JPS6345114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copying machine having a plurality of cleaning means for removing untransferred toner and the like remaining on an electrostatic latent image carrier.

Traditionally, cleaning methods used for copying machines, etc. include fur brushes, blades, rollers,
Various methods such as magnetic brushes are well known. Each cleaning method has its own advantages and disadvantages, and no one has a sufficient cleaning function under all conditions, so each method is currently used appropriately. For example, the fur brush cleaning method requires air suction means, which increases the size of the device, the blade cleaning method requires a large pressure contact, which can easily damage the photoreceptor, and the roller cleaning method requires The disadvantage is that an additional device is required to remove attached toner, etc., and there is a problem of friction on the roller surface, and the magnetic brush cleaning method, which is used only in dry copying machines, does not have a great cleaning effect. There is.

Therefore, recently, attempts have been made to use a plurality of cleaning means of the same type or different types at the same time to further emphasize the advantages of each cleaning means. For example, a copying machine manufactured by Ricoh Co., Ltd.
A typical example is a liquid development type plain paper copying machine such as the DT-1200, in which an elastic foam roller and a cleaning blade are used together.

On the other hand, efforts are being made to make copying machines smaller and lower in cost, but simplification of the copying process and use of a single member for multiple functions also have a high contribution rate. The present invention is based on the latter idea, focusing on static elimination and asking if it is possible to use another member to perform the static elimination function. Conventionally, the static eliminating means has been placed between the cleaning means and the primary charging means, or in front of the cleaning means. This static elimination means mainly uses AC corona discharge, which is intended to reduce the surface potential of the photoreceptor drum to zero, but also to reduce the potential difference between the image area and the non-image area as much as possible. That is the main purpose. If an attempt is made to reduce the surface potential to zero using such an alternating current corona discharge, the mechanism will become complicated and bulky, resulting in high costs, and the installation location must also be considered separately. Static neutralization by AC corona has a large effect on the subsequent formation of electrostatic latent images, and if applied too strongly, the previous electrostatic latent image will appear as a blank image on the next copy, a so-called negative afterimage. If it is too weak, cleaning will be incomplete, and its management and adjustment are troublesome. Furthermore, applying corona discharge to the photoreceptor causes fatigue of the photoreceptor.

In addition, cleaning means that have not only a cleaning function but also a static elimination function have already been published in Japanese Patent Publications No. 40-12831 and No. 44-2036.
Actual Publication No. 11425, Special Publication No. 45-25237, Special Publication No. 45-25237, Special Publication No. 11425
41-14069, Japanese Unexamined Patent Publication No. 49-91651, etc. For example, if an elastic blade is used to remove toner and charge remaining on the photoreceptor drum after transfer, the blade must be conductive, resulting in high hardness and thus the blade tip and photoreceptor. It becomes impossible to increase the contact area with the surface of the body drum. If you try to make it larger and forcefully press the blade against the photoreceptor drum, you will damage the surface of the photoreceptor drum, which is a fatal drawback. Furthermore, due to the increased hardness, it becomes difficult to make the pressing force of the blade against the photoreceptor drum uniform in its length direction, resulting in a problem that uniform charge removal and uniform toner removal cannot be expected.

