JPH06317914A - Electrophotographic photosensitive body - Google Patents

Abstract

PURPOSE:To obtain high sensitivity with small residual potential by using a charge generating material having specified specific surface area in a charge generating layer. CONSTITUTION:By using a charge generating material having >=0.2m<2>/g specific surface area, preferably >=1m<2>/g, the electron transfer reaction can be enough effected and high sensitivity is obtd. To increase the specific surface area of the charge generating material to >=0.2m<2>/g, various methods are used according to materials, and for example, vapor deposition method in a gas or dispersion method with a vigorous shearing force is used. The specific surface area of the charge generating material is measured by sampling only the charge generating material by centrifugal separation or filtering of the charge generating layer or the coating liquid for the photosensensitive layer used for the production of a photosensitive body, and then drying the sample and the then measuring by BET method or the like.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrophotographic photoreceptor.

[0002]

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

[0003]

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

[0004]

According to the present invention, (1)
An electrophotographic photosensitive member having a photosensitive layer in which at least a charge generation layer and a charge transport layer are sequentially laminated on a conductive support, and the specific surface area of the charge generation substance in the charge generation layer is 0.2.
An electrophotographic photoreceptor using m ² / g or more, and (2) an electrophotographic photoreceptor having a photosensitive layer in which at least a charge transport layer and a charge generating layer are sequentially laminated on a conductive support, An electrophotographic photoreceptor using a charge generation material having a specific surface area of 0.2 m ² / g or more in the charge generation layer, and (3) at least a charge generation material and a charge transport material on a conductive support. Provided is a single-layer type electrophotographic photosensitive member having a photosensitive layer contained therein, wherein the specific surface area of the charge generating substance in the photosensitive layer is 0.2 m ² / g or more.

As described above, in the organic electrophotographic photoconductor, the high sensitivity is an important point. Two methods of increasing the quantum efficiency or increasing the mobility can be considered in order to increase the sensitivity of the photoreceptor, but the present inventors have paid attention to the former and have made repeated studies. As a result, in the carrier generation process of the organic electrophotographic photosensitive member, it was clarified that the initial stage of carrier generation is caused by the electron transfer reaction between the charge generating substance and the charge transporting substance. That is, the contact between the charge generating substance and the charge transporting substance plays an important role in the carrier generation and injection process,
It was found that the larger the contact amount between the charge generating substance and the charge transporting substance, the higher the carrier generation efficiency.

That is, it is highly sensitive to have 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) becomes large at the time of producing the photoconductor. It was found that this is one condition for the conversion. In order to increase the contact amount between the charge generating substance and the charge transporting substance, it suffices to increase the contact area between the charge generating substance and the charge transporting substance. It became clear that a large surface area was sufficient.

As a result of further study on this point, the present inventors found that the specific surface area of the charge generating substance is 0.2 m ² / g or more, preferably 1 m ² / g or more, so that the electron transfer reaction is sufficiently performed. The present invention has been completed and found that high sensitivity can be achieved, and completed the present invention.

The specific surface area of the charge generating material is 0.2 m ² / g
The method to do the above depends on the material,
For example, a vapor deposition method in a gas or a dispersion method having a strong market share may be used.

Regarding the measurement of the specific surface area of the charge generating substance, after the charge generating substance alone is taken out and dried by a method such as centrifuging or filtering the charge generating layer or the photosensitive layer coating liquid used for preparing the photoreceptor. , BET method and the like.

Next, the concentrations of the charge generating substance and the charge transporting substance will be described. First, the case where the photosensitive layers are laminated (the photosensitive layer is divided into the charge generation layer and the charge transport layer) will be described.

In this case, the contact between the charge-generating substance and the charge-transporting substance occurs mostly at the interface between the charge-generating layer and the charge-transporting layer, and the concentration of the charge-transporting substance in the portion of the charge-transporting layer that contacts the charge-generating layer. Is higher, the better, and it is desirable that the concentration of the charge transport material is 40% or more. Preferably, only the charge transport material (concentration of the charge transport material is 100%). However, there may be a case where the mechanical strength is lowered. In that case, the charge transport layer may have a multi-layer structure, and the concentration of the charge transport material may be changed stepwise or continuously from the portion in contact with the charge generation layer to the portion farther from the portion. Further, providing a protective layer on the uppermost layer is also an effective means.

