JPH10326022A - Electrophotographic photoreceptor for negative electrification and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoreceptor low in cost, high in productivity and capable of obtaining interchangeability with a conventional laminated type electrophotographic photoreceptor in terms of characteristic by making the mobility of an electron in a photoreceptive layer larger than that of a positive hole. SOLUTION: Charge generating substance 2, charge transporting substance and binding resin are contained in the same photoreceptive layer 4, and the mobility of the electron in the layer 4 is made larger than that of the positive hole. In order to realize the above matter, much electron transporting material having the excellent mobility must be contained in the layer 4. It is desirable that the mobility of the electron in the layer 4 is within 1×10<-6> to 5×10<-5> cm<2> /V.sec on the condition that electric field intensity is 4×10<5> V/cm, and the mobility of the electron is within 5 to 100 times as large as that of the positive hole. In the case of singly using the electron transporting material as the charge transporting material, residual potential easily occurs because the positive hole generated in bulk is easily accumulated. It is effective to add positive hole transporting material in order to prevent the occurrence of the residual potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negatively charged electrophotographic photosensitive member and an image forming method using the same.

[0002]

2. Description of the Related Art In general, an electrophotographic photosensitive member is formed by forming a photosensitive layer made of a photoconductive material on a conductive substrate. In many cases, a laminated electrophotographic photosensitive member having a function-separated type photoconductive layer composed of a charge transport layer is used.

[0003] However, a conventional general laminated electrophotographic photoreceptor generally has a charge transport layer composed of a relatively thick layer laminated on a thin charge-generating layer having a thickness of 1 μm or less. The difficulty of forming a thin film causes a decrease in yield. Further, the charge transporting material used for the charge transporting layer is generally a hole transporting material for reasons of abundance of compounds, electrical stability, safety as a material, etc. Such a laminated electrophotographic photosensitive member inevitably can exhibit sensitivity only by negative charging.

In recent years, demands for electrophotographic photoreceptors tend to be higher in functions such as longer life and higher sensitivity, while demands for lower cost and higher productivity, like other general-purpose products, are extremely persistent.

In response to such demands for the electrophotographic photoreceptor, a conventional single-layer type electrophotographic photoreceptor which can achieve low cost and high productivity due to its advantages such as a simple layer structure is re-evaluated. It is becoming. Therefore, attempts to realize a practical single-layer electrophotographic photosensitive member have been actively made again, but a single-layer electrophotographic photosensitive member that is compatible with a conventional multilayer electrophotographic photosensitive member has been actively developed. At present, no body has been obtained.

[0006] For example, a single-layer electrophotographic method using a poly-N-vinylcarbazole (PVK) / trinitrofluorenone (TNF) complex disclosed in US Pat. No. 3,484,237, which was first practically used as an organic compound. The body has problems such as insufficient mechanical strength of PVK, which is a main component, poor sensitivity due to low charge mobility, and strong toxicity of TNF.

[0007] Also, "Journal of Applied
Physics ”(Journal of Applied Physics) No. 49
Vol. 11, No. 5543-5564 (1978) and the like, a single-layer type electrophotographic photosensitive member in which a hole transport material is used in combination with a eutectic of a thiapyrylium salt and a polycarbonate resin is usable. Because it is limited, it is difficult to improve the characteristics, and the sensitivity wavelength range is narrow, and there is no sensitivity in the long wavelength range, so it is not applicable to electrophotographic devices that use semiconductor lasers that are currently the mainstream as exposure light sources. there were.

Further, as in the phthalocyanine / resin dispersion type electrophotographic photoreceptor disclosed in US Pat. No. 3,397,086, a single-layer type electron having a structure in which a photoconductive pigment is dispersed in an electrically insulating binder. Since the photoreceptor has a high density of charge traps inevitably formed on the pigment surface in the photosensitive layer, the photoresponse characteristics are significantly deteriorated due to a so-called induction effect in which a delay occurs from light irradiation to potential decay. Further, there is a disadvantage that the light attenuation curve is completely different from that of the ordinary laminated type photoreceptor, and compatibility of gradation cannot be obtained. In addition, when used repeatedly, there is also a problem that the charge is accumulated in the trap and the induction effect itself changes, so that stable characteristics cannot be obtained. For this reason, this type of single-layer type electrophotographic photosensitive member is currently used only as a disposable plate-making photosensitive member.

