JPH08190326A - Discharge device for image forming device - Google Patents

Abstract

PURPOSE: To effectively prevent the charge characteristic or the sensitivity of a photoreceptor from being deteriorated, to realize an excellent image forming and to make an image forming device compact by setting the light quantity distribution of a discharge light irradiation part to be such distribution that the light more than the half of total discharge light quantity is emitted toward the half part on an upstream side of the perpendicular at the center of a discharge light source. CONSTITUTION: For example, the discharge light source 2 is provided so as to be inclined to the photoreceptor 1. Then, the light quantity distribution A at the discharge light irradiation part of the surface of the photoreceptor 1 is set so that the light quantity more than 50% of the total discharge light quantity is emitted on the upperstream side of the central part of the light source 2. Therefore, the length of the bottom of the light distribution curve toward a main charger 3 becomes short. So that photoreceptor 1 is hardly affected by flare light and the charge property or the sensitivity is effectively prevented from being deteriorated. Therefore, the light source 2 and the charger 3 can be arranged as near as possible, which serves extremely advantageously for making the image forming device compact.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a static eliminator in an image forming apparatus using an organic photoconductor, and particularly to a static eliminator used in an image forming apparatus using a positively charged organic photoconductor as a photoconductor. It is about.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a main charger, an image exposure device, a developing device, a transfer device, and a cleaning device are usually provided around an endless photoconductor, for example, a drum-shaped or belt-shaped photoconductor. Device and static eliminator
They are provided in this order. A corona charging device is widely used as a main charger, and in image formation, the surface of the photoreceptor is charged to a constant potential by positive or negative corona charging. Then, the image exposure device irradiates the surface of the photoconductor with light reflected from the original image to form an electrostatic latent image corresponding to the original image, and the developing device visualizes the electrostatic latent image to form a toner image. Is formed. This toner image is
The transfer device transfers it to a predetermined sheet, while the photoconductor after transfer is cleaned by a cleaning device to remove the toner remaining on the surface, and then the residual charge is removed by light irradiation by the charge eliminating device, thus One cycle of image formation is completed.

Generally, as the photoconductor, an organic photoconductor is generally used from the viewpoint of cost, and the charge eliminating device is arranged adjacent to the upstream side of the main charger. It is used for machines, laser printers, facsimiles, etc.

By the way, in the case of using a system of charging by corona charging as a main charger, oxygen in the air is oxidized to generate ozone, or nitrogen is oxidized to generate NOx. There is a problem that these discharge products deteriorate the photoreceptor. In particular, when the photoconductor is an organic photoconductor, the deterioration tendency due to discharge products is larger than that of other photoconductors, which causes a reduction in printing durability (lifetime). Therefore, recently, a positive charging type organic photoconductor is used, and when forming an image, an image forming apparatus of a type in which corona charging by a main charger is used as a positive corona discharge to charge the photoconductor is widely used. It is supposed to be done. This is because the negative corona discharge produces a large amount of ozone, whereas the positive corona discharge produces a very small amount of ozone.

[0005]

However, in the above-mentioned image forming apparatus, the charging property and the sensitivity property of the organic photoconductor are low, for example, the surface potential (dark potential) of the photoconductor after the main charging is low, and the image forming device is excellent. There is a problem that an image having a density cannot be obtained or density unevenness of the image occurs. This tendency is particularly remarkable when a single-layer organic photoreceptor is used, and becomes more remarkable as the apparatus is made more compact.

Therefore, it is an object of the present invention to provide an antistatic device in an image forming apparatus using an organic photoconductor, which can effectively prevent the charging characteristics and sensitivity deterioration of the photoconductor and form a good image. To do. Another object of the present invention is to provide a charge eliminating device which solves the above-mentioned problems, particularly in an image forming apparatus using a positive charging type single layer organic photoconductor.

