JPH0333751A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obviate the generation of a memory phenomenon even if this photosensitive body is used for an electrophotographic system having a positive transfer electrostatic charge process by a direct electrostatic charge by constituting a charge transfer layer of a surface layer of two layers and successively increasing the oxidation potential of a charge transfer material used therein from the extreme surface layer toward an internal layer. CONSTITUTION:The surface layer is the charge transfer layer and this charge transfer layer is formed of the two layers; CTL 1, CTL 2. These charge transfer layers are so formed that the oxidation potential of the charge transfer material used therein increases successively from the extreme surface layer toward the internal layer. The positive charge carriers implanted therein stay at the charge transfer layer CTL 1 of the lowest oxidation potential on the surface and the transfer thereof to the inside of the photosensitive body is prohibited. The positive charge carriers implanted into the photosensitive body at the time of the next negative electrostatic charge is, therefore, easily neutralized. The memory phenomenon is hardly generated in this way and the good images having the less change in the image density are obtd.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an electrophotographic system used in an electrophotographic system having a process of applying a positive voltage to an electrophotographic photoreceptor by direct charging in order to transfer a toner image. Regarding photoreceptors.

[Conventional technique #jJ Until now, inorganic photoconductive materials such as selenium, cadmium sulfide, and zinc oxide have been used as photoconductive materials for electrophotographic photoreceptors.
Although rt materials have been mainly used, in recent years, the development and practical application of if-type photoconductors has become active.

Organic pigments and dyes with photoconductivity are easier to synthesize than inorganic materials, and moreover, the variety of compounds that exhibit photoconductivity t(f) in an appropriate wavelength range has been expanded, so many proposals have been made. has been done.

For example, U.S. Pat. No. 4,123,270, U.S. Pat.
Disclosed in Specification No. 1613, Specification No. 4251814, Specification No. 4256821, Specification No. 4280672, Specification No. 4268596, Specification No. 4278747, Specification No. 4293628, etc. Electrophotographic photoreceptors are known in which a disazo pigment exhibiting photoconductivity is used as a charge-generating substance in a photosensitive layer that is functionally separated into a charge-generating layer and a charge-transporting layer.

Conventionally, in the charging process in an electrophotographic process using such an electrophotographic photoreceptor, a high voltage (DC 5 to 8 KV) is applied to a metal wire, and charging is performed by corona generated.

However, with this method, when corona occurs, corona products such as ozone and NOx alter the surface of the photoreceptor, causing image blurring and deterioration, and dirt on the wire affects image quality, resulting in white spots and black lines in the image. There were other problems. On the other hand, in terms of power, the current flowing to the photoreceptor is 5 to 3
Most of it flowed to the shield plate, making it inefficient as a charging means. Directly from the past to compensate for these shortcomings? Methods for generating i'F current have been researched and many proposals have been made (Japanese Patent Application Laid-open No. 1984-10-4351, 57-1782).
Publication No. 67, Publication No. 5B-40566, Publication No. 58-139
No. 156, No. 58-150975, etc.).

A major example is one in which an elastic conductive roller (mainly rubber mixed with conductive carbon black) is brought into pressure contact with the surface of a photoreceptor to perform m-electrification.

According to this method (the voltage required for i'1 voltage is approximately 1 to 2
It is now possible to significantly lower the KV, reducing ozone and N.
Ox generation l,1 is also about 1/10 compared to the corona charging method.
Now it is possible to reduce it to 1/100.

However, when the method of directly pressing a conductive member as described in L is applied to a process of transferring a toner image to transfer paper by positive charging, in particular, iE? There was a problem that a memory phenomenon was likely to occur between the charged part and the directly positively charged part.

&11 In a photoconductor used in an electrophotographic apparatus as shown in FIG.
(in the case of FIG. 1(a)) and a portion that comes into pressure contact with the photoreceptor directly without using the transfer paper 4 (the first part).
In the case of figure (b))

In FIG. 1, 1 is a negative charging roller 22 for image exposure, 3 is a developing device, 6 is a cleaner, and 7 is a pre-exposure.

