JP3287114B2 - Charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device which is used in an image forming apparatus such as a copying machine or a printer to which an electrophotographic method is applied and uniformly charges the surface of a photoreceptor.
In particular, the present invention relates to a charging device that causes a discharge in a minute space close to a photoconductor.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, the surface of a photoreceptor is charged by a charging device, and thereafter, an electrostatic latent image is formed on the surface by irradiating image light. Visualize the latent image. As a charging device used in such an image forming apparatus, a charging device using corona discharge and a charging device using a contact charging method using a charging roll or the like are conventionally known.

In a charging device using corona discharge, a wire is stretched in a shield case so as to be close to or apart from the surface of a photoreceptor, and a high voltage is applied to the wire to cause a corona discharge. A predetermined charge is provided. Although such a charging device is excellent in uniform charging, a high voltage of several kV must be applied in order to charge the photosensitive member to a predetermined surface potential. In addition, since a large amount of discharge products such as ozone are generated during corona discharge, the rubber parts and the photoconductor are deteriorated. For this reason, it is necessary to install an exhaust fan and the like, and there is a drawback that the apparatus becomes large and the cost is increased. Further, the wire is easily stained by dust or fuser oil in the air, causing unevenness in an image. In order to solve this problem, it is necessary to provide a wire cleaning device.

Therefore, recently, as an alternative to the above-described device using corona discharge, a charging device using a contact charging method in which a charging electrode is brought into direct contact with a photosensitive member and charged is widely used. Examples of such a charging device include, for example, JP-A-63-14669 and JP-A-63-20888.
As disclosed in Japanese Patent Laid-Open Publication No. 1 (1994), a roll-shaped conductive member is disposed in contact with the surface of a photoreceptor, and a DC voltage or a superimposed DC / AC voltage is applied to generate a discharge in a minute gap near a contact portion. To charge the surface of the photoreceptor.

In such a charging device, the amount of ozone generated is extremely small because corona discharge is not used, and the conductive member is arranged so as to be in contact with the photoreceptor, which is suitable for miniaturization and weight reduction of the device. ing. In addition, since the gap near the contact portion between the conductive member and the photoconductor is extremely small as compared with the corona discharge device, there is an advantage that a uniform charging potential can be obtained even by using a low voltage. .

However, the contact-type charging device requires a device for supporting the charging roll, and has a drawback that the structure is complicated and the manufacturing cost is increased. In addition, in order to perform uniform charging, it is necessary to improve the adhesion between the roll and the surface of the photoreceptor to form a stable minute gap, and to take measures such as lowering the hardness of the roll surface made of rubber or the like. Required. Therefore, a large amount of process oil must be contained in the rubber, and this process oil has a disadvantage that it tends to transfer to the charge acceptor and adversely affect the image quality.
On the other hand, there is a method of increasing the outer shape accuracy of the roll in order to solve such a drawback. However, it is very difficult to increase the outer shape accuracy of the elastic roll such as rubber, which leads to an increase in cost due to a decrease in yield and the like.

Therefore, in order to avoid the above-mentioned drawback, a charging device disclosed in Japanese Patent Application Laid-Open No. 4-249270 has been proposed. As shown in FIGS. 5A and 5B, this charging device uses a flexible film-like member 102 as a conductive member, and a free end 102 of the film-like member.
a is arranged so as to be in contact with the surface of the photoconductor 101. Then, by applying a DC voltage from the power supply 104, a discharge is caused in the minute gap A shown in FIG. 5B, and the surface of the photoconductor is charged to a predetermined potential. The charging device shown in FIG. 5 has the advantages that the cost of the member itself is lower than other conductive members, the structure is simple, and the manufacturing cost can be reduced.

