JPH08160771A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device which achieves an improvement in image quality by facilitating the decitaticization of the potosensitive layer of an intermediate transfer belt. CONSTITUTION: The device is equipped with a photosensitive drum 9 on which a toner image is formed, the intermediate transfer belt 19 to which the toner image on the photosensitive drum 9 is once transferred in a primary transfer part A, and a transfer charge 106 which retransfers the toner image on the intermediate transfer belt 19 onto transfer paper 24 in a secondary transfer part B. The intermediate transfer belt 19 is composed of a base-material layer and a photosensitive layer whose resistance is higher than that of the base- material layer, and an exposure device 103 for destaticizing the photosensitive layer is provided on the path along which the intermediate transfer belt 19 moves from the secondary transfer part B to the primary transfer part A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile or a printer, and more specifically, a toner image on a latent image carrier is once transferred onto an intermediate transfer belt,
Further, the present invention relates to an image forming apparatus having a transfer device for transferring the toner image on the intermediate transfer belt onto a transfer paper.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an intermediate transfer belt, various materials such as a low resistance material, a high resistance material and a combination thereof are used as the material of the intermediate transfer belt (for example, a material having a high resistance). Japanese Patent Laid-Open No. 1-27
3075, Japanese Patent Laid-Open No. 1-243085).

[0003]

According to the above construction, when the intermediate transfer belt is made of a material having a low resistance, it is added to the intermediate transfer belt, especially when transferring from the latent image carrier to the intermediate transfer belt. Since the electric charges are easily moved, the toner holding force is weakened, and as a tendency, a blurred image is likely to be generated due to the toner being scattered in areas other than the dot portions. On the other hand, when a high resistance material is used, the electric charge added to the intermediate transfer belt becomes hard to move, so that the toner holding force becomes strong and the blurred image is hard to occur. However, since a high-resistance material makes it difficult for electric charges to move, if continuously applied images are formed, if the previously applied electric charges remain on the intermediate transfer belt, they will accumulate. . Therefore, the optimum transfer bias for the image changes, and the image cannot be stabilized. In addition, since the amount of charge accumulated on the intermediate transfer belt is different between where toner is present and when toner is absent, when continuous image formation is performed, an appropriate amount of charge is applied where toner was present in the previous image formation. The toner cannot be supplied, and the toner is less likely to be transferred from the latent image carrier to the intermediate transfer belt, resulting in a defect that a negative afterimage appears on the next image in an overlapping manner. As a countermeasure for this, it is possible to remove the electric charge by corona discharge, etc., but it is difficult to remove the electric charge at the same time because it is easy to hold the charge with a high resistance material, and it is quite difficult compared to the electrostatic charge removal of the latent image carrier. There was also a problem with it. Further, a transfer method in which a voltage is applied to the rollers as shown in FIG. 7 described later cannot be adopted because a current does not flow between the rollers. Further, if the corona transfer by the transfer charger is adopted, the cost is increased together with the above-mentioned charge eliminating means, and the problem of ozone generation also occurs. For this reason, it is very difficult to set the resistance so that there is no problem with the blurred image and no charge eliminating means is necessary.In the conventional device, the belt with medium resistance is unavoidably used to divide the blurred image. There is also
There is also a problem that this is one of the main causes of image quality deterioration.

The present invention has been made in view of the above problems, and it is an object of the present invention to improve the image quality by facilitating charge elimination of the photosensitive layer of the intermediate transfer belt. A forming device is provided.

[0005]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention is a latent image carrier for forming a toner image, and a primary transfer unit for transferring the toner image on the latent image carrier. In an image forming apparatus having an intermediate transfer belt that temporarily transfers the intermediate transfer belt and a transfer unit that retransfers a toner image on the intermediate transfer belt onto a transfer material at a secondary transfer portion. And a photosensitive layer, and an exposing unit for destaticizing the photosensitive layer is provided on a moving path along which the intermediate transfer belt moves from the secondary transfer section to the primary transfer section. .

Here, the volume resistivity is 10 ⁶ Ω · c
Less than m is low resistance 10 ⁶ Ω ・ cm to 10 ¹² Ω ・
Those with cm are classified as medium resistance and those with more than 10 ¹² Ω · cm as high resistance.