Thus, for example, Japanese Patent Application Laid-Open No. 54-1633 discloses a charge generation material such as phthalocyanine of 0.005.
A photosensitive material obtained by dispersing about 0.15 mol part in a binder resin together with 1 mol part of a hole transport material such as oxadiazole and 0.05-0.3 mol part of an electron transport material such as dinitrofluorenone. A single-layer electrophotographic photosensitive member having a layer provided on a conductive support is disclosed. This type of single-layer type electrophotographic photoreceptor is different from a conventional phthalocyanine / resin dispersion type single-layer type electrophotographic photoreceptor in that charge generation and charge transport are performed by the same material. Since the generation is performed by different materials, the concentration of the charge generation material can be significantly reduced as compared with the conventional case, and the induction effect, which is a problem in the single-layer type photoreceptor, is not observed. In addition, there is an advantage that a photosensitive member having both positive and negative charges can be realized.

However, in the technology disclosed above, although the photoreceptor has both positive and negative charging properties, it has been developed mainly for use in positive charging. This is only about half of that of the conventional photoconductor, and does not match the sensitivity at all with the laminated photoconductor conventionally used with negative charging. In addition, in the single-layer type electrophotographic photoreceptor having such a configuration, since charge generation occurs in the photosensitive layer, electrons having low mobility are easily trapped, and the light attenuation characteristic shows a unique tailing tendency. However, even if only sensitization could be sensitized, compatible characteristics could not be obtained.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic photosensitive member that can be manufactured at low cost and with high productivity. An object of the present invention is to provide an electrophotographic photoreceptor for negative charging having preferable performance excellent in compatibility with the above characteristics, and an image forming method using the same.

[0012]

According to the present invention, there is provided an electrophotographic photoreceptor comprising a charge-generating substance, a charge-transporting substance and a binder resin in the same photosensitive layer.
A negative charge electrophotographic photosensitive member, wherein the mobility of electrons in the photosensitive layer is larger than the mobility of holes; and forming a latent image by negatively charging the photosensitive layer of the negative charge electrophotographic photosensitive member. And then developing using negatively charged toner. In order to realize the object of the present invention, in particular, the mobility of electrons in the photosensitive layer is 1 × 10 ⁻⁶ to 1 × 10 ⁻⁶ when the electric field intensity is 4 × 10 ⁵ V / cm 2.
It is desirable to be within the range of 5 × 10 ⁻⁵ cm ² / V · sec. Further, under the condition of the electric field intensity of 4 × 10 ⁵ V / cm, it is 5 to 100 times the mobility of the holes in the photosensitive layer. Preferably, the charge transport material contains an electron transport material and a hole transport material. Further, according to the present invention, high image quality in which defects such as background stains do not appear due to image characteristics can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the structure of a photosensitive layer of an electrophotographic photosensitive member for negative charging according to the present invention. Here, the thickness of the photosensitive layer is preferably in the range of 5 to 50 μm. When the photosensitive layer is formed by dip coating, the desired thickness can be easily obtained by adjusting various physical properties such as a coating speed, a viscosity of a paint, and a cutting power. In addition to the single-layer photosensitive layer, a functional layer such as an intermediate layer or a surface protective layer may be appropriately used.

