JPH07271200A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus in which the separation performance of a transfer material from an image carrier is good and the image quality is improved. In an image forming apparatus that performs transfer by a transfer belt 2 formed of a material having medium resistance, the transfer paper 10 is electrically grounded in proximity to a position separated from the transfer belt 2. Since the property guide plate 21 is provided, even if electric charges are present on the toner image bearing surface of the transfer material, this does not cause peeling discharge and prevents the occurrence of abnormal images.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an optical printer such as a laser printer using an electrophotographic process, a copying machine, and a facsimile machine.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a laser printer, the surface of a drum-shaped or belt-shaped photosensitive member (image carrier) is charged by a charger and then exposed by an exposure device. An electrostatic latent image is formed, the latent image is visualized with a developer from a developing device, and then the latent image is transferred onto a transfer material (transfer paper, OHP sheet, etc.) from a paper feeding device using a transfer device. It is then transferred to and fixed by a fixing device.

A corona transfer charger is conventionally used as a transfer device in such an image forming apparatus. The transfer process by the corona transfer charger will be described in detail. By applying a charge to the transfer material by corona discharge,
An electric field is created between the transfer material and the surface of the image carrier, and the developer (toner) having a charge is attracted to the transfer material side by the electric field and transferred.

In the transfer process using the corona transfer charger, the transfer material is electrostatically adsorbed to the image carrier by the charge applied to the transfer material, so that the transfer material is separated from the image carrier after the transfer. In addition, a static eliminator that appropriately removes the charge of the transfer material is required. In this static elimination process, if the charge of the transfer material is removed too much, the force of attracting the toner becomes weak and transfer failure occurs. On the contrary, if the charge is removed too little, the transfer material cannot be separated. However, since the amount of electric charge applied to the transfer material by the corona transfer charger changes depending on the environment and the like, it is difficult to always perform proper charge removal, and due to variations in the charge removal process, separation defects or transfer defects occurred. .

In order to solve the above problems, in recent years, a belt transfer system has been used in which transfer is performed by a transfer belt having a medium resistance to which a voltage is applied and the transfer paper is brought into contact with the surface of the photosensitive drum to perform transfer. . FIG. 3 shows an example of a conventional image forming apparatus adopting a belt transfer method. In FIG. 3, the transfer paper 10 is transported while being guided by the entrance guide plates 12 and 13 by the transport roller pair 11, and reaches the vicinity of the contact portion between the photosensitive drum 1 and the transfer belt 2. And
The transfer paper 10 is a photosensitive drum 1 that rotates in the direction of arrow A,
It is made of a medium resistance material, is wound around a driving roller 3 and a driven roller 4, and is sandwiched by a transfer belt 2 which rotates in the direction of arrow B, and comes into contact with the surface of the photosensitive drum 1.

At this time, the bias applying roller 5 has a power supply 2
A voltage is applied by 0. Therefore, the transfer paper 10
Is transferred by the toner by the electric field generated by the electric charge of the transfer belt 2 at the contact portion with the photosensitive drum 1.
Here, the surface of the transfer paper 10 in contact with the transfer belt 2 is dielectrically polarized by the electric charge of the transfer belt 2 and
Since 0 is electrostatically adsorbed on the transfer belt 2, the transfer paper 10 is transferred to the photosensitive drum 1 without providing any special means.
Easily separated from. Therefore, in the image forming apparatus adopting the belt transfer system having such a medium resistance transfer belt, the separability of the transfer paper 10 from the photosensitive drum 1 is very good.

Then, the transfer paper 10 having undergone the transfer is conveyed while being attracted by the transfer belt 2 and separated from the transfer belt 2 at the position of the driving roller 3. Here, a feed back plate 6 which is a metal plate connected to a power source 20 is disposed in contact with the inner peripheral surface of the transfer belt 2 between the bias applying roller 5 and the driving roller 3 for driving. Since the electric potential of the transfer belt 2 near the roller 3 is low, the transfer paper 10 is easily separated from the transfer belt 2. And the transfer paper 1
0 is guided by the exit guide plates 14 and 15 and conveyed to the fixing roller pair 16 so that the toner image on the transfer paper 10 is fixed.

