JPH04329571A - Method and device for transferring electrostatically charged toner - Google Patents

Abstract

PURPOSE:To easily obtain many transferred images from the same electrostatic latent image formed on a photosensitive body with high transfer efficiency. CONSTITUTION:A transfer belt 41 which has medium resistance and which is easily deformed is stretched by three conductive rollers 42-44 and brought into tight contact with the photosensitive drum 1 where the electrostatic latent image is formed on its surface and developed with toner 7. A transfer paper 6 being a toner carrier is inserted between the photosensitive drum 1 and the transfer belt 41 and voltage having the same polarity as the electrostatic latent image is impressed on the three conductive rollers 42-44, respectively. Then, the voltage whose absolute value is larger than the voltage impressed on the rollers 42 and 44 is impressed on the middle roller 43.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for transferring charged toner in image forming apparatuses such as electrophotographic copying machines, printers, and plain paper fax machines.

0002

[Prior Art] In an electrophotographic image forming apparatus, the surface of a photoreceptor is uniformly charged and then exposed to light in accordance with the image to be formed to form an electrostatic latent image, into which toner is applied. The charged toner is attached and developed, and the developed image formed by the charged toner is transferred to a toner carrier such as plain paper. For that transcription,
Conventionally, transfer chargers have generally been used.

However, when corona discharge transfer is performed using an electrostatic charger, the electrostatic latent image on the photoreceptor is destroyed, so only one transferred image (copy) can be obtained from the same electrostatic latent image. I couldn't. Further, there is also the problem that ozone and NOx are generated during the transfer.

[0004] Therefore, in recent years, a transfer method has been developed in which a medium resistance rubber roller (transfer roller) is placed in rolling contact with the photoconductor, and a toner carrier is inserted between the rollers to transfer the charged toner on the photoconductor to the toner carrier. It was done. In this case, a voltage of about 800 V is applied to the transfer roller, but the voltage on its surface becomes about 400 V due to the voltage drop due to the resistance of the rubber layer. According to this transfer method, the electrostatic latent image on the photoreceptor is not destroyed during transfer, so by repeatedly developing and transferring the same electrostatic latent image, dozens of transferred images (copies) can be created. Moreover, there is an advantage that ozone and NOx are not generated.

[0005]

However, in the conventional transfer method using such a transfer roller, the transfer voltage was as low as about 400 V, resulting in low transfer efficiency and low density of the transferred image. Therefore, it is possible to increase the transfer efficiency by increasing the voltage applied to the transfer roller, but if this is done, an electric field greater than the Pasche discharge curve will be applied to the thin air layer between the transfer roller and the photoreceptor, causing ionization. As a result, ozone and NOx are generated, and the electrostatic latent image on the photoreceptor may be destroyed.

[0006] In order to solve this problem, two films charged with different polarities are used. First, the high-potential film is superimposed on a transfer paper serving as a toner carrier, and the toner is sufficiently transferred.
Next, a method has been proposed in which a film of low potential and opposite polarity is further stacked, and an electric field below Pasche's discharge curve is created without reversely transferring the toner, and then the transfer paper is peeled off from the photoreceptor. Although this method is correct in principle, it is difficult to put it into practical use as a device.

The present invention has been made in view of the above points, and has an object to easily obtain a large number of transferred images with high transfer efficiency from the same electrostatic latent image on a photoreceptor. purpose.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an endless belt with medium resistance and easy deformation for a photoreceptor on which an electrostatic latent image is formed and developed with toner. Three conductive rollers are stretched and brought into close contact, and a toner carrier such as plain paper is inserted between the photoreceptor and the endless belt, and the same electrostatic latent image is applied to each of the three conductive rollers. A charged toner transfer method characterized by applying a polar voltage and making the absolute value of the voltage applied to an intermediate transfer roller larger than the absolute value of the voltage applied to rollers on the entrance side and exit side of the toner carrier. I will provide a.

[0009] It is desirable to apply a voltage to the rollers on the entrance side and the exit side so as not to cause dielectric breakdown of the air between them and the photoreceptor. Further, it is desirable to form an electric field between the roller on the exit side and the photoreceptor so that no reverse displacement occurs.

Furthermore, a medium-resistance, easily deformable endless belt is stretched by three conductive rollers and brought into close contact with the photoreceptor, on which an electrostatic latent image is formed and developed with toner. , configured so that a toner carrier such as plain paper is inserted between the photoreceptor and the endless belt,
A voltage having the same polarity as that of the electrostatic latent image is applied to each of the three conductive rollers, and the voltage applied to the intermediate roller has a higher absolute value than the voltage applied to the rollers on the entrance and exit sides of the toner carrier. The present invention also provides a charged toner transfer device provided with voltage application means for applying a large voltage.

