JPH1091013A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent releasing property between a toner image formed on an intermediate transfer belt and a belt surface from being deteriorated and to form the image of excellent quality by preventing the occurrence of a worm- eaten image with the toner image secondarily transferred on transfer material. SOLUTION: When the toner image transferred on the intermediate transfer belt 21 is secondarily transferred on the transfer material 7, bias voltage is applied from a bias applying part 34 provided on the downstream side of a contact area between the intermediate transfer belt 21 and a secondary transfer belt 31, and an electric field generated on the upstream side of the contact area between the intermediate transfer belt 21 and the secondary transfer belt 31 is suppressed, so that transfer dust is prevented from being generated and stuck to the tranfer material 7.

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. As shown in FIG. 4, this transfer method employs a medium resistance (surface resistance; 1 × 10 ⁷ to 10 ¹³ Ω).
A secondary transfer roller 26 having a medium resistance is provided in contact with the inside of the intermediate transfer belt 21 and a paper transfer roller 41 is provided at a position outside the intermediate transfer belt 21 opposed to the secondary transfer roller 26.
When the toner image 6 transferred to the intermediate transfer belt 21 is transferred to the transfer paper 7, the toner image 6 is in contact with the secondary transfer roller 26 while applying a transfer bias to the paper transfer roller 41. The toner image 6 is transferred to the transfer paper 7 passing between the intermediate transfer belt 21 and the paper transfer roller 41 by bringing the paper transfer roller 41 into pressure contact with the position of the intermediate transfer belt 21.

[0003]

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. 4, an electric line of force (electric field) φ is formed by this paper transfer bias, 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.

[0006]

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 a toner image transferred to the intermediate transfer belt to a transfer material. The secondary transfer unit of the intermediate transfer belt has a predetermined interval along a moving direction of the transfer material. The intermediate transfer belt has two medium-resistance secondary transfer rollers, and the secondary transfer unit has a medium-resistance secondary transfer belt and bias applying means. The transfer belt is wound in the direction of movement of the transfer material, and the bias applying means is opposed to a secondary transfer roller provided downstream of the two transfer rollers in the direction of movement of the transfer material. The secondary transfer belt is provided within the secondary transfer belt.

Preferably, the bias applying means is a direct applying means by corona transfer. Further, it is preferable that the bias applying unit is configured integrally with the driving unit of the secondary transfer belt.

[0008]

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 having a medium resistance, a primary transfer unit, and a secondary transfer unit. The secondary transfer section has two medium-resistance secondary transfer rollers disposed in the intermediate transfer belt at regular intervals in the direction of movement 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 medium-resistance secondary transfer belt wound along the movement path of the transfer material, and a bias applying section provided inside the secondary transfer belt. 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.

A bias applying section is provided in a secondary transfer belt facing a secondary transfer roller provided downstream of the two secondary transfer rollers in the moving direction of the transfer material. When the toner image transferred to the intermediate transfer belt is secondarily transferred to the transfer material, the lines of electric force (electric field) generated on the upstream side of the contact area between the intermediate transfer belt and the secondary transfer belt are suppressed. It is prevented from being generated and adhering to the transfer material.

The bias applying section is constituted by direct application means by corona transfer, so that the pressure applied to the contact surface between the secondary transfer belt and the intermediate transfer belt during the secondary transfer is further reduced.

Further, the bias applying section is formed integrally with the driving section of the secondary transfer belt so that the position of the bias applying section with respect to the secondary transfer belt is always kept constant, and the distance between the bias applying section and the secondary transfer belt at the time of transfer is increased. Prevents the resistance from fluctuating due to fluctuations in the resistance.

[0013]

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
And a primary transfer section 22 having a bias application roller 23 and an earth roller 24; a secondary transfer section having a tension roller 25 and two secondary transfer rollers 26 and 27; And a roller 29 facing the cleaning section 28. The intermediate transfer belt 21 has a surface resistance of 1 × 10 ⁷ to 10 ¹³ Ω
Formed of a material having medium resistance electrical characteristics
Roller 24, bias applying roller 23, tension roller 25, secondary transfer rollers 26 and 27, and opposing roller 2.
It is wound around 9. 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 27 provided inside the intermediate transfer belt 21 are provided with 0.3 mm thick hydrin rubber on metal rollers 261 and 271 as shown in the partial configuration diagram of FIG. 262, 272, and the surface resistance is 1 ×
It is formed at about 10 ⁷ to 10 ⁹ Ω. The two secondary transfer rollers 26 and 27 are arranged in the intermediate transfer belt 21 at a constant interval L along the moving direction of the transfer material 7.

