JPH0764302A - Electrophotographic photoreceptor and electrophotographic device provided with the same - Google Patents

Abstract

PURPOSE:To provide an electrophotographic and electrophotographic device provided with the same capable of obtaining an excellent image uniformly electrified without the image defect such as a stripe. CONSTITUTION:In the photoreceptor 2 used in the electrophotographic device provided with the photoreceptor 2 and an electrifying member 1 being arranged in contact with the photoreceptor 2 and capable of electrifying the surface of the photoreceptor 2 by only applying DC voltage from the electrifying member l to the photoreceptor 2, the photoreceptor and the device are constituted so that the capacitance C per cm<2> of the photoreceptor 2 is >=95pF. Thus, photoreceptor 2 and the device provided the same capable of obtaining the excellent image uniformly electrified without the image defect such as the stripe.

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 and an electrophotographic apparatus, and more particularly to an electrophotographic photosensitive member and an electrophotographic apparatus which directly charge a direct current voltage.

[0002]

2. Description of the Related Art In an electrophotographic method, an electrophotographic photosensitive member such as selenium, cadmium sulfide, zinc oxide, amorphous silicon or an organic photoconductor is charged, exposed,
When an image is obtained by performing basic processes such as development, transfer, fixing, and cleaning, the charging process is conventionally performed by applying a high voltage (DC 5 to 8 KV) to a metal wire and charging by a corona generated. However, with this method, corona products such as ozone and NO _x deteriorate the surface of the photoconductor when corona occurs, causing image blurring and deterioration, and wire stains affect image quality, resulting in white spots and black streaks. There were problems such as occurrence. In particular, the electrophotographic photoconductor whose photosensitive layer is mainly composed of an organic photoconductor has lower chemical stability than other selenium photoconductors and amorphous silicon photoconductors, and a chemical reaction when exposed to corona products ( Oxidation reaction mainly occurs and tends to deteriorate. Therefore, when it is repeatedly used under corona charging, image blurring due to the aforementioned deterioration and low copy density due to a decrease in sensitivity tend to occur, resulting in a shorter printing (copying) resistance life.

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

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

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

However, although there are many proposals for the direct charging method, there is almost no market record. The reasons for this are the non-uniform charging and the occurrence of discharge dielectric breakdown of the photoconductor due to direct application of voltage. Due to the non-uniformity of charging, the length is 2 to 200 mm and the width is 0.5 mm in the direction perpendicular to the moving direction of the surface to be charged.
White streaks (a phenomenon that white streaks appear in solid black or halftone images) that occur in the case of the positive development method, or black streaks that occur in the case of the reversal development method. Image defects.

In order to solve such problems and improve the uniformity of charging, a method has been proposed in which an AC voltage is superimposed on a DC voltage and applied to a charging member (Japanese Patent Laid-Open No. 63-63).
No. 149668). In this charging method, a pulsating voltage is applied by superimposing an _AC voltage (VAC) on a DC voltage ( _VDC ) to perform uniform charging.

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

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

[0010]

The object of the present invention is to:
There is no generation of streaks with a length of 2 to 200 mm and a width of 0.5 mm or less (direction perpendicular to the moving direction of the surface to be charged) due to non-uniformity of direct current direct charging, and the copying life of the photoconductor is long. Another object of the present invention is to provide an electrophotographic photosensitive member and an electrophotographic apparatus capable of stably supplying a high quality copy image.

[0011]

As a result of repeated studies on the above-mentioned problems, the inventors of the present invention have found that even when a DC voltage is applied to the photoconductor when the photoconductor is contact-charged by the charging member, the photoconductor is not charged. We have found that improvements can solve the problem.

That is, the present invention has an electrophotographic photosensitive member and a charging member disposed in contact with the photosensitive member, and applies only a direct current voltage from the charging member to the photosensitive member. An electrophotographic photosensitive member used in an electrophotographic apparatus for charging a surface thereof, wherein the electrostatic capacity C per 1 cm ^{2 of the} photosensitive member is 95 pF or more, and an electrophotographic apparatus having the same. .

The present invention will be described in detail below.

The contact charging method, in which a charging member is brought into contact with an electrophotographic photosensitive member to perform charging, is performed by a void breaking discharge in accordance with Paschen's law in a minute space near the contact portion between the photosensitive member and the charging member. . Generally, in an electrophotographic apparatus, a drum-shaped or belt-shaped photosensitive member is used, and both are charged while rotating or moving with respect to a charging member. That is, with the position where the photosensitive member and the charging member are in contact as a boundary, the photosensitive member is divided into an upstream side and a downstream side, and charging is performed in both the upstream and downstream minute spaces. At this time, void-breaking discharge according to Paschen's law is performed. Due to the nature of such a charging mechanism, the relative dielectric constant of the photoconductor, the film thickness (electrostatic capacity), the resistance value of the charging member,
It is not easy to charge uniformly due to many factors such as applied voltage. As one of the countermeasures, a method of applying a pulsating current voltage on which an AC voltage is superimposed has been proposed.

