JP3267710B2 - Electrophotographic photoreceptor - Google Patents

Description

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 In an organic electrophotographic photoreceptor, high sensitivity is an important point for practical use. In the case of an organic electrophotographic photosensitive member, there are two points to increase the sensitivity. One is to increase the carrier mobility, and the other is to increase the quantum efficiency.

[0003]

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

[0004]

According to the present invention, there is provided (1) an electrophotographic photosensitive member having a charge generating layer and a charge transporting layer laminated in order on a conductive support, wherein the charge generating layer is a Benard cell. an electrophotographic photosensitive member having a structure, (2) before the surface roughness Ra of the charge generating layer is 50Å or more
(3) The electrophotographic photoconductor according to (1) or (2), wherein the relationship between the thickness d of the charge generation layer and the surface roughness Ra satisfies the following expression (1). Photoconductor, 0.01 <Ra / d <0.5 (1) is provided.

[0005] As described above, in the organic electrophotographic photosensitive member, 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 repeated their studies focusing on the former. Was. 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.

In other words, it is highly sensitive to make the structure (form) such that the contact amount between the charge generating substance and the charge transporting substance (the contact area between the charge generating layer and the charge transporting layer) becomes large when the photoreceptor is formed. It was found that this was one of the conditions for the conversion.

As a result of studying a structure (form) in which the amount of contact between the charge generating substance and the charge transporting substance (the contact area between the charge generating layer and the charge transporting layer) is increased, it was found that It has been found that in an electrophotographic photoreceptor formed by laminating layers, this can be achieved by increasing the surface roughness Ra of the charge generation layer to 50 ° or more.

Although the reason for this is not clear, if the surface roughness Ra of the charge generating layer is smaller than 50 °, it is not possible to secure a sufficient contact amount between the charge generating substance and the charge transporting substance so that the electron transfer reaction proceeds smoothly. It is thought to be.

Furthermore, it has been found that the relationship between the surface roughness Ra and the film thickness d of the charge generation layer is achieved by satisfying the following equation (1).

0.01 <Ra / d <0.5 (1) Although the reason is not clear, Ra / d is 0.0
It is considered that if it is 1 or less, it is impossible to secure a sufficient contact amount between the charge generating substance and the charge transporting substance so that the electron transfer reaction proceeds smoothly. If it is more than 0.5, the surface roughness with respect to the film thickness is too rough, which may adversely affect the function of the electrophotographic photoreceptor as a charge generation layer (for example, a defective image due to uneven sensitivity). ).

In the present invention, Ra is the center line average roughness.

Next, a method for increasing the surface roughness of the charge generation layer will be described.

1) Method for Roughening the Surface at the Time of Coating the Charge Generating Layer The size of the charge generating material particles contained in the coating solution used for coating the charge generating layer is relatively large. In this case, if it is too large, there may be a problem in coatability, but a preliminary experiment or the like may be performed to determine in advance a range in which there is no problem.

By using a solvent having a relatively high evaporation rate as a solvent contained in a coating solution used for coating the charge generation layer, a film having a relatively rough surface can be formed. Usually, by using a solvent having a relatively low evaporation rate, a leveling effect is obtained at the time of touch drying, but in the present invention, the reverse is performed.

In forming the charge generation layer, Benard cells are formed in the coating film. The Benard cell is a phenomenon in which the surface of a coating film is divided into small sections by convection between the inside and the surface of the coating film in a drying step immediately after the coating of the coating material. Usually, the formation of the Benard cell deteriorates the surface properties of the film and causes various inconveniences. Therefore, measures are taken to suppress the formation of the Benard cell. In the present invention, this is positively used. Thereby, the coating film can be uniformly roughened to some extent. In order to positively generate Benard cells, for example, use a pigment having a wide particle size distribution, use a solvent and / or a resin having a large surface tension, set the film thickness to be collected, and determine the thixotropy of the paint by the ratio of the pigment and the resin. And selecting an appropriate pigment dispersion. These can be combined to form a Benard cell, but the invention is not limited in its method or formulation.

[0017]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory sectional view showing an example of the structure of a photoreceptor used in the present invention, in which a charge generation layer 13 and a charge transport layer 15 are laminated on a conductive support 11. .

FIG. 2 is a cross-sectional view showing another configuration example, in which an intermediate layer 17 is provided between a conductive support 11 and a charge generation layer 13. FIG. 3 is a sectional view showing still another configuration example, in which a protective layer 19 is provided on the charge transport layer 15.

As the conductive support 11, a volume resistance 10
Those having a conductivity of ¹⁰ Ω or less and capable of penetrating the tip for image formation, for example, metals such as aluminum, nickel, chromium, nichrome, copper, silver, gold, platinum, and oxides such as tin oxide and indium oxide Coated on a film or cylindrical plastic, paper or the like by vapor deposition or sputtering.

