JPH06337571A - Electrifier - Google Patents

Abstract

PURPOSE:To uniformly and evenly electrify a body to be electrified without causing the irregularity of electrification finally and to excellently form an image even in the case a high voltage part is locally generated on the surface of a conductive roller used for main electrification. CONSTITUTION:The cylindrical conductive roller 13 made of a flexible material, where a brush roller made of a conductive material is incorporated and which is rotatably held by the brush roller, is used in this electrifier; and the electrifier is constituted by setting a pre-electrifier 1 made of a conductive elastic body 11, which abuts on the surface of the body to be electrified, on the upstream side of a main electrifier 2 electrifying the body to be electrified by impressing voltage on the roller 13 and physically bringing it into contact with the body to be electrified. The body to be electrified is previously electrified before the main electrification by impressing the voltage twice or more as high as the starting voltage for electrifying the body to be electrified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device, and more particularly to a charging device in which uneven charging of a photosensitive member is effectively prevented.

[0002]

2. Description of the Related Art In an electrophotographic apparatus, a system in which an electrostatic latent image is formed by uniformly charging the surface of a photosensitive member and exposing the charged photosensitive member to a direct image is employed. Conventionally, corona wires have been widely used for charging charged bodies such as photoconductors.However, corona charging requires a high voltage generator for corona generation, which is costly, and corona discharge requires ozone. There was a problem that harmful components such as In addition, in the former method that does not use corona discharge, brush charging, a method using a conductive roller, etc., the contact between the brush and the photosensitive member is point contact, so that there is a part that is not charged,
The disadvantage is that the charging becomes non-uniform. In the latter case, if the surface of the photoconductor is uneven, or if dust, paper powder, toner, etc. are attached, the charging cannot be performed evenly and the roller is high. It has a drawback that the photoconductor is significantly worn when a pressure is applied.

To solve such problems in charging devices, the Applicant has incorporated a conductive brush roller into the contact which comprises a cylindrical conductive flexible layer rotatably held by the brush roller. A charging device has been proposed which uses a charging roller and applies a DC bias voltage to the brush roller to bring the conductive flexible layer into contact with the surface of the photoconductor by pressing the brush roller to charge the surface of the photoconductor. (Japanese Patent Application No. 5-45549).

Since this charging device contacts the member to be charged without applying a high pressure, it is possible to effectively prevent wear of the member to be charged, and the conductive sheet is flexible and freely deformable. It is a very advantageous charging device in that even if the surface has irregularities, it can make uniform contact with the entire surface and can uniformly and evenly charge the body to be charged.

[0005]

However, in this charging device, in order to impart conductivity to the flexible layer,
Conductive powder such as carbon is dispersed in a flexible resin. Therefore, depending on the degree of dispersion, a dot-like highly conductive portion may occur. On the other hand, since the voltage given by the conductive flexible layer is due to a minute discharge,
Since the high potential is present only in the dot-like highly conductive portion of the conductive flexible layer, there is a problem that uneven charging occurs on the member to be charged. Especially when the surface resistance of the flexible layer is low, such charging unevenness is likely to occur. Therefore, an object of the present invention is to provide a charging device that effectively prevents uneven charging, which is a drawback of the above charging device.

[0006]

According to the present invention, there is provided a cylindrical conductive roller made of a flexible material, which contains a brush roller made of a conductive material and is rotatably held by the brush roller. In the charging device, which applies a voltage to the charged body to bring it into physical contact with the charged body to charge the charged body, the charging start voltage of the charged body is twice or more the upstream side of the conductive roller. There is provided a charging device characterized in that a conductive elastic body to which a voltage is applied is installed so as to come into contact with the surface of a body to be charged.

