JPH06222593A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To provide an excellent electrophotographic sensitive body having satisfactory electrophotographic characteristics such as electrification ability, dark attenuation, environmental stability and repetition stability, high sensitivity, low background potential and a low residual potential. CONSTITUTION:This electrophotographic sensitive body has a photosensitive layer on the electric conductive substrate and the photosensitive layer contains a bisazo compd. represented by the formula and a benzidine compd. satisfying the relation of WS-WB>=-0.1eV (where WB is the work function of the bisazo compd. and WS is the work function of the benzidine compd.). In the formula, Y is H, an alkyl, alkoxyl, halogen, cyano, nitro or hydroxyl and A is a divalent arom. hydrocarbon group or a divalent heterocyclic group contg. N in the ring.

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, and more particularly to an organic photosensitive member for electrophotography.

[0002]

2. Description of the Related Art Conventionally, selenium has been used as an electrophotographic photoreceptor.
Although a photoconductor using an inorganic photoconductive substance such as cadmium sulfide and zinc oxide has been used, recently, a drum, a sheet, which is pollution-free and easy to be manufactured and handled,
Organic photoconductors that use organic photoconductive compounds, which have many advantages such as the ease of obtaining photoconductors of various shapes such as belts, will become the mainstream as photoconductors for plain paper copiers. It has become. These organic photoconductors are roughly classified into a photoconductive layer having a single layer type and a photoconductive layer having a photoconductive layer.

The photoconductive layer contains an organic photoconductive compound called a charge generating material as an essential component and is dispersed in a polymer binder resin. For these photoconductive layers, the charge generation material is not used alone, not only in the laminated type but also in the single layer type, and an organic compound that transports charge carriers generated in the charge generation material called a charge transport material is used. Is included. In addition, the photoconductive layer may contain an organic compound for increasing the efficiency of charge generation in the photosensitivity region of the charge generating material, a so-called chemical sensitizing material. It is also known that transport materials provide a sensitizing effect. As the charge generation material, various organic compounds have been proposed, but mainly bisazo pigments, phthalocyanine pigments, benzopyrylium pigments,
Perylene pigments and the like are known, and as the charge transport material, there are pyrazoline, hydrazone, polyvinylcarbazole and the like, and as the chemical sensitizing material, trinitrofluorene, tetracyanoquinodimethane, tetracyanoethylene and the like are known. Has been. These charge generating material, charge transporting material and chemical sensitizing material are not necessarily used in combination. That is, a charge transport material or a chemical sensitizing material effective for a specific charge generating material is not always effective for another charge transport material, and when the combination of both substances is inappropriate, Not only the electrophotographic sensitivity is lowered, but also the residual potential is increased,
In the worst case, the potential increases with each repeated use,
It cannot be practically used for electrophotography. As described above, there is no general guideline for obtaining the optimum combination, and the fact is that a large number of compounds are selected and determined by accumulation of experiments.

[0004]

Problems to be Solved by the Invention JP-A-63-3625
Japanese Unexamined Patent Publication No. 8 discloses a bisazo compound represented by the following general formula (I). This bisazo compound is a charge-generating material that has sensitivity in the near-infrared region and has wider color reproducibility than a bisazo compound that does not have a cyano group, and as a charge-generating material for semiconductor lasers. Also has the potential. However, no suitable charge transport material has been found for this bisazo compound.
For example, as the charge transport material, N, N'-diphenyl-
N, N'-bis (3-methylphenyl)-[1,1'-
When biphenyl] -4,4′-diamine is used,
The sensitivity is lower than that of charge generation materials that do not have cyano groups,
It has a drawback that the residual potential is also high.

The present invention has been made for the purpose of solving the above-mentioned problems in the prior art. That is, the object of the present invention is to obtain good electrophotographic properties such as chargeability, dark decay, environment and repetitive stability, good sensitivity, and good background potential and background potential even when the bisazo compound represented by the formula (I) is used. An object is to provide an excellent electrophotographic photoreceptor having a low residual potential.

