JPH0447827B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a color electrophotographic method using a three-color overlapping transfer method.

Prior Art An outline of a color electrophotographic copying system using a three-color overlapping transfer method will be explained with reference to FIG. 1. In this system, a photosensitive drum 1 rotates three times to obtain one copy. The light reflected by the original 3 placed on the contact glass 2 is passed through three color filters of blue, green, and red, which are switchably inserted into the optical path of the exposure optical system 4, which exposes the photoreceptor drum 1 as an image. 5 to form three types of latent images on the photosensitive drum 1. Around the photoreceptor drum 1, developing devices 6, 7, and 8 each having a developer containing toner of three colors of yellow, magenta, and cyan are arranged in this order following the exposure position, and a blue filter is installed. The latent image formed by the passing light beam was developed by a yellow developing device, and the toner image was wound on a transfer drum 9 provided in contact with the photoreceptor drum 1 at a later position by three developing devices. The image is transferred onto the transfer paper S by the transfer charger 10 in the transfer drum 9. Next, the latent image formed by the light beam passing through the green filter is developed by a magenta developing device 7, and the toner image is superimposed with the yellow toner image on the same transfer paper S on the transfer drum 9 that has rotated once. transcribed. Next, the latent image formed by the red filter is developed by a cyan color developing device 8, and the toner images thereof are similarly transferred onto the same transfer paper in a superimposed manner. The transfer paper S on which the three-color toner images have been superimposed and transferred is separated from the transfer drum 9 by the charger 11 and separation claw 12, fixed by the fixing device 13, and discharged to a tray 14 outside the machine to complete copying. do.

As shown in FIG. 2, the transfer drum 9 includes a metal frame 15 consisting of annular portions 15a provided at both ends and connecting portions 15b connecting these to each other.
An insulating film 16 such as Mylar film is attached to the metal frame 15 to cover the cylindrical window formed by the annular portions 15a and the connecting portions 15b at both ends of the metal frame 15. , and a clamper 17 provided along the connecting portion 15b of the metal frame 15.The transfer paper fed from the paper feed section 18 is moved by registration rollers 19 to the image on the photoreceptor at the transfer position. The paper is fed at a timing such that the leading edge matches the transfer paper, and the leading edge is gripped by the clamper 17. As the transfer drum 9 rotates, the transfer paper S is wound around the transfer drum and is electrostatically attracted to the Mylar film 16. The film is tightly attached to the circumferential surface of the transfer drum 9 to prevent it from peeling off or shifting. When the three transfers are completed, the electric potential of the mylar film is reduced to almost zero by double static eliminating chargers 11 provided around the transfer drum to facilitate separation.

Now, in order to ensure that the transfer paper is attracted to the transfer drum 9, the cylindrical surface of the transfer drum 9 is sandwiched between the separating claw 12 and the registration roller 19 shown in FIG. It has been proposed that after each transfer, the film potential is reduced to approximately zero volts by the static elimination charger 11 after the transfer is completed three times. However, this method requires five chargers to be placed inside and outside the transfer drum, making the structural arrangement complicated, and because static electricity is removed each time, the adsorption force of the transfer paper to the film drum becomes weaker. Especially under high-humidity conditions, the transfer paper may peel off and the image may be rubbed, and since the pre-charge is charged at about 1KV, the primary transfer voltage is low and the discharge becomes unstable at around 4.0KV. There are drawbacks. You will also need a power pack for pre-charging.

Therefore, in order to simplify the equipment, a pre-charge charger was not provided, and yellow, magenta,
A method of further increasing the cyan transfer voltage three times is adopted. However, in this case, the output of the power pack for transfer is 5.0KV for the primary and 5.0KV for the secondary.
5.5KV, 6.0KV in the 3rd transfer, high voltage, and the voltage of the film on the transfer drum at the end of the 3rd transfer.
If the voltage of static elimination charger 11 exceeds 2KV and is AC
The voltage will be higher than 5KV, and leak phenomena will easily occur. As a result, under low temperature and low humidity conditions where the static neutralization effect is poor, there is a difference in the film potential after static neutralization.
A phenomenon in which the image density of the first and second images differs may be observed.

Purpose This invention eliminates the above-mentioned drawbacks of the conventional color electronic copying method using the three-color superimposed transfer method.
To provide a color electronic copying method that has a simple configuration, does not cause a leak phenomenon, and can obtain stable images from the first sheet.

