JP5043366B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image forming apparatus that transfers a toner image carried on a belt-like image carrier onto a transfer material using a transfer belt. .

A conventional transfer method will be described with reference to FIG. FIG. 5 is a configuration diagram of a secondary transfer unit of a general roller transfer system. In the conventional roller transfer system, the transfer material 104 is conveyed by the registration rollers 22 and 23. The intermediate transfer belt 100 and the transfer material 104, which are belt-shaped image carriers, are sandwiched by the secondary facing roller 103 and the secondary transfer roller 102, and a contact region (nip region and nip region) is interposed between the intermediate transfer belt 100 and the transfer material 104. Called) is formed.
By applying a transfer electric field to the secondary facing roller 103 or the secondary transfer roller 102, the toner image formed on the intermediate transfer belt 100 is transferred to the transfer material 104 in the nip region.

By the way, in this transfer method, a gap is generated between the intermediate transfer belt 100 and the transfer material 104 in the region A immediately before the transfer material 104 enters the nip region. Due to this gap, electric discharge easily occurs in the region A. Due to the electric discharge generated between the transfer material 104 and the toner image on the intermediate transfer belt, the charge of the toner particles forming the toner image on the intermediate transfer belt 100 is reversed in polarity. As a result, even if a transfer electric field is applied in the nip region, a phenomenon in which the toner image is not transferred to the transfer material 104 occurs, causing image quality defects.
Even in the case where no discharge occurs in the region A, the region A is close to the nip region to which the transfer electric field is applied. Originally, pre-transfer is performed at a position deviated from the position of the transfer material 104 onto which the toner particles are transferred, which causes image quality defects such as transfer dust. As described above, there is a problem that the gap in the region A causes a transfer failure.

A technique for solving this problem will be described with reference to FIG. FIG. 6 is a configuration diagram of a secondary transfer portion of a roller transfer system that is an improvement of the roller transfer system of FIG. In this method, the secondary transfer roller 102 is disposed on the upstream side in the moving direction of the intermediate transfer belt 100, and further wound around the outer surface of the intermediate transfer belt 100, so that the intermediate transfer belt 100 just before entering the nip region A gap between the transfer material 104 and the transfer material 104 can be eliminated. As a result, it was possible to suppress the discharge that occurred immediately before the nip region, and to suppress image quality defects due to the discharge.
However, when the transfer is attempted at a higher speed, the time required to pass through the nip region is shortened, so that it is considered that the transfer electric field necessary for transferring the toner image on the intermediate transfer belt 100 to the transfer material 104 is increased. .
For this reason, as shown in FIG. 6, if only the secondary transfer roller 102 is wound around the intermediate transfer belt 100, the transfer material 104 is positioned between the transfer material 104 and the intermediate transfer belt 100 on the upstream side in the moving direction of the intermediate transfer belt 100. Since it is impossible to suppress the discharge in the gap that can be reduced, it is considered that the image quality is deteriorated.

Therefore, a method using the transfer belt 101 shown in FIG. 7 has been proposed as a method for suppressing discharge even with a high transfer electric field. In the method of FIG. 7, the assist roller 106 can be disposed at an arbitrary position, so that the transfer material 104 and the intermediate transfer belt 100 can be brought into close contact with each other at an upstream position in the moving direction of the intermediate transfer belt 100. Become.
As a result, the discharge can be suppressed even when the transfer electric field is high, and a good image quality can be obtained. A related technique is disclosed in Japanese Patent Application Laid-Open No. 11-15298.
Japanese Patent Laid-Open No. 11-15298

In the conventional technique, the intermediate transfer belt 100 and the transfer material 104 are brought into close contact with each other before the transfer electric field is applied, so that discharge can be suppressed and a high-quality image can be obtained. The transfer belt assist roller 106 must be used in order to be in close contact with the roller 100. As a result, a new problem arises in that the structure becomes complicated and the cost increases.
The present invention has been made in consideration of the above-described circumstances, and presupposes a belt transfer system, and suppresses discharge generated in the gap at the entrance of the nip region, thereby suppressing image quality defects such as transfer omission and transfer dust. In addition, it is an object of the present invention to provide an image forming apparatus that does not require a complicated mechanism and does not use an extra member so that the cost can be reduced.

