JPH1055092A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form a high-quality image without a defect such as a worm- eaten spot. SOLUTION: When a toner image 6 transferred to an intermediate transfer belt 21 is secondarily transferred to a transfer material, a secondary transfer belt 31 is brought into press-contact with the intermediate transfer belt 21 between two secondary transfer rollers 26 and 27, of a primary transfer unit, to make pressure applied to the contact surfaces of the transfer belts 31 and 21 smaller, so that the application of excess pressure to the toner image 6 formed on the belt 21 can be prevented. Since the secondary transfer roller 27 facing a bias applying part 34 is connected to a ground with a resistor having middle resistance or more, the leakage of an electric charge from the secondary transfer roller 27 in a transferring region is prevented to secure an effective electric field at the time of performing the transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a full-color image, and more particularly to a high-quality image without defects.

[0002]

2. Description of the Related Art In an image forming apparatus for forming a full-color image, toner images of a plurality of colors formed on a photosensitive member are transferred onto an intermediate transfer belt, and the toner images transferred onto the intermediate transfer belt are transferred. An apparatus employing a transfer method based on an intermediate transfer belt system for transferring an image onto transfer paper is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-28.
JP-A-2491, JP-A-5-210316, JP-A-5-3135
No. 25, etc. In this transfer method, as shown in FIG. 5, a secondary transfer roller 26 having a medium resistance is provided by grounding the inside of the intermediate transfer belt 21 having a medium resistance (surface resistance: 10 ⁷ to 10 ¹³ Ω). A paper transfer roller 41 is provided at a position outside the intermediate transfer belt 21 facing the secondary transfer roller 26,
The toner image 6 transferred to the intermediate transfer belt 21 is transferred to a transfer paper 7.
When a transfer bias is applied to the paper transfer roller 41, the paper transfer roller 41 is brought into pressure contact with the position of the intermediate transfer belt 21 that is in contact with the secondary transfer roller 26. The toner image 6 is transferred to a transfer sheet 7 passing between the intermediate transfer belt 21 and the paper transfer roller 41.

Further, toner is applied to the first surface (front surface) of the transfer paper 7.
After the image 6 is transferred and fixed, the toner image 6 is transferred and fixed on the second surface (back surface) of the transfer paper 7, or the image is formed not only on plain paper but also on thick transfer paper. ing.

[0004]

As described above, when the toner image is transferred to the transfer paper by bringing the paper transfer roller into pressure contact with the intermediate transfer belt, the toner transferred to the intermediate transfer belt is transferred. The layer is compressed by the local pressure of the paper transfer roller, the releasability between the toner and the belt surface is reduced, and a part of the toner remains on the intermediate transfer belt, and the transfer paper or the like is removed. There is a possibility that a so-called insect-eating image in which a part of the transferred image is defective, that is, there is a defect.

Further, an air gap exists near the paper transfer entrance, and as shown in FIG. 5, an electric line of force (electric field) φ is formed by the paper transfer bias at this portion, and the toner is transferred to the transfer paper before the nip. However, there is a disadvantage in that transfer dust is generated on the transfer paper, and a defect occurs in the image transferred on the transfer paper.

SUMMARY OF THE INVENTION It is an object of the present invention to improve such disadvantages and to provide an image forming apparatus capable of forming a high quality image without defects.

[0007]

An image forming apparatus according to the present invention comprises: a primary transfer unit for transferring toner images of a plurality of colors formed on a photosensitive member onto an intermediate transfer belt having a medium resistance;
And a secondary transfer unit for transferring the toner image transferred to the intermediate transfer belt to a transfer material. It has two secondary transfer rollers arranged in the transfer belt, and the secondary transfer roller on the downstream side of the two secondary transfer rollers is the two secondary transfer rollers. The secondary transfer unit is connected to an earth via a resistor having a resistance value equal to or greater than the resistance value of the intermediate transfer belt between the rollers. Bias transfer means, the secondary transfer belt is wound along the moving direction of the transfer material, and the earth roller faces an intermediate position between the two secondary transfer rollers of the primary transfer unit. The bias application means is provided in a secondary transfer belt that performs transfer between the two secondary transfer rollers. 2 transfer b provided on the downstream side in the moving direction of the - provided La opposed to the downstream side of the secondary transfer inner belt, characterized by comprising a conductive elastic member in contact with the secondary transfer belt.