An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, in which the photosensitive layer of the intermediate transfer belt is charged immediately before the toner image on the latent image carrier is transferred to the intermediate transfer belt. It is characterized in that it is provided with a charging device.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the base material layer has a volume resistivity of 1 or less.
It is characterized in that it is made of a material smaller than 0 ⁶ Ω · cm.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the base material layer has a volume resistivity of 1 or less.
A transfer device for transferring a toner image from the latent image carrier to the intermediate transfer belt is constructed by using a material of 0 ⁶ Ω · cm to 10 ¹² Ω · cm. It is characterized in that it is provided on the material layer side.

An image forming apparatus according to a fifth aspect is the image forming apparatus according to the fourth aspect, in which the intermediate transfer belt is supported upstream or downstream of a portion where the latent image carrier and the intermediate transfer belt are in contact with each other. The toner image on the latent image carrier is transferred to the intermediate transfer belt by applying a voltage to the supporting roller that is operating.

[0011]

In the image forming apparatus according to the present invention, since charges are less likely to move in the photosensitive layer having a high resistance, when the toner image on the latent image carrier is transferred to the photosensitive layer side of the intermediate transfer belt. The toner image holding power is strong, and the toner image does not shake on the intermediate transfer belt. In addition, after the transfer from the intermediate transfer belt to the transfer material by the exposure unit,
Since the electric charge remaining on the intermediate transfer belt is eliminated, the photosensitive layer can be easily eliminated.

According to another aspect of the image forming apparatus of the present invention, the charging device provided immediately before the transfer section provides the photosensitive layer of the intermediate transfer belt with electric charges sufficient to transfer the toner image from the latent image carrier. Therefore, even when the toner amount is large, the transfer charge is not insufficient.

In the image forming apparatus of claim 3, since the volume resistivity of the base material layer is smaller than 10 ⁶ Ω · cm,
The charges on the base material layer are easily moved. Therefore, the exposure and charge removal of the intermediate transfer belt can be performed more smoothly.

In the image forming apparatus of claim 4, an electric field is formed between the intermediate transfer belt and the latent image carrier by the transfer device provided inside the intermediate transfer belt. The toner image on the image carrier is electrostatically transferred to the intermediate transfer belt. Here, by setting the volume resistivity of the base material layer to be 10 ⁶ Ω · cm to 10 ¹² Ω · cm, the transfer device from the side of the base material layer on which electric charges are more easily transferred than the photosensitive layer is used. Since the electric charge applied to the intermediate transfer belt is less likely to move as compared with the case where the volume resistivity of the base material layer of the intermediate transfer belt is smaller than 10 ⁶ Ω · cm, it is electrostatically applied to the intermediate transfer belt. The transferred toner image is not blurred.

In the image forming apparatus of the fifth aspect, a voltage is applied to the roller on the upstream side or the downstream side to generate a potential gradient between both rollers, and the potential of the photosensitive layer in the transfer portion is kept constant. Then, the toner image is transferred by the electric field formed between the intermediate transfer belt and the latent image carrier.

[0016]

First, an example of a color copying apparatus which is an image forming apparatus to which the present invention can be applied will be described. FIG. 1 is a schematic configuration diagram of a color copying apparatus, and FIG. 2 is an enlarged view around a photoconductor / intermediate transfer belt. A color image reading device (hereinafter, referred to as a color scanner) 1 forms an image of a document 3 on a color sensor 7 via an illumination lamp 4, a mirror group 5, and a lens 6 to obtain color image information of the document, for example, Blue (Blu, hereinafter B), Green (Gree
n, hereinafter referred to as G) and red (Red, hereinafter referred to as R) color-separated light are read and converted into electrical image signals.
Then, based on the B, G, and R color-separated image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter referred to as Bk) and cyan ( Cyan, hereinafter referred to as C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) color image data are obtained. This is visualized with Bk, C, M, and Y by a color image recording device (hereinafter referred to as a color printer) 2 described below, and the toner images thus obtained are superimposed to form a four-color full-color image. Form.

The writing optical unit 8 of the color printer 2 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 9. To do. The photoconductor drum 9 rotates counterclockwise as indicated by the arrow, and around it, a photoconductor cleaning unit (including a pre-cleaning charge eliminator) 10, a charge erasing lamp 11, a charger 12, a potential sensor 13, and Bk developing. Unit 14, C development unit 1
5, M developing unit 16, Y developing unit 17, optical sensor 18 for developing density pattern detection, intermediate transfer belt 1
9 and the like are arranged.

