JPH03257467A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To prevent the lowering of sensitivity accompanying the endurable use of an organic photoconductor system photosensitive body for positive electrostatic charging and to obtain a good-quality image by providing an electrostatic charging device for making the surface potential of the photosensitive body negative between a destaticizing stage and a primary electrostatic charging stage. CONSTITUTION:After uniformly applying charges on the surface of the organic photoconductor system photosensitive body for positive electrostatic charging 1 by a primary electrostatic charger 2, the inverted latent image of the image which should be copied is formed on the surface of the photosensitive body 1 and the inverted image is developed by adding toner by a developing device 7. When the photosensitive body 1 rotates further, it contacts with and accompanies a transfer material and the toner image is transferred to the transfer material by a transfer charger 6. When it rotates further, the toner remaining on its surface is scraped by a cleaning blade 5 and residual charge is neutralized by a destaticizing lamp 4, then a non-charge state is obtained and the surface potential is made negative by a negative electrostatic charging unit 3. By actively electrostatically charging the surface of the photosensitive body 1 to be negative by the unit 3, the lowering of the sensitivity accompanied with the endurable use of the photosensitive body 1 is prevented and the excellent image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the quality of images obtained by electrophotographic apparatus.

[Prior Art] Current electrophotographic devices use Cd5-resin dispersion systems, ZnO-resin dispersion systems, Se, 5e-Te vapor deposition systems, or amorphous silicon systems, as well as organic photoconductors that are inexpensive and easy to manufacture (
Charging, exposure, development,
The structure is such that a copy is obtained through the basic steps of transfer, cleaning, neutralization, and fixing. In the charging process at this time, a high voltage (D) has traditionally been applied to the metal wire.
Charging is performed by corona generated by applying a voltage of about C5 to 8 kV). However, OPC photoreceptors are inferior in potential stability compared to inorganic photoreceptors. In particular, in the currently widely used negatively charged OPC photoreceptor, when a large drop in potential occurs (a phenomenon in which the bright area potential and dark area potential decrease with continued use), the density decreases during positive development. In reversal development, image defects such as "fogging" occur.

In order to suppress this fall in potential, a method has been adopted in which the value of the current flowing through the charging wire is increased using a scorotron device that is equipped with a discharge current control member (hereinafter referred to as a "grid"). . However, increasing the current value causes an increase in corona products such as ozone and NOx. This is due to negative charging. As a result, in the case of an electrophotographic apparatus using an OPC photoreceptor, which has lower chemical stability than an inorganic photoreceptor, problems such as image blurring and image deletion may occur. Furthermore, the influence that the increase in the amount of ozone or NO generated has on the environment around the electrophotographic apparatus cannot be ignored.

In order to solve such problems such as an increase in the amount of ozone and NOX generated, the development and commercialization of positively charging OPC photoreceptors are progressing. However, the positive charging OPC photoreceptor also has various problems, and in particular, a definitive solution to the decrease in sensitivity due to long-term use has not yet been found.

[Problems to be Solved by the Invention] An object of the present invention is to suppress a decrease in sensitivity caused by long-term use of a positively charging OPC photoreceptor and to provide a good image.

[Means for Solving the Problems] The object of the present invention is achieved by providing a charging device that makes the photoreceptor surface potential negative between the static elimination and primary charging steps.

The present invention will be specifically explained below.

In the positively charging electrophotographic photoreceptor used in the apparatus of the present invention, the photosensitive layer is composed of an organic photoconductor.

Examples of the organic photoconductor used in the photosensitive layer include organic photoconductive polymers such as polyvinyl carbazole or low molecular weight organic photoconductive substances, which are mixed in a binder (binder resin) made of an insulating polymer. It is often used in a dispersed form. The photoreceptor includes a conductive substrate (a functionally separated photoreceptor in which a charge transport layer is laminated, followed by a charge generation layer when viewed from the illumination), or a photoreceptor containing a charge transport material and a charge generation material in the same layer. There are also single-layer type photoreceptors in which the photoreceptor is bound with a binder.

[Means to solve the problem] Hereinafter, the apparatus of the present invention will be specifically explained based on the drawings.

FIG. 1 is a schematic cross-sectional view of an electrophotographic apparatus according to the present invention.

In the figure, after the surface of the photoreceptor l is uniformly charged by the primary charger 2, it rotates in the direction of the arrow, and an inverted latent image of the image to be copied is formed on the surface in an exposure section (not shown). , in developer 7, toner is applied to the surface to develop an inverted image. When it rotates further, it comes into contact with the transfer material (not shown), such as paper, and carries it with it, and the transfer charger 6
The toner image is transferred to the transfer material in the step. When it rotates further, the toner remaining on the surface is scraped off by the cleaning blade 5, and when it rotates further, it is irradiated with the neutralization lamp 4, thereby neutralizing the residual charge and becoming uncharged.