[0011]

[Function] According to such a charged toner transfer method and transfer device, the potential difference between the endless belt and the photoreceptor at the entrance and exit of the toner carrier can be made equal to or less than Pasche's discharge curve. Ionization due to dielectric breakdown does not occur, and no harmful ozone or NOx is generated.

On the other hand, an intermediate conductive roller (transfer roller)
By creating a sufficient potential difference with the photoreceptor, it is possible to increase the transfer efficiency of charged toner. Since corona discharge is not used, the electrostatic latent image remains undestructed on the photoreceptor even after transfer, and by repeating development and transfer, any number of transferred images (copies) can be obtained from the same latent image. be able to.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a configuration diagram around the photoreceptor of an electrophotographic apparatus using a charged toner transfer device according to the present invention.
FIG. 1 is an enlarged view of the vicinity of the transfer device for explaining the transfer action.

In FIG. 2, reference numeral 1 denotes a photosensitive drum rotated in the direction of arrow A, and the outer periphery of the drum 11 made of metal such as aluminum is coated with selenium (Se) or organic optical semiconductor (OPC).
The photosensitive layer 12 is formed as shown in FIG. A charging device 2, a developing device 3, a transfer device 4, and a cleaning device 5 are arranged around the photosensitive drum 1.

The charging device 2 is a conventionally known contact type charging device, in which a charging belt 21 made of an endless belt made of a conductive flexible material such as conductive rubber is stretched by three conductive rollers 22. The conductive roller 2b is then brought into close contact with the surface of the photosensitive layer 11 of the photosensitive drum 1, and a charging voltage is applied to the conductive roller 2b, so that the charging belt 21 is rotated following the rotation of the photosensitive drum 1 in the direction of arrow A. While moving the photosensitive layer 12
The surface of the device is uniformly charged, in this example, positively (+).

The surface of the photosensitive layer 11 of the photosensitive drum 1 charged by the charging device 2 is exposed to light in accordance with the image to be formed by an exposure device (not shown), and the positive charge on the exposed portion is dissipated to become static. Forms an electrolatent image. This photosensitive layer 1
The electrostatic latent image on 1 is developed by a developing roller 31 that rotates in the direction of arrow B when passing through the developing device 3 and is developed by attaching negatively charged toner 7 to the developing roller 31 .

The developed image formed by the charged toner 7 is transferred by a transfer device 4 onto a transfer paper (plain paper) 6 which is a toner carrier. As shown enlarged in FIG. 1, this transfer device 4 includes:
A transfer belt 41, which is an endless belt with medium resistance and easy to deform, is stretched by three conductive rollers 42 to 44 and brought into close contact with the photosensitive layer 12 of the photosensitive drum 1. Rotate it so that it moves with the rotation.

Then, the photoreceptor layer 12 and the transfer belt 4
A transfer paper 6 is inserted between the paper 1 and the paper 1. Hereinafter, the roller 42 on the entrance side of the transfer paper in this transfer device 4 will be referred to as an entry roller.
The intermediate roller 43 is called a transfer roller, and the exit side roller 44 is called a separation roller.

At this time, the entrance roller 42 is powered by a power source 45, the transfer roller 43 is powered by a power source 46, and the separation roller 44 is powered by a power source 47, each of which has the same polarity as the electrostatic latent image on the photosensitive layer 12 (the example shown in the figure). In this case, a positive voltage is applied, and the voltage E2 is applied to the transfer roller 43 by the power source 46.
The absolute value of is made larger than the absolute value of voltages E1 and E3 applied to the entrance roller 42 and separation roller 44 by the power supplies 45 and 47, respectively. Although the power supplies 45 to 47 are shown individually, it goes without saying that the applied voltages E1 to E3 may be output from a common power supply circuit.

To explain a more specific numerical example of this transfer device 4, the transfer belt 41 has an electrical resistance of 10
It is a polyester film with a thickness of 75 μm adjusted to 6 to 10 9 Ω/cm 2 . Each of the rollers 42 to 44 is made of pure aluminum and a low resistance rubber layer (for example, 5 mm thick, specific resistance value 105
~106Ω/cm).

[0021] When the latent image potential is set to +700V (
It is assumed that the toner 7 is negatively charged), E1 = +350V is applied to the entrance roller 42, and E1 = +350V is applied to the transfer roller 43.
E2 = +1500V to the separation roller 44, E3= to the separation roller 44
Apply +350V to each.

In this way, the transfer belt 41 (+350V) and the photosensitive drum 1 are connected at the entrance and exit of the transfer paper 6.
Since the difference between the upper latent image potential (+700 V) and the background potential (~0 V) is less than Pasche's discharge curve, ionization due to dielectric breakdown of the air does not occur at that point.

