JPH09305010A - Image forming device and image forming unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which is compact as a whole and, at the same time, reduces the effects of discharge products on a photoreceptor and, ensures the steady, smooth processes of electrophotography over a long period of time. SOLUTION: In this image forming device for forming an image through the electrification of a photoreceptor drum 1, exposure, development, and transfer, a developing means also serves as a means for clearing away toner remaining on the photoreceptor. Also, an electrifying means 2 positions a scorotron electrifier within ±45 deg. from a vertical line P drawn down from the center C of the photoreceptor drum 1 and has a hole 4 opposite an electrification opening 3. An electric field E. between the wire of the scorotron electrifier and a grid is set greater than an electric field E. between the wire and a shield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly, it is possible to reduce the influence of discharge products on a photoconductor while reducing the size of the apparatus as a whole. The present invention relates to an image forming apparatus in which each step in photography is performed stably and smoothly for a long period of time. The present invention also relates to an image forming unit used in this image forming apparatus.

[0002]

2. Description of the Related Art In electrophotographic image formation, a photosensitive member is charged and exposed to form an electrostatic latent image, and the electrostatic latent image on the photosensitive member is developed with a developer containing charged toner to form a toner image. An image is formed by forming the toner image, transferring the toner image to a transfer material such as paper, and fixing the transferred toner image.

As the electrophotographic photoreceptor, a selenium photoreceptor,
a- Various types of photoreceptors such as silicon photoreceptors and organic photoreceptors are known, but in terms of manufacturing cost, easy disposal and environmental friendliness, and adaptability to small copiers, fax machines and printers. In this respect, the organic photoreceptor is superior.

The organic photoreceptor includes a single-layer organic photoreceptor in which a charge generating agent (CGM) is dispersed in a medium containing a charge transporting agent (CTM), and a charge transporting layer (CGL) on the charge transporting layer (CGL). A laminated photoconductor provided with a CTL) is known.

Generally, a corona charging method is widely used for charging the photoconductor, but it has a drawback in that discharge products such as ozone and NOx are generated. That is, in the latter case of the laminated photoreceptor described above, a large amount of ozone is generated because negative charging is required,
On the other hand, since the former single-layer photoconductor can be positively charged, the amount of ozone generated is relatively smaller than that of the latter, but it is affected by NOx.

[0006]

[Problems to be Solved by the Invention]
In printers, compact copiers, etc., it is essential to reduce the diameter of the photosensitive drum in order to make the image forming apparatus compact and lightweight, but various problems occur as the drum diameter decreases. To do.

First, in the charging section of the photosensitive drum, ozone and NOx are generated by corona discharge, but in the case of a small diameter drum, the entire drum surface is easily exposed to the ozone atmosphere and the surface area of the drum is small, so that a plurality of rotations occur. As described above, the ozone deterioration of the photoconductor occurs in a relatively short operating time in association with the formation of one image.

Further, if the diameter of the drum, and hence the peripheral length of the drum, is reduced, various mechanisms to be arranged around the photosensitive drum, that is, mechanisms for carrying out various steps of electrophotography are also restricted. There is a problem that a sufficient space for arranging the mechanism to be implemented cannot be secured.

Conventionally, there is also known a system in which charging and image exposure are carried out without cleaning the toner remaining on the surface of the photoconductor after toner transfer, and the residual toner is cleaned in the developing step. Can be said to be a desirable method for an image forming apparatus using a small-diameter drum, but this cleaning-less method has a disadvantage that residual toner after transfer is scattered and adhered to a charger or the like, which impairs charging performance. is there.

Accordingly, an object of the present invention is to form an image in which the influence of discharge products on the photoconductor is reduced and the respective steps in electrophotography are stably and smoothly performed for a long period of time while the entire apparatus is made compact. To provide the equipment.

Another object of the present invention is to use ozone or N
(EN) It is possible to provide a compact type image forming apparatus in which deterioration due to Ox is reduced and the photosensitive member is stably charged for a long period of time, and an image forming unit used in this image forming apparatus.

[0012]

According to the present invention, in an image forming apparatus for forming an image through charging, exposing, developing and transferring of a photosensitive drum, the developing means cleans residual toner on the photosensitive member. In addition, the means for performing the charging is such that the scorotron charger is positioned within ± 45 ° from the vertical line from the center of the photosensitive drum to the lower side and the hole is provided on the opposite side of the charging opening. And the electric field E ₁ between the wire and the grid in the scorotron charger is the electric field E ₂ between the wire and the shield.
An image forming apparatus is provided that is set larger than the above.

The photosensitive drum used in the present invention is: 1. A photosensitive layer made of an organic material is provided. 2. It has a single-layer dispersion type organic photosensitive layer, in particular, a positive charge type organic photosensitive layer, in which at least a charge generating material and a charge transporting material are contained in a binder resin. A small-diameter drum having a peripheral length shorter than ½ of the image size in the drum rotation direction, a photosensitive drum set to form one image by multiple rotations of the drum, and the like. is there.

The charging means used in the present invention is a scorotron charger having a ventilation hole on the side opposite to the charging opening, that is, a shield and a discharge wire to which a high voltage is applied, which is housed in the shield. A charging device including a grid provided in the charging opening and a ventilation hole provided on the opposite side of the charging opening, wherein an electric field E ₁ between the wire and the grid in the scorotron charging device is an electric field E between the wire and the shield. It is set larger than ₂ .

The developing means used in the present invention is preferably a reversal developing means using a one-component toner.

The transfer means used in the present invention are: 1. A roller charging unit located above the photoconductor. It is preferable that the toner image on the transfer paper surface is transferred downward by using a charging roller that is not in contact with the photosensitive drum having the toner image.

According to the present invention, further, the image forming is performed by charging, exposing, developing and transferring the photoconductor drum, and the developing means also serves to clean the residual toner on the photoconductor. An image forming unit used in an apparatus, wherein the image forming unit includes a photosensitive drum having a photosensitive layer made of an organic material, a first frame that rotatably supports the photosensitive drum, and a lower portion from a center of the photosensitive drum. And a developing unit and a developing unit and a developing unit provided with the frame so as to be positioned within ± 45 ° from a vertical line to the charging unit and having a ventilation hole on the opposite side of the charging opening. And a developing unit comprising a second frame which also serves as a toner container and also serves as a toner container. The first frame and the second frame have a common fulcrum and a fulcrum. Opposite and a resilient engagement means, and the electric field between the electric field E ₁ between wire and grid in the scorotron charger wire and shield E ₂
An image forming unit is provided that is set to be larger than the above.

[0018]

DETAILED DESCRIPTION OF THE INVENTION

[Operation] Ozone and N
Occurrence of discharge products such as Ox cannot be avoided. However, in the present invention, since the main charger is also provided under the photoconductor,
It is possible to avoid the influence of discharge products (having a larger specific gravity than air) on the surface of the photoconductor. At the same time, by providing a hole on the opposite side of the charging opening, the discharge products accumulated in the charger at the end of image formation (stopping the rotation of the photosensitive drum and turning off the charger) can be quickly discharged downward, Toner that constantly falls was also made to flow out of the hole to prevent toner from adhering to the corona wire and the like. When the main charger is provided on the lower side of the photoconductor, the transfer means is located on the upper side of the photoconductor in the small diameter drum, but in the present invention, the transfer means is not the corona charge but the roller charge, Corona discharge on the top side of the photoreceptor was avoided. In addition, since the transfer by roller charging is also performed by using the non-contact type roller and the back surface transfer, the contact between the toner supporting photoconductor and the transfer roller is blocked by the paper, and even when the transfer is not performed, the transfer roller does not contact the toner supporting photoconductor. Since it is separated from the transfer roller, the transfer roller is prevented from being contaminated, and thus the rear surface of the transfer paper is prevented from being contaminated.
This is a particularly important function for double-sided printing of paper.
Moreover, by using the non-contact roller, the transfer paper is not pressed against the photoconductor, the hollow characters are prevented, and the image quality is significantly improved. By providing the transfer means on the upper side of the photoconductor, the conveyance path between the paper feeding means and the printed matter discharge means placed on the upper part of the apparatus can be minimized, and the apparatus can be made extremely compact. Becomes The photoconductor drum and the charging unit are attached to the first frame to form a photoconductor unit, the developing unit is attached to the second frame to form a developer unit, and a fulcrum and an elastic member common to the first and second frames are provided. By providing the coupling means, the developing means and the photoconductor drum can be securely engaged with each other, the structure of the image forming unit can be simplified, and the detaching and mounting from the apparatus can be performed very easily. .

