JPH0493866A - Corona discharger - Google Patents

Abstract

PURPOSE:To effectively prevent the image flow and void generated in the part of a photosensitive body facing the corona discharger by constituting the corona discharger rotatably in such a manner that the aperture or grid part thereof faces the photosensitive body at the time of image formation and the cylindrical wall faces the photosensitive body and shields the part between a charge wire and the photosensitive body at the time of non-image formation. CONSTITUTION:A hollow metallic cylindrical body 13 in which the charge wire 11 passes is disposed in a shield case 12. This cylindrical body 13 has the aperture or grid part 14 having a specified width in the circumferential direction and a prescribed width in the axial direction in the cylindrical part and is formed rotatable at need. The photosensitive body 1 is positioned to face the aperture or grid part 14 of the cylindrical body 13 at the time of the image formation. The cylindrical body 13 is rotated about 180 deg. to shield the part between the charge wire 11 and the photosensitive body with the cylindrical wall at the time of the non-image formation. The transfer of the corona products formed by the corona discharge and stuck to the inside of the cylindrical part and the grid part 14 to the photosensitive body is, therefore, prevented. The generation of the image flow and void is prevented in this way.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a corona discharge device that prevents image deletion and white spots in image forming apparatuses such as electrophotographic copying machines, laser printers, and facsimiles. It is related to.

(Prior Art) In image forming apparatuses such as electrophotographic copying machines, laser printers, and facsimile machines, amorphous silicon (a
-3i irritating photo), Se, As2Se3゜5eTe
Inorganic photoconductive materials (Se photoreceptor) such as poly-N
- Photoreceptors using organic photoconductive materials (OPC photoreceptors) such as vinyl carbazole, trinitrofluorenone, and various azo pigments are generally known.

For example, OPC photoreceptors have good electrical properties and spectral sensitivity, are inexpensive to manufacture, are non-polluting, and can be relatively easily processed into belt- or drum-shaped photoreceptors.
It is widely used in everything from low-speed to medium-speed machines.

On the other hand, although the a-3i photoreceptor has inferior charging ability compared to other photoreceptors, it has high sensitivity and high abrasion resistance, so it is used in high-speed copying machines, laser printers, and the like.

An example of an image forming apparatus using such a photoreceptor is shown in the fourth example.
As shown in the figure. The photoreceptor 1 is uniformly charged by a charging corona discharger (charger) 2 .

The corona discharger 2 includes a corotron type in which a tungsten wire with a diameter of 40 to 100 μm is stretched, and a scorotron type in which a grid is further stretched near the opening of the corona discharger in order to equalize uneven discharge. , 4000~
A high voltage of 5ooo volts is applied.

After imagewise exposure is performed in the exposure section 3 to form an electrostatic latent image, a toner image is formed in the developing device 4.

The toner image is transferred to a transfer corona discharger (transfer charger) 5.
After the image is transferred onto a copy paper 9, the copy paper is separated from the photoreceptor by a separation corona discharger (separation charger) 6, and fixed by a fixing device 10 to become a hard copy.

On the other hand, the photoreceptor 1 after the transfer is cleaned by a cleaning device 7 to remove residual toner, and the charge is eliminated by a discharge lamp 8, thereby completing a series of copying steps.

By the way, in an image forming apparatus using a corona discharger, corona products, such as ozone and nitrogen oxides, are generated during corona discharge, and when these corona products adhere to the surface of the photoreceptor, the photoreceptor It is known that the surface resistance of the body surface layer decreases and the photosensitive characteristics of the photoreceptor deteriorate, resulting in a decrease in image quality. In particular, the surface resistance decreases with humidity, causing image blurring, and in the worst case, no image may be formed at all. Therefore, in order to maintain the initial image for a long period of time, it is necessary to eliminate the influence of corona products. The degree of occurrence of such image blurring differs depending on the material that makes up the photoreceptor, and there are also differences in the substances that cause image blurring, but in all cases, corona products are the trigger for image blurring. There is.

The following are known as devices designed to prevent the deterioration of image characteristics caused by corona products as described above.

As a first example, by improving the constituent materials of the photoreceptor itself,
Products that prevent a decrease in surface resistance are known. Specifically, photoreceptors include those in which a photosensitive layer is formed on a conductive support, and those in which a protective layer is further laminated on the photosensitive layer. When these photosensitive layers and protective layers are formed by spraying or coating methods, antioxidants (amines, hydroxylamines) are added or rubbed in from the outside to eliminate the effects of corona products. I try to do that.