The charge mobility defined in the present invention means a general characteristic value defined as a charge moving speed per unit electric field intensity. To measure such a characteristic value,
Usually, a technique called a time-of-flight (TOF) method is used. This measurement method is described in, for example, “Journal of Applied Physics”
(Journal of Applied Phisics), Vol. 43, No. 12 (1972), pages 5033-5040, etc., as a means for evaluating the charge transport ability of an organic photoconductive substance. Is very common. The details of the measurement are given to the same document, etc., but as an overview, an electric field is formed by applying a voltage between the electrodes using a sample called a sandwich cell having a structure in which both surfaces of the photosensitive layer are sandwiched between electrodes, and then The pulse light is applied to the sample through the electrodes, and a waveform of a transient current flowing between the electrodes is observed in a process in which generated charges move from one surface of the sample to the opposite surface. The charge mobility can be easily derived by analyzing the transient current waveform. Further, according to this method, it is possible to easily evaluate the mobility of electrons and holes separately from the direction of the light irradiation surface and the direction of the electric field.
It should be noted that the charge mobility of the organic photoconductive substance greatly depends on setting conditions such as electric field strength. Therefore, the value obtained by the measurement under the condition of the electric field strength of 4 × 10 ⁵ V / cm is used as the charge mobility defined by the present invention as a reference.

In the electrophotographic photoreceptor for negative charging of the present invention, it is necessary that the mobility of the electrons in the photosensitive layer is higher than the mobility of the holes. It is necessary to make the photosensitive layer contain a large number of electron transporting materials having a good degree. The mobility of electrons in the photosensitive layer is 1 × 10 ^{−6 to} 5
It is desirable to be within the range of × 10 ⁻⁵ cm ² / V · sec, and it is particularly preferable that the electron mobility is within the range of 5 to 100 times the hole mobility. In addition, it is possible to use the electron transport material alone as the charge transport material. However, in this case, the holes generated in the bulk are easily accumulated, so that the residual potential is likely to increase. To prevent this, it is effective to add a hole transport material.

Examples of the electron transporting material include organic compounds such as benzoquinone, tetracyanoethylene, tetracyanoquinodimethane, fluorenone, xanthone, phenanthraquinone, phthalic anhydride, and diphenoquinone. , Amorphous silicon, amorphous selenium, tellurium, selenium-tellurium alloy, cadmium sulfide,
Examples include inorganic materials such as antimony sulfide, zinc oxide, and zinc sulfide.

Examples of the hole transport material include low molecular weight compounds such as pyrene, carbazole, hydrazone, oxazole, oxadiazole, pyrazoline, arylamine, arylmethane, benzidine, and thiazole compounds. , Stilbene compounds, butadiene compounds and the like. Further, as the polymer compound, for example, poly-N-vinylcarbazole, halogenated poly-
Examples include N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine, pyrene-formaldehyde resin, ethylcarbazole-formaldehyde resin, ethylcarbazole-formaldehyde resin, triphenylmethane polymer, and polysilane.

The charge transporting material used in the present invention is not limited to those listed here, and can be used alone or in combination of two or more. A mixture of transport materials can be used.

The charge generating material used in the present invention includes:
For example, azo pigments, quinone pigments, perylene pigments,
Indigo pigment, thioindigo pigment, bisbenzimidazole pigment, phthalocyanine pigment, quinacridone pigment, quinoline pigment, lake pigment, azo lake pigment, anthraquinone pigment, oxazine pigment, dioxazine pigment, triphenylmethane pigment Pigments, azulenium dyes, squarium dyes, pyrylium dyes, triallylmethane dyes, xanthene dyes, thiazine dyes, various organic pigments such as cyanine dyes, dyes, and further amorphous silicon, amorphous selenium,
Examples include inorganic materials such as tellurium, selenium-tellurium alloy, cadmium sulfide, antimony sulfide, zinc oxide, and zinc sulfide.

When using the charge generating material, the materials mentioned here can be used alone, but two or more kinds of charge generating materials can be mixed and used.

The photosensitive layer of the present invention was prepared by dispersing an electron transporting material, a hole transporting material, a charge generating material, a binder resin, and a solvent using a ball mill, a homomixer or the like to obtain a coating liquid. Apply the coating liquid. As the coating method, a known method such as a dip coating method, a roll coating method, a spray method, or a spin coating method can be appropriately selected. The ratio of the charge generation material to the solid content in the paint,
The range of 0.2 to 5% by weight at which the sensitivity of the electrophotographic photoreceptor is good and the charge retention ability and the charge transportability are good is preferable.

