JP3153651B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member used for a copying machine, a laser printer, and the like. More specifically, the present invention relates to an electronic device having both stable corona charging characteristics and good light attenuation characteristics. It relates to a photoreceptor.

[0002]

2. Description of the Related Art As one type of electrophotographic photoreceptor, an electrophotographic photoreceptor having an undercoat layer between a conductive substrate and a photosensitive layer is known. For example, Japanese Patent Application Laid-Open No. 58-86556 describes that a material containing a polymer or copolymer of a (meth) acrylate and a conductive polymer is used as the undercoat layer of the photoreceptor. ing. In addition, Japanese Unexamined Patent Publication
JP-A-3-85754 discloses that an organic photoreceptor substrate surface
It is described that a gas barrier resin such as a vinylidene chloride-acrylonitrile copolymer is provided.

It has already been proposed to impart conductivity to the undercoat layer. Japanese Patent Application Laid-Open No. 55-30030 discloses the provision of a conductive particle layer as an undercoat layer.
Japanese Patent No. 80048 discloses that an undercoat layer is provided with a dry film of a polymer emulsion in which conductive material particles are dispersed, and Japanese Patent Application Laid-Open No. 64-73352 discloses that an undercoat layer contains magnesium oxide, calcium oxide, It is described that at least one metal oxide selected from beryllium and lanthanum oxide is contained.

[0004]

Generally, an undercoat layer in an electrophotographic photoreceptor is used as a blocking layer for preventing charges opposite to surface corona charges from being injected from a conductive substrate. The purpose of using the undercoat layer in this case is to obtain stable corona charging characteristics. Other purposes include improving the adhesion between the conductive substrate and the photosensitive layer, improving the coating properties of the photosensitive layer, covering defects on the conductive substrate, preventing electrical corrosion of the conductive substrate, and so on. It is being studied for the purpose of preventing the occurrence of upper defects.

However, the conventional undercoat layer has a problem that it is difficult to achieve both stable corona charging characteristics and good light attenuation characteristics. That is, if the undercoat layer is thickened or its electric resistance is increased in order to secure corona charging property, a high residual potential is generated upon light irradiation, which causes fogging. On the other hand, if the undercoat layer is made thinner or its electric resistance is lowered to improve the light attenuation characteristics, the opposite charge is injected from the substrate during corona charging, and the charging potential is reduced or becomes unusable. The problem of becoming stable arises. Also, when the undercoat layer is thinned,
There is also a problem that a surface defect of the conductive substrate affects the photosensitive layer and causes a defect on an image at this portion.

The present inventors have solved the above problem by using a varistor type non-linear conductive property as an undercoat layer interposed between a conductive substrate and a photosensitive layer. I found it.

That is, an object of the present invention is to provide an electrophotographic photosensitive member having both stable corona charging characteristics and good light attenuation characteristics.

Another object of the present invention is to provide an electrophotographic photoreceptor which can be provided thicker than a conventional undercoat layer, thereby effectively preventing image defects due to defects on the surface of the conductive substrate. To offer.

[0009]

According to the present invention, in an electrophotographic photosensitive member having an undercoat layer between a conductive substrate and a photosensitive layer, the undercoat layer is a varistor-type non-linear conductive layer.
Characteristics and a film thickness (Lu) of 0.5 to 10 μm,
The photosensitive layer has a thickness (Lp) of 5 to 50 μm, and
The thickness ratio (Lp / Lu) of the photosensitive layer and the undercoat layer is 1
And an electrophotographic photoreceptor having a range of from 500 to 500 .

The undercoat layer used in the present invention is notable for having a varistor-type non-linear conductive property.
The following formula:

[0011]

## EQU1 I = a * V ^b formula, I is a current, V is voltage, a is a proportional constant, b is the voltage nonlinearity coefficient. It is preferable that the voltage nonlinearity coefficient (b) defined by the above is in the range of 3 or more, particularly 5 to 50. Further, it is desirable to have a volume resistivity of 10 ¹³ Ω · cm or more in an electric field lower than the threshold value.

