JPH11184275A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing a transfer dust, and obtaining the clear image. SOLUTION: In this image forming device provided with, a photoreceptor drum 100 carrying the toner image, an intermediate transfer belt 501 held in contact with the photoreceptor drum 100, for transferring the toner image on the photoreceptor drum 100, and a bias applying member 513 disposed on a rear side of the intermediate transfer belt 501 being the opposite side with respect to a nip part 520 side, in the nip part 520 between the photoreceptor drum 100 and the intermediate transfer belt 501, applying the transfer bias of the reverse polarity to the toner, the bias applying member 513 is held in contact with the intermediate transfer belt 501 on an area straddling over both the nip part 520 and the downstream side section 525 on the downstream side thereof. In such a constitution, the device is made possible to obtain the clear image by preventing the transfer dust.

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, and more particularly to an image forming apparatus having an intermediate transfer member and a bias applying member for applying a bias having a polarity opposite to that of toner to the intermediate transfer member.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus, FIG.
As shown in FIG. 2, between the image carrier 10 (hereinafter, referred to as a “photoconductor drum”) and a transfer unit that transfers a toner image to transfer paper,
Some intermediate transfer members employ an intermediate transfer system in which an intermediate transfer belt 11 is disposed. This type of intermediate transfer system generally includes an indirect application system and a direct application system. In the indirect application method, as shown in FIG. 13, the rotation of the intermediate transfer belt 11 is separated from a contact surface 13 (hereinafter, referred to as a “nip portion”) between the photosensitive drum 10 on which the toner image is formed and the intermediate transfer belt 11. In this method, a bias is applied by a bias roller 15 disposed on the downstream side in the direction, and the toner image on the photosensitive drum 10 is transferred to the intermediate transfer belt 11. In the direct application method, as shown in FIG.
This is a method in which an application member 17 for applying a bias is provided in the nip portion 13 and a transfer bias is applied therefrom. In both types, the ground roller 19 is disposed on the upstream side of the intermediate transfer belt, away from the nip portion 13, so that the configuration does not require static elimination. Further, as the intermediate transfer belt 11 used for these intermediate transfer members, a so-called medium resistance belt having a volume resistivity of less than 10 ¹³ Ω · cm has been mainly used.

[0003] In addition, as shown in FIG.
The ground brush 12 is provided at the inlet end 14 on the upstream side of
A configuration for preventing transfer dust due to toner scattering from the photosensitive drum to the intermediate transfer belt 11 is known.

[0004]

However, in the indirect application method, as is apparent from FIG. 13, even if a bias of, for example, 2 kV is applied from the bias roller 15, the bias at the nip 13 is 1.5 kV. Will decrease. This is because the intermediate transfer belt 1 has a medium resistance as described above.
1 and the applied bias is the earth roller 1
This is because it flows to 9. For this reason, the toner holding force of the intermediate transfer belt 11 is weakened. Therefore, as shown in FIG. 12
As shown in (1), image blur called transfer dust occurs.

On the other hand, the volume resistivity is 10 ¹³ Ω · cm
The above high resistance (in this specification, the high resistance standard is 10
^Even if an intermediate transfer belt of ( ¹³ Ω · cm or more) is used, the resistance is too high and current does not easily flow, so that an electric field is not easily generated in the nip portion 13. Therefore, in such a high-resistance intermediate belt, a conductive layer having a volume resistivity of less than 10 ¹³ Ω · cm is preferable on the back surface of the intermediate transfer belt 11,
Since current flows to the ground roller 19 and an electric field is hardly generated, there is a problem that transfer is inferior.

In the direct application method, as is apparent from FIG. 14, even when a bias of, for example, 2 kV is applied from the application member 17, the discharge at the outlet end 16 on the bias roller side of the nip 13 is weak. However, since the toner holding power cannot be increased, there is a disadvantage that transfer dust is deteriorated.

In the configuration in which the ground brush 12 is provided in FIG. 15, the electric field stops at the position of the ground brush 12 and the electric field at the entrance end 14 which is the other end of the nip 13 disappears. Can be prevented from scattering. However, the electric field at the outlet end 16 is 1 kV even when a bias of 2 kV is applied from the bias roller 15, for example. Therefore, since the electric field is reduced as compared with the above-described indirect method, transfer dust tends to occur.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of preventing transfer dust and obtaining a clear image.

