JPS6236220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrophotographic copying machines, particularly color electrophotographic copying machines.

In a color electrophotographic copying machine, each visible image formed on a photoreceptor is separately superimposed and transferred onto the same transfer paper to obtain a single copy.

This is called a color electrophotographic copying machine that uses a visible image transfer method. Specifically, it separates a color original image into each color component using, for example, blue, green, and red color separation filters. The photoreceptor is exposed to the decomposed light, and the electrostatic latent images obtained by this exposure are developed using yellow, magenta, and cyan color developers, which are complementary colors to the above-mentioned colors. A color copy image is obtained by visualizing the images and sequentially overlapping them and transferring them onto a transfer sheet carried on a transfer drum.

One such color copying machine uses a bias type transfer device. The above bias type transfer device applies a bias voltage of opposite polarity to the toner image on the photoreceptor to a conductive transfer drum that rotates in pressure contact with the drum, and transfers this toner image to transfer paper on the transfer drum. It is something that makes you
The advantages of this device are that the transfer paper is reliably held on the transfer drum, that the transfer drum is easy to control, and that the transfer paper has good conveyance performance.
For example, it is easy to control bias application during transfer. Disadvantages include, first of all, that the transfer drum lacks precision and material stability. In the case of this apparatus, conductive rubber is often used as the material of the transfer drum in order to bring the transfer drum into close contact with the photoreceptor and apply a bias voltage. For this reason, it is difficult to increase precision due to its hardness and conductivity, and it also lacks material stability due to changes over time. In addition, this device suffers from problems such as worm-eaten and hollow spots in image quality due to abnormal discharge during transfer. this is,
This occurs when the contact pressure of the transfer drum against the photoreceptor is increased in order to obtain sufficient adhesion. Furthermore, if a carrier such as iron powder is mixed into the toner image in order to bring the transfer drum into pressure contact with the photoreceptor, the surface of the photoreceptor or the transfer drum may be damaged by this hard carrier. Furthermore, since the surface resistance of the transfer drum easily changes due to environmental changes such as temperature and humidity, the transfer characteristics are sensitive to these changes.

Another type of transfer device is a charge type transfer device. In this method, a portion of a loop-shaped flexible dielectric supported by several rotating bodies is brought into contact with the photoreceptor, and a corona charger with a polarity opposite to that of the toner image is placed on the inside of the loop-shaped flexible dielectric. . The transfer paper is electrostatically brought into close contact with the dielectric sheet and is conveyed, and the toner image is transferred to the transfer paper side by the opposite polarity charge applied from the corona charger. Overall, this device has extremely stable image quality, but the positioning and conveyance of the transfer paper are unstable and color shift is likely to occur. In addition, the entire device becomes very complex, making it difficult to control and lacking in reliability.

As described above, bias type and charger type transfer devices each have advantages and disadvantages.

In the present invention, an optical image of an original to be copied is projected onto a photoreceptor that is uniformly charged by a charger through a filter to form an electrostatic charge image, and then an image of a color corresponding to the filter is formed. In a color electrophotographic copying machine, the process of developing with toner and transferring it to paper by electric force is repeated at least twice by changing the filter and toner. The toner image of
The photoreceptor moves in synchronization with the photoconductor and transfers the image onto the dielectric material that comes into contact with the surface of the photoreceptor, forming a superimposed image, and then transfers this superimposed image onto the paper conveyed from the paper feeder. In this way, when the three color toner images are superimposed, the positional deviation of each toner image is extremely minimized to obtain a clear color image, and the clamping mechanism of the transfer paper is eliminated to avoid mechanical troubles that occur in this mechanism. Another object of the present invention is to provide a color electrophotographic copying machine in which a control mechanism can be eliminated, and the structure can be simplified by eliminating the need for attachment and detachment of a paper separation mechanism.

A feature of the present invention is that the toner image formed on the photosensitive drum is transferred onto a dielectric material and then onto paper.

The present invention will be explained below based on the illustrated embodiments.

The figure schematically shows a color electrophotographic copying machine according to an embodiment of the present invention, in which the photosensitive drum 1 is
Rotates at a constant speed counterclockwise. A photoconductive layer is provided on the surface of the photosensitive drum 1, and this surface is uniformly charged to a predetermined polarity by a corona charger 2.

When an original image is projected by the exposure optical system 3 onto the surface of the photoreceptor that retains an electric charge, the electric charge on the photoconductive layer is dissipated according to the density of the image area of the original image, and an electrostatic latent image is formed there. be done. This electrostatic latent image is transferred to the developing device 4.
Visualized by .

In the case of a color copying machine, the developing device is at least
Three devices are provided: a device 4a for yellow development, a device 4b for magenta development, and a device 4c for cyan development. Accordingly, the exposure optical system 3 is equipped with color separation filters corresponding to each of blue, green, and red colors. In addition to this, the developing device 4 may be equipped with a device for black development in order to adjust the image tone.

