JPH1184812A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently keep the attracting performance of a recording material with respect to a carrying belt and to perfectly evade transfer irregularity. SOLUTION: This device is constituted so that the recording material 6 is attracted and held on the carrying belt 2 by an attraction means 7 and the images of respective color components formed by respective image forming units 1 are successively transferred on the material 6. As the attraction means 7, the device is provided with a roll for laying 3 positioned on the upstream side of the image forming unit la set on the most upstream side among the rolls for laying 3 and 4 of the belt 2 and an attracting member 8 arranged so as to press-contact with the belt 2 opposed to the roll 3. Then, the bias of attraction VAB is homopolar with respect to the bias of transfer VTB impressed on a transfer means 5 is impressed on the roll 3. Besides, the attracting member 8 is grounded directly or through a high resistance 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called tandem type image forming apparatus in which a plurality of image forming units on which respective color component images are formed are arranged in parallel, and more particularly, at least along an arrangement direction of each image forming unit. The present invention relates to an improvement in an image forming apparatus in which a transport belt that is circulated and transported by being wound around a pair of tension rolls is provided, and a recording material is suction-held and transported by the transport belt.

[0002]

2. Description of the Related Art Conventionally, as a tandem type image forming apparatus of this kind, for example, a plurality of image forming units (for example, adopting an electrophotographic system) are arranged on a paper transport path along a horizontal direction, and a paper transport path is provided. A so-called tandem type in which a toner image is sequentially transferred from each of the image forming units to a sheet moving along the sheet so as to form a color image in which each color toner image is superimposed on the sheet is known. (For example, JP-A-5-53412).

In this type of image forming apparatus, from the viewpoint of maintaining good color registration, it is indispensable to transport the paper stably to the transfer point of each color toner image for each image forming unit. Under such a request, conventionally, an endless transport belt rotating and moving at a constant speed is stretched over a plurality of stretching rolls, and the image bearing member such as a photosensitive drum of each image forming unit is placed on the image carrier. The transport belts are arranged to face each other, and the paper is electrostatically attracted to the transport belts, thereby achieving stable paper traveling. In a belt transport system using such a transport belt, a metal suction roll is pressed against the surface of the transport belt located upstream of the most upstream image forming unit in order to electrostatically attract paper to the transport belt. In addition to the arrangement, a corona discharge device such as a corotron is arranged on the back side of the transport belt facing the suction roll, and the paper is passed between the suction roll and the transport belt, thereby electrostatically attracting the paper. A technique for performing the operation stably has already been proposed.

[0004]

However, this type of paper suction system requires expensive parts such as a corona discharge device (using a high voltage power supply) such as a corotron, which leads to an increase in cost. Includes fundamental technical challenges. On the other hand, as a low-price paper suction system, a suction roll is pressed against the surface of the conveyor belt facing the upstream belt tension roll of the conveyor belt,
There has been provided a technique of applying a predetermined suction bias to the suction roll (for example, Japanese Patent Application Laid-Open No. 8-8714).
No. 5).

[0005] However, in this type of paper suction system, a suction bias is applied to the suction roll.
Since the belt tension roll is in a floating state, it cannot be said that the counter electrode facing the suction roll is clearly present, charge injection (or discharge) from the suction roll is unlikely to occur, and the charge application to the paper is uneven. Easy to be. For this reason, when the toner image from each image forming unit is transferred to paper,
There was a technical problem that transfer unevenness easily occurred.

As a means for solving such a technical problem, it is conceivable that the belt tension roll is grounded so that the belt tension roll functions as a counter electrode of the suction roll. According to experiments by the present inventors, it has been found that even if such a method is employed, it is still insufficient to completely prevent transfer unevenness.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and an image forming apparatus capable of maintaining good adsorption performance of a recording material to a conveying belt and completely preventing transfer unevenness. An apparatus is provided.

[0008]

That is, according to the present invention, as shown in FIG. 1, a plurality of image forming units 1 (for example, 1a to 1d) on which respective color component images are formed are arranged in parallel, and 1 and a conveyor belt 2 that is circulated and conveyed over at least a pair of stretching rolls 3 and 4 along the direction of arrangement, and is provided on the back side of the conveyor belt 2 facing each image forming unit 1. A transfer unit 5 to which a transfer bias is applied is provided, and a recording material 6 is suction-held on a conveyance belt 2 by a suction unit 7, and each color component image formed by each image forming unit 1 on the recording material 6. In the image forming apparatus in which the suction means 7 is sequentially transferred.
Of the stretching rolls 3 and 4 of the transport belt 2, the stretching roll 3 located upstream of the most upstream image forming unit 1 a and the transporting belt 2 opposed to the stretching roll 3 are pressed and arranged. A suction bias VAB having the same polarity as the transfer bias VTB applied to the transfer means 5 is applied to the tension roll 3;
Is grounded.

