JPH10186805A - Electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly electrify a body to be electrified and to keep this function extending over a long term by effectively eliminating a foreign matter attached to an electrifying electrode or the body to be electrified when the body to be electrified is electrified by executing continuous electric discharge in a very small gap between the electrifying electrode and the body to be electrified. SOLUTION: The electrifying electrode 1 is the electrical conductive cylindrical body and provided with a spiral projection part 2 at the circumferential surface. The projection part 2 is made to abut on a photoreceptor drum 10 being the body to be electrified and both of them are driven to be rotated at different peripheral speed. Then, the gap corresponding to the height of the projection part 2 is formed between the electrode 1 and the drum 10. By executing the electric discharge in the gap, the drum 10 is uniformly electrified and the foreign matter is prevented from being attached. Since the contact position of the projection part 2 is moved by the difference of the peripheral speed, electrifying irregularity is prevented from occurring and the foreign matter is carried in an axial direction and eliminated by the projection part 2. Then, the foreign matter attached to the electrode 1 is scraped by a cleaning member 7 so as to be prevented from being fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an image forming apparatus such as a copying machine or a printer to which an electrophotographic technique is applied, and uniformly charges an object to be charged such as a photosensitive drum prior to image exposure. It is about.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer to which an electrophotographic process is applied, a charge acceptor (charged body) such as a photosensitive drum is charged by a charging device and then subjected to image exposure to thereby achieve static electricity. An electro-latent image is formed and visualized by attaching toner to it. Then, a process of transferring and fixing the toner image on recording paper or the like is performed. Conventionally, as a charging device used in such an image forming apparatus, a non-contact charging system using corona discharge or the like and a contact charging system that generates a continuous discharge in a minute gap using a charging roll or the like have been conventionally used. Are known.

[0003] The non-contact charging method using corona discharge is as follows.
A wire is stretched in the shield case so as to be close to or separated from the surface of the member to be charged, and a high voltage is applied to the wire to cause corona discharge to give a predetermined charge to the surface of the member to be charged. Things. Although such a charging method is excellent in uniform charging, since a large amount of discharge products such as ozone are generated, which causes deterioration of the device, it is necessary to treat the device, and the device becomes large. It is easy to cause cost increase and cost increase.

For this reason, recently, a contact charging system in which a charging member is brought into direct contact with a member to be charged to perform charging has been studied. In the contact charging method, a direct current or a superimposed voltage of a direct current and an alternating current is applied to a rubber roll, a brush, or the like that is brought into contact with a member to be charged to cause a discharge in a minute space near the contact portion to charge the member to be charged. Things. In this method, in addition to the advantage that the amount of generated ozone is small, there is an advantage that the device can be reduced in size and weight because the small charging member is arranged so as to be in contact with the member to be charged. .

On the other hand, in such a contact-type charging device, since the charging member such as a rubber roll is constantly in contact with the member to be charged, the toner or its additive remaining on the member to be charged is left. Alternatively, the surface of the charging member is contaminated with foreign matter such as paper powder, and abnormal discharge or unstable discharge occurs, thereby deteriorating the charging uniformity of the charged member. As a technique for improving such a defect, for example, there are techniques described in JP-A-2-272589 and JP-A-3-240076. The technique described in Japanese Patent Application Laid-Open No. 2-272589 discloses a technique in which a cylindrical charging member is brought into contact with a member to be charged, and a cleaning member is rubbed against the surface of the charging member to sweep foreign substances and the like adhered to the charging member. It is intended to be taken. In the technique described in Japanese Patent Application Laid-Open No. HEI 3-240076, spacer members are attached to both ends of a cylindrical charging member, and the charging member is arranged close to the member to be charged to prevent the adhesion of the foreign matter. Is what you do.

[0006]

However, the devices of the above-mentioned technologies proposed to solve the problem of contamination of the surface of the charging member, which is a defect of the contact charging system, have the following problems. At present, it is not a sufficient solution.

In the apparatus proposed in Japanese Patent Application Laid-Open No. 2-272589, a cleaning member such as a cleaning roller or a cleaning pad is simply pressed against a charging roller serving as a charging member and rubbed against the foreign matter. Therefore, foreign substances generated by repeatedly rubbing the surface of the charging roller adhere to the surface of the charging roller and clogging of the cleaning member occurs. For this reason, maintenance is complicated, and it is difficult to maintain the charged object uniformly over a long period of time.

