JP2000105513A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which does not include a process for forming an image again on a transfer material curled by a fixing process, generates no conveyance failure of the transfer material, and prevents image defect, etc., due to the image transferred to the curled transfer material, so that excellent images can be formed on the both sides of the transfer material. SOLUTION: This image forming device, which can form images on both sides of a transfer material P, is provided with an image carrier 1 as an electrophotographic photoreceptor, an electrification means 2 to electrify the surface of the image carrier 1, an exposure means E to perform the exposure L of the surface of the electrified image carrier 1 and to form an electrostatic latent image, at least two developing devices 4 and 5 which respectively have a positively electrified toner-containing developer and a negatively electrified toner-containing developer for developing the electrostatic latent image formed on the surface of the image carrier 1 to obtain an toner image, an intermediate transfer body 6 which can support the toner image formed on the image carrier 1, a first transfer means to transfer the toner image on the image carrier 1 to an intermediate transfer body 6, and a second transfer means to transfer the toner image on the image carrier 1 and the toner image on the intermediate transfer body 6 to the transfer material P.

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 for forming an image using an electrophotographic method, and more particularly to an image forming apparatus for forming an image on both sides of a transfer material.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, there is an image forming apparatus capable of forming an image on both sides of a transfer material. FIG. 8 shows a schematic configuration of an example of a conventional image forming apparatus capable of forming a two-sided image.

That is, for example, a charging means 102 uniformly charges a surface of an electrophotographic photosensitive member (hereinafter, simply referred to as a "photosensitive member") in the form of a drum, and an exposure system E charges the surface in accordance with image information. Light is emitted, for example, by exposure to a laser beam L to form an electrostatic latent image. Thereafter, the developing device visualizes the electrostatic latent image, and a so-called toner image is formed on the photoconductor 102. On the other hand, the transfer material P is fed into the image forming apparatus from the paper feed cassette 111 by the paper feed roller 112,
The toner image on the photoconductor 101 is further conveyed by the conveying unit 113 and is electrostatically transferred to the first surface by the operation of the transfer unit 107. Next, heat and pressure are applied to the transfer material P carrying the unfixed toner image by the fixing device 110 to form a permanent image on the first surface.

When an image is formed on both sides of a transfer material, after the image on the first surface is fixed, the transfer path is set via the flapper F such that the second surface of the transfer material P is on the front side of the photoreceptor 101. The transfer material P is again conveyed to the transfer section where the transfer unit 107 and the photoconductor 101 face each other via 114. On the other hand, the photoconductor 10
A toner image for the second surface of the transfer material P is formed on the transfer material P by the same process as described above, and the newly formed toner image is transferred to the second surface of the transfer material P by the action of the transfer means. I do. Thereafter, the transfer material P reaches the fixing device 110 again, receives the unfixed toner image on the second surface, and is finally discharged out of the image forming apparatus by switching the flapper F.

[0005]

However, when an image is formed on both sides of the transfer material P in the above-described conventional image forming apparatus, there are the following problems.

That is, in order to form an image on both sides of the transfer material P, conventionally, the image on the first surface of the transfer material P is first transferred and fixed, and then the transfer material P is transported to the transfer section again. ,
The image on the second surface is transferred and fixed. Therefore, at the time of fixing the first surface, the transfer material P curls due to heat and pressure,
Since the curled transfer material P passes through the transport path 114,
There is a problem that jams frequently occur in the middle of the transport route.

Further, the toner image on the second surface is not sufficiently transferred to the curled transfer material P at the transfer portion, which causes a problem that an image defect occurs.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of forming a good image on both sides without causing a transfer failure of the transfer material when forming images on both sides of the transfer material. To provide.

[0009]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image forming apparatus capable of forming an image on both surfaces of a transfer material, comprising: an image carrier serving as an electrophotographic photoreceptor; charging means for charging a surface of the image carrier; and the charged image carrier Exposure means for exposing the surface of the image carrier to form an electrostatic latent image, and a developer containing a positively chargeable toner for developing the electrostatic latent image formed on the surface of the image carrier into a toner image,
At least two developing devices each having a developer containing a negatively chargeable toner, an intermediate transfer member capable of supporting the toner image formed on the image carrier, and the intermediate transfer of the toner image on the image carrier. First transfer means for transferring to the body;
An image forming apparatus comprising: a second transfer unit configured to transfer a toner image on the image carrier and a toner image on the intermediate transfer member to the transfer material.