[0009]

According to a first aspect of the present invention, there is provided an image bearing member for carrying a toner image, an intermediate transfer member in contact with the image bearing member and transferring the toner image on the image bearing member, An image forming apparatus comprising: a bias applying member that is provided on the back surface of the intermediate transfer body opposite to the contact surface side at a contact position between the carrier and the intermediate transfer body and that applies a transfer bias having a polarity opposite to that of the toner. The bias applying member is in contact with the intermediate transfer member in a region that covers both the contact position and a non-contact position downstream of the contact position.

According to the first aspect of the present invention, the transfer bias is applied by the bias applying member that is in contact with the contact position on the back side of the intermediate transfer belt and the non-contact position. Since the image can be transferred without being transferred, the image becomes clear. Further, since the bias applying member partially contacts the contact position and applies the transfer bias, the potential of the transfer bias is not impaired. Therefore, the potential holding power is increased, and the toner holding property is enhanced by increasing the potential holding power, thereby preventing transfer dust. Further, a minute discharge is generated from a portion of the bias applying member that is not in contact with the intermediate transfer belt, and this discharge prevents toner from scattering.

According to a second aspect of the present invention, in the first aspect, the intermediate transfer member has a volume resistivity of 10 ¹² Ω · cm or more.

According to the second aspect of the invention, since the intermediate transfer belt has a high volume resistivity, it is difficult for current to flow, and the potential of the applied transfer bias is hard to decrease, so that the toner holding power is improved and transfer dust is reduced. To prevent.

[0013] The invention according to claim 3 is the invention according to claim 1 or 2.
In the invention described in (1), the bias applying member is constituted by a brush-like member.

According to the third aspect of the present invention, a brush-like member is used as the bias applying member, so that the configuration is simplified and the apparatus is downsized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming section 90 of a color copying machine to which the present invention is applied. This color copier includes an image forming unit 90 shown in FIG. 1, a color image reading unit (hereinafter, referred to as a “color scanner”) (not shown), a paper feeding unit, a control unit, and the like.

The color scanner reads color image information of a document for each color separation light of red, green, and blue, for example, and converts it into an electric image signal. Then, based on the red, green, and blue color separation image signal intensity levels obtained by the color scanner, a color conversion process is performed by an image processing unit to obtain black, cyan, magenta, and yellow color image data. I have.

The image forming section 90 includes a photosensitive drum 100,
A charger 200 as a charging unit, a photoconductor cleaning device 300 including a cleaning blade and a fur brush, a writing optical unit (not shown) as an exposure unit, and a revolver developing unit 4 as a developing unit
00, intermediate transfer unit 500, paper transfer unit 60
0 and a fixing unit using a fixing roller pair 701.

The photoreceptor drum 100 rotates in the direction of the arrow in the figure, and around it, a charger 200, a photoreceptor cleaning device 300, a selected developing device of the revolver developing unit 400, and an intermediate transfer member of the intermediate transfer unit 500. And an intermediate transfer belt 501 are disposed.

The writing optical unit converts the color image data from the color scanner into an optical signal, performs optical writing corresponding to the image of the document on the surface of the photosensitive drum 100 uniformly charged by the charging charger 200, and An electrostatic latent image is formed on the body drum 100. This writing optical unit can be composed of, for example, a semiconductor laser as a light source, a laser emission drive control unit, a polygon mirror and its rotation motor, an f / θ lens, a reflection mirror, and the like.

The revolver developing unit 400 includes a black developing device 401 using a black toner, a cyan developing device 402 using a cyan toner, a magenta developing device 403 using a magenta toner, a yellow developing device 404 using a yellow toner, and an arrow indicating the entire unit. It comprises a developing revolver drive unit and the like which rotate in the direction. Each developing device installed in the revolver developing unit 400 includes a developer paddle and a developing roller, which rotate by bringing a spike of developer into contact with the surface of the photosensitive drum 100 to develop an electrostatic latent image, by an arrow. It is composed of a developing roller driving unit which rotates in the direction.

