JPH10291336A - Image forming system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracking of image due to breakage of an electrostatic latent image by providing a surface electrode layer. SOLUTION: The image forming system comprises an image carrying belt 2 having a dielectric layer 25 formed on a conductive layer 23, and a photosensitive body 9 having a photosensitive layer 93 and a patterned surface electrode layer 94 having a plurality of slits formed on a conductive layer 92. They are arranged such that the dielectric layer 25 faces the surface electrode layer 94 and the photosensitive layer 93 is subjected to imagewise exposure under a state where a potential difference is set between both conductive layer 23, 92 and a bias voltage is applied to the surface electrode layer 94. A latent image is formed on a traveling image carrying belt 2 through discharge between the photosensitive body 9 and the image carrying belt 2. The width W at a conductive part 98 of the surface electrode layer 94 for making a slit is set at about 20 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an electrostatic latent image on an image carrier, such as a copying machine and a printer.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a printer, an electrostatic latent image carrier such as a photosensitive member is charged by a charging device and then exposed to form an electrostatic latent image. There is generally known an image forming process in which a latent image is developed with a toner to form a visible image, and this is transferred to a transfer material and fixed.
However, in the conventional image forming method involving corona discharge,
It leads to environmental destruction such as generation of a large amount of ozone,
In recent years, it has been desired to provide an image forming method in which generation of ozone is suppressed because the influence on the photoreceptor surface is greatly reduced and the life of the photoreceptor is reduced.

As a low-ozone image forming method, for example, a method described in Japanese Patent Application Laid-Open No. Hei 1-293358 has been proposed. In this image forming method, as shown in FIG. 7, a photosensitive member 101 composed of small pieces and a cylindrical charge holding medium 102 are separately provided. Photoconductor 101 is a photosensitive layer support 1
03, a photoreceptor electrode 104 and a photosensitive layer 105 are sequentially laminated. On the other hand, the charge holding medium 102 is obtained by sequentially stacking an insulating layer support 106, a charge holding medium electrode 107, and an insulating layer 108. This photoconductor 1
01 and the charge storage medium 102 are arranged such that the photosensitive layer 105 and the insulating layer 108 face each other with a gap therebetween.

Then, a voltage is applied between the photosensitive member electrode 104 and the charge holding medium electrode 107, and the photosensitive member 101 is placed in a dark place.
When light is incident on the charge holding medium 102 and the light is scanned in the axial direction (main scanning direction), the light incident portion of the photosensitive layer 105 shows conductivity, and the portion of the photosensitive layer 105 and the insulating layer 108 of the charge holding medium 102 An electric discharge is generated during that time, and electric charges are accumulated in the insulating layer 108 of the electric charge holding medium 102 rotated and driven in the direction of the arrow b in the figure to form an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 109 to become a toner image,
The toner image is transferred to paper or film by the transfer charger 110.

As shown in FIG. 8A, an original composed of a plurality of long and short lines long in the sub-scanning direction is exposed in the main scanning direction to form an electrostatic latent image by the above-described apparatus. Then, FIG.
As shown in (b), the rear end of the electrostatic latent image formed on the charge holding medium 102 extends by ΔL. This elongation is more noticeable in a longer line image.

When the present inventors examined the cause of the extension of the trailing edge of the image, the excess carriers generated in the photoconductor were gradually released after the end of the exposure, and the discharge continued. It was found that the stop did not coincide, and the rear end of the latent image was elongated. Here, the excess carrier includes a carrier of a component having a very low moving speed among the free carriers, and is a carrier that is not discharged during the exposure among the carriers generated by the exposure.

Therefore, the present inventors formed a patterned surface electrode layer having a plurality of slits on the surface of the photosensitive layer facing the charge holding medium, and applied a bias voltage thereto in order to prevent the generation of the excess carriers. By keeping the inside of the photosensitive layer constantly at a high electric field, it has been found that the movement of free carriers in the photosensitive layer can be accelerated to prevent accumulation of excess carriers. Thus, the end of exposure and the end of discharge can be synchronized, and an image faithful to a document having no extension at the rear end of the image can be formed.

[0008]

However, by providing the patterned surface electrode layer having slits on the surface of the photosensitive layer, the image portions corresponding to the conductive portions forming the slits are blanked out linearly. That is, there was a problem of so-called image cracking. This image cracking occurs because the lines of electric force do not extend in the direction directly below the conductive part of the surface electrode layer, and the charges generated by the discharge are not transported, so that the insulating layer immediately below the conductive part is not charged. It turns out.