[0015] In the present invention, charging is also in application of a DC voltage only, the electrostatic capacitance C of ² per 1cm of the photosensitive member 95p
By setting it to F or more, it is possible to charge uniformly as in the case of applying the pulsating voltage.

That is, by setting the electrostatic capacitance C per 1 cm ^{2 of} the photosensitive member to 95 pF or more, it is possible to stably suppress the generation of an electric field in the opposite direction, which is considered to be the cause of streak images, etc. As for the characteristics, it is considered that uniform charging without a streak image or the like could be performed, as in the case of applying the pulsating voltage. Furthermore, since the AC voltage is not superposed, the above-mentioned harmful effects do not occur.

Further, the resistance value of the charging member is 5 × 10 ⁵ Ω.
It is more effective if the resistance is increased to cm or more.

FIG. 1 shows the basic construction of the electrophotographic apparatus of the present invention. The charging member 1 is disposed in contact with the electrophotographic photosensitive member 2, and charges the photosensitive member 2 with a voltage applied from an external power source 3 that is in contact with the charging member 1. 2a is a photosensitive layer,
2b is a conductive support.

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

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

The electrophotographic photosensitive member of FIG. 2 has a conductive support 1
0 is provided with a photosensitive layer 11, and the photosensitive layer 11
Is a laminated structure of a charge 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 substance.

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
The charge generation material 12 and the charge transport material (not shown) are contained in the binder resin.

Further, an overcoat layer may be applied in addition to the structure shown in FIGS.

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

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

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

As the charge generating substance, pyrylium, thiopyrylium dye, phthalocyanine pigment, anthanthrone pigment, dibenzpyrenequinone pigment, pyratron pigment, azo pigment, indigo pigment, quinacridone pigment, asymmetric quinocyanine, quinocyanine, etc. should be used. You can

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 generating layer 13 includes a binder resin and a solvent in an amount of 0.3 to 4 times the amount of the above charge generating substance, and a homogenizer, ultrasonic wave, ball mill, vibrating ball mill, sand mill, attritor, roll mill, or the like. It is formed by being well dispersed by a method, applied and dried. Its thickness is 5μ
m or less, particularly preferably 0.01 to 1 μm.

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

As the binder resin used for forming 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,
Examples thereof include styrene-acrylonitrile copolymer, polycarbonate resin or diallyl phthalate 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, a protective layer may be further coated on the photosensitive layer.

A specific example of an electrophotographic apparatus using the electrophotographic photosensitive member of the present invention is shown in FIG. In this apparatus, a roller-shaped charging member 1, an image exposure unit 4, a developing unit 5, a transfer charger 6, a cleaner 7, and a pre-exposure unit 8 are arranged on the peripheral surface of the electrophotographic photosensitive member 2. G ₁ and G ₂ are discharge parts, and N is a contact part.

In the image forming method, first, a voltage is applied to the charging member 1 arranged in contact with the electrophotographic photosensitive member 2 to charge the surface of the photosensitive member 2 and the image exposing means 4 is used to correspond to the original. The image is exposed on the photoreceptor 2 to form an electrostatic latent image. Next, the toner in the developing device 5 is attached to the photoconductor 2 to develop the electrostatic latent image on the photoconductor 2 (visualization).
To do. Further, the toner image formed on the photoconductor 2 is transferred onto the transfer material P such as paper supplied by the transfer charger 6, and is left on the photoconductor 2 without being transferred onto the transfer material by the cleaner 7. Collect toner. If residual charges remain inside the photoconductor, it is better to remove light by applying light to the photoconductor 2 by the pre-exposure means 8. On the other hand, the transfer material on which the toner image is formed is sent to a fixing device 9 by a conveying unit (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. Also, other auxiliary processes may be added if necessary.

FIG. 6 is a block diagram showing an example of using the electrophotographic apparatus of the present invention as a printer for a facsimile.

The controller 111 controls the image reading section 110 and the printer 119. The entire controller 111 is controlled by the CPU 117. Image reading unit 1
The read data from 10 is transmitted to the partner station via the transmission circuit 113. The data received from the other station is the receiving circuit 1
12 to the printer 119. The image memory 116 stores predetermined image data. The printer controller 118 controls the printer 119.
114 is a telephone.

The image information received from the line 115 (image information from a remote terminal connected via the line) is
After being demodulated by the receiving circuit 112, a decoding process is performed by the CPU 117 and sequentially stored in the image memory 116. When the image information of at least one page is stored in the memory 116, the image recording of that page is performed. CPU1
Reference numeral 17 reads out one page of image information from the memory 116 and sends the decoded one page of image information to the printer controller 118. Printer controller 118
Receives the image information of one page from the CPU 117, controls the printer 119 to record the image information of the page.

The CPU 117 receives the next page during recording by the printer 119.

