JP2001255754A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of providing an excellent image by bringing an endless belt type image carrier into contact with transfer material and preventing toner scattering due to a void from occurring. SOLUTION: A pressing member 30 is provided at a position where it is opposed to the surface K of a transfer material carrying guide 31 so that it can press-contact with the back surface of an intermediate transfer belt 10, and has a curved surface part projecting downward. The member 30 is provided so that its curved surface part may press the back surface side (inside) of the belt 10 toward the outside at a more upstream position than the transfer nip part 51 of the belt 10. The length L of the linear part of a secondary transfer part is set to L<=10 (mm), the pressing force for the transfer material 22 to the belt 10 is kept strong, and the material 22 is brought into contact with the belt 10, whereby the toner scattering is prevented from occurring.

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 copying machine, a printer, a facsimile, etc., and more particularly to an image forming apparatus using an endless belt-shaped image carrier. .

[0002]

2. Description of the Related Art In a conventional image forming apparatus, a toner image on a photoreceptor is transferred onto a transfer material, and the toner image on the transfer material is heated and pressed by a fixing device and fixed. In such an image forming apparatus, it is also possible to use an endless belt-shaped photoconductor stretched and supported by a plurality of rollers as the photoconductor. The advantage of this case is that the degree of freedom of the photoreceptor shape by the roller arrangement is higher than that of the photoreceptor drum, and the curvature can be increased by the diameter of the support roller. It will be easier.

As an image forming apparatus for forming a full-color image, a transfer material is held on a transfer material carrier such as a transfer drum, and yellow, magenta, cyan, and black developed on a photoreceptor are transferred to the transfer material. The transfer material is sequentially transferred to the transfer material, and then the transfer material peeled off from the transfer material carrier is fixed by a fixing device.

On the other hand, instead of transferring the toner image to the transfer material on the transfer material carrier, the four color toner images once superimposed on the intermediate transfer member are collectively transferred to the transfer material and then fixed by a fixing device. There is also an image forming apparatus that performs the operation. In this image forming apparatus, there is no need to hold the transfer material on the transfer material carrier, and there is an advantage that the versatility of paper is high. Therefore, it is possible to form an image on a small-size paper (for example, an official postcard), a thick paper (for example, 200 g / m ² paper), an envelope, or the like. Note that an intermediate transfer drum and an endless belt-shaped intermediate transfer belt are known as the intermediate transfer member. As a prior art of an image forming apparatus using such an intermediate transfer member, one described in Japanese Patent Application Laid-Open No. 5-313525 is known.

[0005] The image forming apparatus using the endless belt-shaped photosensitive member and the intermediate transfer belt as described above has the following problems. This will be described with reference to FIG. FIG. 5 shows the toner image on the intermediate transfer belt 10 as the transfer material 2.
FIG. 4 is an enlarged view of a secondary transfer portion that transfers to No. 2; Since the polarity of the toner on the intermediate transfer belt 10 is negative in this example, a positive bias is applied to the secondary transfer roller 14 by the high voltage power supply 100. At this time, a transfer electric field E is formed, and the toner is transferred to the transfer material 22 by the transfer electric field E.
If the toner particles 2 cannot be brought into close contact with each other before the secondary transfer and a gap is formed, the toner flies in the gap toward the transfer material 22 due to the transfer electric field E, so that toner dust scatters around the image. For this reason, as shown in FIG. 6, the leading end of the transfer material 22 is located at a position upstream of the secondary transfer portion.
The abutting position is regulated by the transfer material transport guide 31 so that the abutting position is zero.