[0007]

According to the present invention, an image forming apparatus in which a main charger and a charge eliminating light irradiating portion upstream of the main charger are arranged adjacent to each other around an endless organic photoreceptor. In the above, there is provided a static eliminator which is characterized in that the light quantity distribution of the static eliminator irradiating part is set to a distribution such that more than 50% of the total static eliminator quantity is radiated in the upstream half from the center line of the static eliminator light source. It

In the present invention, a positive charging type organic photoconductor is particularly preferably used as the organic photoconductor, and a remarkable effect appears when a single-layer organic photoconductor is used.

[0009]

According to the present invention, the light irradiation is performed so that the light quantity distribution in the static elimination light irradiation portion on the surface of the photoconductor is more than 50% of the total static elimination light quantity in the half upstream from the central portion of the static elimination light source. It succeeded in achieving the task.

The reason for this will be described with reference to FIGS. 1 and 2. That is, in FIG. 1 schematically showing the static eliminator of the present invention, this device is composed of a static eliminator light source 2 disposed on an organic photoconductor 1, and a main charger 3 is disposed adjacent to the static eliminator light source 2. There is. The static elimination light source 2 is composed of a lamp 5 and a lamp house 6 which is provided so as to surround the lamp 5 and which has a single opening. Further, the main charger 3 is composed of a shield 7 having a discharge opening surface and a corona wire 8 stretched in the shield 7.

In the present invention, for example, the static elimination light source 2 is provided to be inclined with respect to the photoconductor 1, and the light quantity distribution (the distribution curve is indicated by A) at the static elimination light irradiation portion on the surface of the photoconductor 1 is It can be understood that the skirt on the main charger 3 side of the distribution is shortened because it is set to be more than 50% of the total amount of static elimination light in the upstream half of the static elimination light source 2. .

On the other hand, in FIG. 2 which shows a conventionally known static eliminator in a simplified manner, in this device, the static eliminator light source 2 is not inclined with respect to the photoconductor 1 and the light quantity distribution is a normal distribution. The bottom of the distribution curve (indicated by B) on the main charger 3 side is long.

Therefore, in the conventionally known static eliminator, when the main charging of the organic photoconductor 1 is performed, the static charge is neutralized by the flare light to the side just below the main charger 3 or to the portion just below the main charger 3 as a result. Is charged while the carriers generated on the photoconductor 1 by the irradiation of 1 exist in the bulk, the chargeability is lowered, it becomes difficult to uniformly charge the photoconductor surface to a constant potential, and the sensitivity is also lowered. To do. In particular, in the case of a single-layer organic photoconductor, the carrier life is long, so that the charging property and the sensitivity decrease remarkably under the influence of flare light.

However, according to the static eliminator of the present invention shown in FIG. 1, since the skirt of the light amount distribution curve A on the side of the main charger 3 is short, it is less susceptible to the flare light, and the charging property and the sensitivity are lowered. It is possible to effectively prevent it. Therefore, in the present invention, the static elimination light source 2 and the main charger 3 can be arranged as close to each other as possible, which is extremely advantageous in terms of downsizing the image forming apparatus.
The distance between the static elimination light source 2 and the main charger 3 is preferably set such that the amount of flare light on the surface of the photoconductor immediately below the side wall of the shield 7 of the main charger 3 is substantially zero.

In the present invention, the setting of the above-mentioned light amount distribution curve can be easily performed by providing the static elimination light source in an inclined manner as shown in FIG. It can also be carried out by the means shown in.

For example, FIG. 3 shows that a black light absorbing sheet 10 is provided on the wall surface of the lamp house 6 on the side of the main charger 3, and FIG. 4 is the same as FIG. The black light absorbing sheet 10 is provided on the lamp house 6. Further, in FIG. 5, the wall surface on the upstream side of the lamp house 6 (the side opposite to the main charger 3) is transparent.
In the present invention, from the viewpoint of shortening the skirt of the light amount distribution curve A on the main charger 3 side, it is particularly desirable to adjust the light amount distribution by the means shown in FIG.

[0017]

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(Organic Photoreceptor) The organic photoreceptor used in the present invention has a single-layer or laminated photosensitive layer provided on a conductive substrate, and it is particularly preferable to use a positive charging type organic photoreceptor. That is, if the photosensitive member is charged by positive corona discharge using a positively chargeable organic photosensitive member, the amount of ozone generated is extremely small, and therefore the deterioration of the photosensitive member due to ozone can be effectively prevented.

