JP2001249511A - Color image forming device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device capable of preventing ozone from being produced and realizing the improvement of maintainability and the recycling of toner left after transfer while restraining the device's getting large and cost rising. SOLUTION: This color image forming device is equipped with plural photoreceptor drums (image carriers) 1a to 1d, plural electrifying means 2a to 2d electrifying the drums 1a to 1d, plural developing devices (developing means) 4a to 4d forming respective color toner images by developing electrostatic latent images formed on the electrification surfaces of the drums 1a to 1d with developer of plural colors, and plural transfer rollers (transfer means) 10a to 10d successively transferring the plural color toner images to recording paper (body to be transferred) P. In the device, the electrifying means 2a to 2d are composed of a flexible electrifying roller (electrifying member) forming a contact part with the drums 1a to 1d. Voltage being <=1000 V is applied to the electrifying rollers 2a to 2d, and the developer remaining on the drums 1a to 1d after transferring the toner image is recovered by the developing devices 4a to 4d.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer having a plurality of photosensitive members and forming images of a plurality of colors by sequentially superimposing images formed on respective image carriers on the same transfer material. The present invention relates to a color image forming apparatus using an electrophotographic recording system such as a copying machine and a facsimile, and a process cartridge detachably mounted on the color image forming apparatus.

[0002]

2. Description of the Related Art Various color image forming apparatuses for forming a color image on a transfer material using an electrophotographic system have been proposed.
Some of them have been put to practical use.

As a typical example of a color image forming apparatus using an electrophotographic recording system, for example, a color image forming apparatus with a built-in rotary developing device is known. This type of color image forming apparatus includes a rotating body (rotary developing apparatus) therein, and for example, along a rotating peripheral surface of the rotating body, for example, yellow (Y), magenta (M), cyan (C) and An electrostatic latent image formed on a photoconductor, which is an electrostatic latent image carrier, is provided for each color by providing a rotary developing device including a developing device containing toners, which are developers of four colors of black (Bk). Can be sequentially developed using the above toner.

In an image forming apparatus having such a rotary developing device, an electrostatic latent image of each color formed on a common photoreceptor is visualized as a toner image at a predetermined developing position by each developing device. A multi-color toner image is formed by repeating the process of transferring the image onto a sheet-like recording paper (transfer material) such as paper every time an image is obtained.

[0005] Another example is an apparatus of a system in which toner images of respective colors are selectively superimposed sequentially on a photoreceptor surface to form a multi-color toner image on the photoreceptor surface, and then collectively transferred to recording paper. Has also been devised.

Further, a toner image of each color is separately formed by a developer of each color using a plurality of photoconductors, and the transfer material is conveyed while transferring the transfer material sequentially from each photoconductor to a transfer material. An image forming apparatus adopting a so-called tandem system for forming an image has been proposed.

Here, there has been proposed a type in which a plurality of color toner images are formed by sequentially superimposing toner images of respective colors on an intermediate transfer member instead of directly on recording paper, and then collectively transferred to recording paper. ing.

Each of the typical methods of the color image forming apparatus using the electrophotographic recording method has advantages and disadvantages, but the tandem method is superior from the viewpoint of speeding up in accordance with recent market needs. There are many products that have been put to practical use with this method.

FIG. 9 is a schematic configuration diagram of a color image forming apparatus employing a tandem system, and schematically shows a main internal structure of a color image forming apparatus of a four-drum multiple transfer system (hereinafter, referred to as a tandem color printer). Show.

The tandem color printer 12 sequentially arranges photosensitive drums 1a to 1d, which are electrostatic latent image carriers, opposed to developing means 4a to 4d containing toners of respective colors in a transfer material conveying direction. While sequentially transferring each color toner image formed on each of the photosensitive drums 1a to 1d by the developing means 4a to 4d onto the recording paper P conveyed by the transfer belt 6,
A full-color image is obtained by using four primary colors of yellow, magenta, cyan and black toners, and is configured as follows.

In FIG. 9, an endless transfer belt 6 is suspended by a driving roller 7, a driven roller 9, and a tension roller 10 and rotates in the direction of the arrow shown in FIG. The four photosensitive drums 1a, 1b, 1c, 1 are opposed to the transfer belt 6.
d are arranged in series, for yellow, for magenta,
Each color image station Y for cyan and black,
M, C, and Bk.

Each color image station Y, M, C, B
k image forming means include photosensitive drums 1a to 1d, charging means 2a to 2d, exposing means 3a to 3d, and developing means 4a to 4d.
And cleaning means 5a to 5d, which are disposed around the photosensitive drums 1a to 1d, respectively.

Image forming means for each color includes developing means 4a to 4
It has almost the same configuration except that the developer storage sections d contain yellow (Y), magenta (M), cyan (C) and black (Bk) toners, respectively.

Next, an image forming operation will be described.

The photosensitive drums 1a to 1d uniformly charged by the respective charging means 2a to 2d rotate in the direction of the arrow shown in the figure,
The surface of the photosensitive drum 1a is irradiated with a laser beam modulated to image data by exposure means 3a to 3d.
1d, a desired electrostatic latent image is formed for each color. Then, the electrostatic latent image is reversely developed at a developing site by developing means 4a to 4d including toners of respective colors disposed opposite thereto, and is visualized as a toner image.

The toner image is fed by a paper feeding means (not shown) and transferred to a recording paper P conveyed by a conveyor belt 6 from the right direction (arrow B direction) in FIG. Are transferred electrostatically in the order of yellow (Y), magenta (M), cyan (C), and black (Bk).

The color toner image multi-transferred onto the recording paper P is fused and fixed by fixing means (not shown), and is permanently fixed on the recording paper P to obtain a desired color print image.

Further, the photosensitive drum 1 is not transferred after the transfer.
The toner remaining on a to 1d is removed by cleaning means 5a to 5d including a cleaning blade or the like, and the photosensitive drums 1a to 1d are prepared for the next image forming step.

Although various types of charging means 2a to 2d have been proposed, non-contact charging, such as corona charging and contact charging, roller charging are generally used.
In general, two types of charging methods are generally used for roller charging. Specifically, in order to obtain a surface potential Vd on the photosensitive drum, an AC voltage having a peak-to-peak voltage of 2 × Vth or more is added to a DC voltage corresponding to a desired Vd disclosed in JP-A-63-149669. Is superimposed, and there is a "DC charging system" in which Vd + charging start voltage (Vth) is applied. In particular, in the “DC charging method”, it is necessary to apply a DC voltage of about 1000 to 1500 V in order to obtain a desired surface potential Vd.

Although various types of developing systems have been conventionally proposed, the tandem color printer 12 shown in FIG. 9 may employ either a contact type or a non-contact type. It can be applied regardless of the type of one component or two components. One example is a contact development method using a non-magnetic one-component toner.

On the other hand, in a single-color image forming apparatus,
JP-A-59-133573, JP-A-64-20587
Japanese Patent Application Laid-Open No. 6-51672 discloses a miniaturization of the entire apparatus, an ecological solution that does not generate waste toner, a long life of the photosensitive member, and a reduction in toner consumption per page. A method called "simultaneous development cleaning" or "cleanerless" that eliminates the need to provide a cleaning unit as a dedicated device by also using a cleaning unit for the transfer residual toner remaining on the photoreceptor surface after transferring the toner image. There is an image forming apparatus that employs an image forming apparatus.
In this method, the toner remaining on the photoconductor after transfer is recovered by a potential difference Vback between the DC voltage applied to the developing device and the surface potential of the photoconductor at the time of development in the next process. In a conventional cleaner-less image forming apparatus,
In order to eliminate the history of the toner remaining after transfer, an auxiliary cleaning means such as a so-called flyer member for scattering the toner by contacting the surface of the photoreceptor after the transfer step has been required.

[0022]

However, in the conventional color image forming apparatus, it is difficult to reduce the size of the apparatus because of the presence of the cleaning container. Specifically, since a cleaning container is provided for each image forming unit of each color, the volume occupied by each image forming unit is increased, and the apparatus is increased in size. Further, as the toner capacity of the developing device increases, the amount of waste toner increases accordingly. Therefore, it is necessary to increase the size of the cleaning container in order to avoid puncturing of the cleaning container due to waste toner, resulting in an increase in the size of the image forming apparatus. I was

Further, a cleaner-less structure proposed in a single-color image forming apparatus is provided with a plurality of photoconductors, and an image formed on each photoconductor is sequentially superimposed on the same transfer material to form a plurality of colors. When applied to a tandem-type color image forming apparatus for forming an image, there is a problem of color mixing by retransfer. Specifically, during the transfer of the second and subsequent colors, a part of the toner of a different color already transferred onto the transfer material is charged to the opposite polarity by the transfer device, attracted to the photoconductor by the transfer electric field, and adheres to the photoconductor. Alternatively, the toner having a large adhesive force adheres to the photoreceptor by being pressed against the photoreceptor, and is collected in a developing device through a charging and exposure process as it is, and is transferred to a transfer material during subsequent development and transfer by the developing device. Toner adheres. When such color mixing progresses, it becomes difficult to accurately reproduce a color tone, and image quality deteriorates.

As a charging method, a corona charging method, which is a non-contact charging method, is suitable for realizing a cleaner-less configuration, but has a problem such as generation of ozone.

