JPH08240964A - Electrifyier - Google Patents

Abstract

PURPOSE: To prevent uneven electrification due to deformation of an electrifying electrode or sticking, etc., of toner to the electrifier that is provided with an electrifying electrode arranged in contact with a charge receptor by making a semiconducting film cylindrical and also to prevent the electrification potential from fluctuating in according with the frequency of AC component when the electrifying electrode is impressed with an AC/DC-superimposed voltages. CONSTITUTION: The electrifying electrode 2 is supported by a supporting roller 3 and is also driven to rotate so as to move in the same direction as the charge receptor 1 at an opposing part to each other. A pressing member 5 is also arranged to press the charging electrode onto the supporting roller 3. When a DC voltage is impressed on the charging electrode 2, a circumferential speed ratio of the supporting roller to the electrifying electrode is set equal to 1 or below. By this method, the electrifying electrode 2 gets bulged toward the downstream side, increases in discharging area on the upstream side of the contact nip and the potential by electrification becomes uniform. On the other hand, the circumferential speed ratio is set equal to 1 or more in the case of impressing an AC/DC-superimposed voltages.

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 which uniformly charges the surface of a photoconductor which is a charge acceptor. In particular, the present invention relates to a charging device in which a charging electrode is arranged so as to come into contact with a charge acceptor and discharge is caused in a minute gap near the contact portion.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, the surface of a photoconductor, which is a charge receptor, is charged by a charging device, and an electrostatic latent image is formed on the surface by irradiation of image light, and a developer is attached. To visualize this electrostatic latent image. As a charging device used in such an image forming apparatus, conventionally, a device using corona discharge and a device using a contact charging system using a charging roller or the like are known. A charging device using corona discharge stretches a wire in the shield case close to and away from the surface of the charge receptor, applies a high voltage to this to cause corona discharge, and causes a predetermined amount of charge on the charge receptor surface. To give the electric charge of. Although such a charging device is excellent in uniform charging, it has a drawback in that a large amount of discharge products such as ozone is required to be treated, which makes the device larger and more expensive.

Therefore, recently, a contact charging type charging device has been used in which a charging electrode is charged by directly contacting the charging electrode with the charging electrode. In this charging device, a conductive elastic roller or brush is placed in contact with the surface of the charge receptor, and a charging voltage is applied to this conductive member to cause discharge in a minute gap near the contact portion, It is for charging. In addition, JP-A-1-93760 and JP-A-3
As disclosed in JP-A-203754, there is also known a device in which a blade-shaped charging electrode pressed against a charge receptor is used as a cleaning blade for removing residual toner on the surface of the charge receptor. There is. Further, as disclosed in Japanese Patent Laid-Open No. 4-249270, there is also known a charging device in which a flexible film-like member is used as a charging electrode and its tip portion is arranged so as to contact the surface of a charge receptor. There is. In this type of charging device,
Since corona discharge is not used, the amount of ozone generated is extremely small, and since high voltage is not used, it is suitable for downsizing and weight saving of the device.

However, among the above-mentioned contact type charging devices, the one using a conductive roller requires a supporting device for the roller and the like, and has a drawback that the structure tends to be complicated. Further, in order to perform uniform charging, it is necessary to improve the adhesiveness between the elastic roller and the charge receptor to form stable microscopic voids, and it is necessary to take measures such as lowering the hardness of rubber. Therefore, it is necessary to contain a large amount of process oil in the rubber, and this process oil is liable to transfer to the charge acceptor and adversely affect the image quality. On the other hand, in order to eliminate such a defect, there is a method of increasing the outer shape accuracy of the roller, but it is very difficult to increase the outer shape accuracy of rubber or the like, which leads to an increase in cost due to a decrease in yield and the like.

Further, in the charging device using a conductive brush, it is easier to make the contact uniform as compared with the elastic roller, but it takes a lot of time and labor to manufacture the brush, and the sweeping of the brush is difficult. There is a drawback that uneven charging is likely to occur in an image. Further, in the method in which the blade-shaped charging electrode is also used as the cleaning blade, it is difficult to achieve both the cleaning accuracy and the setting of minute voids required for discharging, and it is difficult to perform uniform and good charging. .

On the other hand, the one using a film-shaped charging electrode has an advantage that a stable contact can be easily obtained with a simple structure and the manufacturing cost of the member is low as compared with other conductive members. However, since the tip end of the film-shaped member comes into contact with the charge acceptor, the friction thereof causes the charging electrode to vibrate, causing a change in the space for discharging, and the charging potential is likely to become unstable. In addition, foreign matter such as toner and external additives adheres to the contact portion between the film-shaped member and the charge acceptor, and a so-called creeping discharge causes streak-shaped charging defects.
In order to improve such a drawback, there is a method of applying a superimposed voltage of direct current and alternating current to the film-shaped member, but there is a drawback that the film-shaped member vibrates in accordance with the frequency of the alternating current and generates a charging sound. There is.

Therefore, in order to avoid the above-mentioned drawbacks, charging devices disclosed in JP-A-4-232977 and JP-A-5-72869 have been proposed. This charging device uses a film-shaped member formed in a cylindrical shape as a charging electrode. The film-shaped member is brought into contact with the peripheral surface of the support roller, and in contact with the charge acceptor in a bent state, the support roller is rotated. With this, it is designed to move endlessly. In such a charging device, the film-shaped member is set so as to move in the same direction at the contact portion with the charge acceptor, so that the generation of electric charges due to friction and the vibration of the film-shaped member as the electrode are eliminated. There are advantages.

