JPS5926947B2 - Copy background stain prevention device for wet color electrophotographic copying machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing copy background stains in a wet color electrophotographic copying machine.

Generally, in a color copying machine, an image carrier, such as a photoreceptor, photosensitive paper, transfer paper, or recording paper, is developed three to four times with a developer such as yellow, magenta, cyan, or black. A color image is obtained, but if the performance equivalent to the initial development characteristics or transfer characteristics, that is, the development potential or transfer potential to satisfy the required density cannot be obtained when the development is repeated, a sufficiently clear color image cannot be obtained. I can't.

Furthermore, due to the capabilities of the toner and developing device, when an electrostatic latent image formed on an image carrier is developed, it is not possible to completely neutralize the charges forming the electrostatic latent image, so the image after development cannot be completely neutralized. A large amount of charge remains on the holder, regardless of whether it is an image area or a non-image area, and if the next color is developed in this state, unnecessary next color toner will adhere to this residual charge. This creates a color cast.

For this reason, the image carrier after development is generally irradiated with light or ions to remove residual charges, but even with this method, the physical properties of the image carrier itself may cause residual charges to be removed. It is not possible to completely eliminate the charge.

Therefore, color cast inevitably occurs, which significantly deteriorates the repeatability of color copying machines. For example, the first
The figure shows changes in the surface potential of the image carrier, in this case transfer paper, during the process in an electrostatic latent image transfer type color copying machine.As is clear from this figure, the initial color After completing yellow development, even if the residual potential on the transfer paper is removed using a static eliminator, the residual potential does not become zero, and the same transfer potential is applied on top of some of the remaining potential. Therefore, as the transfer potential increases, the residual potential also increases in response to this increased potential even during static elimination after the magenta development of the next color is completed.

This increase in residual potential causes color fog, particularly in the background area, and is a cause of background stains. In addition, transfer paper (recording paper) such as electrostatic latent image transfer type copying machines using plain paper and direct development type color copying machines using special paper.
For the type that develops by exposing it directly to the developer,
The surfaces of these papers are smoothed to some extent in order to improve the ease of adding notes to the finished copies and to improve the adhesion of toner.

Therefore, contamination by toner on the paper inevitably occurs, and in color copying machines, since development is repeated three to four times on the same sheet of paper, background stains are particularly likely to occur in non-image areas. SUMMARY OF THE INVENTION An object of the present invention is to easily and reliably prevent copy background stains in a wet color copying machine as described above, and to obtain clear copy images.

According to this purpose, a direct current bias is applied to a squeeze roller for squeezing the developing solution, which has a potential equal to or higher than the potential of the non-image area of the image carrier and has a polarity different from that in the developing solution. Wet-type color electrophotographic copying characterized in that unnecessary and excess toner adhering to the image carrier after development is made to adhere to one side of the squeeze roller by applying electric potential in different amounts that gradually increase for each color. A method for preventing copy background stains in a copying machine is provided. The present invention will be described below with reference to the drawings.

First, FIG. 2 is a schematic configuration diagram showing an example of an electrostatic latent image transfer type color copying machine to which the present invention is applied. The copying machine main body 1 is supported on a floor 13 by casters 12, and various parts and devices are incorporated therein. Copy machine 1
A flexible document holding cover 4 is provided on the top surface so that it can be opened and closed around one end, and on the bottom side,
A transparent document mounting table 5 is arranged.

The document is placed on the document table 5, covered by the document presser cover 4, and illuminated by exposure lamps 6 and 7. The reflected light from the original passes through the opening provided in the shielding plate 8, passes through the first reflecting mirror 9, the color separation filter 10, the lens 11, and the second reflecting mirror 12, and then onto the belt-shaped photoreceptor 13. and an electrostatic latent image is formed thereon. The photoreceptor 13 is made by depositing aluminum on a Mylar (trade name) film and providing an organic photoconductive insulating layer thereon.
The locking shaft 1 of the photoreceptor winding drum 16 rotates while being supported by the
7, and the other end is fixed to slider 18.

