JP2001066908A - Belt type feeding device and image forming device provided with the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always execute stable transfer and separation though the endurance and the using environment of an elastic belt are changed in a belt type feeding device. SOLUTION: A transfer belt 18 constituted of the elastic belt is laid between a driving roller 16 and a tension roller 17. Then, the belt 18 is pressed to a photoreceptor drum 19 from the back surface side by transfer rollers 20a and 20b arranged inside the belt 18 so as to form a transfer area (contact area) T. By applying transfer bias to the rollers 20a and 20b, a toner image formed on the drum 19 is transferred on the surface of a transfer material carried on the surface of the belt 18. By widening the area T, the latitude of a transfer current can be widened. Thus, the stable transfer can be maintained even when the volume resistivity of the belt 18 is changed because the endurance and the environment are changed. Besides, such an image defect that the transfer image is scattered is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt conveying device used for a transfer belt, an intermediate transfer belt, a photosensitive belt, and the like in a copying machine, a laser beam printer, and the like, and an image forming apparatus having the same.

[0002]

2. Description of the Related Art FIG. 9 is a sectional view showing an image forming apparatus (copier) equipped with a conventional belt conveying device.

In FIG. 1, a toner image formed by an image forming unit 2 for performing a known image forming process is transferred to a transfer material P stored in a cassette 1 which can be pulled out to the near side in the figure. Then, the sheet is fixed to the fixing device 4 by the heat and pressure of the fixing device 4, and is discharged to the outside of the image forming apparatus main body 5 from a sheet discharge port 7 by a discharge roller 6 of the image forming apparatus main body 5. The transfer material P discharged to the outside of the image forming apparatus main body 5 is transferred to the entrance 9 of the sheet separating apparatus 8.
The sheet is then discharged to the outside of the sheet separating device 8 by the sheet discharging roller 10 of the sheet separating device 8 and stacked on the sheet discharging tray 11. When the original is set on the pressure plate 12, the original is read by the exposure device 52 and is transferred to the transfer material P as a toner image by the image forming unit 2. When two or more copies of a plurality of originals are to be copied, the transfer material P changes its path in the direction of the roller 14 by the flapper 13 which is the sheet transport path changing means in the sheet separating device 8, and Is discharged. The paper discharge tray 11 has a configuration in which a plurality of bins are stacked in multiple stages, and is indexed and moved in the direction of arrow A by a paper discharge tray driving means (not shown). And classify them by the number of copies. In the above description, the cassette 1, the transport unit 3, and the fixing device 4 can be pulled out to the near side in a direction perpendicular to the plane of the drawing to maintain the apparatus and supply the transfer material P.

Next, a description will be given of a transport unit 3 for transferring the toner image formed by the image forming section 2 to a transfer material P and transporting the toner image to a fixing device 4.

In FIG. 9, an endless transfer belt (elastic belt) 18 is stretched with a predetermined tension between a drive roller 16 to which drive is transmitted from the image forming apparatus main body 5 and a tension roller 17. I have. Drive roller 1
6. The tension roller 17 is rotatably supported by a side plate (not shown) of the transport unit 3 with a predetermined distance between the axes. The transfer belt 18 has a base layer made of NBR rubber and a surface layer made of fluorine rubber, and a volume resistivity of 1.0.
It is set to a high resistance of × 10 ¹³ Ω · cm.

The transfer belt 18 is in contact with the photosensitive drum 19 by being urged with a predetermined pressure by a transfer roller 20 disposed inside the transfer belt 18.

The transfer roller 20 is composed of a high-resistance EPDM rubber layer, and a predetermined voltage is applied to the transfer roller 20 from a power supply (not shown) to charge the surface of the transfer belt 18 and retain the charge. Let

When the transfer material P comes into contact with the transfer belt 18 of the transport unit 3, it is attracted to the surface by electrostatic attraction and transported. Then, the toner image formed on the photosensitive drum 19 by the image forming section 2 (charging device 51, exposure device 52, developing device 53) is transferred around the nip portion between the photosensitive drum 19 and the transfer roller 20. The image is transferred, and after the transfer, the sheet is conveyed to the fixing device 4 while being adsorbed on the transfer belt 18.

