JPH05224566A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain a toner image of high quality with a strong contrast without unintentionally recovering even toner on an exposed part when the toner on a photosensitive surface of an unexposed part is recovered in the electrophotographic device where the toner developing is carried out from a front surface at the same time the photosensitive body has its image exposed from backside. CONSTITUTION:In the electrophotographic device where recovering bias voltage is impressed to recover the toner stuck to the unexposed part of the photosensitive body 10 from the photosensitive body surface by a developing means 21 and provided with the toner recovering means 22 placed facing the photosensitive body 10, the recovering bias voltage of the above mentioned toner recovering means 22 is constituted to be the same polarity as developing bias voltage of the developing means 21 and to be a voltage at a level between electrified voltage of the exposed part and-the electrified voltage of the unexposed part of the surface of the photosensitive body 10 at the position facing the toner recovering means 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus in which a photoreceptor is imagewise exposed from the back side and at the same time toner development is performed from the front side.

As an electrophotographic apparatus, a
The so-called Carlson process including the steps of pre-charging, image exposure, development, transfer, fixing, charge removal, and cleaning is widely used.

However, in the Carlson process, the number of steps is large, the apparatus becomes complicated and large, and the corona discharger, which is often used for precharging, transferring and discharging, has an odor and is harmful to the human body. There is a problem that ozone is generated.

Therefore, an electrophotographic apparatus of a type that can be formed simply and compactly with a small number of steps, and that exposure and development can be performed simultaneously from both front and back surfaces of a photoreceptor without using a corona discharger. Is proposed.

[0005]

2. Description of the Related Art In a conventional electrophotographic apparatus of this kind, as shown in FIG. 7, a conductive material having a developing bias voltage applied to the front surface side of a photosensitive drum 80 exposed from the back surface side by an exposure device 91. The developing roller 92 made of a material is brought into contact with the developing roller 92 to develop the toner, and the collecting roller 9 is applied with a collecting bias voltage having a polarity opposite to that of the developing bias voltage.
3 is brought into contact with the surface of the photosensitive drum 80, and the photosensitive drum 8
The toner adhering to the non-exposed portion of the 0 surface is removed and collected.

In the photosensitive drum 80, a transparent conductive layer 82 serving as a ground electrode is formed on the outside of a transparent substrate 81, and a photoconductive layer 83 for generating electron-hole pairs by exposure is formed on the outside of the transparent conductive layer 82. It has a three-layer structure.

[0007]

In the developing roller 92 portion of the electrophotographic apparatus as described above, image-exposure causes electron-hole pairs in the photoconductive layer 83, of which the voltage applied to the developing roller 92 is Charges of opposite polarity are applied to the photoconductive layer 83.
Of the latent image charge.

FIG. 8 shows the state of electric charges in that portion. As described above, since the electrostatic capacitance of the photoconductive layer 83 apparently increases in the exposed portion, it is transferred from the developing roller 92 and attached. The amount of the toner 100 to be used increases, and a toner image having a certain degree of contrast between the exposed portion and the non-exposed portion is formed. However, the toner 100 also adheres to the non-exposed portion.

Next, in the collecting roller 93, by applying a voltage having a polarity opposite to that at the time of development, the toner in the non-exposed portion is transferred to the collecting roller 93 by electrostatic force.
At this time, in the exposed portion, the toner remains on the surface of the photosensitive drum 80 due to the electrostatic binding force of the latent image charge and the toner charge, and as a result, a clear toner image is formed.

However, the recovery roller 93 has a developing roller 9
Since a voltage having a polarity opposite to that of 2 is applied, as shown in FIG. 9, the electric field acts in the same direction as arrow A not only on the toner of the exposed portion but also on the toner of the non-exposed portion. To do.

As a result, the peeling force due to the electric field in the direction of arrow A becomes larger than the attractive force due to the electrostatic restraint force with the latent image charge, and the toner in the exposed area is transferred to the collecting roller 93 together with the toner in the unexposed area. However, the contrast of the toner image may decrease.

Therefore, according to the present invention, when the toner is collected from the surface of the photoconductor in the non-exposed area, the toner in the exposed area is not collected, and a high-quality toner image with high contrast can be obtained. An object is to provide an electrophotographic apparatus.

[0013]

In order to achieve the above object, the electrophotographic apparatus of the present invention is applied with a developing bias voltage for transferring the toner 100 adhered to the surface to the surface of the photoconductor 10. The developing means 21 is disposed so as to face the surface of the photoconductor 10, and the photoconductor 10 is exposed from the back surface side of the photoconductor 10 at a position facing the developing means 21 to electrostatically charge the photoconductor 10. The exposure unit 1 for forming a latent image and the photoconductor 10 by the developing unit 21.
An electrophotographic apparatus having a toner collecting means 22 arranged facing the photoconductor 10 by applying a collection bias voltage for collecting the toner adhering to the non-exposed portion from the surface of the photoconductor 10. The toner collecting means 22
Of the charging voltage of the exposed portion of the surface of the photoconductor 10 and the charging voltage of the non-exposed portion which have the same polarity as the developing bias voltage of the developing means 21 and face the toner collecting means 22. It is characterized by being set to a height between.

