JPH0862927A - Charging method for photorecertor applied to electrophotographic method and charging device used therefor - Google Patents

Abstract

PURPOSE: To prolong the effective life of a charge roller and to effectively and uniformly charge the surface of a photoreceptor because pre-charge is performed simultaneously with cleaning by a preroller by providing the preroller on the upstream side of the charge roller and allowing the charge roller to charge the photoreceptor while impressing DC voltage equal to or above the charge start voltage on the preroller. CONSTITUTION: In this charging method for charging the photoreceptor 10 by bringing the charge roller 2 consisting of an endless conductive flexible sheet into contact with the movable photoreceptor 10 and impressing the voltage on the roller 2 in such a state: at least one preroller 3 consisting of a conductive flexible roller is arranged in contact with the surface of the photoreceptor in the vicinity of the upstream side of the roller 2 in the moving direction of the photorecetor 10, and it is rotated following the photoreceptor 10 while impressed with the DC voltage equal to or above the charge start voltage of the photoreceptor 10 to perform the charge by the roller 2 at the same time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method for performing main charging on the surface of a photosensitive member by contact charging and a charging device used in the method.

[0002]

2. Description of the Related Art In an image forming method by electrophotography, 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. Is developed and transferred to form an 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: JP-A-63-149669 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, in order to perform uniform charging, it is not enough to apply the DC bias voltage, and it is necessary to apply the AC bias voltage as well.

As a charging method in which such a problem is solved, the present applicant first made a charging roller made of an endless flexible conductive sheet having a built-in brush roller frictionally contact with the surface of the photosensitive member, A method of contact charging while applying a DC voltage to the charging roller has been proposed (Japanese Patent Laid-Open No. 6-119).
No. 52).

In this charging roller, since the flexible conductive sheet is pressed by the brush roller and adheres to the surface of the photosensitive member, only a low DC bias voltage is applied without applying an AC bias voltage. It is extremely excellent in that contact charging can be performed by applying the voltage to.

By the way, also in the above charging roller,
When there is a cleaning failure on the surface of the photoconductor, the toner or the like remaining on the surface of the photoconductor gradually moves to the surface of the charging roller (the surface of the endless conductive sheet). For this reason,
A sponge roller or the like is usually provided on the surface of the charging roller so that it can be driven by the charging roller, and the surface of the charging roller is cleaned.

[0007]

However, when the charging roller is used for a long period of time, the toner collected on the surface of the sponge roller is clogged, the cleaning action of the sponge roller is deteriorated, and the surface of the charging roller is not covered with toner or the like. Therefore, uniform charging is impaired. Further, since the sponge roller and the like are driven to rotate due to friction with the charging roller, if a large amount of toner migrates or accumulates on the surface of the charging roller due to long-term use, friction between the sponge roller and the charging roller may occur. The toner fuses to the surface of the charging roller, which also impairs uniform charging. Therefore, there is still room for improvement in terms of its effective life. The flexible conductive sheet on the surface of the charging roller is made of plastic, and the conductivity is imparted by the conductive powder such as carbon black dispersed in the plastic sheet. Therefore, the electric resistance value on the surface of the charging roller is not always uniform, and there is still room for improvement in terms of uniform charging property.

Therefore, an object of the present invention is to avoid a reduction in device life due to contamination of the surface of a charging roller in a contact charging method for the surface of a photosensitive member using a charging roller composed of an endless flexible conductive sheet. At the same time, it is to provide a charging method capable of effectively improving the uniform charging property. Another object of the present invention is to provide a charging device effectively applied to the above charging method.

[0009]

According to the present invention, a charging roller made of an endless conductive flexible sheet is brought into contact with a movable photosensitive member, and in this state, a voltage is applied to the charging roller to expose the photosensitive member. In a charging method for charging a body, at least one pre-roller composed of a conductive flexible roller is arranged in contact with the surface of the photoconductor in the vicinity of the upstream side of the charging roller with respect to the moving direction of the photoconductor, A charging method is provided, in which a DC voltage equal to or higher than the charging start voltage of the photoconductor is applied to the pre-roller, the photoconductor is driven to rotate, and at the same time, charging is performed by the charging roller.

