JP2001166546A - Image forming method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method and an image forming device concerning the stabilization of the surface potential of an electrophotographic photoreceptor having a high-hardness surface protective layer. SOLUTION: The electrophotographic photoreceptor is electrified by an electrifying electrode and an electrostatic latent image is formed on the photoreceptor by digital exposure, and the electrostatic latent image is developed by a developing device to which developing bias voltage is applied, so that a visible image is obtained in this image forming method. The photoreceptor is provided with at least the surface protective layer. The surface potential of the photoreceptor is detected, and at least any one of an electrifying current or electrifying grid voltage applied to the electrifying electrode and the developing bias voltage applied to the developing device and digital exposure output is controlled based on the detected potential information, whereby the photoreceptor is continued to be used to form an image even after the surface protective layer is worn out and vanished.

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 for stabilizing the surface potential of an electrophotographic photosensitive member and an image forming apparatus using the method.

[0002]

2. Description of the Related Art In a conventional electrophotographic image forming method or an image forming apparatus using the method, the surface potential (charging potential) of a photoreceptor which most affects a visible image is repeatedly changed by image formation. This change in the surface potential is largely due to the thickness wear of the photoconductor due to the repetition of image formation. This decrease in film thickness due to abrasion causes a decrease in charging ability and a change in sensitivity. In particular, the organic photoreceptors most frequently used in the market at present have a large decrease in film thickness due to abrasion, and a method of correcting a change in charging potential due to a change in film thickness has been studied. Conventionally, various methods have been proposed as a method for correcting the change in the surface potential of the photoconductor due to the abrasion of the film thickness. However, in general, the wear speed of the photoconductor can be obtained by image formation in conventional organic photoconductors. The charging current, the charging grid voltage, the exposure laser power, and the like are changed in accordance with the number of copies and the traveling distance of the photoconductor because the number of copies is proportional to the number of copies and the traveling distance of the photoconductor.

However, the present inventors have developed a highly durable organic photoreceptor having a high hardness surface protective layer (Japanese Patent Application No. 11-703).
No. 08), and the image formation using the photoreceptor is performed by a conventional method of correcting the surface potential in proportion to the number of copies or the traveling distance of the photoreceptor. It has been found that the action of potential correction is not good. In other words, since the wear rate of the image forming is different in each layer in the photoconductors having different wear rates of the surface protective layer and the photosensitive layer thereunder, when the correction for the film thickness wear is performed in anticipation by the number of copies and the travel distance of the photoconductor, The correction at the layer boundary is not sufficient, and the correction may be deviated and a potential abnormality may occur.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method and an image forming apparatus for stabilizing the surface potential of an electrophotographic photosensitive member having a high hardness surface protective layer.

[0005]

The object of the present invention is achieved by the following constitution.

[0006] 1. An image forming method in which an electrophotographic photosensitive member is charged by a band electrode, an electrostatic latent image is formed on the photosensitive member by digital exposure, and the electrostatic latent image is developed by a developing device to which a developing bias voltage is applied to obtain a visible image. In the photoreceptor has at least a surface protective layer, detects the surface potential of the photoreceptor, based on the detected potential information, a charging current applied to the band electrode, or charging grit voltage, the developing device An image forming method, comprising controlling at least one of a developing bias voltage to be applied and a digital exposure output, and continuing to use the photoreceptor for image formation even after the surface protective layer is worn away.

[0007] 2. An image forming method in which an electrophotographic photosensitive member is charged by a band electrode, an electrostatic latent image is formed on the photosensitive member by digital exposure, and the electrostatic latent image is developed by a developing device to which a developing bias voltage is applied to obtain a visible image. Wherein the photoreceptor has at least a photosensitive layer and a surface protective layer laminated thereon, and the film wear rate of the surface protective layer (V ₁ ) and the film wear rate of the photosensitive layer (V ₂ ) Ratio (V ₂ / V ₁ ) is 0.5
The following, detecting the surface potential of the photoreceptor, based on the detected potential information, a charging current applied to the band electrode,
Alternatively, an image forming method includes controlling at least one of a charging grid voltage, a developing bias voltage applied to a developing device, and a digital exposure output.

[0008] 3. 3. The image forming method according to claim 1 or 2, wherein a correction based on a running value of the photoconductor is added to the control based on the detected potential information.