In the device proposed in the above-mentioned Japanese Patent Application Laid-Open No. 3-240076, a discharge is generated in a minute gap in the same manner as in the contact charging system, but a space provided at both ends of the charging member is provided. Since the charging member and the member to be charged do not come into contact with each other and the minute gap is set by the surging member, there is a possibility that foreign substances and contaminants on the member to be charged hardly adhere to the charging member. However, the set gap is 0.3 mm (30 mm).
0 μm) or less, which makes it impossible to manufacture a charging roller as a charging member into a perfect cylinder, and there is a limit to the precision of the components of the spacer member. It is extremely difficult to maintain a uniform gap over the entire area, and it is difficult to obtain expected effects.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a charging device that uses a continuous discharge in a minute gap, wherein the charging device adheres to a charging member or a member to be charged. It is an object of the present invention to provide a charging device capable of uniformly removing a foreign substance, thereby uniformly charging an object to be charged, and maintaining this function for a long period of time.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 has a charging electrode disposed so as to face a member to be charged whose surface moves. A charging device that performs charging by generating a continuous discharge in a minute gap formed between the electrode and the member to be charged,
Provided is a charging device, wherein the charging electrode has, on a surface thereof, a convex portion which is in contact with the object to be charged, and the surface of the charging electrode is driven to move relatively to the surface of the object to be charged. .

In the charging device as described above, a projection is provided on the surface of the charging electrode, and the projection is brought into contact with the object by pressing the charging electrode against the object. It faces the member to be charged with a gap. Therefore, by setting the height of the convex portion to correspond to a minute gap suitable for generating a sustained discharge, a discharge can be generated in the gap and the surface of the member to be charged can be charged.

The above-mentioned gap is formed when the surface of the charged body has some irregularities, when the charged body has a cylindrical curved surface and there is some eccentricity during rotation, or when the shape is distorted. Even if there is, it is maintained substantially constant corresponding to the height of the convex portion. In other words, the deformation of the charging electrode caused by pressing the charging electrode against the member to be charged allows the surface of the member to be charged to follow the state of the surface of the member to be charged. Is governed by the height of the protrusions,
It is almost always constant.

Further, since the charging electrode is driven so that its surface moves relatively to the surface of the member to be charged, the contact position of the projection on the surface of the member to be charged always moves.
Although the surface of the member to be charged cannot be charged at the position where the convex portion is in contact, it is possible to charge substantially uniformly by constantly moving this position.

On the other hand, in the charging device according to the present invention, the charging electrode and the member to be charged face each other in close proximity by the convex portion provided on the surface of the charging electrode.
Compared with a contact charging type charging device in which both are completely in contact with each other, the amount of foreign substances and the like adhering to the charging electrode is significantly reduced.

Further, even if foreign substances (for example, toner, paper powder, etc.) on the charged body adhere to the charged electrode, the surface of the charged electrode is relatively moved with respect to the surface of the charged body. Therefore, the foreign matter does not stay in one place, and even if the charge is in a defective state in this portion, the surface of the charged body is charged almost uniformly.

In the charging device according to the second aspect, the charging electrode is a substantially cylindrical member, and a spiral convex portion is formed on the outer peripheral surface. Therefore, when the peripheral surface of the charged electrode is rotated around the axis while being in contact with the member to be charged, the foreign matter on the member to be charged is conveyed in the axial direction of the charging electrode by the above-mentioned convex portion and discharged out of the charged area. Is done. Therefore, substantially uniform charging can be performed over a long period of time without causing poor charging or the like.

Further, in the charging device according to the third aspect, the convex portion formed on the outer peripheral surface of the charging electrode is fixed by winding a thread-like or narrow band-like member. With such a configuration, it is possible to easily form a projection having a minute width and a minute height with high accuracy.

Further, as in the charging device according to the fourth aspect, by providing a cleaning member that is in contact with the outer peripheral surface of the cylindrical charging electrode, foreign substances and the like attached to the charging electrode are wiped off. . Therefore, poor charging due to the adhesion of foreign matter and the like is prevented, and uniform charging can be performed over a long period of time.

According to a fifth aspect of the present invention, there is provided a charging device having a charging electrode arranged so as to face a member to be charged, the surface of which moves, and a minute gap formed between the charging electrode and the member to be charged. A charging device that generates a continuous discharge to perform charging, wherein the charging electrode is in contact with the surface of the member to be charged via a thread-like or strip-like spacer.
The spacer is provided so as to move relatively to the surface of the member to be charged. As the charging electrode used in this charging device, a cylindrical member, an elongated plate-shaped member, or the like can be appropriately used.

