JP2000298408A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent the scattering of a toner image transferred to an intermediate transfer belt. SOLUTION: This image forming device is equipped with an image carrier 1 on which a toner image T in accordance with image information is formed and carried, an intermediate transfer belt 3 stretched and laid and supported on a plurality of roll members 2 turnably and arranged to be opposed to the image carrier 1, a primary transfer means 4 successively transferring toner images T on the carrier 1 to the belt 3, and a secondary transfer means 6 collectively transferring the toner image T on the belt 3 to a recording medium 5. In the device, a 1st contact member 7 with which the belt 3 comes in contact first after passing through the means 4 is provided with a potential holding means 8 holding the surface potential of the member 7 equal to or above the electrification potential of the back surface of the belt 3. Then, all the contact members 9 with which the belt 3 comes in contact until reaching the means 6 after passing through the means 4 are provided with a potential holding means holding the surface potential of the member 9 equal to or above the electrification potential of the back surface of the belt 3.

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 an electrophotographic copying machine and a laser printer, and more particularly, to a toner formed on an image carrier such as a photosensitive drum via an intermediate transfer belt. The present invention relates to an improvement in an image forming apparatus that transfers an image to a recording medium such as a sheet.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, for example, black (Bk), yellow (Y), magenta (M), and cyan (C) color components are provided around an image carrier such as a photosensitive drum. A developing device is provided, a transfer drum is arranged to face the image carrier, and a sheet as a recording medium is held on the transfer drum in advance, and the transfer drum is formed on the image carrier at each rotation of the image carrier. There is known an apparatus in which the respective color component toner images are sequentially transferred onto a sheet.
However, in this type, since the unfixed toner image of each color component is directly transferred onto the paper by multiple transfer, there are many characteristics such as the thickness and surface characteristics of the paper, and the transport characteristics of the paper to the image carrier. There is a problem that the quality of a color image formed on a sheet is easily influenced by factors.

[0003] As a means for solving such a problem,
Image forming apparatuses using an intermediate transfer member are already known (for example, Japanese Patent Publication No. 49-209, Japanese Patent Application Laid-Open No. 62-20 / 1987).
6567, JP-A-2-213879). This means that, for example, black (Bk), yellow (Y), magenta (M) and cyan (C) color developers are provided around an image carrier such as a photosensitive drum. For example, a belt-shaped intermediate transfer body (intermediate transfer belt) is arranged to face each other, and an unfixed toner image of each color component formed on the image carrier is sequentially primary-transferred to the intermediate transfer belt every rotation of the image carrier. Thereafter, the composite primary transfer image superimposed on the intermediate transfer belt is secondarily transferred to a sheet as a recording medium to form a desired image on the sheet. According to this type, since the composite toner image that has already been subjected to multiple transfer on the intermediate transfer belt is collectively transferred to the recording medium, the above-mentioned unstable factor can be eliminated, and the image of the image during multiple transfer can be eliminated. There is an advantage that disturbance and color shift can be effectively prevented.

[0004]

However, in the above-described image forming apparatus, after the primary transfer, the toner image on the intermediate transfer belt scatters, and a phenomenon that the linear image portion of the toner image is blurred (hereinafter referred to as blur) occurs. Technical problem was seen.

It is to be noted that such a technical problem is caused not only by the above-described image forming apparatus but also by, for example, arranging a plurality of image forming units in parallel and circulating along the arrangement direction of each image forming unit. An intermediate transfer belt is provided, and each color component (eg, black, cyan, magenta, yellow) image formed by each image forming unit is primarily transferred sequentially to the intermediate transfer belt, and then a color superimposed image on the intermediate transfer belt is recorded. Secondary transfer to paper as a medium (batch transfer)
So-called tandem type image forming apparatus (for example, Japanese Patent Application Laid-Open No. 10-260593).
The same occurs in Japanese Patent Application Laid-Open Publication No. H10-26095).

The present invention has been made to solve the above technical problem, and provides an image forming apparatus capable of effectively preventing a toner image transferred on an intermediate transfer belt from scattering. Things.

[0007]

That is, according to a first aspect of the present invention, as shown in FIG. 1, an image carrier 1 on which a toner image T corresponding to image information is formed and carried, and a plurality of roll members are provided. 2, an intermediate transfer belt 3 rotatably supported on the image carrier 2 and disposed opposite to the image carrier 1, and a toner image T on the image carrier 1.
Transfer means 4 for sequentially transferring the toner images onto the intermediate transfer belt 3
And the secondary transfer means 6 for transferring the toner image T on the intermediate transfer belt 3 onto the recording medium 5 at a time, the intermediate transfer belt 3 having passed through the primary transfer means 4 comes into contact first. The first contact member 7 is attached to the first contact member 7.
A potential holding means 8 for holding the surface potential of the intermediate transfer belt 3 above the charged potential of the back surface of the intermediate transfer belt 3 is provided.

In such technical means, the first embodiment of the present invention is not limited to the embodiment in which one image carrier 1 is rotated a plurality of times and the toner image T is primarily transferred to the intermediate transfer belt 3. This also includes a mode in which a plurality of image carriers 1 are provided (for example, a mode in which four image carriers are arranged in parallel and the toner image T on each image carrier 1 is primarily transferred to the intermediate transfer belt 3). Regardless of the form of the image carrier 1, whether it is in the form of a drum or a belt, the method of forming the toner image T may be appropriately selected, such as an electrophotographic method or an electrostatic recording method.

The intermediate transfer belt 3 is of a type that is stretched and supported by a plurality of roll members 2 and has a resistivity enough to electrostatically carry the toner image T. It can be selected appropriately.

Further, the primary transfer means 4 is of a type which transfers a toner image T formed on the image carrier 1 to the intermediate transfer belt 3 by forming a transfer electric field. And a non-contact transfer method using a corotron or the like.

The first contact member 7 is a member to which the intermediate transfer belt 3 that has passed through the primary transfer means 4 comes into contact first, and other than the roll member 2 that stretches and supports the intermediate transfer belt 3, Can be assumed. In FIG. 1,
An example in which one of the plurality of roll members 2 is the first contact member 7 is illustrated.

Further, the potential holding means 8 is provided on the first contact member 7 and has a function of holding the surface potential of the first contact member 7 above the charged potential of the back surface of the intermediate transfer belt 3. It can be selected appropriately.

As a specific example of the configuration of the potential holding means 8, there is an embodiment in which the first contact member 7 is disposed non-grounded.