Reference numeral 100 in FIG. 1 denotes a cleaning device for removing toner (residual toner) remaining on the surface of the photosensitive drum 1 after the transfer of the toner image.

[0010]

However, in the above-described conventional example, the nip area of the transfer roller 20 is narrow because the transfer roller 20 is brought into contact with the photosensitive drum 19 with light pressure.

Therefore, an area (transfer area) for transferring the toner image onto the transfer material P and the transfer material P
The area (adsorption area) to be adsorbed on 8 becomes narrow.

As a result, the latitude (degree of freedom) of the transfer to the transfer material P is reduced, and when the transfer voltage (current) is increased, an image defect such that the transferred image is scattered occurs, and it is difficult to control the transfer voltage (current). become. Further, since the volume resistivity of the transfer belt 18 changes depending on durability and environment, it is difficult to always maintain stable transfer if the transfer latitude is narrow.

An adverse effect caused by the narrowing of the suction area is a poor separation of the transfer material P from the photosensitive drum 19.

If a sufficient charge is not applied to the transfer material P in the nip of the transfer roller 20, a sufficient attraction force cannot be obtained between the transfer belt 18 and the transfer material P. As a result, when the transfer material P is separated from the photosensitive drum 19, the attraction force between the transfer material P and the photosensitive drum 19 is superior, and separation failure occurs. Then, the transfer material P that has caused the separation failure rubs the transfer surface with, for example, the cleaning device 100 in FIG. 9, causing an image failure or a jam.

The separation failure is caused by a high-resistance belt having a volume resistivity of the transfer belt 18 of 1.0 × 10 ¹³ Ω · cm, a thin paper having a transfer material P of 52 g / cm ² , and an environment of 20.
It occurs remarkably at ° C / 5% (normal temperature / low humidity).

As a countermeasure for the image defect and the separation defect described above, for example, a method of expanding a transfer region and a separation region shown in FIGS. 10 and 11 has been proposed.

FIG. 10 shows an example in which the rubber layer of the transfer roller 20 is thickened to produce a transfer roller 20 having a large elastic modulus, the urging force of the transfer roller 20 to the photosensitive drum 19 is increased, and the nip area is reduced. Spread out.

However, according to this method, the nip area cannot be made larger than the outer diameter of the transfer roller 20, and a sufficient area satisfying both transfer and separation cannot be secured. In addition, since the transfer roller 20 is strongly pressed and rotated in the direction of the photosensitive drum 19, the transfer belt 18 is greatly damaged and the durability of the transfer belt 18 is reduced.

The countermeasure shown in FIG.
By raising the tension roller 17 on the photosensitive drum 19 side, the contact area between the transfer belt 18 and the photosensitive drum 19 is increased,
This is to secure a transfer / suction area.

However, according to this method, a certain area can be secured on the upstream side of the transfer roller 10, but not so much on the downstream side. In order to secure the area on the downstream side, it is necessary to raise the position of the drive roller 16 further upward, so that the transport path is limited. Further, since the tension of the transfer belt 18 decreases as the durability increases, it is difficult to always secure a stable contact area according to the method of FIG.

The present invention has been made in view of the above-mentioned circumstances, and has a belt conveying device capable of constantly performing stable transfer and separation regardless of a change in durability of an elastic belt or a change in a use environment. It is an object of the present invention to provide an image forming apparatus.

[0022]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: an elastic belt that is wound around a plurality of rollers including a driving roller; In a belt conveying device that forms an area and transfers the toner image formed on the image carrier to the surface of the elastic belt through the contact area, the elastic belt is formed from the back side inside the elastic belt. A first roller and a second roller for pressing against the image carrier are provided, and the contact area is formed between the first roller and the second roller of the elastic belt. .

According to a second aspect of the present invention, in the belt conveying device of the first aspect, the first roller and the second roller transfer charges for transferring a toner image on the image carrier to the surface of the elastic belt. To give to the elastic belt.

