JP2002202653A - Image forming device - Google Patents

Abstract

(57) [Problem] A multicolor toner image is formed on a photoconductor by repeating a series of steps including charging, image exposure, and development for each color, and then formed on a transfer material. Provided is a color image forming apparatus that performs collective transfer, which can support full-color to two-color images, has high color image clarity, can be compact, and can be operated at high speed. SOLUTION: In a color image forming apparatus for forming a color image by sequentially repeating each step of charging, exposure and development for different colors, a developing step of a specific color;
Between the charging process for the next color, a static eliminator is provided for neutralizing the dark portion potential and the bright portion potential on the photoreceptor to almost the same level. The developing bias in the developing step corresponding to the unnecessary color is turned off or switched to the reverse polarity according to the type of the color.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus utilizing electrophotography, and more particularly, to forming a multicolor toner image of two or more colors on a photoreceptor and transferring the image to a medium such as paper. The present invention relates to a color image forming apparatus that performs batch transfer.

[0002]

2. Description of the Related Art An electrophotographic system, an ink jet system, and the like are used as an apparatus for converting a color original into a faithful or desired color and reproducing the image, or as an apparatus for forming a color image based on an output image from a computer. There have been proposed two-color, multi-color or full-color analog or digital image forming apparatuses utilizing various methods such as a thermal method.
Of these, the inkjet method or the thermal method
Although it has the advantage of being able to provide a relatively simple and inexpensive device as compared with the electrophotographic system, it has problems such as problems of sharpness of color images and ink clogging when left for a long time. Have left. On the other hand, an apparatus utilizing electrophotography provides a relatively stable and good color image, although the configuration is complicated.

Many conventionally known electrophotographic color image forming apparatuses use two color (for example, black and red) to four color (cyan, magenta, yellow, and black) color toners for charging, image exposure, and image formation. A series of steps of development and transfer are performed for each color, and a color image is formed by superimposing toner images of each color on a transfer material. For example, in a full-color forming apparatus using four color toners, along a drum-shaped photoconductor,
A charging unit, an image exposing unit, a developing unit (cyan developing unit, magenta developing unit, yellow developing unit, black developing unit) and a transferring unit are sequentially arranged, and a toner image formed for each color is transferred onto a transferring unit (for example, a transfer drum). A full-color image is formed by superimposing on a transfer material such as paper carried on a sheet.

In the image forming apparatus having such a configuration, the process of charging, developing, and transferring must be repeated for each color, so that the printing speed is limited. An additional means such as a transfer drum must be required in order to ensure the superposition accuracy of the toner images.

On the other hand, a proposal has been made to simplify the structure and improve the printing speed by superimposing toner images of respective colors on the surface of the photoreceptor and collectively transferring them (one shot) onto a transfer material. Has been made. In such a configuration, a charging unit, an image exposing unit, a developing unit (a four-color developing unit), and a transferring unit are sequentially arranged along a drum-shaped photoconductor, and one rotation of the photoconductor, that is, the photoconductor is rotated four times. Thus, a superposed toner image of four colors is formed.

[0006]

In such a configuration, the transfer drum and the like are not required, so that the configuration can be simplified. However, the surface of the photoreceptor already carrying the toner image is recharged, and Because of the configuration in which the toner images are superimposed, the sharpness of the color image is poor, and in some cases, an uneven image is formed. One of these causes is the above-described uneven charging at the time of recharging, and is considered to be attributable to the transfer problem.

The present invention has been made in view of the above points, and is directed to an image forming apparatus for forming a multi-color or full-color image. The present invention also provides a color image forming apparatus capable of achieving high clarity of a color image, reducing the size of the apparatus, and increasing the speed of the apparatus.

