JP2002099162A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a transfer unit of simple constitution which can prevent blur transfer at a part in front of a transfer material entrance of a transfer nip part when a toner image is transferred to a transfer material entering the transfer nip part. SOLUTION: An upper guide member 33 is arranged so that the end part 33a of the upper guide member 33 on the downstream side in the conveyance direction of the transfer material is positioned more upstream than the end part 2a of a 1st belt plane part 2A formed of a plane part forming member 38 on the upstream side in the transfer material conveyance direction. Consequently, the transfer material 3 conveyed by a register roller 19 is so guided by the upper guide member 33 as to come into contact with the belt plane part 2A from the upstream-side end part 33a of the belt plane part 2A and then enters the transfer nip part N while keeping contact with the nearly entire surface of the belt plane part 2A, so that no gap G is formed in a blur transfer area in front of the transfer nip part N.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copier, a printer or a facsimile, and more particularly, to an endless belt-like intermediate transfer member or an endless belt-like image bearing member such as a photoreceptor. The present invention relates to an image forming apparatus provided with a transfer unit for transferring a toner image formed on an image carrier to a transfer material using a body.

[0002]

2. Description of the Related Art As this type of image forming apparatus, for example,
As shown in FIG. 4, a toner image charged to a predetermined polarity formed on a photosensitive drum 1 as a latent image carrier is transferred to an intermediate transfer member (hereinafter, referred to as an image carrier) comprising an endless belt.
"Intermediate transfer belt 2")
The next transfer is known. The toner image primary-transferred onto the intermediate transfer belt 2 is secondary-transferred onto a transfer material 3 such as a transfer paper or an OHP sheet fed by a registration roller 19 using electrostatic force.

The image forming apparatus provided with such an intermediate transfer belt 2 can form the toner image formed on the photosensitive drum 1 by superimposing the toner image on the intermediate transfer belt 2. 3 is widely used as a color image forming apparatus for forming a color image.

Further, as shown in FIG. 5, the transfer means of the image forming apparatus includes a secondary transfer bias roller 10 as a transfer member which comes into contact with the surface of the intermediate transfer belt 2, and sandwiches the intermediate transfer belt 2. The secondary transfer bias roller 1
Secondary transfer facing roller 22 as a facing member facing 0
And a transfer device having the following. In this transfer device, a transfer nip N is formed between the intermediate transfer belt 2 and the secondary transfer bias roller 10 by the secondary transfer bias roller 10 and the secondary transfer opposing roller 22. Then, a transfer bias is applied by the secondary transfer bias roller 10 to the transfer material 3 conveyed so as to enter the transfer nip portion N. Thus, the toner image on the intermediate transfer belt 2 is transferred onto the transfer material 3.

[0005] As shown in FIG. 4, the intermediate transfer belt 2 is formed by a belt driving roller 21, a secondary transfer facing roller 22, a tension roller 23, and a driven roller 24 as a plurality of tension members. It is stretched rotatably. When the secondary transfer bias roller 10 is used as a transfer member, toner adheres to the secondary transfer bias roller 10, deformation of the secondary transfer bias roller 10 due to pressing force during transfer, or intermediate transfer due to heat. In order to avoid deterioration of the belt 2, the secondary transfer bias roller 10 is often separated from the intermediate transfer belt 2 except during transfer. Particularly, in an image forming apparatus that forms a color toner image by sequentially superimposing toner images of a plurality of colors on the intermediate transfer belt 2, secondary transfer is performed until the formation of the color toner image on the intermediate transfer belt 2 is completed. The bias roller 10 is configured to be separated from the intermediate transfer belt 2.

[0006]

In a conventional image forming apparatus having this type of transfer device, in FIG. 5, a transfer material 3 enters a transfer nip portion N and a toner image on an intermediate transfer belt 2 is formed. When the image is transferred onto the transfer material 3, pre-transfer occurs in a region on the near side of the transfer material entrance of the transfer nip portion N, and an abnormality occurs in the image transferred on the transfer material 3. Has been a major issue in the past.

