JPH10198123A - Electrifier and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of suppressing noise and always obtaining stable electrification performance so as to avoid a defect in image quality such as the ghost of a latent image without being influenced by conditions that processing speed is made high, the diameter of a body to be electrified such as a latent image carrier is made small and the device itself is miniaturized. SOLUTION: This device is provided with a movable electrifying film 2 arranged through a specified contact nip area (n) on the body to be electrified 1 moving, capable of moving in the same direction as the moving direction of the body 1 and having conductivity, and a bias power source 3 impressing specified electrifying bias on the film 2. A minute recessed part 4 capable of discharging between the body 1 and the part 4 is formed at the spot of the film 2 facing to the contact nip area (n) between the film 2 and the body 1. Furthermore, the device is provided with a film shape regulating member 5 by which the radius of curvature in the vicinity of the contact nip area (n) of the film 2 is set large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used in an electrophotographic system or the like and an image forming apparatus using the same. The present invention relates to an improvement of an image forming apparatus using the same.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus such as an electrophotographic copying machine or a printer, a latent image carrier is written on a latent image carrier such as a photosensitive drum in order to write an electrostatic latent image thereon. In an image forming apparatus using a charging device that charges in advance or using an intermediate transfer member such as an intermediate transfer belt, the toner image formed on the latent image carrier is primarily transferred to the intermediate transfer member. A charging device (corresponding to a transfer device) for charging an intermediate transfer member for transfer is used.

Here, taking a conventional charging device for charging a latent image carrier as an example, as a conventional charging device of this type,
Non-contact charging methods such as corotrons and contact charging methods such as charging rolls are roughly classified. Non-contact charging methods such as corotrons using corona discharge generate discharges such as ozone and nitrided oxide. Many things occur. The discharge product adheres to the discharge wire, and the discharge operation is likely to be unstable, and if adhered to the surface of the photoreceptor, the performance of the photoreceptor is significantly reduced. For this reason, post-processing of the generated discharge products becomes indispensable, and accordingly, it is not always sufficient to meet the demands for reliability, miniaturization, and cost reduction of the device.

[0004] As means for solving such a problem,
Recently, various contact charging systems such as charging rolls have been proposed and are currently widely used. As a charging device using this type of contact charging system, for example, as shown in FIG. 18A, a charging roll 201 made of a conductive elastic roll is brought into contact with a photosensitive drum 200 serving as a latent image carrier. By connecting a bias power supply 202 to the charging roll 201 and applying a charging bias composed of, for example, a DC voltage (an AC voltage may be superimposed), a contact nip area between the charging roll 201 and the photosensitive drum 200 is formed. A device in which charging is performed in the vicinity of n is already known.

According to this method, the discharge operation due to the discharge product is hardly destabilized by the extremely small amount of ozone generated, and the charging roll 201 may be arranged in contact with the photosensitive drum 200. Therefore, the requirements for miniaturization and weight reduction of the charging device itself are met.

[0006]

However, in the contact charging type charging device described above, the charging roll 20
A mechanism for rotatably supporting the charging roller 1 is indispensable, which not only complicates the apparatus configuration but also causes an error between the charging roller 201 and the photosensitive drum 200 due to an eccentricity error and a supporting error of the charging roll. The contact nip condition is easy to change,
To that extent, charging tends to be uneven.

In order to perform uniform charging with the charging roll 201, for example, it is necessary to form the charging roll 201 from a material which is easily elastically deformed to some extent, and to stabilize the adhesion between the charging roll 201 and the photosensitive drum 200. However, for example, as shown in FIG. 18 (b), no discharge is actually generated in the contact nip region n, and the region where the discharge is actually generated is the adjacent region A, near the contact nip region n. B. However, since the charging roll 201 is elastically deformed to some extent to form the contact nip region n, the adjacent regions A and B near the contact nip region n rapidly rise from the surface of the contact nip region n. In the areas A and B, a very small gap capable of discharging between the charging roll 201 and the photosensitive drum 200 is secured only in a very small part.
A technical problem has been found in that the substantial discharge area is rather reduced. Such a technical problem appears more remarkably as the charging roll 201 is reduced in size.

