JP2002333748A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of carrying a transfer material without disturbing a transferred image during image formation on the back in both-sided image formation, by controlling and decreasing electrification of a fixed and ejected transfer material. SOLUTION: A fixing ejection roller 12 and a pre-transfer carrying roller 8 are positioned so as to longitudinally match. An electrified portion of the transfer material P, electrified by the fixing paper ejection roller 12, is again passes through the pre-transfer carrying roller 8. The carrying roller 8 is provided with a power source 22 or a diode 24, which serves as a bias application means, thereby controlling or decreasing electrification of the fixed and ejected transfer material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus and an image forming apparatus including the same, such as a copying machine and a laser printer, and more particularly, to transferring an image formed on an image carrier onto a transfer material. The present invention relates to an image forming apparatus to be used as an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as this type of image forming apparatus,
For example, there is a method in which development is formed on an image carrier such as a photoreceptor by electrophotography or the like, and the developments are transferred to a transfer material and used.

[0003] In these image forming apparatuses, a transfer material feeding and conveying device that feeds and conveys a transfer material from a transfer material feeding section,
A transfer member for transferring the transfer material to the image carrier transfer position, an image forming unit for transferring an image to the transferred transfer material to form an image, and a fixing device for permanently fixing the image transferred to the transfer material after transfer A fixing discharge roller for discharging the transfer material after fixing, and a discharge roller for sending the transfer material to a discharge tray are arranged. Further, in an image forming apparatus equipped with a double-sided printing unit, various transfer material conveying members such as a double-sided conveying roller for conveying a transfer material to a back surface process are arranged.

FIG. 7 is a schematic sectional view showing an example of the configuration of a conventional image forming apparatus. Image forming apparatus M 'shown in FIG.
, A paper feed cassette 7 is used as the transfer material feed section.
However, a paper feed roller 15 as the transfer material paper feeder is
A transport roller 8 is disposed as the transport member.

In the image forming section, a photosensitive drum 1 as the image carrier is arranged, and around the photosensitive drum 1, a charging roller 2, an exposing means 3, a developing device 4, a transfer roller 5. A cleaning device 6 is provided. A typical image forming apparatus M 'as a conventional example has the above configuration.

[0006]

However, in the case of the above prior art, the following problems have occurred. When the transfer material is nipped and conveyed by such a device, the transfer material is more or less charged by the contact friction with each conveying member. If the charge amount is large, the image is disturbed by frictional charging in the image forming process, and image defects such as image scattering are generated. In particular, this tendency was remarkable when used in a low-humidity environment or when the transfer material was left in a low-humidity environment.

On the other hand, in the case where the double-sided printing function is not provided, no problem occurs on the image even if frictional electrification occurs in the discharge section after the fixing step. When the paper roller is charged, the frictional charging unit enters the image forming step on the back surface while maintaining the charged potential, so that there is a problem that the image is scattered at the time of transferring the back surface. This phenomenon also tends to occur when the speed of the apparatus is increased or when the developer to be transferred is a developer having a high fluidity.

As described above, in the case where the double-sided printing function is provided, the paper is again conveyed to the paper feeding section via several conveying rollers after the fixing and discharging, and the back side printing is performed. Occasionally, the transfer material may be highly frictionally charged by the fixing discharge roller. After the fixing and discharging, the transfer material heated in the fixing step has a higher resistance, so that triboelectric charging tends to occur more easily.

Further, in a low-temperature and low-humidity environment or when the transfer material is left unopened, triboelectric charging is more likely to occur. In particular, when the charge amount is large, the transfer material on the back surface is largely charged. During image formation, the image may be disturbed by the transfer nip on the back side during image formation.

[0010] The present invention has been made to solve the above-mentioned problems of the prior art.
It is an object of the present invention to provide an image forming apparatus capable of controlling the transfer amount of the transfer material after the fixing and discharging and thereby reducing the charge amount of the transfer material so that the transfer material can be conveyed without disturbing the transfer image on the back surface even during the double-sided image formation.

[0011]

Means for Solving the Problems In order to achieve the above object, a first means according to the present invention comprises a plurality of conveying members which are arranged on a conveying path of a transfer material and are in pressure contact with each other. In an image forming apparatus that transports a developer image formed on an image bearing member onto a transfer material while transporting while nipping, a pair of transport members for transporting at least the transfer material while nipping the transfer material between transfer portions, After fixing, a sheet discharging member for conveying and discharging the sheet while nipping was held, and the longitudinal position of the conveying member was made to coincide with the longitudinal position of the sheet discharging member.

