JPH0844142A - Electrifying device used in electrophotographic method - Google Patents

Abstract

PURPOSE:To perform excellent uniform electrification, prevent output from a power source from lowering even in the case of a fault such as a pinhole exists on the surface of a photoreceptor and to stably perform electrification by forming a conductive flexible sheet of a laminate sheet constituted of an inside low electric resistance layer and an outside high electric resistance layer. CONSTITUTION:The flexible laminate sheet 3 is constituted of a low resistance inner layer 3a and an outer layer 3b having higher resistance than the inner layer 3a. The outer layer 3b prevents a substance to be electrified such as a photoreceptor drum and the inner layer 3a from coming into contact with each other. Then, the volume resistivity of the inner layer (low resistance layer) 3a is <=10<5>OMEGA.cm. In the case the volume resistivity is higher than 10<5>OMEGA.cm difficult to uniformly and effectively electrify the surface of the photoreceptor. The outer layer(high resistance layer) 3b is set so that its &K resistivity is >=10<6>OMEGA/squ. and <10<7>OMEGA/squ. By such a sheet resistivity, the uniform electrification is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used in an electrophotographic method, and more particularly to a charging device for performing main charging on the surface of a photoreceptor by contact charging.

[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.

[0006]

However, the charging device composed of this charging roller still has room for improvement in the charging property. For example, charging unevenness is more likely to occur than the charging device by corona discharge, and the charging device should be charged. When there is a defect such as a pinhole on the surface of the photoconductor, the conductive sheet comes into contact with the defective part, so that a large current flows into the defective part and the output of the power source is lowered to cause charging failure. There's a problem.

Therefore, an object of the present invention is to provide a charging device comprising a charging roller provided with an endless flexible conductive sheet on the surface thereof, which is excellent in uniform charging property and has a defect such as a pinhole on the surface of the photosensitive member. An object of the present invention is to provide a charging device capable of performing stable charging without causing a reduction in the output of the power supply even when it is present.

[0008]

According to the present invention, in a charging device used in an electrophotographic method, which comprises a charging roller having an endless conductive flexible sheet on its surface, the conductive flexible sheet is A laminated sheet of an inner low electric resistance layer and an outer high electric resistance layer, wherein the high electric resistance layer has a surface resistivity of 10 ⁶ Ω / □ or more and less than 10 ⁷ Ω / □, The low electrical resistance layer has a volume resistivity of 10 ⁵ Ω · cm or less, and a charging device is provided.

[0009]

The charging by the charging roller having the endless conductive flexible sheet on the surface is performed by applying a DC voltage of a constant polarity to the sheet while the sheet is in contact with the charged body such as the photoconductor. Done. Therefore, in order to improve the charging property, it is usually considered that the electric resistance value of the sheet should be lowered. However, according to the experiments conducted by the present inventors, it has been found that even if the electric resistance of the conductive flexible sheet is reduced, the charging property is not necessarily improved, and on the contrary, the uniform charging property is impaired.

Although the reason for this is not clear, the present inventors consider that the cause is the dispersed structure of the conductive flexible sheet. That is, the conductive flexible sheet is one in which conductivity is imparted by dispersing an inorganic conductive powder such as carbon black in an originally electrically insulating plastic. Therefore, when the electric resistance of the conductive flexible sheet becomes low, the amount of the inorganic conductive powder dispersed in the sheet increases, so that the powder partially aggregates and tends to be unevenly distributed on the sheet surface. is there. As a result, when the conductive flexible sheet is brought into contact with the surface of the photoconductor for charging, the discharge from the surface of the sheet becomes non-uniform, which makes it difficult to perform uniform charging. On the other hand, when the electric resistance of the conductive flexible sheet becomes high to some extent, the amount of the inorganic conductive powder present on the sheet surface decreases, so that the discharge unevenness is large and it becomes difficult to perform uniform charging. .

