JP2000181241A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the splashing and transfer blur of toners even with high- rigidity paper while stably separating transfer material from an image carrying member by pre-transfer-exposure without raising a cost and to have good transfer, separation and transportation executed by executing exposure through the transfer material by an exposure means. SOLUTION: An electrostatic latent image meeting image information is formed by a primary electrostatic charger 2 and a laser beam 3 on the surface of the image carrying member 1 rotationally moved in an arrow R1 direction. The electrostatic latent image is adhered with the toners and is developed as a toner image by a developing device 4 and after the charge quantity of the toners is made uniform by the pre-transfer electrostatic charger 13, the unnecessary potential on the image carrying member 1 is destaticized by the pre-transfer-exposure 16. Since the pre-transfer exposure 16 is constituted integral with a transfer lower guide 9, the exposure by the pre-transfer-exposure 16 may be executed through the transfer material P. If the exposure by the transfer pre-exposure 16 is executed through the transfer material P, the destaticization meeting the rigidity of the transfer material P is executed.

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 using an electrophotographic system such as a copying machine or a printer, and more particularly, to a method in which a toner image formed on an image carrier is electrostatically transferred onto a transfer material surface. The present invention relates to an image forming apparatus provided with a transfer device for transferring a sheet to an image carrier and a separating device for separating a transfer material from an image carrier.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a general electrophotographic copying machine, an electrostatic transfer method is used as a transfer device for transferring a toner image formed on an image carrier to a transfer material such as paper. An image forming apparatus provided with is well known.

In an image forming apparatus provided with such a transfer device, as shown in FIG. 7, an image carrier (photosensitive drum) 1
01, primary charger 102, laser beam 10
3. After the toner image is formed by the developing device 104 and the pre-transfer charger 113, the image carrier 1 is exposed by the pre-transfer exposure 116.
The unnecessary electric potential on the upper side is eliminated. Then, the feeding and conveying means 11
2. The toner image is transferred to the transfer material P conveyed to the transfer portion via the registration roller 107, the upper transfer guide 108, the lower transfer guide 109, and the like by the operation of the transfer charger 105. At this time, a transfer bias is applied to the transfer charger 105, whereby the transfer of the toner image is performed by the transfer electric field formed at the transfer portion between the transfer charger 105 and the image carrier 101. Then, the transfer material P after the transfer of the toner image is separated from the surface of the image carrier 101 by the separation charger 106, and the transfer belt 110, the fixing guide 114
Is transferred to the fixing device 115 through which the toner image on the surface of the transfer material is fixed, and a final image formed product (copy) is formed.
Becomes

On the other hand, the image carrier 101 after the transfer of the toner image
In the process, the transfer residual toner remaining on the surface of the image carrier 101 without being transferred to the transfer material P is removed by the cleaning device 111, and is used for the next image formation starting from primary charging.

Next, a part of the operation of the image forming apparatus will be described with reference to FIGS.

[0006] As shown in FIG.
8 is uniformly charged to +400 V (Vd) by the primary charger 2, and as shown in FIG. 8B, a +50 V (Vl) electrostatic latent image is formed by irradiation with the laser beam 103.

Next, as shown in FIG. 8C, a DC voltage of +300 V is applied to the developing sleeve 104a of the developing device 104.
By applying (Vs), the electrostatic latent image is reversely developed with the positively charged toner to form a toner image. Then, the charge amount of the toner is made uniform by the pre-transfer charger 113. Here, Vd in the figure is a non-image portion potential where the toner is not developed, and Vl is an image portion potential where the toner is developed. Vt is the toner layer after the toner is developed to the image portion potential Vl, and is + 150V.

[0008] Then, as shown in FIG. 8 (4), the image carrier 101 is neutralized by the exposure 116 before transfer, and
The electrostatic latent image of 0 V (Vd) becomes +200 V (Vd).
At this time, the electrostatic latent image of +50 V (Vl) is hardly discharged due to the presence of the toner. Also, the toner layer potential Vt
Also remains at + 150V.

Next, as shown in FIG. 8 (5), a negative charge is applied to the back surface of the transfer material P by the transfer charger 105, the back surface potential of the transfer material P is set to -450 V, and the toner image is transferred to the transfer material P. Transferred to P.

