JP2001194932A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent an image defect accompanying the generation of a tension line from occurring. SOLUTION: This image forming device is provided with an image carrier 1 for forming and carrying a toner image T corresponding to image information, a recording and feeding belt 2 fed in circulation at a part opposed to the carrier 1 and a transfer means 3 forming a transfer nip area N between the carrier 1 through the belt 2 and the transfer means 3 and transferring the toner image T formed on the carrier 1 on the belt 2 directly or the through a recording material K. Besides, it is provided with a holding force adjustment means 4 adjusting the holding force of toner so that the holding force of the toner transferred in an area corresponding to the tension line L becomes larger than the peeling force by electric discharge on a condition that the line L is formed at the belt 2 along the feeding direction of the belt 2.

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 such as an electrophotographic copying machine, and more particularly to an image forming apparatus for transferring an image onto a recording / transporting belt directly or via a recording material.

[0002]

2. Description of the Related Art Conventionally, for example, as an intermediate transfer type image forming apparatus, a photosensitive drum on which a toner image corresponding to an electrostatic latent image is formed, and a toner image on the photosensitive drum are intermediately transferred. An intermediate transfer belt, a primary transfer device for transferring the toner image on the photosensitive drum to the intermediate transfer body, and a secondary transfer device for collectively secondary transferring the toner image transferred on the intermediate transfer belt to paper A device provided with a transfer device is known. Here, as the primary transfer device, for example, a transfer roll or the like that is arranged in contact with the intermediate transfer belt is used. The transfer roll forms an electric field between the photosensitive drum and the intermediate transfer belt to move the toner image on the photosensitive drum toward the intermediate transfer belt.

[0003]

In this type of image forming apparatus, the intermediate transfer belt is usually stretched over a plurality of rolls. In this case, for example, the tension applied to the intermediate transfer belt is reduced. If it is too large, a streaky concave or convex portion (hereinafter, referred to as a tension line) may be generated on the intermediate transfer belt in the direction in which the tension is applied, that is, in the transport direction of the intermediate transfer belt.

[0004] When such a tension line is generated, a gap (gap) is formed between the photosensitive drum and the intermediate transfer belt in the primary transfer section, and the holding force of the toner transferred to the tension line forming section is reduced. There is a technical problem in that when a gap discharge occurs in the gap, a round stamp-shaped image quality defect occurs.

Japanese Patent Application Laid-Open No. 9-152791 discloses that
A technique for preventing the image quality defect at the primary transfer portion by defining the relative position between the photosensitive drum and the primary transfer device is described. However, depending on such technical means, the above-mentioned circular stamp-shaped image quality defect may be provided. Cannot be completely prevented.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problem, and an object of the present invention is to provide an image forming apparatus capable of effectively preventing an image quality defect due to the occurrence of a tension line.

[0007]

That is, according to the present invention, as shown in FIG. 1, an image carrier 1 on which a toner image T corresponding to image information is formed and carried, and a portion opposed to the image carrier 1. Transfer nip area N between the recording transport belt 2 circulated and transported and the image carrier 1 via the recording transport belt 2.
And a transfer unit 3 for transferring the toner image T formed on the image carrier 1 directly or via the recording material K to the recording / conveying belt 2.
Under the condition that the tension line L is formed on the recording and conveying belt 2 along the conveying direction of the recording and conveying belt 2,
It is characterized by comprising a holding force adjusting means 4 for adjusting the holding force of the toner such that the holding force of the toner transferred to the area corresponding to the tension line L becomes larger than the peeling force due to the discharge.

In such technical means, as an image forming method of the image forming apparatus to which the present invention is applied, an electrophotographic method, an electrostatic recording method, or the like may be appropriately selected. A method of transferring the toner image T, a method of transferring the toner image T to the recording material K carried and conveyed on the recording conveyance belt 2, and the like may be appropriately selected.
Further, the number of the image carriers 1 may be singular or plural. In FIG. 1, the toner image T formed on one image carrier 1 is transferred to a recording / transporting belt 2 (intermediate transfer belt) by a transfer unit 3 and the toner image transferred onto the recording / transporting belt 2 is transferred. An example is shown in which T is collectively transferred to the recording material K via the collective transfer means 5. The recording transport belt 2 is not limited to the intermediate transfer belt shown in FIG. 1, but includes a recording material transport belt that carries and transports the recording material K. The present invention is directed to a recording / transporting belt 2 in which a round stamp-shaped image quality defect is likely to occur.
This is particularly effective in a mode using the recording transport belt 2 having a volume resistivity of 2 logΩcm or more. Further, in the present application, the tension line L refers to a line formed along the transport direction of the recording and conveying belt 2, which means that the tension line L includes a component in the transport direction. Includes those formed obliquely with respect to