That is, in the above-described conventional image forming apparatus, as shown in FIG. 5, when the sheet enters the transfer nip N and is conveyed, the transfer nip between the transfer material 3 and the intermediate transfer belt 2 is transferred. A minute gap G is generated in a portion on the front side (upstream side in the moving direction of the intermediate transfer belt 2) of the transfer material entrance portion N. When such a gap G occurs, a discharge occurs between the transfer material 3 at the transfer material entrance portion of the transfer nip N and the intermediate transfer belt 2. The discharge causes the toner image on the intermediate transfer belt 2 to fly on the transfer material 3 before reaching the transfer nip N, and the pre-transfer occurs. Hereinafter, a region on the near side of the transfer material entrance portion of the transfer nip where the pre-transfer occurs, is referred to as a “pre-transfer region”.

Particularly, in a color image forming apparatus using the intermediate transfer belt 2, since an overlapped image of a plurality of colors is collectively transferred from the intermediate transfer belt 501 to the transfer material 3, a transfer to the transfer image by the pre-transfer is performed. The effect is so great that, for example, overlapping dust and dot dust of each color toner and excessive transfer of halftone occur.

As a method for preventing the occurrence of the pre-transfer as described above, it is effective to eliminate the gap G between the transfer material 3 and the intermediate transfer belt 2 in the pre-transfer area. Therefore, conventionally, for example, at a portion of the secondary transfer bias roller 10 on the upstream side in the moving direction of the intermediate transfer belt 2,
An upper guide member 33 and a lower guide member 35 are provided as transfer material guide members for guiding the transfer material toward the transfer nip N, and the transfer material 3 and the intermediate transfer belt 2 So that they adhere in advance in the transfer area,
The transfer material 3 is formed by the guide member 33 and the lower guide member 35.
The method of guiding is taken.

That is, the upper guide member 33 and the lower guide member 35 are arranged with the conveyance path of the transfer material 3 conveyed by the registration rollers 19 interposed therebetween. here,
When the transfer material 3 is relatively strong, the transfer material 3 conveyed by the registration rollers 19 is guided by the upper guide member 33. Then, as shown by a broken line in FIG. 6, the transfer material 3 has the leading end portion of the transfer material 3 abutting on the intermediate transfer belt 2 on the front side of the transfer nip portion N, and preliminarily performs intermediate transfer in the pre-transfer area. The sheet enters the transfer nip portion N in a state of being in close contact with the belt 2. on the other hand,
When the transfer material 3 is relatively stiff, the transfer material 3 conveyed by the registration rollers 19 is guided by the lower guide member 35. As a result, first, the leading end of the transfer material 3 comes into contact with the intermediate transfer belt 2 on the front side of the transfer nip N. Thereafter, the transfer material 3 having a weak waist is brought into close contact with the intermediate transfer belt 2 in the pre-transfer area by the electrostatic force of the intermediate transfer belt 2 and the transfer nip portion is formed.
Enter N.

However, in such a conventional method, although it depends on the thickness and type of the transfer material, in practice, as shown by a solid line in FIG. Since the transfer material 3 is separated from the intermediate transfer belt 2, the transfer material 3 and the intermediate transfer belt 2 are often not adhered to each other in the pre-transfer area as desired.