The undercoat layer used in the present invention can be used without any particular limitation as long as it exhibits the above-mentioned varistor-type non-linear conductive characteristics. However, a dispersion composition of antimony-containing tin oxide or molybdenum disulfide and a resin is used. It was found that the conductive properties of the layer were particularly excellent.

[0013]

According to the present invention, by selecting and using a varistor-type non-linear conductive material as the undercoat layer, it has a high resistance at the time of charging, and suppresses the injection of opposite charges from the substrate to achieve high charging. On the other hand, the resistance becomes low under a high electric field at the time of light irradiation, so that the voltage can be reduced due to the movement of electric charges, and both high corona charging characteristics and good light attenuation (sensitivity) characteristics can be achieved.

Further, since the undercoat layer can be provided thick without adversely affecting the light attenuation characteristics, surface defects of the conductive substrate are concealed, and the influence of the surface defects on the photosensitive layer is eliminated. It is possible to effectively prevent the occurrence of a defect on the image caused by the image. As used herein, a varistor is defined as a non-linear resistor that is sensitive to voltage changes. That is, the resistance is extremely high below a certain critical voltage, and almost no current flows, but when the critical voltage is exceeded, the resistance rapidly decreases and a current flows.

FIG. 1 is a plot of the relationship between applied voltage (V) and current density (A / cm ² ) for an example of an undercoat layer used in the present invention (for details, see Example 1 described later). It is. According to FIG. 1, almost no current flows until the applied voltage reaches a critical (threshold) voltage Vcr, but as the applied voltage increases beyond this critical voltage, the current may increase exponentially. It becomes clear.

In the electrophotographic method using the photoreceptor of the present invention,
A photoreceptor having a varistor-type undercoating layer between the photosensitive layer and the substrate is used, and charging is performed under the condition that the electric field of the undercoating layer is equal to or less than a threshold electric field, and the electric field of the undercoating layer is set to It is another remarkable feature that the exposure charge elimination is performed under the condition exceeding the threshold electric field.

That is, at a voltage applied to the photoreceptor in the dark, the photosensitive layer has a high resistance, and the electric field applied to the undercoat layer is lower than the threshold electric field and is maintained at a high resistance. The surface is stably charged to a high potential, but during light irradiation (during exposure to static elimination), the photoconductive layer becomes conductive due to photo-generated carriers in the photoconductive layer. Since the electric resistance of the undercoat layer is higher than the electric field and the electric resistance of the undercoat layer is lowered, the charge is transferred between the photosensitive layer and the conductive substrate through the undercoat layer, thereby increasing the sensitivity and the contrast. is there.

In FIG. 2, which illustrates the photoreceptor of the present invention and the principle of electrophotography using the same, A shows a charging step, and B shows a light irradiation step. The photoreceptor 1 comprises a conductive substrate 2, an undercoat layer 3 provided on the substrate, and a photosensitive layer 4 provided on the undercoat layer. Consisting of conductive properties.

In the charging step A, the photoreceptor surface is positively charged by the positive corona charging mechanism 5. Thus, the surface of the photosensitive layer 4 is positively charged at a constant voltage Vs according to the saturation charging potential and the dark decay rate. In the present invention, the electric field E of the varistor-type undercoat layer 5 is determined by the threshold electric field E
Perform as if it were cr or less. This relationship is expressed as follows: When the thickness of the photosensitive layer is Lp and the thickness of the varistor type undercoat layer is Lu, the electric field intensity Eo applied to the undercoat layer is approximately expressed by the following equation

[0020]

(Equation 2) It is expressed by the following relationship.

Next, in the light irradiation step, the charged photoreceptor is exposed to an image through the image exposure mechanism 6. In the light portion L of the photosensitive layer 4 due to this image exposure, electrons out of the photo-generated charges quickly neutralize to surface charges (positive), but holes transiently stay at the boundary with the undercoat layer 3. , The electric field intensity E ₁ applied to the undercoat layer 3 is approximately calculated by the equation

[0022]

(Equation 3) It is expressed by the following relationship.

The thickness Lu of the undercoat layer is considerably smaller than the total thickness Lp + Lu of the photosensitive layer and the undercoat layer.