The binder resin is preferably a high molecular polymer capable of forming an electrically insulating film. Such high-molecular polymers, for example, polycarbonate, polyester,
Methacrylic resin, acrylic resin, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, styrene-butadiene copolymer, vinylidene chloride
Acrylonitrile polymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicon-alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin, poly-N-vinylcarbazole , Polyvinyl butyral, polyvinyl formal, polysulfone, casein, gelatin, polyvinyl alcohol, ethyl cellulose, phenolic resin, polyamide, carboxy-methyl cellulose, vinylidene chloride-based polymer latex, polyurethane, and the like, but are not limited thereto. These binder resins are used alone or in combination of two or more.

In addition to these binder resins, additives such as a dispersion stabilizer, a plasticizer, a surface modifier, an antioxidant and a light deterioration inhibitor can be used.

Examples of the plasticizer include biphenyl, biphenyl chloride, terphenyl, dibutyl phthalate, diethylene glycol phthalate, dioctyl phthalate, triphenylphosphoric acid, methylnaphthalene, benzophenone, chlorinated paraffin, polypropylene, polystyrene and various fluorohydrocarbons. No.

Examples of the surface modifier include silicone oil, fluororesin and the like.

Examples of the antioxidant include phenol-based, sulfur-based, phosphorus-based, and amine-based compounds.

Examples of the photo-deterioration inhibitor include benzotriazole compounds, benzophenone compounds, hindered amine compounds and the like.

Examples of the solvent used in the coating preparation method of the present invention include alcohols such as methanol, ethanol and n-propanol; acetone, methyl ethyl ketone,
Ketones such as cyclohexanone; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; ethers such as tetrahydrofuran, dioxane and methyl cellosolve; esters such as methyl acetate and ethyl acetate; dimethyl sulfoxide, sulfolane and the like Sulfoxides and sulfones; aliphatic halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride, and trichloroethane; and aromatics such as benzene, toluene, xylene, monochlorobenzene, and dichlorobenzene.

The electrophotographic photoreceptor of the present invention has a feature that it has excellent electrophotographic characteristics at the time of negative charging. Particularly, when the electrophotographic photoreceptor is used in an image forming method by a so-called reversal developing method using a negatively charged toner, a high resolution is obtained. Thus, the true value that there are few printing defects can be exhibited. Such an image forming method uses a laminated negative charging electrophotographic photoconductor in which a hole transporting charge transport layer is laminated on a conventional charge generation layer,
This is a method generally used in an electrophotographic apparatus such as a laser printer, and has a developing feature of attaching toner to a light irradiation unit. According to this method, there is an advantage that the light irradiation area can be reduced in printing with a large number of white backgrounds such as a text document, and the load on the apparatus and the photoconductor can be reduced.

[0030]

The electrophotographic photoreceptor for negative charging of the present invention can achieve low cost and high productivity because of its simple layer structure, and further, contrary to the conventional general single-layer type electrophotographic photoreceptor. That the mobility of the electrons in the photosensitive layer is greater than the mobility of the holes,
It has remarkable characteristics, thereby realizing practically preferable characteristics having good compatibility in electrical characteristics with the conventional laminated electrophotographic photosensitive member and excellent image quality.
The reason will be described below.

In a conventional single-layer type electrophotographic photoreceptor, for example, the photoreceptor described in the above-mentioned embodiment of JP-A-54-1633, the hole transport material is about 10 times as large as the electron transport material. Because of the high content, the electrons do not have sufficient electron transport capability to be transported across the photosensitive layer,
The charge generation at the time of negative charging must necessarily be performed in the vicinity of the interface between the photosensitive layer and the conductive support. For this reason, incident light that has passed through the photosensitive layer and reached the vicinity of the support contributes to charge generation, but since the charge generating substance is dispersed in the photosensitive layer, light is A considerable portion is absorbed, resulting in a significant decrease in sensitivity as compared to the case of positive charging. Also, since the electron concentration in the photoreceptor is originally low, the mobility of the electrons is further reduced by the reduction of the electric field intensity accompanying the light attenuation, and the electrons are easily retained in the bulk, and the light attenuation is reduced. The hemming becomes larger. For this reason, compatibility with the conventional laminated electrophotographic photosensitive member in terms of electrical characteristics was not obtained at all.