According to a preferred embodiment of the present invention, the electrostatic latent image on the image carrier is developed with a positive toner, and the electrostatic latent image on the image carrier is developed with a negative toner. Both toner images are transferred to both surfaces of the transfer material at once. Further, a toner image on the image carrier corresponding to an image on one surface of the transfer material is transferred onto the intermediate transfer member by the first transfer means, and then an image on the other surface of the transfer material is transferred. Is formed on the image carrier, and a voltage of the same polarity as that of the toner transferred on the intermediate transfer member is applied to the second transfer means, so that the second transfer means The toner image on the intermediate transfer member and the toner image on the image carrier are transferred onto both surfaces of the transfer material at one time. Further, an electrostatic latent image to be developed by a developing device having a toner having a polarity opposite to that of the charged potential of the surface of the image carrier is formed by subjecting the surface of the image carrier to background exposure by the exposure unit and then subjected to regular development. And an electrostatic latent image to be developed by a developing device having a toner having the same polarity as the charged potential of the surface of the image carrier is formed by exposing the surface of the image carrier by image exposure by the exposure unit. Develop by reversal development.

According to one embodiment of the present invention, one of the positively or negatively chargeable toners is a magnetic toner and the other is a non-magnetic toner.

According to another embodiment of the present invention, one of the positively chargeable and negatively chargeable toners is a pressure fixing toner and the other is a heat fixing toner.

According to another embodiment of the present invention, the positively or negatively chargeable toners are both magnetic toners.

According to still another embodiment of the present invention, both the positively chargeable and negatively chargeable toners are heat fixing toners.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention.

According to the present embodiment, the image forming apparatus includes a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1 rotatably provided in an arrow D direction. When the image forming operation is started, a charging bias voltage (for example, an AC voltage of 342 Hz and 580 μA is superimposed on a negative DC voltage of −670 V) is applied to a charging roller 2 as a charging unit from a bias power supply 3, and the charging roller 2 is charged. Is, for example, 3
While contacting the surface of the photosensitive drum 1 rotating at 7 mm / sec and being driven to rotate, the surface of the photosensitive drum 1 is rotated by about -65.
It is charged to a uniform negative surface potential of 0V.

Thereafter, a host computer (not shown)
The output image information such as characters converted into electric signals is input to an interface controller (not shown). According to this information, a laser driving circuit causes a laser diode E as an exposure unit to emit light appropriately, By exposing the surface to the laser beam L, an electrostatic latent image is formed on the surface.

Here, the image forming apparatus of this embodiment includes developing devices 4 and 5 for developing the electrostatic latent image on the photosensitive drum 1 to form a toner image. The developing device 4 contains a developer containing a positively charged magnetic toner T1.
The developing device 5 contains a developer containing a negatively charged magnetic toner T2. Further, the toners T1 and T2 are toners for heat fixing.

In this embodiment, the developing device 4 having the toner T1 is used to form an image on the first surface of the transfer material P, and the developing device 5 having the toner T2 is used to form an image on the second surface.

In the case of forming an image on both surfaces of the transfer material P, in this embodiment, the surface of the uniformly charged photosensitive drum 1 is first exposed to a non-image portion of image information of the first surface, a so-called exposure. Perform background exposure. Further, the image on the first surface is not directly transferred onto the transfer material P, but is visualized and then once transferred onto an intermediate transfer belt 6 as an intermediate transfer member, as described later, and then transferred to the transfer material P. Since the image is transferred onto the photosensitive drum 1, exposure is performed on the photosensitive drum 1 so as to form a normal image.

Thereafter, the developing device 4 having moved the electrostatic latent image corresponding to the image on the first surface of the transfer material P from the surface of the photosensitive drum 1 by a solenoid (not shown) to a distance sufficient for the developing process, By performing a jumping development using a positive polarity magnetic toner, a normal development is performed on an image portion where the negative surface potential on the photosensitive drum 1 is held without attenuating, and a toner image is formed by the toner T1. FIG. 1 shows a state in which a toner image is formed on the surface of the photosensitive drum 1 by the toner T1 corresponding to the image on the first surface of the transfer material P.

