JPH0973241A - Transfer device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device provided with an excellent transfer property by a low electric power source. SOLUTION: At the time of non-transferring, a transferring member 8 held in contact with a photoreceptor 1 in the shaft direction, is mounted to an image forming device main body 20 through an elastic body (spring) 22. At the time of transferring, on the way for the transfer material 10 to pass in-between the photoreceptor 1 and the transfer member 8, the transfer member 8 is lowered while allowed to form a gap K whose thickness size is the same as the transfer material 10 between the photoreceptor 1 surface and the transfer member 8, therefore, the transferring member 8 is restrained from contact to the photoreceptor 1 in a non-transferring area, shift of an electric current from the transfer material 8 is prevented, therefore the toner fogging by electrification defect is restrained. Moreover, since the current shift is prevented, the transfer power source voltage can be lowly suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine,
The present invention relates to a transfer device of an image forming apparatus that electrostatically transfers a toner image on a transfer material such as a printer.

[0002]

2. Description of the Related Art As a contact roller type transfer device using a transfer roller, an elastic roller made of a conductive member covered with a conductive roller shaft provided facing a photoconductor as an image carrier is used. A sheet that is a transfer material is conveyed in a nip formed by a photoconductor and a transfer roller, and a transfer voltage is applied to a conductive roller shaft to apply a charge necessary for transfer to the back surface of the transfer material. Is well known. Such a roller transfer device has the characteristics that the transfer efficiency is good even with a low current, the generation of ozone is minute, the transfer material is fixed, and the image can be faithfully transferred.

However, since such a roller type transfer device uses an elastic body such as a conductive rubber or a conductive sponge as a transfer roller, it is said that the paper is contaminated particularly when it is transferred to a small size paper. There was a problem. This is because when the paper passes through the transfer nip, the roller and the photoconductor come into contact with the non-paper passing part, and the transfer current that should originally flow from the transfer roller to the back surface of the paper also flows to the photoconductor surface. It is a thing. For this reason, the charging current having a polarity opposite to the transfer current is canceled out, resulting in poor charging, which causes fogging of the toner and smearing of the sheet.

Therefore, in the conventional apparatus, the resistance value of the transfer roller is set to be extremely high in order to prevent the occurrence of charging failure in the non-sheet passing portion. For example, the resistance of the transfer roller is set to a high resistance value of 10 ⁸ to 10 ⁹ Ω or higher. As described above, by increasing the resistance value of the transfer roller, it was possible to suppress the phenomenon in which a larger amount of current flows to the surface of the photoconductor than to the back surface of the paper. However, in order to obtain a high resistance value, the voltage applied to the transfer roller is usually 3 to 5 kV.
Therefore, there is a problem that a very high voltage is required, which causes an increase in the power supply of the device and an increase in cost.

Therefore, it is conceivable to keep the resistance of the transfer member low in order to lower the transfer power supply voltage. However, if the resistance is lowered as described above, the paper passes through the transfer nip because the transfer member is an elastic body. At this time, the sheet passing portion is dented due to elastic deformation, and the portion where the sheet does not pass directly contacts the photoconductor, resulting in toner fogging due to poor charging in the non-sheet passing portion.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a transfer device of an image forming apparatus that maintains good transfer performance even under a low power supply voltage.

[0007]

In order to solve the above-mentioned problems, a transfer device of an image forming apparatus according to the present invention has at least a transfer member (transfer roller) which is in contact with the entire area in the axial direction of the photosensitive member at the time of non-transfer. The transfer member is formed of a rigid material, and the transfer member is movable in the direction away from the photoconductor when the transfer material passes through.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A transfer device of an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an image forming apparatus according to the present invention. The image forming apparatus according to the present invention mainly includes a photoconductor 1 which is an image carrier, a charger 3, a magnet roller 2, a transfer roller 8 which is a transfer member, a laser 4, a paper feed roller 7, and a fixing device. 9
Consists of A power source (not shown) is connected to the transfer roller 8.

FIG. 2 is an enlarged block diagram of a mounting portion of the transfer roller to the main body, and FIG. 3 is a block diagram of the transfer roller 8.
The configuration of the transfer roller will be described in detail with reference to FIGS. 2 and 3. The transfer roller 8 has a resistance layer 8a provided on the surface of a shaft 8b, and conductive bearings 21 provided at both ends. The transfer roller 8 is fixed to the image forming apparatus main body 20 via a conductive spring 22 fixed to the bearing 21. The pushing force of the spring 22 at this time is about 500.
gf. With such a pressing force, when the sheet 10 passes through the transfer nip, the PVdF layer, which is the surface layer 8a of the transfer roller 8, is deformed, and the transfer roller 8 does not pass through the non-sheet passing portion.
And the photoconductor 1 do not come into contact with each other. The resistance layer 8
a has almost no influence on the transfer performance, and its purpose is to protect the surface of the transfer roller 8 and prevent electric shock. At this time, the maximum applied voltage of the transfer power source is about 1 in 2 μA constant current control.
It is kV.

The operation of the image forming apparatus in this embodiment will be described. The charger 3 uniformly charges the photoconductor 1, and the portion exposed by the laser beam 5 is developed by the magnet roller 2 to form a toner image on the photoconductor. The toner is uniformly applied onto the magnet roller 2 by the action of the layer thickness regulating member 11. The paper 10 is sent out by the paper feed roller 7, the leading end of the paper 10 is aligned by the registration roller 6, and is conveyed to a transfer nip formed by the photoconductor 1 and a transfer roller 8 provided facing the photoconductor. It The toner remaining on the photoconductor 1 is scraped off by the cleaning blade 12.