The toner collecting means 22 may be a roller formed of a conductive elastic material and may be pressed against the surface of the photoconductor 10, and the collecting bias voltage may be set to the non-exposing portion. The charging voltage may be closer to the charging voltage of the exposed portion than the above charging voltage.

Around the photoconductor 10, in addition to the developing means 21 and the toner collecting means 22, a charging means for charging the photoconductor 10 and the photoconductor 10 are provided.
It is not necessary to provide a cleaning means for removing the toner adhering to the surface of the photosensitive member, a discharging means for eliminating the charged state of the surface of the photoconductor 10 and the like.

[0016]

Since the collecting bias voltage is between the charging voltage of the exposed portion and the charging voltage of the non-exposed portion, the electric field direction of the exposed portion and the electric field direction of the non-exposed portion are opposite at the position of the toner collecting means 22. become.

As a result, the toner in the non-exposed area is not transferred to the photosensitive member 1.
By the electric field moving from the 0 side to the toner collecting means 22 side, the toner is separated from the surface of the photoconductor 10 and transferred to the toner collecting means 22, and the toner in the exposed portion acts on the electric field between the photoconductor 10 and the toner collecting means 22. And the attractive force of the latent image charge on the surface of the photoconductor 10 presses the surface of the photoconductor 10.

[0018]

Embodiments will be described with reference to the drawings. Figure 2
1 illustrates a printer device to which the present invention is applied. The present invention can be applied to a copying machine, a facsimile machine and other electrophotographic apparatuses.

Reference numeral 10 denotes a photosensitive drum which is rotationally driven in the direction of arrow P by a drive motor (not shown). The transparent conductive layer 12 is an indium tin oxide vapor deposition film serving as a ground electrode on the outside of the transparent substrate 11 made of glass. Is formed, and a photoconductive layer 13 in which electron-hole pairs are generated by exposure is formed on the outer side thereof to form a three-layer structure. In addition,
The photoconductive layer 13 has a structure in which α-Si having a thickness of, for example, about 15 μm is sandwiched between an inner charge injection blocking layer and an outer protective layer.

A light emitting diode array 1 for emitting image light is arranged inside the photosensitive drum 10, and image exposure is performed on the back side of the photosensitive drum 10 through a self-converging converging lens array 2.

In the developing device 20 containing the toner 100, a developing roller 21 and a collecting roller 22 both of which are made of a conductive elastic member are opposed to the photosensitive drum 10 so as to contact the entire width of the photosensitive drum 10. Are pressed against.

The developing roller 21 and the collecting roller 22 are rotationally driven in directions Q and R, respectively, by a drive motor (not shown). As the toner 100, a non-magnetic and electrically insulating one-component developer is used.

The developing roller 21 includes a developing bias power source 2
3, the developing bias voltage of, for example, +10 to +1000 V (preferably +100 to +600 V) of the positive electrode is applied.

The toner 100 in the developing device 20 adheres to the outer peripheral portion of the rotating developing roller 21 and is conveyed, and when it is formed in a thin layer by the doctor blade 24, it is rubbed by the doctor blade 24. It is charged to about 10 to 20 μC / g.

The collecting roller 22 is made of a conductive elastic rubber material, and is pressed against the photosensitive drum 10 by a spring 25 as shown in FIG. Is elastically deformed.

The contact portion of the collecting roller 22 with the photosensitive drum 10 is rotationally driven in the same direction as the photosensitive drum 10 at a peripheral speed 1.2 to 1.3 times faster than that of the photosensitive drum 10. Two
Reference numeral 7 denotes a recovery blade for scraping off the toner 100 attached to the recovery roller 22 and recovering it in the developing device 20.

The collecting roller 22 has a collecting bias power source 2
The recovery bias voltage of the positive electrode is applied by 6.
As shown in FIG. 4, the recovery bias voltage V is higher than the charging voltage V1 of the exposed portion of the surface of the photosensitive drum 10 facing the recovery roller 22, and the charging voltage V2 of the non-exposed portion.
Set to a lower voltage.

Returning to FIG. 2, reference numeral 5 denotes a transfer roller to which a transfer voltage is applied by the transfer power supply 6, and the photosensitive drum 1
The toner image formed on the 0 surface is transferred to the recording paper 200. A fixing roller 7 thermally fixes the toner image on the recording paper 200.

Around the photosensitive drum 10, the developing device 2
0 and the transfer roller 5, in addition to charging means for charging the photosensitive drum 10, cleaning means for removing toner adhering to the surface of the photosensitive drum 10, and for eliminating the charged state of the surface of the photosensitive drum 10. No static elimination means etc. are provided. Therefore, the configuration of the entire device can be made simple and small.

According to the apparatus of the embodiment thus constructed, electron-hole pairs are generated in the photoconductive layer 13 by the image exposure from the light-emitting diode array 1 in the developing roller 21 part, and among them, development is performed. Negative charges having the opposite polarity to the voltage applied to the roller 21 move to the surface side of the photoconductive layer 13 to become latent image charges.

