JPH0483256A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain the electrophotographic sensitive body which has a high sensitivity and good repetitive stability by forming a charge transfer layer of two layers which respectively contain different charge transfer materials and specifying the ionization potentials of the respective layers to satisfy a specific relation. CONSTITUTION:This photosensitive body is constituted by successively laminating a charge generating layer 2, the charge transfer layer 3 and the charge transfer layer 4 on a conductive base body 1 and specifying the ionization potentials of the respective layers so as to satisfy the relation expressed by formula I. In the formula, Ig(G) denotes the ionization potential of the charge generating layer 2; Ip(T1) denotes the ionization potential of the charge transfer layer 3 in contact with the charge generating layer 2; Ip(T2) denotes the ionization potential of the charge transfer layer 4 in contact with the charge transfer layer 3. The higher sensitivity and better repetitive stability than the sensitivity and repetitive stability of the separated function type electrophotographic sensitive body formed by using one layer of the charge transfer layer are obtd. by laminating two layers of these charge transfer layers in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor having a novel IFli structure.

[Prior art]

In recent years, electrophotographic photoreceptors have been widely used in copying machines and digital printers, and their uses are becoming more widespread.

As the electrophotographic photoreceptor, a-3e type photoreceptor, a-3i
It is known as an organic photoreceptor or an organic photoreceptor.

Among these, organic photoreceptors have been actively researched in recent years as non-toxic and inexpensive electrophotographic photoreceptors, and their practical use is progressing.

It is said that the drawback of this organic photoreceptor is that it has inferior sensitivity and durability compared to other photoreceptors.

In order to overcome these drawbacks, a functionally separated photoreceptor in which the charge generation function and the charge transport function are shared by separate substances has attracted attention, and rapid progress has been made in recent years.

In this function-separated photoreceptor, materials with each function can be selected from a wide range of materials and combined, so depending on the combination of materials, it is possible to create a photoreceptor with high sensitivity and high durability. It is. However, even with this function-separated type photoreceptor, the sensitivity and durability are still insufficient compared to the a-Se or a-3i photoreceptors, and improvements are desired. .

[Invention or problem to be solved]

An object of the present invention is to provide an electrophotographic photoreceptor with good sensitivity and repeated stability (air durability).

[Means to solve the problem]

The inventors of the present invention believe that the above problem is caused by carriers generated in the charge generation layer or not being efficiently injected into the charge transport layer, and as a result of intensive study on this point, the inventors have devised the structure of each layer in particular. We have discovered that by doing so, it is possible to easily obtain an electrophotographic photoreceptor with high sensitivity and good repeatability stability (electrical durability) even with existing material systems.
The present invention has now been completed.

That is, the present invention provides a functionally separated electrophotographic photoreceptor having a charge generation layer and a charge transport layer on a conductive substrate, in which the charge transport layer is composed of two layers each containing a different charge transport substance, and the ionization potential of each layer is The electrophotographic photoreceptor is characterized in that the electrophotographic photoreceptor is laminated so as to satisfy the following relationship: Ip(G)≧1p(T,)≧1p(T2).

However, [p(G) is the ionization point of the charge generation layer, Ip(T1) is the charge transport layer (1) in contact with the charge generation layer.
[11(T2) is the ionization potential of the charge transport layer (2) in contact with the charge transport layer (1).

FIG. 1 shows the concept of the layer structure of the photoreceptor in the present invention.

In the present invention, as shown in FIG.
A structure in which a charge generation layer 2, a charge transport layer (1) 3, and a charge transport layer (2) 4 are laminated in this order, or a structure in which a charge transport layer (2) is laminated on a conductive substrate 1 as shown in (b). ) 4, a charge transport layer (1) 3, and a charge generation layer 2 are all sequentially laminated.

The relationship between the ionization potentials of each layer is important, and it is necessary to satisfy the following relationship.

Ip(G)≧Ip(T,)≧Ip(T2) However, Ip(
G) is the ionization potential of the charge generation layer, Ip(T1
) is the ionization potential of the charge transport layer (1) in contact with the charge generation layer, and Ip(T2) is the ionization potential of the charge transport layer (2) in contact with the charge transport layer (1).

The feature of the present invention is that two charge transport layers are laminated as described above, and this allows unexpectedly high sensitivity and repeatability compared to a functionally separated electrophotographic photoreceptor using a single charge transport layer. Stability can be achieved.