In the electrophotographic photosensitive member for negative charging of the present invention, since the mobility of electrons is larger than the mobility of holes, a remarkable effect that charge generation at the time of negative charging is performed near the surface of the photosensitive layer is produced. . Therefore, the incident light does not need to be transmitted to the vicinity of the substrate in the photosensitive layer, so that the loss is small and high sensitivity can be realized. In addition, since most of the charge generation occurs in the portion closest to the charged charge, the charge is less likely to accumulate in the bulk, and light attenuation characteristics close to those of the conventional negative-type stacked electrophotographic photoreceptor can be obtained. In addition, there is a feature that compatibility in electrical characteristics can be obtained.

Further, the electrophotographic photosensitive member for negative charging of the present invention is extremely advantageous from the viewpoint of image formation. That is, since the charge generation at the time of negative charging is performed in the vicinity of the surface of the photosensitive layer, the incident light is transmitted to the vicinity of the substrate as in the case of a conventional single-layer type electrophotographic photosensitive member or a laminated type electrophotographic photosensitive member. In addition, since there is no absorption or scattering in the photosensitive layer and no charge is diffused from the substrate side to the surface, an extremely high-resolution latent image can be obtained.

Further, in the case of a photosensitive layer mainly having a hole transporting property, such as a conventional single-layer type electrophotographic photosensitive member, in the case of negative charge, holes injected from the substrate side easily reach the surface and charge. In many cases, the potential holding ability cannot be sufficiently obtained. In addition, if the substrate has dirt or defects, it becomes a nucleus for charge injection, causing a local potential drop, which is known to cause fatal black spots and background dirt defects in the reversal development method. I have. On the other hand, in the single-layer type electrophotographic photoreceptor of the present invention, since the hole transport from the substrate side hardly occurs because the electron transporting property is the center, the image defect especially in the reversal development method is obtained. There is an effect that a clear image without any blur can be obtained.

[0035]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the examples. In the following examples and comparative examples, “parts” indicates “parts by weight”.

Example 1 0.3 part of α-type titanyl phthalocyanine, formula (1)

[0037]

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8 parts of an electron transport material represented by the following formula (2)

[0039]

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5 parts of a hole transporting material represented by the following formula: and a polycarbonate resin ("Iupilon Z-" manufactured by Mitsubishi Gas Chemical Company, Inc.).
200 ") was dissolved in 76 parts of chloroform and dispersed using a vibration mill to prepare a coating for a photoreceptor.

Using this coating material, dip coating is applied to the surface of a 30 mm-diameter aluminum tube so that the film thickness after drying becomes 15 μm, and then dried to form a photosensitive layer. I got a body. Further, a plate-shaped electrophotographic photosensitive member having a similar photosensitive layer formed on an aluminum plate having a thickness of 0.3 mm using the same coating material was also manufactured.

Example 2 Example 1 was repeated except that the electron transporting material was changed to 9 parts and the hole transporting material was changed to 4 parts.
An electrophotographic photoreceptor was obtained in the same manner as described above.

Example 3 In Example 1, an electron transporting material represented by the formula (3)

[0044]

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8 parts of a compound represented by the formula (4)

[0046]

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An electrophotographic photoreceptor was obtained in the same manner as in Example 1 except that 5 parts of the compound represented by the following formula was used.

Example 4 An electrophotographic photosensitive member was obtained in the same manner as in Example 3, except that 10 parts of the electron transporting substance and 3 parts of the hole transporting substance were used.

Comparative Example 1 An electrophotographic photosensitive member was obtained in the same manner as in Example 1, except that 1.5 parts of the electron transport material and 8 parts of the hole transport material were used. The molecular weight of each material of the photoreceptor was 576.44 for α-type titanyl phthalocyanine, and 32 for the electron transport material of the formula (1).
4.46, since the hole transport material of the formula (2) is 425.57, the molar ratio is 0.028: 0.24: 1, which is disclosed in Japanese Patent Application Laid-Open No. 54-1633. This corresponds to the disclosed photoconductor.

