JP2007304302A - Processing cartridge, image forming device, and image forming method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a processing cartridge which can reduce contaminations on the charging component and maintain its stability over a long period by suppressing resistance increase over aging, and an image forming device thereof. <P>SOLUTION: This image forming device has a photoreceptor 40 and a static charging roller 70. The charging roller 70 has a metal core, a static charging member formed around the core but not in contact with the photoreceptor 40 surface, gap keepers arranged on its both ends and also a discharger to discharge the charging member. Further, this image forming device has a charging voltage regulator to regulate the voltage to apply to the charging roller 70 by detecting the current in the charging member. The current detector 82 of the voltage regulator is arranged in the ground wiring of the photoreceptor 40. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an image forming apparatus such as a copying machine or a printer, a process cartridge applied to the image forming apparatus, and an image forming method using the same.

Conventionally, as charging means for image forming apparatuses, charger-type charging devices such as scorotron have been the mainstream, but there is a problem that a large amount of discharge products such as ozone are generated. Has been applied.
By the way, in order to reduce the contamination of the charging roller as the charging means, it is advantageous to dispose the charging roller and the photosensitive member as the image carrier in a non-contact manner. In order to apply such a non-contact charging device, it is necessary to keep the gap between the charging member surface and the photoreceptor surface as uniform as possible. Generally, a rubber roller used as a charging member changes its hardness with changes in ambient temperature or humidity, so that the gap between the photoreceptor and the charging member surface (hereinafter referred to as a charging gap) is stably maintained. It is difficult to do.
To solve such a problem, it is conceivable to stabilize the charging gap by applying a high hardness resin material as the charging roller. Further, it is known that by using an ion conductive material as a charging roller, uniform charging can be achieved without charging unevenness due to abnormal discharge as compared with the case where an electron conductive material is used. However, when an ion conductive material is applied as the charging roller, there is a problem that the resistance of the charging roller increases due to energization with time and the charging potential decreases.

In order to solve such problems, for example, Patent Document 1 proposes an operation method for a conductive member that reverses the sign of the current applied to the charging roller by a predetermined amount of charge at predetermined intervals. However, in this method, since the photosensitive member is charged with a reverse polarity, the photosensitive member is liable to deteriorate such as an increase in residual potential, which is disadvantageous in terms of the life of the photosensitive member. Further, there is a problem that normal image forming operation cannot be performed while a reverse polarity current is applied, and productivity is lowered.
Incidentally, in an image forming apparatus in which a gap is provided between the photosensitive member and the charging roller, it is effective to detect and adjust the charging current in order to set the charging bias to an appropriate value. As disclosed in Patent Document 3, in an image forming apparatus provided with a discharging unit that discharges a charging unit, a current flows through the discharging unit when the discharging unit is grounded or a bias is applied. Therefore, there is a problem that it is difficult to accurately detect a charging current that contributes to charging of the photosensitive member. On the other hand, in Patent Document 4, in an image forming apparatus in which a gap is provided between a photosensitive member and a charging roller, the voltage applied to the charging roller is changed stepwise to detect the current flowing through the charging roller. A method for uniformly charging is disclosed.

Japanese Patent Application Laid-Open No. 07-049604 JP 09-062061 A JP 2000-181252 A JP 2002-108059 A

However, any of the above prior arts eliminates the contamination of the charging member in the charging means, and suppresses the increase in resistance over time to provide a charging means with a long life, and thus a process cartridge or an image forming apparatus. Was not necessarily satisfied.
The present invention has been made in view of the above-mentioned problems of the prior art, and its object is to reduce the contamination of the charging member and suppress the increase in resistance over time, and the configuration including the charging means. It is an object of the present invention to provide a process cartridge, an image forming apparatus, and an image forming method using the process cartridge which have a long life and are excellent in long-term stability.

In order to achieve the above object, an image forming apparatus according to the present invention includes an image carrier and a charging unit that charges the image carrier. The charging unit includes a cored bar and the cored bar. A charging member formed around the charging member and disposed in a non-contact manner with respect to the surface to be charged of the image carrier, and a gap having a circumferential surface disposed at both ends of the charging member and protruding from the surface of the charging member A holding member, and the charging unit is provided with a discharging unit for discharging the charging member.
In this case, it is preferable that the static elimination unit functions also as a cleaning unit that cleans the charging unit.
In addition, it is preferable to include a charging voltage adjusting unit that detects a current flowing through the charging member and adjusts an applied voltage applied to the charging unit.
In this case, the current detection means in the charging voltage adjustment means can be provided on the ground wiring of the image carrier.

The process cartridge according to the present invention is a process cartridge in which an image carrier and a charging unit that charges the image carrier are integrated, and is detachably attached to the main body of the image forming apparatus. Gold, a charging member formed around the core bar and disposed in non-contact with the surface to be charged of the image carrier, and disposed at both ends of the charging member and projecting from the surface of the charging member A gap holding member having a circumferential surface, and the charging unit is provided with a discharging unit for discharging the charging member.

