JPH0497174A - Color image forming device - Google Patents

Abstract

PURPOSE:To suppress the occurrence of all sorts of irregularities and to improve the quality of a full color image by separating low and high density parts at each color, executing a copying process, and simultaneously, carrying out a slit-like full surface exposure on the surface of a photosensitive body only on the low density part. CONSTITUTION:The image forming processes of color resolution, toner development, a transfer, etc., are carried out in such a manner that the low and high density parts are separated at each color, and simultaneously, a slit-like exposure is uniformly carried out on the surface of the photosensitive body between an electrifying part and a developing part, when the image forming process of the low density part is executed. In other words, in the copying process of the low density part side on the copying processes of tow times, a slit-like full surface exposing device 16 is provided between electrifying and exposing processes and the slit-like full surface exposure is carried out on the photosensitive drum 1 uniformly electrified by an electrifier 15. Thus, a difference between the base fogging of a slit-like electrifying part and that of an image part is increased, influence caused by the sensitive irregularity of the photosensitive body, the brightness irregularity of an optical system, an electrifying irregularity, etc., are avoided, and a density irregularity is resolved to obtain a stable low density image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention separates an original color into three or more colors, develops each color with toner, and sequentially transfers this toner image onto transfer paper to create a full-color image. The present invention relates to a color image forming apparatus that obtains a color image forming apparatus.

[Conventional technology]

In general, in a color image forming apparatus, in order to obtain a copy image that is faithful to the original, the γ characteristics of the original and the copy image are
A relationship like that shown in Figure 7a is good. However, in reality, it only has the characteristics shown in the figure.

As a means to solve this problem, there is a superimposition method in which two developed images of the same color with different γ characteristics are superimposed on transfer paper. This process separates the original into three colors: R (red), G (green), and B (blue), and then divides each color into low-density areas and high-density areas, and performs a total of six copying processes to create the original. This is a method to obtain a good copy image with close γ characteristics (see Figure 8).
.

Here, images in low density areas are generally obtained by setting the photoreceptor charging potential and the amount of exposure light to be lower than in a normal copying process. Furthermore, images in high density areas can be obtained by setting the photoreceptor charging potential and the exposure light amount higher than in a normal copying process.

[Problem to be solved by the invention]

However, in the above process, twice as much toner as usual is applied to high-density areas, which has the disadvantage that the transfer paper curls after fixing due to the difference in reduction ratio due to heat between the toner and the transfer paper. .

In addition, in the copying process for low-density areas, the difference between the background and image areas becomes smaller, which makes density unevenness more likely to occur due to the effects of uneven sensitivity of the photoreceptor, uneven brightness of the optical system, uneven charging, etc. Problems such as this occurred.

Note that, in order to improve the image quality in low density areas, a technique is known in which slit-like full-surface exposure is performed between the charging and developing processes.

That is, when slit-like exposure is performed on the surface of the photoreceptor, toner is not deposited on the slit-like exposed portions even if they are developed because they are not charged with any charge. In addition, in the non-exposed area, a latent image due to electric charge is formed on the surface of the photoreceptor depending on the intensity of light coming from the optical system, and toner is deposited on the surface of the photoreceptor. An image obtained by superimposing this non-toner area and the developed toner area is visible to the human eye, and the overall appearance can be reproduced in an upper neutral color.

Further, in order to place more toner on the toner-covered portion by the difference from the non-toner portion, it is necessary to set the charging potential and the exposure amount to be high. This allows for a large difference between the background area and the image area, making it possible to reduce the effects of uneven sensitivity of the photoconductor, uneven brightness of the optical system, uneven charging, etc., and eliminate density unevenness in low density areas. This made it possible to reproduce stable neutral colors.

However, if slit-like full-surface exposure is performed during the copying process for high-density areas, a problem arises in that the image quality of the high-density areas is affected by the slits and the density decreases.

In addition, as a prior art, Japanese Patent Laid-Open No. 60-209755 can be mentioned.

The present invention has been made in view of the above-mentioned background, and an object of the present invention is to provide a color image forming apparatus that can improve the image quality of full-color images.