When the photoreceptor 1 further rotates in the direction of the arrow, it encounters the pre-charger 3, which is the main point of the device of the present invention. 3, the surface of the photoreceptor 1 is positively charged negatively.

Figure 2 shows the negative charging unit 3 in the device of the present invention.
3 is a circuit diagram in which a DC power source 31 for charging the battery and an AC power source 32 for superimposing the same are connected to the unit 3. FIG. In the figure, 31 and 32 are connected in parallel to each other.

The laminated organic photoreceptor used in the present invention preferably has the following configuration.

A photosensitive layer is provided on the conductive substrate.

The substrate may be made of a material that itself has conductivity, such as
Metals such as aluminum, its alloys, copper, zinc, corrosion-resistant steel (stainless steel), vanadium, molybdenum, chromium, titanium, nickel, indium, gold, and platinum can be used. Other materials include aluminum, aluminum alloys, indium oxide-tin oxide alloys, etc., formed on the surface of plastic materials such as polyethylene, polypropylene, polyvinyl chloride, acrylic resin, and polyfluoroethylene by vacuum deposition, carbon black, etc. A liquid material in which tin oxide particles or the like are dispersed in a suitable binder may be coated on a plastic material, or a material obtained by impregnating paper, cloth, etc., a plastic material having a conductive binder, etc. can be used.

A subbing layer having both a barrier function and an adhesive function can be provided between the conductive substrate and the photosensitive layer.

The core layer is, for example, casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamides (e.g., nylon-6, nylon-6,6, nylon-610, nylon-11, nylon-12, copolymerized nylon, etc.) , polyurethane, gelatin, aluminum oxide, etc.

The thickness of the subbing layer is usually 5 μm or less, preferably 0.5 to 3 μm.
μm, and in order to fully exhibit its function as a barrier layer, it is desirable that its specific resistance is 10′Ω·cm or more.

The charge transport layer can be formed by dissolving a charge transport substance in a film-forming resin.

Examples of organic charge transport materials include pyrene, N-ethylcarbazole, N-isopropylcarbazole, and N-methylcarbazole.
N-phenylhydrazino-3-methylidene-9-ethylcarbazole, NN diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine, N,N-diphenyl hydrazino-3-methylidene-1
0-Ethylphenoxazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-N
-Phenylhydrazone, p-pyrrolidinobenzaldehyde-N, N diphenylhydrazone, 1,3.5-trimethylindolenine-ω-aldehyde-NN-diphenylhydrazone, p-ethylbenzaldehyde-3-methylbenzthiazolinone-2- Hydrazones such as hydrazone; 2,5-bis(p-diethylaminophenyl)-1,3
, 4-oxadiazole, i-phenyl-3-(p-diethylaminostyryl)-5(p-diethylaminoethylphenyl)pyrazoline, 1-[quinolyl(2)] -
3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl(2
)]-3-(p-diethylaminostyryl)-5-(p
-diethylaminophenyl)pyrazoline, l-[6-medoxybilidyl(2)]3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1[pyridyl(3)]-3-(p -diethylaminostyryl)-5-(p-diethylaminophenyl)pyralizone, l-[Revidyl (2)] -3(p-diethylaminostyryl)-5-(p-diethylaminophenyl)
Pyrazoline, 1-[pyridyl(2)]-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminostyryl)pyrazoline, 1-[pyridyl(2)
] -3(α-methyl-p-diethylaminostyryl)5-(p-diethylaminophenyl)pyrazoline,
1-phenyl-3-(p-diethylaminostyryl)-
Pyrazolines such as 4-methyl-5-(p-diethylaminophenyl)pyrazoline, niphenyl-3-(α-benzyl-p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, and spirvilamicin; 2- (p-diethylaminostyryl)-6-ethylaminobenzoxazole, 2-(p-diethylaminophenyl)-4-(p-diethylaminophenyl)-
Oxazole compounds such as 5-(2-chlorophenyl)oxazole, 2-(p-diethylaminostyryl)
-thiazole compounds such as 6-ethylaminobenzothiazohel; triarylmethane compounds such as bis(4-diethylamino-2-methylphenyl)-phenylmethane 1,l-bis(4-N,N-dimethyl Polyaryl alkanes such as amino-2-methylphenyl)ethane, nitriphenylamine; poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinyl acridine, poly-
One type or a combination of two or more types selected from 9-vinylphenylanthracene, pyrene-formaldehyde resin, ethylcarbazole-formaldehyde resin, etc. can be used.

