JP3293970B2 - Contact charging method for photoreceptor surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method capable of performing main charging of the surface of a photoreceptor without performing corona discharge.

[0002]

2. Description of the Related Art In an image forming method using an electrophotographic method, the surface of a photoreceptor is uniformly charged, and an image is exposed to form an electrostatic latent image corresponding to a document image on the surface of the photoreceptor. Image formation is performed by developing and transferring the latent image. In such an image forming method, the charging (main charging) of the photoreceptor surface is generally performed by corona charging. However, in this method, the problem of environmental pollution such as generation of ozone is unavoidable. Recently, in order to avoid generation of ozone, a method has been proposed in which a conductive rubber roller is brought into frictional contact with the surface of a photoreceptor while applying a bias voltage to perform main charging on the surface of the photoreceptor. 63-1496
No. 69 and JP-A-1-267667).

[0003]

However, in the above-described charging method by frictional contact, uniformity of charging is impaired when foreign matter such as dust and paper powder is caught between the conductive rubber roller and the photosensitive member. Therefore, it has been difficult to perform stable charging. In addition, when forming an image, there is a problem that cleaning of the surface of the photoconductor is defective, and if toner remains on the surface, there is a problem that the remaining toner is fixed to the surface of the photoconductor, and the durability of the photoconductor is reduced. The problem also arises. Furthermore, in order to perform uniform charging, it is not sufficient to apply only a DC bias voltage, and it is necessary to apply an AC bias voltage.

As a charging method in which such a problem has been solved, the present applicant has previously made a flexible conductive sheet frictionally contact the surface of a photoreceptor using a conductive brush roller. (Japanese Patent Application No. 4-68148).

In this charging method, since a flexible conductive sheet is pressed by a conductive brush roller and closely adheres to the surface of a photoreceptor, only a low DC bias voltage is applied without applying an AC bias voltage. This is a very significant charging method in that frictional charging can be performed uniformly. However, in this charging method, if there is a defect such as a pinhole on the surface of the photoconductor, the conductive sheet comes into contact with the pinhole portion, so that a large current flows into the portion and the output of the power supply decreases. Charging failure occurs.

Accordingly, an object of the present invention is to provide a charging method capable of uniformly and effectively performing triboelectric charging without causing a decrease in output of a power supply even when a defect such as a pinhole is present on the surface of a photoreceptor. Is to do.

[0007]

According to the present invention, an endless conductive flexible sheet containing a brush roller is brought into physical contact with the surface of a photoreceptor, and a voltage is applied to the conductive flexible sheet. a method of performing charging of the photosensitive member surface and the
The brush roller is an insulating brush planted on a conductive roller.
The conductive flexible sheet is composed of a first resistance layer located on the brush roller side and a second resistance layer located on the outer surface, and the second resistance layer is A method for contact charging the surface of a photoreceptor, characterized in that the layer has a higher electric resistance than the first resistance layer.

[0008]

That is, according to the present invention, the conductive flexible sheet is composed of a low-resistance first resistance layer and a high-resistance second resistance layer. Since the high-resistance second resistance layer is interposed between the photoconductor and the photoconductor surface, even if a defect such as a pinhole exists on the photoconductor surface, the low-resistance first resistance layer and the second Direct contact with the defective part is prevented, and the inflow of large current due to electrical leakage is prevented,
As a result, the voltage drop of the output power supply is effectively avoided,
Thus, it is possible to prevent poor charging.

In addition, since the contact between the conductive flexible sheet and the surface of the photoreceptor is forced by the brush roller, dust,
Even when foreign matter such as paper powder is caught between the photosensitive members, the flexible sheet bends and the close contact (contact) with the surface of the photoreceptor is effectively maintained, so that charging can be performed effectively and uniformly. For example, uniform charging can be performed without applying an AC bias voltage in addition to a DC bias voltage.