[0007]

As described above, the contact charging mechanism using the conductive roller is a charging by a minute discharge in which the member to be charged and the conductive roller are brought into contact with each other by a small pressure applied by the conductive brush. A point-like high potential portion is generated on the surface of the body to be charged corresponding to the portion of the roller where the conductive material is present, and uneven charging occurs. In the present invention, the main charging is performed by pre-charging the charged body in advance before the main charging which charges the charged body such as the photoconductor using such a conductive roller. Even when a high-voltage part is locally generated on the surface of the conductive roller used, the charged body can be finally charged uniformly and uniformly without causing uneven charging. It is possible to form.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In FIG. 1 showing an example in which an example of the charging device of the present invention is applied to an electrophotographic copying apparatus, a charging device 3 of the present invention comprising a pre-charging device 1 and a main charging device 2 is an electrophotographic photosensitive layer. A pre-charging device 1 and then a main charging device 2 are arranged from the upstream side in the rotation direction of the drum 5 indicated by an arrow around a rotary drum 5 provided with (member to be charged) 4. Further, an image exposure mechanism 6, a developing mechanism 7, a toner transfer mechanism 8, a cleaning mechanism 9 and an exposure charge eliminating mechanism 10 are sequentially arranged on the downstream side of the charging device 3.

In the pre-charging device 1, a sheet-shaped conductive elastic body 11 is connected to a DC power source 12a and an AC voltage 12b.
Are connected via a switch, and one side of the conductive elastic body 11 is arranged so as to contact the photosensitive drum 5 with a constant pressure, and the DC power source 12a (or the AC power source 12b).
When a direct current (AC) bias voltage is applied between the conductive elastic body 11 and the photoconductor 4, the precharge of the surface of the photoconductor is performed. The photoconductor 4 that has been pre-charged is then charged by the main charging device 2 in accordance with its rotation.

FIG. 2 for explaining an example of the main charging device 2.
In FIG. 1, the charging member 13 of the main charging device 2 is roughly, as is clear from the cross-sectional view (a) thereof, a flexible hollow conductive roller 14 and coaxially inside the flexible roller 14. The brush roller 15 is provided so as to be rotatable relative to each other. Further, from the sectional view (b), the brush roller 1
The numeral 5 comprises a drive shaft 16 and a brush 17 having hairs implanted on this shaft. The hollow conductive roller 14 has rigid ends 18 at both ends, and the ends 18 have a large diameter portion 19 and a small diameter portion 20 tapered from the large diameter portion. A drive gear 21 is fixed to 20. Also, in the center of the end 18, there is a hole 22 passing therethrough.
The drive shaft 16 of the brush roller passes through the hole 22 and extends to the outside of the end 18. A bearing 23 is provided between the end 18 and the brush drive shaft 16 to allow relative rotation between the two. The flexible hollow roller 14 is supported on the outer circumference of the large-diameter portion 19 of the end 18, and the end thereof is fastened by the fastening member 24.
It is fixed to the small-diameter portion 8 of.

The inner surface of the flexible hollow roller 14 is in contact with the brush 17 accommodated therein and is supported by the brush 17. The large-diameter portion 19 of the end 18 is a body to be charged (not shown) via a flexible roller around it.
Abutting portions 25 to the
In the meantime, the flexible hollow roller 14 is supported by a brush and is in a state in which the outer diameter of the abutting portions 25, 25 is slightly increased. Further, in order to properly position the flexible hollow roller 14, push springs 28, 28 are provided between the end portion 26 of the brush 17 and the inner end portion 27 of the end 18, and the flexible conductive hollow roller is provided. 14 is given a slight tension in the axial direction. The main charging device 2 is brought into contact with the photosensitive drum 4 with a constant pressure by means such as a spring. In addition, the flexible hollow conductive roller 14 is the photosensitive drum 4
The brush roller 15 is driven at a speed different from that of the hollow conductive roller 14 via the drive shaft 16 thereof. Further, the drive shaft 16 is in a state of being electrically insulated from the machine frame and the drive system, and the DC power source 12a is connected via a current collector (not shown), the wiring 29, and the switch 30.
Alternatively, it is connected to the AC power supply 12b.

In the main charging device 2 of the present invention, since the photosensitive layer 4 is uniformly charged without wearing the photosensitive layer 4, an electrostatic latent image with high contrast and no disturbance is formed by image exposure. be able to. Moreover, since the photosensitive layer 4 is charged to a constant voltage by the pre-charging device 1 prior to the main charging, even if a point-like high voltage portion is generated on the flexible hollow roller 14, uniform and uniform charging is performed. Can be done.