[Means to solve the problem]

The above purpose is to separate the original color into three or more colors, develop each color with toner sequentially, superimpose and transfer onto transfer paper using this developer, and fix the transfer paper after all colors have been transferred using a fixing device. In a full-color color image forming apparatus, image forming processes such as color separation, toner development, and transfer are performed separately for each color into low-density areas and high-density areas. This is achieved by providing a means for controlling uniform slit-like exposure on the surface of the photoreceptor between the development stage and the development stage.

[Effect]

The copying process is performed separately for each color into a low-density area and a high-density area to obtain an image with gamma characteristics close to that of the original. At the same time, a slit-shaped full-surface exposure is performed on the photoconductor surface only for the low-density area. , suppresses the occurrence of various types of unevenness caused by a decrease in the difference between the background area and the image area.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. In the following description, the same reference numerals are given to the same parts as in the conventional example described above, and redundant description will be omitted.

FIG. 2 is a schematic diagram showing an example of a three-primary color separation type color image forming/copying apparatus to which the present invention is applied.

When a copy start button (not shown) is pressed, the photosensitive drum 1 and the transfer drum 2 start rotating in synchronization, while the light #3
is turned on, and the light source 3 and mirror group 4 scan the surface of the document by a driving device.

This reflected light then passes through a color separation filter 5 and forms an electrostatic latent image on the photoreceptor drum 1.

During the first document scan, the electrostatic latent image created on the photoreceptor drum 1 by the blue color separation filter is Y (yellow).
A visible image is created on the photosensitive drum 1 by the developing device 6a.

On the other hand, the transfer paper stored in the cassette 7 is fed by a paper feed roller 8, aligned with the visualized image on the photosensitive drum 1 by a registration roller 9, and sent to the transfer drum 2. .

The tip of the sent-out transfer paper is clamped by a clamper provided on the transfer drum 2, and the visible yellow image on the photosensitive drum 1 is transferred to the transfer paper on the transfer drum 2 by the transfer charger 10.

In the second scan of the document, the color separation filter 5 is switched to green, an electrostatic latent image is created on the photoreceptor drum 1 in the same manner as described above, and a visible image is transferred to the photoreceptor drum 1 by the M (magenta) developer 6b. make on top. Thereafter, a magenta image is superimposed on the yellow visible image on the transfer paper on the transfer drum 2 in the same manner as described above.

In the third scan of the document, the color separation filter 5 is switched to red, an electrostatic latent image is created on the photoreceptor drum 1 in the same manner as above, and a visible image is formed on the photoreceptor drum 1 by the C (cyan) developer 6C. make it.

As described above, after the color-separated three-color images are superimposed and the same color tone as the original is transferred onto the transfer paper, the transfer paper is separated from the transfer drum 2 by the separation static eliminator 11 and the separation claw 12, and fixed. Fixed by roller 13 and placed on tray 1
It is discharged at 4.

The present invention improves image quality in high-density areas and low-density areas by performing both the same-color twice-copying process and the slit-like full-surface exposure copying process in the above-mentioned copying process. There's a lot to do.

In other words, in the copying process on the low-density side of the two-time copying process, a slit-like full-surface exposure device is provided between the charging and exposure processes, and the slit-like full-surface exposure is applied to the photoreceptor drum l, which has been uniformly charged by the charging device. When this is performed, a slit-like charge is formed on the photoreceptor drum 1. Thereafter, the photoreceptor is exposed to light coming from the optical system, forming a latent image. The formed latent image is visualized with toner in the development order, but the toner does not reach the slit exposure area. An image formed by superimposing the non-toner part exposed through this slit and the developed toner-covered part enters the human eye, making it possible to reproduce an upper neutral color in appearance as a whole. Note that in order to obtain the same image quality as the normal low-density side copying process, more toner is placed on the toner-covered area by the difference from the non-toner part, so the photoreceptor is charged less. It is necessary to set the potential and exposure light amount relatively high. This increases the difference between the background of the slit-shaped charged area and the image area, and avoids the effects of uneven sensitivity of the photoreceptor, uneven brightness of the optical system, uneven charging, etc., and eliminates uneven density, resulting in a stable low-density area image. can be obtained. In the next copying process on the high-density side,
By setting the photoreceptor charging potential and the amount of exposure light higher than in a normal copying process, the latent image of the image in the low-density area near the background area is skipped, and an image in the high-density area is obtained. By transferring the high-density image and the low-density image thus obtained onto transfer paper, the images are superimposed and a color copy with good gradation is obtained. Note that even on the high-density side, the amount of toner on the low-density side decreases due to the effect of the slit-like full-surface exposure copying process, so the amount of toner when the two processes are overlapped decreases, and the effect of curling of the transfer paper decreases. It became possible to eliminate.

