JPH09319186A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent images with excellent electrifiability, without an image having fog, even if the application of ACC weight is attained by obtaining setting so that the volume resistivity of an overcoat layer as the surface layer of a photoreceptor satisfies a specific condition. SOLUTION: A voltage is applied to an electrifying member arranged in contact with an electrophotographic photoreceptor 2, thereon, to electrify the surface of the photoreceptor 2, and it has an image exposure with the image corresponding to an original by an image exposure means 4, to form an electrostatic latent image. Then, toner in a developing unit 5 is stuck to the photoreceptor 2, to develop the electrostatic latent image on the photoreceptor 2. Further, a toner image formed on the photoreceptor 2 is transferred to a fed transfer paper P such as a paper sheet by a transfer electrifier 6. At this time, the relation of the volume resistivity R(Ω.cm) of the overcoat layer of the photoreceptor 2, the peak-to-peak voltage Vpp(V) of an AC voltage and frequency F(Hz) is set to satisfy the equation of log (R/3E13)<=R<=-0.4386×(Vpp/F).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus for directly charging a voltage to an electrophotographic photosensitive member, and more particularly, to a system in which charging is predominantly injecting an electric charge directly onto the photosensitive member. The present invention relates to an electrophotographic apparatus that exposes the photoconductor to light.

[0002]

2. Description of the Related Art In the electrophotographic method, for example, selenium, cadmium sulfide, zinc oxide, amorphous silicon, organic photoconductors, and other electrophotographic photoreceptors are used as the basis for charging, exposing, developing, transferring, fixing, cleaning and the like. In this charging process, most of the conventional charging processes apply a high voltage (DC 5 to 8 kV) to a metal wire, and the generated corona charges the image when an image is obtained. . However, in this method, when corona is generated, the surface of the photoconductor is deteriorated by corona products such as ozone and NO _x , and image blurring or deterioration is caused.
The dirt on the wire affects the image quality, causing problems such as white spots and black streaks on the image.

In particular, an electrophotographic photosensitive member whose photosensitive layer is mainly composed of an organic photoconductor has lower chemical stability than other selenium photosensitive members and amorphous silicon photosensitive members and is exposed to corona products. If this happens, a chemical reaction (mainly an oxidation reaction) occurs and tends to deteriorate. Therefore, when repeatedly used under corona charging, there is a tendency that the image blurring due to the above-mentioned deterioration and the sensitivity decrease, the copy density becomes low due to the increase of the residual potential, and the printing (copying) resistance life becomes short.

In the case of corona charging, in terms of electric power, the current flowing to the photoconductor is only 5 to 30%, and most of the current flows to the shield plate, which is inefficient as a charging means. Further, since the ozone concentration is increased by repeating the electrophotographic process by corona charging, it has been a serious problem in providing a comfortable use environment.

Therefore, in order to compensate for such problems,
For example, JP-A-57-178267 and JP-A-56
-104351, JP-A-58-40566, JP-A-58-139156, JP-A-58-1
As proposed in Japanese Patent No. 50975, a method of contacting and charging without using a corona discharger has been studied. To put it concretely, 1-2k from the outside
This is a system in which a charging member such as a conductive elastic roller to which a DC voltage of about V is applied is brought into contact with the surface of the photoconductor to charge the surface of the photoconductor to a predetermined potential.

However, the direct charging method is disadvantageous in comparison with the corona charging method in terms of nonuniform charging and occurrence of dielectric breakdown of the photosensitive member due to discharge when a voltage is directly applied. Here, due to the non-uniformity of charging, stripe-shaped charging unevenness is generated in a direction at a length of 2 to 200 mm and a width of 0.5 mm or less in a direction perpendicular to the moving direction of the surface to be charged. This causes image defects such as white stripes (a phenomenon in which white stripes appear in a solid black or halftone image) that occur in the case of the positive development method and black stripes that occur in the case of the reverse development method.

By solving these problems, it is possible to obtain uniform charging.
In order to improve the
Then, a method of applying the voltage to the charging member has been proposed (Japanese Patent Laid-Open Publication No. Sho.
63-149668). This charging method is
Current voltage (V_DC) To AC voltage (V _AC) By superimposing
To obtain a pulsating voltage and apply it to achieve uniform charging.
Is Umono.

