JP2000321884A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image defect in company with the separation discharge occurring at the time of separating transfer paper from a transfer belt. SOLUTION: The image forming device prevents the image defect in company with the separation discharge occurring when separating the transfer paper P from the transfer belt 8 by restraining the discharge on a rear side of the transfer paper P parting from the transfer belt by stimulating the discharge on the surface of the transfer paper P by means of a discharge stimulating roller 140. Moreover, the device prevents the scattering or the worsening of offsetting of toner in company with the generation of ozone or lowering of the electrostatic attraction force between the transfer paper P and the toner, by unnecessitating the use of corona separation charger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic apparatus, and more particularly, to an image forming apparatus for transferring a toner image to a transfer material on a transfer belt.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses have been improved in speed, function and color, and various types of printers have been commercialized.

In recent years, the need for automatic double-sided printing has been more and more demanded from the viewpoint of enhancing the functions of printers. For this purpose, the following electrophotographic system has been proposed. .

(1) An in-line type image forming apparatus in which a plurality of image forming units of different colors are arranged in series and a transfer paper as a transfer material is conveyed by a belt-shaped conveying unit, and a toner image is sequentially multiplex-transferred. Is capable of forming a color image at high speed, and has wide potential for business use.

In order to reduce the size of the apparatus, an in-line type printer has been proposed in which stations are arranged vertically and transfer papers are conveyed vertically to reduce the installation area of the apparatus. . Further, the printer of this type has a feature that the main body is vertically divided along a transfer paper transport path so that jam easiness and consumable parts can be easily replaced.

However, in such a vertical transport path, it is necessary to transport the transfer paper against gravity, so that the transportability is deteriorated, and image defects due to jams and wobble of the transfer paper are likely to occur.

(2) On the other hand, an electrophotographic apparatus using a solid drum type intermediate transfer member is expected to have a large market for personal use because it is inexpensive and advantageous in color registration and the like.

However, when an intermediate transfer drum is employed, it is necessary to superpose four color toner images corresponding to the maximum transfer paper size on the circumference thereof. 180 in the case of
mm intermediate transfer drums are required,
Since the curvature of the next transfer portion is small, it is difficult to separate the curvature, the separation of the transfer paper from the intermediate transfer drum is not stable, and there is a problem that the possibility of a jam is large.

Therefore, in order to solve the instability of vertical conveyance in the above-described in-line system and the instability of conveyance such as separation failure in the intermediate transfer drum, a transfer belt system capable of simultaneously performing transfer and paper conveyance is adopted. It becomes necessary to adopt this transfer belt system, so that the degree of freedom in the layout of the main body is increased and the transfer of the transfer paper can be stabilized.

When a high-resistance transfer sheet is separated from a contacting member, a peeling discharge occurs due to a voltage applied to an air gap that rapidly increases between the transfer sheet and the member in a separation process. appear.

For example, when a transfer belt is used in the above-described image forming apparatus, a peeling discharge generated when the transfer paper is separated from the transfer belt may cause an image defect.

That is, when the transfer / conveying means is a transfer roller system as shown in FIG.
The separation discharge occurs at two places between the surface of the photosensitive drum 150 and the photosensitive drum 150 and between the back surface of the transfer paper P and the transfer roller 5, so that the discharge shock at each part is relatively small. Become.

On the other hand, the transfer / conveying means is shown in FIG.
In the case of a transfer belt system as shown in FIG.
Does not occur on the front side of the transfer paper P,
, The discharge amount is relatively large, and image defects tend to occur.

As a result, due to the intense discharge that occurs on the back surface of the transfer paper P, a so-called triassic discharge mark or a so-called explosion image in which toner scatters due to a discharge shock in a high-density image to which a large amount of toner has adhered. Image failure may occur.

In order to prevent this, generally, a method is employed in which the transfer paper P on the transfer belt 8 is neutralized by a corona separation charger 110 as shown in FIG. That is, by removing the charge of the transfer paper P by the corona separation charger 110, peeling discharge and image defects generated on the back surface of the transfer paper P and the surface of the transfer belt 8 are prevented.

More specifically, an AC voltage having a peak-to-peak voltage of about 9 kV is applied to the corona wire to remove electricity from the transfer paper P on the transfer belt 8 and to separate the transfer belt 8 from the transfer paper P. Suppress discharge in the part.