According to the present invention, a charging roller made of an endless conductive flexible sheet and arranged in contact with a movable photosensitive member, to which a predetermined charging voltage is applied, and a moving direction of the photosensitive member. And at least one pre-roller, which is disposed near the upstream side of the charging roller in contact with the surface of the photoconductor and is composed of a conductive flexible roller, and a DC voltage is applied to the pre-roller. A charging device for a photoconductor is provided.

[0011]

An important feature of the present invention is that at least one pre-roller composed of a conductive flexible roller is arranged near the upstream side of the charging roller. That is, a DC voltage equal to or higher than the charging start voltage of the photoconductor is applied to this pre-roller,
As a result, some charging is performed before the charging by the charging roller. Therefore, according to the present invention, it is understood that since the charging is performed repeatedly, the uniform charging property becomes extremely good.

The pre-roller also has a function as a cleaning roller. That is, by contacting the surface of the photoconductor, the toner remaining on the surface of the photoconductor due to poor cleaning is collected, and a DC voltage having a polarity opposite to the electric charge of the toner is applied.
The Coulomb force promotes the transfer of toner to the pre-roller. Therefore, even if the toner remains on the surface of the photoconductor due to poor cleaning or the like, the residual toner is collected before the contact between the charging roller and the photoconductor, so that the residual toner does not migrate to the charging roller. This is effectively prevented, and the effective life of the charging roller is dramatically increased.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific examples shown in the accompanying drawings. FIG. 1 is a side sectional view showing an example of a charging device used in the charging method of the present invention together with a photosensitive drum,
FIG. 2 is a front sectional view of a charging roller used in the charging device of FIG. 3 to 6 show other aspects of the charging roller, and a to d of FIG. 7 and a to d of FIG. 8 show various forms of the charging device.

As shown in FIG. 1, the charging device indicated as a whole by 1 comprises a charging roller 2 and a pre-roller 3 which are arranged in contact with the photosensitive drum 10, respectively. On the other hand, it is arranged on the upstream side in the rotation direction of the photoconductor drum 10. The charging roller 2 and the pre-roller 3 are housed in, for example, a housing 5, a sponge roller 6 for cleaning is provided so as to be in contact with the charging roller 2, and a cleaning blade 7 is attached to the pre-roller 3. It is provided so as to abut.

The charging roller 2 is connected to a DC power source 8a and optionally an AC power source 8b, and the pre-roller 3 is connected to a DC power source 9. That is, the pre-roller 3 removes toner and other foreign matter remaining on the surface of the photoconductor 10 due to poor cleaning and precharges the surface of the photoconductor 10, and the charging roller 2 performs main charging on the surface of the photoconductor drum 10. Be seen.

Taking a copying machine as an example, the photosensitive drum 1
An image exposure device, a developing device, a transfer device, a cleaning device, and a charge removing mechanism known per se are provided on the downstream side of the charging device 1 along the rotation direction of 0. That is, after the main charging is performed by the charging device 1, the image of the original is exposed by the image exposure device to form an electrostatic image on the surface of the photosensitive drum, and the electrostatic image is developed by the developing device. A toner image is formed, and this toner image is transferred to a predetermined paper by a transfer device. After the transfer of the toner image, residual toner and the like are removed from the surface of the photoconductor by the cleaning device, and the surface of the photoconductor drum 10 is destaticized by the charge removing device, whereby one cycle of image formation is completed and the next image is formed. A forming process is performed.

(Charging Roller) In FIG. 2, the charging roller 2 used above is roughly speaking a hollow conductive roller 20 and a brush roller 21 coaxially and rotatably provided in the roller 20. And consists of. The hollow conductive roller 20 is formed by fixing both ends of a flexible endless conductive sheet 22 to a rigid flange ring 23, while the brush roller 21 is formed.
Consists of a drive shaft 25 and a brush 26 which is planted on this shaft. In this case, the brush 26 is the conductive sheet 2
2 is in contact with the inner surface of the conductive sheet 2.
2 is held so as not to be recessed inward. The flange ring 23 is rotatably provided on the drive shaft 25 by a bearing 27.

