JPH06214406A - Single layer type electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To provide the org. electrophotographic sensitive body which prevents the generation of ozone as far as possible, is of the single layer type (of a type having a photosensitive layer consisting of a single layer) producible by fewer coating stages and is particularly suitable for positive electrostatic charge. CONSTITUTION:The photosensitive layer (single layer) 2 which is formed by dispersing at least a charge generating pigment, org. hole transfer material and org. acceptor type compd. in a binder, is approximately equal or smaller in the ionization potential (Ip) value of the charge generating material 2 to or than the Ip value of the org. hole transfer material and is more preferably further approximately equal or smaller in the electron affinity (Ea) value of the charge generating pigment to or than the Ea value of the org. acceptor compd. is formed on a conductive base body 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrophotographic photosensitive member, and more specifically, it is a single-layer type electrophotographic photosensitive member (having a single photosensitive layer) particularly useful in a positive charging process in an electrophotographic copying machine or printer. It is about the body.

[0002]

2. Description of the Related Art Since the electrophotographic process uses the visualization of a latent image by electrostatic force as a principle, the electrophotographic photosensitive member used in the process has a good charging property in a dark place and a rapid irradiation by light irradiation. Attenuation of a large surface potential is required. The properties required for these processes depend on the high dark resistance, which is a physical property value, good quantum efficiency, and high charge mobility.

In order to satisfy these physical property values, a photoconductor composed of an inorganic compound such as selenium, selenium-tellurium alloy, and selenium arsenide has been conventionally used, and has been used in many copying machines and printers. It was However, these materials have some problems in terms of environment, are difficult to handle because they are used in an amorphous state, and have high cost because they need to be vacuum-deposited to a thickness of several μm. However, it cannot be said that the conditions for the photoconductor are sufficiently satisfied.

In order to improve these drawbacks, electrophotographic photoreceptors (OPC) using organic materials have been actively developed and put into practical use. Most of the practically used OPCs have a layer (CG) having a charge generation function.
L) and a layer having a charge transporting function (CTL), which is a laminated structure and is mainly used in a negative charging process.

The reason for this is that the photosensitive member formed by mixing the materials used as a single layer reveals the drawback that the fatigue phenomenon of charging property, sensitivity, and electrostatic property is reduced to less than a practical level. In many cases, these defects are suppressed as much as possible in the laminated type, the mechanical strength is high, and a CTL capable of designing a thick film is arranged on the surface, and thus it is sufficient in a state where it is subjected to the process. This is because it is possible to maintain the mechanical durability of the photoconductor. In addition, since the organic materials exhibiting a high charge mobility that does not hinder the high-speed copying process are limited to the donor compounds having only the property of hole transfer at present, the CTL formed by the donor compounds is not used. This is because the charging polarity of the photoconductor arranged on the front side is negative. However,
Such a function separation structure raises a new problem.

The first is derived from the negative charge on the photoconductor. A highly reliable charging method in the electrophotographic process is based on corona discharge, and this method is used in most copying machines and printers. However, as is well known, the negative polarity corona discharge is unstable as compared with the positive polarity, and therefore, the charging method by the scorotron is adopted, which is one of the factors of cost increase. Also,
Because negative corona discharge accompanies more ozone generation,
Ozone filters are used in negatively-charged copying machines and printers in order to prevent discharge to the outside, which also causes an increase in the cost of the apparatus. With the positive charging method, the amount of ozone generated is originally very small. further,
When a two-component developer which is widely used at present is used, a positively charged photosensitive member produces a stable image with less environmental fluctuation. From this aspect, it is desirable to use a positively charged photosensitive member.

The second one is derived from the laminated structure of the photosensitive layer. Although it is possible to use a solution coating method that is cheaper than the vacuum deposition method for a photoreceptor using an organic material,
In order to manufacture such a laminated type photoreceptor, at least 2
Repeated coating, usually by providing an undercoat layer immediately above the substrate (between the substrate and the photosensitive layer) to ensure the charging property of the photoreceptor 3
Needs to be applied twice. An increase in the number of solution coating steps causes an increase in the cost of the photoconductor. Further, in order to maintain the balance between sensitivity and durability and obtain a good image, the thickness of CGL must be within the submicron range with considerable accuracy, which is a factor of increasing the manufacturing cost.