On the other hand, since a potential difference of 800 V or more is generated between the transfer roller 43 and the photosensitive layer 12, about 90% of the toner 7 is transferred from the photosensitive layer 12 onto the transfer paper 6. As the transferred toner 7 approaches the separation roller 44 (+350V), an electric field is applied in the direction of reverse transfer onto the photosensitive layer 12, but the toner 7 is applied to the transfer paper 6 not only by electrostatic force but also by van der Wals force, etc. Because it is attached, there is almost no reverse transfer in a weak electric field.

Note that if the potential of the latent image is lowered by uniform exposure before transfer, the voltage applied to each of the rollers 42 to 44 can be lowered accordingly. In addition, rollers 42 and 43
, and between 43 and 44, no current leak occurs because the transfer belt 41 has medium resistance, and the potential changes little by little. Toner remaining on the surface of the photosensitive drum 1 after transfer is removed by a cleaning brush 51 and a cleaning blade of the cleaning device 5.

However, since the electrostatic latent image remains on the photosensitive layer 12 of the photosensitive drum 1 without being destroyed even after the transfer,
If multiple sheets of the same transferred image (copy) are required, the same image can be transferred to the next transfer paper 6 by repeating the development and transfer process again. According to the transfer method and transfer device of this embodiment described above, the following effects can be obtained.

(1) One endless transfer belt
The structure of the transfer device is relatively simple because the conductive roller of the book rotates the photoreceptor in the same direction and at the same speed. (2) Therefore, jams at the entrance and exit of the transfer paper are less likely to occur when using the conventional corona discharge type transfer device.

(3) Since a medium-resistance transfer belt is used, there is no current leakage, and a predetermined potential can be obtained at each part of the transfer belt. (4) At the entrance and exit where a thin air layer is formed, the potential difference between the transfer belt and the photoreceptor is less than Pasche's discharge curve, which eliminates harmful ozone and NO caused by air ionization.
There is no occurrence of x.

(5) Since there is almost no extra air layer between the transfer roller and the photoreceptor, transfer efficiency can be increased by applying a high voltage to the transfer roller. (6) Since no corona transfer current flows, there is almost no deterioration of the electrostatic latent image after transfer, and it is possible to obtain a large number of transferred images (copies) by repeating development and transfer from the same latent image.

[0029]

As explained above, according to the present invention, a large number of transferred images can be obtained from the same electrostatic latent image on a photoreceptor with high transfer efficiency, and jamming of the toner carrier can be avoided. It also does not generate harmful ozone or NOx. Moreover, the configuration of the transfer device is relatively simple and can be easily implemented.

[Brief explanation of drawings]

FIG. 1 is an enlarged view of essential parts for explaining the transfer action of a transfer device 4 shown in FIG. 2, which is an embodiment of the present invention.

FIG. 2 is a diagram showing the configuration around a photoreceptor of an electrophotographic apparatus using a charged toner transfer device according to the present invention.

[Explanation of symbols]

1 Photosensitive drum 2 Charging device
3 Developing device 4 Transfer device 5 Cleaning device 41 Transfer belt 42
Entry roller 43 Separation rollers 45, 46, 47 Power supply

Claims (4)

[Claims] Claim 1: A medium-resistance, easily deformable endless belt is stretched by three conductive rollers and brought into close contact with a photoreceptor on which an electrostatic latent image is formed and developed with toner. A toner carrier such as plain paper is inserted between the photoreceptor and the endless belt, and a voltage of the same polarity as the electrostatic latent image is applied to each of the three conductive rollers, and the voltage is applied to the middle roller among them. A method for transferring charged toner, characterized in that the absolute value of the voltage applied to the toner carrier is made larger than the absolute value of the voltage applied to the rollers on the entrance side and the exit side of the toner carrier. 2. The charged toner transfer method according to claim 1, wherein a voltage of a magnitude that does not cause dielectric breakdown of air between the rollers and the photoreceptor is applied to the rollers on the entrance side and the exit side. Characteristic charged toner transfer method. 3. The charged toner transfer method according to claim 1 or 2, wherein an electric field is formed between the exit side roller and the photoreceptor so that no reverse displacement occurs. . 4. A medium-resistance, easily deformable endless belt is stretched by three conductive rollers and brought into close contact with a photoconductor on which an electrostatic latent image is formed and developed with toner. , a toner carrier such as plain paper is inserted between the photoreceptor and the endless belt, and a voltage of the same polarity as the electrostatic latent image is applied to each of the three conductive rollers, A charged toner transfer device characterized in that a voltage applying means is provided to an intermediate roller for applying a voltage whose absolute value is larger than the voltage applied to the rollers on the entrance side and the exit side of the toner carrier.