According to the first means, at least a pair of conveying members for conveying at least the transfer material while nipping the transfer portion, and a discharge member for conveying and discharging while nipping the transfer material after fixing. By making the longitudinal position of the conveying member coincide with the longitudinal position of the paper discharging member, the frictional charging portion of the fixing paper discharging member abutting portion is again passed through the conveying member before transfer during double-sided printing. It is possible to obtain a good transferred image free from image scattering.

The second means has a plurality of pairs of conveying rollers which are disposed on the conveying path of the transfer material and are in pressure contact with each other, and conveys the transfer material while nipping it, and forms the developer image formed on the image carrier. And a pair of transport rollers for transporting at least a transfer material while nipping the transfer material, and a paper discharge for transporting and discharging while nipping the transfer material after fixing the transfer material. A roller was held, and the longitudinal position of the transport roller portion was made to coincide with the longitudinal position of the discharge roller portion.

According to the second means, since the transporting member is a transporting roller, the transporting of the transfer material can be stabilized, and the overcharged portion of the transfer material can be stably discharged or alleviated. A good transfer image free from scattering can be obtained.

The third means has a plurality of conveying members which are arranged on the conveying path of the transfer material and are in pressure contact with each other. The conveying member conveys the transfer material while nipping the transfer material, and transfers the developer image formed on the image carrier. In an image forming apparatus for transferring onto a transfer material, at least a pair of pre-transfer transfer members for transferring the transfer material while holding the transfer material between the transfer portions, and a discharge for transferring and discharging while holding the transfer material while holding the transfer material therebetween Member, and an intermediate transport member that transports the transfer material to the next process after fixing and discharging. The longitudinal position of the pre-transfer transport member, the longitudinal position of the paper discharge member, and the longitudinal position of the intermediate transport member. Matched.

According to the third means, a pair of pre-transfer transport members for transporting the transfer material while nipping the transfer portion, and a paper discharge for transporting and discharging while nipping the transfer material after fixing. And a middle part conveying member for conveying the transfer material to the next step after fixing and discharging, and the longitudinal position of the pre-transfer conveying member, the longitudinal position of the paper discharging member, and the longitudinal position of the intermediate conveying member coincide with each other. By causing the frictional charging portion of the discharge member contact portion to pass again through the intermediate conveyance member and the conveyance member before transfer, the potential of the overcharged portion of the transfer material can be more neutralized and reduced. Even on the back side, a good transfer image free from image scattering can be obtained.

In the fourth means, the width of the transfer member before transfer is set wider than the other transfer member widths. According to this means, all areas closely charged by the discharged paper member after fixing can be accommodated in the contact area of the pre-transfer conveyance member,
It is possible to reliably discharge the charged portion over the entire area of the longitudinal contact portion.

The fifth means is to form a pair of transport members for transporting the transfer material to the transfer section by using a conductive member,
A means for applying a bias was provided to at least one of the transport members, and the other was connected to ground. As a result, the charge amount can be reliably controlled irrespective of the charge state of the transfer material, and a good transfer image without image scattering can be obtained.

The sixth means is to form a pair of transport members for transporting the transfer material to the transfer section with conductive members,
Connecting a diode to at least one of the transport members,
The other was connected to ground. According to the sixth aspect, instead of applying the bias from an external power supply, the use of a diode makes it possible to reliably control the charge amount irrespective of the charge state of the transfer material, and to provide a simpler and less expensive image. A good transferred image free from scattering can be obtained.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings. However, the dimensions, material, shape,
Unless otherwise specified, the relative arrangement etc.
It is not intended to limit the technical scope of the present invention only to them. In the following drawings, the same reference numerals are given to members described in the drawings used in the description of the related art and members similar to the members described in the drawings described above.

(First Embodiment) Referring to FIGS. 1 and 2,
An image forming apparatus according to the first embodiment will be described.
FIG. 1 is a cross-sectional view illustrating a configuration example of an image forming apparatus provided with a duplex unit. First, the configuration of the image forming apparatus M will be described with reference to FIG. Image forming apparatus M shown in FIG.
Has a drum-type electrophotographic photosensitive member (photosensitive drum 1) as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in a counterclockwise direction (direction of an arrow R1 in the figure) by a driving unit (not shown).