In the charging device having such a configuration, a minute gap is formed between the charging electrode and the member to be charged by the spacer, and the surface of the member to be charged is charged by the continuous discharge generated here. . Further, the gap is maintained substantially constant by the deformation of the charging electrode following the unevenness and runout of the surface of the member to be charged, and substantially uniform charging becomes possible. Furthermore, the presence of a gap between the charging electrode and the member to be charged can prevent the attachment of foreign objects and the like. Foreign substances can be discharged out of the charged area while preventing the occurrence of charging.

In the charging device according to the sixth aspect, the spacer is a plurality of thread-like or narrow band-like members provided so as to bridge between two substantially parallel tension members, and But,
For example, in the case of a cylindrical or non-born belt that is driven to rotate, the circumferential surface can be charged substantially uniformly by moving the stretching member in a direction substantially perpendicular to the rotating direction.

Further, by providing a cleaning member which comes into contact with the spacer as in the charging device according to the present invention, foreign substances such as toner adhered to the spacer can be wiped, and the charging by the foreign substance can be performed. Defects can be prevented.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view showing a charging device according to an embodiment of the present invention described in claim 1, claim 2, claim 3, or claim 4. This charging device charges a rotating photosensitive drum 10 (charged member) substantially uniformly, and includes a cylindrical charging electrode 1 that is in contact with the peripheral surface of the photosensitive drum 10. ing. The charging electrode 1 has a convex portion 2 formed by spirally winding a thread made of a synthetic resin on the outer peripheral surface of a cylindrical member, and is arranged such that the axis is parallel to the photosensitive drum 10. The photosensitive drum 10 is pressed against the outer peripheral surface of the photosensitive drum 10 with a predetermined load by springs 4 attached to both ends of the rotating shaft 3. The outer peripheral surface of the photosensitive drum 10 is
Only the protrusions 2 formed by the spirally wound yarns are in contact with each other, and a minute gap for generating a continuous discharge is formed between the peripheral surface of the charging electrode 1 and the peripheral surface of the photosensitive drum 10. It is formed. A rotating driving force in the direction of the arrow shown in FIG. 1 is transmitted from a motor 6 to a rotating shaft 3 of the charging electrode 1 via a driving force transmitting device such as a gear 5. The peripheral surface is driven at a different speed at a position facing the drum 10. The driving means of the charging electrode 1 is not limited to the motor 6 described above,
For example, a configuration may be adopted in which a gear engaged with the driving unit of the photoconductor drum 10 is provided, and driving is performed via the gear.

A power supply (not shown) is provided to the charging electrode 1.
For example, a voltage of about -1.0 to 1.5 kV is applied, and a discharge is generated in a minute gap between the cylindrical charging electrode 1 and the photoreceptor drum 10 which is a member to be charged. The peripheral surface of the photosensitive drum 10 is uniformly charged. The voltage applied between the charging electrode 1 and the photosensitive drum 10, that is, the charging voltage is a DC voltage or a DC superimposed AC voltage obtained by superimposing a DC on an AC voltage twice or more of the charging start voltage. can do. However, it is desirable to use a DC voltage because a DC superimposed AC voltage increases the surface energy of the photoconductor drum 10 and the charging electrode 1 and further adversely affects the photoconductor layer.

The photosensitive drum 10 of the charging electrode 1
A cleaning member 7 that comes into contact with the peripheral surface of the charging electrode 1 is provided behind a position facing the charging electrode 1. This cleaning member 7
A brush 9 made of acrylic fiber is implanted in a metal holder 8. The brush 9 is supported so as to be in contact with the surface of the cylindrical charging electrode 1. In accordance with this, the surface is rubbed to wipe off foreign substances adhering to the charging electrode 1. The cleaning member 7
Various materials such as nylon, rayon, polyester and the like can be used as the material of the brush 9 in addition to the above acrylic fiber.

Various materials having semi-conductivity can be used as the material of the charging electrode 1. For example, polyester, polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, Polyimide, PEN, PEK, PES,
Resins such as PPS, PFA, PVdF, ETFE, CITE, or silicone rubber, EPDM, urethane rubber,
Ethylene propylene rubber, butyl rubber, acrylic rubber,
Synthetic rubber such as nitrile rubber mixed with conductive powder such as carbon black, metal powder and metal oxide can be used. Further, a conductive filler such as carbon black, metal powder, or metal oxide is added to a polymer binder such as acryl or epoxy on the surface of the cylindrical body molded from the above synthetic resin or synthetic rubber material. A film in which resistance is adjusted, for example, titanium oxide or impurity-added a-Si on the peripheral surface of a thin-walled hollow pipe made of metal, resin, etc. It is also possible to use a member formed with the above, and a member having a thin hollow pipe itself having conductivity.