When the ionization potential of the charge generation layer is smaller than the ionization potential of the charge transport layer in contact with the charge generation layer (
[p(G) <Ip(T+)), the sensitivity decreases significantly because charge injection from the charge generation layer to the charge transport layer is inhibited, and the ionization potential of the charge transport layer (1) is lower than that of the charge transport layer (2). ) when (Ip(T+) <
rp(T2)), not only is there no increase in sensitivity due to lamination, but the electrophotographic characteristics are deteriorated.

The ionization potential in the present invention can be measured by the following method. That is, a sample in which a charge generation layer or a charge transport layer is formed with an appropriate thickness on a conductive substrate is exposed to spectroscopic ultraviolet light of 200 to 360 nm in a sweeping wavelength manner, and the photoelectrons emitted by the photoelectric effect are measured. Then, we can find out the excitation energy at which photoelectron emission begins. This energy is called photoelectric ionization potential, and in the present invention, this value is defined as ionization potential. Specifically, such a measurement can be suitably carried out using, for example, a surface analyzer model AC-1 manufactured by Riken Keiki Co., Ltd. This method is very simple compared to the conventional oxidation potential measurement using cyclic portammetry, and has the feature that it can directly measure the growth of the photoreceptor, that is, the layer.

The configuration of the present invention will be explained in more detail.

A photosensitive layer having a laminated structure of a charge generation layer and a charge transport layer is provided on a conductive support. As the conductive support, aluminum, aluminum alloy, copper,
Metal plates such as zinc, stainless steel, and nickel, plastic sheets or plastic films such as polyester, on which conductive materials such as aluminum, aluminum alloy, tin oxide, and indium oxide are deposited, or conductive treated paper or resin. used.

The charge-generating layer can be obtained by coating a substrate with a coating liquid in which a charge-generating substance is uniformly dispersed in a suitable binder resin solution, or by forming a vapor-deposited film of a charge-generating substance using a vacuum evaporation device. It will be done.

As the charge-generating substance, any substance that has charge-generating ability can be used, including phthalocyanine-based, perylene-based, perinone-based, indigo-based, polycyclic quinone-based, cyanine-based, azo-based, quinacridone-based, and benzimidazole. Examples include organic dyes and pigments.

As the binder resin used in the charge generating substance dispersion system, an insulating polymer with good dispersion of the charge generating substance is used, such as polystyrene, polyacrylamide, polyester resin, polycarbonate resin, epoxo resin, and phenoxy resin. , polyamide, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, polysulfone resin, polymethacrylate resin, polyarylate resin, cellulose resin, urethane resin, polyvinyl alcohol, polyvinylpyrrolidone, etc. Ru. Also, BoIJ-N-vinylcarbazole, which itself has charge transport ability, can also be used as a binder.

These binder resins may be used alone or in combination of two or more.

The ratio of these binder resins to the charge-generating substance is 0.1 to 5.0, more preferably 0.3 to 2.0; if it is less than this, the adhesion to the base will be poor, and if it is more than this, it will not be sensitive to light. Physical characteristics worsen.

Organic solvents for dissolving these binder resins include:
It needs to have affinity with the charge-generating substance and dissolve the binder resin well. Specifically, esters such as methyl acetate, ethyl acetate, butyl acetate, and dibutyl phosphate, acetone, methyl ethyl ketone, and methyl Ketones such as isobutyl ketone, cyclohexanone, and isophorone; ethers such as oxane, tetrahydrofuran, and ethylene glycol monomethyl ether;
Cellosolves such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve, alcohols such as methanol, ethanol, and isopropanol, chlorinated hydrocarbons such as methylene chloride, ethylene chloride, dichloroethylene, trichloroethylene, chloroform, and carbon tetrachloride, toluene , aromatic hydrocarbons such as xylene, monochlorobenzene, and dichlorobenzene, amides such as N,N-dimethylacetamide, N,N-dimethylformamide, and dimethylsulfoxide.

These solvents may be used alone or in a mixture of two or more.

The coating liquid is prepared by adding a charge generating substance to a solution of the binder resin dissolved in an organic solvent and dispersing the mixture using various conventionally known dispersion methods.

Dispersing machines include ball mills, sand mills, roll mills,
It can be used as a paint shaker.

The charge generation layer is applied by applying the above-mentioned coating liquid using a conventional coating method such as dip coating, spray coating, spin coating, doctor blade coating, wire bar coating, or roll coating. For drying, it is preferable to dry to the touch at room temperature and then to stand still at 30 to 200°C or to heat dry under blowing air.

When forming a deposited film using a vacuum deposition apparatus, the charge-generating substance is directly deposited without using the binder resin, solvent, etc. described above.