As a second example, it is known that corona dischargers are improved to suppress the generation of corona products and prevent corona products from adhering to the photoreceptor. The former is
For example, JP-A-64-68774, JP-A-47-3
Au, Ag, Pt, and Pd are described in JP-A No. 7547, JP-A-49-40739, JP-A-49-84660, etc., and serve as ozone decomposers.

The charge wire, shield case, or grid is plated with a metal or metal oxide such as Ni, Fe, Ni2O3, BaO, alumina, or chromium oxide to suppress the generation of corona products during corona discharge. on the other hand,
The latter is described, for example, in Japanese Patent Application Laid-Open No. 63311365, in which the inner wall and grid of the shield case are treated with activated carbon fiber, manganese oxide, or a metal chelate compound to absorb corona products and adhere to the photoreceptor. I'm trying to prevent that from happening. In addition, other measures have been taken, such as making the grid carbon fiber-based, adding an absorbing member (for example, see Japanese Patent Application Laid-Open No. 1-210974), or creating a shield case shape that takes into account wind flow. There is also. Furthermore, there are also shield cases that use a combination of Pt or Ag plating and an absorbent made of activated carbon.
This is described, for example, in JP-A-50-34828 and JP-A-52-133894.

As a third example, it is known that the photoreceptor is heated with a heater or dried with hot air to eliminate the influence of humidity and prevent a decrease in the surface resistance of the photoreceptor (for example, , JP-A-59-208558, JP-A-60-09
5467, JP-A-61-132977, and JP-A-62-262065).

As a fourth example, one is known in which corona products adhering to the surface of the photoreceptor are removed by polishing or wet cleaning. For polishing, for example, a roller or blade made of a looped steel wire is used (for example, see JP-A-1-161281), and for wet cleaning, corona products on the surface of the photosensitive layer are removed using water or a solvent. I'm trying to remove it.

In addition to the above-mentioned four examples, for example, Japanese Patent Application Laid-Open No. 58-285
No. 81, JP-A-60-95459, JP-A-6
0-189769, JP-A-60-102659, JP-A-59-219770, JP-A-60-
No. 134254, Japanese Patent Application Laid-open No. 17765/1983,
The one described in Japanese Patent Application Laid-Open No. 55-155369 is known.

(Problems to be Solved by the Invention) In the image forming apparatus shown in FIG.
A corona discharger is used to perform the separation, but
With discharge, corona products such as ozone (03) and nitrogen oxides (NOX) are generated from the corona discharger. As a result, these corona products are converted into hydrophilic compounds such as nitrogen compounds, aldehyde groups, and carboxyl groups due to the action of discharge energy and atmospheric moisture, carbon dioxide gas, nitrogen gas, etc., resulting in oxidation of the photoreceptor surface. The electrical resistance (surface resistance) of the photoreceptor decreases due to adsorption of compounds and moisture absorption from atmospheric moisture, resulting in image blurring and even worse, white spots due to image deletion, which significantly reduces copy quality. There is.

This phenomenon occurs in most photoreceptors to a greater or lesser degree, but in particular, in photoreceptors using an a-3i layer, hydrophilic substances such as 5i02 are generated on the surface of the photoreceptor, which tends to cause image smearing. It has been found that a photoreceptor using a-C:H as a protective layer, which was thought to have excellent durability and weather resistance, has the same problem as the a-8i photoreceptor.

In these photoreceptors, the higher the temperature is, the more the image fades, and sometimes the image does not appear at all.

In particular, in laser printers equipped with an OPC photoreceptor with a-C:8 layer as a protective layer, the surface of the photoreceptor facing the negative corona discharger for charging may adhere to the corona discharger during the stoppage after copying. contaminated by corona products,
Even at a humidity of more than 30%, the phenomenon of missing images and white spots occurs, and even with A-3I exposure, it may also occur at the part facing the AC corona discharger for static elimination.

This phenomenon occurs when corona products attached to the corona discharger volatilize and release from the opening of the corona discharger toward the photoreceptor. It is characterized by

Note that in some cases, the image completely disappears in the white areas, but in mild cases, white areas may appear in some areas or a state of image deletion may be observed.