In order to achieve the above object, according to the first aspect of the present invention, an opposing roller for urging the belt-like image carrier in the direction of the transfer belt is provided on the inner periphery of the belt-like image carrier. A transfer roller that urges the transfer belt in the direction of the belt-shaped image carrier is provided on the inner periphery, and a potential difference is generated between the opposing roller and the transfer roller, so that a contact area between the image carrier and the transfer belt In the image forming apparatus , the transfer roller is arranged so that the transfer roller is wound around the image carrier upstream of the counter roller in the moving direction of the image carrier without contacting the transfer roller with the counter roller via the image carrier. Main features.
The invention according to claim 2 is characterized in that, in the image forming apparatus according to claim 1, the image forming apparatus in which the volume resistivity of the transfer belt is made lower than the volume resistivity of the belt-shaped image carrier.
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, a line segment that passes through the center point of the opposing roller and is perpendicular to the tangential direction when the belt-like image carrier is in contact with the opposing roller is provided. The distance between the line segments passing through the center point of the transfer roller and parallel to the line segment is defined as an offset amount L, the volume resistivity R of the transfer belt, the width m of the transfer belt, the thickness d of the transfer belt, and the belt-like image. When the transfer current value necessary to transfer the toner image formed on the carrier onto the transfer material is I, the voltage V = I × R × L / (m × d) applied to the transfer belt is the transfer current. An image forming apparatus having an offset amount L that satisfies the upper limit value of the voltage that can be supplied by the transfer bias power supply for supplying the image is a main feature.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the image forming apparatus includes a plurality of photoconductors on which toner images are formed, and the image carrier is an intermediate transfer belt. The toner images on the plurality of photoconductors are respectively transferred to the intermediate transfer belt.

According to the present invention, the opposed roller for urging the belt-shaped image carrier in the transfer belt direction is provided on the inner periphery of the belt-shaped image carrier, and the transfer belt is belt-shaped on the inner periphery of the transfer belt. By providing a transfer roller that urges in the direction of the image carrier , generating a potential difference between the opposing roller and the transfer roller, and forming a transfer electric field in a contact area between the image carrier and the transfer belt, In an image forming apparatus for transferring a toner image formed on a solid image carrier onto a transfer material conveyed by a transfer belt, the transfer roller is not brought into contact with the opposing roller via the image carrier, but from the opposing roller. also assumes belts transfer system upstream the transfer roller in the direction of movement is arranged by winding the image carrier of the image bearing member, than the discharge in the nip region entrance gap becomes difficult to occur, transfer void, transfer dust, etc. of Suppressing quality defects, besides, does not require a complicated mechanism, by not applying an extra member, it is possible to provide an image forming apparatus capable of suppressing the cost.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an image forming system of an image forming apparatus according to an embodiment of the present invention. First, the configuration and operation of the image forming unit and the transfer unit will be described with reference to FIG.
The image forming unit and the primary transfer unit include chargers 10a to 10d, exposure units 11a to 11d, developing units 12a to 12d, static eliminators 13a to 13d, cleaners 14a to 14d, photoconductors 15a to 15d, and primary transfer rollers. The intermediate transfer belt 100 is an image carrier composed of endless belts 16a to 16d.
The photoconductors 15a to 15d rotate in the illustrated direction. The intermediate transfer belt (image carrier) 100 is stretched by rollers 30 and 31 and is in contact with the photoreceptors 15a to 15d. Each of the devices is in contact with the intermediate transfer belt 100 in the rotational direction of the photoconductor 15, and around the photoconductors 15a to 15d, the static eliminators 13a to 13d, the cleaners 14a to 14d, the chargers 10a to 10d, and the exposure. The devices 11a to 11d and the developing devices 12a to 12d are arranged in this order.
The primary transfer rollers 16a to 16d are arranged to be pressed from the back side of the region where the photoconductors 15a to 15d are in contact with the intermediate transfer belt 100. In this embodiment, the roller that drives the intermediate transfer belt 100 is the roller 30, and the intermediate transfer belt 100 is moved in the direction of the arrow by the roller 30.