In this embodiment, the toner in each developing unit is charged to a negative polarity by stirring with the ferrite carrier, and a negative DC voltage is applied to each developing sleeve by a developing bias power supply as a developing bias applying means (not shown). Vd
A developing bias power source in which an AC voltage Vac (AC component) is superimposed on c (DC component) is applied, and the developing sleeve is biased to a predetermined potential with respect to the metal base layer of the photosensitive drum 100.

In the standby state of the color copying machine, the revolver developing unit 400 is stopped at the home position where the black developing device 401 is located at the developing position. The reading of the color image data is started, and the optical writing by the laser beam 91 and the formation of the electrostatic latent image are started based on the color image data (hereinafter, the electrostatic latent image based on the black image data is referred to as “black electrostatic latent image”). And cyan, magenta and yellow). Before the electrostatic latent image tip reaches the black developing position so that development can be performed from the tip of the black electrostatic latent image, the black electrostatic latent image is developed with black toner by the black developing device 401. Thereafter, the developing operation of the black electrostatic latent image area is continued, but when the rear end of the black electrostatic latent image passes through the black developing position, the developing unit for the next color is immediately moved to the developing position. Revolver developing unit 400
Rotates. This is completed at least before the leading end of the electrostatic latent image based on the next image data arrives.

The transfer unit 500 includes an intermediate transfer belt 501 as an intermediate transfer member stretched over a plurality of rollers. Around this intermediate transfer belt 501, a precharger (hereinafter referred to as a pre-transfer charging means) is provided.
502, a secondary transfer belt 601 as a transfer material carrier of the paper transfer unit 600, and a secondary transfer bias roller 60 as a secondary transfer bias applying unit.
5, a conductive brush roller 514 as a conductive brush member also serving as an intermediate transfer neutralizing unit and an intermediate transfer body cleaning unit, and a lubricant applying brush 5 as a lubricant applying unit
05 and the like are arranged to face each other.

The intermediate transfer belt 501 is driven to rotate in the direction of the arrow and transmits a rotational force to the intermediate transfer belt 507, a belt drive roller 508, a belt tension roller 509, a secondary transfer opposed roller 510, a cleaning opposed roller 511, It is stretched around an earth roller 512 as a pre-transfer neutralization unit. Each roller is formed of a conductive material and is grounded.

As shown in FIG. 2, the intermediate transfer belt 501 includes a surface layer 501a, an intermediate layer 501b, and a base layer 5a.
It is preferable to use a belt material having a multilayer structure made of a material having a volume resistivity of 10 ¹² Ω · cm or more.
In this embodiment, a belt having a volume resistivity of 10 ¹³ Ω · cm is used. The outer peripheral side contacting the photosensitive drum 100 is the surface layer 501a, and the inner peripheral side is the base layer 50a.
1c. Further, the intermediate layer 501b and the base layer 501c
An adhesive layer 501d for bonding the two layers is interposed between the two.

In a transfer section (hereinafter referred to as a primary transfer section) for transferring the toner image on the photosensitive drum 100 to the intermediate transfer belt 501, a float roller 507 and an earth roller 5
At 12, the intermediate transfer belt 501 is stretched so as to be pressed against the photosensitive drum 100 side, so that the photosensitive drum 1
A nip 520 is formed in a predetermined area where the intermediate transfer belt 501 and the intermediate transfer belt 501 are in contact with each other.

As shown in FIG. 3, the nip 520 has an outlet 521 at one end on the downstream side and an inlet 523 at the other end on the upstream side. Further, the float roller 507 and the ground roller 512 are apart from the nip 520. Therefore, the intermediate transfer belt 501 forms a downstream portion 525 that is not in contact with the photosensitive drum 100 between the outlet 521 and the float roller 507. Similarly, between the entrance 523 and the ground roller 512, the photosensitive drum 100
, And forms an upstream portion 526. A bias applying member 51 for applying a transfer bias is provided on the inner peripheral surface of the intermediate transfer belt 501 in the nip portion 520.
3 are provided.