Next, the charge generation layer 13 will be described. The charge generation layer 13 is a layer containing a charge generation substance as a main component, and may use a binder resin as needed. As the binder resin, polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, poly-
N-vinyl carbazole, polyacrylamide and the like are used. These binder resins can be used alone or as a mixture of two or more.

Known materials can be used as the charge generating substance. 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 pigments having fluorenone skeleton, azo pigments having oxadiazole skeleton, azo pigments having bis-stilbene skeleton, azo pigments having distyryl oxadiazole skeleton, azo pigments having distyrylcarbazole skeleton, perylene-based Pigments, anthraquinone-based or polycyclic quinone-based pigments, quinone imine-based pigments, diphenylmethane and triphenylmethane-based pigments, benzoquinone and naphthoquinone-based pigments, cyanine and azomethine-based pigments, Goido based pigments, and bisbenzimidazole pigments. These charge generating substances can be used alone or as a mixture of two or more kinds. Among them, azo pigments can be used favorably.

Next, the charge transport layer 15 will be described. The charge transport layer 15 can be formed by dissolving or dispersing a charge transport material and a binder resin in an appropriate solvent, and applying and drying this.

The charge transport material includes a hole transport material and an electron 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-
Electron accepting substances such as trinitro-4H-indeno [1,2-b] thiophene-4one and 1,3,7-trinitrodibenzothiophene-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 derivative, poly-γ-carbazolylethyl gourmet and its derivative, pyrene-formaldehyde condensate and its derivative, polyvinylpyrene, polyvinylphenanthrene, oxazole derivative, oxadiazole derivative, imidazole derivative , Triphenylamine derivative, 9- (p-diethylaminostyrylanthracene), 1,1-bis-
(4-dibenzylaminophenyl) propane, styryl anthracene, styryl pyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, thiophene derivatives and the like. No. These hole transporting substances can be used alone or as a mixture of two or more kinds.

The binder resin used for the charge transport layer 23 includes polycarbonate (bisphenol A type, bisphenol Z type), polyester, methacrylic resin, acrylic resin, polyethylene, vinyl chloride,
Vinyl acetate, polystyrene, phenol resin, epoxy resin, polyurethane, polyvinylidene chloride, alkyd resin, silicone resin, polyvinyl carbazole, 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.

The intermediate layer provided between the conductive support 11 and the charge generation layer 13 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. Also in this case, a material that can transmit light for image formation is selected and used. As a method of forming the intermediate layer, in the case of an inorganic material alone, a method such as sputtering and vapor deposition, and in the case of using an organic material,
A normal coating method is employed. The thickness of the intermediate layer is 5 μm.
m or less is appropriate.

The protective layer 19 is provided for the purpose of protecting the surface of the photoreceptor. Examples of materials used for the protective layer 19 include ABS resin, ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, allyl resin, and polyacetal. , Polyamide, polyamideimide, polyacrylate, polyallyl sulfone, polybutylene, polybutylene terephthalate, polycarbonate, polyether sulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic resin, polymethylpentene, polypropylene, polyphenylene oxide, polysulfone, polystyrene, AS resin , Butadiene-styrene copolymer, polyurethane, polyvinyl chloride, epoxy resin and the like, and among them, a cured product of a curable material and a curing agent.

The protective layer may further include a fluororesin such as polytetrafluoroethylene for the purpose of improving abrasion resistance;
Silicone resins and those in which an inorganic material such as titanium oxide, tin oxide, or potassium titanate is dispersed in these resins can be added. As a method for forming the protective layer, a normal coating method is employed. The thickness is 0.5 to 10
About μm is appropriate.

[0031]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. All parts used in the examples are parts by weight.

REFERENCE EXAMPLE 1 A coating liquid for a charge generation layer, a coating liquid for a charge transport layer, and a coating liquid for a protective layer having the following compositions were successively coated and dried on an Al cylindrical support having a diameter of 80 mm. 5 μm charge generation layer and 20
A μm charge transport layer was formed to form an electrophotographic photosensitive member of the present invention.

Coating solution for charge generation layer 5 parts of charge generation material having the following structure

[0034]

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Polyester (Toyobo Byron 200) 1 part Methyl ethyl ketone 300 parts Coating solution for charge transport layer 9 parts of charge transport material having the following structure

[0036]

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Polycarbonate (Panlite C1400: Teijin Chemicals) 10 parts Methylene chloride 81 parts Comparative Example 1 All were prepared in the same manner as in Reference Example 1 except that the coating solution for charge generation was changed to the following composition.