[0008]

However, in the charging device shown in FIG. 5, when an attempt is made to discharge at a low voltage, the range of the appropriate minute gap for the discharge is reduced, and the range in which the discharge occurs is reduced. That is, there is a problem that the discharge range B in the circumferential direction of the photoconductor becomes narrow. Further, the film-like member vibrates due to friction between the photoreceptor and the film-like member, and the minute gap A between the film-like member and the photoreceptor cannot be stably maintained almost constant. Further, when an AC voltage is applied to the film-shaped member in a superimposed manner in order to stabilize the charging, the film-shaped member may be vibrated as described above. If the minute gap A fluctuates in this manner, there is a problem that a uniform charging potential cannot be obtained, and charging unevenness occurs on the surface of the photoconductor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to maintain a small gap between the conductive member and the surface of the photoreceptor so that stable charging can be performed at low cost. It is to provide a charging device that can be obtained.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a flexible conductive or semiconductive film-like member, and has a surface. In a charging device having a charging electrode provided to be close to or in contact with the photoconductor supported rotatably, and a power supply for applying a charging voltage to the charging electrode,
A gap holding material made of an insulating material is adhered to a portion of the film-shaped member constituting the charging electrode, which is opposed to both ends of the peripheral surface of the photoconductor, so that the film-shaped member has a curved surface. It is curved and comes into contact with the photoconductor via the gap holding material at or near the curved surface.

In the above charging device, the gap holding material attached to both ends of the film-like member can maintain a distance between the film-like member and the photosensitive member in a gap capable of appropriately discharging. If so, the shape and the like can be appropriately set. Further, the gap holding material may be provided at least in a portion that comes into contact with the photoconductor, avoiding a portion where an image is formed. The material for forming the gap holding material can be appropriately selected from insulating materials that smoothly slide the photoconductor surface.

The shape of the film-like member may be any shape as long as it is curved so as to contact the surface of the photoreceptor with a constant contact pressure via the above-mentioned gap holding material. For example, as in the invention described in claim 2, the film-shaped member can be curved to have a substantially annular shape supported at both edges. Further, it is desirable that the film-shaped member is formed of a material having appropriate rigidity in order to stabilize the contact with the photoconductor surface.

[0013]

In the charging device according to the first aspect of the present invention, an insulating gap holding material is attached to both ends of the film-like member constituting the charging electrode so that the gap holding material contacts the photoconductor. , The gap between the film-shaped member and the photoconductor can be kept substantially constant. For this reason, the range set to an appropriate gap where discharge can occur is expanded, and uniform and stable charging can be performed. Further, the film-shaped member is curved so as to form a curved surface, and is in contact with the photoreceptor via the gap holding material at or near the curved surface, so that the contact pressure with the photoreceptor is stabilized, and the contact with the photoreceptor is stabilized. It is possible to reduce the vibration of the charging electrode due to friction between the electrodes and application of an AC voltage. Therefore, the occurrence of charging unevenness is prevented, and a good image is obtained.

In the charging device according to the second aspect of the present invention, since the charging electrode is formed in a ring shape by bending the film-shaped member, the gap between the film-shaped member and the photosensitive member is formed by the rigidity of the film-shaped member. Can be more reliably kept constant in the width direction of the image forming range. For this reason, it is possible to perform more uniform and stable charging.

[0015]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic configuration diagram showing a charging device according to an embodiment of the first aspect of the present invention. FIG. 2A is a cross-sectional view in the axial direction of the photoconductor, and FIG. FIG. The charging device 10 is supported at a position facing the photoreceptor 1, and is formed by bending a flexible and conductive film-shaped member 7 into a substantially U-shape. A conductive support 3 for supporting the photoconductor 2 at an appropriate contact pressure while supporting the photoconductor 1
And Further, the charging electrode 2 is connected to a DC power source 4.
And the AC power supply 5 in series.
Is applied with a voltage obtained by superimposing an AC component on a DC component.

The charging electrode 2 has a structure in which the film-shaped member 7 is curved and the free end 7a is disposed in the direction of rotation of the photosensitive member 1, and the photosensitive members at both ends of the film-shaped member 7 are provided. A plate-shaped gap holding member 8 made of an insulating material is attached to the side facing 1. The charging electrode 2 is disposed so as to be in contact with the surface of the photoconductor at a part of the curved surface of the gap holding member 8. By bending in this manner, the rigidity of the film-shaped member 7 is utilized, the film-shaped member 7 and the surface of the photoreceptor 1 are held at a constant gap, and the contact pressure of the gap holding material against the photoreceptor surface is substantially uniform. Is to be held.