The present invention has been made on the basis of the above-mentioned findings, and does not adjust the electric resistance value of the conductive flexible sheet, but of the sheet which is in direct contact with a charged body such as a photoconductor. By setting the surface resistance to a certain range,
It succeeded in preventing uneven charging. That is,
In the present invention, it is important to set the electric resistivity of the conductive flexible sheet surface (outer layer surface) to a range of 10 ⁶ Ω / □ or more and less than 10 ⁷ Ω / □. As a result, the appropriate amount of the inorganic conductive powder is evenly distributed on the surface of the conductive flexible sheet, and charging can be performed by uniform discharge. If the electrical resistivity is lower than the above range, the amount of the inorganic conductive powder distributed on the sheet surface is large, and thus there is a portion where the inorganic conductive powder is agglomerated as described above, and as a result, Discharge unevenness occurs and uniform charging cannot be performed. On the other hand, when the surface resistivity is higher than the above range, the amount of the inorganic conductive powder distributed on the surface of the sheet is small, discharge unevenness also occurs, and uniform charging becomes difficult.

In the present invention, it is also important that the endless conductive flexible sheet on the surface of the charging roller is a laminated sheet having a low resistance inner layer and a high resistance outer layer. That is, with such a laminated structure, it is possible to prevent the low resistance inner layer from directly contacting the surface of the charged body such as the photoreceptor. Therefore, even if there is a defect such as a pinhole on the surface of the body to be charged, the defective portion and the low-resistance inner layer do not come into direct contact with each other, so that a large current is prevented from flowing due to electrical leakage. As a result, the voltage drop of the output power source is effectively avoided, and the charging failure is effectively prevented.

In the present invention, the low resistance inner layer should have a volume resistivity in the range of 10 ⁵ Ω · cm or less. That is,
If the volume resistivity of this inner layer is higher than the above range, it becomes difficult to effectively perform charging.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific examples shown in the accompanying drawings. FIG. 1 is a front cross-sectional view showing an example of the charging device of the present invention having a built-in brush roller, and FIG. 2 shows another example of the charging device having a built-in brush roller. 3 to 5 show another aspect of the charging device of the present invention, and FIG. 6 is an explanatory view showing a charging state by the charging device of FIG.

(Charging Device with Built-in Brush Roller) The charging device of the present invention of the type shown in FIG. 1 (generally indicated by 2).
Is a flexible laminated sheet 3 in the form of a seamless tube,
It is composed of a brush roller 4 incorporated therein, and the brush roller 4 is composed of a conductive roller 4a and a brush 4b in which the bristles are planted. Both ends of the flexible laminated sheet 3 are fixed to flange rings 5 provided on the conductive roller 4a. That is, by integrally fixing the flange ring 5 to the conductive roller 4a, the flexible laminated sheet 3 can be provided so as to rotate integrally with the brush roller 4 at the same speed. Further, if the flange ring 5 is provided so as to be rotatable independently of the conductive roller 4a, the laminated sheet 3 can be separated from the brush roller 4 by connecting an appropriate drive transmission mechanism such as a gear to the flange 5. It is also possible to rotate the brush roller 4 and to rotate the brush roller 4 and the moving direction of the laminated sheet 3 in opposite directions.

Generally speaking, it is preferable that the moving speed of the laminated sheet 3 and the moving speed of the brush roller 4 are different from each other in order to prevent the laminated sheet 3 from being deformed due to twisting during contact charging. If the moving directions are the same, it is preferable to set the moving speed of the brush roller 4 (brush 4b) to 1.1 to 5 times the moving speed of the laminated sheet 3. When these moving directions are opposite to each other, the moving speed of the brush 4b is preferably set to 1.1 to 3 times the moving speed of the laminated sheet 3.

The flexible laminated sheet 3 is fixed to the flange ring 5 by using an appropriate heat-shrinkable resin ring 6, and the end portion of the flexible laminated sheet 3 is fixed to the ring 6 and the flange ring 5.
It may be carried out by sandwiching it with a suitable adhesive agent.

