JPH09138550A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device where material to be transferred such as paper is easily peeled from a photoreceptor and developer does not adhere to a non-image area by providing a means for performing exposure to the specified area of a photoreceptor and a means for uniformly irradiating all the surface of the photoreceptor with specified light quantity. SOLUTION: The photoreceptor drum 3 uniformly electrified by an electrifying charger 5 is irradiated with a laser beam in accordance with an image signal by a 1st exposure part 7 so as to form an electrostatic latent image. All the surface of the photoreceptor drum 3 where the electrostatic latent image is formed is uniformly exposed by a 2nd exposure part 9. Therefore, the potential of the photoreceptor 3 starts lowering uniformly both in an image area and the non-image area. The surface potential of the photoreceptor 3 which is exposed by the 2nd exposure part 9 is kept lowering until the photoreceptor 3 is in a transfer stage after a developing stage. Therefore, the surface potential of the non-image area of the photoreceptor 3 becomes completely small at the time of transferring, and a medium on which an image is formed is prevented from being electrostatically attracted to the photoreceptor 3 at the time of transferring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming technique for forming an image from a dry developer used in copying machines, facsimiles, printers and the like.

[0002]

2. Description of the Related Art As a conventional image forming technique, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent No. 167915, by uniformly irradiating the surface of the photoconductor bearing the toner image with light before the transfer, the surface potential of the photoconductor is lowered and the releasability of the transferred material is improved. The technology is widely used. In particular, when an image is formed by reversal development, the light is applied only to the colored portions such as the character portion of the document, so when forming an electrostatic latent image, it is more exposed than the exposed area (hereinafter referred to as the image area). The non-image area (hereinafter referred to as the non-image area) is often larger. When the area where the potential does not drop is large as described above, it is effective to reduce the surface potential of the photoconductor by the pre-transfer static elimination in order to improve the peeling property of the transferred material.

However, in such pre-transfer charge removal, even if the photoconductor is uniformly exposed, if the toner image is formed in the image area, the toner image blocks light, so the charge is removed. Lightning does not reach the surface of the photoconductor.
On the other hand, in the non-image area, there is nothing to shield the light, so the charge is completely removed. As described above, the potential of the image area does not drop as compared with the non-image area, and there is a problem that the surface potential drops (the absolute value of the potential is small) in the non-image area.

In the reversal process, the toner has a characteristic that it exists stably in a region where the absolute value of the surface potential is smaller. Therefore, when a portion where the surface potential drops is generated in the non-image area as described above, the toner moves from the image area to the non-image area and adheres to the image-receiving area. Thus, if the toner image on the photoconductor is transferred in the state where the toner is attached to the non-image area, a poor image is formed. As described above, conventionally, there is a problem that the image quality is deteriorated when the transfer target material is easily peeled off by the pre-transfer charge elimination.

[0005]

As described above, in the conventional image forming apparatus, when it is attempted to easily remove the transfer material by performing the static elimination before the transfer, the developer carried in the image area is removed. However, there is a drawback that a part of the image is easily transferred to the non-image area and the image quality is deteriorated.

It is an object of the present invention to eliminate the above-mentioned drawbacks and to provide an image forming apparatus in which a transfer material such as paper can be easily peeled off from a photoconductor and a developer does not adhere to a non-image area.

[0007]

In order to achieve the above object, the image forming apparatus of the present invention comprises a charging means for charging a photoconductor and the charging means for forming a desired image. First exposure means for exposing a specific region of the photoreceptor to form an electrostatic latent image corresponding to the image;
Second exposure means for uniformly irradiating the entire surface of the photoconductor exposed by the first exposure means with a predetermined amount of light;
Developing means for developing the electrostatic latent image formed on the photoconductor exposed by the first and second exposing means to form a developer image; and a developer image formed by the developing means. A transfer means for transferring the image onto the image forming medium.

In the image forming apparatus constructed as above,
The second exposure unit uniformly irradiates a predetermined amount of light onto the entire surface of the photoconductor on which the electrostatic latent image is formed by being uniformly charged and exposed by the first exposure unit. For this reason, the potential of the photoconductor is not exposed by the first exposure unit (hereinafter referred to as non-image region) even in the region exposed by the first exposure unit (hereinafter referred to as image region). () Also begins to decrease uniformly. The electrostatic latent image formed by the exposure by the first exposure unit remains immediately after the exposure by the second exposure unit. This electrostatic latent image is developed to obtain a developer image.

Even before the photoconductor reaches the transfer means after development, the surface potential of the photoconductor exposed by the second exposure means continues to decrease. For this reason, the surface potential of the non-image area of the photoconductor during transfer is sufficiently small, and it is possible to prevent the image forming medium from being electrostatically attracted to the photoconductor during transfer.

