JPH0777857A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain almost the same potential by electrification in the formation of the latent images of each color and to form the color image of high sharpness by destaticizing the face of a photoreceptor up to an equal level after the development of the first color is completed, reelectrifying the face and then, forming the latent image of the second color. CONSTITUTION:In a process A, a developing unit 6 develops an electrostatic charge image on the photoreceptor 1 with cyan toner by a toner brush formed on a sleeve. Processes B, C and D following the process A have almost the same constitution as that of the process A, except that the colors of each toner of the processes B, C and D are magenta, yellow and black, and a full color image is formed through each process. However, after the process B, the photoreceptor face is temporarily destaticized by destaticizers 7 and 8, 12 and 13 and 17 and 18, prior to the formation of the image. The discharged photoreceptor face is uniformly electrified by electrifiers 9, 14 and 19 and then, optical information is inputted by an exposing unit.

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 using an electrophotographic method, and more particularly, it forms a multicolor toner image of two or more colors on a photoconductor and forms the image on a medium such as paper. The present invention relates to a color image forming apparatus of the type of batch transfer.

[0002]

2. Description of the Related Art As a device for faithfully converting a color original document into a desired color and reproducing it, or as a device for forming a color image based on an output image from a computer, an electrophotographic system, an inkjet system. 2 colors using various methods such as method, thermal method,
Alternatively, an analog or digital image forming apparatus such as multi-color or full-color has been proposed. Among them, the inkjet method or the thermal method has an advantage that it is possible to provide an inexpensive apparatus which is relatively simple in configuration as compared with the electrophotographic method, but lacks in sharpness of a color image and is left for a long time. In some cases, problems such as ink clogging remain. On the other hand, the apparatus using the electrophotographic method provides a relatively stable and good color image although the construction is complicated.

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

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

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

[0006]

In such a structure, the transfer drum and the like are not required, so that the structure can be simplified. However, the surface of the photoconductor which already carries the toner image is recharged and the following steps are taken. Since the toner images are superposed on each other, the definition of the color image is poor and, in some cases, uneven images are formed. One of the causes is the above-mentioned uneven charging at the time of recharging, and it is considered to be attributed to the transfer problem.

The present invention has been made in view of the above points, and provides a color image forming apparatus which has a high definition of a color image, a compact apparatus, and a high speed.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, according to the present invention, a multicolor toner image is formed on a photoconductor by repeating a series of steps of charging, image exposure and development for each photoconductor. In the color image forming apparatus in which the image is formed on the transfer material after being formed, the dark potential and the light potential on the photoconductor are almost the same between the developing step and the charging step for the next color. It is characterized in that a static eliminating means for eliminating static electricity to a level is provided.

In particular, in the color image forming apparatus according to the present invention, at least a means for forming a first color toner image by subjecting the photoconductor to the first charging, image exposure and development, and a photoconductor. A first charge removal unit for removing charge from the upper dark portion potential and the light portion potential to almost the same level, and second charging, image exposure, and development on the photoconductor carrying the first color toner image after the charge elimination. Means for forming a second color toner image in addition to the color toner image, a means for uniformly applying a charge having the same polarity as the polarity of the toner image to the photoconductor carrying the toner image, and then the toner image for the toner image. And a means for transferring the toner image onto the transfer material by charging with a polarity opposite to the polarity.