The present invention is particularly effective when the positively chargeable organic photoconductor is a single layer dispersion type organic photoconductor. That is, by using the positive charging type organic photoconductor, it is possible to use the positive corona, and it is possible to reduce the generation of ozone as compared with the case of using the negative corona. On the other hand, in organic photoreceptors, particularly in single-layer dispersion type organic photoreceptors, the effect of exposure to discharge products is greater than that of inorganic photoreceptors. The effects of the product are considerably reduced. Since the electric field E ₁ between the wire and the grid in the scorotron charger is set to be larger than the electric field E ₂ between the wire and the shield, the charging efficiency of the photoconductor is improved. That is, the inflow current (Icc) into the charging wire is smaller than that in the case of E ₁ <E ₂ , and as a result, the amount of discharge products is reduced. Further, at the time of charging, fresh air flows from a hole provided on the opposite side of the charging opening by ion wind corresponding to the electric field, and the replacement of the fresh air in the charger with the fresh air is performed quickly.

[Arrangement of Charging Means] Referring to FIG. 1 for explaining the arrangement relationship between the photoconductor drum and the charging means, in the present invention, + from the perpendicular line P extending downward from the center C of the photoconductor drum 1.
The charging means 2 is arranged within the range A from the line a of 45 ° to the line b of −45 ° from the perpendicular P.

As shown in an example described later, when the charging means 2 is arranged above the line a or the line b, ozone or NO accumulated in the charger immediately after the image formation is completed.
When x falls on the stopped photosensitive drum and local deterioration of the photosensitive drum occurs, a local decrease in charging potential and a decrease in sensitivity occur. When the charging means is arranged within the range A, it is possible to remarkably reduce the degree of local decrease in the charging potential and the decrease in sensitivity.

This is ozone (O ₃ ) generated by the charging means 2.
It is considered that even if NOx or NOx is generated, ozone or NOx having a larger specific gravity (molecular weight) than that of air in the range A flows downward, and contact with the photoconductor is avoided or reduced.

In the present invention, the ventilation hole 4 is provided on the opposite side of the charging opening 3 to the charging means 2. This hole 4
By providing, the heavy ozone generated in the charger 2 becomes a downward flow S and quickly moves away from the photoconductor 1, and the influence of ozone on the photoconductor 1 is further reduced.

In addition, the holes 4 provided in the charger 2 bring about an extremely effective operation in the above-mentioned cleaningless electrophotographic system. That is, the toner remaining on the surface of the photoconductor after transfer is scattered and adheres to the corona wire, the shield, the grid, or the like of the charger 2, which adversely affects the charging performance and the stability thereof. Since the hole 4 is provided on the opposite side of the charging opening 3 of the charger 2, the toner discharged from the charging opening 3 through the hole 4 to the outside is prevented from adhering to the corona wire, the shield, or the grid. This will prevent adverse effects on the charging performance and its stability.

In summary of the above, according to the present invention, the influence of discharge products on the photoconductor is reduced while the entire apparatus is made compact, and each step in the electrophotographic process is stable and smooth for a long period of time. And the ozone deterioration of the photoconductor is effectively prevented.

[Image Forming Apparatus] In FIG. 2 showing the overall arrangement of an example of the image forming apparatus of the present invention, the photosensitive drum 1 is shown.
The charging means 2, the image exposure means 20, and the
The developing means 30, the toner transfer means 45, and the foreign matter removing means 50 such as paper dust are arranged in this order. In addition, the transfer material 47
From the transfer material supply means (not shown) to the transfer means 45.
Between the photosensitive drum 1 and the photosensitive drum 1, and then the fixing unit 6
It is provided so that the transfer material 47 is discharged to the outside after passing 0.

The image forming process by this electrophotographic apparatus will be briefly described as follows. First, the surface of the photoreceptor drum 1 is charged with a positive charge by the charging means 2. Then
The charged photosensitive drum 1 is irradiated with a light image by the image exposure means 20 to form an electrostatic latent image (negative image) corresponding to the original image. This electrostatic latent image is visualized by the developing unit 30 to form a toner image. The transfer material 47 is supplied at the position of the toner transfer unit 45 so as to be in contact with the drum surface, and the toner image is transferred to the transfer material 47. The transfer paper 47 on which the toner image has been transferred is separated from the drum 1 and sent to the fixing unit 60, where the toner is fixed by passing between the support roller 61 and the heating roller 62. After the transfer of the toner, the photosensitive drum 1 comes into contact with the foreign matter removing means 50 to remove foreign matter such as paper dust. The toner remaining on the photosensitive drum after the transfer of the toner is cleaned by the developing unit 30 after passing through the charging and image exposing steps described above.

[Photoreceptor] The photoreceptor used in the present invention is not particularly limited, but it is preferably a single-layer photoreceptor, and generally, a single-layer organic photoreceptor in which a charge generating agent is dispersed in a charge transport medium, Particularly, it is a positive charging type organic photoconductor, and this photoconductor is particularly effective for a small diameter, and has a diameter of 20 mm or less, particularly 10
Used in the form of small diameter drums up to 20 mm.

Examples of the charge generating agent include selenium, selenium-tellurium, amorphous silicon, pyrylium salt,
Examples include azo pigments, disazo pigments, trisazo pigments, anthanthrone pigments, phthalocyanine pigments, indico pigments, slene pigments, toluidine pigments, pyrazoline pigments, pyranthrone pigments, perylene pigments, and quinacridone pigments. One kind or a mixture of two or more kinds is used so as to have an absorption wavelength region in a desired region.

Among these, phthalocyanine pigments,
Perylene pigments and disazo pigments are preferable.

Various resins can be used as the resin medium in which the charge generating agent is dispersed. Examples of the resin medium include styrene polymers, acrylic polymers, styrene-acrylic polymers, ethylene-vinyl acetate copolymers, polypropylene,
Olefin polymers such as ionomers, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyester,
Alkyd resin, polyamide, polyurethane, epoxy resin, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, polyether resin,
Various polymers such as a phenol resin and a photocurable resin such as an epoxy acrylate can be exemplified. These binder resins may be used alone or in combination of two or more.
Suitable resins are styrenic polymers, acrylic polymers,
Styrene-acrylic polymer, polyester, alkyd resin, polycarbonate, polyarylate and the like.

Particularly suitable resins are polycarbonate, Panlite manufactured by Teijin Chemicals, PCZ manufactured by Mitsubishi Gas Chemical Co., Ltd., and the following general formula (1):

[0033]

Embedded image In the formula, R ₁ and R ₂ are a hydrogen atom or a lower alkyl group, and R ₁ and R ₂ may be linked together to form a cyclo ring such as a cyclohexane ring together with a bonding carbon atom. Polycarbonate derived from bisphenols and phosgene.

As the charge transfer agent (CTM), those having an electron transporting property and those having a hole transporting property can be used, and these can be used in combination. A suitable example is as follows.

