JPH0360427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus that transfers image-like toner or image-like charged toner on a toner carrier such as a photoreceptor or a non-magnetic sleeve to a dielectric transfer material.

2. Description of the Related Art Conventionally, a method of transferring toner to the same transfer material multiple times has been implemented in color copying machines and the like to which electrophotography is applied. Generally, in such color copying machines, dielectric film materials such as polyester and triacetate have been used as OHP sheets to create projection films for overhead projectors (hereinafter referred to as OHP). These dielectric materials have a very high surface resistance of 1×10 ¹⁴ to 1×10 ¹⁷ Ω.
In the above-mentioned color copying machine, a high resistance dielectric sheet or a mesh screen may be used for the sheet carrying and conveying means. With this configuration, the dielectric sheet is electrostatically attracted onto the sheet carrying and conveying means by the action of an electric field such as corona discharge, and in a system in which multiple transfers are performed on this dielectric sheet, the following problems occur. In other words, since a high-resistance material is used as the transfer material, there is no attenuation of the electric charge caused by the transfer corona, and therefore, there is no discharge between the sheet and the conductive member located near the sheet immediately after transfer and during transportation, and even in the air. Electric discharge occurs, causing disturbances in the transferred image and a decrease in transfer efficiency due to a charge-up phenomenon on the sheet surface.

The above phenomenon is noticeable in the second color and even the third color during multiple transfer, and in particular, in the third color, not only the transfer efficiency is extremely reduced but also the image disturbance becomes large.

As a countermeasure for the above-mentioned development, it is possible to remove the charge from the transfer sheet immediately after each transfer during multiple transfers, but this method has the following disadvantages.

(1) Due to static elimination, the electrostatic adhesion between the transfer sheet and the sheet carrying/conveying means is reduced, which tends to cause the sheet to shift, causing color misregistration and degrading the image quality.

(2) Improvements have been made in the materials used for OHP films, but there are cases in which low-resistance materials are used for OHP films. However, conventional low-resistance OHP films are mainly made by mixing surfactants (ammonium salts, aliphatic sulfonates, higher alcohol sulfate ester salts, alcohol ethylene oxide, betaine, etc.) with a binder and attaching them to a dielectric base layer such as polyester. The resistance is lowered by coating it. Therefore, the electrical resistance of the surface is approximately 1×10 ⁹ to 1×10 ¹¹ Ω, and not only is it still not possible to obtain a good multiple transfer image, but the surface resistance increases when the humidity decreases to, for example, 30% RH or less. , almost no effect was obtained by the low resistance treatment.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-mentioned problem of transfer to a dielectric sheet and enables good transfer to a dielectric sheet without using a special device.

To achieve the above object, the present invention includes an image carrier, a transfer charging means for transferring a toner image formed on the image carrier onto a dielectric sheet, and a transfer charging means for transferring a toner image formed on the image carrier to a dielectric sheet, and a transfer charging means for transferring a toner image formed on the image carrier to a dielectric sheet. In the image forming apparatus, the dielectric sheet has a surface resistance of 10 ⁸ Ω or less, and the static eliminating means is inoperative during the transfer. As for the form of the toner on the toner carrier, in addition to the case where the toner is adhered in an image form, it is also possible to apply a form in which a uniform thin layer of toner has a charged pattern in an image form. Furthermore, the toner colors used for multiple transfer are not limited to conventional color toners.
In some cases, it is a monochromatic toner such as black. As for the characteristics of the toner, an insulating toner or a high resistance toner can be used. Of course, the dielectric sheet may be not only a transparent sheet but also an opaque sheet. In this case, if a transparent sheet is used that can be used by viewing the sheet in a transmissive manner, and the toner is translucent, it can also be used as a projection film.

According to the above configuration of the present invention, the transfer electric field is emitted well without using any special means, and the sheet surface does not charge up even during multiple transfers, so it is possible to form a high-quality image. becomes.

Hereinafter, the present invention will be explained in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an example of a transfer type color electrophotographic copying machine to which the present invention is applicable. This diagram is
Although a dielectric mesh screen is shown as a means for supporting the dielectric sheet, it is also possible to use a dielectric sheet in addition to the screen.

