JPH0720683A - Electrifier - Google Patents

Abstract

PURPOSE:To stably and uniformly electrify a photoreceptor drum by contact electrification without causing the deterioration of the durability of the photoreceptor drum nor the twist of a sheet. CONSTITUTION:This electrifier electrifies the photoreceptor drum by impressing electrifying voltage on a conductive roller 1 through a brush roller 3 while rotating the roller 1 by physically bringing the roller 1 into contact with the photoreceptor drum. Both ends of a flexible conductive sheet 2 are fixed to roller flanges 6 provided on the shaft of the roller 3 so as to be rotatable independently, and the roller flange 6 is provided with a driving transmitting gear 10 transmitting the driving of the photoreceptor drum. The roller 1 is rotated in the same direction and at nearly the same circumferential speed as that of the drum, and, a driving transmitting gear 11 transmitting the driving of the drum is provided on the roller 3, and rotated in the same direction as the moving direction of the drum.

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 the surface of a photoconductor used in an electrophotographic apparatus, and more particularly to a charging device capable of performing main charging of the photoconductor surface without corona discharge. Regarding the device.

[0002]

2. Description of the Related Art In an image forming method using an electrophotographic method, the surface of a photoconductor is uniformly charged and imagewise exposed to form an electrostatic latent image corresponding to an original image on the surface of the photoconductor. An image is formed by developing and transferring the latent image. In such an image forming method, charging (main charging) of the surface of the photoconductor is generally performed by corona charging, but this method inevitably suffers from the problem of environmental pollution such as generation of ozone. Recently, in order to avoid generation of ozone, a method has been proposed in which a conductive rubber roller is frictionally brought into contact with the surface of the photoconductor while applying a bias voltage to perform main charging of the surface of the photoconductor (special feature. Kaisho 63-1496
69 and JP-A-1-267667).

However, in the charging method using frictional contact as described above, if foreign matter such as dust or paper dust is sandwiched between the conductive rubber roller and the photosensitive member, there is a problem in that the charging uniformity is impaired and stable. It was difficult to carry out charging. Further, when the image is formed, there is a cleaning failure on the surface of the photoconductor, and if toner remains on the surface,
There is a problem that the residual toner is fixed to the surface of the photoconductor, and there is a problem that durability of the photoconductor is reduced. Further, in order to perform uniform charging, it is not enough to apply the DC bias voltage alone, and it is necessary to apply the AC bias voltage as well.

As a charging method in which such a problem has been solved, the applicant of the present application has previously used a charging device equipped with a conductive brush roller to bring a flexible conductive sheet into frictional contact with the surface of a photosensitive member. A method of frictionally charging while applying a DC voltage to the roller has been proposed (see Japanese Patent Application No. 4-68148). The charging device used in this charging method is usually composed of a conductive brush roller and a flexible hollow conductive roller which is built in the brush roller and is provided so as to come into contact with the brush.

In this charging device, since the flexible conductive sheet forming the hollow conductive roller is pressed by the conductive brush and adheres to the surface of the photosensitive member, a low voltage is applied without applying an AC bias voltage. It is extremely excellent in that it is possible to uniformly perform triboelectrification by applying only the DC bias voltage to the conductive brush.

[0006]

However, since the flexible conductive sheet that constitutes the hollow conductive roller is rotated by being pressed against the surface of the photosensitive member only by the pressing force of the brush, The rotation of the conductive sheet is unstable, uneven rotation and slip with the photoconductor occur, and friction with the surface of the photoconductor occurs. As a result, there is a problem that the photoconductor is worn and the durability of the photoconductor is lowered. In addition, since the conductive sheet is generally quite thin, the sheet is twisted by the rotational driving force of the brush roller to induce uneven charging, and if the twist is continuously increased, the sheet is broken. It may occur.

Therefore, the object of the present invention is to effectively solve the above-mentioned problems, to stabilize the charging of the photosensitive member by contact charging without lowering the durability of the photosensitive member and without causing twisting of the sheet. An object of the present invention is to provide a charging device in an electrophotographic apparatus that can be uniformly used.

[0008]

According to the present invention, a flexible hollow conductive roller composed of an endless flexible conductive sheet and coaxially and mutually rotatable within the hollow conductive roller. A conductive brush roller provided on the inner surface of the hollow conductive roller, and a charging voltage is applied to the hollow conductive roller through the conductive brush roller, and the hollow conductive roller is brought into physical contact with the photosensitive member to rotate while being exposed. In a charging device for charging a body, both ends of the endless flexible conductive sheet are fixed to roller flanges that are rotatably provided independently of the shaft of the conductive brush roller. The flange is provided with a drive transmission member for transmitting the drive of the photoconductor, and the hollow conductive roller can rotate in the same direction as the moving direction of the photoconductor and at substantially the same peripheral speed. The rotation axis of the brush roller, the drive transmission member is provided for transmitting the driving of the photosensitive member, said brush roller, a charging device is provided, characterized in that rotates at the same direction as the moving direction of the photosensitive member.