The sheet 10 having entered the transfer nip forms a gap K in the non-sheet passing portion between the photoconductor 1 and the transfer roller 8 by pushing down the transfer roller 8 which is a rigid body. In the paper passing portion, the toner image developed on the photoconductor 1 is transferred to the paper 10 in the transfer nip, and then fixed by the fixing device 9 and discharged.

The uppermost (resistive) layer 8a of the transfer roller 8 in contact with the photosensitive member 1 is formed of PVdF (polyvinylidene fluoride) having a thickness of about 30 to 100 μm and containing carbon black as a conductive agent. The layer 8a is formed on an iron shaft 8b which is a conductive layer. At this time, the resistance value of PVdF which is the resistance layer 8a is, for example, A4 longitudinal feed 1
In a printer of about 0 ppm, it may be about 10 ⁸ Ω or less. This is because if the impedance of the photoconductor and the paper calculated from the electrostatic capacity is about 10 ⁹ Ω, and the resistance value of the surface layer of the transfer roller as a transfer member is about 10 times less than 10 ⁸ Ω. Has almost no effect on the power supply voltage.

As described above, when the sheet 10 enters the transfer nip, a gap K is formed between the photoconductor 1 and the transfer member 8 in the non-sheet passing portion by the thickness of the sheet 10, so that the transfer member is formed. Therefore, no current flows through the non-sheet passing portion of the photoconductor, and toner fogging due to poor charging does not occur. as a result,
The transfer power supply voltage can be suppressed to a low level, and good transfer performance can be obtained at a voltage of about 1/3 to 1/5 of the transfer power supply voltage of the conventional apparatus.

Next, a second embodiment of the transfer device of the image forming apparatus according to the present invention will be described. FIG. 4 is a schematic configuration diagram of the transfer device of this embodiment. The configuration other than the transfer member 80 is the same as that of the first embodiment, and the description thereof is omitted. Transfer member 80
The contact portion 26 that comes into contact with the photoconductor 1 is a plate member 2 made of iron.
5 is coated with PVdF similar to that of Example 1. The transfer member 80 is fixed to the image forming apparatus main body 20 via an elastic member 24 made of an elastic plate material such as silicon sponge. At this time, the pressing force of the transfer member 80 against the photoconductor 1 is set to about several hundred gf. The pressing force of several hundred gf does not prevent the sheet 10 as the transfer material from entering the transfer nip. Further, as in the first embodiment, when the sheet 10 enters the transfer nip, a gap K is formed between the photoconductor 1 and the transfer member 80 in the non-sheet passing portion by the thickness of the sheet, and the transfer power supply voltage is increased. Can be reduced.

Next, a third embodiment of the transfer device of the image forming apparatus according to the present invention will be described. FIG. 5 is a schematic configuration diagram of the transfer device of this embodiment. Example 1 except for the transfer member 30
Since the configuration is the same as the above, only the transfer member 30 will be described.
The portion 36 of the transfer member 30 that comes into contact with the photoconductor 1 is formed by coating the same plate-like member 35 made of iron with PVdF as in Example 1. One end of the transfer member 30 is rotatably fixed to a rotary shaft 34 fixed to the main body 20. The other end of the transfer member 30 is supported by a spring 33, which is an elastic member, and is pressed toward the photoconductor 1. At this time, the pressing force of the transfer member 30 against the photoconductor 1 is several hundred gf.
Because of this, the sheet 10 as the transfer material does not prevent the sheet 10 from entering the transfer nip. Further, as in the first embodiment, when the sheet enters the transfer nip, the non-sheet passing portion has a gap K between the photoconductor 1 and the transfer member 30 by the thickness of the sheet.
Is formed, and the effect of lowering the transfer power supply voltage is similar.

[0016]

As described above, according to the present invention, at the time of transfer, a gap can be formed between the transfer member and the photoconductor in the non-sheet passing portion by the thickness of the transfer material, so that the transfer can be performed. No current flows from the member to the non-sheet passing portion of the photoconductor, and toner fogging due to poor charging does not occur. As a result, the transfer member does not need to have a high resistance value for preventing current from flowing to the non-sheet passing portion, and even if the resistance value is low, toner fogging can be prevented.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a transfer device of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram of how a transfer member is attached to the apparatus main body.

FIG. 3 is a schematic configuration diagram of a transfer member in the first embodiment.

FIG. 4 is a schematic configuration diagram of a transfer member according to a second embodiment.

FIG. 5 is a schematic configuration diagram of a transfer member according to a third embodiment.

[Explanation of symbols]

1 photoconductor, 2 magnet roller, 3 charger, 4 laser, 5 laser light, 6 registration roller, 7 paper feed roller, 8 transfer roller,
9 fixing device, 10 paper, 12 cleaning blade, 13 transport path, 21 bearing, 22, 33
Spring, 24 elastic sponge, 25, 35
Iron conductive layer, 26, 36 resistance layer, 34 rotating shaft.

Claims (3)

[Claims] 1. A transfer device of an image forming apparatus, comprising: a photoconductor that comes into contact with a transfer material to transfer a toner image according to image information; and a transfer member that comes into contact with the entire region in the axial direction of the photoconductor when not being transferred. A transfer device of an image forming apparatus, wherein at least a portion of the transfer member that is in contact with the photoconductor is formed of a rigid material and is movable in a direction in which the transfer member is separated from the photoconductor when passing through the transfer material. 2. The image forming apparatus according to claim 1, wherein the transfer member is formed of a rigid material, is fixed to the image forming apparatus main body via an elastic member, and is biased toward the photoconductor. Transfer device. 3. The transfer device of the image forming apparatus according to claim 1, wherein the transfer member is formed of a rigid material and an elastic member, and a part of the elastic member is fixed to a main body of the image forming apparatus.