Preferably, the conductive elastic member of the bias applying means is formed of a conductive brush.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention has an image forming unit, a primary transfer unit, a secondary transfer unit, and a fixing unit. The image forming unit forms a plurality of toner images on the photoreceptor surface. The primary transfer unit has an intermediate transfer belt, a primary transfer unit, and two secondary transfer rollers arranged in the intermediate transfer belt at a predetermined interval along the moving direction of the transfer material. Then, the toner image formed on the surface of the photoreceptor is primarily transferred to an intermediate transfer belt at a primary transfer section.

The secondary transfer unit has a secondary transfer belt wound along a moving path of the transfer material, a bias applying unit provided inside the secondary transfer belt, and an ausroller. When the toner image transferred to the intermediate transfer belt is secondarily transferred to a transfer material, the secondary transfer belt is pressed against the intermediate transfer belt between the two secondary transfer rollers of the primary transfer unit, The secondary transfer belt and the intermediate transfer belt are brought into contact with each other with a relatively large area, the pressure applied to the contact surface between the secondary transfer belt and the intermediate transfer belt is reduced, and the toner of the toner image formed on the intermediate transfer belt is contacted. Prevents excessive pressure.

An earth roller is provided in a secondary transfer belt facing an intermediate position between the two secondary transfer rollers of the primary transfer unit, and a bias applying section is provided with two secondary transfer rollers. The toner image transferred to the intermediate transfer belt is provided in the secondary transfer belt facing the secondary transfer roller provided downstream of the transfer material in the moving direction of the transfer material. At the time of transfer, the contact area between the intermediate transfer belt and the secondary transfer belt on the upstream side of the art roller is set as a non-transfer area, and the contact between the intermediate transfer belt and the secondary transfer belt on the downstream side of the art roller is performed. Using the region as a transfer region, lines of electric force (electric field) generated on the upstream side of the contact region are suppressed, and transfer dust is prevented from being generated and attached to the transfer material.

Further, the secondary transfer roller of the transfer area is connected to the ground via a resistor having a medium resistance or higher, and the secondary transfer roller of the transfer area is connected to the ground.
Leakage of electric charge from the secondary transfer roller is prevented, and the current flowing in the secondary transfer belt between the bias applying section and the earth roller, the intermediate transfer belt having a medium resistance and the secondary transfer roller are supplied to the secondary transfer roller. A parallel electric field is formed by the flowing current to secure an effective electric field during transfer.

The secondary transfer unit is arranged such that the secondary transfer belt is pressed against the intermediate transfer belt when the toner image is secondary-transferred onto the transfer material, and the intermediate transfer belt and the secondary transfer belt are used during the secondary transfer. To prevent an air gap from occurring.
Further, when the secondary transfer is not performed, the secondary transfer belt is separated from the intermediate transfer belt to prevent an abnormal image from being generated when a plurality of toner images are superimposed on the intermediate transfer belt.

Further, the bias applying section is constituted by a brush having conductivity, and the pressing force at the time of transfer is further reduced.

[0015]

FIG. 1 is a block diagram showing an embodiment of the present invention. As shown in the figure, the image forming apparatus has an image forming unit 1, a primary transfer unit 2, a secondary transfer unit 3, a transport unit 4, and a fixing unit 5. The image forming unit 1 includes a charging charger arranged around the photoconductor 11.
The irradiating part of the jar 12 and the laser beam 13 and the yellow
(Y), magenta (M), cyan (C), and black (B).