Further, as the potential holding means 8, a resistance grounding means for grounding the first contact member 7 via a high resistance body may be used. Here, the resistance value of the high-resistance body is determined by the surface potential of the first contact member 7.
It is necessary to have a size enough to hold the charged potential on the back surface or higher. As a method of arranging the high-resistance body, various methods may be selected. However, from the viewpoint of simplification of the configuration and downsizing of the device, the surface of the first contact member 7 is coated with high resistance. It is preferable to form a layer and use it. The material constituting the coating layer is PE
T (polyethylene terephthalate) resin or PFA
It is preferable to use a (perfluoroalkoxy) resin.

Further, as the potential holding means 8, a bias applying means for applying a DC bias having the same polarity as the potential of the back surface of the intermediate transfer belt 3 to the first contact member 7 may be used. Here, the DC bias applied by the bias applying means needs to be large enough to keep the surface potential of the first contact member 7 equal to or higher than the charging potential of the back surface of the intermediate transfer belt 3.

[0016] The first aspect of the present invention is as follows.
As shown in FIG. 1, an image carrier 1 on which a toner image T according to image information is formed and carried, and supported by a plurality of roll members 2 so as to be rotatably stretched and opposed to the image carrier 1. An intermediate transfer belt 3, a primary transfer means 4 for sequentially transferring the toner image T on the image carrier 1 onto the intermediate transfer belt 3, and a secondary transfer means for collectively transferring the toner image T on the intermediate transfer belt 3 to a recording medium 5 In the image forming apparatus provided with the transfer unit 6, the charge removal on the back surface side of the intermediate transfer belt 3 is prevented from contacting the first contact member 7 with which the intermediate transfer belt 3 first contacts after passing through the primary transfer unit 4. In other words, it can be said that a prevention means is provided.

According to a second aspect of the present invention, as shown in FIG. 2, an image carrier 1 on which a toner image T corresponding to image information is formed and carried, and a plurality of roll members 2 are rotatable. An intermediate transfer belt 3 that is stretched and supported and disposed opposite the image carrier 1, a primary transfer unit 4 that sequentially transfers the toner image T on the image carrier 1 onto the intermediate transfer belt 3, And a secondary transfer means 6 for collectively transferring the toner image T to the recording medium 5 by the time the intermediate transfer belt 3 after passing through the primary transfer means 4 reaches the secondary transfer means 6. It is characterized in that all the contact members 9 that come into contact with each other are provided with potential holding means 10 for holding the surface potential of the contact members 9 higher than the charged potential of the back surface of the intermediate transfer belt 3.

In such technical means, the second embodiment of the present invention is not limited to the embodiment in which one image carrier 1 is rotated a plurality of times and the toner image T is primarily transferred to the intermediate transfer belt 3. This also includes a mode in which a plurality of image carriers 1 are provided (for example, a mode in which four image carriers are arranged in parallel and the toner image T on each image carrier 1 is primarily transferred to the intermediate transfer belt 3). Further, the image carrier 1, the intermediate transfer belt 3,
The primary transfer means 4 may be appropriately selected from those similar to those shown in the first embodiment of the present invention.

The contact members 9 are all members that come into contact with the intermediate transfer belt 3 after passing through the primary transfer means 4 until the intermediate transfer belt 3 reaches the secondary transfer means 6. Various members other than the roll member 2 to support can be assumed. FIG. 2 illustrates an example in which two of the roll members 2 are contact members.

Further, the potential holding means 10 is appropriately provided as long as it has a function of holding the surface potential of all the contact members 9 at or above the charging potential of the back surface of the intermediate transfer belt 3. You can choose it.

As a specific configuration example of the potential holding means 10, first, there is a mode in which all the contact members 9 are arranged in a non-grounded state.

Further, as the potential holding means 10, a resistance grounding means for grounding all the contact members 9 via a high resistance body may be used. Here, the resistance value of the high-resistance element needs to be large enough to keep the surface potential of all the contact members 9 above the charged potential of the back surface of the intermediate transfer belt 3. As a method of arranging the high-resistance body, various methods may be selected. However, from the viewpoint of simplification of the configuration and compactness of the device, all the contact members 9 have high resistance on the surface. It is preferable to form a coating layer before use. It is preferable to use PET resin or PFA resin as a material for forming the coating layer.

Further, as the potential holding means 10, a bias applying means for applying a DC bias having the same polarity as the potential of the back surface of the intermediate transfer belt 3 to all the contact members 9 may be used. Here, the DC bias applied by the bias applying means needs to be large enough to keep the surface potentials of all the contact members 9 above the charged potential on the back surface of the intermediate transfer belt 3. Further, for example, in a mode in which there are a plurality of contact members 9, it is preferable to share the bias applying means for the plurality of contact members 9.

The first aspect of the present invention described above is as follows:
As shown in FIG. 2, an image carrier 1 on which a toner image T according to image information is formed and carried, and supported by a plurality of roll members 2 so as to be rotatably stretched and opposed to the image carrier 1. An intermediate transfer belt 3, a primary transfer means 4 for sequentially transferring the toner image T on the image carrier 1 onto the intermediate transfer belt 3, and a secondary transfer means for collectively transferring the toner image T on the intermediate transfer belt 3 to a recording medium 5 In the image forming apparatus provided with the transfer unit 6, all the contact members 9 that come into contact with the intermediate transfer belt 3 after passing through the primary transfer unit 4 until reaching the secondary transfer unit 6 are
In other words, it can be said that a charge elimination preventing means for preventing charge elimination of the charge on the back surface side of the intermediate transfer belt 3 is provided.

Next, the operation of the above technical means will be described. In FIG. 1, a toner image T formed on an image carrier 1 is transferred to an intermediate transfer belt 3 by a primary transfer unit 4.
The primary transfer is performed. Then, on the back side of the intermediate transfer belt 3 onto which the toner image T has been transferred, a charge having a polarity opposite to the charge polarity of the toner is induced corresponding to the toner image T. After the primary transfer, the intermediate transfer belt 3 to which the toner image T has been transferred is
It moves with the rotation and moves to the contact portion with the first contact member 7. At this time, the surface potential of the first contact member 7 is held by the potential holding means 8 at or above the charged potential of the back surface of the intermediate transfer belt 3. Accordingly, the charge on the back side of the intermediate transfer belt 3 does not decrease at the time of contact, and the electrostatic force for holding the toner image T on the intermediate transfer belt 3 is maintained, so that scattering of toner is prevented. You.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 3 shows a schematic configuration of a color image forming apparatus (a color electrophotographic copying machine in the present embodiment) to which the present invention is applied.
In the figure, reference numeral 11 denotes a photosensitive drum (latent image carrier)
With the rotation in the direction of arrow A, the surface thereof is charged with a charging device 12 and an exposure device (not shown in FIG.
An electrostatic latent image corresponding to the image information is formed by a well-known electrophotographic process such as that shown in FIG. Around the photosensitive drum 11, developing units 14 including developing units 15 to 18 corresponding to yellow (Y), magenta (M), cyan (C), and black (Bk) are provided. The electrostatic latent image formed on the photosensitive drum 11 is developed by one of the developing devices to form a toner image T. In the present embodiment, the photosensitive drum 11 is configured to be negatively charged, and development is performed by a reversal development method. Therefore, all the toners used are of a type that is negatively charged.

