyvinyl acetate, polystyrene, Phenol resin, epoxy resin, polyurethane, polyvinylidene chloride, alkyd resin, silicon resin, polyvinyl butyral, polyvinyl formal, polyacrylate, polyacrylamide, phenoxy resin and the like are used. These binders can be used alone or as a mixture of two or more.

As the charge generating substance, a known material can be used. For example, metal phthalocyanine, phthalocyanine pigments such as metal-free phthalocyanine, azulhenium salt pigment, methine squaric acid pigment, azo pigment having a carbazole skeleton, azo pigment having a triphenylamine skeleton, azo pigment having a diphenylamine skeleton, dibenzothiophene skeleton Azo pigment having a fluorenone skeleton, azo pigment having an oxadiazole skeleton, azo pigment having a bisstillene skeleton, azo pigment having a distyryl oxadiazole skeleton, azo pigment having a distyryl carbazole skeleton, perylene Pigments, anthraquinone or polycyclic quinone pigments, quinone imine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and azomethine pigments, i Jigoido pigments, etc. bisbenzimidazole pigments. These charge generating substances can be used alone or as a mixture of two or more kinds.

Next, the charge transport material will be described. The charge transport materials include an electron transport material and a hole transport material. Examples of the electron transporting substance include chloranil, bromanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,
4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophene-4
ON, 1,3,7-trinitrodibenzothiophene-
Electron accepting substances such as 5,5-dioxide are exemplified. These electron transport materials can be used alone or as a mixture of two or more.

As the hole transporting material, the following electron donating materials can be used, and are preferably used. For example, poly-N-vinylcarbazole and its derivatives,
Poly-γ-carbazolylethyl gourmet and its derivatives, pyrene-formaldehyde condensate and its derivatives, polyvinylpyrene, polyvinylphenanthrene,
Oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-
Diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane, styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, Benzofuran derivatives, benzimidazole derivatives, thiophene derivatives and the like can be mentioned. These hole transport materials can be used alone or as a mixture of two or more.

The intermediate layer 19 provided between the conductive support 11 and the photosensitive layer 15 is provided for the purpose of improving adhesiveness, and may be made of SiO ₂ , Al ₂ O ₃ , a silane coupling agent, Inorganic materials such as titanium coupling agents and chromium coupling agents, polyamide resins, alcohol-soluble polyamide resins, binder resins having good adhesive properties such as water-soluble polyvinyl butyral, polyvinyl butyral, and PVA are used. In addition, those obtained by dispersing ZnO, TiO ₂ , ZnS, and the like in the binder resin having good adhesiveness can also be used. As a method of forming the intermediate layer, a method such as sputtering or vapor deposition is used when the inorganic material is used alone, and a normal coating method is used when an organic material is used. The thickness of the intermediate layer is suitably 5 μm or less.

The protective layer 17 is provided for the purpose of protecting the surface of the photoreceptor.
ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, allyl resin, polyacetal, polyamide, polyamideimide, polyacrylate, polyallyl sulfone, polybutylene, polybutylene terephthalate, polycarbonate, polyether sulfone, polyethylene, polyethylene terephthalate, Polyimide,
Acrylic resin, polymethylbenten, polypropylene,
Examples thereof include polyphenylene oxide, polysulfone, polystyrene, AS resin, butadiene-styrene copolymer, polyurethane, polyvinyl chloride, and epoxy resin, and among them, cured products of a curable material and a curing agent. Other protective layers include fluororesins such as polytetrafluoroethylene, silicone resins, and inorganic materials such as titanium oxide, tin oxide, and potassium titanate dispersed in these resins for the purpose of improving abrasion resistance. Can be used. As a method for forming the protective layer, a normal coating method is employed. The thickness is about 0.5 to 10 μm.