The primary transfer unit 2 includes an intermediate transfer belt 21
, A bias application roller 23, a primary transfer section 22 having an earth roller 24, a tension roller 25, two secondary transfer rollers 26 and 27, a cleaning section 28, and a cleaning section. It has an opposing roller 29 of the part 28. The intermediate transfer belt 21 is formed of a material having medium resistance electrical characteristics having a surface resistance of 10 ⁷ to 10 ¹³ Ω, and includes an earth roller 24, a bias application roller 23, a tension roller 25, and a secondary roller. Transfer ro
Rollers 26 and 27 and an opposing roller 29. The intermediate transfer belt 21 is separated from the surface of the photoconductor 11 by a contact / separation mechanism (not shown) except when the toner image on the photoconductor 11 is primarily transferred, and the surface of the photoconductor 11 is only used for the primary transfer to the intermediate transfer belt 21. Is pressed against. Two secondary transfer rollers 26 and 2 provided inside the intermediate transfer belt 21
Reference numeral 7 is disposed in the intermediate transfer belt 21 at a predetermined interval L along the moving direction of the transfer material 7, as shown in the partial configuration diagram of FIG. Among the secondary transfer rollers 26 and 27, a secondary transfer roller 27 provided on the downstream side in the moving direction of the transfer material 7 is an intermediate transfer belt between the two secondary transfer rollers 26 and 27. 21 or more, for example, 10 ⁶ to 10 ¹²
It is connected to the earth via a resistor 271 having a resistance value of Ω or more.

The secondary transfer unit 3 includes a secondary transfer belt 31 wound around a driving roller 32 and a driven roller 33 provided along a moving path of the transfer material 7, and a secondary transfer belt 31.
, A bias applying section 34 and an earth roller 35 provided inside. The secondary transfer belt 31 has a surface resistance of 10 ⁷
It is formed of a material having an electrical characteristic of medium resistance of about 10 ¹³ Ω. The earth roller 35 is connected to the primary transfer unit 2 2.
2 which faces the intermediate position between the secondary transfer rollers 26 and 27 of the book
A bias application unit 34 provided in the next transfer belt 31
Is a roller made of, for example, a conductive member, and is opposed to a secondary transfer roller 27 provided on the downstream side in the moving direction of the transfer material 7 among the two secondary transfer rollers 26 and 27. And is in contact with the secondary transfer belt 31. The secondary transfer unit 3 is provided rotatably in the direction of the primary transfer unit 2 around a driving roller 32 as shown in the partial configuration diagram of FIG. At the time of the next transfer, the secondary transfer belt 31 is pressed against the intermediate transfer belt 21, and when the secondary transfer is not performed, the secondary transfer belt 31 is separated from the intermediate transfer belt 21.

When a full-color image is formed by the image forming apparatus constructed as described above, the charging charger 12 is used.
The surface of the photoreceptor 11 charged with the laser beam 13 is irradiated with a laser beam 13 to form an electrostatic latent image. The latent image on the photoreceptor 11 is visualized with toner attached to each color by a color developing unit 14 composed of yellow (Y), magenta (M), cyan (C), and black (B). The toner image on the photoreceptor 11 is primarily transferred onto the intermediate transfer belt 21 of the primary transfer unit 2 and then removed by the drum cleaning unit 15. When the toner image on the photoconductor 11 is primarily transferred to the intermediate transfer belt 21, the intermediate transfer belt 21 contacts the surface of the photoconductor 11 and indirectly applies a charge in the primary transfer unit 22 to Y,
The primary transfer is performed for each of the M, C, and B toners. That is, when the first toner image formed on the photoconductor 11 is primarily transferred onto the intermediate transfer belt 21, the intermediate transfer belt 21 is pressed against the surface of the photoconductor 11 by a contacting / separating mechanism (not shown) to perform the first transfer. The first transfer of the toner image is performed. When the first transfer of the toner image is completed, the intermediate transfer belt 21
Is separated from the surface of the photoconductor 11, the rotation of the intermediate transfer belt 21 is controlled so that the next toner image is superimposed accurately, and the toner image is again pressed against the surface of the photoconductor 11 to perform the first transfer of the second toner image. . This primary transfer is sequentially repeated for each toner, and the toner images of Y, M, C, and B are sequentially superimposed on the intermediate transfer belt 21. The full-color toner image 6 transferred onto the intermediate transfer belt 21 is secondarily transferred to the transfer material 7 conveyed onto the secondary transfer unit 3.