The gap holding member 8 is formed of a member that can follow the bending of the film-shaped member 7, and is made of an insulating material so as not to charge both ends of the photoreceptor 1. Further, a material that can reduce the friction coefficient in consideration of direct contact with the photoconductor 1 is used, and a material that does not deteriorate the photoconductor 1 is selected. As the gap holding material 8, for example, a fluororesin is desirable, and in this embodiment, Teflon (registered trademark of DuPont) is used. In this embodiment, the thickness of the gap holding member 8 is set to 300 μm,
A slight gap (300 mm) between the film member 7 and the photoconductor 1
(about μm).

The film member 7 has a thickness of about 0.1 to 1 mm and a volume resistivity of 10 ² to 10 ⁹ Ω ·
cm conductive or semiconductive member is used, the film-shaped member has appropriate rigidity, and maintains a stable contact state with the surface of the photoreceptor. The film-shaped member 7 is formed by mixing conductive particles such as carbon black in a film of, for example, polyester, polyamide, polyethylene, polycarbonate, polyolefin, or polyurethane. , A predetermined volume resistivity can be obtained. In this embodiment, a conductive member is used as the film-shaped member 7.

A voltage obtained by superimposing an AC component having a peak-to-peak voltage of 1.5 V on a DC component of -500 V is applied to the charging electrode 2 from the DC power source 4 and the AC power source 5. In this embodiment, the AC component is superimposed, but only a DC voltage may be applied.

The photoreceptor 1 has, for example, a structure in which a photoconductive layer is laminated on a cylindrical conductor base, and the conductor base is electrically grounded. The surface of the photoreceptor 1 is charged by discharging in a minute gap between the film member 7 of the charging electrode 2 and the surface of the photoreceptor.

In such a charging device 10, the DC power supply 4
When a predetermined voltage is applied from the AC power supply 5 to the charging electrode 2, a discharge is generated in a minute gap between the film member 7 and the photoconductor 1 constituting the charging electrode 2, and ionization of air occurs. If the negative side of the DC power supply 4 is connected to the charging electrode 2, negative ions or electrons flow to the photoconductor 1 side to charge the surface to a predetermined potential, and positive ions reach the charging electrode 2 side. Neutralized. Charging device 10 of the present embodiment
In this case, the contact pressure to the photoconductor 1 is stabilized by the curvature of the film member 7, and the film member 7 is held at a constant gap over a relatively wide range with the surface of the photoconductor. It can be carried out.

FIG. 1 is a schematic structural view showing an image forming apparatus to which the charging device 10 is applied. The image forming apparatus includes a photoconductor 50 on which a latent image is formed by irradiating image light after uniform charging, and around the photoconductor 50,
The charging device 10 of this embodiment for charging the surface of the photoconductor 50
In addition, an exposure device 51 for irradiating the surface of the photoreceptor with image light, a developing device 52 for forming a toner layer on a developing roll 52a and developing a latent image on the photoreceptor, and transferring the developed toner image onto paper The transfer roller 53 has a cleaning device 57 that cleans residual toner by a cleaning blade 53a pressed against the photoconductor. The apparatus further includes a paper cassette 54 for storing paper, a paper transport path 55 for transporting the paper, a fixing device 56 for fixing the toner image by a fixing roll 56a, and the like. The photosensitive member 50, the charging device 10, the developing device 52, and the cleaning device 57 are integrally accommodated in a cartridge 58, and are exchangeably supported by the apparatus main body.

In such an image forming apparatus, the charging device 1
After the photosensitive member 50 is charged to a predetermined potential by 0, the exposure device 51 irradiates a laser beam corresponding to the image information to form an electrostatic latent image on the surface of the photosensitive member 50. This electrostatic latent image is developed by the developing device 52, and a visible image is formed by the adhesion of the toner. Further, the paper is transported from the paper cassette 54 along the paper transport path 55 between the photoconductor 50 and the transfer roll 53, and the toner image is transferred onto the paper by the transfer roll 53. The transferred toner image is fixed by the fixing device 56 to form one copy image. On the other hand, after the transfer process, the toner remaining on the photoconductor 50 is cleaned by the cleaning device 57, and the rotation of the photoconductor 50 starts the charging process by the charging device 10 again.

A print image was formed by using such an image forming apparatus, and a reliability test of the charging device 10 was performed. As a result, in the conventional charging device shown in FIG.
While the charging became non-uniform due to the vibration and the like, the charging device 10 of the present embodiment hardly vibrated the charging electrode 2, the charging potential was uniform, and a good image without unevenness was obtained.