The film thickness for charge generation is preferably 0.01 to 5 μm, more preferably 0.1 to 2 μm. If it is less than 0.01μ, it becomes difficult to uniformly form a charge generation layer, and if it exceeds 5μ, electrophotographic properties tend to deteriorate.

The charge transport layer is a charge transport layer in contact with the charge generation layer (1)
Both of the charge transport layer (2) in contact with the charge transport layer (1) are prepared by applying a solution of a charge transport agent and a binder resin dissolved in a suitable solvent.

As the charge transport material, any organic material that has the property of transporting holes or electrons can be used, and there are no particular restrictions as long as the material transports charges.As the hole transport material, poly-N-vinylcarbazole can be used. Polymers containing heterocyclic compounds such as those represented by, triazole derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, imidazole derivatives, pyrazoline derivatives, polyarylalkane derivatives, phenylenediamine derivatives,
Examples include electron donating substances that easily transport holes, such as hydrazone derivatives, amino-substituted chalcone derivatives, triarylamine derivatives, carbazole derivatives, stilbene derivatives, and tetraphenylthiophene derivatives.

Examples of the electron-transporting substance include electron-accepting substances that easily transport electrons, such as trinitronefluorenone and tetranitrofluorenone.

These charge transport materials may be used alone or in a mixture of two or more.

As the binder resin of the charge transport layer, an insulating polymer having good compatibility with the charge transport substance is used, such as polystyrene, acrylonitrile-ru-styrene copolymer, acrylonitrile-butadiene copolymer, polyacrylamide, Polyester resins, polycarbonate resins, epoxy resins, phenoxy resins, polyarylates, polysulfone resins, polyamide resins, polymethacrylate resins, etc. are used. Additionally, polyN-hinylcarharpur, which itself has charge transport ability, can also be used as a binder.

The charge transport layer contains a charge transport material in an amount of 10 to 95% by weight, preferably 30 to 90% by weight. The charge transport material is 1
If it is less than 0% by weight, almost no charge transport occurs, and 9
If it exceeds 5% by weight, the mechanical strength of the photoreceptor deteriorates, which is not practical.

The thickness of the charge transport layer is determined by the thickness of the charge transport layer in contact with the charge generation layer (
In the case of 1), the thickness is preferably 0.1 to 20μ, more preferably 0.2 to 10μ. If the film thickness is less than 0.1 g, there will be little effect of lamination, and if it exceeds 20 μm, the sensitivity will tend to decrease, which is not preferred for practical purposes.

In the case of the charge transport layer (2) in contact with the charge transport layer (1),
Preferably 3 to 50μ, more preferably 5 to 30μ
μ. If the film thickness is less than 3g, the amount of charge is insufficient.
If it exceeds 50μ, the residual potential will be high and it is not practical.

An intermediate layer having both a barrier function and an adhesive function can be provided between the photosensitive layer and the conductive support, but materials such as polyamide, nitrocellulose, casein, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyurethane, oxidized Aluminum or the like is suitable, and the film thickness is preferably 1 μm or less.

Further, an overcoat layer may be further provided on the charge transport layer for the purpose of preventing ozone deterioration and improving mechanical strength.

[Action and effect]

The electrophotographic photoreceptor of the present invention has high sensitivity and good repeat stability, making it an excellent electrophotographic photoreceptor.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the embodiments of the present invention are not limited thereby.

Example 1 The following azo compound (I
) was added and dispersed for 72 hours in a ball mill with an internal volume of 80 mm. The dispersion was further diluted by adding 30 g of cyclohexanone to obtain a coating liquid.

First, the above coating solution was applied to a degreased aluminum plate using a dip coater, and dried at 80''C for 2 hours to form a charge generation layer with a thickness of about 0.5μ.

The ionization potential of this layer was measured using a surface analyzer model AC-1 manufactured by Riken Keiki ■ and was found to be 5.91 eV.
There was.

The following stilchen compound (II) Ig and polycarbonate resin (
Manufactured by Kijin Kasei Co., Ltd., product name: ``Panlight 1300 J''
A solution of 1 g dissolved in 20 g of chloroform was applied using a wire bar and dried at 80° C. for 2 hours to form a charge transport layer (1) with a thickness of about 1 μ. The ionization potential of this layer was measured to be 5°59 eV.

Furthermore, a tetraphenylthiophene derivative (I[[)Ig] having the following structure is added thereto as a charge transport substance.

and polycarbonate resin (manufactured by Kijin Kasei Co., Ltd., product name:
Add 1 g of 1300 J to Panlite and add 1 g of chloroform.
.