The image forming method according to the present invention is characterized in that when the charging unit of the image forming apparatus described above is neutralized, a neutralizing bias for neutralizing the charging unit is applied to the neutralizing unit.
In this case, it is preferable that a bias having a polarity opposite to the charging polarity of the image carrier is applied as the charge eliminating bias.
Further, as the charge eliminating bias, a bias having a polarity opposite to the charging polarity of the toner attached to the image carrier can be applied, and the charge eliminating unit can also function as a cleaning unit.
Furthermore, instead of applying a static elimination bias to the static elimination means, a DC voltage and an AC voltage may be applied to the charging means to ground the static elimination means.
In the image forming method according to the present invention, it is preferable to perform charging voltage adjustment using a charging voltage adjusting unit during non-image formation, and not to apply a bias to the charge eliminating unit during charging voltage adjustment.
In this case, instead of applying a bias to the charge eliminating unit, the charge eliminating unit may be separated from the charging unit.

According to the image forming apparatus of the present invention, it is possible to reduce the contamination of the charging member to reduce the increase in resistance over time, and to extend the life and stability of each member including the charging unit and the entire apparatus. .
According to the process cartridge of the present invention, adjustment of the charging gap is unnecessary even when high charging gap accuracy is required, and the maintainability is improved.
According to the image forming apparatus of the present invention, it is possible to form a stable image for a long period of time by reducing the contamination of the charging member and reducing the increase in resistance over time.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an overall configuration of a tandem intermediate transfer type full-color copying machine, which is an image forming apparatus according to an embodiment of the present invention.
In FIG. 1, this full-color copying machine includes a copying machine main body 100, a paper feed table 200 on which the copying machine main body 100 is placed, a scanner 300 mounted on the copying machine main body 100, and an automatic document placed on the scanner 300. It is mainly composed of a transfer device (ADF) 400.
Near the center of the copying machine main body 100, a tandem image forming apparatus 20 in which four image forming units 18 (Y, C, M, Bk) of Y, C, M, and Bk are arranged side by side is provided. Each image forming unit of the tandem image forming apparatus 20 includes a photoreceptor 40 (Y, C, M, Bk) on which toner images of respective colors Y, C, M, and Bk are formed.
An exposure device 21 is provided above the tandem image forming apparatus 20. The exposure device 21 is arranged in four laser diode (LD) light sources prepared for each color, a set of polygon scanners composed of a six-sided polygon mirror and a polygon motor, and an optical path of each light source. It is composed of a lens such as an fθ lens, a long WTL, or a mirror. The laser light emitted from the laser diode in accordance with the image information of each color is deflected and scanned by the polygon scanner and applied to the photoconductor 40 of each color.

Below the tandem image forming apparatus 20, an endless belt-like intermediate transfer belt 10 is installed. As a material of the intermediate transfer belt 10, for example, a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, polyethylene terephthalate, or the like can be applied, and this is molded into a seamless belt and used. These materials can be used as they are, or can be applied by adjusting the resistance with a conductive material such as carbon black. In addition, the surface layer can be formed by a method such as spraying or dipping using these resins as a base layer to form a laminated structure.
For example, the intermediate transfer belt 10 is stretched around three support rollers 14, 15, and 16 and can be rotated and conveyed in the clockwise direction in the drawing, and the first support roller 14 rotates, for example, the intermediate transfer belt 10. It is a drive roller. Further, a primary transfer roller 62 (Y, C, M) is provided between the first support roller 14 and the second support roller 15 as primary transfer means for transferring a toner image from the photosensitive member of each color to the intermediate transfer belt. , Bk) are provided so as to face the respective photoreceptors 40 (Y, C, M, Bk) via the intermediate transfer belt 10.
An intermediate transfer belt cleaning device 17 for removing residual toner remaining on the intermediate transfer belt 10 after image transfer is provided downstream of the third support roller 16 in the conveyance direction of the intermediate transfer belt.

A secondary transfer device 22 is disposed below the intermediate transfer belt 10. The secondary transfer device 22 is configured, for example, such that a secondary transfer belt 24 that is an endless belt is stretched between two rollers 23 and is in contact with the third support roller 16 via the intermediate transfer belt 10. The image on the intermediate transfer belt 10 is transferred to a transfer material. As the secondary transfer belt 24, the same material as that of the intermediate transfer belt 10 can be used.

A fixing device 25 for fixing the image on the transfer material is provided adjacent to the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt. Note that the above-described secondary transfer device 22 has a sheet conveying function for conveying the transfer material after image transfer to the fixing device 25. Of course, a transfer roller or a transfer charger may be disposed as the secondary transfer device 22, and in such a case, it is necessary to separately provide a transfer material conveying function. Below the secondary transfer device 22 and the fixing device 25, in parallel with the tandem image forming device 20, the transfer material is reversed and discharged, or the transfer material is reversed and formed again to form images on both sides of the transfer material. A reversing device 28 for feeding paper is provided.