In view of the above problems, it is understood that the photoconductor is preferably a single-layer photoconductor using an organic material, particularly used in a positive charging process. Further, it is also understood that if the photoconductor can be used as it is or with a slight modification in the negative charging process, a photoconductor can be produced which has an advantage of being inexpensive and having a high degree of freedom in use environment. However, there are very few examples of photoreceptors that satisfy these conditions. As a single-layer type photoconductor, a charge transfer complex photoconductor of polyvinylcarbazole and trinitrofluorenone, a eutectic complex photoconductor of thiapyrylium dye and polycarbonate, a photoconductor in which a perylene pigment and a hydrazone donor are dispersed in a resin. Only count. Among them, the former two examples have a problem in that they have low sensitivity and are repeatedly used, and they are used exclusively in the negative charging process, and therefore have a drawback of ozone generation. The last example has drawbacks that make it unsuitable for high speed copying processes due to the low sensitivity of the photoreceptor. Furthermore, in the case where the components of the laminated-type photoconductor that have been put into practical use are simply dispersed, both the charging potential and the sensitivity are low, and in particular, it is not possible to overcome the disadvantage that they greatly fluctuate in repeated copying operations. is there.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a single-layer type organic material which is excellent in charging property and sensitivity and is stable in electrostatic characteristics against repeated copying processes, and is particularly useful for positive charging. An electrophotographic photoreceptor is provided.

[0010]

The first object of the present invention is to provide a single-layer type electrophotographic photoreceptor in which a single-layer organic photosensitive layer is provided on a conductive substrate directly or via an undercoat layer. Is at least a charge generating substance (pigment), an organic hole transfer substance and an organic acceptor compound dispersed in a binder, and the charge generating pigment has an ionization potential value (Ip).
The value) is about the same as or smaller than the Ip value of the hole transfer material.

A second aspect of the present invention is a single-layer type electrophotographic photosensitive member comprising a single-layer organic photosensitive layer directly or via an undercoat layer on a conductive substrate, wherein the photosensitive layer is at least p-type charge. The generating substance (pigment), the organic hole transfer substance and the organic acceptor compound are dispersed in the binder, and the ionization potential value (Ip value) of the charge generation pigment is the same as the Ip value of the hole transfer substance. Comparable or smaller,
Further, it is characterized in that the electron affinity (Ea) value of the charge generating substance is the same as or smaller than the Ea value of the organic acceptor compound.

The inventors of the present invention have made various studies on a single-layer type organic electrophotographic photosensitive member which is particularly suitable for positive chargeability. As a result, a specific charge generating substance is used as a photosensitive layer forming component. It was confirmed that a desirable photoconductor can be obtained by using an organic hole transfer material having a certain relation with the charge generating material and an organic acceptor compound together with this. That is, in the conventional single-layer type photoconductor in which the charge generation pigment is dispersed in the resin, the charge generation pigment also has a charge transfer function, and the charge characteristics of both holes and electrons are good. Since there is no pigment, the sensitivity is low, the chargeability decreases due to repeated accumulation of a small number of charges, and the electrostatic latent image latitude is narrow due to the induction period in which the charging potential does not decrease immediately after light irradiation. was there. Further, in order to improve the hole mobility of such a photoconductor, a photoconductor to which a hole-transporting substance is simply added has a drawback that the chargeability is low, and the charging potential is remarkably lowered with repetition, which cannot be overcome. Further, since the photoconductor in which the charge generating pigment, the organic hole transfer material, and the organic acceptor compound are dispersed was not considered in consideration of the present invention, there were not a few drawbacks in the charging property, the repeating property and the like. On the other hand, in the present invention, as a result of considering the Ip value and further the Ea value, an appropriate pigment, hole-transporting substance or acceptor compound is selected to improve the above-mentioned drawbacks. The present invention is made by this.

The present invention will be described in more detail below.
In the drawing, 1 is a conductive substrate, 2 is a photosensitive layer, 21 is a (p-type) charge generating substance, and 22 is an organic hole-transporting substance and an organic acceptor compound dispersed in a binder in a molecular form. Each represents a matrix of states.