In this case, while maintaining the uniformity of charging, white spots in the positive development system, black spots in the reversal development system,
In order to prevent image defects such as fogging, it is necessary that the AC voltage to be superimposed has a peak-to-peak potential difference (V _pp ) that is at least twice the discharge start voltage Vth according to Paschen's law.

However, in order to prevent image defects, when the AC voltage to be superimposed is increased, the maximum applied voltage of the pulsating current voltage causes a slight defect in the inside of the photoconductor.
Dielectric breakdown occurs due to discharge. In particular, when the photoconductor is an organic photoconductor having a low withstand voltage, this dielectric breakdown is remarkable. In this case, in the positive development method, the image is white in the longitudinal direction of the contact portion (width direction of the recording material), and in the reverse development method, black streaks occur. Further, when there is a pinhole, that portion becomes a conduction path, current leaks, and the voltage applied to the charging member drops. Further, since the discharge is generated in the minute voids, there is a problem that the damage to the photoconductor is large, the abrasion amount of the photoconductor is large, and the durability is poor.

In order to solve these problems, the present inventors have investigated a process of directly injecting an electric charge onto a photosensitive member to perform charging. Further, it was also found that even in the process of direct injection of electric charges, the superposition of the AC voltage makes the charging more stable than the case of applying only the DC voltage. There is a big difference between the case where the charging that directly injects the charges onto the photoconductor is dominant and the case where the discharging is dominant. That is, the difference is that the peak-to-peak voltage (Vpp) of AC is smaller than twice the discharge start voltage (Vth) as shown in the following equation (2), but the following equations (3) and ( 4) is established.

[0011]

In the charging system in which such charges are directly injected onto the photosensitive member, there is no generation of streaks due to nonuniform discharge of DC direct discharge charging, and photosensing by AC superposition type direct discharge charging. Less damage to the body,
Further, since NO _x , ozone, etc. are hardly generated due to discharge charging, the photoconductor has a long copy life, and a high-quality copy image can be stably provided. Further, a system for superimposing an AC voltage has been studied in order to make the charging more uniform.
In the process of supplying the AC voltage superimposed on the voltage,
There was a problem that it became a fogging image.

Therefore, as a result of repeated studies on the above-mentioned problems, the inventors of the present invention applied a voltage obtained by superimposing a direct current to an alternating current from a charging member in contact with the photoconductor to directly charge the photoconductor. We have found the conditions under which a high quality copy image can be obtained without any fog image even in the charging process for injection.

That is, the present invention has been made based on the above circumstances, and in the process of directly injecting charges from the charging member to the photosensitive member, the DC voltage from the charging member is changed to A.
Even in a system in which the C voltage is superimposed and applied, there is no fog image and a high quality copy image can be stably supplied.
It is an object of the present invention to provide an electrophotographic photosensitive device that produces less x and ozone and is ecologically good.

[0014]

Therefore, in the present invention,
An electrophotographic photosensitive member and a charging member disposed in contact with the photosensitive member are provided, and by applying a voltage from the charging member to the photosensitive member, charging for directly injecting electric charge to the surface of the photosensitive member is performed. In a dominant electrophotographic apparatus, the voltage applied from the charging member to the surface of the photoconductor is a DC voltage superposed with an AC voltage, and the peak-to-peak voltage Vpp (V) of the AC voltage and the discharge start voltage Vth. When the relationship of the following equation (2) is satisfied, the dark potential Vd (V) of the photoconductor is
And the DC applied voltage Vdc, the Vpp and Vth
In the charging method in which the following formulas (3) and (4) are established, the volume resistance R (Ω ·
cm), Vpp (V) of the AC voltage, and frequency F (H
z) satisfies the following formula (1).

Log (R / 3E13) ≦ R ≦ −0.4386 × (Vpp / F) − (1) Vpp <2Vth − (2) | Vdc-Vd | ≤ 200 (V)-(3) | Vd |> | Vpp / 2 | + | Vdc | + | Vth |-(4) The following describes the condition of the present invention. Generally, the charging member is brought into contact with the electrophotographic photoreceptor,
The so-called direct charging method for charging is performed by discharging in a minute space near the contact portion between the photosensitive member and the charging member when a conventional photosensitive member is used.