Development is performed for each color. That is, when a color original image is first projected onto the surface of a photoreceptor using a blue filter, an electrostatic latent image consisting of a yellow component, which is a complementary color to blue, is formed. This is visualized by the yellow developing device 4a. The yellow developing device 4a contains a developer consisting of yellow toner and carrier iron powder, and the two are stirred and mixed to be triboelectrically charged, and the toner has a polarity opposite to that of the electrostatic latent image. charged. The toner and carrier are both attracted to the developing roller 41 and conveyed to a developing position close to the photoreceptor 1.

At the development position, only the toner charged to the opposite polarity is attracted to the electrostatic latent image and becomes a visible image.

Note that while the yellow developing device 4a is performing development, the other developing devices 4b and 4c are moving away from the surface of the photoreceptor 1, and the yellow toner image on the photoreceptor moves toward the next transfer position.

The transfer drum 7 has the same diameter as the photosensitive drum 1, and rotates in the same direction and at the same speed at the contact point where it comes into pressure contact with the photosensitive drum 1, that is, at the transfer position. The transfer drum 7 is made of a dielectric material, and is provided with a first transfer corona charger 8 on the inside facing the transfer position with the photosensitive drum.

The first transfer corona charger 8 is the transfer drum 7
It is slidably attached via a suitable member (not shown) to a transfer drum support member (not shown) disposed inside the transfer drum at a position facing the transfer position. The first transfer corona charger 8 is located at the first transfer drum 7.
It is now a transcription department. This first transfer corona charger 8 is used for transferring each color.

The static elimination charger 9 is disposed at a position where the transfer drum 7 has finished passing through the transfer position, and consists of a charger 9a provided on the outside of the transfer drum 7 and a charger 9b provided on the inner side opposite thereto. The transfer drum 7 is neutralized to an appropriate potential. Static elimination by this static elimination charger 9 is as follows:
This is performed every time the photoreceptor 1 is transferred.

The paper feeding device 10 is disposed behind the static elimination charger 9 and in front of a second transfer charger described later. This paper feeding device 10 includes a cassette 12 containing transfer paper 11, and a rotatable pull-out roller 13 that comes into contact with the uppermost transfer paper in the cassette 12 and pulls out the transfer paper from the cassette at the start of paper feeding. It also includes a paper feed roller 14 and a guide member 15 for introducing the drawn-out transfer paper 11 into a second transfer section, which will be described later. This paper feeding device 10
The rotation of the pull-out roller 13 and the paper feed roller 14 is controlled so that the timing of the operation on the photosensitive drum 1 and the timing of feeding the transfer paper to the transfer drum are synchronized.

The second transfer corona charger 16 is disposed behind the paper feeding device 10, and the transfer paper 11 conveyed from the paper feeding device 10 comes into contact with the transfer drum 7 to transfer the overlapping images on the transfer drum. It serves as the second transfer section.

This second transfer charger 16 includes a corona charger 16a provided outside the transfer drum 7,
This consists of a pair of corona chargers 16b provided inside the opposing drum, and when the final overlapping image is formed on the transfer drum, the toner image on the transfer drum is electrically attracted onto the transfer paper. The charging state is set so that this occurs.

The separation device 17 includes a peeling piece 17a extending toward the immediate rear of the second transfer section, and a roller that conveys the transferred transfer paper 11 peeled from the transfer drum 7 by the peeling piece 17a to the fixing device. 17b
and a loop-shaped belt 17c that comes into contact with this.

This separating device 17 is normally separated from the transfer drum surface. When the final transfer by the transfer drum is completed, the peeling piece 17 of the separating device 17
a comes into contact with the surface of the transfer drum, and the leading edge of the transfer paper 11, which is advancing together with the transfer drum 7, is peeled off and heads toward a fixing device, which will be described later.

The fixing device 18 is located on an extension of the conveyance path of the transfer paper 11 separated from the transfer drum 7 by the separating device 17, and is equipped with a hot air dryer or other known heat fixing mechanism.

On the other hand, the surface of the transfer drum 7 that has finished transferring the toner image onto the transfer paper in the second transfer section is cleaned by the cleaning device 19.

The cleaning device 19 is conventionally known and includes a scraping roller 19a made of urethane or sponge, a scraping plate 19b in contact with the scraping roller 19a, and a wiping roller 19c made of rubber or metal. away from In response to a cleaning command issued after the transfer paper 11 is separated from the transfer drum 7, the cleaning device 19 is brought into contact with the transfer drum 7 and cleans the surface of the transfer drum.

