JPH0756364A - Electrophotographic photoreceptor - Google Patents

Abstract

PURPOSE:To improve sensitivity without decreasing mobility when two or more kinds of charge transfer materials are mixed and used by controlling the ionizing potential to a specified value. CONSTITUTION:A hydrazone compd. expressed by chemical formula I (with 5.05eV ionizing potential) and a diamine compd. expressed by formula II (with 5.10eV ionizing potential) as charge transfer materials in total 5 pts.wt. and 5 pts.wt. of polycarbonate resin are dissolved in dichloromethane to prepare a coating liquid for transfer of charges. Then a charge transfer layer is formed on a polyester terephthalate film on which aluminum is vapor deposited. In this process, when the difference of ionizing potentials between charge transfer materials is less than 0.1eV, the number of hole traps in the photosensitive layer decreases and sensitivity can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoconductor used in electrophotographic printers, copying machines, and the like.
In particular it relates to a charge transport material for the photosensitive layer.

[0002]

2. Description of the Related Art Conventionally, as a photosensitive material for an electrophotographic photoreceptor (hereinafter also referred to as a photoreceptor), an inorganic photoconductive substance such as selenium or a selenium alloy, or an inorganic photoconductive substance such as zinc oxide or cadmium sulfide is used as a resin. An organic photoconductive substance such as poly-N-vinylcarbazole or polyvinylanthracene dispersed in a binder, or an organic photoconductive substance such as a phthalocyanine compound or a bisazo compound is dispersed in a resin binder. The thing and the thing vapor-deposited by vacuum are used.

Organic photoconductive materials have advantages such as flexibility, thermal stability, film forming property, transparency, and cost as compared with inorganic photoconductive materials, but they are inferior in terms of dark resistance and photosensitivity. ing.
Therefore, by taking advantage of the film-forming property, the photosensitive layer is formed into a layer in which the layer mainly contributing to the charge generation and the layer contributing to the surface charge in the dark place and the layer contributing to the charge transport at the time of light reception are separated, and suitable for the function of each layer. We are working to improve the electrophotographic characteristics by selecting different materials and put them into practical use.

This type of laminated photoreceptor has a structure in which a charge generating layer containing an organic charge generating substance and a charge transporting layer containing an organic charge transporting substance are formed. The charge generation layer is made of a phthalocyanine compound having an absorption peak in the infrared light region for a laser beam printer, and an azo compound having an absorption peak in the visible light region for a copying machine as a charge generation substance. It is formed by coating with a coating liquid dispersed in a binder substance binder.

For example, the Carlson method is applied to the image formation by the electrophotographic method using these photoconductors. Image formation by this method is performed by corona discharge to a photoconductor in a dark place, formation of an electrostatic latent image such as characters and pictures of an original on the surface of the charged photoconductor, and electrostatic latent image formed. Of the toner image, the developed toner image is fixed on a support such as paper, and the photoconductor after the toner image transfer is neutralized, residual toner is removed, and light is neutralized before reuse. To be done.

In recent years, electrophotographic photoreceptors using organic materials have been put into practical use because of their advantages such as flexibility, thermal stability and film-forming property. For example, a photoreceptor composed of poly-N-vinylcarbazole and 2,4,7-trinitrofluoren-9-one (described in US Pat. No. 3,484,237), a photoreceptor containing an organic pigment as a main component (JP 47-3
No. 7543), a photoconductor containing a Kyosho complex composed of a dye and a resin as a main component (described in JP-A-47-10735), and the like.

[0007]

Although the organic photoreceptor has many advantages as described above, the characteristics required for the photoreceptor are charging characteristics, dark decay characteristics, light decay characteristics, repetitive characteristics, light fatigue characteristics, At present, there is no one that satisfies all characteristics such as spectral characteristics and response characteristics.

The development of charge transport materials has been used as one strategy to improve properties. The charge transport material has advantages and disadvantages, and since one type of charge transport material cannot obtain sufficient characteristics, a plurality of charge transport materials are mixed to improve the characteristics. For example, when a charge transport material having a poor charge retention rate in the dark is mixed with a charge transport material having a good charge retention rate in the dark to improve the charge retention rate in the dark or a charge transport material having a poor solubility, another charge transport material is mixed. In order to facilitate the preparation of the coating solution. However, there is a problem that the mobility decreases when the two charge transport materials are mixed.