Further, it is known that it is preferable to apply an AC voltage (oscillation voltage) in order to maintain uniform charging over the charging roll 201 for a long period of time. Then, the electrostatic attraction generated between the photosensitive drum 200 and the charging roll 201 vibrates, and the charging roll 201 vibrates, repeatedly hitting the photosensitive drum 200, and generates a technical problem. Occurs.

As means for solving such technical problems, an apparatus using a charged film has already been proposed (for example, Japanese Patent Application Laid-Open No. 4-249270). As shown in FIG. 19, as shown in FIG. 19, the base end of the flexible charging film 211 is fixed to the metal base 210, and the free end of the charging film 211 is arranged in contact with the surface of the photosensitive drum 200, Bias power supply 212 on base 210
Are connected, and a charging bias composed of a DC voltage or the like is applied, so that the charging film 211 and the photosensitive drum 20 are
The charging is performed in a contact nip region n with zero. In this type, stable contact can be easily obtained with a simple configuration, the cost of the charging film 211 itself is lower than other charging members (charging rolls), and the weight of the charging film 211 is lighter. It is possible to reduce noise.

However, in such a charging device using a charged film, since the charged film 211 is disposed in a fixed state, discharge products such as ozone generated at the time of discharge are discharged from the surface of the charged film 211. This causes a technical problem of preventing normal charging by adhering to the surface and generating streak-like image defects. This is considered that the discharge products generated in the minute gap A between the charging film 211 and the photosensitive drum 200 lose their place and adhere to the surface of the charging film 211, and the discharge products on the charging film 211 are effectively used. It is indispensable to add some kind of cleaning means in order to remove the toner, and the configuration of the apparatus becomes complicated accordingly.

In order to solve such a problem, the present inventor has previously arranged, for example, a predetermined contact nip area with respect to the photosensitive drum and rotated in the same direction as the rotation direction of the photosensitive drum. A movable charged film,
A charging device provided with a bias power supply for applying a predetermined charging bias to the movable charging film is provided (Japanese Patent Application No. 7-1995).
No. 2070335), noise generation is suppressed, and stable and uniform charging performance is ensured at low cost.

However, even with this type of charging device, if the process speed is set high, the diameter of the photosensitive drum is reduced, or the charging device itself is reduced in size,
Inevitably, the charging performance deteriorates, and accordingly, Cy
cle1-2 (the difference between the charging potential of the photoconductor drum 200 in the first charging cycle of the Cycle1-2 and the charging potential of the photoconductor drum 200 in the second charging cycle) increases, and a latent image ghost occurs. A technical problem that a defect occurs in image quality has been found.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and suppresses the generation of noise, increases the process speed, and reduces the diameter of a member to be charged such as a latent image carrier. , Without being affected by the miniaturization of the device itself,
An object of the present invention is to provide a charging device capable of always obtaining stable charging performance and reliably avoiding a defect in image quality such as generation of a latent image ghost, and an image forming apparatus using the same.

[0014]

That is, as shown in FIG. 1, the present invention is arranged with a predetermined contact nip area n with respect to a moving object 1 and in the same direction as the moving direction of the object 1. And a bias power source 3 for applying a predetermined charging bias to the movable charging film 2. The contact nip between the movable charging film 2 and the member 1 to be charged is provided. A small concave portion 4 capable of discharging between the member 1 and the member to be charged 1 is provided in a portion facing the region n.

In such technical means, the object of application of the present invention may be appropriately selected according to the type of the object to be charged 1 as long as the object to be charged 1 is charged. For example, when the member to be charged 1 is a latent image carrier such as a photoconductor or a dielectric on which an electrostatic latent image is carried by an electrophotographic system or an electrostatic recording system, the latent image carrier is charged in advance. In the case where the object to be charged 1 is an intermediate transfer member such as an intermediate transfer belt or a final recording medium, the toner image on the latent image carrier via the intermediate transfer member or the recording medium is used. (Transfer device) that transfers a toner image to an intermediate transfer member or the like by applying an electric charge of the opposite polarity to the above. Further, an image forming apparatus provided with the charging device according to the present invention is also applicable to the present invention.

