JP2003015442A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color copying machine provided with a paper transfer roller 23a so that the roller 23a may press-contact with the surface of an intermediate transfer belt 19 wound round a supporting roller 21 also having a function to drive the belt, which is improved to restrain faulty transfer caused by the change of the circumferential speed of the belt in a paper transfer part (LPT) between both rollers 21 and 23a, the fluctuation of the circumferential speed of the belt caused by the adhesion of toner to the roller 21 and that of the circumferential speed of the belt caused by temperature change in the machine. SOLUTION: By making the paper transfer roller 23a having elasticity press-contact with the supporting roller 21 having rigidity, the roller 23a is deformed to secure the width of the paper transfer part. At least the back side of the belt 19 is constituted of material, such as fluororesin, which has releasing property and to which the toner hardly adheres, and the toner is prevented from adhering and being accumulated on the roller 21 through the back surface of the belt. The surface layer 21a of the roller 21 is constituted of material excellent in gripping property for the belt 19, and the thickness thereof is set so that the fluctuation of the circumferential speed of the belt by the fluctuation of thickness caused by heat may not be out of tolerance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, etc.
After transferring the toner image formed on the image bearing member to a transfer material such as paper using an intermediate transfer member such as an intermediate transfer belt,
The present invention relates to an image forming apparatus that fixes a transfer material using a fixing unit.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus using such an intermediate transfer member, for example, toner images of different colors sequentially formed on an image carrier are sequentially transferred onto the intermediate transfer member. 2. Description of the Related Art A color image forming apparatus is known in which, after being superposed, they are collectively transferred from an intermediate transfer member to a transfer material such as paper. Further, it is also known that the intermediate transfer member is composed of a plurality of support rollers and an intermediate transfer belt wound around these.

[0003]

By the way, it is considered that the life of the intermediate transfer belt due to repeated use greatly depends on the material of the intermediate transfer belt, and various materials have been examined in experiments by the inventors. At the same time as this study, regarding the material of the support roller surface that affects the belt grip of the support roller, and the material of the transfer roller surface that is pressed against the belt part wound around the support roller to form the transfer part on the transfer material such as paper. The appropriate material was examined using various materials. Through these studies, it was found that the life of the intermediate transfer belt due to repeated use depends not only on the material of the belt but also on the surface material of the transfer roller and the material of the supporting roller facing the transfer roller. Therefore, the inventors of the present invention have made earnest studies on the cause, and have found that the bending direction of the belt in the transfer portion affects the life of repeated use. Also,
A running test was carried out using a supporting roller having a surface layer made of rubber to improve grip on the intermediate transfer belt, and as a result, problems such as image elongation and image deletion in the circumferential direction of the intermediate transfer belt occurred over time. It was
As a result of diligent research on the cause of this, the outer diameter of the support roller that also functions as a belt drive changes depending on the temperature inside the device, and the floating toner inside the device that adheres to the back surface of the intermediate transfer belt adheres to the support roller. It was found that the peripheral speed of the intermediate transfer belt fluctuated due to the accumulation and increase in the apparent outer diameter of the support roller, resulting in a peripheral speed difference with the photoconductor.

The present invention has been made in view of the above background. A first object of the present invention is to improve the repeated use durability of the intermediate transfer belt by the mechanism structure of the apparatus, and there is room for selection of the material of the intermediate transfer belt. A second object of the present invention is to provide an image forming apparatus capable of forming a good image while suppressing fluctuations in the peripheral speed of the intermediate transfer belt.