[0008]

In order to solve such a problem, the present invention provides at least a first charging / charging method for a photosensitive member.
Means for performing image exposure and then developing with a charged toner of a predetermined polarity under a predetermined developing bias to form a first color toner image, and a dark portion potential and a bright portion potential on the photoreceptor at substantially the same level. A second charge / image exposure is performed on the photoreceptor carrying the first color toner after the charge is removed, and then the developing is performed with the charged toner having a predetermined polarity under a predetermined developing bias. Means for forming a second color toner image in addition to the first color toner image, and uniformly applying a charge having the same polarity as that of the toner image to the photoreceptor carrying the toner image. Means for equalizing the potentials of the first and second color toner images, and means for transferring the toner image onto a transfer material by charging the toner image with a polarity opposite to the polarity of the toner image. Unnecessary color development bar depending on the color Off the astigmatism, or to, characterized in that switching to the charged toner of the same polarity as the bias.

In particular, the present invention relates to a color image forming apparatus for forming a color image by superimposing four color toner images of cyan, magenta, yellow and black on a photoreceptor. A first static eliminator for uniformly discharging the body surface, a first charger for applying a first charge to the photoconductor surface, and exposing a light image corresponding to a first color on the charged photoconductor surface, A first exposure unit for forming an electrostatic latent image on the photoconductor, and a predetermined developing bias for applying a first color toner on the photoconductor surface carrying the electrostatic latent image to form a first toner image; A first developing device applied thereto, a second static eliminator for neutralizing the dark portion potential and the bright portion potential of the photoconductor surface carrying the toner image to substantially the same level, and a second charger for applying a second charge to the photoconductor surface And a light image corresponding to the second color is formed on the charged photoreceptor surface. A second exposure means for illuminating and forming an electrostatic latent image on the photoreceptor, and a second exposure means for applying a second color toner on the surface of the photoreceptor to form a second toner image; A third unit that removes a dark portion potential and a bright portion potential of the developing device and the photosensitive member surface carrying the toner image to substantially the same level;
A static eliminator, a third charger for applying a third charge to the photoreceptor surface, and a light image corresponding to a third color is exposed on the charged photoreceptor surface to form an electrostatic latent image on the photoreceptor An exposure means for applying a third color toner on the photoreceptor surface to form a third toner image; and a dark portion potential and a bright portion potential of the photoreceptor surface carrying the toner image to substantially the same level. 4th static elimination
A static eliminator, a fourth charger for applying a fourth charge to the photoreceptor surface, and exposing a light image corresponding to a fourth color on the charged photoreceptor surface to form an electrostatic latent image on the photoreceptor Fourth exposure means;
A fourth developing device to which a fourth color toner is applied to form a fourth toner image on the photoconductor surface and to which a predetermined developing bias is applied; A charger that increases the toner potential of each color toner image by uniformly applying a charge having the same polarity as the image polarity and makes the potential uniform, and transfers the toner image by charging with a polarity opposite to the polarity of the toner A transfer unit that transfers images onto a material, a cleaner that removes residual toner on the photoconductor surface, and development of unnecessary colors according to the type of color image that is to be sequentially formed along the direction of movement of the photoconductor. Turn off the bias of the
Alternatively, the developing bias is switched to a bias having the same polarity as the toner.

[0010]

As described above, according to the structure of the present invention, after the development of the first color is completed, the surface of the photosensitive member is neutralized to a uniform level, then recharged, and then a latent image of the second color is formed. Therefore, almost the same charged potential can be obtained in the formation of the latent image of each color, whereby a color image with high definition is formed. Further, in the color superimposed toner image on the photoconductor surface thus formed, after the final development,
The surface of the photoreceptor is uniformly charged with the same polarity as the polarity of the toner image, thereby increasing the toner potential and realizing excellent transfer.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Note that a full-color system including four-color development will be described by taking the configuration of FIGS. 1 and 2 as an example. However, the present invention is not limited to a full-color system. Can be applied.

FIG. 1 shows an example of a color image forming apparatus according to the present invention, and an image forming process unit corresponding to each color of cyan, magenta, yellow and black along a moving path X of a photoreceptor 1 according to the moving direction. A, B, C, and D, a pre-transfer charging section E, a transfer / separation section F, and a cleaning section G are arranged. The image forming process sections A, B, C, and D are not particularly limited in the order of colors to be formed, but typically, A forms cyan, B forms magenta, C forms yellow, and D forms black. It will be described as.