In another image forming apparatus of the present invention, a charging unit for charging the photosensitive member and a specific region of the photosensitive member charged by the charging unit are exposed to form a desired image, First exposure means for forming an electrostatic latent image corresponding to the image on the surface of the photoreceptor, and the electrostatic latent image formed by the first exposure means is developed to form a developer image. Second exposure for uniformly irradiating a developing unit and the photosensitive member carrying the developer image formed by the developing unit with a predetermined amount of light from the back surface of the photosensitive member to the entire surface of the photosensitive member. And a transfer means for transferring the developer image on the photoconductor exposed by the second exposure means onto the image forming medium.

In the image forming apparatus configured as described above,
After the developer image is formed on the photoreceptor and before the developer image is transferred from the photoreceptor onto the image forming medium, the second exposure unit exposes the entire surface of the photoreceptor from the back surface of the photoreceptor. To do.

Since the back surface of the photoconductor is exposed, the developer on the photoconductor does not block the light. Therefore, even after exposure after development, the potential of the photoconductor is uniformly reduced in both the image area and the non-image area. Since the surface potential of the photoconductor is lowered in this manner, the attraction force acting between the image forming medium and the photoconductor at the time of transfer can be reduced.

Furthermore, in the image forming apparatus of the present invention, since the charging means for charging the photosensitive member and the desired image are formed,
By exposing the photoreceptor charged by the charging means,
First exposure means for forming an electrostatic latent image corresponding to the image on the surface of the photoreceptor, and the electrostatic latent image formed by the first exposure means is developed to form a developer image. The developing means, the transfer means for transferring the developer image formed by the developing means onto the image forming medium, and the image forming medium having the developer image transferred by the transferring means are separated from the image carrier. And a second exposure unit that irradiates a predetermined amount of light from the back surface of the photoconductor to the entire surface of the photoconductor during the peeling by the peeling unit.

In this image forming apparatus, the exposure by the second exposing means is performed while the image forming medium on which the developer image is transferred is separated from the photoconductor. By uniformly exposing the entire surface of the photoconductor from the back of the photoconductor during peeling,
The potential of the photoconductor is lowered to reduce the attraction force acting between the image forming medium and the photoconductor. By reducing the attraction force between the image forming medium and the photoconductor, the image forming medium can be easily peeled off.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of a main part of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, the photosensitive drum 3 has a cylindrical shape with a diameter of 100 mm and is rotatably provided in the direction of arrow a.

The following are arranged around the photosensitive drum 3 along the rotation direction. First, the photosensitive drum 3
The charging charger 5 that uniformly charges the photosensitive drum 3 is
Are provided opposite to each other. A first exposure unit 7 that exposes the charged photoconductor drum 3 to form an electrostatic latent image is provided downstream (upper side in FIG. 1) of the charger 5. The first exposure unit 7 has a light source made of a semiconductor laser (not shown) and a polygon mirror 7a for scanning the laser beam generated by this light source. The semiconductor laser emits light according to image data corresponding to a desired image, and the emitted laser beam is reflected by the polygon mirror 7 a toward the photosensitive drum 3. In addition, the first exposure unit 7 is a polygon mirror 7
It has a mirror 7b, a mirror 7c and a mirror 7d which guide the laser beam reflected by a onto the photosensitive drum 3.

A second exposure unit 9 is provided downstream of the first exposure unit 7 to uniformly irradiate the entire surface of the photosensitive drum 3 exposed by the first exposure unit 7 with a predetermined amount of light. . Second
Since the exposure unit 9 is closely related to the present invention, the second exposure unit will be described later in detail.

Downstream of the second exposure unit 9, a toner T, which is a minus component developer, is accommodated, and the first exposure unit 7 and the second exposure unit 9 are accommodated.
A developing device 11 is fixedly provided to reversely develop the electrostatic latent image on the photosensitive drum 3 exposed in step 1 to form a toner image. The developing device 11 is a developing roller 1 for attaching a developer to an electrostatic latent image.
3 and the regulating roller 15 for forming a thin layer of the charged toner T on the developing roller 13. Further, in the developing device 11, a stirring roller 17 for stirring the toner T and a supply roller 19 for supplying the toner T stirred by the stirring roller 17 to the developing roller 13 are arranged.

A transfer charger 21 for transferring the toner image formed on the photosensitive drum 3 onto the paper P which is an image forming medium is provided downstream of the developing device 11. The transfer charger 21 has a corona wire 22b stretched around a charger case 22a for DC corona discharge. Adjacent to the downstream side of the transfer charger 21, there is provided a peeling charger 23 for peeling the paper P electrostatically attached to the photosensitive drum 3 during transfer. The peeling charger 23 has a corona wire 24b stretched around a charger case 24a for performing AC corona discharge.

A cleaning device 25 for removing the toner T remaining on the photosensitive drum 3 after the transfer is provided downstream of the peeling charger 23. A charge eliminator 29 that removes the surface charge of the photosensitive drum 3 is provided downstream of the cleaning device 25.