Around the photosensitive drum 1, a charging roller (charging device) 2, an exposing unit 3, a developing device 4, a transfer roller (transfer unit, transfer device) 5, and a cleaning device 6 are arranged in this order along the rotation direction. Are located. Further, a paper feed cassette 7 containing a sheet-like transfer material P such as paper is disposed below the apparatus main body M. Then, in order from the upstream side along the transfer path of the transfer material P, the sheet feeding roller 15 and the transfer roller
(Conveyance member, pre-transfer conveyance member) 8, top sensor 9, conveyance guide 10, fixing device 11, fixing discharge roller (discharge member) 12, discharge roller 13, and discharge tray 14.

Next, the operation of the image forming apparatus M having the above configuration will be described. The photosensitive drum 1, which is rotationally driven in the direction of arrow R1 by a driving unit (not shown), is uniformly charged to a predetermined polarity and a predetermined voltage on the charging roller. The exposed surface of the charged photosensitive drum 1 is subjected to image exposure L based on image information by exposure means 3 such as a laser optical system, and the charge of the exposed portion is removed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller 4a. A developing bias is applied to the developing roller 4a to attach toner to the electrostatic latent image on the photosensitive drum 1 and develop the toner as a toner image (developer material image). Imaging).

The transfer roller 5 transfers the toner image to a transfer material P such as paper. The transfer material P is stored in a paper feed cassette 7, fed by a feed roller 15, transported by a transport roller 8, and transferred between the photosensitive drum 1 and the transfer roller 5 via a top sensor 9. Nip 5
conveyed to a. At this time, the transfer material P is
As a result, the leading edge is detected, and synchronization with the toner image on the photosensitive drum 1 is achieved. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the transfer material P.

The transfer material P carrying an unfixed image on the surface by transfer is conveyed to a fixing device 11 along a conveyance guide 10, where the unfixed toner image is heated and pressed to be fixed on the surface of the transfer material P. You. The transfer material P after fixing the toner image is conveyed by a fixing discharge roller 12 and is discharged by a discharge roller 13 onto a discharge tray 14 on the upper surface of the apparatus main body M.

On the other hand, on the photosensitive drum after the transfer of the toner image, the toner (transfer residual toner) which has not been transferred onto the transfer material P and remains on the surface is removed by the cleaning blade 6a of the cleaning device 6.
And is subjected to the next image formation. By repeating the above operation, images can be formed on the transfer material P one after another.

Next, an image forming process at the time of double-sided printing when the present configuration is used will be described as a subsequent process. As shown in FIG. 1, a reversing roller 20 for reversing the transfer material P for double-sided printing and transporting the same to the back surface process, a reversing transport roller (intermediate transport member)
21. After the step of fixing and discharging the front surface, the rear end of the transfer material P comes out of the fixing and discharging roller 12. Then, the reversing roller 20 stops while the transfer material P is held between the reversing rollers 20, and the image formation on the front surface ends.

After the front side image is formed, the reversing roller 20 is rotated in the reverse direction to enter a back side image forming step. The transfer material P is sent to the reverse transport roller 21 and enters a back-side paper feeding process in synchronization with the image forming timing on the back side. After the back side paper is fed, the back side is fixed and discharged through the same image forming process as that for the front side image formation, and the duplex printing is completed.

In the conventional apparatus, when performing double-sided printing,
In the case where the resistance of the transfer material P is high, the transfer material P is charged by the fixing discharge roller at the front surface or the conveyance roller portion immediately after the transfer roller P, and image scattering on the back surface may be observed at the roller. . This is because the transfer material P dries when the surface is fixed, and further increases the resistance.
Is more likely to occur when the resistance is high, and more pronounced when the device is used in a low humidity environment.

As described above, in the case of high-resistance paper or use in a low-humidity environment, the transfer material P becomes extremely
The surface resistance of the paper becomes high.
When rubbed, it becomes very easy to be charged. Depending on the environment and paper type, it may slightly exceed +3.0 kV.