However, when a strong transfer material strained such as cardboard (e.g. 200 g / m ² paper) In this configuration, the transfer material 22 tip will be pressed against the intermediate transfer belt 10, intermediate transfer The belt 10 is slightly bent by the pressing force. Here, the peripheral speed of the pair of registration rollers 21 is set slightly higher than the transfer material transport speed in the secondary transfer section. This is because if the peripheral speed of the pair of registration rollers 21 becomes slower than the transfer material transport speed in the secondary transfer unit, the transfer material transport is hindered and image shrinkage and image blurring during secondary transfer are caused. Therefore,
Due to the peripheral speed difference described above, even after the leading end of the transfer material 22 has passed the contact position, the intermediate transfer belt 10
Is kept pressed by the transfer material 22.

FIG. 7 is a diagram for explaining the above-mentioned phenomenon. The intermediate transfer belt 10 pushed up by the transfer material 22 cannot be in close contact with the transfer material 22 and a minute gap s is generated.
The toner dust is generated.

In order to prevent the occurrence of the toner dust, the applicant of the present invention disclosed in Japanese Patent Application No. 11-96053, in which the endless belt-shaped image carrier was pressed from the back side (inside) to prevent bending, and An image forming apparatus for preventing generation of voids has been proposed. FIG. 8 is a diagram showing a configuration in which a pressing member 30 for pressing the intermediate transfer belt 10 as an endless belt-shaped image carrier from the back side is provided.

The pressing member 30 is located near the upstream side of the transfer nip 51 with respect to the rotation direction of the intermediate transfer belt 10 and presses from the back side of the intermediate transfer belt 10. The leading end of the transfer material 22 sent out from 31 is disposed at a position downstream of the contact position A where the transfer material 22 contacts the intermediate transfer belt 10. By arranging the pressing member 30 at such a position, even if the transfer material 22 such as thick paper that has a strong stiffness is sent out, the pressing member 30 is located on the back side, so the intermediate transfer belt is moved by the transfer material 22. 10 is not deflected. Accordingly, the air gap s as described in FIG. 7 does not occur, and the generation of toner dust can be prevented.

As shown in FIG. 9, the transfer material conveying guide 31 has a surface J whose extension is directed to the curved surface of the pressing member 30 and a surface that is continuous with the surface J and faces the curved surface. K along the intermediate transfer belt 10 and the surfaces J and K
Has a mountain-like shape having a curved boundary portion P that forms a boundary with the boundary, and has a wedge-like shape as a whole. Here, an extension line from the portion of the intermediate transfer belt 10 located between the pressing member 30 and the transfer nip portion 51 is denoted by L1.
, The boundary portion P was disposed at an arbitrary position on the intermediate transfer belt 10 side including the extension line L1.

With such a configuration, as shown in FIG. 10, the boundary P pushes up the transfer material 22, and the transfer material 22 is always moved from the boundary P to the transfer nip 51. Is applied to the intermediate transfer belt 10. Due to this pressing force F, the transfer material 22 is brought into close contact with the intermediate transfer belt 10 regardless of its type,
Generation of toner dust can be prevented.

Japanese Patent Application No. 11-96053 proposes an invention in which a radius of curvature r (see FIG. 8) of a portion of the pressing member that contacts the endless belt-shaped image carrier is r ≧ 5 mm. However, this is to prevent curling of the endless belt-shaped image carrier. This curl is generated when the endless belt-shaped image carrier is left in a stretched state for a long period of time, which hinders the close contact with the transfer material during transfer and causes horizontal streak-like transfer failure. In order to prevent this curl, it is desirable that the radius of curvature r of the pressing member is large.

[0013]

However, increasing the radius of curvature r of the pressing member is effective for preventing the curl of the endless belt-shaped image carrier, but the pressing member becomes larger than the transfer portion because the pressing member becomes large. As a result, the length L of the linear portion of the endless belt-shaped image carrier formed by the transfer nip portion and the pressing member becomes longer. For this reason, as shown in FIG. 11, even when the transfer material 22 is pressed against the intermediate transfer belt 10 by the transfer material transfer guide 31, the length L of the linear portion is long, so that the transfer material 22 is not moved in the transfer direction of the transfer material 22. The pressing force F per unit length becomes small, and a gap s is generated on the way, so that a sufficient effect on toner dust may not be obtained.

