JPH08272227A - Transfer device - Google Patents

Abstract

PURPOSE: To provide a transfer device capable of eliminating an image irregularity phenomenon by performing a transfer, when a photoreceptor belt and an intermediate transfer belt are nearly in close contact with each other and also preventing irregularities in the image and a deterioration in the photoreceptor belt by reducing the transfer memory effect of the photoreceptor belt. CONSTITUTION: The transfer device is provided with the photoreceptor belt 3 for carrying toner after development, the intermediate transfer belt 1 abutted on the belt 3 with prescribed length and two transfer rollers 50a and 50b disposed on the rear side of the intermediate transfer belt 1 in the vicinities of the contact/uncontact points of the intermediate transfer belt 1 with the photoreceptor belt 3 respectively. A voltage having the same polarity as that of the toner or zero volt is applied to the transfer roller 50a on a side where the belts 1 and 3 make an approach each other and a transfer voltage having a polarity opposite to that of the toner is applied to the other transfer roller 50b. Moreover, an alternating voltage whose maximum value is larger than that of the transfer voltage is superimposed and applied to the transfer roller 50b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device for temporarily transferring a toner image developed on a photosensitive member onto an intermediate transfer belt.

[0002]

2. Description of the Related Art FIG. 5 shows, for example, JP-A-2-212870.
It is a block diagram which shows the conventional transfer apparatus shown by the publication.
In the figure, reference numeral 1 denotes an intermediate transfer belt, which is made of a dielectric sheet material, for example, in which carbon black is dispersed to adjust the specific electric resistance to a desired value. Intermediate transfer belt 1
Is stretched around a drive roller 2a, a driven roller 2b, and a backup roller 2c. The driven roller 2b applies tension to the intermediate transfer belt 1 by a biasing mechanism (not shown). 3 is a photoconductor belt, which is a driving roller 2a,
The drive roller 4 that is in contact with the intermediate transfer belt 1 between the driven rollers 2b and stretches the photosensitive belt 3 presses the photosensitive belt 3 to the intermediate transfer belt 1. Photoconductor belt 3
A toner image is drawn by a developing device (not shown). 5
Reference numerals a and 5b denote conductive first transfer rollers, which are disposed on the surface of the intermediate transfer belt 1 opposite to the surface on which the photosensitive belt 3 is abutted, and each transfer voltage 6 of 600 V having a polarity opposite to that of the toner. Is being applied. The toner image on the photosensitive belt 3 is transferred to the intermediate transfer belt 1 between the transfer rollers 5a and 5b. Reference numeral 7a denotes a second transfer roller. When the second transfer roller 7a moves upward, the second transfer roller 7a comes into pressure contact with the backup roller 2c via the intermediate transfer belt 1 and transfers the toner image on the intermediate transfer belt 1 onto the sheet 8. . At the time of this second transfer, a transfer voltage 7b of 1600 V is applied to the second transfer roller 7a via the intermediate transfer belt 1 between the second transfer roller 7a and the earth roller 7c.

The pressure contact positions of the transfer rollers 5a and 5b with respect to the intermediate transfer belt 1 are set as follows. The point where the intermediate transfer belt 1 and the photoconductor belt 3 contact each other is P1,
If the point to be separated is P2, the transfer rollers 5a and 5b are arranged outside from this point by a distance d (about 10 to 15 mm). Then, in a state where the intermediate transfer belt 1 is stretched around the rollers 2a to 5c and the driving roller 4, the transfer rollers 5a and 5b move the intermediate transfer belt 1 to the driving roller 4 side by a gap p (0.5 to 1. It is arranged at a position where it is pressed. As a result, the intermediate transfer belt 1 lightly presses the intermediate transfer belt 1 toward the photosensitive belt 3 side without contacting the driving roller 4 of the photosensitive belt 3, and the toner image developed on the photosensitive belt 3 becomes toner. Transfer is performed to the intermediate transfer belt 1 by the conductive transfer rollers 5a and 5b to which the transfer voltage 6 having the opposite polarity is applied.