Once charged, the charging potential may not be attenuated even when the transfer material P is conveyed as it is, and may remain charged during image formation on the back surface. When the transfer material P is sent to the transfer position in such a state, when the negatively-developed developer is carried on the image carrier, the transfer is performed in the vicinity of the nip before the image carrier and the transfer material P come into close contact with each other. The transfer of development starts due to the force received from the positive charge on the surface of the material P. This phenomenon is particularly remarkable in the case of a developer having high fluidity. Further, the transfer of the developer in a state where there is a gap in the vicinity of the nip before the close contact is displaced from a predetermined position where the development is transferred in the close contact state, and the developer is liable to be scattered. Will occur.

As a result, the image is scattered from the leading end to the trailing end of the transfer material P at the contact portion of the transfer material P at the fixing paper discharge roller, and appears remarkably as an image of the fixing paper discharge roller 12. The image pattern is very noticeable in the case of a one-dot pattern such as a halftone.

FIG. 2 shows the positional relationship of the rollers of the image forming apparatus used in the present embodiment, and is a schematic projection view of the apparatus viewed from above. In FIG. 2, the longitudinal position of the fixing discharge roller 12 and the longitudinal position of the transport roller 8 before transfer are made to match. Thus, the charging section of the transfer material P charged in the fixing discharge roller section is configured to pass through the pre-transfer conveyance roller 8 again. As a result, the charged portion of the transfer material P once charged by the fixing paper discharge roller 12 passes through the pre-transfer conveyance roller 8 again during the formation of the back surface image, thereby controlling and relaxing the charge amount. This makes it possible to reduce scattering.

Specifically, the transfer material has a high resistance immediately after fixing and discharging, and tends to be more susceptible to charge-up due to triboelectric charging by passing through the fixing and discharging roller in that state. In the case of the configuration described above, since the portion once charged by the fixing discharge roller enters the image forming process for both sides without directly contacting any roller, the overcharged portion is held as it is, and as a result, In the image forming step, the charge is sufficiently maintained even in the image forming step, and image defects are likely to occur.

On the other hand, the transfer material, which had a high resistance immediately after fixing and discharging, has a somewhat reduced resistance in the transfer material transporting process in the double-sided process, so that the charge becomes unstable, and
Since the electric charge becomes unstable due to the fluttering of the transfer material during the transfer of the transfer material, the charged portion is again held and conveyed by the conveyance roller before the transfer during the double-sided image formation in such a state. As a result, it is possible to suppress the charge amount to a smaller amount than the charge-up in the high resistance state immediately after fixing and discharging.

Tables 1 and 2 show changes in the charge amount of the transfer material P when the conventional apparatus is used and when the apparatus according to the present embodiment is used. This is measured and compared at two points (B) immediately before the transfer nip 5a at the time of the back surface.

The experiment was conducted in a low-temperature and low-humidity environment of 15 ° C./10% (hereinafter referred to as an L / L environment). Further, in the second embodiment and the third embodiment described below, the same experiment environment is used. In the paper type, thin paper, high-resistance paper, recycled paper, etc. are more likely to be charged up, and the roller mark is remarkable. In this embodiment, the paper of Badger Bond 60g paper (PAPER MILLS, INC) which is thin paper The comparison was made between two types: immediately after opening (paper type 1) and after leaving for L / L for 24 hours (paper type 2). In the second embodiment and the third embodiment, a comparison is made for similar paper types.

[Table 1]

[Table 2]

As shown by the results in the above table, in the case of the conventional apparatus, the potential charged in the fixing and discharging section is maintained almost as it is, and the charged state is introduced into the transfer nip 5a on the back side. Thus, it has been found that in the apparatus of the present embodiment, charging is assisted in the pre-transfer conveyance unit during the back surface image formation.

Next, Tables 3 and 4 show the evaluation results of image scattering due to paper type and image pattern difference for each of the conventional apparatus and the image forming apparatus used in the present embodiment. Here, as the evaluation of image scattering, there are five ranks: rank 1: occurrence in all areas, rank 2: light in all areas, rank 3: light in some areas, rank 4: slight occurrence, and rank 5: no occurrence. Evaluation was used.

[Table 3]

[Table 4]

As a result of the above table, the difference in the occurrence state of image scattering between the apparatus of the present embodiment and the conventional apparatus became remarkable especially in the halftone image at the time of the back side. As described above, by employing the configuration of the present embodiment, it is possible to suppress scattering on the back surface and maintain a good image.

