JP4210138B2 - Image forming system using amorphous silicon photoconductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming system such as a copying machine, a facsimile machine, and a laser printer, and more particularly to an image forming system using an amorphous silicon photoreceptor.
[0002]
[Prior art]
In electrophotography, the surface of a photoconductor is uniformly charged to a predetermined polarity, and then image exposure is performed by light irradiation based on predetermined document information to form an electrostatic charge image. An image is formed, the toner image is transferred to a predetermined paper, and the toner image is fixed on the paper by heating and pressurizing with a fixing roller, thereby forming an image. In addition, after the toner image is transferred, the surface of the photosensitive member is cleaned by a cleaning blade or the like to remove the remaining toner, and further, if necessary, neutralization is performed by light irradiation or the like, and the next image forming cycle is performed.
[0003]
In the image forming system as described above, ozone is generated by discharge when charging the surface of the photoreceptor, and moisture in the air is decomposed by the ozone to generate ionic substances such as nitrogen oxides and ammonium salts. It is known. Since this ionic substance is water-soluble, when it adheres to the surface of the photoreceptor, it takes in moisture in the atmosphere and lowers the electrical resistance of the surface of the photoreceptor (this tendency becomes more prominent as the atmosphere becomes hot and humid). As a result, when an image is formed, a potential lateral flow occurs at the edge portion of the electrostatic latent image formed on the surface of the photosensitive member, and a so-called image flow phenomenon occurs.
[0004]
In recent years, environmental problems have been greatly taken up, and in the above-described electrophotographic image forming system, reduction of consumables and longer life are desired, and contribution to environmental conservation is demanded. In terms of meeting such demands, amorphous silicon having high durability is most suitable as the above-mentioned photoreceptor, but the amorphous silicon photoreceptor is more suitable than other photoreceptors such as organic photoreceptors. In particular, it has a high hygroscopic property, and thus has a drawback that the above-described image flow phenomenon is remarkable.
[0005]
As a means for preventing such image flow, a heater is provided inside the photosensitive member, and the photosensitive member is heated to evaporate moisture taken in by the ionic substance attached to the surface of the photosensitive member. However, it has been attempted to prevent a decrease in electrical resistance on the surface of the photoreceptor and to suppress image flow. However, such means requires heat control means and the like, resulting in a complicated apparatus structure and increased cost. In addition, it takes time until the surface of the photoconductor is heated to a predetermined temperature, and it takes time until an image is printed, resulting in an increase in power consumption.
[0006]
Therefore, when the image forming cycle is not executed, a developing operation is performed on the surface of the photosensitive member so that a large amount of toner (abrasive-containing toner) is adhered, and the surface of the photosensitive member is polished by this toner. Means for removing the generated ionic substance has been proposed (see Patent Document 1).
[0007]
[Patent Document 1]
JP 11-3014 A (Claims)
[0008]
[Problems to be solved by the invention]
The method proposed in Patent Document 1 is advantageous in that it does not use a heating means such as a heater, and therefore it is possible to avoid inconveniences such as a complicated apparatus structure and an increase in cost and power consumption. .
[0009]
Recently, the toner image formed on the surface of the photoconductor is not directly transferred to the transfer paper, but is temporarily transferred to the intermediate transfer body, and then the toner image on the intermediate transfer body is secondarily transferred onto the transfer paper. An image forming system has been adopted. That is, when forming a full-color image, it is necessary to superimpose toner images of a plurality of colors. However, rather than superimposing toner images on transfer paper, each color toner is temporarily formed on the intermediate transfer member. Transferring the images (primary transfer) and superimposing them, and transferring the full-color toner image from the intermediate transfer member onto the transfer paper (secondary transfer) causes inconveniences such as color misregistration due to misalignment of the transfer paper. This is because a full-color image can be formed without this.