The diameter of the cylindrical charging electrode 1 is not particularly limited, but is preferably about 8 to 20 mm when applied to a small and medium-sized image forming apparatus.

Further, in manufacturing the charging electrode 1,
It is necessary to adjust the mixing amount of the conductive powder so that the volume resistivity becomes a preferable value.
^If it is less than ² Ω · cm, spark discharge is likely to occur and 10 ¹¹ Ω · cm
cm or more, dot-shaped charging failure is likely to occur.
It is desirable to adjust so as to be in the range of 10 ³ Ω · cm to 10 ¹⁰ Ω · cm. In particular, from 10 ³ Ω · cm to 10
^In the range of ⁶ Ω · cm, the charging voltage applied to the charging electrode 1 can be set relatively low, and the process speed is 150 mm / sec. When used in the above-described high-speed machine, it is most preferable because voltage fluctuation can be suppressed to be small.

As the material of the convex portion 2, a material having relatively high strength, abrasion resistance and an insulating property of 10 ⁹ Ω · cm or more can be used. For example, nylon, polyester, rayon And the like are preferably used.
In the charging device of the present embodiment, both ends are adhered and fixed after the yarn serving as the convex portion 2 is spirally wound around the cylindrical charging electrode, but the fixing method is not limited to this. Instead, for example, a method of bonding over the entire length of the yarn can be adopted.

In the charging device having the above-described structure, a gap corresponding to the height of the convex portion 2 is formed between the charging electrode 1 and the photosensitive drum 10, and a continuous discharge occurs in the gap. Then, the surface of the photosensitive drum 10 is charged. At this time,
Since the size of the gap is uniformly maintained by the convex portion 2 abutting on the photosensitive drum 10, the charging potential becomes substantially uniform. Further, since the charging electrode 1 and the photosensitive drum 10 are driven to rotate at different peripheral speeds, the position where the convex portion 2 formed in a spiral shape on the peripheral surface of the charging electrode 1 comes into contact with the photosensitive drum 10 is The toner moves in the axial direction, and the toner remaining on the photoconductor drum with this is transported in the axial direction as shown in FIG. Then, the sheet is discharged out of the image forming area. Further, even at the position where the cleaning member 7 is in contact with the charging electrode 1, the toner applied to the brush 9 is similarly swept out of the image forming area, and the fixation to the charging electrode 1 or the photosensitive drum 10 is prevented. .

Next, an experiment performed to confirm the charging ability of the charging device will be described. <Experiment 1> This experiment was performed to confirm the state of the minute gaps in the charging device and the charging ability of the device, and was performed using an apparatus as shown in FIG. In addition,
In order to compare the effects of the above-described charging device, a similar experiment using a conventional contact charging type charging device was also performed. In this experiment, the charging device 21 of the above embodiment was used.
Is supported so as to face the surface potential measuring drum 25 as shown in FIG. Surface potential measurement drum 25
Is formed by forming a dielectric layer made of polycarbonate having a thickness of 20 microns on a metal drum having a diameter of 30 mm.
It is rotationally driven by a driving device (not shown). Further, a rotational driving force is transmitted from a motor 24 to a charging electrode 22 of the charging device 21 via a gear 23, and the charging electrode 22 is rotated at a peripheral speed different from that of the surface potential measuring drum 25. Then, a charging voltage is applied between the charging electrode 22 and the surface potential measuring drum 25 between the charging electrode 22 and the surface potential measuring drum 25.
Is discharged in the gap with the outer peripheral surface of the substrate 25, and the dielectric layer of the surface potential measuring drum 25 is charged. When charging is performed in this manner, the charging electrode 22 and the surface potential measuring drum 2 are charged.
The rotation with 5 is stopped. The peripheral surface of the surface potential measuring drum 25 is scanned in the axial direction by the detector 28 of the surface potential meter 27, and the potential distribution on the surface of the surface potential measuring drum 25 is detected and recorded on the recorder 29.