According to a third aspect of the present invention, a contact area is formed by bringing an elastic belt stretched over a plurality of rollers including a driving roller into contact with an image carrier, and formed on the image carrier. In a belt conveyance device for transferring a toner image to a surface of a transfer material carried on the elastic belt via the contact area, a first member for pressing the elastic belt against the image carrier from the back side inside the elastic belt. A roller and a second roller are provided to form the contact area between the first roller and the second roller of the elastic belt.

According to a fourth aspect of the present invention, in the belt conveying device of the third aspect, the first roller and the second roller transfer charges for transferring the toner image on the image carrier to the surface of the transfer material. To give to the elastic belt.

According to a fifth aspect of the present invention, in the belt conveying device of the third aspect, the first roller is disposed on an upstream side along a moving direction of the elastic belt, and the second roller is disposed on a downstream side. And a charge for transferring the toner image on the image carrier to the surface of the transfer material is transferred to the first material.
The toner is applied to the elastic belt by a roller, and after the transfer of the toner image, the charge of the elastic belt is removed by the second roller.

According to a sixth aspect of the present invention, in the belt transport device of the fifth aspect, the moving direction of the elastic belt after passing through the contact area is disposed below the image carrier and the image carrier. The roller is set so as to face upward from a tangent to the second roller.

The present invention according to claim 7 is based on claims 1 and 2,
3, 4, 5, or 6, wherein the first roller and the second roller are not in contact with the elastic belt.

According to an eighth aspect of the present invention, in the belt conveying device of the seventh aspect, cylindrical spacers are disposed at both ends in the longitudinal direction of the first roller and the second roller, respectively. By contacting the back surface of the portion corresponding to the non-image forming area of the elastic belt, the first
The distance between the roller and the second roller and the elastic belt is kept constant.

According to a ninth aspect of the present invention, in the image forming apparatus, an image carrier, a toner image forming means for forming a toner image on the image carrier, and the belt according to any one of the first to eighth aspects. And a transfer device.

[0031]

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

<Embodiment 1> FIGS. 1 to 4 show an example of a belt conveying apparatus according to the present invention. FIG. 1 is a partially cutaway perspective view, FIG. 2 is a vertical cross-sectional view along a transfer material conveying direction, FIG. 3 is a vertical cross-sectional view schematically showing a belt conveying device and an image forming apparatus having the same, and FIG. FIG. 4 is a longitudinal sectional view showing transfer / separation of a transfer material. Note that, among the members and the like in these drawings, those having the same configurations and operations as those in FIGS. 9 to 11 described above are denoted by the same reference numerals, and description thereof will be appropriately omitted.

In FIG. 1, reference numeral 21 denotes a belt conveying device according to the present invention. The belt transporting device 21 includes the driving roller 1
6, a driven roller 17, and a transfer belt 18 as an elastic belt stretched between them with a tension of about 8 kg in total.

The drive roller 16 has a non-conductive bearing 2 at both ends.
2, the belt conveying device 21 is rotatably supported between the front plate 23 and the rear plate 24 of the belt conveying device 21.

Reference numeral 25 denotes a stay for keeping the distance between the front side plate 23 and the rear side plate 24 constant and fixing the same. A drive motor 26 which is a DC motor is fixed to the rear side plate 24. The output shaft of the drive motor 26 is coaxially connected to the shaft on the rear plate 24 side of the drive roller 16. Drive motor 2
6, a drive / stop signal is input from a ROM 101 provided in an image forming apparatus main body 105 (see FIG. 3) via a motor driver 102.

The transfer roller (first roller) 20a and the transfer roller (second roller) 20b are rotatably supported at both ends by conductive bearings 28. The bearing 28 has a pin 29 as a center of rotation. Transfer rollers 20a, 20b
Is supplied to R provided in the image forming apparatus main body 105.
A high-voltage generation signal is transmitted from the OM 101 to the high-voltage power supply 104, and the high-voltage power supply 104 performs the operation by applying a voltage via the pin 29.

The transfer rollers 20 a and 20 b are urged vertically upward by the compression coil spring 30, and charge is applied to the transfer belt 18.

