JPS6363902B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic photoreceptor having a specific disazo pigment in a photosensitive layer. It has been known for a long time that disazo pigments are useful as photoconductive substances for electrophotographic light-sensitive materials (for example, Japanese Patent Application Laid-open No. 37453/1983). However, in the field of electrophotographic reproduction there is a constant demand for increasing copying speeds, and from this point of view the development of highly sensitive photoconductive pigments is always expected. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrophotographic photoreceptor containing a photosensitive layer containing a disazo photoconductive pigment that has increased sensitivity compared to conventional disazo photoconductive pigments. Another object of the present invention is to provide an electrophotographic photoreceptor using a disazo photoconductive pigment that can form both positive and negative charge images with high sensitivity. According to the present invention, the following formula An electrophotographic photoreceptor comprising a photosensitive layer containing a disazo pigment represented by the following formula, wherein each of R ₁ and R ₂ represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a halogen atom. is provided. The disazo pigment used in the present invention has the above general formula (1).
As is clear from the above, it has a chemical structure in which a tetrazotized product of 4,4'-diaminodiphenylamine and 3-hydroxy-2-naphthanilide are coupled. Therefore, the present invention provides that a disazo pigment in which the above-mentioned specific tetrazonium salt and an azo coupling component are combined exhibits unique photoconductive properties compared to disazo pigments conventionally used as photoconductive pigments. This is based on this knowledge. In general, when disazo photoconductive pigments are used as a photoreceptor consisting of a single photoconductive layer and a conductive substrate, they exhibit relatively high sensitivity when charged positively; In this case, the sensitivity tends to be low. For example, known disazo-based photoconductive pigments are derived by coupling 3,3'-dimethoxybiphenyltetrazonium salt and 3-hydroxy-2-naphthanilide, as shown in the above-mentioned publication. However, in the case of negative charge, the sensitivity is low. On the other hand, the disazo pigment used in the present invention has a structural feature in that the tetrazonium salt used has a diphenylamine skeleton, which makes it excellent not only for positive charging but also for negative charging. This is a significant advantage of the present invention. The above general formula showing the disazo pigment used in the present invention
In (1), as the lower alkyl group (lower in this specification means having 4 or less carbon atoms), a methyl group is preferable, but an ethyl group, n
-propyl group, iso-propyl group, etc., and as a lower alkoxy group, methoxy group is preferred, but ethoxy group, propoxy group, etc. may also be used. The halogen atom may be a bromine atom in addition to a chlorine atom. The tetrazonium salt used in the production of the disazo pigment of general formula (1) can be obtained by tetrazotizing 4,4'-diaminophenylamine with sodium nitrite in accordance with a conventional method. In order to prevent the -NH- group from becoming nitroso (>N-NO), -
It is necessary to keep the NH- group in salt form.
A disazo pigment can be easily obtained by coupling this tetrazonium salt and an azo coupling component in a suitable solvent such as water or dimethylformamide in the presence of an alkali. In the electrophotographic light-sensitive material of the present invention, the disazo pigment can be used in various embodiments as long as the disazo pigment is contained in the photosensitive layer. For example, the disazo pigment can be dispersed as a photoconductive pigment in an electrically insulating binding medium, and the composition can be used as a photoconductive layer on an electrically conductive substrate. Disazo pigments have a particle size of 5 microns or less,
In particular, it is preferable to finely disperse the particles to a size of 2 microns or less. In this embodiment, as the electrically insulating binding medium, polyester resin, acrylic resin, styrene resin, epoxy resin, silicone resin, alkyd resin, vinyl chloride-vinyl acetate copolymer, etc. are used. Disazo pigment is a binder 100
It is preferred to use amounts of 5 to 100 parts by weight, especially 10 to 50 parts by weight. As the conductive substrate, a metal substrate in the form of a sheet or drum, or conductively treated paper is used, and the coating amount of the photoconductive layer is 3 to 20 g/m ² on a dry basis, especially 5 to 10 g/m 2 .
