JPS62280873A - Multiplex image forming device - Google Patents

Abstract

PURPOSE:To prevent the drop of a transfer rate and a color smear at every transfer at the time of transferring toner images of plural colors successively onto a transfer material, by providing a destaticizing corona discharging device on a position immediately before a transfer position. CONSTITUTION:As for a corona discharging device 12, the gripper of a transfer drum 4 is provided in the down stream of a position A for holding the tip of a transfer material and in a position immediately before a transfer position, and also, an opposed electrode 13 grounded in order to increase a discharge efficiency is provided on the inside of the transfer drum by clamping a transfer material sheet. In such state, after the toner image of a first color is transferred onto the transfer material, a color discharge is started immediately before the toner image of a second color is superposed and transferred, and a charge on the transfer material is destaticized by a prescribed quantity. When the destaticization is executed, the area of an area in which an electrostatic attraction force to the carrying sheet of the transfer material is decreased remains in a small area extending from the projected area of the corona discharging device 12 to the projected area of a transfer corona discharging device 5, and the fall of the electrostatic attraction force to the carrying sheet of the whole transfer material is suppressed to the minimum. In such way, the generation of a color shift can be prevented.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Scope of Industrial Application] The present invention provides a method for transferring a transfer material onto a rotating transfer material carrying sheet. City = 77 Neo to day ↓Old
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7. Applicable to devices that apply an electric field to sequentially form a plurality of toner images on an image bearing member such as a photosensitive drum or an insulated drum and transfer them onto a transfer material by sequentially overlapping them, such as a color copying machine or a color print machine. The present invention relates to a multiple image forming apparatus having a transfer process.

(Prior Art) FIG. 3 is a schematic diagram of a conventional color image forming apparatus.
After the photosensitive drum 1, which is an image carrier, is charged to a predetermined polarity by a corona discharger 2, information exposure I is applied to form an electrostatic latent image, and the latent image is transferred to a predetermined color among the developers 3a, 3b, and 3c. Developed using a developing device containing toner. On the other hand, as shown in a perspective view in FIG. 4, the transfer drum 4 includes a cylinder frame 41, a gripper 42 that grips the leading edge of the transfer material, and an insulating film or insulating film stretched over an opening area on the circumferential surface of the cylinder frame 41. Transfer material supporting sheet 4 such as mesh screen
3, the tip of the fed transfer material is gripped by the gripper 42 and the transfer material is wrapped around the carrier sheet, and then the toner image on the photosensitive drum 1 is transferred onto the transfer material by the transfer corona discharger 5. At the same time, the transfer material is electrostatically attracted onto the transfer material carrying sheet. Next, latent images based on different information exposures are formed on the photosensitive drum 1, developed using a developing device of a predetermined color, and the resulting toner image is aligned with the previously transferred toner image on the transfer material. Transcribe. When the transfer of the three-color toner image is completed and the leading edge of the transfer material approaches the separation position, the gripper 42 is released, the separation claw 10 approaches the transfer drum 4, and the transfer material on the transfer material carrying sheet is separated. be done. At the same time, an alternating current voltage is applied to two corona dischargers 6 and 7 provided with the transfer material carrying sheet sandwiched therebetween, so that static electricity is removed from the front surface of the transfer material and the back surface of the carrier sheet.

The purpose of the charge removal by the corona dischargers 6 and 7 is to remove the electrostatic adhesion between the transfer material and the carrier sheet and to prevent the toner image from scattering due to air discharge when the transfer material is separated.

After the transfer material is thus separated, the transfer material is transported to the fixing device by the transport belt 11, where it is heated and fixed, and a color image is obtained. However, conventional methods have had the following problems.

That is, when multiple color toner images sequentially formed on the image bearing member, which is the photosensitive drum 1, are sequentially overlaid and transferred onto a transfer material on a transfer material carrying sheet, the transfer rate is 2 times higher than that of the first color toner. This was a problem because the transfer rate decreased as the color and third colors were transferred. The main cause of this development is thought to be that when the transfer material separates from the image carrier after transfer, the surface of the transfer material is charged with the opposite polarity to the transfer corona discharge charge, and the charged charge accumulates with each transfer. .

Conventionally, to deal with this problem, corona discharger 6'EL
and 7), a method has been considered in which charges are removed from the surface of the transfer material and the back surface of the transfer material carrying sheet every time transfer is performed. However, if static electricity is removed by the corona dischargers 6 and 7 after each transfer, the electrostatic attraction force of the transfer material to the supporting sheet will decrease, and color misregistration may occur between the toner images of each color, or in severe cases,
The transfer material peels off from the carrier sheet and comes into contact with structures around the transfer drum, such as separation claws and transfer material guides, causing problems such as loss of the toner image transferred on the transfer material, which is impractical. there were.

[Problems to be solved by the invention] The present invention aims to eliminate the above-mentioned problems,
It is an object of the present invention to provide an image forming apparatus having a transfer process capable of preventing a reduction in transfer rate and color shift for each transfer when toner images of a plurality of colors are sequentially transferred onto a transfer material.

