JPH08254870A - Color image forming device - Google Patents

Abstract

PURPOSE: To provide a color image forming device which prevents toner from scattering from an exposed part, is small in size and obtains a high quality image. CONSTITUTION: The color image forming device comprises an electrifier 11, an exposure optical system 12 and a developing unit 13, which are disposed outside or inside the periphery of a photoreceptor drum 10, forms toner images one on top of the other by the repetition of electrification, image exposure and development during one rotation of the photoreceptor drum 10, then cleans the periphery of the photoreceptor drum 10 by a cleaner after the toner image are transferred to a transfer material all at once. In the color image forming device, the electrifier 11 has a saw-teeth-like discharge electrode 111, in the vicinity of the developing unit 13, a toner scatter prevention electrode 13B is provided, the potential of a bias voltage which is applied to the side plate 113 of the electrifier 11 is set higher than the electrification potential of the photoreceptor drum 10 but is set equal to the potential of a bias voltage which is applied to the toner scattering prevention electrode 13B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention arranges a plurality of sets of charging means, image exposing means and developing means on the peripheral surface of an image forming body so that toner is superposed on the image forming body during one rotation of the image forming body. The present invention relates to an electrophotographic color image forming apparatus that is also formed.

[0002]

2. Description of the Related Art As a method for forming a multicolor image, an image forming member, a charger, a developing device, etc., which are the same in number as the necessary colors for the image, are provided, and a single color toner image formed on each image forming member is used. A device that creates a color image by overlaying it on the paper (A)
Or a device (B) that forms a color image by repeating charging, image exposure and development for each color by rotating one image forming body a plurality of times, or charging for each color within one rotation of one image forming body. An apparatus (C) for forming a color image by sequentially performing image exposure and development is known.

Of these, the above-mentioned device (A) has a drawback that the volume of the device becomes large because it requires a plurality of photoconductors and intermediate transfer members. On the other hand, the device (B) requires charging means, image exposure means and photoconductors. Since there is only one, the volume is reduced, but the size of the image formed is limited to the surface area of the photoreceptor or less.

On the other hand, the device (C) is excellent in that there is no restriction on the image size and high-speed image formation can be realized.

Corona discharge type charging means used in the electrophotographic image forming apparatus includes wire discharge type (corotron, scorotron, dicorotron, etc.) and pin discharge type (pin electrode type, sawtooth electrode type, etc.). It is roughly divided into. Since the latter produces less ozone, it has recently been used in electrophotographic copying machines, printers and the like. In particular, Japanese Patent Laid-Open No. 63-75272 and Japanese Patent Laid-Open No. 5-45999 disclose charging means having a structure in which a plurality of sawtooth electrode portions are used on one thin plate member.

[0006]

However, in the apparatus (C), a plurality of sets of charging means, image exposing means and developing means must be arranged, so that the apparatus becomes large and the apparatus is formed in the previous step. Exposure to form a toner image on the toner image causes photo-elimination to cause toner scattering and stains on the formed image and on the charging means.However, it is extremely difficult to clean this stain. There is a problem in that the efficiency is lowered and the image quality is lowered.

An object of the present invention is to provide a color image forming apparatus which solves this problem and enables high-efficiency and uniform charging, and is small in size and capable of obtaining high-quality images.

[0008]

The above-mentioned object is to provide a plurality of sets of charging means, image exposing means and developing means on the outside or inside of the peripheral surface of the image forming body so that one rotation of the image forming body is performed. Electrification,
In a color image forming apparatus, which repeats image exposure and development to form toner images in a superimposed manner, transfers the toner images to a transfer material at once, and then cleans the peripheral surface of the image forming body by a cleaning unit, The charging means has a sawtooth discharge electrode, and a toner scattering prevention electrode is provided in the vicinity of the developing means. The potential due to the bias voltage applied to the side plate of the charging means is the charging potential of the image forming body. This is achieved by the color image forming apparatus, which is set to a higher value and has the same potential as the bias voltage applied to the toner scattering prevention electrode.

