JPH02213885A - Transfer device for electrophotographic device - Google Patents

Abstract

PURPOSE:To uniformly bring a toner picture forming medium and a paper into press-contact and to prevent deterioration in toner picture quality by forming the core bar of a backup roller, which has an insulating rubber roller part, from steel. CONSTITUTION:The backup roller 20c employs a steel pipe 20c1 as the core bar, and its pheriphery is coated with the silicone rubber 20c2 as the roller part. In this case, the pressure of a second transfer roller 22 is applied to the steel pipe 20c1 via the silicone rubber 20c2 of the backup roller 20c; however, the steel pipe 20c1 is scarcely deformed by the pressure of the second transfer roller 22 since the steel pipe 20c1 is sufficiently rigid. Therefore, an intermediate transfer belt 20d and the paper 23, both of which are brought into press-contact, receive uniform pressure between both the rollers 20c and 22 irrespective of a position in the axial direction. Thus, a toner picture on the intermediate transfer belt 20d is uniformly transferred regardless of a position in the axial direction, and deterioration in copying quality, caused by ununiform pressure distribution, can be prevented.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is used in electrophotographic devices such as copying machines to transfer images onto a belt-shaped photoreceptor or intermediate transfer medium that is wound and supported around a backup roller via paper. The present invention relates to a transfer device that transfers a toner image formed on a photoreceptor or an intermediate transfer medium onto a sheet of paper by pressing a roller.

[Conventional technology]

2. Description of the Related Art Electrophotographic apparatuses use a transfer device to transfer a toner image formed on a photoreceptor onto a sheet of paper. Further, in a full-color copying machine, for example, the toner image formed on the photoreceptor is once transferred to an intermediate transfer medium, and then transferred from the intermediate transfer medium to a sheet of paper by a transfer device.

In addition to using a corona transfer method using a transfer charger, the transfer device may also employ a transfer roller method.

The transfer roller method transfers the toner image formed on the photoreceptor or intermediate transfer medium onto the paper by pressing a rotating transfer roller to which an electric charge is applied onto the photoreceptor or intermediate transfer medium through the paper. This is what I did.

When the toner image forming medium consisting of the photoreceptor and intermediate transfer medium is formed in the form of a belt, the belt-like toner image forming medium is supported by being wound around a backup roller, and is held at this position. The transfer roller is brought into pressure contact with the paper.

The overall structure of a full color copying machine employing the above transfer roller system and having an intermediate transfer belt will be described with reference to FIG.

A document table 13 on which a document 12 is placed is provided on the upper surface of the device frame 11 . A photoreceptor bell I/device 15 is disposed below the document table 13 within the apparatus frame 11 via an optical system section 14 . The optical system section 14 is
The document I2 is scanned with light from the copy lamp 14a, and the reflected light from the document 12 is guided to the exposure section of the photoreceptor belt device 15. Note that the lens 14b of the optical system section 14 is provided with three types of color filters consisting of blue, green, and red, and since the original 12 is scanned three times while replacing these filters, the photoreceptor belt device 15
Then, exposure using the transmitted light is performed for each filter in turn.

The photoreceptor belt device 15 is configured such that an endless photoreceptor belt 15c is passed around a drive roller 1.5a and a driven roller 15b, and the photoreceptor belt 1.5c is circulated and transported. The photoreceptor belt 15C has an organic photoreceptor (OPC) film formed on the outer surface of the belt. Further, a main charger 1 is provided around the photoreceptor belt device 15.
6. A developing device 17, a cleaner 18, and a static elimination lamp 19 are arranged in this order along the direction of transport of the photoreceptor belt 15c, forming an electrophotographic apparatus. Therefore, an electrostatic latent image is formed by exposing the outer surface of the photoreceptor belt 15c charged by the main charger 16 to the reflected light from the original 12 guided through the optical system section 14, and this electrostatic latent image is formed. A toner image is formed by the developing device 17 developing the electrolatent image. Note that the developing device 17 has developer tanks loaded with toner of three colors, yellow, magenta, and cyan, and performs development by switching the developer tank used for each of the three scans of the document 12. It looks like this. For this reason, the photoreceptor belt 15 that is circulated is transferred.
Toner images of yellow, magenta, and cyan toners are sequentially formed on C''2. The yellow, magenta, and cyan colors are complementary to the blue-green and red colors in the filter of the lens 14b, respectively.