[0017]

However, newly providing the corona separation charger 110 generates ozone, which leads to an increase in size and cost of the apparatus.

Further, when the corona discharge of the transfer paper P is performed in the separation section, not only the transfer paper P but also the toner is simultaneously discharged, and the electrostatic attraction force between the transfer paper P and the toner is reduced. As a result, adverse effects such as scattering of toner in the fixing unit and deterioration of offset occur.

As described above, in the conventional image forming apparatus,
If a corona separation charger is installed to prevent the occurrence of image defects due to peeling discharge when separating the transfer paper from the transfer belt, a new problem arises, so an image called triasi without using the corona separation charger There is a need to prevent defects.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide an image forming apparatus which eliminates image defects caused by peeling discharge generated when a transfer material is separated from a transfer belt. I do.

[0021]

In order to achieve the above object, an image forming apparatus according to the first aspect of the present invention has an image carrier on which a toner image is formed on a surface thereof, and carries and transports the image on the surface. A transfer belt on which a toner image on the image carrier is transferred to a transfer material, wherein a separation unit provided at a downstream end of the transfer belt separates the transfer material after the transfer of the toner image from the transfer belt. A discharge excitation member is provided so as to sandwich the transfer material separated by the separation unit between the transfer belt and the transfer belt, and the shape of the discharge excitation member is changed from the back surface of the transfer material by the separation unit. The transfer belt is curved so as to gradually move away from the surface of the transfer material with respect to the transfer belt moving away gradually.

According to the second aspect of the present invention, the discharge excitation member is a discharge excitation roller having a dielectric layer on a surface.

According to the third aspect of the present invention, the discharge excitation member is a discharge excitation plate having a dielectric layer on a curved surface where the surface of the transfer material gradually separates.

According to the fourth aspect of the present invention, the discharge excitation member is provided on the first side of the transfer material after printing.
It is provided so as to be able to come into contact with and separate from the transfer belt when printing on a surface.

According to a fifth aspect of the present invention, a plurality of image forming units each having the image carrier are arranged along the transfer material conveying direction of the transfer belt, and are arranged at the most downstream side. The image carrier of the image forming unit is used as the discharge excitation member.

According to the invention described in claim 6, the most downstream image carrier also serving as the discharge excitation member has a diameter of 50 mm.
It is as follows.

[Operation] According to the invention based on the above configuration, the discharge on the back surface of the transfer material separated from the transfer belt is suppressed by exciting the discharge on the surface of the transfer material by the discharge excitation member.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<First Embodiment> FIG. 1 is a schematic structural view showing a first embodiment of an image forming apparatus according to the present invention.

In FIG. 1, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as a first image carrier, and has a predetermined peripheral speed (counterclockwise) in a direction indicated by an arrow R1 in FIG. (Process speed).

The photosensitive drum 1 includes a primary charging roller 2 for uniformly charging the photosensitive drum 1 along the rotation direction, an exposure unit 3 for forming an electrostatic latent image on the photosensitive drum 1, and a photosensitive drum 1. Rotary developing means 4 for visualizing the electrostatic latent image formed on the photosensitive drum 1;
Intermediate transfer drum 13 as second image carrier for next transfer
0 and a cleaner 6 for removing the toner remaining on the photosensitive drum 1 are sequentially arranged.

Exposure means 3 includes a laser diode, a polygon scanner, a lens group, a folding mirror, and the like, and receives an image exposure to form an electrostatic latent image corresponding to a first color component image (for example, a yellow component image) of a target color image. An image is formed. The developing means 4 includes a yellow developing device 41, a magenta developing device 42, a cyan developing device 43, and a black developing device 44. 42, 43, and 44 oppose the photosensitive drum 1 during the developing process to visualize the electrostatic latent image. Each toner is a so-called non-mag toner containing no magnetic material, and is developed by a non-magnetic one-component contact developing method.

The intermediate transfer drum 130 has an arrow R13 shown in the figure.
It is driven to rotate in the 0 direction (clockwise) at the same peripheral speed as the photosensitive drum 1 and has a diameter of 180 mm in order to correspond to the maximum paper size of A3.

A transfer belt 8 is provided in contact with the lower surface of the intermediate transfer drum 130. The transfer belt 8 includes a transfer roller 5 as a transfer member having a diameter of 20 mm and a drive roller (tension roller) 170. It is stretched and wound. A desired secondary transfer bias is applied to the transfer roller 5 by a secondary transfer bias source (not shown), and the drive roller 170 is connected to the ground. The drive roller 170 is provided with a discharge excitation roller 140 as a discharge excitation member to be described later so as to be able to contact and separate from the downstream end of the transfer belt 8.