Comparative Example 2 An electrophotographic photosensitive member was obtained in the same manner as in Example 3, except that 5 parts of the electron transporting material and 8 parts of the hole transporting material were used.

Comparative Example 3 An electrophotographic photosensitive member was obtained in the same manner as in Example 3, except that the electron transporting material was changed to 7 parts and the hole transporting material was changed to 6 parts.

(Comparative Example 4) 2 parts of α-type titanyl phthalocyanine and 1 part of a polyvinyl butyral resin (trade name “Eslec BM-1” manufactured by Sekisui Chemical Co., Ltd.) were dispersed together with 100 parts of methylene chloride in a vibration mill for 2 hours. A paint for a charge generation layer was prepared.

Next, using this paint, it is applied on an aluminum pipe and an aluminum plate, and after drying, a film thickness of 0.4 μm
Was formed.

On the charge generation layer, a coating solution obtained by dissolving 10 parts of the hole transport material of the formula (2) together with 14 parts of a polycarbonate resin (“Iupilon Z-200” manufactured by Mitsubishi Gas Chemical Company) in 76 parts of chloroform. After coating and drying, film thickness 15
A μm charge transport layer was formed to obtain a negatively charged laminated electrophotographic photosensitive member.

(Measurement of Charge Mobility) In order to measure the charge mobility of the prototype photoreceptor, TOF measurement was performed on the samples obtained in each of the examples and comparative examples. For the measurement, titanyl phthalocyanine for charge generation was vapor-deposited to a thickness of 500 ° on the surface of each plate-like sample, and aluminum was thinly vapor-deposited thereon to form a translucent electrode, thereby producing a sandwich cell. The reason why a new charge generation layer was formed on the surface is that, in the single-layer type photoreceptor manufactured in the example, since charge generation is performed in the bulk near the surface, errors in the depth direction are likely to occur, This is because a layer intended only for charge generation is provided and its influence is excluded.

Next, the sample was placed in a constant temperature / humidity chamber set at 23 ° C. and a humidity of 50% RH, a voltage was applied to the electrodes on both sides, and the electric field strength inside the photosensitive layer was 4 × 10 ⁵ V. / Cm
In this state, pulsed light was emitted from a vapor-deposited aluminum surface using a dye laser having a wavelength of 650 nm excited by a nitrogen laser. Table 1 collectively shows the mobility of electrons and holes in the photosensitive layer of each photosensitive member derived from the transient current waveform obtained at this time.

[0057]

[Table 1]

(Electrical Characteristics) In order to evaluate the electrical characteristics of the electrophotographic photosensitive members obtained in each of the examples and comparative examples, each of the drum photosensitive members was tested using a drum photosensitive member test apparatus (“Cynthia-30” manufactured by Gentec). ") Was used to measure the electrophotographic properties. The measuring method was such that the drum photoreceptor was charged by corona discharge at an applied voltage of −6 kV while rotating at 60 rpm in a dark place, and the surface potential immediately after this was used as an initial potential V ₀ for evaluation of charging ability. Next, the potential V ₁₀ after being left in a dark place for 10 seconds was measured, and the potential holding ability was evaluated by V ₁₀ / V ₀ . Then, the exposure intensity on the surface was set to 1 μW / cm ² with 780 nm monochromatic light, the photosensitive layer was irradiated with light, and the decay curve of the surface potential was recorded.
Here, the surface potential by light irradiation determined amount of exposure until reduced to 1/2 of V _10, were evaluated sensitivity as half decay exposure E _1/2. The results are summarized in Table 2.