An elastic ring 7 such as a silicone rubber ring is provided on the inner end of the flange ring 5, and the end of the flexible laminated sheet 3 is fixed to the flange ring 5 so as to be in close contact with the elastic ring 7. Preferably. With this, by applying an appropriate tension to the flexible laminated sheet 3, it is possible to effectively prevent the occurrence of twist or the like when the sheet 3 is physically brought into contact with the surface of the charged body such as the photosensitive drum. Therefore, it is not always necessary to provide a speed difference between the laminated sheet 3 and the brush 4b, a drive mechanism necessary for setting the speed difference is not necessary, and the charging device can be made compact. There is an advantage.

In this case, in the upper surface area A of the laminated sheet 3 corresponding to the elastic ring 7, the sheet 3 comes into close contact with the end portion of the charged body such as the photosensitive drum and is rotated by the rotation of the charged body. Therefore, in order to rotate the laminated sheet 3,
It is not always necessary to provide a special drive mechanism. further,
The size of the elastic ring 7 is preferably set so that the contact width between the laminated sheet 3 and the surface of the photosensitive drum 1 is generally about 2 to 10 mm.

In the present invention, the flexible laminated sheet 3 is composed of an inner layer 3a having a low resistance and an outer layer 3b having a resistance higher than that of the layer 3a, and the outer layer 3b is a charged body such as a photosensitive drum. It prevents contact between the body and the inner layer 3a.

The inner layer (low resistance layer) 3a has a volume resistivity of 10
It is preferably ⁵ Ω · cm or less, particularly preferably 10 to 10 ⁴ Ω · cm. That is, if the volume resistivity is higher than the above range, it tends to be difficult to uniformly and effectively charge the surface of the photoconductor. The outer layer (high resistance layer) 3b
As described above, the surface resistivity is in the range of 10 ⁶ Ω / □ or more and less than 10 ⁷ Ω / □, and having such a surface resistivity results in uniform charging. It becomes possible to do. Since the outer layer 3b has the above-mentioned surface resistivity, the volume resistivity as a layer has a higher resistance than that of the inner layer 3a, but it is usually in a state of being laminated with the inner layer 3a, that is, a laminated sheet. The volume resistivity as 3 is 10 ^{6 to} 10 ⁹ Ω · cm, especially 10 ^{7 to} 10 ⁸
It is preferable to have a volume resistivity in the range of Ω · cm. If the volume resistivity of the laminated sheet 3 is higher than this range, it is difficult to effectively perform contact charging, and if it is lower than this range, there is a defective portion such as a pinhole on the charged body such as the photoconductor. In such a case, it tends to be difficult to prevent the inflow of a large current due to the leakage with the defective portion.

In the present invention, the inner layer 3a and the outer layer 3 are
As b, any material may be used as long as it satisfies the conditions that it has a predetermined conductivity and flexibility, but in general, various conductive agents are used. A compounded resin or rubber is used.

As the resin, various thermoplastic elastomers such as polyester elastomers, polyamide elastomers, polyurethane elastomers, soft vinyl chloride resins, styrene-butadiene-styrene block copolymer elastomers and acrylic elastomers are preferable. , Nylon 6, Nylon 6,6, Nylon 6
-Nylon 6,6 copolymer, Nylon 6,6 -Nylon 6,10
Copolymers, polyamides such as alkoxymethylated nylon such as methoxymethylated nylon, copolyamides or modified products thereof, silicone resins, acetal resins such as polyvinyl butyral, polyvinyl acetate, ethylene-
Vinyl acetate copolymers, ionomers and the like can also 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.

Further, as the inner layer 3a, for example, a seamless metal foil can be used. Examples of the metal foil include nickel, aluminum, copper, brass, tin and the like, and these are obtained by an electroforming method or extrusion.

Further, as the resin or rubber for the outer layer 3b, in addition to those described above, a fluorine-based resin or rubber such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexa. Fluoropropylene copolymer (PTFE
HFP), perfluoroalkoxy fluororesins, etc. are preferably used. When these resins or rubbers are used as the high resistance layer 3b, it is inactive and has a small friction coefficient, so that there is a great advantage in terms of the life of the photoconductor and the life of the sheet.

