JPH07271059A - Electrophotographic photoreceptor and electrophotographic device - Google Patents

Abstract

PURPOSE:To provide an electrophotographic photoreceptor and electrophotographic device which make it possible to obtain good images without uneveness in surface potential in spite of presence of the uneven film thicknesses of photosensitive layers with the electrophotographic device which causes contact electrostatic charge by impression of only the DC voltage. CONSTITUTION:This electrophotographic device has an electrophotographic photoreceptor and an electrostatic charging member arranged in contact therewith and electrostatically charges the photoreceptor by impressing only the DC voltage thereto from the electrostatic charging member. The electrophotographic photoreceptor has the value of (n) satisfying 0.45<=n<=4.0 when the relation between the electrophotographic quantum efficiency PHI and electric field intensity E of the photoreceptor is expressed by the equation PHI=PHI0E<n> (where PHIg is a constant).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an electrophotographic photosensitive member and a charging member arranged in contact therewith, and is charged by applying only a DC voltage from the charging member to the photosensitive member. The present invention relates to an electrophotographic photosensitive member used in an electrophotographic apparatus, and an electrophotographic apparatus.

[0002]

2. Description of the Related Art In an electrophotographic method, for example, selenium,
Charge, expose, and develop electrophotographic photoreceptors such as cadmium sulfide, zinc chloride, amorphous silicon, and organic photoconductors.
When an image is obtained by performing basic processes such as transfer, fixing, and cleaning, the charging process is conventionally performed by applying a high voltage (DC 5 to 8 KV) to a metal wire and charging by a corona generated. However, in this method, when corona occurs, corona products such as ozone and NOx deteriorate the surface of the photoconductor to cause image blurring and deterioration, and wire stains affect image quality, resulting in white spots and black streaks. There was a problem such as. In particular, the electrophotographic photoconductor whose photosensitive layer is mainly composed of an organic photoconductor has lower chemical stability than other selenium photoconductors and amorphous silicon photoconductors, and a chemical reaction when exposed to corona products ( Oxidation reaction mainly occurs and tends to deteriorate. Therefore, when it is repeatedly used under corona charging, image blurring due to the above-mentioned deterioration and low copy density due to reduction in sensitivity tend to occur, and the printing durability life tends to be short.

In the case of corona charging, the electric current flowing to the photoconductor is only 5% to 30% in terms of electric power, and most of them flow to the shield plate and are inefficient as charging means.

In order to make up for such a problem, without using a corona discharger, Japanese Patent Laid-Open No. 57-178267 has been proposed.
JP-A-56-104351, JP-A-58-405
As proposed in Japanese Patent Laid-Open No. 66, Japanese Patent Application Laid-Open No. 58-139156, Japanese Patent Application Laid-Open No. 58-150975, etc., a method of contact charging has been studied.

Specifically, the surface of the photoconductor is charged to a predetermined potential by contacting the surface of the photoconductor with a charging member such as a conductive elastic roller to which a DC voltage of about 1 to 2 KV is applied from the outside. .

However, although there are many proposals for the direct charging method, there is almost no market record. The reason for this is as follows: non-uniform charging, and discharge dielectric breakdown of the photoconductor due to direct voltage application.

In order to make the charging uniform, a method of superimposing an AC voltage on a DC voltage and applying it to a charging member has been proposed (JP-A-63-149668). In this charging method, a pulsating voltage is applied by superimposing an _AC voltage (VAC) on a DC voltage ( _VDC ) to perform uniform charging.

In this case, while maintaining the uniformity of charging, white spots in the positive development system, black spots in the reversal development system,
In order to prevent image defects such as fogging, the superimposed AC voltage is at least twice the peak-to-peak potential difference (V
It is necessary to have a _PP ).

However, if the superposed AC voltage is increased in order to prevent image defects, the maximum applied voltage of the pulsating voltage causes discharge dielectric breakdown at a minute defect portion inside the photoconductor. In particular, when the photoconductor is an OPC photoconductor having a low withstand voltage, this dielectric breakdown is remarkable. In this case, in the normal development method, the image is blanked in the longitudinal direction of the contact portion, and in the reversal development method, black blemishes occur. Further, when there is a pinhole, there is a problem in that the portion of the pinhole serves as a conduction path, current leaks, and the voltage applied to the charging member drops.