Photoreceptor belt 15c in the photoreceptor belt device 15
The portion where the toner image is wound around the driven roller 15b forms a first transfer portion 15d for transferring the toner image formed by the developing device 17 to the intermediate transfer belt device 20 side. Intermediate transfer bell I to device 20, drive roller 20a and driven roller 2
An endless intermediate transfer belt 20d is hung in a triangular manner between the backup roller 20c and the intermediate transfer belt 20c.
0d is transferred in a circular manner. and,
The outer surface of the intermediate transfer bell l-20d located between the drive roller 20a and the driven roller 20b is brought into pressure contact with the photoreceptor bell I□15c of the first transfer section 15d. Further, a first transfer roller 21 to which an electric charge is applied is provided on the inner surface side of the intermediate transfer belt 20d that is pressed against the first transfer portion 15d. Therefore, the toner image formed on the photoreceptor bell 15c in the photoreceptor belt device 15 is attracted by the electric charge of the first transfer roller 21 and is transferred onto the intermediate transfer belt l-20d. The yellow, magenta, and cyan toner images formed on the photoreceptor belt 15c are sequentially transferred onto the intermediate transfer belt 20d in an overlapping manner to form a full-color toner image.

Intermediate transfer belt l- in this intermediate transfer belt device 20
The part where 20d is wound around the bank up roller 20c is
A second transfer section 20e for transferring the transferred toner image onto the paper 23 is formed.

Furthermore, a second transfer roller 22 to which an electric charge is applied is arranged below the second transfer portion 20e. The second transfer roller 22 is provided to be movable up and down, and the paper 23 is transferred to the second transfer roller 22.
When passing through the transfer section 20e, the paper 23 is moved upward and brought into pressure contact with the outer surface of the intermediate transfer belt 20d.

Therefore, the full-color toner image transferred onto the intermediate transfer belt I-20d is attracted to the electric charge of the second transfer roller 22, and is transferred to the second transfer portion 20. The image will be transferred onto the paper 23 passing through e. The outer surface of the intermediate transfer bell I-20d after the transfer has been completed in this way is cleaned by the cleaner 24.
The toner image is cleaned by cleaning the toner image, making it possible to transfer a new toner image. Further, a grounded back electrode roller 28 is brought into contact with the inner surface of the intermediate transfer belt l-20d on the side slightly closer to the driven roller 20b than the second transfer section 20e, and a closed circuit of electrical charges is formed in the intermediate transfer belt assembly W20. It is now possible to do so.

A paper feeding section 25 arranged below the photoreceptor belt device 15 supplies the paper 23 to the second transfer section 20e of the intermediate transfer belt device 20. Here, two paper feed cassettes 26, 26 can be attached to the device frame 11, and the paper 23 is supplied from either one of these paper feed cassettes 26, 26 by the paper feed section 25. . Further, the paper 23 that has passed through the second transfer section 20e has a toner image fixed thereon by a fixing device 27 disposed on the side of the intermediate transfer belt device 20, and is further discharged to the outside of the device frame 11. It has become.

The transfer roller method uses the second transfer roller 22 in the second transfer section 20e of the intermediate transfer belt unit W20 that transfers the toner image onto the paper 23 as described above.

Here, since the backup roller 20c in the intermediate transfer belt device 20 needs to have insulation properties,
The roller portion is made of insulating rubber such as silicone rubber. Further, the second transfer roller 22 is made of stainless steel because it must be conductive in order to apply electric charge, and must have rigidity and corrosion resistance for pressing.

[Problem to be solved by the invention]

However, conventionally, an aluminum pipe has been used for the mandrel of the backup roller 20c, so when the pressing force from the second transfer roller 22 is applied to the backup roller 20c, the mandrel is deformed, and both rollers 20c, 22
The pressure distribution between them becomes uneven. That is, as shown in FIG. 5, the pressure at each axial position between the rollers 20c and 22 has an uneven distribution in which the pressure is stronger at both ends where the rollers are supported and weaker at the center.

