JPH075772A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the irregularity of a toner image on a transfer paper and to obtain a high-quality image when the transfer paper is separated from a transfer belt by providing a means pressing the transfer belt toward a photoreceptor from the back surface of the transfer belt facing the photoreceptor. CONSTITUTION:The pressing member 9 pressing the transfer belt 1 toward the photoreceptor 4 from the back surface of the belt 1 is provided at a nip part 6 formed by the belt 1 and the photoreceptor 4. The pressing member 9 is constituted of an insulating body and provided with an elastic flat part and a U-shaped part. Then, the U-shaped part of the belt 1 is pressed toward the photoreceptor 4 from the back surface of the belt 1. The pressing member 9 may be constituted of an electrically conductive material such as metal. In such a case, it is preferable that the pressing member 9 is grounded. This reason is that the abnormal image is prevented from being formed by causing abnormal electric discharge at the pin-hole of the photoreceptor 4 from the pressing member 9 if there is the pin-hole on the photoreceptor 4 when the pressing member 9 is electrically charged. It is proper that the pressing force thereof is 25g/cm<2>.

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 a copying machine, a facsimile and a printer.

[0002]

2. Description of the Related Art Conventionally, a transfer sheet is supported and conveyed on a transfer belt, and the transfer sheet is conveyed to a nip portion formed by the transfer belt and a photoconductor to form a toner image formed on the photoconductor. There is known an image forming apparatus that transfers a sheet onto a transfer sheet.

In the image forming apparatus of this type, in JP-A-3-167579, a conductive roller is arranged in a portion of the transfer belt facing the transfer portion so as to contact the conductive layer of the transfer belt. A device is disclosed.

[0004]

However, in the apparatus disclosed in the above publication, since the conductive roller is only brought into contact with the conductive layer of the transfer belt, the transfer is performed at the nip portion where the photoconductor and the transfer belt are in contact with each other. When the paper enters, a gap is generated between the photoconductor and the transfer paper and between the transfer paper and the transfer belt.

Then, due to the action of the void, the flow of the transfer current in the void portion is deteriorated, so that the transfer charge amount is reduced. As a result, the amount of electric charge of the toner transferred onto the transfer paper also decreases, and the holding force of the toner on the transfer paper decreases.

Since the holding force of the toner on the transfer paper is small, there is a drawback that the toner image on the transfer paper is disturbed by a change in charge on the transfer paper side which occurs when the transfer paper is separated from the transfer belt. there were.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks that occur when the transfer sheet is separated from the transfer belt, and to provide an image forming apparatus in which the toner image on the transfer sheet is not disturbed. .

[0008]

SUMMARY OF THE INVENTION An image forming apparatus of the present invention comprises a photosensitive member carrying a toner image formed by developing an electrostatic latent image, a nip portion formed on the photosensitive member, and a transfer member. In an image forming apparatus having a transfer belt that supports and conveys paper, and a unit that applies a transfer bias to the transfer belt,
And a means for pressing the transfer belt toward the photoconductor from the back surface of the transfer belt facing the photoconductor.

[0009]

Function: The transfer belt is pressed toward the photoconductor by the pressing means from the back surface of the transfer belt facing the photoconductor.

[0010]

1 is a schematic sectional view of an image forming apparatus showing an embodiment of the present invention. A transfer belt 1 made of a medium resistance rubber material is wound around a driving roller 2 having a metal core whose surface is covered with a rubber material, and a driven roller 3 which is a metal roller. The photoconductor 4 and the nip portion 5 are formed and rotated in the arrow direction. A conductive rubber layer is formed on the back surface of the transfer belt 1, and the rubber layers having a high friction coefficient come into contact with each other between the transfer belt and the driving roller, so that the driving belt can be driven without slipping. The rotating force of the roller is transmitted to the transfer belt.

On the back surface of the transfer belt 1, a metal bias applying roller 7 for applying a transfer bias from a power source 6,
A metal feedback roller 8 that feeds back the applied transfer current to the power source 6 contacts.

A nip portion 5 formed by the transfer belt 1 and the photoconductor 4 is provided with a pressing member 9 for pressing the transfer belt from the back surface of the transfer belt 1 toward the photoconductor 4. The pressing member 9 is made of an insulating material and, as shown in detail in FIG. 2, is composed of an elastic flat surface portion 9-1 and a U-shaped portion 9-2. The U-shaped portion 9-2 is transferred. The transfer belt is pressed from the back surface of the belt toward the photoconductor.

