JPH07113790B2 - Color image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention forms a latent image on an image bearing member for each color and visualizes the latent image with a selected color developing device to obtain the visible image. The present invention relates to a color image forming apparatus configured to successively and sequentially transfer the same onto a same transfer material.

2. Description of the Related Art Conventionally, various color image forming apparatuses have been proposed for copying multicolor originals. Among them, the one that is often used is a color electrophotographic copying apparatus, and in particular, it has a plurality of image forming units. A color electrophotographic copying apparatus in which toner images of different colors are formed in respective image forming units and the toner images are sequentially transferred onto the same transfer material.

An example of such a color copying apparatus will be briefly described with reference to FIG. 2. First, second, third and fourth image forming portions Pa, Pb, Pc and Pd are provided in the apparatus body of the color copying apparatus. It is installed side by side. The image forming portions Pa, Pb, Pc and Pd are respectively dedicated image carriers, in this example, the electrophotographic photosensitive drums 1a, 1b, 1c and
Equipped with 1d.

The photosensitive drums 1a, 1b, 1c and 1d have latent image forming parts 2a, 2b, 2c, 2d, developing parts 3a, 3b, 3c, 3d, transfer discharging parts 4a, 4b, 4c, 4d and cleaning on the outer peripheral side thereof. The parts 5a, 5b, 5c, 5d are arranged.

With such a configuration, first, the latent image forming unit 2a forms a latent image of the yellow component color in the original image on the photosensitive drum 1a of the first image forming unit Pa. The latent image is formed into a visible image with the developer having yellow toner in the developing section 3a, and the yellow toner image is transferred to the transfer material 6 in the transfer section 4a.

On the other hand, while the yellow image is being transferred to the transfer material as described above, a latent image of a magenta component color is formed in the second image forming portion Pb, and then a toner image with magenta toner is obtained in the developing portion 3b. . The magenta toner image is the first
When the transfer material 6 that has been transferred in the image forming portion Pa is carried into the transfer portion 4b, it is transferred to a predetermined position of the transfer material 6.

Thereafter, the third and fourth image forming units P are formed by the same method as described above.
Cyan and black images are formed by c and Pd, and the cyan color and black color are transferred to a predetermined position on the same transfer material. When such an image forming process is completed, the image on the transfer material is fixed on the transfer material by the fixing unit 7, and a multicolor image is obtained. On the other hand, the remaining toner is removed from the photosensitive drums 1a, 1b, 1c and 1d, which have been transferred, by the cleaning units 5a, 5b, 5c and 5d to prepare for the subsequent latent image formation.

In the image forming apparatus having the above-described structure, the transfer material 6 is conveyed from the right side to the left side in FIG. 2 by the conveyor belt 8 and moves together with the conveyor belt 8 to transfer the image forming sections Pa, Pb, Pc, and Pd.
It is configured to pass through 4a, 4b, 4c and 4d.

Problems to be Solved by the Invention However, according to the research and experiment conducted by the present inventors, in the image forming apparatus having the above-described structure, especially when copying a document image in which characters and halftone images are mixed, each color is required. The resolution is different, black, cyan, magenta,
It has been found that a high spatial frequency, that is, a high resolution is required in the order of yellow color, or in the order of black color, magenta color, cyan color, and yellow color.

In addition, for example, in the electrophotographic method by the Carlson process including the steps of charging, exposing, developing, and transferring, the resolution at the time of latent image formation is generally the resolution at the time when the visible image is formed on the photoconductor after the developing step. It turns out that it is much higher than that. Specifically, the resolution at the time of latent image formation is 100 lines / mm or more, while the resolution at the end of the development process is a resolution equivalent to three developer (toner) particles, that is, a toner having a particle diameter of 12 μm. 30 when using
It was difficult to obtain a resolution higher than about book / mm.

