JPH063973A - Color electrophotographic method - Google Patents

Abstract

(57) [Abstract] [Purpose] When a toner image is laminated and transferred from a latent image bearing medium to an intermediate transfer medium plural times, the intermediate transfer medium is prevented from deteriorating transferability of the toner image due to charge accumulation on the intermediate transfer medium. Provided is a color electrophotographic method capable of reducing the reverse transfer phenomenon of a toner image from a toner to a latent image bearing medium as much as possible. [Structure] Toner images sequentially formed on the latent image bearing medium 1 are layered and transferred a plurality of times by applying a bias voltage from the back surface of the intermediate transfer medium 7 to obtain a color toner image on the intermediate transfer medium. Further, the color toner image is recorded on the recording medium 11
A color electrophotographic method for batch transfer to. After each transfer process from the latent image carrier medium 1 to the intermediate transfer medium 7, after the toner image on the intermediate transfer medium 7 is presumably fixed or fixed by the presumably fixing unit 8, the entire surface of the intermediate transfer medium 7 is neutralized by the intermediate transfer medium erasing unit. 9
To eliminate static electricity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic method effective when used in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art As a color electrophotographic method, JP-A-1-
Toner sequentially formed on the latent image bearing medium by applying a bias voltage from the back surface of the intermediate transfer medium carried into the latent image bearing medium, as used in the color electrophotographic apparatus disclosed in Japanese Patent No. 282571. By transferring the image by stacking the images on the intermediate transfer medium a plurality of times to obtain a color toner image on the intermediate transfer medium, and by collectively transferring the color toner image to a recording medium carried into the intermediate transfer medium, In a method for obtaining color printing on a recording medium, a method is already known in which each time a toner image is transferred from a latent image bearing medium onto an intermediate transfer medium, the toner image on the intermediate transfer medium is discharged.

By the way, when the toner is laminated and transferred a plurality of times on the intermediate transfer medium, the transferred toner image is destaticized and then the next toner image is transferred. It is possible to prevent the phenomenon that the transfer electric field is weakened by the charge accumulation and the toner transfer property is deteriorated. However, the charge of the toner that has already been transferred onto the intermediate transfer medium is reduced by the charge removal or the charge polarity is reversed, so that the toner adsorbability to the intermediate transfer medium is reduced, and the toner is transferred in the next transfer step. However, there is a problem that the so-called reverse transfer phenomenon in which the toner returns to the latent image bearing medium cannot be prevented.

The present invention has been made in view of the above circumstances, and a color electrophotographic method capable of reducing the reverse transfer phenomenon of a toner image as much as possible while preventing deterioration of transferability due to charge accumulation on an intermediate transfer medium. The purpose is to provide.

[0005]

According to the present invention, in order to achieve the above object, a bias voltage is applied from the back surface of an intermediate transfer medium carried into the latent image bearing medium, and the intermediate transfer medium is sequentially formed on the latent image bearing medium. A latent image is a color electrophotographic method in which a toner image is transferred onto an intermediate transfer medium by stacking the toner images a plurality of times, and then the transferred toner image is transferred to a recording medium carried into the intermediate transfer medium. After completion of each transfer process from the carrier medium to the intermediate transfer medium, the toner image on the intermediate transfer medium is assumedly attached or fixed, and then the entire surface of the intermediate transfer medium is discharged.

[0006]

When each toner image on the intermediate transfer medium is assumedly attached or fixed and the front surface of the intermediate transfer medium is discharged, the attraction force of the toner image transferred from the latent image carrier onto the intermediate transfer medium increases, and When the toner images are layer-transferred onto the transfer medium, the reverse transfer phenomenon in which the toner image already transferred onto the intermediate transfer medium returns to the latent image carrying medium again is prevented.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a printing apparatus using the color electrophotographic method according to the present invention. This apparatus includes a latent image carrier medium 1, a charging unit 2, an image exposing unit 3, a developing unit 4, a pre-transfer charging unit 5, a transfer roller 6, a toner image presuming unit 8, an intermediate transfer medium charge eliminating unit 9, and a thermal transfer unit 1.
0, a cleaning unit 13, a charge removing unit 14, and the like, each of which is configured as follows.

The latent image bearing medium 1 is an organic photosensitive drum. In addition, a photosensitive drum such as selenium or amorphous silicon can also be used. In addition to the photosensitive drum, a photosensitive belt can be used. The charging unit 2 uniformly charges the surface of the latent image carrying medium 1 with a corona charger. Other than the corona charger, a contact charging device using a conductive roller can be used.

The image exposing means 3 is a laser optical system and exposes the surface of the latent image carrying medium 1 with light according to color image information, thereby sequentially forming electrostatic latent images. As image exposure means,
An LED optical system or the like can also be used. The arrow A in the figure indicates the position of image exposure by the image exposure means 3. The developing means 4 is
A liquid developing apparatus using a known roller developing method, which is composed of four independent developing devices containing developing solutions using yellow, magenta, cyan, and black toners, and is moved by an unillustrated moving means to cause an arrow in the figure. It can be moved in the B direction. The four developing devices include developing rollers 41, 43, 45, 47 for developing the electrostatic latent image, and a developing roller 41, 43, 45, 47 for removing the excess developer adhering to the rollers during development. The squeezing rollers 42, 44, 46 and 48 are independently provided. As the developer, a liquid carrier in which toner particles are dispersed is used.