Incidentally, the above-mentioned problem is not limited to the intermediate transfer belt, but may occur in the case of a photosensitive member which is an endless belt-shaped image carrier.

The present invention has been made in view of the above background. An object of the present invention is to make the endless belt-shaped image carrier and the transfer material adhere to each other so as to prevent the generation of toner dust due to the gap, and to provide a good image. An object of the present invention is to provide an image forming apparatus capable of obtaining an image.

[0016]

According to a first aspect of the present invention, there is provided an endless belt-shaped image carrier which is rotated while carrying a toner image. A transfer material transport guide that guides the transfer material so as to be sent out toward an upstream position in the rotation direction of the endless belt-shaped image carrier at a transfer portion provided at an arbitrary position, and a transfer material that is fed by the transfer material transport guide. Transfer means for transferring the toner image on the endless belt-shaped image carrier to a transfer material, a transfer opposing roller disposed opposite to the transfer means, and the endless belt-shaped image carrier more than the transfer means. And a pressing member for pressing the endless belt-shaped image carrier from the upstream rear surface in the rotation direction of the endless belt-shaped image carrier formed by the transfer opposing roller and the pressing member. Straight section The length was set so that no gap was formed between the transfer material and the endless belt-shaped image carrier until the transfer material reached the transfer portion after contacting the endless belt-shaped image carrier. It is characterized by the following.

In the image forming apparatus according to the first aspect, the length of the linear portion is set to be equal to the length of the transfer material after the transfer material contacts the endless belt-shaped image carrier and reaches the transfer portion. Since the gap is set so as not to generate a gap between the endless belt-shaped image carrier and the endless belt-shaped image carrier, a good image can be obtained by preventing generation of toner dust.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, when the length of the linear portion is L, L ≦ L
10 (unit: mm).

The transfer material is guided by the transfer material conveying guide, and a force for pressing the endless belt-shaped image carrier is applied to the transfer material. When the length L of the linear portion is larger than 10 mm by an experiment, the transfer material becomes an endless belt shape. The length in contact with the image carrier increases, and the pressing force per unit length decreases. When the pressing force is reduced, a gap is generated between the transfer material and the endless belt-shaped image carrier, and toner dust may be generated from the gap. In the image forming apparatus according to the second aspect, since the length L of the linear portion satisfies L ≦ 10 mm, the air gap does not occur, and generation of toner dust is prevented regardless of the thickness of the transfer material or the size of the transfer material. And a good image can be obtained.

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the pressing member makes the endless belt-shaped image carrier uniformly in a direction orthogonal to a rotation direction of the endless belt-shaped image carrier. Characterized in that they are arranged so as to be pressed.

In the image forming apparatus according to the third aspect, when the endless belt-shaped image carrier rotates, the distribution of the pressing force by the pressing member in a direction orthogonal to the rotation direction of the endless belt-shaped image carrier. Since no deviation occurs, stable rotation of the endless belt-shaped image carrier can be obtained.

According to a fourth aspect of the present invention, in the image forming apparatus of the first, second or third aspect, the pressing member is arranged to be swingable about a rotation axis of the transfer opposing roller. It is assumed that.

In the image forming apparatus according to the fourth aspect, the pressing member is swung to separate the pressing member from the inner peripheral surface which is the back surface of the endless belt-shaped image carrier, and the pressing member is moved by the pressing member. The pressing of the endless belt-shaped image carrier can be released.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] An example of an embodiment in which the present invention is applied to a full-color laser printer (hereinafter simply referred to as a "printer") as an image forming apparatus will be described with reference to the drawings. explain. FIG.
2 illustrates an image forming unit of the printer according to the embodiment. A drum-shaped photoreceptor 1 that rotates in the direction of the arrow in the figure is provided in an image forming unit of the printer. Around the photoreceptor 1, a photoreceptor cleaning unit 2 having a rubber blade 3, a charger 4, an exposure unit 5 for irradiating the photoreceptor 1 with light 5L containing image information, and a developing device in the order of rotation indicated by arrows. 6. An intermediate transfer belt 10 and the like are provided as an endless belt-shaped image carrier.

