JPH06148923A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To provide the photosensitive body with which a stable corona charge characteristic and a good light attenuation characteristic are compatible and which can be provided with an under coat layer thicker than the conventional under coat layer and can effectively prevent the generation of defects on images caused to the defect on the conductive base body by interposing the under coat layer having a nonlinear conductive characteristic of a varistor type between a conductive base body and a photosensitive layer. CONSTITUTION:This photosensitive body 1 consists of the conductive substrate 2, the under coat layer 3 provided on the substrate 2 and the photosensitive layer 4 provided on the under coat layer 3. The under coat layer having the nonlinear conductive characteristic of the varistor type is selectively used as the under coat layer 3, by which the high resistance is attained to suppress the implantation of the opposite charges from the base body 2 and the high electrostatic charge is enabled at the time of electrostatic charge. On the other hand, the low resistance is attained and the high voltage is lowered by the transfer of the charges under a high electric field at the time of illumination with light. The high corona charge characteristic and the good light attenuation characteristic are thus compatible. Since the under coat layer 3 is provided thickly without adversely affecting the light attenuation characteristic, the surface defect of the conductive base body 2 is concealed.

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 in a copying machine, a laser printer or the like, and more specifically, to an electronic device having both stable corona charging characteristics and good light attenuation characteristics. The present invention relates to a photoconductor.

[0002]

2. Description of the Related Art As one type of electrophotographic photosensitive member, one having an undercoat layer provided between a conductive substrate and a photosensitive layer is known. For example, Japanese Unexamined Patent Publication (Kokai) No. 58-86556 discloses that an undercoating layer containing a (meth) acrylic acid ester polymer or copolymer and a conductive polymer is used as the undercoating layer. ing. In addition, JP-A-6
Japanese Patent Laid-Open No. 3-85754 discloses that on the substrate surface of an organic photoconductor,
It is described that a gas barrier resin such as vinylidene chloride-acrylonitrile copolymer is provided.

It has already been proposed to impart conductivity to the undercoat layer, and JP-A-55-25030 discloses that a conductive particle layer is provided as the undercoat layer.
In Japanese Patent No. 80048, a dry film of a polymer emulsion in which conductive material particles are dispersed is provided as an undercoat layer, and in Japanese Unexamined Patent Publication No. 64-73352, magnesium oxide, calcium oxide, and oxides are contained in the undercoat layer. It is described that each contains at least one metal oxide selected from beryllium and lanthanum oxide.

[0004]

Generally, an undercoat layer in an electrophotographic photosensitive member 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 adhesion between the conductive substrate and the photosensitive layer, improving coatability of the photosensitive layer, covering defects on the conductive substrate, and preventing electrical corrosion of the conductive substrate. 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 the corona charging property, a high residual potential is generated at the time of light irradiation, which causes fog. On the contrary, if the undercoat layer is thinned or its electric resistance is lowered in order to improve the light attenuation characteristic, the opposite electric charge is injected from the substrate during the corona charging, and the charging potential is lowered or the electric potential is lowered. The problem of becoming stable arises. Also, if you make the undercoat layer thin,
There is also a problem that the surface defect of the conductive substrate affects the photosensitive layer and causes an image defect at this portion.

The present inventors have found that the above problems can be solved by using an undercoating layer having 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 which has both stable corona charging characteristics and good light attenuation characteristics.

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

[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 has a varistor type non-linear conductive characteristic. An electrophotographic photosensitive member having the above is provided.

The undercoat layer used in the present invention is characterized in that it has a varistor type non-linear conductive characteristic.
It is preferable that the threshold electric field is in the range of 3 × 10 ^{5 to} 1 × 10 ⁶ V / cm.

[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. The voltage non-linearity coefficient (b) defined by is preferably 3 or more, and particularly in the range of 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 particular limitation as long as it exhibits the above-mentioned varistor type non-linear conductive characteristics, but a dispersion composition of antimony-containing tin oxide or molybdenum disulfide and a resin is undercoated. It has been found that the layer has particularly excellent conductive properties.

[0013]

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

Further, since the undercoat layer can be formed thick without adversely affecting the light attenuation characteristics, the surface defects of the conductive substrate can be hidden and the influence on the photosensitive layer can be eliminated, and the conductive substrate can be prevented. It is possible to effectively prevent the occurrence of a defect on the image due to it. Varistors are defined herein as non-linear resistors that are sensitive to changes in voltage. That is, below a certain critical voltage, the resistance is very high, and almost no current flows. However, above this critical voltage, the resistance sharply decreases and a current flows.