[0024]

The charge elimination satisfying E ₁ > Ecr ≧ E ₀ can be sufficiently satisfied, and the electron transport in the undercoat layer 3 and the electron injection from the undercoat layer 3 to the photosensitive layer 4 can be sufficiently performed. To sufficiently neutralize the surface positive charge.

Further, in the dark portion D of the photoreceptor, a sufficient potential is maintained on the surface and the electric resistance is sufficiently high, so that a high density image excellent in resolution and contrast can be formed even during development. It becomes.

FIG. 3 shows the surface potential during charging and exposure.

In the present invention, by using a varistor-type undercoat layer, accumulation of a residual potential in the exposed portion (L) when charging and exposure and charge elimination are repeated can be prevented, and a decrease in the initial saturation potential can be suppressed. There is an unexpected effect.
FIG. 4 is a graph in which the number of repetitions of charge / exposure static elimination is plotted on the horizontal axis, the effective initial potential and the residual potential of the exposed portion are plotted on the vertical axis, and the relationship between the two is plotted. The solid line and the solid line are the values for those using the varistor-type undercoat layer according to the present invention. From FIG. 4, it can be seen from FIG. 4 that in the conventional photoreceptor using the undercoat layer, the repetitive use causes an increase in the residual potential and a decrease in the effective surface potential due to charge trapping. It is clear that it has been almost completely eliminated.

In the present invention, it is important that the voltage nonlinearity coefficient is within the above range in order to increase the photosensitivity and reduce the residual potential. In particular, by providing between the positively charged photosensitive layer and the conductive substrate, excellent charging characteristics, image forming ability, etc. can be obtained while exhibiting sufficient effects such as abrasion resistance and printing durability. .

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION (Varistor-type undercoat layer) In the present invention, the varistor-type undercoat layer may have any of the above-mentioned characteristics, and its composition and dispersion form are not particularly limited.

This undercoat layer is composed of a continuous phase of a resin, particularly an electrically insulating resin, and conductive fine powder dispersed therein.

As the conductive fine powder, any one can be used as long as it provides the above-mentioned properties. Preferred examples thereof include tin oxide containing antimony (Sb / SnO ₂ ) and molybdenum disulfide (MoS ₂ ). it can. Molybdenum disulfide tends to color the varistor layer gray, but in the case of the present invention, since the varistor is used as an undercoat layer,
One of the advantages is that there is no influence of coloring. Particularly preferred conductive fine powders are those containing 2 to 20% by weight of antimony oxide per tin oxide. Of course, other conductive agents can be used as long as they have a volume resistivity of 10 ⁶ Ω · cm or less and a fine particle size, particularly, an average particle size of 0.3 μm or less.

As the resin, those used for forming this kind of undercoat layer are all used. For example, melamine resin, urea resin, silicone resin, epoxy resin,
Thermosetting resin such as phenolic resin and polyester resin,
Thermoplastic resins such as polycarbonate resin, polyamide resin, fluorine-based resin, polyarylate resin, and acrylic resin are used alone or in combination of two or more, but those having excellent wettability and dispersibility of conductive fine powder are used. desirable.

In order to obtain the above characteristics of the varistor-type undercoat layer, it is preferable to adjust the mixing ratio and the degree of dispersion of the two in the dispersion system.

When the compounding ratio of the conductive fine powder exceeds a certain range, the conductive fine particles take a dispersed structure in which the conductive fine particles are chained or tufted. Tend to be close to a straight line or the threshold electric field becomes small, so that the characteristics of the present invention tend not to be obtained. If the compounding ratio of the conductive fine powder is less than a certain range, the effect of the electrically insulating resin interposed between the conductive fine particles becomes dominant on the electrical characteristics, and thus the protective layer is rather close to the electrical insulation. Becomes

The nonlinear voltage in the underlayer according to the present invention.
In contrast to the above two cases, the current characteristics are achieved by a dispersion system in which the influence of the interface between the conductive fine particles and the electrically insulating resin is dominant in terms of electric characteristics. There are certain restrictions on the compounding ratio and the dispersion state of.

First, from the above viewpoint, it is desirable that the conductive fine powder is present in an amount of 10 to 40% by weight, particularly 20 to 30% by weight, based on the whole coating, although it varies depending on the kind thereof.