The image forming apparatus of the present embodiment has a paper feed cassette (not shown) for containing the paper P. In the vicinity of the transfer charger 21, a registration roller pair 33 is provided for supplying the paper P taken out by the take-out roller (not shown) from the paper feeding cassette between the photoconductor drum 3 and the transfer charger 21. ing. A transport belt 35 for transporting the sheet P on which the toner image is transferred toward a fixing device (not shown) is provided downstream of the peeling charger 23 along the traveling direction of the sheet P.

An image forming process of the image forming apparatus of the present embodiment having the above-mentioned configuration will be described. When an instruction to start image formation is issued from an operation panel (not shown), the photosensitive drum 3 starts rotating, and the charging charger 5 uniformly charges the surface of the photosensitive drum 3 to about -800V.

The first exposure unit 7 irradiates the photosensitive drum 3 uniformly charged by the charging charger 5 with a laser beam according to an image signal to form an electrostatic latent image. The second exposure unit 9 uniformly exposes the entire surface of the photosensitive drum 3 on which the electrostatic latent image is formed. After the exposure by the first exposure unit 7 and the second exposure unit 9, the developing device 11 adheres the toner charged to about −20 μc / g to the electrostatic latent image to perform the reversal development, and the toner image on the photoconductor drum 3. To form.

On the other hand, the registration roller pair 33 supplies the paper P between the photosensitive drum 3 and the transfer charger 21 at a predetermined timing. As a result, the toner image formed on the photosensitive drum 3 and the paper P are superposed. The transfer charger 21 applies a voltage of +5 kV to the corona wire 22b to perform DC corona discharge, and
The upper toner image is transferred onto the paper P. At the time of transfer, the transfer charger 21 charges the paper P positively.
Is electrostatically attracted to the negatively charged photosensitive drum 3. Subsequently, the peeling charger 23 is the corona wire 24b.
By applying an AC voltage of +6 kV to corona discharge, the paper P is discharged, and the paper P is separated from the photosensitive drum 3.

After the transfer, the cleaning device 25 removes the toner remaining on the photosensitive drum. After cleaning, the photosensitive drum 3 is discharged by the static eliminator 29 to complete one cycle of the image forming process, and is charged again by the charging charger in the next image forming process.

Here, in order to describe the features of the image forming process of the image forming apparatus of the present embodiment in detail, the configurations of the photosensitive drum 3 and the second exposure section 9 will be described in detail. FIG. 2 is a sectional view of the photosensitive drum 3. The photoconductor drum 3 is an organic photoconductor (hereinafter referred to as OPC) in which an organic photoconductive layer 43 having a layer thickness of 30 μm is formed on a substrate 41. The organic photosensitive layer 43 is composed of a charge transport layer 45 and a charge generation layer 47 laminated on the surface of the charge transport layer 45. The charge generation layer 47 is made of a phthalocyanine-based material,
It has a negative charging property and generates a carrier pair composed of holes and electrons when irradiated with light. The generated holes neutralize the negative charges held on the surface of the charge generation layer 47.
The charge transport layer 45 causes the electrons generated in the charge generation layer 47 to travel to the substrate 41 side.

In general, the performance of the photoreceptor is the generation efficiency of carrier pairs with respect to the irradiated light, so-called photoelectric conversion performance,
It depends on how much the generated carriers reach the counter electrode and the charge transfer performance. In this embodiment, the substrate 41 corresponds to the counter electrode. Factors that determine charge transfer performance include
There is a carrier mobility μ and a carrier lifetime τ, and generally, if the product μ · τ satisfies μ · τ ≧ 10 ⁻⁷ cm ² / V, the charge transfer performance is satisfied. However, the characteristics of the photoconductor differ depending on the ratio of μ and τ.
Type photoconductor) and life type photoconductor (hereinafter referred to as τ type photoconductor).

FIG. 3 is a diagram showing a photoelectric flow rate flowing when each of the μ type photoconductor and the τ type photoconductor is irradiated with light. As shown in FIG. 3, in the μ-type photoconductor, a photocurrent starts to flow at the same time when the light irradiation is started, but the flowing photoelectric flow rate gradually decreases, and the current stops flowing when the light irradiation is stopped. On the other hand, in the τ type photoconductor, a photocurrent starts to flow at the same time when the light irradiation is started, and a substantially constant amount of the photocurrent flows during the light irradiation. The photocurrent continues to flow for a while after the light irradiation is stopped, and the amount of current gradually decreases after that and the current stops flowing.