[0005]

In order to achieve the above object, the invention of claim 1 is an intermediate transfer in which a toner image formed on an image bearing member is wound around a plurality of supporting rollers and is driven in a circular manner. In an image forming apparatus, in which an intermediate transfer member is transferred to a transfer material such as paper by using a transfer unit after being transferred to a belt, and is fixed to the transfer material by using a fixing unit, the transfer unit is a belt wound around a support roller. A transfer roller that is in pressure contact with a portion of the transfer roller, the transfer roller being made of an elastic material, and the support roller facing the transfer roller being made of a material having a hardness higher than that of the transfer roller. is there. According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the transfer roller is pressed against a belt portion wound around a support roller that also functions as a belt drive, and a material that causes a thickness change due to heat of the support roller is used. The thickness of the surface layer is set such that the fluctuation of the belt peripheral speed due to the temperature change of the outer diameter of the supporting roller is within the allowable range. The invention of claim 3 is the same as claim 2
In the image forming apparatus of, at least the back surface of the belt is formed of a material such as a fluororesin that toner hardly adheres to, and the surface layer of the support roller has a predetermined friction coefficient such as rubber and has a grip property with respect to the belt. It is characterized by being formed of a good material.

[0006]

According to the invention of claim 1, the transfer roller is made of an elastic material, and the support roller facing the transfer roller is made of a material having a hardness higher than that of the transfer roller. The transfer part that presses with the
While the support roller has almost the original outer shape, the surface portion of the transfer roller is deformed and becomes a concave shape. Therefore, unlike the case where the transfer roller side has a higher hardness than the support roller and the support roller side is deformed to form a recess, the intermediate transfer belt portion that winds around the support roller and passes through the transfer portion is peeled. No deformation is added.

According to the second aspect of the present invention, the thickness of the surface layer of the supporting roller which also functions as a belt is set so that the fluctuation of the belt peripheral speed due to the temperature change of the outer diameter of the supporting roller is within the allowable range. Therefore, it is possible to prevent the fluctuation of the belt peripheral speed exceeding the allowable range.

Further, in the invention of claim 3, since at least the back surface of the belt is formed of a material such as a fluorine-based resin to which toner hardly adheres, adhesion of toner floating in the apparatus to the back surface of the belt can be suppressed. . Therefore, it is possible to suppress the fluctuation of the belt peripheral speed due to the apparent increase of the outer shape of the support roller due to the toner deposited and deposited on the support roller which also functions as the belt drive via the back surface of the belt. Further, since the surface layer of the supporting roller is formed of a material having a predetermined friction coefficient such as rubber and having a good grip property with respect to the belt, it is possible to exhibit a good grip property with respect to the belt.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a color copying machine which is an image forming apparatus will be described. FIG. 1 is an explanatory diagram of a paper transfer section in a color copying apparatus according to an embodiment, FIG. 2 is a schematic configuration diagram of the entire color copying apparatus, FIG. 3 is a schematic configuration diagram of a main part of the color copying apparatus, and FIG. ),
FIG. 3B is an explanatory diagram of an intermediate transfer belt 19 support mechanism as an intermediate transfer member of the copying apparatus. In FIG. 2, the color copying apparatus includes a color image reading apparatus (hereinafter, referred to as a color scanner) 1 and a color image recording apparatus (hereinafter, referred to as a color image recording apparatus).
It is called a color printer) 2. First, the color scanner 1 forms an image of the original 3 on the color sensor 7 via the illumination lamp 4, the mirror group 5, and the lens 6, and the color image information of the original is, for example, blue (hereinafter referred to as B). ), Green (Green, hereinafter G)
), Red (Red, hereinafter referred to as R) color-separated light is read and converted into an electrical image signal. Then, based on the B, G, and R color-separated image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter referred to as Bk),
Cyan (hereinafter C), Magenta (Magent)
a, hereinafter referred to as M), and yellow (Yellow, hereinafter referred to as Y) color image data.

Next, in the color printer 2, the writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal and performs optical writing corresponding to the original image, and a photosensing as an image carrier. An electrostatic latent image is formed on the body 9. The photoconductor 9 rotates counterclockwise as indicated by an arrow, and around the photoconductor cleaning unit (including a pre-cleaning charge eliminator) 10 and a charge eliminating lamp 1.
1, charger 12, potential sensor 13, Bk developing device 14,
C developing device 15, M developing device 16, Y developing device 17, optical sensor 18 for developing density pattern detection, intermediate transfer belt 1
9 and the like are arranged. Each developing device rotates a developing sleeve (14a, 15a, 16a, 17) in which the brush of the developer is brought into contact with the surface of the photoconductor 9 to develop the electrostatic latent image.
a), a developing paddle (14b, 15b, 16b, 17b) that rotates to draw up and agitate the developer, and a toner concentration sensor (14c, 15c, 16c) of the developer.
17c) and the like.