The transfer roller support plate 31 is hung between the rear plate 24 and the front plate 23 of the belt conveying device 21. The transfer roller indicating plate 31 is positioned by inserting the pin 32 into a positioning hole (not shown) of the rear plate 23 and fixing the screw 33 to the front plate 23.

In the front plate 23, an insertion hole (not shown) is provided to facilitate insertion of the transfer roller support plate 31 from the front in the figure.
The transfer roller support plate 31 is easily detached.

The voltage applied to the transfer rollers 20a and 20b is such that the transfer material P is positively (+) when the toner charge transferred to the transfer material P is negative (-), for example. , For example, +2.0 to 2.3k
V, a transfer voltage of about the drum direction current (20 to 30 μA) needs to be applied.

With respect to the arrangement of the transfer rollers 20a and 20b, as shown in FIG. 2, the transfer roller 20b is arranged vertically below the photosensitive drum (image carrier) 19, and the transfer roller 20a is opposite to the transfer roller 20b. They are arranged at an angle of about 25 ° clockwise.

The urging force of the transfer roller 20b in the direction of the photosensitive drum 19 is about 400 g in total pressure, and the transfer roller 20a is about 600 g in pressure.
The compression coil spring 30 is set to be g.

A transfer area (contact area where the photosensitive drum 19 and the transfer belt 18 are in contact) T formed by the transfer rollers 20a and 20b has a length along the circumferential direction of the photosensitive drum 19 of at least 20 mm or more. There is a need.
With respect to the tangent S between the transfer roller 20b and the photosensitive drum 19,
The drive roller 16 is arranged so that the transfer belt 18 forming the transfer path of the transfer material P has a clockwise angle α (α> 0). By providing such an angle α, separation failure is prevented. As shown in FIG. 4, when the transfer material P separates from the photosensitive drum 19, the transfer material P
A force F is applied in the tangential direction between b and the photosensitive drum 19. On the other hand, since the transfer belt 18 forms a transport path upward at an angle α, that is, the moving direction K of the transfer belt 18 is set to be higher than the tangent S, The material P is pressed against the surface of the transfer belt 18 by the force F at the time of separation. Therefore, there is no possibility that the transfer material P is lifted from the transfer belt 18 to cause a separation failure.

In this embodiment, transfer and separation are performed by applying the above-described transfer voltage to both the transfer rollers 20a and 20b. However, the transfer voltage is applied to the transfer roller 20a, and the charge is removed from the transfer roller 20b. A voltage may be applied.

The transfer material P having received the transfer of the toner image from the surface of the photosensitive drum 19 in the nip of the transfer roller 20a and the area around the nip is separated from the photosensitive drum 19 in the charge removal area formed by the transfer roller 20b. This static elimination voltage (current) corresponds to the transfer material P and the transfer belt 18.
Is set so as to weaken the surface charge of the transfer material P on the transfer side while maintaining the suction force of the transfer material P to some extent. Further, the charge removal voltage is set to be much smaller than the transfer voltage so that the toner image transferred on the transfer material P is not re-transferred to the photosensitive drum 19 side.

Second Embodiment FIGS. 5 to 7 show a second embodiment. 5 is a longitudinal sectional view showing a schematic configuration of the belt transport device, FIG. 6 is a view taken along line BB of FIG. 5, and FIG. FIG. 6 is a VI curve diagram showing a relationship with a current value flowing in the direction of the photosensitive drum. Note that among the members and the like in these figures, those having the same configurations and operations as those in FIGS. 9 to 11 and FIGS. 1 to 4 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

The belt transport device 2 according to the second embodiment
1A is different from the first embodiment in the configuration of the transfer roller 20b shown in FIG.