FIG. 4 shows changes in the surface potential of the photosensitive drum 3 when the charged photosensitive drum 3 is irradiated with light as in FIG. Since the τ of the μ-type photoconductor is about 10 ⁻⁴ to 10 ⁻⁵ sec, the photocurrent does not flow in the μ-type photoconductor after the light irradiation is stopped, and within 1/10000 seconds after the light irradiation, The surface potential becomes almost constant. On the other hand, in the τ type photoreceptor, the surface potential continues to decrease for some time after the light irradiation is completed. Therefore, when the τ-type photoconductor is used, the time from the formation of the electrostatic latent image by exposing the charged photoconductor to the development unit is set to a certain value or more,
The surface potential of the exposed portion is usually used after being attenuated to a desired potential suitable for development.

The photoconductor drum 3 used in this embodiment is a τ type photoconductor. Next, the second exposure unit 9 will be described. FIG. 5 shows an enlarged cross-sectional view of the vicinity of the second exposure unit 9, and FIG.
The perspective view of the 2nd exposure part 9 is shown in FIG.

The second exposure section 9 is an LED array formed by arranging a plurality of LEDs 53 on the base material 51. The second exposure unit 9 has a filter 55 made of frosted glass for eliminating light unevenness at a portion facing the photosensitive drum 3. The width d of the filter 55 is 3 mm, and it is configured to perform thin and uniform exposure on the photosensitive drum 3. According to experiments, a filter width of 2 to 5 mm was suitable for uniform exposure.

The image forming process of this embodiment will be described with reference to FIG. The peripheral speed of the photosensitive drum 3 is 480.
It is rotating at a speed of mm / sec. The rotating photoconductor drum 3 is uniformly charged by the charging charger 5 to about -800V. With respect to the charged photosensitive drum 3, the first exposure unit 7 changes the surface potential of the photosensitive drum 3 by exposing a portion (hereinafter referred to as an image area) where toner adheres and an image is formed, Form an electrostatic latent image. As shown in FIG. 7, when the potential changes most, the photosensitive drum 3
Has a surface potential of about -30V. Further, the potential of a portion (hereinafter, referred to as a non-image area) where the light from the first exposure unit 7 is not applied and the toner is not attached is maintained at about -800V.

The surface of the photosensitive drum 3 exposed by the first exposure section 7 is uniformly exposed by the second exposure section 9.
Since the second exposure unit 9 uniformly exposes both the image area and the non-image area, the surface potential of the photosensitive drum 3 immediately after the exposure by the second exposure unit 9 is as shown in FIG. The electrostatic latent image is slightly and uniformly lowered to such an extent that it does not disappear.

Immediately after the exposure by the second exposure unit 9, the photosensitive drum 3 faces the developing device 11. The time from the start of the exposure of the photosensitive drum 3 by the first exposure unit 7 to the arrival of the portion exposed by the first exposure unit 7 at the developing device 11 is 0.2.
(s). The time from the start of the exposure of the photosensitive drum 3 by the second exposure unit 9 to the arrival of the portion exposed by the second exposure unit 9 at the developing device 11 is 0.02 (s). The light irradiation intensity of the second exposure unit 9 is such that when the non-image region exposed by the second exposure unit 9 reaches the position facing the developing device 11, the surface potential of the non-image region becomes about −550V. Set to intensity.

When exposure is performed by the first exposure section 7, a predetermined potential difference is generated between the image area and the non-image area.
If the potential difference is too small, the toner T adheres to the non-image area during development. Therefore, the potential difference needs to be a certain value or more.

After the exposure by the first exposure unit 7, the second exposure unit 9
When the exposure is performed again, the surface potential of the photosensitive drum 3 decreases in both the image area and the non-image area. However, since the time from the exposure by the second exposure unit 9 to the start of the development by the developing device 11 is as short as 0.02 s, the potential of the non-image area is not significantly lowered, and the development is performed. It can be performed.

That is, the non-image area is about -55 after the second exposure.
Since the potential is 0 V, a sufficient potential difference is held between the image area and the non-image area. Therefore, the electrostatic latent image formed by the first exposure unit 7 is not lost by the exposure by the second exposure unit 9, and good development can be performed.

After the development, the photosensitive drum 3 is further rotated to face the transfer charger 21. The time from the completion of development to the transfer charger is 0.2 s. The photoconductor drum 3 used in the present embodiment has τ as described above.
Since it is a photoconductor of the type, the surface potential continues to decay for a while even after the exposure by the second exposure unit 9 is completed. That is, the surface potential of the photosensitive drum 3 is attenuated even after the development, and when the transfer charger 21 and the photosensitive drum 3 face each other, the surface potential of the non-image area is lowered to about -200V.

As described above, the surface potential of the non-image area is small at the time of transfer. Therefore, at the time of transfer, the photoconductor drum 3
It is possible to reduce the electrostatic attraction force between the paper P and the photoconductor drum 3, which is generated when the paper P is charged with a charge having a polarity opposite to the charging polarity of. By thus reducing the electrostatic attraction force between the paper P and the photoconductor drum 3, the paper P can be easily peeled from the photoconductor drum.