The image is received and recorded as described above.

The electrophotographic photoreceptor of the present invention can be used not only in electrophotographic copying machines but also in laser beam printers, C
RT printer, LED printer, liquid crystal printer,
It can be widely used in electrophotographic application fields such as laser plate making.

[0043]

EXAMPLES The present invention will be described below with reference to examples. [Example 1] Using a φ80 mm x 360 mm aluminum cylinder as a support, a 5 wt% methanol solution of a polyamide resin (trade name: Amilan CM8000, manufactured by Toray) was applied to the support by a dipping method, and a 0.5 μm thick undercoat was applied. Layered.

Next, the following structural formula

[0045]

[Chemical 1]

2 parts of bisazo pigment of (part by weight, the same applies hereinafter), 1 part of resin (a) represented by the following structural formula and

[0047]

[Chemical 2]

100 parts of cyclohexanone was dispersed in a sand mill using φ1 mm glass beads for 20 hours.
Tetrahydrofuran (100 parts) was added to this dispersion, and the solution was coated on the undercoat layer.

Next, 9 parts of compound (2) having the following structural formula

[0050]

[Chemical 3]

10 parts of bisphenol Z type polycarbonate (trade name: Z-200, Mitsubishi Gas Chemical Co., Inc.) was dissolved in 100 parts of monochlorobenzene. This solution was coated on the charge generation layer, dried at 100 ° C. for 1 hour with hot air, and then dried.
The charge transport layers of μm, 25 μm and 28 μm were formed.

Example 2 The same procedure as in Example 1 was carried out except that the compound (3) shown below was used instead of the charge transport material (2) in Example 1, and the charge transport layers of 20 μm and 25 μm were used. Was formed.

[0053]

[Chemical 4]

Example 3 The following compound (4) was used in place of the charge transport material (2) in Example 1, and polymethylmethacrylate resin (4) was used in place of bisphenol Z type polycarbonate. Except for the above, the same procedure as in Example 1 was carried out.

[0055]

[Chemical 5]

[Comparative Example 1] The same preparation and coating as in Example 1 were carried out except that the film thickness of the charge transport layer was 30 μm and 35 μm.

[Comparative Example 2] The same procedure as in Example 2 was carried out except that the thickness of the charge transport layer was 28 μm and 30 μm.

[Comparative Example 3] The same procedure as in Example 3 was carried out except that the thicknesses of the charge transport layers were 32 μm and 35 μm.

The photoconductor thus prepared was evaluated as follows.

100 parts by weight of urethane rubber was melt-kneaded with 4 parts by weight of conductive carbon, and a roller-shaped charging member was formed into a size of φ20 mm × 330 mm with a stainless core having a diameter of 5 mm and a length of 350 mm as a central axis. The volume resistance value was 10 ⁶ Ω · cm.

A sample for measuring electrostatic capacity was prepared by spreading an aluminum sheet on an aluminum cylinder and then applying a photosensitive layer under the same conditions. The capacitance was measured with an impedance measuring device (YHP 4192A).

The electrophotographic apparatus is based on Canon NP3525 as a base, and the image exposure means, developing device, paper feeding system, transfer charger, transport system and pre-exposure means are used as they are, and the above-mentioned roller is used as the primary charging means. The shape charging member and cleaner were modified so that cleaning is performed only by blade cleaning with a silicone rubber blade. The voltage applied to the charging unit is DC-1500V
Only (no AC voltage is superimposed). Further, copying was performed in an environment of 23 ° C./50%.

As for the image, halftone and solid black images were copied by the above-mentioned image forming apparatus, and the uniformity of charging was evaluated from image defects such as stripes. The results are shown in Table 1.

[0064]

[0065]

As described above, according to the present invention, charging is uniform and a good image without image defects such as stripes can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic configuration of an electrophotographic apparatus of the present invention.

FIG. 2 is a schematic diagram showing a basic configuration of an electrophotographic photosensitive member of the present invention.

FIG. 3 is a schematic view showing a basic configuration of an electrophotographic photosensitive member of the present invention.

FIG. 4 is a schematic diagram showing a basic configuration of an electrophotographic photosensitive member of the present invention.

FIG. 5 is a schematic view showing a specific example of the electrophotographic apparatus of the present invention.

FIG. 6 is a block diagram of a facsimile using the electrophotographic apparatus of the present invention as a printer.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Koji Goto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hiroyuki Omori 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (2)

[Claims] 1. An electrophotographic photosensitive member and a charging member disposed in contact with the photosensitive member, and the surface of the photosensitive member is charged by applying only a DC voltage to the photosensitive member from the charging member. An electrophotographic photosensitive member used in an electrophotographic apparatus, wherein the electrostatic capacity C per 1 cm ^{2 of the} photosensitive member is 95 pF or more. 2. An electrophotographic apparatus comprising the electrophotographic photosensitive member according to claim 1.