When the full-color toner image 6 transferred onto the intermediate transfer belt 21 is secondarily transferred to the transfer material 7,
The secondary transfer unit 3 is rotated toward the primary transfer unit 2 to press the secondary transfer belt 31 against the intermediate transfer belt 21 between the secondary transfer rollers 26 and 27 as shown in FIG. A bias is applied by a bias applying unit 34 to charge the toner image, and the toner image 6 on the intermediate transfer belt 21 is secondarily transferred onto the transfer material 7 conveyed between the intermediate transfer belt 21 and the secondary transfer belt 31. At the time of the secondary transfer, the secondary transfer belt 31 is rotated about the drive roller 32 to rotate the secondary transfer roller 31.
Since the intermediate transfer belt 21 is in pressure contact with the intermediate transfer belt 21 between 6 and 27, it can be pressed with a small pressing force F. Further, since the secondary transfer belt 31 and the intermediate transfer belt 21 come into contact with each other with a relatively large area, the pressure applied to the contact surface between the secondary transfer belt 31 and the intermediate transfer belt 21 can be reduced, and the intermediate transfer belt 21 Applying an excessive pressure to the toner of the formed toner image 6 can be prevented, and the releasability between the toner image 6 formed on the intermediate transfer belt 21 and the belt surface is reduced. Can be prevented. Therefore, it is possible to prevent a so-called worm-eating image from being generated in the toner image secondarily transferred to the transfer material 7.

The toner image 6 on the intermediate transfer belt 21
When the secondary transfer roller 27 in the transfer area is directly connected to the ground when the image is transferred to the transfer material 7, the secondary transfer roller 27 from the intermediate transfer belt 21 having a medium resistance is used. This causes the transfer charge to leak through the device, resulting in a shortage of the effective electric field during transfer. Therefore, the secondary transfer roller 27 is connected to the earth via a resistor 271 having a medium resistance of, for example, 10 ⁶ to 10 ¹² Ω or more, and the bias applying section 34 and the earth roller 3 are connected.
A parallel electric field is formed by a current flowing in the secondary transfer belt 31 between the intermediate transfer belt 5 and the current flowing in the intermediate transfer belt 21 and the secondary transfer roller 27 having a medium resistance, thereby securing an effective electric field at the time of transfer. An even image can be stably formed.

Further, a bias applying section 34 is provided between the two secondary transfer rollers 26 and 27 of the primary transfer unit 2 on the downstream side in the moving direction of the transfer material 7.
7 is provided in the secondary transfer belt 31 facing the intermediate transfer roller 7, and the earth roller 35 is provided in the secondary transfer belt 31 facing the intermediate position between the secondary transfer rollers 26 and 27. When the toner image 6 on the transfer belt 21 is secondarily transferred to the transfer material 7, a contact area between the secondary transfer belt 31 and the intermediate transfer belt 21 on the upstream side of the athlet roller 35 is set as a non-transfer area, Secondary transfer belt 3 downstream of the art roller 35
The contact area between the transfer belt 1 and the intermediate transfer belt 21 can be a transfer area. And the secondary transfer belt 3 sandwiching the transfer material 7
1 and the intermediate transfer belt 21 are substantially parallel and move at the same speed, so that the secondary transfer can be performed without generating an air gap between the secondary transfer belt 31 and the intermediate transfer belt 21. . Therefore, at the time of the secondary transfer, the transfer bias applied to the intermediate transfer belt 21 causes
Lines of electric force (electric field) generated upstream of the next transfer roller 26
Can be suppressed, transfer dust can be prevented from being generated and attached to the transfer material 7, and a high-quality image can be stably formed on the transfer material 7.

When the secondary transfer is not performed, the secondary transfer belt 31 is separated from the intermediate transfer belt 21. Therefore, it is necessary to prevent an abnormal image from occurring when a plurality of toner images are superimposed on the intermediate transfer belt 21. Can be.

Although the above embodiment has been described with respect to the case where the bias applying section 34 is constituted by a roller having conductivity, the bias applying section 34 is constituted by a brush 34a having conductivity as shown in FIG. Can be made lower.