[0009]

Accordingly, in the present invention, an image carrier having a dielectric layer formed on a conductive layer, a photoelectric conversion layer and a patterned surface electrode layer on the conductive layer are provided in order to eliminate image cracks. Are arranged in such a manner that the dielectric layer and the surface electrode layer face each other, a potential difference is formed between the two conductive layers, and the photoelectric conversion is performed with a predetermined bias voltage applied to the surface electrode layer. In an image forming apparatus for performing image exposure on a layer and forming a latent image on a moving image carrier by a discharge charge between a photoelectric conversion element and an image carrier, the surface electrode layer forms a slit or a mesh-like gap. And a plurality of strip-shaped conductive portions provided so as to have a width of about 20 μm or less.

In the image forming apparatus according to the present invention, a potential difference is formed between the conductive layer of the photoelectric conversion element and the conductive layer of the image carrier, and the bias voltage is applied to the surface electrode layer. When the conversion element is exposed, a carrier pair is generated in the photoelectric conversion layer. Free carriers in the carrier pair move to the surface of the photoelectric conversion layer, and this phenomenon causes an electric field between the photoelectric conversion layer and the image carrier to rise, thereby causing discharge. At this time, by forming the width W of the conductive portion of the surface electrode layer to be about 20 μm or less, the charge generated by the discharge can be transported to the dielectric layer immediately below the conductive portion by the electric field and then charged. it can. As a result, an almost continuous electrostatic latent image can be formed on the surface of the dielectric layer, and image breakage can be prevented.

On the other hand, excess carriers among the generated carrier pairs are quickly accumulated on the surface of the photoelectric conversion layer without accumulating in the photoelectric conversion layer due to an electric field between the conductive portion of the photoelectric conversion element and the patterned surface electrode. And is discharged or trapped in the surface electrode layer. Therefore, the excess carriers are continuously discharged even after the completion of the exposure, and the continuous discharge prevents the latent image formed on the dielectric layer of the image carrier from extending.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration of an image forming apparatus 1 according to one embodiment of the present invention, and FIG. 2 is a partially enlarged view of a photosensitive member 9 and an image bearing belt 2 as main parts.

At the center of the image forming apparatus 1, an image bearing belt 2 as an image bearing member is disposed. The image bearing belt 2 is moved in a direction indicated by an arrow a by a driving roller 3 rotated by a driving device (not shown) and a heating roller 4 provided in parallel with the driving roller 3.

As shown in FIG. 2, the image bearing belt 2 has a structure in which a conductive layer 23 is formed on a surface of a base 21 made of a dielectric, and a dielectric layer 25 is formed thereon. Specifically, a conductive layer 23 was provided on a substrate 21 made of a polyimide film having a thickness of 50 μm, a width of 25 cm, and a circumference of 30 cm, and a dielectric layer 25 made of a fluororesin having a thickness of several μm was provided thereon. Configuration. The conductive layer 23 is grounded by the conductive line 12. The configuration of the image carrier is not limited to such a belt, but may be a drum shape. Around the image bearing belt 2, the latent image forming device 5, the developing device 6, and the transfer roller 7 are sequentially arranged in the direction of arrow a.

The latent image forming apparatus 5 comprises an optical system 8 and a photosensitive member 9 which is a photoelectric conversion element disposed between the optical system 8 and the image carrying belt 2. The optical system 8 includes a housing 81 in which a semiconductor laser generator, a collimator lens, a polygon mirror, an Fθ lens, a reflection mirror, and the like are arranged.
2 are formed. The optical system 8 is configured such that a laser beam 83 generated by a semiconductor laser
To the photoreceptor 9 from above, so that image exposure can be performed. In the present embodiment, 300 dpi
An optical system for performing the scanning exposure is used.

Here, the scanning direction of the laser beam 83 is the width direction of the image bearing belt 2 (the front and back direction in FIG. 1).
This direction is hereinafter referred to as a main scanning direction. The traveling direction of the image bearing belt 2 perpendicular to the main scanning direction (the vertical direction in FIG. 1) is referred to as a sub-scanning direction.