Furthermore, the charging noise due to AC charging is amplified by the photoconductor cylinder, which causes a problem of noise.
As a countermeasure against this, it is considered to fill the inside of the cylinder with aluminum lumps, but there are problems such as an increase in cost and an increase in assembling steps.

In order to solve such a problem, direct charging in which only a DC voltage (V _DC ) is applied without superposing an _AC voltage (V _AC ) has been studied.

However, when only the DC voltage is applied,
Charging largely depends on the electrostatic capacity of the photoconductor, and under the same applied voltage condition, the dark potential is high when the electrostatic capacity is large,
It is known that the dark potential becomes low when the capacitance is small. Regarding the bright potential, when a generally used charge generation layer is used, the bright potential is high when the capacitance is large, and is low when the capacitance is small. In other words, in a direct charging system using only a DC voltage, the bright potential is further increased by the high dark potential in addition to the normal sensitivity reduction amount when the electrostatic capacitance is large, and conversely when the electrostatic capacitance is small. In addition to high sensitivity, is lower due to low dark potential.

In other words, if there is a difference in electrostatic capacitance in the longitudinal direction or the circumferential direction of the photoconductor, that is, if there is a film thickness difference in the charge transport layer, the bright potential is combined with the low dark potential at the thick film thickness. Further, when the film thickness becomes thinner, the bright potential becomes
Combined with the high dark potential, it becomes even higher. That is, even if there is a slight film thickness difference, the bright potential difference becomes large, and the image density also becomes large.

[0014]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is that even in an electrophotographic apparatus in which only a DC voltage is applied and contact charging is performed, there is unevenness in the thickness of the photosensitive layer (back / front and circumferential direction). In addition, it is an object of the present invention to provide an electrophotographic photosensitive member and an electrophotographic apparatus that can obtain good images without unevenness in surface potential.

[0015]

DISCLOSURE OF THE INVENTION As a result of repeated studies on the above problems, the present inventors have improved the electrophotographic photosensitive member to provide a DC voltage when the photosensitive member is contact-charged from a charging member. It has been found that the above problem can be solved by applying only the voltage.

That is, the present invention has an electrophotographic photosensitive member and a charging member disposed in contact with the photosensitive member, and an electron charged by applying only a DC voltage from the charging member to the photosensitive member. an electrophotographic photosensitive member used in the photographic apparatus, the relationship between the electrophotographic quantum efficiency [Phi and the electric field strength E of the photoreceptor satisfies the following formula _{(1) Φ = Φ 0 E} n (1) ( where, [Phi ₀ is a constant) The electrophotographic photosensitive member is characterized in that the value of n represented by the formula (2) satisfies the formula: 0.45 ≦ n ≦ 4.0 (2).

Further, the present invention has an electrophotographic photosensitive member and a charging member arranged in contact with the photosensitive member, and is charged by applying only a DC voltage from the charging member to the photosensitive member. in the electrophotographic apparatus, the relationship between the electrophotographic quantum efficiency [Phi and the electric field strength E of the photosensitive member is represented by the following formula _{(1) Φ = Φ 0 E} n (1) ( where, [Phi ₀ is a constant) when expressed in The value of n satisfies the equation (2) 0.45 ≦ n ≦ 4.0 (2).

The present invention will be described in detail below.

The direct charging method, in which a charging member is brought into contact with an electrophotographic photosensitive member to perform charging, is performed by a void breaking discharge according to Paschen's law in a minute space near the contact portion between the photosensitive member and the charging member. Due to the nature of such a charging mechanism, the surface potential greatly depends on the electrostatic capacity of the photoconductor. Similarly, the surface potential of corona discharge, which has been widely used in the past, depends on the electrostatic capacity of the photoconductor.
Unlike the case of C direct charging, the dark potential is low when the capacitance is large, and the dark potential is high when the capacitance is small.
On the contrary, when a commonly used charge generation layer is used, the bright potential is high when the electrostatic capacity is large, and the bright potential is low when the electrostatic capacity is large.

That is, even if there is unevenness in the film thickness of the photosensitive layer in the same photoconductor in the generatrix direction and the circumferential direction, in the case of corona discharge, the bright potential (including the halftone potential) important for electrophotography is: Due to the (+) and (-) effects of the bright potential difference and the sensitivity difference, the potential difference is not so large, and the image density is almost uniform. Further, when the AC voltage is superposed, the dark potential is substantially independent of the film thickness and is constant even if the film thickness of the photoconductor is uneven. That is, the bright potential difference is only the sensitivity difference caused by the unevenness of the film thickness of the photoconductor, and the bright potential difference is neither large nor small due to the dark potential difference.