8 to 10 show how the surface potential changes in each of the non-image area and the image area of the photosensitive drum 3. In FIGS. 8 to 10, the horizontal axis represents the time from the charging to the steps such as exposure and development necessary for image formation, and the vertical axis represents the exposure when each step is performed. The surface potential of the body drum 3 is taken to represent the relationship between the two. Note that FIG. 9 corresponds to an intermediate area in the image area, and FIG. 10 corresponds to a solid image area.

In the image forming apparatus of this embodiment, various images are formed in FIG. 11 by changing the surface potential of the photosensitive drum 3 during development (hereinafter referred to as developing portion potential) from -30V to -550V. The result is shown. FIG. 11 shows the photosensitive drum 3 when the photosensitive drum 3 reaches the transfer charger 21.
Of the surface potential (hereinafter referred to as the transfer portion potential), the fine line portion of the obtained image (dirt generation state), and the peeling performance of the transferred material are shown. Three types of transfer materials, OHP, 64 g paper and 50 g, were prepared and evaluated in each case.

For comparison, FIG. 11 shows a conventional pre-transfer charge erasing method in which an image is formed by an image forming apparatus which does not perform pre-transfer charge erasing, and in which the pre-transfer charge erasing is performed after development without the second exposure unit 9. The evaluation results when an image is formed by the image forming apparatus are also shown.

As is apparent from FIG. 11, the developing portion potential is −
Regarding the solid image portion of about 30 V, the transfer portion potential is almost the same in all image forming apparatuses. However, the development potential is
Regarding the non-image area of about 550 V, the surface potential was lowered when the conventional charge removal before transfer or the charge removal according to the present embodiment was performed, and the peeling property of the transferred material was improved as compared with the case where the charge removal before transfer was not performed. . However, in the conventional image forming apparatus of the pre-transfer charge eliminating system, the transfer portion potential of the halftone image portion where the developing portion potential is about −300 V does not drop below the transfer portion potential of the non-image portion, and the absolute value of the potential is It became large), and dust was generated in the thin line image.

On the other hand, in the image forming apparatus of this embodiment, the transfer portion potential is sufficiently lowered even in the halftone image portion.
(The absolute value of the electric potential is small), and no dust is generated. The peelability of the transferred material is not jammed even through 50 g paper, and the same performance as that of the conventional pre-transfer charge erasing is obtained.

As described above, according to the image forming apparatus of this embodiment, it is possible to favorably separate the material to be transferred from the photosensitive member while suppressing the occurrence of dust. FIG. 12 shows an example in which the image forming apparatus shown in FIG. 1 is modified so that the substrate 41 of the photosensitive drum 3 is connected to a + 200V DC power supply 61 instead of being grounded. The result of forming an image with this image forming apparatus is also shown in FIG.

By applying a voltage having a polarity opposite to the charging polarity of the photosensitive drum 3 to the substrate 41, the first exposure unit 7
The photosensitive drum 3 exposed in step (2) loses the negatively charged electric charge, and at the same time, becomes slightly positively charged in the part where the electric charge is lost. At the time of transfer, since the paper P is positively charged, the positive charge of the photoconductor drum 3 and the positive charge of the paper P repel each other to improve the peeling property. When an image was formed by the image forming apparatus shown in FIG. 12, the releasability was further improved as compared with the image forming apparatus shown in FIG.

Although the first embodiment of the present invention has been described above, it goes without saying that the first embodiment can be variously modified without departing from the spirit of the invention. The first exposure unit 7,
The irradiation intensity of the second exposure unit 9 is adjusted according to the type, size, peripheral speed, etc. of the photosensitive drum 3. In the non-image area, the change in the surface potential of the photosensitive drum 3 from the charging to the exposure by the first exposure unit 7 is due to dark decay, and the surface potential can be regarded as almost constant. Therefore, the charging potential is 5
When the voltage is from 00 to 800V, it is 4 by the exposure by the second exposure unit 9.
The intensity of the second exposure unit 9 may be adjusted so as to be about 00 to 700V.

Further, in the above-described embodiment, as the photoconductor drum 3, a laminated type τ type photoconductor comprising the charge generation layer 47 and the charge transport layer 45 was used. In the laminated type photoconductor, the charge transport layer 47 is greatly related to the life of the photoconductor and the mobility of carriers. As the charge transport layer 47 capable of forming the τ type photoreceptor, as shown in FIG. 13, a hydrazone-based material, a pyrazoline material, an oxadiazole-based material, and the like can be given.

The light of the LED forming the second exposure unit 9 may be guided onto the photosensitive drum 3 via the reflecting plate 63 as shown in FIG. The second exposure unit 9 may be an array of miniature balls or the like as long as it can uniformly expose the photosensitive drum 3 in addition to the LED array.