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

In the electrophotographic method using the photoconductor of the present invention,
A photoreceptor having a varistor type undercoat layer between the photosensitive layer and the substrate is used, and charging is performed under the condition that the electric field of the undercoat layer is equal to or lower than the threshold electric field, and the electric field of the undercoat layer is Another feature is that the exposure charge removal is performed under the condition of exceeding the threshold electric field.

That is, at the voltage applied to the photosensitive member in the dark, the photosensitive layer has a high resistance, and therefore 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 electric potential, but during light irradiation (during charge removal by exposure), the photoconductive layer becomes conductive due to photogenerated carriers in the photoconductive layer, so that the electric field applied to the undercoat layer is a threshold voltage. Higher than the electric field, the electrical resistance of the undercoating layer is reduced, causing the transfer of charge between the photosensitive layer and the conductive substrate through the undercoating layer, resulting in increased sensitivity and increased contrast. is there.

In FIG. 2 for explaining the principle of the photoconductor of the present invention and the electrophotography method using the same, A shows a charging step and B shows a light irradiation step. The photoreceptor 1 is composed of a conductive substrate 2, an undercoat layer 3 provided on the substrate, and a photosensitive layer 4 provided on the undercoat layer. The undercoat layer 3 is a varistor type non-linearity. It is composed of those exhibiting conductive properties.

In the charging step A, the surface of the photoreceptor is positively charged by the positive corona charging mechanism 5. As a result, the surface of the photosensitive layer 4 is positively charged with a constant voltage Vs according to the saturated charging potential and the dark decay rate. In the present invention, the electric field E of the varistor type undercoat layer 5 is changed to the threshold electric field E in the present invention.
Do so that it is less than or equal to cr. This relationship indicates that when the thickness of the photosensitive layer is Lp and the thickness of the varistor type undercoat layer is Lu, the electric field strength Eo applied to the undercoat layer is approximately expressed by

[0020]

[Equation 2] It is expressed by the relationship.

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

[0022]

[Equation 3] It is expressed by the 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]

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

Moreover, in the dark portion D of the photoconductor, a sufficient potential is held on the surface and the electric resistance thereof is sufficiently high, so that a high density image excellent in resolution and contrast can be formed even during development. It will be.

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

In the present invention, by using the varistor type undercoat layer, it is possible to prevent the residual potential from accumulating in the exposed portion (L) when the charging and exposing and discharging are repeated, and to suppress the decrease of the initial saturation potential. There is an unexpected effect.
FIG. 4 is a plot of the number of repetitions of charge / exposure elimination on the horizontal axis, the effective initial potential and the residual potential on the exposed portion on the vertical axis, and the relationship between the two. The solid line and the solid line are values for those using the varistor type undercoat layer according to the present invention. It can be seen from FIG. 4 that the photoreceptor using the conventional undercoat layer has a residual potential increase and a decrease in the effective surface potential due to the trapping of charges by repeated use. It becomes clear that it is almost completely eliminated.

In the present invention, it is important that the threshold electric field of the varistor-type undercoat layer is within the above-mentioned range in order to improve the charging property and to retain the charge on the surface of the undercoat layer. It is important that the voltage non-linearity coefficient is also within the above range in order to increase the photosensitivity and decrease the residual potential, and a varistor type undercoat layer satisfying these is a photosensitive layer, particularly a positive charge type photosensitive layer. When it is provided between the conductive substrate and the conductive substrate, excellent charging characteristics, image forming ability and the like 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 is not particularly limited as long as it has the characteristics described above, and its composition and dispersion form are not particularly limited.

The 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 gives the above-mentioned characteristics, but as preferable ones, there are listed antimony-containing tin oxide (Sb / SnO ₂ ) and molybdenum disulfide (MoS ₂ ). it can. Molybdenum disulfide tends to color the varistor layer gray, but in the present invention, since the varistor is used as the undercoat layer,
One of the advantages is that there is no effect of coloring. A particularly suitable electrically conductive fine powder contains antimony oxide in an amount of 2 to 20% by weight per tin oxide. Of course, other conductive agents can be used as long as the volume resistivity is 10 ⁶ Ω · cm or less and the particle size is fine, especially the average particle size is 0.3 μm or less.

As the resin, all those used for forming the undercoat layer of this type are used, and examples thereof include melamine resins, urea resins, silicone resins, epoxy resins,
Thermosetting resin such as phenol resin or polyester resin,
Thermoplastic resins such as polycarbonate resin, polyamide resin, fluorine resin, polyarylate resin, and acrylic resin are used alone or in combination of two or more kinds, and those having excellent wettability and dispersibility of conductive fine powder are preferable. desirable.