Paradiphenoquinone derivatives, benzoquinone derivatives, naphthoquinone derivatives, tetracyanoethylene,
Tetracyanoquinodimethane, chloranil, bromoanil, 2,4,7-trinitro-9-fluorenone, 2,
4,5,7-tetranitro-9-fluorenone, 2,
4,7-trinitro-9-dicyanomethylenefluorenone, 2,4,5,7-tetranitroxanthone, 2,
An electron-withdrawing substance such as 4,8-trinitrothioxanthone or a polymer of these electron-withdrawing substances.

Of these, paradiphenoquinone derivatives, particularly asymmetrical paradiphenoquinone derivatives, are preferable because they are excellent in solubility and electron transporting property.

As the paradiphenoquinone derivative, the following general formula (2)

[0038]

Embedded image In the formula, each of R ₃ , R ₄ , R ₅ and R ₆ is a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, an alkoxy group or the like. R ₃ , R ₄ , R ₅ and R ₆ are preferably substituents having an asymmetric structure, and among R ₃ , R ₄ , R ₅ and R ₆ ,
It is preferable that two are lower alkyl groups and the other two are branched chain alkyl groups, cycloalkyl groups, aryl groups or aralkyl groups.

Suitable examples thereof include, but are not limited to:
3,5-dimethyl-3 ′, 5′-di-tert-butyldiphenoquinone, 3,5-dimethoxy-3 ′, 5′-di-tert-butyldiphenoquinone, 3,3′-dimethyl-5,5 '-Di-t-butyldiphenoquinone, 3,5'-dimethyl-
3 ′, 5-di-tert-butyldiphenoquinone, 3,5
3 ', 5'-tetramethyldiphenoquinone, 2,6
2 ′, 6′-tetrat-butyldiphenoquinone, 3,
5,3 ′, 5′-tetraphenyldiphenoquinone, 3,
5,3 ′, 5′-Tetracyclohexyldiphenoquinone and the like can be cited, but these diphenoquinone derivatives have low interaction between molecules due to low molecular symmetry and are excellent in solubility. Preferred for.

On the other hand, as the hole transporting substance, for example, the followings are known, and among them, those having excellent solubility and hole transporting property are used. Pyrene; N-
Ethylcarbazole, N-isopropylcarbazole,
N-methyl-N-phenylhydrazino-3-methylidene-9-carbazole, N, N-diphenylhydrazino-
Carbazoles such as 3-methylidene-9-ethylcarbazole; phenothiazines such as N, N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine; N, N-diphenylhydrazino-3-methylidene Phenoxazines such as -10-ethylphenoxazine; p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-α-naphthyl-N-phenylhydrazone, p-pyrrolidinobenzaldehyde-N, N- Diphenylhydrazone, 1,3,3-trimethylindolenine-ω-aldehyde-N, N-diphenylhydrazone, p-diethylbenzaldehyde-3-methylbenzthiazolinone-2
-Hydrazones such as hydrazones;

2,5-bis (p-diethylaminophenyl) -1,3,4-oxazizole, 1-phenyl-3
-(P-Diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [quinonyl (2)]-3- (p-diethylaminostyryl) -5-
(P-Diethylaminophenyl) pyrazoline, 1- [pyridyl (2)]-3- (p-diethylaminostyryl)
-5- (p-diethylaminophenyl) pyrazoline, 1
-[6-Methoxy-pyridyl (2)]-3- (p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [pyridyl (3)]-3- (p
-Diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [lepidil (3)]-3
-(P-Diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [pyridyl (2)]-3- (p-diethylaminostyryl) -4-
Methyl-5- (p-diethylaminophenyl) pyrazoline, 1- [pyridyl (2)]-3- (α-methyl-p-
Pyrazolines such as diethylaminostyryl) -3- (p-diethylaminophenyl) pyrazoline, 1-phenyl-3- (p-diethylaminostyryl) -4-methyl-5- (p-diethylaminophenyl) pyrazoline and spiropyrazolin;

2- (p-diethylaminostyryl) -3
-Oxazole compounds such as diethylaminobenzoxazole and 2- (p-diethylaminophenyl) -4- (p-dimethylaminophenyl) -5- (2-chlorophenyl) oxazole; 2- (p-diethylaminostyryl) -6 -Thiazole compounds such as diethylaminobenzothiazole; bis (4-diethylamino-2-
Triarylmethane compounds such as methylphenyl) phenylmethane; 1,1-bis (4-N, N-diethylamino-2-methylphenyl) heptane, 1,1,2,2
-Polyarylalkanes such as tetrakis (4-N, N-dimethylamino-2-methylphenyl) ethane;

N, N'-diphenyl-N, N'-bis (methylphenyl) benzdiene, N, N'-diphenyl-N, N'-bis (ethylphenyl) benzidine, N,
N'-diphenyl-N, N'-bis (propylphenyl) benzidine, N, N'-diphenyl-N, N'-bis (butylphenyl) benzidine, N, N'-bis (isopropylphenyl) benzidine, N , N'-diphenyl-N, N'-bis (secondary butylphenyl) benzidine, N, N'-diphenyl-N, N'-bis (tertiary butylphenyl) benzidine, N, N'-diphenyl-
Benzidine compounds such as N, N'-bis (2,4-dimethylphenyl) benzidine and N, N'-diphenyl-N, N'-bis (chlorophenyl) benzidine; triphenylamine, poly-N-vinylcarbazole , Polyvinylpyrene, polyvinylanthracene, polyvinylarucdin, poly-9-vinylphenylanthracene, pyrene-formaldehyde resin, ethylcarbazole formaldehyde resin.

Among these, aromatic amine-based transport agents, especially those represented by the general formula (3),

[0045]

Embedded image In the formula, Ar ₁ , Ar ₂ , Ar ₃ and Ar ₄ are each an aryl group, an alkaryl group or an aralkyl group, Y is a direct bond or a divalent organic group, and n is zero or 1 Is. And a carbazolehydrazone-based transport agent, especially the general formula (4)

[0046]

Embedded image In the formula, each Ar ₅ may be the same or different,
It is an alkaryl group or an aralkyl group. The transport agent represented by is preferable because it has good solubility and hole transportability.

In the monodisperse type photosensitive material used in the present invention, the charge generating agent (CGM) is preferably contained in the photosensitive layer in an amount of 1 to 7% by weight, particularly 2 to 5% by weight, based on the solid content. , And the charge transfer agent (CTM) is 20 per solid content.
It is preferable that it is contained in the photosensitive layer in an amount of from 70 to 70% by weight, particularly from 25 to 60% by weight.

Further, from the viewpoint of sensitivity and a wide range of applications to enable reversal development, it is preferable to use an electron transporting agent (ET) and a hole transporting agent (HT) in combination. In this case, the weight ratio of ET: HT is 10: 1 to 1:10,
In particular, the range of 1: 5 to 1: 1 is the best.

The composition for forming a photoreceptor used in the present invention includes:
Various additives known per se, such as antioxidants, radical scavengers, singlet quenchers, UV absorbers, softeners, surface modifiers, defoaming, as long as they do not adversely affect the electrophotographic properties. Agents, extenders, thickeners, dispersion stabilizers, waxes, acceptors, donors, and the like.

When a sterically hindered phenolic antioxidant of 0.1 to 50% by weight based on the total solid content is blended,
The durability of the photosensitive layer can be significantly improved without adversely affecting the electrophotographic characteristics.

As the conductive drum on which the photosensitive layer is provided, a raw tube made of pure aluminum or aluminum alloy is used, and this drum may be anodized so as to have a film thickness of 1 to 50 μm.

In order to form a monodispersed layer type photoreceptor, a charge generation material, a charge transporting agent and a binder resin are mixed with a conventionally known method, for example, a roll mill, a ball mill, an attritor, and the like.
It may be prepared using a paint shaker, an ultrasonic disperser, or the like, coated by a conventionally known coating means, and dried. The thickness of the photosensitive layer is not particularly limited.
It is desirable that the thickness be in the range of 40 to 40 μm, particularly 20 to 35 μm.