First, as a comparative example, an experiment was conducted on a case where a conventional charging device having no projection on the surface of the charging electrode was directly in contact with the surface potential measuring drum 25. The charging electrode of the charging device of this comparative example is E
A charging roll of a type obtained by coating a conductive material obtained by adding carbon black to an acrylic binder onto the surface of a rubber roll made conductive by adding carbon black to PDM rubber. Used. Then, the surface potential measuring drum 25 is rotated at a peripheral speed of 100 mm / sec. The peripheral speed of the charged electrode is 90 mm / sec. Rotate with power 2
A voltage of -1 kV was applied from 6 to perform charging. Thereafter, each rotation was stopped, and the surface potential distribution in the axial direction of the surface potential measurement drum 25 was measured while scanning the detector 28 of the surface potential meter 27. At this time, the pressing load of the charging electrode is 0, that is, the case where the charging electrode is brought into contact only by its own weight, and the pressing load is 500 g, 10 g.
An experiment was conducted depending on the case where the weight was set to 00 g.

FIG. 4 shows the measured surface potential distribution of the drum 25 in the axial direction. As shown in this figure, when the pressing load is small, the charging potential is low at the central portion in the axial direction, and the uniformity of charging is deteriorated. And, as the pressing load is increased, the charging uniformity is improved.
This is considered to be due to the outer diameter accuracy of the charging electrode. In other words, in the charged electrode used in this experiment, as shown in FIG. 5, due to an error in manufacturing, the central part has a shape closer to a drum shape than the both ends, and the central part is the surface to be charged. It is considered that it is floating from the potential measurement drum 25. That is, as shown by the generally known Paschen's equation, the firing voltage is a function of the gap distance, and as shown in FIG. 6, the larger the gap, the higher the firing voltage. For example, the discharge start voltage when the charging electrode is in contact is about -600 V, and the discharge start voltage when the gap is 0.1 mm is about -1000 V. Therefore, when discharging is performed at the same applied voltage, the potential of the surface potential measuring drum 25 becomes lower at the center of the drum. From the above results, in this comparative example, by increasing the pressing load and elastically deforming the charging electrode so that the entire surface is in contact, the discharge starting voltage at the center thereof is reduced by −60.
It is possible to approach 0 V to make the charging in the axial direction uniform, but on the other hand, foreign substances on the charged body are easily pressed and fixed to the surface of the charged electrode, thereby increasing the possibility of image deterioration. Have the problem of

Next, a similar experiment was performed using the charging device shown in FIG. This charging device 21 has the same charging roll as that of the comparative example as the charging electrode 22, and has a diameter of 0.1 mm.
Is wound at a pitch of 10 mm, and both ends are adhesively fixed to the roll surface, and this is used as a projection on the charging roll surface. As in the case of the comparative example, the surface potential measuring drum 25 was rotated at a peripheral speed of 100 mm / sec. ,
When the charging electrode 22 is 90 mm / sec. While rotating with
A voltage of -1 kV was applied from the power supply 26 between the charging electrode 22 and the surface potential measuring drum 25, and after charging, the surface potential distribution was measured. At this time, the charging electrode 2
As in the case of the comparative example, the experiment was carried out by changing the pressing load to 2, 0 (only the own weight of the charging device), 500, and 1000 g.

FIG. 7 shows an axial surface potential distribution of the surface potential measuring drum 25 measured in the above experiment.
As shown in this figure, when the pressing load is small, the uniformity of charging is poor, and as the load is increased, the uniformity of charging becomes better. This tendency is the same as that of the comparative example. However, even when the load is relatively large, the discharge starting voltage is as high as -900 V, and the applied voltage is -1.
At 0 kV, the charging potential of the drum 25 has risen only to about -100V. On the other hand, even when the pressing load is increased and the charging uniformity is improved, the fineness of about 0.1 mm is set between the charging roll as the charging electrode and the drum 25 as the charged body. This indicates that the appropriate gap is uniformly held in the axial direction. Note that the charging potential was -400 V as in the case where the charging electrode of the comparative example was in contact with the entire surface.
In this case, a voltage of about -1.3 kV is applied from the power supply 26. From the above, in the charging device of the embodiment shown in FIG. 1, uniform minute gaps can be formed in the axial direction between the charging electrode 1 and the photosensitive drum 10 which is the member to be charged. To prevent foreign matter from adhering to
It was confirmed that the member to be charged can be uniformly charged.

