JPH0764370A - Electrifier - Google Patents

Abstract

PURPOSE:To effectively avoid a foreign matter such as toner or paper powder from being accumulated on a flexible conductive roller coming in contact with the surface of a photoreceptor, to prolong the life of the electrifier, to execute stable uniform electrification over a long term, and to effectively prevent slip or friction from being caused on the surface of the photoreceptor. CONSTITUTION:In this electrifier constituted of a flexible hollow conductive roller 1, and a conductive brush roller 5 coaxially provided in the roller 1 so that they can mutually rotate; the photoreceptor is electrified while the roller 1 is rotated in a state where it is physically brought into contact with the photoreceptor by impressing electrifying voltage on the roller 1 through the roller 5. The roller 1 is provided with a cleaning roller 2 coming into contact with the roller 1 and rotating in the same direction, and the roller 1 is driven and energized to be rotated at the same circumferential speed as the roller 2.

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 electrophotographic image forming method, the surface of a photoconductor is uniformly charged, and image exposure is performed 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 the generation of ozone, a method has been proposed in which a conductive rubber roller is brought into frictional 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, when the charging device is used for a long period of time, foreign matter such as toner and paper powder adheres to the hollow conductive roller that contacts the photoconductor and accumulates, so that it becomes gradually uniform. There is a problem that it becomes difficult to perform charging. In addition, since the flexible conductive sheet that constitutes the hollow conductive roller is generally quite thin, the rotational driving force of the brush roller causes twisting of the sheet and induces charging unevenness. If the twist is continuously increased, the sheet may be broken. Further, since this conductive sheet rotates by being pressed against the surface of the photoconductor only by the pressing force of the brush, the rotation of the conductive sheet is unstable, and uneven rotation or slip with the photoconductor occurs. Occurs and friction with the surface of the photoconductor occurs. As a result, there is also a problem that the photoconductor is worn and the durability of the photoconductor is reduced.

Therefore, an object of the present invention is to effectively solve the above-mentioned problems, to prevent the deterioration of the durability of the photosensitive member, to prevent the sheet from being twisted, and for a long period of time, to contact-charge the photosensitive member. It is an object of the present invention to provide a charging device in an electrophotographic apparatus that can perform charging stably and uniformly.

[0008]

According to the present invention, a flexible hollow conductive roller and a conductive brush roller coaxially and rotatably provided in the hollow conductive roller are provided. 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 to charge the photosensitive member. The conductive roller is provided with a cleaning roller that comes into contact with the cleaning roller and rotates in the same direction, and the hollow conductive roller is drivingly biased so as to rotate at the same peripheral speed as the cleaning roller. A charging device is provided.

[0009]

In the present invention, since the cleaning roller is provided in contact with the flexible hollow conductive roller, the surface of the roller is always cleaned and foreign matters such as toner and paper dust are accumulated. It is possible to carry out stable uniform charging over a long period of time without having to do so. Further, since the hollow conductive roller is drivingly biased so as to follow the cleaning roller, setting the peripheral speed of rotation of the cleaning roller so as to match the moving speed of the photoconductor causes the hollow conductive roller to move. It is possible to effectively prevent the occurrence of twisting due to variations in the rotation of the conductive roller, and to prevent abrasion of the photosensitive member effectively without causing slip between the photosensitive member and the hollow conductive roller. As a result, the problem of reduced durability of the photoconductor is effectively solved.

The above-mentioned drive biasing of the hollow conductive roller can be easily performed by transmitting the rotation of the cleaning roller to the hollow conductive roller by using an appropriate drive transmission mechanism.

Further, in the charging device of the present invention, the hollow conductive roller contacting the surface of the photosensitive member is flexible and thus 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 two have a uniform surface contact, and have a basic characteristic that uniform charging can be performed.

[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 the structure of a charging device of the present invention, and FIG. 2 is a side sectional view of the charging device shown in FIG. 1 together with a photosensitive drum to be charged.

This charging device is roughly composed of a hollow conductive roller 1 and a cleaning roller 2. The hollow conductive roller 1 has a flexible endless conductive sheet 3 and both ends thereof. It is composed of a rigid flange ring 4 provided therein, and inside thereof, a conductive brush roller 5 provided coaxially and rotatably with respect to each other is provided. The brush roller 5 comprises a drive shaft 6 and a brush 7 planted on the shaft.