Regarding the charge generation layer, the higher the concentration of the charge generation substance in the portion in contact with the charge transport layer, the better, and the concentration of the charge generation substance is preferably 70% or more. Preferably, only the charge generating substance (charge generating substance concentration 100
%). In this case, the charge generation layer may have a multi-layered structure, and the concentration of the charge generation substance may be changed stepwise or continuously from the part in contact with the charge transport layer to the part farther from it.

In the case where the photosensitive layer has a laminated structure (consisting of a charge generation layer and a charge transport layer), the present invention becomes more effective by laminating at least the upper layer by a wet method. It is considered that this is because the contact between the charge generating substance and the charge transporting substance is improved by forming the upper layer by the wet method.

Next, the case where the photosensitive layer is a single layer (meaning that the charge generating substance and the charge transporting substance are present in the same layer) will be described. In this case, carrier generation rarely occurs in the entire photosensitive layer (except when the photosensitive layer is very thin), and most carriers are generated on the exposure incident side for image formation. . Therefore, the contact amount between the charge generating substance and the charge transporting substance at this portion may be increased.
In this portion, the higher the concentration of the charge generating substance and the concentration of the charge transporting substance, the better. However, the binderless method is not practical because it is difficult to form a film.

Therefore, the photosensitive layer may be of a laminated type, and the binder concentration may be increased stepwise from the side closest to the incident side for image formation to the side farther from the side.
It is also possible to make the photosensitive layer a single layer type and continuously increase the binder concentration from the side closest to the exposure incident side for image formation to the side farther. In any case, it is desirable that the binder concentration on the side closest to the exposure incident side for image formation be 40% or less. Also in this case, providing a protective layer on the uppermost layer is an effective means.

Here, the exposure incident side for forming an image will be described. For example, when exposure is performed from the surface side of the photoconductor as usual, the exposure side for image formation means the support side. The effects of the present invention are further enhanced by configuring the photosensitive layer, charge generation layer, and charge transport layer as described above.

Next, the present invention will be described with reference to the drawings. Figure 1
FIG. 3 is a cross-sectional explanatory view showing a constitutional example of a photoconductor used in the present invention, which has a constitution in which a photosensitive layer 15 is laminated on a conductive support 11. FIG. 2 is a cross-sectional explanatory view showing another configuration example, in which the photosensitive layer 15 has a configuration in which a charge generation layer 21 and a charge transport layer 23 are sequentially stacked. FIG. 3 is a cross-sectional explanatory view showing still another configuration example, in which the photosensitive layer 15 has a configuration in which the charge transport layer 23 and the charge generation layer 21 are sequentially stacked. FIG. 4 is a cross-sectional explanatory view showing still another configuration example, in which an intermediate layer 19 is provided between the conductive support 11 and the photosensitive layer 15. The photosensitive layer may be either a single layer or a laminated layer.

FIG. 5 is a cross-sectional explanatory view showing a further structural example, in which a protective layer 17 is provided on the photosensitive layer 15. The conductive support 11 has a volume resistance of 10 ¹⁰ Ω or less, for example, a metal such as aluminum, nickel, chromium, nichrome, copper, silver, gold or platinum, or an oxide such as tin oxide or indium oxide. Is coated with film-shaped or cylindrical plastic, paper, or the like by vapor deposition or sputtering, or a plate of aluminum, aluminum alloy, nickel, stainless steel, or the like and D. I. , I. I. A tube or the like which has been surface-treated by cutting, superfinishing, grinding or the like can be used after being formed into a raw tube by a method such as extrusion or drawing.

Next, the charge generation layer 21 will be described. The charge generating layer 21 is a layer containing a charge generating substance as a main component, and a binder resin may be used if necessary. As the binder resin, polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, poly-
N-vinylcarbazole, polyacrylamide, etc. are used. These binder resins can be used alone or as a mixture of two or more kinds.

A known material can be used as the charge generating substance. For example, phthalocyanine-based pigments such as metal phthalocyanine and metal-free phthalocyanine, azurenium salt pigments, squaric acid methine pigments, azo pigments having a carbazole skeleton, azo pigments having a triphenylamine skeleton, azo pigments having a diphenylamine skeleton, and dibenzothiophene skeletons. Having an azo pigment, an azo pigment having a fluorenone skeleton, an azo pigment having an oxadiazole skeleton, an azo pigment having a bisstilbene skeleton, an azo pigment having a distyryl oxadiazole skeleton, an azo pigment having a distyrylcarbazole skeleton, a perylene-based Pigments, anthraquinone-based or polycyclic quinone-based pigments, quinoneimine-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, the azo pigment can be effectively used. In the present invention, the specific surface area of the charge generation substance is 0.2 m ² / g by a suitable method suitable for the material.
Use above.

