JPH0619339A - Electrostatic transfer method - Google Patents

Abstract

PURPOSE:To prevent toner and electrostatic charges from remaining on the surface of a photosensitive body by applying the highest voltage after the head edge of transfer paper reaches a transfer part and turning OFF a transfer unit after the tail edge of the transfer paper leaves the transfer part. CONSTITUTION:The head edge of the transfer paper reaches the transfer part of a photosensitive body a time Ta after the clutch of a register roller is turned ON. For the purpose, the transfer unit is turned ON a time Tb before the head edge of the transfer paper reaches the transfer paper and the transfer output is gradually increased. At this time, the transfer unit is controlled so that the transfer output reaches a prescribed output in a time Tc. The tail edge of the transfer paper reaches the transfer part a certain time Td after a register sensor detects the tail edge of the transfer paper at the tail edge part of the transfer paper. Therefore, the transfer output begins to be decreased in a time Te a little bit shorter than the time T and is turned OFF in a time Tf so that the transfer unit is turned OFF after the tail edge of the transfer paper finishes passing through the transfer part. Thus, the transfer output is adjusted at the head edge part and tail edge part of the transfer paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electrostatic transfer method for electrostatically transferring toner on a photoconductor to a transfer paper in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing a main configuration of an electrophotographic image forming apparatus.

The photoconductor 1 having photoconductivity is formed in a drum shape and is rotatably provided in the direction of the arrow in the figure. A charger 2, a developing device 3, a registration roller 4, a transfer device 5, a peeling device 6, a cleaner 7, and a charge eliminator 8 are arranged in this order around the photoconductor 1. The surface of the photoconductor 1 is charged by the charger 2 and exposed by image forming light such as document reflection light and laser light to form an electrostatic latent image. Toner is attached to the electrostatic latent image by the developing device 3 to form a toner image. On the other hand, the transfer paper fed from a paper feeding unit (not shown) hits the registration roller 4 and is temporarily stopped, and then the registration roller 4 starts to rotate at a predetermined timing and is fed to the photoconductor 1. The timing of feeding is the photoconductor 1
It is set so that the leading edge of the toner image that moves by the rotation of and the leading edge of the transfer sheet to be fed match. The transfer device 5 is turned on in a state where the toner image on the photoconductor 1 and the leading edge of the transfer paper are superposed on each other, and corona discharge is generated to transfer the toner image on the photoconductor 1 to the transfer paper. At this time, the voltage applied to the transfer device 5 is set so that the Coulomb force between the toner and the transfer paper generated by the transfer device 5 is stronger than the Coulomb force between the photoconductor 1 and the toner. The transfer paper on which the toner image has been transferred is peeled off from the surface of the photoconductor 1 by the peeling device 6 and conveyed toward the fixing device 9. On the other hand, photoconductor 1
The toner remaining after the transfer remains, and the toner is removed by the cleaner 7. Then, the electric charge remaining on the surface of the photoconductor 1 is removed by the charge remover 8.

[0004]

An electrostatic transfer device equipped with a transfer device 5 has conventionally been controlled as shown in FIG. The transfer paper passes through the position of the transfer device (hereinafter referred to as the transfer unit) at the timing shown in the figure. On the other hand, the transfer device 5 is turned on before the transfer paper starts passing through the transfer portion, and is turned off after the transfer paper finishes passing through the transfer portion. By setting the on / off timing in this way, the toner image on the photoconductor is reliably transferred to the transfer paper.

However, when the on / off control of the transfer device 5 is performed as shown in FIG. 7, there is a problem that a potential remains on the surface of the photoconductor 1 after the transfer process. As shown in the lower side of FIG. 7, the transfer device 5 is set in the range of A on the photoconductor 1.
Is turned on, and the transfer paper passes through the range B. The transfer paper passage portion B is an area where a toner image is formed. During the transfer process, the surface of the photoconductor 1 is charged by the discharge of the transfer device 5 in the region before and after the transfer paper passage portion B, and a residual potential is generated on the surface of the photoconductor 1. At this time, in particular, the electric field concentrates on the edge portions (immediately before the front edge of the transfer paper and immediately before the rear edge of the transfer paper) through which the transfer paper passes, and the residual potential at the edge portions becomes very high. In such a portion (edge portion) where the residual potential becomes extremely high, the toner in the cleaner 7 is reversely adhered at the time of subsequent cleaning, so that the toner cannot be cleaned, that is, the toner is not attached to the surface of the photoconductor 1. There was a problem that it remained. Further, when the static eliminator 8 performs static elimination, the electric charge in the edge portion may not be completely removed and may remain (become an image memory).

