JP5509020B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image using a transfer belt.

  In this type of image forming apparatus, an electrophotographic system is used. When the charger precharges an image carrier, for example, a photosensitive drum, and the exposure device irradiates light on the surface of the photosensitive drum, the photosensitive drum An electrostatic latent image is formed on the surface. Further, the developing device carries toner, and when a developing bias voltage is applied, the toner charged in advance adheres to the electrostatic latent image, and a toner image is formed.

Then, this toner image is transferred and fixed to a recording material on a transfer belt or to a recording material via an intermediate transfer belt.
Here, a technique for running the transfer belt or the like with the driving force of a driving roller is known (see, for example, Patent Document 1). As a result, on the transfer belt or the like, a loose side from the driving roller to the driven roller and a tension side from the driven roller to the driving roller are generated.

JP 2006-171075 A

  However, the above-described conventional technique has a problem of causing a transfer failure of the toner image. This is because the driving roller of the technology is arranged on the downstream side of the transfer position of the toner image. More specifically, the tension side of the belt in this case is close to the transfer position of the toner image, whereas the loose side is separated from the transfer position of the toner image, so that the surface of the belt and the photosensitive drum are in contact with each other. The range (wrapping amount) is reduced.

  This problem becomes prominent when the transfer belt has a structure that vertically conveys the recording material from the bottom to the top rather than in the horizontal direction. Since the loose side is separated further downward from the toner image transfer position under the influence of the gravity of the belt, the contact range between the tension side surface and the surface of the image carrier can be further reduced. is there.

Also, in solving this problem, if a cleaning unit that rubs and cleans the surface of the belt is provided, the damage on the surface leads to poor transfer of the toner image, so that the damage is avoided. There is a need to.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can solve the above-described problems and that can favorably transfer a toner image.

  A first invention for achieving the above object has an image carrier, and by driving the latent image on the image carrier, the latent image on the image carrier is developed with toner, and a toner image is formed. Hanging around each driven roller, the recording material is transported vertically from below to above, and the recording material is placed on the transport surface and travels between the image carrier and the transfer roller. A transfer belt that directly transfers the image to the recording material, and the driving roller is disposed on the upstream side of the transfer position of the toner image as viewed in the running direction of the transfer belt, and is connected to the loose side of the transfer belt. The loose contact is provided closer to the image carrier than the toner image transfer position.

According to the first invention, the transfer belt is a belt that vertically conveys the recording material from below to above, and is wound around the drive roller and the driven roller in an inclined manner. The toner image formed on the image carrier is transferred to the recording material.
Here, when viewed in the running direction of the transfer belt, the drive roller is disposed upstream of the transfer position of the toner image, and the loose side of the transfer belt from the drive roller to the driven roller is close to the image carrier and is driven. The tension side of the transfer belt from the roller toward the driving roller is separated from the image carrier. Therefore, the transfer belt conveyance surface is easily wrapped around the surface of the image carrier.

  Further, the winding angle of the transfer belt in the driving roller is defined from the loose side contact to the tight side contact with the tight side of the transfer belt. In the present invention, the loose side contact is the transfer of the toner image. Since it is provided closer to the image carrier than the position, the winding amount of the transfer surface of the transfer belt is larger than when the loose contact is further away from the image carrier than the toner image transfer position. .

As a result, the back side of the recording material can be strongly pressed toward the image carrier, and the toner image can be transferred satisfactorily.
According to a second aspect of the invention, in the configuration of the first aspect of the invention, the amount of wrapping between the surface of the image carrier and the transfer surface of the transfer belt at the toner image transfer position is set to about 1.0 mm to about 5.0 mm. It is characterized by that.

According to the second invention, in addition to the action of the first invention, the amount of wrapping of the conveying surface is set to a large value of about 1.0 mm to about 5.0 mm. While achieving good transfer performance, if it is within the range, it is possible to prevent the recording material from being wrapped around the image carrier and to obtain good separation performance.
According to a third aspect of the present invention, in the configuration of the first or second aspect of the invention, the distance from the loose side contact to the toner image transfer position is such that the driven roller contacts the loose side of the transfer belt from the toner image transfer position. It is characterized by being set shorter than the distance to the slack side contact.