[0020]

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples. All parts used in the examples are parts by weight. Example 1 A photosensitive layer 1 coating solution and a photosensitive layer 2 coating solution having the following composition were applied and dried on a polyethylene terephthalate film on which aluminum was deposited, and the photosensitive layers 1 and 2 having a thickness of 20 μm were formed.
An m-thick photosensitive layer 2 (the photosensitive layer according to claim 1 of the present invention) was formed to prepare an electrophotographic photoreceptor of the present invention. Coating solution for photosensitive layer 1 Charge generating substance of the following structure (formula 1) 0.6 part

Embedded image 10 parts of a charge transport material having the following structure (formula 2)

Embedded image Polycarbonate (Teijin Chemical Co., Ltd .: Panlite L-1250) 10 parts Tetrahydrofuran 200 parts Photosensitive layer 2 coating liquid 1 part of charge generating substance of the above structure (formula 1) 1 part of charge transport material of the above structure (formula 2) 10 parts polycarbonate (Teijin Chemical Co., Ltd .: Panlite L-1250) 5 parts Tetrahydrofuran 200 parts

Example 2 On the same support as in Example 1, an undercoat layer coating solution, photosensitive layer 1 coating solution and photosensitive layer 2 coating solution having the following composition were sequentially applied and dried, and each was coated with 0%. A 0.3 μm thick undercoat layer, a 17 μm thick photosensitive layer 1 and a 3 μm thick photosensitive layer 2 (the photosensitive layer of claim 1 in the present invention) were formed to produce an electrophotographic photoreceptor of the present invention. Undercoat layer coating solution 25% aqueous solution of water-soluble polyvinyl butyral 50 parts (Sekisui Chemical Co., Ltd .: Esrec W-201) Water 100 parts Methanol 200 parts Photosensitive layer 1 coating solution Charge generation of the following structure (Formula 3) Substance 0.8 parts

Embedded image 9 parts of a charge transport material having the following structure (Formula 4)

Embedded image Polycarbonate (Teijin Chemical Co., Ltd .: Panlite k-1300) 10 parts Methylene chloride 150 parts Coating solution for photosensitive layer 2 Charge generating material of the above structure (Chemical Formula 3) 2 parts Charge transporting material of the above structure (Chemical Formula 4) 9 parts Polycarbonate (Teijin Chemical Co., Ltd .: Panlite k-1300) 6 parts Methylene chloride 100 parts

Example 3 On a polyethylene terephthalate film provided with a Hastelloy conductive layer, a coating solution for an undercoat layer having the following composition was applied and dried, and then a coating solution for photosensitive layer 1 was applied thereon, and the wet state was obtained. The photosensitive layer 2 is coated by a spray method to form a photosensitive layer (the photosensitive layer of claim 2 of the present invention).
An undercoat layer having a thickness of μm and a photosensitive layer having a thickness of 25 μm were formed to prepare an electrophotographic photosensitive member of the present invention. Undercoat layer coating solution Titanium dioxide 5 parts Polyester (Toyobo Co., Ltd. Byron 200) 5 parts Toluylene-2,4-diisocyanate 0.5 parts 2-butanone 100 parts 4-methyl-2-pentanone 50 parts Photosensitive layer 1 Coating liquid 1 part of charge generating substance of the following structure (Chemical Formula 5)

Embedded image 10 parts of a charge transport material having the following structure (Formula 6)

Embedded image Polyarylate (U-100 manufactured by Unitika Ltd.) 10 parts Tetrahydrofuran 180 parts Coating solution for photosensitive layer 2 Charge generating material of the above structure (Formula 5) 4 parts Charge transporting material of the above structure (Formula 6) 10 parts Polyarylate ( Unitika U-100) 5 parts Tetrahydrofuran 200 parts

Example 4 On the same support as in Example 3, a coating solution for photosensitive layer 1 having the following composition was applied, and a coating solution for photosensitive layer 2 was laminated by a spray method in a wet state to form a photosensitive layer ( The photosensitive layer according to claim 2 of the present invention was formed and dried to form a photosensitive layer having a thickness of 22 μm, thereby producing an electrophotographic photoreceptor of the present invention. Photosensitive layer 1 coating solution 3 parts of charge generating substance having the following structure (Chem. 7)

Embedded image 9 parts of a charge transport material having the following structure (formula 8)

Embedded image Methylene chloride 8 parts Coating solution for photosensitive layer 2 Charge generating material of the above structure (Formula 7) 0.9 parts Charge transporting material of the above structure (Formula 8) 9 parts Polycarbonate (GE Corporation: Lexan-141) 10 Parts methylene chloride 190 parts

Comparative Example 1 An electrophotographic photosensitive member was produced in exactly the same manner as in Example 1 except that the photosensitive layer in Example 1 was formed using only the coating solution for photosensitive layer 1.