In each developing unit, a developing sleeve (14a, 15a, 16a, 17) which rotates by bringing the brush of the developer into contact with the surface of the photosensitive drum 9 to develop the electrostatic latent image.
a), a developing paddle (14b, 15b, 16b, 17b) that rotates to scoop up and agitate the developer, and a toner concentration sensor (14c, 15c, 16c, 1) for the developer.
7c) and the like.

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

The Bk toner image formed on the photoconductor drum 9 is transferred onto the surface of the intermediate transfer belt 19 which is driven at the same speed as the photoconductor drum 9 (hereinafter, the toner image transfer from the photoconductor to the intermediate transfer belt is performed). It is called belt transfer, and this transfer position is called primary transfer part A). The intermediate transfer belt 19
Bk, C, M and Y sequentially formed on the photosensitive drum 9
The toner images of 1 are sequentially aligned on the same surface to form a belt transfer image of four colors, and then they are collectively transferred to a transfer paper (hereinafter, this transfer position is referred to as a secondary transfer portion B). The intermediate transfer unit 190 will be described later.

On the side of the photosensitive drum 9, the Bk process is followed by the C process, but the color scanner 1 starts from a predetermined timing.
C image data reading is started by C, and a C latent image is formed by writing a laser beam by the image data. The C developing unit 15 starts rotating the developing sleeve 15a after the trailing end of the previous Bk latent image has passed and before the leading end of the C latent image has reached the developing position, thereby developing the C latent image. Develop with C toner. After that, the development of the C latent image area is continued, and when the trailing edge of the latent image passes, the development is inoperable as in the case of the previous Bk developing unit. This is also completed before the leading edge of the next M latent image arrives. In each of the steps M and Y, the operations of reading image data, forming a latent image, and developing are performed in the same manner as the steps Bk and C described above.

Next, the intermediate transfer unit 190 will be described. The intermediate transfer belt 19 is stretched around a drive roller 21, transfer bias rollers 20a and 20b, and a group of driven rollers, and is drive-controlled by a drive motor (not shown) as described later. The belt cleaning unit 22 includes a brush roller 22a, a rubber blade 22b, a contact / separation mechanism 22c from the intermediate transfer belt 19, and the like.
While transferring the second, third, and fourth colors on the belt, the contact / separation mechanism 2
It is separated from the surface of the intermediate transfer belt 19 by 2c.

The paper transfer unit 23 comprises a paper transfer bias roller 23a, a roller cleaning blade 23b, and a contact / separation mechanism 23c from the intermediate transfer belt 19. The bias roller 23a is normally separated from the surface of the intermediate transfer belt 19, but when the four-color superimposed image formed on the surface of the belt 19 is collectively transferred onto the transfer paper 24, the biasing roller 23a is brought into contact with and separated from the transfer paper 24 at a timing. The sheet is pressed by 23c, and a predetermined bias voltage is applied to the bias roller 23a to perform transfer to the transfer paper 24. In addition, this transfer paper 2
4 is a paper feed roller 25 and a registration roller 26,
The leading end of the four-color superimposed image on the surface of the intermediate transfer belt is fed at the timing of reaching the paper transfer position.