  According to the third invention, in addition to the effects of the first and second inventions, the image carrier is made closer to the drive roller than the driven roller, and the transfer belt has an extension amount of the image carrier. Compared to the case where the roller is placed close to the roller, the amount is less, and this point also contributes to obtaining good transfer performance. Further, the transfer surface of the transfer belt can be reliably wound around the surface of the image carrier.

According to a fourth invention, in the configurations of the first to third inventions, the rotation speed of the image carrier is set to be higher than the rotation speed of the drive roller, and the linear velocity ratio thereof is 1.01 to 1.03. It is controlled within the range.
According to the fourth invention, in addition to the effects of the first to third inventions, if the rotational speed of the image carrier is set larger than the running speed of the transfer belt within the above range, the transfer performance and separation are achieved. Ensure that both performances are met.

  According to a fifth aspect of the invention, in the configurations of the first to fourth aspects of the invention, the transfer belt applies a voltage having a polarity opposite to that of the toner adhering to the latent image to the transfer roller to directly transfer the toner image to the recording material. And a cleaning unit provided on the tension side of the transfer belt for recovering residual toner adhering to the conveying surface by electrostatic force and cleaning the conveying surface. The driven roller is disposed at a position deviating from the winding angle of the transfer belt, contacts the transfer surface of the transfer belt in the trail direction, and its rotational speed is about 1.0 to about 1 with respect to the running speed of the transfer belt. It is characterized in that the speed is set twice.

  According to the fifth invention, in addition to the actions of the first to fourth inventions, the transfer belt is a belt for electrostatically conveying the recording material, and has a voltage having a polarity opposite to that of the toner adhering to the latent image. When applied to the transfer roller, the toner image is transferred to the recording material. In other words, this toner moves positively from the image carrier toward the recording material and can adhere strongly to the conveying surface, but the cleaning unit uses the electrostatic force to collect the residual toner adhering to the conveying surface. Therefore, it is possible to prevent the recording material from being stained.

  Here, simply cleaning the conveyance surface causes damage to the conveyance surface. However, in the present invention, the cleaning roller is not brought into direct contact with the conveyance surface but is in contact with the transfer surface, and the surface of the cleaning roller is the transfer belt. Along with the traveling direction of the belt, the conveyance surface is abutted against the conveyance surface in the trail direction to hold down the conveyance surface, so that the conveyance surface can be prevented from being damaged and a long-life transfer belt can be obtained. On the other hand, the rotation speed of the cleaning roller is set to a speed that does not become slower than the traveling speed of the transfer belt, so that the cleaning performance can be maintained.

In addition, if a transfer belt that electrostatically conveys is used, it is easy to prevent the image carrier from being wound, so that the separation of the recording material is improved, and it is conveyed while being adsorbed until the next fixing. As a result, it contributes to stabilizing the performance of high-speed machines.
According to a sixth aspect of the invention, in the configuration of the fifth aspect of the invention, the cleaning roller imparts tension to the transfer belt so as to set the extension ratio of the transfer belt to about 3% to about 5%.

  According to the sixth invention, in addition to the action of the fifth invention, if the cleaning roller applies the above tension to the transfer belt, the cleaning performance can be improved. Further winding on the surface of the body contributes to the improvement of transfer performance.

  According to the present invention, it is possible to provide an image forming apparatus in which the wrapping amount of the transfer surface of the transfer belt is increased and the contact by the cleaning roller is improved, and the toner image can be transferred satisfactorily. it can.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is an explanatory diagram around a transfer unit in FIG. 1. It is explanatory drawing of the transfer unit of FIG. FIG. 3 is an enlarged view around a transfer roller in FIG. 2.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 schematically shows the structure of a printer 1 for monochrome printing which is an example of an image forming apparatus. The cross section shown in FIG. 1 is seen from the left side of the printer 1. Therefore, the front surface of the printer 1 is located on the right side of FIG.