Further, since the contact between the flexible sheet and the surface of the photoreceptor by the urging of the brush roller is extremely soft, even if residual toner is present on the surface of the photoreceptor,
This is not fixed to the surface of the photoconductor, and as a result, charging can be performed stably, and the durability of the photoconductor does not decrease.

[0011]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is an explanatory diagram for explaining a contact charging method of the present invention, and FIG. 2 is a diagram showing a side cross section of a contact charging roller used for contact charging in FIG.

As is particularly apparent from FIG. 1, in the method of the present invention, a contact charging roller 2 is disposed on the surface of a rotatable photosensitive drum 1 so as to come into contact therewith.

The contact charging roller 2 is composed of a flexible laminated sheet 3 in the form of a seamless tube and a brush roller 4 incorporated therein. The brush roller 4 is composed of a conductive roller 4a and a flocking thereon. Brush 4b. Both ends of the flexible laminated sheet 3 are fixed to a flange ring 5 provided on the conductive roller 4a. That is, the flange ring 5 is connected to the conductive roller 4a.
Fixed to the flexible laminated sheet 3
Can be provided so as to rotate integrally with the brush roller 4 at the same speed. If the flange ring 5 is provided so as to be rotatable independently of the conductive roller 4a, an appropriate drive transmission mechanism such as a gear can be connected to the flange 5 to separate the laminated sheet 3 from the brush roller 4. For example, the rotation direction of the brush roller 4 and the moving direction of the laminated sheet 3 can be set in opposite directions.

Generally speaking, in order to prevent deformation of the laminated sheet 3 such as twisting, it is preferable that the moving speed of the laminated sheet 3 and the moving speed of the brush roller 4 be different. When 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 the moving directions are opposite to each other, the moving speed of the brush 4b is preferably set to be 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 so that the end of the flexible laminated sheet 3 is fixed to the ring 6 and the flange ring 5.
And a suitable adhesive may be used.

As shown in FIG. 2, an elastic ring 7 such as a silicone rubber ring is provided at the inner end of the flange ring 5, and the flexible laminated sheet is brought into close contact with the elastic ring 7. It is preferable to fix the end of 3 to the flange ring 5. Thereby, the flexible laminated sheet 3
If the sheet 3 is physically brought into contact with the surface of the photoreceptor drum 1, the occurrence of twisting or the like can be effectively prevented by applying an appropriate tension to the laminated sheet 3.
There is no need to provide a speed difference between the brush and the brush 4b, and a drive mechanism required for setting the speed difference is not required, and there is an advantage that the developing device can be made compact.

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 of the photosensitive drum and rotates following the rotation of the photosensitive drum 1. Therefore, it is not always necessary to provide a special driving mechanism for rotating the laminated sheet 3. Further, the contact width between the laminated sheet 3 and the surface of the photosensitive drum 1 is generally 2
It is preferable that the size of the elastic ring 7 is set to be about 10 mm to about 10 mm.

In the present invention, the flexible laminated sheet 3 has a low resistance first resistance layer (hereinafter, referred to as a low resistance layer) 3a and a second resistance layer having a resistance higher than that of the layer 3a. (Hereinafter referred to as a high-resistance layer) 3b, and the high-resistance layer 3b is located on the photosensitive drum side and has a low-resistance layer 3a.
And the photosensitive drum 1 are prevented from contacting with each other.

The low resistance layer 3a has a volume resistivity of 10 ⁷ Ω ·
cm or less, and particularly preferably in the range of 10 ^{6 to} 10 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 volume resistivity of the high resistance layer 3b is:
Although it depends on the volume resistivity of the low-resistance layer 3a, it is generally at least 10 ⁸ Ω · cm, preferably from 10 ^{9 to} 10 ¹² Ω · cm, and most preferably from 10 ^{9 to} 10 ¹¹ Ω · cm. If the volume resistivity is lower than this range, it is difficult to prevent the inflow of a large current due to leakage with a defective portion on the surface of the photoconductor 1, and if it is higher than 10 ¹² Ω · cm, the surface resistivity of the photoconductor 1 There is a tendency that it is difficult to effectively perform contact charging.