On the other hand, there are an AC charging system and a DC charging system as the roller charging system as a contact charging system. In the DC charging system, the charging start voltage is changed due to a resistance change due to the environment of the charging member or a change in the thickness of the photosensitive member. Due to the fluctuation of Vth, it is difficult to keep the potential Vd on the photoconductor constant. Also, A
In the C-charging method, although the amount of ozone generated is smaller than that of corona charging, an ozone product adheres to the photoreceptor due to the use of electric discharge, which causes a problem such as image deterioration. Further, in the cleaner-less configuration, a problem common to the contact charging method is a problem such as poor charging due to contamination of the charging member by transfer residual toner.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to realize a cleaner-less system with a simple configuration to suppress an increase in the size and cost of the apparatus and to reduce ozone. Another object of the present invention is to provide a color image forming apparatus and a process cartridge capable of improving maintainability and reusing transfer residual toner.

[0027]

In order to achieve the above object, the present invention provides a plurality of image carriers, a plurality of charging means for charging each of the image carriers, and a charging surface of each image carrier. The image forming apparatus includes a plurality of developing means for developing the formed electrostatic latent image with a plurality of color developers to form toner images of the respective colors, and a plurality of transfer means for sequentially transferring the plurality of color toner images to a transfer target. In the color image forming apparatus, each of the charging units is formed of a flexible charging member that forms a contact portion with each of the image carriers, and a voltage of 1000 V or less is applied to each of the charging members. The developer remaining on each image carrier is recovered by the developing means.

Further, the present invention provides at least a plurality of image carriers, a plurality of charging means for charging each of the image carriers, and a plurality of electrostatic latent images formed on the charged surface of each image carrier. And a process cartridge for each color, which is formed by integrating a plurality of developing means for forming a toner image of each color by developing with the developer, respectively, is detachably mountable to the color image forming apparatus.

[0029]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus according to Embodiment 1 uses an electrostatic transport belt. The tandem type full-color image forming apparatus employs a direct injection charging method and a toner recycling process (cleanerless system).

The full-color image forming apparatus according to the present embodiment is a tandem color printer. In the tandem color printer, image forming means includes photosensitive drums 1a to 1d as image carriers, charging means 2a to 2d, and developing means. The means 4a to 4d are integrated to form a process cartridge 5a (to 5d) as shown in FIG.
FIG. 2 shows only one process cartridge 5a.

The process cartridges 5a to 5d are configured to be detachable from the apparatus main body. In the tandem color printer shown in FIG. 1, the amount of toner remaining in each of the process cartridges 5a to 5d is detected and detected. It has a means for informing the user, and when the process cartridge of a certain color runs out of toner and runs out of life, the user can continue using the process cartridge simply by replacing the process cartridge. It is not necessary to perform maintenance by a service person as performed in the above.

Further, by forming the process cartridge, a good image without any trouble can be always obtained until the life of the process cartridge is reached, and the process cartridge can be replaced at the end of the life. There is an advantage that the user can easily perform the operation. If the cartridge system is adopted, the photoconductor, the charger, and the
There is no need to separately replace the developing device or the toner container, etc., and the frequency of maintenance can be considerably reduced.

Further, since the cleanerless system is realized with a simple configuration, the size of the process cartridge can be reduced without using a cleaner container for collecting the transfer residual toner or the auxiliary cleaning means.

In FIG. 1, Y, M, C and K are image forming means for forming images of different colors, respectively.
Is with yellow toner, M is with magenta toner,
C forms an image with cyan toner and Bk forms an image with black toner. Here, the Y, M, C, and Bk developing units 4a to 4d have the same configuration except that toners, which are developers of respective colors, are included in the developing containers.

The details of the image forming operation will be described below.

The surfaces of the photosensitive drums 1a to 1d, which are uniformly charged by the charging units 2a to 2d, are irradiated with laser beams modulated in accordance with image data from a host such as a personal computer from the exposure units 3a to 3d. Thus, a desired electrostatic latent image is formed for each color on the photosensitive drums 1a to 1d. Then, each of the electrostatic latent images is reversely developed at a developing site by developing means 4a to 4d disposed opposite thereto, and is visualized as a toner image.

First, in the first color image forming means Y,
A yellow toner image is formed on the photosensitive drum 1a. During this time, the recording paper P is fed from a transfer material storage unit 6 such as a cassette by a paper feeding means 7 such as a paper feeding roller. 8. This recording paper P
The electrostatic transport belt 11 suspended by the driving roller 9a and the driven roller 9b after being stopped by the registration roller pair 8 once.
At a predetermined timing by a suction roller 19, and receives a transfer of a yellow toner image at a nip portion with the transfer roller 10a.

Next, in the image forming means M, C, and Bk for the second, third, and fourth colors, magenta, cyan, and black toner images are recorded from the respective photosensitive drums 1b, 1c, and 1d through the same steps as described above. A color toner image is formed by sequentially performing multiple transfer on the paper P.

The color toner image transferred onto the recording paper P is melted by fixing means 12 such as a fixing device and is permanently fixed on the recording paper P, and the recording paper P on which the color toner image is fixed is fixed. Is discharged from the paper discharge unit to the paper discharge tray 13 in a face-up direction, whereby a desired color print image is obtained. When the recording paper P is output in a face-down direction, the recording paper P is discharged to a discharge tray 15 by a discharge roller pair 14 via a predetermined conveyance path.

Next, the schematic configuration of the image forming section will be described. Here, the image forming unit Y for yellow toner will be described as a representative, but other image forming units M, C, and
Since the operation of Bk is the same, a description thereof will be omitted. The subscripts a correspond to yellow, b corresponds to magenta, c corresponds to cyan, and d corresponds to black. (1) Schematic Configuration of Image Forming Unit: In FIG. 2, reference numeral 1a denotes a photosensitive drum serving as an image carrier, which has a diameter of 30 m.
m, a rotating drum type OPC photosensitive member (negative photosensitive member), and is driven to rotate at a peripheral speed (process speed) of 50 mm / sec in a direction indicated by an arrow (clockwise) in the figure.

Reference numeral 2a denotes a conductive elastic roller (hereinafter referred to as a charging roller) as a contact charging member. The charging roller 2a is formed of a rubber or foam as a flexible member on a cored bar 2x. It is constituted by forming the medium resistance layer 2y. Here, the medium resistance layer 2y is formulated with a resin (for example, urethane), conductive particles (for example, carbon black), a sulfide agent, a foaming agent, and the like, and is formed in a roller shape on the cored bar 2x. Thereafter, the surface of the medium resistance layer 2y is polished as necessary, and the charging roller 2a as a conductive elastic body having a porous body surface having a diameter of 12 mm and a longitudinal length of 250 mm.
Was prepared.

When the resistance of the charging roller 2a used in this embodiment was measured, it was 100 kΩ. With respect to the resistance of the charging roller 2a, a voltage of 100 V is applied between the core metal 2x and the aluminum drum in a state where the charging roller 2a is pressed against an aluminum drum having a diameter of 30 mm so that a load of 1 kg is applied to the core metal 2x. It was measured.

Here, the charging roller 2 which is a conductive elastic body
It is important that a functions as an electrode. That is, it is necessary that the charging roller 2a has elasticity so as to obtain a sufficient contact state with the member to be charged and, at the same time, has a resistance low enough to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage when a defect site such as a pinhole is present in the member to be charged. When a photoreceptor for electrophotography is used as a member to be charged, a resistance of 10 ⁴ to 10 ⁷ Ω is desirable in order to obtain sufficient chargeability and leak resistance.

If the hardness of the charging roller 2a is too low, the shape is not stable, so that the charging roller 2a is permanently deformed due to contact with the member to be charged, and the desired roller shape cannot be secured. Not only cannot a uniform charging contact portion be secured with the member to be charged, but also microscopic contact with the surface of the member to be charged deteriorates. For this reason, the hardness of the charging roller 2a is preferably in a range of 25 to 50 degrees in Asker C hardness (manufactured by Kobunshi Keiki Co., Ltd.).

The material of the charging roller 2a is not limited to urethane.
(Ethylene / propylene / diene terpolymer), NB
A rubber material in which a conductive substance such as carbon black or metal oxide is dispersed in R, silicone rubber, IR, or the like for resistance adjustment, or a foamed material thereof is used. In addition, it is also possible to adjust the resistance by using an ionic conductive material without dispersing the conductive substance.

The charging roller 2a is disposed in pressure contact with the photosensitive drum 1a as a member to be charged with a predetermined pressing force against elasticity, so that a predetermined amount of charging nip is formed. The nip width is 3 mm. In the present embodiment, the surface of the charging roller 2a and the surface of the photosensitive drum 1a are moved at a peripheral speed of about 1.3 times in a direction opposite to each other at the charging nip portion at a speed of about 65 mm / sec. Was driven to rotate in the counter direction (clockwise direction in FIG. 2). That is, the photosensitive drum 1 as a member to be charged is placed on the surface of a charging roller 2a as a contact charging member.
A speed difference is provided for the surface a. Here, the peripheral speed is a surface moving speed when the charging roller is not in contact with the photoconductor.

Further, a DC voltage of -700 V was applied as a charging bias from a charging bias applying power source S1 to the core metal 2x of the charging roller 2a. In this embodiment, the surface of the photosensitive drum 1a is
The charging is uniformly performed by the direct injection charging method at a potential (−680 V) substantially equal to the voltage applied to a.

FIG. 10 shows the difference in the charging effect between the conventional "DC charging system" and the "direct injection charging system" used in the present embodiment.

The “DC charging method” is, as shown by a broken line in FIG. 10, a discharge threshold Vth (about 6 in the present embodiment).
00V), the surface potential of the photosensitive drum starts to rise, and thereafter, the surface potential of the photosensitive drum linearly increases with a slope of 1 with respect to the applied voltage.