Next, the image forming apparatus of the second embodiment will be described with reference to FIG. The overall configuration of the image forming apparatus according to the present embodiment is almost the same as that of the image forming apparatus shown in FIG. 1 described above.
5, the same reference numerals as those in FIG. The difference between the image forming apparatus shown in FIG. 15 and the image forming apparatus shown in FIG. 1 is the configuration of the photosensitive drum 71 and the second
This is the arrangement position of the exposure unit 73.

FIG. 16 is a sectional view of the photosensitive drum 71. The photoconductor drum 71 has an indium tin oxide film (hereinafter referred to as an ITO film) 76 as a transparent conductive material on the surface of a plastic transparent tube 75 as a substrate 74. An organic photosensitive layer 77 having a layer thickness of 30 μm is formed on the ITO film 76. The organic photosensitive layer 77 includes a charge transport layer 79 and a charge generation layer 81. As the charge transport layer 79 and the charge generation layer 81, the same ones as those used for the photosensitive drum 3 described above were used. That is, the photoconductor drum 71 is also a τ type photoconductor.

The second exposure section 73 is located inside the photosensitive drum 71 so that the photosensitive drum 71 is exposed from the substrate 74 side, slightly upstream of the developing device 11 along the rotation direction of the photosensitive drum 71. It is provided in.

The diameter and peripheral speed of the photosensitive drum 71, the time from the arrival of the photosensitive drum 71 at the second exposure unit 73 to the development unit 11, the charging potential of the photosensitive drum 71, and the second exposure unit. Regarding the intensity of the exposed portion of No. 73, etc.
The same as in the above embodiment. Even when the second exposure unit 73 performs the exposure from the back surface of the photosensitive drum 71 as in the second embodiment, the same effect as that of the first embodiment can be obtained.

Photoreceptor drum 73 as in the second embodiment
When the pre-transfer charge removal is performed from the back surface of the toner image, even if light irradiation is performed after development, the toner image is not exposed.
Therefore, the static elimination effect does not differ between the non-image area and the image area due to the presence of the toner image. Therefore, FIG.
In the image forming apparatus shown in FIG. 5, the second exposure unit 73 performs the exposure from the back side of the photoconductor drum 71 after the exposure by the first exposure unit 7 and before the peeling by the peeling charger 23 is completed. If

The image forming apparatus shown in FIG. 17 is the image forming apparatus shown in FIG. 15 in which the second exposure section 73 is arranged at a position (a) near the boundary between the transfer charger 21 and the peeling charger 23.

The peripheral velocity of the photosensitive drum 71 was set to 480 mm / s, and the initial charging potential of the photosensitive drum 71 was adjusted so that the developing portion potential in the non-image area was −550V. Also the second
In the exposure unit 73, the photoconductor drum 71 has a peeling charger 23.
The exposure intensity was set so that the potential of the non-image area of the photoconductor drum 71 would be −100 V or less at the end of passing through.

In the transfer area where the transfer charger 21 and the photoconductor drum 71 face each other, the movement of the toner T starts from the moment when the photoconductor drum 71 and the paper P come into close contact with each other and a transfer electric field is formed. Then, even after the movement of the toner T is completed, the contact between the sheet P and the photosensitive drum 71 and the application of the transfer electric field continue. When the peeling charger 23 and the paper P face each other, the peeling charger 23 gradually removes the electric charge applied to the paper P. Charge removal by the peeling charger 23,
Due to the resilience of the paper P itself, the paper P is the photosensitive drum 7
Separate from 1. By disposing the second exposure unit 73 as in the present embodiment, the exposure can be performed from the back surface of the photoconductor drum 71 when the toner has almost completely moved onto the paper P, and the photoconductor drum 71 can be exposed. Can be easily separated.

Note that, in FIG. 17, the second exposure section 73 may be arranged at the position (b) between the developing device 11 and the transfer charger 21. FIG. 18 shows the results of forming images under the following six conditions by the image forming apparatus shown in FIG. The evaluation items are the same as those shown in FIG.

Condition 1: The second exposure section 73 is placed at the position (a) to perform charge removal after transfer. Condition 2: The second exposure unit 73 is arranged at the position (b), and charge removal is performed after transfer. Condition 3: Under the condition 1, a voltage of +200 V is further applied to the substrate 74 of the photosensitive drum 71.

Condition 4: Under condition 2, a voltage of +500 V is further applied to the substrate 74 of the photosensitive drum 71. Condition 5: In condition 1, a voltage of +500 V is further applied to the substrate 74 of the photosensitive drum 71, and the exposure by the second exposure unit 73 is continued until the peeling is completed.

