JP3201612B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method using electrophotography.

[0002]

2. Description of the Related Art In a conventional image forming method, the surface of a photoreceptor is uniformly charged to a specific polarity by a corona discharge means, and then the charge on the photoreceptor is selectively eliminated by image exposure to form an electrostatic image. Is formed, and a toner is supplied to the surface of the photoreceptor by a developer supply member to which an appropriate developing bias is applied to develop an electrostatic image.

[0003] By the way, an apparatus using a corona discharge means is susceptible to the use environment such as humidity and dust.
It is known that there is a problem of odor and harm to the human body due to the release of ozone due to corona discharge.

In order to solve this problem, in recent years, an image forming method using a charging roller or a transfer roller to which an external voltage has been applied has attracted attention.

In this type of conventional method, a conductive substrate of a photoconductor is grounded, and a charging roller to which a bias voltage is applied is pressed against the surface of the photoconductor to uniformly charge the surface of the photoconductor. Next, an electrostatic image corresponding to the image is formed by image exposure. The electrostatic image is developed under a predetermined developing bias by a developing sleeve connected to an appropriate developing bias power supply,
The developed image is transferred onto an appropriate transfer material by the action of a transfer roller to which a bias voltage has been applied. The developer remaining on the surface of the photoconductor without being transferred is removed from the surface of the photoconductor by a cleaning brush to which an appropriate cleaning bias is applied.

[0006]

In such a conventional charge injection type contact charging method using a contact charging member , the above-mentioned problems such as the generation of ozone when corona discharge means are used. Can be resolved,
On the other hand, there remains a problem that the image is easily covered with the ground.

Further, in the above conventional method,
A power source is required for each component of image formation, that is, a large number of power sources are required, such as a power source for a charging roller, a power source for a developing bias, a power source for a transfer roller, and a power source for a cleaner bias. It has been difficult to provide a compact image forming apparatus.

[0008] Therefore, the present invention provides a method for forming a photoconductor on the electrode.
As well as applying the ass voltage,
Induction of electric charge toward the photoconductor surface causes the photoconductor surface
Is charged to a predetermined potential by a new method.
"Charge injection type" contact charging described in the first prior art
Non-uniform contact between the charging roller and photoconductor caused by the method
Troubles such as uneven charging caused by touch or insufficient contact
It is another object of the present invention to provide a novel image forming method which can reduce the power required for image forming means such as a transfer roller and minimize the size and cost of the apparatus.

[0009]

Means for Solving the Problems An image forming method according to this end the present invention, set at least a photoconductive layer on a conductive base
An AC voltage or a bias voltage obtained by superimposing a DC voltage on an AC voltage is applied to a conductive substrate of the photoconductor, and a conductive or semiconductive grounded inducing member is applied to the surface of the photoconductor. directly or by inducing a predetermined polarity charge on the photoreceptor surface in accordance with the applied voltage by contacting with the dielectric to charge the photosensitive member surface to a predetermined potential, and then forming an electrostatic image by exposing the image In an image forming method in which a toner image is transferred onto a transfer material after supplying and developing the toner, a conductive or semiconductive transfer disposed in contact with or close to the photosensitive member By grounding the roller via a diode, a potential of a polarity opposite to that of the toner image is induced on the transfer roller to transfer the toner image. Further, the transfer roller may have an insulating layer on the outer peripheral surface.

[0010]

As described above, when an AC voltage or a voltage obtained by superimposing a DC voltage on the AC voltage is applied to the conductive substrate of the photoreceptor and the inducing member is brought into contact with the surface of the photoreceptor, the photoconductive layer, the air layer, and the inducing member are brought into contact. The applied voltage is divided according to the impedance, and the surface of the photoreceptor has a lowered predetermined potential. Then, by performing image exposure, the potential of the bright image portion approaches the potential applied to the photosensitive member, and an electrostatic image corresponding to image information is formed. After the electrostatic image is developed with toner, it is transferred onto a transfer material by a transfer roller in which a predetermined potential is induced by the action of a diode.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming method according to the present invention will be described with reference to the drawings.

FIG. 1 shows an example of an apparatus for implementing an image forming method according to the present invention. The photoreceptor 1 includes a drum-shaped conductive base (collectively including a layered base) 11 and a base 1
1. Photoconductive layer 1 provided by vapor deposition or coating
2 and rotate in the direction indicated by arrow A. Photoconductive layer 1
2 is OPC, Se, ZnO, CdS, a-Si, etc.
Any type of P-type semiconductor or N-type semiconductor is suitable for use. Further, in addition to the above configuration, a configuration in which a dielectric layer is further provided on the photoconductive layer 12 may be employed. The conductive substrate 11 of the photoreceptor is electrically connected to a bias power supply 6. In this example, the bias power supply 6 applies a voltage obtained by superimposing a DC voltage on an AC voltage to the conductive substrate 11.
AC voltages having a frequency in the range of 80 Hz to 30 kHz are particularly suitable. The superimposed DC voltage has a positive polarity for the N type photoconductor and a negative polarity voltage for the P type photoconductor.