Next, the transfer of the toner image formed by the toner T1 with the transfer roller 7 as a transfer unit and the photosensitive drum 1 is brought into contact via the intermediate transfer belt 6 with the rotation of the photosensitive drum 1 in the direction of arrow D. To the department. A negative transfer bias voltage of −2 kV is applied to the transfer roller 7 by the bias power supply 8, and the toner image formed by the toner T <b> 1 on the photosensitive drum 1 is transferred onto the intermediate transfer belt 6 driven in the arrow direction. FIG. 2 shows a state in which the toner image by the toner T1 is transferred to the surface of the intermediate transfer belt 6.

Here, the intermediate transfer belt 6, which is a belt-shaped intermediate transfer member, is not particularly limited, but usually has a thickness of 100 μm to 200 μm and a volume resistivity of 10 ¹¹ Ω.
A resin film such as PVdF, nylon, PET, polycarbonate, or the like having a resistance of about 10 cm to about 10 ¹⁶ Ωcm, where necessary, is used. Further, as the transfer roller 7, a roller having a volume resistivity of 10 ⁵ Ωcm or less at a transfer portion is generally used.

As described above, by using a thin film as the intermediate transfer belt 6, several hundred pF to several thousand pF
Since a large capacitance can be formed at the transfer site of pF, a stable transfer current can be obtained.

Next, image formation on the second surface of the transfer material P will be described.

After the toner image for forming an image on the first surface of the transfer material P is transferred to the intermediate transfer belt 6, the surface of the photosensitive drum 1 is uniformly charged to -650 V by the charging roller 2 in the same manner as described above. I do. Thereafter, in accordance with the image information input to the image forming apparatus in the same manner as described above, the laser diode E emits a laser beam L as appropriate to form on the second surface of the transfer material P. Performs exposure corresponding to an image portion of image information, that is, image exposure. Thus, the negatively charged potential on the surface of the photosensitive drum 1 corresponding to the image portion is attenuated, and an electrostatic latent image is formed. still,
In the present embodiment, since the toner image formed on the second surface of the transfer material P is directly transferred onto the transfer material P as described later, a mirror image electrostatic latent image is formed here.

Thereafter, the developing device 5 is moved to a predetermined position facing the surface of the photosensitive drum 1 by a solenoid (not shown), and the developing device 5 performs jumping development using a negatively charged toner T2. The electrostatic latent image on the photosensitive drum 1 is reversely developed, and a toner image corresponding to the image formed on the second surface of the transfer material P is formed on the surface. FIG.
This shows how a toner image corresponding to the first surface of the transfer material P and a toner image corresponding to the image on the second surface are carried on the intermediate transfer belt 6 and the photosensitive drum 1, respectively.

Here, as understood from FIG. 3, the toner image corresponding to the image on the second surface of the transfer material P is first placed on the front end of the image forming area of the transfer material P and on the intermediate transfer belt 6. Control is performed by timing such as exposure so that the transferred toner image enters the transfer unit in synchronization with reaching the transfer unit.

As described above, in the transfer section, the toner image corresponding to the image on the first surface of the transfer material P carried on the intermediate transfer belt 6 and the second surface of the transfer material P carried on the photosensitive drum 1 When the leading end of the image forming area of the transfer material P and the toner image corresponding to the image of the transfer material P reaches the transfer portion, the power supply 8 is switched to apply a positive transfer bias voltage to the transfer roller 7 and drive the transfer roller 7 continuously. As the photosensitive drum 1 and the intermediate transfer belt 6 rotate, respective toner images are simultaneously transferred onto respective surfaces of the transfer material P.
Such transfer is hereinafter referred to as “double-sided simultaneous transfer”.

That is, the positively charged toner T1 on the intermediate transfer belt 6 moves in the direction of the transfer material P by electrostatic repulsion, and the negatively charged toner T2 on the photosensitive drum 1 moves by electrostatic attraction. Transfer is performed.

The transfer material P on which the toner images are transferred on both sides is
The transfer material P is conveyed to the fixing device 10 located above by the conveyance force between the intermediate transfer belt 6 and the photosensitive drum 1, and enters the fixing device 10 substantially vertically with the rigidity of the transfer material P itself.

The fixing device 10 of this embodiment has a pair of heat rollers 10a and 10b, and both rollers have a halogen heater. The roller 10a is a roller 10b.
, And the unfixed toner images formed on both surfaces of the transfer material P are fixed by the fixing device 10 by heat and pressure.