Such a photoreceptor of the present invention is excellent in chargeability and sensitivity and is suitable for low speed to high speed copying processes.
In addition, the spectral sensitivity region can be controlled by changing the charge generating pigment (charge generating substance), and it is possible to apply from a monochrome analog copying machine to a photoconductor of a page printer using LD light for optical writing. . As I mentioned earlier,
What is particularly important in the present invention is that the (p-type) charge generating pigment has an Ip value smaller than the Ip value of the hole-transporting substance, and more preferably, its Ea value is the Ea value of the organic acceptor compound. That is, a material having a smaller value was used. By securing this relationship, it is possible to secure chargeability in particular, and further extend the life of sensitivity and electrostatic characteristics. Here, “p-type” refers to a substance in which charge carriers that move in a substance that bears the type are mainly holes, and the determination thereof is, for example,
When a photoconductor in which a charge generating substance is dispersed in an electrically insulating binder is prepared and the photosensitivity is measured by charging the photoconductor to the same positive or negative surface potential, the positive charge type is used. Is made by showing high sensitivity. According to the study by the present inventors, the mechanism for ensuring the realization of the excellent electrostatic characteristics of the present invention is estimated as follows.

That is, when the photoconductor in which the charge generating pigment used in the photoconductor is dispersed in the matrix doped with the hole-transporting substance is charged, the chargeability is such that it cannot be practically used in a combination that does not satisfy the above Ip value relationship. Is low. Therefore, it is considered that free or lightly trapped holes are present in the charge-generating pigment particles at such a concentration that the chargeability of the photoconductor is affected. The presence of the hole transport material around the pigment particles causes the holes in the charge generating pigment to be injected into the donor. The injection of the holes is performed by the assistance of the electric field, and if the injection degree is high, the charging potential of the photoconductor and the charging speed are lowered. The lower the energy barrier in implantation, the higher the degree of implantation. Since holes move the ionization potential level of each material, in the combination of Ip (charge generation pigment)> Ip (hole transfer substance),
The holes existing in the pigment particles are injected into the photosensitive body matrix without any barrier at the time of charging, whereby a photosensitive body having a low charging property is formed. On the other hand, Ip (charge generation pigment)
It is considered that a combination of ≦ Ip (hole-transporting substance) creates a barrier against hole injection, so that it is possible to form a single-layer type photoreceptor excellent in charging.

Since the hole transfer substance originally has a small Ip value in the organic compounds, the charge generating pigment having a smaller Ip value is classified as a so-called p type. In such a charge generating substance, the movement of electrons is much worse than that of holes, and the level of Ea value is usually at a high level (Ea takes a small value). Therefore, it is considered that the electrons generated by the light irradiation are accumulated in the pigment particles, resulting in a decrease in photosensitivity and a decrease in repetition.

If an organic acceptor compound is introduced to enable electron injection from the charge generating pigment particles to the organic acceptor compound, generation of electron accumulation is suppressed, leading to higher sensitivity and improved repeatability. Since the electron transfer efficiency of the (p-type) charge generation material is poor, the concentration of free electrons originally inherent in the charge generation material is considered to be such that the charging potential is not significantly lowered. Therefore, the relationship between the Ea value of the charge generating substance and the Ea value of the organic acceptor compound is a sequence in which electrons are easily injected from the charge generating substance to the organic acceptor compound Ea (charge generating substance) ≦ Ea (organic acceptor compound ) Is preferred.

The role of the binder in the photoreceptor is not only good dispersion of the charge generating pigment and molecular dispersion of the organic hole transport material, but also mechanical strength of the photoreceptor required in the copying process. ing. Therefore, these properties are impaired when the proportion of the binder in the photosensitive layer is low. Therefore, the blending ratio of the binder cannot be unnecessarily low. As the binder that can be used in the present invention,
Polyethylene, polypropylene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd resin, polycarbonate resin, silicone resin, melamine resin, etc. -Type resins, polycondensation-type resins, and copolymer resins containing two or more of these repeating units, such as vinyl chloride-
Examples thereof include vinyl acetate copolymer resin and vinyl chloride-vinyl acetate-maleic anhydride copolymer resin.
The amount of these binders in the entire photosensitive layer is 30 to 90% by weight, preferably 40 to 70% by weight, more preferably 5%.
It is about 0% by weight.