Further, the bias voltage applied to the side plate and the toner scattering prevention electrode is obtained by being grounded via a varistor or a diode, and the potential due to the bias voltage is 200 to 200 times the charging potential. The above-mentioned color image forming apparatus, which is set to be 1000 V higher, is a preferred embodiment.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and function of a color image forming apparatus according to the present invention will be described with reference to FIGS.

(First Embodiment) FIG. 3 shows a structure in which the base of the photosensitive drum 10 is formed of a transparent member, and each exposure optical system 12 is arranged so as to face the inner peripheral surface of the base. 1 illustrates a color image forming apparatus configured to perform image exposure through a sheet.

The photosensitive drum 10 used in this apparatus is
A transparent conductive layer is formed on the outer periphery of a substrate formed of a transparent member such as optical glass or transparent acrylic resin, and an organic photoconductive layer (OPC) is applied on the transparent conductive layer to form a photosensitive layer. The transparent conductive layer is grounded. It is rotated clockwise in this state.

Reference numeral 11 denotes a scorotron charger, which is a charging means to be described later, which performs a charging action on the photosensitive layer of the photosensitive drum 10 by a control electrode held at a predetermined potential and corona discharge by a sawtooth discharge electrode. The control electrode is a charger that is held so as to maintain a predetermined gap with respect to the peripheral surface of the photoconductor drum 10 and applies a uniform potential to the photoconductor drum 10.

FIG. 1 is an enlarged cross-sectional view showing the vicinity of the charging device 11 and the developing device 13 of FIG. 3. In FIG. 1, 111 is a sawtooth-shaped point of equal length projecting toward the photoconductor drum 10 at a constant pitch. Is a sawtooth discharge electrode for corona discharge, and is made by etching a stainless steel plate having a thickness of 0.1 mm as shown in FIG.
a is a pitch of 5 mm, and the radius R of its tip is processed to 30 μm or less. Reference numeral 113 is a side plate which is a stainless steel shield plate having an opening having a U-shaped cross section. The above-mentioned sawtooth discharge electrode 111 is attached to the supporting member 120 made of an insulating resin, pressed down by the pressing member 121 also made of an insulating resin, and fixed so as to drop into the side plate 113. On the opening side of 113, for example, a stainless plate having a thickness of 0.1 mm is etched to form a mesh having a width of 1 mm.
The control electrode 115 formed in the above is provided.
The photosensitive drum 10 and the charging device 11 are held so as to always maintain a predetermined gap.

Reference numeral 12 denotes an exposure optical system which is an image exposure means composed of light emitting elements such as LEDs, FL, EL, PL arranged in the axial direction of the photoconductor drum 10 and a SELFOC lens, which is a separate image reading. The image signals of the respective colors read by the apparatus are sequentially taken out from the memory and input to the respective exposure optical systems 12 as electric signals. The emission wavelength of the light emitting device used in this example is 600-80.
It is in the range of 0 nm. Each of the exposure optical systems 12 is attached to a columnar support member 40 and is housed inside the base of the photosensitive drum 10.

The exposure optical system 12 includes an L
It may be composed of a combination of optical shutter members such as CD, LISA, and PLZT, and an imaging lens such as SELFOC lens.

The exposure optical system 12 is composed of the exposure optical systems 12 (Y), 12 (M), 12 (C) and 1 respectively.
2 (K) have the same central angle with respect to the rotation center of the photosensitive drum 10, and are installed at positions where the distances in the drum circumferential direction are equal.

Reference numerals 13Y, 13M, 13C and 13K denote developing units which are developing means for accommodating each of yellow (Y), magenta (M), cyan (C) and black (K) developers.
The developing sleeves 130 rotate in the same direction while maintaining a predetermined gap with respect to the peripheral surface of the photoconductor drum 10.