(Pre-Charging Device) As the conductive elastic body used in the pre-charging device, resins or rubbers containing various conductive agents are used. As the resin, various heat-flexible elastomers such as polyester-based elastomer, polyamide-based elastomer, polyurethane-based elastomer, soft vinyl chloride resin, styrene-butadiene, styrene / block copolymer elastomer, and acrylic elastomer are preferably used. , Nylon 6, nylon 6,6,
Nylon 6-nylon 6,6 copolymer, nylon 6,6
Polyamides such as nylon 6,10 copolymers and alkoxymethylated nylons such as methoxymethylated nylon,
Copolyamides or modified products thereof are also used. Of course, the resin used is not limited to those exemplified above, and for example, silicone resin, acetal resin such as polyvinyl butyral, polyvinyl acetate, ethylene vinyl acetate copolymer, ionomer and the like can be used. As the rubber, natural rubber, butadiene stereo rubber, styrene-butadiene rubber, nitrile-butadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-non-conjugated diene copolymer rubber, chloroprene rubber, butyl rubber, silicone rubber, urethane Examples thereof include rubber and acrylic rubber.

As the conductive agent, conductive carbon black, metal powder such as silver, gold, copper, brass, nickel, aluminum and stainless steel, and powder conductive agent such as tin oxide type conductive agent can be used. Alternatively, a nonionic, anionic, cationic, amphoteric organic conductive agent or an organic tin conductive agent may be used. Conductive resin or rubber is
Generally speaking the electrical resistance (resistivity) of 10 ² to 10 ⁸ [Omega] cm, particularly preferably in the range of 10 ² to 10 ⁶ [Omega] cm. The conductive agent varies depending on the type of the conductive agent, but 1 to 60 parts by weight to 100 parts by weight of resin or rubber,
In particular, it is mixed in an amount of 5 to 50 parts by weight so that the above resistance value can be obtained.

The conductive elastic body may be made of a single-layer material, or may be made of a laminated or multi-layer material. The tip of the conductive elastic body that contacts the charged body,
When it is formed of a high resistance layer, it is effective in preventing leakage such as discharge even if there are conductive scratches or protrusions on the surface of the photosensitive layer. The specific resistance of the high resistance layer is preferably in the range of 10 ^{8 to} 10 ¹³ Ωcm, particularly 10 ^{9 to} 10 ¹² Ωcm, and the thickness thereof is preferably in the range of 5 to 60 μm. The electric resistance can be easily adjusted by adjusting the blending amount of the conductive agent to be blended with the resin or rubber. As the high resistance layer, a fluorine resin or rubber such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene, a copolymer (PTFE / HF).
The use of P), perfluoroalkoxy-based fluororesins, and the like has a great advantage in terms of the life of the photoconductor and the life of the flexible conductive sheet, because these resins are inactive and have a small friction coefficient. When using a metal foil, coating or laminating of a high resistance layer is particularly recommended. The high resistance layer is formed by coating, co-lamination extrusion or the like.

The conductive elastic body may have various shapes as long as it has a tip portion that is pressed against the surface of the body to be charged and does not damage the body to be charged. preferable. The thickness of the sheet is generally 0.05 to 2 mm,
In particular, the range of 0.1 to 1 mm is preferable from the viewpoint of preventing the scratches on the member to be charged and the charging performance. As described above, in the pre-charging, the applied voltage of the conductive elastic body is twice or more the charging start voltage of the body to be charged, particularly 2.5 to 3
It is preferably doubled. If it is 2 times or less, it becomes difficult to sufficiently eliminate the local potential difference generated in the main charging. The upper limit varies depending on the type of the photoconductor to be used and the film pressure, but when it exceeds 3 times, the humidity of the environment to be used becomes high even if there is no problem at room temperature, for example, 70 If it exceeds%, electric charge may leak to the photoconductor due to the discharge phenomenon, and the photoconductor may be damaged. The contact pressure between the conductive elastic body and the body to be charged is preferably in the range of generally 1 to 10 g / cm as a linear pressure.