In the present invention, the low-resistance layer 3a and the high-resistance layer 3b may be made of any material as long as they satisfy the condition that they have predetermined conductivity and flexibility. , But generally, a resin or rubber containing various conductive agents is used.

As the resin, various thermoplastic elastomers such as polyester elastomer, polyamide elastomer, polyurethane elastomer, soft vinyl chloride resin, styrene-butadiene-styrene block copolymer elastomer, and acrylic elastomer are preferable. , Other nylon 6, nylon 6,6, nylon 6
-Nylon 6,6 copolymer, Nylon 6,6-Nylon 6,10
Copolymers, polyamides such as alkoxymethylated nylons such as methoxymethylated nylons, 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. As the rubber, natural rubber, butadiene rubber, styrene rubber, butadiene-styrene rubber, nitrile-butadiene rubber, ethylene-propylene copolymer rubber, ethylene-
Preferred are propylene-non-conjugated diene copolymer rubber, chloroprene rubber, butyl rubber, silicone rubber, urethane rubber, acrylic rubber and the like.

Further, as the low resistance 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, which are obtained by electroforming or extrusion.

In particular, as the resin or rubber for the high resistance layer 3b, in addition to those described above, fluorine-based resins and rubbers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and tetrafluoroethylene -Hexafluoropropylene copolymer (PTFE
• HFP), perfluoroalkoxy-based fluororesins and the like are preferably used. When these resins or rubbers are used as the high resistance layer 3b, they are inactive and have a small coefficient of friction, so that there is a great merit in terms of the life of the photoconductor and the life of the sheet.

In order to adjust the volume resistivity of each of the layers 3a and 3b, the conductive agent to be added to the above resin or rubber includes conductive carbon black, silver, gold, copper, brass, nickel, aluminum and stainless steel. Metallic powders such as steel and powdered conductive agents such as tin oxide-based conductive agents can be used. In addition, organic conductive agents such as nonionic, anionic, cationic and amphoteric, and organic tin-based A conductive agent can also be used. In general, higher conductivity is obtained when these conductive agent particles form a chain structure in a resin or rubber, but in this case, a point-like high potential portion is generated when a voltage is applied. , Charging unevenness may occur. Therefore, it is preferable that these conductive agents are uniformly and finely dispersed in the resin or the rubber. For this purpose, it is important to sufficiently knead the resin or the rubber containing the conductive agent. Further, in order to effectively perform uniform dispersion of the conductive agent, it is necessary to partially use an acid-modified resin or rubber obtained by copolymerizing an ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, and maleic anhydride. Is also effective.

The molding of the laminated sheet 3 can be easily performed by integral molding such as simultaneous lamination extrusion or coating. In this case, it is desirable to select and use a resin or rubber having a melting point or a softening point close to the resin or rubber for forming the low-resistance layer 3a and the high-resistance layer 3b in order to increase the adhesive strength between the two layers.

Although the thickness of the laminated sheet 3 varies depending on its flexibility, generally speaking, the thickness of the low resistance layer 3a is 5
0 to 400 μm, especially 100 to 300 μm, and the thickness of the high resistance layer 3 b is 15 to 100 μm, particularly 2
It is desirable that the thickness be in the range of 0 to 60 μm. The surface of the laminated sheet 3, particularly the surface of the high resistance layer 3b, is preferably as smooth as possible, and the average roughness according to JIS B0601 is preferably 5 μm or less, particularly preferably 1 μm or less.

In the present invention, as the brush roller 4, a brush 4b made of insulating organic or inorganic fibers is used.
What is planted on the conductive roller 4a is used .

It should be noted that the brush 4 is outside the scope of the present invention.
When a conductive fiber is used as b, an insulating resin ring is used as the above-mentioned flange ring 5, and a voltage is applied to the laminated sheet 3 via the conductive roller 4a and the brush 4b. Use conductive fiber for reference
I will also explain when there is .