In such technical means, as an image forming apparatus to which the present invention is applied, a plurality of image forming units 1 for forming respective color component images are arranged in parallel, and a recording material 6 is formed.
What is necessary is just a so-called tandem type in which each color component image is sequentially superimposed and transferred, and the arrangement direction of each image forming unit 1 is a horizontal arrangement,
This applies to any of the vertical arrangements. Here, in a mode in which the image forming units 1 are arranged horizontally, the transport belt 2 must be disposed along the horizontal direction.
It is necessary to pull the transport belt 2 with a relatively high tension on the tension rolls 3 and 4 from the viewpoint of effectively avoiding the deflection due to the own weight of the transport belt 2. On the other hand, in a mode in which the image forming units are vertically arranged, the transport belt 2
Are arranged in the vertical direction, so that the conveying surface of the recording material 6 of the conveying belt 2 can be vertically arranged without setting the tension of the conveying belt 2 so high.
Therefore, it is preferable in that the recording material 6 is stably conveyed while the driving load on the conveying belt 2 is reduced. In particular, in a mode in which the transport belt 2 is disposed in the vertical direction, it is preferable that the tension roller on the upper side be used as a drive unit and the recording material transport surface side of the transport belt 2 be positively stretched.

The image forming unit 1 may be appropriately selected as long as it forms an image (such as a toner image) for each color component, and may employ an electrophotographic system or an electrostatic transfer system. For example, an electrostatic latent image is written on the image carrier, and the electrostatic latent image can be appropriately selected as long as the electrostatic latent image can be visualized with toner of each color component. Here, the image carrier may be any as long as it can carry at least a toner image, and may be a photoconductor,
A suitable material such as a dielectric may be selected, and the form may be a drum shape or a belt shape.

Further, as long as the transfer belt 2 can electrostatically adsorb the recording material 6, any material such as rubber or resin may be appropriately selected, but the leakage current from the transfer means 5 to the adsorption member 8 is minimized. From the viewpoint of reducing the amount, it is preferable to provide a certain high resistance layer (for example, 10 ⁶ to 10 ¹² Ω · cm) on the conveyor belt 2 as long as the transfer performance is not impaired. As for the method of stretching the conveyor belt 2, at least two stretching rolls 3 and 4 may be used, one of which may be a driving roll and the other may be a driven roll. Stretch rolls can be added. In this case, the added tension roll may be a simple follower roll, a tension roll for applying tension, or a steering roll for correcting the meandering of the transport belt 2, It can be selected appropriately.

Further, as the transfer means 5, a device such as a transfer corotron may be used.
From the viewpoint of stably conveying the image, for example, in an embodiment using the image forming unit 1 of the electrophotographic type or the electrostatic transfer type, the image forming unit 1 is pressed against the image carrier via the conveying belt 2 and rotated. It is preferable that the transfer roll be used.

The adsorbing member 8 constituting the adsorbing means 7 only needs to be at least conductive and semi-conductive, and may be in the form of a roll-shaped member or an elastic member on the surface of the conveyor belt 2. A flexible sheet or the like to be in contact may be appropriately selected. In this case, from the viewpoint of suppressing the leakage current from the transfer unit 5 to the suction member 8, it is preferable that the suction member 8 is grounded via the high-resistance body 9. The layout of the high-resistance element 9 includes all elements that interpose a resistor in an electric circuit, and may use a resistance component separate from the suction member 8 or may be integrated with the surface of the suction member 8. It may be appropriately selected, for example, by forming a high resistance layer. The resistance value of the high-resistance element 9 depends on the relationship with the resistance value of the conveyor belt 2 itself, but is usually 10 ⁷ Ω · cm or more, preferably 10 ⁹ Ω · cm or more, and the upper limit thereof. With regard to, the charges on the conveyor belt 2 are not unnecessarily accumulated,
What is necessary is just to select within the range which does not interfere with spontaneous emission.