The pressing member may be a conductive material such as metal, and in this case, it is desirable that the pressing member is grounded. This is because when the pressing member is charged, the pin
This is effective in preventing the abnormal image from being generated due to abnormal discharge from the pressing member to the pinhole of the photoconductor.

Next, the operation of this embodiment will be described with reference to FIG. The driving roller 2 is rotated by receiving a driving force from a driving source (not shown), and thereby the transfer belt 1 is rotated.

A transfer current I1 from a power source 7 is applied to the transfer belt 1 via a bias applying roller 7.
The applied current I1 flows in the layer direction of the transfer belt and flows into the photoconductor to contribute as a transfer current. A part of the current I1 passes through the transfer belt 1 and is fed back by the feedback roller 8. Flow into. In this embodiment, in order to keep the current (I1-I2) contributing to the transfer constant, the power supply 7 detects the feedback current I2 and controls it so that I1-I2 becomes a constant value.

The transfer sheet 10 conveyed from a sheet feeding device (not shown) is adjusted in resist, and is conveyed while being supported on the transfer belt. The transfer paper is polarized by the electric charge applied to the transfer belt, static electricity is generated by the true electric charge on the transfer belt and the separation electric charge of the transfer paper, and the static electricity is adsorbed on the transfer belt to be supported and conveyed by the transfer belt. .

The transfer paper 10 is conveyed to the nip portion 5 formed by the photoconductor 4 and the transfer belt 1, and the toner image on the photoconductor is transferred to the transfer paper by the action of the transfer current.

At the nip portion 5, the pressing member 9 presses the transfer belt 1 from the back surface thereof toward the photosensitive member 4 so that no gap is formed between the transfer belt 1 and the photosensitive member 4.

As a result of the experiment, this pressing force is 25 g / square c.
When m is appropriate and is more than m, it becomes difficult to convey the transfer paper to the nip portion, and jams and wrinkles of the transfer paper are likely to occur. When it is less than m, between the photoconductor and the transfer paper, and A gap was generated between the transfer paper and the transfer belt, and the toner image on the transfer paper was disturbed.

By making the pressing force 25 g / cm 2,
The adhesion between the photoconductor, the transfer belt, and the transfer paper is increased, the formation of voids between the members does not occur, and the transfer current applied from the bias applying roller 7 easily flows to the photoconductor 4. The charge amount of the toner transferred onto the transfer paper is sufficient and uniform. Since the toner on the transfer paper has a sufficient and uniform charge amount, the toner image will not be disturbed even if the charge on the transfer paper side changes at the separation portion from the transfer belt.

The charge amount of the transfer belt gradually decreases toward the downstream side with respect to the transfer belt conveyance direction at the transfer position, the electrostatic attraction force between the transfer belt and the transfer paper gradually weakens, and at the drive roller portion. The transfer paper is separated from the transfer belt by the curvature separation of the drive roller and the transfer paper strain, the toner image is fixed at the fixing portion, and the transfer paper is ejected outside the machine.

FIG. 3 shows another embodiment of the pressing member, in which the portion corresponding to the U-shaped portion of the pressing member of FIG. 2 is divided in the longitudinal direction.

[0023]

As described above, according to the present invention, a photoreceptor and a transfer paper,
In addition, since no gap is generated between the transfer paper and the transfer belt, the charge amount of the toner on the transfer paper becomes sufficient and uniform, and the toner image on the transfer paper is disturbed when the transfer paper is separated from the transfer belt. High quality images can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a transfer unit according to the present exemplary embodiment.

FIG. 2 is a perspective view of a pressing member of this embodiment.

FIG. 3 is a perspective view showing another embodiment of the pressing member of this embodiment.

[Explanation of sign]

 1 Transfer Belt 7 Biasing Roller 8 Feedback Roller 9 Pressing Member

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Eda 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A photoconductor carrying a toner image formed by developing an electrostatic latent image, a transfer belt which forms a nip portion on the photoconductor and supports and conveys a transfer paper, and the transfer belt. An image forming apparatus having a means for applying a transfer bias to the image forming apparatus, comprising: a means for pressing the transfer belt toward the photoconductor from the back surface of the transfer belt facing the photoconductor. apparatus. 2. The image forming apparatus according to claim 1, wherein the pressing unit is an insulator. 3. The image forming apparatus according to claim 1, wherein the pressing unit is a grounded conductor.