The operation of the full-color copying machine having such a configuration will be described below.
When copying using this full-color copying machine, first, the original is set on the original table 30 of the ADF 400, or the ADF 400 is opened and the original is set on the contact glass 32 of the scanner, and then the ADF 400 is closed and the original is set. Hold down.
Next, when the start switch of the operation unit (not shown) is pressed and a document is set on the ADF 400, the document is conveyed onto the contact glass 32, and then when the document is set on the other contact glass 32, the scanner is immediately To drive the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source, and the reflected light from the document surface is further reflected toward the second traveling body, reflected by the mirror of the second traveling body, and read through the imaging lens 35. It is put in the sensor 36 and the original content is read. Thereafter, when the mode setting in the operation unit or the automatic mode selection is set in the operation unit, the image forming operation is started in the full color mode or the monochrome mode according to the reading result of the document.

When the full color mode is selected, each photoconductor 40 (Y, C, M, Bk) is rotated in the counterclockwise direction in the drawing, and the surface of each photoconductor 40 is fixed by a charging roller as a charging device. It is charged like this. Next, each color photoconductor 40 is irradiated with laser light corresponding to the image of each color from the exposure device 21 to form a latent image corresponding to the image data of each color. Next, by rotating the photoconductor 40, each latent image is developed by a developing device for each color to form a toner image for each color. The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 10 along with the conveyance of the intermediate transfer belt 10 to form a full color image on the intermediate transfer belt 10.
On the other hand, one of the paper feed rollers 42 of the paper feed table 43 is selectively rotated, the transfer material is sent out from one of the paper feed cassettes 44 provided in multiple stages on the paper feed table 43, and separated one by one by the separation roller 45. Then, the sheet is put into the sheet feeding path 46, conveyed by the conveying roller 47, guided to the sheet feeding path 48 in the main body, and abutted against the registration roller 49 and stopped. At this time, the transfer roller 50 is rotated to feed the transfer material on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped. May be. Then, the registration roller 49 is rotated in synchronization with the full-color image on the intermediate transfer belt 10, the transfer material is fed between the intermediate transfer belt 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. The toner image is transferred onto the transfer material.

The transfer material on which the toner image has been transferred is conveyed by the secondary transfer device 22 and sent to the fixing device 25, where it is fixed to the transfer material by applying heat and pressure, and then switched by the switching claw 55 and discharged. The paper is discharged by a roller 56 and stacked on a paper discharge tray 57. At this time, the transfer material is switched by the switching claw 55 and introduced into the sheet reversing device 28, where it is reversed and fed again to the transfer position 28 to record the image on the back surface, and then discharged by the discharge roller 56. The paper may be discharged onto the paper tray 57. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is sequentially repeated.

On the other hand, when the monochrome mode is selected, the support roller 15 that supports the intermediate transfer belt 10 moves downward to separate the intermediate transfer belt 10 from the photosensitive member 40 (Y, C, M). That is, only the photoconductor 40Bk is rotated counterclockwise in FIG. 1, the surface of the photoconductor 40Bk is uniformly charged by a charging roller, and a laser beam corresponding to the Bk image is irradiated to form a latent image. And Bk toner to develop a toner image. This toner image is transferred onto the intermediate transfer belt 10. At this time, the three color photoconductors 40 (Y, C, M) other than 40Bk and the developing device are stopped, and unnecessary consumption of the photoconductor and the developer is prevented.
On the other hand, the transfer material is fed from the paper feed cassette 44 and conveyed by the registration roller 49 at a timing coincident with the toner image formed on the intermediate transfer belt 10. The transfer material onto which the toner image has been transferred is fixed by the fixing device 25 in the same manner as in the case of a full-color image, and processed through a paper discharge system corresponding to the designated mode. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is repeated.

  Next, features of the present invention will be described in detail. FIG. 2 is an enlarged view showing the configuration of the image forming unit of FIG. In FIG. 2, a photoconductor 40 as an image carrier and a charging roller 70 as a charging means for uniformly charging the surface of the photoconductor 40 are integrated, and are detachably attached to the copier body. The process cartridge is formed. Around the photoconductor 40 as an image carrier, there are a charging roller 70 as a charging means for uniformly charging the surface of the photoconductor 40 along its rotation direction, a potential sensor 71 for detecting the potential of the photoconductor 40, A developing device 60 that develops the electrostatic latent image formed on the photoconductor 40, a static elimination lamp 72 that neutralizes the surface of the photoconductor 40 after the toner image is transferred, and a brush roller as a cleaning device that cleans residual toner after transfer. 73 and 74 and a cleaning blade 75 are arranged. The case of the image forming unit 18 is provided with an opening (not shown) for allowing the exposure light 76 from the exposure device 21 to pass therethrough.