The movable charging film 2 may be of any type as long as it can be moved. The movable charging film 2 may be formed in a tubular shape and circulated and rotated, or may be wound on a take-up reel. A mode of winding sequentially (winding method) may be appropriately selected, but from the viewpoint of simplification of the configuration, a tubular shape is preferable. Further, as the charging bias by the bias power supply 3, only a DC voltage may be used, but from the viewpoint of further improving the charging performance, it is preferable to use a DC voltage superimposed on an AC voltage.

Further, from the viewpoint of ensuring a wide discharge area near the contact nip area n between the movable charging film 2 and the member 1 to be charged, the movable charging film is located in the adjacent area near the contact nip area n. What is necessary is to secure a wide gap capable of discharging between the member 2 and the member 1 to be charged. In this case, as a specific mode, a film shape regulating member 5 having a large radius of curvature near the contact nip region n of the movable charging film 2 may be provided. In particular, the contact nip region of the movable charging film 2 may be provided. n
It is preferable that the radius of curvature in the vicinity is set so as to be substantially close to the radius of curvature of the member 1 to be charged.

As the film shape regulating member 5 here, for example, it may be arranged inside the tube-shaped movable charging film 2, may be arranged outside the movable charging film 2, or It may be arranged on both the inside and outside of the movable charging film 2, and the number, shape, arrangement position and the like may be appropriately selected. Further, from the viewpoint of minimizing the moving load of the movable charging film 2, it is preferable to reduce the contact resistance between the movable charging film 2 and the film shape regulating member 5.

The movable charging film 2 may be moved in accordance with the movement of the charged body 1 or may be driven separately from the charged body 1. May be. Here, in the aspect of driving the movable charging film 2, from the viewpoint of further improving the charging performance, it is preferable that the moving speed of the movable charging film 2 is set to be faster than the moving speed of the member 1 to be charged.

Further, the fine concave portions 4 of the movable charging film 2 are used for uniformly charging the charged body 1.
It is preferable that they are arranged substantially uniformly in the moving direction and the direction orthogonal thereto. In this case, as the mode of the minute concave portions 4, the minute concave portions 4 are formed of concave streaks that are continuous in the direction perpendicular to the moving direction of the movable charged film 2, and are arranged at equal pitch intervals in the moving direction of the movable charged film 2. May be formed, or may be formed in, for example, a zigzag pattern having the same ratio everywhere in the moving direction of the movable charged film 2, or may be formed, for example, in the center line of the tube-shaped movable charged film 2. However, it may be appropriately selected such as a spiral shape. Further, the fine concave portion 4 may be at least narrower than the contact nip region n, and is not limited to one in the moving direction of the movable charging film 2 in the contact nip region n, and a plurality of fine concave portions may be arranged.

Further, it is necessary to select an appropriate value of the depth of the minute concave portion 4 within a dischargeable gap determined by the charging bias of the bias power supply 3, the resistance value of the movable charging film 2, and the like. Therefore, the projections 6 that define the minute recesses 4 are arranged such that the surface of the minute recesses 4 facing the member 1 is located within the minute gap where discharge is possible.
Any shape may be used as long as it restricts the depth of the film, and the shape may be selected as appropriate, such as a protrusion, a triangle, or a trapezoid. However, charging unevenness is reduced, and the moving load of the movable charging film 2 is reduced. From the viewpoint of reduction, it is preferable to set a small contact area of the convex portion 6 with the member 1 to be charged. Further, the contact portion of the convex portion 6 with the member to be charged 1 may be subjected to anti-leak processing as necessary. For example, when a defect such as a pinhole is present in the photoreceptor, a current is not concentrated on the pinhole by providing a leakage-resistant layer on the charging device side, and the image quality defect becomes inconspicuous.

Japanese Patent Application Laid-Open No. 8-74835 discloses a method of charging a photosensitive drum in order to solve the problems of reducing contamination (toner fusing characteristics) and vibration noise when an AC voltage is applied as a charging bias. Although a technique of providing irregularities on the surface of the roll is disclosed, it is a technique premised on a charging roll and is not only related to the movable charging film 2 but also has a "concavo-convex" of the prior art and a wider discharge area. Since the idea is completely different from that of the minute concave portion 4 of the present application provided under the problem, the prior art and the present invention are completely unrelated.