Further, when the present invention is applied to a full-color image forming apparatus which is formed by superposing toner images of four colors of cyan, magenta, yellow and black, at least the surface of the photoconductor is uniformly discharged. A static eliminator, a first charger for applying a first charge to the surface of the photoconductor, and a light image corresponding to the first color exposed on the surface of the charged photoconductor to form a latent electrostatic image on the photoconductor. 1 exposure means, a first developing device for forming a first toner image by applying a first color toner on the surface of the photoconductor carrying the electrostatic latent image, a dark portion potential and a bright portion of the surface of the photoconductor carrying the toner image A second charge eliminator for removing the electric potential to almost the same level, a second charger for applying a second charge to the surface of the photoconductor, and a light image corresponding to the second color is exposed on the charged surface of the photoconductor to expose it. Second exposure means for forming a latent electrostatic image on the body, and a second exposure means on the surface of the photoreceptor. Second developing device for forming a second toner image by applying the color toner of the above, a third static eliminator for neutralizing the dark portion potential and the light portion potential of the surface of the photoconductor bearing the toner image to substantially the same level, and the photoconductor surface A third charging device for imparting a third charge to the surface, an exposing unit for exposing a light image corresponding to the third color on the charged surface of the photoconductor to form a latent electrostatic image on the photoconductor, and a photoconductor surface. A third developing device that applies a third color toner to the toner to form a third toner image, and a fourth static eliminator that neutralizes the dark part potential and the light part potential of the surface of the photoconductor bearing the toner image to approximately the same level, Fourth for applying a fourth charge to the photoconductor surface
A charger, a fourth exposure unit that exposes a light image corresponding to a fourth color on the charged surface of the photoconductor to form a latent electrostatic image on the photoconductor, and a toner of the fourth color is applied to the surface of the photoconductor. And a fourth developing device for forming a fourth toner image, a charging device for uniformly applying a charge having the same polarity as the polarity of the toner image onto the surface of the photoconductor carrying the superimposed color toner images, and a toner. A transfer device that transfers a toner image onto a transfer material by charging with a polarity opposite to the polarity of the image and a cleaner that removes residual toner on the surface of the photoconductor are sequentially arranged along the moving direction of the photoconductor.

[0011]

As described above, in the structure of the present invention, after the development of the first color is completed, the surface of the photoconductor is neutralized to a uniform level,
Then, after recharging, the process of forming a latent image of the second color is performed, so that almost the same charging potential can be obtained in the formation of the latent image of each color, and accordingly, a color image with high definition is formed. To be done. In addition, in the color-superimposed toner image formed on the surface of the photoconductor in this way, after the final development, the surface of the photoconductor is uniformly charged with the same polarity as the polarity of the toner image, thereby raising the toner potential. And excellent transfer can be realized.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. A full-color system consisting of four-color development will be described with reference to the configurations of FIGS. Can be applied in.

FIG. 1 shows an example of a color image forming apparatus according to the present invention.
Accordingly, the image forming process units A, B, C, D corresponding to cyan, magenta, yellow, and black, the pre-transfer charging unit E, the transfer / separation unit F, and the cleaning unit G are arranged. The image forming process units A, B, C, and D do not specifically limit the order of colors to be formed, but typically, A forms cyan, B forms magenta, C forms yellow, and D forms black. As described below.

The photoconductor 1 has a structure in which an optical semiconductor layer is formed on a conductive substrate. A belt-shaped photoconductor is shown in FIG. 1, but the present invention is not limited to this. For example, an optical semiconductor layer is formed on an aluminum drum. It may be a drum-shaped photoreceptor.
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 the conductive substrate, and an optical semiconductor layer of an organic optical semiconductor (OPC) is formed on the outer surface thereof. The belt-shaped photoconductor is stretched by two support rollers 33 and 34 that are rotatably arranged, and is driven in a direction indicated by an arrow X at a constant speed by driving one of the support rollers 33 and 34. The reference numerals 35, 36, 3 arranged inside the photoconductor 1
Each of the rollers denoted by reference numerals 7 and 38 is a guide roller for supporting the photoconductor 1, and is arranged at a position facing a developing sleeve of the developing device 6 described later. The support roller 3
3, 34 are composed of conductive rollers, and the rollers 33,
The photoconductor 1 is grounded via 34. The optical semiconductor layer is not limited to OPC and may be Se, CdS, a-Si.
Other optical semiconductor materials may be used.

Next, the image forming process section will be described.
The image forming process unit A includes static eliminators 2 and 3 for uniformly removing 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. And an developing device 6 for developing the electrostatic latent image on the photoconductor formed by this exposure with cyan toner. In the static eliminators 2 and 3, 2 is A on the photoconductor surface.
An AC corona discharger 3 for giving a C discharge is a static elimination light source for irradiating the surface of the photoconductor with infrared rays or rays of other wavelengths, and both 2 and 3 and, if necessary, either 2 or 3 It may be configured to operate.