Condition 6: No second exposure unit 73 is provided. As can be seen from the results of FIG. 18, in the case of condition 6, the dust of the fine line portion did not occur, but the separation was impossible with 50 g paper. When exposure is performed by the second exposure unit 73 before transfer, jam does not occur and dust is small. Further, when the exposure by the second exposure unit 73 is performed after the transfer, the separation performance of the transfer material is excellent, and further, regarding the dust of the fine line portion, when the exposure by the second exposure unit 73 is performed before the transfer. Compared with the above, the number of images was even smaller and a high quality image was obtained. When a voltage is applied to the substrate 74 of the photosensitive drum 71, the peeling property is further improved.

Although some embodiments of the present invention have been described above, as is apparent from the above description, according to the present invention, the second exposure unit is formed after the electrostatic latent image is formed and before the development. By irradiating the entire surface of the photoconductor with a predetermined amount of light, it is possible to uniformly perform the pre-transfer charge elimination on the entire surface of the photoconductor without the light being blocked by the toner image.

Since the second exposure means irradiates the entire surface of the photosensitive member with light before development, the image area is exposed regardless of whether the exposure is from the surface of the photosensitive member or the rear surface of the photosensitive member. And the non-image area can have the same effect of pre-transfer charge elimination.

Further, by using the organic photoconductor in the present invention, the surface potential of the photoconductor exposed by the second exposure means can be changed to a desired value by utilizing the potential decay characteristic of the photoconductor. .

In the present invention, the substrate of the organic photoreceptor is
By applying a voltage having a polarity opposite to the charging polarity of the photoconductor, the electrostatic repulsion force between the photoconductor and the transfer material can be strengthened, and the releasability of the transfer material is improved.

Further, according to the present invention, since the second exposing means irradiates the entire surface of the photosensitive member from the back surface of the photosensitive member after development,
It is possible to perform pre-transfer charge removal without being affected by the toner image. In this case, by applying a voltage having a polarity opposite to the charging polarity of the photoconductor to the substrate of the photoconductor, the releasability of the transferred material is further improved.

Further, the exposure by the second exposing means after the development is performed after the transfer and before the peeling of the material to be transferred is completed, so that the potential of the photoconductor at the peeling can be efficiently lowered.

It is needless to say that the present invention is not limited to the above-mentioned embodiment and can be variously modified without departing from the spirit of the present invention. In the image forming apparatus shown in FIGS. 15 and 17, a τ type OP is used as the photosensitive drum 71.
A C drum was used. However, when performing exposure from the back surface of the photoconductor drum 73 by the second exposure unit 73, particularly when the OPC
Since it is not necessary to use the potential attenuation characteristic of the drum, aS
An i photoreceptor or an inorganic photoreceptor can also be used.

[0069]

As described above, according to the image forming apparatus of the present invention, the transfer material such as paper can be easily peeled off from the photoconductor without adhering the developer to the non-image area.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a photoconductor used in the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram of each of a μ type photoconductor and a τ type photoconductor.

FIG. 4 is a characteristic diagram of each of a μ type photoconductor and a τ type photoconductor.

FIG. 5 is a cross-sectional view of the vicinity of a second exposure unit used in the image forming apparatus according to the first embodiment of the present invention.

FIG. 6 is a perspective view of second exposure means used in the image forming apparatus according to the first embodiment of the present invention.

FIG. 7 is a diagram showing changes in the surface potential of a photoconductor.

FIG. 8 is a diagram showing changes in the surface potential of a photoconductor.

FIG. 9 is a diagram showing changes in the surface potential of a photoconductor.

FIG. 10 is a diagram showing changes in the surface potential of a photoconductor.

FIG. 11 is a diagram showing a result of forming an image by the image forming apparatus according to the first embodiment of the present invention.

FIG. 12 is a diagram illustrating a modified example of the image forming apparatus according to the first embodiment of the invention.

FIG. 13 is a diagram showing a material of a photoconductor.

FIG. 14 is a diagram illustrating a modified example of the second exposure unit used in the image forming apparatus according to the first embodiment of the present invention.

FIG. 15 is a sectional view of a main part of an image forming apparatus according to a second embodiment of the present invention.

FIG. 16 is a sectional view of a photoconductor used in an image forming apparatus according to a second embodiment of the present invention.

FIG. 17 is a sectional view of a main part of an image forming apparatus according to a third embodiment of the present invention.

FIG. 18 is a diagram showing a result of forming an image by the image forming apparatus according to the third embodiment of the present invention.