Next, the charge transport layer 23 will be described. The charge transporting layer 23 can be formed by dissolving or dispersing a charge transporting substance and a binder resin in a suitable solvent, coating and drying the solvent, and is a single layer (in some cases, laminated).

The charge transport material includes a hole transport material and an electron transport material. Examples of the electron transport material include chloranil, bromanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, and 2,4. , 5,7-Tetranitroxanthone,
2,4,8-trinitrothioxanthone, 2,6,8-
Examples thereof include electron-accepting substances such as trinitro-4H-indeno [1,2-b] thiophen-4one and 1,3,7-trinitrodibenzothiophene-5,5-dioxide. These electron transport materials can be used alone or as a mixture of two or more kinds.

Examples of the hole-transporting substance include the electron-donating substances shown below, which are preferably used. For example, poly-N-vinylcarbazole and its derivative, poly-γ-carbazolylethylgourmet tart 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, styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, thiophene derivatives, etc. Can be mentioned. These hole transport materials can be used alone or as a mixture of two or more kinds.

As the binder resin used in the charge transport layer 23, 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, polyvinylcarbazole, 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 kinds.

The photosensitive layer 15 will be described. Photosensitive layer 15
Is a layer containing a charge generating substance and a charge transporting substance as a main component, and is a single layer (laminated in some cases). As the charge generating substance, the charge transporting substance and the binder resin, those shown for the charge generating layer 21 and the charge transporting layer 23 are used.

The intermediate layer provided between the conductive support 11 and the charge generation layer 21 is provided for the purpose of improving the adhesiveness, and its material is SiO ₂ , Al ₂ O ₃ , a silane coupling agent, An inorganic material such as a titanium coupling agent or a chromium coupling agent, a polyamide resin, an alcohol-soluble polyamide resin, a water-soluble polyvinyl butyral, a polyvinyl butyral, or a binder resin having good adhesiveness such as PVA is used. In addition, it is also possible to use one in which ZnO, TiO ₂ , ZnS or the like is dispersed in the binder resin having good adhesiveness. As a method for forming the intermediate layer, when the inorganic material is used alone, a method such as sputtering or vapor deposition is used.
When an organic material is used, a usual coating method is adopted. The thickness of the intermediate layer is appropriately 5 μm or less.

The protective layer 17 is provided for the purpose of protecting the surface of the photoconductor, and examples of materials used therefor 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 these, a cured product of a curable material and a curing agent.

The protective layer may also include a fluororesin such as polytetrafluoroethylene for the purpose of improving wear resistance.
Silicone resins and those obtained by dispersing an inorganic material such as titanium oxide, tin oxide or potassium titanate in these resins can be added. As a method for forming the protective layer, a usual coating method is adopted. The film thickness is 0.5 to 10
About μm is appropriate.

[0029]

EXAMPLES 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.

Example 1 On a polyethylene terephthalate film on which aluminum was vapor-deposited, a charge generation layer coating solution and a charge transport layer coating solution having the following compositions were successively applied by a roll coating method and dried to generate 0.2 μm of charge respectively. A layer and a charge transport layer having a thickness of 20 μm were formed to form an electrophotographic photoreceptor of the present invention.

Charge Generating Layer Coating Solution 5 parts of charge generating substance having the following structure

[0032]

[Chemical 1]

Polyvinyl butyral resin [Sekisui Chemical Co., Ltd .: S-REC BL-1] 0.5 part Cyclohexanone 300 parts 2-butanone 90 parts Charge transport layer coating liquid 9 parts Charge transport material having the following structure

[0034]

[Chemical 2]

Polycarbonate (Teijin Kasei: Panlite K-1300) 10 parts Methylene chloride 250 parts The charge generation layer coating solution was prepared by ball milling for 10 days. The specific surface area of the charge generating substance in the charge generating layer is
It was 0.25 m ² / g.

Example 2 On a polyethylene terephthalate film provided with a Hastelloy conductive layer, a charge generating layer coating solution and a charge transporting layer coating solution having the following compositions were successively coated by a roll coating method and dried,
A charge generation layer having a thickness of 0.3 μm and a charge transport layer having a thickness of 24 μm were formed to prepare an electrophotographic photoreceptor of the present invention.