As the solvent used for forming the coating liquid, various organic solvents can be used, and alcohols such as methanol, ethanol, isopropanol and butanol,
n-hexane, octane, aliphatic hydrocarbons such as cyclohexane, benzene, toluene, aromatic hydrocarbons such as xylene, dichloromethane, dichloroethane, carbon tetrachloride, halogenated hydrocarbons such as chlorobenzene, dimethyl ether, diethyl ether, tetrahydrofuran, Various solvents such as ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; ketones such as acetone, methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate and methyl acetate; dimethylformamide and dimethyl sulfoxide; Used as a mixture. In general, the solid content of the coating solution is preferably 5 to 50%.

[Charging] The charging means 2 used in the present invention is a scorotron charger, and as shown in FIG. 2, it is arranged in a pair of shields 5 facing each other and an opening on the side of the photosensitive drum 1. It is composed of a grid 6 and a corona wire (discharge member) 7. The shield 5 is housed in a housing 8 made of resin, for example, and a hole 4 communicating with the inside of the charger 2 is formed below the housing 8.

As already pointed out, the charging means 2 is shown in FIG.
As shown in FIG. 3, the photosensitive drum 1 is provided even in a compact device by providing the ventilation opening 4 in the range A defined by the line a and the line b and at a specific portion of the charging means. Is significantly reduced from being affected by ozone and NOx, and even in the case of cleaning-less image formation,
Toner adhesion to the corona wire 7 and the grid 6 is effectively prevented.

Regarding the size of the hole 4 provided in the charging means 2, it is good that the hole 4 is provided over the entire length of the charging means 2 in terms of breathability, and the opening width is between the maximum shields 5 and 5. Width (W), but at least 1 of W
It is preferable that the width is / 5 times or more.

As shown in FIG. 3A, the discharge member 7 is electrically insulated from the shield 5 and the housing and is connected to the high voltage power source 9. The grid member 6 is electrically insulated from the housing together with the shield 5, and is grounded via a Zener diode (constant potential diode) or a varistor 10. Further, FIG.
As shown in (B), the grid member 6 and the shield 5 are provided as independent zener diodes or varistor 10 respectively.
And 10 'can also be grounded.

In the scorotron charger, the current (I _cc ) flowing into the discharge member 7 is the effective charging current (I _pc ) into the photosensitive member 1, the current (I _sc ) into the shield 5, and the current flowing into the grid 6. It is represented by the sum total of the currents (I _Gc ), that is, the formula (I) I _CC = I _PC + I _SC + I _GC . The current flowing into the discharge member in the ordinary corotron charger is the discharge current ( _IGc ) to the grid member 6 in the above formula (I).

In the scorotron charger used in the present invention, the electric field E ₁ between the wire 7 and the grid 6 is set to be larger than the electric field E ₂ between the wire 7 and the shield 5. When the voltage of the wire is V _W , the voltage of the grid is V _G , the voltage of the shield is V _S , the distance between the wire and the grid is y, and the distance between the wire and the shield is x, the electric field E
₁ becomes the following formula (II) E ₁ = | V _W −V _G | / y (II), while the electric field E ₂ becomes the following formula (III) E ₂ = | V _W −V _S | / x It becomes (III). Now, as shown in FIG. 3A, if V _G = V _S , then E ₁ / E ₂ = x / y, and it is possible to satisfy the above condition by making y smaller than x. Understood. In the present invention, it is preferable that the range is 4 ≧ E ₁ / E ₂ > 1, particularly 2 ≧ E ₁ / E ₂ ≧ 1.2.
Further, as shown in FIG. 3B, the zener diode 10 of the grid 6 and the zener diode 10 'of the shield 5 have different constant potentials, and V _S > V _G , so that E ₁ > E ₂ It is also possible to satisfy the conditions.

In FIG. 4 showing a specific example (an embodiment described later) of setting the electric field E ₁ between the wire and the grid and the electric field E ₂ between the wire and the shield, the distance (y) between the wire and the grid is 2.5 mm. It can be understood that the distance (x) between the wire and the shield is set to 3.65 mm, and thus the electric field strength ratio (E ₁ / E ₂ ) is 1.462. In this specific example, the closest distance between the grid and the surface of the photosensitive drum is set to 1.4 mm.

In the present invention, the scorotron charger is arranged so that the width of the opening of 0.5 to 3 mm from the surface of the photosensitive drum on the photosensitive drum side is 10 to 30% of the circumference of the photosensitive drum. However, it is preferable for preventing image defects due to leak. The reason why image defects due to leakage in the single-layer photoconductor are prevented by this is as follows.

That is, in the single-layer organic photoconductor, the charge generating agent is exposed on the surface, and in the small diameter drum having a diameter of 20 mm or less, the charging portion is concentrated in a very narrow area in the circumferential direction of the drum due to the large curvature. Although a large current flows as a cause of the leak, in the combination of the small diameter drum and the scorotron charger of the specific opening width used in the present invention, the control grid potential becomes a constant potential, and the surface of the charged portion of the photosensitive layer When the electric potential approaches this, the discharge current (Ip
c) becomes small, which seems to suppress the occurrence of leak.

Surface potential of single-layer photoconductor small-diameter drum (Sp)
Is effective to form a high-density and high-contrast image while preventing leakage, while maintaining the grid potential at 600 to 1300 volts while preventing leakage. Especially 70
Suitably, it is maintained in the range of 0 to 1100 volts.

Further, the decrease in surface potential (ΔSp) of the single-layer photoconductor during repetition was 100K sheets (1K = 1000).
Later, the corotron charger reached the order of 100V, and the shield earth type scorotron charger reached the order of 60V, and the image density reduction due to this was remarkable, but if the shield was maintained at a high potential as shown in FIG. It becomes possible to suppress.

The charging potential on the surface of the photosensitive member and the potential on the grid should be in the above-mentioned ranges, but for this purpose, it is preferable to apply a voltage of plus 3 KV to 7 KV to the scorotron charger.

Maintaining the shield with a high electric resistance is also effective in preventing image defects due to leakage,
At least the surface of the shield may be formed of a high electric resistance resin such as an olefin resin, a fluororesin, a vinyl chloride resin, an epoxy resin, a silicone resin or the like. As the Zener diode or varistor, one that can maintain the grid or the like at a predetermined potential is used.

In the Zener diode or varistor, almost no current flows in these elements up to a certain voltage, and when the voltage exceeds this certain voltage, the current suddenly starts to flow, which causes the control grid and shield of the charger to pass. with an effect of holding a constant set voltage, the discharge current (I _GC) and further discharging current to the shield (I _sc) of the control grid can be reduced.

Of course, a separate power supply may be provided instead of the Zener diode or varistor to apply a predetermined voltage.

As the grid, a parallel line grid or a grid grid having an opening area ratio of about 70 to 98% is used.

[Exposure] In the image exposure means 20 of the present invention,
It is also possible to perform exposure on the photoconductor after the main charging through a known laser beam or exposure device using a light emitting diode (LED) array. As the exposure light source 21,
A monochromatic light source such as an LED for red, yellow, green or the like may be used, or a laser light source such as a semiconductor laser light may be used.

[0071] bright portion exposure at this time (I _B) is an amount such as the residual potential in a bright portion (E _R) is a potential lower than the bias potential (E _B), the more preferred, The residual potential (E _R ) in the bright portion is expressed by the formula (II) E _R = E _B −nED ₀ ... (II) In the formula, E _B is the developing bias potential, and E _D0 is the relationship between the photoconductor and the developer. With respect to the development sensitivity characteristics of the combination, it is preferable to set the exposure amount so as to satisfy a potential at which the fog density is substantially zero and n is a number of 0.4 to 2.5.