The bias applying member 513 shown in FIG. 4 includes a contact portion 516 made of a brush-like member and a primary transfer power source 530. This bias applying member is a primary transfer charge applying unit, and is controlled to a predetermined current or voltage by a primary transfer power supply 530 controlled by a constant current or a constant voltage according to the number of superimposed toner images. For example, a transfer bias of 2 kV is supplied. The contact portion 516 is in contact with the back surface of the intermediate transfer belt at the nip portion 520 opposite to the contact surface with the photosensitive drum 100. In addition, the contact portion 516
It abuts across the outlet 521. In this embodiment,
The width of the contact portion 516 in the moving direction of the intermediate transfer belt (hereinafter, simply referred to as “width”) is set to, for example, 8 mm. The contact part 516 is connected to the nip part 5 from the outlet part 521.
A first abutment portion 516a abutting on the outlet 20;
The second contact portion 51 abutting from 1 to the downstream portion 525
6b. The width (a) of these first contact portions 516a,
The width (b) of the second contact portion 516b is uniform.

The PTC 502 uniformly charges the toner image on the intermediate transfer belt 501 transferred from the photosensitive drum 100 in the primary transfer section before the toner image is transferred to a transfer sheet as a transfer material. is there.

The conductive brush roller 514 removes and cleans the intermediate transfer belt 501 after the secondary transfer. A DC voltage having the same polarity as the surface potential of the intermediate transfer belt 501 after the secondary transfer is used for charge removal. It is applied by the power supply 804. An AC voltage may be superimposed on this DC voltage in order to increase static elimination efficiency. The conductive brush roller 514 can be switched between contact with the intermediate transfer belt 501 and separation from the belt by a separation / contact mechanism (not shown).

The conductive brush roller 514 is ON / OFF controlled as follows. For example, in the case of forming one full-color image, at least the intermediate transfer belt 501 makes one rotation after the completion of the secondary transfer. The conductive brush roller 514 is brought into contact therewith. Further, in the case of forming a full-color image repeat, the conductive brush roller 514 is brought into contact after the end of the secondary transfer until the leading end of the next toner image reaches the neutralization position and the cleaning position, respectively. In the case of forming a single monocolor image, the conductive brush roller 514 is brought into contact at least until the intermediate transfer belt 501 makes one rotation after the primary transfer. Further, in the case of forming a repeat of a monocolor image, after the primary transfer is completed, the conductive brush roller 514 is used until the leading end of the next toner image reaches the neutralization position and the cleaning position, respectively.
Contact.

The lubricant applying brush 505 grinds a zinc stearate 506 as a lubricant molded into a plate shape,
The polished fine particles are applied to the intermediate transfer belt 501. The lubricant application brush 505 is also configured to be able to contact and separate from the intermediate transfer belt 501, and is controlled so as to contact the intermediate transfer belt 501 at a predetermined timing.

The paper transfer unit 600 is composed of a secondary transfer belt 601 and the like stretched over three support rollers 602 to 604, and can be pressed against the intermediate transfer belt 501. One of the three support rollers 602 to 604 is a driving roller that is rotationally driven by a driving unit, and the driving roller drives the secondary transfer belt 601 in the direction of the arrow. The secondary transfer bias roller 605 is disposed so as to sandwich the intermediate transfer belt 501, the transfer paper, and the secondary transfer belt 601 between the secondary transfer opposing roller 510 and the secondary transfer power supply 802 controlled at a constant current. A transfer bias of a predetermined current is applied. Further, the supporting roller 602 and the secondary transfer bias roller 605 are arranged so that the secondary transfer belt 601 and the secondary transfer bias roller 605 can take a position separated from a position where the secondary transfer belt 601 is pressed against the secondary transfer transfer opposing roller 510. A driving mechanism (not shown) is provided. The secondary transfer belt 601 at the separated position is indicated by a two-dot chain line in FIG.

The fixing roller pair 70 of the secondary transfer belt 601
A transfer sheet static elimination charger 606 as a transfer material static elimination means is provided on a portion wound around the first support roller 603.
And a belt static elimination charger 607 as a transfer material carrier static elimination means. Also, the secondary transfer belt 60
A cleaning blade 608 as a transfer material carrier cleaning unit is in contact with a portion wound around the lower support roller 604 in FIG.

The transfer paper discharging charger 606 discharges the electric charges held in the transfer paper so that the transfer paper can be separated from the secondary transfer belt 601 by the strength of the transfer paper itself. is there. The belt static elimination charger 607 eliminates the charge applied by the secondary transfer bias roller 605 and remaining on the secondary transfer belt 601. Further, the cleaning blade 608 includes
The cleaning is performed by removing deposits attached to the surface of the secondary transfer belt 601.