Hereinafter, the outline of the copying operation will be described by taking the example of the developing operation order (color toner image forming order) as Bk, C, M and Y (however, the image forming order is not limited to this. ). When the copying operation is started, the color scanner 1 starts reading Bk image data from a predetermined timing, and optical writing by a laser beam and latent image formation start based on the image data (hereinafter, electrostatic image by Bk image data is used. The latent image is called Bk latent image C, M, Y
About C latent image, M latent image, and Y latent image).
Before the latent image front end reaches the developing position of the Bk developing device 14 so that the front end of the Bk latent image can be developed, the developing sleeve 14a is started to rotate to develop the Bk latent image with Bk toner. After that, the development operation of the Bk latent image area is continued,
When the trailing edge of the latent image has passed the Bk development position, the development is disabled. This is completed at least before the leading edge of the C latent image by the next C image data arrives.

Then, the Bk toner image formed on the photoconductor 9 is transferred onto the surface of the intermediate transfer belt 19 which is driven at the same speed as the photoconductor (hereinafter, the toner image transfer from the photoconductor to the intermediate transfer belt is performed). Called transcription). The belt transfer is performed by applying a predetermined bias voltage to the transfer bias roller 20a while the photoconductor 9 and the intermediate transfer belt 19 are in contact with each other. The intermediate transfer belt 19 has
The Bk, C, M, and Y toner images sequentially formed on the photoconductor 9 are sequentially aligned on the same surface to form a four-color superposed belt transfer image, and then bulk transfer is performed on the transfer paper. . This intermediate transfer belt unit will be described later.

Here, on the side of the photoreceptor 9, C is carried out after the Bk step.
In the process, the C image data reading by the color scanner 1 starts at a predetermined timing, and the C latent image is formed by writing a laser beam with the image data. C
The developing device 15 starts to rotate the developing sleeve 15a with respect to the developing position after the trailing edge of the previous Bk latent image has passed and before the leading edge of the C latent image reaches the C latent image by the C latent image. Develop with toner. After that, the development of the C latent image area is continued, and when the trailing edge of the latent image passes, the development is inoperative as in the case of the previous Bk developing device. This is also completed before the leading edge of the next M latent image arrives. In each of the steps M and Y, the operations of reading image data, forming a latent image, and developing are performed in the same manner as the steps Bk and C described above.

Next, the outline of the intermediate transfer belt unit will be described. In FIG. 3, the intermediate transfer belt 19 is
The drive roller 21, the transfer bias roller 20a, and the driven roller groups 20b and 20c are stretched around and are driven and controlled by a drive motor (not shown) as described later. Further, a separation / contact mechanism as shown in FIGS. 4A and 4B is provided so that the intermediate transfer belt 19 can be contacted / separated from the photoconductor 9. That is, this contact / separation mechanism rotatably supports the bias roller 20a facing the photoconductor 9 and can swing about the fulcrum 50a.
0 and the driven roller 20b adjacent to the bias roller 20a
And a cam member 52, which rotatably supports and is swingable around a fulcrum 51a. Both support members 50 and 51 are pressed against the cam member 52 by a biasing member (not shown). As a result, the rotation of the cam member 52 allows the support members 50 and 51 to move in the same direction with respect to the photoconductor 9 with the same distance. The structural materials of the intermediate transfer belt 19 and the rollers 20a, 20b, 21 will be described later in detail.

A belt cleaning unit 22 is provided at a predetermined position facing the surface of the intermediate transfer belt 19. The unit 22 is composed of a brush roller 22a, a rubber blade 22b, and a contact / separation mechanism 22c from the belt. After the Bk image of the first color is transferred by the belt, the second, third, and fourth colors are transferred by the belt. During this time, the contacting / separating mechanism 22c separates the belt surface from the belt surface, and contacts the surface of the intermediate belt 19 for cleaning at a predetermined timing thereafter.