Coating solution for charge generation layer 5 parts of charge generation material having the following structure

[0039]

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Polyester (Toyobo Byron 200) 1 part Cyclohexanone 300 parts Reference Example 2 On the same support as in Reference Example 1, a coating liquid for an undercoat layer, a coating liquid for a charge generation layer, and a charge transport layer The coating solution was sequentially applied and dried to form a 0.3 μm undercoat layer, a 0.5 μm charge generation layer and a 22 μm charge transport layer, thereby forming an electrophotographic photoreceptor of the present invention.

Coating solution for undercoat layer Alcohol-soluble nylon (Amilan CM8000: Toray) 3 parts Methanol 70 parts Butanol 30 parts Charge generation layer coating solution 10 parts of charge generation material having the following structure

[0042]

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Phenoxy resin (VYHH: UCC) 1 part Cyclohexanone 250 parts Tetrahydrofuran 250 parts The above mixture was dispersed by ball milling for 2 days.

Coating solution for charge transport layer 8 parts of charge transport material having the following structure

[0045]

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Polycarbonate (Panlite L1250: Teijin Chemicals) 10 parts Methylene chloride 100 parts Comparative Example 2 All were prepared in the same manner except that the charge generation coating solution in Reference Example 2 was dispersed by ball mining for 20 days.

Example 1 A coating liquid for a charge generation layer and a coating liquid for a charge transport layer having the following compositions were sequentially coated and dried on an Al cylindrical support having a diameter of 60 mm.
A 0.7 μm charge generation layer and a 25 μm charge transport layer were formed to form the electrophotographic photoreceptor of the present invention.

Coating solution for charge generation layer 2.5 parts of charge generation material having the following structure

[0049]

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Polysulfone (P1700: Nissan Chemical) 1 part Tetrahydrofuran 150 parts Coating solution for charge transport layer 7 parts of charge transport material having the following structure

[0051]

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Polycarbonate (A2500: Idemitsu Petrochemical) 10 parts Methylene chloride 90 parts After coating the charge generating layer, the surface was observed. As a result, formation of Benard cells was observed on the entire surface of the coating film.

Comparative Example 3 The same procedure was carried out except that the charge generation coating solution in Reference Example 1 was changed to the following composition.

Coating solution for charge generation layer 2.5 parts of charge generation material having the following structure

[0055]

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Polysulfone (P1700: Nissan Chemical) 1 part Tetrahydrofuran 150 parts Silicon oil (KF-50: Shin-Etsu Chemical) 0.02 parts No formation of Benard cells was observed.

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

Example 1, Reference Examples 1 and 2, and Comparative Example 1
The electrostatic characteristics of the photoreceptors prepared in Examples 1 to 3 are described in
The measurement was performed as follows using a measuring device disclosed in JP-A-1000016.

First, a corona discharge was performed at a discharge voltage of -6.0 kV for 20 seconds, then attenuated dark for 20 seconds, and then irradiated with a 6.0 lux tungsten lamp light for 20 seconds. At this time, the surface potential V ₆₀ (−
V), and the exposure amount E _1/2 (lux · sec) required to attenuate the surface potential at the start of exposure to half the potential. Table 1 shows the results.

[0080]

[Table 1]

[0081]

As described above, according to the present invention, it is possible to obtain an electrophotographic photosensitive member having extremely high sensitivity and low residual potential.

[Brief description of the drawings]

FIG. 1 is a cross-sectional explanatory view showing a configuration example of a photoconductor,

FIG. 2 is an explanatory cross-sectional view illustrating a configuration example of a photoconductor;

FIG. 3 is an explanatory cross-sectional view illustrating a configuration example of a photoconductor.

[Explanation of symbols]

 Reference Signs List 11 conductive support 13 charge generation layer 15 charge transport layer 17 intermediate layer 19 protective layer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-143762 (JP, A) JP-A-54-2737 (JP, A) JP-A-4-14053 (JP, A) JP-A-3-3 260657 (JP, A) JP-A-3-33859 (JP, A) JP-A-1-109355 (JP, A) JP-A-61-238060 (JP, A) JP-A-4-125652 (JP, A) JP-A-4-125563 (JP, A) JP-A-60-32056 (JP, A) JP-A-60-252359 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 5/00

Claims (3)

(57) [Claims] 1. An electrophotographic photoreceptor comprising at least a charge generation layer and a charge transport layer sequentially laminated on a conductive support, wherein the charge generation layer has a Benard cell structure . 2. The charge generating layer has a surface roughness Ra of 50 ° or more.
2. The electrophotographic photosensitive member according to claim 1, wherein Claims wherein the relationship of the film thickness d and the surface roughness Ra of the charge generating layer, and satisfies the following formula (1)
3. The electrophotographic photosensitive member according to 1 or 2 . 0.01 <Ra / d <0.5 (1)