Therefore, also in the direct charging method, the charging ionizes the molecules in the air and the ions flow to the surface of the photoconductor, so that the charge is not directly injected from the charging member to the surface of the photoconductor. Absent. As a matter of course, the charging in such a charging mechanism largely depends on the surface shapes of the charging member and the photosensitive member, and unevenness of charging occurs due to the roughness of each surface. Further, since the discharge is in a minute gap, the ions move in a strong electric field, so that the damage to the photoconductor is large, the amount of abrasion is large, and the durability is lowered. Further, compared with corona charging, the number of orders of magnitude is incomparably smaller, but still, image blur occurs due to generation of ozone, NO _{x, and the} like.

On the other hand, the present inventors have proposed that the surface layer of the photoreceptor should be a layer in which conductive particles are dispersed in a resin,
By providing an overcoat layer of another medium resistance layer, it is possible to directly inject charges from the charging member, which eliminates the charging unevenness seen by discharge and also reduces the damage given to the photoreceptor and makes it durable. Further, it is possible to improve the property, and furthermore, ozone, NO _x, etc. are hardly generated, and image blurring, etc. are also eliminated, and the problem is greatly improved.

That is, the present invention is largely different from the charging in which discharge in a simple AC superposition system is dominant. In the charging method in which the discharge is dominant, if the following expression (2) is satisfied, the charging becomes non-uniform and the DC applied voltage Vd
Absolute value of difference between c (V) and dark potential Vd (V) of photoconductor |
Vdc-Vd | does not satisfy the following expressions (2) and (4). Further, in the case of the process of directly injecting the charges, even under the condition that the formula (2) is satisfied, the dark potential Vd of the photoconductor has a value almost equal to the DC applied voltage, and the following formulas (3) and ( 4) can be satisfied, but in this case, when the AC voltage is superimposed, there is a problem that a fog image is generated.

Vpp <2Vth− (2) | Vdc-Vd | ≤ 200 (V)-(3) | Vd |> | Vpp / 2 | + | Vdc | + | Vth |-(4) On the other hand, in the present invention, the surface layer of the photoconductor is Volume resistance R of a certain overcoat layer and AC applied to the charging member
When the relationship between the voltage Vpp and the frequency F (Hz) satisfies the above expression (1), the direct injection of charges can be stabilized, and a good image can be obtained without a fog image.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the basic construction of an electrophotographic apparatus of the present invention. Here, the charging member 1 is in contact with and disposed on the electrophotographic photosensitive member 2, and the photosensitive member 2 is charged by the voltage applied from the external power source 3 connected to the charging member 1. Reference numeral 2a is a photosensitive layer and 2b is a conductive support.

The charging member 1 used in the present invention may have any shape such as a fur brush in addition to the magnetic brush as shown in FIG. It can be selected according to the specifications and form of the photographic device.

The magnetic brush is preferably composed of various ferrite particles such as Zn-Cu ferrite as a charging member and a non-magnetic conductive sleeve for supporting the charging member and a magnet roll contained therein. Further, as the material of the fur brush, it is preferable to use carbon, copper sulfide, a metal, a polymer electrically conductive with a metal oxide, or the like. Examples of the polymer material include rayon, acrylic, polypropylene, PET, polyethylene and the like.

By winding or sticking these conductively-treated furs around a metal or other conductively-conductive core metal, a charging device is obtained. The resistance of the charging brush was measured from the value of the current flowing when an aluminum cylinder was contacted instead of the photoconductor and a voltage of 100 V was applied under the same conditions as in actual use.

The photosensitive layer according to the present invention has a single layer or a laminated structure. In the case of a single layer structure, generation and movement of photocarriers are performed in the same layer. In the case of a laminated structure, a charge generation layer that generates photocarriers and a charge transport layer that moves carriers are laminated.

