JPH1020621A - Contact electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contact electrifying device capable of selecting the material of an electrifying member from a wide range and completely restraining scaly electrification irregularity. SOLUTION: In this contact electrifying device 2; a photoreceptor drum 1 (body to be electrified) is electrified by applying DC voltage on the electrifying member 21 arranged in contact with the drum 1 from a power source PW, and the surface resistance ρs of the electrification contributing surface (fs) of the member 21 is >0Ω/square and <=1×10<5> Ω/square, and a potential difference between the surface potential V0 of the drum 1 before electrification by the member 21 and applied DC voltage VC is >=550V and <=750V.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging device for an image forming apparatus such as an electrophotographic copying machine and a printer.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a printer, an electrostatic latent image carrier such as a photosensitive drum is charged by a charging device, and the charged area is exposed to an image to form an electrostatic latent image. Is formed and the latent image is developed into a visible image, which is transferred to a transfer material and fixed. As described above, a charging device is employed to charge the surface of the electrostatic latent image carrier before forming the latent image. In addition, a transfer charger for transferring a visible image formed on an electrostatic latent image carrier to a transfer material, a separation charger for separating a transfer material onto which a visible image has been transferred from an electrostatic latent image carrier, and the like are also available. A charging device is employed.

As the charging device, corona charging devices such as corotrons and scorotrons utilizing corona discharge have been conventionally used. These corona charging devices have an advantage that they can perform stable charging, but require a high voltage. And the large amount of ozone generated, there is a problem in terms of safety and environmental conservation. In order to solve such a problem, various types of contact charging devices and proximity charging devices have recently been proposed.

[0004] The contact charging device brings a charging member to which a voltage is applied into contact with a member to be charged, and mainly includes an area of the charging member which is in contact with the member to be charged and a region which is separated from the member to be charged. The object to be charged is charged by a discharge generated in a gap with the surface. As the charging member, there are various forms such as a charging roller and a charging brush, and a charging blade, a charging film and the like have been proposed.

In the proximity charging device, a charging member to which a voltage is applied is disposed very close to a member to be charged to generate a discharge, thereby charging the surface of the member to be charged. Various types of charging members in the proximity charging device have been proposed. These contact charging devices and proximity charging devices are particularly advantageous in that the amount of ozone generated is significantly smaller than that of corona charging devices. Further, the voltage to be applied can be set lower than that of the corona charging device.

[0006]

However, when looking at the contact charging device, if a charging member made of a low-resistance material such as metal is used, the surface of the member to be charged is non-uniformly charged like a scale. Therefore, when the member to be charged is an electrostatic latent image carrier, for example, one dot / dot as shown in FIG.
When a halftone image of four dots is formed, dot missing or missing dots of halftone dots occur, causing shading of the halftone image. When an image for evaluating the state of charge as described later is created in order to check the state of charge on the surface of the member to be charged by the charging member at this time, a scale-like image as shown in FIG. 8 is seen. this is,
This indicates that the surface of the member to be charged is not uniformly charged and scale-like uneven charging has occurred. This problem does not occur when a charging member made of a high-resistance material is employed. Therefore, a charging member made of a low-resistance material such as metal cannot be used, and a charging member made of a high-resistance material such as rubber or resin in which a conductive material is dispersed has to be used.

[0007] In addition, a flaw may be generated on the surface of the charged member due to scratches generated at the contact portion of the charging member with the charged member and foreign matter such as toner clogging there. In order to suppress the charging, it is conceivable to employ a charging member made of a material having high hardness. As one example of such a material, a metal material is conceivable, but cannot be adopted for the above-mentioned reason. Therefore, it is necessary to employ a charging member made of a material in which a conductive material typified by conductive carbon is dispersed in a specific resin having high hardness. The same was true when trying to adopt a charging member that was hard to wear.

For this reason, there is a problem that the range of choice of the material of the charging member is limited. Therefore, the present invention provides a contact charging device that includes a charging member that is disposed in contact with a member to be charged, and applies a DC voltage to the charging member to charge the member to be charged. It is an object of the present invention to provide a contact charging device that can be selected and that can suppress the occurrence of scale-like uneven charging to a practically acceptable level.

[0009]

A contact charging device according to the present invention for solving the above-mentioned problems comprises a charging member which is arranged in contact with a member to be charged, and the charging member is charged from a power source to charge the member to be charged. A contact charging device for applying a DC voltage,
The surface resistance ρs of the surface contributing to the charging of the charging member is 0Ω.
/ □ and 1 × 10 ⁵ Ω / □ or less, and the potential difference between the surface potential of the member to be charged before charging by the charging member and the DC voltage applied to the charging member is 550 V or more and 750 or more.
V or less.