Further, the same effect can be expected even if a slit-shaped exposure device is inserted between exposure and development.

FIG. 1 is a diagram showing the configuration around a photosensitive drum of a color image forming apparatus according to an embodiment of the present invention.

In the figure, 15 is a charger, 16 is a slit exposure device, 17 is a normal optical writing system, 18 is an eraser for a non-image area, and 19 is a cleaning unit. Further, 6 is a color developing unit, 6d is a black developing device, and P is a transfer paper.

As described above, the slit exposure device 16 exposes the entire surface of the photoreceptor drum 1 in a slit-like manner when performing the image processing of the low-density portion for each color.

FIG. 3 is a perspective view of a slit exposure device, and this slit exposure device 16 includes a substrate 16a, an exposure LED 16b and an LED current limiting resistor 16c attached to the substrate 16a, and a condensing lens 16d. It is composed of a slit film 16e.

FIG. 4 is a lighting control circuit diagram of the slit exposure device, and L
ED 16 b is on, off signal S is transistor 20
When the transistor 20 is turned on, a current flows through the DC power supply 21 and emits light.

FIG. 5 is a conceptual diagram of slit exposure using a slit exposure device, in which the emitted light passes through a condensing lens 16d and becomes parallel rays, passes through a slit film 16e with alternating transparent parts and black parts, and forms a slit. The light is exposed and hits the photosensitive drum 1.

FIG. 6 is an explanatory diagram showing potential changes on the surface of the photoreceptor drum before and after slit exposure.
The photosensitive drum 1, whose photoconductive layer 1a is uniformly charged, is exposed to light in the form of a slit, so that the charges in the areas exposed to light escape from the photoconductive layer 1a toward the conductive substrate 1b, and the charges in areas not exposed to light are reduced. remain. The remaining charge is exposed to light from the optical system 17, and toner is attached to the remaining charge of the latent image pattern by the color developing unit 6, and this latent image pattern is visualized.

〔Effect of the invention〕

As described above, according to the present invention, the copying process is performed separately for each color into a low-density area and a high-density area to obtain an image with a γ characteristic close to that of the original, and only for the low-density area.
Since the entire surface of the photoreceptor is exposed in a slit-like manner, it is possible to suppress the occurrence of various unevenness caused by a reduction in the difference between the background area and the image area, thereby improving the image quality of a full-color image.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram around the photosensitive drum of a color image forming apparatus according to an embodiment of the present invention, FIG. 2 is a configuration diagram of the entire color image forming apparatus, and FIG. 3 is a perspective view of a slit exposure device.
Fig. 4 is a lighting control circuit diagram of the slit exposure device, Fig. 5 is a conceptual diagram of slit exposure by the slit exposure device, Fig. 6 is an explanatory diagram showing potential changes on the surface of the photoreceptor drum before and after slit exposure, and Fig. 7 is a general γ characteristic diagram, and FIG. 8 is a γ characteristic diagram when the present invention is implemented. l... Photosensitive drum, 3... Color separation filter, 6.
...Color developing unit, 16...Slit exposure device. fN 2 Figure 31 χ1 Figure 4 /6e /6d Figure 6 Figure 7 To1 ? , ■ θ diagram

Claims (1)

[Claims] A full-color process in which the original color is separated into three or more colors, each color is developed with toner, and the developed order is superimposed and transferred onto transfer paper, and the transfer paper after all colors have been transferred is fixed by a fixing device. In a color image forming apparatus, the image forming process including color separation, toner development, and transfer is performed separately for each color into a low-density area and a high-density area. A color image forming apparatus characterized by comprising a control means for uniformly performing slit-like exposure on the surface of a photoreceptor between parts.