Conductive agents to be added to the above resins or rubbers to adjust the volume resistivity or surface resistivity of the layers 3a and 3b are conductive carbon black, silver, and the like.
Metal powders such as gold, copper, brass, nickel, aluminum, and stainless steel, and powdered conductive agents such as tin oxide-based conductive agents can be used. In addition, nonionic, anionic,
It is also possible to use a cationic or amphoteric organic conductive agent or an organic tin conductive agent. Generally, higher conductivity is obtained when these conductive agent particles form a chain structure in resin or rubber, but in this case, a dot-shaped high potential portion is generated when a voltage is applied. , There is a risk of uneven charging. 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. In order to effectively disperse the conductive agent uniformly, acrylic acid, methacrylic acid,
It is also effective to partially use an acid-modified resin or rubber obtained by copolymerizing an ethylenically unsaturated carboxylic acid such as maleic anhydride.

The laminated sheet 3 can be easily formed by, for example, integral molding such as simultaneous laminating extrusion or coating. In this case, it is desirable to select and use a resin or rubber for forming the low resistance layer 3a and the high resistance layer 3b, which have a melting point or a softening point in a range close to each other, in order to increase the adhesive strength of both layers.

Although the thickness of the laminated sheet 3 varies depending on its flexibility, it is preferably in the range of generally 100 to 300 μm, particularly 120 to 280 μm,
Usually, the inner layer 3a has a thickness of 50 to 300 μm, especially 10
It is preferable that the thickness is in the range of 0 to 200 μm, and the thickness of the outer layer 3b is in the range of 15 to 150 μm, and particularly 25 to 100 μm. The surface of the laminated sheet 3, especially the outer layer 3b
The surface of is preferably as smooth as possible.
Average roughness according to B0601 is 5μm or less, especially 1μm
The following is desirable.

In the charging device 2 described above, as the brush roller 4, a brush 4b made of insulating or conductive organic or inorganic fiber is planted on the conductive roller 4a.

When conductive fibers are used as the brush 4b, an insulating resin ring is used as the flange ring 5 described above, and a voltage is applied to the laminated sheet 3 via the conductive roller 4a and the brush 4b. Is done. In this case, the volume resistivity of the conductive brush is 10 ^{2 to} 10 ⁸ Ω
-Cm, particularly preferably in the range of 10 ^{3 to} 10 ⁶ Ω · cm. The thickness of the brush fiber is 2 to 10 denier (d), especially 3 to 6 d, the fiber length (length of the bristle foot) is preferably 2 to 7 mm, particularly 3 to 5 mm, and the hair transplant density is 1 The range of 10,000 to 200,000 lines / square inch, particularly 30,000 to 100,000 lines / square inch, 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 laminated 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.

When an insulating fiber is used as the brush 4b, a metal conductive ring is used as the above-mentioned flange ring 5, and a voltage is applied to the laminated sheet 3 by
It is performed through the conductive roller 4a and the flange ring 5. Generally, when the brush 4b is conductive, if there is a defect such as a pinhole on the surface of the charged body such as the photosensitive drum, a local current from the tip of the brush 4b flows into the defective portion. However, in the mode in which the brush 4b is insulative, the current flows from the laminated sheet 3, so that no local current is generated and there is no fear of the above troubles, which is extremely advantageous. .

As the above-mentioned insulating fiber, the above-mentioned organic fiber is used except that the conductive agent is not mixed, and the fineness and the fiber length may be in the ranges described above. However, the flocking density is preferably in the range of 30,000 to 100,000 / square inch, particularly 40,000 to 90,000 / square inch.

The charging device 2 with a built-in brush roller is not limited to the one shown in FIG. 1. For example, as shown in FIG. 2, the flange ring 5 is not used and the brush roller 4 is installed. A rubber ring 20 is provided at an end, and both ends of the laminated sheet 3 are fixed shafts 21 made of a heat-shrinkable resin ring or the like to a drive shaft 22 of the brush roller 4.
It may be fixed to. In this case, brush 4
An insulating material is used as b.