The present invention has been made in view of the above-mentioned points, and has made it possible to combine a plurality of different cleaning means in order to improve the cleaning effect, and thereby make it possible for the cleaning means to also serve as a charge eliminating function.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a compact and inexpensive copying machine that improves the cleaning effect and simplifies various devices around the electrostatic latent image carrier.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a copying machine using a liquid developer according to an embodiment of the present invention. The photosensitive drum 1 rotates around its axis in a counterclockwise direction, and a corona charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are arranged in this order around the photosensitive drum 1. The developing device 4 includes a developer tank 8 that stores a developer 7 in which toner particles are dispersed.
, a photosensitive drum 1, a developing electrode 9 arranged with a predetermined gap, and a pump 10 for supplying a developer 7 between the developing electrode 9 and the photosensitive drum 1.
and a developer receiving tray 11 for collecting the developer overflowing from the developing electrode 9 into the developer tank 8. The developer 7 is maintained at a constant toner concentration by a toner concentration control device (not shown). Immediately after the developing electrode 9, an excess developer removing device 12 is arranged to remove excess developer.
Specifically, it is composed of a squeeze roller that rotates in the direction of the arrow with a gap of several hundred microns to 1 mm between the surface of the photoreceptor drum and the surface of the photoreceptor drum. Cleaning device 6
is composed of a first cleaning means 13 and a second cleaning means 14. As the first cleaning means 13, a conductive elastic roller 15 is used and rotates clockwise around an axis. The elastic roller 15 is constructed by forming a layer of foam-like rubber such as rubber foam, plastic foam, or urethane foam mixed with conductive powder such as carbon on a conductive shaft 16. Furthermore, various types of elastic open-cell rollers coated with a conductive paint, such as a quaternary ammonium-based or sulfonate-based conductive resin paint, or a resin paint in which carbon powder, silver powder, etc. are dispersed, can also be used. This elastic roller 15
The appropriate volume resistivity is 10 ¹¹ Ωcm or less. The elastic roller 15 is grounded or applied with a voltage or alternating current voltage having a polarity opposite to that of the electrostatic latent image. When applying voltage, the voltage must be at a level that does not cause electrical damage to the photoreceptor.
When the photosensitive layer is a selenium photoconductive layer, a minute current of 10 ² μA may be applied. An electric current obtained by superimposing a direct current on an alternating current is more effective than a direct current. Therefore, the AC voltage of this embodiment is of this DC superposition type. On the other hand, as the second cleaning means 14, the elastic cleaning blade 1
7 is used.

The leading edge of the blade 17 is in near-line contact with the photoreceptor drum 1, extending in a direction opposite to the moving direction of the photoreceptor drum 1 and being pressed into contact with the photoreceptor drum 1.

Next, the operation of this embodiment will be explained. The photoreceptor drum 1 is positively and uniformly charged by a corona charging device 2, and an optical image of a document is projected onto the photoreceptor drum 1 by an exposure device 3. The latent image thus formed is visualized by the developing device 4. A voltage that is the same as or slightly higher than the potential of the non-image area is applied to the developing electrode 9, and proper development is performed by such a developing bias voltage. After development, since there is excess developer on the photosensitive drum 1, the excess developer is removed by the excess developer removing device 12 without contacting the developed surface. Of course, the necessary developer solution must remain so that the toner on the drum can move electrophoretically under the electric field. The developer removed by the surplus developer removing device 12 is returned to the developer tank 8 and used again. Next, the photoreceptor drum 1 is brought into close contact with a transfer paper 18 fed from a paper feeding device (not shown), and the toner image on the photoreceptor drum 1 is transferred to the transfer paper by corona discharge from the transfer device 5 from the surface of the transfer paper 18. 18 electrostatically. Transfer paper 1
8 is separated from the photoreceptor drum 1 by a known separating device (not shown), passes through a drying or fixing device, and is discharged to the outside of the machine. On the other hand, not only an untransferred toner image remains on the photoreceptor drum 1 after the transfer is completed, but also the potential difference between the image area and the non-image area is quite large. First, the first cleaning means 13 loosens the electrostatically adhered toner on the photoreceptor drum 1 by mechanical rubbing, and at the same time, eliminates the charge on the photoreceptor drum 1. FIG. 2 is a graph showing a comparison between the static elimination effect of the first cleaning means 13 and the static elimination effect of conventional corona discharge. Lines a and c indicate the potential of the image area and the potential of the non-image area, respectively, when a conventional AC static elimination corona discharge device is used, and the lines b and d
1 shows the potential of the image area and the potential of the non-image area in the apparatus of the present invention, respectively. Here, the neutralization voltage of zero means that it is not used in the conventional corona discharge device, and in the case of the present invention, it means that it is grounded. According to this, the static elimination effect of the first cleaning means 13 of the present invention is not much different from that of conventional corona discharge, and the elastic roller 1
It was confirmed that the effect is sufficient even if 5 is grounded.