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

When the compounding ratio of the conductive fine powder exceeds a certain range, the conductive fine particles have a dispersed structure in which the conductive fine particles are chained or tufted, so that the influence of the conductive agent becomes dominant on the electric characteristics and the voltage-current characteristics. Is close to a straight line, or the threshold electric field becomes small, so that the characteristics of the present invention cannot be obtained. Also, 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, so that the protective layer that is closer to the electrical insulating property is obtained. Becomes

Nonlinear Voltage in Undercoat Layer of the Invention-
In contrast to the above two cases, the current characteristics are achieved in a dispersed system in which the influence of the interface between the conductive fine particles and the electrically insulating resin is dominant in terms of electrical characteristics. There are certain restrictions on the compounding ratio and dispersion state of.

First, it is desirable from the above viewpoint 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 entire coating, although it varies depending on the type.

According to a study by the inventors of the present invention using an electron microscope, in the dispersion system of the undercoat layer exhibiting a non-linear voltage-current characteristic, the conductive fine particles substantially have the above-mentioned chain or tufted structure. Exist as an independent dispersed structure without them, 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 having excellent dispersibility with each other, and the excellent wettability between them, that is, the adhesiveness at the interface, also has a significant influence on the electrical characteristics. In this sense, the conductive fine powder should be treated with a silane coupling agent, zirconium coupling agent, titanate coupling agent, aluminum coupling agent, tin coupling agent, etc. which are known per se. Is especially desirable. Coupling agent is conductive fine powder 1
It is preferably used in an amount of 0.1 to 5 parts by weight per 00 parts by weight.

Although the thickness of the undercoat layer varies depending on the resin, it is generally 0.5 to 10 μm, and particularly preferably 1 to 5 μm.

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

(Photoreceptor) The conductive base material used for forming the varistor type undercoat layer is aluminum,
Metal alloys such as aluminum alloys, steel, tin, platinum, gold, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass, and films of these listed metals or their metal oxides. Examples thereof include glass substrates and plastic substrates formed by means such as vapor deposition. The conductive substrate may have 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 single dispersion layer type photosensitive layer in which a charge generating substance is dispersed in a medium containing a charge transporting substance or charge is 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 the photosensitive layer.

As the charge transporting material, chloranil, tetracyanoethylene, fluorenone compounds such as 2,4,7-trinitro-9-fluorenone, nitration compounds such as 2,4,8-trinitrothioxanthone and dinitroanthracene, N, N-diethylaminobenzaldehyde, N, N-diphenylhydrazone, N-methyl-3-
Carbazolylaldehyde, hydrazone compounds such as 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. To be done. The photoconductive polymer such as poly-N-vinylcarbazole is
It can also be used as a binder resin described later. These charge transport materials may be used alone or in combination of two or more.

As the charge generating material, various conventionally known materials such as selenium, selenium-tylur, amorphous silicon, pyrrole, azo compounds, disazo compounds, trisazo compounds, anthanthrone compounds, phthalocyanines. Compounds, indigo compounds, triphenylmethane compounds, slene compounds, toluidine compounds, pyrazoline compounds, perylene compounds,
Examples include quinacridone compounds, and these may be used alone or in combination of two or more.

As the resin (binder), a styrene 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, diallylphthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, polyether resin,
In addition to phenolic resins, various polymers such as photo-curable resins such as epoxy acrylate and urethane acrylate are exemplified. These polymers may be used alone or in combination of two or more.

In the case of a single dispersion layer type photosensitive layer, the amount of the charge transport material is 15 to 70% by weight, particularly 30 to 60% by weight, and the charge generating material is 1 to 30% by weight, based on the whole layer.
Particularly in an amount of 5 to 15% by weight and the resin is 15 to 70%.
It is preferably present in an amount of% by weight, in particular 30 to 60% by weight. The thickness of the photosensitive layer is usually 2 to 100 μm, preferably 10 to 30 μm.

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

In forming the charge transport layer, the ratio of the charge transport material to the binder resin may be appropriately selected. Usually, 30 to 500 parts by weight of a binder resin or the like is used with respect to 100 parts by weight of the charge transport material. The charge transport layer may be formed to have an appropriate thickness. Usually, it is formed to a film thickness of about 2 to 100 μm.

In the preparation of the coating liquid for the charge generating layer and the coating liquid for the charge transporting layer, an appropriate organic solvent is added, if necessary, in order to improve the coating property depending on the kind of the resin contained in each layer. Any solvent that can be used and does not redissolve the underlying layer should be used.