[0010]
However, in the image forming system using the intermediate transfer body as described above, when the image flow prevention means as proposed in Patent Document 1 is applied, the image flow prevention effect is halved. There's a problem. That is, when water adheres to the surface of the intermediate transfer member, even if the water adsorbing ionic substance is removed by polishing the surface of the photosensitive member, the water is removed from the intermediate transfer member disposed in contact with the photosensitive member. Because it will be replenished. For example, the intermediate transfer member is generally of a roller type in which a conductive elastic layer is provided on a metal drum such as aluminum or a belt type consisting of a conductive elastic belt. A high-quality material is in contact with an elastic body having a high heat capacity (a belt-type intermediate transfer body is disposed in contact with a metal transfer roller). As understood from this, the intermediate transfer member has a property that moisture easily adheres to the surface, and there is a demand for prevention of image flow in an image forming system when the intermediate transfer member is used. .
[0011]
Accordingly, an object of the present invention is to effectively prevent an image flow caused by moisture adhesion without using a heating means such as a heater in an electrophotographic image forming system using an amorphous silicon photoreceptor and an intermediate transfer member. It is to provide a method that can be prevented.
[0012]
[Means for Solving the Problems]
According to the present invention, an electrostatic latent image formed on an amorphous silicon photoconductor is developed with an abrasive-containing toner, and the toner image formed on the photoconductor is temporarily transferred to an intermediate transfer member. In an image forming system for forming an image by executing an image forming cycle in which a transfer toner image transferred onto a body is secondarily transferred to a predetermined sheet,
At the time of non-execution of the image forming cycle, the toner-containing toner is adhered on the photoreceptor, and the toner adhered on the photoreceptor surface is temporarily transferred onto the intermediate transfer body at least over the entire length of the intermediate transfer body , A refresh that polishes the surface of the photoconductor by reversely transferring the toner from the surface of the intermediate transfer body onto the photoconductor, and sliding and rubbing the reversely transferred toner on the surface of the photoconductor by a polishing member provided in a cleaning device. An image forming system characterized in that a mode is executed is provided.
[0014]
In the present invention, a refresh mode is set separately from a mode for executing an image forming cycle (hereinafter sometimes referred to as a printing mode). For example, when the main power supply of the image forming apparatus is turned on or energy saving is performed. The refresh mode is executed when the print mode is not executed, such as when returning from the mode. In such a refresh mode, the toner-containing toner is transferred (transferred) from the surface of the amorphous silicon photosensitive member to the intermediate transfer member, and the toner absorbs moisture on the surface of the intermediate transfer member. (Reverse transfer) and polishing the surface of the photoreceptor with the toner according to a conventional method, moisture can be removed from the intermediate transfer body and the photoreceptor surface at the same time. Can be effectively prevented, and image flow due to moisture adhesion can be effectively avoided.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
[0016]
In FIG. 1 showing a schematic structure of an image forming apparatus in which the image forming system of the present invention is suitably executed, the amorphous silicon photosensitive drum 1 provided rotatably is sequentially arranged along the rotation direction. A charging device 2, an exposure optical system 3 such as an LED, developing devices 4 to 7, and a cleaning device 10 are arranged.
[0017]
The developing units 4 to 7 perform development with toner of each color. For example, the developing unit 4 is a yellow developing unit, the developing unit 5 is a magenta developing unit, the developing unit 6 is a cyan developing unit, and the developing unit 7 is a black developing unit. It has become.
[0018]
The cleaning device 10 includes a polishing roller 10a and a cleaning blade 10b. The polishing roller 10a is positioned on the upstream side and the cleaning blade 10b is positioned on the downstream side with respect to the rotation direction of the photosensitive drum 1. .
[0019]
Further, an intermediate transfer body roller 12 is provided so as to come into contact with the photosensitive drum 1 in a region between the developing device 7 and the cleaning device 10. The intermediate transfer body roller 12 includes a secondary transfer roller 12. The transfer roller 13 and the cleaning device 14 are arranged in contact with each other, and a transfer sheet 20 on which an image is to be formed is passed between the intermediate transfer body roller 12 and the secondary transfer roller 13. Note that the secondary transfer roller 13 and the cleaning device 14 are both retractable so as to be separated from the intermediate transfer body 12. Although not shown, a fixing device including a roller pair of a heat roller and a pressure roller is disposed on the discharge side of the transfer paper 20.