(Main Charging Device) As the hollow conductive roller in the main charging device, a flexible conductive sheet can be used. As the flexible conductive sheet, any material is used as long as it satisfies the condition that it is conductive and has flexibility. For example, it may be made of the above-mentioned conductive resin or rubber, or a metal such as a foil, or a laminate of metal and resin or rubber. Any conductive agent can be used as the conductive agent dispersed in the sheet, and for example, the conductive agent described above can be used. For conductive particles, higher conductivity can be obtained by forming a chain structure in a conductive resin or rubber, but in this case, uneven charging, that is, a tendency to generate dot-like high potential parts Therefore, the conductive particles are preferably uniformly and finely dispersed in the resin or rubber.
For this purpose, it is important to sufficiently knead the conductive agent-containing resin or rubber, for example, as at least a part of the resin or rubber, an acid-modified resin or rubber, that is, acrylic acid,
It is also effective to use a resin or rubber obtained by copolymerizing an ethylenically unsaturated carboxylic acid such as methacrylic acid or maleic anhydride.

The conductive resin or rubber sheet used in the present invention generally varies depending on the flexibility thereof, but is generally 5
It preferably has a thickness of 0 to 400 μm, particularly 100 to 300 μm. The surface is preferably as smooth as possible, and the average roughness according to JIS B0601 is preferably 5 μm or less, and particularly preferably 1 μm or less. Molding into a seamless tube or seamless belt can also be carried out by extrusion molding using a ring die, and a fluidized dipping method of resin or rubber powder into a mandrel or cylindrical mold coated with a release agent, or latex, It can also be carried out by an emulsion, suspension, or solution dip coating film formation method. A seamless metal foil can also be used as the flexible conductive sheet. 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 20 to 80 μm, especially 30
It is desirable to be in the range of 50 to 50 μm.

The flexible conductive sheet forming the conductive roller can be made of a single-layer material, or a laminated or multi-layer material, and the surface of the flexible conductive sheet that contacts the charged body. Is formed of a high resistance layer, it is effective in preventing leakage such as discharge even if there are conductive scratches or protrusions on the surface of the photosensitive layer. The resistivity of this high resistance layer is 1
0 ⁸ to 10 ¹³ [Omega] cm, good especially in the range of 10 ⁹ to 10 ¹² [Omega] cm, the thickness may in the range of 40 to 60 [mu] m, a resin or the like that can be used in other high-resistance layer of the pre-charging device The same material as the conductive elastic body can be used.

As the brush, either a conductive brush or an insulating brush can be used. As the conductive brush, conductive organic or inorganic fibers are used, and it is preferable that the volume resistivity is in the range of 10 ^{2 to} 10 ⁸ Ωcm, particularly 10 ^{3 to} 10 ⁶ Ωcm. The fiber thickness is 2 to 10 denier (d),
Especially 3 to 6d, fiber length (hair length) is 2 to 7mm,
Especially, it should be 3 to 5 mm, and the density of the hair is 100.
00 to 200,000 lines / square inch, especially 30,000
It is preferably in the range of 100 to 100,000 lines / square inch in order to provide a smooth and uniform pressing force. In addition, rounding the tip of the brush is suitable for suppressing abrasion of the flexible conductive sheet.

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. As the conductive agent, those mentioned above are 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 electrically insulating brush, the above organic fiber is used except that it does not contain a conductive agent. The fineness, the fiber length and the hair density can be in the ranges described above.

In the main charging device, the flexible conductive roller is driven or driven at a speed synchronized with the moving speed of the body to be charged, and the brush is driven at a speed different from that of the conductive roller. The brush may be driven in the same direction as the conductive roller or in the opposite direction.
In the same direction, the roller moving speed is generally 1.1 to 5
It is preferable that it is in the range of 1 to 3 times, especially 1.5 to 3 times, and in the opposite direction, it is in the range of 1.1 to 3 times, especially 1.5 to 2 times the moving speed of the roller. It is desirable in that the conductive conductive sheet and the surface of the body to be charged are brought into contact with each other uniformly and steadily. In the main charging device, the charging voltage applied to the conductive roller is preferably set to 1.5 to 3.5 times, particularly 2 to 3 times, the charging start voltage value of the member to be charged.