As the charge transport layer, phenoxy resin, polyacrylamide, polyvinyl butyral, polyarylate, polysulfone, polyamide, acrylic resin, acrylonitrile resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, phenol resin, epoxy resin, polyester, alkyd resin, Polycarbonate, polyurethane, or a copolymer containing two or more types of repeating units constituting these resins, such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer,
Examples include styrene-maleic acid copolymer. It can also be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene.

The thickness of the charge transport layer is usually 5 to 50 μm, preferably 8 to 50 μm.
20 um, and the weight ratio with the binder is former: latter = 5 =
1, preferably about 3:1 to 1:3.

As the coating method, a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a Meyer bar coating method, a blade coating method, a roller coating method, a curtain coating method, etc. can be used.

As the charge generation layer, Sudan Red, Guianpuru-
, azo pigments such as Jenas Green B, quinone pigments such as Algol Yellow, Binone Quinone, and Indanthrene Brilliant Violet PR, indigo pigments such as quinocyanine pigments, perylene pigments, indigo and thioindigo pigments, and bis-based pigments such as India First Orange Toner. It can be formed by vapor deposition of one or more of benzimidazole pigments, phthalocyanine pigments such as copper phthalocyanine, quinacridone pigments, or by dispersion coating together with a suitable binder if necessary.

A suitable binder can be selected from insulating resins and organic photoconductive polymers.

For example, insulating resins include polyvinyl butyral,
Polyarylates (condensation polymers of bisphenol A and phthalic acids, etc.), polycarbonate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide resin, polyamide, polyvinylpyrrolidine, cellulose resin, urethane resin, epoxy resin, casein , polyvinyl alcohol, polyvinylpyrrolidone, and the like.

Examples of organic photoconductive polymers include poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, and the like.

The thickness of the charge generation layer is usually 0.01 to 15 μm, preferably 0.05 to 5 μm, and the weight ratio of the charge generation layer to the binder is usually 10:1 to 1:20.

The solvent used in the paint for the charge generation layer can be selected based on the solubility and dispersion stability of the resin and charge transport material used.

Specifically, alcohols such as methanol, ethanol, isopropanol, acetone, methyl ethyl ketone,
Ketones such as cyclohexanone, N such as N,N-diethylformamide, N,N-dimethylacetamide,
N-dialkyl carbonamides, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, esters such as methyl acetate, ethyl acetate, chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, Aliphatic halogenated hydrocarbons such as trichloroethylene, aromatic compounds such as benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, etc., and ligroin can be used.

As the coating method, a method similar to that used in the preparation of the charge transport layer can be used.

In addition, the production of the single-layer organic photoreceptor used in the present invention is as follows:
The above-mentioned charge-transporting substances and charge-generating substances can be bound by mixing them with the above-mentioned binder = Dyes, pigments, organic charge-transporting substances, etc. are generally resistant to deterioration due to ultraviolet rays and/or ozone, stains due to oil, etc., and metals. Since it is susceptible to scratches caused by powder, it is possible to provide a protective layer if necessary.

Now, since these OPC photoreceptors are inexpensive, easy to manufacture, and non-toxic, their market is rapidly developing. In particular, the development of a positive charging OPC photoreceptor that is advantageous in dealing with the problems of ozone and NOl has become an important theme.

However, positively charging OPC photoreceptors are associated with several major problems. One of them is a decrease in sensitivity due to long-term use. This phenomenon often results in image defects such as image fogging in the case of a normal development system and light density in the case of a reversal development system. It is no exaggeration to say that this phenomenon is unique to OPC photoreceptors.

The present invention applies an external electric field as a means to eliminate residual positive charges. By taking this measure, we succeeded in preventing a decrease in sensitivity due to long-term use of the positively charging OPC photoreceptor while maintaining normal photocarrier generation. The external electric field can be formed, for example, by installing various chargers between the static elimination process and the primary charging process (hereinafter referred to as "pre-charging").

The type of charger is a corotron device consisting of a corona discharge electrode connected to a high-voltage power supply and a shield plate surrounding the corona discharge electrode, a scorotron device in which a grid is provided on the corotron device, or a scorotron device in which a conductive member is brought into contact with the photoreceptor. Any type of charging method, such as a direct charging method in which the electrically conductive member is charged by applying a voltage to the electrically conductive member, can be used.

It is also possible to use a DC (direct current) charge with negative polarity, or to use a power source in which DC and AC (alternating current) are superimposed. The strength of pre-charging depends on the ability and charging settings of the primary charger and the charging ability of the photoreceptor, but the surface potential of the photoreceptor after pre-charging is usually O to -1000V, preferably -toov to -300 parts. Choose according to the degree.

The present invention will be explained below according to examples.

Example 1 Base body: wall thickness 0.5 mm x diameter 60 mm x length 2
A 60 mm aluminum cylinder was prepared.