[Development] The developing means 30 used in the present invention is
As shown in FIG. 2, the developing device for a one-component non-magnetic toner includes an elastic developing roller 32 for applying a non-magnetic one-component toner to a photoconductor inside a developing container 31. A sub roller 33 for supplying toner and an agitator 34 for stirring and charging the toner are stored. An opening 3 is provided on the side of the developing container close to the photoconductor.
5, the developing roller 32 is located in the opening 35, and the sub roller 33 is provided in the vicinity of the developing roller 32.

A toner cartridge 37 having a slit-like opening 36 at the lower end is provided at the upper part of the developing container 31, and a toner supply roller 38 is provided at the opening 36. Further, a blade 39 for controlling the toner layer to a constant thickness and additionally charging the toner is provided on the toner layer sending side of the elastic developing roller 32.

The one-component toner 40 contained in the toner cartridge 37 is transferred by the toner supply roller 38.
The fixed amount is supplied into the developing container 31 and is stirred and charged by the agitator 34. The charged toner is applied on the sub-roller 33 and then on the elastic developing roller 32. The thickness of the toner layer on the developing roller 32 is controlled by a blade 39 so as to have a constant layer thickness, and the toner on the developing roller 32 is strongly charged by rubbing with the blade.

The developing roller 32 is a conductive elastic roller, and the photosensitive drum 1 and the developing roller 32 holding the one-component toner are brought into contact with each other to form an image by reversal development. This reversal development is performed so that the charging polarity of the toner is the same as the charging polarity of the dark portion (unexposed portion) of the photoconductor, and the residual toner amount in the dark portion of the photoconductor becomes substantially zero. As a result, the reversal development is effectively performed by the same repulsive action of the toner and the dark area of the photoconductor and the suction action of the charge and the toner induced to the light area of the photoconductor, and the cleaning of the dark area of the photoconductor is also effective at the time of development. Done in It is desirable to apply a bias voltage slightly higher than the bias voltage applied to the developing roller 32 so that the toner can be smoothly transferred from the sub roller 33 to the developing roller 32.

In the present invention, the non-magnetic one-component toner can be obtained by, for example, a pulverizing method, a spray drying method or a polymerization method. This toner contains a fixing resin component, a colorant, a high-molecular weight or low-molecular weight charge control agent, a release agent and the like as a composition, and preferably has a median diameter of 3 to 20 μm, particularly 5 to 12 μm and D25 / D75
The particle size is represented by monodisperse particles having a dispersity of 1.50 or less, particularly 1.40 or less, or particles close to this. still,
In the present specification, D25 and D75 represent particle diameters corresponding to 25% and 75% of the total volume of toner particles.

The polymerization toner will be specifically described below. The polymerization method spherical toner is obtained by suspension-polymerizing a toner-forming composition containing at least a radical polymerization initiator, a vinyl-based monomer that can be a fixing resin, and a colorant in an aqueous medium.

The vinyl-based monomer capable of forming the fixing resin is water-insoluble and is capable of forming a thermoplastic resin having a fixing property and an electroscopic property. For example, a suitable example thereof is It is not limited to, but is a vinyl aromatic monomer, an acrylic monomer, a vinyl ester monomer, a vinyl ether monomer, a diolefin monomer, a monoolefin monomer, or the like.

As the vinyl aromatic monomer, the following formula (5) is used.

Embedded image In the formula, R ₉ is a hydrogen atom, a lower alkyl group or a halogen atom, and R ₁₀ is a hydrogen atom, a lower alkyl group, a halogen atom, an alkoxy group, a nitro group or a vinyl group. Vinyl aromatic hydrocarbons such as styrene, α-methylstyrene, vinyltoluene, α-chlorostyrene,
Examples thereof include o-, m-, p-chlorostyrene, p-ethylstyrene and divinylbenzene, which may be used alone or in combination of two or more.

The acrylic monomer is represented by the following formula (6)

[Chemical 6] In the formula, R ₁₁ is a hydrogen atom or a lower alkyl group, R ₁₂ is a hydrogen atom, a hydrocarbon group having up to 12 carbon atoms, a hydroxyalkyl group, or a vinyl ester group, an acrylic monomer such as methyl acrylate. , Ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, hexyl methacrylate, methacrylic acid-2
-Ethylhexyl, ethyl β-hydroxyacrylate,
γ-Hydroxy acrylate, δ-hydroxy butyl acrylate, β-hydroxy methacrylate,
Examples thereof include ethylene glycol dimethacrylic acid ester and tetraethylene glycol dimethacrylic acid ester.

Other monomers include vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, etc .: vinyl ethers such as vinyl-n-butyl ether, vinyl phenyl ether, vinyl cyclohexyl ether, etc .: diolefins, especially butadiene. , Isoprene, chloroprene and the like: monoolefins, particularly ethylene, propylene, isobutylene, butene-1, pentene-1, 4-methylpentene-1 and the like. Suitable monomers are styrene monomers, acrylic monomers, styrene-acrylic monomers and the like.

Inorganic or organic pigments or dyes are used as the colorant for the toner, and suitable examples are as follows. The colorant is preferably used in an amount of 3 to 20% by weight based on the resin in the toner. Black pigment carbon black, acetylene black, lamp black, aniline black. Yellow pigment Yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, hanzer yellow G,
Hansar Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Rake, Permanent Yellow NCG, Tartrazine Lake. Orange pigment Red lead yellow molybdenum, molybdenum orange, permanent orange GTR, pyrazolo orange, vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK. Red pigment Bengala, cadmium red, lead red, cadmium mercury sulfide, permanent red 4R, lithol red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B. Purple pigment Manganese purple, fast violet B, methyl violet lake. Blue pigment Navy blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, fast sky blue, indanthrene blue B
C. Green pigment chrome green, chromium oxide, pigment green B,
Malachite Green Lake, Fanal Yellow Green G. White pigment Zinc white, titanium oxide, antimony white, zinc sulfide. Extender barite powder, barium carbonate, clay, silica, white carbon, talc, alumina white.

As the radical polymerization initiator, known radical polymerization initiators such as azo compound type, hydroperoxide type, peroxide type, peracid type initiator and redox type initiator are used. Suitable examples of initiators include, but are not limited to: 2,2'-Azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2-cyclopropylpropionitrile), 2,2'-azobis (4-
Methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis (1-cyclohexanecarbonitrile), benzoyl peroxide, (1-phenylethyl) azodiphenylmethane.

In the toner-forming composition for forming the spherical toner, a toner auxiliary agent known per se can be incorporated.
Examples of the toner auxiliary agent include a charge control agent and a release agent.

As the release agent, polypropylene wax, polyethylene wax, acid modified products of these, etc. are used, and these can be contained in the toner forming composition in the emulsion particle size.

As the charge control agent, those known per se, for example, oil-soluble dyes such as nigrosine base (CI 5045), oil black (CI 26150) and spiron black,
In addition to a naphthenic acid metal salt, a fatty acid metal soap, a metal-containing complex salt dye or the like, a water-soluble monomer having a charge controllable functional group and copolymerizable with the vinyl monomer can be used. Such monomers include sulfonic acid, phosphoric acid, carboxylic acid type anionic groups, or cationic groups such as primary-, secondary- or tertiary-amino groups and quaternary animonium groups. Radical polymerizable monomers having an electrolytic group of,
A suitable example is as follows.

Styrene sulfonic acid, sodium styrene sulfonate, 2-acrylamido 2-methylpropane sulfonic acid, 2-acid phosphooxypropyl methacrylate, 2-acid phosphooxyethyl methacrylate, 3-chloro 2-acid phosphooxypropyl methacrylate, acrylic Acid, methacrylic acid, fumaric acid, crotonic acid, tetrahydroterephthalic acid, itaconic acid, aminostyrene, aminoethyl methacrylate, aminopropyl acrylate, diethylaminopropyl acrylate, γ-N- (N ′, N′-diethylaminoethyl) aminopropyl methacrylate , Trimethylammonium propyl methacrylate.