The present invention has been made in view of the above points, and an object thereof is to provide an electrophotographic photosensitive member having excellent characteristics by preventing a large decrease in mobility during mixing of a charge transporting substance.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on the relationship between the mixture of charge transport materials and their properties, and have found that the ionization potential has a relationship with mobility and sensitivity. Came to make. According to the first aspect of the present invention, a photosensitive layer is provided on a conductive substrate, and the photosensitive layer contains a plurality of charge transporting substances, and the ionization potentials of the charge transporting substances are different from each other by 0.1 eV.
This is achieved by:

According to the second invention, the photosensitive layer is provided on the conductive substrate, and the photosensitive layer contains two charge transporting substances, and the difference in ionization potential of the charge transporting substance is 0.1 eV.
It is achieved by making the content ratio of the charge transport material having a small ionization potential higher than that of the charge transport material having a large ionization potential.

[0012]

When the difference between the ionization potentials of the charge transport materials is 0.1 eV or less, the number of hole traps in the photosensitive layer is reduced and the sensitivity is improved. Even if the difference in ionization potential is 0.1 eV or more, if the content ratio of the charge transport material having a small ionization potential is larger than that of the charge transport material having a large ionization potential, the number of hole traps in the photosensitive layer decreases and the sensitivity is decreased. Is improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a sectional view showing a negatively charged electrophotographic photosensitive member according to an embodiment of the present invention. FIG. 4 is a sectional view showing a positively charged electrophotographic photosensitive member according to an embodiment of the present invention.

In the negative charging laminated type photoreceptor, the charge generation layer 12 and the charge transport layer 13 are sequentially laminated on the conductive substrate 11. 1
Reference numeral 4 denotes a photosensitive layer, which is a function separation type in which a charge generation layer and a charge transport layer are separated. In the positive charging laminated type photoreceptor, the charge transport layer 13, the charge generation layer 12, and the surface coating layer 15 are sequentially laminated on the conductive substrate 11. 14 is a photosensitive layer.

The conductive substrate 11 serves not only as an electrode of the photoconductor but also as a support for each of the other layers, which may be cylindrical, plate-shaped or film-shaped, and is made of aluminum, stainless steel, A metal such as nickel, glass, resin, or the like that has been subjected to a conductive treatment may be used.
The charge generation layer 12 is formed by applying a material in which particles of a charge generation substance are dispersed in a resin binder or by a method such as vacuum deposition, and receives light to generate charges. Further, it is important that the charge generation efficiency is high, and at the same time that the generated charge is injectable into the charge transport layer 13 or the surface coating layer 15, and the electric field dependency is small and the injection is good even in a low electric field. As the charge generating substance, phthalocyanine compounds such as metal-free phthalocyanine and titanyl phthalocyanine, dyes such as various azo, quinone, indigo pigments or cyanine, squarylium, azurenium and pyrylium compounds, selenium or selenium compounds, etc. are used for image formation. A suitable substance can be selected according to the light wavelength region of the exposure light source used. Since the charge generation layer 12 only needs to have a charge generation function, its thickness is determined by the light absorption coefficient of the charge generation substance and is generally 5 μm or less, preferably 1 μm or less. The charge generation layer may be mainly composed of a charge generation substance and a charge transporting substance or the like may be added thereto. As a resin binder,
Polycarbonate, polyester, polyamide, polyurethane, vinyl chloride, phenoxy resin, polyvinyl butyral, diallyl phthalate resin, methacrylic acid ester polymers and copolymers and the like can be appropriately combined and used.

The charge-transporting layer 13 is a coating film in which a charge-transporting substance is dispersed in a resin binder. The charge-transporting layer 13 holds an electric charge of the photoconductor as an insulating layer in a dark place, and the charge injected from the charge-generating layer when receiving light. Exert the function of transporting. As the resin binder, polymers and copolymers of polycarbonate, polyester, polystyrene, methacrylic acid ester, etc. can be used, but in addition to mechanical, chemical and electrical stability and adhesiveness, charge transfer substances Compatibility is important.