Note that a photoconductor cleaning device 20 having a similar configuration to the above-described cleaning device 19 is installed in front of the corona charger 2 of the photoconductor drum 1.
is installed. The photoreceptor cleaning device 20 is configured to clean the photoreceptor after the three-color superimposed image has been transferred onto the transfer paper by the transfer drum 7 and before a new document image is exposed. Clean the surface.

Next, the operation of the color electrophotographic copying machine as an embodiment of the present invention constructed as described above will be described.

Now, when a copy start command is issued via an operation button or the like (not shown) provided on the main body of the copying machine,
The photoreceptor drum 1 begins to rotate and is subjected to discharge of a predetermined polarity by the corona charger 2. Furthermore, the developing device 4 is also started, and the toner of each color and the carrier are stirred and mixed.

The charged photosensitive drum 1 receives exposure of an original image onto its photoconductive layer through an exposure optical system 3 equipped with a color separation filter. The photosensitive drum 1 that has been exposed to the original image forms an electrostatic latent image corresponding to the original image in that color on the photoconductive layer through color separation by a filter.

The photosensitive drum 1 holding the electrostatic latent image on the photoconductive layer is turned into a visible image by a developing device. This development is performed for each color of the original image. That is, when a color original image is first projected onto the surface of a photoreceptor using a blue filter, an electrostatic latent image consisting of a yellow component, which is a complementary color to blue, is formed.
This latent image is visualized by a yellow developing device 4a.

In this way, the photosensitive drum 1 carrying the yellow visible image repeatedly transfers magenta and cyan visible images corresponding to green and red onto the transfer drum in the same way, and finally A superimposed image of three colors is formed on a transfer drum.

On the other hand, on the transfer drum 7, the image is transferred from the photosensitive drum 1 by the first transfer corona charger 8, and when the image transfer is completed, the charge is removed to an appropriate potential by the charger 9. This process is performed for each color, and a three-color superimposed image is carried on the surface.

The transfer drum 7 rotates in synchronization with the photoreceptor drum 1 and has a three-color superimposed image formed on its surface by transferring visible images of each color from the drum 1. When the image is formed, it matches the transfer paper 11 that begins to be conveyed at the second transfer section.
The transfer paper 11 is transported at a transport speed determined so that its leading edge coincides with the leading edge of the three-color superimposed image in the second transfer section.

When the superimposed image and the transfer paper move while matching, the second transfer corona charger 16 starts discharging. As a result, the three-color superimposed image on the transfer drum is transferred to the transfer paper. The second transfer corona charger automatically stops discharging when the transfer is completed.

After the transfer is completed, the transfer paper 11 is transferred to the separating device 1.
The leading end is peeled off by the peeling piece 17a of No. 7, and transported toward the fixing device 18, where the image is fixed.

On the other hand, the photosensitive drum 1 with the three-color superimposed image formed on the transfer drum is cleaned by a cleaning device 20.
Its surface is cleaned.

According to the present invention, by transferring the overlapping images of each color formed on the photoreceptor to the transfer drum that rotates in synchronization with the photoreceptor drum, the transfer paper is transferred to the photoreceptor drum. This eliminates the need for a transfer paper clamp mechanism, eliminates the need for transfer paper misalignment, prevents misalignment of overlapping images on the transfer paper, and eliminates the need for complicated and special mechanisms such as transfer paper separation mechanisms for the transfer drum. By removing the charge after transferring the image onto the transfer drum, it is possible to prevent the previous transfer charge from remaining and interfering with the transfer during the second image transfer. Therefore, it is only necessary to set a uniform charging potential for the first transfer charger.
The structure of the charger can be simplified.

Effects such as this can be obtained.

[Brief explanation of the drawing]

The figure is a schematic diagram showing a color electrophotographic copying machine which is an embodiment of the present invention. 1... Photosensitive drum, 2... Corona charger,
3... Exposure optical system, 4... Developing device, 7... Transfer drum, 8... First transfer charger, 10... Paper feeding device, 11... Transfer paper, 16... Second transfer charger.

Claims (1)

[Claims] 1. An electrostatic charge image is formed by projecting an optical image of the original to be copied onto a photoreceptor that has been uniformly charged by a charger through color separation filters for the original image. , the electrostatic charge image is visualized by developing it with toner of a color corresponding to the filter, and this visible image is electrostatically transferred to transfer paper by changing the filter and toner. At least 2
In a color electrophotographic copying machine that repeats the process several times, a transfer drum having a dielectric surface that comes into contact with the photoreceptor surface; a first transfer charger provided inside the transfer drum where the transfer drum and the photoreceptor come into contact; a static elimination charger located behind the first transfer charger in the rotational direction of the transfer drum to eliminate the surface charge after transfer; and a second static elimination charger located behind the static elimination charger in the rotational direction of the transfer drum. The visible image formed on the photoreceptor is
A color electrophotographic copying machine characterized in that the image is first transferred to a transfer drum and then transferred to a transfer paper.