As shown in FIG. 2, the photosensitive member 9 has a light-transmitting conductive layer 92, a photosensitive layer 93 serving as a photoelectric conversion layer, a surface electrode layer 94, and a surface protection layer 95 laminated in this order on a light-transmitting substrate 91. This is the configuration. The translucent substrate 91 is a transparent glass plate,
The translucent conductive layer 92 is made of an ITO film. The first power supply 13 is connected to the translucent conductive layer 92. The photosensitive layer 93 is made of a semiconductor laser light (wavelength 780 nm) or an LED.
A charge separation layer (CGL) 96 which is a function-separated type for negative charging and has a good sensitivity to long wavelength light such as light (wavelength 680 nm) and has a carrier pair generation function, and a free carrier transport function. And a charge transport layer (CTL) 97.

The surface electrode layer 94 has a shape in which four parallel strip-shaped conductive portions 98 are provided in the main scanning direction as shown in FIGS. The width W of the conductive portion 98 is set to 20 μm or less for the reason described later.

The surface protective layer 95 is made of an amorphous carbon film obtained by plasma polymerization of 1,3-C ₄ H _6.
It was formed with a thickness of 5 μm. This surface protection layer 95 is not always necessary. However, in order to prevent oxidation of the surface electrode layer 94 exposed to the discharge and to avoid local abnormal discharge, an insulating surface protection layer 95 is formed on the surface electrode layer 94.
Is preferably provided.

As shown in FIG. 1, a spacer 10 made of fluororesin is provided between the photosensitive member 9 and the image bearing belt 2.
, An air gap is provided, and the surface electrode layer 94 of the photoconductor 9 and the dielectric layer 25 of the image bearing belt 2 are arranged so as to face each other via the air gap. Here, since the photoconductor 9 is not in contact with the image carrying belt 2, even if foreign matter or the like is conveyed as the image carrying belt 2 travels, the surface of the photoconductor 9 is not polluted and a stable latent image is formed. It can be performed. Further, the member serving as the spacer 10 is not particularly limited to a fluororesin, but may be any member having a small coefficient of friction with the image carrying belt 2 and hardly damaging it.

The developing device 6 includes a toner container 61 for storing a one-component developer (hereinafter, referred to as toner), and a developing sleeve 6 disposed in close proximity to the image bearing belt 2.
2 and a supply roller 63 for stirring the toner contained in the toner containing section 61 and supplying the toner to the developing sleeve 62. The toner used in the developing device 6 is a negatively charged toner having a mean particle size of 10 μm obtained by kneading, pulverizing, and classifying a mixture containing a bisphenol A type polyester resin and carbon black as main components by a known method. is there. An appropriate developing bias is applied to the developing sleeve 62 to prevent background fog and the like.

The transfer roller 7 faces the heating roller 4 via the image bearing belt 2, and
It is arranged in pressure contact with. The recording paper S is passed between the transfer roller 7 and the image bearing belt 2.

First, a process of forming a latent image in the image forming apparatus 1 having the above configuration will be described. The first power supply 13 applies, for example, one light to the translucent conductive layer 92 of the photoconductor 9.
A voltage of 600 V (V _C ) is applied, and the surface electrode layer 94 is, for example, −100 V by the second power supply 14.
(V _p ) bias voltage is applied. As a result, an electric field due to a potential difference of 1600 V is applied between the conductive layer 23 and the light-transmitting conductive layer 92 of the grounded image bearing belt 2 and between the surface electrode layer 94 and the light-transmitting conductive layer 92. , An electric field due to a potential difference of 1700 V is formed.

When the photosensitive member 9 is irradiated with laser light 83 emitted from the optical system 8 in the state where such an electric field is formed, the laser light 83 is exposed to the light transmitting substrate 91 and the light transmitting conductive layer. The light reaches the charge generation layer 96 through the light source 92. The charge generation layer 96 generates a carrier pair when absorbing light in the presence of an electric field. Of the generated carrier pairs, the free carriers move in predetermined directions by the action of the electric field. That is, the free positive carriers move to the surface of the photosensitive layer 93 through the inside of the charge transport layer 97. As a result, the electric field in the air gap between the surface of the photosensitive layer 93 and the surface of the image bearing belt 2 increases, and discharge occurs when the electric field exceeds a threshold determined by Paschen's law. The electric charge is transported by this discharge, and the surface of the dielectric layer 25 of the image carrying belt 2 is charged to form an electrostatic latent image.