In the present invention, the electrophotographic quantum efficiency of the photoconductor satisfies the formulas (1) and (2) even in the case of contact charging using only DC voltage, so that the same as in the case of applying by corona discharge. , Or even more uniform bright potential was found. That is, equation (1)
Since the electrophotographic quantum efficiency shown in Fig. 2 depends on the electric field strength and the degree of dependence n satisfies the formula (2), more electric charges are generated in the charge generation layer in the strong electric field and weak electric field is generated in the electric charge generation layer. Suppresses charge generation. That is, even if there is film thickness unevenness in the generatrix direction and the circumferential direction of the photoconductor, the bright potential can be made substantially uniform, so that the image density can be made uniform.

The "electrophotographic quantum efficiency Φ" shown in the above formula (1) is Φ = Δδ / Nλ (4) Δδ: the amount of charge reduced per unit area when irradiated with light of wavelength λ, and the number of electrons Indicates.

Nλ: Number of photons per unit area of incident light Using surface potential, Φ = (εε₀ ΔV) / (dNλ) (5) ε: relative permittivity ε₀ : Dielectric constant of vacuum ΔV: Reduction amount of electric potential d: Thickness of photoconductive layer (cm) When formula (5) is converted into the number of electrons, Φ = {(εΔVnλ) / (dI₀ )} × 8.85 × 10^-6 (6) nλ: Energy (eV) I per photon I₀ : Incident light (μW / cm² ) For the calculation of quantum efficiency, correction for reflection and transmission of incident light
Is required, I ₀ To I₁ Is substituted.

I ₁ = I ₀ (1-Rλ) {1-eexp (-αλd)} (7) Rλ: surface reflectance αλ: layer absorption coefficient

The value of n in the equation (2) is equal to the gradient when the logarithm of the equation (1) is taken, and can be obtained from the gradient of the logarithmic graph of the quantum efficiency Φ and the electric field strength E.

As means for satisfying the formula (2), the charge generating material in the charge generating layer is changed, the binder resin is changed, or two or more kinds of charge generating materials or 2 are used.
It is possible to use more than one kind of binder resin.

Further, the electric field strength E shown in the equation (3) is as follows when a logarithmic graph of the quantum efficiency Φ and the electric field strength E is created.
When the value of the electric field strength E exceeds 8.0 × 10 ⁵ , the linearity tends to be lost, and the value of n, which is the slope of the linearity, becomes meaningless. Further, there is almost no decrease of less than 1.5 × 10 ⁵ in the electrophotographic process, so this value was made the lower limit.

The charging member 1 used in the present invention may have any shape such as a blade and a belt other than the roller as shown in FIG. 5, and can be selected according to the specifications and form of the electrophotographic apparatus. Is. Further, as the material of the charging member, aluminum, iron, a metal such as copper, polyacetylene, polypyrrole, a conductive polymer material such as polytheophene, carbon, rubber or an artificial fiber conductively treated by dispersing a metal, Alternatively, an insulating material such as polycarbonate, polyvinyl, or polyester whose surface is coated with a metal or another conductive material can be used. The volume resistance value of the charging member is 10 ⁰ to 10 ¹² Ω · cm, particularly 10 ² to 10 ⁷ Ω.
-A range of cm is preferable.

FIGS. 1, 2 and 3 show a typical construction of the electrophotographic photosensitive member of the present invention, in which the photosensitive layer is composed mainly of an organic photoconductor.

Examples of the organic photoconductor include those using an organic photoconductive polymer such as polyvinylcarbazole, and those containing a low molecular weight organic photoconductive substance in a binder resin.

The electrophotographic photosensitive member of FIG. 1 has a conductive support 1
0 is provided with a photosensitive layer 11, and the photosensitive layer 11
Is a laminated structure of a charge generation layer 13 containing a charge generation material 12 dispersed in a binder resin and a charge transport layer 14 containing a charge transport material (not shown). in this case,
The charge transport layer 14 is laminated on the charge generation layer 13.

In the electrophotographic photoreceptor of FIG. 2, unlike the case of FIG. 1, the charge transport layer 14 is laminated below the charge generation layer 13. In this case, the charge generation layer 13 may contain a charge transport material.