The developing means 6 comprises four developing devices: a yellow developing device 6Y, a magenta developing device 6M, a cyan developing device 6C, and a black developing device 6BK. At the time of full-color image formation, light 5L including color image information is irradiated from the exposure unit 5 to form a visible image in the order of a yellow developing device 6Y, a magenta developing device 6M, a cyan developing device 6C, and a black developing device 6BK. The visible images of the respective colors are sequentially transferred onto the intermediate transfer belt 10 in a superimposed manner. That is, the primary transfer forms a full-color toner image on the intermediate transfer belt 10 using four color toners.

The intermediate transfer belt 10 includes a primary transfer bias roller 11, a secondary transfer opposing roller 50, and a drive roller 1.
It is stretched by two and two stretching rollers 13, 60 and the like, and is driven by a drive motor (not shown). The intermediate transfer belt 10 has a volume resistance obtained by dispersing a conductive material such as carbon black in PVDF (polyvinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), or the like. The rate is 10 ⁸ to 10 ¹³ Ωcm
It is adjusted to be within the range.

Around the intermediate transfer belt 10, a secondary transfer unit 15, a belt cleaning unit 18, a mark sensor 20, and the like are provided.

The secondary transfer unit 15 includes a secondary transfer bias roller 14 and the secondary transfer bias roller 14.
And a contact / separation mechanism 16 composed of a cam for bringing the medium into and out of the intermediate transfer belt 10.

The belt cleaning unit 18 includes:
It comprises a cleaning blade 17 and a contact / separation mechanism 19 with a cam for bringing the cleaning blade 17 into and out of contact with the intermediate transfer belt 10. The cleaning blade 17 can be separated from the surface of the intermediate transfer belt 10 by the contact / separation mechanism 19 during the belt transfer of the second, third, and fourth colors after the belt transfer of the first color yellow image. I have.

The mark sensor 20 is used for the intermediate transfer belt 1
The belt position detection mark 21 provided at the end of the zero is detected. By starting the image forming process of each color at the timing when the belt position detection mark 21 is detected by the mark sensor 20, the intermediate transfer belt 1 is started.
Accurate color superposition of each color image on 0 becomes possible.

The transfer material 22 to which the superimposed image on the intermediate transfer belt 10 is transferred is sent out from a paper feed roller 23 and consists of four color superimposed images carried on the surface of the intermediate transfer belt 10 by a registration roller 24. The leading end of the full-color image is a press-contact portion between the secondary transfer opposing roller 50 and the secondary transfer bias roller 14 and is fed at the timing when it reaches the transfer nip 51 as the secondary transfer position.

The secondary transfer bias roller 14 of the secondary transfer unit 15 is usually separated from the surface of the intermediate transfer belt 10, but is formed on the surface of the intermediate transfer belt 10.
When the color superimposed images are collectively transferred to the transfer material 22, they are moved by the action of the contact / separation mechanism 16 at a time and pressed by the intermediate transfer belt 10 between the secondary transfer opposed roller 50. The transfer nip 51 as a secondary transfer position including the pressing portion is configured. Then, a predetermined bias voltage is applied to the secondary transfer bias roller 14, whereby the transfer to the transfer material 22 is performed. The transfer material 22 to which the full-color toner image has been transferred in this manner is fixed while passing through the fixing unit 25,
The paper is discharged to a paper discharge unit (not shown).

At the time of continuous printing of a plurality of colors, the bias voltage to the secondary transfer bias roller 14 is turned off at the timing when the rear end of the transfer material 22 passes through the secondary transfer bias roller 14. Thereafter, in order to prevent toner from adhering to the intermediate transfer belt 10 on which the toner image of the next page is to be carried, the secondary transfer bias roller 14 is moved by the contact / separation mechanism 16.
More separated.