[0004]

In the conventional transfer device as described above, since the same voltage having the opposite polarity to the toner is applied to both transfer rollers 5a and 5b, the developed toner image on the photoconductor belt 3 is applied. Is transferred to the intermediate transfer belt 1, the photoconductor belt 3 and the intermediate transfer belt 1 come close to each other, and even if the gap is still wide to some extent, the potential of the transfer roller 5a may cause the transfer of toner on the photoconductor belt 3. Occurs,
This causes a problem of image distortion. Further, when the photoconductor belt 3 and the intermediate transfer belt 1 are separated from each other, the capacitance of the gap is reduced as the gap is increased, the potential between the two is increased, and discharge due to dielectric breakdown occurs. There is a problem that it causes image distortion.

Further, since the same voltage having the opposite polarity to the toner is applied to both transfer rollers 5a and 5b, the voltage having the opposite polarity is applied to the photoconductor belt 3, so that the photoconductor belt 3 has the same voltage. When a reverse charge is applied to the photoconductor and then the photoconductor is immediately charged, the potential of the part to which the reverse charge is applied is lower than that of the part to which the reverse charge is not applied, and the transfer memory effect that affects the charging potential is generated. Occurs, and image distortion occurs. In addition, there is a problem that the portion where the reverse charge is applied and the transfer memory effect occurs causes deterioration of the photosensitive belt.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a transfer device capable of preventing the disturbance of the image transferred to the intermediate transfer belt and the deterioration of the photosensitive belt. .

[0007]

SUMMARY OF THE INVENTION A transfer device according to the present invention is provided with two electrically conductive members on the back side of the intermediate transfer belt near the contact point between the photosensitive member carrying the developed toner and the intermediate transfer belt. A transfer roller is provided, and a voltage of the same polarity as the toner on the photoconductor or 0 V is applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor meet and approach each other, and the polarity opposite to that of the toner is applied to the transfer roller on the approach and away side. Is applied.

Further, the absolute value of the voltage having the same polarity as the toner applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor meet and approaches is applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor meet and separate. The value is smaller than the absolute value of the voltage of the opposite polarity to that of the toner.

Further, the voltage applied to the transfer roller on the side where the intermediate transfer belt and the photosensitive member are separated from each other is set to 400V to 1400V, which has a polarity opposite to that of the toner.

Further, the transfer roller on the side where the intermediary transfer belt and the photosensitive member are separated from each other is supplied with a DC voltage and 20 kHz from 20 Hz.
An alternating voltage of z or a rectangular wave voltage is superimposed and applied.

Then, the intermediate transfer belt is prepared by blending conductive fine powder with a polyimide material to obtain a surface resistance of 10 ⁸ to 1
It was set to ⁰⁹ ohms.

[0012]

In the transfer device configured as described above,
Since a voltage having the same polarity as the toner on the photoconductor or 0 V is applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are close to each other and a voltage having the opposite polarity to the toner is applied to the transfer roller on the side where the photoconductor is mated and separated from each other, When the photoconductor belt and the intermediate transfer belt come close to each other, the electrostatic force on the toner is small and early transfer to the intermediate transfer belt is suppressed.

Further, the absolute value of the voltage having the same polarity as the toner applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are close to each other is applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are separated from each other. Since it is smaller than the absolute value of the voltage of the polarity opposite to that of the toner, the transfer of the toner to the intermediate transfer belt is accurately performed due to the potential gradient between the two transfer rollers.

Further, since the voltage applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are separated from each other is 400 V to 1400 V, which has a polarity opposite to that of the toner, there is no shortage of the transfer voltage and the toner is moved by overcharging. Can be prevented.

Further, a DC voltage and 20 Hz to 2 kHz are applied to the transfer roller on the side where the intermediate transfer belt and the photosensitive member are separated from each other.
Since the AC voltage or the rectangular wave voltage is superposed and applied, the reverse charge given at the time of transfer of the photoconductor belt is eliminated, and the discharge due to the dielectric breakdown due to the high potential between the photoconductor and the transfer roller is prevented, Further, the transfer memory effect of the photoconductor belt is reduced, and image disturbance and deterioration of the photoconductor belt are prevented.

Then, the intermediate transfer belt is prepared by blending a conductive fine powder with a polyimide material to have a surface resistance of 10 ⁸ to 10 ^8.
Since it is set to ⁹ ohms, the surface current due to the potential gradient between the transfer rollers is set to an appropriate value, and a sufficient electric field is applied during toner transfer. Moreover, the polyimide base material is used to suppress the deposition of the conductive material from the intermediate transfer belt and reduce the characteristic deterioration of the photosensitive belt.