[0010] Then, as shown in FIG. 8 (6), the unnecessary charge applied to the back surface of the transfer material P is removed by the separation charger 106, the potential of the transfer material P becomes about 0 V, and the transfer The attraction force between the material P and the image carrier 101 is weakened, and the transfer material P
Is satisfactorily separated from the image carrier 101, and a desired image can be obtained on the transfer material P.

FIG. 9 is an enlarged view of the vicinity of the transfer charger 105, that is, a transfer portion.

Upper transfer guide 108 and lower transfer guide 109
Is a guide member that serves as a guide when the transfer material P is conveyed and supplied to a transfer portion in order to transfer the toner image on the image carrier 101 to the transfer material P, and a transfer gap between the transfer member P and the surface of the image carrier 101 G and a contact area (nip area) N between the image carrier 101 and the transfer material P are appropriately formed.

On the other hand, separating and conveying the transfer material P while performing stable transfer on the transfer material P is performed by the transfer charger 10 described above.
5 and the voltage applied to the separation charger 106.

First, with regard to transfer, generally, when a larger amount of current is passed, the toner image on the image carrier 101 can be efficiently transferred onto the transfer material P. Next, regarding the separation, generally, the voltage for the AC component is large, and the separation can be efficiently performed on the high frequency side, and the DC component is largely biased in the opposite polarity to the transfer, so that the transfer material P is charged on the transfer material P during the transfer. The discharged charge can be removed, and the separation can be performed more efficiently.

However, in practice, the above-mentioned conditions for transfer and separation are not determined simply by one of the conditions, because both influence each other. That is, if the voltage applied to the transfer charger 105 is unnecessarily large, the amount of charge on the transfer material P increases, and the charge removal effect in the separation charger 106 decreases. As a result, separation efficiency decreases, and separation failure occurs. And so on.

On the other hand, if the voltage applied to the separation charger 106 is unnecessarily high, or if the direct current deviation causes the transfer material P to have an excessively neutralizing effect, the toner image once transferred to the transfer material P However, a so-called retransfer phenomenon occurs, which returns from the transfer material P to the image carrier 101 again.

In consideration of the above, the voltage applied to the transfer charger 105 and the voltage applied to the separation charger 106 are set to appropriate ranges. It changes depending on the thickness and type of the transfer material P.

In order to solve these problems, the potential of the image carrier 1 is lowered by using the pre-transfer exposure 116 after the toner image is developed on the image carrier 101, so that the transfer material P and the image carrier Techniques for reducing the attraction force with the body 101 and expanding the appropriate range have already been proposed.

[0019]

However, the above-described conventional image forming apparatus has the following problem of image deterioration during transfer.

The image deterioration includes a so-called scattering phenomenon in which a very small amount of toner scatters near the substantial image to reduce the sharpness of the image. Regarding this phenomenon, the transfer material P
This is remarkable when the contact between the image carrier 101 and the image carrier 101 is unstable. The transfer gap G between the image carrier 101 and the lower transfer guide 109 is reduced as much as possible, the nip area N is increased, and the transfer material P is reduced. It is known that this can be avoided by bringing the image carrier 101 into stable contact.

However, as described above, a large transfer resistance occurs in the transfer gap G that is adjusted to be narrow, and the transfer speed of the transfer material P changes at the transfer portion, so that the image shrinks. there were. Therefore, the nip area N is set to a range in which scattering and transfer blur do not occur. This must be true regardless of the type of the transfer material P. However, since the transfer material P having high rigidity does not easily adhere to the image carrier 101, the nip area N
Was liable to be small and splattered easily.

Further, by the pre-transfer exposure 116, the potential of the transfer material P immediately after the transfer and the non-image portion potential V of the image carrier 101 are
d decreases, the attraction force between the image carrier 101 and the transfer material P decreases, and the transfer material P is stably
However, since the difference between the non-image portion potential Vd and the image portion potential Vl is reduced as shown in FIG. 8D, the force for restraining the toner at the image portion potential Vl becomes weak, and the non-image portion Therefore, the scattering easily occurred when the toner layer potential Vt was higher than the non-image portion potential Vd.

For this reason, in the conventional image forming apparatus, scattering occurred on high-rigidity paper. However, the scattering occurred only in the high-rigidity paper. Therefore, when the pre-transfer exposure 116 was not operated in the high-rigidity paper, the scattering was good. If the pre-transfer exposure 116 is not operated, poor separation from the image carrier 1 may be a problem, but high-rigidity paper can be stably and favorably separated only by its own rigidity.