It is preferable to set it in the range of g/m ² . In another aspect of the invention, the disazo pigment is dispersed as a charge generating pigment in a charge transport material, and the dispersion composition is provided as a photosensitive layer on a conductive substrate. As the charge transport substance, any hole transport substance or electron transport substance known per se can be used for the purpose of the present invention. Examples of suitable hole transport materials are poly-N-vinylcarbazole, phenanthrene,
N-ethylcarbazole, 2,5-diphenyl-
1,3,4-oxadiazole, 2,5-bis-
(4-diethylaminophenyl)-1,3,4-oxadiazole, bis-diethylaminophenyl-1,3,6-oxadiazole, 4,4'-bis(diethylamino)-2,2'-dimethyl Triphenylmethane, 2,4,5-triaminophenyl imidazole, 2,5-bis(4-diethylaminophenyl)-1,3,4-triazole, 1-phenyl-3-(4-diethylaminostyryl)-5 −
(4-diethylaminophenyl)-2-pyrazoline, p-diethylaminobenzaldehyde-(diphenylhydrazone), etc. Examples of suitable electron transport materials are 2-nitro-9-fluorenone,
2,7-dinitro-9-fluorenone, 2,4,
7-trinitro-9-fluorenone, 2,4,
5,7-tetranitro-9-fluorenone, 2-
These include nitrobenzothiophene, 2,4,8-trinitrooxanthone, dinitroanthracene, dinitroacridine, dinitroanthraquinone, and the like. These may be used alone or in combination of two or more. Of course, there is no problem in using a complex of an electron-accepting substance and an electron-donating substance as the charge-transporting substance so that both holes and electrons can be transported. When the charge transport material is a low-molecular material, it is necessary to disperse the charge transport material in the binder resin mentioned above. Even in the case of a molecular substance, it is desirable to use the binder resin exemplified above for the purpose of reinforcing mechanical properties and increasing adhesion. In this embodiment of the invention, the disazo pigment as a charge generating agent is used in an amount of 1 part by weight per 100 parts by weight of the entire photosensitive layer.
It is preferred to use amounts of from 2 to 30 parts by weight, especially from 2 to 20 parts by weight. According to yet another aspect of the invention, a charge generation layer containing the aforementioned disazo pigment is provided on a conductive substrate, and a charge transport layer is provided on the charge generation layer. The charge generation layer may be formed by vapor depositing the above-mentioned disazo pigment on a substrate, or may be formed by coating and drying a dispersion in an appropriate organic solvent. Alternatively, as in the first embodiment, a composition in which a disazo pigment is dispersed in a binder resin may be applied onto a conductive substrate. Also,
The charge transport layer is easily formed by coating with the charge transport material detailed in the second embodiment. The thickness of the charge generation layer is 0.1 in the case of vapor deposition.
It can vary from microns to 3 microns for resin-pigment dispersions, while the charge transport layer is preferably between 5 and 30 microns thick. The disazo pigment used in the present invention exhibits particularly excellent sensitivity when used as the third type of photosensitive layer, that is, a functionally separated photosensitive layer consisting of a charge generation layer and a charge transport layer. The invention is illustrated by the following example. Synthesis example 4,4'-diaminodiphenylamine sulfate 6
parts by weight (hereinafter referred to as parts), 15 parts of 35% hydrochloric acid, 2.5 parts of anhydrous calcium chloride and 75 parts of water were mixed and dissolved,
While cooling to below 10°C, an aqueous solution of 3 parts of sodium nitrite dissolved in 25 parts of water was gradually added dropwise to effect tetrazotization. After evaporation, this liquid was added dropwise to an aqueous solution consisting of 10.5 parts of 3-hydroxy-2-naphthanilide, 6.5 parts of 48% sodium hydroxide, and 400 parts of water, and a coupling reaction was carried out at about 30°C. Immediately after the end of the reaction, add dilute hydrochloric acid to make a slightly acidic solution.
The pH was adjusted and the reaction product was aged while heating. After the reaction was completed, filtration, water washing, drying (100°C), and pulverization were performed to obtain 12 parts of the following disazo pigment. The following disazo pigments are synthesized in the same manner as in the synthesis example.