[0008]

However, in the charging device provided with the film-like member which moves endlessly as described above, the charging electrode is pressed against the charge receptor to bring them into contact with each other, so that the toner adheres to the surface of the charging electrode. May occur, and this toner is apt to induce poor charging. In particular, when a DC voltage is applied to the charging electrode, the adhered toner has a great influence, and the charging potential is likely to become unstable.

In addition, when a superimposed voltage of direct current and alternating current is applied to the charging electrode, the effect of the fixed toner as described above is small, but the charging potential varies depending on the frequency of the alternating current component of the applied voltage. There is a problem in that a large amount of so-called ripple components are included, which causes deterioration in image quality such as uneven density.

Further, in the above charging device, in order to make the contact between the charging electrode and the charge acceptor uniform, Japanese Patent Laid-Open No. 4-2492.
It is necessary to make the thickness of the film thinner than that of the charging electrode described in JP-A-70, and there is a drawback that the charging electrode is easily deformed. Therefore, there is also a problem that a stable charging potential cannot be maintained for a long period of time due to deformation, such as displacement and twisting, caused by the charging electrode due to an unreasonable force applied to the contact portion with the charge receptor.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent toner from sticking to the charging electrode or fluctuation of the charging potential due to damage or deformation of the charging electrode. It is an object of the present invention to provide a charging device which is capable of preventing and uniformly charging the charge receptor for a long period of time.

[0012]

In order to solve the above problems, the invention according to claim 1 is a charging electrode in which a flexible semiconductive film member is formed in a cylindrical shape,
A cylindrical rotating member that is inserted into the charging electrode, supports the charging electrode so as to contact the charge acceptor, and is rotationally driven to move the charging electrode in the circumferential direction; It has a power source for applying a DC voltage for charging and a pressure contact member for pressing the charging electrode against the rotating member, and the rotating member rotates in the same direction at the contact position of the charging electrode with the charge receptor. It is assumed that the rotation speed is set to a direction in which the rotation speed of the rotating member and the peripheral speed of the charge receptor are set to 1 or less.

According to a second aspect of the present invention, a charging electrode in which a flexible semiconductive film member is formed into a cylindrical shape, and the charging electrode is inserted into the charging electrode, and the charging electrode is a charge acceptor. A cylindrical rotating member that is supported so as to be in contact with each other and that is rotationally driven so as to move the charging electrode in the circumferential direction, a power supply that applies a voltage in which a direct current and an alternating current are superimposed on the charging electrode, And a pressing member that presses the charging electrode against the rotating member, wherein rotation of the rotating member is set in a direction in which the charging electrode moves in the same direction at a contact position with the charge acceptor. It is assumed that the ratio between the peripheral speed and the peripheral speed of the charge acceptor is set to 1 or more.

According to a third aspect of the present invention, in the charging device according to the first or second aspect, the rotating member is held with a gap from the charge acceptor.

According to a fourth aspect of the present invention, in the charging device according to the first aspect, the second aspect, or the third aspect, the pressure contact member is made of a conductive material, and the power source is provided through the pressure contact member. It is assumed that a voltage is applied to the charging electrode.

According to a fifth aspect of the present invention, in the charging device according to the third or fourth aspect, the rotating member has engaging means for transmitting a driving force to the charging electrode at both ends in the axial direction. Shall have.

In the invention described in claim 1 or 2, the ratio of the peripheral speed of the rotating member and the peripheral speed of the charge acceptor, that is, the peripheral speed ratio of the charging member to the charge acceptor is the rigidity of the charging electrode. , The circumference, the setting position of the rotating member, the voltage applied to the charging electrode, and the like can be appropriately set.
Further, the material of the film-shaped member constituting the charging electrode can be set appropriately, but it is desirable that the film-shaped member is formed of a semiconductive material having an appropriate volume resistivity. Further, it is desirable that the thickness and the tensile elastic modulus of the charging electrode are appropriately set in consideration of the size and flexibility.

In the invention described in claim 1 or 2, the shape, material, etc. of the pressure contact member can be appropriately set as long as they are in uniform contact with the outer peripheral surface of the charging electrode. For example, foam such as polyurethane, silicone sponge, felt, brush processed into a plate shape or a roller shape, a film, a blade, an elastic rubber roller, a leaf spring, or the like can be used. Of these, foams, sponges, and brushes are preferable in terms of being particularly soft and capable of contacting.

[0019]

In the charging device according to the first aspect of the present invention, the film-shaped member is formed into a cylindrical charging electrode, and the charging electrode is inserted into the charging electrode to support the charging electrode so as to contact the charge receptor. Since the charging electrode contacts the charge acceptor in a bent state, the charging electrode moves endlessly in the circumferential direction by driving the rotating member. Furthermore, since a pressure contact member for pressing the charging electrode against the rotating member is provided,
The contact between the charging electrode and the charge acceptor becomes uniform, and the movement of the charging electrode in the circumferential direction is stabilized. This prevents deformation such as twisting due to the charging electrode.

