JPH0363745B2 - - 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 in electrophotographic light-sensitive materials (for example, Japanese Patent Application Laid-open No. 37543/1983). However, in the field of electrophotography there is a constant demand for increasing the imaging speed, 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, disazo photoconductive pigments exhibit relatively high sensitivity when positively charged when used as a photoreceptor consisting of a single photoconductive layer and a conductive substrate; In some cases, the sensitivity tends to be low. For example, known disazo photoconductive pigments are derived by coupling 3,3'-dimethoxybiphenyltetrazolium salt and 3-hydroxy-2-naphthanilide, as shown in the above-mentioned publication. However, in the case of negative charge, it shows only a small sensitivity. 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 charge but also for negative charge. 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 easily obtained by subjecting 4,4'-diaminodiphenylamine to tetrazotization by reacting it with sodium nitrite according to a conventional method.
At this time, -NH- also easily becomes >N-NO. 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 used as a photoconductive pigment dispersed in an electrically insulating binding medium and the composition applied as a photoconductive layer on an electrically conductive substrate. Disazo pigments have a particle size of 5 μm or less, especially 2 μm.
It is preferable to perform fine dispersion so that the particle size is less than m. In this embodiment, as the insulating binding medium, polyester resin, acrylic resin, styrene resin, epoxy resin, silicone resin, alkyd resin, vinyl chloride-vinyl acetate copolymer, etc. are used. Disazo pigments are preferably used in amounts of 5 to 100 parts by weight, especially 10 to 50 parts by weight, per 100 parts by weight of binder. As the conductive substrate, a sheet or drum-shaped metal substrate or conductively treated paper is used, and the coating amount of the photoconductive layer is 3 to 20 g/m ² , especially 5 to 10 g/m ² on a dry basis. It is recommended that the range be within the range of . In another aspect of the invention, the disazo pigment is dispersed as a charge-generating pigment in a layer containing a charge transport material, and this dispersed 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'-dimethyltriphenylmethane, 2,4,5-triaminophenyl imidazole, 2,5-bis(4-diethylaminophel)-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-trinylo-9-fluorenone, 2,
4,5,7-tetranitro-9-fluorenone,
2-nitrobenzothiophene, 2,4,8-trinitrothioxanthone, dinitroanthracene,
These include dinitroacridine and dinitroatraquinone. These may be used alone or in combination of two or more. Of course, there is no problem in making it possible to transport both holes and electrons by using an electron-accepting substance, an electron-donating substance, and a complex as the charge-transporting substance. 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 0.1μm in case of vapor deposition.
It can vary from 3μm of resin-pigment dispersion,
On the other hand, the charge transport layer preferably has a thickness of 5 to 30 μm. The disazo pigment used in the present invention exhibits particularly excellent sensitivity when used as a photosensitive layer of the third type, 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 (1) 4,4'-diaminodiphenylamine 1.99g
(0.01 mol) in a beaker shielded from sunlight,
Add 36 ml of 18N HCl and stir to dissolve. While maintaining the liquid temperature at 5 to 10°C, 6.0 ml of a 5N aqueous solution of NaNo ₂ is added dropwise using a separating funnel. After the dropwise addition is completed, the mixture is stirred for a while to complete the tetrazotization. Next, the solution is filtered, and 3 ml of a 10N Zncl ₂ hydrochloric acid aqueous solution is added to the solution, followed by a small amount of common salt to precipitate the tetrazonium salt. The precipitated tetrazonium salt was separated, washed with a very small amount of saline, dissolved in 30 ml of N,N'-dimethylformamide, and placed in a separatory funnel protected from sunlight. Also, naphthol AS-
5.82 g (0.02 mol) of MX is dissolved in 100 ml of N,N'-dimethylformamide and cooled to 5-15°C. A concentrated aqueous solution of sodium acetate is added to the mixture to make it slightly alkaline, and a solution of the above tetrazonium salt in N,N'-dimethylformamide is gradually added dropwise from the separating funnel while stirring. During the dropwise addition, maintain the pH between 6.0 and 9.0 with a concentrated aqueous solution of sodium acetate. After the addition was completed, the mixture was further stirred for 1 hour and the temperature was returned to room temperature. Separate the pigment crystals generated by centrifugation,
Disperse in 500 c.c. of water to remove impurities such as inorganic salts, and then perform extraction and purification with acetone using a Soxhlet extractor for 5 days. After purification, the pigment crystals are vacuum dried and used as a sample (No. 1). The analysis results of this sample (No. 1) are shown below, and the structural formula is shown in Table 1. Appearance: Blue-purple crystal yield: 6.07 g (73.0% of theory) IR spectrum: Nitrosamine 1480 cm ^-1 (〓N-O) 1170 cm ^-1 (〓C-N) 1010 cm ^-1 (〓N-N) Acid amide 1660 cm ^-1 (〓C=O) 3300~3200cm ^-1 (〓N-H) Elemental analysis value;