[0009]

In other words, in the present invention, the flexible hollow conductive roller (endless flexible conductive sheet) contacting the photosensitive member is moved in the same direction as the moving direction of the photosensitive member by the drive transmission member (eg gear). Since it is set to be driven in the same direction at substantially the same circumferential speed, friction due to the speed difference between the photoconductor and the hollow conductive roller is prevented, which results in durability of the photoconductor. Is effectively prevented. Also, the conductive brush roller is set to rotate in the same direction as the moving direction of the photoconductor by the drive transmission member that transmits the drive of the photoconductor, so that the rotation of the endless flexible conductive sheet is assisted. Further, since the twisting of the sheet can be effectively avoided, the uniform charging can be stably performed, and the remarkable advantage that the life of the apparatus is long is achieved.

Further, in the charging device of the present invention, the hollow conductive roller that comes into contact with the surface of the photosensitive member is flexible and therefore deformable, and is pressed by the conductive brush roller. Therefore, even if foreign matter such as dust, paper dust, residual toner, etc. adheres to the surface of the photoconductor, the surface of the photoconductor other than the adhering part can be brought into uniform contact with the hollow conductive roller. Moreover, since the individual brushes of the brush of the conductive brush roller act as pressing springs, the contact between the surface of the photoconductor and the hollow conductive roller can be performed minutely and precisely. That is, the contact between the two becomes a uniform surface contact, and uniform charging can be performed.

Further, in the present invention, the driven transmission of the hollow conductive roller with respect to the photoconductor is positively performed by the drive transmission member, which means that the distance between the photoconductor and the roller is kept constant. is doing. Therefore, according to the present invention, by selecting and using an appropriate drive transmission member,
It becomes possible to stably maintain the contact (nip) width between the hollow conductive roller, that is, the endless flexible conductive sheet and the surface of the photosensitive member, which is extremely advantageous for uniform charging.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to specific examples shown in the accompanying drawings. 1 is a front sectional view showing a structure of a charging device of the present invention, FIG. 2 is a side sectional view of the charging device of FIG. 1, and FIG. 3 is a drive used in the charging device of FIG. It is a figure which shows the drive transmission mechanism of a transmission member (gear) simply.

This charging device is roughly composed of a hollow conductive roller 1 composed of a flexible endless conductive sheet 2 and rigid flange rings 6 provided at both ends thereof, and the flexible conductive roller 2. A conductive brush roller 3 which is coaxially and rotatably provided in the elastic roller 1. The brush roller 3 is composed of a drive shaft 4 and a brush 5 planted on the shaft.

The inner surface of the flexible conductive sheet 2 of the flexible roller 1 is in contact with the brush 5 of the conductive brush roller 3 housed therein and is supported by the brush 5. Has become.

Both ends of the flexible sheet 2 are fixed to a flange ring 6 with an adhesive or the like, and the flange ring 6 is rotatably provided on the drive shaft 4 by a bearing 7. That is, since both ends of the sheet 2 are fixed to the flange rings 6, this portion can be pressed against the end portion of the photosensitive drum 30 with sufficient stability.

A gear 10 is integrally provided on the flange ring 6 as a drive transmission member, and the drive rotation of the photosensitive drum 30 is transmitted thereto, while the drive transmission is also transmitted to the drive shaft 4 of the brush roller 3. A gear 11 is provided as a member, and the driving rotation of the photosensitive drum 30 is transmitted.

In the present invention, the gears 10 and 11 described above are used.
This causes the flexible roller 1 and the brush roller 3 to rotate in the opposite direction to the rotation direction of the photosensitive drum 30 (that is, the drum 30).
It is extremely important to set the roller 1 so as to rotate at substantially the same peripheral speed as the drum 30 in the contact direction with the roller 1). An example of this drive transmission mechanism is shown in FIG.