In addition, such uneven pressure distribution is not limited to the case of the above-mentioned full-color copying machine, but also occurs when a toner image is formed on paper by pressing a transfer roller against a belt-shaped toner image forming medium that is wound and supported by a backup roller. This is common to transfer roller type transfer devices that perform transfer.

For this reason, in the transfer device of a conventional electrophotographic apparatus, the pressure distribution of the toner image forming medium and paper that are pressed into contact between the backup roller and the transfer roller is uneven, resulting in poor image quality of the transferred toner image. This has caused the problem of a decline in performance.

In addition, in order to compensate for the reduction in image quality due to such uneven pressure distribution, it is necessary to strictly determine the voltage applied to the transfer roller and the resistance value of the toner image forming medium. Another problem has arisen in that the degree of freedom in designing is restricted.

[Failure to solve the problem]

In order to solve the above-mentioned problems, a transfer device of an electrophotographic apparatus according to the present invention presses a sheet of paper against a belt-shaped toner image forming medium wound and supported by a backup roller by a rotating transfer roller to which an electric charge is applied. In this transfer device of an electrophotographic apparatus for transferring a toner image formed on a toner image forming medium to paper, the core of the backup roller having a roller portion made of insulating rubber is formed of a steel material. It is said that

[For production]

A belt-shaped toner image forming medium is a medium on which a toner image is formed on the surface of the belt in an electrophotographic apparatus. However, in addition to belts such as photoreceptor belts in which toner images are formed by direct development, there are also belts in which toner images formed on photoreceptors are transferred, such as intermediate transfer belts.

For example, if the toner image on the toner image forming medium is positively charged, a negative charge will be applied to the transfer roller. Therefore, when the paper is brought into pressure contact with the toner image forming medium by this transfer roller, the positively charged toner image is attracted to the negative charge of the transfer aperture roller and is transferred onto the paper.

At this time, the pressing force of the transfer roller is applied to the mandrel via the roller portion of the backup roller. For this reason, in the conventional case, the core metal of the backup roller made of an aluminum pipe would be deformed, and the pressure in the axial center portion would decrease. However, in the present invention, since the core metal of the backup roller is formed of a steel material having sufficient rigidity,
There is no possibility of deformation caused by the pressing force of the transfer roller.

Therefore, the pressure distribution between the backup roller and the transfer roller is uniform, and the toner image forming medium and paper are subjected to equal pressure regardless of their axial positions.

Note that the metal core of this backup roller is usually made of steel pipe material. Moreover, this steel material may be a stainless steel material.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 3.

In this embodiment, the present invention is applied to the transfer device of the full-color copying machine shown in FIG. 4. Incidentally, for convenience of explanation, the same reference numerals are added to the constituent members having the same functions as those in FIG. 4.

As shown in FIG. 2, the transfer device in a full-color copying machine includes a second transfer section 20 in an intermediate transfer belt device 20.
e and the second transfer roller 22.

The intermediate transfer belt device 20 is configured such that an endless intermediate transfer belt 20d is passed around a driving roller 20a, a driven roller 20b, and a backing roller 20c in a triangular shape, and the intermediate transfer belt 20d is circulated and transported. . This intermediate transfer belt 20d has a resistance value of 1×108 to 1×
I am using one with 109Ω・cm.

The drive roller 20a is a 50 mm diameter roller whose roller portion is made of conductive rubber. The drive roller 20a is rotated in the direction of the arrow by a copying process drive device (not shown). The driven roller 20b is a row roller made of aluminum and has a diameter of 42 mm, and is arranged on the lower front side than the drive roller 20a. The driven roller 20b is configured to rotate as the intermediate transfer belt 20d circulates.

As shown in FIG. 1, the backup roller 20c has a core made of a steel pipe 20c with a thickness of 2 cylinders, and the outer periphery of the core metal is coated with silicone rubber 20c2 with a thickness of 3 cylinders.
It is a 5mm roller. Silicone rubber 20C2 has a resistance value of 10'2 to 10I4Ω・mark and a rubber hardness of 40 to 70.
° is used. The backup roller 20c is disposed below the drive roller 20a and behind the driven roller 20b, and rotates as the intermediate transfer belt 20d circulates.