The transfer material P on which images are formed on both sides as described above is finally discharged out of the image forming apparatus.

In this embodiment, the first surface and the second surface of the transfer material P
After transferring the toner image corresponding to the image on the surface, the transfer residual toner is set on the surface of the photosensitive drum 1 so that the transfer residual toner does not remain and sufficient transfer efficiency is obtained, and the transfer residual toner on the photosensitive drum 1 is removed. Cleaning means or a cleaning device can be omitted.

The surface of the intermediate transfer belt 6 is cleaned by a cleaning device 9 having a blade-like cleaning means.
Is moved away from the intermediate transfer belt 6 to remove and remove residual toner remaining after the transfer of the toner image from the intermediate transfer belt 6 onto the transfer material P is completed.

In this embodiment, the circumferential length of the intermediate transfer belt must be equal to or longer than the maximum length of an image that can be formed on the transfer material P. In the present invention, the intermediate transfer member is not limited to a belt shape, but may be, for example, a drum shape.

In this embodiment, only the case where an image is formed on both surfaces of the transfer material P has been described. However, it is a matter of course that the image forming apparatus according to the present invention can form an image only on the first surface of the transfer material P. . For example, in the above-described image forming process, the transfer material P
Only the operation of forming the image on the second surface need be performed.

Further, in this embodiment, background image formation and regular development using a positively chargeable toner are performed during image formation on the first surface of the transfer material P, and image exposure is performed during image formation on the second surface. And reversal development using a negatively charged toner. However, the present invention is not limited to this. For example, by switching the power supply 8, the polarity of the transfer bias at the time of double-side transfer is made negative,
It is possible to change the order of image formation on the side and the second side. Further, the polarity of the charging potential of the photosensitive drum 1 (electrophotographic photosensitive member) is not limited to the negative polarity, and the polarity of the toner for performing the normal development and the reversal development can be changed to the positive polarity. is there.

As described above, according to the image forming apparatus of the present invention, the image on one side of the transfer material and the image on the other side are transferred to both sides of the transfer material at once, and then the unfixed toner on both sides of the transfer material is transferred. The image can be permanently fixed in a single fixing step.

Embodiment 2 FIG. 4 shows a schematic configuration of another embodiment of the image forming apparatus according to the present invention. The image forming apparatus according to the present embodiment has basically the same configuration as the image forming apparatus according to the first embodiment, and uses a different developer and a different fixing device 10.

That is, in the first embodiment, the developers contained in the developing devices 4 and 5 each include the magnetic toner. In this embodiment, the developing device 4 has a positively charged non-magnetic toner T3, and the developing device 5 has a negatively charged magnetic toner T4 similar to the first embodiment.

Since the magnetic toner contains magnetite, it generally has poor fixability. Therefore, in the present embodiment, as shown in FIG. 4, the toner image formed using the developing device 4 having the toner T3 containing no magnetite is once transferred onto the intermediate transfer belt 6 and then transferred onto the transfer material P. The transfer material P is conveyed to the fixing device 10 such that the image faces the pressure roller 10a having no halogen heater therein. That is, an image on the first surface of the transfer material P is formed with the toner T3,
An image on the second surface is formed with toner T4.

As described above, according to the present embodiment, the first embodiment
In addition to the operation described in (1), the cost of the fixing device 10 can be reduced.

Embodiment 3 FIG. 5 shows a schematic configuration of another embodiment of the image forming apparatus according to the present invention. The image forming apparatus according to the present embodiment has basically the same configuration as the image forming apparatus according to the first embodiment, and differs only in the fixing device 10 and the developer used.

That is, in the first embodiment, the developers contained in the developing devices 4 and 5 each include a magnetic toner for heat fixing. In this embodiment, the developing device 4 has a positively-charged magnetic toner T5 for pressure fixing, and the developing device 5 has a negatively-charged magnetic toner T6 for heat fixing, as in the first embodiment.

In order to fix the pressure fixing toner on the transfer material P, the fixing nip portion, that is, the roller pair 10 of the fixing device is used.
Pressure is required at the contact portion between a and 10b, and the heat fixing toner requires heat and a lower pressure than the pressure fixing toner requires for fixing.