The charging roller 70 is in contact with a cleaning roller 77 for cleaning the roller surface and a neutralizing roller 78 for neutralizing the charging roller. As the cleaning roller 77, for example, a brush roller, a sponge roller, a melamine foam roller, or the like is used. As the static elimination roller 78, for example, a material obtained by processing a material such as a brush, sponge, rubber, resin tube or the like having a volume resistance of 10 ⁴ to 10 ⁹ Ωcm into a roller shape can be used. A neutralizing bias is applied to the core of the neutralizing roller 78 or grounded. When the volume resistance of the material used for the static elimination roller 78 is too low, the charging bias is liable to leak, and when the volume resistance is too high, the charge hardly flows and a sufficient static elimination effect cannot be obtained. The neutralizing bias applied to the neutralizing roller 78 is, for example, opposite in polarity to the charging polarity of the photosensitive member, so that an electric field having a polarity opposite to that of the charging region is applied to the charging roller 70, and the charging roller can be neutralized more effectively. it can.

The cleaning roller 77 and the charge removing roller 78 may be brought into contact with the charging roller 70 by its own weight and may be rotated along with the rotation of the charging roller 70 or may be driven by a gear. In addition, instead of arranging the cleaning roller 77 and the charge eliminating roller 78 separately, it is possible to reduce the size of the apparatus by consolidating the functions into one roller. At this time, from the viewpoint of cleaning the charging roller 70, it is desirable that the bias to be applied has a polarity opposite to the charging polarity of the toner attached to the photosensitive member. In the case of using a negatively charged photosensitive member and a negatively charged toner in the negative positive system, it is advantageous to set the neutralizing bias to a positive value because the polarity is opposite to that of the photosensitive member and opposite to the charged polarity of the toner.

A solid lubricant 79 is in contact with the brush roller 74 and functions as a lubricant supply member. Solid lubricants include zinc stearate, barium stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, magnesium stearate, zinc oleate, cobalt oleate, Fatty acid metal salts such as magnesium oleate and zinc palmitate, natural waxes such as carnauba wax, and fluorine-based resins such as polytetrafluoroethylene can be used.
The cleaning blade 75 is made of, for example, polyurethane rubber. The toner scraped off from the photosensitive member by the brush roller 73 and the cleaning blade 75 is transported as waste toner to a waste toner storage unit (not shown) by the toner transport coil 80.

3 is a cross-sectional view taken along the longitudinal direction of the charging roller in FIG. A charging roller 70 as a charging means includes a cored bar 101 as a conductive support, a resin layer 102 as a charging member formed so as to cover the peripheral surface of the cored bar 101, and a resin layer (hereinafter referred to as a charging member). The gap holding member 103 is provided at each of both ends of 102. The gap member 103 has a circumferential surface protruding from the surface of the resin layer 102 as a charging member. Since the gap member 103 has a circumferential surface protruding from the surface of the charging member 102, a charging gap is formed between the charging member 102 and the surface of the photoreceptor 40.
As the metal core 101, for example, a metal such as stainless steel is used. If the core metal 101 is too thin, the influence of the deflection when the charging member is cut or pressed against the photoreceptor cannot be ignored, and the required gap accuracy is difficult to obtain. On the other hand, when the core metal 101 is too thick, there is a problem that the charging roller 70 becomes larger or heavier than necessary. Accordingly, the diameter of the cored bar 101 is, for example, about 6 to 10 mm.
The charging member 102 in the charging roller 70 is preferably made of a material having a volume resistance of 10 ⁴ to 10 ⁹ Ωcm, for example. If the resistance is too low, charging bias leakage tends to occur when the photoreceptor has a defect such as a pinhole. On the other hand, when the resistance of the charging member 102 is too high, sufficient discharge is not generated, and a uniform charging potential cannot be obtained.

The volume resistance of the charging member 102 can be adjusted by blending a conductive material with a resin as a base material. As the base resin, for example, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate can be used. Since these base resins have good moldability, they can be easily molded.
As the conductive material for adjusting the resistance of the charging member, an electronic conductive material such as carbon black can be used. However, it is difficult to uniformly disperse such an electronic conductive material in the base resin. Therefore, resistance unevenness is likely to occur. In particular, it is difficult to uniformly charge the photosensitive member with a charging roller arranged in a non-contact manner on the photosensitive member. On the other hand, ion conductive materials made of electrolyte salts such as Li salts can be uniformly dispersed in the base resin. However, these low molecular weight materials easily move in the base resin, and bleed over time. Out problems may occur. Therefore, as the resistance adjusting material, a high molecular weight ion conductive material which is easily dispersed uniformly in the base resin and hardly moves is preferably used. Examples of such a high molecular weight ion conductive material include polyether ester amide.