For this reason, for example, as shown in FIG. 7, the inventors of the present invention set a tension on the back side of the intermediate transfer belt 2 near the transfer nip portion N to stretch the intermediate transfer belt 2. The transfer material 3 is stretched by using a flat portion forming member 38 which is one of the members, and the transfer material 3 is placed on the belt surface of an entrance path portion of the transfer material 3 which enters the transfer nip N of the intermediate transfer belt 2. There has been proposed an image forming apparatus configured to form a belt flat portion 2A substantially along a conveyance path (Japanese Patent Application No. P200-198200). As described above, by forming the belt flat portion 2A on the front side of the transfer nip portion N of the intermediate transfer belt 2, the registration roller 19
The transfer material 3 conveyed by the above-described process enters the transfer nip N along the belt flat portion 2A.
Thereby, the transfer material 3 and the intermediate transfer belt 2 can be brought into close contact with each other in the pre-transfer area in advance, and the generation of the gap G between the transfer material 3 and the intermediate transfer belt 2 in the pre-transfer area can be reduced. Can be resolved.

However, the belt flat portion 2A as described above
7, the end 33a of the upper guide member 33 on the downstream side in the transfer material transport direction is also formed by the belt flat portion formed by the flat portion forming member 38, as shown in FIG. When the transfer material 3 conveyed by the registration roller 19 is located downstream of the end 2a on the upstream side in the transfer material conveyance direction of the transfer material 3A, the upper guide member 33 causes the belt flat portion 2A. Is guided so as to contact a middle part of the belt flat portion 2A.

For this reason, in such a configuration, the transfer material 3 guided by the upper guide member 33 must contact the belt flat portion 2A from the middle of the belt flat portion 2A. The gap G is formed in the pre-transfer area (a part close to the transfer electric field) on the front side of the transfer nip portion N, and a problem due to discharge in the pre-transfer area is likely to occur. Here, as a method of solving the problem due to the discharge in the pre-transfer area, the contact start position of the leading end of the transfer material 3 with respect to the belt flat portion 2A is set as follows.
A method of increasing the length of the belt flat portion 2A so as to be located on the near side (upstream side) of the pre-transfer area can be considered. However, in this method, the registration rollers 19
The transfer span of the transfer paper 3 from the nip to the transfer nip portion N becomes large, so that the secondary transfer unit becomes large or the position between the leading end of the transfer material 3 and the leading end of the toner image on the intermediate transfer belt 2 is changed. Matching becomes difficult.

Further, in such a configuration, the rear end of the transfer material 3 conveyed in a curled state against the rigidity by the upper guide member 33 comes out of the end 33a of the guide member 33. When it hits, it may jump due to its rigidity. When such a jump of the rear end of the transfer material 3 occurs, the belt flat portion 2A of the intermediate transfer belt 2 is hit by the rear end. As a result, the toner image formed on the intermediate transfer belt 2 is disturbed, and the rear end portion and the belt flat portion 2A cannot maintain close contact with each other. A gap G is generated between the gaps, and discharge in the gap G may cause an image defect.

The above is an example of an image forming apparatus in which the image carrier is an intermediate transfer belt.
The image carrier may be a photoreceptor belt, and the same may occur in an image forming apparatus that directly transfers a toner image formed on the photoreceptor belt to a transfer material.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to transfer a toner image onto a transfer material that has entered a transfer nip portion. An object of the present invention is to provide an image forming apparatus provided with a transfer device having a simple configuration capable of preventing pre-transfer at a portion on the front side of an entrance.

[0018]

According to one aspect of the present invention, there is provided an endless belt-shaped image bearing a toner image on a surface thereof and rotatably stretched by a plurality of stretching members. A carrier, a toner image forming means for forming a toner image on the image carrier, a transfer member disposed on the back side of a transfer material conveyed in synchronization with the rotation of the image carrier, and Transfer means for applying a transfer bias between an opposing member opposing the transfer member across the body to transfer a toner image on the image carrier onto the transfer material; An image forming apparatus comprising: a transfer material conveying unit that conveys the transfer material toward a transfer nip between the transfer member and the image carrier formed by being sandwiched between
Stretching the back side of the image carrier on the front side of the transfer nip portion,
A flat portion forming member for forming a flat belt portion substantially along the transfer material conveyance path on the belt surface in front of the transfer nip portion of the image carrier, and a transfer material contacting the flat belt portion. A transfer material guide member disposed between the transfer path of the transfer material and the image carrier for guiding the transfer material toward the flat surface of the belt; The downstream end in the material transport direction is located further upstream than the upstream end in the transfer material transport direction of the belt flat portion of the image carrier formed by the flat portion forming member. It is assumed that.