At this time, if the width W of the conductive portion 98 of the surface electrode layer 94 is large, the line of electric force does not extend directly below the conductive portion 98, and the region of the dielectric layer 25 corresponding to the conductive portion 98 is charged. However, the electrostatic latent image to be continued is interrupted, and image cracking occurs. However, in the present embodiment, since the width W of the conductive portion 98 is formed to be 20 μm or less, the conductive portion 9 of the dielectric layer 25 is formed by the electric field.
The electric charge due to the discharge is transported to the area immediately below the area 8 and charged. As a result, a substantially continuous latent image can be formed on the surface of the dielectric layer, and image breakage can be prevented.

In the photosensitive layer 93, a charge generation layer 96 is provided.
Carriers trapped in traps formed near the boundary between the charge transport layer 97 and free carriers having a very low moving speed in the photosensitive layer 93 are generated as excess carriers. These excess carriers form a space charge in the photosensitive layer 93 when the amount of exposure light is weak and the electric field in the photosensitive layer 93 is small, and have an adverse effect on the latent image after the completion of the exposure. Cause. However, the electric field in the photosensitive layer 93 is always kept high by providing the surface electrode layer 94. Therefore, the excess carrier is quickly generated in the photosensitive layer 9.
Since the discharge reaches the surface of No. 3 or is captured by the surface electrode layer 94, the accumulation of excess carriers in the photosensitive layer 93 does not occur. Therefore, the discharge does not continue even after the end of the exposure, and the rear end of the latent image does not extend. By providing the surface electrode layer 94 in this manner,
The discharge is immediately terminated in synchronization with the end of the exposure, and a desired latent image substantially the same as the exposed image can be formed.

Next, the process after the formation of the latent image will be described. The electrostatic latent image formed on the image carrying belt 2 is conveyed to the developing unit by the rotation of the driving roller 3 and the heating roller 4, and is developed by the developing device 6 with toner. After that, the toner image formed on the image bearing belt 2 is further conveyed by the rotation of the driving roller 3 and the heating roller 4, and is heated by the heating element 11 provided inside the heating roller 4 and simultaneously by the transfer roller 7. The image is transferred to the recording paper S. At this time, the toner image is melted and transferred, so that the toner does not remain on the image bearing belt 2 and is almost completely transferred to the recording paper S and is fixed at the same time.

Next, a description will be given of an experiment in which the effect of eliminating image cracks among the effects of the image forming apparatus of the present embodiment has been confirmed. In this experiment, various conditions were changed for the configuration of the photoconductor 9 and the image bearing belt 2 shown in FIG. 2 and the surface electrode layer 94 having the slit pattern shown in FIG. In all the experimental examples, the thickness d _p of the photosensitive layer 93 was 15 μm, the thickness of the air layer (distance from the surface of the photosensitive layer 93 to the surface of the dielectric layer 25) d _a was 25 μm, and the dielectric constant of the image bearing belt 2 was 25 μm. The thickness d _i of the body layer 25 was set to 15 μm.

Table 1 shows the conditions of each example and the results of the experiment. In Example 1 to 5, 1600 V applied voltage V _c of the transparent conductive layer 92 of the photosensitive member 9, -100 V bias voltage V _p of the surface electrode layer 94, the slit 99 of the surface electrode layer 94
Was set to 50 μm, and the width W of the strip-shaped conductive portion 98 was changed. Next, in Examples 6 to 10, 1700V applied voltage V _c of the transparent conductive layer 92 of the photosensitive member 9, the surface electrode layer 9
4 of the bias voltage V _p 0V, the width L of the slit 99 of the surface electrode layer 94 was set to 70 [mu] m, and changing the width W of the strip-shaped conductive portion 98. Further, in Examples 11 to 16, 1800 V applied voltage V _c of the transparent conductive layer 92 of the photosensitive member 9, 0V bias voltage V _p of the surface electrode layer 94, the surface electrode layer 9
The width L of the slit 99 was set to 100 μm, and the width W of the strip-shaped conductive portion 98 was changed.

In each experimental example, a plurality of vertical line images having a dot diameter of 80 μm and a width of 4 dots were formed, and the lines were enlarged and observed to evaluate image noise and image density unevenness due to image cracking.