Next, the operation of the above technical means will be described. Now, the movable charging film 2 is disposed with a predetermined contact nip region n with respect to the moving member 1 and moves in the same direction as the moving direction of the member 1.
Then, the bias power supply 3 applies a predetermined charging bias to the movable charging film 2. Here, the movable charging film 2
In the portion facing the contact nip region n with the member 1 to be charged,
Since the minute concave portion 4 capable of discharging between the charged object 1 and the movable charged film 2 is provided in the adjacent area near the contact nip area n, the minute concave portion 4 is provided. The minute gap facing the minute concave portion 4 in the nip region n functions as a discharge region, and the movable charging film 2 charges the member 1 to be charged. In particular, if the radius of curvature of the movable charging film 2 in the vicinity of the contact nip region n is set to be large by the film shape regulating member 5, the charged object 1 and the movable charging film 2 in the adjacent region near the contact nip region n can be formed. , A small gap capable of discharging is widely secured.

Further, since the movable charging film 2 is arranged in uniform contact with the member 1 to be charged and moves in the same direction as the member 1 to be charged, the apparent surface area increases as compared with the fixed charging film. In addition, even if the discharge product adheres to the movable charging film 2, the cleaning effect of the discharge product by the air flow and the cleaning effect by the moving contact with the member 1 to be charged are expected. The amount of discharge products remaining as deposited and attached is reduced, and the reliability against contamination is significantly improved as compared with the fixing film.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. Embodiment 1 FIG. 2 shows Embodiment 1 of an image forming apparatus to which the present invention is applied.
Is shown. In the figure, reference numeral 20 denotes a photosensitive drum, 21
Denotes a charging device for charging the photosensitive drum 20, 22 denotes an exposure device such as a laser scanning device for writing an electrostatic latent image on the charged photosensitive drum 20, and 23 denotes an electrostatic device formed on the photosensitive drum 20. A developing device for developing the latent image with toner; 24, a transfer device for transferring the toner image formed on the photosensitive drum 20 onto recording paper 25; 26, a cleaner for cleaning residual toner on the photosensitive drum 20; Is a paper feed cassette for supplying the recording paper 25, 28 is an alignment roll (registration) for supplying the recording paper 25 from the paper feed cassette 27 to the transfer portion at a predetermined timing, and 29 is on the recording paper 25 after the transfer. The fixing device fixes an unfixed toner image.

In the present embodiment, the charging device 21
As shown in FIG. 3, a tube-shaped movable charging film 40 arranged in contact with the photosensitive drum 20, and a movable charging film 40 near and near a contact nip region n of the movable charging film 40 with the photosensitive drum 20. It comprises film shape regulating rods 51 and 52 disposed inside 40 and a bias power source 60 for applying a charging bias to the movable charging film 40.

More specifically, in the present embodiment, the photosensitive drum 20 having an outer diameter of, for example, 30φ is used. On the other hand, as the movable charging film 40, for example, a fluororesin is extruded. It is a molded tube with an outer diameter of about 10φ in a natural state, a film thickness of about 100 to 200 μm (in this example, 150 μm is used),
Further, those having a volume resistivity of about 10 ⁸ Ω · cm are used.

The film shape regulating rods 51, 52
Is composed of, for example, a cylindrical metal rod having an outer diameter of 3φ extending along the axial direction of the movable charging film 40, and both ends thereof are fixedly supported by a support bracket (not shown). The distance between the film shape regulating rods 51 and 52 is set to, for example, about 4 mm, and the gap with the photosensitive drum 20 is set to about 0.5 to 1.0 mm. Therefore, in the present embodiment, as shown in FIG. 3, the film shape regulating rods 51 and 52 slightly move the movable charged film 40 loosely fitted around the rod from the free cylindrical shape shown by the dotted line to the lower side. It is deformed into a deformed shape crushed.