The photoconductor 1 has a structure in which an optical semiconductor layer is formed on a conductive substrate. FIG. 1 shows a belt-shaped photoconductor, but the present invention is not limited to this. For example, the optical semiconductor layer is formed on an aluminum drum. It may be a drum-shaped photoconductor.
The belt-shaped photoreceptor shown in FIG. 1 has a structure in which an endless polyester film having electrode layers formed on both surfaces is used as a conductive substrate, and an optical semiconductor layer of an organic optical semiconductor (OPC) is formed on the outer surface. The belt-shaped photosensitive member is stretched by two rotatable support rollers 33 and 34, and moves in a direction indicated by an arrow X at a constant speed by driving one of the support rollers 33 and 34. Reference numerals 35, 36, 3 arranged inside the photoconductor 1
The rollers denoted by reference numerals 7 and 38 are guide rollers for supporting the photoreceptor 1, and are arranged at positions facing a developing sleeve of a developing unit 6 described later. The support roller 3
Reference numerals 3 and 34 are constituted by conductive rollers.
The photoconductor 1 is grounded via 34. The optical semiconductive layer is not limited to OPC, but may be Se, CdS, a-S
Other optical semiconductor materials such as i may be used.

Next, the image forming process will be described.
The image forming process unit A includes static eliminators 2 and 3 for uniformly eliminating the surface of the photoconductor 1, a charger 4 for uniformly charging the photoconductor surface with a specific polarity, and a first color on the photoconductor surface. An exposure device 5 for exposing image information for image formation, and a developing device 6 for developing an electrostatic latent image formed on the photoconductor by the exposure with cyan toner. In the static eliminators 2 and 3, 2 is A on the photoconductor surface.
An AC corona discharger 3 for applying a C discharge is a light source for irradiating the surface of the photoreceptor with a light beam of infrared rays or other wavelengths, and discharges both 2 and 3 or one of 2 or 3 depending on the case. It may be configured to act.

The photosensitive member 1 thus neutralized is charged to a specific polarity (positive for convenience of explanation) by a charger 4, and then optical image information is input by an exposure device 5. The exposing device 5 is configured by an LED array, and optically plots necessary image information on the photoconductor surface. In this example, the image is exposed as a positive image, but may be a negative image. The exposure device 5 is not limited to the LED array, but may be another digital light image irradiation means such as a laser or an analog exposure. The dot diameter of the light image formed by the LED array is preferably 60 μm or less. For example, a control circuit is obtained to scan the photoconductor in the generatrix direction. When the dot diameter is large, not only the resolving power decreases but also the color reproduction decreases.

The electrostatic latent image formed on the photoreceptor by the exposing device 5 is developed by a negatively charged cyan toner by a developing device 6 to form a cyan toner image.

Although the developing device 6 is not described in detail in the drawings, the developing device 6 includes a conductive non-magnetic developing sleeve 6a that rotates in the forward direction with respect to the moving direction of the photoconductor 1, and
And a magnet roll 6b disposed in the developing sleeve, and develops the electrostatic image on the photoconductor with a toner brush formed on the sleeve. The magnet roll 6b may be fixed or rotating, and a DC developing bias of minus several hundred volts is applied to the developing sleeve 6a.

The distance between the developing sleeve 6a and the surface of the photoreceptor 1 is such that the toner layer carried on the developing sleeve 6a does not contact the surface of the photoreceptor, and is as narrow as possible (for example, 200 to 300 μm). Optimal.

As the developer, a two-component developer composed of a color toner and a carrier is used, but is not limited thereto, and may be a one-component developer. Note that a one-component developer can be positively used for the black toner that forms the final color.

Each of the process units B following the process unit A,
C and D have almost the same configuration and operation as the respective means of the process unit A, except that the toner images to be developed are magenta, yellow, and black, respectively.
The AC corona dischargers 7, 12, and 17 correspond to the discharger 2, the light sources 8, 13, and 18 correspond to the light source 3, the chargers 9, 14, and 19 correspond to the charger 4, and the exposure units 10, 15, and 20 correspond to the exposure unit 5. , Developing devices 11, 16, 21 perform the same function as the corresponding developing device 6. Through such process sections A, B, C, D and E, a full-color or multi-color image is formed on the photoreceptor.