In addition, the driven roller 20b and the backup roller 2
0c is arranged so that the plane connecting the lower ends of each peripheral surface is substantially horizontal.

Note that a grounded back electrode roller 28 is provided slightly forward of the backup roller 20c in the intermediate transfer belt device 20.

This back electrode roller 28 forms a closed circuit for the electrical charges in the intermediate transfer belt assembly W20 by coming into contact with the inner surface of the intermediate transfer belt 20d.

The toner image formed on the photoreceptor belt 15C described in FIG. Become. This toner image is transferred to the intermediate transfer belt 20d in the following order: the driven roller 20b, the backup roller 20c, and the drive roller 20a.
It is transferred in a circular manner. And photoconductor bell) 15c
When the first color toner image is transferred, the next color toner image is superimposed and transferred after one rotation of the intermediate transfer bell I-20d, and the last color toner image is superimposed and transferred after one more rotation. , this results in 3 yellow, magenta, and cyan
A full-color donor image of primary colors is transferred to the intermediate transfer belt 2Od.
It is supposed to be formed on top.

In the second transfer section 20e, the intermediate transfer belt 20d in the intermediate transfer belt device 20 is connected to the backup roller 20c.
It is formed in the part that is wound around. This second transfer section 20
e is a position for transferring the full-color toner image formed on the intermediate transfer belt 20d onto the paper 23.

The second transfer roller 22 is arranged below the second transfer portion 20e. The second transfer roller 22 is a roller made of conductive stainless steel, and is applied with a charge of 1.2 to 2.degree. 0 kV by a power source 29. The second transfer roller 22 is driven by a paper conveyance system drive device (not shown) to rotate in the opposite direction to the backup roller 20c. Further, the second transfer roller 22 is installed so as to be able to move downward by one inch, and is configured to move upward and downward based on instructions from a control device (not shown).

That is, when the second transfer roller 22 descends, a gap is created between the intermediate transfer bell) 20d, and when the second transfer roller 22 rises, a gap is created between the intermediate transfer bell) at the second transfer portion 20e. The outer surface of 20d is pressed. The pressing force when the second transfer roller 22 rises is 5 to 5.
It is set at 10kgf.

A paper conveyance roller 30 and a paper guide 31 are provided below the intermediate transfer belt device 20 and on the front side of the second transfer section 20e. Then, the paper 23 from the paper feed section 25 explained in FIG.
0 and the paper guide 31 to the second transfer section 20e. Further, a peeling plate 32 made of a grounded conductive metal is arranged below the intermediate transfer belt device 20 and on the rear side of the second transfer section 20e. This peeling plate 32 electrostatically attracts the paper 23 that has passed through the second transfer section 20e and removes the paper 23 from the intermediate transfer belt 20.
It is for peeling off from d.

The transfer action of the transfer device configured as described above will be explained.

The second transfer roller 22 is located below except when the paper 23 passes through the second transfer section 20e. When the paper 23 is transported near the second transfer section 20eN by the paper transport roller 30 and the paper guide 31, the second transfer roller 22
rises, and its circumferential surface contacts and presses the outer surface of the intermediate transfer belt 20d in the second transfer portion 20e. Then, the leading edge of the paper 23 that has immediately reached the second transfer portion 20e is caught between the second transfer roller 22 and the intermediate transfer belt 20d. At this time, the paper 23 is transferred to the intermediate transfer belt 2
It is designed to be conveyed in synchronization with the movement of the full color l/ner image formed on the Od.

The paper 23 that has reached the second transfer section 20e in this way is
While being pressed against the intermediate transfer belt 20d by the second transfer roller 22, it is conveyed at the same transport speed as the intermediate transfer belt 20d. Here, assuming that the full-color toner image on the intermediate transfer bell) 2Od is positively charged,
The second transfer roller 22 is negatively charged by the power source 29 as shown in FIG. Then, the toner image on the intermediate transfer belt I-20d is transferred to the second transfer portion 20 by the pressing force of the second transfer roller 22 and the attraction force caused by the negative charge.
The images are sequentially transferred onto the paper 23 passing through e.