As shown in FIG. 3, the gear 10 for driving the flexible roller 1 provided on the flange ring 6 meshes with a large-diameter drum gear 31. The ratio of the number of teeth is set so that the peripheral speed of the photosensitive drum 30 and the peripheral speed of the flexible roller 1 are the same.
It is set according to the diameter of the drum 30 and the diameter of the drum 30. The gear 11 provided on the drive shaft 4 of the brush roller 3 is rotated through the even number (two in FIG. 3) of idle gears 32 in order to rotate in the opposite direction to the rotation direction of the photosensitive drum 30. It meshes with 31. The ratio of the number of gear teeth is also set according to the diameter of the brush roller 3 and the diameter of the drum 30 so that the peripheral speeds of the brush roller 3 and the drum 30 are the same.

According to the present invention, by such a drive transmission mechanism, the flexible roller 1 and the brush roller 3 incorporated therein are driven by the photosensitive drum 30 to flex with the photosensitive drum 30. It is possible to effectively suppress the occurrence of friction between the elastic roller 1 and the durability of the drum 30. Further, since it is possible to avoid the positional deviation between the flexible roller 1 and the brush roller 3 and the positional deviation at both ends of the flexible conductive sheet 2 that constitutes the flexible roller 1, the flexible roller 1 can be avoided. 1 can be effectively prevented, and uniform charging of the surface of the photosensitive drum 30 can be stably performed.

Further, since the center distance between the photosensitive drum 30 and the flexible roller 1 is maintained at a constant value by the sizes of the gear 10 and the drum gear 31, the flexible roller 1 and the photosensitive drum 30 are separated from each other. Since the contact width can be secured within a certain range, uniform charging can be performed more reliably and stably. That is, the center-to-center distance is determined by the number of teeth of the gear 10 and the drum gear 31, so that the flange ring 6 is located at the end of the photosensitive drum 30 within a range in which the peripheral speeds of the drum 30 and the roller 1 can be set to be the same. The number of teeth of these gears may be set so that the gears are pressed against each other. According to the present invention, since the contact (nip) width can be secured by the drive transmission member (gear) in this way, it is not necessary to use a special member such as a pressing spring to secure the nip width, and the device It is understood that it is extremely advantageous in terms of productivity and device cost.

According to the aspect of FIG. 3 described above, the brush roller 3 also rotates at substantially the same peripheral speed as the photosensitive drum 30, but it does not necessarily have to rotate at the same peripheral speed.
For example, in the range of 1.0 to 3 times the peripheral speed of the photosensitive drum 30 (which is substantially the same as the peripheral speed of the flexible roller 1), the twisting of the flexible roller 1 is It can be sufficiently prevented. Outside this range, the speed difference between the brush roller 3 and the flexible roller 1 becomes large, and it may be difficult to prevent the flexible roller 1 from twisting. The speed of the brush roller 3 may be adjusted by separately setting the number of teeth of the idle gear 32 that meshes with the gear 11.

In the present invention, it is preferable that a rubber ring 20 is fitted inside the flange ring 6 in the axial direction, whereby the end portion of the flexible sheet 2 and the end portion of the photosensitive drum 30 are fitted. And the flexible sheet 2 on the rubber ring 20 is effectively pressed.
The portion 21 has a constant width and is in surface contact with the surface of the photosensitive drum 30. Therefore, the nip width of both can be set to be relatively large, which is extremely advantageous for uniform contact charging.

In order to correctly position the flexible sheet 2, a coil spring 13 is provided between the end of the brush 5 and the end of the flange ring 6 in the axial direction, so that the flexible sheet 2 is axially moved. It is preferable to apply a slight amount of tension.

According to the present invention, the endless flexible conductive sheet 2 of the flexible hollow conductive roller 1 is driven at the speed synchronized with the rotation speed of the photosensitive drum 30 as described above, and the brush is used. While rotating 5, the flexible sheet 2 is brought into contact with the surface of the photosensitive drum 30 with a constant nip width over the entire axial direction by the brush 5, and a constant charging voltage is applied to the brush roller 3 in this state. As a result, the photoconductor drum 30 is charged.

In the above-mentioned charging device, the flexible endless conductive sheet 2 is made of any material as long as it satisfies the condition of being conductive and flexible. For example, it may be made of a conductive resin or rubber, a metal such as a foil, or a laminate of metal and a resin or rubber.

As the conductive resin or rubber, resins or rubbers containing various conductive agents are used. As such a resin, various thermoplastic elastomers such as polyester elastomers, polyamide elastomers, polyurethane elastomers, soft vinyl chloride resins, styrene-butadiene-styrene block copolymer elastomers, acrylic elastomers are preferable, but Nylon 6, nylon 6,6, nylon 6-nylon 6,6 copolymer, nylon 6,6-nylon 6,10 copolymer, polyamide such as alkoxymethylated nylon such as methoxymethylated nylon, copolyamide or Modified products thereof can also be used. Of course, the resin used is not limited to these, and for example, silicone resin, acetal resin such as polyvinyl butyral, polyvinyl acetate, ethylene-vinyl acetate copolymer, ionomer and the like can be used. Examples of the rubber include natural rubber, butadiene rubber, styrene rubber, butadiene-styrene rubber, nitrile-butadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-non-conjugated diene copolymer rubber, chloroprene rubber, butyl rubber, silicone rubber. , Urethane rubber, acrylic rubber and the like are preferable.