In the single-layer photoreceptor, the thickness is 5 to
100 μm is preferable, and 10 to 60 μm is more preferable. The content of the charge generation material or the charge transport material is 20 to 8
0 wt% is preferable, and 30 to 70 wt% is more preferable. Further, in the laminated photoreceptor, the thickness of the charge generation layer is preferably 5 μm or less, more preferably 0.01 to 1 μm. The content of the charge generation material is 10 to 100.
Weight% is preferable, and 40-100 weight% is more preferable. The thickness of the charge transport layer is preferably 5 to 100 μm,
5-60 micrometers is more preferable. The content of the charge transport material is preferably 20 to 80% by weight, more preferably 30 to 70% by weight.

The electrophotographic photosensitive member of FIG. 2 has a conductive support 1
0 is provided with a photosensitive layer 11, and the photosensitive layer 11 is
This is a laminated structure of a charge generating layer 13 containing a charge generating substance (not shown) dispersed in a binder resin and a charge transporting layer 14 containing a charge transporting substance (not shown). In this case, the charge transport layer 14 is laminated on the charge generation layer 13.

In the electrophotographic photosensitive member of FIG. 3, unlike the case of FIG. 2, the charge transport layer 14 is laminated below the charge generation layer 13. In this case, the charge generation layer 13 may contain a charge transport material.

The electrophotographic photosensitive member of FIG. 4 has a conductive support 1
0 is provided with a photosensitive layer 11, and the photosensitive layer 11
Contains a charge generating substance and a charge transporting substance in a binder resin. Further, in addition to the configurations of FIGS. 2, 3, and 4, as shown in FIG. 5, an overcoat layer is applied as an injection layer. The inventors of the present invention have found that by dispersing conductive particles in a resin in the overcoat layer, direct injection of electric charges is significantly improved.

As the conductive support 10, a support itself having conductivity, for example, aluminum, aluminum alloy, stainless steel or the like can be used. In addition,
By vacuum deposition, aluminum, aluminum alloy,
A conductive support having a layer formed by coating and forming an indium oxide-tin oxide alloy, plastic, conductive fine particles (for example, carbon black, tin oxide, titanium oxide, silver particles, etc.) together with a suitable binder on plastic or paper. It is possible to use a support impregnated in the above, and further a plastic having a conductive binder.

Further, between the conductive support and the photosensitive layer,
An undercoat layer (adhesive layer) having a barrier function and an adhesive function can be provided. Incidentally, the undercoat layer, the adhesion improvement of the photosensitive layer, the coating property improvement, the protection of the support, the coating of defects of the support,
Casein, which is formed for the purpose of improving the charge injection property from the support, protecting the photosensitive layer against electrical breakdown, etc.
Polyvinyl alcohol, ethyl cellulose, ethylene-
Acrylic acid copolymer, polyamide, modified polyamide,
It is composed of polyurethane, gelatin, aluminum oxide, etc. The thickness of the undercoat layer is preferably 5 μm or less, more preferably 0.2 to 3 μm.

Examples of the charge generating substance used in the present invention include phthalocyanine pigments, azo pigments, indigo pigments, polycyclic quinone pigments, perylene pigments, quinacridone pigments, azurenium salt pigments, pyrylium dyes, thiopyrylium dyes, squarylium dyes, cyanine dyes, Examples thereof include xanthene dyes, quinoneimine dyes, triphenylmethane dyes, styryl dyes, selenium, selenium-tellurium, amorphous silicon, cadmium sulfide, and zinc oxide.

The solvent used for the charge generation layer coating material is selected from the solubility and dispersion stability of the resin and the charge generation material used, but as the organic solvent, alcohols, sulfoxides, ketones, ethers, Esters, aliphatic halogenated hydrocarbons, aromatic compounds and the like can be used.

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

The charge generation layer 13 includes a homogenizer, an ultrasonic wave, a ball mill, a vibrating ball mill, a sand mill, an attritor, a roll mill and the like, together with a binder resin in an amount of 0.3 to 4 times the amount of the charge generating substance and a solvent. In the method, it is well dispersed, coated, dried, and formed. The thickness is
It is preferably 5 μm or less, and particularly preferably 0.01 to 1 μm.