Figures 2(a) and 2(b) diagrammatically illustrate the electrophotographic behavior of the portion of the μ-type carrier. When injected into the photoreceptor, the potential at the next negative-to-next Teiden cycle was not stable, and a memory phenomenon in which the negatively charged potential became lower than the surroundings was likely to occur.

In addition, Fig. 2 (a) shows normal transfer to the photoreceptor? i) This shows a situation in which positive charge carriers are injected from the roller to the photoreceptor when the electric roller makes contact, and the left-hand portion shows that almost no charge carriers are injected because it is through the transfer paper. (b) shows that when the part of the right hand side that directly contacts the positive transfer charging roller is negatively charged by the negative-order 4JF charging roller, the injected positive charge carriers cancel out the surface negative charge. This indicates that negative potential is less likely to be applied to the area compared to the area that is in contact with the area through the transfer paper.

Therefore, as a countermeasure, it was proposed to coat the surface of the positive N charge member with a polymer to prevent the positive charge carriers from being injected into the photoreceptor, but the resistance of the coating layer changes depending on the environment and the charging Problems such as instability have been pointed out.

[Problem to be Solved by Problem 11 J The fourteenth objective of the present invention is to solve the problem in item L. It is an object of the present invention to provide a single-sensitivity photographic photoreceptor that does not cause a memory phenomenon even when used in an electrophotographic system having a positive transfer charge transfer process by direct charging.

[Means for Solving the Problems, Effects] The present invention provides a layered photoreceptor for use in an electrophotographic system that has a process of transferring a toner image onto a transfer paper by positively charging it through a charging member. The layer is a charge transport layer, and the charge transport layer is composed of two layers, and the oxidation potential of the charge transport substance used therein increases in order from the outermost surface debris to the inner layer. The present invention, which comprises an electrophotographic photoreceptor, will be explained with reference to FIGS. 3 and 4.

FIG. 5 shows an example of the layer structure of the electrophotographic photoreceptor of the present invention.

FIG. 3 shows the layer structure of the electrophotographic photoreceptor of the present invention.
It shows that positive charge carriers from the positive transfer charging roller are injected only up to the charge transport layer (II).

FIG. 4 is a schematic diagram of the energy level of each layer in the layer structure of the electrophotographic photoreceptor of the present invention, and shows the charge transport layer (II
) and the charge transport layer (I), and positive charge carriers easily flow in the direction from the charge transport layer (1) to the charge transport layer (TI), but there is a gap between the charge transport layer (II) and the charge transport layer (TI). This shows that it is difficult to flow in the direction of CA).

When a charging roller containing a conductive material with a high work function such as carbon black is pressed against an electrophotographic photoreceptor to positively charge it, in the case of a conventional photoreceptor, positive charge carriers can easily be transferred to the photoreceptor in terms of energy level. However, in the case of the electrophotographic photoreceptor of the present invention (Fig. The photoreceptor remains there and is prevented from moving inside the photoreceptor.

Therefore, the positive '+ injected into the photoreceptor during the first negative charging
ti, the load carrier is easily neutralized and the memory phenomenon is less likely to occur.

In the electrophotographic photoreceptor of the present invention, the thickness of the outermost layer containing the charge transport material having the lowest oxidation potential is 1/2 or less of the total thickness of the charge transport layer, preferably 115%, and The film thickness is set as necessary. In addition, in the materials constituting these charge transport layers, the binder may be the same resin or different resins for the 1 m1 layer and the internal layer.
Either can be used.

Furthermore, it is also possible to coexist in the surface layer various additive materials for improving the mechanical copper strip properties and chemical strip properties of the photoreceptor.

As a coating method, coating methods such as a dip coating method, a spray coach ink method, and a roller coating method can be applied.

The oxidation potential was determined using a saturated calomel electrode as a reference electrode, 0, IN (CH3CHλC)1. cH2) 4 N” 0 sentence 0+Q
Using an acetonitrile solution as an electrolyte, the potential of the working electrode was swept with a potential sweeper, and the peak position of the obtained current-potential curve was directly determined as the value of the oxidation potential. That is, first, the sample was heated to 0.1N (CI
3CHYUCHYUCH)4N C04 Dissolve in an electrolytic solution of acetonitrile solution to a concentration of 5-10 mmol%.