The rotation of the rotating member is set so that the charging electrode moves in the same direction at the contact position with the charge acceptor, and the ratio of the peripheral speed of the rotating member to the peripheral speed of the charge acceptor is set. Since it is set to 1 or less and the rotation of the rotating member is slower than that of the charge acceptor, the charging electrode is pulled in the moving direction of the charge acceptor. Therefore, the charging electrode is attracted to the charge receptor by the electrostatic force generated when a voltage is applied, the contact nip (electrostatic adsorption area) between the charging electrode and the charge receptor increases, and the charging electrode moves in the moving direction of the charge receptor. It looks like a bulge. Therefore, the discharge region in which an appropriate gap is maintained is widened on the upstream side of the contact nip, that is, on the pre-nip side.

In general, when a DC voltage is applied to the charging electrode, the main charging potential rises due to the discharge that occurs in the pre-nip side region, and in the post-nip side discharge, the charging potential that complements this rises to a certain extent. . That is, when a DC voltage is applied to the charging electrode, the discharge on the pre-nip side becomes dominant with respect to the charging of the charge receptor. Therefore, when the charging electrode is pulled in the moving direction of the charge receptor as described above, the charging electrode gradually approaches the charge receptor on the pre-nip side, and the discharge area on the pre-nip side increases. Therefore, uniform charging is possible, and a stable charging potential can be obtained. Further, even if toner or the like adheres to the vicinity of the contact nip of the charging electrode, the discharge area is wide, so that stable charging can be performed and the occurrence of charging failure can be reduced.

In the charging device according to the second aspect of the present invention, the ratio of the peripheral speed of the rotating member to the peripheral speed of the charge acceptor is 1.
The rotation member is rotated faster than the charge acceptor. Therefore, the charging electrode is attracted to the charge receptor by the electrostatic force generated when a voltage is applied, and has a shape that swells toward the upstream side of the charge receptor. Therefore, the discharge region having an appropriate gap is expanded on the downstream side of the contact nip between the charging electrode and the charge receptor, that is, on the post nip side.

In general, when the voltage applied to the charging electrode is a direct current and an alternating current superposed on each other, the positive and negative discharges alternately occur to change the charging potential of the charge acceptor according to the frequency of the alternating current. . At this time, in the region on the post nip side, the distance between the charging electrode and the charge acceptor is increased, so that discharge is less likely to occur, and eventually the charge potential of the charge acceptor tends to converge near the potential of the DC component. is there. That is, the discharge on the post-nip side is dominant with respect to the charging of the charge receptor. Therefore, when the charging electrode has a shape that swells toward the upstream side of the charge receptor as described above, the charging electrode gradually separates from the charge receptor on the post nip side, and the discharge area on the post nip side increases. Therefore, uniform charging with a small ripple component is possible, and a stable charging potential can be obtained. Further, even if toner or the like adheres to the vicinity of the contact nip of the charging electrode, stable charging can be performed because the discharge area on the post nip side is wide, and the occurrence of charging failure can be reduced.

In the charging device according to the third aspect of the present invention, since the rotating member is held with a gap between the charge receiving body and the charge receiving body, the rotating member contacts the charge receiving body while the charging electrode is bent. While being supported as described above, the charging electrode is moved endlessly while being in contact with the charge acceptor by the driving of the rotating member. Therefore, the charging electrode can be stably moved in the circumferential direction, and it is possible to prevent the contact pressure between the charging electrode and the charge receptor from becoming nonuniform. Therefore, the occurrence of charging failure is prevented and a uniform charging potential can be obtained.

In the charging device according to the fourth aspect of the present invention, the pressure contact member is made of a conductive material, and a voltage is applied to the charging electrode via the pressure contact member. It is no longer necessary to use a conductive material in which the conductive powder described above is mixed, and the material setting range is widened.
Therefore, the cost can be reduced by selecting an appropriate resin or the like. In addition, since the voltage is supplied from the pressure contact member located far from the charge acceptor, spark discharge is prevented from occurring even when the charging electrode is damaged.

In the charging device according to the fifth aspect of the invention, since the engaging means for transmitting the driving force to the charging electrode is provided at both ends in the axial direction of the rotating member, when the charging electrode rotates. In addition, it is possible to prevent deformation such as displacement and twisting due to the charging electrode, so that the charging electrode can be stably rotated. Therefore, the contact between the charging electrode and the charge acceptor can be further stabilized, and a more uniform charging potential can be obtained.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a schematic configuration diagram showing a charging device according to an embodiment of the invention described in claim 1 or claim 3.
1A is a sectional view, and FIG. 1B is a side view. The charging device 10 is supported at a position facing a charge receptor 1 (photoreceptor) that can move in a fixed direction, and is a cylindrical member having a semi-conductive film-shaped member having an endlessly movable peripheral surface. And the charging electrode 2 formed on the
It has a supporting roller 3 (rotating member) which is supported so as to be brought into contact with the supporting roller 3 and is rotationally driven in a fixed direction, and a pressure contact member 5 which presses the charging electrode 2 against the outer peripheral surface of the supporting roller 3. Further, the supporting roller 3 is connected to a DC power source 4, and a charging voltage is applied to the charging electrode 2 via the supporting roller 3.

The charge acceptor 1 has a structure in which a photoconductive layer 1b is laminated on, for example, a cylindrical conductor substrate 1a, and the conductor substrate 1a is electrically grounded. Then, the surface of the charge receptor 1 is charged by the occurrence of discharge in the minute gap near the contact portion with the charging electrode 2.

