JPH103201A - Electrifier for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of the filming of toner on the surface of an electrifying roller by improving the contact state of the electrifying roller and a cleaning member in the electrifying device of a roller electrifying system. SOLUTION: The sticking position of a cleaning pad 34 to an electrifying roller case 31 is set so that the end 34a of the pad 34 on a downstream side in the rotating direction B of the electrifying roller 19 may project to the downstream side in the rotating direction of the roller 19 from a center line C in the radial direction of the roller 19 drawn along in a moving direction so as to make the pad 34 press-contact with the roller 19 while setting the center line C as reference. Nip width W3 between the roller 19 and the pad 34 is made different on both sides of the center line C, and the nip width Wu on an upstream side in the rotating direction B of the roller 19 is made considerably larger than the nip width Wd on the downstream side therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for an image forming apparatus, and more particularly to a charging device having improved contact between a charging roller and a member for cleaning the charging roller.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a facsimile, a photoreceptor, a developing device, a charging device and the like are housed in an integrated case to constitute an image forming unit, and an image forming unit is formed. It is becoming more common to reduce the size of the entire apparatus. In this type of image forming unit, a roller charging type charging device is often used.
Such a charging device is shown in FIGS. In this charging device, a charging roller 1 is held in a charging roller case 2, and springs 4, 4 are arranged between a bearing 3 of the charging roller 1 and a lower surface of the charging roller case 2, and a rotating arm (not shown) is provided as a whole. When the charging roller 1 comes into contact with the photoreceptor 5 by being pressed down, the charging roller 1 is evenly pressed against the photoreceptor 5 by the urging force of the spring 4 to rotate with the photoreceptor 5,
This is to uniformly charge the surface of the photoconductor 5.

A cleaning pad 6 is adhered to the lower surface of the charging roller case 2, and the charging roller case 2 is further pushed down by an arm (not shown) during a non-image forming step, so that the cleaning pad 6 made of a sponge or the like is transferred to the charging roller 1. , So that the toner and other foreign matter are removed from the surface of the charging roller 1 by sliding contact with the surface of the charging roller 1 which rotates with the photoreceptor 5. The arrow A in the figure indicates the photoconductor 5
, The arrow B indicates the rotation direction of the charging roller 1.

Incidentally, in such a charging device, it is necessary to take into consideration that toner filming does not occur on the surface of the charging roller 1 due to sliding contact with the cleaning pad 6. The contact pressure between the charging roller 1 and the cleaning pad 6 has a certain appropriate value, and toner filming is more likely to occur as the contact pressure between the charging roller 1 and the cleaning pad 6 increases. Charging becomes impossible, thereby causing a problem that image quality is impaired. The charging roller 1
The longer the contact time between the cleaning pad 6 and the cleaning pad 6, the more easily the toner filming occurs. Therefore, if the contact of the cleaning pad 6 with the charging roller 1 is uniform between the upstream and downstream sides in the rotation direction B of the charging roller 1 as in the example of FIG. 5, the contact length is long and the contact time is long. Since it is long, filming as described above is likely to occur.

In general, a sponge and a felt having a two-layer structure in which the felt is brought into contact with a charging roller are often used. Therefore, when the contact form as shown in FIG. 5 is adopted, for example, a sponge having a relatively large cell diameter has a large frictional force with the surface of the charging roller 1 and the charging roller 1 has a large frictional force.
Of removing the toner and the like adhering to the surface of the charging roller 1 as the cleaning pad 6 and reducing the bite of the cleaning pad 6 into the charging roller 1 to shorten the contact length and reduce the contact pressure. Can be considered. However, as described above, the size of the entire image forming apparatus has been reduced, and accordingly, the charging device has also been reduced in size, and in order to ensure a desired contact state between the charging roller 1 and the cleaning pad 6, it is necessary to make each component part It is necessary to control the dimensional tolerance to be a very small value, and there is a limit to measures for reducing the biting amount of the cleaning pad 6 and reducing the contact pressure as described above. That is, neither the contact pressure nor the contact length becomes too small to satisfy the desired cleaning properties, or the contact pressure and the contact length become too large, so that not only the filming of the toner but also the surface of the charging roller 1 is easily damaged. It was easy to get the result.

