JPH10274873A - Electrifying method of image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a grid potential to approach a cut-off potential, in a state where the voltage of a discharge wire is suppressed low, to reduce the generation of ozone as well and to attain a long life scrotron electrifier. SOLUTION: In the shapes of the opening parts of a grid electrode 3, it is divided into two or more regions 3A and 3B in the moving direction of a photoreceptor, so that the ratios of the grid opening parts of each region are set to make the grid opening parts gradually dense as it goes to the downstream side from the upstream side in the moving direction of the photoreceptor, or division into regions is not attained deliberately, but the ratio of opening areas is set so that it is changed from sparseness to denseness, as it goes to the downstream side from the upstream side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method for an image forming apparatus in which a scorotron charger is provided with a grid electrode, that is, a so-called scorotron charger for charging the surface of a photoreceptor, and more particularly to a grid electrode shape of the scorotron charger. The present invention relates to a charging method in which the shape of the opening is changed to improve the charging ability of the photosensitive member.

[0002]

2. Description of the Related Art Conventionally, there are a contact type and a non-contact type as a charging method for applying a charge to a photoreceptor. The contact type charging method uses a shield case (casing electrode) which occupies a half space around a discharge wire. A scorotron charger having the above configuration, and a scorotron charger having a grid electrode added to an open space facing a photoreceptor of the scorotron charger are often used. The principle of the scorotron charger is
First, corona ions are generated by applying a high voltage to the discharge wires inside the shield case. The generated corona ions are charged to the photoreceptor by being carried to the photoreceptor surface by an electric field generated between the discharge wire, the control grid portion, and the photoreceptor (see JP-A-52-109 as a reference).
943 and many other documents).

Such a scorotron charger controls the corona ion flow generated from the discharge wire by the grid electrode, and controls the amount of ions reaching the photoconductor as a result. And OPC which is apt to cause dielectric breakdown due to overcharging. The grid includes a stainless steel or tungsten wire rod stretched at an interval of 1 to 3 mm or a plate rod meshed by etching into a halftone dot or multi-parallel slit shape. Is often used.

[0004]

On the other hand, in recent years, an a-Si photosensitive drum has been used in view of high durability.
The Si photoreceptor drum requires three to four times the current to charge it to the same potential as the OPC photoreceptor drum. Therefore, when the a-Si photosensitive drum is charged using a scorotron-type charger having a conventional grid in which the grid aperture ratio in the scorotron-type charger is constant over the entire surface, the grid potential and the grid shape are reduced. The charging potential of the photoconductor at the point where it passes through the charging device becomes extremely lower than the determined cut-off voltage (photoconductor surface potential at which no current flows from the charging device to the photoconductor). For this reason, when the voltage of the discharge wire becomes extremely high due to the contamination of the discharge wire due to the adhesion of the surface oxide or the like, there has been a problem that the photoconductor charging potential abnormally increases. .

Also, when the grid electrode is contaminated,
Since the current flowing into the grid electrode decreases, the current flowing into the photoconductor increases, and the charging potential of the photoconductor abnormally rises as in the case where the discharge wire is contaminated. This problem is not always a problem peculiar to the a-Si photosensitive drum, and even when the OPC photosensitive drum is used, the width of the charger, specifically, the charger in the rotating direction of the photosensitive drum is used. A similar phenomenon can occur when the width is reduced.

[0006] In order to solve such a disadvantage, it is necessary to minimize the difference between the cut-off voltage and the charging voltage by increasing the size of the charger and increasing the charging time, or increasing the voltage of the discharge wire. This makes it possible to suppress a change in the charging characteristics when the discharge wire is contaminated. Further, by making the grid pattern of the grid electrode finer and reducing the area of the opening portion of the grid electrode, it is possible to suppress a change in charging characteristics when the grid is contaminated. Therefore, it is only necessary to design so as to make these factors compatible.However, making the grid pattern finer and making the area of the opening relatively small means simultaneously reducing the ratio of the current flowing into the photoconductor. It itself becomes a factor that widens the difference between the cutoff voltage and the charging voltage. Therefore, when the ratio of the opening portions of the grid is reduced, it is necessary to further increase the size of the charger and prolong the charging time. However, increasing the size of the charger is extremely difficult in practice because the space available as the charger around the photoreceptor is limited. Further, when the voltage of the discharge wire is increased, there is a problem that the amount of ozone generated increases and the load on the power supply increases.

SUMMARY OF THE INVENTION In view of the above technical problems, an object of the present invention is to provide a charging method in which the opening capability of a grid electrode of a scorotron charger is changed to improve the charging ability of a photoreceptor. It is another object of the present invention to provide a charging method for an image forming apparatus suitable for charging an a-Si photosensitive drum while achieving downsizing and high speed.