As shown in FIG. 1, a paper discharge tray 36 is provided above the apparatus main body 2 of the printer 1, and a plurality of operation keys used for various operations by the user are provided near the paper discharge tray 36. A front cover 5 on which a screen for displaying various types of information is arranged is provided.
A sheet feeding cassette 4 is disposed below the apparatus main body 2, and a sheet of paper (recording material) is stored in the storage unit 40 in a stacked state.

As shown in FIG. 1, a paper feed roller 46 is provided on the upper right side of the accommodating portion 40, and the paper is sent toward the upper right side of the paper feed cassette 4. It is vertically transported upward along the front surface of the printer 1 inside.
Further, the paper feed cassette 4 is configured to be able to be pulled out to the front side of the printer 1, that is, in the right direction in FIG. 1, and in this pulled out state, a new sheet can be replenished to the storage section 40. The paper can be replaced with another type of paper.

Inside the apparatus main body 2, a conveyance roller 10, a registration roller 14, an image forming unit 16, and a transfer unit 30 are sequentially arranged on the downstream side when viewed in the sheet conveyance direction from the sheet feeding cassette 4.
The image forming unit 16 is provided with a single photosensitive drum (image carrier) 18, which is rotatably installed and is driven counterclockwise in FIG. 1 by a drum motor. Note that the photosensitive drum 18 of this embodiment is an a-Si drum having an amorphous silicon-based layer on the surface thereof.

  As shown in FIG. 1, an exposure unit 15 is provided on the left side of the photosensitive drum 18, and laser light is emitted from the exposure unit 15 toward the photosensitive drum 18. As shown in FIG. 1, a charging device 20, a developing device 24, a transfer roller 31 of the transfer unit 30 and a cleaning unit 25 are provided at appropriate positions around the photosensitive drum 18.

The charger 20 of this embodiment is located obliquely above and to the left of the photosensitive drum 18 as shown in FIG. 1, and has a charging roller that contacts the photosensitive drum 18 and a rubbing roller that polishes and rubs the surface of the charging roller. Then, the surface of the photosensitive drum 18 is charged.
The developing device 24 is disposed obliquely below and to the left of the photosensitive drum 18 and has a developing roller that faces the photosensitive drum 18. This developing roller is driven clockwise by a developing motor in FIG.

A black toner container 23 is disposed between the exposure unit 15 and the paper feed cassette 4.
Here, the transfer unit 30 of the present embodiment has a transfer belt 50 having elasticity that attracts and conveys paper by electrostatic force as will be described later (FIGS. 2 and 3), and the transfer belt 50 is the photosensitive drum 18. 1, and travels clockwise as viewed in FIGS. 1 to 3 by a belt motor.

  The transfer belt 50 is configured to be able to press against the photosensitive drum 18 from the lower right side via the transfer roller 31. The transfer belt 50 and the photosensitive drum 18 form a nip portion for transferring a toner image onto a sheet. The transfer roller 31 of the present embodiment is configured with a size of about 14 mm in diameter, in which EPDM foam rubber is formed on a metal shaft (about 8 mm in diameter), and the back surface of the transfer belt 50 faces the photosensitive drum 18. Pressing.

In addition, a fixing unit 32, a discharge branching unit 34, and a discharge roller 35 are sequentially arranged on the downstream side of the transfer unit 30 when viewed in the sheet conveyance direction (FIG. 1).
In this embodiment, the transfer unit 30 and the manual feed tray 3 are provided with a transfer unit 48 that can be pulled out from the apparatus main body 2 together with the transfer unit 30. A double-sided printing conveyance path 38 is formed. The duplex printing conveyance path 38 branches from the discharge branching portion 34 on the front side of the apparatus main body 2 and extends downward, and is connected to the upstream side of the registration roller 14.