Various measures have been proposed to solve the above-mentioned conventional problems. For example, JP-A-3-101
No. 768 discloses that, as shown in FIG. 7, the downstream end of the cleaning pad 6 in the rotation direction (the direction of the arrow B) of the charging roller 1 is moved from the center of the charging roller 1 to the charging roller case 2.
Perpendicular h drawn on the surface to which the cleaning pad 6 is attached
Or a technique that is positioned upstream of the vertical line h. With this technology,
The contact length between the charging roller 1 and the cleaning pad 6, that is, the nip width is shortened (the nip width W2 in the example of FIG. 7 is less than half as compared with the nip width W1 of the example of FIG. 5). Short contact time.

However, with the above configuration, the contact length between the charging roller and the cleaning pad is too short in the charging roller whose diameter is reduced in accordance with the miniaturization of the entire apparatus, and filming of toner is taken into consideration. Then, since the contact pressure cannot be increased too much, an appropriate contact state cannot be obtained in many cases, and therefore, there is a problem that it is difficult to perform sufficient cleaning. Therefore, the present invention can improve the contact property with the cleaning member even when a small-diameter charging roller is used, properly contact the charging roller with the cleaning member, prevent the occurrence of toner filming, and consequently cause uneven charging and An object of the present invention is to provide a charging device of an image forming apparatus having a structure capable of preventing occurrence of an abnormal image caused by the charging.

[0008]

According to a first aspect of the present invention, there is provided a charging device for an image forming apparatus, comprising: a charging roller for pressing a photosensitive member to charge the photosensitive member in order to achieve the above object; And a cleaning member for cleaning the charging roller while pressing against the charging roller, wherein the charging roller extends in a moving direction for pressing the cleaning member against the charging roller. With respect to the center line in the radial direction, the downstream end of the cleaning member in the rotation direction of the charging roller is disposed so as to be able to press against the surface of the charging roller at a position downstream of the center line in the rotation direction of the charging roller. It is characterized by the following.

According to a second aspect of the present invention, the cleaning member has a two-layer structure of a sponge material and a felt material slidably contacting the surface of the charging roller.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a charging device for an image forming apparatus according to the present invention will be described below with reference to the drawings. First, the configuration of an image forming unit of an image forming apparatus using the charging device according to the present invention will be described. FIG. 1 is a sectional view showing an image forming unit, a transfer / separation device, a fixing device and the like using the charging device according to the present invention, and FIG. 2 is an exploded perspective view of the charging device shown in FIG. In these figures, reference numeral 10 denotes an image forming unit, 11 denotes a transfer / separation device, and 12 denotes a fixing device. The image forming unit 10 is formed in a cartridge shape and is detachably attached to an image forming apparatus main body (not shown). It is possible.
Further, the transfer / separation device 11 includes a transfer roller 13 and is rotatable in a vertical direction in FIG.
The fixing device 12 includes a pressure roller 15 and a heating roller 16.

The illustrated image forming unit 10 comprises a case around a photoreceptor surrounding case 17 and an upper cover 37, inside which a photoreceptor 18, a charging roller 19 constituting a charging device,
The developing device 20, the cleaning device 21, a toner recycling belt 22 for feeding the residual toner collected by the cleaning device 21 to the developing device 11, a toner conveying screw 42, an agent stirring member 43, and the like are provided. Upper cover 3
Reference numeral 7 is attached so as to cover the case 17 around the photosensitive member, and prevents the hand of an operator or a service person from contacting the photosensitive member 18 and the charging roller 19.

As shown in FIG. 2, the charging roller 19 of the charging device has a small hygroscopic property on the outer periphery of a metal core 27,
It is formed by molding a conductive rubber (e.g., epichlorohydrin rubber) 28 having a stable resistance value.
8 is brought into contact with the surface of the photoreceptor 18 and
By applying a high voltage to the photoconductor 7, the surface of the photoconductor 18 is uniformly charged. Both ends of the core metal 27 of the charging roller 19 are rotatably held by bearings 29, 29,
Each of the bearings 29 is attached to the charging roller case 31 so as to be movable in the vertical direction in the figure, and a pressure spring 33 is interposed between the bearing 29 and the inner surface of the charging roller case 31. The charging roller 19 can be pressed against the photosensitive member 18 with a predetermined pressure.