4. An image forming apparatus in which an electrophotographic photosensitive member is charged by a band electrode, an electrostatic latent image is formed on the photosensitive member by digital exposure, and the electrostatic latent image is developed by a developing device to which a developing bias voltage is applied to obtain a visible image. In the photoreceptor has at least a surface protective layer, detects the surface potential of the photoreceptor, based on the detected potential information, a charging current applied to the band electrode, or charging grit voltage, the developing device An image forming apparatus, wherein at least one of a developing bias voltage to be applied and a digital exposure output is controlled, and the photoconductor is continuously used for image formation even after the surface protective layer is worn away.

[0010] 5. An image forming apparatus in which an electrophotographic photosensitive member is charged by a band electrode, an electrostatic latent image is formed on the photosensitive member by digital exposure, and the electrostatic latent image is developed by a developing device to which a developing bias voltage is applied to obtain a visible image. Wherein the photoreceptor has at least a photosensitive layer and a surface protective layer laminated thereon, and the film wear rate of the surface protective layer (V ₁ ) and the film wear rate of the photosensitive layer (V ₂ ) Ratio (V ₂ / V ₁ ) is 0.5
The following, detecting the surface potential of the photoreceptor, based on the detected potential information, a charging current applied to the band electrode,
Alternatively, the image forming apparatus controls at least one of a charging grid voltage, a developing bias voltage applied to a developing device, and a digital exposure output.

6. 6. The image forming apparatus according to 4 or 5, wherein a correction based on a travel value of a photoconductor is added to the control based on the detected potential information.

Hereinafter, the present invention will be described in detail. An example of the production of an electrophotographic photoreceptor having a surface protective layer of the present invention is described below.

Preparation Example of Photoreceptor Preparation of Intermediate Layer Coating Solution A polyamide resin (Amilan CM-8000: manufactured by Toray Industries, Inc.) 60 g methanol 1600 ml 1-butanol 400 ml was mixed and dissolved to prepare an intermediate layer coating solution. This coating solution is applied on a cylindrical aluminum substrate by a dip coating method,
An intermediate layer having a dry film thickness of 0.3 μm was formed.

Preparation of charge generation layer coating solution Titanyl phthalocyanine 60 g Silicone resin solution (KR5240, 15% xylene-butanol solution: manufactured by Shin-Etsu Chemical Co., Ltd.) 700 g A charge generation layer coating solution was prepared. This coating solution was applied onto the intermediate layer by a dip coating method to form a charge generation layer having a dry film thickness of 0.2 μm.

Preparation of charge transport layer coating solution Charge transport substance (4-methoxy-4 '-(4-methyl-α-phenylstyryl) triphenylamine) 200 g Bisphenol Z-type polycarbonate (Iupilon Z300: manufactured by Mitsubishi Gas Chemical Company, Ltd.) 300 g of 1,2-dichloroethane (2000 ml) was mixed and dissolved to prepare a charge transport layer coating solution. This coating solution was applied on the charge generation layer by a dip coating method to form a charge transport layer having a dry film thickness of 20 μm.

Preparation of Resin Layer Coating Solution Polysiloxane resin 1 comprising 80 mol% of methylsiloxane units and 20 mol% of methyl-phenylsiloxane units
Molecular sieve 4A was added to 0 parts by mass, and the mixture was allowed to stand for 15 hours to be dehydrated. This resin was dissolved in 10 parts by mass of toluene, and 5 parts by mass of methyltrimethoxysilane and 0.2 parts by mass of dibutyltin acetate were added thereto to form a uniform solution.

To this, 6 parts by mass of dihydroxymethyltriphenylamine (the following compound 1) and 0.3 part by mass of hindered amine (Sanol LS2626: manufactured by Sankyo Co., Ltd.) were added and mixed to prepare a resin layer coating solution. After applying this coating solution onto the charge transport layer, the coating is heated and cured at 120 ° C. for 1 hour to prepare a photoreceptor having a surface protective layer (siloxane resin layer having charge transport performance) having a dry film thickness of 2 μm. did.

FIG. 1 is an example of a graph showing the abrasion loss of the electrophotographic photosensitive member (hereinafter, also simply referred to as a photosensitive member) to which the present invention is applied. That is, the graph of FIG. 1 shows an electrophotographic photosensitive member having a subbing layer, a photosensitive layer (a charge generating layer and a charge transporting layer), and a surface protective layer (a siloxane-based resin layer having charge transporting performance) on an aluminum drum.
This is data obtained by measuring the amount of abrasion of the photoreceptor with respect to the number of copies mounted on a 50 digital copier under conditions of 24 ° C. and 60% temperature and humidity.