  Here, for the transfer belt 50 described above, an endless belt in which both end portions of a rubber sheet material are overlapped and joined, or a seamless belt without a seam, is used, as shown in FIGS. As shown in the figure, the driving roller 52 disposed on the lower registration roller 14 side and the driven roller 54 disposed on the fixing unit 32 side above are parallelly run and run clockwise in an inclined state. Yes.

  That is, as shown in FIGS. 2 and 3, the loose side of the transfer belt 50 of this embodiment from the driving roller 52 toward the driven roller 54 is close to the photosensitive drum 18. Further, the slack side contact S1 of the driving roller 52 and the slack side contact (other slack side contact) S2 of the driven roller 54 shown in FIG. 3 are provided closer to the photosensitive drum 18 than the transfer position of the toner image. ing.

  Specifically, the winding amount (indicated by L in FIG. 4) between the surface of the photosensitive drum 18 and the transfer surface of the transfer belt 50 at the toner image transfer position is set to about 1.0 mm to about 5.0 mm. As shown in FIG. 3, the loose side contact S <b> 1 and the loose side contact S <b> 2 of FIG. 3 are provided closer to the photosensitive drum 18 than the nip portion between the transfer belt 50 and the photosensitive drum 18.

In addition, the distance from the slack side contact S1 to the nip portion in this embodiment is set shorter than the distance from the slack side contact S2 to the nip portion, and the photosensitive drum 18 is driven more than the driven roller 54. It is provided near the roller 52 (FIGS. 2 and 3).
The rotational speed of the photosensitive drum 18 is set to be about 2 to 3% larger than the rotational speed of the drive roller 52, and is controlled within a range of 1.01 to 1.03 in terms of a linear speed ratio. Yes.

For example, acrylonitrile butadiene rubber (NBR) is used for the rubber sheet material described above, and the surface thereof is coated with fluorine (for example, PTFE) in order to improve the releasability of the toner.
Further, the triboelectric charging characteristic of the transfer belt 50 has a reverse polarity relationship with the triboelectric charging characteristic of the toner adhering to the electrostatic latent image on the photosensitive drum 18.

  A voltage having a polarity opposite to that of the toner attached to the electrostatic latent image is applied between the transfer roller 31 and the photosensitive drum 18. In other words, if the toner used in this embodiment is a positively chargeable toner, when a voltage having a polarity opposite to that of the toner is applied to the transfer roller 31, the positively chargeable toner on the photosensitive drum 18 is It moves away from the photosensitive drum 18 and basically goes to the paper on the transfer belt 50.

  Here, on the conveying surface of the transfer belt 50, positively charged toner separated from the photosensitive drum 18 or negatively charged toner generated due to an increase in the surface potential of the photosensitive drum 18 as residual toner. May adhere. In addition, the positively chargeable toner may include the same positively chargeable residual toner that is gradually charged up by the rotation of the transfer belt 50.

Therefore, the cleaning unit 57 in FIG. 2 removes the residual toner remaining on the transfer surface of the transfer belt 50.
As shown in FIG. 3, the cleaning unit 57 of this embodiment includes a cleaning roller 58, a blade 59, a high-pressure substrate, and a cleaning auxiliary unit 60.

The cleaning roller 58 is disposed on the tension side from the driven roller 54 toward the driving roller 52, specifically, in the vicinity of the downstream side of the driven roller 54 when viewed in the traveling direction of the transfer belt 50, and adheres to the conveyance surface on which the paper is placed. Residual toner is collected by electrostatic force and removed from the conveying surface.
More specifically, as shown in FIG. 3, the rotational axis of the cleaning roller 58 of this embodiment is disposed at a position deviating from the winding angle of the transfer belt 50 on the driven roller 54.