The role of the organic acceptor compound in the single-layer type photoconductor of the present invention is to lower the residual potential and to prolong the life of electrostatic properties of the photoconductor. The cause of these improvements is not clear, but one of them is to prevent the reduction of the internal electric field of the charge generation pigment and the reduction of the electric resistance by extracting the electrons out of the holes and electrons generated in the charge generation pigment by light irradiation. Can be considered. The role of another organic acceptor compound is to increase the charging potential. In a normal copying process, during the charging process of the photoconductor, the photoconductor is not charged up to the electron accepting capacity determined by the capability of the charging unit, and the charge is terminated at a transient potential level. In such a situation, the change in the charging speed of the photoconductor greatly affects the charging potential of the photoconductor. Even with a photoreceptor having a high potential receiving ability, if the charging speed changes, the charging potential will change during repeated copying. However, in the photoconductor of the present invention, the addition of the organic acceptor compound further stabilizes the repetition of the charging potential as compared with the photoconductor in which the organic acceptor compound is not added. It is assumed that this is also related to the above-mentioned electron extraction. in this way,
The organic acceptor compound is an essential component in the single-layer photoconductor according to the present invention. Examples of the organic acceptor compound that can be used in the present invention include quinone compounds, π-electron compounds having a nitrile group, and π-electron compounds having a nitro group. The amount of this substance in the photosensitive layer is 1 to
It is 40% by weight, preferably 5-40% by weight.

The organic hole-transporting substance in the present invention is a compound having a triphenylamine moiety in the molecule, a hydrazone compound, a triphenylmethane compound, an oxadiazole compound, a compound containing a carbazole group, a pyrazoline compound, a styryl compound. , Butadiene compounds,
Examples thereof include polysilane compounds having a linear main chain of Si, and polymer donor compounds such as polyvinylcarbazole. The amount of the organic hole transfer material in the entire photosensitive layer is 15% by weight or more, preferably 20 to 50% by weight, and more preferably 25 to 40% by weight.

Charge generating pigments that can be used in combination with these organic hole transfer substances include bisazo pigments, trisazo pigments, phthalocyanine pigments, quinacridone pigments,
Indigo pigments may be mentioned. Of these, electron-donating groups such as a carbazole group, a styryl group, a diphenylamine group, and a triphenylamine group are preferable as the central skeleton of the azo pigment. The amount of the charge generating pigment in the entire photosensitive layer is 0.1 to 40% by weight, preferably 0.3 to 25% by weight.
Is appropriate.

The thickness of the photosensitive layer of the present invention is preferably 5 to 100 μm. If it is thinner than this, the charging property is lowered, and if it is thick, the sensitivity is lowered.

As the conductive substrate which can be used in the present invention, a metal plate of aluminum, nickel, copper, stainless steel, a metal drum or a metal foil, a plastic on which a thin film of aluminum, tin oxide or copper iodide is vapor-deposited or applied. Examples thereof include film and glass.

In the photoreceptor of the present invention, an undercoat layer may be provided between the photosensitive layer and the conductive substrate for the purpose of improving the charging property. As the material for the undercoat layer, polyamide resin, polyvinyl alcohol, casein, polyvinylpyrrolidone, or the like can be used in addition to the binder material.

To prepare the photoconductor of the present invention, a photosensitive layer forming solution prepared by dissolving or dispersing the above-mentioned materials in an organic solvent by a ball mill, ultrasonic wave or the like is applied by a dipping method or a blade coating method.
The photosensitive layer may be formed by coating the substrate with a spray coating method or the like.

[0026]

EXAMPLES The present invention will be specifically described with reference to Examples.
This does not limit the embodiments of the present invention.