[0006]

The above objects of the present invention are as follows.
In the photosensitive layer, as a charge generating material, the photosensitive layer has the following general formula (I):

[Chemical 3] (In the formula, Y represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group or a hydroxyl group, and A is a divalent aromatic hydrocarbon group or a divalent aromatic group containing a nitrogen atom in the ring. When the work function of the bisazo compound is WB and the work function of the benzidine compound is WS, the relationship of WS-WB ≥ -0.1 eV is obtained. This can be achieved by including a satisfying benzidine compound.

That is, the electrophotographic photoreceptor of the present invention comprises a conductive support and a photosensitive layer provided on the conductive support, and the photosensitive layer comprises a bisazo compound represented by the general formula (I) and a bisazo compound. Assuming that the work function is WB and the work function of the benzidine compound is WS, WS -WB ≥ -0.1
It is characterized by containing a benzidine compound satisfying the relationship of eV.

The present invention will be described in detail below. According to the present invention, the work function of the bisazo compound is WB,
When the work function of a benzidine compound is WS, WS
When a benzidine compound satisfying the relationship of -WB ≥ -0.1 eV is contained, the sensitivity of the bisazo compound is improved and the background potential is reduced. For the mechanism,
It can be considered as follows.

In an electrophotographic photoreceptor in which a charge transporting material or an organic sensitizing material is added in contact with a charge generating material,
Factors that affect the sensitivity, the background potential, and the residual potential are 1) the charge generation efficiency in the charge generation layer,
2) Charge injection efficiency from the charge generating material to the charge transporting material or from the charge transporting material to the charge generating material, 3) Charge transporting performance in the charge generating material and the charge transporting material, and in the case of a laminate, further 4) The charge transport properties of the charge transport layer and the charge generation layer are mentioned. Conventionally, the mechanism of sensitizing a charge-transporting material or an organic sensitizing material by contacting it with a charge-generating material has been explained by the difference in the ionization potential of the material, but it has not been fully clarified yet. Among the above factors, the improvement in sensitivity and the reduction in background potential are particularly related to the charge generation efficiency in the charge generation layer of 1). In the case of the present invention, the charge generation efficiency depends on the bisazo compound and the benzidine. The work function of the system compound is involved. When these work functions satisfy the above relationship, the charge generation efficiency in the charge generation layer is increased and the sensitizing effect is exhibited.

Here, a method of measuring the work function will be described. The work function used in the present invention is the difference between the Fermi level and the vacuum level, and based on the principle of contact potential difference,
It is a physical quantity measured by an ultraviolet electron emission measuring device (UPS) or a Kelvin method using a change in vibration capacity. Note that conventionally, a value measured by a photoelectron spectrometer AC-I manufactured by Riken Keiki Co., Ltd. may be defined as a work function.
The value measured by −I, that is, the value determined by measuring the photoelectron emission at room temperature by AC-I and plotting the power of the yield of photoelectrons against the energy of incident light, is In organic crystals such as charge generation materials,
It means an ionization potential, and does not mean a work function in the present invention. FIG. 1 illustrates the relationship between the work function and the ionization potential in the charge generation material. However, when the metal is measured by the photoelectron spectrometer AC-1 manufactured by Riken Keiki Co., Ltd., the work function can be measured by obtaining the threshold value of electron emission. This difference depends on the different electronic states of metal and semiconductor.

In the present invention, the work functions of the azobis compound and the benzidine compound are obtained by measuring the contact potential difference between the organic compound and the reference electrode with the contact potential difference measuring device according to the Kelvin method shown in FIG. You can In FIG. 2, reference numeral 1 is a reference electrode, which is made of brass plated with gold. Further, 2 is a base, which is also made of brass plated with gold, and the sample 3 is formed on the base. Sample 3 is a coating liquid in which an azobis compound and a benzidine compound are dispersed on a substrate 2 in an appropriate solvent, and the coating liquid is from 10 μm to 10 μm.
It is formed by coating so as to have a thickness of 0 μm and vacuum drying at 150 ° C. for 2 hours. 4 is an ammeter,
5 is an external power supply. The difference between the work function of Sample 3 and the work function of the reference electrode is the contact potential difference, and the measurement principle is as follows. When the sample 3 and the reference electrode, which are formed on the substrate 2 while maintaining electrical contact with each other, are opposed to each other with a gap of 1 to 2 mm, the substrate 2 and the reference electrode are electrically connected as shown in FIG. If the voltage is zero, a potential equal to the contact potential difference between the sample 3 and the reference electrode facing each other is generated. Sample 3 and the reference electrode are capacitors to which an electric potential is applied. When the reference electrode is vibrated,
The capacity of the capacitor changes and current flows through the circuit. Here, when a voltage having the opposite sign and equal to the contact potential is applied between the sample 3 and the reference electrode by the external power supply 5, the voltage applied to both ends of the capacitor becomes zero, and the current stops flowing. When this current is monitored by the ammeter 4 and the voltage when the current stops flowing is obtained, it corresponds to the contact potential difference between the sample 3 and the reference electrode. Here, the work function of the metal reference electrode can be measured by the photoelectron emission device AC-1 manufactured by Riken Keiki Co., Ltd. Therefore, if the contact potential difference with the reference electrode is known, the work function of the sample can be determined.