In the photosensitive layer, terphenyl, halonaphthoquinones, acenaphthylenes, conventionally known sensitizers, plasticizers, ultraviolet absorbers, antioxidants and other deterioration inhibitors, etc.
Various additives may be included. Further, an intermediate layer for facilitating charge transfer between the charge generation layer and the charge transport layer may be formed between the layers.

(Electrophotography) According to the present invention, the above-mentioned photoconductor is used, charging is performed under the condition that the electric field of the undercoat layer is equal to or lower than the threshold electric field, and the electric field of the undercoat layer is The exposure charge is removed under the condition of exceeding the threshold electric field.

First, the electric field control of the undercoat layer of the photoconductor is carried out by the mechanism shown in FIG. 2, but the Lp / Lu ratio is generally set in the range of 1 to 500, particularly 3 to 100. Is good.

The surface potential of the photoreceptor is 400 to 15
It is preferable to set it to satisfy the above condition from the range of 00V, especially 600 to 1000V, and the charging is performed by using the positive charging corona.

Then, the charge is removed 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 between the photosensitive layer and the undercoat layer [Lp / L
[u] is set in the above range, the electric field applied to the undercoat layer during this exposure exceeds the threshold electric field Ecr,
Effectively eliminates static electricity.

The exposure may be slit exposure from an original or scanning exposure using a laser, and the exposure amount is generally 2 l.
ux ・ sec (0.6μJ / cm ² ) to 10 lux ・ sec (3μ
J / cm ² ) is suitable.

According to the electrophotographic method of the present invention, although not limited to this, a sensitivity of about 1 to 3 Lux · sec in terms of half-exposure amount can be easily obtained.

Image formation in the electrophotographic method of the present invention includes
Except for the above points, the method may be any method known 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 type oscillating electric field developing method, a developing method using a one-component non-magnetic developer, etc. may be used. Therefore, the toner image formed on the photoconductor can be transferred and fixed on a copy paper or the like by a known method.

[0058]

The present invention will be described in the following examples. Example 1 Antimony-containing tin oxide (manufactured by Mitsubishi Metals Co., Ltd., T-1) 30
Parts by weight and 70 parts by weight of a vinyl acetate-vinyl chloride copolymer resin (S-REC C, manufactured by Shimizu Chemical Co., Ltd.) are dispersed and dissolved in 900 parts by weight of tetrahydrofuran, and this solution is mixed with 100 parts by weight.
A varistor-type undercoat layer was obtained by applying the composition on an aluminum sheet having a thickness of μm and drying at 110 ° C. 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-Perylene tetracarboxylic acid diimide 10
90 parts by weight of p-diethylaminobenzaldehyde diphenylhydrazone, 100 parts by weight of polycarbonate resin (Z-200 manufactured by Mitsubishi Gas Chemical Co., Inc.) and 90 parts of toluene.
The solution was dispersed and dissolved in 0 part by weight, and the coating solution was applied onto the undercoat layer and dried at 120 ° C. to form a single-layer type photosensitive layer, which was used as a photoreceptor sample. At this time, the film thickness after drying is about 20.
The coating conditions were set so as to be μm.

Example 2 A photoconductor sample was prepared in the same manner as in Example 1 except that molybdenum disulfide was used instead of tin oxide containing antimony.

Example 3 Tin oxide containing antimony (T-1 manufactured by Mitsubishi Metals Co., Ltd.) 30
Parts by weight of a silicone-based cured resin (NSC-made by Nippon Seika Co., Ltd.)
1272) [Solid content / 70 parts by weight] was used as a coating solution, which was applied onto an aluminum sheet having a thickness of 100 μm and dried at 120 ° C. to form 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 added to polyvinyl butyral (300, manufactured by Denki Kagaku Kogyo Co., Ltd.).
0K) together with 50 parts by weight of n-butyl alcohol 35
The dispersion liquid, which was stirred and mixed with 100 parts by weight, was applied onto the undercoat layer and dried at 120 ° C. to form 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 (manufactured by Mitsubishi Gas Chemical Co., Inc., Z -200) 100 parts by weight was dissolved in 900 parts by weight of toluene, and this coating solution was applied onto the carrier generation layer and dried at 120 ° C to form 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 the antimony-containing tin oxide was replaced with 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 photoconductor sample was prepared in the same manner as in Example 2 except that the varistor type undercoat layer was removed.