In the present invention, the transfer means 3 comprises:
In addition to a normal transfer function, that is, a function of transferring the toner image T formed on the image carrier 1, a function of forming a transfer nip area N with the image carrier 1 via the recording and conveying belt 2 is also provided. It is necessary to be. Here, in a mode in which, for example, a contact transfer member (for example, a transfer roll) that is disposed in pressure contact with the recording and conveying belt 2 is adopted as the transfer unit 3,
The contact transfer member also has a function of forming the transfer nip N. On the other hand, in a mode in which a non-contact transfer member (for example, corotron) arranged in non-contact with the recording and conveying belt 2 is used, in addition to the non-contact transfer member, the recording and conveying belt 2 is used as an image bearing member. It is necessary to provide a functional member (pressing member) that presses toward the body 1 side.

Further, the holding force adjusting means 4 adjusts the holding force of the toner such that the holding force of the toner transferred to the area corresponding to the tension line L of the recording and conveying belt 2 becomes larger than the peeling force due to the discharge. If it is a thing, it does not matter if it is selected appropriately, and as a specific mode, for example,
A mode in which the pressing force of the transfer unit 3 is adjusted by the pressing force adjustment unit (hereinafter, referred to as a first mode), and a mode in which the amount of bias applied to the transfer unit 3 is adjusted by the bias adjustment unit (hereinafter, second mode) Is referred to as an embodiment).

In the first embodiment described above, when the recording and conveying belt 2 is made of a material having a large coefficient of hygroscopic expansion, the tension line L is generated on the recording and conveying belt 2 in a high-temperature and high-humidity environment. It's easy to do. Therefore, from the viewpoint of effectively preventing the tension line L generated due to such environmental fluctuation and the image quality defect accompanying the tension line L, the pressing force adjusting unit determines the pressing force of the transfer unit 3 based on environmental information. Is preferably adjusted.

Further, the recording and conveying belt 2 is used as the transfer means 3.
In the case of using the transfer roll in contact with the transfer roll, if the support member on which the transfer roll is supported is made of a material that expands and contracts with environmental changes, it is automatically pushed in response to environmental changes. The support member can be provided with a function as the holding force adjusting means 4 for adjusting the pressure.

On the other hand, also in the second embodiment described above, when the recording and conveying belt 2 is made of a material having a large hygroscopic expansion coefficient, the recording and conveying belt 2 is connected to the recording and conveying belt 2 under a high temperature and high humidity environment. L tends to occur. Therefore,
The tension line L generated due to such environmental change
From the viewpoint of effectively preventing image quality defects associated therewith, it is preferable that the bias adjustment unit adjusts the amount of bias applied to the transfer unit 3 based on environmental information.

The recording and conveying belt 2 is used as the transfer means 3.
In the embodiment using a transfer roll that is arranged in contact with the transfer roller, the bias adjustment unit utilizes the fact that the system resistance of the transfer nip area N fluctuates with environmental fluctuations, and May be adjusted.

By the way, three or more image carriers 1 are arranged opposite to the recording and conveying belt 2 and toner images T of a plurality of colors (for example, yellow, magenta, cyan, or yellow, magenta, cyan, black, etc.) are formed in one pass. In a so-called tandem type image forming apparatus that can be superposed, the recording and conveying belt 2 at a portion facing the plurality of image carriers 1 is used.
When the tension is applied, the end of the recording transport belt 2 at the central portion in the transport direction of the portion is sagged, and the portion becomes a void, and a circular stamp-shaped discharge occurs. There is a possibility that a mark will be generated.