In view of these facts, the pre-transfer exposure 116 is operated on low-rigidity paper, and the pre-transfer exposure 1 is performed on high-rigidity paper.
It can be seen that it is necessary to keep 16 out of operation.

However, it is difficult to detect the rigidity of the transfer material P and to control the operation of the pre-transfer exposure 116 based on the rigidity of the transfer material P because it is difficult to detect the rigidity of the transfer material P. However, even if it can be realized, the cost will increase.

Accordingly, it is an object of the present invention to prevent the toner from scattering and the transfer blur even on high-rigidity paper while stably separating the transfer material from the image carrier by the pre-transfer exposure without increasing the cost. It is another object of the present invention to provide an image forming apparatus capable of performing good transfer, separation, and conveyance.

[0027]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier having a movable surface on which an electrostatic latent image is formed; developing means for developing the electrostatic latent image as a toner image by reversal development; and exposing the image carrier on which the toner image is formed And an exposing unit for transferring the toner image onto a transfer material at a transfer portion, wherein the exposing unit performs the exposure through a transfer material. An image forming apparatus.

It is preferable that a guide member for transporting the transfer material to the transfer site is provided, and the exposure means is provided integrally with the guide member. According to another aspect, it is preferable that the exposure unit is provided integrally with the transfer unit. When the non-image portion potential of the surface of the image carrier is Vd and the toner layer potential is Vt in a state where the transfer material is not transmitted, Vd> Vt, and Vd ≒ Vt.
It is preferable that the exposure amount satisfies the following condition.

It is preferable to have an environmental humidity detecting means for detecting the environmental humidity in the main body of the image forming apparatus, and a means for changing an exposure amount of the exposing means in accordance with a result of the detection of the environmental humidity. It is preferable that a means for changing the exposure amount of the exposure unit is provided so that the relationship between the exposure amount by the exposure unit and the rigidity of the transfer material becomes constant irrespective of a change in environmental humidity.

An image reading device is provided downstream of the transfer portion in the transfer material transport direction, and a means for changing an exposure amount of the exposure device in accordance with a toner image of the transfer material read by the image reading device is provided. Is preferred. It is preferable to have a detecting means for detecting the use of the transfer material for the overhead project, and a means for reducing the exposure amount of the exposing means in accordance with the detection result.

[0031]

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 A first embodiment of the present invention will be described with reference to FIGS.

Referring to FIG. 1, the image forming apparatus of this embodiment will be described. In FIG. 1, the image forming apparatus includes a drum-type photoconductor (image carrier) 1 rotatably supported in an arrow R1 direction by an image forming apparatus main body (hereinafter, simply referred to as “apparatus main body”). Around the image carrier 1,
The primary charger 2, the developing device 4, and the
A pre-transfer charger 13, a pre-transfer exposure 16, a transfer charger 5, a separation charger 6, and a cleaning device 11 are provided.

Below the image carrier 1, a feeding means 12 for feeding and transferring the transfer material P, a registration roller 7 for registering the transfer material P, and the transfer material P transferred by the registration roller 7 to a transfer portion. An upper transfer guide 8 and a lower transfer guide 9 for guiding are provided. Further, on the downstream side of the separation charger 6, the transport belt 10, the fixing guide 14, the fixing device 1
5 are arranged.

The operation of the image forming apparatus having the above configuration will be described.

An electrostatic latent image corresponding to image information is formed on a surface of an image carrier (photosensitive drum) 1 rotated and driven in the direction of arrow R1 by a primary charger 2 and a laser beam 3. The electrostatic latent image is developed by the developing device 4 as a toner image with toner attached thereto, and then charged before the transfer.
After the charge amount of the toner is made uniform, unnecessary electric potential on the image carrier 1 is removed by the pre-transfer exposure 16. Thereafter, the toner image is transferred to the transfer material P which has been conveyed to the transfer portion via the feeding / conveying means 12, the registration roller 7, the upper transfer guide 8, the lower transfer guide 9, and the like by the operation of the transfer charger 5. At this time, a transfer bias is applied to the transfer charger 5, whereby the transfer of the toner image is performed by a transfer electric field formed at a transfer portion between the transfer charger 5 and the image carrier 1.

Then, the transfer material P after the transfer of the toner image is separated from the surface of the image carrier 1 by the separation charger 6, and is conveyed to the fixing device 15 via the conveyance belt 10 and the fixing guide 14, where the surface of the image is fixed. The toner image is fixed to form a final image formed product (copy).