[0017]

【Example】

Example 1. FIG. 1 is a sectional view showing an embodiment of the present invention. In the figure, 1, 2a to 2c, 3, 4, 7a to 7
Since c and 8 have the same configuration as the above-mentioned conventional device, the description thereof will be omitted. The transfer rollers 50a and 50b are the intermediate transfer belt 1
For example, the transfer roller 50a is applied with a potential 9 having a polarity opposite to that of the toner and having a polarity opposite to that of the toner, and the transfer roller 50b has a predetermined transfer voltage 10 having a polarity opposite to the toner. Is being applied. This allows
By reducing the potential difference between the transfer roller 50a and the toner on the side where the photosensitive belt 3 rotates together with the intermediate transfer belt 1 and gradually approaches, the phenomenon of prompting the transfer can be prevented. Then, a potential difference required for toner transfer is applied to the transfer roller 50b in accordance with the movement between the photosensitive belt 3 and the intermediate transfer belt 1 where the intermediate transfer belt 1 is in contact with the transfer roller 50b. Transfer to 1. Further, rollers 11a and 11b are provided at both ends of the transfer rollers 50a and 50b, which are in pressure contact with the photosensitive belt 3 and are driven by the concentric shafts of the transfer rollers to rotate, so that the distance between the photosensitive belt 3 and the intermediate transfer belt 1 is always constant. The contact area between the photosensitive belt 3 and the intermediate transfer belt 1 is kept constant so that the transfer stability is ensured. The pressure contact positions of the transfer rollers 50a and 50b with respect to the intermediate transfer belt 1 are set as follows. Assuming that the point where the intermediate transfer belt 1 and the photoconductor belt 3 contact each other is P1 and the point where the intermediate transfer belt 1 and the photoconductor belt 3 are apart from each other is P2, the transfer rollers 50a, 5
0b is arranged outside the distance d (about 10 to 15 mm). Then, the intermediate transfer belt 1 is connected to the rollers 2a to 2c.
And the transfer rollers 50 a and 50 b in a state where the intermediate transfer belt 1 is stretched around the drive roller 4.
It is arranged at a position where it presses the gap p (about 0.5 to 1.5 mm) toward the side.

According to the above-described embodiment, since the toner remains charged and adheres to the photoconductor belt 3 in the developing device to maintain the charging potential, the transfer roller 50a has no charge.
By applying a potential 9 having the same polarity as that of the toner close to V (ground potential) and a predetermined transfer voltage 10 having the opposite polarity of the toner to the transfer roller 50b, the intermediate transfer in the moving direction of the intermediate transfer belt at this time is performed. As shown in FIG. 2, the belt back surface potential (potential difference with the toner) is low because the back surface potential of the intermediate transfer belt 1 is low in a state where the photoconductor belt 3 and the intermediate transfer belt 1 are close to each other and the gap is wide to some extent (A area). The toner on the body belt 3 is not prematurely transferred, and when the photosensitive belt 3 and the intermediate transfer belt 1 are almost in contact with each other, the back surface potential of the intermediate transfer belt 1 becomes high and transfer is performed. This can prevent image distortion.

As described above, by applying a voltage of the same polarity as the toner or 0 V to one transfer roller of the two conductive rollers and applying a voltage of the opposite polarity to the toner to the other transfer roller. , When the developed toner image on the photoconductor belt is transferred to the intermediate transfer belt, the transfer of toner is not promoted when the photoconductor belt and the intermediate transfer belt are close to each other and the gap is wide to some extent. However, the phenomenon of image distortion disappears because transfer is performed almost at the time of close contact.

Example 2. Although the transfer voltage 10 having a polarity opposite to that of the toner is applied to the transfer roller 50b in the first embodiment, the transfer voltage of 400V to 1400V is in the usable range according to the experimental results of the present inventors. When the voltage applied to the transfer roller 50b is 400 V or less,
Transfer failure occurs due to insufficient electric field during transfer. Also, 1
When the voltage is set to 400 V or more, the toner is excessively charged, and the toner layer on the intermediate transfer belt 1 has a high potential and repels and moves between the toners, resulting in image disturbance. From the above, the setting range is 400V to 1400V, but it is more preferable that the setting range is around 600V.