In this image forming apparatus, the end of the transfer material guide member on the downstream side in the transfer material transport direction is located upstream of the belt flat portion of the image carrier formed by the flat portion forming member in the transfer material transport direction. It is located further upstream than the side end. For example, the end 33a of the upper guide member 33 shown in FIG. 7 is the end on the upstream side in the transfer material transport direction of the intermediate transfer belt 2 and the belt flat portion 2A as the image carrier formed by the flat portion forming member 38. It is located further upstream than 2a. Therefore, in this image forming apparatus, the transfer material 3 conveyed by the registration roller 19 is moved by the upper guide member 33 to the upstream end 33a of the belt flat portion 2A with respect to the belt flat portion 2A.
Guided from contact. As a result, the transfer material 3 conveyed by the registration rollers 19 enters the transfer nip portion N in a state of being in close contact with almost the entire surface of the belt flat portion 2A, and is located on the front side of the transfer nip portion N. No gap G is formed in the pre-transfer region.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the transfer material is provided upstream of the first belt flat portion of the image carrier formed by the flat portion forming member in the belt rotation direction. And a stretching member that stretches the image carrier so as to form a second belt flat portion that is gradually separated from the transfer path of the transfer member, and passes through the end of the transfer material guide member on the downstream side in the transfer material transfer direction. The absolute value of the distance from the intersection of a perpendicular line perpendicular to the extension surface of the first belt flat portion and the extension surface to the end of the transfer material guide member on the downstream side in the transfer material transport direction is defined as The distance from the intersection of the surface of the second belt plane with the perpendicular is set to be smaller than the distance from the intersection of the extension of the first belt plane with the perpendicular. Things.

In this image forming apparatus, the image carrier formed by the flat section forming member is gradually upstream from the transfer path of the transfer material on the upstream side in the belt rotation direction of the first belt flat section. The second belt flat portion is formed in the second belt flat portion. According to the above setting, the end of the transfer material guide member on the downstream side in the transfer material transport direction faces a position separated from the second belt flat portion of the image carrier. Thus, at the moment when the transfer material guide member exits from the end portion on the downstream side in the transfer material transport direction, a predetermined distance is provided between the rear end of the transfer material and the second belt flat portion of the image carrier. Therefore, even if the rear end of the transfer material escapes from the end of the transfer material guide member on the downstream side in the transfer material transport direction and jumps up to the image carrier side, the rear end of the transfer material is It does not come into contact with the image carrier.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, an end of the transfer material guide member on the downstream side in the transfer material transport direction is formed by the flat portion forming member. With the extension surface of the first belt flat part sandwiched,
The transfer material guide member is provided so as to be located on a side facing the image carrier.

As shown in FIG. 3, an end 33a of the guide member 33 as the transfer material guide member on the downstream side in the transfer material transport direction is a first belt flat portion of the intermediate transfer belt 2 as the image carrier. When the intermediate transfer belt 2 is located between the extension surface 2A ′ of the intermediate transfer belt 2 and the intermediate transfer belt 2, the transfer material 3 guided by the guide member 33 and conveyed toward the transfer nip N is transferred to the intermediate transfer belt 2. First belt flat part 2 of belt 2
Prior to contact with the first belt flat portion 2A, the first belt flat portion 2A contacts the upstream end 2a. As a result, the transfer material 3 curls in an arc shape or an S-shape near the end 2a on the upstream side of the belt flat portion 2A, and the gap between the belt flat portion 2A and the transfer material 3 is formed. G sometimes occurred. On the other hand, in the image forming apparatus of the present invention,
The end of the transfer material guide member on the downstream side in the transfer material transport direction faces a position facing the image carrier with the extension surface of the first belt flat portion of the image carrier interposed therebetween. Accordingly, in this image forming apparatus, the transfer material guided by the transfer material guide member and conveyed toward the transfer nip portion is located near the upstream end of the first belt flat portion of the image carrier.
The transfer material surely comes into contact with the first belt flat portion of the image carrier without curling in an arc shape or an S shape.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter, referred to as a "color copying machine") as an image forming apparatus will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a color copying machine using the intermediate transfer belt 2. This color copier is shown in FIG.
, A color image reading unit (hereinafter, referred to as a “color scanner”), a control unit for controlling a driving unit of the color copying machine, and the like.