According to a study by an electron microscope of the present inventors, in a dispersion of an undercoat layer exhibiting non-linear voltage-current characteristics, the conductive fine particles substantially take the above-mentioned chain or tufted structure. Without a dispersion structure, and their average interparticle distance is 100 to 500.
It should be in the Angstrom range.

The conductive agent fine powder and the resin are a combination excellent in mutual dispersibility, and the wettability of the two, that is, the excellent adhesion at the interface, also has a significant effect on the electrical characteristics. In this sense, the conductive fine powder should be treated with a known silane coupling agent, zirconium coupling agent, titanate coupling agent, aluminum coupling agent, tin coupling agent, or the like. Is particularly desirable. The coupling agent is conductive fine powder 1
It is preferably used in an amount of 0.1 to 5 parts by weight per 100 parts by weight.

The thickness (Lu) of the undercoat layer is 0.5 to 1
0 μm, especially in the range of 1 to 5 μm.

The coating of the undercoat layer can also be formed by preparing a solution or dispersion of the above resin, applying it, drying it and, if necessary, baking it.

(Photoreceptor) The conductive base material used for forming the varistor-type undercoat layer is aluminum,
Metals such as aluminum alloy, steel, tin, platinum, gold, silver, panadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, brass, etc., and films of these listed metals or their metal oxides A glass substrate and a plastic substrate formed by means such as vapor deposition. The shape of the conductive substrate may be a sheet shape or a drum shape.

As the photosensitive layer provided on the undercoat layer, any photosensitive layer can be used. For example, a monodispersed layer type photosensitive layer in which a charge generating substance is dispersed in a medium containing a charge transporting substance, or a charge-transporting layer can be used. A function-separated laminated photosensitive layer composed of a combination of a transport layer (CTL) and a charge generation layer (CGL) is used. These charge transporting substances and charge generating substances are dissolved or dispersed in a resin solution known per se and used for forming a photosensitive layer.

Examples of the charge transport material include fluorenone compounds such as chloranil, tetracyanoethylene, 2,4,7-trinitro-9-fluorenone, nitrated compounds such as 2,4,8-trinitrothioxanthone and dinitroanthracene; N, N-diethylaminobenzaldehyde, N, N-diphenylhydrazone, N-methyl-3-
Hydrazone compounds such as carbazolylaldehyde and N, N-diphenylhydrazone; oxadiazole compounds such as 2,5-di (4-dimethylaminophenyl) -1,3,4-oxadiazol; 9- ( Styryl compounds such as 4-diethylaminostyryl) anthracene, carbazole compounds such as N-ethylcarbazole, pyrazoline compounds such as 1-phenyl-3- (p-dimethylaminophenyl) pyrazoline, 2- (p-diethylaminophenyl) -4- (p-dimethylaminophenyl) -5
Oxazole compounds such as (2-chlorophenyl) oxazole, isoxazole compounds, thiazole compounds such as 2- (p-diethylaminostyryl) -6-diethylaminobenzothiazole, triphenylamine,
Amine derivatives such as 4,4′-bis [N- (3-methylphenyl) -N-phenylamino] diphenyl, stilbene compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, indole compounds,
Examples include nitrogen-containing cyclic compounds such as triazole compounds, condensed polycyclic compounds, succinic anhydride, maleic anhydride, dibromomaleic anhydride, poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, and ethylcarbazole-formaldehyde resin. Is done. Incidentally, a photoconductive polymer such as poly-N-vinyl carbazole,
It can be used also as a binder resin described later. These charge transport materials may be used alone or in combination of two or more.

Examples of the charge generating material include various conventionally known materials, for example, selenium, selenium-till, amorphous silicon, billiium salts, azo compounds, disazo compounds, trisazo compounds, anthanthrone compounds, and phthalocyanine. Compounds, indigo compounds, triphenylmethane compounds, sulene compounds, toluidine compounds, pyrazoline compounds, perylene compounds,
Examples thereof include quinacridone compounds, which may be used alone or in combination of two or more.