In FIG. 1, 1 is an electrophotographic photosensitive drum having a surface insulating layer, a photoconductive layer, and a conductive substrate;
It is rotatably supported on a shaft 2 and starts rotating in the direction of arrow 3 in response to a copy command. When the drum 1 rotates to the normal position, the original 0 placed on the original platen glass 4 is illuminated by an illumination lamp 6 integrated with the first scanning mirror 5, and the reflected light is transmitted to the second scanning mirror. Scanned at 7. The reflected light image passes through a lens 8 and a third mirror 9, is color-separated by a color separation filter 10, and further passes through a fourth mirror 11 and a dust-proof sealing glass 12, and is imaged on the drum 1 by an exposure section 13.

After the drum 1 is neutralized by a static eliminator 14 and then charged by a primary charger 15, the image irradiated by the illumination lamp 6 is subjected to slit exposure in the exposure section 13. At the same time, AC or primary charge removal is performed using a charge remover 16, and then the entire surface is exposed using a full surface exposure lamp 17, thereby forming an electrostatic latent image on the drum 1.

The electrostatic latent image on the photosensitive drum 1 is then developed into a toner image by a developing device 18. Developing device 18
are yellow 18a, magenta 18b, cyan 18
It is composed of four developing devices: c, black 18d, and a designated developing device corresponding to the color separation filter used for exposure operates to obtain a toner image of the required color.

The transfer paper 20 using plain paper in the cassette 19 is fed into the machine by a paper feed roller 21, and the rough timing is determined by the first register roller 22, and then the precise timing is determined by the second register roller 23. , whose tip is the gripper 2 of the transfer drum 33
It is gripped by 4. As the transfer drum 33 rotates, the transfer paper 20 is conveyed while being wrapped around a screen attached to the transfer drum, and while the transfer paper 20 passes between the transfer charger 25 and the photosensitive drum 1, the photosensitive drum 1 is placed on the transfer paper. The toner image is transferred, and at the same time, the transfer paper 20 is held on the screen surface by electrostatic attraction.

In the first transfer, the transfer paper 20 is electrostatically attracted to the screen after the transfer charger 25, and the binding force until then is weak, so the transfer paper 20 is pulled against the photosensitive drum 1, causing color misregistration. Therefore, the presser roller 35 prevents this. The presser roller 35 and paper feed guide plate 34 move away from the transfer drum 33 after the first paper passes through them. The transfer drum 33 grips the leading edge of the transfer paper 20 with the gripper 24 and rotates the required number of times while being electrostatically attracted to the screen, thereby transferring images of the required number of colors.

After the transfer is completed, the transfer paper is released from the gripper 24 and separated by the separating claws 2 with the help of the separating static eliminators 36 and 37.
6, and is guided to a conveyor belt 27, and further guided to a pair of fixing rollers 28 and 29, where it is pressurized and
The image is fixed by heating and then discharged onto the tray 30. After the transfer, the surface of the photosensitive drum 1 is cleaned by a cleaning device 31 composed of an elastic blade, and the process proceeds to the next cycle.

On the other hand, the transfer drum 33 is connected to the cleaners 38 and 3.
9, both sides of the screen are cleaned, and if necessary, a charge-up prevention static eliminator 40 removes the charge-up on the screen surface, and the process proceeds to the next cycle.

FIG. 2 shows a perspective view of the transfer drum 33.
The transfer drum 33 includes a screen 33a that carries the transfer paper, a cylinder 33b with a notch that is a supporting member that supports the screen at its edge, and a gripper 3 that grips the leading edge of the transfer paper.
It has 3c.

The above-mentioned screen is made of knitted fibers of nylon, polyester, silk, polypropylene, or the like, or a sheet made of polyester, polypropylene, or the like with holes pressed. In both cases, the aperture ratio of the screen is approximately 30-70%.

In the copying machine described above, a dielectric sheet is used in place of the transfer paper 20, and the dielectric sheet is a transparent sheet in which a tin-doped indium oxide thin film is laminated as a conductive layer on a highly transparent polyester film substrate. When a color image was reproduced on this sheet, a good three-color multi-transfer image with high transfer efficiency and no image disturbance was obtained. The electrical resistance of the surface of the dielectric sheet subjected to conductivity treatment was measured to be about 10 ³ to ^{10 4} Ω. According to experiments, images with no practical problems can be obtained if the surface resistance of the dielectric sheet is 10 ³ Ω or less, but preferably
It was confirmed that better images could be obtained at 10 ⁶ Ω or less.

Note that if the surface resistance is within the above range, conductive treatment may be removed only in the portion of the dielectric sheet that is gripped by the gripper 33c, or insulation may be insulated by pasting an insulating sheet on this gripping portion, or By providing insulation on the contact surface of the gripper 33c with the sheet surface, it is possible to reliably prevent transfer failure (a phenomenon in which toner is not partially transferred) near the gripper or on the entire image area of the dielectric sheet.