An object of the present invention is to provide an electrostatic transfer method capable of preventing toner and charges from remaining on the surface of a photosensitive member by controlling the voltage applied to the transfer device.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a transfer paper is transferred to a transfer unit so that a toner image formed on the surface of a rotating photoconductor is sent to the transfer unit by the rotation of the photoconductor. In the electrostatic transfer method, in which the toner image is electrostatically transferred onto the transfer paper by supplying a voltage to the transfer device at the same time as feeding the paper, a voltage is applied to the transfer device before the front end of the transfer paper reaches the transfer unit. Is applied to gradually increase the applied voltage, reach the maximum applied voltage after the leading edge of the transfer paper reaches the transfer portion, and gradually decrease the applied voltage before the rear end of the transfer paper leaves the transfer portion. The transfer device is turned off after the rear end of the transfer paper is separated from the transfer portion.

[0008]

According to the present invention, when the leading edge of the transfer sheet reaches the transfer section and when the trailing edge of the transfer sheet reaches the transfer section, the voltage applied to the transfer unit is slightly lower than the maximum voltage value. It has become. Therefore, the amount of electric field concentrated on the edge portion of the transfer paper also decreases, and the residual potential at the edge portion decreases.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the main part of a copying machine is as shown in FIG. A block diagram of the essential parts of the electrostatic transfer device is shown in FIG. The CPU 11 outputs an ON signal for the transfer device 5 at a predetermined timing. This ON signal is converted into a voltage value by the D / A converter 12, and a predetermined voltage is applied to the transfer device 5 via the high voltage power supply 13. This causes the transfer device 5 to generate corona discharge according to the voltage value.

FIG. 4 is a diagram showing the relationship between the transfer output (current flowing into the photosensitive member 1) and the transfer efficiency. As shown in the figure, when the transfer output is increased, the transfer efficiency is increased, and within a certain range (-0.3 to -0.4 μA / cm), it becomes saturated, and then the transfer output is increased. However, the transfer efficiency will decrease. This is because if the transfer output is increased too much, discharge will occur in the air gap between the photoconductor and the transfer paper. Therefore, in this embodiment, the transfer output is controlled to be -0.3 .mu.A / cm at the front and rear ends of the transfer paper, and the transfer output is -0.4 .mu.A / cm at the center of the transfer paper. Are controlled.

FIG. 3 is a diagram showing the output of the transfer unit 5 and the potential state of the surface of the photoconductor after the transfer processing. Transfer paper passage section B
On the other hand, the transfer device 5 is turned on within the range of A. However, while the transfer device 5 is turned on, the transfer output is changed between the position corresponding to the front end of the transfer paper and the position corresponding to the rear end of the transfer paper. When the transfer device 5 is turned on, the transfer output is approximately 1/2 (-
The output is gradually increased to 0.2 μA / cm).

At the leading end of the transfer paper, -0.3 μA /
The output is controlled to be about cm, and thereafter, the output is controlled to be a specified output (-0.4 μA / cm) slightly inside the front end of the transfer paper. Conversely, at the trailing edge of the transfer paper, the output begins to drop slightly inside the trailing edge of the transfer paper, and at the leading edge of the transfer paper -0.3μ.
The transfer device 5 is controlled to be about A / cm, and the transfer device 5 is turned off after the rear end of the transfer paper has finished passing through the transfer portion. By controlling in this way, as shown in the drawing, it is possible to prevent the photosensitive member surface potential at the edge portion of the transfer paper after the transfer processing from becoming extremely high. For example, as in the conventional case, the transfer device 15
When the transfer output is raised to the specified value at the same time as when the switch is turned on, the residual potential of the edge portion after the transfer processing becomes about -1500 V, but the transfer output was gradually changed at the edge portion as in this embodiment. In this case, the residual potential of the edge portion after the transfer process is about −700V. When the voltage is about −700 V, the static eliminator 8 can sufficiently remove the static charge when the static eliminator 8 performs the static eliminator. In this way, the transfer device 5
It is possible to lower the potential of the edge portion after the transfer process by adjusting the output of the.

