JPH05333723A - Intermediate transfer device - Google Patents

Abstract

PURPOSE:To provide an intermediate transfer device capable of keeping fluctuation in an effective secondary transfer bias which is generated in accordance with the fluctuation in the surface resistance of an intermediate transfer belt to a minimum, as to the intermediate transfer device using a conductive belt as an intermediate transfer medium. CONSTITUTION:The intermediate transfer device 20 is provided with an endless conductive belt 21 which is extended over plural rollers including a backup roller 22 and for receiving the transfer of a toner image formed on an image carrier 11 and for temporarily carrying the toner image and a secondary transfer roller 26 which is in press-contact with the backup roller 22 through the belt 21 and for transferring the toner image on the belt 21 to a recording paper passing through a secondary transfer part as a press-contact part. The secondary transfer roller 26 is a conductive rigid roller, and the backup roller 22 is a grounded conductive elastic roller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermediate transfer device using a conductive belt as an intermediate transfer medium.

Some image forming apparatuses such as electrophotographic copying machines and printers are provided with an intermediate transfer device. This intermediate transfer device is composed of an endless conductive belt, and is an intermediate transfer medium that temporarily carries a toner image formed on an image carrier, and a primary transfer device that transfers the toner image on the image carrier onto the intermediate transfer medium. A transfer unit and a secondary transfer unit that transfers the toner image on the intermediate transfer medium onto a recording sheet are provided.

This intermediate transfer device is effective as a means for superposing toner images in a color copying machine or printer which forms an output image by superposing a plurality of toner images of different colors, and is currently used in some products. Has been done.

[0004]

2. Description of the Related Art An outline of a conventional intermediate transfer device of this type is shown in FIG. In the figure, 1 is an intermediate transfer belt having conductivity,
Reference numeral 2 is a backup roller, and 3 is a secondary transfer roller (secondary transfer means). The intermediate transfer belt 1 is stretched around each roller as shown in the figure, and is given a transfer force by the drive pulley 4 to run in the direction of arrow A. Reference numeral 5 is a counter electrode arranged near the backup roller 2 for applying a secondary transfer bias in the secondary transfer section.

The toner image formed on the image carrier (not shown) is transferred onto the intermediate transfer belt 1 by the primary transfer means composed of the primary transfer rollers 6a and 6b.
The secondary transfer roller 3 transfers the image onto the recording paper 100 conveyed in the arrow B direction.

[0006]

As described above, the purpose of providing the counter electrode for applying the secondary transfer bias not only increases the cost of the apparatus but also restricts the arrangement of the intermediate transfer belt. It was imposed and was disadvantageous. Further, since the actual secondary transfer bias is defined between the counter electrode and the secondary transfer roller, in this configuration in which the counter electrode has to be separated from the secondary transfer portion to some extent,
The secondary transfer characteristics also tended to become unstable with changes in the surface resistance of the intermediate transfer belt due to environmental factors and the like.

An object of the present invention is to provide an intermediate transfer device capable of minimizing the effective fluctuation of the secondary transfer bias due to the fluctuation of the surface resistance of the intermediate transfer belt.

[0008]

In order to achieve the above object, in the present invention, an endless conductive member for temporarily carrying a toner image formed on an image carrier, which is stretched over a plurality of rollers including a backup roller. Intermediate transfer medium composed of a flexible belt, a primary transfer means for transferring the toner image on the image carrier onto the intermediate transfer medium, and the backup roller pressed against the intermediate transfer medium via the intermediate transfer medium. In an intermediate transfer device having a secondary transfer means for transferring a toner image on the intermediate transfer medium onto a recording sheet passing through a secondary transfer portion, the secondary transfer means is a conductive rigid roller, and
The backup roller is a grounded conductive elastic roller, and a secondary transfer bias is applied to the secondary transfer means when the recording sheet passes through the secondary transfer section. (First configuration).

Further, an intermediate transfer medium formed of an endless conductive belt which is wound around a plurality of rollers including a backup roller and temporarily carries the toner image formed on the image carrier, and the above-mentioned image carrier. A primary transfer unit that transfers a toner image onto the intermediate transfer medium; and a primary roller that press-contacts the backup roller via the intermediate transfer medium, and transfers the toner image on the intermediate transfer medium to a recording sheet that passes through the pressed portion. In an intermediate transfer device having a secondary transfer unit, the backup roller is a grounded rigid roller, and the secondary transfer unit is a plurality of rollers including at least one roller made of an elastic body, and each roller. 1 composed of the elastic body, which is composed of an endless conductive belt that is stretched around
This roller is pressed against the backup roller via the endless conductive belt and the intermediate transfer medium to form a nip portion as a secondary transfer portion, and the nip portion serves as a secondary transfer portion, and the recording paper passes through the secondary transfer portion. A configuration (second configuration) is characterized in that a secondary transfer bias is applied to the secondary transfer unit.