Comparative Example 2 An electrophotographic photoreceptor was produced in exactly the same manner as in Example 2, except that the photosensitive layer in Example 2 was formed using only the coating solution for photosensitive layer 1.

Comparative Example 3 An electrophotographic photosensitive member was produced in exactly the same manner as in Example 3, except that the photosensitive layer in Example 3 was formed using only the coating solution for photosensitive layer 1.

Comparative Example 4 A photosensitive layer was prepared in exactly the same manner as in Example 4 except that the photosensitive layer was formed using only the coating solution for photosensitive layer 2.

Example 5 The procedure of Example 1 was repeated except that the coating solution for the photosensitive layer 2 was changed to the following. Coating solution for photosensitive layer 2 Charge generating substance having the above structure (Chemical formula 1) 1 part Charge transporting material having the above structure (Chemical formula 2) 10 parts Polycarbonate (Teijin Chemical Co., Ltd .: Panlite L-1250) 7 parts Tetrahydrofuran 200 parts

The characteristics of the photoreceptors of Examples 1 to 3 and Comparative Examples 1 to 3 prepared above were measured using an electrostatic copying paper test apparatus (Kawaguchi Electric Works: SP-428) as follows. evaluated. First, a corona discharge was performed for 20 seconds at a discharge voltage of 6.0 kV or -6.0 kV, and then, when the surface potential became 800 V or -800 V after dark attenuation, 6.0 lux tungsten light was applied. The surface potential at this time was measured 400V or exposure required to be _{-400V E 1/2 (lux ·} sec), tungsten light irradiation for 20 seconds after a potential V ₂₀ (V). The photosensitive members of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to lightning from the surface (photosensitive layer side) using the electrostatic copying paper test apparatus,
Further, the photoconductors of Example 4 and Comparative Example 4 were exposed from the back surface (electrode side) using a device obtained by partially modifying the electrostatic copying paper test device, and the electrical characteristics of each photoconductor were measured. In the case of the photoconductors of Example 4 and Comparative Example 4, evaluation was made by negative charging. Table 1 shows the results.

[0030]

[Table 1]

[0031]

The electrophotographic photoreceptor of the present invention has a very high sensitivity and an extremely low residual potential.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electrophotographic photosensitive member having a photosensitive layer having a multilayer structure according to the present invention.

FIG. 2 is a cross-sectional view of an electrophotographic photoreceptor having a single-layered photosensitive layer of the present invention.

FIG. 3 is a cross-sectional view of an electrophotographic photosensitive member provided with a protective layer of the present invention.

FIG. 4 is a cross-sectional view of an electrophotographic photosensitive member provided with an intermediate layer according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Conductive support 15 ... Photosensitive layer 15-1 ... Layer which comprises a multilayered photosensitive layer 15-2 ... Layer which comprises a multilayered photosensitive layer 15-3 ... Layer which comprises a multilayered photosensitive layer 17 ... Protective layer 19 ... Intermediate layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-70844 (JP, A) JP-A-4-263259 (JP, A) JP-A-64-246749 (JP, A) JP-A-4- 162043 (JP, A) JP-A-56-121042 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 5/00

Claims (3)

(57) [Claims] 1. An electrophotographic photosensitive member having a photosensitive layer containing at least a charge generating substance and a charge transporting substance on a conductive support, wherein at least two photosensitive layers are laminated. and, by in each layer of the photosensitive layer
An electrophotographic photoreceptor, wherein the charge generation substance concentration with respect to the undercoat resin is gradually increased from the farthest side of the exposure incident side for forming an image to the side closer to the side. 2. An electrophotographic photosensitive member having a photosensitive layer containing at least a charge generating substance and a charge transporting substance on a conductive support, wherein the photosensitive layer is a single layer, and Wherein the concentration of the charge generating substance with respect to the binder resin is continuously increased from the farthest side of the exposure incident side for forming an image to the side closer thereto. 3. The method according to claim 1, wherein a concentration of the binder resin is 40% by weight or less with respect to a total solid content of a portion of the photosensitive layer closest to an exposure incidence side for forming an image. Electrophotographic photoreceptor.