The charging electrode 2 is formed so that the circumference of the film-shaped member is larger than the circumference of the support roller 3, and is supported so as to contact the charge receptor 1 in a bent state. The charging electrode 2 is designed to move endlessly with the rotation of the support roller 3. As shown in FIG. 2, the charging electrode 2 has a peripheral surface facing the moving direction of the charge receiving body 1 at a position facing the charge receiving body 1. It is set to move in the same direction as. As the film-shaped member forming the charging electrode 2, a flexible semiconductive member having a thickness of about 30 to 200 μm is used. This film-shaped member is formed by mixing conductive particles such as carbon black into a film such as polyester, polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, or polyvinylidene fluoride, and has a preferable volume resistivity. Thus, the mixing amount of the conductive particles is adjusted. At this time, if the volume resistivity is 10 ² Ω · cm or less, spark discharge is likely to occur, and if it is 10 ¹¹ Ω · cm or more, dot-shaped charging failure is likely to occur, so that 10 ³ to 10 ¹⁰ Ω · c.
It is desirable to use in the range of m. Especially 10 ³ to 10 ⁶
Ω · cm is preferable in that the charging voltage to be used can be set to be relatively low, and power consumption can be saved. Further, in consideration of direct contact with the charge receptor 1, the tensile elastic modulus is set to about 10 to 280 Kg / mm ² .

The support roller 3 is a cylindrical member inserted into the charging electrode 2 and is driven to rotate in a fixed direction by a motor or the like (not shown). The rotation direction of the support roller 3 is set such that both peripheral surfaces move in the same direction at the position facing the charge receptor 1, and at this time, the peripheral speed of the support roller 3 and the peripheral speed of the charge receptor 1 are set to be equal to each other. Ratio of 1
It is set as follows. Further, in order to serve also as power supply to the charging electrode 2, the peripheral surface of the support roller 3 is formed of a conductive material, and for example, a metal such as aluminum or SUS, or a volume resistivity of which is equal to or lower than the volume resistivity of the charging electrode 2. A conductive polymer material or the like formed so as to be used is used. Further, the supporting roller 3 is arranged so as to face the charge receptor 1 with a space therebetween, and supports the charging electrode 2 so as to contact the charge receptor 1 with an appropriate contact pressure. That is, when the charging electrode 2 is in contact with the charge acceptor 1 in a bent state, the contact pressure on the charge acceptor 1 is appropriately adjusted, and uniform contact is obtained. The DC power source 4 is
A DC voltage can be applied to the charging electrode 2 in the step of charging the charge receptor 1. The voltage applied to the DC power supply 4 will be described later.

The pressing member 5 is fixedly supported at a position where it contacts the outer peripheral surface of the charging electrode 2, and is a member for lightly pressing the charging electrode 2 so as to make it closely contact with the outer peripheral surface of the supporting roller 3. As a material for forming the pressing member 5, a soft member that does not damage the surface of the charging electrode 2 is desirable, and for example, foam such as polyethylene or polyurethane, or silicone sponge or felt processed into a plate shape is used. .

In such a charging device, when a predetermined voltage is applied to the charging electrode 2 from the power source 4 through the conductive supporting roller 3, the charging electrode 2 generates static electricity between itself and the charge receptor 1. Is attracted to the side of the charge acceptor 1 by force,
The contact nip (electrostatic adsorption area) between the charging electrode 2 and the charge receptor 1 increases. At this time, the ratio of the peripheral speed of the support roller 3 to the peripheral speed of the charge receptor 1 (charge receptor 1 of the support roller 3
The peripheral speed ratio to the charging electrode 2 is set to 1 or less, and the rotation of the supporting roller 3 is slower than that of the charge receptor 1.
Are pulled in the moving direction of the charge acceptor 1. as a result,
As shown in FIG. 2, the charging electrode 2 has a shape that swells in the moving direction of the charge receptor 1, and the discharge region on the upstream side of the contact nip, that is, the pre-nip side expands.

In such a state, a predetermined DC voltage is applied to the charging electrode 2, and a discharge is generated mainly in a minute gap at the contact portion between the charging electrode 2 and the charge receptor 1, mainly on the pre-nip side, and air is discharged. Ionization occurs. Power supply 4 to support roller 3
If the negative polarity side is connected, negative ions or electrons flow to the charge acceptor 1 side and charge it, and positive ions reach the charging electrode 2 side and are neutralized. In the charging device of the present embodiment, by using the semi-conductive member for the charging electrode 2, it is possible to prevent an excessive current from flowing to any part of the void, and to the charge acceptor 1. Uniform charging is possible.

Next, the results of the charging test of the above charging device using the charging test device as shown in FIG. 3 are shown. This charging test apparatus has a surface potential sensor 11 that detects the potential of the surface of the charge receptor 1 and a discharge lamp 13 that exposes the surface around the charge receptor 1, and the surface potential sensor 11 has a surface potential. A total of 12 are connected. The charging device 10 of the present embodiment is arranged on the upstream side of the surface potential sensor 11 in the rotation direction of the charge receptor 1, and the charging electrode 2 is supported so as to contact the surface of the charge receptor 1. A DC power supply 14 is connected to the support roller 3 so that a DC charging voltage is applied. The DC power supply 14 is capable of arbitrarily changing the voltage, and the surface potential of the charge acceptor 1 which changes with this can be measured by the surface electrometer 12.
It is designed to measure at.