Examples of the resin (binder) include a styrene-based polymer, a styrene-butadiene copolymer, a styrene-acrylonitrile copolymer, a styrene-maleic acid copolymer, an acrylic polymer, a styrene-acrylic copolymer, Ethylene-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy resin, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, polyether resin,
In addition to phenol resins and the like, various polymers such as photo-curable resins such as epoxy acrylate and urethane acrylate are exemplified, and these may be used alone or in combination of two or more.

In the case of a monodispersed photosensitive layer,
15 to 70% by weight, especially 30 to 60% by weight of the charge transport material
In amounts by weight, the charge generating substance is present in an amount of from 1 to 30% by weight, especially from 5 to 15% by weight, and the resin is present in an amount of from 17 to 70% by weight, especially from 30 to 60% by weight.
The thickness (Lp) of the photosensitive layer is 5 to 50 μm, particularly
The thickness is set to 10 to 30 μm.

In the case of the photosensitive layer of the function-separated type, when forming the charge generating layer, usually 1 to 300 parts by weight of the binder resin is used per 100 parts by weight of the charge generating material. The charge generation layer may be formed to an appropriate thickness. Usually, it is formed to a thickness of about 0.01 to 5 μm.

In forming the charge transport layer, the ratio between the charge transport material and the binder resin may be appropriately selected. Usually, the binder resin 30 to 5 is added to 100 parts by weight of the charge transporting material.
00 parts by weight are used. The charge transport layer has a thickness of the photosensitive layer.
(Lp) is formed to be 5 to 50 μm.

In preparing the above-mentioned coating solution for the charge generation layer and the coating solution for the charge transport layer, an appropriate organic solvent may be used, if necessary, in order to improve coatability according to the type of resin contained in each layer. A solvent that can be used, but does not re-dissolve the underlying layer, should be used.

In the photosensitive layer, terphenyl, halonaphthoquinones, acenaphthylenes, conventionally known sensitizers, plasticizers, ultraviolet absorbers, deterioration inhibitors such as antioxidants, etc.
Various additives may be contained. Further, an intermediate layer may be formed between the charge generation layer and the charge transport layer to facilitate the transfer of charges between the two layers.

(Electrophotography) According to the present invention, the above-mentioned photoreceptor is used, charging is performed under the condition that the electric field of the undercoat layer is equal to or less than the threshold electric field, and the electric field of the undercoat layer is controlled by the electric field. Exposure static elimination is performed under conditions exceeding the threshold electric field.

First, the electric field control of the undercoat layer of the photoreceptor is performed by the mechanism shown in FIG. 2, but the ratio of Lp / Lu is
It is set in the range of 1 to 500, especially 3 to 100.

The surface potential of the photosensitive member is 400 to 15
The voltage is preferably set to satisfy the above condition from the range of 00 V, particularly 600 to 1000 V, and the charging is performed using a positively charged corona.

Next, static elimination is performed by image exposure. A varistor having a non-linear voltage-current characteristic is used as the undercoat layer, and the charging potential and the thickness ratio of the photosensitive layer and the undercoat layer [Lp / L
u] is set in the above-described range, the electric field applied to the undercoat layer during this exposure exceeds the threshold electric field Ecr,
Effective neutralization is performed.

The exposure may be slit exposure from a document or scanning exposure using a laser.
ux · sec (0.6 μJ / cm ² ) to 10 lux · sec (3 μ
J / cm ² ) is appropriate.

According to the electrophotographic method of the present invention, it is possible to easily obtain a sensitivity of about 1 to 3 Lux · sec in terms of half-exposure, although not limited thereto.

The image formation in the electrophotographic method of the present invention is as follows.
Except for the above points, it can be carried out in any known manner per se. For example, for development, a magnetic brush developing method using a two-component magnetic developer or a one-component magnetic developer, a non-contact oscillating electric field developing method, or a developing method using a one-component non-magnetic developer can be used. The toner image formed on the photoreceptor can be transferred onto a copy paper or the like by a known method and fixed.