Further, at the end of the transfer of the last page during single-sheet printing or continuous printing, the secondary transfer bias roller 14 is not separated from the surface of the intermediate transfer belt 10, and the cleaning bias having the reverse polarity to the bias at the time of transfer is used. In this example, -1 KV is applied for a fixed time (in this example, a time corresponding to four rotations of the secondary transfer bias roller 14). Subsequently, a bias having the same polarity as the transfer bias (1 in this example).
KV) is applied for a certain period of time (corresponding to two rotations of the transfer roller in this example) to transfer the toner adhered to the surface of the secondary transfer bias roller 14 to the intermediate transfer belt 10,
The surface of the secondary transfer bias roller 14 is cleaned, and then separated from the intermediate transfer belt 10.

Here, the reason why the bias having the same polarity as the transfer bias is applied is to release the electric attraction force of the toner having a small charge amount or the toner charged to the opposite polarity to enhance the cleaning property. The toner transferred to the intermediate transfer belt 10 is collected from the surface of the intermediate transfer belt 10 by the belt cleaning unit 18. After the end of a series of printing operations as described above, the rotation of the motor serving as the driving source is stopped, and the printer enters a print standby state.

Next, the features of this embodiment will be described. In FIG. 1, the pressing member 30 is located at a position facing the surface K of the transfer material transport guide 31,
0 is provided so as to be able to be pressed against the back surface of the pressing member 3.
Numeral 0 has a downwardly curved surface in this example. The pressing member 30 has a curved surface portion at a position upstream of the transfer nip portion 51 of the intermediate transfer belt 10.
0 is pressed from the back side (inside) to the outside.

The material of the pressing member 30 is a slidable resin having good slidability. As this sliding resin,
POM (polyacetal), polyamide resin (nylon), PTFE (polytetrafluoroethylene), PVDF
(Polyvinylidene fluoride) and the like, and any of these can be selected and used. By forming the pressing member 30 from a material having high slidability as described above, the intermediate transfer belt 10 is placed inside the intermediate transfer belt 10, that is,
Even in the configuration in which the pressing member 30 is set to be pressed from the back side and the sliding contact is made, the back side of the intermediate transfer belt 10 is not damaged such as being damaged early.

The electric field region in the secondary transfer portion is about 4 mm from the transfer nip portion 51. Therefore, the transfer nip 51
Transfer belt 10 formed by the pressing member 30
It is better that the length L of the straight portion is at least 4 mm and as short as possible. This is because the pressing force F between the intermediate transfer belt 10 and the transfer material 22 is increased, and it is difficult to form a gap between the transfer material 22 and the intermediate transfer belt 10, so that generation of toner dust can be prevented.

In order to find a preferable length L of the linear portion for preventing generation of toner dust due to a gap between the transfer material 22 and the intermediate transfer belt 10, the length L of some linear portions is determined.
Was set and the experiment was performed. Table 1 shows the results. As is apparent from Table 1, the length L of the linear portion is L ≦ 10
It was found that the generation of toner dust can be prevented by setting the unit (mm).

[0040]

[Table 1]

In order to configure the length L of the linear portion of the intermediate transfer belt 10 formed by the transfer nip portion 51 and the pressing member 30 so as to satisfy the above relationship, the pressing member 3
It is effective to reduce the radius of curvature r of the contact portion with the intermediate transfer belt 10 of zero. However, if the radius of curvature r of the pressing member 30 is reduced, as described above, the intermediate transfer belt 1
There is a possibility that a curl of 0 may occur.

In the printer according to this embodiment, in order to prevent the intermediate transfer belt 10 from curling, a pressing member contact / separation mechanism is provided so that the pressing member 30 is moved from the back of the intermediate transfer belt 10 when image formation is not performed. The intermediate transfer belt 30 is released from the pressure, and the pressure on the intermediate transfer belt 30 is released.