[Table] (2) Bisazo pigments No. 2 to No. 6 were synthesized in the same manner as in (1), and their structural formulas are also shown in Table 1.

【table】

[Table] Example 1 No. 1 azo pigment 0.3 parts Hydrazone compound of the following structural formula 2.1 parts Byron 200 (manufactured by Toyobo Co., Ltd.) 3.0 parts Tetrahydrofuran 30 parts were dispersed and mixed in a ball mill for 6 hours, the resulting dispersion was applied onto approximately 50 μm aluminum foil with a wire bar, and heated at 100°C for 30 minutes. Dry for 10 minutes to a thickness of 10 μm.
A photoreceptor was obtained. Using a commercially available surface potentiometer (SP-428 manufactured by Kawaguchi Electric Co., Ltd.), corona discharge of ±6KV was performed for 5 seconds to make it positively or negatively charged, and the surface potential at that time was left in the dark for 5 seconds. Measure V ₀ ,
Next, the sample surface was illuminated with an illuminance of 20° from a tungsten lamp.
The photosensitive layer is irradiated with light so that the surface potential becomes 1/2 of V _{0, and the time (seconds) required for the surface potential to become 1/2 of V 0} is determined and the half-reduced exposure amount E 1/2 (illuminance x time; unit lux seconds) was measured. The results are shown in Table 2.

[Table] Examples 2 to 6 No. 2 to 6 instead of azo pigment No. 1 of Example 1
Table 3 shows the results of the test conducted in the same manner as in Example 1, except that the azo pigment was used.

【table】

[Table] Example 7 1 part of No. 1 bisazo pigment, copolyester resin of terephthalic acid, neopentyl glycol, and 1,4 cyclohexanedimethanol (1:1)
1.5 parts of tetrachloroethane and 10 parts of tetrachloroethane were dispersed and mixed in a ball mill for 6 hours, coated on a 50 μm thick aluminum foil with a wire bar, and dried at 100°C for 30 minutes to form a 0.6 μm thick charge generation layer. Formed. Furthermore, on top of this, the same hydrazone compound 2 as in Example 1 was added.
A mixed yellow solution consisting of 2 parts of Vylon 200, 2 parts of tetrahydrofuran, and 20 parts of tetrahydrofuran was applied using a doctor blade and dried at 80° C. for 30 minutes to form a charge transport layer with a thickness of about 10 μm. The characteristics of this laminated photoreceptor are V ₀ =-474V, E1/
2 = 2.0 lux seconds. In addition, when this laminated photoreceptor is pasted on the surface of an actual photoreceptor drum and copied using a two-component developer using a DC-15 machine manufactured by Sanda Kogyo Co., Ltd., a high-resolution copy image with no capri that is faithful to the original is produced. I got it.

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 in which the disazo pigment is dispersed as a charge-generating pigment in a layer containing a charge transporting substance. 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 according to claim 6, wherein the charge generation layer has a thickness of 0.1 to 3 μm and the charge transport layer has a thickness of 5 to 30 μm.