As is clear from the graph, there is a difference of at least twice between the wear rate (A) of the surface protective layer and the wear rate (B) of the photosensitive layer. Since the bending point of C changes depending on the size of the copy paper, the usage conditions, and the like, it is difficult to estimate the wear amount by the number of copies. The surface protective layer of the present invention is relatively thin, and can be continuously used as a photoreceptor even after the protective layer has been worn away. The present invention relates to a method and an apparatus for stabilizing the surface potential of a photoconductor.

The surface protective layer of the present invention is preferably a high hardness surface layer for protecting the photoreceptor from abrasion due to cleaning or rubbing with a developer or the like. velocity ratio V ₂ / V ₁ it is preferable satisfy 0.5 or less. This surface protective layer may be an insulating layer or a semiconductor layer (meaning a layer having a carrier mobility), but a semiconductor layer is more preferable in order to achieve the intended potential stability.

[0021]

The present invention will be described below in detail with reference to examples.

FIG. 2 is a schematic view showing one embodiment of the control of the surface potential of the photosensitive member having the surface protective layer of the present invention. FIG.
In the figure, reference numeral 50 denotes a photoconductor drum (photoconductor) having a surface protective layer, which is a photoconductor in which an organic photoconductive layer is applied on a conductive drum and a surface protective layer is applied thereon, and is grounded and clockwise. It is driven and rotated. Reference numeral 52 denotes a band electrode, and the photosensitive drum 5
Uniform charging is given to the 0 circumferential surface by corona discharge. Prior to the charging by the charger 52, a charge removing exposure device 51 using a light emitting diode or the like is provided to erase the history of the photoconductor. 53 is a digital image exposure device (polygon mirror,
The developing units 54 and 541 for developing the electrostatic latent image are developing sleeves that incorporate magnets and rotate while holding the developer. On the other hand, the developed toner is transferred to the recording paper P in the area of the transfer pole 58,
Thereafter, the recording paper P is separated from the photoconductor at the separation pole 59 and is conveyed to the fixing device 60.

On the other hand, the photosensitive drum 50 from which the recording paper P has been separated, the residual toner is removed and cleaned by the pressure contact of the blade 611 of the cleaning device 61, and the charge removing exposure device 5 is again removed.
In response to the charge elimination by 1 and the charging by the charger 52, the image forming process starts. A cleaning roller 612 removes paper dust and the like.

The potential sensor 62 for measuring the surface potential of the photosensitive member of the present invention is located between the image exposing unit 53 and the developing unit 54. Hereinafter, a charging potential adjusting process for making the potential difference between the unexposed portion potential and the exposed portion potential constant will be described.

First, the photosensitive member 50 is uniformly charged by the band electrode 52. The charged photoreceptor is digitally exposed by a laser diode image exposure device 53 to form a potential latent patch latent image on the photoreceptor 50. The surface potential (exposure portion potential) of the patch latent image is detected by the potential sensor 62, and the detected potential information is transmitted to the process control portion 63 in FIG. The process controller 63 is a process controller that controls the band electrodes based on a signal from the potential sensor 62. A target charging potential is determined by adding a constant voltage to the potential obtained by the sensor. The high-voltage control unit 64 is a high-voltage control unit that receives a control signal from the process control unit 63 and supplies current and voltage to the band electrode 52. Based on the determined target charging potential, a target signal of a charging current and a charging grid voltage is output from the process controller to the high voltage control unit, and subsequently determined by the high voltage control unit to the corona wire 521 and the scorotron grid 522 of the band electrode 52, respectively. The charged charging current and charging grid voltage are output. Further, the potential of the photosensitive member (unexposed portion potential) charged by the charging output is detected by a potential sensor, and the target charging potential is corrected.

The process for determining the target charging potential can be automatically performed in the above cycle, for example, as follows. That is, a relational expression for determining the target surface potential from the surface potential of the exposed portion obtained from the potential sensor and correcting the target surface potential from the surface potential of the unexposed portion potential, for example, the relationship between the unexposed portion potential and the exposed portion potential A relational expression (for example, a relational expression between the current and voltage value of the strip electrode and the surface potential of the photoreceptor) that makes the difference constant is obtained in advance by an experiment or the like, and this relational expression is further determined by an actual charging potential control cycle. By incorporating a program that can be corrected in the memory of the process control unit 63, the target charging potential can be automatically determined.