[0008]

However, the image forming apparatus adopting the conventional belt transfer system has a problem in that a black spot-like or polka dot-like abnormal image occurs. This is because when the transfer paper 10 is separated from the photosensitive drum 1, peeling discharge occurs between the photosensitive drum 1 and the transfer paper 10 due to the electric charge of the transfer belt 2, and the toner image bearing surface side of the transfer paper 10 is generated. Is charged. And the transfer paper 1
When the transfer paper 10 is separated from the transfer belt 2 in the transport process downstream of the transfer unit of 0, the electric charge on the toner image bearing surface side of the transfer paper 10 increases away from the conductor, and the electric potential rises. Peeling discharge occurs between the paper 10 and the transfer belt 2 having a low potential. Then, it is considered that the toner moves due to the movement of the electric charges at this time and the above-mentioned abnormal image is generated.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus in which the separation property of the transfer material from the image carrier is good and the image quality is improved. .

[0010]

In order to achieve the above-mentioned object, the present invention is made of a material having an electric resistance of medium resistance, and carries and conveys a transfer material so as to pass through the transfer portion, and In an image forming apparatus equipped with a transfer belt for electrostatically transferring an image formed on a transfer material to a transfer material by an applied voltage, the transfer material is placed close to a position where the transfer material is separated from the transfer belt. A conductive guide plate for guiding is provided.

In the image forming apparatus, it is preferable that the distance between the conductive guide plate and the transfer belt is within 5 mm. Further, a conductive brush may be arranged at the downstream end of the conductive guide plate in the transfer direction of the transfer material.

[0012]

According to the present invention, the toner is transferred by the transfer belt.
Even if electric charges are present on the toner image bearing surface of the transfer material that has received the image transfer, peeling discharge does not occur when the transfer material is separated from the transfer belt, and the occurrence of an abnormal image is prevented.

Further, according to the present invention, since the distance between the conductive guide plate and the transfer belt is within 5 mm, the toner image is transferred to the toner image carrying surface of the transfer material which has been transferred by the transfer belt. Even if electric charges are present, peeling discharge when the transfer material is separated from the transfer belt can be surely prevented, and an abnormal image is surely prevented.

Further, according to the present invention, the conductive brush is disposed at the downstream end of the conductive guide plate in the transfer material conveying direction, so that the charge on the toner image bearing surface of the transfer material is gently and surely. Since it is discharged to the outside, the occurrence of abnormal images is prevented under any environment.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a main part configuration diagram showing a first embodiment of an image forming apparatus of the present invention, and the same parts as those in FIG. 3 are designated by the same reference numerals.

In FIG. 1, a photoconductive photosensitive drum 1 is shown.
Is an image carrier, which holds the toner image to be transferred on the peripheral surface and rotates in the direction of arrow A. The transfer belt 2 has a two-layer structure, and the surface layer on the side in contact with the photosensitive drum 1 is made of a material having an electric resistance of 1 × 10 ⁹ Ω to 1 × 10 ¹² Ω, and contacts the bias applying roller 5. Side back layer has an electrical resistance of 1 ×
It is made of a material of 10 ⁹ Ω to 1 × 10 ¹² Ω. The transfer belt 2 is wound around the driving roller 3 and the driven roller 4, and is rotated counterclockwise (in the direction of arrow B) by the driving roller 3.

The drive roller 3 has a rubber layer formed on the outer peripheral surface of the metal roller for enhancing frictional engagement with the transfer belt 2, and is rotated counterclockwise by a drive mechanism (not shown). The driven roller 4 is a metal roller.