Therefore, another embodiment of the present invention relates to a method for forming three or more image carriers 1 on which toner images T corresponding to image information are formed and carried.
A recording and conveying belt 2 circulated and conveyed at a portion opposed to each of the image carriers 1, and a transfer nip area N formed opposite to each of the image carriers 1 via the recording and conveying belt 2. An image forming apparatus including a transfer unit 3 for transferring a toner image T formed on each of the image carriers 1 directly or via the recording material K to the recording / conveying belt 2, wherein each of the transfer units 3 is Regarding the pressing force for pressing the recording and conveying belt 2, the pressing force of the transfer unit 3 disposed on the most upstream side in the conveying direction of the recording and conveying belt 2 and the pressing force of the transfer unit 3 disposed on the most downstream side in the conveying direction of the recording and conveying belt 2. The present invention is characterized in that the pressing force of the transfer means 3 arranged between them is set higher than the pressing force of the transfer means 3.

In still another embodiment of the present invention, three or more image carriers 1 on which a toner image T corresponding to image information is formed and carried, and circulated and conveyed through portions opposed to the respective image carriers 1. And a transfer nip area N formed opposite to each of the image carriers 1 via the recording / transporting belt 2 and forming the transfer nip area N. In the image forming apparatus including the transfer unit 3 for transferring the toner image T formed on each image carrier 1, the amount of bias applied to each of the transfer units 3 is determined based on the amount of bias applied to the recording and conveyance belt 2 in the conveyance direction. The transfer unit disposed between the transfer unit 3 disposed on the upstream side and the transfer unit 3 disposed on the most downstream side in the conveyance direction of the recording and conveying belt 2 is smaller than the bias application amount of the transfer unit 3. 3 bias application Characterized in that the set larger.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a first embodiment of a color image forming apparatus to which the present invention is applied. In FIG. 1, a color image forming apparatus according to the present embodiment includes a plurality of image forming units 100 (specifically, 100Y, 100M, 100C, and 100K) on which respective color component toner images are formed by an electrophotographic method.
And an intermediate transfer belt 110 as a recording and transporting body for sequentially transferring (primary transfer) each color component toner image formed by each image forming unit 100, and an intermediate transfer belt 11
A batch transfer device 120 that batch-transfers (secondarily transfers) the superimposed image transferred onto the sheet P to a sheet P as a recording material, and a fixing device 150 that fixes the batch-transferred image onto the sheet P.
It is provided with.

In this embodiment, the image forming units 100 for the respective color components are arranged from the upstream side in the conveying direction B of the intermediate transfer belt 110 to the yellow image forming unit 100Y, the magenta image forming unit 100M, the cyan image forming unit 100C, and the black image forming unit 100C. The forming units 100K are arranged in this order. Then, each image forming unit 10
0 denotes a uniform charging device 102 on which the photosensitive drum 101 is charged, and an electrostatic latent image is written on the photosensitive drum 101, around the photosensitive drum 101 as an image carrier rotating in the direction of arrow A. Laser exposure device 103 (indicated by an exposure beam Bm in the figure), and a developing device 10 in which toners of respective color components are stored and an electrostatic latent image on the photosensitive drum 101 is visualized.
4. For electrophotography, such as a primary transfer roll 105 as a transfer device for transferring each color component toner image on the photosensitive drum 101 to the intermediate transfer belt 110 and a drum cleaner 106 for removing residual toner on the photosensitive drum 101 Devices are sequentially arranged.

Then, as shown in FIG. 3, each of the primary transfer rolls 105 (specifically, 105Y, 105M, 105
C, 105K), a transfer bias power supply 107 (specifically, 107Y, 10K) to which a DC bias of the opposite polarity (positive polarity in the present embodiment) to the charge polarity of the toner is applied.
7M, 107C, and 107K). Each of these transfer bias power supplies 107 is connected to each of the primary transfer rolls 105.
The constant voltage (30 μm in the present embodiment) is applied to each primary transfer roll 105.
A) is applied.

Further, as shown in FIG. 2, the intermediate transfer belt 110 is stretched around a plurality of (five in this embodiment) support rolls 131 to 135. Here, the support roll 131 is a driving roll of the intermediate transfer belt 110, the support rolls 132 and 135 are driven rolls, the support roll 133 is a tension roll for adjusting the tension of the intermediate transfer belt 110, and the support roll 134 is a batch transfer as described later. Apparatus 1
20 backup rolls.

The intermediate transfer belt 110 is made of a resin such as polyimide or polyamide containing an appropriate amount of an antistatic agent such as carbon black, and has a volume resistivity of 10 ¹⁰ to 10 ¹³ Ωcm. Formed,
The thickness is set to, for example, 0.1 mm.