The charge transport layer 14 is generally formed by dissolving the above charge transport substance and the binder resin in a solvent and applying the solution. The mixing ratio of the charge transport material and the binder resin is about 2: 1 to 1: 2. As the solvent, acetone,
Ketones such as methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as toluene and xylene, chlorinated hydrocarbons such as chlorobenzene, chloroform and carbon tetrachloride are used. When applying this solution, for example, dip coating method,
A coating method such as a spray coating method or a spinner coating method can be used, and the drying is performed at 10 ° C.
To 200 ° C., preferably 20 ° C. to 150 ° C., for 5 minutes to 5 hours, preferably 10 minutes to 2 hours, for example, by blast drying or static drying. it can.

As the binder resin used to form the charge transport layer 14, acrylic resin, styrene resin,
A resin selected from polyester, polycarbonate resin, polyarylate, polysulfone, polyphenylene oxide, epoxy resin, polyurethane resin, alkyd resin, unsaturated resin and the like is preferable. Particularly preferred resins include polymethylmethacrylate, polystyrene, styrene-acrylonitrile copolymer, polycarbonate resin, or diallylphthalate resin.

Further, the charge generation layer or the charge transport layer may contain various additives such as an antioxidant, an ultraviolet absorber and a lubricant. Further, on the photosensitive layer,
Further, an overcoat layer 15 can be applied as a protective layer.

A medium resistance layer is preferably used as the overcoat layer. This is 1E10 to 5E15 in terms of volume resistance, image deletion, and residual potential.
(Ω · cm) volume resistance value, preferably 1E1
The volume resistance value is 1 to 5E13 (Ω · cm). However, this also means that, from the viewpoint of image fog, the AC applied voltage Vpp (V) from the charging member and the frequency F (H
z).

According to the studies of the present inventors, as for the image fog, the lower the volume resistance of the overcoat layer, the better the image obtained, and the smaller the AC applied voltage Vpp and the lower the frequency. The more the image fogging is reduced, the better the image is obtained. Further, if the degree of image fog is 2% or less, there is no problem in practical use, and therefore it can be used as an image.

FIG. 7 shows AC applied voltage Vpp / frequency F
Is plotted on the abscissa and the volume resistance R of the overcoat layer is plotted on the ordinate, and the point where the density of the image fog is 1.9 to 2.0% is plotted. The reason has not been fully clarified yet, but according to the results of the test, the change is almost linear, and in the region below the line,
The image fog density was 2% or less, and a good image was obtained. That is, the above-mentioned formula (1) represents the region below the straight line shown in FIG.

As a method for controlling the resistance value of the medium resistance, any method may be used, such as a system in which conductive particles are dispersed in a binder or a binder having a medium resistance. Here, although a system in which conductive particles are dispersed in a binder will be described, as the conductive particles, zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin-doped indium oxide, Ultrafine particles such as tin oxide and zirconium oxide doped with antimony or tantalum can be used. These metal oxides may be used alone or in combination of two or more. When two or more kinds are mixed, they may be in the form of solid solution or fusion.

As the resin for the surface layer, commercially available polyester, polycarbonate, polyurethane, acryl, epoxy, silicone, alkyd, vinyl chloride-vinyl acetate copolymer and the like can be used. further,
As a result of investigations to improve the strength distribution and dispersibility, the present inventors disperse conductive particles in a photocurable acrylic monomer having two or more acryloyl groups in one molecule. By using the surface layer formed by applying and photo-curing the composition on the photosensitive layer of the photoreceptor, both the film strength and the dispersibility of the conductive particles can be dramatically improved.

Next, FIG. 6 shows a specific example of an electrophotographic apparatus using the electrophotographic photosensitive member according to the present invention. This device is
On the peripheral surface of the electrophotographic photosensitive member 2, the magnetic brush charging member 1,
Image exposure means 4, developing device 5, transfer charger 6, cleaner 7
Is arranged.

In the image forming method, first, a voltage is applied to the charging member 1 which is in contact with and disposed on the electrophotographic photosensitive member 2, the surface of the photosensitive member 2 is charged, and the image exposing means 4 corresponds to the original. The formed image is imagewise exposed on the surface of the photoconductor 2 to form an electrostatic latent image. Next, the toner in the developing device 5 is adhered to the photoconductor 2 to develop (visualize) the electrostatic latent image on the photoconductor 2. Further, the toner image formed on the photoconductor 2 is transferred by the transfer charger 6 onto the supplied transfer material P such as paper.