(Charging Device Not Incorporating Brush Roller) In the present invention, as long as the tubular flexible laminated sheet 3 having the above-mentioned specific surface resistivity is used, the brush roller 4 is used. It is also possible to use a charging device of a type that does not include the. An example of such a charging device of another aspect is shown in FIGS.

The charging device 2 of FIG. 3 is provided with a sponge roller 30 formed of a foam of various synthetic resins such as polyurethane and polystyrene, instead of the brush roller 4 of the charging device of FIG. Further, FIG. 4 shows that a metal roller 31 made of stainless steel or the like is provided instead of the brush roller 4, and FIG. 5 shows that the inside of the tubular flexible laminated sheet 3 is hollow. The charging device of FIG.
It is suitable when used as a small diameter (for example, diameter is 16 mm or less). According to the present invention, even in these types of charging devices, it is possible to improve the uniform charging property and avoid the inconvenience caused when there is a defect such as a pinhole on the surface of the body to be charged.

(Charging Method) The charging using the above-mentioned charging device 2 will be explained by taking the charging device shown in FIG. 1 as an example. For example, as shown in FIG. And the conductive roller 4a.
To the surface of the photosensitive drum 1 which rotates by pressing the laminated sheet 3 with the brush roller 4 while applying a voltage to the flexible laminated sheet 3 via the brush 4b or the flange ring 5 by connecting the DC power source 10 to the Contact the photoconductor drum 1
Charge the surface.

The charging device 2 is housed in, for example, a housing having an opening on one side and arranged in the electrophotographic device, and the laminated sheet 3 is applied to the surface of the photosensitive drum 1 through the opening with a constant pressure and a constant pressure. It is preferable to press using an appropriate spring or the like so that the contact is made within the contact width.

The charging voltage applied to this laminated sheet 3 is
The charging start voltage value on the surface of the photosensitive drum 1 is 1.5 to 3.5.
It is preferable to set double, especially 2 to 3 times. According to the charging using such a charging device, a good linear relationship between the applied voltage and the surface potential is maintained in the effective charging region, and By arranging a surface potential detection sensor around the body and increasing or decreasing the applied voltage based on the surface potential value detected by this sensor, the surface potential of the photoconductor can be kept constant and maintained at an optimum value. Becomes

In the present invention, since the high resistance layer 3b is in contact with the surface of the photosensitive drum 1 when a voltage is applied,
Even when there are defects such as pinholes on the surface of the photosensitive drum 1, the large current is prevented from flowing and the photosensitive drum 1
It is a remarkable advantage that the surface can be uniformly and effectively charged, but it is also an advantage of the present invention that uniform and even charging can be performed only by using a DC voltage. In this case, in order to perform even charging, it is possible to combine the AC power supply 11 with the DC power supply 10 and apply a voltage obtained by superimposing the AC voltage on the DC voltage described above. Such alternating current has a frequency of 300 to 1500 Hz,
Particularly, 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 400 to 1000 Hz.

The charging device of the present invention is useful for charging photoreceptors used in various electrophotographic processes such as copying machines, facsimiles, laser printers, etc., and various photoreceptors having a single-layer or laminated structure, for example, a-Si. The present invention is applicable to charging of any photoconductor such as a photoconductor, a selenium photoconductor, and a single-layer or multi-layer organic photoconductor. Among these, when the charging device of the present invention is applied to the organic photoconductor, ozone and NO _x are not generated, and therefore, the charge-generating pigment, the charge-transporting substance, the binder, the dielectric substance, and the like that compose the photoconductor. It is possible to extend its life without deterioration. Of course, the charging device of the present invention is not limited to the charging in the narrow sense, and it is needless to say that the charging device can be applied to static elimination by applying a bias voltage.