The thickness of the charge transport layer is preferably in the range of 3 to 50 μm, and more preferably 10 to 40 μm in order to maintain a practically effective surface potential. Examples of the charge transport material are represented by chemical formulas (I-1) to (I-6). The ionization potentials of these compounds are as follows. The ionization potential was measured using an atmospheric photoelectron emission device (AC-1 manufactured by Riken Keiki Co., Ltd.). 5.05eV, 5.10eV, 5.25e
V, 5.30 eV, 5.10 eV, 5.10 eV

[0018]

[Chemical 1]

The surface coating layer 15 has excellent durability against mechanical stress and is made of a chemically stable substance.
In a dark place, it has the function of receiving and holding the electric charge of corona discharge, and also has the ability to transmit the light to which the charge generation layer is sensitive, and transmits the light during exposure to reach the charge generation layer,
It is necessary to neutralize and eliminate the surface charges by receiving the injection of the generated charges. Further, as described above, it is desirable that the coating material is as transparent as possible in the wavelength region where the light absorption maximum of the charge generating substance is maximum.

As a coating material for the surface coating layer, a modified silicone resin such as an acrylic modified silicone resin, an epoxy modified silicone resin, an alkyd modified silicone resin, a polyester modified silicone resin, a urethane modified silicone resin, or the like, or a hard coating agent is used. Silicon resin, etc. can be applied. These modified silicone resins can be used alone, but SiO ₂ and Ti are used for the purpose of improving durability.
A mixed material with a condensate of a metal alkoxy compound capable of forming a film containing O ₂ , In ₂ O ₃ and ZrO ₂ as a main component is preferable.

The film thickness of the coating layer itself depends on the composition of the coating layer, but can be arbitrarily set within a range such that the residual potential does not increase when repeatedly used continuously. Example 1 1 part by weight of a bisazo compound represented by the chemical formula (II) as a charge generating substance and 1 part by weight of a diallyl phthalate resin (trade name DAP K, manufactured by Osaka Soda) as a binder resin were mixed with 150 parts by weight of methyl ethyl ketone. Kneading was performed for 3 hours to prepare a coating liquid for the charge generation layer.

5 parts by weight of a hydrazone compound represented by the chemical formula (I-1) as a charge transport material, and a chemical formula (I-2)
5 parts by weight of the diamine compound represented by and 10 parts by weight of a polycarbonate resin (trade name: Panlite L-1225 manufactured by Teijin Chemicals) were dissolved in dichloromethane to prepare a coating solution for the charge transport layer. Next, a charge generating layer (1 μm) and a charge transporting layer (20 μm) were formed in this order on a polyester terephthalate film on which aluminum was vapor deposited to prepare a negative charging photoreceptor.

[0023]

[Chemical 2]

The electrophotographic characteristics of the photoconductor thus obtained were measured by the electrostatic recording paper testing apparatus "SP-428" manufactured by Kawaguchi Electric Co., Ltd.
Was measured using. The surface potential V _S (V) of the photoconductor is the initial surface potential when the surface of the photoconductor is negatively charged by the corona discharge of −6.0 kV in the dark, and then for 2 s after the corona discharge is stopped. The surface potential Vd (volt) when kept in a dark place was measured, and then the surface potential Vd (volt) was measured by irradiating the photoreceptor surface with white light with an illuminance of 2 lx.
Half decay exposure amount E
_{It was set to 1/2} (lx · s). The surface potential when white light with an illuminance of 2 lx was irradiated for 10 s was defined as the residual potential Vr (volt). The measurement results are shown in Table 1.

Next, as a charge transport substance, the chemical formula (I-1)
5 parts by weight of the hydrazone compound represented by and the diamine compound represented by the chemical formula (I-2) in total, and 5 parts by weight of a polycarbonate resin (trade name Panlite L-1225 manufactured by Teijin Kasei) are dissolved in dichloromethane. A coating solution for the charge transport layer was prepared. Next, a charge transport layer (20 μm) was applied on a polyester terephthalate film on which aluminum was vapor deposited, and a semitransparent gold electrode was vapor deposited on this sample to obtain a sample. The mobility of this sample was measured by the usual time-of-flight method. The electric field is 3 × 10 V ⁶ / cm.

