JPH04296785A - Image forming device - Google Patents

Abstract

PURPOSE:To sufficiently clean an intermediate transfer body by a cleaning device whose constitution is simple and which is inexpensive in an intermediate transfer system image forming device. CONSTITUTION:After a multiple toner image which is primarily transferred by being successively superposed on an intermediate transfer belt 18 is collectively secondarily transferred on a transfer material 19, a voltage whose polarity is reverse to that at the transfer time is impressed on a primary transfer roller 9 and a drum cleaner 6 and a belt cleaner 20 are actuated while the reverse voltage is impressed. Besides, the circumferential speed of the belt 18 is made higher than that of a photosensitive drum 5. Thus, toner, dust or the like left on the surface of the belt 18 is efficiently reversely transferred on the drum 5 and eliminated by the cleaner 6. On the other hand, since the toner, the dust or the like left on the belt 18 becomes extremely little, it is easily eliminate by the cleaner 20.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to image forming apparatuses such as copying machines and printers using electrophotography or electrostatic recording.
In particular, but not limited to, the present invention relates to an image forming apparatus that uses an intermediate transfer method in which visible developed images (toner images) of a plurality of different colors are superimposed on an intermediate transfer member and then transferred all at once to a transfer material.

0002

[Prior Art] Conventionally, a visible developed image (toner image) formed on an image carrier is sequentially primarily transferred onto an endlessly running intermediate transfer member, and multiple toner images on this intermediate transfer member are created. In image forming apparatuses that use an intermediate transfer method that performs secondary transfer to a sheet-like transfer material, each time a toner image is secondarily transferred to a transfer material, sufficient amount of residual toner that remains on the intermediate transfer material without contributing to transfer is removed. It is essential to continuously obtain high-quality images. For this reason, various cleaning devices for intermediate transfer bodies have been developed, but most of these cleaning devices employ a brush type or a blade type.

0003

[Problems to be Solved by the Invention] However, the brush type cleaning device not only becomes large in size, but also has a tendency for developer to adhere to the cleaner brush.
The developer has to be scraped off from the cleaner brush, and the scraped developer must be removed using a suction device or the like, resulting in a problem that the apparatus becomes bulky.

On the other hand, in blade-type cleaning devices, improvements have been made to the thickness and contact pressure of the blade, as disclosed in, for example, Japanese Unexamined Patent Publication No. 1-293380. In order to achieve this, the blade thickness is set large and the contact pressure of the blade is also set large. This has the disadvantage that the cleaning device becomes expensive.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus in which an intermediate transfer member can be sufficiently cleaned using a simple and inexpensive cleaning device.

[0006]

Means for Solving the Problems The above objects are achieved by an image forming apparatus according to the present invention. In summary, the present invention provides primary transfer of visible developed images formed on an image carrier by sequentially superimposing them onto an intermediate transfer member, and transfers the multiple developed images transferred onto the intermediate transfer member to a transfer material. In an image forming apparatus that performs secondary transfer at once, at least after the completion of the secondary transfer, an electric field is formed between the intermediate transfer body and the image carrier in a direction opposite to that during the primary transfer, and The image forming apparatus is characterized in that developer, dust, dirt, etc. remaining on the transfer member are made to adhere to the image carrier.

In one embodiment of the present invention, when an electric field is formed between the intermediate transfer member and the image carrier in a direction opposite to that during primary transfer, the intermediate transfer member is moved around the image carrier. The intermediate transfer body is rotated at a circumferential speed different from that of the intermediate transfer body, and a rubbing action is created between the intermediate transfer body and the image carrier to remove developer, dust, dirt, etc. remaining on the intermediate transfer body with high efficiency. It is attached on top.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic sectional view showing a first embodiment of an image forming apparatus according to the present invention, and shows a case where the present invention is applied to an electrophotographic laser beam printer. This laser beam printer includes a photosensitive drum 5 of, for example, an OPC as an image carrier.
Around the image is a pre-exposure lamp 7, a primary charger 8, a laser scanner 1 that irradiates laser light onto the photoreceptor drum 5 according to each color signal, and first and second mirrors 2 and 3. Toner remaining on the exposure area, the developing unit 4 having a developing device that accommodates magenta (M), cyan (C), yellow (Y), and black (BK) developers, and the photoreceptor drum 5. Drum cleaner 6 to remove
etc. are arranged.