FIG. 2 is an enlarged view of the vicinity of the pressing member contact / separation mechanism 70. FIG. 3 is a perspective view of the vicinity of the pressing member contact / separation mechanism 70. The pressing member contact / separation mechanism 70 includes a pressing member 30, a holding member 71 for holding the pressing member 30, a bearing 72 for rotatably holding the holding member 71, a cam 73 for swinging the holding member 71, and a holding member 71. Mainly composed of a spring 74 or the like that presses the cam 73 in the direction of the cam 73.

The pressing member 30 is integrally attached to the holding member 71. The holding member 71 is rotatably mounted on a shaft portion of the secondary transfer opposing roller 50 via a bearing 72 around the axis of the secondary transfer opposing roller 50. Thereby, the pressing member 30 can maintain the parallelism with respect to the secondary transfer opposing roller 50 with high accuracy, and can freely rotate around the rotation axis of the secondary transfer opposing roller 50.

At least one of the longitudinal ends of the holding member 71 is provided with a contact portion 71a that contacts the cam 73. The cam 73 is fixed to the rotation shaft 75, and the rotation of the rotation shaft 75 is interrupted by a clutch mechanism (not shown) so that the cam 73 can be stopped at an arbitrary position. A spring 74 is provided on a surface of the contact portion 71a opposite to a surface that contacts the cam 73. One end of the spring 74 is held by a spring holding member 76 attached to the housing of the printer main body, and the other end is arranged so as to constantly press the contact portion 40 a in the direction of the cam 73. With such a configuration, the pressing member 30 can move toward and away from the intermediate transfer belt 10 according to the stop position of the cam 73.

During the image forming operation, as shown in FIG. 2, since the cam 73 is rotated and stopped at the position where the pressing member 30 presses the intermediate transfer belt 10, the intermediate transfer belt 10 and the transfer material are stopped. 22 and a good image free of toner dust is obtained. Even if the radius of curvature r (see FIG. 3) of the pressing member 30 is small, the intermediate transfer belt 10 is rotating during the image forming operation, and is always in contact with the pressing member 30 at a different portion. Will not be attached. In the present embodiment, for example, the radius of curvature r is set to r = 5.
mm, the intermediate transfer belt 10 did not have a curl.

On the other hand, in a standby state other than the image forming operation,
As shown in FIG. 4, the cam 73 is located in a direction in which the pressing member 30 moves away from the intermediate transfer belt 10. When the cam 73 is stopped at the illustrated position, the spring 74 presses the contact portion 71 a of the holding member 71 and the holding member 71
Is pivoted about the rotation axis of the secondary transfer opposing roller 50 in the counterclockwise direction in the figure. As the holding member 71 swings, the pressing member 30 attached to the holding member 71 separates from the back surface of the intermediate transfer belt 10. This allows
In a standby state other than the image forming operation, since the pressing member 30 does not press the intermediate transfer belt 10, the intermediate transfer belt 10
There is no curl habit.

Further, since the parallelism between the pressing member 30 and the secondary transfer opposing roller 50 is accurately maintained, the intermediate transfer belt 10 is rotated when the intermediate transfer belt 10 is driven to rotate.
There is no deviation in the pressure distribution in the direction perpendicular to the rotation direction of. Therefore, stable rotation of the intermediate transfer belt 10 is obtained, and skewing of the intermediate transfer belt 10 can be prevented.

In the above-described embodiment, an example in which the endless belt-shaped image carrier is applied to the intermediate transfer belt has been described. However, the present invention is not limited to this, and may be applied to an endless belt-shaped photoconductor. .