[Explanation of symbols]

 3,71 Photoreceptor 7 First Exposure Section 9,73 Second Exposure Section 11 Developing Device 21 Transfer Charger 23 Peeling Charger

Claims (8)

[Claims] 1. A charging unit for charging a photoconductor, and an electrostatic latent image corresponding to the image by exposing a specific region of the photoconductor charged by the charging unit to form a desired image. A first exposure unit for forming a light, a second exposure unit for uniformly irradiating the entire surface of the photosensitive member exposed by the first exposure unit with a predetermined amount of light, and the first and second Developing means for developing the electrostatic latent image formed on the photoconductor exposed by the exposing means to form a developer image, and the developer image formed by the developing means on the image forming medium. An image forming apparatus comprising: a transfer unit for transferring. 2. A charging unit for charging a photosensitive member, and an electrostatic latent image corresponding to the image by exposing a specific region of the surface of the photosensitive member charged by the charging unit to form a desired image. A first exposure unit for forming a light source; a second exposure unit for uniformly irradiating a predetermined amount of light on the entire surface of the photosensitive member exposed by the first exposure unit; Developing means for developing the electrostatic latent image formed on the photoconductor exposed by the second exposing means to form a developer image; and the developer image formed by the developing means on the image forming medium. An image forming apparatus comprising: a transfer unit configured to transfer the image onto the image forming apparatus. 3. A charging unit for charging a photosensitive member, and an electrostatic latent image corresponding to the image by exposing a specific region of the surface of the photosensitive member charged by the charging unit to form a desired image. And a first exposure unit for forming an image on the entire surface of the photoconductor exposed by the first exposure unit.
Second exposure means for uniformly irradiating a predetermined amount of light from the back surface of the photoreceptor, and the electrostatic latent image formed on the photoreceptor exposed by the first and second exposure means. An image forming apparatus comprising: a developing unit that develops to form a developer image; and a transfer unit that transfers the developer image formed by the developing unit onto an image forming medium. 4. A charging unit for charging an organic photoconductor, and an electrostatic latent image corresponding to the image by exposing a specific region of the photoconductor charged by the charging unit to form a desired image. First exposure means for forming an image; second exposure means for uniformly irradiating the entire surface of the photosensitive member exposed by the first exposure means with a predetermined amount of light; Developing means for developing the electrostatic latent image formed on the photoreceptor exposed by the second exposing means to form a developer image; and the developer image formed by the developing means for forming an image forming medium. An image forming apparatus comprising: a transfer unit that transfers the image onto the image forming apparatus. 5. A charging unit configured to charge a surface of a photosensitive layer of a photosensitive member having a photosensitive layer formed on a substrate, and a bias voltage having a polarity opposite to a polarity with which the charging unit charges the photosensitive member, And a voltage applying unit for applying a voltage to the substrate, to expose a specific area of the photoconductor charged by the charging unit and to which a voltage is applied by the voltage applying unit to form a desired image. First exposure means for forming a corresponding electrostatic latent image, and second exposure means for uniformly irradiating the entire surface of the photoconductor exposed by the first exposure means with a predetermined amount of light. Developing means for developing the electrostatic latent image formed on the photoconductor exposed by the first and second exposing means to form a developer image, and a developer image formed by the developing means. Transfer means for transferring the image onto the image forming medium An image forming apparatus, comprising. 6. A charging unit for charging a photoconductor, and a specific region of the photoconductor charged by the charging unit to form a desired image is exposed to expose the image on the surface of the photoconductor. First exposure means for forming a corresponding electrostatic latent image, developing means for developing the electrostatic latent image formed by the first exposure means to form a developer image, and forming means by the developing means Second exposure means for uniformly irradiating a predetermined amount of light from the back surface of the photoconductor to the photoconductor carrying the developed developer image; and the second exposure means. And a transfer unit that transfers the developer image on the photoreceptor, which is exposed by the method, onto the image forming medium. 7. A charging unit configured to charge a surface of a photosensitive layer of a photosensitive member having a photosensitive layer formed on a substrate, and a bias voltage having a polarity opposite to a polarity with which the charging unit charges the photosensitive member. Voltage applying means for applying a voltage to the substrate of the photosensitive member, and to expose a specific area of the photoconductor charged by the charging means and to which a voltage is applied by the voltage applying means to form a desired image. First exposure means for forming an electrostatic latent image corresponding to the image on the surface of the body, and developing means for developing the electrostatic latent image formed by the first exposure means to form a developer image. Second exposure means for irradiating the photosensitive body carrying the developer image formed by the developing means with a predetermined amount of light from the back surface of the photosensitive body to the entire surface of the photosensitive body, The above-mentioned feeling exposed by the second exposure means. Image forming apparatus characterized by having a transfer unit that transfers the developer image on the body on an image forming medium. 8. A charging unit for charging a photosensitive member, and exposing the photosensitive member charged by the charging unit to form a desired image, and electrostatically corresponding to the image on the surface of the photosensitive member. First exposure means for forming a latent image, developing means for developing the electrostatic latent image formed by the first exposure means to form a developer image, and developer formed by the developing means Transfer means for transferring the image onto the image forming medium, peeling means for peeling the image forming medium having the developer image transferred by the transferring means from the image carrier, and peeling by the peeling means. The image forming apparatus further comprises: second exposure means for uniformly irradiating a predetermined amount of light from the back surface of the photoconductor to the entire surface of the photoconductor.