Configuration The above object is, according to the present invention, without providing a separate charger for the pre-transfer charger, without applying the voltage of the static elimination charger after the primary transfer, and without applying a charger for the charger before the transfer.
After the next transfer, the potential of the film on the transfer drum is applied so that it is almost equal to the potential after the first transfer, and after the third transfer, the potential of the film on the transfer drum is changed so that it becomes almost zero. It will be achieved.

In this case, the transfer voltage is lower for the primary transfer,
Good results can be obtained by setting the secondary and tertiary values to substantially equal values higher than the primary value.

Examples will be described in detail below.

Embodiment The transfer paper S fed from the paper feeding device 18 to the transfer drum 9 whose electric potential of the film 16 by the static elimination charger 11 has become approximately 0V is held by the clamper 17 and is rotated as the transfer drum 9 rotates. wrapped around the drum. In the first transfer, that is, the transfer of the yellow toner image, the transfer voltage is 5 KV. At this time, the voltage of the film 16 of the transfer drum is -500V as measured by the surface electrometer 21 at point 20 in FIG.

Next, in the second transfer, that is, the transfer of the magenta toner image, the transfer voltage is 5.5 KV, and the potential of the film 16 of the transfer drum 9 is -1 KV. At this point, the transfer drum (film) static elimination charger 11 eliminates the static electricity from the film 16 so that it becomes -500V. At this time, the static elimination voltage of the static elimination charger 11 may be 3.5 to 4.0 KV AC. If the static electricity is removed too much at this time and the voltage is set to zero, the adhesion between the transfer drum film 16 and the transfer paper S will deteriorate, resulting in drawbacks such as the transfer paper peeling off from the film or shifting, resulting in misalignment. Therefore, it is best to set it to around -500V.

Next, during the third transfer, that is, the transfer of the cyan toner image, the transfer voltage may be approximately equal to or slightly higher than that during the second transfer, that is, approximately 5.5 to 5.7 KV. As a result, the voltage of the film 16 of the transfer drum was measured at position 20 and was found to be between -1,000 and
It will be about 1,200V. And static elimination charger 1
1, the potential of the film 16 on the transfer drum becomes almost zero V, and the transfer process is completed, the film is separated by the separation claw 12 and fixed by the fixing device 13. , a color copy is obtained.

Effects As described above, by controlling the voltage to be changed for each of three transfers using one film static eliminator on the transfer drum, the pre-charger for pre-transfer charge on the device can be omitted. In addition to simplifying the device, it also prevents the static elimination voltage from increasing and leaking, or between the first and second sheets.
It is also possible to prevent a change in the image density due to a change in the potential after static electricity removal after the transfer of the first sheet, making it possible to obtain a stable color image.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of a color electrophotographic copying system of a three-color overlapping transfer type to which the present invention is applied, and FIG. 2 is a perspective view showing the configuration of a transfer drum thereof. 1... Photosensitive drum, 5... Three-color separation filter, 6... Yellow developer, 7... Magenta developer, 8... Cyan developer, 9... Transfer drum, 1
1... Transfer drum film static elimination charger, 1
5...Transfer drum metal frame, 16...Transfer drum insulator film, S...Transfer paper.

Claims (1)

[Claims] 1. A document is separated into three colors by three color filters of blue, green, and red and exposed to light on a photoreceptor, and each latent image formed correspondingly on the photoreceptor is colored yellow, magenta, and Developed with cyan toner and transferred overlappingly three times onto the same transfer paper wrapped around a transfer drum made of an insulating film attached to a metal frame, and after completing the three rotations, the insulator of the transfer drum In the color electrophotography method in which a color copy is obtained by removing static electricity from the film using a static electricity removal charger and separating the transfer paper, the voltage of the electricity removal charger described above is not applied after the primary transfer, and the voltage of the transfer drum is applied after the secondary transfer. A color electrophotographic method characterized in that the transfer drum potential is applied so as to be approximately equal to the potential after the primary transfer, and the transfer drum potential is changed to be approximately zero after the tertiary transfer. 2. When the three-color toner image on the photoreceptor is transferred three times onto the transfer paper wrapped around the transfer drum, the transfer voltage is low for the first image, and higher for the second and third images than the first image. A color electrophotographic method according to claim 1, characterized in that the values are set to be equal.