Next, an image forming method and a primary transfer method will be described. The photoreceptor 15 is charged by the charger 10. Thereafter, an electrostatic latent image is generated on the charged photoconductor 15 by irradiating a laser beam from the exposure device 11 based on image data from the scanner or the PC. Thereafter, the toner charged by the developing device 12 is developed on the photoreceptor 15. The toner image formed on the photoreceptor 15 is transferred onto the intermediate transfer belt 100 by applying a transfer electric field with a current or voltage controlled by a constant current or a constant voltage to the primary transfer roller 16.
After the toner image is transferred onto the intermediate transfer belt 100, the photoconductor 15 removes the residual charge remaining on the photoconductor 15 by the static eliminator 13 and removes the toner remaining on the photoconductor 15 by the cleaner 14. The process of returning to the charger 10 is repeated.
The image forming apparatus of FIG. 1 has an image forming portion for each of the four colors of cyan, magenta, yellow, and black, and performs primary transfer of the toner image formed on the photoreceptor 15a onto the intermediate transfer belt 100. After the transfer, the intermediate transfer belt 100 moves to the photoconductor 15b and transfers the toner image formed by the photoconductor 15b onto the toner image transferred by the photoconductor 10a. Thereafter, the photoconductors 15c and 15d and the toner image are sequentially transferred in an overlapping manner.
The toner image transferred onto the intermediate transfer belt 100 is transferred to a secondary transfer portion formed by a secondary opposing roller 103 that holds the intermediate transfer belt 100 and a secondary transfer roller 102 that holds a transfer belt 101 including an endless belt. Transferred to the transfer material 104. Fixing rollers 20 and 21 are disposed on the downstream side of the secondary transfer portion.

Next, the secondary transfer portion which is a feature of the present invention will be described in detail.
FIG. 2 is a detailed configuration diagram in the vicinity of the secondary transfer portion in the image forming apparatus shown in FIG.
In this embodiment, the transfer belt 101 is used, and the secondary transfer roller 102 is not brought into contact with the secondary opposing roller 103 via the intermediate transfer belt 100, and the secondary transfer roller 102 is upstream in the moving direction of the intermediate transfer belt 100. The intermediate transfer belt 100 is wound around the intermediate transfer belt 100.
Compared with the method using the conventional transfer belt 101 shown in FIG. 7, in this embodiment, it is not necessary to use the transfer belt assist roller 106, so that the structure is easy and the cost can be reduced.
Here, the volume resistivity of the transfer belt 101 is limited by the volume resistivity of the intermediate transfer belt 100. 3 is an enlarged view of the secondary transfer portion when the volume resistivity of the transfer belt 101 is lower than the volume resistivity of the intermediate transfer belt 100 in the configuration of FIG. 2, and FIG. 4 is a diagram of FIG. 4 is an enlarged view of a secondary transfer portion when the volume resistivity of the transfer belt 101 is higher than the volume resistivity of the intermediate transfer belt 100. FIG.

When the volume resistivity of the transfer belt 101 is lower than the volume resistivity of the intermediate transfer belt 100, a transfer current flows along the path indicated by the arrow B in FIG. The transfer point C is transferred to the transfer material 104.
In this case, since the intermediate transfer belt 100 and the transfer material 104 can be brought into close contact with the transfer point C at a position separated by the offset amount L, discharge is unlikely to occur and image quality defects can be suppressed.
Conversely, when the volume resistivity of the transfer belt 101 is higher than that of the intermediate transfer belt 100, a transfer current flows along the path indicated by the arrow B in FIG. The transfer point C is transferred to the transfer material 104.
In this case, since the intermediate transfer belt 100 and the transfer material 104 are brought into close contact immediately before the transfer point C, discharge is likely to occur in the gap immediately before the transfer point C, and image quality is liable to occur. Therefore, the volume resistivity of the transfer belt 101 must be set lower than the volume resistivity of the intermediate transfer belt 100.
Here, the offset amount L is limited by the transfer bias power source. Hereinafter, the limitation on the offset amount L will be described with reference to FIG.