As the conductive agent to be blended with the above resin or rubber, conductive carbon black, metal powder such as silver, gold, copper, brass, nickel, aluminum and stainless steel, tin oxide conductive agent and the like can be used. A powder conductive agent can be used, and in addition, a nonionic, anionic, cationic, amphoteric organic conductive agent, or an organic tin conductive agent can also be used.

The conductive resin or rubber is generally
The electric resistance (specific resistance) is preferably in the range of 10 to 10 ⁸ Ω · cm, particularly 10 ^{2 to} 10 ⁶ Ω · cm.
The conductive agent is mixed with 100 parts by weight of resin or rubber in an amount of 1 to 20 parts by weight, particularly 5 to 15 parts by weight, so that the above resistance value can be obtained, though it varies depending on the kind. Generally, higher conductivity can be obtained when the conductive agent particles form a chain structure in the resin or rubber, but in this case, a dot-shaped high potential portion is generated when a voltage is applied, and charging is performed. May cause unevenness. Therefore, it is preferable that these conductive agents are uniformly and finely dispersed in the resin or rubber, and for this purpose, it is important to sufficiently knead the conductive agent-containing resin or rubber.
Further, in order to effectively disperse the conductive agent uniformly, some acid-modified resins or rubbers obtained by copolymerizing an ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, or maleic anhydride should be used. Is also effective.

Although the thickness of the above-mentioned flexible conductive sheet 2 varies depending on its flexibility, it is preferably in the range of 50 to 400 μm, particularly 100 to 300 μm. The surface is preferably as smooth as possible, and the average roughness according to JIS B 0601 is 5 μm or less,
Particularly, it is desirable that the thickness is 1 μm or less.

In the present invention, the flexible conductive sheet 2 is used.
Alternatively, a seamless metal foil can be used. Examples of the metal foil include nickel, aluminum, copper, brass, tin and the like, which are obtained by electroforming or extrusion. The thickness of the metal foil is 20 to 80μ
It is preferably in the range of m, especially 30 to 50 μm.

The flexible conductive sheet 2 may be made of a single layer material or a laminated material. In particular, when the surface of the conductive sheet 2 that comes into contact with the surface of the photoconductor is formed of a high resistance layer, even when there are defects such as pinholes on the surface of the photoconductor, leakage such as discharge can be prevented. This is advantageous in that it can be done. The resistivity of this high resistance layer is 10 ^{8 to} 10 ¹³ Ω · cm, especially 10 ⁹
The thickness is preferably in the range of 10 to 10 ¹² Ω · cm, and the thickness thereof is preferably in the range of 40 to 60 μm. The electric resistance can be easily adjusted by adjusting the amount of the conductive agent mixed in the resin or the rubber. As the conductive agent or rubber, those mentioned above can be used, but in addition to them, fluorine-based resins or rubbers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene. A copolymer (PTFE / HFP), a perfluoroalkoxy-based fluororesin, etc. are preferably used. When these resins or rubbers are used for the high resistance layer, they are inert and have a small friction coefficient, so that there is a great merit in the life of the photoconductor and the life of the sheet.

In the present invention, a brush in which a conductive brush made of conductive organic or inorganic fibers is planted on a conductive roller is preferably used as the brush 5. The brush has a volume resistivity of 10 ² to 10 ^2. It is preferably in the range of 10 ⁸ Ω · cm, particularly 10 ^{3 to} 10 ⁶ Ω · cm. The thickness of the brush fiber is 2 to 10 denier (d), especially 3 to 6 d,
Fiber length (hair length) is 2 to 7 mm, especially 3 to 5 m
m should be in the range and the flock density should be 10,000 to 20
It is preferable that the pressure is in the range of 10,000 / square inch, particularly 30,000 to 100,000 / square inch, in order to provide a smooth and uniform pressing force. Further, it is preferable to round the tip of the brush in order to suppress abrasion of the flexible sheet 2.