The ion conductive material described above is uniformly blended into the base resin by using a means such as a biaxial kneader or a kneader. The blending amount of the ion conductive material and the base resin is desirably 30 to 80 parts by weight of the ion conductive material with respect to 100 parts by weight of the base resin.
The compounded material can be easily molded into a roller shape by injection molding or extrusion molding on the core metal. The thickness of the resin layer formed on the mandrel is, for example, 0.5 to 3 mm. If the resin layer is too thin, molding is difficult and there is a problem in terms of strength. On the other hand, if the resin layer is too thick, the charging roller is increased in size and the actual resistance of the resin layer is increased, so that the charging efficiency is lowered. After the resin layer is molded on the core metal, a gap holding member molded in advance on both ends of the resin layer is fixed to the core metal by press-fitting or bonding or both.

As the material of the gap holding member, an insulating resin such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate can be used as in the base material of the charging member. However, since the gap holding member is brought into contact with the surface of the photosensitive member (photosensitive layer) as the image carrier, it is preferable to use a grade having a hardness lower than that of the charging member in order to prevent the photosensitive layer from being damaged. Polyacetal, ethylene-ethyl acrylate copolymer, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene as resin materials with excellent slidability and less damage to the photosensitive layer Resins such as copolymers can also be used. It is also possible to form a surface layer with a thickness of about several tens of μm on which the toner or the like is difficult to adhere by coating the resin layer or the gap holding member.

After the charging member and gap holding member formed on the metal core are integrated, the outer diameter of the charging roller is adjusted by cutting, grinding, etc., and the phase of the charging member and gap holding member is set to the same phase. Reduce gap variation.
A gap is formed between the charging member and the photosensitive member by applying the gap holding member of the charging roller to the outside of the image area of the photosensitive member. In the charging roller, for example, the gear attached to the end of the core bar meshes with the gear formed on the photosensitive member flange. When the photosensitive member is rotated by the photosensitive member driving motor, the charging roller also has a linear velocity almost equal to that of the photosensitive member. Rotates in the accompanying direction. Since the charging member and the photosensitive member are not in direct contact, even when a hard resin material and an organic photosensitive member are used as the charging roller, the photosensitive layer in the image area is not damaged. If the gap is too wide, abnormal discharge occurs and charging cannot be performed uniformly, so that the maximum gap can be suppressed to 100 μm or less.

When a charging roller having a charging gap is used, it is desirable to superimpose an AC voltage on a DC voltage as a charging bias. Since the charging gap fluctuates with the rotation of the photosensitive member and the charging roller, the high-voltage power supply may not be able to follow the fluctuation of the charging gap in the constant current control method. Therefore, there is provided a charging voltage adjusting means that changes the voltage stepwise while monitoring the charging current using a constant voltage controlled high-voltage power supply and adjusts the applied voltage through which the target charging current flows. Thereby, good charging performance can be obtained. As a method for detecting the charging current, it is common to detect the output current of the high-voltage power supply as shown in FIG. 5a. However, when a neutralizing roller is provided as in the apparatus of the present invention, only the current flowing to the photosensitive member side is used. In addition, since the current flowing to the static elimination roller side is also detected, the detection accuracy is low. Therefore, when the charge voltage adjustment operation is performed, the current flowing to the charge removal roller can be reduced and the detection sensitivity can be improved by turning off the charge removal bias or separating the charge removal roller from the charge roller. Further, as another means, as shown in FIG. 5b, current detection means is provided on the ground wire of the photosensitive member, and only the current component flowing through the photosensitive member can be detected by detecting the current on the ground side of the photosensitive member. In this case, it is necessary to place a detection circuit between the photosensitive element tube and the ground, but this is the configuration in consideration of providing a contact / separation mechanism on the static elimination roller when detecting on the high-voltage power supply side. Is easy.

Employing a non-contact roller charging system for the photoreceptor has the following advantages. That is, by adopting a non-contact roller charging method, the roller is less likely to be contaminated with toner or the like as compared with the charging roller in contact with the photosensitive member. Even if it is non-contact, by setting the charging gap to, for example, 100 μm or less, the generation amount of discharge products is greatly reduced as compared with the charger method in which a gap of about 5 to 15 mm is provided between the photoreceptor and the wire. be able to.

Each developing device for developing a latent image formed on the surface of the photoreceptor has the same configuration, and only the color of the toner used is different. The developing device is, for example, a two-component developing type developing device, and each developing device contains a two-component developer composed of toner and carrier.
That is, in FIG. 2, the developing device 60 mainly includes a developing roller 61 facing the photoreceptor 40, screws 63 and 65 for conveying and stirring the developer, a toner density sensor 64, and the like. Although not shown, the developing roller 61 is composed of an outer rotatable sleeve and a magnet fixed on the inner side. In accordance with the output of the toner concentration sensor 64, a necessary amount of toner is supplied from a toner supply device (not shown).