On the other hand, in the “direct injection charging method” used in the present embodiment, as shown by the solid line in FIG. 10, a charging potential substantially proportional to the applied voltage can be obtained.

In general, the photosensitive drum requires a surface potential of about 400 to 1000 V. Therefore, in the "DC charging system", an applied voltage of about 1000 to 1600 V is required. Then 400-100
An applied voltage of about 0 V is sufficient.

In FIG. 2, reference numeral 3a denotes an exposing device as an image exposing means, which is constituted by a laser beam scanner including a laser diode, a polygon mirror and the like. The exposure unit 3a outputs a laser beam whose intensity is modulated in accordance with a time-series electric digital pixel signal of target image information, and scans and exposes the uniformly charged surface of the photosensitive drum 1a with the laser beam. This scanning exposure causes the photosensitive drum 1
The potential of the exposed portion a becomes about -150 V, and an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1a.

A developing device 4a is a reversal developing device using a non-magnetic one-component insulating toner (negative toner). The developing device 4a comprises a developing section and a developing container section. Have been. By using the non-magnetic one-component developing device as the developing device 4a, it is possible to provide a simple configuration that does not require the control of the T / C ratio (toner / carrier ratio) of the two-component developing device.

Incidentally, the electrostatic latent image formed on the surface of the photosensitive drum 1a is developed by the non-magnetic one-component developer Ta carried on the developing roller 16a and visualized. Here, the non-magnetic one-component developer Ta refers to a mixture of the toner ta and the charge promotion particles m described later. The toner ta is obtained by mixing toner particles with an external additive such as a fluidizing agent.

The developing roller 16a in the developing device 4a containing the non-magnetic one-component developer Ta contacts the photosensitive drum 1a at a predetermined pressure and rotates in the direction indicated by the arrow (counterclockwise).
A voltage of about -300 V is applied to the developing roller 16a from a DC power supply (not shown) as a developing bias.

The developing device 4a includes a developing blade 18a as a toner regulating member, a supply roller 17a, and a stirring member (not shown) for stirring the non-magnetic one-component developer Ta.

In order for the non-magnetic one-component developer Ta contained in the developing device 4a to adhere to the developing roller 16a, the non-magnetic one-component developer Ta is supplied to the supply roller 17a and the developing roller 1a.
At 6a, a charge must be applied by friction. As a material of the supply roller 17a, urethane foam, foam E
Known materials such as PDM rubber and foamed silicone rubber are used. In the present embodiment, the supply roller 17a made of urethane foam rubber is rotated counter (counterclockwise) with respect to the development roller 16a.

The developing roller 16 is supplied by the supply roller 17a.
Next, the amount of the developer ta applied on the surface a is regulated by a predetermined pressure of the developing blade 18a, which is a developer regulating member, and tribo is applied by friction.

By performing contact development in which the developing roller 16a comes into contact with the photosensitive drum 1a, not only the recovery of the developer Ta by simultaneous development cleaning described later is facilitated, but also the charge promotion described later as compared with the non-contact development. Particle m
Can be prevented from flying. Further, since the potential difference acting on the developing unit is small, the charge accelerating particles m
Can be suppressed, and the ratio of the charge accelerating particles m contained in the non-magnetic one-component developer Ta in the developing device 4a can be kept constant. As a result, a predetermined amount of the charge promoting particles m can be supplied to the charging roller 2a just before the end of the durability.

[Simultaneous Development Cleaning] The simultaneous development cleaning method will be described with reference to the schematic diagram of FIG.

In FIG. 6, □ indicates transfer residual toner existing on the photosensitive drum 1a, and ○ indicates new toner carried on the developing roller 16a after passing through the developing blade 18a. The symbol-in the symbol indicates the charging polarity of the toner.

The untransferred toner (toner remaining on the photosensitive drum 1a without being transferred to the recording paper P in the transfer step) is charged at the contact portion between the photosensitive drum 1a and the charging roller 2a with the charge promoting particles m, the photosensitive drum 1a and the charging roller The toner is rubbed with the toner 2a and becomes a negatively charged toner. With respect to the exposed portion (image portion) on the photosensitive drum 1a in the exposure process, the potential on the photosensitive drum 1a becomes about -150 V due to the exposure.
Becomes In the developing step, the transfer residual toner on the exposed portion remains on the photosensitive drum 1a as it is, and new toner on the developing roller 16a is developed on the photosensitive drum 1a by a developing bias (-300V) and a potential difference on the photosensitive drum 1a. Is done. At the same time, the negatively-charged transfer residual toner in the non-exposed portion (non-image portion) is charged with the charged potential (−680) on the photosensitive drum 1a.
V) and the developing bias (−300 V), the image is transferred onto the developing roller 16a. At this time, the developing roller 1
The new toner on 6a remains on the developing roller 16a.

The simultaneous development and cleaning is achieved by the above-described steps. By performing the simultaneous development and cleaning, the size of the apparatus can be significantly reduced and the toner can be reused.

[Developing Roller Configuration] The developing roller 16a is formed by laminating an elastic layer of about 4 mm on a core metal having a diameter of
6 mm. Here, silicone rubber was used for the elastic layer. In addition, as rubber used for the elastic layer,
Other NBR (NBR: nitrile rubber), butyl rubber,
Commonly used rubbers such as natural rubber, acrylic rubber, hydrin rubber, urethane rubber and the like can be mentioned. Usually, the hardness is reduced by increasing the oil impregnation amount of the rubber material. If the rubber hardness is high, the contact pressure at the contact portion between the developing roller 16a and the photosensitive drum 1a must be increased, and if the contact pressure is increased, the toner deteriorates, which is not preferable.

When the developing roller 16a has a single layer,
From the viewpoint of chargeability to the toner, when a negatively chargeable toner is used, urethane rubber, silicone rubber, NBR
Rubber or the like is preferably used. When a positively chargeable toner is used, fluorine rubber or the like is preferably used. When a coating layer is provided on the outer periphery of the elastic layer in consideration of charging of the toner, a polyamide resin, a urethane resin, a silicone resin, an acrylic resin, a fluororesin, or a mixture thereof is preferably used.

[Non-magnetic one-component developer] The non-magnetic one-component developer Ta is composed of the toner ta and the charge accelerating particles (charge assisting particles) m.
And the toner ta has a substantially spherical shape.
A non-magnetic one-component developer Ta is prepared by adding the charge accelerating particles m and a fluidizing agent to the toner ta as an external additive. The weight average particle diameter (D4) of the toner ta is 7 μm
Met. In the present embodiment, conductive zinc oxide particles having a particle diameter of 3 μm are used for the charge promotion particles m, and the toner ta100
2.5 parts by weight of the charge accelerating particles m was added to 1 part by weight of hydrophobically treated silica as an external additive.

[Toner] The toner ta of the non-magnetic one-component developer Ta is substantially in a state in which the wax component is not compatible with the binder resin in the tomographic observation of the toner particles using a transmission electron microscope (TEM). It is preferable that the particles are dispersed in an island shape in a spherical and / or spindle shape. By dispersing the wax component as described above and encapsulating it in the toner, it is possible to prevent deterioration of the toner and contamination of the image forming apparatus, etc., thereby maintaining good chargeability and excellent dot reproduction. It is possible to form a toner image over a long period of time. Further, since the wax component acts efficiently during heating, low-temperature fixability and offset resistance are satisfied.

As a specific method of observing the tomographic plane of the toner particles, the toner particles are obtained by sufficiently dispersing the toner particles in a cold-setting epoxy resin and then curing the same in a 40 ° C. atmosphere for 2 days. The cured product is dyed using ruthenium tetroxide and, if necessary, osmium tetroxide, and then a flaky sample is cut out using a microtome with diamond teeth, and the sample is cut out using a transmission electron microscope (TE
Observe the tomographic morphology of the toner particles using M). In the present invention, it is preferable to use a ruthenium tetroxide dyeing method in order to give a contrast between materials by utilizing a slight difference in crystallinity between the wax component used and the resin constituting the outer shell. FIG. 5 shows a typical example. In the toner particles used in the present embodiment, it was observed that the wax component was encapsulated in the outer shell resin.

In the DSC curve measured by a differential scanning calorimeter, the wax component was heated at a temperature of 40 to 130 ° C.
Those having the maximum endothermic peak in the region are used. By having a maximum endothermic peak in the temperature range, it greatly contributes to low-temperature fixing, and also effectively exhibits releasability. If the maximum endothermic peak is less than 40 ° C., the self-cohesive force of the wax component becomes weak, and as a result, the high-temperature offset resistance deteriorates and the gloss becomes too high. On the other hand, when the maximum endothermic peak exceeds 130 ° C., the fixing temperature becomes high, and it becomes difficult to appropriately smooth the surface of the fixed image. Particularly, when used for a color toner, the color mixing property is preferably reduced. Absent.

The maximum endothermic peak temperature of the wax component is measured according to “ASTM D3418-8”. For the measurement, for example, DSC-7 manufactured by PerkinElmer is used. The temperature correction of the device detection unit uses the melting points of indium and zinc, and the heat quantity correction uses the heat of fusion of indium. An aluminum pan was used as a measurement sample, an empty pan was set as a control, the temperature was raised and lowered once to obtain a pre-history, and then the measurement was performed at a heating rate of 10 ° C./min.

Examples of the wax component include paraffin wax, polyolefin wax, Fischer-Tropsch wax, amide wax, higher fatty acid,
Ester waxes and their derivatives or their graft / block compounds are used.