The volume resistivity of the conductive brush is 10 ^{2 to} 1
0 ⁸ Ω · cm, it is preferable in the range of 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, and the fiber length (length of the hair foot) is 2
To 7 mm, especially 3 to 5 mm,
In addition, the flocking density is 10,000 to 200,000 fibers / square inch, especially 3
It is preferable that the thickness be in the range of 10,000 to 100,000 lines / square inch in order to give a smooth and uniform pressing force. Also, it is preferable to round the tip of the brush in order to suppress the wear 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, and the like.
Examples include polyvinyl alcohol fiber, polyvinyl chloride fiber, rayon, acetate and the like. In order to impart conductivity to the fiber, the method is not limited to the method by the addition of the conductive agent, but may be a method of metallizing the fiber surface. When a 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 conductive ring made of metal is used as the above-mentioned flange ring 5, and a voltage is applied to the laminated sheet 3.
This is performed via 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 photosensitive drum 1,
Since the local current from the tip of the brush 4b flows into the defective portion, the brush tip is easily broken. However, in the case where the brush 4b is insulative, the current flows from the laminated sheet 3 and no local current is generated. This is extremely advantageous in that there is no possibility of the above-mentioned trouble.

The above-mentioned organic fibers are used as the insulating fibers except that no conductive agent is blended, and the fineness and the fiber length may be within the above-mentioned ranges. However, it is preferable that the flocking density is in the range of 30,000 to 100,000 fibers / square inch, particularly 40,000 to 90,000 fibers / square inch.

According to the present invention, as shown in FIG. 1, a DC power supply 10 is connected to the conductive roller 4a, and a voltage is applied to the flexible laminated sheet 3 via the brush 4b or the flange ring 5. While applying the voltage, the laminated sheet 3 is pressed by the brush roller 4 and brought into contact with the surface of the rotating photosensitive drum 1 to charge the surface of the photosensitive drum 1.

The contact charging roller 2 is accommodated in, for example, a box having one side open and disposed in an electrophotographic apparatus, and the laminated sheet 3 is applied to the surface of the photosensitive drum 1 at a constant pressure and constant through this opening. Is pressed by using an appropriate spring or the like so as to make contact with the contact width.

The charging voltage applied to the laminated sheet 3 is:
1.5 to 3.5 of the charging start voltage value of the surface of the photosensitive drum 1
It is preferable to set the value to 2 times, especially 2 to 3 times. FIG.
FIG. 4 is a diagram showing the relationship between the voltage applied to the conductive laminated sheet 3 and the surface potential of the photoconductor drum 1 when the charging method of the present invention is applied when an organic photoconductor is used. As is apparent from this figure, it is understood that a good linear relationship is maintained between the applied voltage and the surface potential in the effective charging region. For this reason, in the charging method of the present invention, for example, a surface potential detection sensor is arranged around the photoreceptor, and the applied voltage is increased or decreased based on the surface potential value detected by the sensor. It will be appreciated that the potential can be kept constant and maintained at an optimum value.

In the present invention, the high-resistance layer 3b is in contact with the surface of the photosensitive drum 1 when a voltage is applied.
Even when a defect such as a pinhole is present on the surface of the photosensitive drum 1, the inflow of a large current is prevented, and
It is a remarkable advantage that the surface can be charged uniformly and effectively, but it is also an advantage of the present invention that the charging can be performed uniformly and without unevenness only by using a DC voltage. In this case, it is also possible to combine the AC power supply 11 with the DC power supply 10 and apply a voltage in which the AC voltage is further superimposed on the above-described DC voltage in order to perform charging with more uniformity. Such alternating current has a frequency of 300 to 1500 Hz,
In particular, 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-mentioned DC voltage at 400 to 1000 Hz.