[0008]

In order to solve the above-mentioned problems, in the invention according to the first aspect, a grid electrode of a scorotron charger and a photoreceptor are arranged facing each other at a predetermined interval, and the photoreceptor is charged. In the charging method of the image forming apparatus for charging the photosensitive member while moving from the upstream side to the downstream side, the shape of the opening of the grid electrode is divided into two or more regions with respect to the photosensitive member moving direction, The ratio of the opening area of each region is set from sparse to dense from the upstream side to the downstream side of the grid electrode with respect to the photoconductor moving direction. The invention according to claim 2 is characterized in that the ratio of the opening area of the grid electrode opening is set to gradually change from sparse to dense from the upstream side to the downstream side with respect to the photoconductor moving direction. Features. The invention according to claim 3 is characterized in that a photoconductor suitable for using the charging method is specified, and the photoconductor is an a-Si photoconductor. In any of the above inventions, it is natural that the distance between the photoconductor and the grid electrode must be maintained at a predetermined distance.

According to this invention, the shape of the opening portion of the grid electrode is divided into two or more regions in the moving direction of the photoconductor, and the area is changed from the upstream side to the downstream side in the moving direction of the photoconductor. By gradually setting the ratio of the grid opening in each region from sparse to dense, or by changing the ratio of the opening area from sparse to dense from the upstream side to the downstream side without intentionally dividing the region. By setting, even when the charger is downsized and the charging time is shortened, it is possible to suppress the rise of the charging potential at the time of contamination as compared with the conventional charger.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. It's just

FIG. 4 is a schematic configuration diagram of an experimental apparatus for explaining an embodiment of the present invention. In FIG. 1, reference numeral 100 denotes a scorotron type charger, and a shield case 2 (occupying a half space around a discharge wire 1). The grid electrode 3 is provided on the side of the open space of the casing electrode facing the photosensitive drum (substituted by the aluminum tube 103). High-voltage power supply 101 is discharge wire 1
And is set so that a constant current of 400 μA flows in the direction of the arrow in the figure. The high-voltage power supply 102 is connected to the Al tube 103 via an ammeter 105, and controls the potential of the Al tube 103. Reference numeral 104 denotes a Zener diode as a constant voltage circuit, which is connected to the shield case 2 and its value is set to 400V. With such an experimental apparatus, the performance of the scorotron-type charger can be evaluated by measuring, with the ammeter 105, the current flowing into the Al tube 103 when the voltage of the high-voltage power supply 102 is changed. With this experimental method, the dependence of the current flowing into the aluminum pipe on the aluminum pipe potential was examined for grids of three types of patterns and when they were contaminated. The experimental results are shown below.

FIG. 5 shows the pattern shapes of three types of grid electrodes on which experiments were performed. Experimental Example No. 1 is 60 ° with respect to the horizontal at 0.8 mm pitch intervals so as to leave a fine line of 0.1 mm width on a 0.1 mmt stainless steel plate.
Etching is performed so as to intersect the right and left at an inclination angle of? To form a rhombic mesh network grid. Experimental Example No.
2 is 6 mm apart from the horizontal at a pitch of 0.8 mm on a 0.1 mmt stainless steel plate so as to leave a thin line of 0.1 mm width.
Etching is performed at a right inclination angle of 0 ° to form a one-sided slit grid. Experimental Example No. 3 is 60 ° with respect to the horizontal at 1.7 mm pitch intervals so as to leave a thin line of 0.1 mm width on a 0.1 mmt stainless steel plate.
To form a slit-shaped grid inclined to one side.

FIG. 6 is a diagram showing the case of No. 3 in FIG. Using 1 to 3 pattern electrodes, control grid potential to 400V, and high voltage power supply 10
The current flowing into the Al tube 103 when the potential of the Al tube 103 is changed by changing the voltage of
Some are measured by: According to this result, No. 1 → No.
2 → No. The current flowing into the aluminum tube 103 increases in the order of 3, and as a result, the larger the area of the opening of the grid pattern is, the larger the current flows into the photoconductor, but the cutoff potential (the potential of the photoconductor at which no current flows into the photoconductor) ,
That is, there is a large difference between the grid potential (400 V) and the point at which the line in the graph of FIG. 6 intersects with the zero point on the horizontal axis, and the current flows into the photoconductor until the potential becomes considerably higher than the grid potential (400 V). is there. On the other hand, when the area of the opening portion of the grid pattern is reduced, the current flowing into the photoconductor is small, but the difference between the cutoff potential and the grid potential is small. Experiments have shown that this cut-off potential does not change even if the voltage of the discharge wire is increased.