This state is exactly the same as the case of FIG.
Since the electrostatic capacity of the photoconductive layer 13 apparently increases in the exposed portion, the toner 10 transferred from the developing roller 21 and attached thereto
The amount of 0 becomes large, and a toner image with a certain degree of contrast is formed between the exposed portion and the non-exposed portion.

The toner 100 transferred to the surface of the photosensitive drum 10 is collected by the collecting roller 2 by the rotation of the photosensitive drum 10.
Move to Part 2. Since the recovery bias voltage applied to the recovery roller 22 is between the charging voltage of the exposed portion and the charging voltage of the non-exposed portion of the photosensitive drum 10, the position of the recovery roller 22 is as shown in FIG. In addition, the electric field direction of the exposed portion and the electric field direction of the non-exposed portion are opposite.

As a result, the toner in the non-exposed portion is generated by the electric field moving from the photosensitive drum 10 to the collecting roller 22 side.
It is separated from the surface of the photosensitive drum 10 and transferred to the collecting roller 22.

On the other hand, the toner of the exposed portion is the photosensitive drum 10
It is pressed against the surface of the photosensitive drum 10 by the electric field acting between the collecting roller 22 and the collecting roller 22 and the attractive force of the latent image charge on the surface of the photosensitive drum 10, and remains on the surface of the photosensitive drum 10 with a strong suction force.

Therefore, almost all of the toner 100 in the non-exposed area is transferred to the collecting roller 22 side, and almost all of the toner 100 in the exposed area remains on the photosensitive drum 10 side, so that a clear toner image with high contrast is obtained. It is sent to the transfer roller 5 and transferred onto the recording paper 200. When the recovery bias voltage V is set closer to the charging voltage of the exposed portion than the charging voltage of the non-exposed portion, a toner image with less fog in the background portion can be obtained.

FIG. 6 shows the experimental results comparing the line density of the image obtained in this example and the fog density of the background portion with the conventional example, and the result of the example shown by the solid line is the broken line. The results show that the line density is high and the fog density is low as compared with the case of the conventional example shown by.

[0037]

According to the electrophotographic apparatus of the present invention, the toner in the non-exposed portion is separated from the surface of the photoconductor by the electric field moving from the photoconductor side to the toner collecting means side, transferred to the toner collecting means, and exposed. The toner of the part is pressed down on the surface of the photoconductor by the electric field acting between the photoconductor and the collecting means and the attractive force of the latent image charge on the surface of the photoconductor, so that a high-quality toner image with high contrast can be obtained. It has an excellent effect.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment.

FIG. 3 is a partial configuration diagram of an embodiment.

FIG. 4 is a diagram showing a recovery bias voltage of an example.

FIG. 5 is a schematic view showing an operation of a collecting roller portion of the embodiment.

FIG. 6 is a diagram showing the density of a toner image of an example in comparison with a conventional example.

FIG. 7 is a configuration diagram of a conventional example.

FIG. 8 is a schematic view showing an operation of a developing roller portion of a conventional example.

FIG. 9 is a schematic view showing an operation of a collecting roller section of a conventional example.

[Explanation of symbols]

 1 Light Emitting Diode Array (Exposure Means) 10 Photosensitive Drum (Photosensitive Body) 21 Developing Roller (Developing Means) 22 Collecting Roller (Toner Collecting Means) 100 Toner

Claims (4)

[Claims] 1. A developing device which is arranged to face the surface of the photoconductor (10) by applying a developing bias voltage for transferring the toner (100) attached to the surface to the surface of the photoconductor (10). The means (21) and the photoconductor (1) at a position facing the developing means (21).
0) from the back surface side of the photoconductor (10) to form an electrostatic latent image on the photoconductor (10), and the photoconductor (1) by the developing unit (21). A toner collecting unit (2) arranged facing the photoconductor (10) by applying a collection bias voltage for collecting the toner adhering to the non-exposed portion of the photoconductor (10) from the surface of the photoconductor (10).
2), the recovery bias voltage of the toner collecting means (22) has the same polarity as the developing bias voltage of the developing means (21) and faces the toner collecting means (22). The electrophotographic apparatus is characterized in that the height is set between the charging voltage of the exposed portion and the charging voltage of the non-exposed portion of the surface of the photoconductor (10). 2. The electrophotographic apparatus according to claim 1, wherein the toner collecting means (22) is a roller formed of a conductive elastic material and is pressed against the surface of the photoconductor (10). 3. The electrophotographic apparatus according to claim 1, wherein the recovery bias voltage is closer to the charging voltage of the exposed portion than the charging voltage of the non-exposed portion. 4. Around the photoconductor (10), in addition to the developing means (21) and the toner collecting means (22),
A charging unit for charging the photoconductor (10), a cleaning unit for removing toner adhering to the surface of the photoconductor (10), and a charge state for eliminating the charged state of the surface of the photoconductor (10). The electrophotographic apparatus according to claim 1, 2 or 3, wherein no charge eliminating means is provided.