[0058]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the following examples. Example 1 Antimony-containing tin oxide (manufactured by Mitsubishi Metals, T-1) 30
Parts by weight and 70 parts by weight of a vinyl acetate-vinyl chloride copolymer resin (Slec C, manufactured by Shimizu Chemical Co., Ltd.) are dispersed and dissolved in 900 parts by weight of tetrahydrofuran.
It was applied on an aluminum sheet having a thickness of μm and dried at 110 ° C. to obtain a varistor-type undercoat layer. At this time, the coating conditions were set so that the film thickness after drying was about 1 μm.

Next, N, N'-3,5-xylyl-3,
4,9,10-perylenetetracarboxylic diimide 10
Parts by weight, 90 parts by weight of p-diethylaminobenzaldehyde diphenylhydrazone, and 100 parts by weight of a polycarbonate resin (Z-200, manufactured by Mitsubishi Gas Chemical Company) in toluene 90
The coating solution was dispersed and dissolved in 0 parts by weight, and this coating solution was applied on the undercoat layer, and dried at 120 ° C. to form a single-layer type photosensitive layer to obtain a photoreceptor sample. At this time, the film thickness after drying is about 20
The coating conditions were set to be μm.

Example 2 A photoconductor sample was prepared in the same manner as in Example 1 except that antimony-containing tin oxide was replaced by molybdenum disulfide.

Example 3 Tin oxide containing antimony (T-1 manufactured by Mitsubishi Metal Corporation) 30
Parts by weight are silicone-based cured resin (NSC-NSC-
1272) A dispersion dispersed in [solid content / 70 parts by weight] was used as a coating liquid, applied on an aluminum sheet having a thickness of 100 μm, and dried at 120 ° C. to obtain a varistor-type undercoat layer. At this time, the coating conditions were set so that the film thickness after drying was about 1 μm.

Next, 100 parts by weight of dibromoanthanthrone was charged with polyvinyl butyral (300 g, manufactured by Denki Kagaku Kogyo KK).
0K) with 50 parts by weight of n-butyl alcohol 35
A dispersion obtained by stirring and mixing 00 parts by weight was applied onto the undercoat layer and dried at 120 ° C. to obtain a carrier generation layer.
At this time, the coating conditions were set so that the film thickness after drying was 0.3 μm.

Subsequently, 100 parts by weight of 1,1-bis (p-diethylaminophenyl) -4,4-diphenyl-1,3-butadiene (anan, T-405) and a polycarbonate resin (Z-Mitsubishi Chemical Co., Ltd.) -200) 100 parts by weight were dissolved in 900 parts by weight of toluene, and this coating solution was applied on the carrier generation layer and dried at 120 ° C. to obtain a carrier transport layer. At this time, the film thickness after drying is about 20 μm.
The coating conditions were set so that This example is a photoreceptor sample having a laminated type photosensitive layer.

Example 4 A photoconductor sample was prepared in the same manner as in Example 3 except that antimony-containing tin oxide was replaced by molybdenum disulfide.

Comparative Example 1 A photoconductor sample was prepared in the same manner as in Example 1 except that the varistor-type undercoat layer was removed.

Comparative Example 2 A photoreceptor sample was prepared in the same manner as in Example 2 except that the varistor-type undercoat layer was removed.

Comparative Example 3 A photoconductor sample was prepared in the same manner as in Example 3 except that the varistor-type undercoat layer was removed.

Comparative Example 4 A photoconductor sample was prepared in the same manner as in Example 4 except that the varistor-type undercoat layer was removed.

The photoreceptor thus manufactured was evaluated for electrostatic characteristics using a commercially available plain paper copying machine (DC-3285, manufactured by Mita Kogyo KK). The exposure was performed by changing the exposure amount on the surface of the photoreceptor in the range of 0 to 6 Lux · sec every 0.2 Lux · sec. The decay of the surface potential with respect to the exposure was evaluated based on the potential at the developing portion position (300 msec after the start of the exposure). From the relationship between the exposure amount thus obtained and the exposed portion potential, the half-life exposure amount and the exposed portion residual potential at an exposure amount of 6 Lux · sec were treated as sensitivity. The corona charging ability of the photoreceptor was evaluated based on the corona discharge current required for charging the surface potential to 800V. The repetition stability of the electrostatic property was evaluated by setting the initial dark portion charging potential at 650 V and the exposure amount at 3.5 Lux · sec, and repeating the charging / exposure charge elimination 300 times. The results are shown in Table 1.