Reference numeral 20 denotes an intermediate transfer belt disposed so as to be in contact with the surface of the photosensitive drum 11, which is stretched over a plurality of (six in the present embodiment) rolls 21 to 26. It turns in the direction of arrow B. Here, in the present embodiment, reference numerals 21 and 25 are driven rolls,
Reference numeral 22 denotes a metal idler roll (Idler) used for positioning the intermediate transfer belt 20 and forming a flat primary transfer surface.
roll, reference numeral 23 denotes a tension roll for controlling the tension of the intermediate transfer belt 20 to be constant, 24 denotes a drive roll of the intermediate transfer belt 20, and 26 denotes an opposing roll (backup roll) for secondary transfer.

In particular, in this embodiment, as shown in FIG. 4, the driven rolls 21, 25, the tension roll 23, and the drive roll 24 are grounded, while the idler roll 22 is not grounded.

In the present embodiment, the intermediate transfer belt 20 contains an appropriate amount of carbon black as an antistatic agent in a resin such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate, acryl, vinyl chloride, or various rubbers. Let
Its volume resistivity is 10 ⁶ to 10 ¹⁴ Ωcm and its thickness is 0.1
mm.

Further, at a portion (primary transfer position) of the intermediate transfer belt 20 facing the photosensitive drum 11, a primary transfer device (primary transfer roll in this embodiment) 27 is provided on the back side of the intermediate transfer belt 20. As shown in FIG. 4, by applying a primary transfer bias Vf (positive in this embodiment) opposite to the charge polarity of the toner to the primary transfer roll 27, the photosensitive drum 11 is provided. The upper toner image T is electrostatically attracted to the intermediate transfer belt 20. Here, in the present embodiment, the distance L1 between the primary transfer position and the opposing position between the intermediate transfer belt 20 and the idler roll 22 is set to 30 mm, while the distance L1 between the primary transfer position and the tension roll 23 is set. Is 11
It is set to 0 mm. Incidentally, in FIG.
Reference numeral denotes a drum cleaner for removing toner remaining on the photosensitive drum 11 after the primary transfer.

Further, a secondary transfer device 40 is provided at a secondary transfer position of the intermediate transfer belt 20 facing the transport path of the paper 30 as a recording medium. And a counter roll (back-up roll) 26 disposed on the back side of the intermediate transfer belt 20 and serving as a counter electrode of the secondary transfer roll 28. I have. In this embodiment, as shown in FIG. 4, the secondary transfer roll 28 is grounded, and the backup roll 26 is provided with a secondary transfer bias Vs having the same polarity as the toner charging polarity. 29 is applied stably. Further, a belt cleaner 41 that removes toner remaining on the intermediate transfer belt 20 after the secondary transfer is provided downstream of the secondary transfer device 40. The secondary transfer roll 28 and the belt cleaner 41 are disposed so as to be able to contact and separate from the intermediate transfer belt 20. When a plurality of color images are formed, the toner image before the final color is formed. These are separated from the intermediate transfer belt 20 until T passes through the secondary transfer roll 28 and the belt cleaner 41.

Further, in the present embodiment, the paper transport system is configured to feed the paper 30 from the paper tray 50 to the feed roll 5.
1, the sheet 30 is once stopped by a registration roll (registration roll) 52, and then sent to the secondary transfer position at a predetermined timing. Further, the sheet 30 after the secondary transfer is transferred to the secondary transfer position. The sheet is guided to a conveyance belt 53 via a sheet conveyance guide (not shown), and is conveyed to a fixing device 54 by the conveyance belt 53.

Next, an image forming process of the image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. First, an electrostatic latent image is written on the photosensitive drum 11 and is developed by a developing device corresponding to the electrostatic latent image. For example, if the electrostatic latent image written on the photosensitive drum 11 corresponds to yellow image information, the electrostatic latent image is developed by the developing device 1 containing yellow toner.
5, and a yellow toner image T is formed on the photosensitive drum 11. Then, the toner image T formed on the photosensitive drum 11 is transferred from the photosensitive drum 11 to the surface of the intermediate transfer belt 20 at a primary transfer position where the photosensitive drum 11 contacts the intermediate transfer belt 20. On the other hand, the toner remaining on the photosensitive drum 11 after the primary transfer is removed by the drum cleaner 19.

At this time, when forming a monochrome image,
The toner image T primarily transferred to the intermediate transfer belt 20 is immediately secondary-transferred onto the paper 30. When a color image in which a plurality of color toner images T are superposed is formed, the toner image T is formed on the photosensitive drum 11. Of the toner image T and the primary transfer process of the toner image T are repeated for the number of colors. For example, when a full-color image is formed by superimposing four color toner images, yellow, magenta, cyan and black toner images T are formed on the photosensitive drum 11 every one rotation thereof.
Are formed, and these toner images T are sequentially transferred to the intermediate transfer belt 2.
0 is primarily transferred. On the other hand, the intermediate transfer belt 20 rotates at the same cycle as the photosensitive drum 11 while holding the toner image T that has been primarily transferred first, and the intermediate transfer belt 20 is driven to rotate magenta, cyan, and black every rotation thereof. The toner image T is transferred.

The toner image T primarily transferred to the intermediate transfer belt 20 in this manner is conveyed to a secondary transfer position as the intermediate transfer belt 20 rotates. On the other hand, the paper 30 is supplied to the secondary transfer position at a predetermined timing by the registration roll 52, and the secondary transfer roll 28 nips the paper 30 with the backup roll 26. Then, at the secondary transfer position, the toner image T carried on the intermediate transfer belt 20 is removed by the action of the transfer electric field formed between the secondary transfer roll 28 as the secondary transfer device 40 and the backup roll 26. At the next transfer position, the image is electrostatically transferred to the sheet 30. Thereafter, the sheet 30 on which the secondary transfer has been performed is transferred to the transport belt 5.
The toner image T on the sheet 30 is conveyed to the fixing device 54 through the fixing device 3 and the toner image T is fixed on the sheet 30. On the other hand, the image carrying surface side of the intermediate transfer belt 20 that has passed the secondary transfer position is cleaned by the belt cleaner 41.