The photoconductor 1 thus neutralized is charged to a specific polarity (having a positive polarity for convenience of explanation) by the charger 4, and then the optical image information is input by the exposure device 5. The exposure unit 5 is composed of an LED array and optically plots necessary image information on the surface of the photoconductor. Although the image is exposed as a positive image in this example, it may be a negative image. In addition,
The exposure device 5 is not limited to the LED array, and may be other digital light image irradiation means such as a laser or analog exposure. In addition, the dot diameter of the light image by the LED array is 60
It is preferably less than a micron. For example, a control circuit is provided to scan the photoconductor in the generatrix direction. If the dot diameter is large, not only the resolution will decrease, but also the color reproduction will decrease.

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

Describing the developing device 6, although not described in detail in the drawing, the developing device 6 includes a conductive non-magnetic developing sleeve 6a which rotates in the forward direction of the moving direction of the photoconductor 1.
It has a magnet roll 6b arranged 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 rotated, and a DC developing bias of minus several hundreds of V is applied to the developing sleeve 6a.

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

As the developer, a two-component type developer composed of a color toner and a carrier is used, but the developer is not limited to this and may be a one-component type developer. A one-component developer can be positively used for the black toner forming the final color.

Each process section B following the process section A,
C and D have substantially the same configuration and operation as each means of the process section A except that the toner images to be developed are magenta, yellow and black, respectively, that is,
The AC corona dischargers 7, 12, 17 are the discharger 2, the light sources 8, 13, 18 are the light source 3, the chargers 9, 14, 19 are the charger 4, and the exposure devices 10, 15, 20 are the exposure device 5. In addition, the developing devices 11, 16 and 21 function similarly to the developing device 6, respectively. Such process parts A, B, C, D
And E, a full-color or multi-color image is formed on the photoconductor.

What is particularly important here is that the surface of the photoconductor is destaticized 7, 8 (or 12,
13 or 17, 18) to eliminate the charge.
As will be described later, since a potential difference between the dark portion and the light portion is generated on the surface of the photoconductor on which the toner image is formed in the previous process portion, even if this is uniformly charged by the chargers 9, 14, 19 the The potential difference remains and a partial unevenness is formed in the potential on the surface of the photoconductor, which appears as an image. For this reason, it is preferable that the above-mentioned charge removal is sufficiently carried out until the dark part potential and the light part potential of the photoconductor drop to almost the same level.

FIG. 2 shows changes in the surface potential on the photoconductor during a series of processes. In the figure, the solid line D indicates the dark part potential and the broken line L indicates the bright part potential. The surface of the photoconductor that has been uniformly discharged by the static removers 2 and 3 is uniformly charged by the charger 4, and then the 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. As described above, when the image exposure is a positive image,
The development is performed on the dark part potential, and a toner image according to the image information is formed. At this time, the dark portion potential fluctuates to some extent due to the adhesion of toner, but a potential difference is still formed on the photoconductor. This potential difference is sufficiently neutralized by the subsequent static eliminators 7 and 8 until the potentials in the dark and light areas drop to substantially the same level, and then recharged for the next image formation.
The static elimination step is effective for uniform recharging. Hereinafter, the same procedure is repeated to form a color image on the surface of the photoconductor.

The toner images of the respective colors may be formed so as to be superposed, or the toners of the respective colors may be formed so as not to overlap each other. Further, in the case of full color, all the image forming process units may be operated, and in the case of multi-color or two-color, only the image forming process unit corresponding to the required color may be operated. For example, by turning off the bias of the developing sleeve or switching the bias to be applied to the bias of the same polarity as the toner, the toner is prevented from adhering to the sleeve surface,
It can be prevented from contributing to the development on the photoreceptor.

In the multicolor toner image thus formed on the photosensitive member, the electric potential is not constant for each color and the electric potential is not sufficient. Therefore, prior to the transfer step, the charger 2 is used.
2 uniformly charges the surface of the photoconductor carrying the toner image with the same polarity as the polarity of the toner image, thereby raising the toner potential, weakening the attraction between the toner and the photoconductor, and excellent transfer. To be possible.

The toner image to which the uniform charge is applied is then transferred onto a transfer material 23 such as paper at a transfer / separation unit F. Reference numeral 26 is a transfer corona charger, which applies a voltage having a polarity opposite to the charging polarity of the toner from the back surface of the transfer material 23,
The toner image is transferred onto the transfer material 23. A transfer roller may be used instead of the transfer corona charger. Reference numeral 27 is an AC neutralizing corona separation device. The paper feed rollers 24 and 25 operate so that the transfer material 23 contacts the toner image on the photoconductor at a controlled timing and comes into contact with the surface of the photoconductor.