Here, the "charged member" is typically a photosensitive member.
Etc., but need not be limited to it.
Without, the charging device of the present invention is to prevent scale-like uneven charging or
The present invention can be applied to an object to be charged. The charging member
May be provided, in which case, the charging unit
For each material, the surface resistance ρ of the surface contributing to charging
s is greater than 0Ω / □ and 1 × 10 ^FiveΩ / □ or less, before
The surface potential of the member to be charged before charging by the charging member and the surface potential
The potential difference from the DC voltage applied to the electrical member is 550 V or more and 7
50 V or less. 550V or more and 750V or less
When voltage is applied to satisfy the condition, only one charging member
Now let the surface potential of the charged object reach
If it is not possible to provide multiple charging members,
The surface potential of the member to be charged reaches
Can be made.

In any case, the surface resistance ρs of the surface contributing to the charging of the charging member is larger than 0Ω / □ and 1 × 10 ⁵ Ω
/ □ or less, but as for the lower limit, the low-resistance material usually considered as a charging member material is a metal material, and even if it is a low-resistance material, its surface resistance is approximately 1 × 10
^-5 Ω / □. From this viewpoint, the surface resistance ρs of the surface contributing to the charging of the charging member is not limited thereto, but is actually selected in a range of about 1 × 10 ⁻⁵ Ω / □ to 1 × 10 ⁵ Ω / □. It is thought to be done.

The surface resistance ρs is larger than 0Ω / □ and 1 ×
The material in the range of 10 ⁵ Ω / □ or less is a material that can be selected from a wide range. However, if the charging member made of this material is used without any consideration, the possibility that scale-like charging unevenness occurs may occur. Material of a certain area. If the potential difference between the surface potential of the member to be charged before charging by the charging member and the DC voltage applied to the charging member is in the range of 550 V to 750 V, the surface resistance ρs of the surface contributing to charging of the charging member
Is larger than 0 Ω / □ and 1 × 10 ⁵ Ω / □ or less, and any charging member selected from a wide range of materials can sufficiently suppress scale-like uneven charging.

When the potential difference becomes larger than 750 V, scale-like uneven charging which cannot be ignored in practical use occurs. If the potential difference is smaller than 550 V, charging of the member to be charged becomes insufficient, making it difficult to use.
Various charging members such as a blade charging member, a film charging member, and a roller charging member can be considered as the charging member in the contact charging device of the present invention.

According to the charging device of the present invention, the charging member is arranged so as to partially contact the member to be charged, a DC voltage is applied to the charging member, and the charging member and the member to be charged move relatively. As a result, the surface of the member to be charged is charged. The surface resistance ρs of the surface contributing to the charging of the charging member is 0Ω /
Larger than □ and 1 × 10 ⁵ Ω / □ or less, that is, a condition in which scale-like charging unevenness occurs or is likely to occur in the past, even though it is a condition prior to charging by the charging member of the member to be charged. Since the potential difference between the surface potential and the DC voltage applied to the charging member is regulated within the range of 550 V or more and 750 V or less, occurrence of scale-like uneven charging is suppressed to a level that causes no practical problem. The surface resistance ρs of the surface contributing to the charging of the charging member is larger than 0Ω / □ and 1 × 10 ⁵ Ω.
/ □ or less, the selection range of the charging member material is sufficiently wide. Within this range, a charging member made of a material having excellent abrasion resistance and high hardness (for example, a suitable metal material) that is resistant to scratching or an inexpensive material can be manufactured.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. All of the contact charging devices according to the present invention described below are used by being incorporated in the printer shown in FIG. The printer shown in FIG. 1 includes a photosensitive drum 1 which is an electrostatic latent image carrier (charged body) at the center, and this drum is driven to rotate by a main motor 100 in the direction of arrow a. Around the drum 1, a charging device 2, a developing device 3, a transfer charger 4, a cleaning device 5, and an eraser 6 are sequentially arranged. The charging device 2 is a contact charging device according to the present invention, and has a charging member 21 as shown in FIG. 2, and upon forming an image, a DC voltage Vc is applied to the charging member 21 from a power source PW in this example. The charging device 2 will be further described later.

An optical system 7 is disposed above the photosensitive drum 1. This optical system is provided in a housing 71 with a semiconductor laser generator, a polygon mirror, a toroidal lens, a half mirror, a spherical mirror, a folding mirror, and a reflection mirror. An exposure slit 72 is formed in the floor of the housing 71 and an image exposure can be performed on the photosensitive drum 1 through the space between the charging device 2 and the developing device 3.

On the right side of the photosensitive drum 1 in the figure, a pair of timing rollers 81, a pair of intermediate rollers 82, and a sheet cassette 83 are provided.
Are sequentially arranged, and a paper feed roller 84 faces the paper feed cassette 83. A pair of fixing rollers 91 and a pair of discharge rollers 92 are sequentially arranged on the left side of the photosensitive drum 1 in the drawing, and a discharge tray 93 faces the pair of discharge rollers 92. The above components are mounted on the printer body 10.

