JP3142326B2 - Image forming device - Google Patents

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 having a transfer belt device.

[0002]

2. Description of the Related Art As is well known, in an image forming apparatus such as a copying machine or a printer, a toner-visible image carried on a photosensitive member is electrostatically transferred to a transfer member such as transfer paper. FIG. 8 shows a structure for this purpose.

FIG. 8 shows an example of a copying machine having a transfer paper transporting structure using a dielectric belt. In this copying machine, a transfer unit has a structure in which a plurality of transfer members are provided at positions facing the photosensitive drum A. A transfer belt D is provided around the rollers B and C, and is movable in the direction of the arrow shown in the figure. The transfer charger E is disposed at a position facing the photosensitive drum A with the transfer belt D interposed therebetween. As a result, the toner having the polarity opposite to that of the toner carried on the photosensitive drum A is charged, so that the transfer belt D
Is attracted by the dielectric polarization while the toner on the photosensitive drum A is electrostatically attracted onto the transfer paper.

In the above-described structure, the transfer belt D is formed of a medium-resistance dielectric belt having an electric resistance of 10 ⁸ to 10 ¹³ Ωcm. At the separation position of the transfer paper,
In order to obtain the characteristic of a low voltage, the so-called electrostatic attraction of the transfer paper due to the so-called residual charge is weakened, so that the transfer paper can be easily separated.

[0005]

However, as a structure that can exhibit the same function as the above-described structure, a structure as shown in FIG. 9, that is, a dielectric belt having the above-described resistance characteristics is used as a transfer belt, and this transfer belt is used. An experiment was conducted on a case in which a roller located on the driving side of the rollers around which the roller was wound was used as a transfer bias means having the same function as the transfer charger. Occurred. First, before describing this problem, the above-described structure will be described. Among the rollers around which the transfer belt D is wound, a roller which is disposed at a transfer position facing the photosensitive drum A and forms a drive side. The pulley B is connected to a transfer bias power source F, the pulley C located on the driven side is grounded, and a contact area with the photosensitive drum A is provided near the pulley B on the driving side. As shown in FIG. 9, a backup roller G for pressing the back surface of the belt is provided for the purpose of expanding the nip width for enlargement.

In the above-described structure, a bias roller is used in place of the transfer charger provided at the transfer position shown in FIG. 8, but this is because ozone generated by corona discharge by the transfer charger. It is used in order to prevent the occurrence and to reduce the power supply and to reduce the cost.

The problem with this structure is that, first, a bias roller is used as the transfer means, and the position of this roller is slightly smaller than the position facing the photosensitive drum A in the moving direction of the transfer belt D. 10 if placed upstream
^When a resistance value of ⁸ to 10 ¹³ Ωcm is set, good transfer can be obtained. On the other hand, transfer unevenness occurs in the rotation cycle of the belt, and uniformity of the resistance value cannot be obtained in the extended portion of the belt. There were places where the resistance value was high.

Secondly, the above-mentioned driven pulley is designed to remove residual charges on the transfer belt D by grounding the pulley. However, some of the charges remain. In some cases, due to the residual charge, peeling discharge occurs at the time of separation of the transfer paper, causing image disorder. This is especially true when a high-resistance material such as an OHP (overhead project) sheet is used as the transfer member.
It is considered that this is caused by the lack of uniformity in the resistance value of the belt because it occurs in accordance with the rotation cycle of the belt.

In the transfer structure using the above-described transfer belt, when the toner adhered to the transfer belt is removed after the transfer, conventionally, the toner is removed by a blade indicated by reference numeral H in FIG. However, when the residual potential of the toner is high due to non-uniformity of the resistance value of the transfer belt, it is difficult to remove the residual potential, and the back of the transfer paper may be stained.

In order to suppress the occurrence of such a problem,
It is important to make the resistance value of the dielectric belt uniform, but it is difficult to make it uniform because it is impossible to eliminate errors on the processing side from the viewpoint of this belt forming process, and as a result, At present, the existence of residual charges is allowed in some parts, and the resistance value becomes uneven.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus having a transfer belt device having a structure that does not cause transfer unevenness, in view of the above-described problems in the conventional transfer belt device.

[0012]

According to a first aspect of the present invention, there is provided an image forming apparatus having a transfer belt for transferring image information held on an image carrier onto a recording medium.
A first contact electrode disposed at a transfer position of the image information, to which a voltage for attracting a toner image on the image carrier to the transfer belt is applied; and a first contact electrode downstream of the transfer position in a moving direction of the transfer belt. Side and near
The second contact electrode to which the transfer belt is pushed up from behind and the nip width at the transfer position is widened and a voltage of the same polarity as the transfer voltage by the first contact electrode is applied, and the recording medium is separated from the transfer belt. It is characterized by comprising a separation position and a contact electrode that is arranged upstream of the separation position and is grounded.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the first contact electrode is a roller, and the transfer belt is stretched over a pair of rollers including the first contact electrode. An endless belt made of an elastic material, wherein a width of the transfer belt is larger than a length of the pair of rollers.