The inducing member 2 is disposed in contact with the surface of the photoreceptor 1 (it does not need to be in strict contact, as the case may be). The inducing member 2 is, in the illustrated example,
It has a roller shape in which a layer 22 made of a conductive elastic rubber material is electrically in contact with a rotatably supported conductive metal core 21 and is packaged. The roller 22 is pressed against the surface of the photoreceptor by an appropriate pressure. It rotates in the forward direction at the contact portion at substantially the same peripheral speed as the peripheral speed. The layer 22 may be made of, for example, NBR or silicon rubber containing a conductive material. In some cases, the inducing member 2 may be provided with a dielectric layer 23 of synthetic resin or the like (an inducing member having such a configuration is shown in FIG. 4) on the outer peripheral surface of the layer 22. Layer 22
Is a semiconductive material (for example, 10
⁵ to 10 ¹⁰ Ωcm) or a rigid metal body.
The core 21 is grounded directly or via a rectifier 8 such as a varistor, a constant voltage diode or a diode. In order to obtain a desired potential on the photoreceptor, an appropriate resistor may be interposed. Further, the inducing member 2 may be in the form of a conductive or semi-conductive blade or brush, in addition to the roller shape as described above.

FIG. 2 is an equivalent circuit for explaining the charging of the photosensitive member 1. In the dark, when a bias voltage having a predetermined value obtained by superimposing an alternating current and a direct current is applied to the conductive substrate 11 of the photoconductor 1 and the induction member 2 that is grounded directly or via a diode or the like comes into contact with the photoconductor surface, An electric charge is induced on the surface, and the surface of the photoreceptor has a divided voltage according to the impedance of the photoreceptor 1, the impedance of the inducing member 2, and the impedance of the air layer between them.

FIG. 3 schematically shows changes in the surface potential of the photoconductor when a superimposed bias voltage deviated to the positive polarity side is applied in the dark to a photoconductor substrate having an N-type photoconductive layer. As described above, a positive charge is induced on the surface of the photoreceptor in contact with the inducing member 2, and the potential drops according to the partial pressure. Then, when image exposure 7 is performed by optical means such as a laser or LED, the surface potential (V _L ) of the bright image portion (exposed area) approaches the value of the bias potential applied to the substrate 11 of the photosensitive member, A potential difference is formed between the potential (V _D ) of the dark part (the area not exposed). Thus, in the electrophotographic method according to the present invention, contrary to the method using the conventional corona discharge, the potential of the image bright portion becomes a high value close to the bias potential to the photoconductor,
An electrostatic image in which the potential of the dark portion of the image becomes a low value is formed.

In FIG. 3, for convenience of explanation, the light portion potential and the dark portion potential are shown linearly. However, in practice, the surface potential of the photoreceptor during the application of the bias has an amplitude in which alternating bias potentials are superimposed. ing. FIG. 4 shows a case where a bias voltage obtained by superimposing an AC voltage of 2500 Vp-p with a frequency of 4 kHz on a DC voltage of plus 400 V is applied to the substrate of the photoreceptor, and thereafter an optical image is irradiated to obtain an electrostatic latent image. Although the potential of the dark portion and the bright portion are shown, the waveform of the amplitude is substantially equal to the waveform of the bias voltage applied to the photosensitive body, and the frequency of the amplitude is also equal to the frequency of the bias voltage.

Similarly, when a negative potential is applied to the substrate of the photoreceptor having a P-type photoconductive layer, a negative potential charge is induced on the surface of the photoreceptor, and an electrostatic image is formed in the same manner as described above. Description will be made again with reference to FIG. The electrostatic images formed by the image exposure are developed by developing means 3 arranged in the following order. The developing means 3 includes a conductive sleeve 31 arranged close to the surface of the photoconductor 1 and a magnet roller 32 provided inside the sleeve. The sleeve 31 and the magnet roller 32 are provided so as to be rotatable independently of each other at different speeds. In this example, both the sleeve 31 and the magnet roller 32 are in the opposite direction to the rotation direction of the photoconductor 1, that is,
It rotates forward at the development site. The surface of the sleeve 31 is shot blasted, and the developer supplied from a storage case (not shown) is attracted to the surface by the magnetic force of the magnet roller 32. The developer is conveyed in the direction opposite to the rotation direction of the photoreceptor 1 (forward direction in the developing portion, direction of arrow B) at substantially the same speed as or slightly higher than the peripheral speed of the photoreceptor, and contacts the surface of the photoreceptor 1. Alternatively, the electrostatic image is developed by rubbing under the action of an alternating electric field and an alternating magnetic field. As the developer, a one-component magnetic toner or a two-component developer is used.