The bisazo compound in the present invention is represented by the above general formula (I), and specifically, for example, the following can be used.

[Table 1]

[0013]

[Table 2]

As the binder resin, polystyrene resin, silicone resin, polycarbonate resin, acrylic resin,
Methacrylic resin, polyester resin, polyvinyl acetal resin, vinyl chloride resin, vinyl acetate resin and copolymer resin containing two or more kinds of monomers constituting these resins, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride Known materials such as vinyl acetate-maleic anhydride copolymer may be used alone or in combination.

In the present invention, when the work function of the charge transport material is WCT and the work function of the bisazo compound represented by the general formula (I) is WB, WCT-WB≥-0.1 eV
In this case, both the sensitization and charge transport functions can be handled by the charge transport material alone. Also, WCT-WB <-
In the case of 0.1 eV, a benzidine compound having a work function WS satisfying WS -WB ≥ -0.1 eV is used together with the charge transport material. In the present invention, as the benzidine compound, those represented by the general formula (II) are preferably used.

[0016]

[Chemical 4] (In the formula, R ₁ represents a halogen atom or a cyano group,
R ₂ and R ₃ each represent a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, an alkoxycarbonyl group or a substituted amino group. )

Specifically, the following compounds can be exemplified.

[Chemical 5]

[0018]

[Chemical 6]

[0019]

[Chemical 7]

[0020]

[Chemical 8]

[0021]

[Chemical 9]

[0022]

[Chemical 10]

[0023]

[Chemical 11]

[0024]

EXAMPLES The present invention will be described below with reference to examples. Example 1 1 part by weight of a polyvinyl butyral resin (trade name: BLX; manufactured by Sekisui Chemical Co., Ltd.) was dissolved in 40 parts by weight of cyclohexanone, and the exemplified compound No. I-2 was mixed in an amount of 3 parts by weight, then well dispersed by a paint shaker, and this was coated on an aluminum sheet by an applicator,
It was dried to form a charge generation layer. The film thickness after drying is 0.2
was μm.

The TPD (N,
9 parts by weight of N'-diphenyl-N, N'-bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine), polycarbonate resin (trade name: Lexan 145, manufactured by GE) , Molecular weight 35,000-40,000
0, work function: 4.7 eV) 10 parts by weight, and the exemplified compound No. 1 part by weight of II-2 and 15 parts of dichloromethane
A uniform solution of 0 parts by weight was applied with an applicator and dried to form a charge transport layer having a film thickness of 20 μm.
Here, exemplary compound I-No. 2 and Exemplified Compound No. II-
The work functions of 2 are 4.9 eV and 4.9 eV, respectively.
And the difference was 0 eV.

The electrophotographic photosensitive member thus obtained is
The following characteristic evaluation was performed using an electrostatic copying paper test apparatus (SP-428, manufactured by Kawaguchi Denki Seisakusho). First, -6K
After negatively charging by corona charging of V, the surface potential Vpo (volt) at that time was measured by leaving it in the dark for 2 hours.
Then, light was irradiated using a tungsten lamp, the time until the surface potential became ½ of Vpo was determined, and the exposure amount E1 / 2 (lux · sec) was calculated. Furthermore, the same measurement was repeated 20 times. The results are shown in Table 3.