According to the present embodiment, the charging unit can be efficiently discharged by applying a bias to the discharging unit. By setting the charge eliminating bias to a polarity opposite to the charging polarity of the image carrier, an electric field in the reverse direction is applied to the charging means, so that the charging means can be discharged efficiently.
Further, according to the present embodiment, the charging unit can be discharged by applying an AC bias to the charging unit in addition to the DC bias and grounding the discharging unit. In this case, since it is not necessary to provide a high-voltage power supply for the charge removal means, the charge means can be discharged at low cost.
According to this embodiment, since the charge removal unit also serves as the cleaning unit, the charge member can be discharged by the charge removal bias, the toner attached to the charge member can be efficiently removed, and the apparatus can be downsized. It becomes.
Furthermore, according to the present embodiment, the charging current detection means is arranged on the image carrier side, for example, the ground wiring of the photosensitive member, so that the charging current can be detected without being influenced by the current flowing through the charge removal means. In addition, since no bias is applied to the charge removal means during current detection, the current flowing through the charging means can be accurately detected. Furthermore, only the current that contributes to charging can be accurately detected by separating the charge removal unit from the charging unit during current detection.
Furthermore, according to this embodiment, since the photosensitive member and the charging roller are integrated into one process cartridge, adjustment of the charging gap is unnecessary even when high gap accuracy is required. Even the user can easily replace it, improving the maintainability.

The toner applied to the developing device is prepared by adding a binder resin, a colorant, and a charge control agent as main components and adding other additives as necessary.
As the binder resin, for example, polystyrene, styrene-acrylic acid ester copolymer, polyester resin, or the like can be used. As the yellow, magenta, cyan and black colorants, known ones can be used. The amount of the colorant is suitably 0.1 to 15 parts by weight, for example, with respect to 100 parts by weight of the binder resin.
As the charge control agent, a nigrosine dye, a chromium-containing complex, a quaternary ammonium salt, or the like is used, and these are properly used depending on the polarity of the toner particles. The amount of the charge control agent is, for example, 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.
It is preferable to add a fluidity-imparting agent to the toner particles. Examples of the fluidity-imparting agent include fine particles of metal oxides such as silica, titania, alumina, etc., and these fine particles as silane coupling agents, titanate coupling agents, etc. Or a polymer fine particle such as polystyrene, polymethyl methacrylate, and polyvinylidene fluoride. The particle size of these fluidity imparting agents is, for example, 0.01 to 3 μm. The addition amount of the fluidity-imparting agent is preferably 0.1 to 7.0 parts by weight with respect to 100 parts by weight of the toner particles.

As a method for producing the toner for the two-component developer applied in the present embodiment, various known methods or a combination thereof are applied. For example, in the kneading and pulverization method, a binder resin, a colorant such as carbon black, and necessary additives are dry-mixed, heated, melted and kneaded with an extruder, two rolls, three rolls, etc., and cooled and solidified. Then, the toner is pulverized by a pulverizer such as a jet mill and classified by an airflow classifier. In addition, a toner can be directly produced from a monomer, a colorant, and an additive by a suspension polymerization method or a non-aqueous dispersion polymerization method.
The carrier is generally made of a core material itself, or a carrier provided with a coating layer on the core material. The core material of the resin-coated carrier that can be applied in the present embodiment is ferrite or magnetite. An appropriate particle size of the core material is about 20 to 60 μm.
Examples of the material used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with a fluorine atom, and vinyl ketone substituted with a fluorine atom. As the coating layer, a resin is applied to the surface of the carrier core particles by means of a spraying method, a dipping method or the like, as in the conventional case.

Here, the configuration of the photoreceptor applied in the present embodiment will be described. FIG. 4 is a cross-sectional view of a photoreceptor applied in the present embodiment. In FIG. 4, the photoconductor includes a conductive support 201, a charge generation layer 203 and a charge transport layer 204 as a photosensitive layer 202 laminated on the conductive support 201, and a protective layer provided as an outermost layer. 205.
The conductive support 201 exhibits conductivity having a volume resistance of 10 ¹⁰ Ωcm or less. For example, a metal such as aluminum, nickel, chromium, nichrome, copper, silver, gold, or platinum, or a metal such as tin oxide or indium oxide. It consists of a film or cylindrical plastic or paper coated with an oxide by vapor deposition or sputtering, or a tube material such as aluminum, aluminum alloy, nickel, or stainless steel that has been surface treated by cutting, superfinishing, polishing, or the like.
The charge generation layer is a layer mainly composed of a charge generation material. As the charge generation material, an inorganic or organic material is used, and typical examples include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squaric. Examples include acid dyes, phthalocyanine pigments, naphthalocyanine pigments, azulenium salt dyes, selenium, selenium-tellurium alloys, selenium-arsenic alloys, and amorphous silicon. These charge generation materials may be used alone or in combination of two or more.

Such a charge generating material is appropriately dispersed together with a binder resin, using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, 2-butanone, dichloroethane or the like by a ball mill, attritor, sand mill, etc. By applying to 201, the charge generation layer 203 is formed. Examples of the binder resin to be appropriately applied include resins such as polyamide, polyurethane, polyester, epoxy, polyketone, polycarbonate, silicone, acrylic, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polyacryl, and polyamide. The added amount of the binder resin is suitably 0 to 2 parts on a weight basis with respect to 1 part of the charge generating material. The charge generation material can be applied by, for example, a dip coating method, a spray coating method, a bead coating method, or the like. The film thickness of the charge generation layer is usually 0.01 to 5 μm, preferably 0.1 to 2 μm.