In FIG. 1, a charger 4 for uniformly charging the surface of the photosensitive drum 1 with a predetermined polarity is provided around a photosensitive drum 1 rotating in the direction of the arrow, and a writing laser beam L is provided.
, An image exposure means (not shown) for forming a latent image on the charged surface of the photosensitive drum 1, and a developing device for developing a latent image formed on the photosensitive drum 1 with a plurality of color toners stored individually. 5, 6, 7, 8 and a photosensitive drum cleaner 18 for removing residual toner on the photosensitive drum 1 are provided.

A toner image is formed on the surface of the photosensitive drum 1 by a well-known electrophotographic process. The toner image formed on the surface of the photosensitive drum 1 reaches the primary transfer section by the rotation of the photosensitive drum 1. On the other hand, the endless belt-shaped intermediate transfer belt 2 includes a driving roller 21, a driven roller 24, a tension roller 23 having a tension control mechanism,
And a secondary transfer opposing roller (hereinafter, simply referred to as an “opposite roller”) 22 constituting a secondary transfer portion, and is brought into close proximity to or in contact with the photosensitive drum 1,
It rotates in synchronization with the peripheral speed of.

In the primary transfer section, a corona charger 9 as primary transfer means is provided on the back side of the intermediate transfer belt 2. The corona charger 9 includes the photosensitive drum 1
By applying a discharge electric field having a polarity opposite to the charging polarity of the toner image formed thereon, the toner image is primarily transferred onto the intermediate transfer belt 2. The intermediate transfer belt 2 on which the toner image has been primarily transferred rotates in the direction of the arrow, and
And a secondary transfer bias roller (hereinafter, simply referred to as a “secondary transfer roller”) 10. The secondary transfer roller 10 is configured to be able to freely contact and separate from the intermediate transfer belt 2.

On the other hand, the residual toner remaining on the surface of the photosensitive drum 1 for forming the next toner image is
It is removed by the photosensitive drum cleaner 18. Further, a residual charge remaining on the surface of the photosensitive drum 1 is removed by a static eliminator (not shown). Here, when a toner image is continuously formed on the photosensitive drum 1, after the residual toner and the residual charge are removed, the surface of the photosensitive drum 1 is re-formed by the charger 4. It is uniformly charged. When a color image is formed, a toner image of each color corresponding to a plurality of image signals is sequentially formed on the photosensitive drum 1, and the toner image of each color formed on the photosensitive drum 1 is In the primary transfer section, the image is transferred onto the intermediate transfer belt 2 while being sequentially superimposed.

When the final toner image is primarily transferred onto the intermediate transfer belt 2 in this manner, the leading end of the toner image primarily transferred and carried on the intermediate transfer belt 2 is transferred to the secondary transfer section. Before starting, the secondary transfer roller 10
Is moved so as to contact the surface of the intermediate transfer belt 2. That is, the secondary transfer roller 10 is retracted to a position away from the surface of the intermediate transfer belt 2 until the final toner image is primarily transferred onto the intermediate transfer belt 2.