Each of the developing devices 13 is the charging device 1 described above.
The electrostatic latent image formed on the photosensitive drum 10 by the charging by 1 and the image exposure by the exposure optical system 12 is reversely developed in a non-contact state by applying a developing bias voltage.

Reference numeral 13B is a toner scattering prevention electrode provided in a portion close to the exposed portion of the developing device 13 after the second development, and a bias voltage having the same polarity as that of the toner is applied to the toner scattering prevention electrode 13B. However, the toner is prevented from scattering from the toner image previously developed and formed.

In the present embodiment, the optical static eliminator 12 further comprises light emitting elements such as LEDs, FL, EL, PL arranged in the axial direction of the photosensitive drum 10 and a SELFOC lens.
Between the separator 14B and the cleaning device 19, L is attached to the support member 40 so as to irradiate the photoconductor drum 10 with light in the emission wavelength range of 600 to 800 nm. As a result, the photoconductor drum 10 is subjected to photo-electrification before cleaning to be more completely cleaned, and then charged by the DC corona discharge of the charger 11 (Y), which is the first charger, which is performed first, and thus is more uniform. Proper charging will be performed.

Next, the process of the color image forming apparatus in this apparatus will be described.

In the image reading apparatus which is separate from this apparatus, the original image is an image read by the image pickup device or an image edited by a computer is once used as an image signal for each color of Y, M, C and K. Stored and stored in memory.

When the image recording is started, the photoconductor drive motor is rotated to rotate the photoconductor drum 10 clockwise.
At the same time, the application of electric potential to the photoconductor drum 10 is started by the charging action of the charging device 11 (Y) that performs the initial charging by the DC corona discharge.

After the photoconductor drum 10 is applied with a potential, the exposure optical system 12 (Y) starts image exposure with an electric signal corresponding to a first color signal, that is, a yellow (Y) image signal, and the drum is started. An electrostatic latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer on the surface by the rotational scanning of.

The latent image is reversely developed by the developing device 13 (Y) with the developer on the developing sleeve 130 in a non-contact state, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10. .

Next, the photosensitive drum 10 is further given a potential on the yellow (Y) toner image by the charging action of the charger 11 (M), and the second color signal of the exposure optical system 12 (M), that is, Image exposure is performed by an electric signal corresponding to the magenta (M) image signal, and non-contact reversal development by the developing device 13 (M) causes the magenta (M) toner on the yellow (Y) toner image. The images are sequentially superimposed and formed. Since the charging in this case is performed by DC corona discharge, the yellow (Y) toner image previously developed and formed is not discharged. However, at the time of exposure by the exposure optical system 12 (M), the yellow (Y) toner image is subject to photo-electrification due to the exposure, and toner scattering occurs. In order to prevent this toner scattering, the toner scattering prevention electrode 13B is provided in the developing device 13 after the second development described above.
Is provided, and a voltage having the same polarity as the charging of the toner is applied to the toner scattering prevention electrode 13B, so that the toner image previously developed and the toner scattering from the developing device 13 are prevented. .

By the same process, the charger 11 (C),
The cyan (C) toner image corresponding to the third color signal is further generated by the exposure optical system 12 (C) and the developing device 13 (C), and finally, the charger 11 (K) and the exposure optical system 12 are used.
(K) and the developing device 13 (K) sequentially form a black (K) toner image corresponding to the fourth color signal, and the color image is formed on the peripheral surface of the photosensitive drum 10 within one rotation. A toner image is formed. Since charging by the second and subsequent charging means is charging by DC corona discharge, the toner images of magenta (M), cyan (C) and black (K) are not discharged, so that the next transfer is efficient. Often done.

The color toner image thus formed on the peripheral surface of the photoconductor drum 10 is a transfer material which is a transfer material which is conveyed from the paper feed cassette 15 in the transfer device 14A and is fed in synchronization with the driving of the timing roller 16. Transferred to paper.