In the charging roller 2 described above, the sheet 22
Both ends of the ring can be easily fixed to the flange ring 23 by using, for example, a heat-shrinkable resin tube 30, and a large diameter rubber ring 31 is provided inside the flange ring 23. Is preferred. This makes it possible to apply an appropriate tension to the sheet 22, effectively prevent the sheet 22 from loosening, and secure a constant nip width (shown by A in the figure) between the sheet 22 and the photosensitive drum 10.

The charging roller 2 presses the roller 2 toward the photoconductor drum 10 by means of, for example, a pressing spring or the like (not shown), so that both end portions of the sheet 22 are attached to the photoconductor drum 10. It can be pressed against the end portion with sufficient stability, the above nip width can be secured, and the hollow conductive roller 20 can be driven to rotate without any difference in peripheral speed from the drum surface.

On the other hand, if the drive shaft 25 of the brush roller 3 is connected to an appropriate drive member 33 such as a belt pulley,
The brush roller 3 can be driven and rotated independently of the hollow conductive roller 20.

In the charging roller 2 described above, the flexible endless conductive sheet 22 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, etc. 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.

The thickness of the above-mentioned flexible conductive sheet 22 varies depending on its flexibility, but 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.

A seamless metal foil may be used as the flexible conductive sheet 22. Examples of the metal foil include nickel, aluminum, copper, brass, tin and the like, which are obtained by an electroforming method or extrusion. The thickness of the metal foil is preferably in the range of 20 to 80 μm, particularly 30 to 50 μm.

The flexible conductive sheet 22 may be made of a single layer material or a laminated material. In particular, when the surface of the conductive sheet 22 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. Is advantageous. The resistivity of this high resistance layer is 10 ^{8 to} 10 ¹³ Ω · cm, especially 10 ^{9 to} 1
The thickness is preferably in the range of 0 ¹² Ω · cm, and the thickness thereof is preferably in the range of 10 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. Further, as the constituent material of the conductive sheet 22, the resins or rubbers described above can be used, but in addition to them, fluorine-based resins or rubbers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetra Fluoroethylene-hexafluoropropylene copolymer (PTFE
HFP), perfluoroalkoxy fluororesins, etc. are preferably used. The high resistance layer using these resins or rubbers is inactive and has a small friction coefficient, so that it has a great advantage in terms of the life of the photoconductor and the life of the sheet.

In the present invention, conductive or insulating organic or inorganic fibers are preferably used as the brush 26 of the brush roller 3. When conductive fibers are used, a conductive sheet is passed through the brush. In order to pass an electric current through 22, the substrate roller on which the fibers are implanted is made electrically conductive, and the volume resistivity of the brush is in the range of 10 ^{2 to} 10 ⁸ Ω · cm, particularly 10 ^{3 to} 10 ⁶ Ω · cm. Is good. The thickness of the brush fiber is 2 to 10 denier (d), especially 3
To 6d, the fiber length (length of the bristle foot) is preferably in the range of 2 to 7 mm, particularly 3 to 5 mm, and the hair transplant density is 1
10,000 to 200,000 / square inch, especially 30,000 to 100,000 /
The range of square inches is suitable for providing 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 22.

As the organic conductive fiber, synthetic or regenerated fiber in which conductive agent particles are dispersed is used. For example, polyamide fiber such as nylon 6, nylon 6,6, polyester fiber such as polyethylene terephthalate, acrylic fiber. , Polyvinyl alcohol fiber, polyvinyl chloride fiber,
Examples include rayon and acetate. To impart conductivity to the fiber, it is not limited to the method of blending a conductive agent,
A method of metallizing the fiber surface may be used. 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.

As the insulating fiber, the above-mentioned conductive fiber containing no conductive agent is used. When the brush 26 is made of an insulating fiber, the conductive sheet 22 may be energized through the flange ring 23, for example.

The charging roller 2 described above is not limited to the one shown in FIG. 2. For example, as shown in FIG. 3, the flange ring 23 is not used and the rubber ring 40 is provided at the end of the brush 26. The flexible conductive sheet 22
It is also possible to fix both ends to the drive shaft 25 by using a fixed tube 41 made of a heat-shrinkable resin ring or the like. In this case, the brush 26 is insulative.