Although not shown in the drawings, each developing device of the developing unit 4 includes a developing cylinder and a non-magnetic blade in this embodiment, and the developer is composed of toner and carrier, which are mixed at a constant ratio. The toner and carrier are charged by friction, so that the toner is negatively charged and the carrier is charged positively. This developer is brush-like on the surface of the developing cylinder by the magnetic field of a fixed magnet, and is formed into a developer layer of uniform thickness by a blade. A developing bias is simultaneously applied to the developing cylinder. Therefore, the negative component of the developing bias is larger than the positive component. The toner is attracted to the bright area of the photoreceptor drum 5 by the surface potential of the photoreceptor drum 5 and the negative component of the developing bias, and the electrostatic latent image formed on the photoreceptor drum 5 is developed into a visible image. In this case, when the image exposure unit irradiates a color-separated light image at a predetermined timing, for example, a color image passed through a green filter, an electrostatic latent image mainly consisting of magenta components of the color image is transferred to the photoreceptor. It is formed on the drum 5. In synchronization with the feeding of this latent image, the developing unit 4
Since the developing device containing the magenta developer is placed at a position facing the photoreceptor drum 5, the magenta color developer (
Toner) flies electrostatically and adheres to the electrostatic latent image on the photoreceptor drum 5, and as a result of a developing operation, only a magenta toner image is formed on the photoreceptor drum 5. .

The magenta toner image formed on the photoreceptor drum 5 is transferred to an intermediate transfer member, in this embodiment, which runs endlessly in contact with or slightly apart from the photoreceptor drum 5 in the primary transfer section. The image is transferred onto the intermediate transfer belt 18. This intermediate transfer belt 18 is stretched between a fixed roller 15 and a tension roller 12 so as to run between a pair of opposing secondary transfer rollers 13A and 13B, and a photosensitive drum is provided at the primary transfer section. A primary transfer roller 9 is arranged on the back side of the intermediate belt 18, facing the intermediate belt 5. The intermediate transfer belt 18 is driven by the motor 16 through the motor control drive circuit 17, and the fixed roller 15 coupled to the motor output shaft rotates, so that the intermediate transfer belt 18 travels in the direction of the arrow in the figure. Note that the pair of secondary transfer rollers 13A
, 13B are disposed on the toner image holding surface (front surface) side of the intermediate transfer belt 18, while 13A is a bias roller configured to be able to approach and separate from this belt 18, and is biased during the transfer operation. It is positioned in contact with the belt 18 or in a slightly spaced state.

The toner image formed on the photoreceptor drum 5 is electrostatically transferred onto the intermediate transfer belt 18 by applying a predetermined positive voltage to the primary transfer roller 9, which serves as a counter electrode of the photoreceptor drum 5. transcribed. During this primary transfer, a paper feed roller (not shown) for feeding the transfer material 19 from the paper feed cassette 30 is not operated. Also, at this time, the secondary transfer rollers 13A and 13B are open (
In other words, the bias roller 13A on the front surface side of the belt is separated), so the magenta toner image transferred onto the intermediate transfer belt 18 is not transferred even if the transfer material 19 is fed, and the magenta toner image is not transferred onto the secondary transfer roller 13A. , 13B, and is held on the intermediate transfer belt 18 as the belt 18 moves, and is conveyed again to the primary transfer section.

After the magenta toner image is thus transferred onto the intermediate transfer belt 18, the remaining toner on the photosensitive drum 5 is completely cleaned by a drum cleaner 6. Furthermore, before forming a latent image of the next color, the pre-exposure lamp 7 is operated to irradiate the surface of the photoreceptor drum 5 with light to erase any residual charge on the drum surface. The series of image forming processes described above, including pre-exposure, primary charging, laser exposure, development, primary transfer, and drum cleaning, are repeated in the same way when forming cyan toner images, yellow toner images, and black toner images, and thus intermediate transfer. On the belt 18, the four color toner images, the magenta toner image, the cyan toner image, the yellow toner image, and the black toner image, are transferred in an overlapping state.