The bias applying roller 5 is a metal roller, and is located at a position displaced from the contact portion between the photosensitive drum 1 and the transfer belt 2 toward the drive roller 3 by a predetermined distance.
It contacts the inner peripheral surface of the transfer belt 2 and rotates following the rotation of the transfer belt 2. The feedback plate 6 is a metal plate, and is in contact with the inner peripheral surface of the transfer belt 2 between the bias applying roller 5 and the driving roller 3. The bias applying roller 5 and the feedback plate 6 are both connected to the power source 20.

During toner image transfer, the transfer paper 10 is fed from the driven roller 4 side of the transfer belt 2 which rotates counterclockwise. That is, the transfer paper 10 is transported by the transport roller pair 11 along the entrance guide plates 12 and 13 to the vicinity of the contact portion between the photosensitive drum 1 and the transfer belt 2, which is the transfer portion.
Then, the transfer paper 10 is sandwiched between the photosensitive drum 1 and the transfer belt 2, and is conveyed to the left in the drawing as the two rotate. At the time of transfer, a voltage is applied to the bias applying roller 5 from the power source 20 and a current I ₁ flows. A part of this current I ₁ flows rightward through the transfer belt 2 having an electric resistance of medium resistance and becomes a transfer current I ₂ , and the toner image on the photosensitive drum 1 is transferred onto the transfer paper 10. The remaining portion I ₃ of the current I ₁ flows through the transfer belt 2 and is fed from the feedback plate 6 to the power source 20.
Return to.

In such a belt transfer system, when the voltage applied to the bias applying roller 5 is kept constant, a change in the resistance value of the transfer belt 2 and the transfer paper 10 due to environmental changes, and the transfer belt 2 itself. Since the resistance value between the bias applying roller 5 and the photosensitive drum 1 changes depending on the resistance unevenness, the type of the transfer paper 10, the area of the image portion formed on the photosensitive drum 1, etc., the transfer to the photosensitive drum 1 is performed. The current I ₂ changes. When the transfer current flowing to the photosensitive drum 1 changes, the transfer efficiency changes accordingly, and stable image formation cannot be performed.

Therefore, it has been conventionally practiced to control the voltage of the power source 20 so that the difference between the current I ₁ flowing from the power source and the current I ₃ flowing from the feedback plate 6 to the power source 20 becomes constant. As a result, the transfer current I ₂ flowing to the photosensitive drum 1 can be kept constant, and a predetermined transfer efficiency can be maintained. In this embodiment, the toner has a positive polarity and the transfer current I ₂ is -50.
It is set to be μA

In this way, the transfer paper 10 having the toner image transferred at the transfer portion is conveyed by the transfer belt 2 and reaches the position of the drive roller 3. At this time, as described above, the transfer belt 2 between the bias applying roller 5 and the driving roller 3
A metal plate connected to the power source 20 is provided on the inner peripheral surface of the fuse.
Since the duck back plate 6 is arranged in contact with the transfer belt 2 in the vicinity of the driving roller 3 and the electric potential of the transfer belt 2 is low, the transfer paper 10 is easily separated from the transfer belt 2. And
The transfer paper 10 is guided by the exit guide plates 14 and 15 and conveyed to the fixing roller pair 16 so that the toner image on the transfer paper 10 is fixed.

In such an apparatus, when the transfer paper 10 is separated from the transfer belt 2 when the transfer paper 10 is conveyed downstream of the transfer portion as described above, the transfer paper is charged by the charge on the toner image bearing surface. A peeling discharge occurs between the transfer belt 10 and the transfer belt 2 having a low potential, which causes an abnormal image.

In this embodiment, a conductive guide plate 21 which is electrically grounded is provided near the position where the transfer paper 10 is separated from the transfer belt 2. by this,
The situation where the charge on the toner image bearing surface of the transfer paper 10 suddenly moves away from the conductor is avoided, and the charge on the toner image bearing surface of the transfer paper 10 is gently passed through the electrically conductive guide plate 21 which is electrically grounded. To be discharged. Therefore, the peeling discharge does not occur, and the occurrence of an abnormal image is prevented. According to experiments, particularly good results were shown when the distance between the conductive guide plate 21 and the transfer belt 2 was within 5 mm. Therefore, the conductive guide plate 21 and the transfer belt 2
Are preferably provided close to each other within 5 mm. In addition, compared to the case of using the conventional insulating guide plate,
Since the transfer paper 10 is conveyed while being attracted to the conductive guide plate 21, the rear end of the transfer paper 10 is not lifted from the transfer belt 2 and the transferability is improved.