On the other hand, in the image carrier 1 after the transfer of the toner image, the transfer residual toner remaining on the surface of the image carrier 1 without being transferred to the transfer material P is removed by the cleaning device 11, and the next image starting from primary charging is removed. Served for formation.

The image forming apparatus of the present embodiment is different from the conventional example in that the pre-transfer exposure 116 of the conventional example is disposed immediately downstream of the pre-transfer charger 113 in the rotation direction of the image carrier 101. In the present embodiment, the pre-transfer exposure 16 is formed integrally with the lower transfer guide 9, whereby the exposure by the pre-transfer exposure 16 can be performed through the transfer material P.

Here, the effect of performing the exposure by the pre-transfer exposure 16 through the transfer material P will be described.

FIG. 2 shows the relationship between rigidity and transmittance of general paper. The rigidity was measured according to JIS 8143-1967.

As shown in FIG. 2, the rigidity of the paper (cm ³
/ 100) and the transmittance (%) have a roughly inversely proportional correlation that the transmittance decreases as the stiffness increases, and conversely, the transmittance increases as the stiffness decreases. It was done.

That is, the pre-transfer exposure 16 through the transfer material P
, The charge is removed in accordance with the rigidity of the transfer material P, and the high-rigidity paper hardly undergoes the exposure by the pre-transfer exposure 16, and the low-rigidity paper performs the exposure. in short,
According to the configuration of the present embodiment, as described in the section of “Problems to be Solved by the Invention”, it is necessary to operate the pre-transfer exposure 16 on low-rigidity paper and not operate the pre-transfer exposure 16 on high-rigidity paper. Can be satisfied.

In the following, experimental results of scattering and poor separation by the image forming apparatus according to the present embodiment will be compared with those of the conventional example.

The experiment was conducted using a copy machine NP67 manufactured by Canon Inc.
50.

In the conventional example, the exposure amount by the pre-transfer exposure is 0.21 (lux) at the position of the image carrier surface opposite to the pre-transfer exposure.
Sec). Hereinafter, the exposure amount by the pre-transfer exposure is measured at the surface position of the image carrier at the facing portion of the pre-transfer exposure. However, in this embodiment, since the exposure is performed while transmitting the transfer material P, the exposure amount is set to 0.31 (lux · sec) without transmitting the transfer material P.

This ensures that a sufficient amount of exposure by the pre-transfer exposure 16 is ensured on the transfer material P where separation failure occurs.
In addition, even when the transmittance is 100%, the non-image portion potential Vd is prevented from being lower than the toner layer potential Vt.
That is, Vd> Vt and Vd ≒ Vt are satisfied.

In this embodiment, the separation failure has a rigidity of 40 (c).
m ^3/100) started to occur from below, rigidity 25 (cm
^3/100) was frequently in the following. Therefore, the rigidity is 25
(Cm ^3/100), when the transmittance using the transfer material P to about 66%, the exposure of the pre-transfer exposure 16 0.21
(Lux · sec) can be secured.

Here, in Table 1 below, in this embodiment, the pre-transfer exposure 16 is configured to expose from the back surface of the transfer material P.
As described above, 0.31 (lux · sec) was used. In Conventional Example 1, the exposure of the pre-transfer exposure 16 is performed directly on the image carrier 1, and the exposure amount is 0.21 (lux · sec).
c) was used. In Conventional Example 2, the pre-transfer exposure 16 is removed, and the exposure amount is 0.

In the above experiment, the transfer charger 5 and the separation charger 6
The same power supply conditions and environmental conditions were used. The experiment was performed at a temperature of 20 ° C. and a humidity of 50% RH.

Table 1 summarizes the evaluation results of toner scattering and separation failure. The evaluation was performed according to the following criteria. The value of the rigidity of the transfer material P shown here uses the value of the transfer material P which is generally used.

(Splattering) で: Scattering is observed around some characters at the level of microscopic observation, but hardly noticeable. ：: Cannot be determined by visual observation. Δ: Although discrimination can be made by visual observation, characters are not bleeding. ×: Characters can be easily discriminated by visual observation, and characters appear to be blurred.

(Defective separation) A: Very good without fluttering or floating. ：: Floating can be confirmed very rarely. Δ: Floating or fluttering, but the apparatus does not stop due to paper jam. ×: The apparatus stops due to a paper jam.