The timing for applying the attraction bias may be appropriately selected within a range in which the operation of attracting the recording material 6 to the transport belt 2 can be effectively performed, but unnecessary charges are stored in the transport belt 2. From the viewpoint of effectively avoiding the situation, the suction bias applying unit 11 stops the operation of applying the suction bias VAB when the recording material 6 passes through the transfer area of the most downstream image forming unit 1d. Is preferred. Further, the suction bias applying means 11 is normally provided separately from the transfer bias applying means 10, but from the viewpoint of simplification of the device configuration, the suction bias applying means 11 is applied to the transfer means 5. At least one of the transfer bias applying means 10 may be used in combination.

Next, the operation of the above technical means will be described. In FIG. 1, a transfer means 5 is
The suction bias VAB having the same polarity as the transfer bias VTB applied to the transfer member is applied, while the suction member 8 is grounded.
Therefore, the suction member 8 effectively functions as a counter electrode with respect to the tension roll 3, and the charge accompanying the suction bias VAB is uniformly applied to the recording material 6 via the transport belt 2. Further, since the attracting bias VAB having the same polarity as the transfer bias VTB is applied to the stretching roll 3, the charge polarity on the recording material 6 up to the most upstream image forming unit 1a is different between the other image forming units (1b- 1c, 1c-1d), and the image forming units 1 (1a-1d) accordingly.
Transfer conditions approach each other.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. Embodiment 1 FIG. 2 shows an embodiment of a color image forming apparatus to which the present invention is applied. In the figure, the color image forming apparatus vertically arranges image forming units 22 (specifically, 22a to 22d) of four colors (black, yellow, magenta, and cyan in this embodiment) in a main body housing 21. And a paper feed cassette 23 for accommodating sheets for supply is disposed below the image forming unit 22.
A paper transport path 24 which is a transport path for paper (not shown) from the paper feed cassette 23 is vertically arranged at a location corresponding to.

In this embodiment, the image forming units 22 (22a to 22d) form toner images for black, yellow, magenta, and cyan in order from the upstream side of the paper transport path 24. , A photoreceptor cartridge 30 and an exposure unit 40. Here, the photoconductor cartridge 30 includes, for example, a photoconductor drum 31 and
A charging roll 32 for charging the photosensitive drum 31 in advance
And a developing unit 3 that develops the electrostatic latent image formed by exposure on the charged photosensitive drum 31 by the exposure unit 40 with a corresponding color toner (for example, negative polarity in this embodiment).
3 and a cleaner 34 for removing residual toner on the photosensitive drum 31 are integrally formed as a cartridge.
On the other hand, the exposure unit 40 stores a semiconductor laser (not shown), a polygon mirror 42, an imaging lens 43, and a mirror 44 in a case 41, deflects and scans light from the semiconductor laser (not shown) with the polygon mirror 42, The optical image is guided to an exposure point on the photosensitive drum 31 via the image lens 43 and the mirror 44.

Further, in the present embodiment, as shown in FIGS. 2 and 3, the paper transporting circulating along the paper transport path 24 is performed at a position corresponding to each photosensitive drum 31 of each image forming unit 22. A belt 80 is provided. The paper transport belt 80 is made of a belt material (rubber or resin) capable of electrostatically attracting the paper 25, and has a surface
A high resistance coat layer 80a of about ¹⁰ Ω · cm (see FIG. 4) is formed. Then, the paper transport belt 80
Is stretched over a pair of metal stretching rolls 81 and 82. In the present embodiment, the upper stretching roll 82 is a driving roll, and the lower stretching roll 81 is a driven roll. .

Further, a transfer roll 50 is provided on the back side of the paper transport belt 80 corresponding to the photosensitive drum 31 of each image forming unit 22.
The paper 25 on the paper transport belt 80 is nipped and held between the photosensitive drum 31 and the photosensitive drum 31. A transfer bias power supply 51 is connected to the transfer roll 50, and a predetermined transfer bias VTB (positive in this embodiment) is applied at an appropriate timing via a switch 52.

In the present embodiment, the sheet cassette 2
3 is provided with a paper feed roll 61 for feeding the paper 25 at a predetermined timing, and the paper feed roll is fed to the paper transport path 24 located between the paper feed roll 61 and the transfer portion of the uppermost stream image forming unit 22a. Delivery roll 62 is provided. Further, a fixing device 64 is provided in the sheet transport path 24 located on the downstream side of the most downstream image forming unit 22d, and a discharge roller 66 for discharging the sheet is provided downstream of the fixing device 64.
Is provided, and the discharge paper is stored in a storage tray 67 formed on the upper part of the main body housing 21. In FIG. 2, reference numeral 65 denotes a paper guide for guiding the paper 25 sent from the paper transport belt 80 to the fixing device 64.