Further, the collective transfer device 120 includes a secondary transfer roll 113 disposed in pressure contact with the toner transfer surface of the intermediate transfer belt 110 and a secondary transfer roll 113 disposed in contact with the back surface of the intermediate transfer belt 110. A backup roll 114 serving as an electrode (also used as a support roll 134) is provided. As shown in FIG. 3, the backup roll 114 stably receives a bias having the same polarity as the toner charging polarity from the bias power supply 112. A metal-made power supply roll 115 to be applied is disposed in contact with the metal.

In the present embodiment, the secondary transfer roll 1
13 is a tube of urethane rubber in which carbon is dispersed on the surface, the inside is made of urethane foam in which carbon is dispersed, and the surface of the roll is further coated with fluorine, the volume resistance is 10 ³ to 10 ¹⁰ Ω and the roll diameter is 28 mm. The hardness is set to, for example, 30 ° (Asuka C).

The backup roll 114 is made of a blend rubber tube of EPDM and NBR in which carbon is dispersed on the surface, and the interior thereof is made of EPDM rubber. The surface resistivity is 10 ⁷ to 10 ¹⁰ Ω / □ and the roll diameter is 28 mm. The hardness is set to, for example, 70 ° (Asuka C).

The secondary transfer roll 113 is provided with a roll brush 161 to remove the stain attached to the secondary transfer roll 113, thereby preventing the back surface of the paper P from being stained. Reference numeral 136 denotes a belt cleaner that cleans the surface of the intermediate transfer belt 110 after the secondary transfer, and 137 denotes an image density sensor that detects the image density of an image formed on the intermediate transfer belt 110.

Further, in the present embodiment, the paper transport system feeds out the paper P from the paper tray 116 at a predetermined timing by the pickup roll 117, and moves to the secondary transfer position via the transport roll 118 and the transport chute 119. The paper P after the secondary transfer is guided to a transport belt 140, and the transport belt 14
At 0, the sheet is conveyed to the fixing device 150.

Next, a method of disposing each primary transfer roll 105 according to the present embodiment will be described in detail. In this embodiment, the primary transfer roll 105 is made of urethane foam rubber in which carbon is dispersed, has a diameter of 28 mm, has a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm, and has a hardness of, for example, 35 ° ( Asuka C) is set.

In the present embodiment, as shown in FIG. 4, the intermediate transfer belt 11 is attached to each primary transfer roll 105.
Pressing mechanism 18 for adjusting the pressing force to zero (not shown)
0 is provided. The pressing mechanism 180 has an eccentric cam 181 that is arranged in contact with the rotation shaft 105 a of the primary transfer roll 105, and a motor 183 that transmits a driving force to the eccentric cam 181 via a gear 182. Are rotated in the forward and reverse directions, so that the pressing force of the primary transfer roll 105 against the intermediate transfer belt 110 can be varied. The pressing mechanism 180 is not limited to the type driven by a motor, but may be driven by, for example, a solenoid.

Further, the intermediate transfer belt 110 according to the present embodiment has a high coefficient of hygroscopic expansion and tends to generate a tension line in a high temperature and high humidity environment. Therefore, in the present embodiment, as shown in FIG. 5, the control device 2 controls the pressing force of each primary transfer roll 105 according to the environmental conditions.
00 is provided.

In this embodiment, the control device 200
The input interface 2 receives a temperature detection signal from the temperature sensor 171 and a humidity detection signal from the humidity sensor 172.
01 to the CPU 202, and then the CPU 202
202 performs appropriate data processing between the ROM 203 and the RAM 204 and then outputs the primary transfer rolls 105 (specifically, 105Y, 105Y,
105M, 105C, and 105K) (specifically, a yellow transfer roll pressing mechanism 180).
Y, a drive signal is sent to each of the magenta transfer roll pressing mechanism 180M, the cyan transfer roll pressing mechanism 180C, and the black transfer roll pressing mechanism 180K).

Next, an image forming process of the color image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. More specifically, for example, when the color image forming apparatus is configured as a digital color copying machine, a document set on a document table (not shown) is read by a color image reading device, and the read signal is read by an image signal processing unit. , And temporarily store the digital image signals in a memory. Based on the stored digital image signals of four colors (Y, M, C, and K), toner images of each color are formed. .