In the specific example shown in FIG. 1, a flexible conductive laminated sheet 3 is provided in a tube shape. In addition, for example, as shown in FIG. ,
Of course, it is also possible to adopt a structure in which the conductive brush roller 4 is provided inside the driving or driven roller 20a, 20b, 20c, 20d as an endlessly stretched belt. In this case, the contact width between the belt-shaped laminated sheet 3 and the surface of the photosensitive drum 1 is maintained within a certain range by the same pressing force as shown in FIG. Can be performed.

The charging method of the present invention is useful for charging a photosensitive member used in various electrophotographic methods such as a copying machine, a facsimile, a laser printer, etc., and various photosensitive members having a single layer or a 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, applying the charging method of the present invention to organophotoreceptors, since there is no generation of ozone and NO _X, a charge generating pigment constituting the photoreceptor, the charge transport material, a binder, a dielectric such as , And its life can be extended. Needless to say, the charging method of the present invention is not limited to charging in a narrow sense, but can also be applied to static elimination by applying a bias voltage.

[0039]

EXAMPLE 1 Mita Kogyo Co., Ltd. using an organic photoreceptor 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 and charging conditions of each member of the charging device were set as follows. In addition, the volume resistivity of each resistance layer constituting the endless flexible conductive sheet was measured using a volume resistivity meter Loresta or Hiresta manufactured by Mitsubishi Yuka Co., Ltd. at an applied voltage of 10 V. A measurement was made.

Endless flexible conductive sheet (two layers); high resistance layer (surface layer): polyvinylidene fluoride (thickness: 0.
04 mm, volume resistivity: 1.4 × 10 ⁸ Ω · cm) Low resistance layer (brush roller side): polyvinyl chloride elastomer (thickness: 0.2 mm, volume resistivity: 8.8 × 10 ² Ω · c
m) Inner diameter of roller (inner diameter of endless sheet): 20mm

Material: Insulating rayon Outer diameter: 19.8 mm Fiber thickness: 6 denier Fiber length: 3 mm Flocking density: 86,000 / inch ²

Charging condition; applied DC voltage: +1600 V (charging start voltage: +
600V) Brush roller rotation speed: 150 rpm (photosensitive member and driven rotation) Endless sheet rotation speed: 150 rpm (fixed to brush roller,
Photoreceptor and driven rotation) Photoreceptor 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 carried out under the same conditions using a photoreceptor having a pinhole, no image defects such as white stripes caused by a concentrated leakage of the charging current to the pinhole portion occurred.

Example 2 The same experiment as in Example 1 was carried out except that the members constituting the charging device and the charging conditions were changed as follows.

Endless flexible conductive sheet (two-layer structure); high resistance layer (surface layer): fluorine-based rubber (thickness: 0.03 mm, volume resistivity: 2.8 × 10 ¹⁰ Ω · cm) Low resistance layer (brush roller side): polyurethane elastomer (thickness: 0.3 mm, volume resistivity: 2.4 × 10 ⁸ Ω · cm) Roller inner diameter (inner diameter of endless sheet): 20 mm

Brush roller; Material: conductive rayon (volume resistivity: 1.0 × 10 ³⁾
Ω · cm) Outer diameter: 19.8mm Fiber thickness: 6 denier Fiber length: 3mm Flocking density: 100,000 fibers / inch ²

Charging condition; applied DC voltage: +1700 V (charging start voltage: +
600 V) Brush roller rotation speed: 225 rpm (rotation direction is the same as the endless sheet) Endless sheet rotation speed: 150 rpm (photosensitive member and driven rotation) Photoconductor peripheral speed: 157 mm / sec

As a result of charging under the above conditions, the surface potential of the photoreceptor was +790 V, and the obtained copy was a good image without black spot-like unevenness as in Example 1. Also, in an experiment using a photoreceptor having a pinhole, no image defect such as a white stripe caused by the concentrated leakage of the charging current to the pinhole portion occurred.

Comparative Example 1 The same experiment as in Example 1 was carried out except that the members constituting the charging device and the charging conditions were changed as follows.