When the image forming cycle is started in the above-described color copying machine, first, the photosensitive drum 100 rotates in the direction of the arrow in the figure, and the intermediate transfer belt 501 rotates in the direction of the arrow in the figure. With the rotation of the intermediate transfer belt 501, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed. A toner image is formed overlapping.

The black toner image is formed as follows. The charger 200 uniformly charges the photosensitive drum 100 to a potential of about 600 V with negative charge by corona discharge. Then, raster exposure is performed by the writing optical unit based on the black color image signal. When this raster image is exposed, in the exposed portion of the photosensitive drum 100, which is initially uniformly charged to about 600 V, the charge proportional to the amount of exposure light disappears, and a black electrostatic latent image is formed. Then, when the black electrostatic latent image contacts the black toner of negative charge on the black developing roller 401, the toner does not adhere to the portion where the charge of the photosensitive drum 100 remains, and the portion without charge, Black toner is adsorbed on the exposed portion, and a black toner image similar to the electrostatic latent image is formed. The black toner image formed on the photosensitive drum 100 is attracted to the bias applied by the bias applying member 513 in the nip portion 520 of the intermediate transfer belt 501 that is driven at a constant speed in contact with the photosensitive drum 100. And transferred to the surface. Thereafter, the photosensitive drum 100 is moved from the intermediate transfer belt 5
01 is referred to as “belt transfer”. still,
Here, the second contact portion 516 in contact with the downstream portion 525
The discharge is slightly smaller than that of b.

A small amount of untransferred residual toner remaining on the surface of the photosensitive drum 100 after the belt transfer is used to prepare the photosensitive drum 100 for reuse.
Clean at 0.

On the photosensitive drum 100 side, the process proceeds to the cyan image forming process after the black image forming process, and starts reading cyan image data by a color scanner at a predetermined timing. An electrostatic latent image is formed. Then, after the rear end of the previous black electrostatic latent image has passed and before the front end of the cyan electrostatic latent image has arrived, the revolver developing unit 40
A rotation operation of 0 is performed to move the next magenta developing device 403 to the developing position. This is also completed before the leading end of the next magenta electrostatic latent image reaches the developing position. In the magenta and cyan image forming processes, the operations of reading the color image data, forming the electrostatic latent image, and developing are the same as those of the above-described black and cyan processes, and thus the description thereof is omitted.

On the intermediate transfer belt 501, black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive drum 100 are sequentially superimposed and transferred on the same surface. As a result, a maximum of 4
A toner image in which colors are superimposed is formed. The superimposed toner image on the intermediate transfer belt 501 is a PTC 50
After being uniformly charged in Step 2, the toner is transferred onto the transfer paper at a time in the next secondary transfer step.

At the time when the image forming operation is started, the fed transfer paper is fed from a paper feeding unit such as a transfer paper cassette or a manual feed tray, and stands by at a nip of a pair of registration rollers. When the leading edge of the toner image on the intermediate transfer belt 501 approaches the secondary transfer portion where the nip is formed by the secondary transfer facing roller 510 and the secondary transfer bias roller 605, the leading edge of the transfer paper is just The registration roller pair is driven so as to coincide with the leading end of the sheet, and the transfer sheet and the toner image are aligned. Thereafter, the transfer paper is superimposed on the toner image on the intermediate transfer belt 501 and passes through the secondary transfer portion. At this time, the transfer bias formed by the transfer bias applied to the secondary transfer bias roller 605 causes the four-color superimposed toner image on the intermediate transfer belt 501 to be collectively transferred onto the transfer paper. The transfer paper is discharged when passing through a portion opposed to the transfer paper static elimination charger 606 disposed on the downstream side of the secondary transfer portion in the moving direction of the secondary transfer belt 601, and is separated from the intermediate transfer belt 501 to form a fixing roller pair. 701 is sent. Then, the toner image is fused and fixed at the nip portion of the fixing roller pair 701, and sent out of the apparatus to obtain a full-color copy.

On the other hand, the surface of the intermediate transfer belt 501 after the transfer of the toner image onto the transfer paper is removed and cleaned by the brush roller 514 pressed against the intermediate transfer belt 501 by the contact / separation mechanism.