That is, each of the image forming units 100 (specifically, 100Y, 100M, 100C, 1C) corresponds to a digital image signal of each color input from the image signal processing means.
00K). Then, in each image forming unit 100, an electrostatic latent image corresponding to the digital signal is written by the laser exposure device 103 on the photosensitive drum 101 uniformly charged by the uniform charger 102. Then, each of these electrostatic latent images is developed by the developing device 104 containing the toner of each color to form a toner image of each color. When this color image forming apparatus is configured as a device such as a printer, it is only necessary to form toner images of each color based on an image signal input to the image signal processing means from the outside.

Then, the toner image formed on each photosensitive drum 101 is transferred to a primary transfer roll 10 at a primary transfer position where each photosensitive drum 101 contacts the intermediate transfer belt 110.
5, from the photosensitive drum 101 to the intermediate transfer belt 11
0 is sequentially transferred to the surface. The toner remaining on the photosensitive drum 101 after the primary transfer is transferred to the drum cleaner 1.
It is cleaned at 06.

The toner image primarily transferred to the intermediate transfer belt 110 in this manner is superimposed on the intermediate transfer belt 110, and is conveyed to the secondary transfer position as the intermediate transfer belt 110 rotates. On the other hand, the paper P is supplied to the secondary transfer position at a predetermined timing, and
14, the secondary transfer roll 113 nips the paper P.

Then, at the secondary transfer position, the transfer electric field formed between the secondary transfer roll 113 serving as the batch transfer device 120 and the backup roll 114 acts,
The toner image carried on the intermediate transfer belt 110 is
Is transferred in batch. Paper P on which this toner image has been transferred
Is transported by the transport belt 140 to the fixing device 150 to fix the toner image. Further, the toner remaining on the intermediate transfer belt 110 after the secondary transfer is cleaned by the belt cleaner 136.

Next, the control of the pressing force on each primary transfer roll 105 by the control device 200 will be described in detail with reference to the flowchart shown in FIG. In the image forming apparatus according to the present embodiment, it is known that there is a relationship shown in FIG. 7 between the environment (temperature and humidity) and the load (primary nip load) applied to the primary transfer nip area. . That is, if the primary nip load is too large, the intermediate transfer belt 11
0 or the photoreceptor drum 101 is damaged, resulting in image quality defects.
On the other hand, if the primary nip load is too small, the holding power of the toner transferred to the tension line forming portion becomes weak, and a round stamp image quality defect (discharge mark) occurs. A region where such a defect does not occur (a region where no defect occurs) is slightly different between a low-temperature and low-humidity environment, a normal temperature and normal humidity environment, and a high-temperature and high humidity environment.

When image formation is started, a temperature detection signal from the temperature sensor 171 and a humidity detection signal (environmental information) from the humidity sensor 172 are input. It is determined that no tension line is formed on the intermediate transfer belt 110, and the primary nip load of each primary transfer roll 105 is set to 98 mN / c.
m (10 gf / cm). On the other hand, in a high-temperature and high-humidity environment, it is determined that there is a risk that a tension line is formed on the intermediate transfer belt 110, and the primary transfer nip load of each primary transfer roll 105 is doubled by 19 times.
Set to 6 mN / cm (20 gf / cm). And
The primary transfer from the photosensitive drum 101 to the intermediate transfer belt 110 is performed, and this process is repeated until the image formation is completed.

In this embodiment, the intermediate transfer belt 110
In an environment where a tension line is likely to occur, that is, in a high-temperature and high-humidity environment, the pressing force (primary nip load) on the primary transfer roll 105 is set to be large to forcibly smooth the intermediate transfer belt 110 in the primary transfer nip area. As a result, it is possible to increase the holding force of the toner transferred to the area where the tension line is formed, and thus obtain good transfer performance while preventing the occurrence of image quality defects in the shape of a round stamp. Can be.

In this embodiment, the primary transfer nip load is 98 m in a low-temperature and low-humidity environment and in a normal temperature and normal humidity environment.
N / cm, the primary nip load in a high-temperature and high-humidity environment was set to 196 mN / cm. However, the present invention is not limited to this. For example, the primary nip load in a low-temperature and low-humidity environment and a normal temperature and normal humidity environment is as follows. 98-147mN /
cm (10 to 15 gf / cm), and a primary nip load in a high temperature and high humidity environment is 196 to 294 mN.
/ Cm (20 to 30 gf / cm).