On the other hand, the charge transport layer can be formed by dissolving or dispersing the charge transport material and the binder resin in an appropriate solvent, and applying and drying the solution. If necessary, a plasticizer, a leveling agent or the like can be added to the charge transport layer.
Among charge transport materials, low molecular charge transport materials include electron transport materials and hole transport materials. Examples of the electron transport material include chloroanil, bromanyl, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2, 4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophene-4-one, 1,3,7-tri Examples thereof include electron accepting substances such as nitrodibenzothiophene-5,5-dioxide. An electron transport material may be used independently and may be used as a 2 or more types of mixture.

Examples of hole transport materials include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane. , Styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, thiophene derivatives, and the like. The hole transport material may be used alone or as a mixture of two or more.
When a polymer charge transport material is used as the charge transport material, the charge transport layer may be formed by dissolving or dispersing in a suitable solvent, coating and drying. The polymer charge transport material may be a material having a charge transporting substituent in the main chain or side chain in the low molecular charge transport material. If necessary, an appropriate amount of a binder resin, a low molecular charge transport material, a plasticizer, a leveling agent, a lubricant and the like can be added to the polymer charge transport material.

Examples of the binder resin used in the charge transport layer together with the charge transport material include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, and vinyl chloride. Vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy, polycarbonate, cellulose acetate, ethyl cellulose, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, acrylic, silicone, epoxy, melamine, urethane, phenol, alkyd, etc. A thermoplastic or thermosetting resin is mentioned.
Examples of the solvent include tetrahydrofuran, dioxane, toluene, 2-butanone, monochlorobenzene, dichloroethane, methylene chloride and the like.

The thickness of the charge transport layer is appropriately selected in the range of 5 to 30 μm according to desired photoreceptor characteristics.
Examples of the plasticizer that can be added to the charge transport layer include general-purpose plasticizers for resins such as dibutyl phthalate and dioctyl phthalate. About 30% is appropriate.
Examples of leveling agents that can be added to the charge transport layer include silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having a perfluoroalkyl group in the side chain. About 0 to 1% is appropriate for the binder resin on the basis.

In the photoreceptor applied in this embodiment, an undercoat layer may be formed between the conductive support and the photosensitive layer. In general, the undercoat layer is mainly composed of a resin. However, considering that the photosensitive layer is applied using a solvent, the resin is a resin having high resistance to general organic solvents. Is desirable. Such resins include water-soluble resins such as polyvinyl alcohol, casein, sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine, alkyd-melamine, epoxy, etc., three-dimensional Examples thereof include a curable resin that forms a network structure.
Further, fine powder of metal oxide such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, and indium oxide may be added to the undercoat layer in order to prevent moire and reduce residual potential. The undercoat layer can be formed using an appropriate solvent and coating method, as in the case of the photosensitive layer.
Furthermore, it is also useful to use a metal oxide layer formed by, for example, a sol-gel method using a silane coupling agent, a titanium coupling agent, a chromium coupling agent or the like as the undercoat layer. In addition, the undercoat layer which the _Al 2 _{O 3} was formed by those anodized, organic matter such as polyparaxylylene _{(parylene), SiO, SnO 2, TiO} 2, ITO, Ce0 2 , etc. inorganic It is also effective to form the film by a vacuum thin film manufacturing method. The thickness of the undercoat layer is suitably from 0 to 5 μm.