The sleeve 31 is grounded via an induced bias means such as a varistor, a constant voltage diode, or a high resistor. In the illustrated example, the sleeve 31 is grounded via a varistor 33, and develops an electrostatic latent image on the photoconductor with a bias potential induced by a potential applied to the photoconductor. The bias potential of the sleeve 31 depends on the rated value of the induced bias means such as a varistor and a constant voltage diode connected to the sleeve 31. For example, when reversal development is required as in a digital printer, the bias voltage is determined by setting the potential of the sleeve 31 to the photoconductor. Is selected so as to be a value close to the dark portion potential.

The toner image thus visualized is transferred by a transfer roller 4 onto a transfer material such as paper. The transfer roller 4 has substantially the same configuration as the inducing member 2, and includes a diode 5
1, a conductive metal core 41, 10 ³ -1
It includes a conductive or semiconductive layer 42 of 0 ¹⁰ Ωcm, and optionally further includes a dielectric layer 43 (FIG. 4) on its outer peripheral surface. The transfer roller 4 is provided in contact with or close to the photoconductor 1, and transfers a toner image on the photoconductor with a transfer potential having a polarity opposite to that of the toner image induced by a bias voltage applied to the photoconductor. Transfer to material.

For example, transfer when reversal development is performed using an N-type photosensitive member will be described. The inducing member 2 is grounded via the diode 8 (the cathode side is grounded),
The polarity of the electrostatic image potential on the photoreceptor surface becomes negative polarity,
In the case of reversal development, development is performed with N type toner. Therefore, the transfer roller 4 is grounded (the anode side of the diode is grounded) via the diode 51 so that a positive charge is induced, so that a positive half-wave voltage is induced on the transfer roller 4, and the induced voltage causes Transfer can be performed. The same applies to the case where only the AC bias is applied to the substrate of the photoreceptor. Next, the transfer material is separated from the photoreceptor surface by a separating unit (not shown), and sent to a fixing unit (not shown) to form a permanent copy image thereon. still,
Dirt adhering to the transfer roller is removed from its surface by an elastic blade (not shown) or the like and is cleaned.

On the other hand, the photoreceptor after the transfer is cleaned by a cleaning unit 5 to remove the toner remaining on the photoreceptor, and is prepared for the next image formation. In this example, the cleaning means 5 is a brush-type cleaner in which a conductive brush is implanted on a conductive substrate 51. The conductive substrate 51 is grounded,
As a result, the toner remaining on the photoconductor is electrostatically and physically attracted to the conductive brush and removed from the photoconductor.
The toner attached to the brush is removed by a scraper (not shown).

FIG. 5 shows that the bias voltage applied to the conductive substrate of the photoreceptor 1 is only an AC voltage (no DC voltage is superimposed).
In this case, the induction member 2 is grounded via the rectifying means 8. Other parts have the same configuration as the example of FIG.

EXPERIMENTAL EXAMPLE 1 In the configuration of FIG. 1, a photosensitive body having an N-type organic photoconductive layer on a conductive base was applied with a DC voltage of about 900 V and an AC voltage of 2500 Vp-p (frequency was 80 Hz).
(Up to 30 kHz) was applied, and the photosensitive member was rotated at a peripheral speed of 40 mm / Sec. For this photoconductor, NBR
Alternatively, a grounded induction roller having an elastic layer made of silicon rubber containing conductive powder was pressed in the dark, and then irradiated with laser light to form an electrostatic image, followed by reversal development.

The developer used was a mixture of 5 parts of a toner mainly composed of an acrylic resin and 100 parts of a ferrite carrier having a resistance of about 10 ⁷ to 10 ⁹ Ω · cm and a spherical average particle diameter of 50 μm. . The surface of the developing sleeve is about 4
A SUS304 sleeve having an outer diameter of 18 mm and shot-blasted with 00 mesh was used and connected to a DC bias power supply. A six-pole magnet roller is rotated in the developing sleeve so that an alternating magnetic field of about 600 gauss acts on the toner on the surface of the sleeve.
The development was performed by bringing the toner on the developing sleeve into contact with the surface of the photoconductor at 3 mm. Next, a transfer roller grounded via a diode (using the same configuration as the induction roller)
As a result, a clear image without background contamination could be obtained.