Further, in the present embodiment, the AC power supply VAC (1.5 to 2.5 kV) is used as the bias power supply 60.
_PP (peak-to-peak voltage), frequency: 400-20
00 Hz) is superimposed on the DC voltage VDC (−350 to −7).
That which applies a charging bias of (00 V) is used. Note that the AC power supply may be a constant current control. In the present embodiment, the film shape regulating rods 51,
A bias power source 60 is connected to 52, and the film shape regulating rods 51 and 52 also serve as a power supply member for the movable charging film 40.

Further, in the present embodiment, as shown in FIG. 4, minute concave portions 41 are regularly provided on the outer peripheral surface of the movable charging film 40.
Is formed by arranging a large number of recesses having a substantially trapezoidal cross section extending along the axial direction (corresponding to a direction perpendicular to the rotation direction) of the movable charging film 40 at a predetermined pitch. The depth d of the minute concave portion 41 is selected to be an appropriate value within the dischargeable gap determined by the applied voltage of the charging bias, the resistance value of the movable charging film 40, and the like. It is set to about 0.1 mm. Further, the width dimension m (corresponding to the dimension along the rotation direction of the movable charging film 40) of the minute concave portion 41 may be set at least in a range narrower than the contact nip area n of the movable charging film 40. It is set to about 0.05 to 1 mm. Further, as the convex portions 42 that partition the minute concave portions 41, for example, those having the same trapezoidal shape as the minute concave portions 41 are used.

Next, the operation of the charging device according to the present embodiment will be described. In FIG. 3, the charging bias from the bias power supply 60 is applied to the film shape regulating rods 51 and 5.
2 is applied to the movable charging film 40. on the other hand,
When the photosensitive drum 20 rotates, the photosensitive drum 20
The movable charging film 40, which is arranged in contact with the photosensitive drum 20, rotates following the rotation of the photosensitive drum 20.

At this time, as shown in FIG. 5A, adjacent areas A and B near the contact nip area n between the movable charging film 40 and the photosensitive drum 20 are provided with the photosensitive drum 20 and the movable charging film 40. And a small gap capable of discharging is also formed in a region C corresponding to the small concave portion 41 in the contact nip region n. On the other hand, in the comparative embodiment (movable charged film without the minute concave portion 41), as shown in FIG. 5B, an adjacent area A near the contact nip area n between the movable charged film 40 and the photosensitive drum 20 is used. , B, a small gap capable of discharging is formed between the photosensitive drum 20 and the movable charging film 40. In this comparison, no discharge phenomenon actually occurred in the contact nip region n. Therefore, the discharge area of the present embodiment is larger than that of the comparative embodiment, and the charging efficiency for the photosensitive drum 20 is improved. Then, even if there is a difference in the surface potential of the photosensitive drum 20 that enters the charged area, the difference in the surface potential after passing through the charged area becomes small, and there is no defect in image quality due to insufficient charging.

As shown in FIG. 7, the present inventor fixed the photosensitive drum 20 to φ30 and changed the charging member to a φ6 charging roll, φ10 charging roll, and Flatbar, respectively. When the performance (Cycle1-2) was evaluated, the results shown in FIG. 8 were obtained. In addition, Cycl
e1-2 is the photosensitive drum 2 in the first charging cycle
It shows the difference between the charging potential of 0 and the charging potential of the photosensitive drum 20 in the second charging cycle. The smaller this value is, the better the charging performance is. According to the figure, it is understood that the flat bar has an infinite radius of curvature at the contact portion with the photosensitive drum 20, and the charging performance at this time is the best. This indicates that the wider the discharge area near the contact nip area, the better the charging performance.

In particular, in the present embodiment, the shape of the movable charging film 40 is regulated by the film shape regulating rods 51 and 52 so as to construct a state close to Flatbar described above. That is, as shown in FIGS. 6A and 6B, the film shape regulating rod 51 (52) moves the movable charging film 40 near the contact nip area n to the photosensitive drum 2.
It works to make it closer to the 0 side. Therefore, in the present embodiment, in the adjacent area near the contact nip area n, the radius of curvature R of the movable charging film 40 does not include the film shape regulating rods 51 (52) (FIG. 6B).
R ′ (R5), it is understood that the dischargeable minute gaps A and B between the movable charging film 40 and the photosensitive drum 20 are widely secured, and the charging performance is more excellent. Will be kept.