The behavior of the toner image T primarily transferred onto the intermediate transfer belt 20 in the above-described image forming process will be described in detail. In the primary transfer process, when the toner image T is transferred onto the intermediate transfer belt 20, a position corresponding to the toner image T on the back side of the intermediate transfer belt 20 is
In accordance with the charge amount of the toner, a charge having a polarity opposite to the charge polarity of the toner (positive in this embodiment) is induced. Accordingly, a positive charge distribution corresponding to the toner image T is formed on the back surface side of the intermediate transfer belt 20.

The amount of charge on the back side of the intermediate transfer belt 20 increases each time the toner image T is transferred in an overlapping manner. That is, the charge amount is larger when the magenta toner image T is transferred onto the yellow toner image T than when the yellow toner image T is transferred. Further, a potential is induced on the back side of the intermediate transfer belt 20 by the charge on the back side of the intermediate transfer belt 20, and this potential also increases as the charge amount increases.

After the primary transfer, the intermediate transfer belt 20 contacts the idler roll 22 while carrying the toner image T. At this time, since the idler roll 22 is not grounded, the idler roll 22 is charged to substantially the same potential as the back surface of the intermediate transfer belt 20. Therefore, the intermediate transfer belt 20
The situation in which the charge on the back side flows into the idler roll 22 is avoided, and the electrostatic force for holding the toner image T on the intermediate transfer belt 20 is maintained, so that the situation in which the toner is scattered is avoided. The Rukoto. Further, in the present embodiment, since the idler roll 22 is made of metal, the contact surface of the idler roll 22 with the intermediate transfer belt 20 has substantially the same potential, and the intermediate transfer belt 20 may be locally discharged. Absent.

In this embodiment, the idler roll 2
The tension roll 23 disposed downstream of the second transfer belt 2 is grounded. However, even if the back surface of the intermediate transfer belt 20 is neutralized by the tension roll 23, it has been found that there is almost no effect. The details will be described later.

Embodiment 2 The present embodiment is almost the same as Embodiment 1, except that the idler roll 22 is grounded by a ground resistor 61 as shown in FIG. Here, the resistance value of the ground resistor 61 is 2000 MΩ. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and a detailed description thereof will be omitted.

In the present embodiment, since the idler roll 22 is grounded via the grounding resistor 61 having a very large resistance value, the charged state at the same potential as the back surface of the intermediate transfer belt 20 is maintained. . As a result, similarly to the first embodiment, the situation where the charge on the back side of the intermediate transfer belt 20 flows into the idler roll 22 is avoided, and the electrostatic force for holding the toner image T on the intermediate transfer belt 20 is maintained. As a result, scattering of toner and retransfer to the photosensitive drum 11 are prevented.

Embodiment 3 This embodiment is almost the same as Embodiment 1, but as shown in FIG. 6, a bias applying device for setting the idler roll 22 to a potential higher than the potential of the back surface of the intermediate transfer belt 20. 62 are provided. In the present embodiment, the bias VB applied to the idler roll 22 by the bias applying device 62 is set to 1000V. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and a detailed description thereof will be omitted.

In the present embodiment, the bias applying device 62
The potential of the idler roll 22 causes the intermediate transfer belt 2
0 is set to be higher than the potential of the back surface. As a result, similarly to the first embodiment, the situation where the charge on the back side of the intermediate transfer belt 20 flows into the idler roll 22 is avoided, and the electrostatic force for holding the toner image T on the intermediate transfer belt 20 is maintained. As a result, scattering of toner and retransfer to the photosensitive drum 11 at the time of primary transfer of the next color can be prevented.

Fourth Embodiment FIG. 7 shows a color image forming apparatus according to a fourth embodiment of the present invention. In the figure, a color image forming apparatus according to the present embodiment includes a plurality of image forming units 100 (specifically, 100K, 100Y, 100M, and 100C) on which respective color component toner images are formed by an electrophotographic method.
And an intermediate transfer belt 110 for sequentially transferring (primary transfer) each color component toner image formed by each image forming unit 100 and a superimposed image transferred on the intermediate transfer belt 110 to a sheet 117 as a recording medium. Batch transfer device 120 for batch transfer (secondary transfer) and intermediate transfer belt 1
Cleaner 140 for removing residual toner on the belt 10
And a fixing device 150 for fixing the batch-transferred images on the sheet 117.

In the present embodiment, the image forming unit 100 for each color component (specifically, 100K, 100Y, 1
00M, 100C) is a latent image carrier 10 such as a photosensitive drum.
1, a uniform charger 102 for charging the latent image carrier 101, a laser exposure device 103 for writing an electrostatic latent image on the latent image carrier 101, and a latent image carrier for accommodating each color component toner. Developing device 10 for visualizing an electrostatic latent image on body 101
4. An electrophotographic device such as a primary transfer roll 105 for transferring each color component toner image on the latent image carrier 101 to the intermediate transfer belt 110 and a cleaner 106 for removing residual toner and the like on the latent image carrier 101 They are arranged sequentially. Also in this embodiment, each latent image carrier 101
Are negatively charged, and development is performed by a reversal development method. Therefore, all the toners used are of a type that is negatively charged. Then, as shown in FIG. 8, the primary transfer roll 105 (specifically, 10K, 105Y, 105
M, 105C) have positive DC biases Vf1 to Vf1, respectively.
Vf4 is applied.

The intermediate transfer belt 110 is stretched over a plurality of (six in the present embodiment) support rolls 131 to 136. Here, the support roll 131 is a driving roll of the intermediate transfer belt 110, and the support rolls 132 and 135.
Is a driven roll, and the support roll 133 is the intermediate transfer belt 11.
A meandering regulating correction roll in a direction substantially perpendicular to the movement direction of 0 (steering roll: provided so as to be tiltable with one axial end as a fulcrum), and a support roll 134 are used as backup rolls of the collective transfer device 120 as described later. The support roll 136 is an idler roll used for positioning the intermediate transfer belt 110 and forming a flat secondary transfer surface.