In the hollow conductive roller 1 described above, the inner surface of the flexible conductive sheet 3 is in contact with the brush 7 of the conductive brush roller 5 housed therein, and is supported by the brush 7. It is in a state of Both ends of the flexible sheet 3 are fixed to a flange ring 4 with an adhesive or the like, and the flange ring 4 is rotatably provided on the drive shaft 6 by a bearing 8.
That is, since both ends of the sheet 3 are fixed to the flange rings 4, this portion can be pressed into contact with the end portion of the photosensitive drum (indicated by 30 in FIG. 2) in a sufficiently stable manner. It is possible to secure a constant contact (nip) width between the flexible conductive sheet 3 of the conductive roller 1 and the surface of the photosensitive drum 30.

Further, in the present invention, a pulley 20 is provided integrally with the flange ring 4 on the outer side in the axial direction, and a belt 21 wound around the pulley 20 makes it possible to
The hollow conductive roller 1 rotates integrally with the cleaning roller 2. In this case, the hollow conductive roller 1 is in the direction opposite to the rotating direction of the photosensitive drum 30 (the moving direction in the contact portion is the same), and the peripheral speed thereof is the drum 30.
The rotation of the cleaning roller 2 is set so as to be the same as that. Therefore, with such a drive bias,
Slip between the photosensitive drum 30 and the hollow conductive roller 1 is effectively prevented, and twisting of the flexible sheet 3 or deterioration of durability of the photosensitive drum 30 can be effectively avoided.

Further, it is preferable that a rubber ring 11 is fitted on the inner side of the flange ring 4 in the axial direction, whereby the end portion of the flexible conductive sheet 3 and the end portion of the photosensitive drum 30 are connected. It is extremely advantageous for effective pressure contact and ensuring a constant nip width. For example, if a means such as a spring is used to press the entire charging device toward the photosensitive drum 30, the rubber ring 11 is recessed, and the portion 3a of the flexible conductive sheet 3 above the rubber ring 11 has a constant width. Surface-contact with the surface of the photosensitive drum 30. Therefore, since a constant nip width is secured between the two, the photosensitive drum 30
The contact charging can be effectively performed.

In order to correctly position the flexible conductive sheet 3, a coil spring 12 is provided between the end of the brush 7 and the inner end of the flange ring 4 in the axial direction, and the sheet 3 is axially moved in the axial direction. It is preferable to give some tension. As a result, the slack of the sheet 3 can be avoided.

On the other hand, the drive shaft 6 of the brush roller 5 is provided with a suitable drive member 10 such as a belt pulley,
The hollow conductive roller 1 is driven by a suitable driving source (not shown).
The brush roller 5 is driven and rotated independently of the flange ring 4. Therefore, this brush roller 5
It is possible to prevent the flexible conductive sheet 3 and the surface of the photosensitive drum 30 from slipping by independently controlling the rotation of the. For example, the rotation speed of the brush roller 5 is
It is preferable to rotate in the same direction as the hollow conductive roller 1 and at a peripheral speed of the roller 1, that is, a peripheral speed of 0.9 to 0.95 times the moving speed of the photosensitive drum. Thus, by setting the speed of the brush roller 5 to be slightly slower than that of the hollow conductive roller 1, the brush roller 5 acts on the roller 1 like a brake, so that the roller 1, that is, the flexibility. The occurrence of twisting of the conductive sheet 3 is more effectively prevented.

In the present invention, the drive shaft 22 of the cleaning roller 2 which is provided so as to come into contact with the hollow conductive roller 1 is connected to an appropriate drive source (not shown) to be driven and rotated. At the same time, the shaft 22 is provided with a pulley 23.
Is connected to the pulley 20 of the hollow conductive roller 1 via. That is, as described above, the cleaning roller 2
Are set to rotate at the same peripheral speed as the photosensitive drum 30. In this case, the rotation direction of the cleaning roller 2 is set to rotate in the same direction as the rotation direction of the photosensitive drum 30. As a result, the hollow conductive roller 1 is drivingly biased so as to rotate at the same peripheral speed as the photosensitive drum 30 and in the opposite direction.

Further, the cleaning roller 2 is provided with a cleaning blade 25 which is in contact with the cleaning roller 2 to remove foreign matters such as toner and paper dust collected by the roller 2 and always perform good cleaning. Is made like.