The drive control of the intermediate transfer belt 19 will be described here. As a method of driving the intermediate transfer belt 19, the following three methods are conceivable as an operation method after the belt transfer of the Bk toner image of the first color is completed up to the end portion. From the surface, the intermediate transfer belt 19 is driven by efficiently combining a plurality of these methods according to the copy size. (1) First, a constant speed forward movement method will be described as a first method. Even after the Bk toner image is transferred onto the belt, it continues to move at a constant speed. When the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position of the contact portion with the photosensitive drum 9 again, the front end portion of the next C toner image on the photosensitive drum 9 side is just at that position. The image is formed at the right time. As a result, the C image is accurately aligned with the Bk image and is transferred onto the intermediate transfer belt 19 in a superimposed manner. After that, the same operation is followed to the M, Y image process,
A belt transfer image of four colors is obtained. Subsequent to the belt transfer process of the Y toner image of the fourth color, the four color superposed toner image on the belt surface is moved forward as it is,
As described above, they are collectively transferred onto the transfer paper 24. (2) Next, a skip forward method will be described as a second method. When the belt transfer of the Bk toner image is completed, the intermediate transfer belt 19 is separated from the surface of the photosensitive drum 9, and the intermediate transfer belt 19 is skipped at a high speed in the forward direction as it is, and after moving a predetermined amount, the initial forward speed is restored. In addition, after that, the photoconductor drum 9 again
The intermediate transfer belt 19 is brought into contact with. When the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position again, the photosensitive drum 9 side takes an image at a timing so that the front end of the next C toner image is exactly at that position. Has been formed. as a result,
The C image is accurately aligned with the Bk image and is superimposed and transferred onto the belt. After that, the same operation is performed to proceed to the M and Y image process.
Obtain a belt transfer image with color overlap. Following the Y color toner image belt transfer process for the fourth color, the four color superimposed toner images on the surface of the intermediate transfer belt 19 are collectively transferred onto the transfer paper 24 at the same forward speed. (3) Next, a reciprocating (quick return) system will be described as a third system. When the belt transfer of the Bk toner image is completed, the intermediate transfer belt 19 is separated from the surface of the photosensitive drum 9, and the forward movement is stopped, and at the same time, the intermediate transfer belt 19 is returned at a high speed in the opposite direction. In the return, the front end position of the Bk image on the surface of the intermediate transfer belt 19 passes through the position corresponding to the belt transfer in the opposite direction, and after moving by a preset distance, it is stopped and put in a standby state. Next, when the front end of the C toner image on the photosensitive drum 9 side reaches a predetermined position before the belt transfer position, the intermediate transfer belt 19 is restarted in the forward direction. Further, the intermediate transfer belt 19 is brought into contact with the surface of the photosensitive drum 9 again. Also in this case, the C image is B on the surface of the intermediate transfer belt 19
The belt transfer is performed under the condition that the k image is accurately overlapped. After that, the same operation is performed to proceed to the Y and M image process.
Obtain a belt transfer image with color overlap. Subsequent to the belt transfer process of the Y toner image of the fourth color, the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred onto the transfer paper 24 by moving forward at the same speed without returning.

As described above, the transfer paper 24 to which the four-color superposed toner images are collectively transferred from the intermediate transfer belt surface is conveyed to the fixing device 28 by the paper conveying unit 27, and the fixing roller 28a controlled to a predetermined temperature. And pressure roller 28b
Then, the toner image is fused and fixed, and is carried out to the copy tray 29 to obtain a full color copy.

The photosensitive drum 9 after the belt transfer is
Photoconductor cleaning unit 10 (pre-cleaning static eliminator 10a, brush roller 10b, rubber blade 10c)
The surface is cleaned by, and the charge is removed uniformly by the discharge lamp 11. In addition, the intermediate transfer belt 19 after the toner image is transferred onto the transfer paper 24 is not cleaned by the cleaning unit 2.
2 is pressed again by the contact / separation mechanism 22c to clean the surface.

At the time of repeat copying, the color scanner 1
And the image formation on the photosensitive drum 9
(4th color) After the image process, 2 at a predetermined timing
Proceed to the Bk (first color) image step for the first sheet. Further, the intermediate transfer belt 19 has a transfer paper 24 for the first four-color superimposed image.
Subsequent to the batch transfer process to, the second Bk toner image is belt-transferred to the area whose surface is cleaned by the cleaning unit 22. After that, the same operation as the first sheet is performed. The transfer paper cassettes 30, 3
Transfer papers of various sizes are stored in 1, 32, and 33, and the registration roller 2 is stored at a timing from a storage cassette of size paper designated by an operation panel (not shown).
Paper is fed and conveyed in six directions. Reference numeral 34 is a manual paper feed tray for OHP paper or thick paper.

The above is the description of the copy mode for obtaining four full colors, but in the case of the three-color copy mode and the two-color copy mode, the same operation as above is performed for the designated color and the number of times. It will be. In the case of the single-color copy mode, until the predetermined number of sheets are finished, only the developing unit of that color is in the developing operation (agent standing) state, and the intermediate transfer belt 19 contacts the surface of the photoconductor drum 9. Drives in the forward direction at a constant speed, and the belt cleaner 2
The copy operation is also performed in a state in which 2 also contacts the belt 19. (Hereinafter, margin)

Next, the intermediate transfer unit 1 according to the present embodiment.
90 will be described. FIG. 3 shows the intermediate transfer unit 19
FIG. 3 is an enlarged view of the primary transfer portion at 0. The intermediate transfer belt 19 has a structure in which the photosensitive layer 101 is formed on the base material layer 102. The photosensitive characteristic of the photosensitive layer 101 needs to correspond to the polarity of the toner on the photosensitive drum 9. For example, when a toner composed of a polyester-based resin, a styrene-based resin, or a polyol-based resin is used, the toner T is negatively charged on the photosensitive drum 9, and therefore, as shown in FIG. In order to transfer the charged toner T onto the intermediate transfer belt 19, the intermediate transfer belt 19
The photosensitive layer 101 is made of a material such as Se that is positively charged, and it is necessary to inject a positive charge into the photosensitive layer 101 of the intermediate transfer belt 19.