As the charging electrode 2, a cylindrical film having a thickness of 50 μm, which is formed of polyvinylidene fluoride, nylon, and polycarbonate so as to have volume resistivities of 10 ³ , 10 ⁵ , and 10 ⁷ Ω · cm, respectively, is used. . The diameter of the charging electrode 2 was set to 11 mm and 12.5 mm, and the supporting roller 3 was a conductive rubber roller set to Φ8, Φ10, and Φ12 mm. The peripheral speed ratio of the support roller 3 to the charge receptor 1 is set to 0.5, and the pressure contact member 5
Urethane foam was used for.

FIG. 4 shows the relationship between the applied voltage when a DC voltage is applied to the charging electrode 2 and the surface potential of the charge receptor 1 in the charging test using the above charging test apparatus. In this figure, 0 to -20 from the DC power supply 14
When a DC voltage of 00V was applied, it was confirmed that the surface potential of the charge acceptor 1 began to rise sharply from an applied voltage of about -550V and reached about -1450V at an applied voltage of -2000V. During this period, no abnormal discharge was generated by the charging device 10. In addition, with the combination of the material of the charging electrode 2 and the support roller 3, good results were obtained in all of the above cases. Further, when the shape of the charging device 2 when the charge receptor 1 was rotated was observed, it was almost the same shape as in FIG. 1 when no voltage was applied, but when the applied voltage was increased, At -200V, the post-nip side became bulged. This is because when the voltage applied to the charging electrode 2 exceeds a certain value, the charging electrode 2
Is attracted to the side of the charge receptor 1 by electrostatic force,
Furthermore, since the rotation of the support roller 3 is slower than that of the charge receptor 1, the charging electrode 2 is pulled in the moving direction of the charge receptor 1 between the contact nip portion and the pressure contact member 5 due to the balance between the forces of the two. is there.

Next, in order to investigate the influence of the peripheral speed ratio of the support roller 3 to the charge receptor 1 on the charging characteristics,
Using the charging test apparatus shown in FIG. 3, the charging potential was measured by changing the peripheral speed ratio. Here, the film used for the charging electrode 2 is polyvinylidene fluoride having a volume resistivity of 10 ⁵ Ω.
A 50 μm cylindrical film produced so as to have a size of cm was used. The diameter of the charging electrode 2 is 12.5 mm,
A rubber roller having a diameter of 10 mm was used as the support roller 3. Further, urethane foam was used for the pressure contact member 51. Figure 5
FIG. 4 is a diagram showing the surface potential of a charge acceptor measured after application of a voltage to a charging electrode is started with time. In this figure, the peripheral speed ratio between the support roller 3 and the charge receptor 1 is set to 1. Power source 4 for charging electrode 2
When a DC voltage of −1000 V is applied from the charge acceptor 1, the charge potential V _HIGH of the charge acceptor 1 is changed to the charge acceptor 1 as shown in FIG.
The first rotation reached -330V and the second rotation reached -360V. That is, in the initial state where the charge acceptor 1 is not charged (V ₀ = 0), the potential difference ΔV _1-2 between the first rotation and the second rotation is 40V. Further, the difference ΔV between the maximum value and the minimum value of the charging potential V _HIGH in the second rotation
_HIGH was about 20V.

FIG. 6 shows that in such a charging device, the peripheral speed ratio of the support roller 3 to the charge acceptor 1 is changed in steps of 0.5 from 0 to 4, and ΔV _1-2 and ΔV _HIGH are measured. The result is shown. In the figure, the peripheral speed ratio is 2.
It can be seen that by setting the ratio to 5 or less, both ΔV _1-2 and ΔV _HIGH tend to decrease. Particularly, when the peripheral speed ratio is 1 or less, a more stable charging potential can be obtained.

Here, the mechanism by which the uniformity of the charging potential changes due to the difference in peripheral speed ratio will be described. As shown in FIG. 2, the force applied to the charging electrode 2 when a voltage is applied is the force F _E that the charging electrode 2 is attracted by the electrostatic force with the charge acceptor 1 and is pulled along the charge acceptor 1, and the charge electrode 2. 2 and the frictional force F _S acting between the pressure contact member 5 and the directions of the respective forces are as shown in the drawing. Therefore,
As shown in FIG. 7, when the peripheral speed ratio is 1 or less, the contact nip is generated in the downstream side portion of the portion facing the support roller 3, and as a result, the charging electrode 2 appears to bulge in the moving direction of the charge receptor 1. It becomes a shape. Generally, the charge acceptor 1 is charged by discharge occurring in a minute gap near the contact portion with the charging electrode 2. However, when a DC voltage is applied to the charging electrode 2, the discharge mainly occurs in the region on the pre-nip side. As a result, the charging potential rises, and in the discharge on the post nip side, the charging potential that complements it rises to a certain extent. That is, when a DC voltage is applied to the charging electrode 2, the discharge on the pre-nip side becomes dominant with respect to the charging of the charge receptor 1. Therefore, when the discharge on the pre-nip side is stable, the charging potential of the charge acceptor 1 is stabilized, and it is understood that the discharge area on the pre-nip side is preferably wide.

In this embodiment, as shown in FIG. 7A, the charging electrode 2 has a shape bulging in the moving direction of the charge receptor 1, and the charging electrode 2 and the charge receptor 1 on the pre-nip side.
Is smaller than the angle theta ₂ angle theta ₁ is a post-nip side with. That is, since the charging electrode 2 gradually separates from the charge acceptor 1 on the pre-nip side, the discharge area on the pre-nip side increases as compared to the post-nip side as shown in FIG. 7B. Therefore, more uniform and stable charging is possible.

