JPH0764421A - Image forming device - Google Patents

Abstract

PURPOSE:To suppress the influence of heat generated by a heat fixing device on a transfer belt and to ensure that a transfer material is conveyed to the heat fixing device. CONSTITUTION:A transfer belt 2 is spaced sufficiently from a heat fixing device 8 to be free from the influence of heat generated by a fixing roller 8a, and an intermediate conveying roller 7 for conveying transfer paper 10 is provided between the transfer belt 2 and the heat fixing device 8. At least the surface of contact of the intermediate conveying roller 7 with the transfer material is installed electrically as a conductive member so as to obtain a static eliminating effect. Also, the amount of suspended toner attaching to the transfer paper 10 can be reduced by fuzzing the surface of contact.

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, and the latent image is visualized with a developer from a developing device, and then transferred onto a transfer material (transfer paper, OHP sheet, etc.) from a paper feeding device using a transfer device. Then, the heat is fixed by a fixing roller.

In such an image forming apparatus, the process in which the developer is transferred from the photoconductor to the transfer material will be described in detail. When the transfer material imparts an electric charge to the transfer material, the transfer material and the surface of the photoconductor are exposed. An electric field is generated between the two, and the developer (toner) having a charge is attracted to the transfer material side and transferred by the electric field.

Conventionally, a corona charger has been used as a transfer device for applying an electric charge to a transfer material. FIG. 6 shows an example of a main configuration of an image forming apparatus including a transfer device using the corona charger. In FIG. 6, the transfer paper 10, which is the transfer material that has received the transfer of the developer by the corona charger 31 from the photosensitive drum 1 that is an image carrier, is neutralized by the static eliminator 32 and then thermally fixed by the transport belt 33. It is conveyed to the apparatus 8 and thermally fixed.

However, since the corona charger gives electric charges to the transfer material by corona discharge, ozone is generated at the time of transfer. Therefore, in the image forming apparatus including the transfer device using the corona charger, a device for removing the generated ozone is required, which complicates the configuration and causes a cost increase.

In order to solve the above problems, in recent years, a belt transfer system has been used in which a transfer material is conveyed by a transfer belt and brought into contact with the surface of a photosensitive member to perform transfer. FIG. 7 shows an example of a conventional image forming apparatus adopting a belt transfer method. In FIG. 7, the transfer paper 10 is
The transfer belt 2 wound around the drive roller 3 and the driven roller 4 and rotated in the direction of arrow B conveys the paper to the left in the drawing, and is sandwiched between the photosensitive drum 1 and the transfer belt 2 which rotate in the direction of arrow A. , Comes into contact with the surface of the photosensitive drum 1.

At this time, a voltage is applied from the power source 20 to the bias applying roller 5, and the transfer current I ₁ flows to the photosensitive drum 1 through the transfer belt 2 whose electric resistance is medium resistance, so that transfer is performed. A part of the current I ₂ flows to the left on the transfer belt 2 and returns from the feedback plate 6 to the power source 20. The transfer paper 10 that has received the transfer of the developer is transferred to the transfer belt 2
Is conveyed to the heat fixing device 8. Reference numeral 9 is a fixing entrance guide plate.

In such a belt transfer system, the transfer current flows through the contact portion between the photosensitive member and the transfer belt, and corona discharge is not performed, so that ozone is not generated. Also,
In this method, the transfer belt conveys the transfer material from the transfer section to the fixing section.

[0009]

However, the conventional belt transfer type image forming apparatus has a problem that the transfer efficiency is changed. In the belt transfer method, the transfer efficiency is determined by the transfer current flowing to the photoconductor, but the magnitude of the transfer current depends on the resistance value of the transfer belt. Therefore, the resistance value of the transfer belt is generally strictly controlled at the time of production. However, since the transfer belt is extended to the vicinity of the thermal fixing device for transporting the transfer material, the resistance value of the transfer belt changes due to the heat of the thermal fixing device, which may change the transfer efficiency. understood.

As described above, the transfer belt is required to have a constant resistance value as a transfer function. Further, it is required that the transfer belt does not chemically affect the photoconductor because it comes into contact with the photoconductor and that the transfer belt does not chemically affect the photoconductor because it comes into contact with the photoconductor. . Therefore, although a material that satisfies all of these requirements is used for the transfer belt, there is a problem that the resistance value changes due to heat.

Since the transfer belt is required to have various characteristics as described above, it is usually used for the transport belt 33 which is required to have only the transport function in the image forming apparatus shown in FIG. It is not possible to select materials such as silicone rubber and urethane rubber, which have high heat resistance. Therefore, in the transfer belt extended to the vicinity of the heat fixing device, there is a problem that the transfer belt is mechanically deformed by the heat of the heat fixing device.