The evaluation results in Table 1 show a preferable state where there is no noise and density unevenness due to image cracking. A state where image noise and image density unevenness are not bothersome. A state in which there was no problem was represented by Δ, and a state in which image noise and image density unevenness were remarkable and had a practical problem was represented by ×.

[0032]

[Table 1]

From these experimental results, it can be seen that, when the width W of the conductive portion 98 of the surface electrode layer 94 is at a boundary of 20 μm, image noise and image density unevenness due to image cracking become severe, causing a problem in practical use. I understand. Therefore, it is preferable that the width W of the conductive portion 98 be 20 μm or less.

FIGS. 4 to 6 show modified examples of the surface electrode layer 94. FIG. In each figure, reference numeral 19 indicates an exposure spot for main scanning. The one shown in FIG. 4 has four strip-shaped conductive portions 98a parallel to each other arranged in the main scanning direction.
The slits are formed in a mesh shape by arranging a number of strip-shaped conductive portions 98b parallel to each other in the sub-scanning direction. In this case, the width of each of the conductive portions 98a and 98b is formed to 20 μm or less. FIG. 5 shows a configuration in which one strip-shaped conductive portion 98a is arranged in the main scanning direction and a plurality of strip-shaped conductive portions 98 parallel to each other.
The slits 99 are formed obliquely by arranging b so as to be inclined in both the main scanning direction and the sub-scanning direction. In this case, since the strip-shaped conductive portion 98a is out of the exposure area and has nothing to do with image breakage, the width W of the strip-shaped conductive portion 98b may be formed to 20 μm or less. Further, the one shown in FIG.
The slits 99 are formed by arranging 8a in the main scanning direction and arranging a number of strip-shaped conductive portions 98b parallel to each other in a comb shape in the sub-scanning direction. In this case, similarly, the width W of the strip-shaped conductive portion 98b may be formed to 20 μm or less.

[0035]

As described above, according to the image forming apparatus of the present invention, the patterned surface electrode layer having a plurality of slits (or meshes) is provided on the surface of the photoelectric conversion layer facing the image carrier. The width of the conductive portion of this electrode layer is formed to 20 μm or less. As a result, problems such as image cracking and image elongation can be solved, and image formation faithful to a document and excelling can be stably performed.

As a result, as compared with a conventional electrophotographic image forming apparatus, a charging device is not required, a bar-shaped photoconductor can be used in place of the photoconductor drum, and the photoconductor is a mere photoelectric conversion device. Just have a function,
Unlike photoreceptor drums, there is no mechanical stress due to blades or toner, so there is no deterioration such as film abrasion, the photoreceptor is not a consumable item, and image formation is performed on a belt or drum-shaped dielectric so simultaneous transfer The fixing method can be adopted, and there is an advantage that a cleaner is not required by increasing the transfer efficiency. For these reasons, an inexpensive, compact, and high-quality image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a side view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of a main part of the image forming apparatus shown in FIG.

FIG. 3 is a view showing the shape of a surface electrode layer of a photoconductor.

FIG. 4 is a view showing a modification of the shape of the surface electrode layer.

FIG. 5 is a view showing another modification of the shape of the surface electrode layer.

FIG. 6 is a view showing still another modification of the shape of the surface electrode layer.

FIG. 7 is a diagram illustrating a conventional image forming apparatus.

FIG. 8A is a diagram illustrating a test pattern of a document image, and FIG. 8B is a diagram illustrating a toner image having image expansion formed based on the test pattern.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image carrying belt (image carrying body), 9
... Photoconductor (photoelectric conversion element), 23 ... conductive layer, 25 ... dielectric layer, 92 ... conductive layer, 93 ... photosensitive layer (photoelectric conversion layer) 94
... surface electrode layer, 98 ... conductive part, 99 ... slit.

Claims (1)

[Claims] An image bearing member having a dielectric layer formed on a conductive layer, and a photoelectric conversion element having a photoelectric conversion layer and a patterned surface electrode layer formed on the conductive layer in order are provided with a dielectric layer and a surface electrode. The photoelectric conversion layer is exposed in a state where a potential difference is formed between the two conductive layers and a bias voltage is applied to the surface electrode layer, and a discharge charge between the photoelectric conversion element and the image carrier is formed. Thus, in an image forming apparatus that forms a latent image on a running image carrier, the surface electrode layer includes a plurality of strip-shaped conductive portions provided so as to form slits or mesh-shaped gaps. An image forming apparatus having a width of about 20 μm or less.