On / off control of the transfer unit 5 is performed as follows, for example.

In FIG. 6, a registration sensor 4a is provided immediately before the registration roller 4 (in the conveyance direction of the transfer paper) to detect the insertion of the transfer paper. The registration sensor 4a is turned on when the front end of the transfer paper reaches the registration roller 4, and is turned off when the rear end of the transfer paper has finished passing the registration roller 4. 2 shows registration rollers 4,
3 is a timing chart showing the operation of the transfer device 5, and FIG. 1 is a flowchart showing the control procedure thereof.

The registration roller 4 is normally in an off state, and after the registration sensor 4a is turned on, it is turned on (clutch on) at a predetermined timing to start feeding the transfer sheet to the photoconductor 1 (n1 → n2). ). Then, when the registration sensor 4a is turned off, the rotation is stopped (clutch off) (n6 → n7). As a result, the transfer sheet is fed to the transfer section and superposed on the toner image on the photoconductor 1. On the other hand, since the distance between the registration roller 4 and the transfer section of the photoconductor 1 is constant and the transfer sheet conveyance speed by the registration roller 4 is also constant, the transfer sheet is transferred after the clutch of the registration roller 4 is turned on. The time to reach is constant. That is, after the clutch of the registration roller 4 is turned on, T
After a time, the front end of the transfer paper reaches the transfer portion of the photoconductor.
Therefore, the transfer device 5 is turned on at time Tb before the leading edge of the transfer paper reaches the transfer portion, and the transfer output is gradually increased. At this time, the transfer output is the specified output (−0.4 μm) at the time Tc.
A / cm) is controlled (n3 → n4 → n5).
On the other hand, at the trailing edge of the transfer sheet, the trailing edge of the transfer sheet reaches the transfer section after a predetermined time Td after the registration sensor 4a detects the trailing edge of the transfer sheet. Therefore, the transfer output is started to decrease at a time Te slightly earlier than Td, and the transfer device 5 is turned off after the trailing edge of the transfer paper has finished passing through the transfer portion.
Turn off the transcription output over time (n6 → n8 → n9 →
n10 → n11). In this way, the transfer output is adjusted at the leading end and the trailing end of the transfer paper.

[0016]

According to the present invention, by adjusting the transfer output at the position corresponding to the edge portion of the transfer paper, the residual potential on the surface of the photoconductor after the transfer processing can be reduced. This facilitates charge removal of the photoconductor, and prevents the potential from remaining in the image memory. Further, it is possible to prevent the toner from being reversely attached to the cleaner portion.

[Brief description of drawings]

FIG. 1 is a flowchart showing an on / off control procedure of a transfer device.

FIG. 2 is a time chart of on / off control of a transfer device.

FIG. 3 is a diagram showing a relationship between a transfer output control state and a residual potential of a photoconductor.

FIG. 4 is a graph showing the relationship between transfer current and transfer efficiency.

FIG. 5 is a block diagram of a main part of a transfer device.

FIG. 6 is a diagram showing a main configuration of an electrophotographic image forming apparatus.

FIG. 7 is a diagram showing a relationship between a transfer output control state and a residual potential of a photoconductor in a conventional apparatus.

[Explanation of symbols]

 1 photoconductor 4 registration roller 4a registration sensor 5 transfer device 7 cleaner 8 static eliminator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshikazu Harada 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (1)

[Claims] 1. A transfer sheet is fed to a transfer unit and is transferred to a transfer device so that a toner image formed on the surface of a rotating photoconductor coincides with a timing when the toner image is sent to the transfer unit by the rotation of the photoconductor. In an electrostatic transfer method in which a voltage is supplied to electrostatically transfer the toner image onto the transfer paper, a voltage is applied to the transfer device to gradually increase the applied voltage before the leading edge of the transfer paper reaches the transfer portion. The maximum applied voltage is reached after the leading edge of the transfer paper reaches the transfer section, and the applied voltage is gradually lowered before the trailing edge of the transfer paper separates from the transfer section. An electrostatic transfer method characterized in that the transfer device is turned off after the transfer unit is separated from the transfer unit.