<Experiment 2> Next, an experiment for forming an image on the image forming apparatus 30 as shown in FIG. 8 using the charging device shown in FIG. 1 and evaluating the image quality will be described. In this image forming apparatus, a charging device 21 is provided so as to face a photosensitive drum 31 which is a member to be charged, and a charging voltage is applied from a power supply 38 to a roll-shaped charging electrode 1 to rotate the charging electrode 1. The outer peripheral surface of the driven photosensitive drum 31 is charged. On the outer peripheral surface of the charged photosensitive drum 31,
The exposure device 32 irradiates image light to form an electrostatic latent image. The toner is selectively transferred from the developing device 33 to this electrostatic latent image, and a visible image is formed. The toner image is transferred to a paper tray 35 at a position where the transfer device 34 is provided.
Is transferred onto the paper supplied from the fixing device 36.
To form a fixed image on the sheet. After the transfer device 34 transfers the toner image, the photosensitive drum 3
The toner remaining on the photosensitive drum 1 is removed by the cleaning device 39, and the photosensitive drum 31 is subjected to the next image forming process.

In this experiment, the effect of the diameter of the nylon fiber spirally wound around the charging electrode 1 of the charging device 21 and the rotation speed of the charging electrode 1 on the image quality was confirmed. The winding pitch of the nylon fiber is 10 mm, and the diameter is
Using four types of charging electrodes of 0.01, 0.03, 0.06, and 0.1 mm, an image is formed for each of them, and the image quality is evaluated. The rotation speed (peripheral speed) of the photosensitive drum 31 is kept constant at 100 mm / sec, while the rotation speed of the charging electrode 1 is 0 (stop), 100 m / sec.
m / sec (constant speed with photosensitive drum), 200 (double speed) m
m / sec. Then, each of the charging electrodes is sequentially mounted on the image forming apparatus 30, and the charging electrode 1 is charged.
After applying a voltage of about -1.1 to 1.4 kV from the power source 36 to charge the photosensitive drum 31 to -500 V, the photosensitive drum 31 is formed through the steps of image light irradiation, development, transfer, and fixing. The image quality of the image was evaluated. Table 1 shows the evaluation results.

[0038]

[Table 1]

In Table 1, when the diameter of the nylon fiber is large and thus the gap distance is large,
Is stopped or rotating at the same speed as the photosensitive drum, a vertical black line corresponding to the nylon fiber winding pitch as shown in FIG. 9 (b), or shown in FIG. 9 (c). Such oblique black lines are generated. It is considered that this is because the nylon fiber cuts off the discharge and the position on the photosensitive drum that contacts the nylon fiber does not fluctuate quickly. From the above experimental results, it can be seen that good image quality can be obtained by setting each rotation speed so that the peripheral surface of the charging electrode 1 and the peripheral surface of the photosensitive drum 31 move relatively.
Although the black line is less likely to be generated by reducing the diameter of the nylon fiber, it is not preferable to reduce the diameter too much in consideration of the image quality characteristic when copying a large number of sheets described below.

<Experiment 3> Next, the influence of the diameter of the nylon fiber wound around the charging electrode, that is, the size of the gap between the charging electrode 1 and the photosensitive drum 31 on the contamination of the image when copying a large number of sheets was investigated. An experiment was performed. In this experiment, diameters of 0.01, 0.03, 0.06, 0.
Four types of charging devices in which a 1 mm nylon fiber was wound around the charging electrode 1 were used, and the rotation speed of the charging electrode 1 was set to 100 mm / sec, which was the same speed as that of the photosensitive drum 31, and 10
0000 sheets of images were formed. In this experiment, the cleaning device 37 was removed from the image forming apparatus 30 in order to accelerate toner contamination. In addition,
In this experiment, in order to make a comparison with the above-described charging device according to the present invention, an experiment of similarly performing image formation using a charging electrode on which a nylon fiber was not wound was also performed. Table 2 shows the evaluation results of the image quality in this experiment. (Below)

[0041]

[Table 2]

In Table 2, in the conventional contact-type charging device, which was tested as a comparative example, fogging occurred on the entire surface of the paper in a short period of time, resulting in poor image quality. However, in the charging device according to the embodiment of the present invention, It can be seen that the larger the diameter of the nylon fiber, that is, the larger the gap between the charging electrode 1 and the photosensitive drum 31, the less fogging due to dirt occurs even when the number of copies increases. Also, in the image forming apparatus used in this experiment, it is found that the diameter of the nylon fiber is preferably 0.06 mm or more. In addition, the diameter of the nylon fiber is 0.03
Even if the thickness is less than mm, it is considered that the toner cannot be prevented from adhering at all, but has an effect of reducing the contact pressure between the toner and the surface of the charging electrode to prevent the toner from sticking.