[0020]
[Image formation process]
The image forming process (printing mode) in the above apparatus is executed as follows.
[0021]
The photoconductive drum 1 is provided with an amorphous silicon photoconductive layer on a conductive element tube such as aluminum and is known per se. For example, the element ratio composition of the photoconductive layer is expressed by the following formula:
a-Si _1-X C _X : H
In the surface layer, in the surface layer, x is in the range of 0.95 ≦ x <1, and the Vickers hardness of the outermost surface is 300 or less, and the innermost side (conductive element tube side) than the outermost surface side The hardness is preferably large, and it is particularly desirable that the hardness gradually increases toward the back side. By having such a hardness change, the photoconductive layer itself is scraped off together with the removal of the ionic substance generated by charging by polishing in the refresh mode described later, and the photoconductive layer always has a virgin surface. Thus, it is possible to constantly maintain the chargeability and other characteristics at the same level as in the initial stage.
[0022]
For image formation, first, the charger 2 is used to uniformly charge the surface of the photosensitive drum 1 uniformly. At this time, the main charging potential on the surface of the photosensitive drum 1 is set to +200 to + 600V. This main charging potential is extremely low compared to the case where an image is formed using another photoconductor. As the charger 2, a corona charger, a charging roller or the like is generally used.
[0023]
Next, based on predetermined image information, the optical system 3 irradiates light such as laser light to form an electrostatic latent image on the surface of the photosensitive drum 1. That is, by this image exposure, the portion irradiated with light has a low potential.
[0024]
The electrostatic latent image formed as described above is reversely developed with a developer containing toner of each color charged to positive polarity by any of the developing devices 4 to 7. That is, a toner image is formed by the toner adhering to a portion that is irradiated with light and has a low potential.
[0025]
In such development, a development bias voltage is usually applied between the developer supply side (developer) and the photosensitive member. For example, the developing device is grounded, and a potential of +130 to +350 V is applied as the developing bias voltage (potential applied to the photosensitive drum 1).
[0026]
The toner image formed on the surface of the photosensitive drum 1 by the development is primarily transferred to the intermediate transfer body roller 12. The primary transfer is performed by applying a primary transfer bias potential (usually about −200 to −500 V) to the intermediate transfer roller 12. In the primary transfer, the secondary transfer roller 13 and the cleaning device 14 are both retracted from the intermediate transfer body roller 12.
[0027]
The intermediate transfer body roller 12 as described above usually has a conductive drum made of aluminum or the like as a base, and an elastic body layer formed of a resin having toner releasability such as a fluorine-containing resin on the surface thereof. It is what you have.
[0028]
After the toner image is transferred to the intermediate transfer body 12, the toner remaining on the surface of the drum 1 is removed by the cleaning device 10, particularly the cleaning blade 10b, and then the same charging, developing, primary transfer and cleaning are performed, and the other colors The toner image is primarily transferred to the intermediate transfer roller 12. In this manner, the toner images of the respective colors are transferred to the intermediate transfer body roller 12, and the toner images of the respective colors are superimposed on the intermediate transfer body roller 12, thereby forming a full color image.
[0029]
After the full-color image is formed on the intermediate transfer body roller 12, the secondary transfer roller 13 and the cleaning device 14 return from the retracted position and come into contact with the intermediate transfer body roller 12 to perform the secondary transfer and intermediate transfer body of the full-color image. The roller 12 is cleaned. That is, by passing the transfer paper 20 while applying a secondary transfer bias potential (usually about −500 to −2000 V) to the secondary transfer roller 13, a full color image is transferred onto the transfer paper 20, and the transfer paper. 20 is introduced into a fixing device (not shown), and a full-color image is fixed on the transfer paper 20. On the other hand, the toner remaining on the intermediate transfer roller 12 after the secondary transfer is removed by the cleaning device 14, thereby completing one cycle of full-color image formation. When forming a monochrome image, only the black developing device is used, and the above-described image forming cycle is performed without performing color superposition.