A charging roller 2 of still another embodiment is shown in FIGS. The charging roller 2 of FIG. 4 is provided with a sponge layer 45 formed of a foam of various synthetic resins such as polyurethane and polystyrene instead of the brush 26 of the charging roller of FIG. Further, FIG. 5 shows that a metal roller 46 made of stainless steel or the like is provided in place of the brush roller 3, and FIG. 6 shows that the brush 26 is not provided at all and the portion where the brush 26 is provided is hollow. is there.
According to the present invention, the charging roller 2 having any of these structures can be used. In particular, the charging roller of FIG. 6 is suitable when used as a roller having a small diameter (for example, a diameter of 10 mm or less).

(Pre-roller) Returning to FIG. 1 again, as the pre-roller 3 provided on the upstream side of the charging roller 2, the pre-roller having the same structure as the above-mentioned charging roller 2 can be used. For example, FIGS. 3, a structure having a brush roller inside, a flexible conductive sheet provided on the sponge layer shown in FIG. 4, a metal roller shown in FIG. A pre-roller having exactly the same structure as the one having a flexible conductive sheet directly provided on the surface thereof, the one having a hollow inside the flexible conductive sheet shown in FIG. Can be used as Of course, in addition to these, a conductive sponge roller in which a conductive sponge layer is simply formed on the surface of the metal roller or a conductive rubber roller in which a conductive rubber layer is formed can be used as the pre-roller.
In this case, the electric resistance of the conductive sponge layer or the conductive rubber layer is preferably set in the same range as that of the flexible conductive sheet 22 described above by blending the conductive agent.

(Charging Method) In the present invention, cleaning by the pre-roller 3 is performed at the same time as charging by the charging roller 2. For this cleaning, a DC voltage having a polarity opposite to that of the charged toner is applied to the pre-roller 3 by the DC power supply 9. Then do. Accordingly, for example, even when cleaning failure occurs due to a cleaning device (not shown) provided on the upstream side of the charging device 1, the toner remaining on the surface of the photosensitive drum 10 can be effectively removed, so that the charging roller It is possible to effectively prevent the toner from adhering to the toner 2 and the contamination of the sponge roller 6 for removing the adhered toner, and it is possible to significantly improve the effective life of the charging roller 2. The toner collected by the pre-roller 3 is scraped off by the cleaning blade 7 and always kept clean.

The DC voltage applied to the pre-roller 3 must be equal to or higher than the charging start voltage of the photosensitive drum 10 (for example, about 600 V for the selenium photosensitive drum) as described above. As a result, pre-charging is performed at the same time as cleaning, and charging by the charging roller 2 is performed in addition to the pre-charging, so that the uniform charging of the photosensitive drum 10 can be effectively performed, and a uniform image without density unevenness can be obtained. Can be formed.

The charging by the charging roller 2 is performed by the DC power source 8a.
Is applied by applying a DC voltage to the charging roller 2 by means of 1.5 to 3.5 times, especially 2 to 3 times, the charging start voltage value on the surface of the photosensitive drum 10. Is preferred. Further, it is possible to perform uniform and even charging by applying only a DC voltage to the charging roller 2. However, in order to perform more uniform charging, as shown in FIG. It is also possible to combine the above and apply a voltage obtained by superimposing an AC voltage on the above DC voltage. For such alternating current, the frequency is 3
00 to 1500 Hz, especially 400 to 1000 Hz
And the peak-to-peak voltage is 2.5 to 4 times the DC voltage, especially
It is preferred to use 2.8 to 3.5 times the alternating current.

Further, in the present invention, the same power source can be used as the power source 9 for applying the DC voltage to the pre-roller 3 and the power source 8a for applying the DC voltage to the charging roller 2. That is, the charging roller 2 and the pre-roller 3
When and are electrically connected, there is also an advantage that the voltage applied to the charging roller 2 necessary for giving a predetermined surface potential to the photosensitive drum can be reduced. This is extremely advantageous in that current leakage from the charging roller 2 to the defective portion of the photoconductor drum 10 can be prevented even when the surface of the photoconductor drum 10 is defective.