In particular, in the present embodiment, a paper suction device 90 is provided at the entrance of the paper transport belt 80.
In the sheet suction device 90, a suction roller 91 is pressed and arranged at a position corresponding to the tension roll 81 on the entrance side of the sheet conveyance path 24 of the sheet conveyance belt 80, and a suction bias power supply 92 is connected to the tension roll 81. A suction bias VAB having the same polarity as the transfer bias VTB is applied at an appropriate timing through a switch 93, while the suction roll 91 is grounded. Further, in the present embodiment,
As shown in FIG. 3, a paper passage sensor 94 (for example, using an optical sensor or a limit switch) for detecting that the paper 25 has passed is disposed downstream of the transfer site of the most downstream image forming unit 22d. Switch 93
Is turned on in synchronization with the operation timing of the paper feed roll 61 at the start of an image forming job (one or a plurality of image forming jobs), and the last sheet of the image forming job has passed the sheet passing sensor 94. It is turned off at the time. As the suction roll 91, for example, a hollow metal roll 91a having a surface coated with a conductive elastic layer 91b such as EPDM is used.

Next, the operation of the color image forming apparatus according to this embodiment will be described. 2 and 3,
First, when the number of images to be formed is designated and an image formation start switch (not shown) is pressed, the paper 25 in the paper feed cassette 23 is sent out by the paper feed roll 61 and then nip-conveyed by the feed roll 62. The sheet reaches the sheet suction device 90. At this time, in the paper suction device 90, the switch 93 is turned on at the timing when the first paper 25 of the image forming job is sent out, and the suction bias V AB is applied to the stretching roll 81.
(Positive voltage) is applied and the suction roll 91 is grounded.
Is formed as a counter electrode. For this reason, when the paper 25 enters the nip portion between the suction roll 91 and the stretching roll 81 of the paper suction device 90, a positive charge is uniformly applied to the paper 25, and the paper transport belt 80 is electrostatically attracted and held.

In this state, the sheet 25 is conveyed by the sheet conveying belt 80, and each image forming unit 22
When the color component toner images on the photosensitive drum 31 are sequentially passed through the transfer portions (22a to 22d), the color component toner images are sequentially transferred onto the paper 25 by the transfer electric field generated by the transfer roll 50. Then, when the leading end of the sheet 25 enters the fixing device 64 and finishes passing, the sheet 25 on which the unfixed toner image is fixed is discharged to the storage tray 67 through the discharge roll 66.
Note that the last sheet 25 of the image forming job is
4, the switch 93 is turned off, the application of the suction bias VAB to the paper suction device 90 is stopped, and the residual charges on the paper conveyance belt 80 are spontaneously discharged via the suction roll 91.

In such an image forming process, the paper 2
In No. 5, a good color image without transfer unevenness was obtained. Such conclusions are based on the following experiments.

That is, an experiment was conducted for examining the level of occurrence of transfer unevenness in the working model according to the present embodiment and each comparative model. Here, the execution model according to the present embodiment is in the form of “stretch roll: + bias application, suction roll: grounding”, whereas each comparative model is “stretch roll: −bias application, + This is a mode in which “bias application, grounding, float” and “sucking roll: −bias application, + bias application, grounding, float” are appropriately combined. The results of the experiment are shown in FIG. In the figure, it is understood that in the comparative model in which either the stretching roll or the suction roll is in the floating state, the paper suction is impossible or the suction power is insufficient, and the paper suction performance itself is impaired. . On the other hand, in a mode in which either the stretching roll or the suction roll is grounded, although the paper suction performance is ensured, a difference occurs in the transfer unevenness level,
In the execution model, no transfer unevenness was observed (◎), Comparative model 1 (“stretch roll: grounding, suction roll: + bias application”), and comparison model 2 (“stretch roll: −bias application, suction roll: It was confirmed that the level of occurrence of transfer unevenness deteriorated (Δ, ×, XX) in the order of “grounding”) and Comparative Model 3 (“stretch roll: grounding, suction roll: −bias application”).