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.
And a bias applying section 34 provided inside the inside. 2
The secondary transfer belt 31 is formed of a material having a medium resistance electrical characteristic having a surface resistance of 1 × 10 ⁷ to 10 ¹³ Ω. The bias applying section 34 is composed of a corona transfer means, and the secondary transfer roller 26 is opposed to the 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. It is provided in the transfer belt 31 and is configured integrally with a driving unit of the secondary transfer belt 31 so as to always maintain a fixed position with respect to the secondary transfer belt 31. This secondary transfer unit 3
3 is provided so as to be rotatable around the driving roller 32 in the direction of the primary transfer unit 2 as shown in the partial configuration diagram of FIG. When the secondary transfer belt 31 is pressed against the intermediate transfer belt 21 and 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 voltage is applied and charged by the bias applying unit 34,
The toner image 6 on the intermediate transfer belt 21 is transferred onto the transfer material 7 conveyed between the intermediate transfer belt 21 and the secondary transfer belt 31.
Next transfer. At the time of this secondary transfer, the secondary transfer belt 3
1 is rotated about the driving roller to rotate the secondary transfer roller 2
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 are in 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. Further, the bias applying section 34 is constituted by corona transfer means,
At a position facing the secondary transfer roller 27, the secondary transfer belt 3
Since the bias voltage is applied directly to the transfer roller 1, the pressure applied to the contact surface between the secondary transfer belt 31 and the intermediate transfer belt 21 during transfer can be further reduced. Therefore, it is possible to prevent an excessive pressure from being applied to the toner of the toner image 6 formed on the intermediate transfer belt 21, and to separate the toner image 6 formed on the intermediate transfer belt 21 from the belt surface. It is possible to prevent the moldability from being reduced. For this reason, the toner image secondarily transferred to the transfer material 7
It is possible to prevent the occurrence of a so-called insect image.

A bias applying section 34 is a secondary transfer roller facing the 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. Since the secondary transfer belt 31 having a medium resistance is provided directly in the belt 31 and the toner image 6 on the intermediate transfer belt 21 is secondarily transferred onto the transfer material 7 by the transfer bias, the transfer bias is applied to the transfer entrance. Lines of electric force (electric field) generated near the nip can be suppressed, and transfer dust can be prevented from being generated and adhering to the transfer material 7, so that a high-quality image can be stably formed on the transfer material 7. be able to.

Further, the secondary transfer rollers 26 and 2 having a medium resistance are used.
7, the intermediate transfer belt 21 and the secondary transfer belt 31 are used, and the applied voltage is directly applied at a position facing the secondary transfer roller 27, so that the applied charges can be uniformly distributed and a uniform image can be obtained. It can be formed stably.

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.

Further, since the bias applying section 34 is formed integrally with the driving section of the secondary transfer belt 31, the secondary transfer belt 31 is rotated to contact the intermediate transfer belt 21 for performing the secondary transfer. When this is done, the position of the bias applying unit 34 with respect to the secondary transfer belt 31 can always be kept constant. Therefore, it is possible to prevent the resistance or the like between the secondary transfer belt 31 and the bias applying unit 34 from fluctuating. Further, maintenance and the like of the secondary transfer unit 3 can be easily performed.

[0022]

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.

A bias applying section is provided in a secondary transfer belt facing a secondary transfer roller provided downstream of the two secondary transfer rollers in the moving direction of the transfer material. When the toner image transferred to the intermediate transfer belt is secondarily transferred to a transfer material, the toner image may be in the vicinity of the nip at the transfer entrance or in the intermediate transfer belt.
Forming a defect-free image on the transfer material by suppressing lines of electric force (electric field) generated on the upstream side of the contact area of the next transfer belt and preventing transfer dust from being generated and adhering to the transfer material. Can be.

Further, the bias application means is constituted by direct application means by corona transfer, so that the pressure applied to the contact surface between the secondary transfer belt and the intermediate transfer belt during the secondary transfer is made smaller and constant. Thus, an image free from insect erosion can be stably formed.

Further, the bias applying means is formed integrally with the driving section of the secondary transfer belt so that the position of the bias applying means with respect to the secondary transfer belt is always kept constant.
Since it is possible to prevent the resistance and the like from fluctuating due to a change in the distance to the next transfer belt, it is possible to stably transfer the image and easily perform maintenance of the secondary transfer unit.

[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 illustrating 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 unit 21 Intermediate transfer belt 26 Secondary transfer roller 27 Secondary transfer roller 31 Secondary transfer belt 34 Bias applying unit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Jun Okamoto Ricoh Co., Ltd. 1-3-6 Nakamagome, Ota-ku, Tokyo

Claims (3)

[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. And an image forming apparatus having a secondary transfer unit for causing the secondary transfer portion of the intermediate transfer belt to have a fixed position along the moving direction of the transfer material. A secondary transfer roller having a resistance, the secondary transfer unit having a secondary transfer belt having a medium resistance and a bias applying means, the secondary transfer belt being wound along a moving direction of the transfer material; The bias applying means is a secondary transfer roller provided on the downstream side in the moving direction of the transfer material among the two secondary transfer rollers.
An image forming apparatus provided in a secondary transfer belt facing the image forming apparatus. 2. An image forming apparatus according to claim 1, wherein said bias applying means is a direct applying means by corona transfer. 3. The image forming apparatus according to claim 1, wherein said bias applying unit is integrated with a driving unit of a secondary transfer belt.