[0010]

In the case of the first construction, the secondary transfer means is a conductive rigid roller, and the backup roller opposed thereto is a grounded conductive elastic roller, so that the secondary transfer bias is directly transferred to the secondary transfer roller. It is possible to apply the voltage in the area, and the device cost can be suppressed by omitting the counter electrode as in the conventional case, and the fluctuation of the effective secondary transfer bias due to the fluctuation of the surface resistance of the intermediate transfer medium can be minimized. Therefore, it is possible to perform highly stable transfer.

Further, by using an elastic roller as the backup roller, it is possible to improve the adhesion of the recording paper to the belt at the secondary transfer portion, and it is possible to obtain a high quality transferred image with less toner scattering. Become. Further, by using a rigid roller as the secondary transfer means, it becomes possible to easily perform highly efficient cleaning.

In the case of the second construction, the secondary transfer means is constituted by an endless belt which is wound around a plurality of rollers including a roller made of an elastic body (opposed to the backup roller), so that the backup roller is made of metal. Even if it is made of a rigid body such as, the adhesiveness can be enhanced in the secondary transfer portion. Further, by making the backup roller a rigid body, it is possible to suppress the meandering of the intermediate transfer belt to be small, to reduce the positional deviation between the superimposed toner images, and to suppress the stress applied to the intermediate transfer belt to extend its life. It also becomes possible. Furthermore, the surface of the belt that is soiled with toner can be cleaned with high efficiency.

[0013]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 and FIG. 2 show a first embodiment.

FIG. 1 is a schematic explanatory view of the structure of a color printer to which the intermediate transfer device of this embodiment is applied. In the figure, 11 is a photosensitive drum (image carrier) and 20 is an intermediate transfer device. The photoconductor drum 11 is rotated in the direction of the arrow by a driving source (not shown), and is charged to a constant potential by the conductive brush charger 12, and then an image is exposed by the laser optical system 13 to form an image depending on the presence or absence of electric charge. .. The charge image on the photoconductor drum 11 is first a yellow developing device 14 containing yellow toner.
It is developed by Y to form a yellow toner image.

The intermediate transfer device 20 includes a backup roller 22, a driving roller 23, primary transfer rollers (primary transfer means) 24a and 24b, and an endless conductive intermediate transfer belt (intermediate transfer medium) 21 which is wound around a tension roller 25.
And a metal secondary transfer roller (secondary transfer means) 26 facing the backup roller 22. The tension roller 25 applies a constant tension to the intermediate transfer belt 21 with a spring, and the drive roller 23 sends the intermediate transfer belt 21 in the arrow direction. The intermediate transfer belt 21 is
It is made of polycarbonate or polyimide and has a thickness of 50 to 150 μm and a volume resistivity of 10 ⁸ to 10 ^10.
Ωcm.

The yellow toner image formed on the photosensitive drum 11 as described above is transferred onto the intermediate transfer belt 21 by the primary transfer bias applied by the primary transfer rollers (primary transfer means) 24a and 24b. At this time, the toner remaining on the photosensitive drum 11 without being transferred is removed by the cleaner 15. The yellow toner image transferred onto the intermediate transfer belt 21 circulates once again and enters the primary transfer portion, but at this time, the secondary transfer roller (secondary transfer roller is used so as not to damage the toner image on the intermediate transfer belt 21). Means) 26
The belt cleaner 16 is separated from the intermediate transfer belt 21.

A magenta toner image is formed on the photoconductor drum 11 by the magenta developing unit 14M in the same manner as the yellow toner image in accordance with the timing when the yellow toner image again enters the primary transfer portion. Then, the magenta toner image is transferred and superposed on the yellow toner image at the primary transfer portion. After that, cyan developer 1
The cyan toner image formed by 4C and the black toner image formed by the black developing device 14B are respectively superposed, and a toner image in which the toner images of four colors are superposed is formed on the intermediate transfer belt 21.