  The cleaning roller 58 is made of metal (for example, SUS430), and extends in the width direction of the transfer belt 50 so as to be rotatable. Further, the cleaning roller 58 rotates counterclockwise in FIG. 3 at the same or larger speed (linear speed ratio: for example, 1.0 to 1.2) as that of the transfer belt 50, and follows the trail direction on the conveyance surface of the transfer belt 50. Abut. More specifically, the cleaning roller 58 of this embodiment applies a tension to the transfer belt 50 to set the extension rate of the transfer belt 50 to about 3% to about 5%.

The blade 59 is made of urethane, extends in the width direction of the transfer belt 50, and contacts the cleaning roller 58 in the counter direction on the side opposite to the conveyance surface.
The driven roller 54 described above is grounded, and a voltage having a polarity opposite to that of the toner adhering to the electrostatic latent image on the photosensitive drum 18 is applied between the cleaning roller 58 and the driven roller 54 from the high voltage substrate. Therefore, an electric field is generated from the transfer surface of the transfer belt 50 toward the cleaning roller 58.

As a result, the positively chargeable toner adhering to the conveyance surface of the transfer belt 50 is collected from the conveyance surface and adheres to the cleaning roller 58. Residual toner adhering to the cleaning roller 58 is scraped off by a blade 59 and collected in a collection container.
On the other hand, the cleaning assisting unit 60 is disposed in the vicinity of the upstream side of the driving roller 52 in the traveling direction of the transfer belt 50 and extends in the width direction of the transfer belt 50 so as to be rotatable.

The cleaning assisting unit 60 is configured by a brush whose frictional charging characteristic has a relationship opposite to that of a regular charged toner (negative charging property in this embodiment). Then, it rotates clockwise in FIG. 3 at the same speed as the transfer belt 50 (linear speed ratio: 1.0), and abuts against the transport surface of the transfer belt 50 in the counter direction.
As a result, even if the negatively chargeable toner adhering to the transport surface passes through the cleaning roller 58, it is disturbed by the cleaning assisting unit 60 and is all adjusted to positively chargeable toner.

A sheet is placed near the registration roller 14 on the transport surface on which the prepared positively charged toner is adhered, and is directed to the photosensitive drum 18.
Next, when a voltage having a polarity opposite to that of the toner is applied to the transfer roller 31, the positively chargeable toner on the photosensitive drum 18 moves away from the photosensitive drum 18 toward the paper, but adheres to the conveyance surface of the transfer belt 50. The positively charged toner that has been applied does not go to the back side of the paper but continues to adhere to the transport surface.

According to the cleaning unit 57, since the electric field from the conveyance surface to the cleaning roller 58 is generated by the high-pressure substrate, the positively chargeable toner that continues to adhere to the conveyance surface can be collected from the conveyance surface, and then Residual toner is difficult to accumulate on the transport surface.
Reference numeral 55 in FIG. 2 is a support table, and a density sensor capable of detecting toner on the transfer belt 50 is installed on the support table 55.

  Returning to FIG. 1 again, when the printer 1 performs printing, the paper feed roller 46 separates and feeds the paper from the paper feed cassette 4 one by one. The fed paper reaches the registration roller 14 from the transport roller 10. The registration roller 14 feeds the paper to the transfer unit 30 at a predetermined paper feed timing while correcting the oblique feeding of the paper and measuring the image transfer timing with the toner image formed by the image forming unit 16. .

On the other hand, the input port 91 in FIG. 2 is configured to be able to receive image data as a printing source from the outside. This image data is data in which various images such as characters, codes, figures, symbols, diagrams, and patterns are converted into data. Based on this data, the controller 90 controls laser light irradiation and the like.
Specifically, after the surface of the photosensitive drum 18 is neutralized, the charger 20 charges the surface of the photosensitive drum 18.

Next, when the exposure unit 15 irradiates the surface of the photosensitive drum 18 with laser light, an electrostatic latent image is formed on the surface of the photosensitive drum 18, and a black toner image is formed from the electrostatic latent image. .
This toner image is transferred onto a sheet conveyed by the transfer belt 50. The toner remaining on the surface of the photosensitive drum 18 is removed by the cleaning unit 25, and the residual toner and the like adhering to the conveyance surface of the transfer belt 50 is removed by the cleaning unit 57.