Charge Generating Layer Coating Solution 5 parts of the charge generating substance having the following structure

[0038]

[Chemical 3]

Polyester [Toyobo: Byron 300] 1 part Cyclohexanone 300 parts Charge transport layer coating liquid 7 parts charge transport material having the following structure

[0040]

[Chemical 4]

Polycarbonate (GE company: Lexan L-141) 10 parts Tetrahydrofuran 300 parts The charge generation layer coating solution was prepared by ball milling for 8 days. The specific surface area of the charge generating substance in the charge generating layer is
It was 0.5 m ² / g.

Example 3 An undercoat layer coating solution, a charge generation layer coating solution, and a charge transport layer coating solution having the following compositions were sequentially applied on an Al plate (JIS 1080) having a thickness of 0.3 mm by a dipping method. Then, it was dried to form an undercoat layer of 0.2 μm, a charge generation layer of 0.2 μm, and a charge transport layer of 18 μm, to prepare an electrophotographic photoreceptor of the present invention.

Undercoat layer coating liquid Soluble nylon (Toray: Amilan CM8000) 2.5 parts Methanol 70 parts Butanol 30 parts Charge generating layer coating liquid 10 parts of charge generating substance having the following structure

[0044]

[Chemical 5]

Polyvinyl butyral [UCC: XYHL] 1 part Cyclohexanone 500 parts Tetrahydrofuran 200 parts Charge transport layer coating liquid 8 parts Charge transport material having the following structure

[0046]

[Chemical 6]

Polyarylate (Unitika: U polymer U-100) 10 parts Tetrahydrofuran 200 parts The charge generation layer coating solution was prepared by ball milling for 6 days. The specific surface area of the charge generating material in the charge generating layer is 5
It was m ² / g.

Example 4 On the same support as in Example 3, a charge transport layer coating solution and a charge generating layer coating solution having the following compositions were sequentially applied by a spray method and dried to obtain a charge transport layer having a thickness of 22 μm. , 0.5μ
A charge generation layer of m was formed to prepare an electrophotographic photoreceptor of the present invention.

Charge transport layer coating liquid 8 parts of charge transport material having the following structure

[0050]

[Chemical 7]

Polycarbonate resin [Z type, molecular weight 20000] 10 parts Tetrahydrofuran 400 parts Charge generation layer coating liquid 5 parts charge generation material having the following structure

[0052]

[Chemical 8]

Polycarbonate (A type) 2 parts Cyclohexanone 100 parts Tetrahydrofuran 100 parts The coating liquid for the charge generation layer was prepared by ball milling for 12 days. The specific surface area of the charge generating substance in the charge generating layer was 20 m ² / g.

Example 5 On the same support as in Example 1, a charge generation layer coating liquid and a charge transport layer coating liquid having the following compositions were sequentially applied by a roll coating method and dried to obtain 0.25 μm each. Charge generation layer, 2
A charge transport layer having a thickness of 1 μm was formed to prepare an electrophotographic photoreceptor of the present invention.

Charge Generating Layer Coating Solution 6 parts of charge generating substance having the following structure

[0056]

[Chemical 9]

Phenoxy resin [UCC: VYHH] 2 parts Cyclohexanone 400 parts 2-Methyl-4-pentanone 150 parts Charge transport layer coating liquid 10 parts Charge transport material having the following structure

[0058]

[Chemical 10]

Polycarbonate (Teijin Kasei: Panlite L-1250) 10 parts Tetrahydrofuran 300 parts The charge generation layer coating solution was prepared by ball milling for 8 days. The specific surface area of the charge generating substance in the charge generating layer is
It was 33 m ² / g.

Comparative Example 1 The same preparation as in Example 1 was carried out except that the following charge generation layer coating solution was changed.

Charge Generating Layer Coating Solution 5 parts of the charge generating substance having the following structure

[0062]

[Chemical 11]

Polyvinyl butyral resin [Sekisui Chemical Co., Ltd .: S-REC BL-1] 0.5 parts Cyclohexanone 300 parts 2-butanone 90 parts The charge generation layer coating solution was prepared by ball milling for 1 day. The specific surface area of the charge generating substance in the charge generating layer is
It was 0.1 m ² / g or less.

Comparative Example 2 The same preparation as in Example 2 was carried out except that the following charge generation layer coating solution was used.