At this time, the pressing force of the second transfer roller 22 is applied to the steel pipe 20c via the silicone rubber 20c2 of the backup roller 20c. However, since this steel pipe 20c1 has sufficient rigidity unlike the conventional aluminum vibrator which is a mandrel, almost no deformation occurs due to the pressing force of the second transfer roller 22. Therefore, as shown in FIG. 3, the intermediate transfer belt 20d and the paper 23 that are in pressure contact are subjected to equal pressure between the rollers 20c and 22 regardless of their axial positions. Therefore, the toner image on the intermediate transfer belt 2Od is also transferred uniformly regardless of the position in the axial direction, and it becomes possible to prevent deterioration in copy quality due to uneven pressure distribution.

Furthermore, once the unevenness of the pressure distribution in the transfer device is corrected, the voltage applied to the second transfer roller 22, which conventionally had a narrow tolerance range of about 1.5 to 7 kV, can be reduced as in this embodiment. It will be possible to expand it to 1.2 to 2.0. Also, conventionally 3 x 108 ~ 5 x 10" Ω・C
In this embodiment, the resistance value of the intermediate transfer belt 20d, which should have been approximately 1×10B to 1×109Ω・c
m is now allowed.

Note that the leading edge of the sheet 23, which receives the toner image transfer as described above and is discharged from the second transfer section 20e, approaches the leading edge of the peeling plate 32. At this time, the paper 23 is negatively charged by the pressure of the second transfer roller 22 to which a negative charge is applied. However, when the paper 23 approaches the peeling plate 32, a positive charge is induced in the peeling plate 32, and this positive charge attracts the paper 23. Therefore, the intermediate transfer belt 20d has a positive charging tendency.
The peeling plate 32 can pull back the paper 23 that is being attracted by the paper 23 and try to move upward, thereby promoting normal conveyance.

〔Effect of the invention〕

As described above, the paper peeling device in the electrophotographic apparatus according to the present invention presses the paper against the belt-shaped toner image forming medium wound and supported by the backup roller by the rotating transfer roller to which an electric charge is applied. Accordingly, in a transfer device of an electrophotographic apparatus that transfers a toner image formed on a toner image forming medium to a sheet of paper, a mandrel of a bank up roller having a roller portion made of insulating rubber is formed of a steel material. There is.

As a result, the core of the backup roller is made of a steel material with sufficient rigidity, so that the pressure distribution between the backup roller and the transfer roller is uniform, and the toner image forming medium and paper are They will experience almost equal pressure.

Therefore, the present invention has the effect that it is possible to uniformly press the toner image forming medium and the paper into contact with each other, thereby preventing deterioration in the quality of the transferred toner image.

Further, since this allows a margin to be given to the appropriate range of the voltage applied to the transfer roller and the resistance value of the toner image forming medium, it also has the effect of facilitating the design of the electrophotographic apparatus itself.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention, in which FIG. 1(a) is a front view of the backup roller;
FIG. 2B is a side view of the backup roller, FIG. 2 is a side view of the transfer device, and FIG. 3 is a graph showing the pressure distribution in the axial direction in the transfer device. FIG. 4 is a schematic side view of the structure of the full-color copying machine. Fifth
The figure shows a conventional example, and is a graph showing the pressure distribution in the axial direction in the transfer device. 20c is a backup roller, 20c1 is a steel pipe (mandrel made of steel), 20C2 is silicone rubber (insulating rubber L of the roller part), 20d is an intermediate transfer belt (toner image forming medium), and 22 is a second transfer roller (transfer roller). , 23 are sheets of paper.

Claims (1)

[Claims] 1. By a rotating transfer roller to which an electric charge is applied,
In a transfer device of an electrophotographic device that transfers a toner image formed on a belt-shaped toner image forming medium to a sheet of paper by pressing the sheet against a belt-shaped toner image forming medium that is wound and supported by a backup roller, an insulating rubber 1. A transfer device for an electrophotographic apparatus, characterized in that a core metal of a backup roller having a roller portion is made of steel.