Further, electrolysis of the above-mentioned sulfonic acid, phosphoric acid, carboxylic acid type anionic groups, or cationic groups such as primary-, secondary- or tertiary-amino groups and quaternary animonium groups. It is also possible to introduce a charge control group at the polymer terminal by using a radical initiator having a polymerizable group.

In the production of the toner by the polymerization method, the toner-forming composition containing a vinyl monomer or the like is suspended in water. In this case, the concentration of the composition is generally 1 to 50.
%, Especially 5 to 30% by weight is suitable, the size of the suspended particles is generally 3 to 20 .mu.m, especially 5 to 12 .mu.m.
It is suitable to adjust to m.

A dispersion stabilizer may be used, if necessary, in order to stabilize the suspension state of the toner-forming composition. Examples of such dispersion stabilizers include polymers soluble in a medium such as polyvinyl alcohol, methyl cellulose, ethyl cellulose, polyacrylic acid, polyacrylamide, polyethylene oxide, poly (hydroxystearic acid-g-methyl methacrylate-CO. -Methacrylic acid) copolymer, nonionic or ionic surfactant, inorganic powder such as calcium phosphate, etc. are appropriately used. The dispersion stabilizer is preferably added to the system in an amount of 0.1 to 10% by weight, particularly 0.5 to 5% by weight.

The amount of the initiator in the toner forming composition is preferably 0.3 to 30% by weight, particularly 0.5 to 10% by weight, based on the amount of the monomer.

At the time of polymerization, the reaction system is replaced with an inert gas such as nitrogen, and the polymerization is carried out at a temperature of 40 to 100 ° C., particularly 50 to 90 ° C. while maintaining the above-mentioned suspension state. Of course, mild agitation may be performed to homogenize the reaction system. Since the polymerization product after the reaction is obtained in the form of granules having the above-mentioned particle size range, the produced particles are filtered, washed with water or a suitable solvent if necessary, and dried to obtain toner particles.

If necessary, the toner particles are sprinkled with a fluidity-improving agent such as carbon black, hydrophobic fine amorphous silica, hydrophobic fine alumina, fine titanium oxide or the like to obtain a final toner. The fluidity improver is preferably used in an amount of 0.1 to 2% by weight per toner.

In order to improve the fluidity, heat resistance and offset resistance of the polymerized toner, the resin in the toner has a maximum molecular weight of 50,000 to 500,000 and a maximum value of the high molecular weight component, and a low molecular weight of 1,000 to 50,000. It is preferable to have a gel permeation chromatogram (GPC) having the maximum value of the component. The molecular weight can be adjusted by seeding polymerization or the like.

As the elastic developing roller 32, a roller obtained by molding a composition in which an electrically conductive powder is mixed with an elastomer polymer is used.

The surface resistance of this elastic developing roller is generally 10 ^{5 to} 10 ¹² Ω · cm, especially 10 ^{7 to} 10 ¹⁰ Ω.
The range is preferably in the range of cm. If the range is higher than the above range, it is difficult to apply the bias voltage.

The surface hardness (Rockwell JIS A) of the elastic developing roller is 30 to 70, especially 40 to 6.
It is preferably in the range of 0, and when it is higher than the above range, it tends to be difficult to uniformly contact the toner layer on the surface of the photoreceptor or the abrasion of the photoreceptor tends to occur. If it is lower than the above range, it becomes difficult to transmit a sufficient pressure contact force, or the developing roller is liable to be worn.

Examples of the elastomer polymer include nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), polybutadiene (BR), polyisoprene (IIB), butyl rubber, natural rubber, ethylene- Propylene rubber (EP
R), ethylene-propylene-diene rubber (EPD)
M), polyurethane, silicone rubber, fluorine rubber, chlorinated polyethylene, chlorinated polypropylene, soft vinyl chloride resin and the like can be used. In order to adjust the surface hardness, a foam (sponge) can be used, or a plasticizer or a softener can be blended.

As the conductive powder, conductive carbon black, tin oxide doped with indium, antimony or the like, metal powder such as copper, silver or aluminum can be used, but conductive carbon black is preferable. The content of the conductive powder may be such that the electric resistance and hardness of the roller are within the ranges described above.

In forming the conductive rubber roller,
A compounding agent known per se, for example, a sulfur or organic vulcanizing agent, a vulcanization accelerator, a softening agent, an antioxidant, a filler, a dispersant, a plasticizer, a foaming agent, etc. Can be blended. The molded rubber roller is heated to be vulcanized or vulcanized and foamed to obtain an elastic developing roller having a predetermined hardness.

The present invention can be advantageously applied to an organic photoconductor drum having a relatively small diameter, for example, an organic photoconductor having an outer diameter (D _p ) of 10 to 20 mm. A roller having D _d ) of 6.5 to 20 mm, particularly 7.0 to 16 mm is used, and the ratio of the diameter of the elastic developing roller to the diameter of the organic photosensitive drum (D _d / D _p ).
Is preferably in the range of 65 to 100%.

If the diameter of the elastic developing roller is smaller than the above range, the problem of toner scattering tends to occur. On the other hand, if it is larger than the above range, the area of the developing section becomes too large, which is not preferable.

At the time of development, the elastic roller is used in an amount of 0.05 to 1 kg / dm, particularly 0.08 to 0.
The pressure roller is brought into pressure contact with a linear pressure of 5 kg / dm, and the peripheral speed of the elastic roller is 1.
The peripheral speed is preferably 2 to 3 times, particularly 1.5 to 2.5 times.

When the pressure contact force is lower than the above range or when the peripheral speed of the elastic developing roller is lower than the above range,
It is difficult to sufficiently improve the image density, and there is a tendency that cleaning in the dark portion of the photoconductor cannot be performed sufficiently. On the other hand, when the pressure contact force is higher than the above range or the peripheral speed of the elastic developing roller Is larger than the above range, the amount of abrasion of the photoconductor increases, and the life of the photoconductor tends to be shortened.

The elastic roller has the same polarity as the charging potential of the toner and the photosensitive member potential (dark portion potential) of 0.2 to 0.
It is preferable to apply a bias potential of 8 times, especially 0.3 to 0.7 times. If the bias potential is lower than the above range, a sufficient image density cannot be obtained. The toner cleaning of the dark portion of the photoreceptor is not performed sufficiently, and fogging occurs. Also, the supply of toner is insufficient, and the image density tends to decrease.

In the developing device shown in FIG. 2, it has already been pointed out that a bias voltage is applied to the sub roller, but the bias voltage applied to the sub roller has the same polarity as the bias voltage applied to the elastic developing roller, and It is preferable that the voltage is higher by about 0 to 200 V in order to smoothly transfer the toner from the sub roller to the elastic developing roller.

The thickness of the toner layer on the elastic developing roller is
Although regulated by a blade, it is generally preferable to form about two times the toner particle size, that is, to form about two toner layers.

[Toner Transfer] In the present invention, a conductive elastic roller is used as the transfer means 45, and the photosensitive drum 1 and the transfer roller 45 are larger than the thickness of the transfer material 47 and transfer the toner. Toner transfer is performed by arranging them so as to be separated from each other by a small distance that allows transfer to the material 47.

As the conductive elastic body, those described for the developing roller are generally used, but the rubber hardness is 5
A roller formed from a conductive polyurethane rubber composition having a rubber hardness of preferably 70 °, which is cured so as to exceed 0 ° (JIS A), is used. Thereby, occurrence of image defects such as white spots is prevented, and a good and stable transfer image can be formed over a long period of time.

Polyurethane rubber comprises a soft segment based on polyester or polyether in the polymer chain,
It exhibits rubbery elasticity due to the presence of a hard segment based on an aromatic chain linked through a urethane or urea bond.