Charge Generating Layer Coating Solution 5 parts of charge generating substance having the following structure

[0066]

[Chemical 12]

Polyester [Toyobo: Byron 300] 1 part Cyclohexanone 300 parts Tetrahydrofuran 200 parts The charge generation layer coating liquid was prepared by ball milling for 36 hours. The specific surface area of the charge generating substance in the charge generating layer was 0.1 m ² / g or less.

Comparative Example 3 The same preparation as in Example 3 was carried out except that the charge generation layer coating liquid was changed to the following.

Charge Generating Layer Coating Solution 10 parts of charge generating substance having the following structure

[0070]

[Chemical 13]

Polyvinyl butyral [UCC: XYHL] 1 part Cyclohexanone 500 parts The charge generation layer coating liquid was prepared by ultrasonic dispersion for 2 hours. The specific surface area of the charge generating substance in the charge generating layer is
It was 0.1 m ² / g or less.

Comparative Example 4 The same preparation as in Example 4 was carried out except that the coating liquid for charge generating layer was changed to the following liquid.

Charge Generating Layer Coating Solution 5 parts of charge generating substance having the following structure

[0074]

[Chemical 14]

Polycarbonate [A type] 2 parts Cyclohexanone 100 parts Tetrahydrofuran 100 parts The coating liquid for the charge generation layer was prepared by ball milling for 12 hours. The specific surface area of the charge generating substance in the charge generating layer was 0.13 m ² / g.

Comparative Example 5 The same procedure as in Example 5 was carried out except that the charge generation layer coating solution was changed to the following.

Charge Generating Layer Coating Solution 6 parts of charge generating substance having the following structure

[0078]

[Chemical 15]

Phenoxy resin [UCC: VYHH] 2 parts Cyclohexanone 400 parts 2-Methyl-4-pentanone 150 parts The charge generation layer coating solution was prepared by ball milling for 20 hours. The specific surface area of the charge generating substance in the charge generating layer was 0.18 m ² / g. The specific surface areas of the charge generating substances of Examples 1 to 5 and Comparative Examples 1 to 5 are BET.
It was measured by the method.

The characteristics of the photoconductors of Examples 1 to 5 and Comparative Examples 1 to 5 were evaluated as follows using an electrostatic copying paper test apparatus (Kawaguchi Denki Seisakusho: SP-428 type). .
First, corona discharge was performed for 20 seconds at a discharge voltage of -6.5 kV (or 6.5 kV), and then dark decay was performed to bring the surface potential to -800 V (or 800 V). Was irradiated.

At the time of light irradiation at this time, the surface potential was -800.
The exposure amount E ₄₀₀ (lux · sec) required to change from V to −400 V (or 800 V to 400 V) and the potential V ₂₀ (V) 20 seconds after the tungsten light irradiation were measured.
The results are shown in Table 1.

[0082]

[Table 1]

[0083]

As described above, the electrophotographic photosensitive member of the present invention has extremely high sensitivity, has a small residual potential, and can prevent abnormal images such as background stain and fog.

[Brief description of drawings]

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

FIG. 2 is another cross-sectional explanatory view showing a configuration example of a photoconductor,

FIG. 3 is still another cross-sectional explanatory view showing a configuration example of a photoconductor.

FIG. 4 is another cross-sectional explanatory view showing a configuration example of a photoconductor.

FIG. 5 is still another cross-sectional explanatory view showing a configuration example of a photoconductor.

[Explanation of symbols]

 11 Conductive Support 15 Photosensitive Layer 17 Protective Layer 19 Intermediate Layer 21 Charge Generation Layer 23 Charge Transport Layer

Claims (3)

[Claims] 1. An electrophotographic photoreceptor having a photosensitive layer comprising a conductive support and at least a charge generation layer and a charge transport layer laminated in this order, wherein the specific surface area of the charge generation substance in the charge generation layer is 0. An electrophotographic photosensitive member characterized by using a material having a weight of ² m ² / g or more. 2. An electrophotographic photosensitive member having a photosensitive layer formed by laminating at least a charge transport layer and a charge generating layer on a conductive support, wherein the specific surface area of the charge generating substance in the charge generating layer is 0. An electrophotographic photosensitive member characterized by using a material having a weight of ² m ² / g or more. 3. In a single-layer type electrophotographic photoreceptor having a photosensitive layer containing both a charge generating substance and a charge transporting substance on a conductive support, the specific surface area of the charge generating substance in the photosensitive layer is An electrophotographic photosensitive member characterized by using one having a density of 0.2 m ² / g or more.