In this embodiment, as shown in FIG. 2, the width of the transport roller 8 in the longitudinal direction is set to be the same as the width of the fixing discharge roller 12 in the longitudinal direction. It is not the purpose. The width in the longitudinal direction of the conveyance roller 8 may be configured to be wider than the width of the other conveyance rollers in the longitudinal direction as long as the longitudinal position of the fixing discharge roller 12 is covered. With this configuration, all the areas closely charged by the fixing discharge roller 12 can be accommodated in the contact area of the transport roller 8 before transfer, and the charging unit can more reliably control the charge amount over the entire area of the longitudinal contact section. , Can be relaxed.

(Second Embodiment) FIGS. 3 and 4 show a second embodiment. In the second embodiment, the transport roller 8 is provided with a bias applying unit. Other configurations and operations are the same as those of the first embodiment, so that the same components are denoted by the same reference numerals, and
The description is omitted.

In the prior art, when double-sided printing is performed using a transfer material P left unopened in a low-temperature and low-humidity environment,
It has been found that the transfer material P triboelectrically charged at the fixing and discharging portion is more likely to be introduced into the transfer nip 5a while maintaining the charged charge when the back surface is formed, and the occurrence of image scattering becomes more remarkable. Under such an environment, even in the configuration of the first embodiment, it may be difficult for the transport roller 8 before transfer to reduce the frictional charging potential of the fixing discharge roller 12 on the back side.

On the other hand, as means for controlling the charging potential of the pre-transfer conveying roller to suppress image scattering, as the prior invention by the present applicant, the conveying roller 8 is a conductive roller, one of the pair of rollers is grounded, and the other is grounded. A method is proposed in which a bias applying unit (power supply 22) or a charge control unit such as a diode 24 is provided to control the charge on the transport roller 8 to prevent overcharging, thereby avoiding an image defect.

FIG. 3 is a schematic sectional view for explaining the second embodiment. In this embodiment, as shown in FIG. 2, the longitudinal position of the fixing discharge roller and the longitudinal position of the transport roller before transfer are made to coincide with each other, and here, the transport roller before transfer is electrically conductive for the reason described above. Roller pair, conveying roller 8
Both a and 8b are conductive rollers, a power supply 22 as bias applying means is provided in 8a, and a ground 23 is connected to 8b to ground.

The current path is provided in the conveying roller 8 before transfer in this way, a bias is applied while the transfer material P passes through the conveyance roller nip, and a current flows through the transfer material P, so that a charge is always applied to the conveyance nip. As a result, the image forming surface and the non-image forming surface of the transfer material P can be maintained at a predetermined potential up to the transfer nip 5a.

Here, the conveying roller 8 is used as an applied bias.
A power supply 22 of -500 V was connected to a, and a ground 23 was connected to the transport roller 8b to ground. Here, the applied bias is
The reason for setting the voltage to 500 V is that if the voltage is lower than 500 V, the effect may be insufficient, and if the voltage is higher than necessary, other image problems such as leakage may occur. It should be noted that the optimum bias value for this set value differs depending on the device configuration.

Tables 5 and 6 show the change in the charge amount of the transfer material P between the conventional apparatus, the image forming apparatus used in the first embodiment, and the image forming apparatus of the present embodiment. (A) and immediately before the transfer nip 5a at the back side
(B) are measured and compared at two points.

[Table 5]

[Table 6]

As shown in the results of the above table, in the case of the conventional apparatus, the potential charged in the fixing and discharging section is almost maintained as it is, and the charged state is introduced into the transfer nip 5a on the back side. Thus, it has been found that in the apparatus of the present embodiment, charging is assisted in the pre-transfer conveyance unit during the back surface image formation. Further, regarding the charge amount of the transfer material P immediately before the transfer nip 5a at the time of the back side, the apparatus of the first embodiment and the apparatus of the present embodiment are compared. As a result, the charge amount was reduced.

As described above, the charging portion of the transfer material P charged by the fixing paper discharging roller 12 is passed again by the transport roller 8 before the back surface transfer provided with the charge control means, so that The charge control effect of the first embodiment or more can be obtained, and as a result, image defects can be suppressed.

Tables 7 and 8 show evaluation results of image scattering due to paper type and image pattern difference for each of the conventional apparatus, the image forming apparatus of the first embodiment, and the image forming apparatus used in the present embodiment. is there. Here, there are five-level evaluations of image splattering: Rank 1: dark occurrence in all areas, rank 2: light occurrence in all areas, rank 3: light occurrence in some areas, rank 4: slight occurrence, and rank 5: no occurrence. Was used.