From these facts, when the grid pattern is coarse, the current flowing into the photoreceptor is large.
Even if the grid potential is relatively low, the photoconductor can be charged to a predetermined potential. However, since the cut-off voltage is higher than that, the discharge wire may be contaminated, and if the voltage on the surface of the discharge wire rises, the photoconductor may be charged to a considerably high potential. On the other hand, as compared with the case where the grid pattern is coarse, the cutoff voltage itself is lower,
Since the current flowing into the photoreceptor itself is small, it cannot be charged to a predetermined potential unless the grid potential is set high. As a result, the difference between the cut-off voltage and the charging potential is not so large as when the pattern is coarse, but becomes large, causing an increase in the charging potential.

Next, experimental results when the grid is contaminated will be described. FIG. 1 {Fig. 7 (a)} and N
o. 2 {FIG. 7 (b)} A graph showing the relationship between the potential of the aluminum pipe and the current flowing into the aluminum pipe for the grids (solid line) and the grids not polluted (dashed line) for each of the grids. FIG. As can be understood from FIG. 7, when a contaminated grid electrode is used, the current flowing into the photoconductor and the cutoff voltage increase in either pattern grid. As a result, it can be inferred that the charging potential increases, but it can also be understood that the change in the charging characteristics and the increase in the cut-off voltage are smaller when the aperture ratio of the grid is smaller.

FIG. 8 is a schematic diagram showing the state of the surface potential when the photosensitive member actually passes through the charger. FIG. 8A is an operation diagram showing a state in which the photoconductor 10 passes through the scorotron charger 100, and FIG. 8B is a pattern grid (No. 1, No. 2, and No. 3) shown in FIG. FIG. 7 is a conceptual diagram of a change in surface potential when charged by a charger using the method (1).
The solid line is No. 1; 2, the broken line is No. 3
In the case where the pattern grid of No. 3 is used, the bold two-dot chain line increases the opening ratio of the upstream portion of the pattern grid (No. 3 pattern grid), and decreases the opening ratio of the downstream side (No. 3). 1 pattern grid). In such a configuration, the grid pattern is coarse on the upstream side. The charging rises in the same manner as the grid of No. 3, but the aperture ratio of the grid on the downstream side is small and the potential itself is already high. Charging will be much slower than charging with one grid.

In the grid pattern shown in FIG. No. 1 and No. 1 having a large aperture ratio. FIG. 9A shows the charging status on the upstream side (charging device entrance side A) and downstream (charging device exit side B) side of the charging area when each of the three devices is charged by the device configuration of FIG. In FIG. 3B, a solid line indicates a state where the discharge wire is not contaminated, and a broken line indicates a state where the discharge wire is contaminated. As is clear from these figures,
If the discharge wire is contaminated, the charging speed will increase,
In both cases (a) and (b), the grid is charged to a potential near the cutoff voltage of each grid. The opening ratio of the grid is large. In the case of No. 3, (a), since the grid cutoff voltage is considerably higher than the charging potential immediately after entering the charger at the charger inlet side A, the potential rise when the discharge wire is contaminated is inevitably large. . In addition, in the case of the grid having a small aperture ratio, In the case of No. 1, the opening ratio of the grid is large. Even when the grid potential is the same value as in the case of No. 3, the charging potential at the point passing through the charger outlet side B decreases. Also in this case, similarly to the case where the pattern is coarse, the difference between the charging potential and the blocking potential when not contaminated is large, and the charging potential increases when the discharge wire is contaminated. Regardless of the grid of any pattern, the charging potential increases due to the contamination of the discharge wire. Further, when the grid is contaminated, the cut-off voltage itself increases, so that the charging potential increases further.
The finer the grid pattern, the smaller the rise in the cutoff voltage.

An embodiment for solving the increase in the charging potential when the grid electrode of the charger is contaminated will be described with reference to FIG. FIG. 1 is a configuration diagram of a main portion of a charging portion of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a high-voltage power supply connected to a discharge wire 1, which is fixed in a direction indicated by an arrow in FIG. Set to flow current. The several kV is applied to the discharge wire 1 by applying the high voltage power supply 11.
And generate discharge ions. Reference numerals 2 and 3 denote a shield case and a grid electrode, respectively, which are connected to a zener diode 104 as a constant voltage circuit. The photosensitive drum 10 is grounded. With such a configuration, an electric field generated between the discharge wire 1, the shield case 2, the grid electrode 3, and the photoconductor drum 10 causes charges to be transferred onto the photoconductor 10, thereby charging the photoconductor.