In the case of a repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 100 are performed at a predetermined timing following the second image formation process for the yellow image which is the first image. Then, the process proceeds to a black image forming process of the first color. Further, the intermediate transfer belt 50
The first is such that the second black toner image is belt-transferred to the area cleaned by the brush roller 514 on the front surface following the batch transfer process of the first four-color superimposed toner image onto the transfer paper. To After that, the operation is the same as that of the first sheet.

The above is the copy mode for obtaining a four-color full-color copy. However, in the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Become. In the case of the single-color copy mode, only the developing device of the predetermined color of the revolver developing unit 400 is in the developing operation state until the predetermined number of sheets is completed, and the brush roller 514 is pressed against the intermediate transfer belt 501. The copy operation is continuously performed as it is.

In this embodiment, the bias applying member 513
Abuts across the outlet 521,
Since the transfer bias is applied, the intermediate transfer belt 50
The transfer can be performed without being affected by the resistance of the first.

Further, 2k is applied by the bias applying member 513.
When a bias of V is applied, the potential does not decrease at the nip 520 as in the related art, and substantially 2 kV can be maintained.
Therefore, transfer dust at the outlet 521 is prevented. This is because the first contact portion 516a of the bias applying member 513 is in contact with the nip portion 520, so that the potential holding force in the nip portion 520 can be increased.

Based on the above-described embodiment, the transfer dust state was measured while changing the bias potential variously. In this measurement, the potential of the bias applied from the bias applying member 513 is changed, the image discharged from the color copier is visually measured with a loupe for each potential value, and the degree of scattering of the dots of the discharged image is checked. And ranked them in five levels. The results are shown in FIGS. FIG. 5 is a graph in which the horizontal axis indicates the potential value (kV) of the applied transfer bias, and the vertical axis indicates the transfer dust rank in five stages. In this transfer chile rank, a state in which the transfer chile is conspicuous is defined as a transfer chile rank of 1, and, contrary to the transfer chile rank, a state in which there is almost no transfer chile is set as a transfer chile rank of 5, and the evaluation is divided into five levels. is there. The vertical axis of FIG. 6 is the same as FIG. 5, and the horizontal axis is the graph showing the surface potential value (V) of the outlet 521. In addition, this exit part 521
Is a portion having the highest potential in the nip portion 520. As is apparent from these two graphs, the higher the bias applied to the intermediate transfer belt 501, the more the transfer dust is eliminated. This is the photosensitive drum 10
The toner image held on the intermediate transfer belt 50
This is because the image is definitely transferred to the corresponding position (hereinafter referred to as a transfer toner portion) on No. 1.

The mechanism of the occurrence of transfer dust will be described with reference to FIGS. 7 to 9, the vertical axis represents the photoconductor 10.
Bias (V) between the toner on 0 and the intermediate transfer belt 501
, And the time (t) is plotted on the horizontal axis. (C) shows the time when the toner image on the photosensitive drum 100 is in the nip 520, 0 to (c) shows the time up to the entrance 523, and (c) and thereafter show the exit. 52
Indicates the time after 1. As shown in FIG.
The potential (a) of the upper toner image portion is 600 V, and when the potential (b) of the intermediate transfer belt greatly exceeds 100 V, the toner scatters in places other than the transfer toner portion, and transfer dust occurs. However, according to the configuration of this embodiment, as shown in FIGS. 8 and 9, the potential (b) of the intermediate transfer belt is 400 V or 700 V, and the potential (a) of the toner image portion of the photosensitive drum 100 is 600 V. Approach and surpass. That is, when the configuration of the present embodiment is adopted, the toner holding force is increased by increasing the potential holding force of the intermediate transfer belt 501, so that the toner is less likely to scatter in places other than the transfer toner portion. As a result, transfer dust is prevented.

Since the second contact portion 516b is not in contact with the photosensitive drum 100, a minute discharge occurs in the downstream portion 525. This discharge can prevent toner from scattering. Further, by using a high-resistance belt having a volume resistivity of 10 ¹³ Ωcm for the intermediate transfer belt 501, the potential of the applied bias is hardly reduced. As a result, the toner holding force is increased, and transfer dust is more effectively prevented. In addition, since a brush-like member is used as a member for applying a bias, the configuration is simplified, and the device is downsized.

Next, a description will be given of a modification of the embodiment of the present invention. In the description, portions having the same functions as those described above are denoted by the same reference numerals, and description thereof will be omitted.