Subsequently, the sheet is fed toward the fixing unit 32 with an unfixed toner image carried thereon, and is heated and pressed by the fixing unit 32 to fix the toner image. Thereafter, the sheet sent from the fixing unit 32 is discharged to the discharge tray 36 via the discharge roller 35 and stacked in the height direction.
When double-sided printing is performed on this single-sided printing, the conveyance direction of the paper discharged from the fixing unit 32 is switched by the discharge branching unit 34.

That is, the sheet printed on one side is pulled back into the apparatus main body 2 and conveyed to the duplex printing conveyance path 38. Subsequently, the sheet is sent toward the upstream side of the registration roller 14 and is sent again toward the transfer unit 30. As a result, the toner image is transferred to the surface of the paper that has not been printed.
As described above, according to this embodiment, the transfer bell 50 is a belt that vertically conveys a sheet from below to above, and is wound around the drive roller 52 and the driven roller 54 in an inclined manner. It runs between the photosensitive drum 18 and the transfer roller 31, and the toner image formed on the photosensitive drum 18 is transferred to a sheet.

  Here, when viewed in the running direction of the transfer belt 50, the driving roller 52 is disposed upstream of the toner image transfer position, and the driven roller 54 is disposed downstream of the toner image transfer position. The loose side of the transfer belt 50 from 52 to the driven roller 54 is close to the photosensitive drum 18, and the tight side of the transfer belt 50 from the driven roller 54 to the driving roller 52 is away from the photosensitive drum 18. Therefore, the conveyance surface of the transfer belt 50 is easily wound around the surface of the photosensitive drum 18.

  The winding angle of the transfer belt 50 on the driving roller 52 is defined from the loose side contact S1 to the tight side contact with the tight side of the transfer belt 50. In this embodiment, the loose side contact is provided. Since S1 is provided closer to the photosensitive drum 18 than the transfer position of the toner image, the slack side contact S1 is closer to the photosensitive drum 18 than the transfer position of the toner image. The amount of wrap around the transport surface becomes larger.

As a result, the back side of the paper can be strongly pressed toward the photosensitive drum 18, and the toner image can be transferred satisfactorily.
Further, since the amount of wrap around the transfer belt 50 is set to a large value of about 1.0 mm to about 5.0 mm, the transfer from the photosensitive drum 18 to the paper can be achieved while maintaining the good transfer performance. Thus, it is possible to prevent the paper from being wound around the photosensitive drum 18 and to obtain good separation performance.

  Further, the photosensitive drum 18 is closer to the driving roller 52 than the driven roller 54, and the amount of extension of the transfer belt 50 is smaller than that in the case where the photosensitive drum 18 is close to the driven roller 54. This also contributes to the acquisition of good transfer performance. Further, the conveyance surface of the transfer belt 50 can be reliably wound around the surface of the photosensitive drum 18.

Furthermore, if the rotational speed of the photosensitive drum 18 is set larger than the traveling speed of the transfer belt 50 within the above range, both the transfer performance and the separation performance are surely satisfied.
The transfer belt 50 is a belt that electrostatically conveys and conveys a sheet. When a voltage having a polarity opposite to that of the toner adhering to the latent image is applied to the transfer roller 31, the toner image is transferred to the sheet. That is, the toner moves positively from the photosensitive drum 18 toward the paper and can adhere strongly to the conveyance surface of the transfer belt 50, but the cleaning unit 57 uses the electrostatic force to leave the residue adhered to the conveyance surface. The toner is collected, and the backside of the paper can be prevented.