FIG. 2 is an enlarged view of a main part of the charger portion of FIG.
As is clear from this figure, the grid pattern of the grid electrode 3A on the upstream side in the grid electrode is roughened (N
o. 3), and the grid pattern of the grid electrode 3B on the downstream side is made finer (the one of No. 1 is used).
Accordingly, it is possible to suppress a rise in the potential of the charger when the inside of the charger including the grid electrode 3 is contaminated. That is, as described in more detail, the finer the grid pattern, the smaller the cutoff voltage and the rise in the cutoff voltage when the grid is contaminated. This characteristic is a characteristic of the grid that is required on the downstream side of the charger after the potential has increased to some extent in the process of the photoconductor 10 passing through the charger.
On the upstream side of the charger where the charging potential of the photoconductor is low, it is important that the charging speed is high and the potential rises quickly to a certain potential. Therefore, by making the grid pattern on the upstream side coarse and the grid pattern on the downstream side fine, it is possible to quickly charge the photoconductor to a certain extent, and then to control the photoconductor so that an unnecessary current does not flow to the photoconductor. is there. Note that FIG. 1 and No.
2 shows the relationship between the Al tube potential and the current flowing into the Al tube for each of the two grids and the grid shown in FIG. Therefore, by adopting the configuration of the control grid as in the present embodiment, the contamination of the charger progresses, and even when the surface potential is considerably increased only in the upstream portion of the charger, the current flows in the direction of the photoconductor downstream. Since the current does not flow and the grid and the shield case all draw current, there is an effect that the surface potential rise can be suppressed to be lower than in the case where the grid is all uniform.

In the grid structure, as shown in FIG. 3, the diameter of the circular opening 30 is gradually reduced so that the ratio of the opening area of the grit opening to the upstream side with respect to the rotation direction of the photosensitive drum 10 is adjusted. The same effect can be obtained even when it is set to gradually change from sparse to dense from downstream to downstream.

[0021]

As described above, according to the present invention, since the grid potential and the cut-off potential can be brought close to each other while keeping the voltage of the discharge wire low, the generation of ozone is reduced.
In addition, a long-life charger is realized. In particular, it is possible to obtain a charging method suitable for charging the a-Si photosensitive drum while achieving high speed.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of a charged portion of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of a charger section of FIG. 1 and corresponds to the invention described in claim 1;

FIG. 2 is an enlarged view of a main part of a charger portion shown in FIG. 1 and corresponds to the invention described in claim 2;

FIG. 4 is a schematic configuration diagram of an experimental apparatus for explaining an embodiment of the present invention.

FIG. 5 shows three types of grid electrode pattern shapes that were tested with the apparatus of FIG.

FIG. Using 1 to 3 pattern electrodes, A
It is the graph figure which measured the inflow electric current of the aluminum pipe when changing the electric potential of the 1 pipe.

FIG. 1 (A) and No. 1 2 (B)
7 is a graph showing the relationship between the potential of the aluminum pipe and the current flowing into the aluminum pipe for the grids (solid line) and the grids not polluted (broken line) for each of the grids of FIG.

FIG. 1 (A) and No. 1 2 (B)
Grid when each grid is contaminated (solid line)
FIG. 4 is a graph showing the relationship between the potential of the aluminum shell and the current flowing into the aluminum shell for the grid which is not contaminated.

FIG. 9 is a graph showing a change in charging in a charging device area as a photoconductor surface potential when a discharge wire is contaminated.

FIG. 1 and No. 2 grid and the grid shown in FIG.
It is a graph which shows the relationship with the inflow current of a base tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge wire 2 Shield case 3 Grid electrode 3A Upstream grid electrode 3B Downstream grid electrode 10 Photoconductor drum 11 High voltage power supply 104 Zener diode

Claims (3)

[Claims] 1. An image forming apparatus in which a grid electrode of a scorotron charger and a photoconductor are arranged facing each other at a predetermined interval, and the photoconductor is charged while moving the photoconductor from an upstream side to a downstream side of the charger. In the charging method of the device, the shape of the opening of the grid electrode is divided into two or more regions with respect to the photoconductor moving direction, and each of the openings is divided from the grid electrode upstream to the downstream with respect to the photoconductor moving direction. A charging method for an image forming apparatus, wherein the ratio of the opening area of the region is set from sparse to dense. 2. An image forming apparatus, comprising: a grid electrode of a scorotron charger and a photoreceptor facing each other at a predetermined interval; and charging the photoreceptor while moving the photoreceptor from an upstream side to a downstream side of the charger. In the charging method of the apparatus, the ratio of the opening area of the grit electrode opening is set to gradually change from sparse to dense from the upstream side to the downstream side with respect to the photoconductor moving direction. Charging method for an image forming apparatus. 3. The charging method according to claim 1, wherein the photoconductor is an a-Si photoconductor.