[0030]
[Refresh mode]
In the present invention, a refresh mode is executed in addition to the print mode as described above, whereby the removal of ionic substances from the surface of the photosensitive drum 1 and the removal of moisture from the intermediate transfer body roller 12 are performed. The occurrence of image flow can be effectively avoided.
[0031]
In the refresh mode, first, the toner filled in any of the developing devices 4 to 7 is attached to the surface of the photosensitive drum 1. This toner adhesion is basically performed in the same manner as the development in the above-described printing mode. In this case, the toner is adhered to the entire surface of the image forming area of the photosensitive drum 1 by the entire surface exposure.
[0032]
Thus, the toner (hereinafter referred to as a solid image) adhering to the entire surface of the photosensitive drum 1 is transferred to the intermediate transfer roller 12 in the same manner as the primary transfer in the print mode. When transferring the solid image, the secondary transfer roller 13 and the cleaning device 14 are both retracted from the intermediate transfer roller 12. In this way, a solid image is transferred at least over the entire circumference of the intermediate transfer roller 12, and the water adhering to the surface of the intermediate transfer roller 12 is absorbed and removed from the surface by the transferred solid image (toner). The In order to transfer a solid image over the entire circumference of the intermediate transfer roller 12, a development bias may be applied for a time during which such an amount (size) of solid image is formed.
[0033]
After the moisture on the surface of the intermediate transfer body roller 12 is removed in this way, the solid image is reversely transferred to the surface of the photosensitive drum 1. In this reverse transfer, a potential having a polarity opposite to that of the primary transfer bias (that is, positive polarity) may be applied to the intermediate transfer roller 12.
[0034]
The solid image reversely transferred from the intermediate transfer roller 12 to the surface of the photosensitive drum 1 is introduced into the cleaning device 10, and the surface of the photosensitive drum 1 is polished by passing the solid image through the polishing roller 10a. By this polishing, ionic substances and moisture adhering to the surface of the photosensitive drum 1 are removed, and more desirably, the surface of the photoconductive layer itself of the drum 1 is also scraped off to form a virgin surface. The
[0035]
As the polishing roller 10b, an elastic roller such as foamed polyurethane is usually used. In order to effectively polish the surface of the photosensitive drum 1, the surface hardness H is preferably 30 degrees or more. It is preferable that the contact is made with a linear pressure of 50 g / cm or more. Further, the polishing roller 10b is provided so as to rotate in the opposite direction to the photosensitive drum 1, and its peripheral speed (absolute value) is 1.2 times or more the peripheral speed of the photosensitive drum. It is preferable in order to maximize the polishing effect.
[0036]
After the surface of the photosensitive drum 1 is polished by the polishing roller 10b, a solid image is collected from the surface of the photosensitive drum 1 by the cleaning blade 10b, and the refresh mode is completed.
[0037]
The above-described refresh mode can be performed at any time when the print mode is not executed. In general, image flow due to moisture adsorption or the like is performed for a long time under a certain environmental condition (especially high temperature and high humidity) in the image forming apparatus. Occurs when held. Therefore, in order to prevent such image flow, it is preferable to set the image forming apparatus so that it is automatically performed when the main power supply of the image forming apparatus is turned on or when returning from the energy saving mode. Of course, when an image flow or the like occurs, it is necessary to execute it at any time by an input from the operation panel of the apparatus.
[0038]
[toner]
In order to execute the refresh mode as described above, the toner (yellow, magenta, cyan, black, etc.) used as the developer needs to contain an abrasive. Such an abrasive is not limited as long as it has a polishing action, but generally, titanium oxide, alumina, silicon carbide, magnetite, tin oxide, strontium titanate, inorganic powder subjected to surface conductive treatment In general, it is preferable that the fine particles having a particle size of 0.1 to 3.0 μm are externally added to the toner particles, and in order not to deteriorate the charging characteristics of the toner, the volume solid resistance The value is in the range of 1 × 10 ^{2 to} 1 × 10 ¹⁰ Ωcm, and the addition amount is preferably in the range of 0.3 to 5 parts by weight per 100 parts by weight of the toner particles.