In the laminated type organic photoconductor, a photosensitive layer is formed by providing a charge generating layer in which a charge transfer agent is dispersed in a resin medium on a charge generating layer in which a charge generating agent is dispersed in a resin medium. However, the present invention has remarkable advantages especially when a positively charged single-layer organic photoreceptor is used. That is, as described above, in the positive charging type single layer organic photoconductor, the carrier life generated by light irradiation is long, and the degree of reduction in charging property and sensitivity due to the influence of flare light is remarkable. According to the present invention, even when such a positive charging type single-layer organic photoreceptor is used, it is possible to effectively prevent a decrease in charging property and sensitivity due to flare light, and it is possible to make the apparatus compact. Of.

This positively chargeable single-layer organic photoreceptor has a single-layer photosensitive layer in which a charge-generating agent and a charge-transporting substance are dispersed in a resin medium, which is provided on a conductive substrate. As the substance, a combination of a hole transport material and an electron transport material is used.

Of the charge transfer agents, the electron transfer agent is
Diphenoquinone compounds, benzoquinone compounds, naphthoquinone compounds, malononitrile, thiopyran compounds, tetracyanoethylene, tetracyanoquinodimethane, chloranil, bromoanil, 2,4,7-trinitro-9-fluorenone, 2,4,5,5 7-Tetranitro-9-fluorenone, 2,4,7-trinitro-9-
Dicyanomethylene fluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitroxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, dibromo Maleic anhydride, and the following formula (1):

[0021]

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[Wherein, l, m and n are l ≧ 0, m ≧
2, an integer of n ≧ 1, X is nitro, OH, a halogen atom, CN, aryl optionally having a substituent, aralkyl, NR ₂ , OR, OCOR, COOR, CONHR,
CONR ₂ , COR, SOR, and SO ₂ R (R is an alkyl, aryl, or aralkyl which may have a substituent), and when n ≧ 2, X may be the same or different, Y represents an alkyl group which may have a substituent, and the like, and electron-withdrawing materials such as compounds represented by these, and polymers obtained by polymerizing these electron-withdrawing materials can be exemplified.

Particularly, as the electron transfer agent, a diphenoquinone compound, particularly an asymmetric substitution type compound is preferable. As the diphenoquinone compound, those represented by the following formula (2) can be used alone or in combination of two or more kinds.

[0024]

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In the above formula, each of R ¹ , R ² , R ³ and R ⁴ is a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group or the like. More specifically, 3,
5-Dimethyl-3 ′, 5′-dit-butyldiphenoquinone, 3,3′-dimethyl-5 ′, 5′-dit-butyldiphenoquinone, 3,5′-dimethyl-3 ′, 5 -Di-t-butyldiphenoquinone, 3,5,3 ', 5'-tetramethyldiphenoquinone, 3,5,3', 5'-tetra-t-butyldiphenoquinone, 3,5,3 ', Examples thereof include 5'-tetraphenyldiphenoquinone and 3,5,3 ', 5'-tetracyclohexyldiphenoquinone, which satisfy the following formula (3), (4) or (5). The diphenoquinone derivative having a substituent is preferable because the molecule has low symmetry, the interaction between the molecules is small, and the solubility is excellent.

(Carbon number of R ¹ = carbon number of R ³ )> (carbon number of R ² = carbon number of R ⁴ ) ... (3) (carbon number of R ¹ = carbon number of R ² )> (R ³ carbons = R ⁴ carbons) (4) (R ¹ carbons = R ⁴ carbons)> (R ² carbons = R ³ carbons) (5)

As the hole-transporting agent, any hole-transporting substance can be used. For example, oxadiazole compounds, styryl compounds, carbazole compounds, organic polysilane compounds, pyrazoline compounds, hydrazone compounds,
Nitrogen-containing cyclic compounds such as triphenylamine compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds,
Fused polycyclic compounds and the like are used, and those having an ionization potential in the range of 5.3 to 5.6 eV are preferably used. The electrolytic strength is 3 × 10 ⁵ V / cm and 1 × 1.
Those having a mobility of 0 ⁻⁶ cm ² / V · sec or more are particularly preferable.