FIG. 6A shows the results of such an experiment, for example, by comparing the actual model with the comparative model 3.
It is estimated as shown in FIG. That is, in the implementation model “stretch roll: + bias application, suction roll: ground”,
As shown in FIG. 6A, since the suction bias VAB having the same polarity as the transfer bias VTB is applied to the stretching roll 81, the transfer roll facing the image forming unit 22 (for example, the most upstream image forming unit 22a). The leakage current IL1 from the sheet 50 flows to the suction roll 91 side through the paper conveyance belt 80. However, if a certain high resistance coating layer 80a is formed on the surface of the paper conveyance belt 80, the leakage current IL1 is extremely small. Can be suppressed. On the other hand, in the comparative model 3 (“stretch roll: grounding, suction roll: −bias application”), as shown in FIG.
1 is grounded, a leakage current IL2 from the transfer roll 50 facing the image forming unit 22 (for example, the most upstream image forming unit 22a) is directly transmitted to the grounded roll 81 via the paper transport belt 80. The leakage current IL2 is the leakage current IL1 of the working model.
Considerably more than. In FIG. 6B, reference numeral 92 'denotes a suction bias power supply. Therefore, in the case of the comparative model 3, the transfer current IT injected from the transfer roll 50 to the photosensitive drum 31 in the image forming unit 22 varies due to a large amount of leakage current IL2. On the other hand, in the case of the working model, the transfer current IT is stably injected with almost no unevenness, while the occurrence level is deteriorated. Therefore, it is assumed that no transfer unevenness is observed at all.

Second Embodiment An image forming apparatus according to a second embodiment is substantially the same as that of the first embodiment, but is different from the first embodiment.
It has. FIG. 7A shows a paper suction device 90 used in the second embodiment. In the same drawing, the sheet suction device 90 has a suction roller 91 pressed against the surface of a sheet conveyance belt 80 facing the tension roller 81 and has the same polarity as the transfer bias VTB on the tension roller 81, as in the first embodiment. And the suction roller 91 is grounded via a high-resistance component 95 of, for example, about 10 ¹⁰ Ω · cm.

According to the present embodiment, as shown in FIG. 8, since the attracting bias VAB having the same polarity as the transfer bias VTB is applied to the stretching roll 81, the image forming unit 22 (for example, the most upstream image forming) The leakage current IL from the transfer roll 50 facing the unit 22a) flows to the suction roll 91 through the paper transport belt 80, but the high resistance component 95 is added to the high resistance coat layer 80a on the surface of the paper transport belt 80. Since it functions as a resistor, the leakage current IL is further suppressed to an extremely small level as compared with the first embodiment.
Therefore, according to the present embodiment, the image forming unit 22
The transfer current IT injected from the transfer roll 50 to the photosensitive drum 31 is more stable because the leakage current IL is further reduced, and a higher quality color image without transfer unevenness can be obtained. In this embodiment, FIG.
As shown in FIG. 7, a high-resistance component 95 is used. However, the present invention is not limited to this. For example, as shown in FIG. The high resistance layer 96 may be formed on the surface of the roll 91.

Third Embodiment FIG. 9 shows a color image forming apparatus according to a third embodiment of the present invention. In the figure, the color image forming apparatus according to the present embodiment is substantially the same as the first embodiment, but differs from the first embodiment in that the transfer roll 50 and the sheet suction device 90 of the most downstream image forming unit 22d are different. Tension roll 81
A common bias power supply 100 is connected to the transfer bias VTB from the common bias power supply 100 to the transfer roll 50, and a suction bias VAB (VAB = VTB in this embodiment) to the stretching roll 81 via the switch 101. Thus, it is applied at an appropriate timing. However, in the present embodiment, the distance from the nip between the suction roll 91 and the stretching roll 81 to the nip between the photosensitive drum 31 of the most downstream image forming unit 22d and the transfer roll 50 is A,
When the length in the transport direction of the paper 25 to be used is B, A>
B is required. The same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the detailed description thereof will be omitted.

Therefore, according to the present embodiment, the paper 25
Are the suction roll 91 and the stretching roll 81 of the paper suction device 90
While the trailing end of the paper 25 passes through the suction roll 91, the leading end of the paper 25 is in the nip between the photosensitive drum 31 of the most downstream image forming unit 22d and the transfer roll 50. Has not reached. For this reason, while the suction operation of the paper 25 by the paper suction device 90 is performed,
The transfer operation in the most downstream image forming unit 22d is not performed. On the other hand, while the transfer operation is performed in the most downstream image forming unit 22d, the paper suction device 90 does not perform the suction operation on the sheet 25. Therefore, the voltage fluctuation due to the paper entry at the nip portion of the paper suction device 90 does not affect the transfer operation of the most downstream image forming unit 22d.
The voltage fluctuation due to the entry of the sheet at the nip portion of the most downstream image forming unit 22d does not affect the sheet suction operation of the sheet suction device 90. Therefore, it is possible to configure the suction bias power supply to the stretching roll 81 of the paper suction device 90 and the transfer bias power supply to the transfer roll 50 of the most downstream image forming unit 22d with the shared bias power supply 100, and the paper suction device The cost can be reduced because the 90 dedicated power supplies can be omitted.