The conductive layer of the dielectric sheet having the above-mentioned surface resistance value has no charge retention property when itself is grounded. However, this conductive layer is provided on an insulating film, and the dielectric sheet having this conductive layer is held on an insulating transfer material holding member, so the conductive layer on the surface is There is no contact with conductive members near the surrounding area. Therefore, during transfer, the transfer electric field applied to the back surface of the dielectric sheet or the back surface of the transfer material carrying and conveying means is not blocked and works well.

In addition, since the conductive layer of this dielectric sheet allows charges to move relatively freely, the increase in potential when peeling the transfer material from the photoreceptor immediately after transfer is caused to shift toward a lower potential. hold it down. This prevents uneven transfer and puddle-like patterns that tend to occur when the dielectric sheet is peeled off. Furthermore, the conductive layer is thought to have the effect of suppressing the charge-up phenomenon of the dielectric sheet as a result of leaking the charge due to the peeling discharge generated during the peeling.

By the way, when a dielectric sheet having such a conductive layer is used in a general copying machine, if the conductive layer comes into contact with a conductive member along the conveyance path, transfer failure is likely to occur. However, in the multiple transcription system mentioned above,
Since the means for holding and conveying the dielectric sheet is a completely insulating sheet or the above-mentioned screen, leakage of the transfer electric field is not a problem. Furthermore, when a three-layered photoreceptor having an insulating layer on the surface as described in FIG. 1 is used as a toner carrier, since there is an insulating layer on the surface of the photoreceptor, there is There is no need to worry about leaks.

The dielectric sheet laminated with the above indium oxide thin film has a light transmittance of 80 to 88%, and is fully usable as an OHP film or a slide film. Other sheets with high transparency that can be used as OHP films include those in which a thin metal film such as gold, palladium, or aluminum is laminated on the surface of a polyester film, SnO ₂ , TiO ₂ , ZrO ₂ , Cd ₂ SnO ₄ ,
It is also possible to use a polyester film laminated with a semiconductor thin film such as CuI. Further, the conductive laminated layer made of these metals or the like may be a single layer or a plurality of thin layers of different types.

With the same effect as described above, multiple transfer of three colors can also be performed on the surface of a metal foil such as a thin layer of aluminum attached to a dielectric sheet such as a resin film. Note that transfer is also possible using only an aluminum foil sheet without using a dielectric sheet. However, in this case, it is possible to do this simply by insulating the part of the aluminum sheet that is held in the gripper, but since the rigidity is different from that of paper or dielectric sheets, it will not be transported well in a copying machine. Therefore, when an aluminum sheet is used as a dielectric sheet, it is desirable to attach the aluminum sheet to plain paper and then convey and transfer the sheet.

Incidentally, when the dielectric sheet described above is applied to the copying machine shown in FIG. 1, the separation static eliminators 36 and 37 are not operated during the transfer to prevent transfer failure. but,
If the rear end of the dielectric sheet has already passed through the transfer area, the static eliminators 36 and 37 may be activated.

As explained above, in a system in which a transfer sheet is electrostatically attracted to a transfer sheet carrying means for multiple transfer, the toner image supporting surface of the dielectric sheet is made to have an electrical resistance of 10 ⁸ Ω or less, and the transfer sheet is used. The transfer efficiency can be increased during multiple transfers, and furthermore, the completed image can be transferred without causing any disturbance. Further, since the material used for the conductive treatment is a metal or semiconductor material, there is almost no change in resistance due to the temperature and humidity environment, especially the humidity environment, and the stability against the environment is extremely excellent and good transfer can be performed.

[Brief explanation of drawings]

FIG. 1 is a side view showing an embodiment of a color electrophotographic copying machine to which the present invention is applied, and FIG. 2 is a perspective view of a transfer drum used in the transfer device shown in FIG. In the figure, 1...a photosensitive drum, 33...a drum serving as a means for carrying and conveying transfer paper, and 33c...a gripper.

Claims (1)

[Scope of Claims] 1. An image bearing member, a transfer charging means for transferring a toner image formed on the image bearing member onto a dielectric sheet, and a transfer charging means provided on the downstream side of the transfer charging means in the direction in which the dielectric sheet moves. and a static eliminator, wherein the dielectric sheet has a surface resistance of 10 ⁸ Ω or less, and the static eliminator is inactive during the transfer.