FIG. 2 shows the construction of the essential parts of a second embodiment of the present invention. In the second embodiment, a conductive brush 22 that is electrically grounded is arranged at the downstream end of the conductive guide plate 21 with respect to the transfer paper conveyance direction.

That is, in the first embodiment, the transfer paper 10 separated from the transfer belt 2 does not generate the peeling discharge and is conveyed to the fixing roller pair 16. At this time, however, the transfer paper 10 depends on the environment. Since the resistance value of No. 1 changes, there is a possibility that the above-mentioned conductive guide plate 21 does not sufficiently eliminate static electricity under a special environment. If the charge is not sufficiently removed, the transfer paper 10 moves away from the conductive guide plate 21 while the charges are present on the surface of the image carrier, which causes peeling discharge and an abnormal image. In this embodiment,
Since the electrically conductive brush 22 that is electrically grounded and has a better charge removal property than the conductive guide plate is provided, in order to gently and sufficiently discharge the electric charge remaining on the toner image bearing surface of the transfer paper 10. It is possible to reliably prevent the occurrence of peeling discharge and prevent the occurrence of abnormal images in any environment.

[0027]

As described above, according to the present invention, even if electric charge exists on the toner image bearing surface of the transfer material which has received the transfer of the toner image by the transfer belt, the transfer material is transferred to the transfer belt. Separation discharge does not occur at the time of separating from, and the generation of an abnormal image is prevented. Therefore, it is possible to provide the image forming apparatus in which the transfer material has a good separability from the image carrier and the image quality is improved.

Further, according to the present invention, since the distance between the conductive guide plate and the transfer belt is within 5 mm, the toner image bearing surface of the transfer material on which the toner image is transferred by the transfer belt is transferred. Even if electric charges are present, peeling discharge when the transfer material is separated from the transfer belt can be surely prevented, and an abnormal image is surely prevented. Therefore,
It is possible to provide an image forming apparatus in which the transfer material has good separability from the image carrier and which has improved image quality.

Further, according to the present invention, the conductive brush is disposed at the downstream end of the conductive guide plate in the transfer material conveying direction, so that the charge on the toner image bearing surface of the transfer material is gently and surely ensured. Since the discharge is performed, it is possible to prevent the occurrence of an abnormal image in any environment. Therefore, it is possible to provide the image forming apparatus in which the transfer material has a good separability from the image carrier and the image quality is improved.

[0030]

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a main part configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a main part configuration diagram showing an example of an image forming apparatus adopting a conventional belt transfer system.

[Explanation of symbols]

 1 image carrier 2 transfer belt 3 driving roller 4 driven roller 5 bias applying roller 6 feed back plate 10 transfer paper 21 conductive guide plate 22 conductive brush

Claims (3)

[Claims] 1. A transfer material is formed of a material having an electric resistance of medium resistance, carries a transfer material so as to pass through a transfer portion, and electrostatically forms an image formed on an image carrier by an applied voltage. In an image forming apparatus provided with a transfer belt for transferring to a transfer material, an electrically grounded conductive guide plate for guiding the transfer material is provided near a position where the transfer material is separated from the transfer belt. An image forming apparatus characterized by the above. 2. The image forming apparatus according to claim 1, wherein
The distance between the conductive guide plate and the transfer belt is 5 mm.
An image forming apparatus characterized by being within the range. 3. The image forming apparatus according to claim 1, further comprising a conductive brush electrically grounded at a downstream end of the conductive guide plate with respect to a transfer direction of the transfer material. A characteristic image forming apparatus.