FIG. 9 shows a modification of the charging device used in the first embodiment. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here. In the figure, the basic configuration of the charging device 21 is substantially the same as that of the first embodiment, but is different from the first embodiment, and the film shape regulating rods 51 and 52 of the first embodiment are substantially U-shaped in cross section. Film shape regulating plate (for example, SUS304, plate thickness t = 0.5 mm) 5
3 is replaced. In this modification, the minimum gap between the film shape regulating plate 53 and the photosensitive drum 20 is 0.1 to 1.0 mm, and the width of the film shape regulating plate 53 is set to about 9 mm. As in the first embodiment, the radius of curvature of the regulating plate 53 in the adjacent area near the contact nip area n of the movable charging film 40 is set to be larger than that in the free state (R5). Also,
The film shape regulating plate 53 is also used as a charging bias power supply member. It is needless to say that a conductive resin, an aluminum deformed material, or the like can be used as a material of the film shape regulating plate 53.

Second Embodiment FIG. 10 shows a charging device according to a second embodiment of the present invention. In the figure, the basic configuration of the charging device is such that a tube-shaped movable charging film 40 is wound around an elastic roll 54 made of non-conductive urethane foam, for example. Photoreceptor drum 2
0, and a pair of outer shape regulating rods 56, 56 are disposed above the elastic roll 54.
The elastic roll 54 is deformed so as to be slightly crushed, so that the radius of curvature of the adjacent region near the contact nip region n of the movable charging film 40 is set to be larger than the radius of curvature in the free state. In particular, in the present embodiment, the lower the hardness of the elastic roll 54, the better, and the Asker C hardness is desirably 30 degrees or less, preferably 20 degrees or less. In the present embodiment, the outer shape regulating rods 56 also serve as a charging bias power supply member. Therefore, also in the present embodiment, the same operation and effect as those of the first embodiment can be obtained.

As a modification of this embodiment, as shown in FIG. 11, for example, the elastic roll 57 is made of conductive urethane foam (resistance value is about 10 ⁶ Ω · cm). May be used also as a power supply member to the movable charging film 40 by using a spring member 55 that presses the outer shape control rods 56, 56, or in place of the outer shape control rods 56, 56, the outer shape control plates 58, 58 having an elliptical inner shape. It may be used.

Further, as shown in FIG.
An elastic roll 71 made of urethane foam having an outer diameter of φ8 is included in the movable charging film 40 of the above-mentioned. The film shape regulating plates 72, 72 having an inner side of an elliptical shape are made of a conductive material. The shapes of the movable charging film 40 may be regulated by 72 and 72.

Third Embodiment The charging device according to the third embodiment includes a movable charging film 40 different from the first embodiment. That is, the movable charging film 40 according to the present embodiment is, for example, as shown in FIG.
As shown in (a), a convex portion 42 that partitions a minute concave portion 41.
Are formed as arc-shaped protrusions 43 at the tip, and the contact area between the protrusion 42 and the photosensitive drum is set smaller than that in the first embodiment. As shown in FIG. 13B, even if the convex portion 42 is formed as a triangular chevron portion 44 or a trapezoidal portion having a narrow top, the contact area between the convex portion 42 and the photosensitive drum is reduced. It is possible to

According to the present embodiment, since the contact area between the convex portion 42 and the photosensitive drum is reduced, the moving load of the movable charging film 40 is reduced, and the contact between the convex portion 42 and the photosensitive drum is reduced. Leakage at the time of discharge from the part can be suppressed to a smaller extent. Further, the small interval area required for the discharge can be set large.

Fourth Embodiment FIG. 14 is an explanatory diagram showing an outline of a fourth embodiment to which the present invention is applied. In the figure, the basic configuration of the charging device is substantially the same as that of the first embodiment, but differs from the first embodiment in that a film driving mechanism 80 for rotating the movable charging film 40 is added. Embodiment 1
The same components as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the detailed description is omitted here. In the present embodiment, the film drive mechanism 80 includes the drive motor 8
An elastic drive roll 82 rotated by 1 is disposed in contact with the outside of the movable charging film 40, and a backup roll 83 is fixedly provided on the back side of the movable charging film 40 facing the elastic drive roll 82. In the present embodiment, the moving speed vf of the movable charging film 40 is set to be higher than the moving speed vp of the photosensitive drum 20.