A wire 20 wound around and fixed to a wire winding shaft 19 is fixed to the slider 18 via a pulley 21, and the wire winding shaft 19 is connected to a spiral constant force spring 2.
2 gives the wire 20 the habit of always winding it up. When the photoreceptor winding drum 16 is rotated counterclockwise by a drive system (not shown) with a force stronger than the tensile force of the constant force spring 22, the photoreceptor 13
A certain amount is wound around the circumferential surface of 6.

When this first drive is released, the photoreceptor 13 is pulled back by the tensile force of the constant force spring 22. At this time, the surface of the photoreceptor 13 is uniformly charged by a charging device 23 disposed near the photoreceptor winding drum 16. Then, when the photoreceptor 13 stops at a fixed position, an electrostatic latent image is formed on the photoreceptor 13 by the exposure. On the other hand, a roll of transfer paper 24 and a pair of paper feed rollers 2
5, 26, 27 and paper feed guides 28, 29, the shaft 3
The transfer paper is fed toward the rotating transfer paper winding drum 31 supported by the drum 31, and its tip is held by a clamp device 32 provided on the drum 31, and is attached to the circumferential surface of the drum 31. 33, the sheet rotates clockwise together with the drum 31, and after being fed a certain length, the rear portion thereof is cut by a cutter 34 provided between the pair of sheet feeding rollers 25 and 26.

On the other hand, the photoreceptor winding drum 16 rotates counterclockwise again and winds the photoreceptor 13 on which the electrostatic latent image has been formed around its circumferential surface, and the photoreceptor winding drum 16 is attached to the circumferential surface of the transfer paper winding drum 31. The electrostatic latent image is pressed against the transfer paper which rotates clockwise, and the electrostatic latent image is transferred.

The transfer paper to which the electrostatic latent image has been transferred is transferred to the transfer paper winding drum 3.
Support rollers 35, 36 provided in pressure contact with the circumferential surface of 1
, 37, while being securely held on the circumferential surface of the drum, the toner image is first developed by a developing device 38, which will be described in detail later, and then dried with hot air by blowers 39, 40 to fix the toner image. , the copying cycle for the first color is completed by temporarily stopping at the starting position.

Entering the second color copying cycle, the transfer paper winding drum 3 is started again.
1 rotates clockwise, the electric potential remaining on the transfer paper is removed by the static eliminator 41 disposed above the clamp device 32 in the figure.

On the other hand, after completing the transfer, the photoreceptor winding drum 16 is rotated in the reverse direction, that is, clockwise, and the potential remaining on the photoreceptor 13 is transferred to the photoreceptor winding drum 16 provided below the photoreceptor winding drum 16 in the figure. The static electricity is removed by the static eliminator 42, and the static electricity is removed by the charging device 2.
It stops at the fixed exposure position while being newly charged by 3. This process is repeated in the order of yellow, magenta, cyan, and black, and after the final cyan or black development, the transfer paper is transferred to the transfer paper winding drum 3.
The clamping device 32 attached to the drum 1 unclamps the transfer paper, and the peeling claw 43 provided at the lower left of the drum 31 peels the transfer paper from the drum 31. The sheet is held between the conveyor belts 44 and 45, is dried by a fan 46, and sent through a guide 47 to a pair of paper feed rollers 48, where the excess edges are cut off by a cutter 49, and a pair of paper feed rollers 50, The paper is sent to a copy tray 53 through a guide 51 and a paper feed roller pair 52.

The cut chips are collected in a scrap box 54. Next, details of the developing device will be explained.

The developing device 38 includes a yellow developing device 38a, a magenta developing device 38b, a cyan developing device 38c, and a black developing device 38d, each of which is supported by a rail 55 and slides to a predetermined developing position. It is configured to be arranged sequentially. Note that the transfer paper winding drum 31 is provided with a notch so as not to obstruct movement of the developing device 38. FIG. 3 is a schematic cross-sectional view of the developing device, in which the developing tray 60 has a corresponding electrode 61 formed along the circumferential surface of a transfer paper winding drum 31 made of a conductive member, for example, a conductive rubber material. , a bottom plate 63 provided via a support plate 62, and a side plate 6 provided in the axial direction of the drum 31.
4, and the upper surface of the side plate 64 coincides with the circular arc portion of the drum 31.
They are always in pressure contact with each other by a compression coil spring 66 provided between them. Further, a developer supply pipe 67 is provided on the bottom plate 63 of the developer tray 60, and a developer supply port 6 connected to the developer supply pipe 67 is provided inside the developer tray 60.
8 and a collision plate 6 arranged horizontally above the supply port.
A developer supply section 70 having 9 is provided.