Endless flexible conductive sheet (two-layer constitution): The layer constitution of the sheet used in Example 1 was reversed. That is, the surface layer was a low resistance layer, and the brush roller side was a high resistance layer.

The brush roller used was exactly the same as that used in Example 1.

Charging conditions; applied DC voltage: +1620 V (charging start voltage: +
600V) Brush roller rotation speed: 150 rpm (photosensitive member and driven rotation) Endless sheet rotation speed: 150 rpm (fixed to brush roller,
Photoreceptor and driven rotation) Photoreceptor peripheral speed: 157 mm / sec

As a result of charging under the above conditions, the surface potential of the photosensitive member was +790 V, and the obtained copy was an image having black spots and unevenness. In an experiment using a photoreceptor having a pinhole, image defects such as white stripes occurred due to concentrated leakage of charging current to the pinhole.

Comparative Example 2 The same experiment as in Example 1 was carried out except that the members constituting the charging device and the charging conditions were changed as follows.

Endless flexible conductive sheet (single layer configuration); Material: polyvinyl chloride elastomer (thickness: 0.3 mm, volume resistivity: 5.2 × 10 ² Ω · cm) Roller inner diameter (endless) Inner diameter of sheet-like sheet): 20mm

Brush roller: exactly the same as that used in Example 2 was used.

Charging condition; applied DC voltage: +1600 V (charging start voltage: +
600 V) Brush roller rotation speed: 225 rpm (rotation direction is the same as the endless sheet) Endless sheet rotation speed: 150 rpm (photosensitive member and driven rotation) Photoconductor peripheral speed: 157 mm / sec

As a result of charging under the above conditions, the surface potential of the photoreceptor became +800 V, and the obtained copy was an image having black spots and unevenness. In an experiment using a photoreceptor having a pinhole, image defects such as white stripes occurred due to concentrated leakage of charging current to the pinhole.

[0059]

According to the present invention, even when a defect such as a pinhole occurs on the surface of the photosensitive member, the surface of the photosensitive member can be uniformly and stably charged without lowering the output of the power supply. It can be done without reducing body life.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining an example of a charging method of the present invention.

FIG. 2 is a diagram illustrating a side surface of a charging roller used in the charging method of FIG. 1;

FIG. 3 is a diagram showing the relationship between the applied voltage and the surface potential of the photoconductor when the charging method of the present invention is applied to an organic photoconductor.

FIG. 4 is a diagram showing an embodiment in which a flexible conductive laminated sheet is provided in a belt shape and the charging method of the present invention is performed.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akinori Nishida 1-2-28 Tamatsukuri, Chuo-ku, Osaka-shi Inside Mita Kogyo Co., Ltd. (72) Inventor Takeshi Hori 1-2-28 Tamatsukuri, Chuo-ku, Osaka-shi Mita Kogyo (56) References JP-A-6-75458 (JP, A) JP-A-6-11945 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 101

Claims (3)

(57) [Claims] 1. A method in which an endless conductive flexible sheet containing a brush roller is physically brought into contact with the surface of a photoreceptor, and a voltage is applied to the conductive flexible sheet to charge the surface of the photoreceptor. In the above, the brush roller is made of an insulating material implanted in a conductive roller.
The conductive flexible sheet comprises a first resistive layer located on the brush roller side and a second resistive layer located on the outer surface, and the second resistive layer comprises: A method for contact charging a surface of a photoreceptor, wherein the layer has a higher electric resistance than the first resistance layer. 2. The volume resistivity of the first resistance layer is 10
2. The contact charging method according to claim 1, wherein the resistivity is ⁷ Ω · cm or less, and the volume resistivity of the second resistance layer is 10 ⁸ Ω · cm or more. 3. The endless conductive flexible sheet is fixed to a conductive flange ring provided on a rotating shaft of the conductive roller, and by applying a voltage to the conductive roller, The contact charging method according to claim 1 , wherein a voltage is applied to the endless conductive flexible sheet via a flange ring.