In this embodiment, when the charging performance (Cycle 1-2) with respect to the speed difference between the movable charging film 40 and the photosensitive drum 20 was evaluated, the result shown in FIG. 15 was obtained. According to the figure, when the speed difference between the movable charging film 40 and the photosensitive drum 20 is increased, the portion where the movable charging film 40 and the convex portion 42 first contact each other also becomes Δ.
Since the minute concave portion 41 shifts after tsec, a minute gap capable of discharging is formed, and it is understood that the discharging performance (charging performance) increases accordingly. still,
FIG. 15 shows a comparative example (movable charging film 40).
A similar experiment was performed for the movable charging film 40 and the photosensitive drum 2.
As the speed difference from 0 increases, the discharge performance slightly increases, but it is understood that the degree of the improvement is smaller than in the present embodiment.

The film drive mechanism 80 may be appropriately selected according to the support structure of the movable charging film 40. For example, as shown in FIG. The elastic roll 71 may be directly driven by the drive motor 84, or, as shown in FIG.
A drive roll 85 is provided inside the movable charging film 40 for a structure similar to that of (Type), and a certain amount of tension is applied to the movable charging film 40 by the driving roll 85 and the pair of film shape regulating rods 51 and 52. , The driving roller 85 may be driven by a driving motor 86 to drive the movable charging film 40.

Others In each embodiment, the present invention is applied to the charging device 21. However, the present invention is not limited to this. For example, the present invention is applied to the transfer device 24 of the image forming apparatus shown in FIG. You may make it apply. Further, the image forming apparatus to which the present invention is applied may be appropriately selected. For example, as shown in FIG. The present invention is also applicable to a configuration in which the primary transfer device 101 is provided at a primary transfer portion of the transfer belt 100 and the secondary transfer device 102 is provided at a secondary transfer portion of the intermediate transfer belt 100. . In FIG. 17, reference numeral 103 denotes a group of rolls for extending the intermediate transfer belt 100, and reference numeral 104 denotes a belt cleaner for removing residual toner and the like on the intermediate transfer belt 100. In such an intermediate transfer type image forming apparatus, the present invention may be applied not only to the charging device 21 but also to the primary transfer device 101 and further to the secondary transfer device 102. Although the image forming apparatus shown in FIGS. 2 and 17 is for a single color, it is needless to say that the image forming apparatus can be applied to a color image forming apparatus. in this case,
For example, the developing device 23 may be replaced with a rotary developing device for color or a plurality of developing devices for each color component, and the process may be controlled by a process for color.

[0045]

As described above, according to the present invention,
The movable charging film is placed in contact with the charged object, and the discharge phenomenon occurs in the contact nip area with the charged object in addition to the adjacent area near the contact nip area between the charged object and the movable charged film. , A larger discharge area can be secured than before, and the charging efficiency can be further increased accordingly.
For this reason, even if the process speed is increased, the diameter of the member to be charged such as the latent image carrier is reduced, or the charging device itself is downsized, stable charging performance can always be obtained, and the latent image ghost can be obtained. Defects in image quality such as generation can be reliably avoided. In particular, if the radius of curvature near the contact nip region of the movable charging film is set to be large by the film shape regulating member, discharge between the member to be charged and the movable charging film in the adjacent region near the contact nip region is possible. It is possible to secure a large minute gap, and it is possible to more effectively increase the charging efficiency.

Further, in the present invention, since the movable charging film is used, the noise caused by the vibration generated when an AC voltage is used as the charging bias can be greatly reduced as compared with the embodiment using the charging roll. Furthermore, since the movable charging film is arranged in uniform contact with the member to be charged and moves in the same direction as the member to be charged, the apparent surface area increases as compared with the fixed charging film. Even if an object adheres to the movable charging film, it can be expected that the cleaning action of the discharge product by the air flow and the cleaning action by the moving contact with the member to be charged can be expected, and the discharge product remains deposited and attached to the movable charging film. Nothing happens. For this reason, it is possible to effectively prevent poor charging over time due to deposition of the discharge product.

