JPH06337570A - Electrifier - Google Patents

Abstract

PURPOSE:To prevent the durability of a photoreceptor from lowering, to prevent a sheet from being twisted, and to stably and uniformly electrify the photosensitive body by rotating a conductive brush roller at specified circumferential speed. CONSTITUTION:This electrifier is constituted of a flexible hollow conductive roller 1 consisting of a flexible endless conductive sheet 2 and rigid flange rings 6 provided at both ends of the sheet 2, and the conductive brush roller 3 coaxially and mutually rotatably provided in the roller 1. The brush roller 3 is constituted of a driving shaft 4 and a brush 5 planted on the shaft 4. The endless conductive sheet 2 in the roller 1 is driven or submissively moved at speed synchronizing with the rotating speed of the photoreceptor drum, and the brush 5 is rotated at the moving speed of the photoreceptor drum, that is, at the circumferential speed which is 0.9-0.95 times as high as the moving speed of the roller 1. The driving direction of the brush 5 is made the same as the driving direction of the conductive sheet 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, 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 driven by a photoconductor and a conductive material coaxially and rotatably provided in the hollow conductive roller. A charging roller that is composed of a brush roller and applies a charging voltage to the hollow conductive roller through the conductive brush roller to charge the photosensitive member while physically rotating the hollow conductive roller in contact with the photosensitive member. In the apparatus, there is provided a charging device characterized in that the conductive brush roller is rotated at a peripheral speed of 0.9 to 0.95 times a moving speed of a photosensitive member.

[0009]

In the present invention, the flexible hollow conductive roller is driven by the photosensitive member to rotate at substantially the same speed (peripheral speed). By the way, in manufacturing this hollow conductive roller, since some irregularities or wrinkles are formed especially at both end portions, some twisting occurs when driven by the photoconductor. Therefore, when the hollow conductive roller is continuously driven, that is, the charging operation is continuously performed, the twisting gradually expands due to a slip with the photoconductor, and finally the flexible sheet constituting the roller is broken. Will occur until.

Thus, according to the present invention, since the rotation speed of the brush roller for pressing the hollow conductive roller is set to be slightly slower than that of the hollow conductive roller, slip between the hollow conductive roller and the photosensitive member is caused. In addition to effectively avoiding the above, a stable driven relationship is maintained, and since the brush roller acts as a brake on the hollow conductive roller, the expansion of twist is effectively prevented.

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 contact between the two becomes a uniform surface contact, and 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 the charging device of the present invention, and FIG. 2 is a side sectional view of the charging device of FIG.

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 in a sufficiently stable manner. It can be driven and rotated with no difference in peripheral speed. In order to perform the driven rotation more reliably, a drive gear 8 is provided on the outer side in the axial direction of the flange ring 6 if necessary, and the drive gear 8 is flexed through the gear 8 at a speed synchronized with the photosensitive drum 30. The sex roller 1 can be driven or driven to rotate.

On the other hand, the drive shaft 4 of the brush roller 3 is connected to an appropriate drive member such as a belt pulley so that the brush roller 3 can be driven and rotated independently of the flexible roller 1.

According to the present invention, the endless conductive sheet 2 of the flexible hollow conductive roller 1 is driven or driven at the speed synchronized with the rotation speed of the photosensitive drum 30 as described above, and the brush is used. 5 is the moving speed of the photosensitive drum, that is, 0.9 of the moving speed of the hollow conductive roller 1.
Rotate at a peripheral speed of 0.95 times. The driving direction of the brush 5 is the same as the driving direction of the conductive sheet 2.
By setting this moving speed within the above range, it is possible to effectively prevent the twisting or expansion of the conductive sheet 2 from occurring. If the moving speed is lower than the above range, the braking action of the brush 5 becomes too large, and conversely the generation or expansion of twisting is promoted. Therefore, it is impossible to prevent the occurrence or expansion of twist.

Further, in the present invention, it is preferable that a rubber ring 11 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. Thus, the flexible sheet 2 can be reliably driven by the flexible sheet 2 with respect to the photosensitive drum 30. In order to properly position the flexible sheet 2, a coil spring 13 is provided between the end of the brush 5 and the inner end of the flange ring 6 in the axial direction. It is preferable to apply tension.

The charging device described above is a box 2 having an opening on one side.
5 and is arranged so as to abut on the photoconductor drum 30 by means of a push spring 26 or the like (see FIG. 2).

In the above 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, 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 2 varies depending on its flexibility, it is preferably in the range of generally 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 in 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, the brush 5 is preferably a conductive roller made of conductive organic or inorganic fibers and is brushed on a conductive roller. 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 conductive brush 5, and the flexible conductive sheet 2 is pressed by the brush 5 and brought into contact with 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 electrically conductive sheet 2 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. Figure 5
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.

According to the present invention, uniform and even charging can be performed only by using a DC voltage. However, in order to perform even charging, the AC power supply 21 is replaced by the DC power supply 20.
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.

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.

[0033]

According to the present invention, it is possible to effectively prevent twisting of the flexible conductive roller that comes into contact with the surface of the photosensitive member, and to perform stable and uniform charging for a long period of time. Further, since the conductive roller follows the photoconductor without any speed difference from the photoconductor, the occurrence of slip or friction on the photoconductor surface is effectively prevented, and the durability of the photoconductor does not deteriorate.

[Brief description of drawings]

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

FIG. 2 is a side sectional view of the charging device shown in FIG. 1 together with a photosensitive drum. .

FIG. 3 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 conductive hollow brush comprising a flexible hollow conductive roller driven by a photosensitive member and a conductive brush roller coaxially and rotatably provided in the hollow conductive roller. A charging device that applies a charging voltage to a hollow conductive roller through a roller to charge the photosensitive body while rotating the hollow conductive roller in physical contact with the photosensitive body, wherein the conductive brush roller is A charging device characterized by rotating at a peripheral speed of 0.9 to 0.95 times the moving speed of a photoconductor. 2. The charging device according to claim 1, wherein the hollow conductive roller rotates at a peripheral speed substantially the same as the moving speed of the photosensitive member.