Then, a voltage is applied to this sample solution, the voltage is changed linearly from a low potential, and the change in current is measured to obtain a current-potential curve.

The potential value corresponding to the first inflection point of the current value in this Tti current-potential curve was defined as the oxidation potential in the present invention.

The charge transport layer is formed by dissolving a charge transport material in a film-forming resin.

Examples of organic charge transport materials include pyrene, N-ethylcarbazole, N-isopropylcarbazole, N-methyl-N-7enylhydrazino-3-methylidene-9-
Ethylcarbazole, N.

N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-
Methylidene-10-ethylphenothiazine, N,N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine, P-diethylamide/benzaldehyde-
N,N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-N-phenylhydrazone, p-virolidinobenzaldehyde N,
Hydrazones such as N-diphenylhydrazone, 1,3.5-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone, p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone, 2.5 -bisCP-diethylaminophenyl)-1,
3,5-oxadiazole, l-phenyl-3-(p-
diethylaminostyryl)-5-(p-diethylaminoethylphenyl)pyrazoline, l-[quinolyl (2)]
-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, l[pyridyl(2
)]-3-(p-diethylaminostyryl)-5-(p
-diethylaminophenyl9-pyrazoline, 1-[6-medoxypyridyl(2)] -3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)hylazoline, 1-[pyridyl(3)]-3-( p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, l-[lepidyl (2)]-3-(p-
diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, l-[pyridyl(2)]-3
-(p-diethylaminostyryl)-4-methyl-5-
(p-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-3-(α-methyl-P-diethylaminostyryl)-5-(p-diethylaminophenyl)
Pyrazoline, l-phenyl-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenylpyrazoline, l-phenyl-3-(α-benzyl-P-diethylaminostyryl)-5-(p -diethylaminophenyl)pyrazoline, pyrazoline compounds such as spirpyrazoline, 2-(p-diethylaminostyryl)-6-diethylaminobenzoxazole, 2-(
Oxazole compounds such as p-diethylaminophenyl)-4-(p-diethylaminophenyl)-5-(2-chlorophenyl)oxazole, thiazole compounds such as 2-(p-diethylaminostyryl)-6-diethylaminobenzothiazole, bis Triarylmethane compounds such as (4-diethylamino-2-methylphenyl)-phenylmethane, 1. l-bis(4-N, N
polyarylalkane compounds such as -dimethylamino-2-methylphenyl)ethane, triphenylamine,
Poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinyl acridine 2 poly-
Examples include 9-vinylphenylanthracene, pyrene-formaldehyde resin, and ethylcarbazole formaldehyde resin. Further, these ``Yuu Yue'' transportation materials can be used alone or in combination of two or more.

Examples of binders used in the charge transport layer include phenoxy resin, polyacrylamide, polyvinyl butyral, polyarylate, polysulfone, polyamide, acrylic resin, acrylonitrile resin, methacrylic resin, vinyl chloride phase opening, vinyl acetate citrus, phenolic resin, and epoxy resin. , polyester, alkyd resin, polycarbonate, polyurethane, or copolymers containing two or more repeating units of these resins, such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, and the like. It can also be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene.

Further, in the electrophotographic photoreceptor of the present invention, the photosensitive layer is provided on a support having a conductive layer.

As the support having a conductive layer, the support itself has conductivity, such as aluminum, aluminum alloy,
Copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, platinum, etc. can be used, and in addition, aluminum, aluminum alloy, indium oxide-tin oxide alloy, etc. can be used to form a film by vacuum coating. A support made of plastic or paper impregnated with conductive particles (e.g. carbon black, tin oxide particles, etc.) with a suitable binder. , plastic having a conductive binder, etc. can be used.

An undercoat layer having barrier and adhesive functions can also be provided between the conductive layer and the photosensitive layer. The undercoat layer can be formed of casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer polyamide (nylon 6, nylon 66, nylon 610, copolymerized nylon, etc.), polyurethane gelatin, f/# aluminum, and the like. The thickness of the undercoat layer is suitably 5 μm or less, preferably 0.5 to 3 pm. It is desirable that the barrier layer has a resistance of 10 7 Ωcm or more in order to exhibit its function.

The photosensitive layer is composed of a charge generation layer and the charge transport layer described above.