<Experiment 4> Next, an experiment for confirming the effect of the cleaning member provided in contact with the charging electrode will be described. In this experiment, as shown in FIG. 10, a cleaning member 7 having a brush 9 made of acrylic fiber planted on a metal holder 8 is provided so as to be in contact with the peripheral surface of the charging electrode 1. Then, the charging device is connected to the image forming apparatus 30 described above.
And make many copies as in Experiment 3,
The output image was evaluated. Table 3 shows the evaluation results.

[0044]

[Table 3]

As is clear from the comparison between Table 3 and Table 2,
It can be seen that by providing the cleaning member 7, the effect of preventing contamination confirmed in Experiment 2 can be maintained for a longer period. This is because of the minute gap formed between the charging electrode 1 and the photosensitive drum 10 which is the member to be charged.
This is because the adhesion of the foreign matter to the surface of the charging electrode 1 is prevented, and the foreign matter attached to the surface of the charging electrode 1 is swept away by the rubbing action of the brush 9 of the cleaning member 7. Then, by the rotation of the charging electrode 1 and the rubbing of the cleaning member,
The toner and the like are conveyed in the axial direction and are swept out of the image area. Also, by using the cleaning member 7,
It can be seen that even when a charged electrode having a projection formed of a nylon fiber having a diameter of 0.03 mm or less is used, the generation of black lines is prevented and good image quality can be obtained over a long period of time.

Next, an embodiment of the invention described in claim 5, claim 6, or claim 7 will be described with reference to FIG.
The charging device includes a plate-shaped charging electrode 61 pressed against the peripheral surface of the photosensitive drum 10, and an endless belt-shaped sliding member partially inserted between the charging electrode 61 and the photosensitive drum 10. A main part is constituted by 63, a driving roller 64 and a driven roller 65 that rotatably support the sliding member 63, and a cleaning member 67 provided to be in contact with the surface of the sliding member 63.

The charging electrode 61 is a member that is long in the axial direction of the photosensitive drum 10, and a shallow groove-shaped projection on which the belt-shaped sliding member 63 is loosely fitted has a surface. It is provided in the axial direction. Then, a plurality of coil springs 6 inserted between the support members (not shown)
2 urges the surface of the photosensitive drum 10. The charging electrode 61 has such a thickness that elastic deformation easily occurs. The charging electrode 61 is pressed with substantially uniform pressure in the axial direction of the photosensitive drum 10 by the urging force of the coil spring 62. I have. The sliding member 63 is made of a film having a small coefficient of friction with a thickness of about 0.06 mm, provided with a large opening, and having continuous both ends 63a.
And a portion 63b connecting these components. The connecting portion 63b is a spacer inserted between the charging electrode 61 and the photosensitive drum 10. A driving force is transmitted from the motor 66 to the sliding member 63 via the driving roller 64, and the sliding member 63 is driven to rotate in the axial direction. The cleaning member 67 has a brush made of an acrylic fiber, and the brush wipes off toner, paper powder, and the like attached to the sliding member 63.

In such a charging device, a minute gap is formed between the charging electrode 61 and the peripheral surface of the photosensitive drum 10 by pressing the charging electrode 61 through the spacer. When a charging voltage is applied between the charging electrode 61 and the photosensitive drum 10, a continuous discharge is generated in the minute gap, and the peripheral surface of the photosensitive drum 10 is charged. At this time, since the minute gap is formed substantially uniformly in the axial direction of the photoconductor by the spacer, substantially uniform charging is performed. In addition, the spacer is moved around the photosensitive drum 10 in the axial direction together with the both end portions 63a, so that the portion in contact with the spacer is moved, thereby preventing the occurrence of uneven charging.
Further, even if the residual toner or paper dust adheres to the photosensitive drum 10, it is swept out of the image forming area by this orbital movement, and the adhesion to the charging electrode is prevented. Therefore, it is possible to prevent the occurrence of poor charging due to foreign matter such as toner. Further, the foreign matter adhering to the spacer is removed by the cleaning member 67 and is prevented from being sent again to the area facing the photosensitive drum 10.

When this charging device was mounted on the image forming apparatus 30 and images obtained by copying a large number of sheets were evaluated in the same manner as in Experiment 3, it was confirmed that good images could be formed over a long period of time. .