Examples 1 to 5 Five kinds of photoconductors were prepared by variously changing the kinds of organic hole transporting substances. That is, after 0.5 g of the following azo pigment was ball milled with 10 g of a polycarbonate Z (PC-Z) solution (dissolved in tetrahydrofuran so as to be 10% by weight) and 9 g of tetrahydrofuran, the pigment component was 6% by weight, PC-Z component is 50% by weight, the following organic acceptor compound is 12% by weight, and the following organic hole-transporting substance is 32% by weight.
A Z layer solution, an organic acceptor compound, and an organic hole transfer substance were added to prepare a photosensitive layer forming liquid. This solution was applied onto an aluminum substrate and dried by heating to prepare a single layer type photoreceptor having a thickness of about 15 μm. Further, the oxidation potential Eox (a value corresponding to the Ip value) of the hole transfer material dissolved in acetonitrile and a film in which the azo pigment was dispersed in PC-Z and coated on ITO glass was measured with respect to the reference electrode SCE. did. The Eox of the azo pigment was about 0.76V.

These photoconductors were halved in charge potential Vs (surface potential value 20 seconds after the start of charging) and surface potential after light irradiation by an electrostatic copying paper tester (SP-428) manufactured by Kawaguchi Electric Co., Ltd. The amount of exposure (E1 / 2) required to attenuate was measured. The results shown in Table 1 were obtained, and Eox of the organic hole transfer material was obtained.
It was found that when the value was lower than that of the charge generating substance, the charging property was significantly lowered.

[Chemical 1]

[Chemical 2] (Example 1)

[Chemical 3] (Example 2)

[Chemical 4] (Example 3)

[Chemical 5] (Example 4)

[Chemical 6] (Example 5)

[Chemical 7]

Examples 6 to 10 Five types of photoconductors were prepared by changing the type of the organic acceptor compound or the organic hole transfer substance. That is, 0.5 g of the same azo pigment as used in Example 1 was added to Polycarbonate Z.
10 g of (PC-Z) solution (10 in tetrahydrofuran)
After being ball-milled with 9 g of tetrahydrofuran, the pigment component is 2% by weight, the PC-Z component is 50% by weight, the organic acceptor compound described below is 20% by weight, and the organic positive electrode described below is used. 2 hole transfer substances
A 10% by weight PC-Z solution, an organic acceptor compound, and an organic hole-transporting substance were added so as to be 8% by weight to prepare a photosensitive layer forming liquid. This solution was applied onto an aluminum substrate and dried by heating to prepare a single layer type photoreceptor having a thickness of about 15 μm. Furthermore, the above-mentioned azo pigment is dispersed in PC-Z to form ITO.
The reduction potential Ered (value corresponding to the Ea value) of the film coated on glass and the Eed of the organic hole transfer substance dissolved in acetonitrile were measured with respect to the reference electrode SCE. Ered of the azo pigment was about -1.2V or less, and Ered of the organic acceptor compound was about -0.53V.

In the same manner as in Example 1, these photoconductors were irradiated with light with a charging potential Vs (surface potential value 20 seconds after the start of charging) and light irradiation using an electrostatic copying paper tester (SP-428) manufactured by Kawaguchi Electric Co., Ltd. The amount of exposure required to reduce the surface potential to 1/2 (E1 /
2) was measured. The results shown in Table 1 were obtained, and again, it was found that when the Eox value of the organic hole-transporting substance was lower than that of the charge-generating substance, the charging property was significantly lowered. Further, these photoreceptors were attached to a drum having a linear velocity of 260 mm / s, and positive charging, exposure and light quench were repeated.
The results shown in Table 2 were obtained, and Ip of the organic hole transfer material was obtained.
The value was found to be less repeatable than the charge generating material.

[Chemical 8] (Example 6)

[Chemical 9] (Example 7)

[Chemical 10] (Example 8) The same organic hole transfer material as in Example 3. (Example 9) The same organic hole transport material as in Example 4. (Example 10) The same organic hole transport material as in Example 5.

