JPH06138743A - Color image forming method - Google Patents

Abstract

PURPOSE:To prevent scattering of toner and to obtain a sharp image by dividing into a character line image part and a picture pattern part excepting the character line image part, and writing the character line image part later. CONSTITUTION:In the case of an original 16 where the picture pattern parts 12 and the character line image parts 13 overlap, the picture pattern parts 12 of four colors are first written by the use of a fullcolor image forming device, thereafter the character parts 13 of the four colors are written in order. In this case, image data separated into the picture pattern part and the character part by an image processing part is converted into an LD light emission intensity signals and are sent to an LD drive circuit in sequence. And the images are formed in order. By forming the images this way, exposure is not carried out at least next to the vicinity of the toner image of the character part 13. Therefore, conspicuous dusts can be reduced most.

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 method using an electrophotographic copying machine, a facsimile, a printer or the like,
More specifically, the present invention relates to a color image forming method in which a plurality of color images are superposed on a photoconductor.

[0002]

2. Description of the Related Art Conventionally, by using a color image forming method in which a plurality of color superposed toner images are repeatedly formed on a photoconductor by repeating charging, optical writing, and development, K (black), When an image is sequentially formed with Y (yellow), M (magenta), and C (cyan), there is a problem that K dust is generated in the Y portion around K. This is often seen, for example, when a map document or the like is copied.

Such development is carried out by (a), (b) and (c) of FIG.
It will be described based on. First, as shown in FIG.
In the Y image forming process, corona charging is performed in a state where the black toner 18 is attached on the photoconductor. At this time, the toner 18
The charging potential of the part without toner is -900V, that of the part with toner 18 is -100V, and that of the photosensitive member below is -8.
It is charged to 00V. Here, as shown in (b) of FIG.
When the Y image signal is exposed to the peripheral portion, the photoconductor potential is -1.
Although it drops to 00V, the photoconductor potential under the black toner 18 remains at about -800V. Therefore, at the boundary,
Due to the potential difference between the both parts, the negatively charged black toner 18 scatters to the peripheral part as shown in FIG. This is toner dust.

Therefore, in the prior art, a method of preventing dust by a potential "cover" by providing a non-image portion when adjacently exposing the toner image formed in the previous step (Japanese Patent Laid-Open No. 62-2620).
No. 68), and a method of reducing the charging potential during Y image formation (Japanese Patent Laid-Open No. 133073) for the purpose of reducing the potential difference at the boundary between the black toner portion and the peripheral portion.

[0005]

However, in the former case, there is a problem that even a small amount of non-image portion causes a problem in faithful image formation, especially in reproduction of a document in a copying machine. Further, in the latter case, if the charging potential is lowered and the developing bias voltage is fixed, the background stain is caused. Therefore, it is necessary to lower the developing bias at the same time as the charging potential, and as a result, the developing potential becomes small. There is a problem that a sufficient concentration cannot be obtained.

Therefore, the present invention does not have such a problem, and prevents the toner scattering due to the exposure of the previously developed toner to the adjacent portion, thereby obtaining a clear image. Is to provide.

[0007]

In order to solve the above-mentioned problems, the present invention forms a plurality of color superposed toner images on a photoconductor by repeating charging, optical writing and development, and transfers them to a transfer material at once. In the color image forming method, a character line drawing portion and a pattern portion other than the character line drawing portion are separated, and the character line drawing portion is written later.

Colors which do not need to be developed are passed through the image forming process.

Further, when the character / line drawing portion is formed, the image forming speed may be faster than when the pattern portion is formed.

[0010]

By forming the pattern portion first, the toner image is not written adjacent to the character / line image portion toner image, so that dust in the conspicuous character / line image portion can be prevented.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a full-color image forming apparatus used for carrying out the present invention. First, an outline of an image forming operation by the apparatus will be described.

In the full color mode, the photoreceptor 2 uniformly charged to -900V by the scorotron charger 1.
Then, a Y (yellow) image is written by the laser exposure L, thereby forming an electrostatic latent image of the Y image in which the potential of the image portion, which is the portion to which the toner should adhere, is lowered. In addition,
At this time, the potential of the image area has dropped to −100V.
This Y latent image is reversely developed by the Y developing device 3 having negatively charged toner to form a Y toner image. The developer uses a single non-magnetic component. Then, the transfer unit 7 and the cleaning unit 8 are configured so that the photosensitive member 2 can be used during the overdeveloping.
Since the image is being retreated from the surface, the image forming process (image forming process) for the second color is started without transferring or cleaning.

Next, the photosensitive member 2 on which the Y toner image is still formed is charged again, and then the M (magenta) image is written with the leading edge of the image aligned with the Y image, and the electrostatic charge of M of the negative image is written. A latent image is formed. This M latent image is an M developing device 4 provided with negatively charged M toner without disturbing the image of the first color by non-contact.
Is subjected to reversal development by means of a toner image. Similarly, a C (cyan) image is similarly formed by the C developing device 5, and a K (black) image is also formed by using the K developing device 6 if necessary.