On the other hand, while the toner image is being formed on the intermediate transfer belt 2, the transfer materials 3 stored in the paper feed tray 12 are taken out one by one by the rotation of the feed roller 11. . The transfer material 3 taken out of the paper feed tray 12 is kept on standby while being held between the nips of the registration rollers 19. Then, the intermediate transfer belt 2
The transfer material 3 is conveyed by the registration roller 19 at a timing such that the front end of the toner image carried on the transfer material coincides with the front end of the image transfer area of the transfer material.

As a result, the transfer material 3 is conveyed to the transfer nip N between the intermediate transfer belt 2 and the secondary transfer roller 10, and the transfer bias applied to the transfer nip N causes the transfer bias to be applied to the intermediate transfer belt. 2 is secondarily transferred onto the transfer material 3 at a time. The transfer material 3 on which the toner image has been secondarily transferred in this manner is sent to the fixing device 15 by the conveyor belt 14, and after the toner image is fixed by heating / pressing, is discharged outside the machine. .

On the other hand, the intermediate transfer belt 2 on which the secondary transfer of the toner image has been completed is removed by an intermediate transfer belt cleaner 16 to remove the residual toner and paper dust adhered to the surface. Further, the toner adhered to the peripheral surface of the secondary transfer roller 10 is removed by the cleaning blade 25.

Next, the configuration of the secondary transfer section, which is a feature of the present invention, will be described. As shown in FIG. 2, the secondary transfer unit of the image forming apparatus according to the present embodiment includes an upper guide member 33 for guiding the transfer material 3 conveyed toward the transfer nip N, and a lower guide member. 35.
A back surface of the intermediate transfer belt 2 on the front side of the transfer nip portion N is a stretching member for stretching the intermediate transfer belt 2.
It is configured to be stretched by using a flat portion forming member 38 which is one of them. As a result, a belt plane portion 2A is formed on the belt surface of the transfer path portion of the transfer material 3 entering the transfer nip portion N of the intermediate transfer belt 2 along the transfer path of the transfer material 3. The length D of the belt flat portion 2A in the circumferential direction of the belt is required to maintain the transfer of the transfer material 3 without being guided by the upper guide member 33 or the lower guide member 35. The following is preferable, and more preferably, about 10 mm is desirable.

As described above, by forming the belt flat portion 2A on the front side of the transfer nip portion N of the intermediate transfer belt 2, the transfer material 3 conveyed by the registration roller 19 is transferred to the belt flat portion 2A. Along the transfer nip portion N, along the direction. As a result, the transfer material 3 and the intermediate transfer belt 2 come into close contact with each other before the transfer electric field in the pre-transfer area increases. Therefore, no gap G is generated between the transfer material 3 and the intermediate transfer belt 2 in the pre-transfer area, and occurrence of an image defect due to discharge in the gap G is prevented.

However, as shown in FIG. 7, the end 33a of the upper guide member 33 on the downstream side in the transfer material transport direction is
If the belt flat portion 2A formed by the flat portion forming member 38 is located downstream of the end 2a on the upstream side in the transfer material transport direction of the belt flat portion 2A, the registration roller 19
Is transferred by the upper guide member 33 to the belt flat portion 2A with respect to the belt flat portion 2A.
Is guided to contact the middle part of As a result, in the case of such a configuration, as described above, the transfer material 3 guided by the upper guide member 33 only contacts the belt flat portion 2A from the middle of the belt flat portion 2A. In addition, the gap G is formed in the pre-transfer area (a part close to the transfer electric field) on the front side of the transfer nip portion N, and a problem due to discharge in the pre-transfer area is likely to occur.

Therefore, in the image forming apparatus according to the present embodiment, as shown in FIG. 2, the end 33a of the upper guide member 33 on the downstream side in the transfer material transport direction is formed by the flat portion forming member 38. The first belt flat part 2
The upper guide member 33 is disposed so as to be located further upstream than the end 2a on the upstream side in the transfer material transport direction of A.
That is, the position of the end 33a of the upper guide member 33 is
The position is shifted from the position of the end 2a of the first belt flat portion 2A by the distance C to the upstream side in the transfer material transport direction.