Therefore, it is conceivable to increase the distance between the rear end portion of the transfer belt 2 and the heat fixing device 8 as shown in FIG. 8, but then, the transfer paper 10 is a small size thick paper such as a postcard. In this case, when curled on the transfer belt 2 during the conveyance, there is a possibility that the conveyance force of the transfer belt 2 may make it impossible to convey to the fixing device 8.

The present invention has been made in view of the above points, and it is possible to maintain good transfer quality by reducing the influence of heat on the transfer belt by the heat fixing device and to reliably transfer the transfer material. An object is to provide an image forming apparatus.

[0014]

In order to achieve the above object, the present invention electrostatically transfers an image formed on a material having a medium electric resistance and formed on an image carrier onto a transfer material. An image forming apparatus including a transfer belt that conveys the transfer material, and a heat fixing device that fixes the transferred image on the transfer material conveyed by the transfer belt by heat,
Intermediate transfer means for transferring the transfer material is provided between the transfer belt and the heat fixing device.

In the image forming apparatus, it is preferable that the contact portion of the intermediate conveying means with the transfer material is made of a conductive member and is electrically grounded. Further, it is preferable that the contact portion of the intermediate conveying means with the transfer material is formed into a bristle brush shape.

[0016]

According to the present invention, since the intermediate conveying means is interposed between the transfer belt and the heat fixing device, the influence of the heat of the heat fixing device on the transfer belt is reduced and the transfer material is surely conveyed. Can be sent to a heat fixing device.

If the contact portion of the intermediate conveying means with the transfer material is conductive and is electrically grounded, the charge of the transfer material provided by the transfer belt can be removed during the conveyance by the intermediate conveying means. . Further, when the contact portion of the intermediate conveying means with the transfer material is in the shape of a bristle brush, it is possible to make it difficult for the floating toner attached to the intermediate conveying means to adhere to the transfer material.

[0018]

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. 7 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 is made of a rubber material having an electric resistance of medium resistance, and the driving roller 3
And the driven roller 4 and are rotated counterclockwise (direction B in the arrow) by the drive 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. Both the bias applying roller 5 and the feedback plate 5 are connected to the power source 20.

At the time of toner image transfer, the transfer paper 10 as a transfer material is fed from the driven roller 4 side of the transfer belt 2 which rotates counterclockwise. The transfer paper 10 rides on the right end portion of the upper flat surface portion of the transfer belt 2 as shown in the figure, is conveyed leftward as the transfer belt 2 rotates, and contacts the peripheral surface of the photosensitive drum 1 at the transfer portion. .

At the time of transfer, a voltage is applied from the power source 20 to the bias applying roller 5, 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, so that the toner image on the photosensitive drum 1 is transferred onto the transfer paper 10. The remaining part I ₂ of the current I ₁ flows leftward in the transfer belt 2 and returns from the feedback plate 5 to the power source 20.

The transfer paper 10 on which the toner image is transferred is a thermal fixing device 8 comprising a fixing roller 8a and a pressure roller 8b for fixing the toner on the transfer paper by heat as the transfer belt 2 rotates. Be transported to. Further, in this embodiment, an intermediate conveyance roller 7 as an intermediate conveyance means is provided between the transfer belt 2 and the thermal fixing device 8, and the transfer paper 10 conveyed by the transfer belt 2 is Upon receiving the carrying force of the intermediate carrying roller 7 which rotates in the direction of arrow C, it is guided by the fixing inlet guide plate 9 and reliably carried to the fixing device 8.

Therefore, it is possible to sufficiently separate the distance between the transfer belt 2 and the fixing device 8 to a distance where the heat of the fixing roller 8a does not affect the transfer belt 2. Also,
Even if the distance between the transfer belt 2 and the fixing device 8 is set according to the minimum size of the transfer paper to be used, and the transfer paper 10 is a card such as a postcard and curls during transportation, that Since the transfer paper 10 receives the carrying force by the intermediate carrying roller 7, it is reliably carried to the fixing device 8.

FIG. 2 shows a second embodiment of the present invention. In the second embodiment, two rollers, that is, intermediate transfer rollers 11 and 12 that rotate in the arrow direction are provided as the intermediate transfer means, and the distance between the transfer belt 2 and the fixing device 8 is set. Even when the sheets are further separated, the transfer sheet can be satisfactorily conveyed from the transfer belt 2 to the fixing device 8.