Next, the intermediate transfer belt 21 for the toner image.
As the upper tip position enters the secondary transfer portion, the cam 27 is rotated by a motor (not shown), so that the metal secondary transfer roller 26 moves to the intermediate transfer belt 21.
It is pressed against the backup roller 22 via. On the other hand, the recording paper 100 is sent by the registration rollers 17 at the same timing, and passes between the secondary transfer roller 26 and the backup roller 22 which is grounded together with the intermediate transfer belt 21.

At this time, a secondary transfer bias is applied to the secondary transfer roller 26, and the toner image on the intermediate transfer belt 21 is transferred to the recording paper 100. Backup roller 2
Since 2 is made of conductive rubber such as silicone rubber and urethane rubber having an upper limit of volume resistivity of 10 ⁶ Ωcm, recording paper 10
0 is in good contact with the intermediate transfer belt 21, and a clean transfer image without toner scattering can be obtained.

The surface of the secondary transfer roller 26 is made of a substance such as a fluororesin having a high resistivity (10 ¹⁰ Ωcm).
Since it is a metal roller having a thin layer of ~ 500 μm,
Optimal transfer voltage fluctuations due to the type and thickness of the recording paper 100 are suppressed to a minimum, and stable secondary transfer characteristics can be obtained. The belt cleaner 16 is pressed against the intermediate transfer belt 21 and transferred by the cam 16a being rotated by a motor (not shown) in accordance with the position of the tip of the toner image on the intermediate transfer belt 21. The toner remaining on the intermediate transfer belt 21 is removed.

When the recording paper 100 on which the toner image is transferred passes through the secondary transfer portion, the fixing belt 1 is fixed by the conveyor belt 18.
Then, the toner image is fixed on the recording paper. The recording paper 100 that has been fixed is discharged to an external stacker or the like.

When the recording paper 100 does not reach the secondary transfer portion due to a paper jam or the like, the toner adheres to the secondary transfer roller 26, and if it is left as it is, the rear surface of the recording paper may be soiled during the next secondary transfer. In order to occur, the secondary transfer roller 26 has to be cleaned, but the secondary transfer roller 26 having a thin layer of a high-resistivity material on the surface of the metal roller is used.
Blade cleaner that is simple and inexpensive because it uses
8 can be used, which is advantageous in terms of cost.

By the way, as described above, the conductive rubber backup roller 22 has a volume resistivity (upper limit of 10 ⁶ Ωcm) sufficiently smaller than the volume resistivity of the intermediate transfer belt 21 (10 ⁸ to 10 ¹⁰ Ωcm). By doing so, it becomes possible to always perform stable secondary transfer without being affected by manufacturing variations in the resistance of the backup roller and variations due to environmental factors. This will be described in detail with reference to the equivalent circuit of the secondary transfer portion of FIG.

In FIG. 2, R _b , R _belt and R _r are the effective resistances of the backup roller, the intermediate transfer belt and the secondary transfer roller, respectively, and R _p and C _p are the secondary transfer portions of the recording paper. Is an effective resistance and capacitance between the secondary transfer roller and the intermediate transfer belt when passing through the sheet, and I is a current flowing through the secondary transfer portion. When the variation rate of the backup roller resistance value is α, the relative variation rate of the intermediate transfer belt surface potential at the secondary transfer portion is αR _b / R.
_{Since belt} + R _b , if R _belt >> R _b , this value becomes a very small amount with respect to 1. Therefore, the effective fluctuation of the secondary transfer bias can be made extremely small.

On the other hand, when the secondary transfer roller is a metal roller having a thin layer made of a substance having a high resistivity on the surface, the fluctuation of the optimum transfer voltage depending on the type of recording paper can be suppressed. To explain this in detail, FIG.
As can be seen from the above, the secondary transfer electric field is almost constant if the current I is constant. In order to suppress the fluctuation of the current I, it is sufficient to suppress the fluctuation of the total combined resistance of the secondary transfer portion. Since it is R _p that varies depending on the type of recording paper, if the resistance R _r of the secondary transfer roller is large, the variation rate of the total combined resistance can be small.

As described above, according to this example, the following various excellent effects can be obtained. (1) In the intermediate transfer device using the conductive belt, the secondary transfer bias is directly applied between the secondary transfer roller and the conductive backup roller to prevent the surface resistance of the intermediate transfer belt from fluctuating. Therefore, stable transfer can be performed. (2) By forming the backup roller with a conductive elastic material, the adhesion between the intermediate transfer belt and the recording paper can be enhanced, and a clean transferred image with less toner scattering can be obtained. (3) The conductive elastic body forming the backup roller is
By making the volume resistivity sufficiently smaller than that of the intermediate transfer belt, stable secondary transfer characteristics can be obtained against variations in the resistance of the backup roller. (4) Since the secondary transfer roller is a metal roller having a thin layer made of a high-resistivity material on its surface, the fluctuation of the optimum transfer voltage depending on the type of recording paper can be suppressed to a minimum and stable. Secondary transfer can be performed.