It is expected that there will be a large amount of corona products attached to the white area, and since this is hydrophilic, if there is even a small amount of water, the surface resistance will decrease, and after the image fades, the white area will change to the white area. It is thought that this will be achieved.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that effectively prevents image deletion and white spots occurring at the portion of the photoreceptor facing the corona discharger.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a charge wire and a shield case that surrounds the charge wire and is open on the side facing the photoreceptor, through which the charge wire penetrates. A hollow metal cylindrical body is disposed within the shield case, and the cylindrical body has an opening or grid portion having a constant width in the circumferential direction and a predetermined length in the axial direction in the body. , so that it can be rotated as needed.

Further, a cleaning member is provided between the shield case and the cylindrical body to clean the outer surface of the cylindrical body as the cylindrical body rotates.

(Function) In the above configuration, the opening or grid portion of the cylinder is positioned to face the photoreceptor when forming an image, and the cylindrical wall shields between the charge wire and the photoreceptor when not forming an image. Rotate the cylinder approximately 180 degrees. This results in
Since corona products generated by corona discharge and attached to the cylindrical body or the grid portion can be prevented from transferring to the photoreceptor, white areas can suppress the occurrence of the phenomenon.

In addition, during long-term use, corona products gradually accumulate on the outer surface of the cylinder, but in particular, corona products attached to the grid, which is closest to the photoreceptor and easily contaminates the photoreceptor, are removed. There is a need to. In the present invention, by rotating the cylindrical body, the outer surface of the cylindrical body is cleaned by the cleaning member disposed between the shield case and the cylindrical body, so that contamination of the photoreceptor is further reduced. As the cleaning member, one mainly made of activated carbon fiber is suitable.

(Example) Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 shows the basic configuration of a corona discharger in an embodiment of the present invention, where 11 is a charge wire;
Tungsten wire with a diameter of 40-100 μm is commonly used. 12 is a shield case that surrounds the charge wire 11 and is open on the side facing the photoconductor; 13 is a hollow metal cylindrical body that is rotatably disposed within the shield case 12 so that the charge wire 11 passes through the inside thereof; and
Metal that is resistant to bending, e.g. thickness 0.1-0.51nITl
It is made of 18-8 stainless steel or phosphor bronze with rust prevention, and etching is applied to a part of the body, that is, approximately 1/4 of the circumferential width and the required length in the axial direction. It forms a grid portion 14 (sometimes an opening). The area other than the grid area is a wall. Reference numeral 15 denotes a counter electrode to the charge wire, which is used to operate corona discharge efficiently and stably, and can be made of a chrome-plated or nickel-plated iron plate, a stainless steel plate, or the like. Note that the shield case 12 holds, protects, and holds the cylindrical body 13.
It plays the role of preventing the spread of corona discharge current and corona products, installing a fixture on the image forming apparatus, and also holding a cleaning member as described below.

FIG. 3 shows this embodiment in more detail.

An end block 16 holds the charge wire 11, the counter electrode 15, and the high voltage terminal 17, and also supports the cylindrical body 13 in a rotatable manner. A spring (not shown) is installed in the end block 16 for tensioning the charge wire. Reference numeral 18 denotes a base plate that fixes and holds the end block 16. 19 is a drive motor that rotates the cylindrical body 13, and a gear 20 attached to the motor shaft rotates the cylindrical body I.
It meshes with the gear 21 provided at the end of 3 and rotates the cylindrical body for 15 seconds/
Rotate at the speed of rotation.

Next, specific effects of this embodiment will be explained.

First, the Ninoop hardness on the OPC photoconductor is 1500 to 2000.
A photoreceptor 1 in which a-C:H layers with a thickness of 7,500 to 8,000 kg/mm are laminated by plasma CVD is mounted on an experimental laser beam printer. When the main switch of the printer is turned on, the grid portion 14 of the cylindrical body 13 faces the photoreceptor, and after the copying process is completed, a control system is incorporated in which the grid portion 14 faces the photoreceptor. However, this circuit has a switch so that it can be turned on and off. The latent image potential was set to -250V for the bright area and -920V for the dark area.

Copy in A-4 size for 5 days at a rate of 3000 sheets/day, leave it overnight, and the next day, 50-55% RH, 21-23
The phenomenon of white spots occurring on the opposing part of the corona discharger in an environment of ℃ was observed.

As a result, when the cylindrical body 13 is not rotated after the copying process is completed and the grid portion 14 is always opposed to the photoreceptor 1, white spots are observed slightly wider than the grid width after each number of copies are completed. Ta.