A paper transfer unit 23 is provided so as to face the portion of the intermediate transfer belt 19 wound around the drive roller 21. The unit 23 includes a paper transfer roller 23a, a roller cleaning blade 23b,
And a belt contact / separation mechanism 23c. The structural material of the paper transfer roller 23a will be described later in detail. The paper transfer roller 23a is usually separated from the surface of the belt 19, but the contact / separation mechanism is arranged at a timing when the four-color superposed images formed on the surface of the intermediate transfer belt 19 are collectively transferred to the transfer paper. 23c is pressed by the roller 23
A predetermined bias voltage is applied to a and transfer to paper is performed.
The transfer paper 24 is fed by the paper feed roller 25 and the registration roller 26 at the timing when the leading edge of the four-color superimposed image on the intermediate transfer belt surface reaches the paper transfer position.

As a method of driving the intermediate transfer belt 19, there are a constant speed forward movement method, a skip forward movement method, and a quick return as an operation method after the belt transfer of the Bk toner image of the first color is completed to the end. Three methods are conceivable. One of these methods is used, or a plurality of methods are efficiently combined according to the copy size in terms of copy speed, the intermediate transfer belt 19 is driven, and the photosensitive member is sequentially driven. 9
The toner images transferred from are superposed on the intermediate transfer belt 19 and are collectively transferred onto the transfer paper 24.

The transfer paper 24 on which the four-color superposed toner images have been collectively transferred from the surface of the intermediate transfer belt in this manner is conveyed to the fixing device 28 by the paper conveying unit 27, and the fixing roller 28a controlled to a predetermined temperature. Then, the toner image is melted and fixed by the pressure roller 28b and carried out to the copy tray 29 to obtain a full color copy.

The photosensitive member 9 after the belt transfer is the photosensitive member cleaning unit 10 (pre-cleaning static eliminator 10).
The surface is cleaned with a, the brush roller 10b, the rubber blade 10c), and the charge is removed uniformly by the charge removing lamp 11. Further, the surface of the intermediate transfer belt 19 after the toner image is transferred onto the transfer paper 24 is cleaned by pressing the cleaning unit 22 again by the contact / separation mechanism 22c.

At the time of repeat copy, the color scanner 1
The operation and the image formation on the photosensitive member 9 proceed to the second Bk (first color) image process at a predetermined timing after the first Y (fourth color) image process. Further, in the intermediate transfer belt 19, the second Bk toner image is formed in the area where the surface is cleaned by the cleaning unit 22, following the batch transfer process of the first four-color superimposed image onto the transfer paper. Allow the belt to be transferred. After that, the same operation as the first sheet is performed. The transfer paper cassettes 30, 31, 32,
The reference numeral 33 stores transfer sheets of various sizes, which are fed and conveyed in the direction of the registration rollers 26 at a timing from a storage cassette of size sheets designated by an operation panel (not shown). Reference numeral 34 is a manual paper feed tray for OHP paper or thick paper.

The above is the description of the copy mode for obtaining four full colors, but in the case of the three-color copy mode and the two-color copy mode, the same operation as above is performed for the designated number of colors and the number of times. It will be. In the single-color copy mode, until the predetermined number of sheets are finished, only the developing device of that color is in a developing operation (agent standing) state, and the intermediate transfer belt 19 remains in contact with the surface of the photoreceptor 9. Drives in the forward direction at a constant speed, and the belt cleaner 22
The copy operation is performed in the state of being in contact with 9.

Next, the structures and materials of the intermediate transfer belt 19, the support rollers 20a, 20b and 21, and the paper transfer roller 23a will be described. The intermediate transfer belt 19 is made of a fluorine-based resin, and the fluorine-based resin is exposed on the back surface of the intermediate transfer belt 19 to prevent toner from adhering.