The charge generation layer is made of azo pigments such as Sudan Red, Guianplugenus Green B, Algol Yellow, Pyrenequinone, Indanthrene Brilliant Violet)
Quinone pigments such as RRP, quinocyanine pigments, perylene pigments, indigo pigments, indigo pigments such as thioindigo pigments, bisbenzimidazole pigments such as India First Orange toner, phthalocyanine pigments such as copper phthalocyanine, and one or more charge-generating substances such as quinacridone pigments. It can be formed by vapor depositing two or more types, or by dispersing them together with a suitable hainder (or without a binder) and coating. The binder can be selected from a wide range of insulating resins or organic photoconductive polymers. Examples of the insulating resin include polyvinyl butyral, polyarylates (condensation polymers of bisphenol A and phthalic acid, etc.),
Examples include polycarbonate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide, polyamide, polyvinylpyridine, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol, and polyvinylpyrrolidone. In addition, as organic photoconductive polymers, carbazole polymers,
Examples include polyvinylanthracene and polyvinylpyrene. The thickness of the charge generation layer is 0. O1 to 15ILm, preferably 0.05 to 5gm, and the weight ratio of the 5Ml load-generating layer to the binder is 10:1 to 1:20. The solvent used in the paint for the charge generation layer is selected based on the solubility and dispersion stability of the resin and charge transport material used. Specifically, organic solvents include alcohols such as methanol, ethanol, and impropanol; Amides such as acetone, methyl ethyl ketone cyclohexanone, N,N-dimethylformamide, N,N-dimethylacetamide, ethers such as tetrahydrofuran, dioxane, ethylene gelicol, monomethyl ether, esters such as methyl acetate, ethyl acetate, etc. 011ff Holm,
Examples include aliphatic halogenated hydrocarbons such as methylene chloride, dichloroethylene, carbon tetrachloride, and trichloroethylene, and aromatic compounds such as benzene, toluene, xylene, ligroin, chlorobenzene, and dichlorobenzene. For coating, coating methods such as a dip coating method, a spray coating method, a spinner coating method, a beat coach ink method, a Meyer bar coating method, a blade coating method, a roller coating method, and a curtain coating method can be applied.

The electrophotographic photoreceptor of the present invention is used not only for electrophotographic copying machines, but also for laser beam printers, LED printers,
It can also be used in electrophotographic applications such as CRT printers and electrophotographic plate making systems.

[Examples] Example 1 An aluminum sill with a wall thickness of 0.5 mm and a size of 60φ×260 mm was prepared as a support.

Copolymerized nylon (trade name 0M8000, Toshi-!Ii Ri 4ffl (parts by weight, same below) and type 8 nylon (trade name Laccamite 5003, manufactured by Dainippon Ink ■) 4
A coating solution was prepared by dissolving 50 parts of methanol and 50 parts of n-butanol, and this was dip-coated onto the above support to form a 0.6 gm polyamide undercoat layer.

Next, add 10 parts of a disazo pigment having the following structure.

10 parts of polyvinyl butyral to 120 parts of cyclohexanone
30 parts of methyl ethyl ketone was added to the zero dispersion which was dispersed in a sand mill for 10 hours together with 30 parts of methyl ethyl ketone, and the mixture was coated on the undercoat layer to form a charge generating layer having a thickness of 0.15 parts m.

Next, a polycarbonate (bisphenol zz) io portion having the following structure with a weight average molecular fi of 120,000 and an oxidation potential of 0.
10 parts of a styryl-based charge transport material having the following structure and having a voltage of 81V were dissolved together in 80 parts of chlorobenzene.

This liquid was applied onto the charge generation layer to form a charge transport layer (I) having a thickness of 18 lumen.

Thereafter, 10 parts of the same polycarbonate and 7 parts of a styryl charge transport material having the following structure and an oxidation potential of 0.78V were dissolved together in 80 parts of chlorobenzene.

This liquid was applied onto the charge transport layer (CI) by a spray coating method to form a charge transport layer (H) with a thickness of 2 μm to prepare an electrophotographic photoreceptor.

The layer structure of this electrophotographic photoreceptor is shown in FIG.