Thus, the transfer material 3 conveyed by the registration roller 19 is moved by the upper guide member 33 to the belt flat portion 2A with respect to the belt flat portion 2A.
The transfer nip portion is guided in such a manner that the transfer material 3 conveyed by the registration roller 19 is in close contact with almost the entire surface of the belt flat portion 2A. You will enter N. As a result, the gap G is not formed in the pre-transfer area on the front side of the transfer nip N.

Here, the end 33 of the upper guide member 33
a extension surface 2A 'of the first belt flat portion 2A
From the intersection of a perpendicular line perpendicular to
The absolute value of the distance B to the end 33a of the upper guide member 33 is determined by the flat portion forming member 38 and the tension roller 2
3 from the intersection of the surface of the second belt flat portion 2B formed by the first belt flat portion 3 and the perpendicular.
Is desirably set to be smaller than the distance A to the intersection between the extension surface 2A ′ of the above and the perpendicular. That is, by setting the distance B as described above, the end portion 33a of the upper guide member 33 faces a position separated from the second belt flat portion 2B along the perpendicular. Thereby, the end 3 of the upper guide member 33 is formed.
At the moment when the transfer material 3 comes out of the transfer material 3a, a predetermined distance is secured between the rear end of the transfer material 3 and the second belt flat portion 2B. However, even if it comes out of the end 33 a of the guide member 33 and jumps up to the intermediate transfer belt 2 side, the intermediate transfer belt 2 is not hit by the rear end of the transfer material 3.

As described above, the end 33a of the guide member 33 is positioned between the extension surface 2A 'of the first belt flat portion 2A of the intermediate transfer belt 2 and the intermediate transfer belt 2. 3, the transfer material 3 guided by the guide member 33 and conveyed toward the transfer nip N is transferred to the first belt flat portion 2A of the intermediate transfer belt 2 as shown in FIG. Before the contact, the first belt flat portion 2A contacts the upstream end 2a. As a result,
The transfer material 3 curls in an arc shape or S-shape near the end 2a on the upstream side of the belt flat portion 2A, and the gap G is generated between the belt flat portion 2A and the transfer material 3. Sometimes.

Therefore, the end 33a of the guide member 33
As shown in FIG. 2, it is desirable that the first member is located on the side facing the intermediate transfer belt 2 with the extension surface 2A ′ of the first belt flat portion 2A interposed therebetween. As a result, the transfer material 3 guided by the guide member 33 and conveyed toward the transfer nip N is curled in an arc shape or an S shape near the upstream end of the first belt flat portion 2A. And the first belt flat portion 2A is reliably brought into contact with the first belt flat portion 2A.

[0041]

According to the first to third aspects of the present invention, the transfer material conveyed by the registration roller is brought into close contact with almost the entire surface of the belt flat portion on the front side of the transfer nip portion of the endless belt-shaped image carrier. In this state, it enters the transfer nip portion. As a result, a gap is not formed between the image carrier and the transfer material in the pre-transfer area on the front side of the transfer nip portion, and the occurrence of an abnormal image due to discharge in the gap can be prevented. Has an effect.

In particular, according to the second aspect of the present invention, at the moment when the transfer material guide member comes out of the end portion on the downstream side in the transfer material transport direction, the rear end portion of the transfer material and the second belt flat portion of the image carrier. A predetermined distance is secured between the transfer material guide member and the transfer material guide member. There is an excellent effect that the rear end of the transfer material does not come into contact with the image carrier and abnormal image generation due to the contact of the rear end of the transfer material with the image carrier can be prevented.

According to the third aspect of the present invention, the transfer material guided by the transfer material guide member and conveyed toward the transfer nip portion is the upstream end of the first belt flat portion of the image carrier. There is an excellent effect that the transfer material surely comes into contact with the first belt flat portion of the image carrier without being curled in an arc shape or an S shape near the portion.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming unit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a secondary transfer unit of the image forming apparatus.