The transfer paper on which the toner image has been transferred is separated from the peripheral surface of the drum by removing the charge in the separator 14B, and is fused and fixed on the transfer paper by the fixing device 17 via the conveyor belt 20. After that, the paper feed roller R ₁ ,
It is discharged onto the tray 200 at the upper part of the apparatus via R ₂ , R ₃ and 18.

On the other hand, the photosensitive drum 10 from which the transfer paper is separated
The cleaning device 19 removes and cleans residual toner to continue forming the toner image of the original image, or temporarily stops and waits for formation of a new toner image of the original image.

(Embodiment 2) FIG. 4 is a constitution in which the image exposure means is arranged so as to face the outer peripheral surface of the image forming body, and image exposure is carried out from the outside of the image forming body to the photoreceptor on the peripheral surface. The same color image forming apparatus is shown, and the members having the same function are indicated by the same reference numerals as those of the apparatus shown in FIG.

Reference numeral 10 denotes a photosensitive drum which is an image forming body, which is a photosensitive layer formed by applying OPC which is an organic photoconductor on a drum-shaped substrate made of a conductor such as aluminum. The substrate is grounded. It is driven and rotated clockwise in the closed state.

Reference numeral 11 denotes a scorotron charger, which is a charging means, and corona discharge by a control electrode and a sawtooth discharge electrode held at a predetermined potential with respect to the above-mentioned photosensitive layer of the photosensitive drum 10 as in the first embodiment. The charging operation is performed by means of the first charging device 11 (Y) and the second charging device as in the first embodiment.
~ The charging devices 11 (M) to 11 (K), which are the fourth charging devices, perform charging by DC corona discharge. As a result, the photosensitive drum 10 is uniformly charged.

Reference numeral 12 denotes an exposure optical system which is an image exposure means, and includes LEDs, FL, E arranged in the axial direction of the photosensitive drum 10.
It is composed of light emitting elements such as L and PL and a Selfoc lens. The image signals of the respective colors read by the separate image reading device are sequentially taken out from the memory and input as electric signals to the respective exposure optical systems 12.
The emission wavelength of the light emitting device used in this example is 600 to
It is in the range of 800 nm.

The exposure optical system 12 includes an L
It may be composed of a combination of optical shutter members such as CD, LISA, and PLZT, and an imaging lens such as SELFOC lens.

13 is yellow (Y), magenta (M),
A developing device, which is a developing unit that contains cyan (C) and black (K) developers, is provided with a developing sleeve 130 that rotates in the same direction with a predetermined gap from the peripheral surface of the photosensitive drum 10. ing.

Each of the developing devices 13 is in a non-contact state by applying a developing bias voltage to the electrostatic latent image formed on the photosensitive drum 10 by charging by DC corona discharge and image exposure by the exposure optical system 12. Reverse development with.

Further, a toner scattering prevention electrode 13B is provided in a portion close to the exposed portion of the developing device 13 after the second exposure. A voltage having the same polarity as the charging of the toner is applied to the toner scattering prevention electrode 13B to prevent the toner image previously developed and formed and the toner scattering from the developing device 13.

Image formation by the apparatus of the second embodiment,
The recording is also performed by the same process as that of the apparatus shown in the first embodiment.

In the first and second embodiments described above, assuming that the photosensitive drum 10 is charged to -700 V, the DC power source E ₁ is applied to the control electrode 111 of the charger 11 as shown in FIG. -700V, charger 1
No. 1 side plate 113 and toner scattering prevention electrode 13
B is -1.2 kV by DC power supply E ₂ and discharge electrode 1
A bias voltage of -4 kV is applied to each of 11 by the DC power source E ₃ . Thus, the side plate 11
3 potential and toner scattering prevention electrode 13
By setting the potential of the bias voltage of B to the same potential, the power source for the bias voltage is shared and the increase in the number of power sources is avoided.