The transfer current flows along the arrow B. At this time, the volume resistivity R of the transfer belt 101, the width m of the transfer belt 101, the thickness d of the transfer belt 101, and a transfer current value necessary for transferring the toner image 105 on the intermediate transfer belt 100 to the transfer material 104. Is I, the shared voltage V along the moving direction of the transfer belt 101 is expressed by I × R × L / (m × d). From this equation, it can be seen that the shared voltage along the moving direction of the transfer belt 101 is proportional to the offset amount L.
Therefore, if the offset amount L is excessively long, the shared voltage along the moving direction of the transfer belt 101 becomes too large, which may exceed the upper limit value of the voltage value of the transfer bias power source.
In this case, a transfer electric field sufficient to transfer the toner image 105 on the intermediate transfer belt 100 to the transfer material 104 at the transfer point C cannot be applied. As a result, a phenomenon that the toner image 105 on the intermediate transfer belt 100 is not transferred to the transfer material 104 occurs, resulting in poor image quality. For the above reasons, the offset amount L is limited.
As an actual value, when the upper limit value of the transfer bias power supply is 5 kV, a polyimide belt is used as the transfer belt 104, the volume resistivity is 108 Ω · cm, the transfer current is 30 μA, the transfer belt width is 30 cm, and the thickness is 100 μm, the offset amount L is 0. It must be kept below 5 cm.

1 is a schematic configuration diagram illustrating an image forming system of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a detailed configuration diagram in the vicinity of a secondary transfer unit in the image forming apparatus illustrated in FIG. 1. FIG. 3 is an enlarged view of a secondary transfer portion when the volume resistivity of the transfer belt is lower than the volume resistivity of the intermediate transfer belt in the configuration of FIG. 2. FIG. 3 is an enlarged view of a secondary transfer portion when the volume resistivity of the transfer belt is higher than the volume resistivity of the intermediate transfer belt in the configuration of FIG. 2. It is a block diagram (the 1) of the secondary transfer part of a general roller transfer system. FIG. 5 is a configuration diagram (part 2) of a secondary transfer unit of a general roller transfer system. It is a block diagram of the secondary transfer part of a general belt transfer system.

Explanation of symbols

100 Intermediate transfer belt (belt-shaped image carrier)
101 Transfer belt 102 Secondary transfer roller (transfer roller)
103 Secondary opposed roller (opposed roller)

Claims (4)

A counter roller for urging the image carrier in the direction of the transfer belt is provided on the inner periphery of the image carrier composed of an endless belt, and the transfer belt is disposed in the direction of the image carrier on the inner periphery of the endless belt. A transfer roller that urges the image bearing member , generates a potential difference between the opposing roller and the transfer roller, and forms a transfer electric field in a contact area between the image carrier and the transfer belt, thereby In the image forming apparatus for transferring the toner image formed on the transfer material conveyed by the transfer belt,
The image forming apparatus is characterized in that the transfer roller is not brought into contact with the opposing roller via the image carrier , and the transfer roller is disposed around the image carrier upstream of the opposing roller in the moving direction of the image carrier. apparatus.   2. The image forming apparatus according to claim 1, wherein the volume resistivity of the transfer belt is made lower than the volume resistivity of the image carrier.   3. The image forming apparatus according to claim 2, wherein a line segment that passes through a center point of the counter roller and is perpendicular to a tangential direction when the image carrier is in contact with the counter roller, and a center point of the transfer roller are defined. The distance between the line segments parallel to the line segment is defined as an offset amount L, the volume resistivity R of the transfer belt, the width m of the transfer belt, the thickness d of the transfer belt, and the toner formed on the image carrier. When a transfer current value necessary for transferring an image to a transfer material is I, a voltage V = I × R × L / (m × d) applied to the transfer belt is a transfer bias power source for applying a transfer current. Is an offset amount L satisfying the upper limit of the voltage that can be applied. The image forming apparatus according to any one of claims 1 to 3,
Comprising a plurality of photoreceptors on which toner images are formed;
  The image carrier is an intermediate transfer belt,
  An image forming apparatus, wherein toner images on the plurality of photosensitive members are respectively transferred to the intermediate transfer belt.

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