Therefore, in this embodiment, as shown in FIG. 5, the toner image formed by using the developing device 4 having the toner T5 for pressure fixing is once transferred to the intermediate transfer belt 6 and then transferred onto the transfer material P. The transfer material P is transferred to the fixing device 10 such that the image is directed to the pressure roller 10 a having no halogen heater therein. That is, the image on the first surface of the transfer material P is formed with the toner T5, and the image on the second surface is formed with the toner T6.

As described above, according to the present embodiment, the first embodiment
In addition to the operation described in (1), the cost of the fixing device 10 can be reduced.

Embodiment 4 FIG. 6 shows a schematic configuration of another embodiment of the image forming apparatus according to the present invention. The image forming apparatus according to the present embodiment has basically the same configuration as the image forming apparatus according to the first embodiment, and differs mainly in the arrangement of the fixing device 10.

In this embodiment, the fixing device 10 is located substantially below the transfer portion where the photosensitive drum 1 and the intermediate transfer belt 6 are in contact with each other, passes through the transfer portion, and carries the unfixed toner image on both surfaces. The material P is conveyed toward the fixing device 10 by the conveying force of the photosensitive drum 1 and the intermediate transfer belt 6, and enters the fixing nip substantially vertically by its own weight.

Accordingly, there is no need to provide any special means for pressing the leading end of the transfer material and guiding the transfer material to the fixing device, even if the rigidity of the transfer material P itself is low.

Embodiment 5 FIG. 7 shows a schematic configuration of another embodiment of the image forming apparatus according to the present invention. The image forming apparatus according to the present embodiment has basically the same configuration as the image forming apparatus according to the first embodiment, and differs mainly in the arrangement of the fixing device and the arrangement and the arrangement of the intermediate transfer belt 6.

As shown in FIG. 7, when the fixing device 10 is disposed in a substantially horizontal position with respect to the transfer portion, the leading end of the transfer material P having passed through the transfer portion and carrying the unfixed toner image on both sides thereof is fixed to the fixing device 10. In the meantime, it tends to fall downward by its own weight. Therefore, when the fixing device 10 and the transfer unit have such a positional relationship, it is necessary to bring the fixing device 10 close to the transfer nip so that the transfer material P enters the fixing nip by the rigidity of the transfer material P itself. is there. In addition, the circumferential length of the intermediate transfer belt 6 needs to be equal to or longer than the maximum length of an image that can be formed on the transfer material P.

Therefore, in the present embodiment, the fixing device 10 is moved in such a manner that the intermediate transfer belt 6 having passed through the transfer roller 7 is directed substantially vertically downward with respect to a straight line connecting the transfer portion and the fixing nip. It was configured to approach.

More specifically, the width of the intermediate transfer belt is set to be larger than the width of the image forming area of the transfer material P (the length in the direction perpendicular to the direction in which the transfer material P is transported). A pair of conveying rollers 12 (only one roller 12 at one end in the width direction of the conveying belt is shown in the figure) is provided so as to guide the toner image outside the both ends in the width direction of the toner image.
The intermediate transfer belt 6 after passing through the transfer section can be directed substantially vertically downward.

[0057]

As described above, the image forming apparatus according to the present invention is an image forming apparatus capable of forming an image on both sides of a transfer material, and includes an image carrier as an electrophotographic photosensitive member, Charging means for charging the surface of the image carrier, exposure means for exposing the charged surface of the image carrier to form an electrostatic latent image, and developing the electrostatic latent image formed on the surface of the image carrier. At least two toners each including a developer containing a positively charged toner and a developer containing a negatively charged toner for forming a toner image
Developing devices, an intermediate transfer member capable of holding a toner image formed on the image carrier, a first transfer means for transferring the toner image on the image carrier to the intermediate transfer member, and a toner on the image carrier And a second transfer means for transferring the image and the toner image on the intermediate transfer member to the transfer material, so that the image on one surface and the image on the other surface of the transfer material are transferred to both surfaces of the transfer material. It is possible to transfer the image at once, and then permanently fix the unfixed toner images on both sides of the transfer material in a single fixing step. Therefore, when an image is formed on both surfaces of the transfer material, a step of forming an image again on the transfer material curled by the fixing process is not included, so that transfer failure of the transfer material does not occur, and furthermore, the transfer material to the curled transfer material can be formed. It is possible to prevent image defects and the like generated for image formation, and to form a good image on both sides.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a state in which a toner image corresponding to an image on a first surface of a transfer material is formed on a photosensitive drum in an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram illustrating a state in which a toner image corresponding to an image on a first surface of a transfer material is carried on an intermediate transfer belt in an embodiment of the image forming apparatus according to the present invention.