The thus prepared electrophotographic photoreceptor was developed by image exposure using negatively charged semiconductor laser light (input = 788 nm) (reversal development* using negative toner).

A charger for a laser beam printer using a reversal development method that has the processes of forward transfer charging, cleaning, and pre-exposure is made by melting and kneading 5 parts of conductive carbon with 2752100 parts of Chlorob, and forming it into a diameter of 20 x 260 mm with a stainless steel shaft in the center. Roller-shaped charging member (volume resistance 3X
The installation was evaluated using an evaluation machine (Fig. 1) modified to a temperature of 10+Ωcm, 22°C/60%).

For comparison, in the preparation of the electrophotographic photoreceptor described above, the charge transport layer (II) was not provided, and only the charge transport layer (1) was formed.
0JLml)! An electrophotographic photoreceptor was prepared by coating 2 thick layers: /Ii.

The primary charging condition is the application of a pulsating current voltage in which a DC voltage of -750V is superimposed with an AC peak-to-peak voltage of 1500V, and the transfer charging condition is the application of a DC voltage of +2000V.

In addition to evaluation under normal temperature and normal humidity (22°C/60%) environment,
Evaluation results under a low temperature, low humidity (15° C./10%) environment are shown.

Example 122/60 700 150 15/10 710 180 Comparative example 22/60 690 14015/10
700 150 is negative - order f? This indicates that the negative potential after the F-electrode is lower than that of the portion that contacted the positive transfer roller via the transfer paper.

The same applies to ΔVL, which indicates the positive band 1 line memory at the bright area potential, and in the case of reversal development, the bright area is developed, so ΔV
The larger L is, the larger the density difference on the image becomes.

Example 122/60 -20V -10V15/1
0 -40V -20V comparative example 22/60
-100V -800V15/lo -150V
-100V In the table, ΔvD indicates the difference in the absolute value of the dark area potential between the part that contacted the normal transfer roller through the transfer paper and the part that directly contacted the pressure transfer roller, and when the sign is -, the normal transfer roller Example 12 of the part directly in contact with
2/60 Almost no image 15/10 Same comparative example 22/60 Significant density unevenness 15/10
From the above results, the photoreceptor according to Example 1 has a small positive charging memory, and does not cause density changes or fog on images, especially as a memory of paper traces.

Example 2 Using the same conductive support/subbing layer as in Example 1, 10 parts of a trisazo pigment having the following structure as a charge generating material, 5 parts of polymethyl methacrylate, and 12 parts of cyclohexanone.
A dispersion solution prepared by dispersing the mixture with 0 parts in a sand mill for 10 hours and adding 30 parts of the dispersion residue methyl ethyl ketone was applied onto the above-mentioned undercoat layer to form a charge generation layer having a thickness of 0.15 μm.

10 parts of polycarbonate (mentioned above) and 10 parts of a hydrazone charge transport material having the following structure and an oxidation potential of 0.76V were both dissolved in 80 parts of chlorobenzene, and this was coated on the charge generation layer to form a charge transport material of 18 parts m. Layer CI) was formed.

Thereafter, 10 parts of the following styrene-acrylic copolymer and 7 parts of a biphenyl-based charge transport material having the following structure and an oxidation potential of 0.69V were dissolved in 80 parts of chlorobenzene.

The above charge transport layer (I) is formed by spray coating this solution.
A charge transport layer (II) having a thickness of 2 ILm was formed on top of the photoreceptor to prepare an electrophotographic photoreceptor.

As a comparative example, the charge transport material of the charge transport layer (■) was used for the charge transport layer (TI) in Example 1, and the oxidation potential was 0.
．． As an example, an electrophotographic photoreceptor prepared in place of a styryl-based charge transport material having a voltage of 76V will be described.

These electrophotographic photoreceptors were attached to the same evaluation machine as in Example 1, and evaluated in the same manner. Show the results.

Example 2 22/60 680 17015/1 00 Comparative example 2 2/6 0 00 30 15/10 10 40 Example 2 22/60 15/10 Comparative example 22/60 15/10 -20V -20V -40V -20V -80V -60V -100V -70V Example 2 22/60 Almost absent on image 15/10
Same as above Comparative example 22760 Concentration difference 15710
From the above results, it can be seen that the electrophotographic photoreceptor according to Example 2 has a small positive charge memory and little density change.
In the electrophotographic photosensitive pair of the comparative example in which the oxidation potential difference of the charge transport material between the charge transport layers (I) and (If) was eliminated, the positive (;7 charge memory) became large and the density difference was significant.