4 parts of copolymerized nylon [trade name: CM-8000 (manufactured by Toshi ■)] and 4 parts of type 8 nylon [trade name: Niratsukamite 5003 (manufactured by Dainippon Ink ■)] in 5 parts of methanol.
The solution was dissolved in a mixed solution of 0 parts of n-butanol and 50 parts of n-butanol, and dip-coated on the above conductive layer to form a polyamide undercoat layer with a thickness of 0.6 μm.

Next, polycarbonate resin [product name: Panlite L-
1250 (manufactured by Yojin Kasei)] was prepared and dissolved in 80 parts of monochlorobenzene together with 10 parts of a hydrazone compound having the following structural formula.

This was applied onto the undercoat layer to form a charge transport layer with a thickness of 16 μm.

Next, 10 parts of a disazo pigment having the following structural formula and 1 part of a polyvinyl butyral resin [trade name: S-LEC BM2 (manufactured by Building Block Chemical Co., Ltd.]) were mixed and dispersed together with 120 parts of cyclohexanone in a sand mill for 10 hours. A photoreceptor was prepared by adding 30 parts of methyl ethyl ketone to the dispersion and coating it on the charge transport layer to form a charge generation layer with a thickness of 2.0 μm.

A normal development type copying machine [product name: PC-20 (manufactured by Canon)] was modified for positive charging, and a corotron device as shown in Figure 1↓ was installed between the primary charger and the static elimination lamp.
I connected it to a power source that superimposed AC on C. The photoreceptor is installed in the copying machine, and the potential after pre-charging is 1100 or -
The potential of the photoreceptor and the image were observed before and after the durable use by running 1000 sheets under a setting of 300V. The results are shown in Table 1.

Example 2 Base material: wall thickness 0.5 mm x diameter 60 mm x length 2
A 60 mm aluminum cylinder was prepared.

4 parts of copolymerized nylon [trade name: CM-8000 (manufactured by Azuma)] and 4 parts of type 8 nylon [trade name: Niratsukamite 5003 (manufactured by Dainippon Ink ■)] with 5 parts of methanol
The solution was dissolved in a mixed solution of 0 parts of n-butanol and 50 parts of n-butanol, and dip-coated on the above conductive layer to form a polyamide undercoat layer with a thickness of 0.6 μm.

Next, a solution was prepared by dissolving 15 parts of a stilbenzene compound with the following structure and 1 part of polycarbonate resin [trade name: Panlite L-1250 (manufactured by Kijin Kasei)] in a mixed solution of 50 parts of dichloromethane and 10 parts of monochlorobenzene. It was coated on the above subbing layer to form a charge transport layer with a thickness of 15 gm.

Furthermore, 10 parts of a disazo pigment having the following structural formula and 1 part of polyvinyl butyral resin [trade name: S-LEC BM2 (manufactured by Tanezu Kagaku ■)] were mixed and dispersed together with 120 parts of cyclohexanone in a sand mill for 10 hours. A photoreceptor was prepared by adding 30 parts of methyl ethyl ketone to the dispersion and coating it on the charge transport layer to form a charge generation layer with a thickness of 2.0 μm.

Evaluation was conducted using the same modified copying machine as in Example 1 with the same settings. The results are shown in Table 1.

90 Comparative Example 1 A photoreceptor was installed in a modified copying machine similar to that in Example 1, except that no pre-charging was performed, and the same evaluation as in Example 1 was conducted under the same settings. The results are shown in Table 1.

Comparative Example 2 The same copying machine and photoreceptor as in Example 2 were used except that pre-charging was not performed, and the same evaluation as in Example 2 was performed. The results are shown in Table 1.

[Effects of the Invention] According to the present invention, it is possible to prevent a decrease in sensitivity due to long-term use of a positively charging OPC photoreceptor, and moreover, it is possible to provide high-quality images.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the electrophotographic apparatus of the present invention,
FIG. 2 is a diagram showing the connection relationship with a power source for negatively charging the electrophotographic apparatus of the present invention. 1...OPC photoconductor 2...-forming charger 3...Negative charging unit 4...Static elimination lamp 5...Cleaning blade 6...Transfer charger 7...Developer

Claims (3)

[Claims] (1) At least primary charging and exposure using an organic photoreceptor;
In an electrophotographic apparatus in which the primary charging step of the image forming process, which includes the steps of development, transfer, cleaning, static elimination, and fixing, is of positive polarity, a negative charging unit that charges the photoreceptor surface potential to negative between the primary charging and static elimination. An electrophotographic device characterized in that: (2) The electrophotographic apparatus according to claim 1, wherein the power source of the negative charging unit that negatively charges the surface potential of the photoreceptor is a DC power source. (3) The electrophotographic apparatus according to claim 1, wherein the power source of the negative charging unit for negatively charging the surface potential of the photoreceptor is a superimposed power source of direct current and alternating current.