Embodiment 2 This embodiment is almost the same as Embodiment 1, but further controls the primary transfer current according to environmental conditions. Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In this embodiment, the control device 200
As shown by broken lines in FIG. 5, the transfer bias power supplies 107 (specifically, the yellow transfer bias power supply 107Y, the magenta transfer bias power supply 107M, and the cyan transfer bias power supply 1) are output via the output interface 205.
07C and a black transfer bias power supply 107K).

Next, the control of the pressing force and the transfer bias for each primary transfer roll 105 by the control device 200 is as follows.
This will be described in detail based on the flowchart shown in FIG.
In the image forming apparatus according to the present embodiment, it is known that the relationship shown in FIG. 9 exists between the environment (temperature and humidity) and the primary transfer current. That is, if the transfer current is too large, discharge due to the excessive transfer current and primary transfer retransfer accompanying the discharge occur. On the other hand, if the transfer current is too small, a round stamp-shaped image defect due to insufficient transfer current occurs. A region where such a defect does not occur (a region where no defect occurs) is slightly different between a low-temperature and low-humidity environment, a normal temperature and normal humidity environment, and a high-temperature and high humidity environment.

When image formation is started, a temperature detection signal from the temperature sensor 171 and a humidity detection signal (environmental information) from the humidity sensor 172 are input. It is determined that no tension line is formed on the intermediate transfer belt 110, and the primary nip load of each primary transfer roll 105 is set to 98 mN / c.
m (10 gf / cm) and the primary transfer current applied to each primary transfer roll 105 is set to 30 μA. On the other hand, in a high temperature and high humidity environment, it is determined that there is a risk that a tension line is formed on the intermediate transfer belt 110, and the primary transfer nip load of each primary transfer roll 105 is doubled to 196 mN / cm. (20gf / c
m) and the primary transfer current applied to each primary transfer roll 105 is set to 35 μA, which is larger than the primary transfer current under the above environment. Then, primary transfer from the photosensitive drum 101 to the intermediate transfer belt 110 is performed, and this process is repeated until image formation is completed.

In this embodiment, the intermediate transfer belt 110
In an environment where a tension line is likely to occur, that is, in a high-temperature and high-humidity environment, the pressing force (primary nip load) on the primary transfer roll 105 is set to be large to forcibly smooth the intermediate transfer belt 110 in the primary transfer nip area. In addition, since the primary transfer current is further increased, the holding force of the toner transferred to the area where the tension line is formed can be further increased.

Embodiment 3 The present embodiment is almost the same as Embodiment 1, except that the primary transfer current is controlled in accordance with the system resistance of the primary transfer section. Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In this embodiment, the control device 300
As shown in FIG. 10, a resistance detection signal from a resistance measuring device 173 for measuring a system resistance of a primary transfer unit is fetched into a CPU 302 via an input interface 301. Next, the CPU 302
After appropriately performing data processing with the transfer bias power supply 107,
(Specifically, a bias control signal is sent to each of the yellow transfer bias power supply 107Y, the magenta transfer bias power supply 107M, the cyan transfer bias power supply 107C, and the black transfer bias power supply 107K).

Next, the control of the transfer bias for each primary transfer roll 105 by the control device 300 will be described in detail with reference to the flowchart shown in FIG. When the image formation is started, a resistance detection signal (resistance information) from the resistance measuring device 173 is input. When the resistance value R is equal to or more than a predetermined resistance value Rs, a low-temperature low-humidity environment or a normal-temperature normal-humidity environment is used. It is determined that the tension line is not formed below, that is, the intermediate transfer belt 110, and each primary transfer roll 1
05 is set to 30 μA. On the other hand, when the resistance value R exceeds the predetermined resistance value Rs, it is determined that there is a risk that a tension line is formed in the high-temperature and high-humidity environment, that is, the intermediate transfer belt 110, The primary transfer current applied to 105 is set to 35 μA. Then, primary transfer from the photosensitive drum 101 to the intermediate transfer belt 110 is performed, and this process is repeated until image formation is completed.

In the present embodiment, the primary transfer current applied to the primary transfer roll 105 is set large in an environment where the system resistance is reduced, that is, in a high temperature and high humidity environment where a tension line is likely to be generated on the environmental intermediate transfer belt 110. As a result, it is possible to increase the holding force of the toner transferred to the area where the tension line is formed in the primary transfer nip area, and to obtain good transfer performance while preventing the occurrence of image quality defects in a round stamp shape. be able to.