A positive DC bias is applied to the superimposed toner image by the transfer roller 7a which has returned to the normal position,
The image is transferred onto a transfer paper (transfer material) sent from the registration roller 9, further fixed by a fixing device 10, and ejected from a paper ejection unit 11. On the other hand, the transfer residual toner on the photoconductor 2 is cleaned by the conductive fur brush cleaning 8a of the cleaning unit 8 which has also returned to the normal operating position after the pre-cleaning charge removal by the DC superimposed AC charge.

In the above example, the toner images are formed in the order of Y, M, C, and if necessary K, but the present invention is not limited to this, and the toner images may be formed in any preset order. You may form.

In the present invention, in the case of the original 16 in which the picture portion 12 and the character line drawing portion (hereinafter, simply character portion) 13 are overlapped with each other as shown in FIG. 12 is written in 4 colors first, and then the character portion 13 is written in 4 colors sequentially. In this case, as shown in the block diagram of FIG. 3, the image processing unit 14 converts the image data (see FIG. 4) separated into the pattern portion and the character portion into the LD emission intensity signal, and sequentially outputs the LD drive circuit (writing unit). ) 15 sent to. That is, the Y pattern portion, the M pattern portion, the C pattern portion, the K pattern portion, the Y character portion, the M character portion, the C character portion, and the K character portion are formed in this order.

By thus forming an image,
At least the periphery of the toner image of the character portion 13 is not exposed adjacently. Therefore, the most conspicuous dust can be reduced. As a result, as shown in (a) of FIG. 5, the copy 17 in which the characters 13a are conventionally scattered is somewhat mixed with the toner of the picture part in the character part as shown in (b) of FIG. The characters 13a will not be scattered. That is, although the dust in the picture part toner does not disappear, even if dust is generated, it is dust from the picture part to the picture part, or from the picture part to the character part, so there is no practical problem.

Next, another embodiment of the present invention will be described with reference to the flowchart shown in FIG. In the above embodiment, the pattern portion and the character portion are imaged once for all colors and the photosensitive member is rotated 8 times in total, but in the present embodiment, when there is no pattern portion or character portion data for each color, Only pass the image formation process. In this case, after the image formation of the picture part is completed, the image formation of the character part is started, but it is judged whether or not there is image data for each color, and if there is not, the process proceeds to the image formation of the next color. To By doing so, it is possible to prevent the image forming speed from decreasing even a little.

Further, for the character portion, it is possible to increase the speed a little because the developing ability exceeds that of the picture portion due to the edge effect, and high gradation such as a photograph of the picture portion is not desired. However, it is desirable to pass the fixing at a standard speed in terms of energy.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0021]

As described above, according to the color image forming method of the present invention, since the character line drawing portion is formed after the image other than the character line drawing portion is formed, dust is generated in the character line drawing portion. A sharp image can be obtained without doing this, and the speed is reduced by making it possible to pass the image forming process of the color that is not developed and by making the image forming speed at the time of character line drawing faster than others. It has an excellent effect that it can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a color image forming apparatus used for carrying out a color image forming method of the present invention.

FIG. 2 is a conceptual diagram of an image.

FIG. 3 is a block diagram of a color image forming apparatus.

FIG. 4 is a conceptual diagram of write data.

FIG. 5 is a comparison of the dust generated on the copy.
(A) is a diagram showing a conventional example, and (B) is a diagram showing a case according to the present invention.

FIG. 6 is a flowchart showing another embodiment of the present invention.

7A and 7B show a mechanism of dust generation. (A) shows a state of potential during development, (B) shows a state of potential during next-color charging / exposure, and (C) shows a state of potential after exposure. It is a conceptual diagram which shows each state.

[Explanation of symbols]

 1 Scorotron charger 2 Photoreceptor 3 Y developing device 4 M developing device 5 C developing device 6 K developing device 12 Picture part 13 Character line drawing part 14 Image processing part 15 LD drive circuit L Laser exposure

Claims (3)

[Claims] 1. A color image forming method for forming a color superposed toner image of a plurality of colors on a photoconductor by repeating charging, image signal exposure and development, and transferring the color image onto a transfer material at a time. In the case of an image in which images other than the character and line drawing are overlapped, a toner image of the character and line drawing is formed after forming a color-superimposed toner image other than the character and line drawing. 2. The color image forming method according to claim 1, wherein the color image forming step for passing through the color of the image which is not developed is passed. 3. The color image forming method according to claim 1, wherein the image forming speed at the time of forming the character line image is made higher than that at the time of forming an image other than the character line image.