In the present embodiment, as shown in FIG. 6, a bias roller (second roller) 34 made of conductive metal has a cylindrical shape with both ends formed of non-conductive resin. Both ends thereof are supported by abutting rollers (spacers) 35, and are urged toward the photosensitive drum via the transfer belt 18. The abutting roller 35 is fixed to the bias roller 34, and the driving force of the transfer belt 18 is transmitted to the bias roller 34 by a frictional force acting between the transfer belt 18 and the abutting roller 35. An electronic voltage of about +4 to +6 kV is applied to the bias roller 34 from the high voltage power supply 104 shown in FIG.
Gap discharge is generated between the transfer belt 18 and the surface of the bias roller 34, and transfer charges are formed on the transfer belt 18. The gap distance h from the surface of the bias roller 34 to the transfer belt 18 shown in FIG. 6 is preferably about 0.2 to 0.5 mm.

The contact position of the abutting roller 35 with the transfer belt 18 is located outside the transfer area, and the abutment roller 35 abuts, for example, about 10 mm away from the transfer area.

It goes without saying that the transfer roller 20a may have the same configuration as the bias roller 34.

Further, a transfer voltage may be applied to the transfer roller 20a, and a neutralization voltage may be applied to the bias roller 34.

As shown in FIG. 7, the slope of the graph of the correlation between the voltage applied to the bias roller 34 and the static elimination current flowing toward the photosensitive drum 19 is smaller in non-contact transfer charging than in contact transfer. When the region of the static elimination current required at the time of separation is y in the figure, the static elimination voltage region of contact transfer is X1, whereas the static elimination region of non-contact transfer is X1.
2 and the latitude (degree of freedom) of the static elimination voltage increases. This has an advantageous effect on the durability change of the volume resistivity of the transfer belt 18 and the environmental change.

Another advantage of the present embodiment is that the bias roller 34 is not brought into contact with the transfer belt 18 in the transfer area T of the transfer belt 18, so that mechanical damage to the transfer belt 18 can be suppressed. And durability can be improved.

Third Embodiment FIG. 8 shows a third embodiment. FIG. 1 is a longitudinal sectional view showing a schematic configuration of the belt transport device. Note that among the members and the like in these drawings, those having the same configurations and operations as those in FIGS. 9 to 11 and FIGS. 1 to 7 are denoted by the same reference numerals and description thereof will be appropriately omitted.

The belt conveying device 21 according to the present embodiment
B differs from Embodiment 1 in that the transfer roller 20a
The point is that an elastic endless belt 36 having a predetermined volume resistivity is wrapped around 20b.

With such a configuration, the transfer charge applied to the belt 36 by the transfer rollers 20a and 20b is uniformly applied to the transfer belt 18 in the transfer area T formed by the transfer rollers 20a and 20b. be able to.

Further, since the belt 36 urges the transfer belt 18 toward the photosensitive drum 19 in the transfer area T, the transfer material P and the transfer belt 18 adhere to each other when the transfer material P is transferred.
Transfer and adsorption can be performed reliably.

Since the belt 36 circulates in the transfer area T, charges that have not moved from the belt 36 to the transfer belt 18 remain on the belt 36. Therefore, it is not necessary to increase the voltage applied to the transfer rollers 20a and 20b.

In the first to third embodiments described above, an example has been described in which the toner image formed on the photosensitive drum 19 is transferred to the transfer material P carried on the transfer belt 18 as an elastic belt. The present invention is not limited to this, and can be applied to a case where a toner image formed on the photosensitive drum 19 is directly transferred to an intermediate transfer belt as an elastic belt. In this case, the toner image once transferred onto the intermediate transfer belt is then transferred onto a transfer material. This intermediate transfer belt is used, for example, in a color image forming apparatus. Further, the present invention can be applied to a case where the elastic belt is a photosensitive belt.

[0060]

As described above, according to the present invention,
By increasing the transfer area, the latitude of the transfer current can be increased. Thus, stable transfer can be maintained even when the volume resistivity of the transfer belt changes due to durability or environment, and occurrence of image defects such as scattered transferred images can be prevented.

Further, by increasing the transfer area, it is possible to increase the suction area for adsorbing the transfer material on the transfer belt. This increases the attraction force in the direction of the transfer belt acting on the transfer material when the transfer material is separated from the image carrier,
The transfer material can be surely separated from the image carrier. Therefore, it is possible to prevent a jam or an image defect due to a separation failure.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a configuration of a belt conveyance device according to a first embodiment.