[0024]

As described above, according to the present invention, when the toner image transferred to the intermediate transfer belt is secondarily transferred to the transfer material, the secondary transfer belt is used for the two secondary transfer of the primary transfer unit. The secondary transfer belt and the intermediate transfer belt are brought into contact with a relatively large area by pressing against the intermediate transfer belt between the rollers,
The pressure applied to the contact surface between the secondary transfer belt and the intermediate transfer belt is reduced to prevent applying excessive pressure to the toner of the toner image formed on the intermediate transfer belt. It is possible to prevent the releasability between the formed toner image and the belt surface from deteriorating, and to prevent the occurrence of a worm image in the toner image secondary-transferred to the transfer material. An image can be formed.

An earth roller is provided in a secondary transfer belt facing an intermediate position between the two secondary transfer rollers of the primary transfer unit, and the bias applying means is provided with two secondary transfer rollers. −
The toner image transferred to the intermediate transfer belt is provided in the secondary transfer belt facing the secondary transfer roller provided downstream of the transfer material in the moving direction of the transfer material. And the intermediate transfer belt upstream of the
The contact area of the next transfer belt is set as a non-transfer area,
Since the contact area between the intermediate transfer belt and the secondary transfer belt downstream of the contact area is used as the transfer area, lines of electric force (electric field) generated upstream of the contact area are suppressed, and transfer dust is generated and adheres to the transfer material. And a defect-free image can be formed on the transfer material.

Further, the secondary transfer roller in the transfer area is connected to the ground via a resistor having a medium resistance or higher, and the secondary transfer roller in the transfer area is connected to the ground.
Leakage of electric charge from the secondary transfer roller is prevented, and the current flowing in the secondary transfer belt between the bias applying means and the earth roller, and the intermediate transfer belt and the secondary transfer roller having a medium resistance are supplied to the secondary transfer roller. By forming a parallel electric field with the flowing current, an effective electric field at the time of transfer can be secured, and a stable image can be formed.

In the secondary transfer unit, the secondary transfer belt is pressed against the intermediate transfer belt when the toner image is secondary-transferred onto the transfer material, and the intermediate transfer belt and the secondary transfer belt are used during the secondary transfer. Therefore, it is possible to prevent the occurrence of transfer dust, and to stably form a high-quality image.

Further, by forming the bias applying means with a conductive brush, the pressing force at the time of transfer can be further reduced, and a high quality image can be formed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a partial configuration diagram illustrating a secondary transfer operation state of the embodiment.

FIG. 3 is a partial configuration diagram illustrating a movable state of a secondary transfer unit of the embodiment.

FIG. 4 is a configuration diagram showing another embodiment.

FIG. 5 is a configuration diagram showing a secondary transfer unit of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming unit 2 Primary transfer unit 3 Secondary transfer unit 11 Photoconductor 14 Color developing part 21 Intermediate transfer belt 22 Primary transfer part 26 Secondary transfer roller 27 Secondary transfer roller 31 Secondary transfer belt 34 bias applying part 35 earth roller 271 resistor

Claims (2)

[Claims] 1. A primary transfer unit for transferring a plurality of color toner images formed on a photoreceptor onto an intermediate transfer belt having a medium resistance, and a toner image transferred on the intermediate transfer belt to a transfer material. An image forming apparatus including a secondary transfer unit for causing the two transfer units to be disposed in the intermediate transfer belt at a predetermined interval along the moving direction of the transfer material.
A secondary transfer roller having a secondary transfer roller on the downstream side of the two secondary transfer rollers having the same resistance as an intermediate transfer belt between the two secondary transfer rollers; The secondary transfer unit is connected to an earth via a resistor having a resistance value of about the same level or more. The secondary transfer unit includes a secondary transfer belt having a medium resistance, an earth roller, and bias applying means. The belt is wound along the direction of movement of the transfer material, and the earth roller is a secondary transfer unit of the primary transfer unit.
The bias applying means is provided in the secondary transfer belt facing the intermediate position between the two secondary transfer rollers, and the bias applying means is provided on the downstream side in the moving direction of the transfer material among the two secondary transfer rollers. An image forming apparatus comprising a conductive elastic member provided in a secondary transfer belt on the downstream side facing a secondary transfer roller and in contact with the secondary transfer belt. 2. The image forming apparatus according to claim 1, wherein said conductive elastic member of said bias applying means is formed of a conductive brush.