[0039]
Further, the toner particles may be known per se, for example, a colorant of a predetermined color such as yellow, magenta, cyan, and black, together with a release agent such as a positive charge control agent and wax, and other compounding agents. What was disperse | distributed in binder resin can be used, and the particle size is generally in the range of about 5 to 10 μm. In addition, the toner particles can be used alone as a developer (in this case, a magnetic agent such as magnetite is blended), and further a two-component developer in combination with a magnetic carrier such as ferrite. It can also be used as
[0040]
Furthermore, any toner can be used as the toner for forming the solid image at the time of executing the refresh mode described above. However, it is generally preferable to use a black toner having a low cost.
[0041]
In the apparatus of FIG. 1 that executes the image forming system of the present invention described above, the intermediate transfer roller 12 is used as an intermediate transfer member. However, the present invention may be applied to an apparatus that uses a belt as an intermediate transfer member. Of course it is possible.
[0042]
【Example】
Example 1
A modified Kyocera Mita full-color printer equipped with an a-Si photosensitive member (diameter: 80 mm) having the structure shown in FIG. 1 was left in an environment of 30 ° C. and RH 80% for one day and night.
Then, at the same time as turning on the main power supply of this modified machine, 2 parts by weight of titanium oxide (particle size: 0.1 μm, resistance: 1 × 10 ⁷ Ωcm) and hydrophobic silica 0.5 per 100 parts by weight of toner particles. A refresh mode consisting of solid toner image formation, solid image transfer to the intermediate transfer roller, reverse transfer of the solid image to the photosensitive drum, polishing roll and polishing process with the solid image, with the black toner with the weight part added externally Was executed. The solid image was formed over the entire circumference of the intermediate transfer roller. The specifications of the polishing roll are as follows.
[0043]
Polishing roll:
Made of polyurethane foam (diameter: 14mm)
Surface hardness H: 30 degrees Contact pressure: 60 g / cm
Peripheral speed: 162m / min (1.2 times the photosensitive drum)
Rotation direction: photoconductor drum and forward direction
After executing the above refresh mode, the normal print mode was executed under the following conditions to form a full color image.
Main charging potential: 280V
Development bias: 160V
Primary transfer bias: -400V
Secondary transfer bias: -1200V
Printing rate: 5%
[0045]
When the obtained image was confirmed visually, no image flow occurred.
[0046]
Comparative Example 1
Except that the solid image was not transferred to the intermediate transfer roller, the refresh mode was executed in the same manner as in Example 1, and the print mode was executed in the same manner. As a result, the resulting full color image clearly had an image flow.
[0047]
【The invention's effect】
According to the present invention, in an image forming system using an amorphous silicon photosensitive member and an intermediate transfer member, image flow caused by moisture adhesion on the surface of the photosensitive member and the intermediate transfer member can be effectively performed without using a heating means such as a heater. It became possible to prevent.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic structure of an image forming apparatus in which an image forming system of the present invention is preferably executed.
[Explanation of symbols]
1: Amorphous silicon photosensitive drum 2: Charger 3: Exposure optical system 4-7: Developer 10: Cleaning device 10a: Rub roller 10b: Cleaning blade 10b
12: Intermediate transfer roller 13: Secondary transfer roller 14: Cleaning device 20: Transfer paper

Claims (1)

The electrostatic latent image formed on the amorphous silicon photoconductor was developed with an abrasive-containing toner, and the toner image formed on the photoconductor was temporarily transferred to the intermediate transfer member and transferred onto the intermediate transfer member. In an image forming system that forms an image by executing an image forming cycle in which a transfer toner image is secondarily transferred to a predetermined sheet,
At the time of non-execution of the image forming cycle, the toner-containing toner is attached on the photoreceptor, and the toner attached on the surface of the photoreceptor is temporarily transferred onto the intermediate transfer body at least over the entire length of the intermediate transfer body. A refresh that polishes the surface of the photoconductor by reversely transferring the toner from the surface of the intermediate transfer body onto the photoconductor, and sliding and rubbing the reversely transferred toner on the surface of the photoconductor by a polishing member provided in a cleaning device. An image forming system in which a mode is executed.

Images