Apply a solution dissolved in 80 g using a wire bar,
After drying at °C for 2 hours, the charge transport layer (2
) to produce the laminated photoreceptor shown in Figure 1 (al).The ionization potential of this layer was 5°45 e
There was a V.

Electrostatic copying paper testing device (Kawaguchi Electric, EPA-8100)
The photoreceptor is charged by corona discharge with an applied voltage of -6Kv, the surface potential v0 at that time is measured, and the surface potential V0 is measured after being left in a dark place for 2 seconds. Irradiate the surface with light from a halogen lamp (color temperature 2855 K) at an illuminance of 5 lux, measure the time for the surface potential to reach 1/2 of V, and calculate the half-reduction exposure amount El/2.
(lux −5ee) was calculated. Furthermore, the surface potential VI2, that is, the residual potential, was measured after 10 seconds of light irradiation. Further, the charging and exposing operations were repeated 1000 times to check durability.

Comparative Example 1 A conventional charge generation layer/charge transport layer was prepared by performing the same operation as in Example 1 except that the stacking of the charge transport layer (1) containing the charge transport substance '31F (II) was omitted. (2)
A laminated photoreceptor was fabricated and evaluated.

Comparative Example 2 A conventional charge generation layer/charge transport layer (2) was prepared in exactly the same manner as in Comparative Example 1, except that stilbene compound (II) was used as the charge transport material in the charge transport layer (2). ) was fabricated and evaluated.

Comparative Example-3 A laminated photoreceptor was produced by performing the same operation as in Example-1, except that the charge transporting material in the charge transporting layer (1) and the charge transporting material in the charge transporting layer (2) were replaced. and evaluated it.

Example-2 Azo compound (■) showing the following structure as a charge generating substance
A laminated photoreceptor was produced and evaluated in the same manner as in Example 1, except that .

The ionization potential of this charge generation layer is 5.86.
There was eV.

Comparative Example-4 Ab compound (IV
) was performed in exactly the same manner as in Comparative Example-1, except that the conventional charge generation method was used! A laminated photoreceptor having a charge transport layer (2) was prepared and evaluated.

Comparative Example-5 Azo compound (IV
) was used, except that the same operation as in Comparative Example 2 was performed to prepare a conventional multilayer photoreceptor having a charge generation layer/charge transport layer (2), and evaluation was performed.

Comparative Example-6 Ab compound (IV
) was used, but the same operation as in Comparative Example 3 was performed to produce a laminated photoreceptor, and evaluation was performed.

Example 3 A laminated photoreceptor was produced and evaluated in the same manner as in Example 1, except that a hydrazone compound (V) having the structure shown below was used as the charge transport material in the charge transport layer (1). I did it. In addition, charge transport containing this hydrazone compound (V)
The ionization potential of was 5.54 eV.

Example-4 A tetraphenylthiophene derivative (■) was used as the charge transport material in the charge transport layer (1), and a stilbene compound (VI) having the following structure was used as the charge transport material in the charge transport layer (2).
A laminated photoreceptor was produced and evaluated in the same manner as in Example 1, except that . The ionization potential of the charge transport layer containing this stilbene compound (IV) was 5.24 eV.

Example-5 X-based metal-free phthalocyanine (■) as a charge-generating substance (
A laminated photoreceptor was produced and evaluated in the same manner as in Example 4, except that an ionization potential of 5.53 eV) was used.

The measurement results of Examples and Comparative Examples are shown in Table-1.

From these Examples and Comparative Examples, it can be seen that the sensitivity and repetition stability of the photoreceptor are improved by the present invention.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of the electrophotographic photoreceptor of the present invention. In FIG. 1, each symbol is as follows. l...Conductive support 2...Charge generation layer 3...Charge transport layer (1) 4...-Charge transport layer (2) FIG.

Claims (1)

[Scope of Claims] 1) In a functionally separated electrophotographic photoreceptor having a charge generation layer and a charge transport layer on a conductive substrate, the charge transport layer is composed of two layers each containing a different charge transport substance, and each layer has a An electrophotographic photoreceptor characterized in that the layers are stacked so that the ionization potential satisfies the following relationship. Ip(G)≧Ip(T_1)≧Ip(T_2) However, I
p(G): Ionization potential of charge generation layer Ip(T_1): Charge transport layer (1) in contact with charge generation layer
Ionization potential Ip (T_2): Ionization potential of the charge transport layer (2) in contact with the charge transport layer (1)