FIG. 2 is a longitudinal sectional view of the belt conveyance device according to the first embodiment, taken along a transfer belt moving direction.

FIG. 3 is a longitudinal sectional view of the image forming apparatus to which the belt conveyance device according to the first embodiment is mounted.

FIG. 4 is a diagram illustrating transfer / separation of a belt conveyance device in the first embodiment.

FIG. 5 is a vertical cross-sectional view of a belt conveyance device according to a second embodiment, taken along a transfer belt moving direction.

FIG. 6 is a view taken along line BB of FIG. 5;

FIG. 7 is a diagram showing a correlation between a static elimination voltage and a static elimination current in the second embodiment.

FIG. 8 is a vertical cross-sectional view of a belt conveyance device according to a third embodiment, taken along a transfer belt moving direction.

FIG. 9 is a longitudinal sectional view of an image forming apparatus to which a conventional belt conveying device is mounted.

FIG. 10 is a longitudinal sectional view of a conventional belt conveying device taken along a transfer belt moving direction.

FIG. 11 is a vertical cross-sectional view of another conventional belt conveyance device taken along a transfer belt moving direction.

[Explanation of symbols]

 Reference Signs List 16 drive roller 17 roller (tension roller) 18 elastic belt (transfer belt) 19 image carrier (photosensitive drum) 20a first roller (transfer roller) 20b second roller (transfer roller) 21, 21A, 21B belt transport device 34 2 rollers (bias roller) 35 Spacer (butting roller) K Moving direction of elastic belt P Transfer material S Tangent line T Contact area (transfer area, separation area)

Claims (9)

[Claims] An elastic belt stretched over a plurality of rollers including a driving roller is brought into contact with an image carrier to form a contact area, and a toner image formed on the image carrier is transferred to the contact area. A belt conveying device that transfers the elastic belt to the surface of the elastic belt through a first roller and a second roller that press the elastic belt against the image carrier from the back side inside the elastic belt; The belt conveying device, wherein the contact area is formed between the first roller and the second roller of the belt. 2. The elastic belt according to claim 1, wherein a charge for transferring a toner image on the image carrier to a surface of the elastic belt is applied to the elastic belt by the first roller and the second roller. 3. The belt transport device according to claim 1. 3. A contact area is formed by contacting an elastic belt stretched over a plurality of rollers including a driving roller with an image carrier, and a toner image formed on the image carrier is transferred to the contact area. A belt conveying device for transferring the image onto a transfer material surface carried on the elastic belt via a first roller and a second roller which press the elastic belt against the image carrier from the back side inside the elastic belt. A belt conveying device, wherein the contact area is formed between the first roller and the second roller of the elastic belt. 4. The elastic belt according to claim 3, wherein electric charges for transferring the toner image on the image carrier to the surface of the transfer material are applied to the elastic belt by the first roller and the second roller. 3. The belt transport device according to claim 1. 5. The image forming apparatus according to claim 1, wherein the first roller is disposed on an upstream side along a moving direction of the elastic belt, and the second roller is disposed on a downstream side. The method according to claim 3, wherein an electric charge for transferring to the surface of the transfer material is applied to the elastic belt by the first roller, and the electric charge of the elastic belt is removed by the second roller after the toner image is transferred. The belt conveying device as described in the above. 6. The moving direction of the elastic belt after passing through the contact area is set so as to be above a tangent line between the image carrier and a second roller disposed below the image carrier. The belt conveyance device according to claim 5, wherein: 7. The device according to claim 1, wherein the first roller and the second roller are not in contact with the elastic belt.
3. The belt transport device according to claim 1. 8. A cylindrical spacer is disposed at each of both longitudinal ends of the first roller and the second roller, and the spacer is applied to the back surface of a portion corresponding to a non-image forming area of the elastic belt. The belt conveyance device according to claim 7, wherein a distance between the first roller and the second roller and the elastic belt is kept constant by being in contact with each other. 9. An image comprising: an image carrier; a toner image forming means for forming a toner image on the image carrier; and the belt transport device according to claim 1. Forming equipment.