Examples 11 to 13 The pigment of Example 1 was replaced by 0.5 g of the following azo pigment, the pigment composition was set to 5% by weight, and the following organic hole transfer material was set to 30% by weight.
Further, a single-layer type photoreceptor was prepared in the same manner as in Example 1 except that the following organic acceptor compound was changed to 15% by weight. In addition, Eox and Ered of the film in which the azo pigment was dispersed in PC-Z, the oxidation potential Eox of the organic hole transfer substance, and the Ered of the organic acceptor compound were measured. The Eox of this azo pigment was 0.93V, and the Ered was about -0.62V or less. Vs value and E1 / 2 of these photoconductors were measured in the same manner as in Example 1,
Also, repeatability was measured. As a result, it was found that when the Ea value of the organic acceptor compound was higher than that of the charge generating substance, the sensitivity and repeatability were lowered. The measurement results are summarized in Tables 1 and 2.

[Chemical 11]

[Chemical 12] (Example 11)

[Chemical 13] (Example 12)

[Chemical 14] (Example 13)

[Chemical 15]

[0032]

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Example Eox (V) Ered (V) Vs (V) E1 / 2 (lux ・ s) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1 0.44 110 5.6 2 0.51 260 2.6 ３ 0.73 1380 0.9 4 0.86 1420 1.3 5 0.89 1550 1.1 6 150 5.6 7 240 2.6 8 1410 0.9 9 1420 1.2 10 1510 1.1 11 -0.43 1080 2.8 12 -0.85 1360 5.1 13 -1.01 1580 6.4 ━━━━━━━━━━━━━━━━━ ━━━━━━━━━━━━━

[Table 2] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Example Example Charge potential (V) Post-exposure potential (V) First 5000 times After first After 5000 times ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 6 260 50 40 40 7 510 190 140 160 8 8 830 760 160 180 9 800 700 160 180 10 840 760 180 250 11 810 760 190 210 12 800 610 190 230 13 830 550 240 250 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

[0033]

According to the invention of claim 1, at least the charge generating pigment, the organic hole transporting substance and the organic acceptor compound are dispersed in the binder, and the ionization potential value of the charge generating material is By using a material having an ionization potential value equal to or smaller than the ionization potential value of the organic hole transfer material, a single-layer type electrophotographic photoreceptor having excellent charging property can be obtained. According to the invention of claim 2, at least a (p-type) charge generating pigment, an organic hole transfer material, and an organic acceptor compound are dispersed in a binder, and the ionization potential value of the charge generating pigment is By using a material having an electron affinity value equal to or smaller than the ionization potential value of the organic hole transfer substance and smaller than the electron affinity value of the organic acceptor compound as its electron affinity value, excellent chargeability and sensitivity are obtained,
Further, it is possible to obtain a single-layer type electrophotographic photosensitive member having a long electrostatic property life.

[Brief description of drawings]

FIG. 1 is a schematic view of a typical single-layer type electrophotographic photosensitive member according to the present invention.

[Explanation of symbols]

1 Conductive Substrate 2 Photosensitive Layer 21 Charge Generating Material 22 Matrix in which Organic Hole Transfer Material and Organic Acceptor Compound are Molecularly Dispersed in Binder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masakatsu Shimoda 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Kaoru Teramura 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Inside Ricoh Company (72) Inventor Emi Kawahara 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh (72) Inventor Akio Kojima 1-3-6 Nakamagome, Tokyo Stock Company Ricoh Company

Claims (2)

[Claims] 1. A single-layer organic photosensitive layer is provided on a conductive substrate directly or via an undercoat layer, and the photosensitive layer contains at least a charge generating substance, an organic hole transfer substance and an organic acceptor compound. A single-layer type electrophotography which is dispersed in a binder and has an ionization potential (Ip) value of the charge generating substance which is similar to or smaller than the Ip value of the organic hole transporting substance. Photoconductor. 2. A single-layer organic photosensitive layer is provided on a conductive substrate directly or via an undercoat layer, and the photosensitive layer is at least a p-type charge generating substance, an organic hole transfer substance, and an organic acceptor property. The compound is dispersed in the binder, and the ionization potential (Ip) value of the charge generating substance is equal to or smaller than the Ip value of the organic hole transporting substance,
Furthermore, the electron affinity (Ea) value of the charge generating substance is the same or smaller than the Ea value of the organic acceptor compound, and a single-layer type electrophotographic photoreceptor.