A cleaning pad 34 for cleaning the surface of the charging roller 19 is adhered to the inner surface of the charging roller case 31, which is a holding member of the charging roller 19, with an adhesive such as a double-sided tape. The charging roller 19 keeps in contact with the surface of the photoreceptor 18 during the charging operation. As is well known, the surface of the photoreceptor 18 is easily contaminated by minute toner adhering to the surface of the photoreceptor 18 to cause charging unevenness. The cleaning is performed by pressing the cleaning pad 34 against pressure to remove the adhered toner, thereby preventing charging unevenness caused when the charging roller 19 becomes dirty.

Further, the inside of both ends in the longitudinal direction of the charging roller case 31 and the photosensitive member surrounding case 1 of the image forming unit 10 are formed.
7, springs 36, 36 are interposed between the spring receivers 35, 35, respectively, so that the entire charging device is separated from the photoreceptor 18 in a state other than during the charging operation and when the charging roller 19 is cleaned. The charging roller case 31 is urged upward in the drawing by the urging force of the spring 36. In the figure, reference numerals 40 and 40 denote a pair of swingable pressure arms which constitute a contact / separation mechanism for bringing the charging roller 19 into and out of contact with the photosensitive member 18.
1 by pressing the upper surface of the charging roller case 31
When the pressing arm 40 is separated from the upper surface of the charging roller case 31, the charging roller 19 and the charging roller case 31 are separated from the photosensitive member 18 by the urging force of the spring 36. Has become.

An image forming operation using the image forming unit configured as described above will be briefly described. First, with the image forming apparatus main body mounted at a predetermined position, the photosensitive member 18 can be rotated in a direction indicated by an arrow in FIG. 1 by a driving source (not shown). The surface is neutralized by irradiating static elimination light from a static elimination lamp (not shown), and the surface potential is averaged to a reference potential of, for example, 0 to -150V. Next, a high voltage is applied to the charging roller 19 which is in contact with the surface of the photoreceptor 18 to charge the photoreceptor 18, and the surface potential is set to, for example, about -1100V. Then, the charged potential surface is exposed, and the surface potential to form an image is, for example, 0 to 0.
A latent image portion of -290 V is formed.

When the latent image portion is moved to the position of the developing sleeve 23 of the developing device 20 by the rotation of the photosensitive member 18, the latent image portion is held on the surface of the developing sleeve 23 in which a bias of, for example, about -800 V is applied. The latent toner adheres, and the latent image portion is developed to become a toner image (visible image).

On the other hand, the transfer paper P fed from a paper feed unit (not shown) is moved by the registration roller pair 24 so that the front end of the transfer paper P and the front end of the toner image on the photoreceptor 18 coincide at the position of the transfer roller 13. The timing is adjusted, and the toner image on the photoconductor 18 is transferred to the transfer paper P by the transfer roller 13. The transfer paper P is conveyed between the pressure roller 15 and the heating roller 16 of the fixing device 12, where the transferred toner is fused to the transfer paper P by heat and pressure, and is transferred to a discharge tray (not shown) outside the apparatus. Discharge.

The residual toner remaining on the photoreceptor 18 after the image transfer is scraped off by a cleaning blade 25 of a cleaning device 21. Move to The residual toner collected by the cleaning device 21 is transferred to the developing device 20 by the toner recycling belt 22.
The developer is transported to the developer agitating section 26 and collected.
And the toner is recycled by supplying the toner to the developing sleeve 23 again. In the figure, 41 is the cleaning blade 2
5 holder.

In the present embodiment, the position of the cleaning pad 34 attached to the charging roller case 31 is improved as shown in FIG. That is, a radial center line C of the charging roller 19 drawn along the moving direction to press the cleaning pad 34 against the charging roller 19.
Roller 1 of the cleaning pad 34 with reference to
9 is protruded from the center line C to the downstream side in the rotation direction of the charging roller 19, and the nip width W3 is made different on both sides of the center line C (in the rotation direction B of the charging roller 19). The upstream side is Wu, and the downstream side is Wd.
= Wu + Wd), and the nip width Wu on the upstream side is set to be considerably larger than the nip width Wd on the downstream side.

When the cleaning pad 34 is arranged as described above, the downstream end 3 in the rotation direction B of the charging roller 19 is formed.
4a is pulled by the rotation of the charging roller 19 and deformed as shown in the figure, the contact pressure at this portion where the biting amount is small is the smallest, and the portion on the radial center line h of the charging roller 19 is the smallest. The contact pressure is large, and therefore the contact pressure is also large, and the upstream side in the rotation direction B of the charging roller 19 shows a contact pressure intermediate between them (shown as large, medium, and small in FIG. 3B). In other words, the charging roller 19 is more than the conventional example shown in FIG.
The contact length between the cleaning pad 34 and the downstream end 34a
When a contact pressure in an appropriate range according to the materials of the charging roller 19 and the cleaning pad 34 is applied, not only sufficient cleaning properties can be exhibited but also uniform contact on both sides of the center line C. Since the contact length is shorter and the contact pressure is smaller, filming of the toner hardly occurs.