Comparative Example 3 A photoreceptor 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 electrostatic properties of the thus-produced photoconductor were evaluated using a commercially available plain paper copying machine (DC-3285, manufactured by Mita Kogyo Co., Ltd.). The exposure was performed by changing the exposure amount on the surface of the photoconductor in the range of 0 to 6 Lux · sec in 0.2 Lux · sec steps. The decay of the surface potential with respect to exposure was evaluated by the potential at the position of the developing area (300 msec after the start of exposure). From the relationship between the exposure amount and the exposure portion potential thus obtained, the exposure portion residual potential when the half exposure amount and the exposure amount 6 Lux · sec were treated as the sensitivity. The corona charging ability of the photoreceptor was evaluated by the corona discharge current amount required to charge the surface potential to 800V. The repetitive stability of the electrostatic characteristics was evaluated by repeating the charging / exposure neutralization 300 times with the initial dark part charging potential set to 650 V and the exposure amount set to 3.5 Lux · sec. The results are shown concretely in Table 1.

[0070]

[Table 1]

Further, in order to confirm the electrical property values, Sample A in which only the varistor-type undercoat layer of Example 1 was formed on an aluminum sheet (antimony-doped (1
(0 wt%) tin oxide content = 27 wt%), antimony-doped (10 wt%) tin oxide-free resin component only, so to speak, electrically insulating undercoat layer (corresponding to Comparative Example 1) Sample B (antimony-doped (10 wt% in surface protection layer)
%) Tin oxide content = 0 wt%), and the addition amount of the antimony-doped (10 wt%) tin oxide of Example 1 was changed from 40 parts by weight to 100 parts by weight, so to speak, a low resistance type undercoat layer (comparison). Sample C (corresponding to Example 2) (tin oxide content of antimony-doped (10 wt%) in surface protection layer = 48 wt%) was formed on an aluminum sheet. The film thickness is 2.1 μm for sample A and 1.8 μ for sample B
m and sample C were 2.0 μm.

High resistivity measuring device (TR42 [sample measuring box], TR300C manufactured by Advantest)
[DC stabilized power supply], TR8652 [micro ammeter]), electric field strength was 1 × 10 ⁵ V / cm, and the volume resistivity was measured. As a result, Sample A was 6 × 10 ¹⁵ Ω · c.
m, sample B is 3 × 10 ¹⁷ Ω · cm, sample C is 2 × 10 ¹⁵ Ω · cm
It was Ω · cm.

Further, when the cross sections of the sample A and the sample C were observed with a transmission electron microscope, in the sample A, the antimony-doped (10 wt%) tin oxide microparticles were about 200 to 100%.
In the sample C, antimony-doped (10 wt.
%) Tin oxide fine particles were observed to be aggregated in tufts in some areas, or chained in some areas.

[0074]

According to the present invention, a photoreceptor having a varistor type undercoating layer having a non-linear voltage-current characteristic is used as the undercoating layer, and the electric field of the undercoating layer is below the threshold electric field. By charging under the following conditions, and by performing exposure and charge removal under conditions where 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 The resistance was reduced and the surface charge and intermediate charge were effectively eliminated, and it became possible to obtain excellent photosensitivity, image sharpness and high contrast without impairing the corona charging property. Further, the repetitive property or printing durability could be remarkably improved such that the residual potential could be effectively reduced while keeping the initial potential high.

[Brief description of 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, in which A shows a charging step and B shows an exposure and charge elimination step.

FIG. 3 is a graph showing the surface potential of the surface-protecting photoconductor during charging exposure.

FIG. 4 is a graph showing the relationship between the number of times charging and exposure are eliminated and the effective initial potential and the exposed portion residual potential.

[Explanation of symbols]

 1 Photoconductor 2 Conductive Substrate 3 Undercoat Layer 4 Photosensitive Layer 5 Corona Charging Mechanism 6 Image Exposure Mechanism

Claims (6)

[Claims] 1. An electrophotographic photosensitive member having an undercoat layer provided between a conductive substrate and a photosensitive layer, wherein the undercoat layer has a varistor type non-linear conductive property. 2. The electrophotographic photosensitive member according to claim 1, wherein the undercoat layer is made of a dispersion composition of antimony-containing tin oxide or molybdenum disulfide and a resin. 3. The undercoat layer is 3 × 10 ^{5 to} 1 × 10
^The electrophotographic photosensitive member according to claim 1, which has a threshold electric field in the range of ⁶ V / cm. 4. The electrophotographic photosensitive member according to claim 1, wherein the undercoat layer has a voltage nonlinearity coefficient (b) of 3 or more. 5. The electrophotographic photosensitive member 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. 6. The undercoat layer has a thickness (Lu) of 0.1 to 5 μm, and the photosensitive layer has a thickness (L) of 5 to 50 μm.
p) and the ratio (Lp / Lu) of both film thicknesses is 1 to 5
The electrophotographic photosensitive member according to claim 1, which is in a range of 00.