Of the supporting rollers, the driving roller 21
Is a core metal roller 2 made of aluminum as shown in FIG.
A surface layer 21b made of hydrin rubber is formed on 1a. Since this hydrin rubber is rubber, it has a good grip on the belt 19 from the viewpoint of the coefficient of friction and the adhesion. Since the thickness of the hydrin rubber changes depending on the temperature, the change in the thickness is within a range in which the relative peripheral speed difference is 0.1% or less of the original peripheral speed in consideration of the change in the diameter of the photosensitive member 9 side due to the sensitivity. The thickness at room temperature is set to 0.3 mm so that the surface layer 21b can be kept within the allowable thickness change range. Here, the outer diameter of the driving roller 21 is 39.88 mm, and it is rotationally driven so that the belt peripheral speed becomes 180 mm / s. The hardness is 70 Hs (J
IS-A). The other supporting rollers 20a, 20
b can also be configured with the same structure and material as the drive roller 21. However, these are not limited to the change in outer diameter as much as the drive roller 21, and thus the constituent materials may be appropriately changed.

The paper transfer roller 23a has a core metal roller 40a made of carbon steel pipe, an elastic layer 40b made of hydrin rubber and having a thickness of about 6 mm, and a surface layer 40c made of PFA tube having a thickness of 50 μm. 30.15 mm,
The roller has a hardness of 38 Hs (JIS-A). The paper transfer roller 23a is urged toward the drive roller 21 side by a predetermined pressure by the separating / contacting mechanism, and is deformed into a concave shape as shown in FIG. 1 to form a transfer portion (L _PT ). ing. The width of this transfer portion (so-called nip width) is about 2.5 mm.

The above intermediate transfer belt 19 and drive roller 2
In the color copying machine using No. 1 or the like, sufficient repeating durability of the intermediate transfer belt 19 was obtained, the peripheral speed of the intermediate transfer belt 19 was stable, and a good image could be obtained.

[0026]

According to the first aspect of the invention, the transfer portion where the support roller and the transfer roller are in pressure contact with each other with the intermediate transfer belt interposed therebetween has a deformed surface portion of the transfer roller and is recessed, and is wound around the support roller. On the contrary, unlike the case where the transfer roller side has a higher hardness than the support roller and the support roller side is deformed to form a recess, the intermediate transfer belt portion that passes through the lever transfer portion does not undergo unnecessary deformation. It is possible to improve the repeated use durability of the transfer belt. Therefore, it is possible to widen the scope of selection of the material of the intermediate transfer belt.

Further, according to the second aspect of the invention, even when the surface layer is formed of a material having a good gripping property with respect to the belt, such as rubber, which is a material in which the thickness changes due to heat, the belt circumference exceeding the allowable range is obtained. Since the fluctuation of the speed can be prevented, it is possible to provide the image forming apparatus capable of suppressing the fluctuation of the peripheral speed of the intermediate transfer belt and forming a good image.

Further, according to the third aspect of the present invention, the toner adhering and accumulated on the supporting roller which also functions as a belt driving via the back surface of the belt causes the outer shape of the supporting roller to apparently increase and the belt peripheral speed fluctuates. Therefore, it is possible to provide the image forming apparatus capable of forming a good image by suppressing the fluctuation of the peripheral speed of the intermediate transfer belt. In addition, it is possible to achieve good grip performance with respect to the belt, suppress slippage between the belt and the driving support roller, and stabilize the belt peripheral speed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a toner image transfer unit from an intermediate transfer belt to a transfer material according to an embodiment.

FIG. 2 is a schematic configuration diagram of an entire color copying apparatus according to the embodiment.

FIG. 3 is an enlarged view around a photoconductor and an intermediate transfer belt of the color copying apparatus.

4A and 4B are explanatory views of an intermediate transfer belt 19 support mechanism as an intermediate transfer member of the copying apparatus.