In this embodiment, the driven roll 132
As shown in FIG. 8, a substrate 132 made of stainless steel is used.
a and a coating layer 132b provided on the substrate 132a.
And Here, the coating layer 132b is made of PFA (perfluoroalkoxy) resin and has a thickness of 100
μm, and the resistance is 12 logΩ. And, this base material 13
2a is grounded. In addition, the correction roll 133 and the idler roll 136 also include the driven roll 132
Similarly, the bases 133a, 13a made of stainless steel
6a and covering layers 133b and 136b, and the bases 133a and 136a are grounded.
The drive roll 131 and the driven roll 135 are made of stainless steel, and are each grounded.

The intermediate transfer belt 110 is made of a resin such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate or various rubbers containing an appropriate amount of carbon black or the like, and has a volume resistivity of 10 ⁶ to 10 ¹⁵ Ω · cm. And its thickness is set to 0.1 mm.

Further, the collective transfer device 120 includes a secondary transfer roll 113 disposed in pressure contact with the toner carrying surface of the intermediate transfer belt 110 and a secondary transfer roll 113 disposed on the back side of the intermediate transfer belt 110. A backup roll 114 (also used as a support roll 134) serving as an electrode is provided, and a power supply roll 115 to which a bias having the same polarity as the charged polarity of the toner is stably applied is abutted on the backup roll 114. On the exit side of the nip area of the secondary transfer roll 113, a peeling member 121 is disposed.

In this embodiment, the backup roll 114 is made of EPDM (ethylene propylene diene rubber) having a two-layer structure in which the outer periphery of a metal core is covered with a foamed elastic material layer and an outer conductive layer. Was. The outer conductive layer is a semiconductive EPDM foam rubber in which carbon black is dispersed at 15 to 35% by weight, and the thickness of the conductive layer is 0.5 to 1.5.
mm, and its surface resistivity is 10 ⁷ to 10
It is controlled in the resistance area of ¹⁰ Ω / □.

The secondary transfer roll 113 is provided with a carbon black having a thickness of 5 to 20 μm via a skin layer on a core layer made of a metal core material and a carbon black dispersed and foamed EPDM material fixed around the metal core material. One having a coating layer made of a dispersed fluororesin-based material was used. The volume resistivity between the metal core and the coating layer is 1
0 ⁴ [Omega] cm is to 10 ⁶ [Omega] cm, also roll hardness is 45 ° to 20 ° in Asker C hardness.

As shown in FIG. 8, a collective transfer bias Vs of a negative polarity is applied to the power supply roll 115. As shown in FIG. 7, a cleaning blade 122 made of, for example, urethane rubber is attached to the secondary transfer roll 113 to remove dirt attached to the secondary transfer roll 113, thereby preventing the back surface of the paper 117 from being stained. ing. Further, between the collective transfer device 120 and the belt cleaner 140, there is provided a static eliminator 112 for removing residual charges of the intermediate transfer belt 110 before the cleaning process.

Further, in the present embodiment, the paper transport system feeds the paper 117 from the paper tray 116 to the secondary transfer position at a predetermined timing, and transports the paper 117 after the secondary transfer. The sheet is guided to a belt 118, and is conveyed to the fixing device 150 by the conveyance belt 118.

Next, an image forming process of the color image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. More specifically, for example, when the color image forming apparatus is configured as a digital color copying machine, a document set on a document table (not shown) is read by a color image reading device, and the read signal is read by an image signal processing unit. , And temporarily store the digital image signals in a memory. Based on the stored digital image signals of four colors (K, Y, M, and C), toner images of each color are formed. .

That is, the image forming unit 1 according to the digital image signal of each color inputted from the image signal processing means.
00 (specifically, 100K, 100Y, 100M, 10
0C) are respectively driven. Then, each image forming unit 1
At 00, an electrostatic latent image corresponding to the digital signal is written by the laser exposure unit 103 on the latent image carrier 101 uniformly charged by the uniform charger 102. Then, each of these electrostatic latent images is stored in a developing device 1 containing toner of each color.
04 to form toner images of the respective colors.
When this color image forming apparatus is configured as a device such as a printer, it is only necessary to form toner images of each color based on an image signal input to the image signal processing means from the outside.

The toner image formed on each latent image carrier 101 is connected to each latent image carrier 101 and the intermediate transfer belt 1.
The latent image is transferred from the latent image carrier to the surface of the intermediate transfer belt 110 by the primary transfer roll 105 at the primary transfer position where the transfer belt contacts the intermediate transfer belt 110.

The toner image primary-transferred onto the intermediate transfer belt 110 in this manner is superposed on the intermediate transfer belt 110, and is conveyed to the secondary transfer position as the intermediate transfer belt 110 rotates. On the other hand, the paper 117 is supplied to the secondary transfer position at a predetermined timing, and the secondary transfer roll 113 is
Nip.

Then, at the secondary transfer position, the transfer electric field formed between the secondary transfer roll 113 serving as the collective transfer device 120 and the backup roll 114 causes
The toner image carried on the intermediate transfer belt 110 is
17 are collectively transferred. The sheet 117 to which the toner image has been transferred is conveyed to the fixing device 150 by the conveyance belt 118, and the toner image is fixed. Further, the intermediate transfer belt 110 after the secondary transfer has a residual charge removed by the charge eliminator 112, and the intermediate transfer belt 11 after the secondary transfer.
The toner remaining on 0 is cleaned by the belt cleaner 140.

In this embodiment, before the intermediate transfer belt 110 after the primary transfer reaches the collective transfer device 120, the driven roll 132, the correction roll 133, and the idler roll 136, while carrying the toner image T, However, as described above, these driven rolls 13
2. Since the correction roll 133 and the idler roll 136 are grounded via the resistance of the coating layer 132b, they are charged to the same potential as the potential on the back side of the intermediate transfer belt 110. Therefore, the situation where the charge on the back side of the intermediate transfer belt 110 flows into the driven roll 132, the correction roll 133, and the idler roll 136 is avoided, and the electrostatic force for holding the toner image T on the intermediate transfer belt 110 is maintained. Therefore, the situation in which the toner is scattered is avoided.

Embodiment 5 This embodiment is almost the same as Embodiment 4, but as shown in FIG. 9, the driven roll 132 and the correction roll 133
And a bias applying device 161 for setting the idler roll 136 to a potential equal to or higher than the potential of the back surface of the intermediate transfer belt 110. In the present embodiment, the applied bias VR by the bias applying device 161 is set to 1000V. Note that components similar to those of the fourth embodiment are denoted by the same reference numerals as those of the fourth embodiment, and a detailed description thereof will be omitted.