[0014]

[0015]

[0016]

According to the present invention, the resistance value in the extension direction of the dielectric belt becomes non-uniform by extending the range of action of the bias in the transfer position in the direction of movement of the dielectric belt and the downstream side of the transfer position. Is corrected to suppress the occurrence of transfer unevenness.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a schematic diagram for explaining a configuration of a main part of a transfer belt device according to an embodiment of the present invention. In FIG. 1, a transfer belt device 1 includes a transfer belt arranged to face a photosensitive drum 2. The transfer belt 3 is made of an elastic material such as urethane rubber, for example, and is hung around a pair of conductive rollers 4 and 5 to move in the direction of the arrow shown in the figure. .

As shown in FIG. 2, the transfer belt 3 has a width shorter than the axial length of the rollers 4 and 5, and is opposed to the axial ends of the rollers 4 and 5. The bending position is bent by the elasticity, so that the meandering is prevented by the so-called pre-crown effect by restoring the running position.

One of the rollers 4, 5 is
The drive side is arranged at a transfer position where the photosensitive drum 2 and a transfer sheet as a recording medium are opposed to each other. The rotation center is located upstream of the rotation center 2A of the photosensitive drum 2 in the rotation direction of the drum. 4A, and the transfer belt 3
Is brought into contact with the photosensitive drum 2 from a position on the peripheral surface of the photosensitive drum 2 on the upstream side of a perpendicular line drawn from the rotation center 2A to the transfer belt 3 in the rotation direction of the photosensitive drum 2.

The roller 4 functions as a first contact electrode for the transfer belt 3. Specifically, the photosensitive drum 2
It is connected to a bias power source 6 for setting a potential for electrostatically attracting the toner image carried on the transfer belt 3 side. The roller 5 is grounded.

A back-up roller 7 is disposed on the back side downstream of the transfer position in the moving direction of the transfer belt 3. The backup roller 7 is made up of a conductive roller and constitutes a second contact electrode for the transfer belt 3. By pushing up the transfer belt 3 from the back surface, as shown in FIG. The contact range between the transfer belt 3 and the photosensitive drum 2 is set in addition to the range α where the transfer belt 3 contacts the photosensitive drum 2 by the opposing relationship between the roller 4 and the photosensitive drum 2. The nip width corresponding to the clamping width between the transfer paper and the photosensitive drum 2 is increased. The backup roller 7 is a roller 4
Are connected to a bias power supply 6 to which the roller 4 is connected.

When the charging potential of the photoconductive layer on the photosensitive drum 2 is -800 V and the counter electrode of the toner carried on the photosensitive drum 2 is the positive electrode (+),
Charging potential of the roller 4 and the backup roller 7 is -2 to 3
When KV is applied, the range of the bias applied to the transfer belt 3 is a range from the position where the roller 4 faces the photosensitive drum 2 to the position where the roller 4 faces the backup roller 7.
That is, the bias potential application position is extended as compared with the case where only the position where the roller 4 and the photosensitive drum 2 face each other is set as the bias potential application position.

By the expansion of the bias range, the potential gradient generated between the photosensitive drum 2 and the transfer belt 3 is reduced, and the influence on the transfer unevenness due to the non-uniform resistance value of the transfer belt can be suppressed. In other words, when a bias is applied to only the roller 4 located on the driving side, as in the prior art, the photosensitive drum 2
In order to set a fairly high bias value in consideration of a potential gradient at a position where the transfer belt 3 and the transfer belt 3 are opposed to each other, at the transfer position on the transfer belt, the amount of charged charges due to uneven resistance of the transfer belt 3 becomes extremely large. Phenomena, which cause non-uniformity in the amount of electrostatic attraction of the toner, and as a result,
This causes transfer unevenness.

On the other hand, when a range in which a bias is applied at a constant potential between the roller 4 and the backup roller 7 is set, the above-described potential gradient causes the photosensitive drum 2 and the transfer belt 3 to move. At the opposite position of the transfer belt 3, it is possible to prevent the change in the amount of charged electric charge due to the non-uniformity of the resistance value of the transfer belt 3 from becoming extreme. As a result,
The electrostatic attraction of the toner is also substantially uniform.

Next, a transfer belt device according to another embodiment of the present invention will be described with reference to FIGS. The present embodiment is characterized in that a structure for preventing peeling discharge when separating transfer paper as a recording medium is provided.
The other B in the moving direction of the transfer belt 3 - at the upstream side of La 5, the b - conductive and is the same potential is grounded similarly to the La 5 B - La 8 on the back surface of the transfer belts 3 It is in contact. The conductive roller 8 is set to have a curvature that can be separated by utilizing the self-returning force depending on the stiffness of the transfer paper. The contact position is determined by the time constant (τ = C) of the belt expressed by the product of the resistance (R) of the transfer paper and the capacitance (C).
(R) The position where the relaxation of the charge amount of the transfer paper due to R) is promoted, and at least the position where the potential becomes 0 V immediately before the roller 5 as shown in FIG.