FIG. 1 is a diagram showing the composition dependence of the mobility of the hydrazone compound represented by the chemical formula (I-1). The hydrazone compound represented by the chemical formula (I-1) has an ionization potential of 5.05 eV and a mobility of 1.0 × 10 ^−5.
cm ² / V · s, the ionization potential of the diamine compound represented by the chemical formula (I-2) is 5.10 eV, and the mobility is 1.5 × 10 ⁻⁵ cm ² / V · s. The mobility shows an intermediate value between the two in any mixing ratio. Example 2 A photoreceptor in the same manner as in Example 1 except that 5 parts by weight of the styryl compound represented by the chemical formula (I-3) and 5 parts by weight of the styryl compound represented by the chemical formula (I-4) are used as the charge transport material. Was produced. Example 3 A photoconductor was carried out in the same manner as in Example 1 except that 5 parts by weight of the diamine compound represented by the chemical formula (I-5) and 5 parts by weight of the hydrazone compound represented by the chemical formula (I-6) were used as the charge transport material. Was produced. Comparative Example 1 A photoconductor was prepared in the same manner as in Example 1 except that 10 parts by weight of the hydrazone compound represented by the chemical formula (I-1) was used as the charge transport material. Comparative Example 2 A photoconductor was prepared in the same manner as in Example 1 except that 10 parts by weight of the styryl compound represented by the chemical formula (I-3) was used as the charge transport material. Comparative Example 3 A photoconductor was prepared in the same manner as in Example 1 except that 10 parts by weight of the diamine compound represented by the chemical formula (I-5) was used as the charge transport material. Example 4 A photoreceptor as in Example 1 except that the charge transporting material is replaced by 8 parts by weight of the hydrazone compound represented by the chemical formula (I-1) and 2 parts by weight of the styryl compound represented by the chemical formula (I-3). Was produced.

The electrophotographic characteristics of the photoconductor thus obtained were measured by the electrostatic recording paper testing apparatus "SP-428" manufactured by Kawaguchi Denki Co., Ltd.
Was measured using. The surface potential V _S (V) of the photoconductor is the initial surface potential when the surface of the photoconductor is negatively charged by the corona discharge of −6.0 kV in the dark, and then for 2 s after the corona discharge is stopped. The surface potential Vd (volt) when kept in a dark place was measured, and then the surface potential Vd (volt) was measured by irradiating the photoreceptor surface with white light with an illuminance of 2 lx.
Half decay exposure amount E
_{It was set to 1/2} (lx · s). The surface potential when white light with an illuminance of 2 lx was irradiated for 10 s was defined as the residual potential Vr (volt). The measurement results are shown in Table 1.

Next, as the charge transport material, the chemical formula (I-1) is used.
5 parts by weight of the hydrazone compound represented by and the styryl compound represented by the chemical formula (I-3) in total, and 5 parts by weight of a polycarbonate resin (trade name: Panlite L-1225 manufactured by Teijin Kasei) are dissolved in dichloromethane. A coating solution for the charge transport layer was prepared. Next, a charge transport layer (20 μm) was applied on a polyester terephthalate film on which aluminum was vapor deposited, and a semitransparent gold electrode was vapor deposited on this sample to obtain a sample. The mobility of this sample was measured by the usual time-of-flight method. The electric field is 3 × 10 ⁶ V / cm.