The above four color toner images are transferred to the intermediate transfer belt 18.
When the multiple color toner images are transferred onto the intermediate transfer belt 18, the paper feed roller is driven and the transfer material 19 passes through the pair of registration rollers 10 and 11 and is transferred to the secondary transfer roller 13A in synchronization with the position of the four color toner images on the intermediate transfer belt 18. , 13B are provided. When the transfer material 19 approaches the secondary transfer section, the secondary transfer roller 13A on the belt surface side of the secondary transfer rollers 13A and 13B is urged, and the intermediate transfer belt 18
The intermediate transfer belt 18 and the transfer material 19 are sandwiched between the secondary transfer rollers 13A and 13B. At this time, a predetermined positive voltage is applied to the secondary transfer roller 13A on the front side as shown in the figure, and as a result, the bonding force between the transfer material 19 and the toner is stronger than the bonding force between the intermediate transfer belt 18 and the toner. becomes stronger, the toner on the transfer belt 18 adheres to the transfer material 19, and the four-color toner image is transferred to the transfer material 19.

When the secondary transfer is performed, a transfer material separating means (not shown) is operated, and the transfer material 19 to which the toner image has been transferred is separated from the intermediate transfer belt 18 by this separating means, and then transferred to a pair of fixing members by a conveying means (not shown). The image is sent to a fixing section composed of rollers 14, 14. In this embodiment, each fixing roller 14 has a built-in heater lamp, and when the transfer material 19 passes between the fixing rollers, the four color toner images are fixed all at once by heat and pressure, and a permanent image is created. Convert to

After the secondary transfer is completed, the untransferred toner remains on the surface (toner image holding surface) of the intermediate transfer belt 18, and if this continues, the color image to be copied next will be stained. Occur. Therefore, in this embodiment, after the secondary transfer is completed, a predetermined negative voltage is applied to the primary transfer roller 9, and at the same time, the belt cleaner 20, which has been separated until now, is brought into contact with the intermediate transfer belt 18. The negative voltage applied to the primary transfer roller 9 forms an electric field that attracts the toner (negative polarity) attached to the surface of the intermediate transfer belt 18 toward the circumferential surface of the photoreceptor drum 5, thereby causing the intermediate transfer Most of the toner remaining on the belt 18 without being transferred is reversely transferred onto the circumferential surface of the photosensitive drum 5. The toner remaining on the intermediate transfer belt 18 without being reversely transferred is removed by the belt cleaner 2.
removed by 0. Thus, the intermediate transfer belt 18
is completely cleaned, and stains on the next copy can be reliably prevented. On the other hand, the toner reversely transferred onto the photosensitive drum 5 reaches the position where the drum cleaner 6 is disposed as the drum 5 rotates.
removed by

Furthermore, in this embodiment, the intermediate transfer belt 1
In order to promote reverse transfer of toner from 8 to photoreceptor drum 5 and to remove dust, dirt, etc. on intermediate transfer belt 18, the circumferential speed of intermediate transfer belt 18 is changed during cleaning after completion of secondary transfer. . Note that when the peripheral speed of the intermediate transfer belt 18 is Vm and the peripheral speed of the photosensitive drum 5 is VD, the peripheral speed Vm of the intermediate transfer belt 18 is 0.5V.
It is appropriate that D ≦Vm ≦0.9VD 1.1VD ≦Vm ≦2.0VD.

When the circumferential speed of the intermediate transfer belt 18 is changed in this way, a sliding action occurs between the intermediate transfer belt 18 and the photosensitive drum 5 due to the difference in their circumferential speeds after the completion of the secondary transfer. Reverse transfer of residual toner from the transfer belt 18 to the photoreceptor drum 5 is facilitated, and at the same time, dust, dirt, etc. also adhere to the photoreceptor drum 5. Therefore, the amount of toner, dust, dirt, etc. remaining on the intermediate transfer belt 18 is extremely small and can be easily removed by the belt cleaner 20, which has a simple configuration.
can be cleaned even more effectively.