On the other hand, in the conventional color electrophotographic copying apparatus, each color developing device uses a developer having the same average particle diameter, and therefore the resolution of each color depends on the developer, and the limit resolution is the same. However, it is not possible to achieve the required resolution due to the color difference as described above.
In other words, when the particle size of each color developer is set to have a slightly larger particle size in accordance with the resolution required for yellow color image reproduction, the required resolution for black color image reproduction cannot be satisfied, Also, if the particle size of each color developer is reduced in accordance with the resolution for reproducing a black color image, black color reproduction is achieved, but the fine particle developer is coated with the developer and then the fine particle developer is applied. There is a problem because it has a characteristic that the transfer efficiency is deteriorated when transferred. That is, when the particle size of the magenta, cyan, and yellow color developers to be laminated is also reduced in accordance with the black color, the reproducibility of the yellow color in particular decreases, and the color balance with other colors is achieved. Becomes difficult. Further, since the fine particle developer is expensive, it is not preferable to use the fine particle developer for each color from the viewpoint of running cost.

Object of the Invention An object of the present invention is to achieve the resolution required for color reproduction, to obtain a high-quality full-color image faithful to the original from an image signal obtained by color separation from the original image, and It is an object of the present invention to provide a color image forming apparatus having a low running cost.

Means for Solving the Problems The above object is achieved by the color image forming apparatus according to the present invention. In summary, the present invention has a magenta developing means, a cyan developing means, a yellow developing means and a black developing means for developing an electrostatic image formed in accordance with an image signal, and a transfer in which a plurality of color toner images are laminated. In a color image forming apparatus that fixes a material to form a full-color image, the average particle diameters of magenta toner, cyan toner, and yellow toner are made substantially equal, and the average particle diameter of black toner is calculated from the average particle diameters of these three color toners. Is a color image forming apparatus.

Embodiment Next, an embodiment of the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Referring to FIG. 1, the present invention is embodied in a color electrophotographic copying machine similar to that described in connection with FIG. That is, the image forming apparatus according to the present invention includes the apparatus main body 10
Image forming sections Pa, Pb, Pc, and Pd are arranged inside, and below the image forming section, transfer material conveying means including drive rollers 11, 12 and 76 and a conveyor belt 8 wound around the rollers is provided. The conveyor belt 8 is rotated in the arrow direction.

In FIG. 2, a paper feed mechanism 13 is arranged on the right side of the conveyor belt 8, and the transfer material 6 is fed onto the conveyor belt 8 via the paper feed mechanism 13. The transfer material 6 that has been transferred at each of the image forming portions Pa, Pb, Pc, and Pd is fixed to the fixing device 7 from the left side of the conveyor belt 8.
Is sent to. The fixed transfer material 6 is discharged from the discharge port 14 to the outside of the apparatus main body 10.

The first, second, third and fourth image forming portions Pa, Pb, Pc and Pd, which are arranged side by side above the conveyor belt 8, are the photosensitive drums 1a, 1b,
Chargers 15a, 15b, 15c and 15d are provided on the upper left side of the photosensitive drums 1a, 1b, 1c and 1d, respectively.

Further, laser beams 16a, 16b, 16c and 16d are provided on the photosensitive drums 1a, 1b, 1c and 1d, respectively. These laser beam scanners 16a, 16b, 16c, 16d are composed of a semiconductor laser, a polygon mirror, an fθ lens, etc., receive an electric digital image signal, and charge the laser beam modulated according to the signal with the charger 15a, Photosensitive drums 1a, 1b, 1c, 15b, 15c, 15d and developing devices 3a, 3b, 3c, 3d,
It is formed so that these are exposed by scanning in the direction of the 1d generatrix.

More specifically, in the color image forming apparatus of the present invention, when the electrostatic image is formed according to the image signal, the black image can be separated from the three primary colors, so that each of the magenta, cyan and yellow component images is formed. In addition to the image forming unit, an image forming unit that forms a black component image of a color image is provided. The laser scanner 16a of the first image forming unit Pa receives the pixel signal corresponding to the black component image of the color image, and the laser scanner 16b of the second image forming unit Pb receives the pixel signal corresponding to the magenta component image. It is input respectively, and the laser scanner 16c of the third image forming unit Pc and the fourth
A pixel signal corresponding to a cyan component image and a pixel signal corresponding to a yellow component image are input to the laser scanner 16d of the image forming unit Pd.