Fourth Embodiment FIG. 12 shows a main part of a primary transfer section of an image forming apparatus according to a fourth embodiment. In the figure, a rotating shaft 105a of a primary transfer roll 105 has a support member 1 made of a material having a high hygroscopic expansion property such as a cellophane.
It is supported at 85. Accordingly, the support member 185 expands in a high-temperature and high-humidity environment, and the pressing force of the primary transfer roll is increased accordingly. Therefore, the pressing force is automatically controlled by the surrounding environment without controlling the pressing force. The pressure can be adjusted.

Embodiment 5 This embodiment is substantially the same as Embodiment 1 except that FIG.
In FIG. 3, among the primary transfer rolls 105 (specifically, 105Y, 105M, 105C, and 105K),
A pressing force is applied to the magenta primary transfer roll 105M and the cyan primary transfer roll 105C arranged at the center part by the pressing force applied to the yellow primary transfer roll 105Y and the black primary transfer roll 105K arranged at the end of the intermediate transfer belt 110 in the conveyance direction. The pressure is set high.

FIG. 13 is a top view of the primary transfer surface of the color image forming apparatus shown in FIG. The description of the photosensitive drum 101 is omitted. In the figure, under the condition that excessive tension is applied to the intermediate transfer belt 110, in the vicinity of the drive roll 131 and the driven roll 132, the waving of the intermediate transfer belt 110 in the transport direction of the intermediate transfer belt 110 (the tension line L : Indicated by phantom lines in the figure), while the tension line L is less generated at the center between the driving roll 131 and the driven roll 132, but at the both end portions 110E. Dripping becomes noticeable.

In such a case, the magenta primary transfer section and the cyan primary transfer section between the yellow primary transfer section near the driving roll 131 and the black primary transfer section near the driven roll 132 are on both sides of the intermediate transfer belt 110. End 1
As the sag of 10E increases, the reaction force applied to the primary transfer rolls 105M and 105C from the intermediate transfer belt 110 increases, and the effective value of the pressing force decreases. As a result, voids are generated in the primary transfer nip area of magenta and cyan, and a discharge is generated to cause a round stamp-shaped image quality defect.

Here, the present inventor has proposed that each primary transfer roll 1
Focusing on the pressing force of No. 05, various combinations of the magnitudes of the pressing forces were combined, and an experiment was conducted to confirm whether or not a discharge phenomenon occurred. As a result, as shown in FIG. 14, the yellow primary transfer roll 105Y and the black primary transfer roll 105K
Of the magenta primary transfer roll 105M and the cyan primary transfer roll 105
When the pressing force on C was set high (see No. 1), no discharge phenomenon occurred in the primary transfer nip area, and it was confirmed that a good image without image quality defects was obtained. When the pressing force applied to each of the primary transfer rolls 105 is set to be substantially the same (see No. 2), it is confirmed that a slight discharge phenomenon occurs and a slight image quality defect occurs. When the pressing force on the yellow primary transfer roll 105Y and the black primary transfer roll 105K disposed on the end portions is set higher than the pressing force on the magenta primary transfer roll 105M and the cyan primary transfer roll 105C (see No. 3). In ()), it was confirmed that a discharge phenomenon occurred and image quality defects occurred.

[0055]

As described above, according to the present invention,
Since the holding force of the toner transferred to the area corresponding to the tension line formed on the recording / conveying belt by the holding force adjusting unit is set to be larger than the peeling force due to the discharge, image quality defects due to the occurrence of the tension line are effectively reduced. Can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of Embodiment 1 of the image forming apparatus to which the present invention has been applied.

FIG. 3 is an enlarged view of a primary transfer device of the image forming apparatus according to the first embodiment.

FIG. 4 is an explanatory diagram illustrating a pressing mechanism of a primary transfer roll.

FIG. 5 is a block diagram of a control device of the image forming apparatus according to the first and second embodiments.

FIG. 6 is a flowchart showing a control flow of the control device according to the first embodiment.

FIG. 7 is a graph showing a relationship between an environment and a primary nip load.

FIG. 8 is a flowchart showing a control flow of a control device according to the second embodiment.

FIG. 9 is a graph showing a relationship between an environment and a primary transfer current.

FIG. 10 is a block diagram of a control device of the image forming apparatus according to the third embodiment.

FIG. 11 is a flowchart showing a control flow of a control device according to the third embodiment.