FIG. 2 schematically shows a sequence when copying only one sheet of A4 size transfer material in the image forming apparatus according to the present invention having the above configuration. In response to the copy operation start signal, at time T1, the photosensitive drum 5 and the intermediate transfer belt 18 synchronously start rotating in the direction of the arrow in the figure. At time T2, a predetermined positive DC voltage, which is a primary transfer voltage, is applied to the primary transfer roller 9, and the first color toner image is primary transferred onto the transfer belt 18. The application time of this primary transfer voltage is selected to cover an image area corresponding to the designated transfer material size (A4 in this example). Here, the time when the primary transfer of the toner image of the first color is started is defined as the starting point of the first rotation, and the rotation of the intermediate transfer belt 18 from this starting point until the primary transfer of the toner image of the second color is started. The movement is defined as one rotation of the transfer belt 18. Hereinafter, the same primary transfer voltage is applied for the primary transfer of the second color toner image, the third color toner image, and the fourth color toner image, and the four color toner images are superimposed and transferred onto the intermediate transfer belt 18. A predetermined DC voltage, which is a secondary transfer voltage, is applied to the secondary transfer roller 13A, and the secondary transfer roller 13A comes into contact with the intermediate transfer belt 18. The multiple toner images on the intermediate transfer belt 18 are
It reaches the secondary transfer part at approximately 41/2 rotations (3 and a half rotations) of 8. After the secondary transfer is completed, the secondary transfer voltage is turned off, and the secondary transfer roller 13A is separated from the intermediate transfer belt 18. At the same time, a negative DC voltage of opposite polarity to that during primary transfer is applied to the primary transfer roller 9, and further,
In synchronization with the application of this reverse voltage, the drum cleaner 6 and the belt cleaner 20 are energized and come into contact with the photosensitive drum 5 and the intermediate transfer belt 18, respectively. Further, in synchronization with the application of the reverse voltage, the circumferential speed of the intermediate transfer belt 18 is made faster than the circumferential speed of the photoreceptor drum 5. In this embodiment, the time for applying the reverse voltage to the primary transfer roller 9, the time for contacting both cleaners 6 and 20, and the time for changing the circumferential speed of the intermediate transfer belt 18 is the time for the intermediate transfer belt 18 to rotate approximately once. After this time has elapsed, the reverse voltage applied to the primary transfer roller 9 is turned off, the drum cleaner 6 and the belt cleaner 20 are separated from the photoreceptor drum 5 and the belt 18, and the circumferential speed of the intermediate transfer belt 18 returns to its original speed. be returned. Note that the separation time of these cleaners 6 and 20 may be slightly slower than the off time of the reverse voltage.

As described above, in the above sequence, after the completion of the secondary transfer, a voltage with a polarity opposite to that during transfer is applied to the primary transfer roller 9, and during the time when this reverse voltage is applied, the drum cleaner 6 and Since the belt cleaner 20 is activated and the peripheral speed of the intermediate transfer belt 18 is made faster than the peripheral speed of the photoreceptor drum 5, toner, dust, dirt, etc. remaining on the surface of the intermediate transfer belt 18 are removed from the photoreceptor. The toner is efficiently reversely transferred onto the drum 5, and the reversely transferred toner, dust, dirt, etc. are reliably removed by the drum cleaner 6. On the other hand, since the toner, dust, dirt, etc. remaining on the intermediate transfer belt 18 are extremely small, they can be easily removed by the belt cleaner 20. Therefore, the cleaning performance of the intermediate transfer belt 18 by the belt cleaner 20 is further improved, and the dirt on the surface of the intermediate transfer belt can be completely cleaned with a simple configuration without making the cleaning device large or large-scale. Therefore, the disadvantage that the cleaning device becomes expensive can also be eliminated.