A second embodiment is shown in FIGS. 3 and 4.

In the intermediate transfer device of the preceding example, a conductive roller made of a rigid body such as metal is used as the secondary transfer roller, and a conductive roller made of an elastic body is used as the backup roller to improve the adhesion between the intermediate transfer belt and the recording paper. With a roller,
This will promote the meandering of the intermediate transfer belt that is stretched over the backup roller. When the meandering becomes large, not only the positional deviation between the superimposed toner images of the respective colors becomes large, but also the stress applied to the intermediate transfer belt becomes large and the life of the belt is greatly shortened.

In order to solve these problems, it is conceivable to form the backup roller from a rigid body such as metal and use a conductive elastic body as the secondary transfer means. However, since the secondary transfer means is inevitably soiled by toner, and must be constantly cleaned,
It is difficult to use a roller made of a conductive elastic material without a cleaning means having a sufficiently high efficiency. This example has been made in view of these problems.

FIG. 3 is a schematic configuration diagram showing the principle of the intermediate transfer device 30 of the present embodiment. In the figure, 31 is a backup roller made of a rigid body, and 32 is a secondary transfer means. The same reference numerals are used for the same members as in the previous example. Secondary transfer means 32
The elastic roller 33 is composed of a plurality of rollers, for example, an elastic roller 33, a metal roller 34, a rigid roller 35, and an endless conductive belt 36 wound around these rollers. The elastic roller 33 is the backup roller 31.
Is pressed against the recording paper, and the recording paper passes between them.

With this structure, even if the backup roller 31 is a rigid roller for suppressing the meandering of the intermediate transfer belt 21, the backup roller 31 is high between the recording paper and the intermediate transfer belt 21 in the secondary transfer portion. Adhesion can be realized. In addition, the cleaning of the endless belt 36,
For example, as shown in FIG. 3, it can be easily performed by using the blade cleaner 37 in the portion stretched by the rigid roller 35.

As means for applying the secondary transfer bias, the backup roller 31 is electrically grounded and the endless belt 36 is electrically conductive. And
A conductive roller may be included in the roller around which the endless belt 36 is wrapped (metal roller 34), and a secondary transfer bias may be applied to the conductive roller. At this time, if the other rollers are insulative, they will be charged and affect the secondary transfer. As a means for avoiding this, the other rollers may be grounded rollers of high resistance. ..

Similar effects can be obtained by using another roller as a conductive roller which is grounded via a high resistance. Further, even if all the rollers around which the electroconductive endless belt is wound are made electroconductive and a secondary transfer bias is applied to all of them, stable secondary transfer can be performed. Next, a color printer adopting such a principle will be described.

FIG. 4 is a schematic explanatory view of the structure of the color printer of this example, in which 41 is a secondary transfer means. The same members as those in the previous example and FIG. 3 are designated by the same reference numerals. The secondary transfer means 41 is a conductive elastic roller (secondary transfer roller).
42, a metal roller 43, an endless conductive belt 44 wound around these, a blade cleaner 45, and a cam 2
7 and. The formation of the toner images of the respective colors on the photoconductor drum 11 and the four-color toner image superposition transfer onto the intermediate transfer belt 21 are the same as in the previous example, and the description thereof is omitted. The subsequent action is as follows.

The eccentric cam 27 is rotated by a motor (not shown) in accordance with the leading end position of the toner images transferred on the intermediate transfer belt 21 with the four colors being transferred to the secondary transfer portion. The conductive elastic roller 42 of the next transfer unit 41 is pressed against the backup roller 31 via the intermediate transfer belt 21. On the other hand, the recording paper 100 is sent in the same manner as in the previous example, and passes between the backup roller 31 and the conductive elastic roller 42 which are grounded together with the intermediate transfer belt 22. At that time, a secondary transfer bias is applied to the conductive elastic roller 42 and the metal roller 43, and the toner image on the intermediate transfer belt 21 is transferred to the recording paper 100.

At this time, due to the elasticity of the conductive elastic roller 42, the recording paper 100 is in close contact with the intermediate transfer belt 21 and a clean transferred image without toner scattering can be obtained. Further, since the backup roller 31 is made of metal and has a rigid body, the meandering that accompanies the conveyance of the intermediate transfer belt 21 can be suppressed to be small, and the displacement of the toner image and the stress received by the intermediate transfer belt 21 can be minimized.
At the same time that a beautiful image is obtained, the intermediate transfer belt 21
It also enables a longer life.