The pre-transfer charging means 5 is a corona charger that charges the surface of the latent image carrying medium 1 together with the developed toner image to the same polarity as the charge polarity of the toner. By this pre-transfer charging, the toner image is pressed by the electric field force, and the latent image carrying medium 1
The attraction force between the toner image and the toner image is increased, and the flow and the thickening of the toner image in the process of transferring the toner image to the intermediate transfer medium 7 are suppressed.

The transfer roller 6 is a metal drum and can hold the intermediate transfer medium 7 on its surface. A bias voltage having a polarity opposite to that of the toner is applied to the transfer roller 6 from the back surface of the intermediate transfer medium 7 by a transfer bias applying unit (not shown). The transfer roller 6 may have an appropriate diameter depending on the size of the recording medium. Further, a transfer belt can be used in addition to the transfer roller.

The intermediate transfer medium 7 is formed by laminating a thin silicone layer on a conductive rubber layer. By applying a bias voltage from the back surface of the intermediate transfer medium 7, the toner is transferred to the surface of the silicone layer. The toner image hypothetical fixing means 8 hypothetically adheres the toner image transferred onto the intermediate transfer medium 7 with a halogen lamp. This hypothetical adhesion increases the attraction force between the intermediate transfer medium 7 and the toner image, and when the toner images are stacked and transferred onto the intermediate transfer medium 7, the toner image already transferred onto the intermediate transfer medium 7 carries a latent image. The reverse transfer phenomenon of returning to the medium 1 again is prevented. In addition to the halogen lamp described above, a far infrared heater or other heat source can be used as the toner image presuming means 8. Needless to say, the toner image may be fixed on the intermediate transfer medium 7, and in this case as well, the halogen lamp and other heat sources can be strengthened to be used in the same manner.

The intermediate transfer medium charge-eliminating means 9 is a corona charger, and charges the surface of the intermediate transfer medium 7 including the portion of the toner image transferred onto the intermediate transfer medium 7. This static elimination prevents the surface potential of the intermediate transfer medium 7 from changing in the direction in which the transfer electric field is weakened by the toner images transferred in layers.
Suppresses deterioration of transferability. The thermal transfer means 10 has a heater (not shown) built therein, and is pressed against the intermediate transfer medium 7 by a pressing mechanism (not shown) to heat / apply the color toner images laminated and transferred to the intermediate transfer medium 7. Recording medium 1 by pressing
1 is transferred. Here, when the pressing mechanism transfers the toner image from the latent image carrying medium 1 to the intermediate transfer medium 7, the thermal transfer means 10 is separated from the intermediate transfer medium 7. Then, by the pressing mechanism, the heat fixing unit 10 is pressed against the intermediate transfer medium 7 with a predetermined pressing force by the time the final toner image transferred portion of the four types of toner images arrives. As a result, the thermal transfer means 10 heats and presses the color toner images laminated and transferred onto the intermediate transfer medium 7, and transfers the four types of toner images onto the recording medium 11 supplied from the print medium conveying means 12 at once. To do.

The cleaning means 13 is provided with a non-woven fabric (not shown) and a cleaning blade (not shown) in the cartridge. When the cartridge is mounted on the printer, the cleaning blade comes into contact with the latent image carrying medium 1. . The cleaning means 13 is used for the intermediate transfer medium 7.
After the transfer, the toner image and the liquid toner remaining on the latent image bearing medium 1 are scraped by the cleaning blade,
It is cleaned by wiping it with the non-woven fabric.

The discharging means 14 is a tungsten lamp or L
By exposing the entire surface of the latent image bearing medium 1 with an ED array or the like, residual charges on the latent image bearing medium 1 are removed. In the printing device configured as described above, color printing is
This is done as follows. In the printing apparatus, the latent image bearing medium 1 rotates in the direction of the arrow in the figure, and the surface of the latent image bearing medium 1 is uniformly charged by the charging means 2.

Next, the image exposure means 3 writes an image to be visualized with yellow toner on the latent image carrying medium 1. The electrostatic latent image thus obtained is developed by the developing device of the developing means 4 in which the developing solution using the yellow toner is contained. The development is performed by rotating the developing roller 41 and supplying the developing solution to the latent image carrying medium 1.
The excess developer adhering to the latent image bearing medium 1 in this development is
It is removed by the squeeze roller 42. The developing rollers 43, 45, 47 and the squeezing rollers 44, 46, 48 provided in the developing devices containing the developing solutions of other colors also have the same operation when performing the developing operation using the developing devices.