[0054]

[Table 1]

As shown in Table 1, in this embodiment,
By performing exposure by the pre-transfer exposure 16 through the transfer material P, it is possible to obtain an extremely good image without scattering, separation failure, and the like for all the transfer materials P, and to realize good paper conveyance. Was completed.

The relative position between the pre-transfer exposure 16 and the image carrier 1 needs to be determined with a certain accuracy or higher.
Otherwise, the amount of exposure to the image carrier 1 will vary, causing scattering and poor separation.
For this reason, in the present embodiment, in order to maintain the positional relationship with the image carrier 1 with the same accuracy as that of the transfer lower guide 9, the structure is integrated with the transfer lower guide 9. However, the present invention is not limited to this as long as a certain level of accuracy is ensured. As a modified example of the present embodiment, as shown in FIG. It may be arranged in.

Embodiment 2 Next, a second embodiment of the present invention will be described with reference to FIG.

The rigidity of the transfer material greatly changes depending on environmental conditions, particularly humidity, and at high humidity, the rigidity becomes very small. Further, as the tendency of scattering, the charge amount of the toner becomes large in a low humidity environment, so that the toner layer potential Vt becomes high, which tends to be worse than in a high humidity environment.

Therefore, in the present embodiment, in consideration of the above, the exposure amount of the pre-transfer exposure 16 is changed according to the environmental humidity.

More specifically, in the present embodiment, the humidity is detected by the humidity sensor 17, and the voltage input to the pre-transfer exposure 16 is changed by the control device 18 in accordance with the result to control the exposure amount. .

An experimental result on scattering and poor separation on the transfer material P formed by the image forming apparatus having the above-described configuration was examined in comparison with a comparative example.

The experiment was performed using a copying machine NP6750 manufactured by Canon Inc. in the same manner as in the first embodiment. The results are shown in Table 2 below.

[0063]

[Table 2]

In this embodiment, the amount of light when the sheet does not pass through the transfer material P, the humidity is 15% RH, and the exposure is 0.27 (lu
x · sec), humidity 80 RH, exposure amount 0.37 (lux)
The voltage input to the pre-transfer exposure 16 was changed so as to satisfy (sec). This is because the relationship between the exposure amount by the pre-transfer exposure 16 and the rigidity of the transfer material P in a normal environment (50% RH) is made constant regardless of the environmental humidity.

When the exposure amount of the pre-transfer exposure 16 is not changed according to the environmental humidity as in the comparative example shown in Table 2,
In a high-humidity environment, the exposure amount by the pre-transfer exposure 16 is not sufficient, and separation failure occurs. This is because the stiffness of the transfer material P generally used is limited to the normal environment (humidity 15% R).
In ^{H), 40cm 3 / 100~1280cm 3} /10
0), in a high humidity environment (80% RH), 20 cm ³ /
100-640 cm < ³ > / 100).

On the other hand, as in this embodiment, by appropriately changing the exposure amount of the pre-transfer exposure 16 depending on the environmental humidity, an appropriate pre-transfer exposure according to the rigidity of the transfer material P can be obtained. A good image and good paper conveyance without occurrence of separation and poor separation could be realized.

Embodiment 3 Next, a third embodiment of the present invention will be described with reference to FIG.

In this embodiment, an image reading device 19 for reading the state of the toner image formed on the transfer material P is provided downstream of the transfer portion in the transfer direction of the transfer material P, and the evaluation of the toner image in the image reading device 19 is performed. The present invention is characterized in that the voltage applied to the pre-transfer exposure 16 is appropriately changed according to the result, thereby improving and correcting toner scattering.

More specifically, an image determination pattern (toner image) stored in advance in the control device 18 is formed on the image carrier 1 and transferred onto the transfer material P. The image is read by the image reading device 19 and the read signal is fed back to the control device 18 again. Next, the control device 18 appropriately changes the voltage input to the pre-transfer exposure 16 in accordance with the level of the read signal to improve and correct the scattering of toner.

Embodiment 4 Next, a fourth embodiment of the present invention will be described with reference to FIG.

The present invention is an application of the relationship between paper rigidity and transmittance shown in FIG. In an image forming apparatus to which the present invention is applied, an OHP sheet (transfer material for an overhead projector) is often used in addition to paper. The OHP sheet has a certain degree of rigidity, but has a transmittance of almost 100%, and shows a behavior different from a general paper relationship as shown in FIG. Therefore, in the OHP sheet, when the present invention is applied, scattering tends to occur easily.