In the figure, reference numeral 160 denotes an intermediate transfer member cleaner, and the intermediate transfer member cleaner 160 and the transfer belt 8 sequentially transfer toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer drum 130. In the execution process to be performed, the intermediate transfer drum 130 is configured to be appropriately moved toward and away from the intermediate transfer drum 130.

Next, an image recording operation of a copying machine or a laser printer as an image forming apparatus will be described.

A primary transfer bias is applied to the intermediate transfer drum 130, and a yellow toner image, which is a first color component image formed and carried on the photosensitive drum 1, is transferred between the photosensitive drum 1 and the intermediate transfer drum 130. During the passage through the contacting primary transfer nip, the electric field and pressure formed by the primary transfer bias cause the one
Next is transferred.

Similarly, a magenta toner image as a second color component image, a cyan toner image as a third color component image, and a black toner image as a fourth color component image are sequentially superimposed and transferred onto the intermediate transfer drum 130. Thus, a composite color toner image corresponding to the target color image is formed.

The transfer paper P as a transfer material is fed at a predetermined timing to a transfer nip where the transfer belt 8 and the intermediate transfer drum 130 are in contact with each other, and at the same time, the transfer paper P is transferred from the secondary transfer bias source to the transfer roller 5. By applying the next transfer bias, the composite color toner image on the intermediate transfer drum 130 is secondarily transferred onto the transfer paper P. Thereafter, the transfer paper P is transported to the fixing device 9 and is heated and fixed.

The printer performs automatic double-sided recording.
A flapper that guides the transfer paper P to either a paper discharge tray or an automatic duplex unit is provided downstream of the fixing device 9 in the transport direction of the transfer paper P (both are not shown). Then, by switching the flapper, the transfer paper P is conveyed to a discharge tray or an automatic duplex unit. The automatic double-sided unit is provided with a reversing unit for reversing the transfer paper P. The transfer paper P is reversed at the reversing unit, guided again to the registration roller pair 15, and then transferred to the registration roller pair 15 at the image forming unit. Printing is performed on the unprinted surface.

Also, the transfer paper P
After the transfer of the toner image to the intermediate transfer drum 130, the transfer residual toner remaining on the intermediate transfer drum 130 is removed.
Collect by 0.

The transfer belt 8 of the present embodiment has a surface layer of a fluororesin having a volume resistance of 1 × 10 ¹³ Ωcm and a thickness of 20 μm;
It has a two-layer structure in which a urethane elastomer having a volume resistance value of 1 × 10 ⁶ Ωcm in which carbon is dispersed in the base layer is laminated. By providing a high-resistance resin on the surface layer, leakage of electric charge from the transfer paper P is prevented, Is increasing.

The outer diameter of the transfer belt 8 is φ65 × 300.
The tube has a thickness of 300 μm, and the volume resistivity of the entire belt is 1 × 10 ¹⁰ Ωcm. The volume resistance was measured using a measurement probe conforming to JIS method K6911, using a high resistance meter R8340 manufactured by ADVANTEST.
The value measured by applying a voltage of 100 V is normalized by the belt thickness before use.

Next, a case where automatic double-sided printing is performed using the above-described printer will be described.

The main component of the transfer paper P is cellulose,
Under normal circumstances, it absorbs moisture to some extent, so 1 ×
It has a resistance value of about 10 ⁹ Ωcm. Further, the transfer paper P printed on the first side is heated by passing through the fixing device 9 to evaporate water. Such transfer paper P
Has a high resistance up to about 1 × 10 ¹² Ωcm, and is in a state where charges can be easily held.

In this state, the transfer paper P printed on the second side is strongly charged by the transfer charge, and the transfer belt 8
A very strong adsorbing force works between them.

Accordingly, when the transfer paper P is separated from the transfer belt 8 by a curvature, the charge pairs between the transfer belt 8 and the transfer paper P are separated, and the capacitance between them decreases as the separation process proceeds. As a result, the voltage increases sharply, causing severe discharge.