By the above-described process of controlling the surface potential of the photoconductor, the potential difference between the charged potential of the photoconductor and the potential of the exposed portion is always kept constant even if the film thickness wear of the photoconductor changes due to environmental conditions or the like. As a result, stable image formation can be performed.

Further, in the case of reversal development, after transmitting a surface potential detection signal of the patch latent image by the potential sensor 62 to the process control unit 63, a signal obtained by adding a constant potential to the surface potential of the patch latent image is a high voltage. It is preferable that the developing bias voltage transmitted to the control unit 64 and corresponding to the signal be output to the developing sleeve 541. As a result, the potential difference between the developing bias voltage and the exposed portion potential is kept constant, and stable reversal development is always performed.

Further, by controlling the laser output of the image exposing device based on the surface potential detection signal of the patch latent image obtained from the potential sensor 62, it is possible to control the exposed portion potential of the photosensitive member. In this case, the potential detection signal from the potential sensor 62 is transmitted to the process control unit 63 in the same manner as in the above example, and after the target exposure amount is determined, a signal corresponding to the target exposure amount is transmitted to the exposure control unit 65. A current or voltage output signal corresponding to the signal is output from the exposure control unit 65 to the image exposure device 53, and the exposure amount of the image exposure device 53 is controlled.

Although a laser diode is used as the digital exposure source in the above description, a linear array light source such as an LED, an EL (electroluminescence), a phosphor plasma, etc. may be used as the exposure source in addition to the laser diode.

As described in the above embodiment, according to the photosensitive member surface potential control of the present invention, a photosensitive member having a surface protective layer having a high hardness and a soft photosensitive layer thereunder is repeatedly image-formed. When the same photoreceptor is used continuously after the protective layer is scraped, the conventional method of controlling the surface potential on the assumption that the scraping speed is constant can provide only insufficient control. By performing the control, it is possible to stabilize the charged potential of the photoconductor and the exposed portion potential,
Furthermore, by applying a developing bias control, that is, in the case of reversal development, by maintaining a constant difference between the developing bias voltage and the exposed portion potential, a good image can be obtained continuously even after the surface protective layer of the photoconductor has disappeared. be able to.

In the method for controlling the surface potential of the present invention, the greater the difference in the scraping speed between the surface protective layer and the photosensitive layer thereunder, the more effective the effect of stabilizing the surface potential, for example, the more the difference between the developing bias voltage and the exposed portion potential becomes constant. Is particularly effective when the V ₂ / V ₁ ratio is 0.5 or less.

The method of controlling the change in the surface potential due to the wear of the photoconductor has been described above. However, the change in the surface potential of the photoconductor occurs simultaneously due to causes other than the wear of the film. For example, if the dark decay characteristic of the photoconductor surface potential changes,
According to the information detected by the potential sensor, even when the surface potential of the photoconductor is adjusted to the target value, the surface potential of the photoconductor changes at the developing position where the image is actually developed, and the obtained image is The value may not be reached. Such a change in the dark decay characteristic is a deterioration of the photoconductor that progresses gradually, and thus often deteriorates in proportion to the running value of the photoconductor. Here, the travel value of the photoconductor is an amount related to the history amount of the photoconductor used for image formation, and means an amount that can be measured by a travel distance, a total rotation speed, a copy count, and the like of the photoconductor related to image formation. . In the present invention, it is more preferable to add a correction based on the running value of the photoconductor to the control based on the surface potential information. For example, when adding a correction based on a copy count, a copy count sensor is set on the conveyance path of the recording paper P in FIG. 2, for example, before or after the fixing device (not shown), and a count signal from the sensor is sent to the process control unit. And a target charging potential is determined in accordance with the signal from the potential sensor, and then a current and voltage signal corresponding to the target charging potential is transmitted from the process control unit 63 to the high voltage unit. An output for controlling at least one of a charging current applied to the electrode, a charging grid voltage, a developing bias voltage applied to the developing device, and a digital exposure output is performed. As described above, by adding the correction based on the photoconductor travel value to the control of the photoconductor surface potential by detecting the surface potential of the photoconductor, deterioration of the photoconductor characteristics having different causes can be more appropriately corrected, and the life of the photoconductor is eliminated. (Until the above control cannot be performed on the photosensitive member), a good electrophotographic image can be produced.