[Embodiment 1] FIG. 4 is an embodiment in which the present invention is applied to the intermediate transfer unit 190 of the color copying apparatus shown in FIG. In the present embodiment, unlike in FIGS. 1 and 2, the belt surface of the intermediate transfer belt 19 is stretched by a plurality of rollers, of which two rollers near the photoconductor drum 9 move to the photoconductor drum 9 side. Touching to press. Further, in the paper transfer unit 23, the transfer charger 106 is used in place of the paper transfer bias roller 23 a, and a transfer electric field is formed between the intermediate transfer belt 19 and the transfer charger 106 to perform transfer to the transfer paper 24. ing. Then, the secondary transfer portion B for transferring the toner on the intermediate transfer belt 19 onto the transfer paper 24.
An exposure device 103 as an exposure unit is provided between the first transfer unit A and the primary transfer unit A that transfers the next toner image from the photosensitive drum 9. With this configuration, the toner image formed on the photosensitive drum 9 rotating in the direction of the arrow a in the figure is electrostatically transferred onto the intermediate transfer belt 19 at the primary transfer portion A. The intermediate transfer belt 19 moves in the direction of the arrow b in the figure, and is transferred to the transfer paper 24 by the transfer charger 106 at the secondary transfer portion B of the paper transfer unit 23. The intermediate transfer belt 19 after the transfer onto the transfer paper 24 is cleaned by a belt cleaning unit (not shown), and further, the belt 1 is transferred by the exposure device 103.
The residual charge on 9 is removed to make the potential constant. Next, the optimum transfer bias of the intermediate transfer belt 19 in the primary transfer portion A for transferring the toner image from the photosensitive drum 9 is stabilized. Here, since the photosensitive layer 101 of the intermediate transfer belt 19 is generally a high-resistance dielectric, it is difficult for charged charges to move, and the above-described blurred image is less likely to occur. In contrast,
Since the resistance of the base material layer 102 is lower than that of the photosensitive layer 101,
The positive charge remaining on the belt after the transfer process onto the transfer paper 24 is completed can be easily removed by exposure. The volume resistivity of the base material layer 102 shown in FIG.
If it is smaller than ⁶ Ω · cm, the electric charge added to the base material layer 102 becomes easier to move, so that the charge of the intermediate transfer belt 19 after transfer is further facilitated. Therefore, a blurred image at the time of transfer can be prevented.

[Embodiment 2] FIG. 5 shows another embodiment in which the present invention is applied to the intermediate transfer unit 190 of the color copying apparatus shown in FIG. The basic configuration of this embodiment is the same as that of the first embodiment. The difference is that in this embodiment, the intermediate transfer belt 19 is newly provided immediately before the primary transfer portion A for transferring the toner image from the photosensitive drum 9. The point is that the charging device 104 for charging is arranged. By the way, when the toner adhesion amount on the photoconductor drum 9 is small as in the case of monochromatic copying, even if the potential on the intermediate transfer belt 19 is stabilized only by the charge removal by the exposure device 103, the toner is not transferred onto the intermediate transfer belt 19. Has a certain amount of electric charge that has not been removed yet, and this electric charge alone causes the photosensitive drum 9
The upper toner image can be transferred onto the intermediate transfer belt 19. However, when the toner adhesion amount on the photoconductor drum 9 becomes large as in color copying, the toner image formed on the photoconductor drum 9 is insufficiently charged unless the intermediate transfer belt 19 is newly charged. It is difficult to transfer everything. Therefore, in the present embodiment, the charging device 104 stably provides the photosensitive layer 101 of the intermediate transfer belt 19 with an electric charge enough to transfer the toner image from the photosensitive drum 9, and the toner amount is the same as in the color copying. Even when the number of charges increases, insufficient charging does not occur and a good image can be obtained.