Specific examples of suitable hole transport materials include:
1-bis (p-diethylaminophenyl) -4,4-diphenyl-1,3-butadiene, N, N '-(o, p-
Dimethylphenyl) -N, N'-diphenylbenzidine, 3,3'-dimethyl-N, N, N ', N'-tetrakis (4-methylphenyl-1,1'-biphenyl)-
4,4'-diamine, N-ethyl-3-carbazolylaldehyde-N, N'-diphenylhydrazone, 4-
[N, N-bis (p-toluyl) amino] -β-phenylstilbene and the like can be exemplified.

Examples of the charge generating agent include selenium, selenium-tellurium, amorphous silicon, pyrylium salt, azo pigments, disazo pigments, ansanthuron pigments, phthalocyanine pigments, indico pigments, slene pigments,
Examples include toluidine pigments, pyrazoline pigments, perylene pigments, quinacridone pigments and the like, and one kind or a mixture of two or more kinds is used so as to have an absorption wavelength range in a desired range. Particularly, those having an ionization potential in the range of 5.3 to 5.6 eV are preferable, and most preferable are bisazo pigments, X-type metal-free phthalocyanine,
Oxotitanyl phthalocyanine etc. are illustrated.

Various resins can be used as the resin medium in which the above-mentioned respective agents are dispersed. For example, a styrene polymer, an acrylic polymer, a styrene-acrylic polymer,
Ethylene-vinyl acetate copolymer, polypropylene, olefin polymers such as ionomer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy resin,
Polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone resin,
Various polymers such as polyvinyl butyral resin, polyether resin, and phenol resin, and photocurable resins such as epoxy acrylate can be used alone or in combination of two or more. Particularly suitable resins are styrene polymers, acrylic polymers, styrene-acrylic polymers, polyesters, alkyd resins, polycarbonates, polyarylates and the like.

In the above positive charging type single-layer organic photoreceptor,
The charge generating agent is usually 0.1 to 5% by weight based on the solid content,
In particular, it is preferable to be contained in the photosensitive layer in an amount of 0.25 to 2.5% by weight, and an electron transfer agent (ET) such as a diphenoquinone derivative and a hole transfer agent (HT) are contained in each solid content. It is preferably contained in the photosensitive layer in an amount of 5 to 50% by weight, particularly 10 to 40% by weight. Further, the weight ratio of ET: HT is preferably in the range of 1: 9 to 9: 1, and particularly 2: 8 to 8: 2.

Further, the above-mentioned composition for forming a single photosensitive layer may be incorporated into various compositions known per se, such as an antioxidant, within a range that does not adversely affect electrophotographic characteristics.
A radical scavenger, a singlet quencher, a UV absorber, a softening agent, a surface modifier, an antifoaming agent, a bulking agent, a thickener, a dispersion stabilizer, a wax, an acceptor, a donor and the like can be added. In particular, when the sterically hindered phenolic antioxidant is added in an amount of 0.1 to 50% by weight based on the total solid content, the durability of the photosensitive layer is remarkably improved without adversely affecting the electrophotographic characteristics. You can

The single-layer photosensitive layer is formed by dissolving or dispersing each of the above-mentioned agents and resin components in a solvent and coating the solution on a conductive substrate. As the solvent, various organic solvents such as methanol can be used. , Alcohols such as ethanol, isopropanol and butanol, aliphatic hydrocarbons such as n-hexane, octane and cyclohexane, aromatic hydrocarbons such as benzene, toluene and xylene, dichloromethane, dichloroethane, carbon tetrachloride and chlorobenzene. Halogenated hydrocarbons, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol, and other ethers, acetone, methyl ethyl ketone, cyclohexanone, and other ketones, ethyl acetate, methyl acetate, and other esters, dimethylforma The de ,, dimethyl sulfoxide, can be used alone or in combination. The solid content concentration of the coating liquid is generally preferably 5 to 50%.