If the absolute value of the applied voltage having the same polarity as that of the toner on the transfer roller 50a is set to be equal to or higher than the applied voltage to the transfer roller 50b, even when the photosensitive belt 3 and the intermediate transfer belt 1 are in close contact with each other, the toner has the same polarity as that of the toner. Since the electric field is applied to cause the transfer failure, the transfer failure can be prevented by setting the absolute value of the voltage applied to the transfer roller 50a to be equal to or less than the applied voltage of the transfer roller 50b.

Example 3. In each of the above-described embodiments, since there is a difference in the applied voltage between the transfer roller 50a and the transfer roller 50b, the surface current flows through the intermediate transfer belt 1 due to this voltage difference. A surface current also flows on the intermediate transfer belt 1 and the photoconductor belt 3. The surface resistance of the intermediate transfer belt 1 is 10
If it is less than ⁸ ohms, the current flowing into the photoconductor belt 3 becomes large and the deterioration of the photoconductor belt 3 is promoted. On the other hand, if the surface resistance exceeds 10 ⁹ ohms, a sufficient electric field cannot be generated during transfer, resulting in transfer failure. Therefore, the surface resistance of the intermediate transfer belt 1 is preferably about 10 ⁸ ohms to 10 ⁹ ohms, and the transferability can be secured. Further, the material of the intermediate transfer belt 1 having the surface resistance of this value and having the mechanical strength and hardness is a polyimide material. By using the polyimide material for the intermediate transfer belt 1, it is possible to reduce the abrasion of the intermediate transfer belt 1 due to the contact with the photoconductor belt 3 and to deposit the conductive material such as carbon black mixed for adjusting the surface resistance value. Therefore, the adhesion of the conductive material to the photoconductor belt 3 is reduced, and the characteristic deterioration of the photoconductor belt 3 can be suppressed. Then, the mechanical strength of the intermediate transfer belt 1 is increased and the life of the intermediate transfer belt 1 can be extended.

Embodiment 4 FIG. In the first embodiment, the transfer roller 5
0b is applied with only the transfer voltage 10 having a polarity opposite to the toner of 400V to 1400V, but in the present embodiment, as shown in FIG. 3, the transfer roller 50b has a voltage having a polarity opposite to the toner and a frequency of 20Hz to 2kHz. By superimposing and applying an AC voltage having a maximum value of 10 or more, charge is removed from the photoconductor belt 3 together with the intermediate transfer belt 1, and when the photoconductor belt 3 and the intermediate transfer belt 1 are separated from each other, a gap is created between them. As the capacitance increases, the capacitance of the gap decreases and the potentials of the both increase, which prevents discharge due to dielectric breakdown. Then, the transfer memory effect of the photosensitive belt 3 is reduced, and it is possible to prevent image disturbance and deterioration of the photosensitive belt 3. According to the results of experiments conducted by the inventors, the transfer memory effect is not reduced when the AC frequency is 20 Hz or less, and the transfer efficiency is poor and the transfer becomes defective when the AC frequency is 2 kHz or more.
It is preferable to set the degree. Among them, 40 shown in FIG.
Optimal experimental results were obtained at 0 Hz. Further, the maximum value of the AC voltage needs to be set to a value higher than the voltage value of the opposite polarity in order to eliminate the charge on the intermediate transfer belt 1 and the photoconductor belt 3 and reduce the transfer memory effect of the photoconductor. There is. Therefore, the voltage of the opposite polarity to the toner is 400
The maximum value of AC voltage is about 1.2 for V-1400V.
The AC voltage was doubled.

Example 5. In the fourth embodiment, the transfer roller 5
An alternating voltage is applied to 0b in a voltage having a polarity opposite to that of the toner, but in this embodiment, a rectangular wave voltage as shown in FIG. 4 is applied, and the same effect can be obtained. In this case, the electric charge in the vicinity of the maximum value is larger than that of the sine wave, and the charge removal effect of the photosensitive belt 3 is improved.

[0025]

Since the present invention is configured as described above, it has the following effects.