FIG. 3 is a schematic structural view showing a charging device according to another embodiment of the present invention. This charging device replaces the charging electrode 2 of the charging device shown in FIG.
The charging electrode 12 in which the free end 17a is arranged so that the film-like member 17 is curved toward the upstream side in the rotation direction of the photoconductor 1
have. This charging electrode 12 is used for the film-shaped member 1.
As in the above-described embodiment, plate-like gap holding members 18 are attached to the surfaces of both ends of 7 that face the photoconductor 1.
The film member 17 and the gap holding material 18
2 and the other structure of the charging device are the same as those of the charging device shown in FIG.

When a copying test was performed using an image forming apparatus to which such a charging device was applied, uniform charging was performed similarly to the charging device shown in FIG. 2 and a good copied image was obtained. confirmed.

FIG. 4 is a schematic structural view showing a charging device according to an embodiment of the present invention. This charging device has a charging electrode 22 in which a conductive film-shaped member 27 is curved and both ends are overlapped to form a loop, instead of the charging electrode 2 of the charging device shown in FIG. I have. A gap holding member 28 made of an insulating material is attached to both ends of the film-like member 27. The gap holding member 28 comes into contact with the surface of the photoreceptor 1, and the film-like member 27 and the photoreceptor 1 And a certain gap is maintained. The other structure of the charging device is the same as that of the charging device shown in FIG.

When a copying test was conducted using such an image forming apparatus using the image forming apparatus, the occurrence of uneven charging was prevented, and a good copied image was obtained. Further, since the film-like member 27 is formed in a loop shape, there is an advantage that the gap with the photoreceptor 1 can be more stably kept constant, and the charging potential can be made more uniform.

[0029]

As described above, in the charging device according to the first aspect of the present invention, the film-like member constituting the charging electrode is curved, and the photosensitive member is formed at or near the curved surface via the gap holding material. , And the gap between the film-shaped member and the photoconductor is kept substantially constant. For this reason, the range in which an appropriate gap for causing discharge is formed is expanded,
Uniform and stable charging can be performed. Furthermore, since the contact pressure between the charging electrode and the photoconductor is stabilized, the friction between the charging electrode and the photoconductor and vibration of the charging electrode due to the application of an AC voltage are reduced, and stable charging is achieved. It can be carried out. Therefore, the occurrence of charging unevenness can be prevented with a simple structure, and a good image can be obtained at low cost.

In the charging device according to the second aspect of the present invention, since both edges of the film-like member are supported and are substantially annular, the shape is stable and the contact state between the charging electrode and the photosensitive member is stable. In addition, the charging electrode has sufficient rigidity in the width direction of the image forming range, so that the gap between the film member and the photoconductor can be more reliably kept constant.
Therefore, uniform and more stable charging can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus to which a charging device according to an embodiment of the present invention is applied;

FIG. 2 is a schematic configuration diagram showing a charging device according to an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram showing a charging device according to another embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing a charging device according to an embodiment of the invention described in claim 2;

FIG. 5 is a schematic configuration diagram showing a conventional charging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2, 12, 22 Charging electrode 3, 13, 23 Support 4, 14, 24 DC power supply 5, 15, 25 AC power supply 7, 17, 27 Film-shaped member 8, 18, 28 Gap holding material 10 Charging device Reference Signs List 50 photoconductor 51 exposure device 52 developing device 53 transfer roll 54 paper cassette 55 paper transport path 56 fixing device 57 cleaning device

Claims (2)

(57) [Claims] 1. A charging electrode comprising a flexible conductive or semiconductive film-like member and placed near or in contact with a photoreceptor whose surface is rotatably supported, and the charging electrode A charging device having a power supply for applying a charging voltage to the charging member, wherein a gap holding material made of an insulating material is provided on a portion of the film-like member constituting the charging electrode, which is opposed to both ends of the peripheral surface of the photoconductor. Affixed, the film-shaped member is curved to have a curved surface,
A charging device that contacts the photosensitive member via the gap holding material at or near the curved surface. 2. The charging device according to claim 1, wherein the charging electrode is formed in a substantially annular shape in which the film-shaped member is curved and supported at both edges.