[0050]

According to the present invention, the transfer material and the endless belt-like image carrier are transferred from when the transfer material comes into contact with the endless belt-like image carrier to when the transfer material reaches the transfer portion. Since no gap is formed between the body and the body, there is an excellent effect that a good image can be obtained by preventing generation of toner dust.

In particular, according to the second aspect of the present invention, the length L of the linear portion of the endless belt-shaped image carrier formed by the transfer opposing roller and the pressing member is set to 10 mm or less. There is no gap between the transfer material and the endless belt-shaped image carrier, and there is an excellent effect that a good image without toner dust can be obtained.

In particular, according to the third aspect of the present invention, the endless belt-shaped image carrier rotates stably and the endless belt-shaped image carrier has no skewing or the like, and a good image can be obtained. Has an excellent effect.

In particular, according to the invention of claim 4, in a standby state other than the time of image formation, the pressing member is swung,
By releasing the pressing member from the inner peripheral surface of the endless belt-shaped image carrier and releasing the pressing, an excellent image can be obtained without curling the endless belt-shaped image carrier. effective.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a full-color laser printer showing an example of an image forming apparatus according to an embodiment.

FIG. 2 is an enlarged view of a secondary transfer unit in the image forming apparatus of FIG.

FIG. 3 is a perspective view for explaining a contact / separation mechanism 70;

FIG. 4 is an enlarged view of a secondary transfer unit showing a state where a pressing member is separated from an intermediate transfer belt.

FIG. 5 is a schematic explanatory view of electrostatic transfer according to the related art.

FIG. 6 is a diagram illustrating a state around a transfer unit according to the related art.

FIG. 7 is a diagram illustrating a gap between an endless belt-shaped image carrier and a transfer material according to a conventional technique.

FIG. 8 is a diagram illustrating a state in which a pressing member according to another related art is provided.

FIG. 9 is a diagram illustrating a state in which a pressing member according to another related art is provided.

FIG. 10 is a diagram illustrating a state in which a pressing member according to another related art is provided.

FIG. 11 is a diagram illustrating a gap between an endless belt-shaped image carrier and a transfer material according to another related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 10 intermediate transfer belt 14 secondary transfer bias roller 30 pressing member 31 transfer material transport guide 50 secondary transfer opposing roller 51 secondary transfer nip 70 pressing member contact / separation mechanism 71 holding member 71a cam 73 72 Bearing 73 Cam 74 Spring 75 Rotation axis of cam 76 Spring holding member r Curvature radius of pressing member 30

Claims (4)

[Claims] An endless belt-shaped image carrier which carries a toner image and is rotated; and an endless belt-shaped image carrier having a transfer portion provided at an arbitrary position around the endless belt-shaped image carrier. A transfer material conveyance guide for guiding the transfer material so as to be sent out toward the upstream position in the rotation direction; and a transfer for transferring the toner image on the endless belt-shaped image carrier to the transfer material sent by the transfer material conveyance guide. Means, a transfer opposing roller disposed opposite to the transfer means, and pressing the endless belt-shaped image carrier from the back surface upstream of the transfer means in the rotation direction of the endless belt-shaped image carrier. In the image forming apparatus having the pressing member, the length of the linear portion of the endless belt-shaped image carrier formed by the transfer opposing roller and the pressing member may be set such that the transfer material is the endless belt-shaped image carrier. Above contact Until it reaches the shooting unit, an image forming apparatus characterized by being set so that the gap does not occur between the transfer material and the endless belt-shaped image carrier. 2. The image forming apparatus according to claim 1, wherein when the length of said linear portion is L, L ≦ 10 (unit: mm)
An image forming apparatus that satisfies the following relationship: 3. An image forming apparatus according to claim 1, wherein said pressing member presses said endless belt-shaped image carrier uniformly in a direction orthogonal to a rotation direction of said endless belt-shaped image carrier. An image forming apparatus, which is provided. 4. An image forming apparatus according to claim 1, wherein said pressing member is arranged to be swingable about a rotation axis of said transfer opposing roller. .