[Table 7]

[Table 8]

As a result of the above table, the difference in the state of occurrence of image scattering between the apparatus of the present embodiment and the conventional apparatus became remarkable, especially in the halftone image at the time of the back side. Furthermore, comparing the apparatus of the first embodiment with the apparatus of the present embodiment, in the apparatus of the present embodiment, image scattering does not occur at all with any paper type, and the results show that the image scattering can be more prevented. became. As described above, by adopting this configuration, an image forming apparatus that can maintain a good image with no scattering of an image on the back surface even when using a high-resistance sheet that has been left open in a low-temperature and low-humidity environment is provided. We were able to.

On the other hand, in the present embodiment, the transport rollers 8
A negative (minus) bias is applied to the non-image forming surface side of the a side, and the image forming surface side of the transport roller 8b is connected to the earth 23 and grounded, so that the image forming surface side of the transfer material P is negative.
By inducing a (minus) charge, the unfixed image is prevented from being attracted to the transfer material P before the transfer, thereby preventing the image from being disturbed. However, as shown in FIG. The same effect can be obtained by applying a positive (plus) bias by connecting a power supply 22 as a bias applying means on the image forming surface side of the conveying roller 8b side and connecting the ground to an earth 23, and image disturbance. Can be prevented.

(Third Embodiment) FIGS. 5 and 6 show a third embodiment. In the third embodiment, the transport roller 8 is provided with a diode 24. Other configurations and operations are the same as those of the first and second embodiments, so that the same components are denoted by the same reference numerals and description thereof will be omitted.

FIGS. 5 and 6 are schematic sectional views of the image forming apparatus used in this embodiment. In FIG. 5, unlike the case of the second embodiment, a current flows from the transport roller 8a to the ground 23 between the transport roller 8a and the ground 23 to the transport roller 8a disposed on the non-image forming surface side. It is characterized in that the diode 24 is connected in the direction.

By the diode 24 connected to the transport roller 8a, a negative (negative) charge is always injected into the transport roller 8a, and as a result, a positive charge is applied to the non-image forming surface of the transfer material P.
A (plus) charge and a negative (minus) charge are induced on the non-image forming surface side.

For this reason, similarly to the second embodiment, a negative charge is induced in the overcharged portion of the transfer material P charged in the fixing and discharging portion on the front side when passing through the pre-transfer conveyance roller on the back side,
Since the amount of charge in the overcharged portion can be reduced, the toner on the photosensitive drum 1 before transfer is prevented from being inadvertently transferred before reaching the transfer portion, and as a result, scattering of the image is suppressed. The same effect as that of the second embodiment was obtained. By connecting the diode 24 instead of applying the bias to the conveying roller 8 in this manner, the occurrence of image scattering is suppressed with a simpler and cheaper configuration than in the case of the second embodiment. It is possible to obtain a perfect image.

On the other hand, FIG. 6 shows that the diode 24 is connected to the transport roller 8b disposed on the image forming surface, between the transport roller 8b and the ground 23, in the direction in which current flows from the ground 23 to the transport roller 8b. It is characterized by.
A positive (plus) charge is injected into the transport roller 8b by the diode 24 connected to the transport roller 8b, and as a result, a negative (minus) charge is induced on the image forming surface of the transfer material P.

As a result, as in the case of FIG. 5, a negative charge is induced in the overcharged portion of the transfer material P charged in the fixing and discharging portion on the front side when passing through the pre-transfer conveyance roller 8 on the back side.
By controlling and relaxing the charge amount of the overcharged portion, it is possible to prevent the toner on the photosensitive drum 1 before the transfer from being carelessly transferred before reaching the transfer portion, and as a result, the scattering of the image is suppressed. . Further, the same effect as that of the second embodiment can be achieved with a simpler configuration, and cost reduction can be achieved at the same time.

[0060]

As described above, according to the present invention,
Without requiring a particularly large mechanism, the longitudinal position of the discharge member after fixing and the longitudinal position of the transport member before transfer are matched, and the charged portion of the transfer material charged by the discharge roller is transported by the transport member before transfer. Since the charge amount of the transfer material after fixing and discharging was able to be controlled and relaxed as a configuration that allows the sheet to pass again, the charge amount of the transfer material after fixing and discharging was controlled and relaxed, so that double-sided image formation was achieved. It is possible to provide an image forming apparatus that can transfer a transfer material without causing a transfer image disturbance at the back side.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus illustrating a first embodiment.