It is particularly important that the surface of the photoreceptor is discharged before the image formation in each process section.
13 or 17, 18).
As will be described later, the surface of the photoreceptor on which the toner image has been formed in the previous process section has a potential difference between the dark area and the light area, so that even if this is uniformly charged by the chargers 9, 14 and 19, The potential difference remains to form partial unevenness in the potential on the surface of the photoreceptor, which appears as an image. For this reason, it is preferable that the charge is sufficiently removed until the potential of the dark portion and the potential of the light portion of the photoreceptor decrease to substantially the same level.

FIG. 2 shows changes in the surface potential on the photosensitive member during a series of processes. In the drawing, a solid line D indicates a dark portion potential, and a broken line L indicates a bright portion potential. The photoreceptor surface from which the charges have been uniformly removed by the charge removers 2 and 3 is uniformly charged by the charger 4, and then optical information is input by the exposure device 5. As a result, the light portion potential drops, and a potential difference is formed between the dark portion and the light portion. When the image exposure is a positive image as described above,
The development is performed for the dark part potential, and a toner image is formed according to the image information. At this time, the potential of the dark portion fluctuates somewhat due to the adhesion of the toner, but a potential difference is still formed on the photosensitive member. The potential difference is sufficiently removed by the next charge removers 7 and 8 until the potentials of the dark portion and the light portion fall to substantially the same level, and then recharged for the next image formation. Such a charge removal step is effective for uniformly performing recharging. Hereinafter, a similar procedure is repeated to form a color image on the photoreceptor surface.

The toner images of the respective colors may be formed so as to overlap each other, or the toner images of the respective colors may be formed so as not to overlap. Further, in the present invention, from full color to two-color, according to the type of color of the color image to be formed, in order to obtain an optimal image, in full color, all image forming process units are operated, In the case of multi-color or two-color or the like, only the image forming process section corresponding to a required color needs to be operated. For example, in the developing step alone, by turning off the bias of the developing sleeve, or by switching the applied bias to a bias having the same polarity as the toner, it is possible to prevent the toner of an unnecessary color from adhering to the surface of the sleeve, and It is possible not to contribute to the development on the body, and thus it is possible to obtain an optimal clear image according to the type of the color image as described above.

Since the potential of the multicolor toner image formed on the photoreceptor is not constant for each color, and the potential is not sufficient, the charging device 2 is provided prior to the transfer step.
2, the surface of the photoreceptor carrying the toner image is uniformly charged with the same polarity as that of the toner image, thereby increasing the toner potential, weakening the suction between the toner and the photoreceptor, and providing excellent transfer. Is made possible.

The uniformly charged toner image is then transferred to a transfer material 23 such as paper in a transfer / separation unit F. Reference numeral 26 denotes a transfer corona charger, which transfers the image onto the transfer material 23. A transfer roller may be used instead of the transfer corona charger. Reference numeral 27 denotes an AC neutralizing corona separator. The paper feed rollers 24 and 25 operate at a controlled timing such that the transfer material 23 comes into contact with the surface of the photoconductor by registering with the toner image on the photoconductor.

Next, the transfer material on which the toner image has been transferred is
Conveyor belt 30 supported by support rollers 28 and 29
To the fixing device 31, where the toner image is fixed on the transfer material, and a clear color copy is obtained. The fixing device 31 may have a known configuration in which a transfer material is sandwiched between a heating roller and a pressure roller having a heat source provided inside a roller having silicon rubber as a surface, and fixing is performed by heat and pressure.

On the other hand, foreign matter such as toner remaining on the surface of the photoreceptor to some extent after the transfer is cleaned by a cleaning means 32 such as a cleaning brush or a cleaning blade for the next repetitive use of the photoreceptor.