Example 3 Using the same conductive support/undercoat layer as in Example 1, 10 parts of aluminum chlorophthalocyanine li material having the following structure as a charge generating material, 5 parts of polymethyl methacrylate, cyclo^, xanone 1
After dispersion, 30 parts of methyl ethyl ketone was added to the dispersion solution prepared by adding 20 parts of the dispersion liquid to the undercoat layer to form an IT charge generation layer having a thickness of 0.15 gm.

10 parts of polycarbonate (mentioned above) and 410 parts of a biphenyl-based charge transport material lI having the following structure and an oxidation potential of 0.76 V were both dissolved in 80 parts of chlorobenzene, and this solution was applied onto the charge generation layer at varying film thicknesses. , 10-22IL
Each charge transport layer (I) with a film thickness of m was formed.

Thereafter, 10 parts of polycarbonate (mentioned above) and hydrazone-based charge transport material 7 having the following structure and an oxidation potential of 0.67V were added.
Both parts were dissolved in 80 parts of chlorobenzene, and this solution was spray coated to form the charge transport layer (r).
A charge transport layer (II) having a thickness of 2 to 12 gm was formed by coating the charge transport layer (II) in varying thicknesses to prepare an electrophotographic photoreceptor.

These electrophotographic photoreceptors were attached to the same evaluation machine as in Example 1 and evaluated in the same manner.

Photoreceptor charge transport layer (1) Charge transport layer (■) O 2 5 8 0 2 2 0 10 00 00 90 00 90 10 90 60 80 70 50 15/10 = 80 70 2, // -40-303//
-40-20 4// -30-30 5// -40-30 6// -100-80 115/lo Significant concentration difference 2 tt Almost no concentration difference 3
tt Same as above 4 //
Same as above 5 tt Same as above 6 // From the above results, the electrophotographic photoreceptors of the present invention, Photoreceptors 2 to 5, have a small Seiteiden memory and can obtain good images with little change in density. .

[Effects of the Invention] Even when the electrophotographic photoreceptor of the present invention is used in an electrophotographic process that includes a positive transfer charging process using direct charging, it is said that memory loss does not easily occur, and good images with little change in image density can be obtained. It has a remarkable effect.

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional view of an example in which the photoreceptor 8 and the normal transfer charging roller 5 are in contact with each other via the transfer paper 4 in an electrophotographic apparatus, and FIG. 1(b) is a sectional view of an example in which the electrophotographic apparatus In,
A cross-sectional view of an example in which the photoreceptor 8 and the positive transfer charging roller 5 are in direct contact, the symbol 1 is the negative-order charging roller, 2 is the image exposure, 3 is the developing device 4 is the transfer paper, and 5 is the positive transfer charging roller. ,6
2(a) and 2(b) show the electrophotographic behavior of the portion of FIG. 1(a) and the portion of FIG. 1(b). FIG. 3 is a diagram illustrating that in the layer structure of the electrophotographic photoreceptor of the present invention, positive charge carriers from the positive transfer charging roller are injected only up to the charge transport layer (II).
Figure 1 is a schematic diagram of the energy level of each layer in the layer structure of the electrophotographic photoreceptor of the present invention, and FIG. 5 is a diagram showing the layer structure of the electrophotographic photoreceptor of the present invention.

Claims (1)

[Claims] 1. In a laminated photoreceptor used in an electrophotographic system having a process of transferring a toner image onto a transfer paper by positively charging via a charging member, the surface layer is a charge transport layer; , and the charge transport layer is composed of two layers,
An electrophotographic photoreceptor characterized in that the oxidation potential of the charge transport material used therein increases in order from the outermost layer toward the inner layer. 2. The electrophotographic photoreceptor according to claim 1, wherein the thickness of the outermost layer containing a charge transport material having the lowest oxidation potential is 2/1 or less of the thickness of the entire charge transport layer.