[0025]Experimental example 2 Under the same conditions as in Experimental Example 1, the average particle diameter of the developer was 1
10 at 2μ¹⁴-10^Fifteen Ω · cm using one-component magnetic toner
As a result of conducting similar experiments,
Images were obtained.

Experimental Example 3 Under the same conditions as in Experimental Example 1, 6 g of spherical ferrite powder of 35 to 60 μm was uniformly adhered in advance to the surface of the developing sleeve as a developer carrier.
A similar experiment was performed using a toner of 10 ¹⁴ Ω · cm to 10 ¹⁵ Ω · cm. As a result, a result similar to that of Experimental Example 1 was obtained.

[0027]

As described above, according to the present invention, the electrodes of the photoreceptor are covered with electrodes.
Bias voltage and contact of the inducing member
Charge induced toward the photoreceptor surface, causing the photoreceptor surface
Charge to bring the surface to a predetermined potential, that is, “charge-induced”
By applying the charging method, the original
In the "charge injection type" contact charging method described in
Uneven or insufficient contact between the charged roller and photoconductor
It is possible to eliminate problems such as charging unevenness caused by touch
In addition to this, it does not require many high-voltage power supplies for the charging means and the transfer roller, so that the configuration of the apparatus to be implemented can be made extremely simple and inexpensive, and a clear image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a main part of an example of an image forming apparatus that performs a method according to the present invention.

FIG. 2 is an equivalent circuit relating to a photoconductor and an inducing member.

FIG. 3 is a diagram illustrating a change in the surface potential of the photoconductor when a positive potential is applied to the substrate of the photoconductor having an N-type photoconductive layer according to the present invention.

FIG. 4 is a diagram illustrating a change in the surface potential of a photoconductor when a positive potential is applied to the substrate of the photoconductor having an N-type photoconductive layer according to the present invention.

FIG. 5 is a schematic view showing another example different from FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Inducing member 3 Developing means 4 Transfer roller 5 Cleaning means 6 Bias power supply 11 Conductive substrate 12 Photoconductive layer 31 Developer supply member 51, 52 Diode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-73367 (JP, A) JP-A-63-149668 (JP, A) JP-A-52-35639 (JP, A) JP-A-55-35639 147651 (JP, A) JP-A-56-54447 (JP, A) JP-A-56-110967 (JP, A) JP-A-58-88770 (JP, A) JP-A-60-138566 (JP, A) JP-A-1-156775 (JP, A) JP-A-63-280279 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 13/16 G03G 13/02 G03G 15/02 G03G 15/06

Claims (3)

(57) [Claims] At least a photoconductive layer is provided on a conductive substrate.
An AC voltage or a bias voltage obtained by superimposing a DC voltage on an AC voltage is applied to a conductive substrate of the photoconductor, and a conductive or semiconductive grounded inducing member is applied to the surface of the photoconductor. Is contacted directly or via a dielectric to induce a charge of a predetermined polarity on the surface of the photoconductor in accordance with the applied voltage, thereby charging the surface of the photoconductor to a predetermined potential, and then exposing an image to form an electrostatic image. In an image forming method in which a toner image is transferred onto a transfer material after supplying and developing the toner, a conductive or semiconductive transfer disposed in contact with or close to the photosensitive member An image forming method, wherein the roller is grounded via a diode to induce a potential of a polarity opposite to that of the toner image on the transfer roller to transfer the toner image. 2. At least a photoconductive layer is provided on a conductive substrate.
An AC voltage or a bias voltage obtained by superimposing a DC voltage on an AC voltage is applied to a conductive substrate of the photoconductor, and a conductive or semiconductive grounded inducing member is applied to the surface of the photoconductor. Is contacted directly or via a dielectric to induce a charge of a predetermined polarity on the surface of the photoconductor in accordance with the applied voltage, thereby charging the surface of the photoconductor to a predetermined potential, and then exposing an image to form an electrostatic image. Then, after supplying and developing the toner, in an image forming method in which a toner image is transferred onto a transfer material, a conductive or conductive material coated with an insulating layer disposed in contact with or in close proximity to the photoconductor is used. An image forming method, wherein a semiconductive transfer roller is grounded via a diode to induce a potential of a polarity opposite to that of the toner image on the transfer roller to transfer the toner image. 3. The image forming method according to claim 1, wherein the induction member is grounded via a rectifying unit.