[Table] Example 1 2 parts by weight each of azo pigments No. 1, 2, 3, 4 and 5 (hereinafter referred to as parts), 6 parts of polyester resin (Toyobo Co., Ltd. Vylon 200) and tetrahydrofuran (hereinafter referred to as THF) 65 parts were ground and mixed in a ball mill to prepare a coating solution. This coating solution was applied onto a 100 μm thick aluminum foil using a wire bar, and then dried at 100° C. for 30 minutes to obtain an electrophotographic photoreceptor. After storing these photoreceptors in the dark, they are charged by positive corona discharge, and brought into close contact with a positive original (an image is formed on a transparent film) under a photoreceptor surface illuminance of 80 lux for 1 to 2 seconds. The image was exposed to light, then developed using a negative two-component developer (manufactured by Sanda Kogyo, developer for DC-15), transferred to plain paper (90 μm thick bond paper), and heat-fixed. However, we were able to obtain fog-free, high-contrast copies that were faithful to the originals. Example 2 3 parts of azo pigment No. 2, 30 parts of p-diethylaminobenzaldehyde (diphenylhydrazone),
30 parts of polyester resin and 190 parts of THF were pulverized and mixed in a ball mill, and an electrophotographic photoreceptor was produced in the same manner as in Example 1. After being stored in the dark, the sample was charged by positive or negative corona discharge using a commercially available surface electrometer (Kawaguchi Electric Model SP-428), and the surface potential was measured and then the optical attenuation was measured. Table 1 shows the results.
Shown below.

[Table] The photosensitivity is expressed as the amount of light required to attenuate the light to 1/2 of the surface potential. According to the results, it was found that the disazo pigment of the present invention has high sensitivity in both positive and negative directions. In addition to the hole transport materials used in this example, 2,5-bis-(4-diethylaminophenyl)-1,3,4-oxadiazole, 1-phenyl-3-(4-diethylaminostyryl)- 5
-(4-diethylaminophenyl)-2-pyrazoline or 4,4'-benzylidene-bis(N,N'-diethyl-m-toluidine), etc. could also be used for similar purposes. Example 3 5 parts of Azo Pigment No. 1 and 85 parts of THF were pulverized and mixed in a ball mill, and this dispersion was applied onto a 100 μm thick aluminum foil using a wire bar, and air dried to generate a charge with a film thickness of 1 μm. formed a layer. Next, a coating solution consisting of 3 parts of p-diethylaminobenzaldehyde (diphenylhydrazone), 5 parts of polyester resin, and 30 parts of THF was applied thereon using a doctor blade and dried (100°C, 30 minutes).
Then, a charge transport layer with a thickness of 13 μm was provided. The charging characteristics of this photoreceptor showed a surface potential of -700 V and a photosensitivity of 5.6 lux·sec when negatively charged.

Claims (1)

[Claims] 1. The following formula An electrophotographic photoreceptor comprising a photosensitive layer containing a disazo pigment represented by the following formula, wherein each of R ₁ and R ₂ represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a halogen atom. . 2. The photoreceptor according to claim 1, wherein the photosensitive layer is a photosensitive layer formed by dispersing the disazo pigment in an electrically insulating binding medium. 3 The disazo pigment is 5 parts per 100 parts by weight of the binder.
A photoreceptor according to claim 2, wherein the photoreceptor is present in an amount of from 100 parts by weight. 4. The photoreceptor according to claim 1, wherein the photosensitive layer is a photosensitive layer comprising the disazo pigment dispersed as a charge generating pigment in a charge transporting material. 5. The photoreceptor according to claim 4, wherein the disazo pigment is present in an amount of 1 to 30 parts by weight per 100 parts by weight of the entire photosensitive layer. 6. The photoreceptor according to claim 1, wherein the photosensitive layer comprises a charge generating layer containing the disazo pigment provided on a conductive substrate, and a layer of a charge transporting material thereon. 7. The photoreceptor of claim 6, wherein the charge generation layer has a thickness of 0.1 to 3 microns and the charge transport layer has a thickness of 5 to 30 microns.