As the conductive substrate, various materials having conductivity can be used. For example, aluminum, iron, copper, tin, platinum, gold, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel. Examples include simple metals such as indium, stainless steel, and brass, plastic materials in which the above metals are vapor-deposited or laminated, and glass coated with aluminum iodide, tin oxide, indium oxide, or the like.

In particular, in the case of a single-layered photosensitive layer, since no interference fringes are generated, it is possible to use an ordinary alumite tube that has been subjected to alumite treatment so as to have a film thickness of 1 to 50 μm. That is also one of the advantages.

In order to prepare the coating liquid, the charge-generating material and the like are mixed with the resin and the like by a conventionally known method such as a roll mill,
A ball mill, an attritor, a paint shaker, an ultrasonic disperser or the like may be used, and this may be applied and dried by a conventionally known application means.

The thickness of the single photosensitive layer is not particularly limited, but it is preferably in the range of generally 5 to 100 μm, particularly 10 to 50 μm.

(Image Forming Apparatus) In FIG. 6 showing an example of an image forming apparatus using the static eliminator of the present invention, this apparatus comprises a rotating organic photosensitive drum 1 and a corona provided along the rotating direction thereof. It comprises a charging device 22, an optical system 23 for image exposure, a developing device 24, a charging device 25 for transfer, a cleaning device 26 and a light source 27 for static elimination.

That is, in forming an image, first, the surface of the photosensitive drum 1 is charged positively or negatively by the corona charging device 22. In this case, when a positive charging type organic photoconductor is used as the photoconductor drum 1, the photoconductor drum 1 is positively charged. Next, reflected light from a document (not shown) is irradiated onto the photoconductor drum 1 via the optical system 23 to form an electrostatic latent image corresponding to the document image.

The developing device 24 has toner 30 and
This electrostatic latent image is developed with the toner 30 by the developing device 24 to form a toner image. The charging polarity of the toner is the opposite polarity to the surface of the photoconductor drum 1 in the case of normal regular development, and the same polarity as the photoreceptor surface in the case of reversal development.

The transfer charging device 25 includes a toner transfer charging device 31 and a paper separation AC charging device 32. Corona charging is performed from the back surface of the transfer paper 33 by the charging device 31 to transfer the toner image onto the transfer paper. And transfer to 33. The polarity of the charger 31 is the same as that of the surface of the photosensitive drum 1 on which the toner is attached. The transfer paper 33 on which the toner image is transferred is
The charge is removed from the surface of the photosensitive drum 1 by the charge removal of the AC charger 32, and is sent to a fixing area (not shown) where heat,
The toner image is fixed by pressure or the like.

After the toner transfer, the residual toner is removed from the photosensitive drum 1 by the cleaning device 26 equipped with a cleaning blade and the like, and the residual charge is removed by the entire surface exposure from the light source 27 for static elimination.

In the above-mentioned image forming apparatus, the charge eliminating light source 27 is provided in an inclined manner as shown in FIG.
Of course, it may be provided as shown in FIGS. By providing the static elimination light source 27 in this way, the corona charging device 22 can be provided as close as possible, which is extremely advantageous in terms of making the device compact.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the following examples.

(Production of Photoreceptor) In the following examples, a positive charging type single-layer organic photoreceptor prepared by the following method was used. A photosensitive layer composition having the following composition was uniformly dispersed using a paint shaker for 2 hours to prepare a single-layer photosensitive layer-forming coating solution, which was applied to the surface of an aluminum tube having an outer diameter of 78 mm. It was applied by dipping and dried at 110 ° C. for 30 minutes to form a single-layer photosensitive layer having a film thickness of 30 μm to obtain a positive charging type single-layer organic photoreceptor.