  Here, simply cleaning the conveyance surface of the transfer belt 50 causes damage to the conveyance surface. However, in this embodiment, the cleaning roller 58 is not brought into direct contact with the conveyance surface but is brought into contact with the conveyance surface. Since the surface of the roller 58 is along the running direction of the transfer belt 50 and abuts against the conveyance surface in the trail direction to hold down the conveyance surface, the conveyance surface can be prevented from being damaged, and the transfer belt has a long life. On the other hand, the rotational speed of the cleaning roller 58 is set to a speed that does not become slower than the traveling speed of the transfer belt 50, so that the cleaning performance can be maintained.

In addition, if the transfer belt 50 that is electrostatically attracted and conveyed is used, the winding around the photosensitive drum 18 can be easily prevented, so that the separation of the paper is improved and the toner is kept adsorbed until the next fixing. Since it can be transported, it contributes to stabilizing the performance of high-speed machines.
Further, if the cleaning roller 58 applies the above tension to the transfer belt 50, the cleaning performance can be improved, and the transfer surface of the transfer belt 50 is wound around the surface of the photosensitive drum 18 to improve the transfer performance. Contribute.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims.
For example, in the above-described embodiment, the positively charged toner is described as a regular charged toner. However, the present invention can also be applied to a case where a negatively charged toner is used as a regular charged toner.

In the above embodiment, an example in which a printer is embodied as an image forming apparatus is shown. However, the image forming apparatus according to the present invention can naturally be applied to a multifunction machine, a copier, a facsimile machine, and the like.
In any of these cases, the toner image can be transferred satisfactorily as described above.

1 Printer (image forming device)
16 Image forming unit 18 Photosensitive drum (image carrier)
30 Transfer Unit 31 Transfer Roller 50 Transfer Belt 52 Drive Roller 54 Followed Roller 57 Cleaning Unit 58 Cleaning Roller

Claims (5)

An image carrier having an image carrier and developing a latent image on the image carrier with toner by driving to form a toner image;
The recording material is stretched between the driving and driven rollers, and vertically conveys the recording material from below to above, and the recording material is placed on the conveying surface and travels between the image carrier and the transfer roller. A transfer belt that directly transfers the toner image to the recording material;
A cleaning unit provided on the tension side of the transfer belt with a cleaning roller that collects residual toner adhering to the conveyance surface by electrostatic force and cleans the conveyance surface;
The drive roller is disposed upstream of the transfer position of the toner image as viewed in the running direction of the transfer belt, and when the line connecting the rotation axes of the drive roller and the driven roller is viewed horizontally. wherein provided on the image bearing member toward viewed in the vertical direction from the transfer position of the slack side contacts the toner image is a point of contact with loose side of the transfer belt,
The transfer belt applies a voltage having a polarity opposite to that of the toner attached to the latent image to the transfer roller to directly transfer the toner image to the recording material,
The cleaning roller is disposed at a position where the rotational axis of the driven roller deviates from the winding angle of the transfer belt in the driven roller, and the contact point between the driven roller and the tension side of the transfer belt without facing the driven roller. abut on the conveying surface at a position near, with contacts the conveying surface of the transfer belt in the trail direction about its rotational speed exceeds 1.0 times the running speed of the transfer belt 1.2 An image forming apparatus, wherein the speed is set so as not to be slower than the transfer belt up to double. The image forming apparatus according to claim 1,
An image forming apparatus, wherein a winding amount between a surface of the image carrier and a transfer surface of the transfer belt at a transfer position of the toner image is set to about 1.0 mm to about 5.0 mm. The image forming apparatus according to claim 1, wherein
The distance from the slack side contact to the toner image transfer position is set shorter than the distance from the toner image transfer position to the other slack side contact where the driven roller contacts the slack side of the transfer belt. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The rotational speed of the image carrier is set to be higher than the rotational speed of the drive roller, and the linear speed ratio is controlled within a range of 1.01 to 1.03. . The image forming apparatus according to claim 4 ,
2. The image forming apparatus according to claim 1, wherein the cleaning roller applies tension to the transfer belt so that an extension ratio of the transfer belt is set to about 3% to about 5%.

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