Next, the toner on the photosensitive drum 1 is completely removed by the second cleaning means 14.
Before reaching the second cleaning means 14, the toner has been loosened by the first cleaning means 13 as described above, so the contact pressure of the cleaning blade 17 is higher than that when the toner is used alone in the past. It's good to be weak. Moreover, since the first cleaning means 13 also removes static electricity, the cleaning action is more effective. The toner and developer removed by the cleaning blade 17 are guided along the surface of the photoreceptor drum 1 in the direction of the drum axis, and flow downward from the end of the drum.
The developer is collected into the developer tank 8.

In this way, one rotation of the photosensitive drum 1 is completed, and the next copying process is started again.

FIGS. 3 and 4 show the results of comparative experiments between the present invention and the conventional example. The solid line shows the present invention, and the broken line shows the conventional example. FIG. 3 shows the relationship between image density and static elimination effect, and shows the elastic roller 1 which is the first cleaning means 13 of the present invention.
It was found that there was no difference in image density (ID) whether the electrode 5 was grounded or an alternating current voltage was applied, and there was no difference between the two and the same as those using conventional alternating current corona discharge.

FIG. 4 shows the relationship between the static elimination effect and the occurrence of black streaks. In the present invention, when the elastic roller 15 is grounded, almost no black streaks occur on the copy, and when an AC voltage is applied, Although a small amount of black streaks occurred, the occurrence of black streaks was extremely small compared to the conventional method. Note that the reason why black streaks often appear on copies when AC corona discharge is performed has not yet been fully elucidated.

By the way, as the elastic roller 15, carbon is dispersed in open-cell polyurethane rubber with a foaming rate (number of foams per inch) of 100 cells to obtain a specific volume resistivity.
When a material with a conductivity of 10 ⁶ Ωcm or less was used, the same values as the experimental results described above were obtained.

FIG. 5 is a schematic diagram of a dry type electrophotographic copying machine showing another embodiment of the present invention. In the drawings, the same components and functions as those in the first embodiment will be described using the same reference numerals. The photosensitive drum 1 is positively and uniformly charged by a corona charging device 2, and then irradiated with light by an exposure device 3, so that an electrostatic latent image corresponding to the original image is formed thereon. This electrostatic latent image is visualized by a developing device 19. The developing device 19 employs a magnetic brush developing method, and magnetically attracts the developer 20 to a developer container 21 storing a two-component developer 20 consisting of negatively charged toner and a magnetic carrier. A magnetic brush developing roller 22 on which a magnetic brush is formed and supplies toner to the surface of the photosensitive drum 1; a scraper 23 that scrapes the developer from the developing roller 22 and returns it to the developer container 21; medicine container 2
1, and a stirring member 24 for stirring and mixing the developer 20 in the developer 1. After development, the toner image on the photosensitive drum 1 is brought into close contact with the transfer paper 18 fed from a paper feeding device (not shown), and is electrostatically applied to the transfer paper 18 by positive corona discharge from the transfer device 5 from the back side. transcribed into. The transfer paper 18 is separated from the photosensitive drum 1, the toner image is permanently fixed thereon by a heat fixing device (not shown), and the paper is discharged outside the machine. On the other hand, the cleaning device 25 removes untransferred toner from the photosensitive drum 1 after the transfer, and eliminates unnecessary charges. The cleaning device 25 is also the first cleaning means 2
6 and a second cleaning means 27, the first cleaning means 26 comprising an elastic roller 28 made of a conductive flexible brush. This brush is made of a conductive and flexible material such as carbon or graphite, and is grounded or applied with an alternating current voltage. Conditions such as current when applying voltage are as follows:
This is the same as in the embodiment. This elastic roller 28 rotates counterclockwise, and first removes the toner remaining on the photosensitive drum 1. Since the removed toner adheres to the brush, an impact is applied to the brush with a striking rod 29 to remove the toner adhered to the brush. This dropped toner is collected into a gutter-shaped toner collection container 30 disposed at the bottom.