[0050]

As described above, the charging device according to the present invention has the following effects in addition to the features of the contact charging type charging device. A substantially uniform minute gap is formed between the charging electrode and the member to be charged, and a substantially uniform discharge is generated in the gap to uniformly charge the outer peripheral surface of the member to be charged. In addition, since the surface of the charging electrode and the surface of the charged object are driven to move relatively, a convex portion that is in contact with the charged object to form a minute gap is formed on the surface of the charged object. And the entire surface of the member to be charged is uniformly charged. Further, since a minute gap is maintained between the charging electrode and the member to be charged, the amount of foreign matter attached to the charging electrode is drastically reduced, and charging is performed by the convex portion moving on the member to be charged. It is possible to exclude the outside of the area.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a charging device according to an embodiment of the present invention described in claim 1, claim 2, claim 3, or claim 4;

FIG. 2 is a schematic diagram illustrating the operation of the charging device shown in FIG.

FIG. 3 is a schematic configuration diagram of an apparatus used in an experiment for confirming the effect of the charging device shown in FIG.

FIG. 4 is a diagram showing a surface potential distribution of an object to be charged which is charged by a conventional charging device as compared with the charging device shown in FIG. 1;

FIG. 5 is a diagram showing a distribution of a manufacturing error of external dimensions in a charging roll.

FIG. 6 is a diagram showing a relationship between a discharge starting voltage and a gap size.

FIG. 7 is a diagram showing a surface potential distribution of an object to be charged which is charged by the charging device shown in FIG.

8 is a schematic configuration diagram of an image forming apparatus using the charging device shown in FIG.

FIG. 9 is a diagram illustrating an example of an image defect due to charging failure.

FIG. 10 is a schematic perspective view of a cleaning member used in the charging device of FIG.

FIG. 11 is a schematic perspective view showing a charging device according to an embodiment of the present invention described in claim 5, 6 or 7.

[Explanation of symbols]

1 charged electrode, 2 spiral convex part of charged electrode, 3 rotation axis, 4 spring, 5
Gears, 6 motors, 7 cleaning members, 8 holders, 9 brushes,
10 photoconductor drum, 11 toner,
21 charging device, 22 charging electrode,
23 gears, 24 motors,
25 surface potential measurement drum, 26 power supply,
27 surface electrometer, 28 detector,
29 recorder, 30 image forming apparatus,
31 photoconductor drum, 32 exposure device,
33 developing device, 34 transfer device,
35 paper tray, 36 fixing device, 3
7 cleaning device, 38 power supply for charging,
39 motors, 40 gears, 6
1 charging electrode, 62 coil spring, 63
Sliding member, 64 drive roller, 65 driven roller, 66 motor, 67 cleaning member

Claims (7)

[Claims] 1. A charging device having a charging electrode disposed so as to face a moving object to be charged, wherein a continuous discharge is generated in a minute gap formed between the charging electrode and the object to be charged. A charging device that performs charging by charging, wherein the charging electrode has, on a surface thereof, a convex portion that is in contact with the member to be charged, and the surface of the charging electrode moves relative to the surface of the member to be charged. A charging device characterized in that the charging device is driven as described above. 2. The charging device according to claim 1, wherein the charging electrode is a substantially cylindrical member having a spiral projection formed on an outer peripheral surface. 3. The charging device according to claim 2, wherein the convex portion formed on the outer peripheral surface of the charging electrode is formed by winding a string-like or narrow band-like member around the charging electrode. Characteristic charging device. 4. The charging device according to claim 2, further comprising a cleaning member fixed and supported so as to contact an outer peripheral surface of the charging electrode. 5. A charging device having a charging electrode whose surface is opposed to a moving object to be charged, wherein a continuous discharge is generated in a minute gap formed between the charging electrode and the object to be charged. A charging device that contacts the surface of the member to be charged via a string-shaped or strip-shaped spacer, wherein the spacer includes the charged member. A charging device characterized by moving relative to the surface of a body. 6. The charging device according to claim 5, wherein the spacer is provided between two substantially parallel stretching members stretched in a direction substantially perpendicular to a moving direction of a surface of the charged object. A plurality of thread-like or narrow-band-shaped members provided so as to be bridged, wherein the stretching member is moved in the axial direction thereof. 7. The charging device according to claim 6, wherein the tension member is formed in an endless shape and is supported by a plurality of rollers so as to be able to rotate, and at a position where the tension member is in contact with the spacer. A charging device, wherein a cleaning member is fixedly supported.