FIG. 2 is a schematic diagram illustrating a roller positional relationship for explaining the first embodiment.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus illustrating a second embodiment.

FIG. 4 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus illustrating a second embodiment.

FIG. 5 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus illustrating a third embodiment.

FIG. 6 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus illustrating a third embodiment.

FIG. 7 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus illustrating a conventional example.

[Description of Signs] 1 photosensitive drum 2 charging roller 3 exposure means 4 developing device 4a developing roller 5 transfer roller 5a transfer nip 6 cleaning device 6a cleaning blade 7 paper feed cassette 8 transport roller (pair) 8a (lower in the figure) Roller 8b (upper in the figure) transport roller 9 top sensor 10 transport guide 11 fixing device 12 fixing discharge roller 13 discharge roller 14 discharge tray 15 paper feed roller 20 reversing roller 21 reversing transport roller 22 power supply (bias applying unit) 23 Ground 24 Diode L Image exposure M Main unit M '(Conventional example) Main unit P Transfer material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B65H 5/06 B65H 5/06 F 3F100 29/20 29/20 3F101 29/60 29/60 A 85/00 85/00 G03G 15/16 G03G 15/16 21/14 21/00 372 F term (reference) 2H027 DA21 DA50 DC04 DC05 DE07 DE09 EC06 ED16 ED24 EE02 EF09 2H072 AB15 BA03 CA01 CB01 CB03 FB01 JA02 2H200 FA08 FA16 GA02 GA10 GA23 GA34 GA44 GB26 GB41 HA02 HB12 HB22 JA02 JA18 JA28 JA29 JA30 JB10 JB40 JB48 NA02 NA21 PA12 PB12 PB39 3F049 AA06 CA13 CA31 DA12 LA03 LA07 LB03 3F053 EA03 EA05 EB01 EB04 LA03 LA07 LB03 3A100 CA03A03 CA03

Claims (6)

[Claims] An image forming apparatus includes a plurality of transfer members which are disposed on a transfer path of a transfer material and are in pressure contact with each other. The transfer member is transported while sandwiching the transfer material, and a developer image formed on an image carrier is transferred onto the transfer material. An image forming apparatus having a transfer unit for transferring the transfer material while nipping the transfer material between the transfer unit; An image forming apparatus having a sheet discharging member, wherein a longitudinal position of the conveying member is made to coincide with a longitudinal position of the sheet discharging member. 2. The developer image formed on the image carrier, comprising a plurality of pairs of conveying rollers which are arranged on a conveying path of the transfer material and are in pressure contact with each other, and convey while nipping the transfer material. An image forming apparatus having the transfer unit that transfers the transfer material onto the transfer material, wherein at least one pair of the transport rollers for transporting the transfer material while nipping the transfer material between the transfer units, and nipping the transfer material after fixing the transfer material. 2. The image forming apparatus according to claim 1, further comprising a discharge roller for transporting and discharging the paper, wherein a longitudinal position of the transport roller is made to coincide with a longitudinal position of the discharge roller. 3. A transfer member, which is disposed on a transfer path of the transfer material and is in pressure contact with the transfer member, transfers the transfer material while nipping the transfer material, and transfers the developer image formed on the image carrier onto the transfer material. In the image forming apparatus for transferring, at least a pair of the pre-transfer conveying members for conveying the transfer material while nipping the transfer member, and a discharge for conveying and discharging while nipping the transfer material after fixing. A paper member, and an intermediate conveying member that conveys the transfer material to the next step after the fixing and discharging, the longitudinal position of the pre-transfer conveying member, the longitudinal position of the paper discharging member, and the longitudinal position of the intermediate conveying member. 3. The image forming apparatus according to claim 2, wherein: 4. The image forming apparatus according to claim 1, wherein the width of the conveying member before transfer is wider than the width of other conveying members. 5. A pair of transport members for transporting a transfer material to a transfer portion are formed of conductive members, and means for applying a bias to at least one of the transport members is provided, and the other is connected to ground. The connection is made.
4. The image forming apparatus according to claim 1. 6. A pair of transport members for transporting a transfer material to a transfer section are formed of conductive members, and a diode is connected to at least one of the transport members and the other is connected to ground. The image forming apparatus according to claim 1, wherein: