JPH11249415A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of clearly forming images, even when the images provided with different contrast are adjacently located, without blurring these images boundary part. SOLUTION: This device is constituted by equipping an image carrier 1 provided with a photoreceptor layer 1, an electrifying means 8 uniformly electrifying the photoreceptor layer, an exposing means exposing the image carrier 1 having been electrified by the electrifying means 8 based on the desired image data, and a developing means 3 visualizing the electrostatic latent image formed on the image carrier 1 by the exposure of the exposing means with the developer. In this case, the device is provided with an auxiliary electrode 11 in an developing area formed by the developing means 3 and the image carrier 1 at a position on the upstream side with respect to the traveling direction of the photoreceptor 1.

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 used for an electrophotographic and electrostatic recording apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system, an electrostatic latent image is formed on an image carrier, developed to be visualized as a toner image, and the image is transferred onto a transfer material. And have got the image.

[0003] As for the above-mentioned developing method, a one-component developing method using a one-component developer consisting of toner alone is generally less developed than a two-component developing method using a developer consisting of magnetic particles and toner. There are advantages such as a simple configuration of the apparatus and easy maintenance, and various developing methods and developing apparatuses based on the one-component developer method have been proposed at present.

A developing device shown in FIG. 10 will be described as an example. In the developing device of FIG. 10, a developing sleeve 3 made of a cylindrical non-magnetic material is used as a toner carrier, and the magnetic force of a magnet roller 4 fixed inside the developing sleeve 3 is used.
The one-component magnetic toner T stored in the toner container 5 is carried on the developing sleeve 3, and the developing sleeve 3 is moved by an arrow B in FIG.
The carried one-component magnetic toner T is conveyed by rotating in the direction, and the conveyed one-component magnetic toner T is developed by a concentrated magnetic field formed by the magnetic blade 6 and the magnetic pole N1 of the magnet roller 4 so that the developing sleeve 3 is moved. A thin layer is applied on top. The developing sleeve 3 carrying the one-component magnetic toner T and the photosensitive drum 1 as an image carrier disposed opposite to the developing sleeve 3 have an interval of 50 to 500 μm. 3 and the photosensitive drum 1 have a bias power supply 7
As a result, a developing bias in which a DC voltage is superimposed on an AC voltage is applied, so that the so-called jumping development in which the one-component magnetic toner T flies to the electrostatic latent image on the photosensitive drum 1 and is transferred by the action of this electric field is performed. .

Although the above-described apparatus forms a black-and-white image, a method of forming a color image using a color non-magnetic toner as a developer has been put to practical use in recent years.

[0006]

However, in the developing method described above, when images having different contrasts are adjacent to each other, that is, when the halftone portion H and the solid portion D are adjacent as shown in FIG. A phenomenon that the tone side is whitened by several millimeters often occurs. This phenomenon largely contributes to the edge effect at the boundary portion of the latent image and the stagnation of the toner on the upstream side of the development nip. As shown in FIG. 6, the toner to be developed at the halftone portion H side boundary portion has a large contrast. This is caused by being drawn into the solid portion D.

FIG. 7 shows an electric field vector distribution and an equipotential distribution in the development nip in order to see these details in detail. In the figure, 3 is a developing sleeve, 1 is a photosensitive drum,
H is a halftone portion, D is a solid portion, and point G is a boundary of the image. In the present description, the latent image potential of the halftone portion H is -530 V, the latent image potential of the solid portion D is -250 V, and the potential of the electric field vector when the potential of the opposite developing sleeve 3 is -580 V is equal to the equipotential. The distribution is shown.
The sleeve diameter and the drum diameter are each 20 mm.
φ, 30 mmφ, and the traveling direction is as shown in the figure. Looking at the direction of the electric field vector generated from the development sleeve 3 in the drawing, the direction of the electric field is directed to the solid portion D avoiding the boundary portion, and further from the halftone portion H to the solid portion D at the boundary portion. It can be seen that the electric field wraps around.

That is, when the boundary G approaches the developing sleeve 3 and development starts, the toner that has left the developing sleeve 3 does not fly to the halftone portion H-side boundary and is solid according to the direction of the electric field. Developed in area D, even if halftone area H
Even if the toner is developed at the side boundary, in the region W in the figure,
The toner is peeled off from the photosensitive drum 1, and an excessive force toward the solid portion D acts on the toner.

FIG. 8A shows the normal component Er of the electric field vector E on the photosensitive drum 1 before and after the boundary G.
Here, the vertical axis indicates the intensity of Er, and the direction of the electric field at which the toner is attracted to the center of the photosensitive drum 1 is defined as positive.
Conversely, the direction in which the photosensitive drum 1 is peeled off is represented by a negative value. In the solid portion D, an electric field in a positive direction acts on the boundary portion as a peak, but in the halftone portion H, an electric field in a negative direction, that is, an electric field for peeling the toner from the photosensitive drum 1 acts on the boundary portion. Recognize.

Further, it is known that the area W expands in the direction in which the space between the sleeve and the drum (hereinafter, between SD) expands with the movement of the boundary position G. FIG. 8B shows a change in Er with movement of the boundary G position. Is the absolute value of the angle formed by the line L2 connecting the photosensitive drum 1 and the boundary G with respect to the line L1 connecting the center of the photosensitive drum 1 and the developing sleeve 3, and | θ | = 0 ° , The boundary position is closest to the developing sleeve 3. It can be seen that the negative region has increased at the halftone portion H-side boundary with the increase of | θ |, and the region W has expanded accordingly (W1 → W2 → W).
3). When | θ | = 8 °, the value of W3 is about 1 mm, that is, at both ends of the development nip, the force for peeling off the toner acts on the boundary of the halftone portion H side as much as 1 mm. As described above, when the boundary G enters the developing nip, as shown by the arrow in FIG. 9, the toner on the photosensitive sleeve 1 is solid-sided before developing the boundary on the half-tone part H side. The region W is attracted to the boundary and developed.
When the boundary position G is moved to the center of the nip where the image is minimal, the toner which should contribute to the development is already small on the photosensitive sleeve 1, and the boundary cannot be sufficiently developed. Further, even after the position of the boundary G has passed the closest position, the force for peeling off the toner at the boundary of the halftone portion H increases, so that a large amount of toner is exposed to the photosensitive sleeve from the boundary of the halftone portion H. -Pulled back to step 1. As a result, the boundary portion on the halftone portion H side becomes white. Such a phenomenon makes it difficult to reproduce a good image and degrades the image quality.

Accordingly, it is an object of the present invention to provide an image forming apparatus capable of forming a clear image without blurring an image boundary even when images having different contrasts are adjacent to each other. And

[0012]

According to a first aspect of the present invention, there is provided an image carrier having a photosensitive layer, a charging means for uniformly charging the photosensitive layer, Exposure means for exposing the image carrier charged by means based on image data, and development means for visualizing an electrostatic latent image formed on the image carrier by exposure of the exposure means with a developer. This is achieved by providing an auxiliary electrode in a development area formed by the developing means and the image carrier and at a position upstream of the moving direction of the image carrier.

A second invention according to the present application is characterized in that a bias having the same polarity as the charged polarity of the toner is applied to the auxiliary electrode.

A third invention according to the present application is characterized in that the auxiliary electrode is formed of a wire-shaped conductive member.

A fourth invention according to the present application is characterized in that the auxiliary electrode is formed of a wedge-shaped conductive member.

According to the above arrangement, an auxiliary electrode is provided at a position upstream of the moving direction of the developing means in the developing area formed by the developing means and the image carrier, so that an image having a constant contrast difference is provided. Even if the continuation of, the wraparound of the electric field due to the contrast difference can be suppressed, so that the toner is not drawn into the high contrast image area in the development area. Further, by applying a bias having the same polarity as the charge polarity of the toner to the auxiliary electrode, the toner can contribute to the development at the center of the development nip, so that the influence of the electric field wraparound can be further reduced. Image reproduction becomes possible, and clear image formation can be achieved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier, and 2 denotes a developing device as a developing means, which is rotatable with a toner container 5 for storing a one-component magnetic toner T therein and a magnet roller 4 therein. And a magnetic blade 6 disposed at a distance of 100 to 300 .mu.m from the developing sleeve 3 to regulate the amount of toner on the developing sleeve 3. And about 300
The photosensitive drum 1 is arranged to face the photosensitive drum 1 with an interval of μm.

In the drawing, reference numeral 8 denotes a charging roller for uniformly charging the photosensitive drum 1, reference numeral 9 denotes a transfer roller for transferring a toner image on the photosensitive drum 1 to a transfer material P, and reference numeral 10 denotes a transfer residual toner to the photosensitive drum 1. Cleaner for collecting from garbage, 11
Is a photosensitive drum 1 on the upstream side of the developing area between the drum and the sleeve.
An electrode wire 13, which is an auxiliary electrode for development arranged at about 200 μm above, is a fixing device for fixing a toner image to the transfer material P. Reference numerals 7 and 14 denote power supplies for applying a desired bias to the development sleeve 3 and the electrode wire 11.

Next, an image forming operation in the present embodiment will be described.

The apparatus according to the present embodiment is an image forming apparatus using a laser beam as a light source. A metal optical semiconductor such as amorphous silicon / zinc oxide / selenium / cadmium sulfide or phthalocyanine is formed on a conductive drum 1a as a photosensitive drum 1. / A material in which a photosensitive layer 1b is formed by vapor deposition or coating of a material in which an organic optical semiconductor such as polyvinyl carbazole and a resin are mixed and dispersed is used.

The photosensitive drum 1 is moved in the direction of arrow A, and the surface of the photosensitive drum 1 as an image carrier is uniformly charged to -700 V by a charging roller 8 as a primary charging means. The image of the surface of the photosensitive drum 1 is exposed by the laser driver 12 based on the image data of (1) to form a latent image pattern.
The magnitude of this potential is determined by the sensitivity of the photosensitive layer to light and the amount of exposure light. In this image forming example, the surface potential at the solid portion D is -250 V, and the surface potential at the halftone portion H is -530 V. Exposed. The latent image pattern on the photosensitive drum 1 formed in this manner is conveyed to a portion facing the developing device 2 as a developing unit. On the other hand, the one-component magnetic toner T stored in the toner container 5 is carried on the developing sleeve 3 made of a non-magnetic material as a toner carrier by a magnetic force of a magnet roller 4 fixed inside the sleeve. The one-component magnetic toner T is conveyed by the rotation of the non-magnetic developing sleeve 3 in the direction of arrow B in the figure, and the concentrated magnetic field formed by the magnetic blade 6 and the magnetic pole N1 of the magnet roller 4 causes the developing sleeve to move. A thin layer is applied on the block 3. A non-magnetic developing sleeve 3 is applied with a DC voltage of -580 V superposed on an AC voltage of 1.6 kV by a bias power supply 7, and the one-component magnetic toner T is applied to the photosensitive drum by the action of this electric field. 1 and fly to and adhere to the electrostatic latent image. However, in the present embodiment, the electrode wire 11 is installed on the upstream side in the rotation direction of the photosensitive drum 1 in the developing nip, and a DC bias of −700 V is applied to the electrode wire 11 by the power supply 14. Therefore, the equipotential distribution in the developing region is greatly distorted as compared with the conventional equipotential distribution, and the distortion remarkably suppresses the electric field from flowing around the boundary.

FIG. 2 shows an electric field vector distribution and an equipotential distribution on the upstream side of the developing region. In the upstream of the developing area, an electric field near the developing sleeve 3 acts in the direction of the center of the developing sleeve 3 due to a bias applied to the electrode wire 11, and an electric field wraps around from the halftone portion H to the solid portion D. It can be seen that is greatly suppressed.

That is, when the boundary G approaches the developing sleeve 3 and starts developing near the boundary, an electric field suppressed on the developing sleeve 3 acts on the one-component magnetic toner T.
The one-component magnetic toner T to be developed at the boundary portion of the halftone portion H is prevented from first falling into the solid-side D image area.

Further, comparing the Er before and after the boundary G with the conventional Er at this time, as shown in FIG. 3, the negative electric field region where the one-component magnetic toner T is peeled off from the photosensitive drum 1 is reduced. It can be seen that the unexpected region W has been reduced. Therefore, the one-component magnetic toner T developed on the boundary portion on the halftone portion H side is peeled off from the photosensitive drum 1, and the region W which moves to the image region of the solid portion D is significantly reduced.

The toner image thus formed on the photosensitive drum 1 as an image carrier is transferred onto a transfer material P by a transfer roller 9 as a transfer means, and then onto the transfer material P by a fixing roller 16. It is fixed.

The one-component magnetic toner T remaining on the photosensitive drum 1 is applied to a cleaner 1 such as a blade or a fur brush.
The cleaning is performed by the cleaning means of 0, and the same process is repeated.

[Second Embodiment] The shape of the auxiliary electrode in the present invention is not limited to that described in the first embodiment, and the shape of the auxiliary electrode may be, for example, a wedge shape as shown in FIG. It has been found that the electrode 15 is also effective.
With the wedge-shaped shape, the one-component magnetic toner T can contribute more to the development at the center of the development nip, so that the area of the electric field that draws the toner into the image area on the high contrast side can be further reduced.

[0029]

According to the first, third and fourth aspects of the present invention, the auxiliary electrode is provided at a position upstream of the moving direction of the image carrier in the developing region formed by the developing means and the image carrier. With this arrangement, even when images having a constant contrast difference are continuous, it is possible to suppress the wraparound of the electric field due to the contrast difference, so that the toner is not drawn into the high contrast image area in the development area.

According to the second aspect of the present invention, by applying a bias having the same polarity as the charge polarity of the toner to the auxiliary electrode, the toner can contribute to the development at the center of the development nip. Good image reproduction that can reduce the influence of the wraparound can be achieved, and clear image formation can be achieved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing an image forming apparatus according to a first embodiment of the present invention;

FIG. 2 is a distribution diagram of electric field vectors and equipotentials in an image boundary area according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a normal component of an electric field vector in an image boundary area according to the first embodiment of the present invention.

FIG. 4 is a configuration diagram schematically showing an image forming apparatus according to a second embodiment of the present invention;

FIG. 5 is a conventional image state diagram in an image boundary area.

FIG. 6 is a diagram showing an equipotential pattern in a conventional image boundary area.

FIG. 7 is a conventional distribution diagram of electric field vectors and equipotentials in an image boundary area.

FIG. 8 is a diagram showing a normal component of an electric field vector in a conventional image boundary area.

FIG. 9 is an explanatory diagram showing the operation of toner in a conventional image boundary area.

FIG. 10 is a partial explanatory view of a conventional non-contact developing device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photosensitive drum (image carrier) 2 developing device 3 developing sleeve 4 magnet roller 5 toner container 6 magnetic blade 7 bias power supply (for sleeve) 8 charging roller 9 transfer roller 10 ... cleaner 11 ... auxiliary electrode (electrode wire) 12 ... laser driver 13 ... fixing device 14 ... bias power supply (for wire) 15 ... auxiliary electrode (wedge-shaped electrode)

Claims (4)

[Claims] 1. An image bearing member having a photosensitive layer, charging means for uniformly charging the photosensitive layer, and exposing means for exposing the image bearing member charged by the charging means based on desired image data. An image forming apparatus comprising: a developing unit configured to visualize, by a developer, an electrostatic latent image formed on the image carrier by exposure of the exposing unit, the electrostatic latent image formed by the developing unit and the image carrier. An auxiliary electrode is provided at a position upstream of the moving direction of the image carrier in the developing region. 2. The image forming apparatus according to claim 1, wherein a bias having the same polarity as the charging polarity of the toner is applied to the auxiliary electrode. 3. The image forming apparatus according to claim 1, wherein the auxiliary electrode is formed of a wire-shaped conductive member. 4. The image forming apparatus according to claim 1, wherein the auxiliary electrode is formed of a wedge-shaped conductive member.