Composition of photosensitive layer composition: Bisazo pigment (represented by the following formula (6)) 10 parts by weight N, N, N ′, N′-tetrakis (3-methylphenyl) -m-phenylenediamine 100 parts by weight 3 , 5,3 ', 5'-Tetraphenyldiphenoquinone 50 parts by weight Polycarbonate resin 100 parts by weight Dichloromethane 800 parts by weight

[0047]

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Example 1 The above-mentioned photosensitive drum was attached to a modified electrophotographic copying machine DC-2556 manufactured by Mita Kogyo Co., Ltd., and a light source for static elimination (irradiation light amount: 120 lux.sec.) Was tilted as shown in FIG. Were arranged (inclination angle θ = 30 degrees). At this time, the distance d between the light source for static elimination and the main charger was set to 15 mm. For this copier, the voltage applied to the main charger was variously changed, the inflow current (Ipc) to the photosensitive drum was changed, and the surface potential (SP) of the photosensitive drum was measured. The results are shown in Table 1. Indicated. In addition, the surface of the photoconductor drum is charged to 800 V to perform image exposure and charge removal, and subsequently, after charging,
The relationship between the exposure amount of the second image exposure when image exposure was performed and the drum surface potential (SP) of the light irradiation portion was measured. The results are shown in Table 2.

Comparative Example 1 The same experiment as in Example 1 was carried out except that the static elimination light source was arranged without tilting as shown in FIG. 2 and the light quantity distribution was a normal distribution. The results are also shown in Tables 1 and 2.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

As is clear from the above experimental results, according to the static eliminator of the present invention, by setting the light quantity distribution of the irradiation light of the static elimination light source to be more than 50% in the upstream half. , The deterioration of the charging property and sensitivity of the organic photoreceptor is effectively prevented. As a result, it is possible to dispose the main charging device disposed adjacent to the charge eliminating light source as close to the charge eliminating light source as possible, which is extremely advantageous in terms of downsizing the image forming apparatus.

[Brief description of drawings]

FIG. 1 is a diagram simply showing an example of the structure of a static eliminator of the present invention.

FIG. 2 is a diagram simply showing a structure of a conventionally known static eliminator.

FIG. 3 is a diagram showing the structure of another example of the static eliminator of the present invention.

FIG. 4 is a diagram showing the structure of another example of the static eliminator of the present invention.

FIG. 5 is a view showing the structure of another example of the static eliminator of the present invention.

FIG. 6 is a diagram showing a structure of an image forming apparatus using the static eliminator of FIG.

[Explanation of symbols]

1: Photoconductor 2: Light source for neutralization 3: Main charger 5: Lamp 6: Lamp house 7: Shield 8: Corona wire 22: Corona charging device for main charging 23: Optical system for image exposure 24: Developing device 25: Transfer Charging device 26: Cleaning device 27: Light source for neutralization 30: Toner 31: Charger for toner transfer 32: AC charger for paper separation 33: Transfer paper

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Sako, 1-2-2 Tamatsukuri, Chuo-ku, Osaka City Mita Engineering Co., Ltd. (72) Yukishi Terada 1-2-2 Tamatsukuri, Chuo-ku, Osaka City Mita Kogyo Co., Ltd. (72) Inventor Yuji Tanaka 1-228 Tamatsukuri, Chuo-ku, Osaka Mita Kogyo Co., Ltd. (72) Toru Ueno 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Kogyo Co., Ltd. (72) Inventor Keizo Kimoto 1-228 Tamatsukuri, Chuo-ku, Osaka Mita Engineering Co., Ltd.

Claims (4)

[Claims] 1. In an image forming apparatus in which a main charger and a discharge light irradiating unit upstream of the main charger are arranged adjacent to each other around an endless organic photoconductor, the light amount distribution of the discharge light irradiating unit is The static eliminator is characterized in that the distribution is set so that more than 50% of the total amount of static elimination light is emitted in the upstream half from the center line of the static elimination light source. 2. The static eliminator according to claim 1, wherein the organic photoconductor is a positive charging type organic photoconductor. 3. The static eliminator according to claim 2, wherein the organic photoconductor is a positive charging type single-layer organic photoconductor. 4. The static eliminator according to claim 1, wherein the organic photoconductor is a photoconductor containing a resin medium containing a hole transporting agent and an electron transporting agent, and a charge generating agent dispersed in the medium. .