The electrophotographic photosensitive member of FIG. 3 has a conductive support 1
0 is provided with a photosensitive layer 11, and the photosensitive layer 11
Includes a charge generation material 12 and a charge transport material (not shown) in a binder resin.

In addition to the configurations shown in FIGS. 1, 2 and 3,
It is also possible to apply an overcoat layer.

Of these, a photoreceptor having a structure in which the charge generation layer 13 and the charge transport layer 14 are laminated in this order from the conductive support 10 side as shown in FIG. 1 is preferable in the present invention.

As the conductive support 10, a metal such as aluminum or stainless steel, a cylindrical cylinder such as paper or plastic, a sheet or a film is used. Further, these cylindrical cylinders, sheets or films may have a conductive polymer layer or a resin layer containing conductive particles such as tin oxide, titanium oxide and silver particles, if necessary.

Further, an undercoat layer (adhesive layer) having a barrier function and an undercoat function can be provided between the conductive support and the photosensitive layer.

The subbing layer is for improving the adhesion of the photosensitive layer, improving the coating property, protecting the support, covering defects on the support, improving the charge injection property from the support, protecting the photosensitive layer against electrical breakdown, etc. Formed for. The film thickness is about 0.2 to 2 μm.

As the charge generating material, use is made of pyrylium, thiopyrylium dye, phthalocyanine pigment, anthanthrone pigment, dibenzpyrenequinone pigment, pyratron pigment, azo pigment, indigo pigment, quinacridone pigment, asymmetric quinocyanine, quinocyanine, etc. You can

As the charge transport material, hydrazone compounds, pyrazoline compounds, styryl compounds, oxazole compounds, thiazole compounds, triarylmethane compounds, polyarylalkane compounds and the like can be used.

The charge generation layer 13 includes a homogenizer, an ultrasonic wave, a ball mill, a vibrating ball mill, together with a binder resin in an amount of 0.3 to 4 times the amount of the charge generation material and a solvent.
It is formed by being well dispersed by a method such as a sand mill, an attritor, or a roll mill, coated and dried. Its thickness is 5
It is preferably not more than μm, particularly preferably in the range of 0.01 to 1 μm.
The charge transport layer 14 is generally formed by dissolving the above charge transport material and the binder resin in a solvent and coating the solution. The mixing ratio of the charge transport material and the binder resin is 2: 1 to 1: 1.
It is about 2. As the solvent, ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as toluene and xylene, chlorinated hydrocarbons such as chlorobenzene, chloroform and carbon tetrachloride are used. To be When applying this solution, a coating method such as a dip coating method, a spray coating method or a spinner coating method can be used, and drying is performed at a temperature in the range of 10 ° C to 200 ° C, preferably 20 ° C to 150 ° C. 5 minutes to 5 hours,
Preferably, it can be carried out for 10 minutes to 2 hours under blast drying or static drying. The thickness of the generated charge transport layer is preferably 5 to 30 μm, particularly preferably 10 to 25 μm.

The binder resin used to form the charge transport layer 14 includes acrylic resin, styrene resin, polyester, polycarbonate resin, polyarylate, polysulfone, polyphenylene oxide, epoxy resin, polyurethane resin, alkyd resin and A resin selected from saturated resins and the like is preferable. Particularly preferred resins include polymethylmethacrylate, polystyrene,
Examples thereof include a styrene-acrylonitrile copolymer, a polycarbonate resin or a diallyl phthalate resin. Further, the charge generation layer or the charge transport layer contains an antioxidant,
Various additives such as an ultraviolet absorber and a lubricant can be contained.

A specific example of an image forming apparatus using the electrophotographic process of the present invention is shown in FIG. In this apparatus, a roller-shaped charging member 1, an image exposure unit 4, a developing unit 5, a transfer charger 6, a cleaner 7, and a pre-exposure unit 8 are arranged on the peripheral surface of an electrophotographic photosensitive member 2. In the image forming method, first, a voltage is applied to the charging member 1 arranged in contact with the electrophotographic photosensitive member 2 to charge the surface of the photosensitive member 2 and an image corresponding to the original is exposed by the image exposing unit 4. The body 2 is imagewise exposed to form an electrostatic latent image. Next, the toner in the developing device 5 is removed from the photosensitive member 2.
The electrostatic latent image on the photoconductor 2 is developed (visualized) by being adhered to. Further, the toner image formed on the photoconductor 2 is transferred onto a transfer material such as paper supplied through a paper feed roller and a paper feed guide by a transfer charger 6, and the cleaner 7 does not transfer the toner image onto the transfer material. The residual toner remaining on the body 2 is collected. The pre-exposure unit 8 irradiates the photoconductor 2 with light to remove the charge. On the other hand, the transfer material on which the toner image has been formed is sent to the fixing device 9 by the conveying section and the toner image is fixed.