The cleaner 7 collects the residual toner remaining on the photoconductor 2 without being transferred to the transfer material.
Further, in the case where residual charge remains inside the photoconductor, it is preferable that the image exposure means 4 irradiate the photoconductor 2 with light to remove the charge.

On the other hand, the transfer material on which the toner image is formed is sent to a fixing device 9 by a carrying section (not shown), and the toner image is fixed.

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

[0048]

【Example】

(First Embodiment) The present invention will be described below with reference to embodiments.
Here, an aluminum cylinder having a diameter of 30 mm × 260.5 mm was used as a support, and 5% by weight of a polyamide resin (trade name: Amilan CM8000, manufactured by Toray) was used as the support.
A methanol solution is applied by a dipping method to form a 0.5 μm undercoat layer. Next, in the following structural formula, the diffraction angle 2θ ± 0.2 ° in the X-ray diffraction spectrum of CuKα is 9.
Having strong peaks at 0, 14.2, 23.9 and 27.1 °,

[0049]

Embedded image 4 parts of titanyl oxophthalocyanine pigment (parts by weight, the same applies hereinafter), 2 parts of polyvinyl butyral resin BX-1 (manufactured by Sekisui Chemical Co., Ltd.), and 80 parts of cyclohexanone,
Dispersion was performed for about 4 hours using a sand mill device using φ1 mm glass beads. Furthermore, 100 mL of ethyl acetate was added to this dispersion.
Parts were added and coated on the undercoat layer.

Next, the following structural formula:

Embedded image 10 parts of the compound and 10 parts of bisphenol Z type polycarbonate (trade name: Z-200, manufactured by Mitsubishi Gas Chemical Co., Inc.) were dissolved in 100 parts of monochlorobenzene. This solution was applied onto the charge generation layer and dried in hot air at 105 ° C. for 1 hour to form a 20 μm charge transport layer.

Next, as an overcoat layer, the following structural formula:

Embedded image Acrylic monomer: 25 parts, surface-treated with the following structural formula (treatment amount: 7%) antimony-doped tin oxide ultrafine particles: 50 parts,

[0052]

Embedded image Ethanol: 150 parts was dispersed in a sand mill for 66 hours, and further dispersed by adding 20 parts of polytetrafluoroethylene fine particles (average particle diameter 0.18 μm). Thereafter, as a photopolymerization initiator, 2-methylthioxanthone: 3 parts, and a photopolymerization initiation auxiliary agent represented by the following structural formula: 9 parts were dissolved to prepare a preparation liquid.

[0053]

Embedded image Using this formulation, a film was formed on the above charge transport layer by a dip coating method, and the film was formed with a high pressure mercury lamp at 160 W / cm ^2.
With light intensity of 60 seconds, and then 120
The surface layer was obtained by drying with hot air at a temperature of ° C for 2 hours. At this time, the thickness of the obtained surface layer was 3 μm. Also,
The dispersibility of the surface layer preparation liquid was good, and the surface of the surface layer was a uniform and even surface.

As the charging member of the magnetic brush, the average particle size:
25 μm Zn-Cu ferrite particles and average particle size: 1
Zn-Cu ferrite particles of 0 μm were mixed in a weight ratio of 1: 0.
Magnetic particles prepared by mixing in No. 05 and coated with a medium resistance resin layer of ferrite particles having an average particle diameter of 25 μm and having a peak at the position of each average particle diameter were used.

The contact charging member is composed of the coated magnetic particles prepared as described above, a non-magnetic conductive sleeve for supporting the coated magnetic particles, and a magnet roll contained therein, and the coated magnetic particles are placed on the sleeve. , Thickness: 1m
m to form a charging nip having a width of about 5 mm with the photoreceptor. The gap between the magnetic particle holding sleeve and the photoconductor was about 500 μm. Further, the magnet roll is rotated so that the sleeve surface rubs in the opposite direction at twice the peripheral speed of the surface of the photoconductor, and the photoconductor and the magnetic brush come into uniform contact with each other. I did it. At this time, as for the resistance of the charging member, instead of the photosensitive drum, the aluminum cylinder is brought into contact, and the voltage: 100
It was set to 5 × 10 ⁵ (Ω) depending on the current value when V was applied.