Polyurethane rubber used for the elastic transfer roller is obtained by reacting a polyurethane prepolymer (isocyanate terminated polymer) obtained by reacting a polyol (hydroxyl group terminated polymer) with a polyisocyanate compound with a chain extender (crosslinking agent). Can be obtained. At this time, a desired rubber hardness can be obtained by adjusting the reaction between the isocyanate-terminated prepolymer and the chain extender. For example, by adjusting the temperature and / or the reaction time of the chain extension (crosslinking) reaction, a polyurethane having a desired hardness can be obtained. In general, it indicates that rubber hardness increases with increasing temperature and reaction time.

That is, the free isocyanate group in the prepolymer increases the molecular weight of the polyurethane by reacting with a chain extender (crosslinking agent) to form a urea bond, and reacts with an already existing urethane bond or urea bond. To generate an allophanate bond or burette bond, and to increase the rubber hardness by forming a three-dimensional crosslinked structure, the desired effect of the present invention can be obtained, as well as abrasion resistance, heat resistance, durability And so on.

The polyol used for forming the prepolymer includes polyols having 2 or more, preferably 2 to 3 active hydrogens in one molecule, such as polyether polyols, polyester polyols, polyacryl polyols and polyvinyl polyols. One kind or two or more kinds are used. A polyester polyol is preferable in terms of electrical characteristics and durability, and a known polyester polyol used in production of a polyester polyurethane is applied.

Among them, a preferable polyester polyol is composed of a diol and a dicarboxylic acid, and is a polyester polyol obtained by appropriately reacting at least one kind of an aliphatic diol and at least one kind of an aliphatic carboxylic acid. The polyester polyol may contain a polyester component obtained by ring-opening polymerization such as polycaprolactam.

Examples of the aliphatic diol component include:
1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, , 10-decanediol, neopentyl glycol, ethylene glycol, diethylene glycol, polyethylene glycol,
Dipropylene glycol, polypropylene glycol,
1,4-cyclohexanemethanol, 1,4-cyclohexanediol, 3-methyl-1,5-pentanediol, and the like are preferably used.

Examples of the aliphatic carboxylic acid include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, speric acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid. Acids and 1,4-cyclohexanedicarboxylic acid are preferably used.

The number average molecular weight of the hydroxyl-terminated polymer is 30
It is desirably in the range of 0 to 10000, particularly 1000 to 8000.

As the polyisocyanate compound, a known polyisocyanate compound used for producing polyurethane is applied. Of these, it is preferable to use diisocyanate. For example, tolylene diisocyanate, 4,4
-Diphenylmethane diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, paraphenylene diisocyanate, tetramethyl xylene diisocyanate, hexamethylene diisocyanate, dicyclohexyl methane diisocyanate, isophorone diisocyanate, tolidine diisocyanate and the like are applied. In particular, 4,4-diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate and the like are preferred.

In the production of the prepolymer, one or more polyols and one or more polyisocyanate compounds are used, and the NCO / OH ratio is 1.1 to 4.
And more preferably in the range of 1.3 to 2.5, and reacted under heating at 60 to 130 ° C. for several hours to produce a polyurethane prepolymer.

As the chain extender (crosslinking agent), polyfunctional active hydrogen-containing compounds, particularly low molecular weight polyols and low molecular weight polyamines, especially aliphatic or aromatic polyamines can be used. Suitable chain extenders (crosslinking agents) are aliphatic diol components such as 1,2-propanediol, 1,3-propanediol, 1,3-
Butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-
Octanediol, 1,10-decanediol, neopentyl glycol, ethylene glycol, diethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanemethanol, 1,4-cyclohexanediol,
3-methyl-1,5-pentanediol and the like.

As the aliphatic diamine component, for example,
1,2-propanediamine, 1,3-propanediamine, 1,3-butanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,8-octanediamine, , 10-decanediamine, neopentyldiamine, ethylenediamine,
1,4-cyclohexanediamine, 3-methyl-1,5
-Pentanediamine and the like are preferably used.

On the other hand, examples of aromatic polyamines include tolylenediamine, 4,4-diphenylmethanediamine, xylylenediamine, naphthylenediamine, paraphenylenediamine, tetramethylxylenediamine, dicyclohexylmethanediamine, isophoronediamine and tolidinediamine. Can be mentioned.

The chain extension (crosslinking) reaction is generally carried out at 100 ° C.
The reaction temperature and the temperature at which the polyurethane having the desired hardness is obtained are selected from the temperatures of 300 to 300 ° C. and the reaction time of 0.5 to 5 hours.

As the transfer roller, a roller obtained by molding a composition in which polyurethane is mixed with conductive powder is used. By blending the conductive powder with the composition of the prepolymer and the chain extender (crosslinking agent) prior to crosslinking, uniform and uniform blending and dispersion can be achieved. The volume resistance of this conductive rubber is generally 10 ^{7 to} 10 ¹⁴ Ω · cm.
, Particularly in the range of 10 ^{8 to} 10 ¹² Ω · cm.

As the conductive powder, those described for the conductive elastic developing roller are used, and the compounding amount thereof is determined so that the above-mentioned electric resistance and hardness can be obtained.

At the time of transferring the toner, a DC voltage having a polarity opposite to the main charging polarity of the photoconductor is applied to the transfer roller. Even if this DC voltage is lower than the charging start voltage of the photoconductor,
Although it may be higher than the charging start voltage of the photoconductor, the latter transfer method is desirable in terms of transfer efficiency. The charging start voltage (V _TH ) of the photoreceptor by the transfer roller varies depending on the type of the photoreceptor, but in the case of the monodispersed layer type organic photoreceptor suitably used in the present invention, it is approximately 0.3 to 2 kV. In the range. A preferable applied voltage in terms of toner transfer efficiency is
1.5 times or more, especially 2 times, the charging start voltage (V _TH ) of the photoconductor
More than double.

On the other hand, the upper limit of the voltage applied to the transfer roller is determined by the surface potential of the photosensitive layer after static elimination (residual potential before main charging). That is, the applied voltage should be set so that the absolute value of the residual potential before main charging is 50 V or less, preferably 20 V or less.

[Removal of foreign matter] In the present invention, since the developing means 30 also serves to clean the residual toner on the photoconductor, a so-called cleaning mechanism is not provided, and the toner remaining on the photoconductor is reused for the development. It However, since the photosensitive drum contacts a transfer material such as paper,
Foreign matter such as paper dust tends to adhere to the photoreceptor surface, and it is necessary to provide foreign matter removing means 50 to remove the foreign matter.

As the foreign matter removing means 50, a fur brush is used, and at least a part of the brush fibers is made of a conductive material such as metal, so that the photoconductor can be discharged at the same time.

In the present invention, the toner fixing operation can be carried out by a means known per se under the conditions known per se.

[Image Forming Unit] In the present invention, as shown in FIG. 5, the photoconductor drum 1 and the charging means 2 or the foreign matter removing means 50 may be attached to the frame 70 to form the photoconductor unit 78. This is advantageous in omitting the operation of exchanging the photoconductor and adjusting the positions of the photoconductor and each means in the field. The frame 70 has a side opening 71 that allows the photosensitive drum 1 and the developing means 32 to come into contact with each other.
And an upper surface opening 72 that allows the transfer means 45 to approach the photosensitive drum 1. Further, there may be provided a means 73 for discharging foreign matter such as paper dust removed by the foreign matter removing means 50 (see FIG. 2).

On the other hand, the developing means 32 is supported by the second frame 74 which also serves as a toner container and is supported by the developing unit 79.
Is composed. The first frame 70 and the second frame 74 are detachably provided in the image forming apparatus such that at least one of the first frame 70 and the second frame 74 can swing by a common fulcrum 75. The photosensitive drum and the developing means are engaged by the mechanical engaging means 76.