The developer sent through the developer supply pipe 67 and the supply port 68 hits the collision plate 69 and is diffused, overflowing from both sides of the collision plate 69 to the upper part and reaching the orifice 71 provided in the corresponding electrode 61. The electrostatic latent image flows between the corresponding electrode 61 and the transfer paper 24 to develop the electrostatic latent image on the transfer paper.

The developed transfer paper 24 is then squeezed by a squeeze roller 72 to remove excess developer.

The squeeze roller 72 is a metal pipe whose surface is chromed and then polished, and is always pressed against the transfer paper (transfer paper winding drum) by a spring (not shown). As shown in the schematic plan view of FIG. 4, this squeeze roller 72 has a support shaft 73 supported by an insulating bearing holder 75 via a bearing 74, and is electrically suspended from other members. .

Further, a contact 77 provided at one end of a bias applying contact piece 76 is in contact with the tip of the support shaft 73, and the other end of the contact piece 76 is connected to a terminal 78 by an insulating screw 79. It is attached to a side plate 81 of the developing device housing via an insulating spacer 80. The other end of the bias power cord 82 connected to the terminal 78 applies a DC bias potential for each color, which has a potential equal to or higher than the potential of the non-image area of the transfer paper and has a polarity different from that of the toner in the developer. It is connected to a bias power source (not shown) configured to apply different amounts that gradually increase each time. Therefore, this squeeze roller 72 is
While squeezing the developer, the excess toner adhering to the transfer paper is transferred from the transfer paper to one side of the squeeze roller.
Prevents background stains on copies.

The toner adhering to the squeeze roller 72 is cleaned by a squeeze roller cleaner 83 provided in contact with the circumferential surface of the squeeze roller 72, as shown in FIG.

Note that FIG. 5 is a schematic side view of FIG. 4, and the same members are given the same reference numerals.

As described above, according to the present invention, in a wet color electrophotographic copying machine, the squeeze roller for squeezing the developer adhering to the image carrier such as transfer paper, recording paper, or photosensitive paper after development is attached to the image carrier. Since a DC bias potential of a potential equal to or higher than the potential of the non-image area of the toner and of a different polarity than that of the toner is applied at different amounts that gradually increase for each color, the background potential due to the increase in residual potential due to repeated development is applied. In addition to preventing toner from adhering to areas and obtaining clear copies without background stains, the squeeze roller 1 directly contacts the image carrier to squeeze the developer and has the above-mentioned background stain prevention effect. Since it performs both, it is very efficient and the equipment is simple and economical.

[Brief explanation of drawings]

FIG. 1 is a diagram showing changes in surface potential of transfer paper during a process in an electrostatic latent image transfer color copying machine, and FIG. 2 is an electrostatic latent image transfer color copying machine to which the present invention is applied. FIG. 3 is a schematic cross-sectional view of the developing device in FIG. 2, FIG. 4 is a schematic plan view of a portion of the squeeze roller in FIG. 3, and FIG. FIG. 24...Transfer paper, 31...Transfer paper winding drum, 72...Squeeze roller 1, 73...
...Spindle, 74...Bearing, 75...
・Bearing holder, 76... Bias application contact piece, 77... Contact, 78... Terminal, 79... Insulating screw, 80... ... Insulating spacer, 81 ... Side plate, 82 ...
・Code, 83...Squeeze roller cleaner one.

Claims (1)

[Claims] 1. In a wet color electrophotographic copying machine, a squeeze roller for squeezing the developer adhering to the image carrier after development is charged with toner at a potential equal to or higher than the potential of the non-image area of the image carrier. 1. A method for preventing copy background stains in a wet color electrophotographic copying machine, characterized in that copy background stains are prevented by applying a DC bias potential of a different polarity to each color in a different amount that gradually increases.