In this embodiment, the bias applying device 16
By means of 1, the potentials of the driven roll 132, the correction roll 133, and the idler roll 136 are set to be higher than the potential of the back surface of the intermediate transfer belt 110. Thus, similarly to the fourth embodiment, the electric charges on the back side of the intermediate transfer belt 110 are transferred to the driven roll 132, the correction roll 133, and the idler roll 136.
Is prevented from flowing into the intermediate transfer belt 11.
The electrostatic force for holding the toner image T on the zero is maintained, and as a result, scattering of the toner is prevented.

In the first to fifth embodiments, the image forming apparatus using the negative polarity toner has been described. However, the present invention is not limited to this, and the image forming apparatus using the positive toner may be used. It is also applicable to
However, in the image forming apparatus described in the third embodiment, the idler roll 22 is used, and in the image forming apparatus described in the fifth embodiment, the driven roll 132 and the correction roll 13 are used.
3. It is necessary to reverse the polarity of the bias applied to the idler roll 136.

[0063]

Example 1 Using the image forming apparatus shown in FIGS. 3 and 4, the distance L1 from the primary transfer position to the idler roll 22 was changed to investigate the occurrence of image quality defects. Then, a comparison was made between two cases where the idler roll 22 was grounded and not grounded. The experimental conditions are as follows. ○ Intermediate transfer belt: Polyimide resin with carbon black dispersed ・ Surface resistivity: 10 ¹² Ω / □ (Mitsubishi Yuka Hiresta, using HR Flow®, 100V, 30sec measurement value) ・ Volume resistivity: 10 ⁹ Ωcm (Mitsubishi Oil・ Hiresta, HR flow meter, 100V, 30sec measurement) ・ Thickness: 80μm ・ Time constant: 1.0sec or less ○ Primary transfer condition: 25μA (constant current) ○ Belt transport speed: 220mm / sec ○ Created image: Process Black (solid image of yellow + magenta + cyan) superimposed on the toner image T on the intermediate transfer belt 20
When the toner image T reached the primary transfer position again after passing through the idler roll 22, it was visually confirmed whether the toner image T was re-transferred onto the photosensitive drum 11.

FIG. 10 shows the results. Idler roll 22
When the distance L1 is shorter, the image quality defect is more likely to occur as the distance L1 is shorter, and a completely defective image is obtained when L1 = 30 mm. On the other hand, when the idler roll 22 is not grounded, the image quality defect is lower when L1 = 30 mm. It was confirmed that there was no image quality defect at all.

This can be explained as follows. When the idler roll 22 is grounded, as shown in FIG.
The intermediate transfer belt 20 after the primary transfer is an idler roll 22
When passing through the contact portion, the charge Q for carrying the toner image T induced on the back side of the intermediate transfer belt 20 at the time of the primary transfer flows into the ground side via the idler roll 22 as the current I. . Accordingly, on the back side of the intermediate transfer belt 20 after passing through the idler roll 22, the charge for carrying the toner image T is rapidly removed, and for example, the toner T _{A in the} area where the charge on the back side has not been removed is left. Is to be held on the intermediate transfer belt 20,
Or scattered from the intermediate transfer belt 20 in the rear surface of the charge has been removed area (indicated by reference numeral T _B), also since the adhesion force is very weak as not scattered tentatively, sensitive to the next primary transfer so that the thus re-transferred to the body drum 11 side (in the figure indicated by reference numeral T _C).

On the other hand, when the idler roll 22 is not grounded, when the intermediate transfer belt 20 after the primary transfer passes through the contact portion with the idler roll 22, as shown in FIG. The charge Q on the back surface of the intermediate transfer belt 20 does not flow to the idler roll 22 side.
The electric charge Q on the back surface is held as it is, that is, charge elimination is prevented. Accordingly, it is understood that blurring due to scattering of toner and re-transfer (re-transfer) to the photosensitive drum 11 at the time of the next primary transfer can be prevented. This is because, in this embodiment, the potential of the back surface of the intermediate transfer belt 20 immediately after the primary transfer on which the process black was formed was about 500 V, whereas the potential of the idler roll 22 disposed non-ground was the same potential. (Approximately 500 V).

As another result, idler roll 2
It was confirmed that no image quality defect occurred when L1 = 110 mm even when 2 was grounded. This can be explained as follows. In this embodiment, the intermediate transfer belt 20 is made of a semiconductive material. That is, the intermediate transfer belt 2
0 has self-static elimination performance. When this type of intermediate transfer belt 20 is used, the charge on the intermediate transfer belt 20 gradually decreases with time. In the case of this embodiment, L
At the position of 1 = 110 mm, the electric charge on the back side of the intermediate transfer belt 20 has already been reduced due to the self-static elimination performance of the intermediate transfer belt 20, and the electric charge on the back surface of the intermediate transfer belt 20 when it comes into contact with the grounded idler roll 22. It is considered that no sharp decrease occurred, and no image quality defect was caused. In the first embodiment, the tension roll 23 is disposed 110 mm downstream from the primary transfer position for the same reason. Further, in the image forming apparatus of this embodiment, the distance at which the image quality defect does not occur when the idler roll 22 is in contact with the ground is 110 mm.
0 because it changes depending on the resistance of 0, the moving speed, etc.
It is not always 0 mm.

Example 2 Using the image forming apparatus shown in FIGS. 3 and 5, under the condition that the distance L1 from the primary transfer position to the idler roll 22 was fixed at 30 mm, the resistance value of the ground resistance 61 and the image quality defect were evaluated. An experiment was performed on the correlation with occurrence. The other experimental conditions are the same as in Example 1.

FIG. 12 shows the results. According to this, it was confirmed that the higher the ground resistance of the idler roll 22, the more difficult it is to cause image quality defects. In particular, paying attention to the relationship between the roll potential induced on the idler roll 22 by the ground resistance 61 and the state of occurrence of the image quality defect, under the condition that the ground resistance at which the roll potential is 500 V or more is selected, the image quality defect is low. It turns out that it does not occur. As described in the first embodiment, the potential on the back side of the intermediate transfer belt immediately after the primary transfer on which the process black is formed is about 500 V. Therefore, when a resistance higher than this is selected, the resistance induced on the idler roll 22 is selected. It can be said that static elimination is prevented and image quality defects are prevented.