The belt cleaner 16 is used for the intermediate transfer belt 2
The eccentric cam 16a is rotated by a motor (not shown) in accordance with the position of the leading edge of the toner image on No. 1 and is pressed against the intermediate transfer belt 21 and is not transferred to the intermediate transfer belt 21. Remove the remaining toner. The recording paper 100 onto which the toner image has been transferred and which has passed through the secondary transfer portion is guided to the fixing device 19, where the toner image is fixed and then discharged to the outside.

If the recording paper 100 does not reach the secondary transfer portion due to a paper jam or the like, the endless conductive belt 44
Toner adheres to the endless conductive belt 44, and if left as it is, there is a problem that the back surface of the recording paper is soiled at the time of the next secondary transfer. Therefore, the endless conductive belt 44 must be cleaned. By pressing the blade cleaner 45 against the endless conductive belt 44, it is possible to easily perform highly efficient cleaning.

[0040]

As described above, according to the present invention, the following various excellent effects can be obtained. (1) By directly applying the secondary transfer bias between the secondary transfer roller and the backup roller, it is possible to perform stable transfer regardless of variations in the surface resistance of the intermediate transfer medium. (2) The adhesion between the intermediate transfer belt and the recording paper can be enhanced, and a clean transferred image with less scattering can be obtained. (3) If the backup roller is a rigid roller as in the second embodiment, the meandering of the intermediate transfer roller can be suppressed. (4) It is possible to clean the portion of the secondary transfer unit that contacts the recording paper, and it is possible to solve the problem of toner contamination.

[Brief description of drawings]

FIG. 1 is a structural schematic explanatory diagram of a color printer according to a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a secondary transfer portion according to the first embodiment of the present invention.

FIG. 3 is a schematic configuration diagram showing the principle of an intermediate transfer device according to a second embodiment of the present invention.

FIG. 4 is a structural schematic explanatory diagram of a color printer according to a second embodiment of the present invention.

FIG. 5 is a side view showing an outline of a conventional intermediate transfer device.

[Explanation of reference numerals] 11 photoconductor drums (image carrier) 20, 30 intermediate transfer device 21 intermediate transfer belt (intermediate transfer medium) 22, 31 backup rollers 24a, 24b primary transfer roller (primary transfer means) 26 secondary transfer roller (Secondary transfer means) 32,41 Secondary transfer means 33 Elastic roller 34,43 Metal roller 35 Rigid roller 36,44 Endless conductive belt 42 Conductive elastic roller (secondary transfer roller)

Claims (2)

[Claims] 1. An intermediate transfer medium, which comprises an endless conductive belt which is stretched over a plurality of rollers including a backup roller and temporarily carries a toner image formed on an image carrier, and the above-mentioned image carrier. A primary transfer unit that transfers a toner image onto the intermediate transfer medium; and a backup roller that is in pressure contact with the intermediate transfer medium and a recording paper that passes through the secondary transfer unit, which is the pressure contact portion, onto the intermediate transfer medium. In an intermediate transfer device having a secondary transfer means for transferring a toner image, the secondary transfer means is a conductive rigid roller, the backup roller is a grounded conductive elastic roller, and the recording paper is An intermediate transfer device characterized in that a secondary transfer bias is applied to the secondary transfer means when passing through the secondary transfer portion. 2. An intermediate transfer medium, which comprises an endless conductive belt which is stretched over a plurality of rollers including a backup roller and temporarily carries a toner image formed on the image carrier, and the image carrier. A primary transfer unit that transfers a toner image onto the intermediate transfer medium; and a primary transfer unit that press-contacts the backup roller via the intermediate transfer medium and transfers the toner image on the intermediate transfer medium to a recording sheet passing through the press-contact portion. In an intermediate transfer device having a secondary transfer means, the backup roller is formed of a rigid body, and the secondary transfer means is provided on a plurality of rollers including at least one roller made of an elastic body and the rollers. Endless electroconductive belt, and a roller made of the elastic body, the endless electroconductive belt and the intermediate transfer medium being interposed between the backup roller and the backup roller. The nip portion is brought into contact with the secondary transfer portion to form a secondary transfer portion, and a secondary transfer bias is applied to the secondary transfer means when a recording sheet passes through the secondary transfer portion. Transfer device.