The charging device described above is housed in a box 40 having an opening on one side, and the box 40 is swingably held by a support shaft 41 fixed to a machine frame (not shown) of a copying machine or the like. The flexible conductive sheet 3 is arranged by means of a pressing spring 42 or the like so that both ends thereof come into contact with both ends of the photosensitive drum 30 (see FIG. 2). As a result, both ends of the sheet 3 are pressed against both ends of the photoconductor drum 30, so that the hollow conductive roller 1 comes into contact with the photoconductor drum 30 with a constant nip width to uniformly perform contact charging. Is possible.

According to the charging device of the present invention, the endless flexible conductive sheet 3 of the flexible hollow conductive roller 1 is rotated at the speed synchronized with the rotation speed of the photosensitive drum 30 as described above. While the brush 7 is rotated, the brush 7 brings the sheet 3 into contact with the surface of the photosensitive drum 30 over the entire axial direction with a constant nip width, and in this state, a constant charging voltage is applied to the brush roller 5. By applying the voltage, the photosensitive drum 30 is charged.

In the above-mentioned charging device, the flexible endless conductive sheet 3 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 type 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, these conductive agents are preferably 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 3 varies depending on its flexibility, it is preferably in the range of generally 50 to 400 μm, and 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 3 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 3 may be made of a single layer material or a laminated material. In particular, when the surface of the conductive sheet 3 that comes into contact with the surface of the photoconductor is formed of a high resistance layer, even if 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 as the high resistance layer, they are inactive 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, as the brush 7, a conductive brush made of conductive organic or inorganic fibers is preferably used, and the conductive roller is flocked. The volume resistivity of the brush is 10 ² to 10. 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 conductive sheet 3.

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 50 is connected to the brush roller 5, and the brush 7 presses the flexible conductive sheet 3 to bring it into contact with the surface of the rotating photosensitive drum 30. A DC voltage is applied to the conductive sheet 3 via the brush 7 to charge the surface of the photosensitive drum 30.

The charging voltage applied to the conductive sheet 3 is 1.5 to 3, which is the charging start voltage value of the surface of the photosensitive drum 1.
It is preferably set to 5 times, especially 2 to 3 times. In the present invention, the uniform and even charging can be performed only by using the DC voltage. However, in order to perform the uniform charging, the AC power supply 51 is combined with the DC power supply 50, and the above-mentioned DC voltage is further added. It is also possible to apply a voltage on which an AC voltage is superimposed. Such alternating current has a frequency of 300 to 1500 Hz, especially 400 to 1000 Hz.
, The peak-to-peak voltage is 2.5 to 4 times the DC voltage,
In particular, it is preferable to use an alternating current of 2.8 to 3.5 times.

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. Particularly, 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. Further, in addition to the main charging of the photoconductor, it can be applied to the charge removal thereof.

[0035]

According to the present invention, it is possible to effectively avoid accumulation of foreign matter such as toner or paper powder on the flexible conductive roller that comes into contact with the surface of the photosensitive member. It is possible to stably and uniformly charge the battery. Moreover, since the conductive roller is drivingly biased so as to rotate at substantially the same speed as the photoconductor, the occurrence of slip and friction on the photoconductor surface is effectively prevented, and the durability of the photoconductor is improved. Further, it is possible to effectively prevent the twisting of the flexible conductive roller which does not decrease and is easily deformed, and it is possible to perform stable and uniform charging for a long period of time.

[Brief description of drawings]

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

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

Claims (5)

[Claims] 1. A flexible hollow conductive roller, and a conductive brush roller coaxially and rotatably provided in the hollow conductive roller, wherein the conductive brush roller is hollow. In a charging device that applies a charging voltage to a conductive roller and charges the photosensitive member while rotating the physical contact of the hollow conductive roller with the photosensitive member, the hollow conductive roller is not contacted with this. The charging device is characterized in that a cleaning roller that rotates in the same direction is provided, and the hollow conductive roller is drivingly biased so as to rotate at the same peripheral speed as the cleaning roller. 2. The cleaning roller is provided with a cleaning blade in contact with the cleaning roller.
The charging device according to. 3. The hollow conductive roller is made of an endless flexible conductive sheet, and both ends of the sheet are attached to roller flanges rotatably provided independently of the shaft of the conductive brush roller. The charging device according to claim 1, wherein the charging device is fixed, and the roller flange is provided with a drive transmission mechanism for transmitting rotation of the cleaning roller. 4. The charging device according to claim 4, wherein the drive transmission mechanism is a belt pulley. 5. The charging device according to claim 1, wherein the cleaning roller is set to rotate at the same peripheral speed as the moving speed of the photoconductor.