[0031]

As described above, according to the present invention,
A closed circuit configuration in which a suction member is disposed in pressure contact with the surface of the conveyance belt facing the tension roll of the conveyance belt, and a suction bias having the same polarity as the transfer bias is applied to the tension roll, and the suction member is grounded. Therefore, it is possible to uniformly charge the recording material, to reduce the occurrence of transfer unevenness in each image forming unit, and to stabilize the electrostatic attraction force on the recording material. As a result, the recording material can be stably conveyed to maintain good color registration. Further, according to the present invention, by applying a suction bias having the same polarity as the transfer bias to the tension roll, the charge polarity on the recording material up to the uppermost image forming unit and the charge polarity between the other image forming units are adjusted. The transfer conditions of each image forming unit are different from each other in comparison with a mode in which the charge polarity of the recording material up to the most upstream image forming unit is opposite to the charge polarity between the image forming units. , The transfer conditions of each image forming unit can be easily set, and a good color image with good color balance for each color component can be easily obtained.

Further, in the present invention, if the suction member is grounded via a high-resistance element, the leakage current from the transfer means to the suction member can be extremely reduced, so that the transfer condition of the transfer means can be stabilized. Therefore, a stable color image without transfer unevenness can be obtained.

[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 an explanatory diagram illustrating an overall configuration of the image forming apparatus according to the first embodiment;

FIG. 3 is an explanatory diagram illustrating an outline of a sheet suction device used in the first embodiment.

FIG. 4 is an explanatory diagram showing details of the paper suction device of FIG. 3;

FIG. 5 is an explanatory diagram showing a result of examining a transfer unevenness level with respect to an execution model and a comparison model according to the first embodiment.

FIG. 6A is an explanatory diagram showing a state of a leakage current from a transfer roll in an execution model, and FIG. 6B is an explanatory diagram showing a state of a leakage current from a transfer roll in a comparative model.

FIG. 7A is an explanatory diagram showing a paper suction device used in a second embodiment, and FIG. 7B is an explanatory diagram showing a modification thereof.

FIG. 8 is an explanatory diagram showing advantages of the paper suction device according to the second embodiment.

FIG. 9 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a third embodiment.

[Explanation of symbols]

1 (1a to 1d) image forming unit, 2 transport belt, 3, 4 stretching roll, 5 transfer means, 6 recording material,
7 suction means, 8 suction member, 9 high resistance body, 10 transfer bias application means, 11 suction bias application means, V
AB: adsorption bias, VTB: transfer bias, 22 (22a
22d) image forming unit, 25 paper, 50 transfer roll, 51 transfer power supply, 80 paper transport belt, 81, 82 stretch roll, 90 paper suction device,
91: suction roll, 92: suction bias power supply, 100:
Shared bias power supply

Claims (4)

[Claims] 1. A transport belt in which a plurality of image forming units on which respective color component images are formed are arranged in parallel, and are circulated and conveyed by being wrapped around at least a pair of tension rolls along an arrangement direction of the image forming units. A transfer unit to which a transfer bias is applied is disposed on the back side of the conveyance belt facing each image forming unit, and a recording material is suction-held on the conveyance belt by the suction unit. In the image forming apparatus configured to sequentially transfer each color component image formed by each image forming unit, the suction unit is located on the upstream side of the most upstream image forming unit among the stretching rolls of the transport belt. A stretch roll,
A suction member that is disposed in pressure contact with the transfer belt facing the tension roll, and applies a suction bias having the same polarity as a transfer bias applied to a transfer unit to the tension roll, while applying the suction member to the tension roller. An image forming apparatus, which is grounded. 2. The image forming apparatus according to claim 1, wherein the suction member is grounded via a high-resistance element. 3. The image forming apparatus according to claim 1, wherein the suction bias applying means stops the operation of applying the suction bias when the recording material passes through the transfer area of the most downstream image forming unit. Characteristic image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the attraction bias applying unit also serves as at least one of the transfer bias applying unit applied to the transfer unit.