(Means for Solving the Problems) The apparatus of the present invention is the image forming apparatus described above, in which a corona discharger for static elimination is disposed at a position immediately before the transfer position.

[Example] The present invention will be described below based on an example of a color image forming apparatus shown in FIGS. 1 and 2.

In FIGS. 1 and 2, the same parts as those in FIG. 3 are indicated by the same numerals, and the same explanation as in the color image forming process in the conventional example will be omitted.

In FIG. 1, corona discharger 12. However, at least the gripper of the transfer drum 4 grips the leading edge of the transfer material;-! P5
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13 is provided inside the transfer drum with the transfer material sheet in between. The corona discharge device 12 starts corona discharge after the first color toner image is transferred onto the transfer material and immediately before the second color toner image is superimposed and transferred, and removes a predetermined amount of charge on the transfer material. . The high voltage applied to the corona discharger 12 is an alternating current voltage, a direct current voltage having the same polarity as the transferred corona discharge charge, or an alternating current voltage superimposed with a direct current bias voltage for controlling the amount of charge removed.

The discharge by the corona discharger 12 is at least for the third color,
In a device that transfers four-color toner images, the process continues until the static electricity removal on the transfer material is completed before the fourth-color toner image is superimposed and transferred. Although the voltage applied to the corona discharger 12 may be a constant voltage, it is more effective to gradually increase the ability of the third color pre-transfer static elimination compared to the voltage applied during the second color pre-transfer static elimination. For example, the AC voltage applied to the corona discharger 12 is 4.5 KV when static electricity is removed before transfer of the second color, and 5.5 KV when static electricity is removed before transfer of the third color. The voltage is controlled to OKV, or similarly, the alternating current voltage is set to 5.0KV, and the superimposed bias voltages are controlled to -0.8KV and -0.4KV in order.

Note that, of course, a corona discharger may be provided in place of the counter electrode 13 to remove charges from the back surface of the transfer material carrying sheet.

By removing the charge on the transfer material using the corona discharger 12 as described above, the area of the region where the electrostatic adhesion force of the transfer material to the carrying sheet is reduced is reduced by the transfer corona discharge from the irradiation area of the corona discharger 12. The area up to the irradiation area of the electric device 5 remains small, and the reduction in the electrostatic attraction force of the entire transfer material to the carrier sheet can be minimized, and as a result, the occurrence of color shift can be prevented.

Further, FIG. 2 shows another embodiment of the present invention.

In FIG. 2, a corona discharger 14 is provided at least downstream of A and immediately before the transfer position.

13 is a counter electrode of the corona discharger 14.

The corona discharger 14 is provided so that corona discharge is performed toward the transfer section, and the high voltage application timing is the same as in the above embodiment, and the charge on the transfer material is removed, but at the same time, the photosensitive material carrying the toner image is The charge on the drum 1 is removed. This charge removal on the photosensitive drum 1 removes the charge on the toner to reduce the repulsive force with the toner already transferred onto the transfer material, and also removes the latent image charge that holds the toner to restrain the toner. This is to reduce the force and prevent a drop in multiple transfer efficiency. One corona discharger can eliminate charges on the transfer material and the photosensitive drum, and two corona dischargers are used for each charge elimination. Compared to the case where a discharger is provided, this is advantageous in terms of spatial layout constraints, and the configuration is simpler. When removing the charges on the photosensitive drum, if near-infrared light with high light transmittance is irradiated to the color toner, the latent image charge on the photosensitive drum will be optically attenuated through the toner, making more effective charge removal possible. .

In addition, an insulating material is installed at the opening of the shield member of the corona discharger 12 in FIG. 1 and the corona discharger 13 in FIG. A thread may be strung around it, or several pulleys may be provided.

[Effects] Therefore, due to the static elimination effect of the transfer material according to the present invention, there is an effect that a good multicolor image with no color shift and high multiple transfer efficiency can be obtained. It is also possible to eliminate static electricity from both the transfer material and the toner image carrier at the same time using one corona discharger. In this case, it is possible to obtain a good multicolor image, and it is advantageous in terms of arrangement. This has the effect of simplifying the configuration.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of the main parts of the color image forming apparatus of the present invention, FIG. 3 is an explanatory diagram of the main parts of the conventional apparatus, and FIG. 4 is a diagram of the transfer drum shown in FIGS. FIG. 1-111 photosensitive drum, 2-111 corona discharger, 3 a, 3 b, 3 c----1 developing device, 4-111 transfer drum, 5-111 transfer corona discharger, 8.9---One-separation static elimination corona discharger, 10---One-separation claw, 12, 14---Corona discharger, 13---One counter electrode.

Claims (2)

[Claims] (1) In a transfer device that uses an electric field to superimpose toner images formed on an image carrier onto a transfer material carried on a transfer material carrying sheet, a charge on the transfer material is placed at a position immediately before the transfer. A multiplex image forming apparatus characterized in that a corona discharger is provided to eliminate charges on a transfer material, and the corona discharger eliminates charges on a transfer material prior to every second and subsequent transfer except before the first transfer. (2) The multiplex image forming apparatus according to claim 1, wherein the corona discharger removes static electricity on the image carrier at the same time.