In the modification shown in FIG. 10, the nip 520 is brought into contact with the nip 520 under the bias applying member 513,
An earth brush 517 is arranged. Earth brush 51
7, a brush-like member is used in a portion in contact with the nip portion 520. The ground brush 517 is grounded.

When a bias of 2 kV is applied from the bias applying member 513, the applied bias is released by the ground brush 517. Therefore, no electric field is generated at the entrance 523, and the toner is prevented from scattering from the photosensitive drum 100 to the intermediate transfer belt 501 in the upstream portion 526. Also, this ground brush 51
7 is in contact with the nip 520, so that the nip 5
Since the bias at 20 maintains 2 kV and does not affect the electric field on the intermediate transfer belt 501, the toner holding force does not decrease. Therefore, the image becomes clear.

The present invention is not limited to the above-described embodiment, but can be variously modified without departing from its use. For example, in the present embodiment and the modified example, the bias applying member 513 is uniformly contacted across the outlet 521, but the same effect can be obtained even if the bias applying member 513 is biased to one side. Can be The volume resistivity of the intermediate transfer belt 501 is, for example, 10 ¹⁰ Ωcm or 10 ¹⁰ Ωcm.
It may be ¹¹ Ωcm. Further, the bias applying member 513
Is not limited to a brush, but may be a plate-shaped one or a sponge-shaped one.

[0054]

According to the first aspect of the present invention, since the bias applying member straddles the contact position and the non-contact position between the image carrier and the intermediate transfer belt, the image becomes clear and the transfer dust is reduced. To prevent

According to the second aspect of the present invention, transfer dust is prevented by using a belt having a volume resistivity of 10 ¹² Ωcm or more.

According to the third aspect of the present invention, since the member on the brush is used as the bias applying member, the configuration of the bias applying member is simplified, and the apparatus is downsized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a main part of a copying machine according to an embodiment.

FIG. 2 is a cross-sectional view illustrating a structure of an intermediate transfer belt according to the embodiment.

FIG. 3 is a schematic configuration diagram illustrating a bias application member and a bias application state according to the present embodiment.

4 is a schematic configuration diagram in which a contact portion of a bias applying member according to FIG. 3 and the vicinity thereof are enlarged.

FIG. 5 is a graph showing the relationship between transfer bias and transfer dust.

FIG. 6 is a graph showing the relationship between transfer bias and transfer dust.

FIG. 7 is a graph showing a relationship between a bias applied state of the toner and the intermediate transfer belt.

FIG. 8 is a graph showing a relationship between a bias applied state of the toner and the intermediate transfer belt.

FIG. 9 is a graph showing a relationship between a bias applied state of the toner and the intermediate transfer belt.

FIG. 10 is a schematic configuration diagram showing a modification of the present embodiment.

FIG. 11 is a front view showing a toner image on a photosensitive drum before transfer.

FIG. 12 is a front view showing a state of dust transfer of the toner image on the intermediate transfer member after the transfer.

FIG. 13 is a schematic configuration diagram showing a configuration of a conventional indirect application method.

FIG. 14 is a schematic configuration diagram showing a configuration of a conventional direct application method.

FIG. 15 is a schematic configuration diagram in which a ground brush is installed at an entrance according to a conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 photoconductor drum (image carrier) 501 intermediate transfer belt (intermediate transfer member) 512 ground roller 513 bias applying member 516 contact portion 516a first contact portion 516b second contact portion 517 ground brush 520 nip portion (contact position) ) 525 Downstream part (non-contact position)

Claims (3)

[Claims] An image carrier that carries a toner image, an intermediate transfer member that contacts the image carrier, and transfers the toner image on the image carrier, and an image carrier that is in contact with the image carrier at the contact position An image forming apparatus provided on the back surface of the intermediate transfer body opposite to the surface side, and comprising a bias applying member for applying a transfer bias of the opposite polarity to toner; An image forming apparatus which is in contact with the intermediate transfer member in a region extending over both of the non-contact positions on the side. 2. The image forming apparatus according to claim 1, wherein the intermediate transfer member has a volume resistivity of 10 ¹² Ω · cm or more. 3. The image forming apparatus according to claim 1, wherein the bias applying member is formed of a brush-like member.