As the organic conductive fibers, synthetic or regenerated fibers in which conductive agent particles are dispersed are used. For example, polyamide fibers such as nylon 6, nylon 6,6, polyester fibers such as polyethylene terephthalate, acrylic fibers,
Examples thereof include polyvinyl alcohol fiber, polyvinyl chloride fiber, rayon and acetate. The method of imparting conductivity to the fiber is not limited to the method of blending a conductive agent, and may be a method of metallizing the surface of the fiber. When the conductive agent is used, the conductive agent described above can be used. Carbon fibers are preferably used as the conductive inorganic fibers, but metal fibers such as stainless steel and brass are also used.

According to the present invention, the DC power source 20 is connected to the brush roller 3, and the flexible conductive sheet 2 is pressed by the brush 5 while contacting the surface of the rotating photosensitive drum 30. A DC voltage is applied to the conductive sheet 2 via the brush 5 to charge the surface of the photosensitive drum 30.

The charging voltage applied to the conductive sheet 2 is 1.5 to 3.
It is preferably set to 5 times, especially 2 to 3 times. Figure 4
FIG. 4 is a diagram showing the relationship between the voltage applied to the conductive sheet 2 and the surface potential of the photoconductor drum 30 when the charging method of the present invention is applied when an organic photoconductor is used. As is clear from this figure, it is understood that a good linear relationship between the applied voltage and the surface potential is maintained in the effective charging area. From this, in the charging method of the present invention, for example, a surface potential detection sensor is arranged around the photoconductor, and based on the surface potential value detected by this sensor, the applied voltage is increased or decreased to reduce the surface of the photoconductor. It will be appreciated that it is possible to keep the potential constant and optimal.

In the present invention, the uniform and even charging can be performed only by using the DC voltage, but the AC power supply 21 is replaced by the DC power supply 20 in order to perform the charging evenly.
It is also possible to apply a voltage obtained by superimposing an AC voltage on the DC voltage described above. Such alternating current has a frequency of 300 to 1500 Hz, especially 4
It is preferable to use an alternating current having a peak-to-peak voltage of 2.5 to 4 times, especially 2.8 to 3.5 times the above DC voltage at 00 to 1000 Hz.

In the embodiment shown in the accompanying drawings, the gears (10, 11) are used as the drive transmission member for transmitting the drive of the photosensitive drum 30, but of course,
Other than this, it is also possible to use members such as a belt pulley and a cam.

The charging device of the present invention is extremely useful for charging a photoconductor used in an electrophotographic method such as a copying machine, a facsimile, a laser printer, etc. In particular, as the photoconductor, various organic photoconductors having a single-layer or laminated structure are used. However, of course, in addition to this, it is also suitably applied to contact charging of an inorganic photoconductor such as an a-Si photoconductor or a selenium photoconductor. In addition to the main charging of the photoconductor, it can be applied to, for example, charge removal.

[0039]

According to the present invention, since the flexible conductive roller contacting the surface of the photoconductor can be driven at substantially the same speed as the photoconductor, slippage and friction on the surface of the photoconductor can be prevented. Generation is effectively prevented, the durability of the photoreceptor is not deteriorated, and twisting of the flexible conductive roller that is easily deformed can be effectively prevented, and stable and uniform charging is performed for a long period of time. Can be done over. Further, since no special drive source is used for driving the brush roller, it is very advantageous in terms of downsizing of the device and cost of the device.

[Brief description of drawings]

FIG. 1 is a diagram showing a front sectional view of a charging device of the present invention together with a photosensitive drum.

FIG. 2 is a side sectional view showing the structure of the charging device of FIG.

FIG. 3 is a diagram showing an example of the position of a drive transmission mechanism in the charging device of FIG.

FIG. 4 is a diagram showing the relationship between the applied voltage and the surface potential of the photoconductor when the organic photoconductor is charged by the charging device of the present invention.

Claims (2)

[Claims] 1. A flexible hollow conductive roller composed of an endless flexible conductive sheet, and a conductive brush roller coaxially and rotatably provided in the hollow conductive roller. In the charging device, a charging voltage is applied to the hollow conductive roller via the conductive brush roller, and the hollow conductive roller is brought into physical contact with the photosensitive member to rotate while charging the photosensitive member. Both ends of the endless flexible conductive sheet are fixed to roller flanges that are independently rotatably provided on the shaft of the conductive brush roller, and the roller flanges transmit the drive of the photoconductor. A drive transmission member is provided, and the hollow conductive roller can rotate in the same direction as the moving direction of the photoconductor and at substantially the same peripheral speed. A drive transmission member that transmits the drive of the optical body is provided, and the brush roller is
A charging device characterized in that it rotates in the same direction as the moving direction of the photoconductor. 2. The charging device according to claim 1, wherein the drive transmission members of the roller flange and the brush roller rotation shaft are gears.