The charging device 1 described above is not necessarily the same as that shown in FIG.
The structure is not limited to the structure shown in (1), but two or more pre-rollers 3 may be provided. Further, instead of the cleaning blade 7 provided in contact with the pre-roller 3, a sponge roller can be provided as a cleaning roller, and this cleaning roller can also be provided in the charging roller 2. Representative examples of the charging device using such a sponge roller are shown in FIGS. 7A to 7D and 8A to 8D.

In FIGS. 7 and 8, the cleaning roller is designated by 50. In particular, as shown in FIG. 8d,
It is also possible to provide the cleaning roller 50 in the housing 5 so as to be vertically movable, and control the vertical movement thereof by the solenoid 51 or the like so that the sponge roller 50 is brought into contact with the charging roller 2 and the pre-roller 3 only during charging. According to this aspect, it is possible to minimize clogging of the sponge roller 50 and fusion of the toner due to the toner attached to the charging roller 2 and the pre-roller 3, which is extremely advantageous in terms of device life. In these aspects, a sponge roller is generally used as the cleaning roller 50, but of course, the cleaning roller is not limited to this, and may be replaced with, for example, a belt type cleaning means.

The above-described charging method of the present invention is extremely useful for charging a photoconductor used in various electrophotographic apparatuses such as a copying machine, a facsimile, and a laser printer. Particularly, as the photoconductor, various types of single-layer or laminated structures are used. The organic photoconductor is suitable, but of course, in addition to this, it can be suitably applied to contact charging of an inorganic photoconductor such as an a-Si photoconductor or a selenium photoconductor.

[0041]

According to the present invention, the pre-roller is provided on the upstream side of the charging roller, and the charging roller charges the photosensitive member while applying a DC voltage higher than the charging start voltage to the pre-roller. Since the life can be improved and pre-charging is performed at the same time as cleaning by the pre-roller, uniform charging of the surface of the photoconductor can be effectively performed.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of a charging device used in a charging method of the present invention together with a photosensitive drum.

FIG. 2 is a front sectional view of a charging roller used in the charging device of FIG.

FIG. 3 is a schematic view showing an embodiment of a charging roller used in the present invention.

FIG. 4 is a schematic view showing an embodiment of a charging roller used in the present invention.

FIG. 5 is a schematic view showing an example of a charging roller used in the present invention.

FIG. 6 is a schematic view showing an example of a charging roller used in the present invention.

FIG. 7 is a schematic view showing various examples of the charging device of the present invention.

FIG. 8 is a schematic view showing various other examples of the charging device of the present invention.

[Explanation of symbols]

1: Charging device 2: Charging roller 3: Pre-roller 5: Cleaning roller 7: Cleaning blade 10: Photosensitive drum

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masajun Matsuda 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Industrial Co., Ltd.

Claims (5)

[Claims] 1. A charging method in which a charging roller made of an endless conductive flexible sheet is brought into contact with a movable photosensitive member, and a voltage is applied to the charging roller in this state to charge the photosensitive member. At least one pre-roller composed of a conductive flexible roller is disposed in contact with the surface of the photoconductor in the vicinity of the upstream side of the charging roller with respect to the moving direction of the body, and the pre-roller has a charging start voltage of the photoconductor or more. 2. A charging method characterized in that while the DC voltage is applied, the photoconductor is driven to rotate, and at the same time, charging is performed by the charging roller. 2. The charging method according to claim 1, wherein the charging roller has a brush roller incorporated in an endless conductive flexible sheet. 3. The charging method according to claim 1, wherein the pre-roller is formed by incorporating a brush roller in an endless conductive flexible sheet. 4. The charging method according to claim 1, wherein the pre-roller is a conductive rubber or sponge roller. 5. A charging roller, which is made of an endless conductive flexible sheet, is arranged in contact with a movable photosensitive member, and to which a predetermined charging voltage is applied, and the charging roller in the moving direction of the photosensitive member. At least one pre-roller, which is arranged near the upstream side of the roller in contact with the surface of the photoconductor and is made of a conductive flexible roller, and a DC voltage is applied to the pre-roller. Body charging device.