The process for controlling the surface potential of the photosensitive member based on the surface potential signal from the potential sensor according to the present invention comprises the following steps:
More specifically, by regularly performing image formation on a fixed number of sheets once at a time, a sufficiently stable image can be achieved over the life of the photoconductor. However, if necessary, it is also possible to control the surface potential for each image forming sheet based on the measured value of the surface potential immediately before and to control the developing bias potential.

Here, the life of the photoreceptor may be considered to be sufficiently usable as long as the target surface potential control is achieved even after the surface protective layer has disappeared.

[0036]

As described above, according to the present invention, a photosensitive member having a surface protective layer having a high hardness always has a stable potential difference between the charging potential and the exposure potential or the developing bias voltage and the exposure potential even after the surface protective layer disappears. Can be obtained, and an image forming method and an image forming apparatus capable of maintaining a good image as in the initial stage even after the surface protective layer has been worn out can be provided.

[Brief description of the drawings]

FIG. 1 is an example of a graph showing a wear amount of an electrophotographic photosensitive member according to the present invention.

FIG. 2 is a schematic view showing one embodiment of a surface potential control of a photoreceptor having a surface protective layer of the present invention.

[Explanation of symbols]

 Reference Signs List 50 photoreceptor drum (or photoreceptor) 51 exposure device for slow charging 52 band electrode 53 image exposure device 54 developing device 541 developing sleeve 58 transfer pole 59 separation pole 60 fixing device 61 cleaning device 611 cleaning blade 612 cleaning roller 62 potential sensor 63 Process control unit 64 High voltage control unit 65 Exposure control unit

Claims (6)

[Claims] 1. An electrophotographic photosensitive member is charged by a band electrode,
An image forming method of forming an electrostatic latent image on a photoreceptor by digital exposure and developing the electrostatic latent image by a developing device to which a developing bias voltage is applied to obtain a visible image, wherein the photoreceptor has at least a surface protective layer Having a surface potential of the photoreceptor, based on the detected potential information, a charging current applied to the band electrode, or a charging grid voltage, a developing bias voltage applied to a developing device, and a digital exposure output. An image forming method, comprising controlling at least one of the photoconductors and continuing to use the photoconductor for image formation even after the surface protective layer has been worn away. 2. An electrophotographic photosensitive member is charged by a band electrode,
An image forming method for forming an electrostatic latent image on a photoconductor by digital exposure and developing the electrostatic latent image by a developing device to which a developing bias voltage is applied to obtain a visible image, wherein the photoconductor includes at least a photosensitive layer and And a ratio (V ₂ / V ₁ ) of the film wear rate (V ₁ ) of the surface protective layer to the film wear rate (V ₂ ) of the photosensitive layer is 0. The surface potential of the photoreceptor is detected, and based on the detected potential information, a charging current or a charging grid voltage applied to the band electrode, a developing bias voltage applied to a developing device, and An image forming method, wherein at least one of the exposure outputs is controlled. 3. The image forming method according to claim 1, wherein a correction based on a running value of a photoconductor is added to the control based on the detected potential information. 4. An electrophotographic photosensitive member is charged by a band electrode,
In an image forming apparatus for forming an electrostatic latent image on a photoconductor by digital exposure and developing the electrostatic latent image by a developing device to which a developing bias voltage is applied to obtain a visible image, the photoconductor includes at least a surface protective layer. Having a surface potential of the photoreceptor, based on the detected potential information, a charging current applied to the band electrode, or a charging grid voltage, a developing bias voltage applied to a developing device, and a digital exposure output. An image forming apparatus, wherein at least one of them is controlled, and the photoreceptor is continuously used for image formation even after the surface protective layer is worn away. 5. An electrophotographic photosensitive member is charged by a band electrode,
An image forming apparatus that forms an electrostatic latent image on a photoconductor by digital exposure and develops the electrostatic latent image by a developing device to which a developing bias voltage is applied to obtain a visible image, wherein the photoconductor includes at least a photosensitive layer and a photosensitive layer And a ratio (V ₂ / V ₁ ) of the film wear rate (V ₁ ) of the surface protective layer to the film wear rate (V ₂ ) of the photosensitive layer is 0. The surface potential of the photoreceptor is detected, and based on the detected potential information, a charging current or a charging grid voltage applied to the band electrode, a developing bias voltage applied to a developing device, and An image forming apparatus for controlling at least one of exposure outputs. 6. The image forming apparatus according to claim 4, wherein a correction based on a traveling value of the photosensitive member is added to the control based on the detected potential information.