Unlike the transfer roller system, the discharge is caused by the gap between the transfer belt 8 and the transfer paper P, and the shock causes an image defect called triasi. To prevent this, in this embodiment, A discharge excitation roller 140 is newly provided at a separation portion between the transfer paper P and the transfer belt 8, that is, at a downstream end of the transfer belt 8. This excites the discharge not only on the back surface but also on the front surface of the transfer paper P, thereby preventing image defects such as triad.

In this case, the characteristics required for the discharge excitation roller 140 include a surface potential for suppressing the adhesion of toner to the discharge excitation roller 140 and a high resistance characteristic for suppressing the flow of an excessive current. It is.

In this embodiment, since the negative toner is used as the developer of the developing means 4, the discharge excitation roller 140
Is required to be located on the minus side of the surface potential of the transfer belt 8 in order to prevent toner from adhering.

However, if the potential difference between the discharge excitation roller 140 and the surface of the transfer belt 8 is too large, discharge is generated by Paschen's law upstream of the nip portion between the discharge excitation roller 140 and the transfer belt 8, causing image disturbance. I will.

On the other hand, if the resistance value of the discharge excitation roller 140 is too low, the current will flow too much and the polarity of the toner on the transfer paper P will be inverted, and the toner will be offset to the roller, resulting in an image defect. This is the same phenomenon as the reverse transfer of the toner for cleaning the intermediate transfer drum 130 by reversely transferring the transfer residual toner to the photosensitive drum 1.

For this reason, in the present embodiment, the discharge excitation roller 140 is configured as described below.

The discharge excitation roller 140 is formed by coating an aluminum cylinder having a diameter of 20 mm with a polycarbonate resin as a dielectric layer having a thickness of 20 μm.

The aluminum cylinder is supported by a conductive bearing so as to be rotatable with respect to the transfer belt 8, and at the same time, a bias is applied to the shaft of the aluminum cylinder from a high-voltage power supply.

The discharge excitation roller 140 of the present embodiment
Since a polycarbonate resin having a relative dielectric constant of 3 is coated to a thickness of 20 μm, the discharge starting voltage based on Paschen's law is about 550V. For this reason, the applied voltage is set to the negative side within a range where the difference from the transfer voltage does not exceed 550 V.

That is, for example, when the transfer voltage is +1500 V
In this case, the applied voltage can be selected in the range of +1500 to 950V. In addition, since the surface of the discharge excitation roller 140 is coated with an insulating layer, the current is limited so that an excessive current does not flow, and toner offset and image disturbance do not occur.

Although a voltage may be applied to the discharge excitation roller 140 using a high voltage power supply, a voltage may be applied from the transfer high voltage power supply using a constant voltage element such as a varistor.

Further, in the present embodiment, the discharge excitation roller has been described as an example of the discharge excitation member, but the discharge excitation member is a transfer part that gradually separates from the back surface of the transfer paper P at the separation unit. The discharge excitation plate may have a curved surface with respect to the belt 8 so as to gradually move away from the surface of the transfer paper P. In this case, the curved surface of the discharge excitation plate is coated with a dielectric layer. Of course.

Further, since the discharge excitation roller 140 is configured to be able to contact and separate from the transfer belt 8, the discharge excitation roller 140 is brought into contact with the transfer belt 8 when printing the transfer paper P on the second side of double-sided printing. Thus, the adverse effect on the toner image may be minimized.

As described above, the double-sided printing was performed by disposing the discharge excitation roller 140 at the separation portion between the transfer belt 8 and the transfer sheet P, and the surface of the discharge excitation roller 140 and the transfer sheet P and the transfer were performed. Since the discharge is excited both between the back surface of the paper P and the transfer belt 8, the discharge on the back surface of the transfer paper P is dispersed, and the occurrence of image defects such as trias can be prevented.

Further, by using the discharge excitation roller 140 instead of the corona separation charger, the generation of ozone can be prevented, and good double-sided printing can be performed.

Further, in order to further improve image defects and toner offset, charge-up of the surface of the discharge excitation roller 140 is prevented, and a discharging unit and a cleaning unit are brought into contact with the discharge excitation roller 140. Specifically, it is effective to make the charging roller or the discharging brush to which the AC bias is applied contact.

<Second Embodiment> Next, a second embodiment will be described in detail with reference to FIG.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the image forming apparatus according to the present invention.
The same or equivalent components as those described above are denoted by the same reference numerals, and redundant description will be omitted.

In the present embodiment, in a color printer of an in-line system using a transfer belt, occurrence of image defects such as triass and scattering of toner is prevented without using a corona separation charger.

