JPS58211774A - Transfer and separation method in electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To provide both sepn. and transfer performances by changing over the potential of a sepn. and conveyance member in the short period when the sepn. is started and the period after the same. CONSTITUTION:The surface of a photoreceptor 1 is electrostatically charged to a positive potential and the voltage applied on a transfer charger 3 is of a positive polarity. The electric charge to be applied on copying paper 6 by said voltage is positive. The potential to be applied on the conductive layer 4b of a belt 4 by a voltage application circuit 5 is negative and the paper 6 which is held electrostatically charged positive is attracted surely to the belt 4 at the point of the time when the paper 6 approaches to the belt 4 and the sepn. thereof from the photoreceptor 1 is started. If the polarity of the circuit 5 is changed over to positive at the point of the time when the forward end part of the paper 6 is separated by about 3-10mm. from the photoreceptor 1, the retransfer of the toner having negative charge to the photoreceptor 1 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating and transporting copy paper to which a toner image has been transferred from a photoreceptor.

There is a method in which the force of the separation reservoir depends on an electrostatic force generated between the copy paper and the separating and conveying member, and since the present invention relates to an improvement thereof, this will be explained first.

FIG. 1 shows a separating and conveying device of the above type. ■
is a drum-shaped photoreceptor that rotates in the direction of the arrow. The photoreceptor 1 carries an electrostatic latent image with a positive potential around it, and toner 2 with a negative charge is attracted to it. The copy paper 6 is 1-. The transfer charger 3 is carried in so as to be in close contact with one surface, and is acted on by a transfer charger 3 connected to a positive polarity transfer source 3 from the back surface thereof. As a result, the copy paper is positively charged and the toner 2 is completely absorbed, but it is attracted to the inner surface of the photoreceptor 1 by the attraction force generated between the toner 2 and the conductive substrate 1a of the photoreceptor 1. . A belt 4 that comes into contact with or comes very close to the back side of the adsorbed copy paper 6 is stretched between the boots IJ-7 and 8 and runs in the direction of the arrow 13.

As shown in Figure 2, the front side of the belt hand is 1012.
The insulation layer 4a has a resistance of 108Ω or more on the back side.
It is composed of a conductive layer 4h having a thickness of an or less.

The conductive layer 4b is grounded via a voltage application circuit 5. The voltage application circuit 5 sets the potential of the conductive turtle layer 4h to negative polarity,
The copy paper 6 which has been properly banded is suctioned, separated from the circumferential surface of the photoreceptor (2), adsorbed onto the belt 4, and conveyed. Note that 9 is a charge eliminating charger that removes static electricity from the belt 4, and 10 is a cleaning blade that removes toner adhering to the belt 4.

By the way, in order to attract the copy paper 11 (i) to the belt 4 side, the device applies a negative potential of about 1L to the conductive 1☆74h, that is, the same polarity as the band of toner 2, so that the copy paper is Among the toner 2 adsorbed on the conductive layer Φb
There is a possibility that some of the toner particles are repelled by the electric potential and retransferred to the photoreceptor l side, resulting in defective transfer. In this way, since the separation performance and the transfer performance are contradictory, the conductive layer 4b
The potential to be applied must be determined based on these considerations, and the allowable range is not necessarily wide.

Therefore, it is not possible to cope with changes in paper quality and environmental conditions such as temperature and humidity, resulting in poor separation or poor transfer.

The purpose of the present invention is to solve the problem described in Ail, and to achieve both of the above-mentioned performances by switching the potential of the separation/conveying member for a short period of time at the start of separation and for a period thereafter. The aim is to

Next, the present invention will be explained based on an example in which the present invention is implemented in a positive original/positive copy copying machine using a selenium photoreceptor. In this example, the photoreceptor I has a selenium layer on its surface with a thickness of about 60 .mu.m, and is charged to a positive potential of about 700 to 800 .mu.m. The voltage applied to the transfer charger 3 is of positive polarity, so that the charge applied to the copy paper 6 is positive.

As shown in FIG. 3(a), a time t=to when the copy paper 6 approaches the belt hand and starts to be separated from the photoreceptor l.
In this case, the potential applied to the conductive layer 4b of the belt 4 by the voltage application circuit 5 is negative, and its value is selected from 0 to -800V as shown in FIG.

Therefore, the positively charged copy paper 6 is reliably attracted to the belt 4, separated from the photoreceptor 1 as it travels, and is conveyed by the belt. At this time, a portion of the negatively charged toner 2 is retransferred onto the photoreceptor 1, causing a transfer failure, but since this is only at the leading edge of the copy paper 6, no problem occurs.

As copying progresses, as shown in FIG. 3(h), when the leading edge of the copy paper 6 is separated from the photoreceptor ■ by about 3 to 10 Il+++1 (1 = 11), this is detected and the voltage application circuit 5 Switch the polarity of the

The potential of the conductive layer 4a of the belt 4 after switching is selected to be +400 to 800V, as shown in FIG.