Then, the pre-transfer charging means 5 charges the surface of the electrostatic latent image carrying medium 1 together with the developed yellow toner image. By this charging, the attraction force of the toner image to the latent image carrying medium 1 is increased, and the flow and thickening of the image in the transfer step of transferring the toner image to the intermediate transfer medium 7 are suppressed. The obtained yellow toner image is transferred onto the intermediate transfer medium 7 by applying a transfer bias voltage having a polarity opposite to the charge polarity of the toner from the back surface of the intermediate transfer medium 7. The yellow toner image transferred on the intermediate transfer medium 7 in this way is assumedly fixed on the intermediate transfer medium 7 by the assumed fixing means 8. By this hypothetical attachment, the yellow toner image transferred onto the intermediate transfer medium 7 has an increased attracting force with the intermediate transfer medium 7, and the subsequent transfer of another toner image from the latent image carrier medium 1 to the intermediate transfer medium 7 is continued. At this time, reverse transfer of the yellow toner image on the intermediate transfer medium 7 to the latent image carrier 1 is prevented. Then, the intermediate transfer medium 7 is neutralized by the intermediate transfer medium neutralizing means 9.

By this hypothetical deposition and charge removal, the reverse transfer phenomenon of the toner image is prevented, and the accumulation of electric charges in the direction of weakening the transfer electric field on the intermediate transfer medium 7 is prevented. Image deterioration at the time of stack transfer of the toner images to the toner is suppressed. The residual toner and the residual charge on the surface of the latent image carrying medium 1 after the transfer of the yellow toner image are removed by the cleaning unit 13 and the charge eliminating unit 14.

Next, after the surface of the latent image carrying medium 1 is uniformly charged by the charging means 2, the image to be visualized with magenta toner is written this time. The electrostatic latent image thus obtained is developed by a developing device containing a developing solution containing magenta toner of the developing means 4, and after the excess developing solution on the latent image carrying medium 1 is removed, Charging is performed by the pre-transfer charging unit 5.

The magenta toner image on the latent image bearing medium 1 thus obtained is transferred onto the intermediate transfer medium 7 on which the yellow toner image has already been transferred. Thereafter, by the same process, after the cyan toner image is layered and transferred to the intermediate transfer medium 7, the black toner image is finally layered and transferred. Here, it goes without saying that when the toner images are stacked and transferred onto the intermediate transfer medium 7, the registration of the superposition is performed.

After the color toner images of four colors are laminated and formed on the intermediate transfer medium 7 in this way, the thermal transfer means 10 is pressed against the intermediate transfer medium 7 by the pressing mechanism,
The print medium 11 conveyed from the print medium conveying means 12 is sandwiched between the thermal transfer means 10 and the intermediate transfer medium 7, and the color toner images formed in layers are transferred onto the print medium 11.

In the printing apparatus of the above embodiment, the toner image transferred onto the intermediate transfer medium 7 is assumed to be attached by the toner image attachment means 8. However, by strengthening the halogen lamp and other heat sources, The toner image transferred onto the intermediate transfer medium 7 may be fixed.

[0023]

As is apparent from the above description, after the transfer process of each toner image from the latent image bearing medium to the intermediate transfer medium is completed, the toner image on the intermediate transfer medium is assumedly attached or fixed, and then the intermediate image is transferred. Since the entire surface of the transfer medium is neutralized, the adsorbability between the intermediate transfer medium and the toner image is increased, and even if the charge amount of the toner is reduced due to the neutralization or the charge polarity of the toner is reversed, it is already present during the layered transfer. It is possible to prevent the reverse transfer phenomenon in which the toner image transferred on the intermediate transfer medium returns to the latent image carrying medium again, and it is possible to prevent the accumulation of electric charges in the direction of weakening the transfer electric field on the intermediate transfer medium.

As a result, there is an excellent effect that the image deterioration at the time of the laminated transfer of the toner images to the intermediate transfer medium is suppressed and the print quality can be improved.

[Brief description of drawings]

FIG. 1 shows an embodiment of a printing apparatus using a color electrophotographic method according to the present invention.

[Explanation of symbols]

 1 Latent Image Bearing Medium 2 Charging Means 3 Image Exposure Means 4 Developing Means 5 Pre-Transfer Charging Means 6 Transfer Rollers 7 Intermediate Transfer Media 8 Toner Image Assuming Means 9 Intermediate Transfer Media Eliminating Means 10 Thermal Transfer Means 11 Printing Media 12 Printing Media Conveying Means 13 cleaning means 14 static elimination means 41, 43, 45, 47 developing roller 42, 44, 46, 48 diaphragm roller

Claims (1)

[Claims] 1. A bias voltage is applied from the back surface of an intermediate transfer medium carried into a latent image bearing medium, and toner images sequentially formed on the latent image bearing medium are laminated and transferred on the intermediate transfer medium a plurality of times, Further, a color electrophotographic method for transferring the transferred toner image onto a recording medium carried into the intermediate transfer medium, wherein the intermediate transfer medium is formed after each transfer step from the latent image carrying medium to the intermediate transfer medium. A color electrophotographic method, characterized in that after the above toner image is assumedly attached or fixed, the entire surface of the intermediate transfer medium is discharged.