[0059]

[Table 2]

As is clear from the results shown in Table 2, the electrophotographic photosensitive members obtained in Examples 1 to 4 of the present invention exhibited excellent charging ability and sensitivity. In addition, each electrophotographic characteristic is very close to the conventional electrophotographic photosensitive member for negative charging having a conventional configuration in which the charge generation layer and the charge transport layer obtained in Comparative Example 4 are laminated in this order, and the compatibility is excellent. I understand. On the other hand, Comparative Example 1
The single-layer type electrophotographic photoreceptors in which the hole mobilities obtained in Nos. 1 to 3 are larger than the electron mobilities have significantly higher sensitivities as compared with the electrophotographic photoreceptors obtained in Examples and Comparative Example 4. Obviously, it is inferior and does not provide sufficient compatibility.

(Image Characteristics) To evaluate the image characteristics, a laser printer of a reversal development type (“Laser Jet III Si” manufactured by Hewlett-Packard, Inc.) corresponding to a negatively charged drum-shaped electrophotographic photosensitive member was used. ), The drum-shaped electrophotographic photoreceptors obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were mounted, and an image was formed on copy paper which is usually used in an environment of 23 ° C. and 50% RH. . Table 2 summarizes the image evaluation results. The evaluation of background contamination was performed by observing a white background document on which an image was formed with a 50-fold loupe, calculating the area ratio of the toner adhered in a 2 mm × 2 mm square, and using the following evaluation criteria, ◎, ○, Δ , ×, the degree was evaluated in four stages.

A: The maximum value of the area ratio is less than 0.1%. ：: The maximum value of the area ratio is 0.1% or more and less than 0.5%. Δ: The maximum value of the area ratio was 0.5% or more and less than 1.0%. ×: The maximum value of the area ratio is 1.0% or more.

The image density was determined by measuring the print density of the black background portion of the image with a densitometer (RD918, manufactured by Macbeth).

[0064]

[Table 3]

As is clear from the results shown in Table 3, each of the electrophotographic photoreceptors obtained in Examples 1 to 4 was free from background smear, and images with sufficient print density were obtained. Example 1
In the electrophotographic photoreceptors obtained in Nos. 1 to 3, not only the image density was significantly inferior, but also the evaluation of background contamination was insufficient.
In the conventional electrophotographic photosensitive member having a laminated structure obtained in Comparative Example 4, although sufficient image density was obtained, the evaluation of background contamination was very poor.

Further, when the resolutions of the printed images composed of the halftone dots were compared, the electrophotographic photosensitive members obtained in Comparative Examples 1 and 2 were found to have poor resolution due to the collapse of the halftone dots. Indicate excellent dot reproducibility,
It has been found that good resolution can be obtained.

[0067]

According to the electrophotographic photoreceptor for negative charging of the present invention, the cost can be reduced and the productivity can be increased because of its simple layer structure. Practically preferable characteristics that have compatibility and have high image quality in which no defects appear on the image are realized.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating an example of a layer configuration of an electrophotographic photosensitive member of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conductive support 2 charge generating substance 3 charge transporting substance + binder resin 4 photosensitive layer

Claims (5)

[Claims] 1. An electrophotographic photosensitive member containing a charge generating substance, a charge transporting substance and a binder resin in the same photosensitive layer, wherein the mobility of electrons in the photosensitive layer is higher than the mobility of holes. An electrophotographic photosensitive member for negative charging, characterized by being large. 2. The method according to claim 2, wherein the mobility of electrons in the photosensitive layer is 4
1 × 10 ^{−6 to} 5 × 1 under the condition of × 10 ⁵ V / cm 2
^2. The photoreceptor according to claim 1, wherein said photoreceptor is within a range of 0-5 cm2 / ^Vsec . 3. The method according to claim 1, wherein the mobility of the electrons in the photosensitive layer is 4
3. The photoconductor according to claim 1, wherein the mobility is 5 to 100 times the mobility of holes in the photosensitive layer under the condition of × 10 ⁵ V / cm ³ . 4. The photoconductor according to claim 1, wherein the charge transport material contains an electron transport material and a hole transport material. 5. An image forming method using the electrophotographic photoreceptor for negative charging according to claim 1, wherein:
An image forming method, comprising: forming a latent image on the photosensitive layer of the photoreceptor by negative charging, and developing the latent image with a negatively charged toner.