In this image forming apparatus, the image exposure means 4
As the light source, a halogen light, a fluorescent lamp, a laser light or the like can be used. Also, other auxiliary processes may be added if necessary.

The electrophotographic apparatus of the present invention can be widely applied to electrophotographic application fields such as a laser beam printer, a CRT printer, and an electrophotographic plate making system as well as a copying machine.

[0046]

【Example】

[Example 1] An electrophotographic photosensitive member was produced as follows.

A φ80 mm × 360 mm aluminum cylinder was used as a support, and a 5 wt% methanol solution of a polyamide resin (trade name: Amilan CM8000, manufactured by Toray) was applied to the support by a dipping method to form an undercoat layer having a thickness of 0.5 μm. Provided.

Next, the following structural formula (1)

[0049]

[Chemical 1] 2.5 parts of bisazo pigment (part by weight, the same applies hereinafter), the following structural formula

[0050]

[Chemical 2] 1 part of butyral resin (a) (trade name: BLS, manufactured by Sekisui Chemical Co., Ltd.) and 100 parts of cyclohexanone were dispersed in a sand mill using 1φ glass beads for 20 hours. To this dispersion, 100 parts of tetrahydrofuran was added, coated on the undercoat layer, dried at 80 ° C. for 10 minutes with hot air, and dried.
A charge generation layer of 80 mg / m ² was formed.

Next, the following structural formula (2)

[0052]

[Chemical 3] 9 parts of the compound and 10 parts of bisphenol Z-type polycarbonate (trade name: Z-200, manufactured by Mitsubishi Gas Chemical Co., Inc.) were dissolved in 100 parts of monochlorobenzene.

This solution was applied onto the charge generation layer, and 1
It was dried with hot air at 00 ° C. for 1 hour to form a 25 μm charge transport layer by a dip coating method. Since the dip coating method was adopted, the film thickness difference between the upper part and the lower part of the photosensitive layer was 1 to 2 μm.

The photoconductor thus prepared was evaluated as follows.

Conductive carbon 4 on 100 parts of urethane rubber
The parts were melted and kneaded, and a roller-shaped charging member was molded to have a diameter of φ20 mm × 330 mm with a stainless core having a diameter of φ5 mm and a length of 350 mm as the central axis. Volume resistance value is 10
It was ⁶ Ω · cm.

The basic form of the image forming apparatus is based on Canon NP4835, and the image exposing means, developing device, paper feeding system, transfer charging device, conveying system, and pre-exposure means are used as they are, and the above-mentioned primary charging means is used. The roller-shaped charging member and cleaner were modified so that they could be cleaned only by blade cleaning with a silicon rubber blade. The voltage applied to the charging unit is DC-1400V
However, the AC voltage was not superimposed.

Example 2 As the charge generating material, the following structural formula was used.

[0058]

[Chemical 4] 1.2 parts of I type TiOPc pigment, 1 part of butyral resin (trade name: BX-1, manufactured by Sekisui Chemical Co., Ltd.), and 100 parts of cyclohexanone were dispersed for 4 hours in a sand mill using 1Φ glass beads. . 100 parts of ethyl acetate was added to this dispersion and applied on the undercoat layer, and dried at 95 ° C. for 10 minutes with hot air to form a charge generation layer of 180 mg / m ² .
Other than that was performed like Example 1.

[Example 3] The binder resin in the charge generation layer was represented by the following structural formula (b).

[0060]

[Chemical 5] The same procedure as in Example 1 was carried out except that the benzal resin (trade name: B-80, manufactured by Copia Co., Ltd.) shown in 1 was used.

Example 4 2 parts of the charge generation layer coating used in Example 1 and the charge generation layer coating used in Example 2

The same procedure as in Example 1 was carried out except that 1 part was added and 280 mg / m ^{2 was} applied. Example 5 2.5 parts of the compound represented by the structural formula (1) as a charge generating material, and the following structural formula (c) as a binder:

[0063]

[Chemical 6] Example 1 was repeated except that 0.1 part of the compound of Example 1 and 0.9 part of the compound represented by the structural formula (a) were used.