Therefore, in this embodiment, considering the above, O
When the HP sheet is used, this fact is detected, and the exposure before transfer 16
The input voltage is reduced.

The specific configuration will be described with reference to FIG. 6. To detect the use of the OHP sheet, a measuring device 20 for measuring the transmittance of the transfer material P is provided near the feeding / conveying means 12, and the measurement result is about 100%. It was determined that an OHP sheet was used.

At that time, the transmittance measuring device 20
The fact that the mode is the use mode is sent to the controller 18, and the controller 18 reduces the exposure amount of the pre-transfer exposure 16 by half.

Since the OHP sheet has high rigidity to some extent, there was no problem with the separation failure even if the exposure amount of the pre-transfer exposure 16 was reduced.

As described above, in this embodiment, OH
Even with the P sheet, it was possible to obtain a good image and paper conveyance with respect to extremely poor separation without scattering and poor separation.

The detection of the use of the OHP sheet may be performed by means other than those described above. For example, the detection may be performed by the user of the image forming apparatus pressing an OHP use button of the image forming apparatus. Further, the exposure amount of the pre-transfer exposure 16 does not have to be reduced by half, and may be off.

[0078]

As is apparent from the above description, according to the image forming apparatus of the present invention, the exposing means for exposing the image carrier on which the toner image is formed performs the above-mentioned exposure through the transfer material. By doing so, it is possible to stably separate the transfer material from the image carrier without increasing the cost, and to prevent toner scattering and transfer blurring even on high-rigidity paper, thereby performing good transfer, separation, and conveyance. And high quality images can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a relationship between rigidity and transmittance of general paper.

FIG. 3 is a schematic configuration diagram of an image forming apparatus showing a modification of the first embodiment.

FIG. 4 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment.

FIG. 5 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a third embodiment.

FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to a fourth embodiment.

FIG. 7 is a schematic configuration diagram illustrating an example of a conventional image forming apparatus.

FIG. 8 is a schematic diagram showing a change in surface potential of an image carrier in the image forming apparatus of FIG. 7;

9 is an enlarged view illustrating a transfer portion in the image forming apparatus of FIG. 7;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum (image carrier) 4 developing device (developing means) 5 transfer device (transfer means) 8 upper transfer guide (guide member) 9 lower transfer guide (guide member) 16 exposure before transfer (exposure means) 18 controller 19 Image reading device 20 Environmental humidity detection means

Claims (8)

[Claims] An image carrier having a movable surface on which an electrostatic latent image is formed; developing means for developing the electrostatic latent image as a toner image by reversal development; and a developing device on which the toner image is formed. Exposure means for exposing the image carrier, transfer means for transferring the toner image to a transfer material at a transfer site,
The image forming apparatus according to claim 1, wherein the exposure unit performs the exposure by transmitting a transfer material. 2. The image forming apparatus according to claim 1, further comprising a guide member for transporting a transfer material to the transfer portion, wherein the exposure unit is provided integrally with the guide member. 3. The image forming apparatus according to claim 1, wherein said exposure means is provided integrally with said transfer means. 4. An exposure amount by the exposure unit, where Vd is a non-image portion potential on the surface of the image carrier and Vt is a toner layer potential in a state where the transfer material is not transmitted, Vd> Vt, and Vd 4. The image forming apparatus according to claim 1, wherein the exposure amount satisfies ≒ Vt. 5. An image forming apparatus according to claim 1, further comprising: an environmental humidity detecting means for detecting an environmental humidity in the image forming apparatus main body; and a means for changing an exposure amount of said exposing means in accordance with a result of detecting the environmental humidity. Any of the image forming apparatuses. 6. An image according to claim 5, further comprising means for changing an exposure amount of said exposure means so that a relationship between an exposure amount by said exposure means and rigidity of a transfer material is constant regardless of a change in environmental humidity. Forming equipment. 7. An image reading device downstream of the transfer portion in a transfer material transport direction, wherein an exposure amount of the exposure unit is changed according to a toner image of the transfer material read by the image reading device. 7. Means 1 to 6 having means
Any one of the image forming apparatuses. 8. A detecting means for detecting the use of the transfer material for an overhead projector, and according to the detection result,
The image forming apparatus according to claim 1, further comprising a unit configured to reduce an exposure amount of the exposure unit.