FIG. 3 is a schematic diagram showing a behavior of a transfer material guided by a guide member arranged in the secondary transfer unit.

FIG. 4 is a schematic diagram illustrating a configuration of a secondary transfer unit of a conventional image forming apparatus.

FIG. 5 is an enlarged view of a secondary transfer portion of the conventional image forming apparatus.

FIG. 6 is a schematic diagram illustrating another configuration of a secondary transfer unit of a conventional image forming apparatus.

FIG. 7 is a schematic diagram showing a configuration of a secondary transfer unit previously proposed by the present applicant.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Intermediate transfer belt 2A First belt flat part of intermediate transfer belt 2B Second belt flat part of intermediate transfer belt 2a End part on the upstream side of first belt flat part of intermediate transfer belt 3 Transfer material Reference Signs List 4 charger 5, 6, 7, 8 developing device 10 secondary transfer bias roller 15 fixing device 19 registration roller 21 drive roller, 24 driven roller, 23 tension roller, 22 secondary transfer opposing roller 33 upper guide member 33a upper guide member 35 Lower guide member 38 Plane forming member G Gap between intermediate transfer belt and transfer material N Transfer nip

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiromi Ogiyama 1-3-6 Nakamagome, Ota-ku, Tokyo Stock inside Ricoh Company (72) Inventor Shin Chihara 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Mitsuru Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Hiroshi Ono 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh ( 72) Inventor Toshiaki Motohashi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Katsuya Kawagoe 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H032 AA05 AA15 BA09 BA19 BA23 2H072 AB19 CA07 CB07 HB00 HB05 3F101 FA00 FB04 FC01 FC07 FC12 LA02 LA05 LA07 LB03

Claims (3)

[Claims] 1. An endless belt-shaped image carrier which carries a toner image on its surface and is rotatably stretched by a plurality of stretching members, and a toner image forming means for forming a toner image on the image carrier And a transfer bias between a transfer member disposed on the back side of the transfer material conveyed in synchronization with the rotation of the image carrier and a facing member facing the transfer member with the image carrier interposed therebetween. Transfer means for applying the toner image on the image carrier to the transfer material, and a transfer member and the image carrier formed by being sandwiched between the facing member and the transfer member. Toward the transfer nip portion, in an image forming apparatus provided with a transfer material transporting means for transporting the transfer material, stretching the back side of the image carrier on the front side of the transfer nip portion,
A flat portion forming member for forming a flat belt portion substantially along the transfer material conveyance path on the belt surface in front of the transfer nip portion of the image carrier, and a transfer material contacting the flat belt portion. A transfer material guide member disposed between the transfer path of the transfer material and the image carrier for guiding the transfer material toward the flat surface portion of the belt; The downstream end in the material transport direction is located further upstream than the upstream end in the transfer material transport direction of the belt flat portion of the image carrier formed by the flat portion forming member. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the transfer member is provided with an image carrier formed by the flat portion forming member, which is gradually upstream of a first belt flat portion in a belt rotation direction. A stretching member that stretches the image carrier so as to form a second belt flat portion that is separated from the first belt member; The absolute value of the distance from the intersection of a perpendicular line perpendicular to the extension surface of the belt plane portion and the extension surface to the end of the transfer material guide member on the downstream side in the transfer material transport direction is the second belt plane. From the intersection of the surface of the part and the above perpendicular,
An image forming apparatus, wherein the distance is set to be smaller than a distance between an intersection of an extension surface of the first belt flat portion and the perpendicular line. 3. The image forming apparatus according to claim 2, wherein the end of the transfer material guide member on the downstream side in the transfer material transport direction is a first belt flat surface of the image carrier formed by the flat portion forming member. An image forming apparatus, wherein the transfer material guide member is disposed so as to be located on a side facing the image carrier with an extension surface of the portion interposed therebetween.