The paper feed mechanism 13 includes a paper feed guide 51 and a sensor 52,
When the transfer material 6 is inserted into the paper feed guide 51, the sensor 52 detects the leading end of the transfer material 6 and sends a rotation start signal to the photosensitive drums 1a, 1b, 1c, 1d, and at the same time, the drive rollers 11, 12, 96 also. The conveyor belt 8 is driven to rotate. Further, the transfer material 6 fed to the conveyor belt 8 receives corona discharge from the adsorption chargers 59 and 62 and is reliably adsorbed to the surface of the conveyor belt 8. In this embodiment, the high-voltage polarities of the adsorption chargers 59 and 62 are set to be opposite to each other, and the charger 62 is a transfer charger 4a, 4b, 4c, 4d.
And the same polarity.

When the front end of the transfer paper 6 shuts off each sensor 60a, 60b, 60c, 60d, the signal causes the photosensitive drums 1a, 1b, 1 to rotate.
Image formation for c and 1d is sequentially started. When the transfer material 6 passes through the fourth image forming portion Pd, the transfer material 6 is discharged by the charge remover 61 to which the AC voltage is applied, and is separated from the transport belt 8.

Next, the transfer material 6 enters the fixing device 7 and after fixing the image,
It is discharged from the discharge port 14.

Furthermore, each developing device 3a, which constitutes one of the characteristic parts of the present invention,
Explaining 3b, 3c and 3d, in the present embodiment, the average particle diameter of the developer (toner) contained in the black color developing device 3a is 6 μm, and the magenta color of the other developing devices 3b, 3c and 3d, The average particle size of cyan and yellow toners was set to 12 μm. By using such a developing device 3a, 3b, 3c, 3d,
That is, in order to obtain a full-color image, the particle diameters of the color toners to be laminated are made substantially equal to each other, and only the particle diameter of the black toner not to be laminated is made small, whereby both the color balance and the resolution can be satisfied, and good quality Image was obtained.

The image forming apparatus according to the present invention is not limited to the color electrophotographic copying apparatus having the above-mentioned configuration, and includes, for example, one electrophotographic photosensitive member, and a charger and a laser beam scanner around the photosensitive member. Exposure means such as a plurality of developing devices,
A transfer unit and a cleaning unit are arranged, a latent image is formed on the photoconductor for each color, the latent image is visualized by a selected developing device, and each visualized image of the color is transferred to the same transfer material. The color image forming apparatus may be configured to be superimposed and transferred. Of course, the exposure means is not limited to a digital optical system using a laser beam, and a normal analog type exposure optical system can also be used.

In the present invention, the order of development by each developing device is
As described above, it was experimentally found that the same effect can be obtained in the order of black color, cyan color, magenta color, and yellow color instead of black color, magenta color, cyan color, and yellow color. .

Effects of the Invention The image forming apparatus according to the present invention configured as described above is
By making the average particle size of magenta toner, cyan toner, and yellow toner approximately the same and making the average particle size of black toner smaller than the average particle size of these three color toners, the necessary resolution that meets the qualifications can be achieved without waste. The image signal obtained by color separation from the original image can achieve the color reproduction faithful to the original, a high-quality full-color image can be obtained, and the running cost is low. To do. Further, in the apparatus of the present invention, since the black toner having a small average particle size is used, the edge portion of the black image targeted for the line image such as characters is emphasized, and particularly high resolution can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the image forming apparatus according to the present invention. FIG. 2 is a schematic sectional view of a conventional image forming apparatus. Pa, Pb, Pc, Pd: Image forming parts 1a, 1b, 1c, 1d: Image carriers 3a, 3b, 3c, 3d: Developing device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 9/09 15/01 113 Z G03G 9/08 381 (56) Reference JP-A-59-31971 (JP, A) JP 58-202458 (JP, A) JP 60-186874 (JP, A) JP 55-120046 (JP, A) JP 54-126039 (JP, A) Kai 60-79382 (JP, A)

Claims (1)

[Claims] 1. A transfer material having a magenta developing means, a cyan developing means, a yellow developing means and a black developing means for developing an electrostatic image formed according to an image signal, wherein a plurality of color toner images are laminated. In a color image forming apparatus that fixes and forms a full-color image, the average particle diameters of magenta toner, cyan toner, and yellow toner are made substantially equal, and the average particle diameter of black toner is smaller than the average particle diameter of toners of these three colors. A color image forming apparatus characterized by the above.