FIG. 8 is a schematic structural view showing an image forming apparatus to which the charging device 10 is applied. This image forming apparatus includes a photoconductor (charge receptor) 20 on which a latent image is formed by irradiating image light after uniform charging, and the surface of the photoconductor 20 is charged around the photoconductor 20. In addition to the charging device 10 of this embodiment, an exposure device 21, a developing device 22,
It has a transfer roller 25 and a cleaning device 27.
Further, in the apparatus, a paper cassette 2 for storing paper 24 is provided.
3. It has a fixing device 26 for fixing the toner image.
In such an image forming apparatus, after the photoconductor 20 is charged to a predetermined potential by the charging device 10, a laser beam corresponding to the image information is irradiated by the exposure device 21, and the photoconductor 2 is exposed.
An electrostatic latent image is formed on the surface of 0. This electrostatic latent image is developed by the developing device 22, and a visible image is formed by the adhesion of toner. Further, the paper 24 is transferred from the paper cassette 23 along the paper guide 28 to the photoconductor 20 and the transfer roller 2.
5, the toner image is transferred onto the paper 24 by the transfer roller 25. The transferred toner image is fixed by the fixing device 26 and one image is formed. On the other hand, after the transfer process, the toner remaining on the photoconductor 20 is cleaned by the cleaning device 27, and the photoconductor 20 rotates to start the charging process by the charging device 10 again. The voltage applied to the charging device 10 in the above step is -900.
A direct current voltage of V is set, so that the charge potential of the charge acceptor 1 becomes about -350V.

A print image was formed using such an image forming apparatus, and a reliability test of the charging device 10 was conducted. As a result, it was confirmed that a good image having a uniform charging potential and no image quality defect was obtained. Was done. The charging device 10
The above is applied to the image forming apparatus as shown in FIG. 8 described above. However, for example, the charging device may be integrated with a toner cartridge or the like so as to be detachably supported by the image forming apparatus. As a result, if the used cartridge is collected and only the charging electrode 2 is replaced in the factory, the charging device can be reused, which is effective for recycling and the cost can be reduced.

Further, in the above embodiment, the supporting roller 1 is supported at a distance from the charge receiving body, but as shown in FIG. 9, the supporting roller 1 becomes a charge receiving body via the film-shaped charging electrode 2. It may be pressed and supported.

FIG. 10 is a schematic block diagram showing a charging device which is an embodiment of the invention described in claim 2 or 3. This charging device is equipped with a power supply 34 for applying a voltage obtained by superimposing an alternating current on a direct current to the charging electrode 32, instead of the direct current power supply 4 of the charging device shown in FIG.
It is connected to a support roller 33 that supports the charging electrode 32. The voltage applied from the power source 34 is -35.
Peak-to-peak voltage of 1.5k as AC component in 0V DC component
The voltage is set by superimposing a sin wave of V and a frequency of 170 Hz. The rotation direction of the support roller 33 is the same as that of the charging device shown in FIG. 1, but the ratio of the peripheral speed of the support roller 33 to the peripheral speed of the charge receptor 31 is set to 1 or more. The other structure of this charging device is the same as that of the charging device shown in FIG.

In such a charging device, the support roller 33 is used.
The ratio of the peripheral speed of the charge receiver 31 to the peripheral speed of the charge acceptor 31 is set to 1 or more, and the rotation of the support roller 33 is faster than that of the charge acceptor 1. Therefore, as shown in FIG. The contact nip with is generated in the upstream side portion of the portion facing the support roller 3. Then, the charging electrode 32 is attracted to the charge acceptor 31 by the electrostatic force generated when the charge is applied, and has a shape that swells toward the upstream side with respect to the moving direction of the charge acceptor 1. Therefore, the charging electrode 32 and the charge acceptor 3
The discharge region having an appropriate gap is expanded on the downstream side of the contact nip with 1, that is, on the post nip side.

Next, the influence of the shape of the charging electrode 32 on the charging characteristics of the charge acceptor 31 will be described. FIG.
FIG. 1 is a diagram showing the transition of the charging potential of the charge receptor 31 near the contact portion between the charging electrode 32 and the charge receptor 31. As shown in this figure, when the surface of the charge receptor 31 enters the discharge area on the pre-nip side, the charge electrode 32 is charged by applying a superimposed voltage of direct current and alternating current to the charging electrode 32, and the charge receptor 31 is charged. The potential changes up and down due to repeated charging and discharging depending on the frequency of the AC component of the applied voltage. Furthermore, when the surface of the charge acceptor 31 enters the contact nip, the charging potential becomes a constant value, but when it enters the post nip portion, the charging potential fluctuates up and down according to the frequency of the AC component again due to discharge. At this time, the gap in which the electric discharge is generated gradually increases in the post nip portion, so that the electric discharge is less likely to occur, and eventually the charge potential of the charge acceptor 31 converges near the potential of the DC voltage. From such charging characteristics, it can be seen that when a superimposed voltage of direct current and alternating current is applied to the charging electrode 32, the charge potential of the charge acceptor 31 is dominated by the discharge on the post nip side.

In the charging device of this embodiment, the charging electrode 32 has a shape swelling in the downstream direction of the charge receiving body 31, and the charging electrode 32 gradually separates from the charge receiving body 31 on the post nip side. The discharge area on the post nip side becomes wider. For this reason, the fluctuation of the charging potential gradually converges, and finally a stable potential with less fluctuation is obtained, and uniform charging is possible. Further, even if toner or the like adheres to the vicinity of the contact nip of the charging electrode 32, the discharge area is wide, so that stable charging can be performed and the occurrence of charging failure can be reduced.