In the image forming apparatus of the present embodiment, four color stations of yellow, magenta, cyan and black are arranged in one line with respect to one transfer belt 8, and the transfer belt 8 is rotated. The transfer paper P adsorbed thereon is conveyed, and a toner image corresponding to each color component image is transferred from each station to form a full-color image.

The stations for yellow, magenta, cyan, and black are the photosensitive drums 11, 12,
13, 14, charging rollers 21, 22, 23, 24,
Exposure means 31, 32, 33, 34 and developing units 41, 4
2, 43, 44 and cleaning devices 61, 62, 6
3 and 64.

The photosensitive drums 11 to 14 rotate during the rotation process.
The primary charging rollers 21 to 24 uniformly charge to a predetermined polarity and voltage, and then receive image exposure by exposure means 31 to 34 to form an electrostatic latent image corresponding to each color component image.

Next, the electrostatic latent images are developed by the developing units 41 to 44 of the respective stations. That is, each of the developing devices 41 to 44 is rotated in a direction indicated by an arrow by a rotation driving device (not shown). Note that the yellow, magenta, cyan, and black toners of the present embodiment are so-called non-mag toners (non-magnetic toners) that do not contain a magnetic material, and are developed by a non-magnetic one-component contact developing method.

The transfer belt 8 is driven by the drive roller 170 and the transfer roller 54 as a transfer member so that the transfer belt 8 is driven to rotate at the same peripheral speed as the photosensitive drums 11 to 14 in the direction of the arrow R8 in FIG.
And it is stretched. And the photosensitive drum 1
1 corresponds to a transfer roller 51 via a transfer belt 8,
The transfer roller 52 corresponds to the photosensitive drum 12 via the transfer belt 8, the transfer roller 53 corresponds to the photosensitive drum 13 via the transfer belt 8, and the photosensitive drum 14 also serves as a discharge excitation roller. The transfer rollers 54 are arranged corresponding to each other via the transfer belt 8.

Transfer paper P fed from paper cassette 10
Is transferred to the transfer belt 8 after passing through the registration roller pair 15.
Then, the toner image is electrostatically attracted to the transfer belt 8 through a nip constituted by the transfer roller 8 and the suction roller 7. The suction roller 7 is formed by molding solid rubber on a core metal having a diameter of 6 mm, and is configured so that a high-voltage bias for suction can be applied to the core metal. The suction roller 7 has a diameter of 12 in which carbon black is dispersed in EPDM rubber for resistance adjustment.
It is a solid rubber roller with a thickness of 1 mm, and the resistance is adjusted to 1 × 10 ⁵ Ω when a metal foil having a width of 1 cm is wound around the roller and a voltage of 500 V is applied between the roller and the metal core. .

Each time the transfer paper P attracted to the transfer belt 8 passes through each color station, the photosensitive drums 11 to
The toner images are transferred by transfer rollers 51 to 54 arranged on the back surface of the transfer belt 8 facing the transfer belt 14.

After the transfer paper P is separated from the downstream end side of the transfer belt 8 wound around the transfer roller 54 by a curvature,
The image is fixed by the fixing device 9 and discharged outside the apparatus to obtain a final print.

When performing automatic double-sided printing,
The transfer paper P that has passed through the fixing device 9 passes through the automatic double-sided unit 100 by the flapper 16, is turned upside down by the reversing unit 17, and is conveyed again to the registration roller pair 15 through the flapper 18. Thereafter, printing is performed on the back surface of the transfer paper P.

The transfer belt 8 is made of a single layer of ETFE resin having a thickness of 100 μm and made of carbon black at 1 × 10 ¹² Ωcm.
Is adjusted to the volume resistance value. The volume resistance value of the transfer belt 8 is measured by the measurement method described in the first embodiment.

When automatic double-sided printing is performed using the inline printer of the present embodiment, the fixing device 9 is temporarily stopped.
Is transferred to the registration roller pair 15 after being turned over, the resistance of the transfer paper P is increased, and the transfer paper P is strongly attracted to the transfer belt 8 by the transfer charge.

In the present embodiment, the transfer belt 8 and the transfer paper P
In order to suppress the discharge at the separation section, the separation section is arranged in the most downstream image forming station corresponding to the photosensitive drum 14 as shown in FIG. 2, and the photosensitive drum 14 is used as a discharge excitation roller. It is characterized by the following.

