JPS60208773A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a ghost-free image of high quality and to form a high-potential latent image without forming any pinhole in the surface of a photosensitive body by exposing uniformly an area before the latent image is formed. CONSTITUTION:The photosensitive drum 1 obtained by forming a photoconductive layer on a conductive base drum is exposed uniformly by a pre-exposure light source 2 to prevent the formation of a ghost image of an original. Then, the drum 1 is exposed 4 to an image after plus-porarity discharge is carried out by an electrostatic charger 3, thereby forming a color-separated latent image on the drum 1. A blank exposure light source 5 is turned on during the exposure 4 to perform uniform exposure and thus toner is prevented from sticking a no-image part between image areas.

Description

Detailed Description of the Invention The present invention uses an electrophotographic photoreceptor to obtain a color image by overlapping toner images of different colors, or to form a single image by overlapping a plurality of image information of a single color or multiple colors. The present invention relates to an image forming apparatus.

Conventionally, the process of forming color-separated latent images on an electrophotographic photoreceptor, developing them with corresponding color toners, and transferring the resulting developed images to the same transfer material is repeated multiple times. Color image forming apparatuses that form multicolor images have been put into practical use.

However, in this type of color image forming apparatus, developing devices for three to four colors are fixedly arranged around the endlessly moving photosensitive drum to obtain a 7A/color image, so it is necessary to increase the diameter of the photosensitive drum. there were. On the other hand, in a color image forming apparatus in which developing devices for three to four colors are rotatably moved relative to the photosensitive drum, and only a predetermined developing device corresponding to a latent image is moved to the developing position during development, the photosensitive drum Since the diameter of the drum can be reduced, it is possible to downsize the device and make the photosensitive drum more versatile (
For example, there is a great advantage in achieving common use with photosensitive drums for general black-and-white image forming apparatuses.

FIG. 1 is an explanatory diagram of an embodiment of a color image forming apparatus to which the above-mentioned rotationally movable developing unit is applied.

In FIG. 1, a photosensitive drum 1 having a photoconductive layer made of amorphous silicon or the like on a conductive base drum is uniformly exposed by a pre-exposure source 2. As shown in FIG. This pre-exposure is a well-known means used for the purpose of preventing the generation of ghost images on the original. Next, the photosensitive drum is subjected to positive polarity corona discharge by a charger 3 in order to sensitize the photosensitive drum, and then image exposure 4 is performed, and as a result, a color separation latent image is formed on the drum 1.

Then, between each image exposure, the blank exposure source 5 is turned on to perform uniform exposure and prevent toner from adhering to non-image areas existing between image areas. The lighting time of this blank exposure lamp is set to the minimum time required for the return time after scanning of the scanning exposure optical system of the original, or the travel time required for replacing the developer, or to a value according to that time. , which is generally short compared to normal image exposure time.

In FIG. 1, reference numeral 6 denotes a rotationally movable multicolor developing device group, which includes a yellow developing device 68, a magenta developing device 62, a cyan developing device 68, and a black developing device 64, each having toner of each color. A developing device of a color corresponding to the color separation latent image described above reaches a development position by rotation of the support, and the color separation latent image is developed with negatively charged toner. Then, the developed images are transferred onto a transfer system P held on the surface of a transfer drum 70 covered with a mesh screen, using a transfer charger 7. The images are superimposed and transferred by a positive corona discharge.

On the other hand, the toner remaining on the photosensitive drum 1 without being transferred is
It is cleaned and removed by a cleaning device 8 having a blade plate. After the four-color toner images are aligned and transferred to the transfer side stop, the transfer material P is separated by the separation claw 9, further fixed by a fixing device (not shown), and discharged from the apparatus. , to complete a full-color image on the transfer material.

However, in the above apparatus, although the diameter of the photosensitive drum can be made small (for example, when the diameter is approximately 150 mm or less),
The following problems arise.

That is, since the diameter of the photosensitive drum is small, the pre-exposure sources 2 and 1 are
The distance to the next charger 3 has to be kept close. Therefore, especially when the circumferential speed of the photosensitive drum is high, if the amount of pre-exposure required to erase the ghost image is applied, a large number of 7-otocarriers generated in the photoconductive layer due to the pre-exposure will be charged for the photosensitization. As a result, even after the above-mentioned charging, only a low charge level was obtained as a result of the fact that a large number of particles remained even when the photoconductive layer was charged.

Figure 2 is a diagram showing the relationship between the surface potential Vs of the photosensitive drum after charging and the time t from exposure to charging for photosensitization. When the amount of exposure necessary to obtain the pre-exposure effect is given by each pre-exposure source, generally the time t is 0.
If it is shorter than 3 seconds, the surface potential Vs will drop significantly.

If the voltage applied to the charger is increased to compensate for the decrease in surface potential after charging, pinholes will be created on the photosensitive drum surface, resulting in a significant decrease in the durability of the photosensitive drum. Ta. Therefore, it is necessary to reduce the exposure amount of the pre-exposure sources, and as a result, the ghost image on the original document is not sufficiently erased. Especially when forming a full-color image, the ghost image of the previous color separation latent image is removed from the next color. It appears when a latent image is formed. This phenomenon causes the image to be observed with a difference in color tone, making it unsuitable for practical use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color image forming apparatus that overcomes the above-mentioned problems.

The image forming apparatus of the present invention has means for uniformly exposing a latent image forming area to a color separation latent image or a latent image associated with a subsequent latent image before forming the latent image. As the uniform exposure means, the blank exposure source 5 of the first illustrated apparatus is used, or another exposure means is used. FIG. 3 shows an example of a time sequence when the blank exposure source 5 is used.

FIG. 3 shows a case where the photosensitive drum diameter is, for example, 80 mm and the transfer drum diameter is 160 mm (photosensitive drum diameter: transfer drum diameter is 1=2), and the light source 5 provides uniform exposure to the rotational speed of the photosensitive drum and the transfer drum. time, image exposure time 4, transfer charger 6. For each output time linked to the transfer charging operation time, the size of the transfer material is A4 size and A4 size.
It is shown separately for three sizes.

Note that transfer charging does not necessarily need to be turned off in non-image areas of the photosensitive drum.

Further, in the present invention, the pre-exposure light source 2 shown in the first figure may be used in combination, and the light source 2 may be turned on continuously as long as the exposure amount is small enough not to adversely affect the reduction in the charge level. As described above, instead of performing the uniform exposure of the present invention using the light source 5 shown in the first figure, a light source provided at another position, scanning laser light, light from a document illumination lamp, etc. may be used.

As described above, when using, for example, the color image forming apparatus of the present invention, a high-quality image with sufficient image density and no appearance of gauze or image was observed in the resulting color image. Furthermore, it is possible to form a latent image with a sufficiently high potential without creating pinholes on the surface of the photoreceptor, and the durability of the photoreceptor can be improved h).

The present invention is effective not only for forming full-color images but also for image forming apparatuses that repeatedly use the same photoreceptor and form a composite image by overlapping a first image and a second image. The shape of the photoreceptor is not limited to a drum, but may be belt-shaped, and the circumference of the photoreceptor is not limited to that of the embodiment, and may vary depending on the characteristics of the photoconductive layer of the photoreceptor. Needless to say.

[Brief explanation of drawings]

31 is an explanatory diagram showing the positional relationship of the surface of the drum, and 31 is an explanatory diagram showing a timing chart of each member when the present invention is applied to the apparatus shown in FIG. In the figure, l is a photosensitive drum, 3 is a uniform charger for the photosensitive member, 4 is an exposure light for image information, 5 is a blank exposure light source, and 6
indicates a developing device.

Claims (1)

[Scope of Claim] An image forming apparatus that obtains an image by overlapping a plurality of images formed on a photoreceptor, comprising: a photoreceptor that moves endlessly; a charging means for imparting photosensitivity to the photoreceptor; It has an exposure means for exposing the image information, a developing means for developing the formed latent image, and a uniform exposure means for uniformly exposing the photoreceptor between the charging means and the developing means, and has an exposure means for exposing the image information. An image forming apparatus characterized in that an image information recording light area of a photoreceptor is first exposed by the uniform exposure means.