By applying a voltage having the same polarity as the toner or 0 V to the transfer roller on the side where the intermediate transfer belt and the photosensitive member are close to each other and applying a voltage of the opposite polarity to the toner on the transfer roller on the side where they are separated from each other, When the photoconductor belt and the intermediate transfer belt come close to each other, the electrostatic force on the toner is small and the early transfer to the intermediate transfer belt is suppressed, so that the disturbance of the image can be prevented.

Further, the absolute value of the voltage having the same polarity as the toner applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are close to each other is applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are separated from each other. Since it is smaller than the absolute value of the voltage of the opposite polarity to that of the toner, the transfer of the toner to the intermediate transfer belt is accurately performed due to the potential gradient between the two transfer rollers, and the disturbance of the image can be prevented.

Further, since the voltage applied to the transfer roller on the side where the intermediate transfer belt and the photosensitive member are separated from each other is 400 V to 1400 V, which has the opposite polarity to the toner, there is no shortage of the transfer voltage and the toner is moved by overcharging. Can be prevented.

Further, a DC voltage and 20 Hz to 2 kHz are applied to the transfer roller on the side where the intermediate transfer belt and the photosensitive member are separated from each other.
Since the AC voltage or the rectangular wave voltage is superposed and applied, the reverse charge given at the time of transfer of the photoconductor belt is eliminated, and the discharge due to the dielectric breakdown due to the high potential between the photoconductor and the transfer roller is prevented, Further, the transfer memory effect of the photoconductor belt is reduced, and it is possible to prevent image disturbance and deterioration of the photoconductor belt.

Then, the intermediate transfer belt is constructed by blending a conductive fine powder with a polyimide base material, and has a surface resistance of 10%.
^{Since it is set to 8} to 10 ⁹ ohms, the surface current due to the potential gradient between the transfer rollers is set to an appropriate value, the deposition of the conductive material from the intermediate transfer belt is suppressed, and the characteristic deterioration of the photosensitive belt is reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a transfer device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the state of the back surface potential in the moving direction of the intermediate transfer belt in this embodiment.

FIG. 3 is a waveform diagram showing a voltage applied to the transfer roller in the embodiment of the present invention.

FIG. 4 is a waveform diagram showing a voltage applied to the transfer roller in the embodiment of the present invention.

FIG. 5 is a configuration diagram showing a conventional transfer device.

[Explanation of symbols]

1 Intermediate transfer belt 2a Drive roller
2b Driven roller 2c Backup roller 3 Photosensitive belt
4 Drive rollers 50a, 50b Transfer rollers 9 and 10 Transfer voltage

Claims (6)

[Claims] 1. A photoconductor carrying toner on which a latent image has been developed, an intermediate transfer belt which is brought into contact with the photoconductor with a predetermined length, and a contact and separation between the intermediate transfer belt and the photoconductor. In a transfer device including two conductive transfer rollers respectively disposed on the back side of the intermediate transfer belt near the point, a transfer roller of the transfer rollers on the side where the intermediate transfer belt and the photoconductor are in close contact with each other. And a voltage of 0 V having the same polarity as that of the toner on the photoconductor, and a voltage having the opposite polarity of the toner to the other transfer roller. 2. The absolute value of the voltage of the same polarity as the toner applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor meet and approach each other is applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor meet and separate. 2. The transfer device according to claim 1, wherein the transfer voltage is set to be smaller than the absolute value of the voltage having a polarity opposite to that of the generated toner. 3. The voltage applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are separated from each other is 40
The transfer device according to claim 1 or 2, wherein the transfer device has a voltage of 0V to 1400V. 4. A DC voltage and an AC voltage having a maximum value of 20 Hz to 2 kHz which is equal to or higher than the DC voltage are superimposed and applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are separated from each other. The transfer device according to claim 3. 5. A DC voltage and a rectangular wave voltage having a maximum value of 20 Hz to 2 kHz which is equal to or higher than the DC voltage are superimposed and applied to the transfer roller on the side where the intermediate transfer belt and the photoconductor are separated from each other. The transfer device according to any one of claims 1 to 3. 6. The intermediate transfer belt is formed by mixing conductive fine powder with a polyimide material and has a surface resistance of 10 ⁸ to 10 ^8.
The transfer device according to any one of claims 1 to 5, wherein the transfer device is ⁹ ohms.