FIG. 3 schematically shows a sequence when A4 size transfer materials are continuously copied in the image forming apparatus according to the present invention having the above configuration. In this case,
When the intermediate transfer belt 18 rotates five times and the secondary transfer of the multiple toner image to the first transfer material is completed, and the cleaning of the intermediate transfer belt 18 is completed, the primary transfer of the multiple toner image to the next second transfer material is completed. The transfer operation is started. That is, from the sixth rotation, the operations from the first rotation to the end of the fifth rotation in the sequence shown in FIG. 2 are repeated. Thereafter, the sequence shown in FIG. 2 from the first rotation to the end of the fifth rotation is repeated for the required number of transfer materials. Therefore, the secondary transfer of the multiple toner image to the last transfer material is completed,
Since the operations of 1 to 5 rotations in the sequence shown in FIG. 2 are repeated except that the intermediate transfer belt 18 continues to rotate until cleaning of the intermediate transfer belt is completed, a detailed explanation will be omitted.

FIG. 4 schematically shows the sequence when copying only one sheet of A3 size transfer material in the image forming apparatus according to the present invention having the above configuration. In this case,
Because the size of the transfer material 19 is large, the primary transfer voltage is continuously applied without being turned off between the primary transfers of the toner images of each color, and the secondary transfer voltage is applied continuously during the fourth rotation of the intermediate transfer belt 18. In other words, the operation is the same as the sequence shown in FIG. 3 except that the voltage is applied when the four-color toner image multiplexed onto the intermediate transfer belt 18 reaches the secondary transfer section, so a detailed explanation will be given below. Omitted. In this case, the reverse voltage applied to the primary transfer roller 9 is applied for a period of time during which the intermediate transfer belt 18 rotates approximately once after the completion of the secondary transfer. Further, the drum cleaner 6 and the belt cleaner 20 are also operated during the time period during which the intermediate transfer belt 18 makes approximately one rotation. Further, while the reverse voltage is being applied, the circumferential speed of the intermediate transfer belt 18 is made faster than the circumferential speed of the photoreceptor drum 5.

FIG. 5 schematically shows a sequence when A3 size transfer materials are successively copied in the image forming apparatus according to the present invention having the above configuration. In this case, since the size of the transfer material is large, the primary transfer operation of the multiple toner image to the next second transfer material starts when the intermediate transfer belt 18 makes six rotations (when it enters the seventh rotation). be done. That is, from the seventh rotation, the operations from the first rotation to the end of the sixth rotation in the sequence shown in FIG. 4 are repeated. Thereafter, the operations from the first rotation to the end of the sixth rotation in the sequence shown in FIG. 4 are repeated for the required number of transfer materials. Therefore, the secondary transfer of the multiple toner image to the last transfer material is completed,
Except that the rotation of the intermediate transfer belt 18 continues until the cleaning of the intermediate transfer belt is completed, the operations of the 1st to 6th rotations in the sequence of FIG. 4 are repeated, so a detailed explanation will be omitted.

In each of the above sequences, the intermediate transfer belt 18 is cleaned only during the post-rotation after the secondary transfer of multiple toner images is completed, but cleaning is also performed not only during the post-rotation but also during the pre-rotation of the intermediate transfer belt 18. If this is done, the cleaning performance of the intermediate transfer belt 18 will be further improved. FIG. 6 schematically shows a sequence for copying only one sheet of A4 size transfer material.