FIG. 2 is a diagram showing the composition dependence of the mobility of the hydrazone compound represented by the chemical formula (I-1). The hydrazone compound represented by the chemical formula (I-1) has an ionization potential of 5.05 eV and a mobility of 1.0 × 10 ^−5.
cm ² / V · s, the ionization potential of the styryl compound represented by the chemical formula (I-3) is 5.25 eV, and the mobility is 2.0 × 10 ⁻⁵ cm ² / V · s. The mobility changes greatly depending on the composition. The mobility increases as the content ratio of the charge transporting material having a low ionization potential is higher than that of the charge transporting material having a high ionization potential. Example 5 Photoreceptor similar to Example 1 except that the charge transport material was changed to 8 parts by weight of the diamine compound represented by the chemical formula (I-2) and 2 parts by weight of the styryl compound represented by the chemical formula (I-4). Was produced. Example 6 A photoreceptor was prepared in the same manner as in Example 1 except that the charge transport material was replaced by 8 parts by weight of the hydrazone compound represented by the chemical formula (I-6) and 2 parts by weight of the styryl compound represented by the chemical formula (I-3). Was produced. Comparative Example 4 A photoreceptor was prepared in the same manner as in Example 1 except that 2 parts by weight of the hydrazone compound represented by the chemical formula (I-1) and 8 parts by weight of the styryl compound represented by the chemical formula (I-3) were used as the charge transport material. It was made. Comparative Example 5 A photoreceptor was prepared in the same manner as in Example 1 except that 2 parts by weight of the diamine compound represented by the chemical formula (I-2) and 8 parts by weight of the styryl compound represented by the chemical formula (I-4) were used as the charge transport material. It was made. Comparative Example 6 A photoreceptor was prepared in the same manner as in Example 1 except that 2 parts by weight of the hydrazone compound represented by the chemical formula (I-6) and 8 parts by weight of the styryl compound represented by the chemical formula (I-3) were used as the charge transport material. It was made.

[0030]

[Table 1]

As can be seen from Table 1, in Examples 1 to 6, Vs is a negative value larger than -600V, Vr is a negative value smaller than -25V, and sensitivity E _1/2 is 1.4 lx · s or less. Satisfy the values at the same time. On the other hand, in the comparative examples, none of the above-mentioned numbers are satisfied at the same time, and the superiority of the electrophotographic photoreceptor according to the present invention is clear.

[0032]

According to the first aspect of the present invention, a photosensitive layer is provided on a conductive substrate, and the photosensitive layer contains a plurality of charge transporting substances, and the ionization potentials of the charge transporting substances have a difference of 0.
According to the second invention, the photosensitive layer is provided on the conductive substrate, and the photosensitive layer contains two charge transporting substances, and the difference between the ionization potentials of the charge transporting substances exceeds 0.1 eV. Since the charge transport material having a small ionization potential has a larger content ratio than the charge transport material having a large ionization potential, the difference in the ionization potentials of the charge transport material is 0.
When it is 1 eV or less, the number of hole traps in the photosensitive layer decreases, and as a result, an electrophotographic photoreceptor having excellent sensitivity can be obtained.

Even when the difference in ionization potential exceeds 0.1 eV, the number of hole traps in the photosensitive layer decreases if the content ratio of the charge transport material having a small ionization potential is larger than that of the charge transport material having a large ionization potential. Thus, an electrophotographic photoreceptor having excellent sensitivity can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the composition dependence of the mobility of a hydrazone compound represented by the chemical formula (I-1).

FIG. 2 is a diagram showing the composition dependence of the mobility of a hydrazone compound represented by the chemical formula (I-1).

FIG. 3 is a sectional view showing a negatively charged electrophotographic photoreceptor according to an embodiment of the present invention.

FIG. 4 is a sectional view showing a positively charged electrophotographic photosensitive member according to an embodiment of the present invention.

[Explanation of symbols]

 11 Conductive Substrate 12 Charge Generation Layer 13 Charge Transport Layer 14 Photosensitive Layer 15 Surface Coating Layer

Claims (3)

[Claims] 1. A photosensitive layer is provided on a conductive substrate, wherein the photosensitive layer contains a plurality of charge transporting substances, and the ionization potentials of the charge transporting substances are different from each other by 0.1 eV or less. Electrophotographic photoreceptor. 2. A photosensitive layer is provided on a conductive substrate, and the photosensitive layer contains two charge-transporting substances, and the difference in ionization potential of the charge-transporting substances is more than 0.1 eV, and the ionization potential is small. A photoreceptor for electrophotography, characterized in that the content of the charge transport material is larger than that of the charge transport material having a large ionization potential. 3. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer is a laminate of a charge generation layer and a charge transport layer.