Since the present embodiment has the above configuration,
The period during which the transfer belt 3 is neutralized before reaching the roller 5 is extended. During this period, when the charge amount of the transfer paper is reduced and the transfer paper 3 reaches the roller 5, the remaining charge is removed. There is no charge. Therefore, the transfer paper is a roller 5
Is reliably separated by the self-returning force with respect to the curvature.

FIG. 6 shows a transfer device for surely removing toner adhered on the transfer belt 3. A cleaning device 9 is disposed downstream of the roller 5 in the direction of movement of the transfer belt 3.
Is a rotary brush 9A that can be brought into contact with the transfer paper carrying surface of the transfer belt 3 and a flicker bar 9 that can be brought into contact with and separated from the rotary brush 9A.
B.

Cleaning device 9 with transfer belt 3 interposed
In the position opposite to the rotating brush 9A, an opposing roller 10 which is rotatable in contact with the transfer belt 3 is disposed. The opposing roller 10 is formed of a conductive roller and is connected to a bias power supply 11 having the same polarity as the toner.

When the toner adhered to the transfer paper carrying surface of the transfer belt 3 is, for example, a positive electrode (+),
When the cleaning device 9 is opposed to the cleaning device 9, it is repelled by the bias from the opposing roller 10, flies off the belt surface, and is collected by the rotating brush 9 </ b> A of the cleaning device 9.

In the embodiment shown in FIG.
Since the electrical characteristics of the conductive roller 8 and the conductive roller 8 may be constant and low potential, for example, as shown in FIG. To satisfy this condition.

[0031]

According to the present invention, by extending the range in which the transfer bias acts, it is possible to suppress an extreme change in the charge amount caused when the resistance value of the transfer belt is not uniform due to the potential gradient. As a result, it is possible to reduce unevenness in the amount of electrostatic attraction of the toner and suppress transfer unevenness. In addition, since the charge removing roller is disposed so that the charge amount of the transfer paper until reaching the separation position is reduced through the transfer belt, the charge of the transfer paper at the separation position is almost zero at the separation position. As a result, the separation by the mechanical action can be surely performed through the self-returning property of the transfer paper due to the stiffness of the roll at the separation position, and the residual paper at the time of separation can be obtained. Peeling discharge due to electric charges can be prevented beforehand.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a main configuration of a transfer belt device according to an embodiment of the present invention.

FIG. 2 is a plan view for explaining the relationship between the transfer belt and the rollers around which the transfer belt has the essential configuration shown in FIG.

FIG. 3 is a partially enlarged schematic diagram for explaining an arrangement relationship between a roller around which a transfer belt is wrapped and a photosensitive member in the main configuration shown in FIG. 1;

FIG. 4 is a schematic view corresponding to FIG. 1 for explaining a main configuration of a transfer belt device according to another embodiment of the present invention.

FIG. 5 is a diagram for explaining a potential level of each unit in the main configuration shown in FIG. 4;

FIG. 6 is a schematic view corresponding to FIG. 1 for explaining a main configuration of a transfer belt device according to another embodiment of the present invention.

FIG. 7 is a schematic diagram corresponding to FIG. 4 for explaining a partially modified example of the main part configuration shown in FIG. 4;

FIG. 8 is a layout diagram for explaining an example of a device to which a conventional transfer belt device is applied.

FIG. 9 is a schematic diagram for explaining a problem when an experiment is performed with the same function as the configuration shown in FIG. 8;

[Explanation of symbols]

REFERENCE SIGNS LIST 1 transfer belt device 2 photoreceptor drum 3 transfer belt 4 roller located on the drive side of transfer belt and serving as first contact electrode 5 roller running around transfer belt 6 bias power supply 7 second contact Backup roller forming electrode 8 Conductive roller 9 Cleaning device 10 Opposing roller

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/16

Claims (2)

(57) [Claims] An image forming apparatus having a transfer belt for transferring image information held on an image carrier onto a recording medium, the image forming apparatus being disposed at a transfer position of the image information, A first contact electrode to which a voltage for attracting a toner image to the transfer belt is applied; and a first contact electrode disposed downstream and near the transfer position in a moving direction of the transfer belt, and the transfer belt is moved from behind. A second contact electrode to which a voltage having the same polarity as the transfer voltage by the first contact electrode is applied to increase the nip width at the transfer position, and a separation position where the recording medium is separated from the transfer belt and at a position upstream thereof. An image forming apparatus, comprising: a contact electrode disposed and grounded. 2. The image forming apparatus according to claim 1, wherein the first contact electrode is a roller, and the transfer belt is an endless end made of an elastic material stretched over a pair of rollers including the first contact electrode. An image forming apparatus, wherein the width of the transfer belt is greater than the length of the pair of rollers.