On the other hand, when the cylinder was rotated half a turn after the copying process was completed so that the grid portion was located on the opposite side from the photoreceptor, no white spots were observed.

FIG. 2 shows another embodiment of the present invention, in which a cleaning member 23 is provided between the shield case 12 and the cylindrical body 13 for cleaning the outer surface of the cylindrical body.

In the short term, the configuration shown in Fig. 1 is sufficient to achieve the desired results, but when used for a long period of time, corona products gradually accumulate on the outer wall of the cylindrical body 13, and after the copying process is completed, the corona products are removed. Since the outer wall with the material on it will be facing the photoreceptor, a substantial problem may arise. Therefore, as the cylinder rotates, the cleaning member 23 rubs the outer surface of the cylinder to remove the corona products.

Although corona products are water soluble, wet cleaning methods cannot be used. Therefore, a dry cleaning method is required. Although it is effective to use a general cleaning member, it is insufficient. Activated carbon fiber is suitable as a member that can efficiently remove corona products in a short time and does not cause re-deposition while being absorbed.

Activated carbon fibers have extremely thin fiber diameters of 5 to 30 mm, so they have good NOx and ozone absorption efficiency and can be processed into various forms. However, on the other hand, since each fiber is hard and brittle, dust may be generated depending on the purpose of use. In the case of this embodiment, since it will be rubbed, it must be strong.

The activated carbon fibers that can be used in the present invention are preferably in the form of a woven fabric, with a thickness of about 0.5 to 1.0 mm, so they can be used by folding them together or by sandwiching felt-like activated carbon fibers between them. Possible variations are possible, such as using it with a piece of paper or inserting felt or foam material in between. In any case, using activated carbon fiber as a cleaning member has great effects.

Specifically, activated carbon fibers in the form of a fabric were folded three times on the lower surface of the base plate 18 in the shield case and attached so as not to fray, thereby forming a cleaning member for the cylindrical body 13. At this time, in order to see the effect, the cleaning members were arranged 172 times along the length of the cylindrical body. In this state, the effect over time was confirmed at a rate of 1,500 copies per day for one month (total number of copies: 30,000 copies).

After each copy was completed, cleaning was performed three times, and the control system was set so that the grid part stopped at the opposite side from the photoreceptor. As a result, in the areas where the cleaning member was not placed, slight unevenness of shading occurred, although this level was not a problem for practical use. However, in the area where the cleaning member is placed,
The difference in shading could not be discerned at all.

(Effects of the Invention) As described above, according to the present invention, the opening or grid portion of the cylinder is positioned to face the photoreceptor during copying, and the charging wire is connected to the cylinder wall when copying is stopped. Since the cylinder is rotated approximately 180 degrees to shield the space between the photoreceptors, the photoreceptor is not contaminated with corona products generated by corona discharge and adhered to the cylinder and the grid, and the white Extraction can prevent the phenomenon from occurring.

In addition, even during long-term use, corona products adhering to the outer surface of the cylinder can be cleaned and removed by rotating the cylinder, further reducing contamination of the photoreceptor and improving image quality. can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic configuration of an embodiment of the present invention;
FIG. 2 is a sectional view showing the basic configuration of another embodiment of the present invention, FIG. 3 is an exploded perspective view of the specific configuration of FIG. 1, and FIG. 4 is an image forming system to which the present invention is applied. FIG. 2 is a schematic configuration diagram of the device. 1... Photoreceptor, 11... Charge wire, 12...
...Shield case, 13...Cylindrical body, 14...
Grid portion, 23...Cleaning member. Figure 1 Figure 2 Patent applicant Ricoh Co., Ltd.

Claims (2)

[Claims] (1) A corona discharger for an image forming apparatus, comprising a charge wire and a shield case that surrounds the charge wire and is open on the side facing the photoreceptor, the corona discharger being made of hollow metal through which the charge wire penetrates. A cylindrical body is disposed within the shield case, and the cylindrical body is attached to the body.
It has an opening or a grid portion having a constant width in the circumferential direction and a predetermined length in the axial direction, and the opening or grid portion faces the photoreceptor when an image is formed, and the cylindrical wall faces the photoreceptor when an image is not formed. A corona discharger characterized in that the corona discharger is configured to be rotatable so as to face the charge wire and shield between the charge wire and the photoreceptor. (2) The corona discharger according to claim 1, further comprising a cleaning member disposed between the shield case and the cylindrical body to clean the outer surface of the cylindrical body as the cylindrical body rotates.