Comparative Example 1 Example 1 was repeated except that 1.8 parts of the compound represented by the structural formula (1) was used as the charge generating material and 1 part of the compound represented by the structural formula (c) was used as the binder resin. I went the same way.

Comparative Example 2 The binder resin in Comparative Example 1 was prepared by using the following structural formula (d).

[0066]

[Chemical 7] The same procedure as in Comparative Example 1 was repeated except that the compound of Example 1 was used instead.

Comparative Example 3 Comparative Example 1 was repeated except that the amount of the compound represented by the structural formula (1) in Comparative Example 1 was changed to 1.2 parts.

In the above Examples 1 to 5 and Comparative Examples 1 to 3, in the initial stage, the surface potential (Vd / Vd /) was measured on the back side (135 mm from the center) and the front side (135 mm from the center).
Vl) was performed, and section images were copied and evaluated. Further, when image development and durability were performed on these photoconductors, surface potential in the circumferential direction at the time when film thickness unevenness of about 2 μm was produced in the circumferential direction. The evaluation by unevenness and the evaluation by copying the section image were performed.

Quantum efficiency was measured by Kawaguchi Electric Co., Ltd.
This was done by modifying a paper analyzer made by Japan. The results are plotted by plotting the electric field strength E (V / cm) on the horizontal axis of the log-log graph and the quantum efficiency on the vertical axis. In the range where the electric field strength satisfies the expression (3), these plots lie on a substantially straight line, and the value of n is obtained from the slope of this straight line.

[0070]

[0071]

As described above, according to the present invention, even in an electrophotographic apparatus in which only a DC voltage is applied and contact charging is performed, there is unevenness in the film thickness of the photosensitive layer (back / front and circumferential direction). Even if the surface potential is uneven, a good image can be obtained.

[Brief description of drawings]

FIG. 1 is a partial vertical cross-sectional view showing the configuration of a photoconductor applied to the present invention.

FIG. 2 is a partial vertical cross-sectional view showing the configuration of another photoconductor applied to the present invention.

FIG. 3 is a partial vertical cross-sectional view showing the configuration of still another photosensitive member applied to the present invention.

FIG. 4 is a vertical cross-sectional view showing a main part of an electrophotographic apparatus based on the process of the present invention.

FIG. 5 is a partial vertical cross-sectional view showing a general charging member and a photoconductor.

[Explanation of symbols]

 1 Charging Member 2 Photosensitive Member 3 External Power Supply Device 4 Exposure Light 5 Developing Device 6 Transfer Charging Member 7 Cleaner 8 Pre-Exposure Means 9 Fixing Device 10 Conductive Support 11 Photosensitive Layer 13 Charge Generation Layer 14 Charge Transport Layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Akira Yoshida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. An electrophotographic apparatus having an electrophotographic photosensitive member and a charging member disposed in contact with the photosensitive member, and being charged by applying only a DC voltage from the charging member to the photosensitive member. an electrophotographic photosensitive member used, the relationship between the electrophotographic quantum efficiency [Phi and the electric field strength E of the photoreceptor satisfies the following formula _{(1) Φ = Φ 0 E} n (1) ( where, [Phi ₀ is a constant) was expressed in In this case, the value of n satisfies the formula (2) 0.45 ≦ n ≦ 4.0 (2). 2. The electrophotographic photosensitive member according to claim 1, wherein the electric field strength E satisfies the following formula (3): 1.5 × 10 ⁵ ≦ E ≦ 8.0 × 10 ⁵ (V / cm) (3). . 3. An electrophotographic apparatus comprising an electrophotographic photosensitive member and a charging member disposed in contact with the photosensitive member, and charged by applying only a DC voltage from the charging member to the photosensitive member. , the relationship is represented by the following formula with an electrophotographic quantum efficiency [Phi and the electric field strength E of the photoconductor _{(1) Φ = Φ 0 E} n (1) ( where, [Phi ₀ is a constant) the value of n when expressed in An electrophotographic apparatus satisfying the formula (2) 0.45 ≦ n ≦ 4.0 (2). 4. The electrophotographic apparatus according to claim 3, wherein the electric field strength E satisfies the following formula (3): 1.5 × 10 ⁵ ≦ E ≦ 8.0 × 10 ⁵ (V / cm) (3).