Next, the transfer material on which the toner image has been transferred is
Conveying belt 30 supported by supporting rollers 28 and 29
Is conveyed 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 structure in which a transfer material is sandwiched between a heating roller having a heat source provided inside a roller having a silicon rubber surface and a pressure roller, and fixing is performed by heat and pressure.

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

[0029]

As described above, according to the present invention, since the method of superposing toner images on the photoconductor is adopted, a continuous long color image can be obtained, and not only the apparatus can be downsized but also each color can be obtained. By providing the static elimination step for uniform level in the image forming process section, it is possible to form toner images of substantially the same level for each color, and as a result, a clear color image is formed. Further, by adopting the pre-transfer charging, the transfer efficiency is improved and it contributes to the formation of a clear color image.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining 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 Pre-transfer charging section F Transfer / peeling section G Cleaning section 1 Photoconductor 2,7,12,17 AC corona discharger 3,8,13,18 Static elimination light source 5, 10, 15, 20 Exposure device 6, 11, 16, 21 Developing device 22 Pre-transfer charging device 26 Transfer device

Claims (3)

[Claims] 1. A multi-color toner image is formed on a photoconductor by repeating a series of steps of charging, image exposure and development for the photoconductor, and then transferring the same onto a transfer material at once. In the color image forming apparatus described above, between the developing step and the charging step for the next color, a neutralizing means for neutralizing the dark portion potential and the light portion potential on the photoconductor to almost the same level is provided. Color image forming apparatus. 2. At least a first charge for the photosensitive member
Means for forming a first color toner image by performing image exposure and development, static erasing means for neutralizing the dark portion potential and the light portion potential on the photoconductor to almost the same level, and the first color toner image after the neutralization Means for forming a second color toner image in addition to the first color toner image by subjecting the photoreceptor carrying the second charge, image exposure and development to the photoreceptor carrying the toner image Color image formation characterized by having means for uniformly applying the same polarity as the polarity of the toner image and then means for transferring the toner image onto the transfer material by the opposite polarity to the polarity of the toner image apparatus. 3. A color image forming apparatus for forming a color image by superposing four color toner images of cyan, magenta, yellow and black on a photoconductor to at least uniformly remove static electricity on the photoconductor surface. A static eliminator, a first charger for applying a first charge to the surface of the photoconductor, and a first electrostatic latent image formed on the photoconductor by exposing the charged photoconductor surface with an optical image corresponding to the first color. 1 exposure means, a first developing device for applying a first color toner on the surface of the photoreceptor carrying the electrostatic latent image to form a first toner image, and a dark potential and a bright portion of the surface of the photoreceptor carrying the toner image A second static eliminator that removes the electric potential to almost the same level, a second charger that applies a second charge to the photoconductor surface, and a photoimage corresponding to the second color is exposed on the charged photoconductor surface to expose it. Second exposure means for forming a latent electrostatic image on the body; A second developing device for forming a second toner image by applying a second color toner to the third developing device, and a third discharging device for removing the dark portion potential and the light portion potential of the surface of the photoreceptor carrying the toner image to substantially the same level, A third charger for imparting a third charge to the surface of the photoconductor, an exposure unit for exposing a light image corresponding to the third color on the charged surface of the photoconductor to form a latent electrostatic image on the photoconductor, A third developing device that applies a third color toner to the surface of the body to form a third toner image, and a fourth static eliminator that neutralizes the dark part potential and the light part potential of the photoconductor surface carrying the toner image to almost the same level. And a fourth charger for applying a fourth charge to the surface of the photoconductor, and a fourth exposure for exposing a light image corresponding to the fourth color on the charged surface of the photoconductor to form a latent electrostatic image on the photoconductor. And a fourth developing device for forming a fourth toner image by applying a fourth color toner on the surface of the photoconductor. , A charger that uniformly applies the same polarity of the toner image to the surface of the photoconductor that carries the superimposed color toner images, and a transfer material that transfers the toner image by the opposite polarity of the toner image polarity. A color image forming apparatus in which a transfer device for transferring onto the surface and a cleaner for removing residual toner on the surface of the photoconductor are sequentially arranged along the moving direction of the photoconductor.