[0133]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the following examples. (Production of Organic Photoreceptor Drum of Single Layer Dispersion Type) Component: Metal-Free Phthalocyanine (Charge Generating Material) 5 parts by weight N, N′-bis (O, P-dimethylphenyl) N, N′-diphenylbenzidine ( Hole transport material) 40 parts by weight 3,3 ′, 5,5′-tetraphenyldiphenoquinone (electron transport material) 40 parts by weight polycarbonate (binder resin) 100 parts by weight dichloromethane (solvent) 800 parts by weight After mixing and dispersing with a ball mill, the prepared coating solution is applied onto an aluminum tube having a diameter of 16 mm and 10 mm by dip coating, and then dried with hot air at 60 ° C. for 60 minutes to obtain a single layer dispersion type organic photoreceptor having a film thickness of 30 μm. Obtained.

A copying machine LDC-650 manufactured by Mita Kogyo was modified for this experiment. That is, as shown in FIG. 6, scorotron chargers having grids (dimensions shown in FIG. 4) are arranged at different positions (Examples 1 to 3 and Comparative Examples 1 to 1).
4). Although not shown in FIG. 4, the developing roller pressure contact type non-magnetic one-component toner developing device and the non-contact type transfer roller (photosensitive drum and And a foreign matter removing brush for collecting foreign matter on the photosensitive drum. Also,
Examples 1 to 3 and Comparative Example 4 as scorotron chargers
In the case of Comparative Example 1
No. 3 had no holes.

Using the above-mentioned apparatus, 500 images were continuously formed at a peripheral speed of the photosensitive drum of 56 mm / sec, 500 images were continuously formed after a pause of 60 minutes, and a total of 1000 images were formed. A sample image of Last one
The 000th image was visually evaluated. The results are as follows.

In Examples 1 to 3, good images were obtained for each drum. In Comparative Example 1, black streaks extending in the direction corresponding to the drum circumferential direction were generated.
This is probably due to poor charging. In Comparative Example 2,
Black streaks similar to those observed in Comparative Example 1 were generated, and local background fog was generated at the portion corresponding to the drum axis direction. This background fog is ozone and NO
It is thought that this is caused by the local oxidation of the surface of the photoreceptor due to x. In Comparative Example 3, the same background fog as that observed in Comparative Example 2 was observed. In Comparative Example 4, black streaks and background fog were observed as in Comparative Example 2.

[0137]

According to the present invention, since the main charger is arranged below the photoconductor, it is possible to avoid the influence of discharge products (having a larger specific gravity than air) such as ozone and NOx on the photoconductor surface. At the same time, by providing a hole on the opposite side of the charging opening and providing an air flow path that passes through the inside of the charger, the discharge products can be swiftly discharged downward, and by this flow path,
It is also possible to prevent the toner that is scattered from flowing out from the hole and to prevent the toner from adhering to the corona wire or the like.

When the main charger is provided on the lower side of the photoconductor, the transfer means is located on the upper side of the photoconductor in the small-diameter drum, but in the present invention, the transfer means is not corona charge but roller charge. As a result, the corona discharge on the upper side of the photoconductor can be avoided, and the influence of the discharge products can be more surely eliminated.

The transfer by roller charging also uses the non-contact type roller and the back surface transfer, so that the contact between the toner-supporting photosensitive member and the transfer roller is blocked by the paper, and the transfer roller does not transfer the toner even when the transfer is not performed. Since it is separated from the supporting photoconductor, the transfer roller is prevented from being soiled, and thus the rear surface of the transfer paper is prevented from being soiled. This is an important effect for double-sided printing of paper.

By using the non-contact roller, the transfer paper is not pressed against the photoconductor, preventing the characters from falling out.
The image quality is significantly improved.

By providing the transfer means on the upper side of the photoconductor, the conveying path between the paper feeding means and the printed matter discharging means placed on the upper part of the apparatus can be minimized, and the apparatus can be made extremely compact. It becomes possible.

The photoconductor drum and the charging unit are attached to the first frame to form a photoconductor unit, and the developing unit is attached to the second frame which also serves as a toner container to form a developer unit. By providing a common fulcrum and elastic engaging means in each, the developing means and the photoconductor drum are surely engaged with each other, and the structure of the image forming unit is simplified, so that the image forming unit can be easily removed and attached. Can also be done very easily.

The present invention is particularly effective when the positively chargeable organic photoconductor is a single layer dispersion type organic photoconductor. That is, by using the positive charging type organic photoconductor, it is possible to use the positive corona, and it is possible to reduce the generation of ozone as compared with the case of using the negative corona. On the other hand, in organic photoreceptors, particularly in single-layer dispersion type organic photoreceptors, the effect of exposure to discharge products is greater than that of inorganic photoreceptors. The effects of the product are considerably reduced.

The electric field E ₁ between the wire and the grid in the scorotron charger is equal to the electric field E ₂ between the wire and the shield.
The charging efficiency of the photoconductor is improved because it is set larger than the above. That is, the inflow current (Icc) into the charging wire is smaller than that in the case of E ₁ <E ₂ , and as a result, the amount of discharge products is reduced. Furthermore, at the time of charging, fresh air flows in from the shield vent hole side, and replacement with fresh air in the charger is performed quickly.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining a positional relationship between a photosensitive drum and a charging unit.

FIG. 2 is an overall layout diagram of an example of an image forming apparatus of the present invention.

FIG. 3 is a connection diagram showing an example of electrical connection of a charger.

FIG. 4 is an explanatory diagram showing various dimensions of a charger.

FIG. 5 is a layout view showing an example of an image forming unit used in the present invention.

FIG. 6 is a view showing the arrangement of scorotron chargers in Examples 1 to 3 and Comparative Examples 1 to 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging means 3 Charging opening 4 Hole 5 Shield 6 Grid 7 Corona wire 8 Housing 9 High voltage power supply 10 Zener diode or varistor 20 Image exposure means 21 Light source 30 Developing means 31 Developing container 32 Elastic developing roller 33 Sub roller 34 Agitator 35 Opening 36 Slit-like Opening 37 Toner Cartridge 38 Toner Supply Roller 39 Blade 40 One-Component Toner 45 Toner Transfer Means 50 Foreign Material Removing Means 60 Fixing Means 61 Supporting Rollers 62 Heating Rollers

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromitsu Ogawa 1-22 Tamagaku, Chuo-ku, Osaka Mita Engineering Co., Ltd.

Claims (5)

[Claims] 1. An image forming apparatus for forming an image by charging, exposing, developing and transferring a photosensitive drum, wherein the developing means also serves to clean residual toner on the photosensitive drum. Means for locating the scorotron charger within ± 45 ° of the vertical line from the center of the photosensitive drum to the bottom and providing a hole on the opposite side of the charging opening. An electric field E ₁ between the wires and the shield is set to be larger than an electric field E ₂ between the wire and the shield. 2. The image forming apparatus according to claim 1, wherein the photoconductor is a positive charging type single layer organic photoconductor. 3. The image forming apparatus according to claim 1, wherein the developing unit is a reversal developing unit using a one-component toner. 4. The transfer device is a device for transferring a toner image on a transfer paper surface downward by using a roller not in contact with a photosensitive drum having a toner image. Image forming device. 5. An image forming apparatus for use in an image forming apparatus, wherein an image is formed by charging, exposing, developing and transferring a photosensitive drum, and the developing means also serves to clean residual toner on the photosensitive member. A unit, wherein the image forming unit includes a photosensitive drum having a photosensitive layer made of an organic material, a first frame rotatably supporting the photosensitive drum, and a vertical line extending downward from the center of the photosensitive drum. A photoconductor unit having a scorotron charger provided in the frame so as to be located within ± 45 ° and provided with a ventilation hole on the opposite side of the charging opening; and supporting a developing means and a developing means, and And a developing unit composed of a second frame which also serves as a toner container, wherein the first frame and the second frame have a common fulcrum and an elastic member on the opposite side of the fulcrum. And a coupling means, and said image forming unit electric field E ₁ between wire and grid in the scorotron charger is characterized in that it is set larger than the electric field E ₂ between the wire and the shield.