When a charging test similar to that shown in FIG. 5 was carried out using such a charging device, as shown in FIG.
The surface potential of the charge acceptor 31 is the potential of the DC component −
It was confirmed that the ripple component can be reduced to the extent that it does not cause image density unevenness, although it contains a ripple component that is charged near 350 V and fluctuates up and down according to the frequency of the AC component. Also, as in FIG. 6, ΔV
_{When 1-2} and ΔV _HIGH were measured, ΔV _1-2 was about 20 V and ΔV _HIGH was 5 V or less.

A print test was conducted using such a charging device, and it was confirmed that a good copy image was obtained. On the other hand, when the discharge area on the post-nip side is smaller than that of the charging device of the present embodiment as in the conventional charging device, the charge potential of the charge acceptor changes according to the frequency of the AC component and the halftone This caused deterioration of image quality such as uneven density. It should be noted that in the charging method in which the superimposed voltage of DC and AC is applied, the rotation tends to be unstable as compared with the case in which the DC voltage is applied, but the charging device of the present embodiment can obtain a stable charging potential and charge It also has the effect of reducing sound.

FIG. 14 is a schematic configuration diagram showing a charging device which is an embodiment of the invention described in claim 4. In FIG. This charging device has a supporting roller 43 made of an insulating material and a plate-like pressure contact member 45 made of a conductive material, and a DC power supply 44 is connected to the pressure contact member 45. The pressure contact member 45 has a volume resistivity of about 10 ³ Ω · cm by mixing conductive fine particles such as carbon and copper sulfide into a polymer material such as rayon, acrylic, nylon, polypropylene, and polyethylene terephthalate. Is formed into a plate shape. In this example, carbon was mixed into rayon to set the volume resistivity to about 10 ³ Ω · cm. The supporting roller 43 is made of an insulating polymer material that does not mix conductive fine particles. The shapes of the supporting roller 43 and the pressure contact member 45 are the same as those shown in FIG. 1, and other configurations of this charging device are also shown in FIG.
It is the same as the charging device shown in. When a print test was performed using such a charging device, it was confirmed that a good image could be obtained as in the charging device shown in FIG. Further, the supporting roller 43 does not need to be mixed with a conductive powder such as carbon, so that the cost can be reduced. Further, since voltage is supplied to the pressure contact member 45 located far from the charge acceptor 41, there is an advantage that spark discharge is unlikely to occur even when the charging electrode 42 is damaged.

FIG. 15 is a schematic configuration diagram showing a charging device which is an embodiment of the invention described in claim 5. In this charging device, instead of the charging electrode 2 shown in FIG. 1, a charging electrode 52 having a plurality of openings at equal intervals in the circumferential direction near the edge of the film-shaped member is used, and the support roller 53 is a cylindrical member. Is provided with a plurality of protrusions 53a engaged with the opening. The support roller 53 is rotated by being driven by the charge receptor 51 or the main body of the machine, so that the charging electrode 52 has an opening with the projection 5 of the support roller 53.
It is adapted to rotate while engaging with 3a. Also,
A DC power supply 54 is connected to the support roller 53, and a DC voltage is applied to the charging electrode 52. In addition,
The other structure of the charging device is the same as that of the charging device shown in FIG.

When a charging and printing test was performed using such a charging device, it was confirmed that the charging potential was uniform and a good image was obtained as in the charging device shown in FIG. Further, since the rotation of the charging electrode 52 is stabilized by engaging and driving the charging electrode 52 with the support roller 53, good charging can be performed.
Further, it is possible to increase the frictional force between the pressing member 55 and the charging electrode 52, and increase the pressing force to clean the surface of the charging electrode 52.
Using an image forming apparatus to which such a charging device is applied,
When a print test of 5,000 sheets was performed, there was no twisting or twisting of the charging electrode, and a stable charging potential was obtained for a long period of time. In addition, foreign substances did not adhere to the charging electrode 53, and the image quality defect was not caused by the foreign substances.

[0053]

As described above, in the charging device according to the first aspect of the invention, the charging electrode is pulled in the moving direction of the charge receptor, and the contact nip between the charging electrode and the charge receptor is a rotating member. Since it is formed on the downstream side of the position opposite to, the minute gap formed between the charging electrode and the charge acceptor formed on the pre-nip side expands, and the discharge area on the pre-nip side increases. Therefore, when a DC voltage is applied to the charging electrode,
The charging potential can be stabilized and a uniform charging potential can be stably obtained. Further, even if toner or the like adheres, discharge is generated in a wide range on the pre-nip side, so that the occurrence of charging failure can be minimized and a sufficient charging potential can be obtained. Therefore, the occurrence of image quality defects is reduced, and a good image can be obtained.

In the charging device according to the second aspect of the present invention, since the contact nip between the charging electrode and the charge receptor is formed at the upstream side of the position facing the rotating member, the charging electrode functions as the charge receptor. The contact nip is gradually separated from the post nip side, and the discharge area on the post nip side is increased. Therefore, when a superimposed voltage of direct current and alternating current is applied to the charging electrode, the potential of the charge acceptor gradually converges near the voltage of the direct current component on the post nip side, and the charging potential can be stabilized. Therefore, uniform charging can be stably performed. Further, even if toner or the like adheres to the charging electrode, the occurrence of defective charging can be minimized, and a good image without image quality defects can be obtained.