By the way, this first cleaning means 26 is
Therefore, it is not necessary to have a function to remove all the residual toner, but it is necessary to have a function to forcibly shift the position of the electrostatically attached toner using mechanical sliding force and to remove the static charge on the photoreceptor. It is enough. In this way, the loosened toner is completely removed by the next second cleaning means 27. The second cleaning means is the same as the first embodiment, the elastic blade 1
It consists of 7. Second cleaning means 27
Since it is only necessary to remove the toner existing on the photoconductor which has already been neutralized, the pressing force is weaker than that of conventional methods, there is less risk of damaging the photoconductor, and the photoconductor can be used for a long period of time. body can be used.

In the second embodiment, the first and second cleaning means 26 and 27 may be attached to a position where the surface of the photoreceptor drum 1 is raised or lowered, and the specific configuration of the cleaning means may be determined depending on the attachment position. It can be changed arbitrarily. As the first cleaning means 26, a conductive foam roller as exemplified in the first embodiment can also be used instead of the conductive brush.

In the above embodiment, a case was described in which a photoreceptor was used as an electrostatic latent image carrier, but the invention is not limited to this, and an electrostatic recording device using a dielectric material, electrostatic recording paper, etc. It is also applicable to copying machines such as. Further, the second cleaning means may be made of a conductive material, and may be grounded or applied with alternating current voltage or reverse polarity voltage.

By the way, in the case of a copying machine that performs dry development, when the copy paper is separated from the photoreceptor, a peel discharge occurs, and an abnormally high potential exists on the surface of the photoreceptor corresponding to the leading and trailing edges of the transfer paper. I will do it. When this enters the cleaning device, it is developed with the toner present in the cleaning device, and because the potential is too high, it is not cleaned sufficiently, resulting in horizontal black lines appearing on the image. . To prevent this, light irradiation or corona discharge was applied before cleaning, but the former method causes photoreceptor fatigue, and the latter method requires a high voltage generator, which is expensive. However, in the present invention, such a phenomenon did not occur at all.

As described above, according to the present invention, the cleaning function is divided into two stages, and the first stage cleaning means loosens the electrostatically adhered residual toner and eliminates the charge on the electrostatic latent image carrier, so that the second stage cleaning means loosens the electrostatically attached residual toner and eliminates the charge on the electrostatic latent image carrier. The cleaning burden on the cleaning means can be reduced, and even if an elastic blade is used, the electrostatic latent image carrier can be used for a long period of time without being damaged. Furthermore, by separating the cleaning means into two different cleaning methods and skillfully utilizing the characteristics of both methods, it has become possible to achieve an excellent cleaning effect without the occurrence of black streaks or the like. Furthermore, since a high voltage generator, a corona discharger, etc. are not required, the copying machine can be made compact and has the advantage of providing an inexpensive copying machine.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a liquid development type copying machine showing a first embodiment of the present invention, FIGS. 2 to 4 are graphs showing comparative experiment results between the present invention and a conventional example, and FIG. FIG. 2 is a schematic configuration diagram of a dry type copying machine showing a second embodiment of the present invention. 1...Photosensitive drum, 4, 19...Developing device,
5... Transfer device, 6, 25... Cleaning device, 13, 26... First cleaning means, 1
4, 27...second cleaning means, 15, 28
...Elastic roller, 17...Elastic blade.

Claims (1)

[Scope of Claims] 1. A copying machine having two cleaning means for removing toner, etc. remaining on the electrostatic latent image bearing member after transfer, wherein the first cleaning means has both a cleaning function and a static eliminating function, a conductive elastic roller that rotates in pressure contact with the electrostatic latent image carrier, the second cleaning means being disposed behind the first cleaning means in the moving direction of the electrostatic latent image carrier; A copying machine characterized by an elastic cleaning blade that is in pressure contact with an electrostatic latent image carrier. 2. The copying machine according to claim 1, wherein the elastic roller is grounded and applied with a voltage having a polarity opposite to that of the electrostatic latent image or an alternating current voltage.