[0028]

As described above, the present invention adopts the method of superimposing toner images on the photoreceptor, so that a continuous long color image can be obtained. By providing a static elimination process for a uniform level in the image forming process unit, a toner image of substantially the same level can be formed for each color, and as a result, a clear color image such as a multi-color, full-color, or two-color image can be formed. Is formed. In addition, by adopting pre-transfer charging,
Improves transfer efficiency and contributes to formation of clear color images.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of a color image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a change in surface potential on a photoconductor in the embodiment of FIG.

[Explanation of symbols]

 A, B, C, D Image forming process section E Charging section before transfer F Transfer / peeling section G Cleaning section 1 Photoconductor 2, 7, 12, 17 AC corona discharger 3, 8, 13, 18 Light source for static elimination 5, 10, 15, 20 Exposure device 6, 11, 16, 21 Developing device 22 Pre-transfer charger 26 Transfer device

Claims (2)

[Claims] At least a first charging / charging operation is performed on a photosensitive member.
Means for performing image exposure and then developing with a charged toner of a predetermined polarity under a predetermined developing bias to form a first color toner image, and a dark portion potential and a bright portion potential on the photoreceptor at substantially the same level. A second charge / image exposure is performed on the photoreceptor carrying the first color toner after the charge is removed, and then the developing is performed with the charged toner having a predetermined polarity under a predetermined developing bias. Means for forming a second color toner image in addition to the first color toner image, and uniformly applying a charge having the same polarity as that of the toner image to the photoreceptor carrying the toner image. Means for equalizing the potentials of the first and second color toner images, and means for transferring the toner image onto a transfer material by charging the toner image with a polarity opposite to the polarity of the toner image. Unnecessary color development bar depending on the color Off the astigmatism, or the color image forming apparatus, characterized in that switching to the charged toner of the same polarity as the bias. 2. In a color image forming apparatus for forming a color image by superimposing four color toner images of cyan, magenta, yellow and black on a photoconductor, at least the surface of the photoconductor is uniformly discharged. A first static eliminator, a first charger for applying a first charge to the surface of the photoconductor, and a light image corresponding to a first color is exposed on the surface of the photoconductor, and an electrostatic latent image is formed on the photoconductor. A first exposing unit for forming an image, and a first exposing unit for applying a first color toner on a photoreceptor surface carrying the electrostatic latent image.
A first developing device to which a predetermined developing bias is applied for forming a toner image; a second neutralizer for neutralizing the dark portion potential and the bright portion potential of the photoconductor surface carrying the toner image to substantially the same level; A second charger for applying a second charge, a second exposing means for exposing a charged photoreceptor surface to a light image corresponding to a second color to form an electrostatic latent image on the photoreceptor, A second developing device for applying a second color toner on the body surface to form a second toner image, to which a predetermined developing bias is applied, and a dark portion potential and a bright portion potential of the photoconductor surface carrying the toner image are substantially changed. A third static eliminator that eliminates electricity to the same level, a third charger that imparts a third charge to the surface of the photoconductor, and a light image corresponding to a third color is exposed on the surface of the charged photoconductor to expose the surface of the photoconductor. Exposure means for forming an electrostatic latent image on the surface of the photosensitive member, A third developing device for forming a toner image, a fourth static eliminator for neutralizing the dark portion potential and the bright portion potential of the photoconductor surface carrying the toner image to substantially the same level, and a fourth developing device for applying a fourth charge to the photoconductor surface. A charger, fourth exposure means for exposing a light image corresponding to the fourth color on the charged photoreceptor surface to form an electrostatic latent image on the photoreceptor, and applying a fourth color toner on the photoreceptor surface A fourth developing device to which a predetermined developing bias is applied to form a fourth toner image by applying the toner image to the photoconductor surface carrying the superimposed color toner; A charging device that raises the toner potential of each color toner image and makes the potential uniform,
A transfer device for transferring a toner image onto a transfer material by charging with a polarity opposite to the polarity of the toner, a cleaner for removing residual toner on the photoreceptor surface, and a transfer device are sequentially arranged along the direction of movement of the photoreceptor. A color image forming apparatus, wherein the bias of an unnecessary color developing unit is turned off or the developing bias is switched to a bias having the same polarity as the toner according to the type of a color image to be formed.