[Embodiment 3] FIG. 6 shows still another embodiment in which the present invention is applied to the intermediate transfer unit 190 of the color copying apparatus shown in FIG. The basic structure of this embodiment is similar to that of the first embodiment, except that the base layer 102 of FIG. 3 has a volume resistivity of 10 ⁶ Ω · cm.
10 to ^{12 12} Ω · cm are used, and a transfer charger 105 that applies electric charge to the intermediate transfer belt 19 from the inside of the intermediate transfer belt 19, that is, the base material layer 102 side is provided. Here, by setting the volume resistivity of the base material layer 102 to medium resistance, the base material layer 10 in Example 1 was used.
As compared with the case where the volume specific resistance of 2 is less than 10 ⁶ Ω · cm, it becomes difficult to eliminate the charge. However, it is difficult to eliminate the static electricity, that is, it is difficult for the charges to leak. Therefore, in the present exemplary embodiment, the transfer charger 105 is provided on the side of the base material layer 102 where the charge is more likely to move than the photosensitive layer 101, so that the charge is applied to the intermediate transfer belt 19. As a result, the electric charge applied to the intermediate transfer belt 19 is held on the belt 19 without leaking. With this charge, the toner image on the photosensitive drum 9 can be electrostatically attracted and transferred to the intermediate transfer belt 19 side, and the transferred toner image is charged on the belt 19. Is difficult to move, so blur images do not occur. Further, since the transfer charger 105 can be arranged inside the intermediate transfer belt 19, the transfer charger 105 can be arranged outside the intermediate transfer belt 19.
It is possible to occupy a smaller space than that in which the device is provided, and the device main body space can be effectively used.

[Embodiment 4] FIG. 7 shows still another embodiment in which the present invention is applied to the intermediate transfer unit 190 of the color copying apparatus shown in FIG. The basic configuration of this embodiment is the same as that of the first embodiment, except that in this embodiment, a bias voltage is applied to the bias roller 20c on the downstream side of the primary transfer portion A, and the ground of the upstream side is applied. The point is that the roller 20d is grounded. As a result, a potential gradient is generated between the two rollers 20c and 20d, and the potential of the photosensitive layer 101 at the primary transfer portion A is kept constant. Therefore,
The toner image on the photosensitive drum 9 is transferred onto the intermediate transfer belt 19 by the electric field formed between the photosensitive drum 9 and the photosensitive layer 101 at the primary transfer portion A. Therefore, since a transfer device such as a transfer charger is not required, ozone is not generated unlike when a transfer charger is used, and the influence on the environment can be reduced. Further, since the voltage applied to the bias roller 20c is lower than that of the transfer charger, the cost of the power source can be reduced.

According to the above embodiments, the intermediate transfer belt 1
Since 9 is composed of two layers, the photosensitive layer 101 and the base material layer 102, blurring of the toner image transferred from the photoconductor drum 9 can be prevented by the photosensitive layer 101 in which electric charge is hard to move, and the transfer paper 24 can be prevented. After the transfer is completed, the electric charge remaining on the intermediate transfer belt 19 is quickly removed from the base material layer 102 side where the electric charge is easier to move than the photosensitive layer 101, and the potential on the belt 19 is stabilized for the next transfer process. Therefore, a stable toner image can be obtained. Therefore, it is possible to improve the image quality.

[0035]

According to the image forming apparatus of the present invention, since the toner image holding force on the photosensitive layer is strong and the toner transferred to the intermediate transfer belt does not easily move on the intermediate transfer belt, the conventional method is not used. It is possible to prevent the blurred image which was a problem of. Further, since the position of the static eliminator is set after the transfer from the intermediate transfer belt to the transfer material, it is possible to easily eliminate the electric charge remaining on the photosensitive layer of the intermediate transfer belt after the transfer to the transfer material. Therefore, it is possible to stabilize the optimum transfer bias at the time of transfer from the latent image carrier to the intermediate transfer belt.

According to the image forming apparatus of the second aspect, by the charging device provided immediately before the transfer section, an electric charge enough to transfer the toner image from the latent image carrier is applied to the photosensitive layer of the intermediate transfer belt. In addition to the effect of the first aspect, stable transfer can be performed even when the toner adhesion amount is relatively large.

According to the image forming apparatus of claim 3, since the volume resistivity of the base material layer is smaller than 10 ⁶ Ω · cm, the electric charge on the base material layer easily moves. In addition to this, the exposure and charge removal of the intermediate transfer belt can be performed more smoothly. Therefore, the image quality can be stabilized.