For example, the hardness of the material of the cleaning pad 34, in other words, the number of cells is appropriate (for example, about 50 ± 3).
If a sponge is used, the cleaning ability of the sponge itself is originally high, so there is no need to use a very high contact pressure.
Therefore, the surface of the charging roller 19 is not damaged by a sponge, and the contact length is longer than the downstream end portion 34a of the cleaning pad 34, so that both the contact pressure and the contact time satisfy the condition that can prevent the occurrence of toner filming. Becomes Of course, in the present invention, similar cleaning properties can be exhibited even if a cleaning pad 34 composed of a sponge 34b and a felt 34c is used as shown in FIG.

The cleaning pad 34 is pulled by the rotation of the charging roller 19 on each of the downstream side and the upstream side in the rotation direction B of the charging roller 19, so that the force in the shearing direction is charged on the adhesive surface to the charging roller case 31. It hangs along the inner surface of the roller case 31. However, at the downstream end 34a, a compressive force is applied to the adhesive surface side of the charging roller case 31, and at the upstream end, the force in the shearing direction is very small.

[0023]

As described above, the charging device of the image forming apparatus according to the present invention is based on the radial center line of the charging roller along the moving direction for pressing the cleaning member against the charging roller. Since the downstream end of the cleaning member in the rotation direction of the charging roller can be pressed against the surface of the charging roller at a position downstream of the center line in the rotation direction of the charging roller, the contact property between the charging roller and the cleaning member is improved, and the charging property is improved. There is an effect that the occurrence of toner filming and flaws on the roller surface can be reliably prevented.

[Brief description of the drawings]

FIG. 1 shows an image forming unit using a charging device according to the present invention;
FIG. 3 is a cross-sectional view illustrating a transfer / separation device, a fixing device, and the like.

FIG. 2 is an exploded perspective view of the charging device shown in FIG.

FIG. 3 is a cross-sectional view (A) showing an embodiment of a charging device according to the present invention, and an enlarged cross-sectional view (B) of a main part.

FIG. 4 is a cross-sectional view showing another embodiment of the charging device according to the present invention.

FIG. 5 is a side sectional view showing a configuration of a conventional charging device.

FIG. 6 is a front sectional view of the charging device of FIG. 5;

FIG. 7 is a side sectional view showing the configuration of another conventional charging device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 image forming unit 11 transfer device 12 fixing device 13 transfer roller 14 rotation fulcrum 15 pressure roller 16 heating roller 17 image forming unit case 18 photoconductor 19 charging roller 20 developing device 21 cleaning device 22 toner recycling belt 23 developing sleeve 24 Registration roller pair 25 Cleaning blade 26 Developer stirring section 27 Core bar 28 Conductive rubber 29 Bearing 31 Charging roller case 33 Pressure spring 34 Cleaning pad 34a Downstream end of cleaning pad 34b Sponge 34c Felt 35 Spring receiver 36 Spring 37 Upper Cover 41 Holder of cleaning blade 42 Toner transport screw 43 Agent stirring member A Rotation direction of photoconductor B Rotation direction of charging roller C Center line of charging roller P Transfer paper W1, W2 W3, Wu, Wd nip width

Claims (2)

[Claims] 1. A charging device for an image forming apparatus, comprising: a charging roller that presses against a photoreceptor to charge the photoreceptor; and a cleaning member that presses against the charging roller and cleans the charging roller. With reference to the radial center line of the charging roller along the moving direction for pressing the cleaning member against the charging roller, the rotation-direction downstream end of the cleaning member in the rotation direction of the charging roller is located at a position higher than the center line. A charging device for an image forming apparatus, wherein the charging device is arranged so as to be able to press against the surface of the charging roller at the downstream side in the rotation direction of the charging roller. 2. The charging device for an image forming apparatus according to claim 1, wherein said cleaning member has a two-layer structure of a sponge material and a felt material slidably contacting the surface of said charging roller.