[0027]

[Table 3]

Examples 2 to 4 In Example 1, the exemplified compound No. Instead of I-2, exemplified compounds No. I-15, No. I-17, N
o. I-20 (except that each of Examples 2 to 4 was used,
An electrophotographic photosensitive member was produced in the same manner as in Example 1, and its characteristics were evaluated. Here, exemplary compound No. I-15,
No. I-17, No. The work functions of I-20 were 4.9, 4.9, and 5.0 eV, respectively. The results are shown in Table 4.

[0029]

[Table 4]

Example 5 2 parts by weight of polyvinyl butyral resin (trade name: BLX; manufactured by Sekisui Chemical Co., Ltd.) was dissolved in 80 parts by weight of cyclohexanone, and the exemplified compound No. 6 parts by weight of Exemplified Compound No. 1 part by weight of II-1 was added and mixed, and then well dispersed with a paint shaker, and this was coated on an aluminum sheet with an applicator and dried to form a charge generation layer. The film thickness after drying was 0.2 μm. Here, exemplary compound No. The work function of II-1 is 5.
It was 0 eV, and the difference WS-WB was +0.1 eV. 9 parts by weight of TPD, polycarbonate resin ((trade name: Lexan 145, manufactured by GE, molecular weight 35,000 to 40,000, work function:
A uniform solution of 10 parts by weight (4.7 eV) and 150 parts by weight of dichloromethane was applied with an applicator and dried to form a charge transport layer. The film thickness was 20 μm. The characteristics of the electrophotographic photosensitive member obtained as described above were evaluated in the same manner as in Example 1. The results are shown in Table 5.
It was as shown in.

[0031]

[Table 5]

Comparative Examples 1 to 4 In Examples 1 to 4, the compound No.
An electrophotographic photosensitive member was produced in the same manner as in Examples 1 to 4 except that II-3 was not included, and its characteristics were evaluated. The results are shown in Table 6.

[0033]

[Table 6]

Comparative Example 5 In Example 5, the compound No. of Exemplified Compound No. was added to the charge generation layer. II-
An electrophotographic photosensitive member was produced in the same manner as in Example 5 except that 1 was not included, and its characteristics were evaluated. The results are shown in Table 7.

[0035]

[Table 7]

[0036]

The electrophotographic photoreceptor of the present invention uses the bisazo compound represented by the formula (I) as the charge generating material, and the work function of the bisazo compound, as is clear from the comparison of the above Examples and Comparative Examples. Is WB and the work function of the benzidine compound is WS, WS -WB ≥ -0.1
By containing the benzidine compound satisfying the relationship of eV, the compound has excellent sensitivity as compared with the case where the benzidine compound is not contained, and the electron emission such as charging property, dark decay, photosensitive stability and repetitive stability is improved. It has excellent photographic characteristics and low background potential and residual potential.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining a difference between a work function and an ionization potential in a charge generation material.

FIG. 2 is a schematic diagram of a contact potential difference measuring device by the Kelvin method.

[Explanation of symbols]

1 ... reference electrode, 2 ... substrate, 3 ... sample, 4 ... ammeter,
5 ... External power supply.

Claims (3)

[Claims] 1. An electrophotographic photoreceptor having a photosensitive layer on a conductive support, wherein the photosensitive layer has the general formula (I): (In the formula, Y represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group or a hydroxyl group, and A is a divalent aromatic hydrocarbon group or a divalent aromatic group containing a nitrogen atom in the ring. When the work function of the bisazo compound represented by a heterocyclic group) and the work function of the bisazo compound are WB and the work function of the benzidine compound is WS, WS-
An electrophotographic photoreceptor containing a benzidine compound satisfying the relationship of WB ≥ -0.1 eV. 2. A benzidine compound is represented by the following general formula (I
I) [Chemical 2] (In the formula, R ₁ represents a halogen atom or a cyano group,
R ₂ and R ₃ each represent a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, an alkoxycarbonyl group or a substituted amino group. The electrophotographic photoreceptor according to claim 1, which is a benzidine compound represented by the formula (1). 3. The electrophotographic photosensitive material according to claim 1, wherein the photosensitive layer comprises a charge generation layer and a charge transport layer, and the charge generation layer contains the benzidine compound represented by the general formula (II). body.