Embodiment 3 Using the image forming apparatus shown in FIGS. 3 and 6, the bias application device 62 applies the voltage to the idler roll 22 under the condition that the distance L1 from the primary transfer position to the idler roll 22 is fixed to 30 mm. An experiment was conducted on the correlation between the applied bias VB and the occurrence of image quality defects. Here, the bias V
B is applied through a varistor. The other experimental conditions are the same as in Example 1.

FIG. 13 shows the results. According to this, it was confirmed that the higher the rated voltage of the varistor, the more difficult it is for image quality defects to occur. In particular, focusing on the relationship between the roll potential induced on the idler roll 22 by the bias VB and the state of occurrence of image quality defects, the roll potential is 500
It can be seen that no image quality defect occurs under the condition that a varistor of V or more is selected. As described in the first embodiment, since the potential on the back side of the intermediate transfer belt immediately after the primary transfer on which the process black is formed is about 500 V, when a varistor in which a higher potential is induced by the idler roll 22 is selected. It can be said that static elimination is prevented and image quality defects are prevented.

Embodiment 4 In the image forming apparatus shown in FIG.
The magnitude of the voltage induced in the correction roll 133 and the idler roll 136 was investigated. In this investigation, as shown in FIG. 14, each of the rolls 132, 133, and 136 was made of stainless steel, and voltmeters 171 to 173 were attached to these rolls, respectively. The experimental conditions are as follows. ○ Intermediate transfer belt ・ Volume resistivity: 10 ¹¹ to ¹³ Ωcm ・ Time constant: 1.5 sec or less ○ Primary transfer condition: 3 to 4 kV ○ Belt transfer speed: 264 mm / sec In addition, the primary transfer roll 105c and the driven roll 132 The distance is 200 mm, the driven roll 132 and the correction roll 13
3 is 50 mm, and the distance between the correction roll 133 and the idler roll 136 is 300 mm.

FIG. 15 shows the results. According to this, although the induced voltage decreases with the distance from the primary transfer roll 105c, the idler roll 136 (the primary transfer roll 10c).
5 to 550 mm), a voltage of about 400 V is induced. This is because the resistance and the time constant of the intermediate transfer belt 110 used in the present embodiment are higher than those of the intermediate transfer belt 20 used in the first embodiment.
It is due to the lower than. Another effect is that the conveyance speed of the intermediate transfer belt 110 used in the present embodiment is higher than that of the intermediate transfer belt 20 used in the first embodiment. Further, since the driven roll 132 and the correction roll 133 are arranged close to each other, it can be seen that the voltage induced in both is hardly changed. Thus, in the image forming apparatus shown in FIG. 7, in addition to the driven roll 132, the correction roll 1
It is understood that it is necessary to provide a potential holding unit also for the idler roll 33 and the idler roll 136.

Example 5 The driven roll 1 used in the image forming apparatus shown in FIGS. 7 and 8
In order to examine the optimum materials for the components 32, the correction roll 133, and the idler roll 136, an investigation was conducted using an experimental apparatus shown in FIG. In FIG.
Reference numeral 81 denotes a sheet metal; 182, a DC power supply; 183, an ammeter. The intermediate transfer belt 110 and the driven roll 132 are placed on the sheet metal 181;
The resistance value was calculated from the amount of current when a DC voltage was applied between the sheet metal 181 and the sheet metal 181. In this experiment, as the driven roll 132, a stainless steel substrate 132a alone without a coating layer 132b, a stainless steel substrate 132a with an alumite layer provided as a coating layer 132b, a stainless steel substrate 132a on the coating layer 132b
Provided with a PET layer as a base material of stainless steel 132
The one provided with a PFA layer as the coating layer 132b on a was used. The results are shown in FIG.

Next, the following rolls 132 were incorporated into the image forming apparatus shown in FIGS. 7 and 8, and the scattering of toner images was investigated. As shown in FIG. 18, a sheet metal 191 that is grounded at a distance of 5 mm is disposed at a position facing the driven roll 132, and the toner image T formed on the intermediate transfer belt 110 The evaluation was performed by evaluating the density of toner scattered and adhering to the facing surface 191a side of the sheet metal 191 during the passage.

FIG. 19 shows the results. According to this, when the PET layer and the PFA layer are used as the coating layer 132b, it is understood that the scattering of the toner can be prevented.

According to the experiment of the present inventor, the coating layers 132b, 133b, and 136b of the driven roll 132, the correction roll 133, and the idler roll 136 are respectively PFA, P
It has been found that toner does not scatter in the vicinity of each roll even when it is made of ET and urethane, that is, when a resistance is provided with a gradient from upstream to downstream. This is because the voltage induced on the back surface of the intermediate transfer belt 110 decreases with the distance from the primary transfer roll 105c (see Embodiment 4).

Example 6 In order to determine the bias applied to the driven roll 132 in the image forming apparatus shown in FIGS. 7 and 9, a test was conducted using an experimental apparatus shown in FIG. In this experiment, the driven roll 1
As the driven roll 132, a DC power source 182 capable of applying both positive and negative voltages is connected to the driven roll 132.
The density of the toner scattered and adhered to the opposing surface 191a of the 91 was evaluated.

FIG. 20 shows the results. According to this, it is understood that scattering of toner can be prevented by applying a voltage of +500 V or more to the driven roll 132.
According to the experiment of the present inventor, a gradient is applied to the driven roll 132, the correction roll 133, and the idler roll 136 from the upstream to the downstream (for example, 650 V, 600 V, and 450 V are applied, respectively). Also in this case, it has been found that toner does not scatter near each roll. This is because the voltage induced on the back surface of the intermediate transfer belt 110 decreases with the distance from the primary transfer roll 105c (see Embodiment 4).

[0080]

As described above, according to the present invention,
Potential holding means is provided to the first contact member that the intermediate transfer belt after passing through the primary transfer means first contacts or all the contact members that contact the intermediate transfer belt after passing through the primary transfer means to reach the secondary transfer means. In this case, the charge on the back surface of the intermediate transfer belt is prevented from being eliminated, so that scattering of the toner image transferred onto the intermediate transfer belt can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating Embodiment 1 of the image forming apparatus to which the present invention has been applied.

FIG. 4 is an enlarged view around an intermediate transfer belt of the image forming apparatus according to the first embodiment;

FIG. 5 is an enlarged view around an intermediate transfer belt of the image forming apparatus according to the second embodiment.

FIG. 6 is an enlarged view around an intermediate transfer belt of the image forming apparatus according to Embodiment 3;

FIG. 7 is an explanatory diagram illustrating Embodiment 4 of an image forming apparatus to which the present invention has been applied.