It is preferable to form a protective layer on the photoreceptor as a surface layer for the purpose of protecting the photosensitive layer and improving durability. The protective layer has a structure in which fine metal oxide particles such as alumina, silica, titanium oxide, tin oxide, zirconium oxide, and indium oxide are dispersed in the binder resin for the purpose of improving wear resistance. As the binder resin, a resin similar to the binder resin used for the charge transport layer can be used.
The amount of metal oxide fine particles added to the protective layer is, for example, 5 to 30% on a weight basis. If the amount of the metal oxide fine particles is less than 5%, the effect of improving the wear resistance is small and the durability is inferior. If it exceeds 30%, the bright portion potential is significantly increased at the time of exposure, and the sensitivity reduction cannot be ignored. So undesirable. As a method for forming the protective layer, a normal coating method such as a spray method is employed. The thickness of the protective layer is, for example, 1 to 10 μm, preferably 3 to 8 μm. If the protective layer is too thin, the durability is inferior, and if the protective layer is too thick, not only the productivity at the time of manufacturing the photoreceptor is lowered, but also the residual potential increases with time. The particle size of the metal oxide particles added to the protective layer is, for example, 0.1 to 0.8 μm. If the particle size of the metal oxide fine particles is too large, the irregularities on the surface of the protective layer become large and the cleaning property is deteriorated, and the exposure light is easily scattered by the protective layer, the resolution is lowered and the image quality is inferior. On the other hand, when the particle size of the metal oxide fine particles is too small, the wear resistance is poor.
As a structure of the protective layer, not only a structure in which metal oxide fine particles are dispersed in a binder resin but also a structure using a heat or photocrosslinkable resin is known. By using a photoconductor provided with a protective layer, the wear resistance of the photoconductor is improved, so even if it is used for a long time, the change in photoconductor sensitivity due to the decrease in the photoconductor film thickness is small and stable over a long period of time. An image can be output.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view showing a configuration of the image forming unit in FIG. 1. FIG. 3 is a cross-sectional view taken along the rotation center axis of the charging roller in FIG. 2. 2 is a cross-sectional view of a photoreceptor applied in an embodiment of the present invention. FIG. It is a figure which shows the example of arrangement | positioning of the electric current detection means in a charging voltage adjustment means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 14 Support roller 15 Support roller 16 Support roller 17 Intermediate transfer belt cleaning device 18 Image forming unit 20 Tandem image forming device 21 Exposure device 22 Secondary transfer device 23 Roller 24 Secondary transfer belt 25 Fixing device 26 Fixing belt 27 Pressure roller 28 Reverse device 30 Document table 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Reading sensor 40 Photosensitive body 42 Paper feed roller 43 Paper feed table 44 Paper feed cassette 45 Separating roller 46 Paper feed Path 47 Conveying roller 48 Paper feed path 49 in the body Registration roller 50 Paper feed roller 51 Manual feed tray 52 Separating roller 53 Manual feed path 55 Switching claw 56 Discharge roller 57 Paper discharge tray 60 Developing device 61 Development roller 62 Primary transfer roller 63 Screw 64 Toner density sensor S 65 Crew 70 Charging roller 71 Electric potential sensor 72 Electric discharge lamp 73 Brush roller 74 Brush roller 75 Cleaning blade 76 Exposure light 77 Cleaning roller 78 Electric discharge roller 79 Solid lubricant 80 Toner conveyance coil 81 High voltage power supply 82 Current detection means 100 Copying machine main body 101 Core metal 102 Charging member (resin layer)
103 Gap holding member 200 Paper feed table 201 Conductive support 202 Photosensitive layer 203 Charge generation layer 204 Charge transport layer 205 Protective layer 300 Scanner 400 Automatic document feeder (ADF)

Claims (11)

In an image forming apparatus having an image carrier and a charging means for charging the image carrier,
The charging means includes a cored bar, a charging member formed around the cored bar and arranged in non-contact with the surface to be charged of the image carrier, and disposed at both ends of the charging member. A gap holding member having a circumferential surface protruding from the member surface,
An image forming apparatus, wherein the charging unit is provided with a discharging unit for discharging the charging member. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the charge eliminating unit functions as a cleaning unit that cleans the charging unit. The image forming apparatus according to claim 1, wherein
An image forming apparatus comprising: a charging voltage adjusting unit that detects a current flowing through the charging member and adjusts an applied voltage applied to the charging unit. The image forming apparatus according to claim 3.
The image forming apparatus according to claim 1, wherein the current detection means in the charging voltage adjusting means is provided in a ground wiring of the image carrier. In a process cartridge that integrates an image carrier and a charging unit that charges the image carrier and is detachably attached to the image forming apparatus main body.
The charging means includes a cored bar, a charging member formed around the cored bar and arranged in non-contact with the surface to be charged of the image carrier, and disposed at both ends of the charging member. A gap holding member having a circumferential surface protruding from the member surface,
6. A process cartridge according to claim 1, wherein the charging means is provided with a discharging means for discharging the charging member. In the image forming method using the image forming apparatus according to any one of claims 1 to 4,
An image forming method, wherein when the charging unit is neutralized, a neutralizing bias for neutralizing the charging unit is applied to the neutralizing unit. The image forming method according to claim 6.
An image forming method, wherein a bias having a polarity opposite to a charging polarity of the image carrier is applied as the charge eliminating bias. The image forming method according to claim 6.
An image forming method, wherein a bias having a polarity opposite to a charging polarity of toner adhering to the image bearing member is applied as the charge eliminating bias, and the charge eliminating unit also functions as a cleaning unit. The image forming method according to claim 6.
An image forming method comprising applying a DC voltage and an AC voltage to the charging unit instead of applying a neutralizing bias to the neutralizing unit, and grounding the neutralizing unit. In the image forming method using the image forming apparatus according to claim 3 or 4,
An image forming method, wherein a charging voltage is adjusted using the charging voltage adjusting unit during non-image formation, and a bias is not applied to the charge eliminating unit during the charging voltage adjustment. The image forming method according to claim 10, wherein instead of applying no bias to the charge eliminating unit, the charge eliminating unit is separated from the charging unit.

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