The evaluation of the test results was carried out by Canon Inc. L
The BP-NX was modified and the DC voltage applied to the primary charging was -70.
0V, AC applied voltage Vpp is 1000V (<2Vth =
2 × 580) and a frequency of 1 kHz were applied, the surface potential of the photoconductor was measured, and the quality of the image was evaluated. Table 1 shows the results.

The volume resistance of the overcoat layer was measured by pA meter 4140 manufactured by Yokogawa Hewlett-Packard Co.
B was used.

(Examples 2 and 3) In Example 1,
The test was carried out in the same manner as in Example 1 except that the acrylic monomer was changed to 20 parts and 17 parts.

Comparative Examples 1 to 3 Tests were carried out in the same manner as in Example 1 except that the acrylic monomer was changed to 40 parts, 30 parts, and 10 parts in Example 1.

(Examples 4, 5, and 6) In Example 1,
The test was conducted in the same manner as in Example 1 except that the surface treatment amount of tin oxide was reduced from 7% to 4% and the amount of the acrylic monomer was changed to 30, 25 and 20 parts.

(Comparative Examples 4 to 6) In Examples 4 to 6,
The tests were carried out in exactly the same manner as in Examples 4 to 6 except that the acrylic monomer was changed to 40 parts, 35 parts, and 15 parts.

[0062]

[Table 1]

[0063]

As described above, according to the present invention,
An electrophotographic apparatus comprising an electrophotographic photosensitive member and a charging member in contact with and disposed on the photosensitive member, wherein the surface of the photosensitive member is charged by applying a voltage to the photosensitive member from the charging member, When the volume resistance R (Ω · cm) of the overcoat layer which is the surface layer of the photoconductor satisfies the above formula (1), no fog image is generated even when AC superposition is applied, and the chargeability is good. The effect that a good image can be obtained is exhibited.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a contact charging system.

FIG. 2 is an example of an electrophotographic photosensitive member.

FIG. 3 is an example of another electrophotographic photosensitive member.

FIG. 4 is an example of still another electrophotographic photosensitive member.

FIG. 5 is an example of another electrophotographic photosensitive member.

FIG. 6 is a schematic view of an electrophotographic apparatus using the contact charging member according to the present invention.

FIG. 7 is a graph showing the volume resistance of the overcoat layer according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charging member 2 Photoconductor 2a Overcoat layer 2b Photosensitive layer 2c Conductive support 3 External power supply 10 Conductive support 11 Photosensitive layer 13 Charge generation layer 14 Charge transport layer 15 Overcoat layer

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

Claims (2)

[Claims] 1. An electrophotographic photosensitive member and a charging member disposed in contact with the photosensitive member are provided, and a voltage is applied to the photosensitive member from the charging member to directly charge the surface of the photosensitive member. In an electrophotographic apparatus in which charging is predominantly performed, the voltage applied from the charging member to the surface of the photoconductor is D
When the AC voltage is superimposed on the C voltage and the relationship between the peak-to-peak voltage Vpp (V) of the AC voltage and the discharge start voltage Vth satisfies the following expression (2), the dark potential V of the photoconductor is
In the charging method in which d (V), the DC applied voltage Vdc, and the Vpp and Vth satisfy the following formulas (3) and (4), the volume resistance R (Ω · cm) of the overcoat layer of the photoreceptor and the above An electrophotographic apparatus characterized in that the relationship between Vpp (V) of AC voltage and frequency F (Hz) satisfies the following expression (1). log (R / 3E13) ≦ R ≦ −0.4386 × (Vpp / F) − (1) Vpp <2Vth − (2) | Vdc-Vd | ≤ 200 (V)-(3) | Vd |> | Vpp / 2 | + | Vdc | + | Vth |-(4) 2. The photoconductor contains a charge generating material and a charge transporting material, the charge generating material and the charge transporting material are organic substances, and further has an overcoat layer on the photosensitive layer. The electrophotographic apparatus according to claim 1, which is characterized in that.