FIG. 3 illustrates a toner image on an intermediate transfer belt corresponding to an image on a first surface of a transfer material and a photosensitive drum on a photosensitive drum corresponding to an image on a second surface in an embodiment of the image forming apparatus according to the present invention. FIG. 3 is a schematic configuration diagram illustrating a state in which a toner image is transferred onto a transfer material.

FIG. 4 is a schematic configuration diagram showing another embodiment of the image forming apparatus according to the present invention.

FIG. 5 is a schematic configuration diagram showing still another embodiment of the image forming apparatus according to the present invention.

FIG. 6 is a schematic configuration diagram showing still another embodiment of the image forming apparatus according to the present invention.

FIG. 7 is a schematic configuration diagram showing still another embodiment of the image forming apparatus according to the present invention.

FIG. 8 is a schematic configuration diagram showing a conventional image forming apparatus capable of forming an image on both surfaces of a transfer material.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image carrier, electrophotographic photosensitive member) 2 Charging roller (charging means) 4, 5 Developing device 6 Intermediate transfer belt (intermediate transfer member) 7 Transfer means 10 Fixing device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) G03G 15/20 111 G03G 9/08 101 F term (Reference) 2H005 DA02 DA03 FA06 FA07 FB02 FB06 2H028 BA03 BA06 BA16 BB02 BB06 BC01 2H032 AA05 BA02 BA05 BA09 BA16 BA21 BA23 BA26 BA30 CA04 CA13 DA16 2H033 AA15 AA31 AA46 BA08 BA10 BA25 BB01 BB12 BB18 BB28 BC02 BD01

Claims (8)

[Claims] 1. An image forming apparatus capable of forming an image on both surfaces of a transfer material, comprising: an image carrier as an electrophotographic photosensitive member; a charging unit for charging a surface of the image carrier; Exposure means for exposing the surface of the charged image carrier to form an electrostatic latent image, and a positively chargeable toner for developing the electrostatic latent image formed on the surface of the image carrier into a toner image And a developer containing a negatively chargeable toner, respectively.
One developing device; an intermediate transfer member capable of holding the toner image formed on the image carrier; a first transfer unit for transferring the toner image on the image carrier to the intermediate transfer member; An image forming apparatus comprising: a second transfer unit configured to transfer a toner image on a carrier and a toner image on the intermediate transfer member to the transfer material. 2. An electrostatic latent image on the image carrier is developed with positive polarity toner, an electrostatic latent image on the image carrier is developed with negative polarity toner, and both toner images are transferred to the transfer material. 2. The image forming apparatus according to claim 1, wherein the image is transferred onto both sides of the image at once. 3. A toner image on the image carrier corresponding to an image on one surface of the transfer material is transferred onto the intermediate transfer body by the first transfer means, and then the other of the transfer material is transferred. Forming a toner image corresponding to the surface image on the image carrier,
By applying a voltage having the same polarity as that of the toner transferred onto the intermediate transfer member to the second transfer portion, the toner image on the intermediate transfer member and the toner image on the image carrier are applied by the second transfer portion. 3. The image forming apparatus according to claim 1, wherein the toner image is transferred onto both surfaces of the transfer material at a time. 4. An electrostatic latent image to be developed by a developing device having a toner having a polarity different from that of the charged potential of the surface of the image carrier is formed by exposing the surface of the image carrier to background by the exposure unit. An electrostatic latent image to be developed by post-regular development and then developed by a developing device having a toner having the same polarity as the charged potential of the image carrier is formed by exposing the surface of the image carrier by the exposure means. 4. The image forming apparatus according to claim 1, wherein the image is formed by reversal development after the formation. 5. The toner according to claim 1, wherein one of the positively chargeable and negatively chargeable toners is a magnetic toner and the other is a non-magnetic toner. The image forming apparatus as described in the above. 6. The toner according to claim 1, wherein one of the positively chargeable and negatively chargeable toners is a pressure fixing toner and the other is a heat fixing toner. The image forming apparatus according to the item. 7. The image forming apparatus according to claim 1, wherein both the positively chargeable and negatively chargeable toners are magnetic toners. 8. The image forming apparatus according to claim 1, wherein both the positively chargeable and negatively chargeable toners are heat fixing toners.