[0070]

[Table 1]

Further, in order to confirm the electrical properties, the sample A in which only the varistor-type undercoat layer of Example 1 was formed on an aluminum sheet (the antimony-doped (1
(0 wt%) tin oxide content = 27 wt%), antimony-doped (10 wt%) resin component without tin oxide added, so-called electrically insulating undercoat layer (corresponding to Comparative Example 1) B formed on an aluminum sheet (with antimony dope (10 wt.
%) Of tin oxide of antimony-doped (10 wt%) in Example 1 was changed to 40 parts by weight of 100 parts by weight. Sample C (corresponding to Example 2) was formed on an aluminum sheet (tin oxide content of antimony-doped (10 wt%) in the surface protective layer = 48 wt%). The film thickness was 2.1 μm for sample A and 1.8 μm for sample B.
m and Sample C were 2.0 μm.

Then, a high resistivity measurement device (TR42 [sample measurement box], TR300C, manufactured by Advantest Co., Ltd.)
[Regulated DC power supply], TR8652 [micro ammeter]) using, in the electric field intensity 1 × 10 ⁵ V / cm, was measured for volume resistivity, the sample A is 6 × 10 ¹⁵ Ω · c
m, sample B is 3 × 10 ¹⁷ Ω · cm, sample C is 2 × 10 ¹⁵
Ω · cm.

Further, when the cross sections of Sample A and Sample C were observed with a transmission electron microscope, in Sample A, antimony-doped (10 wt%) fine particles of tin oxide were almost 200 to
The sample C was dispersed at a distance of 500 angstroms, whereas the antimony dope (10 wt.
%) Of tin oxide fine particles were observed to be aggregated in a tufted shape at a certain portion, and to a chain at a certain portion.

[0074]

According to the present invention, a photoreceptor having a varistor-type undercoating layer having non-linear voltage-current characteristics is used as the undercoating layer, and the electric field of the undercoating layer is less than the threshold electric field. By performing charging under a certain condition, and performing exposure and elimination under the condition that the electric field of the surface protective layer exceeds the threshold electric field, the photosensitive layer is stably charged with high resistance in the dark and in the bright state. The resistance has been reduced to effectively remove the surface charge and the intermediate charge, and it has become possible to obtain excellent light sensitivity, clear image and high contrast without impairing the corona charging characteristics. In addition, the repetition characteristics and printing durability were significantly improved, for example, the residual potential could be effectively reduced while maintaining the initial potential high.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between applied voltage and current density for an undercoat layer used in the present invention.

FIG. 2 is an explanatory view showing the principle of the present invention, wherein A shows a charging step, and B shows an exposure and charge removing step.

FIG. 3 is a graph showing a surface potential at the time of charge exposure of a surface protective photoconductor.

FIG. 4 is a graph showing a relationship between the number of repetitions of charging and exposure / elimination, an effective initial potential, and a residual potential of an exposed portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Conductive substrate 3 Undercoat layer 4 Photosensitive layer 5 Corona charging mechanism 6 Image exposure mechanism

Claims (4)

(57) [Claims] 1. An electrophotographic photoreceptor in which an undercoat layer is provided between a conductive substrate and a photosensitive layer, wherein the undercoat layer is a ballistic
Non-linear conductive characteristics and film thickness of 0.5 to 10 μm
(Lu), and the photosensitive layer has a thickness of 5 to 50 μm.
(Lp) and the film thickness of the photosensitive layer and the undercoat layer
An electrophotographic photosensitive member, wherein the ratio (Lp / Lu) is in the range of 1 to 500 . 2. The electrophotographic photoreceptor according to claim 1, wherein the undercoat layer comprises a dispersion composition of antimony-containing tin oxide or molybdenum disulfide and a resin. 3. The electrophotographic photoreceptor according to claim 1, wherein the undercoat layer has a voltage nonlinearity coefficient (b) of 3 or more. 4. The electrophotographic photoreceptor according to claim 1, wherein the undercoat layer has a volume resistivity of 10 ¹³ Ω · cm or more in an electric field lower than a threshold value.