As a result, the polarity of the conductive layer 4a becomes opposite to the polarity of the toner 2, so that transfer defects are eliminated. Copy paper 6 and belt 4
Although the suction force per unit area that acts between the belt 4 and the belt 4 decreases due to the switching, since separation and conveyance have already started and the copy paper 6 and the belt 4 are in close contact with each other over a certain area, the separation force [ (Attraction force per unit area) x (Contact area)
] has reached a sufficient value, and there is no risk of poor separation.

FIG. 5 shows an example in which the present invention is implemented in a negative original F4/positive copy copying machine. In this example, since the charge applied to the copy paper 6 by the transfer charger 3 is of negative polarity, the separation is started at the time t. The potential applied to the belt 4 is positive polarity, and is switched to negative polarity at time t1.

FIG. 6 shows yet another embodiment of the invention. In this example, belt 4 is charged by charger 11 . The charger 11 is connected to a high-voltage AC power supply 12 with a DC bias, and discharges a corona toward the belt 4 to positively and negatively charge it. That is, the DC bias of the high-voltage AC power supply 12 is switched according to the advancing state of the copy paper 6, and the portion A that contacts the leading edge of the copy paper 6 is charged with the opposite polarity of the transfer electric field.
The portion B that contacts the subsequent image portion is charged with the same polarity as the transfer electric field. Since the surface potential of the charged portion A of the belt 4 is opposite to the charged polarity of the copy paper 6, the copy paper 6 is attracted to the surface of the belt 4, moves away from the photoreceptor 1, is attracted to it, and is conveyed.

However, since the charged polarity of the toner is the same, transfer failure occurs, but only at the leading end. Charged part B
When the belt 4 arrives, the polarity of the surface potential of the belt 4 is reversed, so that the transfer performance becomes good. The fact that this polarity reversal has no practical effect on separation performance is the same as in the other embodiments described above.

Note that as means for detecting the progress state of the copy paper 6, in addition to using the output of the sensor, a paper feed registration signal or a signal from the exposure optical system can also be used.

As described above, in the present invention, at the start of separation, the electric potential applied to the conveying unit side is set to the opposite polarity of the transfer electric field, so that the charged polarity of the copy paper and the electric potential of the conveying member become opposite polarities, and sufficient suction is achieved. Force is generated to ensure reliable separation. Since there is an insulating layer on the surface of the conveyance member, even if the conveyance member and copy paper come into contact. Since the amount of charge on the copy paper does not decrease, no transfer defects will occur due to this, and the transfer ability will only be slightly degraded. This state occurs only at the start of separation, and immediately after that, the potential of the conveyance member is made to have the same polarity as the transfer electric field, so that sufficient transfer ability can be maintained. Further, once the separation is started, a decrease in the adsorption force per unit area can be prevented by increasing the adsorption area, and sufficient separation ability can be obtained without any problem.

[Brief explanation of the drawing]

The first figure is a front view of the transfer/separation device, and the second figure is an enlarged sectional view of the belt. FIG. 3 is a front view of a main part showing an example of the present invention, and FIG. 4 is a graph showing changes in belt potential. FIG. 5 is a graph showing changes in belt potential in another example. FIG. 6 is a front view of yet another embodiment. ■...Photoconductor, 2...Toner, 3...Transfer charger, 3a...(Transfer) power supply, 4...Belt, 4α
... Insulating layer, 4h... Conductive layer, 5... Voltage application circuit, 6... Copy paper, 11... Charger, 1
2...High voltage AC power supply. Patent applicant Rico Co., Ltd. - Figure 1 Figure 3 (a) (b) Figure 4 Figure 5 Figure 6

Claims (2)

[Claims] (1) The toner image is transferred from the photoreceptor by applying a transfer electric field from the back side of the copy paper, and a conductive conveyance member having an insulating layer on the surface is contacted or In a method of separating the copy paper from the photoreceptor by an electrostatic attraction force generated between the conveyance member and the copy paper when the conveyance member and the copy paper are brought close to each other, an electric potential is applied to the conveyance member and the electric potential is applied at the time of starting separation. In this case, the polarity of the transfer electric field is reversed. and a transfer/separation method in an electrophotographic copying machine, which is characterized in that the polarity is switched to the same polarity after the separation starts. (2) The toner image is transferred from the photoconductor by applying a transfer electric field from the back side of the copy paper, and a conductive conveyance member having an insulating layer on the surface is brought into contact with the back side of the copy paper after the transfer. In a method in which the copy paper is separated from the photoreceptor by the electrostatic attraction force generated between the conveyance member and the AiI copy paper by bringing them close to each other, an electric charge is injected into the surface of the conveyance member, which causes the copy paper to A transfer/separation method in an electrophotographic copying machine, characterized in that the transfer electric field has an opposite polarity in a portion that comes into contact with or approaches a tip of the transfer electric field, and has the same polarity (even polarity) in other portions.