More specifically, the transfer nip portion where the photosensitive drum 14 of the most downstream image forming station contacts the transfer roller 54 with the transfer belt 8 interposed therebetween is moved to the transfer belt 8
It is possible to excite the discharge by the photosensitive drum 14 on the front surface of the transfer paper P by setting the separation point between the transfer paper P and the transfer paper P. It is possible to prevent the occurrence of defects.

At this time, for example, in the case of a normal in-line type image forming apparatus as shown in FIG. 4, the transfer paper is separated from the photosensitive drum of the most downstream station by the transfer paper P.
The transfer belt 8 is well attracted to the transfer belt P. However, in the configuration of the embodiment shown in FIG. 2, separation of the transfer paper P from the photosensitive drum 14 must rely on curvature separation. Absent. For this reason, the diameter of the photosensitive drum 14 needs to be 50 mm or less at which the curvature can be separated.

In the present embodiment, each photosensitive drum 11,
By setting the diameters of 12, 13, and 14 to 30 mm, good separation could be performed.

In the present embodiment, by adopting the above-described configuration, it is possible to realize a discharge mode such as a transfer roller system in a separation portion between the transfer belt 8 and the transfer paper P, and When the discharge is excited on the front and back of
As in the embodiment, the occurrence of image defects such as trias can be prevented without separately providing a discharge excitation member in the separation section.

[0083]

As is apparent from the above description, according to the present invention, the discharge on the back surface of the transfer material separated from the transfer belt by exciting the discharge on the front surface of the transfer material by the discharge excitation member. Because it is suppressed, it is possible to suppress image defects due to peeling discharge that occurs when the transfer material is separated from the transfer belt, and further, since no corona separation charger is used, generation of ozone and transfer material It is possible to prevent the toner from scattering and the offset from becoming worse due to the decrease in the electrostatic attraction force with the toner.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram illustrating a second embodiment of the image forming apparatus according to the present invention.

3A and 3B are diagrams illustrating a discharge mode in a conventional transfer material separation unit, and FIG. 3A is an explanatory diagram illustrating a discharge mode of a transfer roller system;
(B) is an explanatory view showing a discharge mode of the transfer belt system.

FIG. 4 is a schematic configuration diagram illustrating an example of a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image carrier (photoconductor drum) 5 transfer member (transfer roller) 8 transfer belt 11 image carrier (photoconductor drum) 12 image carrier (photoconductor drum) 13 image carrier (photoconductor drum) 14 image carrier (Photoreceptor drum) 51 Transfer member (transfer roller) 52 Transfer member (transfer roller) 53 Transfer member (transfer roller) 54 Transfer member (transfer roller) 140 Discharge excitation member (discharge excitation roller) P Transfer material (transfer paper)

Claims (6)

[Claims] An image carrier on which a toner image is formed, and a transfer belt on which a toner image on the image carrier is transferred to a transfer material carried and conveyed on the surface, wherein the transfer belt is provided downstream of the transfer belt. An image forming apparatus that separates the transfer material after the transfer of the toner image from the transfer belt by a separation unit provided at an end, wherein discharge is performed so as to sandwich the transfer material separated by the separation unit between the transfer belt and the transfer material. An excitation member is provided, and the shape of the discharge excitation member is curved so as to gradually move away from the front surface of the transfer material with respect to the transfer belt that gradually moves away from the back surface of the transfer material at the separation section. An image forming apparatus, characterized in that: 2. The image forming apparatus according to claim 1, wherein the discharge excitation member is a discharge excitation roller having a dielectric layer on a surface. 3. The image forming apparatus according to claim 1, wherein the discharge excitation member is a discharge excitation plate having a dielectric layer on a curved surface where a surface of the transfer material gradually separates. 4. The apparatus according to claim 1, wherein the discharge excitation member is provided so as to be capable of coming into contact with and separating from the transfer belt at the time of printing on the second surface after printing on the first surface of the transfer material. An image forming apparatus according to any one of claims 1 to 3. 5. A plurality of image forming units each having the image carrier are arranged along a transfer material conveying direction of the transfer belt, and an image of the image forming unit arranged at the most downstream side is provided. The image forming apparatus according to claim 1, wherein a carrier is used as the discharge excitation member. 6. The image forming apparatus according to claim 5, wherein the most downstream image carrier also serving as the discharge excitation member has a diameter of 50 mm or less.