The toner preferably has a shape factor SF-1 value of 100 to 150 and a shape factor SF-2 value of 100 to 140 measured by an image analyzer. The value of 1 is 100 to 140,
More preferably, the value of the shape factor SF-2 is 100 to 120. Further, the above condition is satisfied, and (SF-2)
By setting the value of / (SF-1) to 1.0 or less, not only the various characteristics of the toner but also the matching with the image forming apparatus become extremely good.

Here, the shape factors SF-1 and SF-2 are determined by using FE-SEM (S-800) manufactured by Hitachi, Ltd.
A sample of 100 toner images magnified 500 times is randomly sampled, and the image information is introduced into an image analyzer (Luzex3) manufactured by Nicole via an interface, analyzed, and a value calculated by the following equation is obtained. It is. The shape factors SF-1 and SF-28 are shown in FIGS.

SF-1 = ｛(MXLNG) ² / ARE
A｝ × (π / 4) × 100 SF-2 = {(PERI) ² / AREA} × (1/4
π) × 100 AREA: toner projection area, MXLNG: absolute maximum length,
PERI: circumference The shape factor SF1-1 of the toner indicates the degree of roundness of the toner particles. As this value increases, the shape gradually changes from spherical to irregular. Also, the shape factor SF-
2 indicates the degree of unevenness of the toner particles, and as this value increases, the unevenness of the toner surface becomes more remarkable.

When the shape factor SF-1 of the toner exceeds 160, the shape of the toner becomes indefinite, so that the charge amount distribution of the toner becomes broad and the toner surface is easily crushed in the developing device. This causes a reduction in image density and image fogging.

In order to increase the transfer efficiency of the toner image, the shape factor SF-2 of the toner particles is from 100 to 140,
It is preferable that the value of (SF-2) / (SF-1) be 1.0 or less. The shape factor SF-2 of the toner particles is 140
Larger, the value of (SF-2) / (SF-1) is 1.0
When the value exceeds, the surface of the toner particles is not smooth, the toner particles have many irregularities, and the transfer efficiency from the photosensitive drum 1a to the recording paper P or the like tends to decrease.

Further, in order to faithfully develop minute latent image dots for the purpose of improving the image quality, the toner particles have a weight average particle diameter of 10 μm or less (preferably 4 to 8 μm), and the fluctuation in the number distribution The coefficient (A) is preferably 35% or less. In the case of toner particles having a weight average particle diameter of less than 4 μm, a large amount of toner particles remain untransferred on a photosensitive drum or an intermediate transfer member due to a decrease in transfer efficiency, and further cause non-uniform unevenness of an image due to fog or poor transfer. This is not preferable as the toner used in the present invention. When the weight average particle diameter of the toner particles exceeds 10 μm,
Fusing to members such as the surface of the photosensitive drum and the electrostatic transport belt is likely to occur. The coefficient of variation in the number distribution of toner particles is 35
%, The tendency is further enhanced. The particle size distribution of the toner particles can be measured by various methods. In the present embodiment, the particle size distribution is measured using a Coulter counter.

For example, a Coulter counter TA-II type (manufactured by Coulter) is used as a measuring device, and an interface (manufactured by Nikkaki) for outputting the number distribution and volume distribution and a personal computer are connected. A 1% NaCl aqueous solution is prepared using sodium. For example, ISOTON II (manufactured by Coulter Scientific Japan) can be used. As a measurement method,
0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and the measurement sample is further added to 2 to 20 m.
Add g. The electrolyte in which the sample is suspended is approximately 1
Dispersing treatment for ~ 3 minutes, the Coulter counter TA-
For example, a 100 μm aperture is used as an aperture according to the type II, and the particle size distribution of particles of 2 to 40 μm is measured based on the number, and the value is determined.

Coefficient of variation A in the number distribution of toner particles
Is calculated by the following equation.

Coefficient of variation A = [S / D1] × 100 where S is the standard deviation value in the number distribution of toner particles, and D1 is the number average particle size (μm) of the toner particles.

Further, as the toner particles used in the present invention, particles whose surface is coated with an external additive (including charge accelerating particles) are used so that a desired charge amount is imparted to the toner. Is preferred. Therefore, the coverage of the external additive on the toner surface is 5 to 99%, more preferably 10 to 99%.
Must be%.

To determine the external additive coverage on the toner surface,
Using FE-SEM (S-800) manufactured by Hitachi, 100 toner images are randomly sampled, and the image information is introduced into an image analysis device (Luzex3) manufactured by Nicole via an interface. The obtained image information has a difference in brightness between the toner particle surface portion and the external additive portion.
It is obtained by dividing the value into the area SG of the external additive portion and the area ST of the toner particle portion (including the area of the external additive portion) ST, and is calculated by the following equation.

External additive coverage (%) = (SG / ST) × 100 Examples of the external additive include metal oxides (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, oxide Tin (zinc oxide, etc.), nitride (silicon nitride, etc.), carbide (silicon carbide, etc.), metal salt (calcium sulfate, barium sulfate, calcium carbonate, etc.), fatty acid metal salt (zinc stearate, calcium stearate, etc.), carbon Black silica or the like is used. These external additives are used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the toner particles. In addition, these external additives may be used alone or in combination of two or more, but those subjected to hydrophobic treatment are more preferable.

When the amount of the external additive is less than 0.01 parts by weight, the fluidity of the one-component developer is deteriorated, the transfer and development efficiency is reduced, and the density unevenness of the image and the periphery of the image area Scatter phenomenon occurs in which the toner scatters.

On the other hand, when the amount of the external additive exceeds 10 parts by weight, an excessive amount of the external additive adheres to the photosensitive drum or the developing roller, thereby deteriorating the chargeability to the toner or disturbing the image. I do.

[Charging Promoting Particles] In the present embodiment, the charging promoting particles m having conductivity have a specific resistance of 10 ⁸ Ω · cm,
Although conductive zinc oxide particles having an average particle diameter of 3 μm including secondary aggregates were used, the material of the charge-promoting particles m was selected from conductive inorganic particles such as other metal oxides and various conductive materials such as mixtures with organic substances. Particles can be used.

The particle resistance is required to be 10 ¹² Ω · cm or less, preferably 10 ¹⁰ Ω · cm or less, in order to transfer electric charges via the particles.

The resistance was determined by normalizing by measuring by the tablet method. That is, about 0.5 g of a powder sample was placed in a cylinder having a bottom area of 2.26 cm ² and 15 kg was placed on the upper and lower electrodes.
Was applied and a voltage of 100 V was applied to measure the resistance value, and then normalized to calculate the specific resistance.

The particle size is 50 in order to obtain good charging uniformity.
μm or less is desirable, and the lower limit of the particle size is limited to 10 nm as long as the particles can be obtained stably. More preferably, the particle size should be between 1 and 5 μm. With such a particle size, not only the role as the charge accelerating particles but also the transfer efficiency can be improved.

In the present invention, when the particles are formed as aggregates, the particle size is defined as the average particle size of the aggregates.

In the measurement of the particle diameter, 100 or more particles were extracted from the observation with an optical microscope or an electron microscope,
The volume particle size distribution was calculated based on the maximum chord length in the horizontal direction, and the 50% average particle size was determined.

There is no problem that the charge promoting particles m exist not only in the form of primary particles but also in the form of aggregated secondary particles. Regardless of the state of aggregation, the form is not important as long as the function as the charge promotion particles as the aggregate can be realized.

As the charge accelerating particles m, colorless or nearly white particles are appropriate so as not to hinder the exposure of the latent image particularly when used for charging the photosensitive drum 1a. Further, in the case of performing color recording, considering that the charge accelerating particles m are transferred from the photosensitive drum 1a to the recording material P, a colorless or nearly white color is desirable. Further, in order to prevent light scattering by the charge accelerating particles m at the time of image exposure, the particles are desirably smaller than the constituent pixel size. The charge accelerating particles m are preferably non-magnetic so as not to hinder the exposure.

Next, a method of transferring the toner image on the photosensitive drum 1a to the recording paper P will be described.

The electrostatic transport belt 11 is connected to the four photosensitive drums 1
It arrange | positions so that it may contact all of a-1d. At this time, in a state where the transfer rollers 10a to 10d are not in contact with the electrostatic transport belt 11, the width of the nip formed by the electrostatic transport belt 11 and the photosensitive drums 1a to 1d is set to 0.5 mm or more. deep.

Here, the electrostatic transport belt 11 is supported by two rollers, a driving roller 9a and a driven roller 9b, to which an appropriate tension is applied.
When the driving roller 9a is driven, the electrostatic transport belt 11 moves at substantially the same speed in the forward direction with respect to the photosensitive drums 1a to 1d.

The electrostatic transport belt 11 has a thickness of 5
PVdF (polyvinylidene fluoride), polyamide having a volume reduction efficiency of about 10 ⁸ to 10 ¹⁶ Ω · cm
Polyimide, PET (polyethylene terephthalate),
Resin material such as polycarbonate and thickness 0.5-2mm,
Rubber materials such as chloroprene rubber, EPDM (ethylene-propylene-diene terpolymer), NBR (nitrile butadiene rubber), and urethane rubber having a volume efficiency of about 10 ⁹ to 10 ¹⁶ Ω · cm are used. In some cases, these materials include carbon, ZnO, SnO ₂ , and Ti.
Disperse conductive filler such as O ₂ to reduce volume efficiency by 10 ⁷
It may be adjusted to about 10 ¹¹ Ω · cm.

The photosensitive drums 1a to 1d are respectively provided on the back surface of the electrostatic transport belt 11 in opposition to the photosensitive drums 1a to 1d.
Transfer rollers 10a to 10d as transfer members corresponding to 1d
10d is placed in contact. When transferring the toner image to the recording paper P, an appropriate positive DC bias is independently applied to each of the transfer rollers 10a to 10d.

The recording paper P fed from the cassette 6 or a multi-feeder (not shown) is electrostatically conveyed while being controlled by the registration roller pair 8 so as to be synchronized with the formation of an electrostatic latent image by laser exposure. It is conveyed to the belt 11. Then, the recording paper P is attracted to the electrostatic transport belt 11 by the attracting roller 19, and the photosensitive drum 1 of the first color (yellow) is
a.

An electric field is generated on the recording paper P by the action of the positive DC bias applied to the transfer roller 10a, and the toner image is transferred onto the recording paper P.

Thereafter, the recording paper P is transported by the electrostatic transport belt 11 to the opposite portions of the photosensitive drums 1b to 1d of the second color (magenta), the third color (cyan) and the fourth color (black), and the corresponding transfer roller 10b By applying a positive DC bias to 10 to 10d, the toner images are sequentially transferred onto the recording paper P. After the transfer of the four color toner images onto the recording paper P is completed, the recording paper P is separated from the electrostatic transport belt 11 by the drive roller 9a.

10a to 10d are medium resistances as transfer means
These are transfer rollers of the photosensitive drums 1a to 1d.
The transfer nip is formed by pressing the electrostatic transfer belt 11 at a predetermined pressure.
Form. In the present embodiment, the transfer rollers 10a to 10a
As d, the resistance value is 5 × 10 ⁸ Use the Ω
The transfer was performed by applying a DC voltage of + 2000V.
That is, the recording paper P introduced into the transfer nip portion is
Is transported by being clamped by the
The toner images carried on the surfaces 1a to 1d are
It is sequentially transferred by force and pressing force.

Thereafter, the recording paper P to which the toner image has been transferred in the transfer step is separated from the surfaces of the photosensitive drums 1a to 1d and introduced into the fixing device 12, where the toner image is fixed and an image formed product (print , Copy) out of the apparatus.

The full-color image forming apparatus according to the present embodiment is cleaner-less as described above, and the transfer residual toner remaining on the surfaces of the photosensitive drums 1a to 1d after transferring the toner image onto the recording paper P is as follows. Without being removed by the cleaner, the photosensitive drums 1a to 1d are rotated to reach the developing unit via the charging unit, and are simultaneously cleaned (collected) by the developing units 4a to 4d (toner recycling process).

Thus, in the present invention, the charge accelerating particles m are mixed with the non-magnetic one-component developer Ta, and the developing devices 4a to 4
When supplied from d, the charge promotion particles m also function as a transfer aid, and as a result, it is possible to maintain a predetermined transfer efficiency even when various recording papers P are used as a transfer material. Become.

As described above, the toner ta and the charge accelerating particles m are supplied to the transfer portion without being separated by the development with the DC bias by the contact development as described above. (2) Regarding the direct injection charging of the photosensitive drum: a) The charge-promoting particles m having conductivity and impregnated in the non-magnetic one-component developer Ta of the developing device 4a are charged by the developing device 4a with the electrostatic latent image on the photosensitive drum 1a side. At the time of image development, since the developing contrast (difference between the exposed portion potential of the photosensitive drum 1a and the voltage applied to the developing roller) is as low as 200 V, an appropriate amount moves to the photosensitive drum 1a together with the toner ta without being separated from the toner ta.

The toner image on the photosensitive drum 1a is attracted to the recording paper P side by the influence of the transfer bias in the transfer area and is positively transferred.
Does not follow the electric field very much because it has conductivity. Therefore, a part of the charge accelerating particles m is transferred to the recording paper P by the adhesive force with the toner ta, and the other is substantially adhered and held on the photosensitive drum 1a and remains. Further, the effect of improving the transfer efficiency of the toner image from the photosensitive drum 1a side to the recording paper P side can be obtained by the presence of the charge promoting particles m substantially adhered and held on the surface of the photosensitive drum 1a.

Since the image forming apparatus in the toner recycling process does not use a cleaner, the transfer residual toner and the residual charge accelerating particles m remaining on the surface of the photosensitive drum 1a after the transfer are rotated by the rotation of the photosensitive drum 1a.
Then, it is carried as it is to the charging nip portion of the charging roller 2a, which is a contact charging member, and adheres to and mixes with the charging roller 2a.

Therefore, the photosensitive drum 1a and the charging roller 2a
The contact charging of the photosensitive drum 1a is performed in a state in which the charge promotion particles m are present in the nip portion. Incidentally, in the initial stage of printing, the charge accelerating particles m are not supplied to the surface of the charging roller 2a,
The charging roller 2a cannot be charged satisfactorily.
The surface may be coated with the charge promoting particles m in advance.
If the charge accelerating particles m are not applied to the surface of the charging roller 2a in advance, the charging roller 2a is rotated at a rotation speed more than 1.5 times in the counter direction with respect to the peripheral speed of the photosensitive drum 1a. It is possible to charge the photosensitive drum 1a by substantially increasing the chance of the roller 2a contacting the photosensitive drum 1a.

Thus, due to the presence of the charge accelerating particles m, even if the toner adheres to or mixes with the charging roller 2a, it is possible to maintain the close contact property and contact resistance of the charging roller 2a with the photosensitive drum 1a. Therefore, the contact charging member is a simple member such as the charging roller 2a, and the charging roller 2a performs direct injection charging of the photosensitive drum 1a by the charging roller 2a regardless of the contamination by the transfer residual toner. Can be.

That is, the charging roller 2a is charged with the charge promoting particles m
Contact the photosensitive drum 1a densely through the charging roller 2
a and the charge-promoting particles m present in the nip portion of the photosensitive drum 1a rub the surface of the photosensitive drum 1a without any gap, so that the charging of the photosensitive drum 1a by the charging roller 2a causes a discharge phenomenon due to the presence of the charge-promoting particles m. The stable and safe direct injection charging which is not used becomes dominant, and a high charging efficiency which cannot be obtained by the conventional roller charging or the like is obtained, and a potential substantially equal to the voltage applied to the charging roller 2a is applied to the photosensitive drum 1. And as a result, generation of ozone can be almost eliminated.

The transfer residual toner adhering to and entering the charging roller 2a is negatively charged due to the friction between the charge promoting particles m and the photosensitive drum 1a and the charging roller 2a at the contact portion between the photosensitive drum 1a and the charging roller 2a. Become toner. And
The transfer residual toner is gradually transferred from the charging roller 2a to the photosensitive drum 1
The developer is discharged onto the photosensitive drum 1a, reaches the developing unit with the movement of the surface of the photosensitive drum 1a, and is simultaneously cleaned (collected) with the developing unit 4a (toner recycling process).

As described above, in the simultaneous cleaning for development, the toner remaining on the photosensitive drum 1a after the transfer is developed in the subsequent image forming process (that is, the photosensitive drum 1a is charged and exposed to the latent image on the photosensitive drum 1a). At the time of forming an image and developing the latent image, a fog removing bias of the developing device 4a (that is, a fog removing potential difference which is a potential difference between a DC voltage applied to the developing device 4a and a surface potential of a non-exposed portion of the photosensitive drum 1a). Vback). In the case where the reversal developing method is employed as in the full-color image forming apparatus according to the present embodiment, the simultaneous development cleaning is performed by the electric field for collecting the toner from the non-exposed portion of the photosensitive drum 1a to the developing roller 16a and the developing roller 16a. Photosensitive drum 1
This is performed by the action of an electric field that causes the toner to adhere to the non-exposed portion potential a.

Even if the charge accelerating particles m fall off from the charging roller 2a, the image forming apparatus is operated to
The charge promotion particles m contained in the developer Ta of the developing device 4a move to the surface of the photosensitive drum 1a in the developing process, and
The rotation of “a” carries the toner to the charging unit via the transfer nip and continues to be sequentially supplied to the charging roller 2 a, so that good chargeability due to the presence of the charge promoting particles m is stably secured.

In this manner, the contact charging method, the transfer method,
In an image forming apparatus employing a toner recycling process, a charging roller 2a is used as a contact charging member, and irrespective of contamination of the charging roller 2a by transfer residual toner, ozone-less direct injection charging at a low applied voltage can be performed for a long time. It can be stably maintained throughout. As a result, a uniform chargeability can be given to the photosensitive drum 1a, and a low-cost image forming apparatus can be obtained with a simple configuration free from obstacles due to ozone products and failures due to poor charging.

Therefore, conventionally, in order to eliminate the history of the transfer residual toner, a so-called flyer member or the like for contacting the photosensitive drum surface and scattering the transfer residual toner after the transfer step has been required.
In this embodiment, simultaneous development and cleaning of the full-color image forming apparatus can be performed without requiring these members.

B) By interposing the charge-promoting particles m in the contact nip between the charging roller 2a and the photosensitive drum 1a, a lubricating effect (friction reducing effect) of the charge-promoting particles m is applied to the charge roller 2a and the photosensitive drum 1a. The speed difference can be easily and effectively provided.

By providing the speed difference between the charging roller 2a and the photosensitive drum 1a as described above, the opportunity for the charge promoting particles m to contact the photosensitive drum 1a at the contact nip portion between the charging roller 2a and the photosensitive drum 1a. It is possible to obtain a remarkably increased contact property, and to easily perform direct injection charging.

As a structure for providing a speed difference between the charging roller 2a and the photosensitive drum 1a, preferably, the transfer residual toner on the photosensitive drum 1a carried to the charging section is temporarily collected by the charging roller 2a to be evenly distributed. For this purpose, it is desirable that the charging roller 2a be driven to rotate, and that the rotation direction be opposite to the moving direction of the surface of the photosensitive drum 1a. That is, it is possible to perform the direct injection charging by dominating the transfer residual toner on the photosensitive drum 1a once by the reverse rotation and performing the charging.

If the amount of the charge-promoting particles m in the contact nip between the photosensitive drum 1a as the image carrier and the charging roller 2a as the contact charging member is too small, the lubricating effect of the particles m cannot be sufficiently obtained. Then, the friction between the charging roller 2a and the photosensitive drum 1a increases, and the driving torque becomes excessive.

According to the experiment, the intervening amount of the charge accelerating particles m was 1
0 ³ / mm ² or more is desirable. If it is lower than 10 ³ / mm ² , a sufficient lubricating effect and an effect of increasing the contact chance cannot be obtained. More preferably, 10 ^{3 to} 5 × 10 ⁵ pieces / mm ²
Is preferred. If it exceeds 5 × 10 ⁵ particles / mm ² , the drop of the charge-promoting particles m onto the photosensitive drum 1a increases remarkably, and regardless of the light transmittance of the particles m itself, the photosensitive drum 1
Insufficient exposure to a occurs. If it is 5 × 10 ⁵ particles / mm ² or less, the amount of particles falling off can be suppressed to a low level, and adverse effects can be avoided. In the range of the intervening amount, the photosensitive drum 1
When the amount of the particles m dropped on a is determined, 10 ² to 10 ⁵
Since the number of particles / mm ² is not larger than 10 ⁵ particles / mm ^{2, it} is desired that the abundance has no adverse effect on image formation.

Here, a method for measuring the intervening amount of the charge accelerating particles m and the abundance on the photosensitive drum 1a will be described.

The intervening amount of the charge accelerating particles m is determined by the charging roller 2a.
It is desirable to directly measure the contact surface portion of the photosensitive drum 1a and the photosensitive drum 1a, but most of the particles m existing on the photosensitive drum 1 before coming into contact with the charging roller 2a are peeled off by the contacting charging roller 2a while moving in the opposite direction. Therefore, in the present invention, the amount of particles on the surface of the charging roller 2a immediately before reaching the contact surface portion is defined as the intervening amount. Specifically, the rotation of the photosensitive drum 1a and the charging roller 2a is stopped in a state in which the charging bias is not applied, and the surfaces of the photosensitive drum 1a and the charging roller 2a are moved to a video microscope (OLYMPUS OVM10).
00N) and a digital still recorder (SR-3100 manufactured by DELTAS).

The charging roller 2a is brought into contact with the slide glass under the same conditions as when the charging roller 2a is brought into contact with the photosensitive drum 1a. 1
I photographed more than 0 places. In order to separate the individual particles m from the obtained digital image, binarization processing was performed with a certain threshold value, and the number of regions where the particles m exist was measured using desired image processing software. In addition, the abundance on the photosensitive drum 1a was measured by photographing the photosensitive drum 1a with the same video microscope and performing the same processing. The measurement was performed by photographing the photosensitive drum 1a with the same video microscope and performing the same processing.

Adjustment of the intervening amount of the charge accelerating particles m was performed by setting the blending amount of the charge accelerating particles m in the developer Ta of the developing device 4a. Generally, the toner ta is 100
The charge-promoting particles m are 0.01 to 20 parts by weight with respect to parts by weight.

In the present embodiment, the arrangement of the image forming means is Y → M → C → Bk. Further, in the present embodiment, since the direct injection charging method is used as the charging method, the role of the charge promotion particles m plays a large role.

The charging roller 2 is formed by the first color image forming means Y.
When the number of the charge accelerating particles m attached to a decreases, unevenness in image density is likely to occur. By setting the first color image forming unit Y to yellow, the yellow toner has lower luminosity than the other color toners, so that the image density unevenness is visually small.

In the subsequent image forming means M, C and Bk, if the charge accelerating particles m are not supplied from the developing device 4b for some reason (for example, toner empty), the preceding image is formed. The charge promotion particles m can be supplied from the developer (yellow).

That is, a certain amount of the charge accelerating particles m also adheres to the yellow toner recorded on the recording paper P. The yellow toner image comes into contact with the photosensitive drum 1b at the transfer section of the next magenta image forming unit M. At this time, the charge accelerating particles m are slightly left on the photosensitive drum 1b, and as a result, the charge accelerating particles m are supplied to the photosensitive drum 1b, albeit slightly.

However, in the image forming means Y for the first color, the toner image does not exist on the recording paper P, and the charge accelerating particles m do not exist. Therefore, by setting the first color image forming unit Y to yellow, even when the amount of the charge accelerating particles m attached to the charging roller 2a decreases, it is possible to minimize the influence of the image density unevenness.

<Evaluation of the present embodiment>
Image output durability of 00 sheets was performed.

[Comparative Example 1] In Comparative Example 1, a charging roller was used as a charging member, and a bias weighing AC and DC was applied to the charging roller, and charging was performed by discharging.
In addition, the charge promotion particles m were not mixed with the non-magnetic one-component developer Ta. That is, the apparatus does not use the charge accelerating particles m.

[Comparative Example 2] In Comparative Example 2, a charging roller was used as a charging member, and a DC-only bias was applied to the charging roller. The voltage applied to the charging roller is 1300
V, and the surface potential of the photosensitive drum is 680 V. Here, the charging roller contacts the photosensitive drum, and the total pressure is 1
000 gf, and rotates following the photosensitive drum. In addition, the charge promotion particles m were not mixed with the non-magnetic one-component developer Ta.

[Evaluation]: In each example, the chargeability and the color mixture of the toner were evaluated. The evaluation of the chargeability was made based on the superiority of the ghost image.

In the present embodiment, since the reversal development system is employed, the ghost means a portion where the image is exposed in the first rotation of the photosensitive drum (toner is an image portion) in the second rotation of the photosensitive drum. This means that a ghost image is generated due to insufficient development of the previous image pattern on the photosensitive drum due to shortage.

In the present embodiment, the occurrence of charging failure and the change in color due to color mixing were not observed when 1000 images were output. Regarding color mixing, it is considered that the effect of the charge promoting particles m contributing as a transfer aid is large.

In both Comparative Examples 1 and 2, when printing was continued, toner rapidly adhered to the charging roller, charging ghost occurred on less than 10 sheets, and charging failure occurred at 100 sheets. .

In the first embodiment, the non-magnetic one-component developer T
a) and the particles m can be stably supplied to the charging roller via the photosensitive drum, so that sufficient contact with the photosensitive drum is obtained, and the chargeability is improved. Satisfaction and its chargeability can be maintained. Also, when both the speed of the photosensitive drum and the speed of the charging roller are increased, good chargeability is exhibited. However, when the speed of the charging roller is reduced, a slight charge shortage occurs. Therefore, the charging roller and the photosensitive drum can be charged more efficiently by providing a speed difference.

<Others> 1) The charging roller 2a as the contact charging member is not limited to the charging roller of the embodiment.

As the flexible contact charging member, besides the elastic charging roller, a material and shape such as a fur brush, felt and cloth can be used. It is also possible to obtain a more appropriate elasticity and conductivity by laminating them.

2) Charging roller 2a as a contact charging member
For the applied charging bias or the applied developing bias to the developing roller 16a, the alternating voltage (AC voltage) may be superimposed on the DC voltage.

As the waveform of the alternating voltage, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Alternatively, a rectangular wave formed by periodically turning on / off a DC power supply may be used. As described above, as the waveform of the alternating voltage, a bias whose voltage value periodically changes can be used.

3) The image exposure means for forming an electrostatic latent image is not limited to the laser scanning exposure means for forming a digital latent image as in the first embodiment.
Normal analog image exposure or other light-emitting elements such as LEDs may be used, as long as an electrostatic latent image corresponding to image information can be formed, such as a combination of a light-emitting element such as a fluorescent lamp and a liquid crystal shutter. I don't mind.

The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is primary-charged uniformly to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head or an electrophotographic gun to write and form a desired electrostatic latent image. .

As described above, according to the present invention, there is provided a tandem type full-color image forming apparatus using an electrostatic transport belt, which employs a direct injection charging method and a toner recycling process (cleanerless system). In the forming apparatus, a cleaner-less image carrier is realized with a simple configuration that has not been used in the related art, so that the apparatus can be significantly reduced in size and toner can be reused.

A simple member such as a charging roller or a fur brush is used as the contact charging member, and the transfer efficiency is improved by mixing the charge promoting particles with the developer of the developing means. Direct injection charging can be maintained for a long period of time by reducing the effects of retransfer and paper dust, preventing color mixing, and improving the contact density of the contact charging member to the image carrier.

Further, by adopting the contact developing method, the transfer residual toner and the charge accelerating particles discharged from the charging roller can be efficiently collected by the developing device, and the image forming apparatus can be stabilized. It has become possible.

In this configuration, even when the toner, which is an insulator, is mixed into the contact charging member, the charge accelerating particles, which are conductive particles, are stably supplied at the same time, whereby the charge accelerating particles are brought into contact with the contact charging member. The contact between the contact charging member and the image carrier was improved by being interposed between the carriers, whereby the direct injection charging could be maintained.

Further, the image carrier and the contact charging member are brought into contact with each other with a speed difference. More preferably, the image carrier and the contact charging member are rotated so as to move in opposite directions to charge the image carrier, thereby further increasing the contactability and contact opportunity between the image carrier and the contact charging member, and transferring the image. Good charge can be maintained by suppressing the influence of the residual toner.

Further, by using the electrostatic transport belt, it is possible to balance the amount of the auxiliary charging particles with other image forming means.

<Embodiment 2> Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view showing a schematic configuration of a tandem-type full-color image forming apparatus according to the present embodiment. In this figure, the same elements as those shown in FIG. The description of them is omitted.

The full-color image forming apparatus according to the present embodiment is similar to the image forming apparatus described in the first embodiment, and is a toner for charging the surfaces of the photosensitive drums 20a to 20b as image carriers by a direct injection charging method. This is an image forming apparatus that employs a recycling process (cleanerless system). The toner image formed on the surface of each of the photosensitive drums 20a to 20d is multi-transferred onto the intermediate transfer belt 22,
It is characterized in that a full-color image is formed by secondarily transferring the multiple toner image onto the recording paper P.

In the full-color image forming apparatus according to the present embodiment, the photosensitive drums 20a to 20d serving as image carriers are used.
Embodiment 1 by adjusting the surface resistance of the first embodiment.
As a result, direct injection charging can be performed more stably and uniformly.

That is, the charging roller 2 as a contact charging member
The transfer residual toner adheres and mixes into the photosensitive drums 20a to 2d.
Even when the contact area between the photosensitive drums 20a to 20d is reduced, the presence of the charge promoting particles m and the surface resistance of the photosensitive drums 20a to 20d are set to be low in a region where a latent image can be formed.
Charges can be transferred more efficiently.

In this embodiment, the photosensitive drums 20a to 20a
d, a charge injection layer is provided on the surface of the photosensitive drums 20a to 20a.
The resistance of the 0d surface is adjusted.

FIG. 8 is a sectional view showing the layer structure of the photosensitive drums 20a to 20d having a charge injection layer on the surface used in the present embodiment. That is, the photosensitive drums 20a to 20d
A charge injection layer is formed on a general organic photosensitive drum, which is coated on an aluminum drum substrate (Al drum substrate) 20A in the order of an undercoat layer 20B, a positive charge injection prevention layer 21B, a charge generation layer 20C, and a charge transport layer 20D. The charging performance is improved by applying 20E.

The charge injection layer 20E is made of a photocurable acrylic resin as a binder and SnO ₂ ultrafine particles (having a diameter of about 0.03 μm) as conductive particles (conductive filler).
m) A lubricant such as tetrafluoroethylene resin (trade name: Teflon), a polymerization initiator, and the like are mixed and dispersed, and after coating, a photocuring method is used.
The film is formed by a thermosetting method or the like.

An important point for the charge injection layer 20E is the resistance of the surface layer. In the charge method by direct injection of charges, the transfer of charges can be performed more efficiently by lowering the resistance on the side of the member to be charged. On the other hand, when used as a photoreceptor, since the electrostatic latent image needs to be held for a certain period of time, the volume resistance value of the charge injection layer 20E is 1 × 1
The range of ⁰⁹ to 1 × 10 ¹⁴ Ω · cm is appropriate.

Even when the charge injection layer 20E is not used as in the present configuration, the same effect can be obtained, for example, when the charge transport layer 20D is in the above resistance range.

Further, the volume resistance of the surface layer is about 10 ¹³ Ω · cm.
The same effect can be obtained by using an amorphous silicon photoconductor or the like.

In the first embodiment, since the charge accelerating particles m are mixed with the developer and the particles m can be stably supplied to the charging roller via the photosensitive drum, On the other hand, sufficient contact properties were obtained, and as a result, the chargeability was satisfied and the chargeability was maintained. Also, when the peripheral speed of the photosensitive drum and the peripheral speed of the charging roller are both increased, good chargeability is exhibited. However, when the peripheral speed of the charging roller is reduced, insufficient charging occurs. Therefore, as described above, charging can be performed more efficiently by providing a speed difference between the rotation of the charging roller and the photosensitive drum.

On the other hand, in the present embodiment, by setting the resistance of the surface layers of the photosensitive drums 20a to 20d to be low as long as the electrostatic latent image can be maintained, the contact state can be improved even more efficiently. Since charge transfer can be performed, the peripheral speed of the charging rollers 2a to 2d is applied to the photosensitive drum 20a under the same conditions in which the charge accelerating particles m are mixed with the developer.
d, the photosensitive drums 20a to 20a
20d can be sufficiently charged.

Therefore, in the present embodiment, 50 mm / s
The charging rollers 2a to 2d are driven at a peripheral speed of approximately 50 mm / sec so that the surfaces of the charging rollers 2a to 2d move at a constant speed in the charging nip portion with respect to the surfaces of the photosensitive drums 20a to 20d moving at a peripheral speed of ec. ing.

The charge transport layer 20D and the charge injection layer 20E of the photosensitive drums 20a to 20d are functionally separated into two layers to improve the releasability of the surfaces of the photosensitive drums 20a to 20d. It is possible to add a larger amount of fluorine particles to the charge injection layer 20E than to add the particles to the charge injection layer 20E, thereby improving the slipperiness of the surfaces of the photosensitive drums 20a to 20d and transferring the particles from the photosensitive drums 20a to 20d to the intermediate transfer belt 22. The transfer efficiency of the toner image can be improved.

Further, in the image forming apparatus according to the present embodiment, as the exposure means 21a to 21d, L is used instead of the laser scanner used in the image forming apparatus according to the first embodiment.
An electrostatic latent image is formed on the surface of each of the photosensitive drums 20a to 20d by exposing the photosensitive drums 20a to 20d by the ED array.

The LED arrays 21a to 21d are provided with light emitting elements at a resolution of 600 dpi in the main scanning direction. However, the LED arrays 21a to 21d are smaller than a laser scanner, and require more exposure means than a configuration using a laser scanner. It can be efficiently placed in the device.

Hereinafter, the details of the image forming operation will be described.

The photosensitive drums 20a to 20a used in this embodiment
20d, charging rollers 2a to 2d, exposure means 21a to 21
(d) The functions of the developing units 4a to 4d in the image forming process are the same as those in the first embodiment, and the toner images are formed on the surfaces of the photosensitive drums 20a to 20d as described in the first embodiment.

On the other hand, the intermediate transfer belt 22 is arranged so as to abut against all of the four photosensitive drums 20a to 20d. At this time, with the primary transfer roller 23 not in contact with the intermediate transfer belt 22, the intermediate transfer belt 2
2 and the width of the nip formed by the photosensitive drums 20a to 20d were each set to 0.5 mm or more.

Here, the intermediate transfer belt 22 includes a driving roller 24, a tension roller 25, and a secondary transfer opposing roller 2.
6 are supported by three rollers, which are given an appropriate tension. By driving the driving roller 24, the intermediate transfer belt 22 is moved to the photosensitive drum 2.
It moves at substantially the same speed in the forward direction with respect to 0a to 20d.

The intermediate transfer belt 22 has a thickness of, for example, 50 to 300 μm and a low volume efficiency of 10 ⁹ to 10 ¹⁶ Ω ·
cm of resin material such as PVdF (polyvinylidene fluoride), polyamide, polyimide, PET (polyethylene terephthalate), and polycarbonate, and a thickness of 0.5 to 2 cm.
A rubber material such as chlorobrane rubber, EPDM (ethylene-propylene-diene terpolymer), NBR (nitrile butadiene rubber), urethane rubber, etc., having a volume efficiency of 10 ⁹ to 10 ¹⁶ Ω · cm is used. In some cases, these materials may include carbon, ZnO, Sn
In some cases, a conductive filler such as O ₂ and TiO ₂ is dispersed to adjust the volume efficiency to about 10 ⁷ to 10 ¹¹ Ω · cm. Further, the configuration can be simplified by adopting a configuration in which the intermediate transfer belt 22 is suspended by two rollers according to the main body layout of the image forming apparatus.
Instead, an intermediate transfer drum having a functional layer formed on the peripheral surface of the cylinder can be used as the intermediate transfer member. On the intermediate transfer drum, for example, an elastic body made of silicone rubber, chloroprene rubber, urethane rubber, EPDM, or the like is formed in a solid or foamed form on a cylindrical cored bar, and a urethane resin is further formed as a surface layer with a thickness of urethane resin. Those coated at 1 to 100 μm can be used. A conductive material such as carbon, a metal oxide, or a whisker subjected to a conductive treatment is dispersed in the elastic body. The elastic body and the surface layer have an electric resistance of 10 ⁶ to 10 ¹² Ω · cm. It is configured to be a resistance. Further, a fluorine-based resin or the like can be used for the surface layer coating.

Next, each of the photosensitive drums 20 is placed on the back surface of the intermediate transfer belt 22 and the portion facing the photosensitive drums 20a to 20d.
The primary transfer roller 23 is disposed in contact with the corresponding a to 20d.

At the time of the primary transfer of the toner image to the intermediate transfer belt 22, an appropriate positive DC bias is applied to each of the primary transfer rollers 23 independently.

An electrostatic latent image by exposure is formed on each of the photosensitive drums 20a to 20d while delaying a writing signal from the controller at a constant timing for each color in accordance with the distance between the primary transfer positions of each color. A primary image is sequentially transferred onto the intermediate transfer belt 22 by the action of the electrostatic latent image primary transfer roller 23, so that a multiplex image is formed on the intermediate transfer belt 22.

Thereafter, the secondary transfer roller 27 is disposed opposite to the secondary transfer opposing roller 26 disposed in contact with the back surface of the intermediate transfer belt 22 and in contact with the surface (image carrying surface) of the intermediate transfer belt 22. A bias having a polarity opposite to that of the toner is applied.
At this time, the recording paper P, which is a transfer material fed from the cassette 6 or a multi-feeder (not shown), passes between the intermediate transfer belt 22 and the secondary transfer roller 27 in accordance with the formation of the electrostatic latent image by the exposure. By doing so, the intermediate transfer belt 22
The four-color multiplex toner image carried on the upper surface is collectively secondarily transferred onto the surface of the recording paper P.

As the secondary transfer roller 27, for example, a metal core is covered with an elastic body such as EPDM, urethane rubber, CR and NBR whose volume resistivity is adjusted to 10 ⁶ to 10 ⁹ Ω · cm. A configuration can be employed.

The secondary transfer roller 27 is brought into contact with each of the photosensitive drums 20a to 20d at a linear pressure of about 5 to 15 g / cm, and in a forward direction with respect to the moving direction of the intermediate transfer belt 22. Are arranged to rotate at substantially the same speed.

On the other hand, after the completion of the secondary transfer, the transfer residual toner remaining on the intermediate transfer belt 22 and the paper dust generated by the conveyance of the recording paper P are disposed in contact with the intermediate transfer belt 22. It is removed and collected by the belt cleaning means 28. In the image forming apparatus according to the present embodiment, a brush roller disposed in contact with the surface of the intermediate transfer belt 22 is used as the belt cleaning unit 28,
For example, an elastic cleaning blade made of urethane rubber or the like can be used. Further, a cleaning blade is disposed on the upstream side with respect to the moving direction of the surface of the intermediate transfer belt 22, and a brush roller is disposed on the downstream side. By doing so, the cleaning efficiency can be further improved.

The recording paper P after the completion of the secondary transfer of the toner image is conveyed to the fixing means 12, where the toner image is fixed by the fixing means 12, and an image formed matter (print, copy) is formed. Is discharged out of the image forming apparatus.

In the image forming apparatus according to the present embodiment using the above-described intermediate transfer belt 22, the photosensitive drums 20a to 20a
The transfer efficiency when the toner image is primarily transferred from the 0d surface to the intermediate transfer belt 22 can be made substantially constant irrespective of the material, thickness, resistance, etc. of the recording paper P.

Further, since a high transfer efficiency can be stably obtained under various environments, the photosensitive drum 20a
The amount of untransferred toner remaining on the surface of the developing devices 4a to 4d and remaining on the surface of the developing devices 4a to 4d is substantially constant.

On the other hand, by using the photosensitive drums 20a to 20d provided with the charge injection layer 20E, the transfer efficiency is further improved, and the transfer residue which remains on the surfaces of the photosensitive drums 20a to 20d and is collected by the developing units 4a to 4d. The amount of toner is further reduced.

Therefore, the toner recycle process for directly injecting and charging the surfaces of the photosensitive drums 20a to 20d and collecting the untransferred toner in the developing devices 4a to 4d is always performed efficiently in a more stable state.

Further, since the paper dust generated from the recording paper P together with the secondary transfer residual toner not transferred to the recording paper P is removed by the belt cleaning means 28, the paper dust directly adheres to the photosensitive drums 20a to 20d. Charging roller 2a ~
It does not flow into the 2d or the developing devices 4a to 4d, so that the deterioration of the quality of the image output from the image forming apparatus is prevented.

Thus, the image forming apparatus according to the present embodiment using the intermediate transfer member is an image forming apparatus employing the electrostatic transport belt system according to the first embodiment of the present invention. Compared to the device, it is more advantageous in stabilizing the device.

[0187]

As is apparent from the above description, according to the present invention, a plurality of image carriers, a plurality of charging means for charging the respective image carriers, and a charging surface of each image carrier are provided. The image forming apparatus includes a plurality of developing means for developing the formed electrostatic latent image with a plurality of color developers to form toner images of the respective colors, and a plurality of transfer means for sequentially transferring the plurality of color toner images to a transfer target. In the color image forming apparatus, each of the charging units is formed of a flexible charging member that forms a nip portion with each of the image carriers, and a voltage of 1000 V or less is applied to each charging member. Since the developer remaining on each image carrier is collected by the developing unit, the color image forming apparatus is reduced in size and cost, while achieving ozone-less and improving maintainability. There is an advantage that it is possible to reuse the residual toner.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a color image forming apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a process cartridge of the color image forming apparatus according to Embodiment 1 of the present invention.

FIG. 3 is an explanatory diagram of a toner shape factor SF-1.

FIG. 4 is an explanatory diagram of a toner shape factor SF-2.

FIG. 5 is a diagram illustrating components of a toner.

FIG. 6 is an explanatory view of a simultaneous development cleaning method.

FIG. 7 is a sectional view illustrating a schematic configuration of a color image forming apparatus according to a second embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating a layer configuration of a photosensitive drum of a color image forming apparatus according to Embodiment 2 of the present invention.

FIG. 9 is a cross-sectional view illustrating a schematic configuration of a conventional color image forming apparatus.

FIG. 10 is a diagram illustrating a relationship between a voltage applied to a charging roller and a photosensitive drum surface potential.

[Explanation of symbols]

1a to 1d Photosensitive drum (image carrier) 2a to 2d Charging roller (charging member: charging means) 3a to 3d Exposure device (image exposure means: image information writing means) 4a to 4d Developing device (developing means) 5a to 5d Process cartridges 10a to 10d Transfer rollers (transfer means) 16a to 16d Developing rollers (developer carrier) 20a to 20d Photosensitive drums (image carrier) 22 Intermediate transfer belt (intermediate transfer body) P Recording paper (transfer material: transferred) Body) Ta non-magnetic one-component developer ta toner m charge accelerating particles

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/01 114 G03G 15/01 114A 5/147 503 5/147 503 9/08 9/08 9/09 374 9/08 374 15/02 101 15/02 101 15/08 503A 15/08 503 9/08 361 507 15/08 507L 507B (72) Inventor Katsuhiro Sakaizawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Co., Ltd. (72) Inventor Murasaki Murasaki 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term within Canon Inc. (reference) 2H003 AA12 AA18 CC05 2H005 AA08 AA15 AA21 CB07 DA09 EA01 EA05 FA07 2H030 AA06 AA07 AB02 AD01 AD02 AD03 BB22 BB42 BB71 2H068 AA04 AA08 CA37 FA27 FB13 FC01 FC08 2H077 AA37 AC16 EA14 EA15 GA11 GA13

Claims (15)

[Claims] 1. A plurality of image carriers, a plurality of charging means for charging each of the image carriers, and an electrostatic latent image formed on a charged surface of each image carrier, respectively, by a developer of a plurality of colors. A color image forming apparatus comprising: a plurality of developing means for developing to form toner images of respective colors; and a plurality of transfer means for sequentially transferring the toner images of the plurality of colors to a transfer-receiving body. A flexible charging member forming a contact portion with a body, a voltage of 1000 V or less is applied to each charging member, and a developer remaining on each image carrier after transfer of a toner image is transferred by the developing unit. A color image forming apparatus characterized by being collected. 2. The color image forming apparatus according to claim 1, wherein a speed difference is provided between the surface of each charging member and the surface of each image carrier. 3. A color image forming apparatus according to claim 1, wherein each of said charging members is constituted by an elastic conductive roller. 4. The method according to claim 1, wherein each of the charging member and each of the image carriers are rotationally moved in opposite directions at their contact portions, and the peripheral speed of the charging member is set to be equal to or higher than the peripheral speed of the image carrier. The color image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein at least a nip portion between each of the charging members and each of the image carriers has conductive charge-promoting particles interposed therebetween. Color image forming apparatus. 6. The color image forming apparatus according to claim 5, wherein said charge-promoting particles are contained in at least developers of each color of said developing means. 7. The resistance of the charge-promoting particles is 10 ¹² Ω · c.
The color image forming apparatus according to claim 5, wherein the particle size is 50 μm or less. 8. The transfer member according to claim 1, wherein the transfer member is an intermediate transfer member that transfers a toner image to a transfer material at a time after a transfer material or a toner image of each color is sequentially multiplex-transferred.
The color image forming apparatus as described in the above. 9. The method according to claim 1, wherein the outermost layer of each of the image carriers has a volume resistance of 1 × 10 ⁹ Ω · cm or more and 1 × 10 ¹⁴ Ω · cm or less. 6. A color image forming apparatus according to any one of the preceding claims. 10. The color image forming apparatus according to claim 1, wherein the developer contained in each of the developing units is a non-magnetic one-component toner. 11. The shape factor S of the non-magnetic one-component toner
F-1 is 100 to 150, shape factor SF-2 is 100 to
The color image forming apparatus according to claim 10, wherein the number is 140. 12. Each developing means is a contact developing type developing means, and each developer carrier of the developing means is disposed in contact with each image carrier to develop the electrostatic latent image. And forming a toner image of each color by using
2. The color image forming apparatus according to claim 1. 13. A color toner image having the lowest visibility is formed on an image carrier on which a toner image is formed first among the plurality of image carriers. 13. The color image forming apparatus according to any one of items 12 to 12. 14. The image information writing means for forming an electrostatic latent image on each charged surface of the plurality of image carriers comprises an image exposure means. The color image forming apparatus according to one of the above. 15. At least a plurality of image carriers, a plurality of charging means for charging each of the image carriers, and an electrostatic latent image formed on a charged surface of each image carrier with a developer of a plurality of colors. A process cartridge for each color configured by integrating a plurality of developing units each for developing a toner image of each color, wherein the process cartridge is a color image forming apparatus according to any one of claims 1 to 14. A process cartridge which is detachable.