JPS6236221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transfer device used in electrophotography for reproducing two color components of an original image, such as black and chromatic colors.

Many proposals have been made so far regarding electrophotographic devices that can make two-color copies, but one method that develops a latent image formed on a photoreceptor using two types of toner of different polarity is proposed. The transfer image forming process requires a step of charging the toners of different polarities to one polarity before the transfer.

Here, in order to understand the contents of the present invention, some explanation will be added regarding an example of this image forming process. In FIG. 1, a first photoconductive layer 3 sensitive to white light and a second photoconductive layer 4 sensitive to light other than red light are first charged with negative polarity by a primary charger 5 while irradiating red light. When charging (or positive polarity charging) is performed, and then reverse polarity charging is performed using the secondary charger 6 in a dark place, the negative primary charge on the surface of the second photoconductive layer 4 becomes almost 0, but 1st, 2nd
The induced positive charges on the back surfaces of the photoconductive layers 3 and 4 remain as they are. Image exposure 7 is then performed, and for the red region, the induced positive charges on the back surface of the second photoconductive layer 4 are removed from the conductive layer 4 except for those that are restrained by the negative charges on the surface of this layer 4.
to escape. In the white region, the resistance of the first and second photoconductive layers 3, 4 decreases, so that all the positive charges on the back surface of the second photoconductive layer 4 escape, and in the black region, the same state is maintained. When a positively charged red toner and a negatively charged black toner are applied to the latent image formed through the above process using the developing devices 8 and 9, the red toner is applied to the surface of the second photoconductive layer 4 in the red region. The black toner is attracted by the electric field caused by the induced positive charge maintained on the back surface of the second photoconductive layer 4 in the black area, and adheres here to the photoreceptor 1.
A two-color separated developed image is formed on the surface. moreover,
The pre-transfer charger 10 performs positive or negative polarity charging to align these different polarity toners to one polarity, and then the transfer charger 11 performs charging with the opposite polarity to the pre-transfer charge. This is to move the toner onto the transfer paper 12. In addition, reference numeral 1 in Figure 1
3 is a static eliminator, 14 is a fixing device, 15 is a cleaning device, and 16 is a quenching lamp.

However, as mentioned above, if two types of toners with different polarities are charged to have the same polarity before transfer, there is no problem with the toners with the same polarity as the charged polarity, but with the toners with the opposite polarity, In other words, the above-mentioned positive red toner is changed to negative polarity by this pre-transfer charging, so that it becomes the same as the charge polarity on the surface of the second photoconductive layer 4, and is repelled by the latent image and peeled off. It becomes easier to do. Therefore, the image is easily disturbed by corona ion wind due to pre-transfer charging or contact of the transfer paper 12 onto the photoreceptor 1, etc.
The problem was that good image density and quality could not be obtained.

The present invention is intended to solve the above-mentioned problems faced by transfer-type color electrophotographic apparatuses that perform development using two types of toners of different polarities.

Hereinafter, the details of the present invention will be explained in detail based on the drawings.

FIG. 2 shows a first embodiment of the present invention, and parts common to those of the conventional device shown in FIG. 1 are given the same reference numerals and their explanations will be omitted.

Therefore, the feature of the present invention is that the pre-transfer charger 10 is removed from the conventional transfer type color copying apparatus shown in FIG. Transfer is performed on transfer paper using two transfer chargers,
In the embodiment shown in FIG. 2, the first
The transfer charger 17 first transfers the positively charged red toner onto the transfer paper 12, and then the second transfer charger 18 performs positive charging to remove the negative polarity remaining on the photoreceptor 1. The black toner is transferred onto the transfer paper 12.

Here, there is a concern that the previously transferred positive toner may be separated from the transfer paper 12 by the second positive charge, but the negative charge voltage of the first transfer charger 17 is set to -6.0KV, and the second The positive charging voltage of the transfer charger 18 is set to be slightly lower than the first transfer charging voltage.
It has been confirmed through experiments that good image quality can be obtained by setting the voltage to 5.0KV to +5.5KV.

FIG. 3 shows a second embodiment of the present invention, in which 19 is a corona transfer charger that charges with negative (or positive) polarity, and 20 is a conductor charged with positive (or negative) polarity. 20a is a cleaning roller, 20b is a cleaning blade, and 20c is a toner accumulator.

In this embodiment, positive polarity toner is transferred by a corona transfer charger 19 that performs negative polarity charging,
Next, the bias transfer roller 2 is charged with positive polarity.
0, the negative polarity toner transfer portion is performed. Here, there is a concern that the previously transferred toner may be separated from the transfer paper by the application of the next bias voltage, but the corona transfer voltage is -5.5 to -7 KV and the voltage applied to the bias roller is +0.5 to 1 KV. It was confirmed that good image quality could be obtained without disturbing the previously transferred image.

FIG. 4 shows a third embodiment of the present invention, in which reference numeral 21 denotes a first bias roller transfer charger that performs negative (or positive) polarity charging, and the surface of the photoreceptor 1 is The photoreceptor 1 rotates together with the photoreceptor 1. A second bias roller transfer charger 22 performs positive (or negative) polarity charging. A roller having a slightly larger diameter than the roller of the first transfer charger 21 is used, and it weakly contacts the surface of the photoreceptor 1. There is. Reference numeral 23 indicates a belt stretched between both of the rollers described above so that they rotate at the same time.

In this embodiment, a bias voltage of -1.0 to -1.5 KV is applied to the first bias roller transfer charger 21, and a bias voltage of -1.0 to -1.5 KV is applied to the first bias roller transfer charger 22.
By applying a bias voltage of +0.5 to +1.0KV, which is slightly lower than that of the conventional method, it is possible to obtain a good image without disturbing the previously transferred toner image even if the transfer is performed in two steps. confirmed. Furthermore, according to this embodiment, the diameter of the roller of the second bias transfer charger 22 is set to the diameter of the roller of the first bias transfer charger 22.
Because it is larger than that of the second roller, when both rollers are rotating at the same speed, the second roller has a higher circumferential speed, which tends to pull the transfer paper, eliminating slack in the paper between the two rollers, and improving the transfer speed. There is no shift in the image.

As described above, according to the present invention, an electrostatic latent image formed on a photoconductor according to two original color components is developed with two types of toners of different polarities. In the device, these positively and negatively charged toners are separately moved onto the transfer paper by two transfer chargers with different polarities, one for negative polarity and one for positive polarity, which are arranged in the transfer section. This not only simplifies the process by omitting the pre-transfer charger in the conventional device, which was installed in front of the transfer unit to align the polarities of toners of different polarities, but also simplifies the process. Therefore, there is no fear that unstable toner with aligned polarity will disturb the image, and toner of different polarity can be transferred in a state where it is stably attached according to the latent image polarity. Therefore, it has excellent effects as a color electrophotographic transfer device, such as obtaining good image density and high image quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the layout of a conventional color electrophotographic image forming apparatus, and FIGS. 2 to 4 are layout diagrams of an electrophotographic apparatus equipped with a transfer device according to an embodiment of the present invention. 3...First photoconductive layer, 4...Second photoconductive layer, 5...Primary charger, 6...Secondary charger, 8, 9...Developer, 1
0...Pre-transfer charger, 17...First transfer charger, 18
...Second transfer charger, 20, 21, 22...Bias roller transfer charger.

Claims (1)

[Claims] 1 In a two-color color copying device equipped with an electrostatic latent image forming device and a developing device that develops the two color components of an original image using two types of toners of different polarities, the transfer portion of the device is A transfer device characterized in that two transfer chargers are provided.