FIG. 12 is an explanatory diagram showing a support mechanism of a primary transfer roll in an image forming apparatus according to Embodiment 4.

FIG. 13 is a schematic diagram illustrating a stretched state of an intermediate transfer belt in the image forming apparatus according to the fifth embodiment.

FIG. 14 is a table showing the relationship between the pressing force applied to each primary transfer roll and the occurrence of a discharge phenomenon.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Recording conveyance belt, 3 ... Transfer means, 4
... holding force adjusting means, 5 ... batch transfer means, K ... recording material, L
... Tension line, T ... Toner image

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Hayashi 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Masaaki Takahashi 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Yoko Miyamoto 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Makoto Katayama 2274 Hongo, Ebina-shi, Kanagawa Prefecture F-term inside Fuji Xerox Co., Ltd. AA15 BA09 BA23 BA25 BA30

Claims (10)

[Claims] An image bearing member on which a toner image corresponding to image information is formed and carried; a recording / conveying belt circulating / conveying a portion facing the image bearing member; and the image carrying member via the recording / conveying belt. An image forming apparatus comprising: a transfer unit that forms a transfer nip area between the image bearing member and a transfer unit that transfers a toner image formed on the image carrier to the recording conveyance belt directly or via a recording material. Under the condition that a tension line is formed on the recording transport belt along the transport direction of the recording transport belt, the holding force of the toner transferred to the area corresponding to the tension line is larger than the peeling force due to the discharge. An image forming apparatus comprising: a holding force adjusting unit that adjusts a holding force of toner. 2. The image forming apparatus according to claim 1, wherein the holding force adjusting unit is a pressing force adjusting unit that adjusts a pressing force of the transfer unit. 3. The image forming apparatus according to claim 2, wherein the pressing force adjusting unit adjusts the pressing force of the transfer unit based on environmental information. 4. The image forming apparatus according to claim 2, wherein
In the aspect in which the transfer unit includes a transfer roll that is arranged in contact with the recording and conveying belt, the pressing force adjusting unit supports the transfer roll, and includes a transfer roll support member that can expand and contract with environmental changes. An image forming apparatus comprising: 5. The image forming apparatus according to claim 1, wherein the holding force adjusting unit is a bias adjusting unit that adjusts a bias application amount to the transfer unit. 6. The image forming apparatus according to claim 5, wherein the bias adjustment unit adjusts a bias application amount to the transfer unit based on environmental information. 7. The image forming apparatus according to claim 5, wherein
In the aspect in which the transfer unit includes a transfer roll that is arranged in contact with the recording and conveying belt, the bias adjustment unit adjusts a bias application amount to the transfer roll based on a system resistance in the transfer nip area. An image forming apparatus comprising: 8. The image forming apparatus according to claim 1, wherein the volume resistivity of the recording and conveying belt is 1 at room temperature and normal humidity.
An image forming apparatus having a density of 2 log Ωcm or more. 9. A three- or more image carrier on which a toner image corresponding to image information is formed and carried; a recording / conveying belt circulatingly carried at a portion facing each of the image carriers; And a transfer unit that transfers a toner image formed on each of the image carriers to the recording / transporting belt directly or via a recording material while forming a transfer nip area opposed to each of the image carriers. In the image forming apparatus provided with respect to the pressing force of each transfer unit pressing the recording conveyance belt, the pressing force of the transfer unit disposed on the most upstream side in the conveyance direction of the recording conveyance belt and the conveyance of the recording conveyance belt An image forming apparatus characterized in that the pressing force of the transfer means disposed between them is set higher than the pressing force of the transfer means disposed on the most downstream side in the direction. 10. An image carrier on which three or more toner images corresponding to image information are formed and carried; a recording / conveying belt circulating / conveying a portion facing each of the image carrying members; And a transfer unit that transfers a toner image formed on each of the image carriers to the recording / transporting belt directly or via a recording material while forming a transfer nip area opposed to each of the image carriers. In the image forming apparatus provided with respect to the amount of bias applied to each of the transfer units, the amount of bias applied to the transfer unit disposed on the most upstream side in the conveyance direction of the recording and conveyance belt and the most downstream in the conveyance direction of the recording and conveyance belt An image forming apparatus characterized in that the amount of bias applied to a transfer unit disposed between them is set to be larger than the amount of bias applied to a transfer unit disposed on the side.