When the bias voltage value applied to the control electrode 111 is V ₁ and the bias voltage value applied to the toner scattering prevention electrode 13B is V ₂ , the absolute values |
V ₁ |, | V ₂ | is _{| V 1 | - | V 2} | absolute value of the potential of When ≧ 200 to 1000 (V) toner scattering preventing electrode 13B is higher than the absolute value of the potential of the photosensitive drum 10 Therefore, toner scattering is more effectively prevented, which is preferable. However, at 1000 V or higher, most of the ions generated at the discharge electrode are directed toward the control electrode. As a result, the controllability of the control electrode becomes insufficient, and even ions that are not required for the photoconductor may arrive, resulting in uneven potential.

Further, as shown in FIGS. 2A and 2B, a varistor can be used to reduce the power supply for the bias voltage. This is controlled by the DC power source E ₁ ,
Alternatively, since an ionic current flows between the discharge electrode 111 and the ground through the side plate 113, a predetermined voltage can be generated by inserting the varistors VR ₁ and VR ₂ whose resistance characteristics are selected between them. Is. The DC power supply E ₂ can be omitted in FIG. 2A, and the DC power supply E ₁ and the DC power supply E ₂ can be omitted in FIG. 2B.
Further, the varistors VR ₁ and VR ₂ can be replaced with diodes whose resistance characteristics are selected.

Although the color image forming apparatus of the present invention has been described as having a drum-shaped image forming body, it has a belt-shaped image forming body provided with a plurality of sets of image forming means. Needless to say, the present invention can be applied to a device that forms a color image with one rotation.

[0045]

As described above, according to the present invention, the potentials of the side plate of the charger and the toner scattering prevention electrode are set to be the same and higher than the potential of the control electrode of the charger, so that toner scattering is prevented from the exposed portion. Effectively reduced the power supply for the bias voltage. Further, by inserting a varistor or a diode between the side plate of the charger and the control electrode and the ground, the power supply for the bias voltage is greatly reduced. Therefore, it is possible to provide a color image forming apparatus which is compact in size, reduces manufacturing cost, prevents toner from scattering from an exposed portion, can uniformly and highly efficiently charge, and obtains a high quality image.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing a configuration near a developing device of a color image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view showing a method of applying a bias voltage to the charger of the device of the present invention.

FIG. 3 is a cross-sectional configuration diagram showing an embodiment of a color image forming apparatus of the present invention.

FIG. 4 is a sectional configuration diagram showing another embodiment of the color image forming apparatus of the present invention.

5 is a plan view showing an example of a sawtooth electrode of the charger of FIG.

[Explanation of symbols]

10 Photoreceptor Drum (Image Forming Body) 11 Charging Device (Charging Means) 11 (Y) First Charging Device (First Charging Means) 12 Exposure Optical System (Image Exposure Means) 12L Photo Static Eliminator 13 Developing Device (Developing Means) 13B toner scattering prevention electrode 14A transfer device 14B static eliminator 15 sheet feeding cassette 17 fixing device 19 cleaning device 111 discharge electrode 113 side plate 115 control electrodes E ₁ , E ₂ , E ₃ , E ₄ DC power supply VR ₁ , VR ₂ varistor

Claims (3)

[Claims] 1. A plurality of sets of charging means, image exposing means and developing means are provided outside or inside the peripheral surface of the image forming body, and charging, image exposing and developing are repeated during one rotation of the image forming body. In the color image forming apparatus, the toner images are formed by superimposing them on each other, and then the toner images are collectively transferred to a transfer material, and then the peripheral surface of the image forming body is cleaned by a cleaning unit. A toner scattering prevention electrode is provided in the vicinity of the developing means, and the potential due to the bias voltage applied to the side plate of the charging means is set higher than the charging potential of the image forming body. A color image forming apparatus having the same potential as that of a bias voltage applied to the toner scattering prevention electrode. 2. The color image forming apparatus according to claim 1, wherein the bias voltage applied to the side plate and the toner scattering prevention electrode is obtained by being grounded via a varistor or a diode. 3. The color image forming apparatus according to claim 1, wherein the potential due to the bias voltage applied to the side plate and the toner scattering prevention electrode is 200 to 1000 V higher than the charging potential.