Both of the pre-charging and the main charging can use the DC voltage to perform uniform and even charging, but in order to carry out the charging evenly, the AC voltage is further superimposed on the above-mentioned DC voltage. A voltage can also be applied. Such alternating current has a frequency of 300 to 1500H.
It is possible to use an AC voltage having a peak-to-peak voltage of 2.5 to 4 times, especially 2.8 to 3.5 times the above DC voltage at z, especially 400 to 1000 Hz.

The charging method of the present invention is useful for charging a photoconductor using various electrophotographic methods such as a copying machine, a facsimile, a laser printer, etc. Here, as the photoconductor, various photoconductors having a single-layer or laminated structure, Examples thereof include an a-Si photoconductor, a selenium photoconductor, and a single-layer or multi-layer organic photoconductor. Among these, when the power supply method of the present invention is applied to the organic photoconductor, ozone and NOx are hardly generated. Therefore, charge generating pigments, charge transporting substances, binders, dielectrics and the like which compose the photoconductor are used. It is possible to extend its life without deterioration.

[0025]

EXAMPLES An experiment was conducted to confirm the effect of pre-charging by changing the voltage applied to the pre-charging device using a device having the same structure as the device schematically shown in FIG. The conditions of the experimental apparatus are as follows. As the pre-charging device, a conductive elastic body made of polyurethane resin containing carbon black and having an electric resistance of 10 ³ Ωcm and a thickness of 1 mm is used, and the contact pressure to the photoconductor is set to 3 g / cm. used. The charging start voltage was 600 V when the pre-charging device was used as a photosensitive member and brought into contact with a commercially available selenium photosensitive member. As the main charging device, a device having a surface resistance of 10 ² Ωcm was used, and a direct current voltage of 1500 v was applied as a charging voltage so that the surface of the photoconductor was applied to 800 v. The size of the photoconductor is 78 mm, and the peripheral speed is 310 mm / sec.
And As an experiment for confirming the uniformity of charging, the photosensitive member was uniformly charged under the above conditions and then developed with a commercially available two-component developer without image exposure, and this was transferred to paper, It was carried out by checking the unevenness of the image at that time. The results are shown in Table 1.

[0026]

[Table 1]

[0027]

According to the present invention, a cylindrical conductive roller made of a flexible material which contains a brush roller made of a conductive material and is rotatably held by the brush roller is used. This pre-charging device is combined with a main charging device that applies a voltage to physically contact the charged member and charges the charged member, and a pre-charging device made of a conductive elastic body that contacts the surface of the charged member. The main charging device is installed upstream of the main charging device, and a voltage that is at least twice as high as the starting voltage for charging the charged object is applied to pre-charge the charged object before the main charging. It is possible to effectively prevent the generation of the dot-like high potential portion that occurs when only the charging is performed, and it is possible to perform uniform and uniform charging, and it is possible to improve the image quality.

[Brief description of drawings]

FIG. 1 is a diagram showing an example in which an example of a charging device of the present invention is applied to an electrophotographic copying apparatus.

FIG. 2 is a diagram showing an example of a main charging device used in the present invention.

[Explanation of sign]

 DESCRIPTION OF SYMBOLS 1 Pre-charging device 2 Main charging device 3 Charging device 4 Charged object 6 Image exposure mechanism 7 Development mechanism 8 Toner transfer mechanism 9 Cleaning mechanism 10 Exposure static elimination mechanism 11 Conductive elastic body 12 Power supply 13 Charging member of main charging device 14 Flexible Roller 15 Brush roller 16 Drive shaft

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiji Goto 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Engineering Co., Ltd.

Claims (1)

[Claims] 1. A cylindrical conductive roller made of a flexible material, which has a brush roller made of a conductive material and is rotatably held by the brush roller, is used, and a voltage is applied to the cylindrical conductive roller. A charging device for charging a charged body by physically contacting it with a charged body, comprising: a conductive elastic body having a voltage applied to the upstream side of the conductive roller at least twice as high as a charging start voltage of the charged body. A charging device, which is installed so as to come into contact with the surface of an object to be charged.