In response to the copy operation start signal, the photosensitive drum 5 and the intermediate transfer belt 18 start rotating in the direction of the arrow shown at time T1. At this time, the intermediate transfer belt 18 rotates at a peripheral speed faster than the peripheral speed of the photoreceptor drum 5. At the same time as this rotation of the intermediate transfer belt 18, a reverse voltage is applied to the primary transfer roller 9, and in synchronization with this, the drum cleaner 6 and the belt cleaner 20 are operated, and the photoreceptor drum 5
and comes into contact with the intermediate transfer belt 18. Intermediate transfer belt 1
Charged toner reversely transferred onto the surface of the photoreceptor drum 5 from the surface of the photoreceptor drum 8, as well as toner, dust, dirt, etc. that has adhered to the photoreceptor drum 5 due to the rubbing action, are removed by the drum cleaner 6, and the toner is transferred onto the intermediate transfer belt. The slight remaining toner, dust, dirt, etc. are completely removed by the belt cleaner 20. The reverse voltage applied to the primary transfer roller 6 causes the operation of both cleaners 6 and 20 to be turned off earlier by a time ΔT than the time T3 during which the primary transfer voltage is applied. This is to prevent load fluctuations during rotation of the intermediate transfer belt 18 by the primary transfer roller 9 and belt cleaner 20 from affecting the primary transfer. Intermediate transfer belt 1
8 rotates once and starts its second rotation at time T3, a predetermined positive DC voltage that is the primary transfer voltage is applied to the primary transfer roller 9, and the primary transfer of the first color toner image to the transfer belt 18 is performed. . As shown in the sequence shown in FIG. 2 below, the same primary transfer voltage is applied for the primary transfer of the second color toner image, the third color toner image, and the fourth color toner image. When the toner images of four colors are superimposed and transferred onto the belt at the fifth rotation of the intermediate transfer belt 18, a predetermined DC voltage that is the secondary transfer voltage is applied to the secondary transfer roller 13A, and this secondary transfer roller 13A is intermediate transfer belt 1
8. The multiple toner images on the intermediate transfer belt 18 reach the secondary transfer portion at approximately 51/2 rotations (four and a half rotations) of the intermediate transfer belt 18. After the secondary transfer is completed, as described above, a reverse voltage is applied to the primary transfer roller 9 while the intermediate transfer belt 18 rotates approximately one rotation, so that the circumferential speed of the intermediate transfer belt 18 is lower than the circumferential speed of the photoreceptor drum 5. At the same time, the drum cleaner 6 and belt cleaner 20 are activated to bring them into contact with the photosensitive drum 5 and the intermediate transfer belt 18. As a result, the charged toner on the surface of the intermediate transfer belt 18 is reversely transferred to the surface of the photoreceptor drum 5, and due to the sliding action between the photoreceptor drum 5 and the intermediate transfer belt 18, the intermediate transfer belt 18
Toner, dust, dirt, etc. that are difficult to be reversely transferred on the photosensitive drum 5 are made to adhere to the photosensitive drum 5, thereby improving the cleaning performance of the intermediate transfer belt 18 by the belt cleaner 20.

In this way, when the intermediate transfer belt 18 is cleaned by applying a voltage of opposite polarity to the primary transfer roller 9 during the pre-rotation of the intermediate transfer belt 18, the intermediate transfer belt 18 is cleaned. Since toner, dust, dirt, etc. that have adhered to the intermediate transfer belt 18 while the belt is stopped can be removed by the drum cleaner 6 and the belt cleaner 20, there is an advantage that dirt on the intermediate transfer belt 18 can be removed more reliably. Although not shown, it goes without saying that cleaning can be performed on transfer materials of other sizes in the same sequence during the previous rotation of the intermediate transfer belt.

As a specific example, in an image forming apparatus having the configuration shown in FIG. 1, a dielectric belt having a volume resistivity of 1010 Ω·cm was used as the intermediate transfer belt 18 to output a color image. At this time, the bias voltage applied to the primary transfer roller 9 during the primary transfer is set to 0.8 for the first color (yellow).
The KV was set to 0.9 KV for the second color (cyan), 1.0 KV for the third color (magenta), and 1.1 KV for the fourth color (black). Also,
The bias voltage applied to the secondary transfer roller 13A during secondary transfer was set to 1.5 KV. Furthermore, the reverse bias voltage applied to the primary transfer roller 9 during cleaning is -1.
It was set to 0KV. When these primary transfer voltages, secondary transfer voltages, and reverse bias voltages were turned on and off in the sequences shown in FIGS. 2 to 6, residual toner, dust, and dirt remained on the intermediate transfer belt 18 after the completion of the secondary transfer. etc. were completely removed, making it possible to significantly improve the cleaning performance of the intermediate transfer belt 18.