FIG. 3 shows a third embodiment of the present invention. In this embodiment, 13 is an intermediate conveyance belt as an intermediate conveyance means. This intermediate conveyor belt 13
Is hung between the intermediate conveyor belt drive roller 14 and the intermediate conveyor belt driven roller 15, and the intermediate conveyor belt drive roller 14 is driven by a drive mechanism (not shown) to rotate counterclockwise (arrow The transfer paper 10 is conveyed by rotating in the D direction). At this time, air holes are provided in the intermediate conveyance belt 13,
It is preferable to reduce the pressure inside the belt to suck the transfer paper 10 and improve the conveying force.

Since the intermediate conveyor belt 13 is required only to convey the transfer paper as a function, it has the same heat resistance as the conventional conveyor belt 33 shown in FIG. 6 (silicon rubber,
Since urethane rubber or the like can be used, the fixing device 8 can be sufficiently brought close to the fixing device 8.

FIG. 4 shows a fourth embodiment of the present invention. In this embodiment, reference numeral 16 is an intermediate conveyance roller as an intermediate conveyance means, and at least a contact portion with the transfer material is made of a conductive member such as metal and electrically grounded. . By doing so, it is possible to eliminate the electric charges that are charged on the transfer paper 10 separated by the transfer belt 2, and the electric charges that are generated on the transfer paper 10 due to the local variations in the resistance value of the transfer belt 2. Therefore, it is possible to prevent the occurrence of an abnormal image due to the variation of the charges.

FIG. 5 shows a fifth embodiment of the present invention. In this embodiment, 17 is an intermediate conveyance roller as an intermediate conveyance means, and the contact portion with the transfer material is constituted by a bristle brush member.

As a result, the contact area between the transfer paper 10 and the intermediate transfer roller 17 is reduced, and even if the surface of the intermediate transfer roller 17 is soiled by the floating toner, the back surface of the transfer paper 10 is reduced. There is less chance of getting dirty. If the intermediate conveying roller 17 is also electrically grounded by using a conductive material as a bristle brush-like member, it is possible to obtain the same static elimination effect as in the fourth embodiment.

[0032]

As described above, according to the present invention, it is possible to minimize the influence of heat on the transfer belt by the thermal fixing device and prevent the resistance value of the transfer belt from changing. Therefore, it is possible to provide an image forming apparatus having good transfer quality. Further, the transfer belt is not mechanically deformed by the heat of the heat fixing means.

Further, according to the present invention, it is possible to eliminate the electric charge of the transfer material given by the transfer belt when passing through the intermediate conveying means, and thereby the local variation in the resistance value of the transfer belt can be eliminated. As a result, it is possible to prevent the variation of the charges generated on the transfer material, and it is possible to prevent the occurrence of the abnormal image caused by the variation of the charges. Moreover, the transfer material can always be reliably conveyed to the thermal fixing device regardless of the size and thickness of the transfer material. Further, it is possible to prevent the floating toner attached to the intermediate conveying means from attaching to the transfer material, and to prevent the back side of the transfer material from being soiled as much as possible.

[0031]

[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 a third embodiment of the present invention.

FIG. 4 is a main part configuration diagram showing a fourth embodiment of the present invention.

FIG. 5 is a main part configuration diagram showing a fifth embodiment of the present invention.

FIG. 6 is a main part configuration diagram of an image forming apparatus including a transfer device using a conventional corona charger.

FIG. 7 is a main part configuration diagram showing an example of an image forming apparatus adopting a conventional belt transfer system.

FIG. 8 is a partially enlarged view for explaining the problem as well.

[Explanation of symbols]

 1: Photosensitive drum (image bearing member) 2: Transfer belt 3: Driving roller 4: Followed roller 5: Bias application roller 6 Feedback plate 7, 11, 12, 17: Intermediate conveyance roller LA 8: Thermal fixing device 10: Transfer paper 13: Intermediate conveyance belt 20: Power supply

Claims (3)

[Claims] 1. A transfer belt, which is formed of a material having an electric resistance of medium resistance, electrostatically transfers an image formed on an image carrier onto a transfer material and conveys the transfer material, and the transfer belt. An image forming apparatus having a heat fixing device for fixing the transferred image on the transfer material, which is conveyed by a belt, by heat, an intermediate conveying means for conveying the transfer material between the transfer belt and the heat fixing device. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein
The image forming apparatus, wherein the intermediate conveying means is configured such that a contact portion with the transfer material is formed of a conductive member and is electrically grounded. 3. The image forming apparatus according to claim 1 or 2, wherein the intermediate conveying unit has a bristle brush-shaped contact portion with the transfer material.