FIG. 8 is an enlarged view around an intermediate transfer belt of an image forming apparatus according to a fourth embodiment.

FIG. 9 is an enlarged view around an intermediate transfer belt of an image forming apparatus according to Embodiment 5;

FIG. 10 is a table showing experimental results of Example 1.

FIG. 11A is a schematic diagram illustrating a behavior of toner on an intermediate transfer belt when an idler roll is grounded,
FIG. 4B is a schematic diagram illustrating the behavior of the toner on the intermediate transfer belt when the idler roll is not grounded.

FIG. 12 is a chart showing experimental results of Example 2.

FIG. 13 is a table showing experimental results of Example 3.

FIG. 14 is an explanatory diagram illustrating an induced voltage measuring device according to a fourth embodiment.

FIG. 15 is a graph showing the experimental results of Example 4.

FIG. 16 is an explanatory diagram showing an outline of a resistance measuring device used in Example 5.

FIG. 17 is a chart showing a relationship between a configuration of a driven roll and a resistance value.

FIG. 18 is an explanatory diagram showing an outline of an evaluation device for investigating scattering of toner used in Examples 5 and 6.

FIG. 19 is a graph showing the experimental results of Example 5.

FIG. 20 is a graph showing the experimental results of Example 6.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Roll member, 3 ... Intermediate transfer belt,
4 primary transfer means, 5 recording medium, 6 secondary transfer means,
7 First contact member, 8, 10 Potential holding means (antistatic means), 9 Contact member, 11 Photoconductor drum, 20 Intermediate transfer belt, 21 to 26 Roll, 22 Idler roll, 27 Primary transfer device (primary transfer roll), 28 ...
Secondary transfer roll, 30 ... paper, 40 ... secondary transfer device, 6
DESCRIPTION OF SYMBOLS 1 ... Ground resistance, 62 ... Bias applying device, 100 ... Image forming unit, 105 ... Primary transfer roll, 110 ... Intermediate transfer belt, 120 ... Batch transfer device, 132 ... Follower roll 132a ... Base material, 132b ... Coating layer, 133 ... Correction roll, 136 Idler roll, 161 Bias applying device

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yukio Hayashi 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Nobuka Takahashi 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. F-term (Reference) 2H027 DC04 EA03 EA10 EB04 ED15 ED16 ED24 ED27 EE05 2H030 AB02 AD01 AD17 BB02 BB23 BB24 BB42 BB44 BB54 BB55 BB56 2H032 AA05 AA15 BA01 BA05 BA09 BA18 BA23 BA26 BA30 CA02 CA13

Claims (15)

[Claims] An image transfer member on which a toner image corresponding to image information is formed and supported; an intermediate transfer belt rotatably stretched and supported by a plurality of roll members and arranged to face the image support; An image forming apparatus comprising: a primary transfer unit that sequentially transfers a toner image on a carrier onto an intermediate transfer belt; and a secondary transfer unit that collectively transfers a toner image on the intermediate transfer belt to a recording medium. Image forming characterized in that a first contact member with which the intermediate transfer belt contacts first after passing the means is provided with a potential holding means for holding the surface potential of the first contact member at or above the charged potential of the back surface of the intermediate transfer belt. apparatus. 2. The image forming apparatus according to claim 1, wherein said potential holding means is means for disposing said first contact member in a non-grounded state. 3. The image forming apparatus according to claim 1, wherein the potential holding unit is a resistance grounding unit that grounds the first contact member via a high-resistance body. 4. The image forming apparatus according to claim 3, wherein the high-resistance body comprises a coating layer formed on a surface of the first contact member. 5. The image forming apparatus according to claim 4, wherein the coating layer is made of a PET resin or a PFA resin. 6. The image forming apparatus according to claim 1, wherein the potential holding unit is a bias applying unit that applies a DC bias having the same polarity as the potential of the back surface of the intermediate transfer belt to the first contact member. An image forming apparatus comprising: 7. An image carrier on which a toner image corresponding to image information is formed and carried; an intermediate transfer belt rotatably stretched and supported by a plurality of roll members and disposed opposite to the image carrier; An image forming apparatus comprising: a primary transfer unit that sequentially transfers a toner image on a carrier onto an intermediate transfer belt; and a secondary transfer unit that collectively transfers a toner image on the intermediate transfer belt to a recording medium. Potential holding means for holding the surface potential of the contact member at or above the charging potential of the back surface of the intermediate transfer belt is provided on all the contact members that come into contact with the intermediate transfer belt after passing through the means and reach the secondary transfer means. An image forming apparatus characterized in that: 8. An image forming apparatus according to claim 7, wherein said potential holding means is means for arranging said contact member non-grounded. 9. The image forming apparatus according to claim 7, wherein the potential holding unit is a resistance grounding unit that grounds the contact member via a high resistance body. 10. The image forming apparatus according to claim 9, wherein the high-resistance body is formed of a coating layer formed on the surface of the contact member. 11. The image forming apparatus according to claim 10, wherein the coating layer is made of a PET resin or a PFA resin. 12. The image forming apparatus according to claim 7, wherein the potential holding unit is a bias applying unit that applies a DC bias having the same polarity as the potential of the back surface of the intermediate transfer belt to the contact member. Image forming apparatus. 13. The image forming apparatus according to claim 12, wherein the bias applying unit is shared. 14. An image carrier on which a toner image corresponding to image information is formed and carried; an intermediate transfer belt rotatably stretched and supported by a plurality of roll members and arranged to face the image carrier; An image forming apparatus comprising: a primary transfer unit that sequentially transfers a toner image on a carrier onto an intermediate transfer belt; and a secondary transfer unit that collectively transfers a toner image on the intermediate transfer belt to a recording medium. An image forming apparatus comprising: a first contact member that first contacts the intermediate transfer belt after passing the unit; and a charge elimination preventing unit for preventing charge elimination of charges on the back side of the intermediate transfer belt. 15. An image carrier on which a toner image corresponding to image information is formed and carried; an intermediate transfer belt rotatably stretched and supported by a plurality of roll members and arranged to face the image carrier; An image forming apparatus comprising: a primary transfer unit that sequentially transfers a toner image on a carrier onto an intermediate transfer belt; and a secondary transfer unit that collectively transfers a toner image on the intermediate transfer belt to a recording medium. An image characterized in that all contact members that come into contact with the intermediate transfer belt after passing through the means until the intermediate transfer belt reaches the secondary transfer means are provided with a charge elimination preventing means for preventing charge elimination on the back side of the intermediate transfer belt. Forming equipment.