In the charging device according to the third aspect of the invention, the rotating member is held with a gap between the charge receptor and the charging electrode, and the charging electrode is supported so as to contact the charge receptor in a bent state. It is possible to stabilize the rotation of the charging electrode and prevent the contact pressure between the charging electrode and the charge receptor from becoming non-uniform. Therefore, the occurrence of charging failure can be prevented and a more uniform charging potential can be obtained.

In the charging device according to the fourth aspect of the present invention, since the voltage is applied to the charging electrode through the pressure contact member, it is not necessary to use the rotating member as a conductive material and the material setting range is widened. . Therefore, the cost can be reduced by selecting an appropriate material. Furthermore, when the voltage is supplied from the pressure contact member that is held at a distance from the charge receptor, spark discharge is less likely to occur even when the charging electrode is broken, and a uniform charging potential can be stably obtained. it can.

In the charging device according to the fifth aspect of the present invention, since the rotation of the charging electrode is stabilized by the engaging means, it is possible to prevent deformation such as displacement and twisting due to the charging electrode. The contact between the charging electrode and the charge acceptor can be made uniform. Therefore, a more uniform charging potential can be stably obtained, and a good image without image quality defects can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a charging device that is an embodiment of the invention described in claim 1 or claim 3.

FIG. 2 is a diagram for explaining the operation of the charging device shown in FIG.

FIG. 3 is a schematic configuration diagram showing a charging test device for performing a charging test of the charging device.

FIG. 4 is a diagram showing test results of the charging device shown in FIG. 1 and is a diagram showing a relationship between a DC voltage applied to the charging device and a surface potential of a charged charge receptor.

5 is a diagram showing a test result of the charging device shown in FIG. 1 and is a diagram showing a surface potential of a charge receptor with time.

FIG. 6 is a diagram showing the charging characteristics of the charge receptor when the ratio of the peripheral speed of the support roller and the peripheral speed of the charge receptor is changed in the charging device shown in FIG.

FIG. 7 is a diagram showing the shape of the charging electrode and the discharge region when the ratio of the peripheral speed of the support roller to the peripheral speed of the charge receptor is set to 1 or less.

8 is a schematic configuration diagram showing an image forming apparatus in which the charging device shown in FIG. 1 is used.

FIG. 9 is a schematic configuration diagram showing a charging device according to another embodiment of the invention described in claim 1.

FIG. 10 is a schematic configuration diagram showing a charging device that is an embodiment of the invention described in claim 2 or claim 3.

FIG. 11 is a diagram showing changes in the charging potential of the charge receptor in the vicinity of the contact portion between the charging electrode and the charge receptor in the charging device shown in FIG.

12 is a diagram showing a test result of the charging device shown in FIG. 9 and is a diagram showing a surface potential of a charge acceptor with time.

13 is a diagram showing an operation of the charging device shown in FIG.

FIG. 14 is a diagram showing a charging device according to an embodiment of the invention described in claim 4;

FIG. 15 is a diagram showing a charging device which is an embodiment of the invention described in claim 5;

[Explanation of symbols]

 1, 31, 41, 51 Charge acceptor 2, 32, 42, 52 Charging electrode 3, 33, 43, 53 Support roller 4, 44, 54 DC power supply 5, 35, 45, 55 Pressure contact member 10 Charging device 11 Surface potential Sensor 12 Surface potential meter 13 Static electricity removal lamp 14 DC power source 20 Photoconductor 21 Exposure device 22 Developing device 23 Paper cassette 24 Paper 25 Transfer roller 26 Fixing device 27 Cleaning device 28 Paper guide 34 Power supply

Claims (5)

[Claims] 1. A charging electrode in which a flexible semiconductive film member is formed in a cylindrical shape, and the charging electrode is inserted into the charging electrode and supports the charging electrode so as to come into contact with a charge acceptor. A cylindrical rotating member that is rotationally driven to move the charging electrode in the circumferential direction; a power source that applies a charging DC voltage to the charging electrode; and a pressure contact member that presses the charging electrode against the rotating member. The rotation of the rotating member is set in a direction in which the charging electrode moves in the same direction at the contact position with the charge receptor, and the peripheral speed of the rotating member and the peripheral speed of the charge receptor are set to The charging device is characterized in that the ratio thereof is set to 1 or less. 2. A charging electrode in which a flexible semiconductive film member is formed into a cylindrical shape, and the charging electrode is inserted into the charging electrode and supports the charging electrode so as to come into contact with a charge acceptor. A cylindrical rotating member that is rotationally driven so as to move the charging electrode in the circumferential direction; a power source that applies a voltage in which a direct current and an alternating current are superimposed on the charging electrode; The rotation of the rotating member is set in a direction in which the charging electrode moves in the same direction at the contact position with the charge receptor, and the peripheral velocity of the rotating member and the charge receiving member are set. A charging device, characterized in that the ratio to the peripheral speed of the body is set to 1 or more. 3. The charging device according to claim 1 or 2, wherein the rotating member is held with a gap from the charge receptor. 4. The charging device according to claim 1, 2, or 3, wherein the pressure contact member is made of a conductive material, and the power source applies a voltage to the charging electrode through the pressure contact member. Charging device characterized by being adapted to. 5. The charging device according to claim 3, wherein the rotating member has engaging means for transmitting a driving force to the charging electrode at both ends in the axial direction. apparatus.