[0042]

EXAMPLES Example 1 Mita Industry Co., Ltd. using an organic photoconductor as the charging device of FIG.
It was mounted on a modified electrophotographic copying machine DC-2566, and charged, exposed, developed, transferred and fixed without applying an AC voltage. The physical properties of each member of the charging device and the charging conditions were set as follows. The volume resistivity and surface resistivity of each resistance layer constituting the endless flexible conductive sheet were measured using a volume resistivity meter Loresta or Hiresta manufactured by Mitsubishi Petrochemical Co., Ltd. The measurement was performed at a voltage of 10V.

Endless flexible conductive laminated sheet; Outer layer: polyvinylidene fluoride (thickness: 80 μm, volume resistivity: 6.4 × 10 ⁷ Ω · cm,
Surface resistivity: 8.6 × 10 ⁶ Ω / □ Inner layer: Polyvinyl chloride elastomer (thickness: 200 μm, Volume resistivity: 8.8 × 10 ² Ω ・ c)
m) Inner diameter of laminated sheet: 20 mm Volume resistivity of laminated sheet: 6.4 × 10 ⁷ Ω · cm

Brush roller; Material: Conductive rayon outer diameter: 19.8 mm Fiber thickness: 6 denier Fiber length: 3 mm Flock density: 100,000 fibers / inch ²

Charging conditions: Applied DC voltage: + 1600V (charging start voltage: + 600V) Brush roller rotation speed: 150 rpm (photoconductor and driven rotation) Endless sheet rotation speed: 150 rpm (fixed to brush roller, photoconductor and driven) Rotation) Photoconductor peripheral speed: 157 mm / sec

As a result of charging under the above conditions, the surface potential of the photosensitive member was +800 V, and the obtained copy was a good image without black spots. Further, when charging was performed under the same conditions using a photoconductor having a pinhole, no image defects such as white lines due to concentrated leak of charging current to the pinhole portion occurred.

[0047]

According to the present invention, it is possible to effectively uniformly charge an object to be charged such as a photoconductor, and even if a defect such as a pinhole is generated on the surface of the object to be charged, It is possible to uniformly and stably charge the surface of the photoconductor without lowering the output and without shortening the life of the photoconductor.

[Brief description of drawings]

FIG. 1 is a front cross-sectional view showing an example of a charging device of the present invention in which a brush roller is incorporated.

FIG. 2 shows another example of a type in which a brush roller is incorporated in the charging device of the present invention.

FIG. 3 shows an example of a type in which a brush roller is not incorporated in the charging device used in the present invention.

FIG. 4 shows another example of the charging device used in the present invention, which does not include a brush roller.

FIG. 5 shows still another example of the charging device used in the present invention in which the brush roller is not incorporated.

FIG. 6 is an explanatory view showing a charging state by the charging device of FIG.

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

Claims (6)

[Claims] 1. A charging device used in an electrophotographic method, comprising a charging roller having an endless conductive flexible sheet on a surface thereof, wherein the conductive flexible sheet has a low electrical resistance layer on an inner side and a high electrical resistance layer on an outer side. A laminated sheet with an electric resistance layer, wherein the high electric resistance layer has a surface resistivity of 10 ⁶ Ω / □ or more and less than 10 ⁷ Ω / □, and the low electric resistance layer has a volume resistivity of 10 ⁵
Charging device characterized by being less than Ω · cm. 2. The charging device according to claim 1, wherein the conductive flexible sheet has a volume resistivity in the range of 10 ^{6 to} 10 ⁹ Ω · cm. 3. The charging device according to claim 2, wherein the conductive flexible sheet has a thickness of 100 to 300 μm. 4. The charging device according to claim 1, wherein the charging roller is formed by incorporating a brush roller in an endless conductive flexible sheet. 5. The charging device according to claim 1, wherein the charging roller is formed by incorporating a sponge roller in an endless conductive flexible sheet. 6. The charging roller is a small diameter roller having a diameter of 16 mm or less, and both ends of a conductive flexible sheet are fixed to elastic rings provided on a conductive rotating shaft so that the inside is hollow. The charging device according to claim 1, wherein