Further, since a minute concave portion is provided in the movable charging film for enlarging the discharge area, the contact area between the movable charging film and the member to be charged can be reduced. At this time, even if a charging bias is applied, the probability that the defect (pinhole or the like) on the member to be charged such as the photosensitive drum or the like and the charging device contact with each other is reduced, and the movable charging film and the member to be charged contact each other. There is also a secondary effect that the reactive current leaking through the section can be reduced, and the capacity of the bias power supply can be reduced accordingly.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a charging device according to the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of Embodiment 1 of the image forming apparatus to which the present invention has been applied.

FIG. 3 is an explanatory diagram illustrating an outline of a charging device used in the first embodiment.

FIG. 4 is an explanatory diagram showing a configuration of a movable charging film used in the first embodiment.

FIG. 5A is an explanatory diagram illustrating a charging principle of a movable charging film according to the present embodiment, and FIG. 5B is an explanatory diagram illustrating a charging principle of a movable charging film according to a comparative embodiment.

FIGS. 6A and 6B are explanatory diagrams showing a difference in operation depending on the presence or absence of a film shape regulating rod according to the present embodiment.

FIG. 7 is an explanatory diagram showing the contents of an experiment for examining the relationship between the shape of a movable charged film and the chargeability.

FIG. 8 shows the experimental results of FIG. 7 (tube curvature and cycle).
FIG. 6 is a graph showing the relationship with 1-2).

FIG. 9 is an explanatory diagram showing an outline of a charging device according to a modification of the first embodiment.

FIG. 10 is an explanatory diagram showing an outline of a charging device according to a second embodiment.

FIG. 11 is an explanatory diagram illustrating an outline of a charging device according to a modification of the second embodiment.

FIG. 12 is an explanatory diagram showing an outline of a charging device according to another modification of the second embodiment.

13A is an explanatory view showing a configuration of a movable charging film of a charging device according to Embodiment 3, and FIG. 13B is an explanatory view showing a modified form thereof.

FIG. 14 is an explanatory diagram showing an outline of a charging device according to a fourth embodiment.

FIG. 15 is a graph showing the relationship between the speed ratio of the movable charged film / photosensitive drum and Cycle 1-2 in the fourth embodiment.

FIGS. 16A and 16B are explanatory views showing a modification of the charging device according to Embodiment 4. FIGS.

FIG. 17 is an explanatory diagram illustrating another example of the image forming apparatus to which the present invention has been applied.

FIG. 18A is an explanatory diagram showing an example of a conventional contact charging type charging device, and FIG. 18B is an enlarged explanatory diagram showing the vicinity of a contact nip region n.

FIG. 19 is an explanatory view showing another example of a conventional contact charging type charging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... To-be-charged body, 2 ... Movable charging film, 3 ... Bias power supply, 4 ... Minute concave part, 5 ... Film shape regulating member, 6 ... Convex part

Claims (7)

[Claims] 1. A movable object having a predetermined contact nip area (n) with respect to a moving object to be charged (1) and having a conductivity capable of moving in the same direction as the moving direction of the object to be charged (1). A charging film (2); and a bias power supply (3) for applying a predetermined charging bias to the movable charging film (2). A contact nip area of the movable charging film (2) with the member (1) to be charged. A charging device, characterized in that a minute concave portion (4) capable of discharging with respect to the member to be charged (1) is provided in a portion facing (n). 2. The charging device according to claim 1, wherein the movable charging film is formed in a tubular shape and circulates and rotates. 3. The charging device according to claim 1, further comprising a film shape regulating member having a large radius of curvature near the contact nip region of the movable charging film. Charging device. 4. The charging device according to claim 1, wherein the moving speed of the movable charging film is set higher than the moving speed of the member to be charged. 5. The charging device according to claim 1, wherein the minute concave portions are arranged substantially uniformly in a moving direction of the member to be charged and a direction perpendicular to the moving direction. apparatus. 6. The charging device according to claim 1, wherein the object to be charged (1) has a convex portion (6) defining a minute concave portion (4).
A contact area with the charging device is set to be small. 7. An image forming apparatus comprising the charging device according to claim 1.