[Explanation of symbols]

1 Color image reading device 2 Color image recording device 8 Writing optical unit 9 Photosensitive drum 10 Photoconductor cleaning unit 11 Static elimination lamp 12 Charger 14 Black developer 15 Cyan developer 16 Magenta developer 17 Yellow developer 19 Intermediate transfer belt 20a Belt transfer bias roller 21 Belt drive roller 21a Core bar roller 21b surface 22 Belt cleaning unit 22a brush roller 22b rubber blade 22c Contact / separation mechanism 23 Paper transfer unit 23a Paper transfer roller 23b Roller cleaning blade 23c Contact / separation mechanism 24 Transfer paper 27 Paper transport unit 28 Fixer 28a fixing roller 28b pressure roller 40a core metal roller 40b elastic layer 40c surface

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[Procedure amendment]

[Submission date] June 19, 2002 (2002.6.1)
9)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

[0005]

In order to achieve the above object, the invention of claim 1 is an intermediate transfer in which a toner image formed on an image bearing member is wound around a plurality of supporting rollers and is driven in a circular manner. In an image forming apparatus, in which an intermediate transfer member is transferred to a transfer material such as paper by using a transfer unit after being transferred to a belt, and is fixed to the transfer material by using a fixing unit, the transfer unit is a belt wound around a support roller. configured using a transfer roller which presses the part, and the transfer roller, and a support roller facing the transcription roller have respective elastic layer, or
One, rather high towards the support roller hardness than the transfer roller
It is characterized in that it has formed such that. The invention according to claim 2 is a toner image formed on an image carrier.
While being lapped over multiple support rollers
After transferring to the intermediate transfer belt, use an intermediate transfer
Transfer the image from a copy object to a transfer material such as paper and transfer it using a fixing unit.
In an image forming apparatus for fixing to a copying material, the transfer means
One of the plurality of support rollers
And press contact with the belt part wrapped around the one support roller.
And a pressure roller,
And the pressing roller, each having an elastic layer, and
The one support roller has higher hardness than the pressure roller
It is characterized in that it is formed as follows. According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the transfer roller is brought into pressure contact with a belt portion wound around a support roller which also serves as a belt drive, and a thickness of the support roller is changed by heat. The thickness of the elastic layer made of a material is set so that the fluctuation of the belt peripheral speed due to the temperature change of the outer diameter of the supporting roller is 0.1% or less .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Delete

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Delete

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideya Furuta             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Yoshihiro Sakai             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Miokata             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Hideki Ueyama             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Minoru Sugiyama             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 2H200 FA02 FA17 FA20 GA23 GA47                       GA50 GB03 GB12 GB15 GB22                       GB23 HA03 HB12 HB22 JA02                       JA08 JA23 JA25 JA27 JA28                       JC03 JC07 JC12 JC13 JC15                       JC17 MA01 MA03 MA04 MA20                       MC02 MC05 MC09 MC18 NA01                 3J103 AA02 BA43 FA12 FA18 GA57                       GA58 GA60 GA66 HA12

Claims (3)

[Claims] 1. A toner image formed on an image bearing member is transferred to an intermediate transfer belt which is wound around a plurality of supporting rollers and driven to rotate, and then transferred from an intermediate transfer member to paper using a transfer means. In an image forming apparatus for transferring to a material and fixing to the transfer material by using a fixing means, the transfer means is configured by using a transfer roller that is in pressure contact with a belt portion wound around a support roller, and the transfer roller is made of an elastic material. An image forming apparatus characterized in that a supporting roller facing the transfer roller is formed of a material having a hardness higher than that of the transfer roller. 2. The transfer roller is brought into pressure contact with a belt portion wound around a support roller which also serves as a belt drive, and the thickness of a surface layer made of a material that changes in thickness due to heat of the support roller is determined by the temperature of the outer diameter of the support roller. The image forming apparatus according to claim 1, wherein the belt peripheral speed variation due to the change is set to be within an allowable range. 3. At least the back surface of the belt is formed of a material such as a fluororesin to which toner is unlikely to adhere, and the surface layer of the support roller has a predetermined friction coefficient such as rubber and has a good grip property with respect to the belt. The image forming apparatus according to claim 2, wherein the image forming apparatus is formed of various materials.