According to the image forming apparatus of claim 4, since the volume resistance of the base material layer is medium resistance, it is more difficult to eliminate the charge as compared with claim 3, but the base material inside the intermediate transfer belt. Since the electric charge applied to the intermediate transfer belt from the layer side does not easily move, blurring of the toner image can be prevented. In addition, since the charge can be injected from the side of the base material layer where the charge easily moves as compared with the photosensitive layer, the electrostatic transfer by the electric field between the latent image carrier and the intermediate transfer belt can be performed.
It becomes possible to transfer the toner image more effectively.
Further, since the transfer device can be arranged on the inner side of the intermediate transfer belt, that is, on the base material layer side, a smaller space is required as compared with the case where the transfer device is arranged on the outer side of the intermediate transfer belt. Can be used effectively.

According to the image forming apparatus of the fifth aspect, a potential gradient is generated between the roller on the downstream side and the roller on the upstream side of the transfer section, and the potential of the photosensitive layer in the transfer section is kept constant. Keep it at. As a result, the toner image on the latent image carrier is transferred onto the intermediate transfer belt by the electric field formed between the latent image carrier and the photosensitive layer in the transfer section. Therefore, compared to the fourth aspect, it is not necessary to newly provide a transfer device such as a transfer charger, and ozone generated thereby is not generated, which is also effective as an environmental measure. Further, the voltage applied to the roller on the upstream side or the downstream side can be lower than that when the transfer charger is used, so that the cost of the power source can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color copying apparatus to which the present invention can be applied.

FIG. 2 is an enlarged view around the photosensitive drum and the intermediate transfer belt in FIG.

FIG. 3 is an explanatory diagram showing a charged state of an intermediate transfer belt.

FIG. 4 is an enlarged view of an embodiment in which the present invention is applied to an intermediate transfer unit of a color copying apparatus.

FIG. 5 is an enlarged view of another embodiment in which the present invention is applied to an intermediate transfer unit of a color copying machine.

FIG. 6 is an enlarged view of yet another embodiment in which the present invention is applied to an intermediate transfer unit of a color copying apparatus.

FIG. 7 is an enlarged view of yet another embodiment in which the present invention is applied to an intermediate transfer unit of a color copying apparatus.

[Explanation of symbols]

 9 photoconductor drum 19 intermediate transfer belt 20a, 20b transfer bias roller 20c bias roller 20d earth roller 21 drive roller 21a driven roller 23 paper transfer unit 24 transfer paper 101 photosensitive layer 102 base material layer 103 exposure device 104 charger 105 transfer charger 106 Transfer charger 190 Intermediate transfer unit A First transfer part B Second transfer part T Toner

Claims (5)

[Claims] 1. A latent image carrier for forming a toner image, an intermediate transfer belt for temporarily transferring the toner image on the latent image carrier at a primary transfer portion, and a secondary transfer of the toner image on the intermediate transfer belt. An image forming apparatus having a transfer means for retransferring onto a transfer material at a part thereof, wherein the intermediate transfer belt comprises a base material layer and a photosensitive layer, and the intermediate transfer belt is provided from the secondary transfer part to the primary transfer part. An image forming apparatus comprising: an exposing unit that removes electric charge from the photosensitive layer on a moving path that moves to a transfer unit. 2. The image forming apparatus according to claim 1, further comprising a charging device for charging the photosensitive layer of the intermediate transfer belt immediately before the toner image on the latent image carrier is transferred to the intermediate transfer belt. Forming equipment. 3. The volume resistivity of the base material layer is 10 ⁶ Ω · c.
The image forming apparatus according to claim 1, wherein the image forming apparatus is configured by using a material smaller than m. 4. The volume resistivity of the base material layer is 10 ⁶ Ω · c.
A transfer device for transferring a toner image from the latent image carrier to the intermediate transfer belt is formed on the base material layer side of the intermediate transfer belt by using a material having m to 10 ¹² Ω · cm. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided. 5. A voltage is applied to a supporting roller supporting the intermediate transfer belt upstream or downstream of a portion where the latent image carrier and the intermediate transfer belt are in contact with each other, whereby the latent image is formed. The image forming apparatus according to claim 4, wherein the toner image on the carrier is transferred to the intermediate transfer belt.