In the above embodiment, the present invention was applied to an electrophotographic laser beam printer, but the present invention can be applied to various copying machines, printers, etc. of electrophotography, electrostatic recording, etc. other than the embodiments. It is equally applicable to the following image forming apparatuses. Furthermore, it goes without saying that various modifications and changes can be made to the members, elements, etc. constituting the image forming apparatus as necessary. Furthermore, the sequences related to the primary transfer voltage, secondary transfer voltage, voltage with the opposite polarity to the primary transfer voltage applied during cleaning, changes in the peripheral speed of the intermediate transfer belt, and on/off operations of cleaners, etc. are limited to those shown in the illustrations. It's not something you can do. For example, changing the peripheral speed of the intermediate transfer body does not necessarily have to be added to the sequence.

[0028]

As explained above, the image forming apparatus according to the present invention applies a voltage with a polarity opposite to that during the primary transfer between the intermediate transfer member and the image carrier after the completion of the secondary transfer. Since an electric field is formed in the opposite direction and both cleaners for the image bearing member and the intermediate transfer member are operated during the time when the opposite electric field is being formed, the developer remaining on the intermediate transfer member is A considerable amount of the toner is reversely transferred onto the image carrier, and not much remains on the intermediate transfer member. Therefore, since this slight amount of residual developer can be easily removed with a simple cleaner, the cleaning performance of the intermediate transfer body can be significantly improved without increasing the size or cost of the cleaning device. There is.

Furthermore, by making the circumferential speed of the intermediate transfer member different from the circumferential speed of the image carrier when the above-mentioned electric field in the opposite direction is formed, the developer that is difficult to be reversely transferred remains on the surface of the intermediate transfer member. Dust, dirt, etc. can be efficiently adhered to the image carrier by the frictional action between the image carrier and the intermediate transfer member. Therefore, the amount of developer, dust, dirt, etc. remaining on the intermediate transfer member is extremely small and can be easily removed by a cleaner for the intermediate transfer member. Thus,
The cleaning performance of the intermediate transfer body by the cleaner for the intermediate transfer body has been further improved, and the dirt on the surface of the intermediate transfer body can be completely cleaned with a simple configuration without making the cleaning device large or large-scale, and the cleaning device is expensive. It has the remarkable effect of eliminating the disadvantage of

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an image forming apparatus according to the present invention shown in FIG.
FIG. 4 is a timing diagram showing a sequence when copying only one size transfer material.

FIG. 3 is an image forming apparatus according to the present invention shown in FIG.
FIG. 3 is a timing diagram showing a sequence when successively copying transfer materials of various sizes.

FIG. 4: A3 in the image forming apparatus according to the present invention in FIG.
FIG. 4 is a timing diagram showing a sequence when copying only one size transfer material.

FIG. 5: A3 in the image forming apparatus according to the present invention shown in FIG.
FIG. 3 is a timing diagram showing a sequence when successively copying transfer materials of various sizes.

FIG. 6 is an image forming apparatus according to the present invention shown in FIG.
FIG. 7 is a timing diagram showing another sequence when copying only one size of transfer material.

[Explanation of symbols]

Claims (2)

[Claims] Claim 1: Visible developed images formed on an image carrier are sequentially superimposed and primary transferred onto an intermediate transfer member, and multiple developed images transferred onto the intermediate transfer member are collectively transferred to a transfer material. In an image forming apparatus that performs secondary transfer, at least after the completion of the secondary transfer, an electric field in a direction opposite to that during the primary transfer is formed between the intermediate transfer body and the image carrier, and the electric field is applied to the intermediate transfer body. An image forming apparatus characterized in that developer, dust, dirt, etc. remaining on the image carrier are made to adhere to the image carrier. 2. When an electric field is formed between the intermediate transfer member and the image carrier in a direction opposite to that during primary transfer, the intermediate transfer member is rotated at a circumferential speed different from that of the image carrier. The image forming apparatus according to claim 1, further comprising means for moving the image forming apparatus.