According to this printer, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by the charging device 2, and the charged area is image-exposed from the optical system 7 to form an electrostatic latent image. The electrostatic latent image thus formed is developed by the developing device 3 to become a toner image, and moves to a transfer area facing the transfer charger 4. On the other hand, the transfer paper is pulled out from the paper feed cassette 83 by the paper feed roller 84, reaches the timing roller pair 81 via the intermediate roller pair 82, and is fed to the transfer area in synchronization with the toner image on the drum 1. Thus, in the transfer area, the toner image on the drum 1 is transferred onto the transfer paper by the action of the transfer charger 4, and the transfer paper reaches the fixing roller pair 91, where the toner image is fixed and then discharged by the discharge roller pair 92. The sheet is discharged to the paper tray 93.

After the toner image is transferred to the transfer paper, the toner remaining on the photosensitive drum 1 is cleaned by the cleaning device 5. The residual charges are erased by the eraser 6. The system speed of the printer (the peripheral speed of the photosensitive drum 1) is 3.5 cm / sec. Developing device 3
Is a one-component contact developing device for performing reversal development.

The photoreceptor drum 1 is a negative charge function-separated type organic photoreceptor having sensitivity to long wavelength light. The charge generation layer is formed of a mixture of τ-type metal-free phthalocyanine and polyvinyl butyral resin to a thickness of about 0.4 μm, and then a charge transport layer is formed of a mixture mainly composed of a hydrazone compound and a polycarbonate resin to a thickness of about 18 μm. Have been. The electrostatic latent image carrier to which the charging device of the present invention can be applied is not limited to the above.

Here, the toner used in the developing device 3 is of a negative charge type, and a mixture mainly composed of a bisphenol A type polyester resin and carbon black is kneaded, crushed and classified by a known method, and the average particle diameter is reduced. 10μ
m. Such a toner is stored in the developing device 3 and is developed under a developing bias VB.

The contact charging device 2 will be further described. As shown in FIG. 2, one end f1 of a film F cut into a predetermined size to become a film charging member 21 is cantilevered by a support member 22. The free end f2 is bent upward, the free end side is placed in contact with the surface of the photosensitive drum 1, and the charging member 21 is supplied with a DC voltage Vc from a power source PW.
Is applied.

The voltage Vc applied to the charging member 21 is a potential difference ΔV = | Vc−Vo | between the surface potential Vo of the surface of the photosensitive drum 1 charged by the charging member 21 before charging by the charging member and the voltage Vc. Is 550V or more and 750V
It is set to be as follows. Here, the film F constituting the charging member 21 is a flexible film of the same kind as that disclosed in Japanese Patent Application Laid-Open No. 4-249270.
More specifically, in order to improve the contact property with the member to be charged, as shown in FIG.
_The bending moment Mm required for winding around a core rod R having a circular cross section of ₁ = 1 cm is Mm ≦ 20 (g · cm), preferably Mm ≦ 10 (g · cm). It also has mechanical strength (strength against tearing, tearing, etc.). Where the bending moment Mm
Is ^{EI / ρ (I = bh 3} /12). E is the Young's modulus of the film F (g / cm ² ), I is the cross section 2 of the film F
The next moment (cm ⁴ ), ρ is the radius of curvature (cm) of the film F, the distance between the center O of the core rod R and the neutral plane NS of the film F, and h is the thickness of the film.

The material of the film F is the charge contributing surface f
s has a surface resistance ρs greater than 0Ω / □ and 1 × 10 ⁵ Ω /
□ or less, but here 1 × 10 ⁻⁵ Ω / □ or more and 1 × 10 ⁵ Ω /
□ Selected from the following materials. As described above, in the contact charging device 2, the film charging member 21 has the surface resistance ρs of the charging contributing surface fs as described above.
Is 1 × 10 ⁻⁵ Ω / □ or more and 1 × 10 ⁵ Ω / □ or less,
In other words, the voltage Vc applied to the charging member 21 is reduced by the charging of the surface of the photosensitive drum 1 to be charged by the charging member 21 despite the condition in which the scale-like charging unevenness occurs or is likely to occur in the related art. Since the potential difference ΔV between the surface potential Vo before charging by the member and the voltage Vc is set to be 550 V or more and 750 V or less, occurrence of scale-like uneven charging is sufficiently suppressed.

Next, an experimental example showing that if the surface resistance ρs of the charging contributing surface fs of the charging member 21 in the charging device 2 and the voltage applied to the charging member 21 are as described above, the scale-like charging unevenness is sufficiently suppressed. Table 1 shows Experimental Examples 1 to 4 in which various materials of the film F constituting the charging member were adopted and the voltage Vc was variously changed for each of the materials. In addition, Comparative Experimental Examples 1 to 4 performed for comparison
Table 2 also shows No. 2.

All experiments were performed using the printer. Developing bias voltage V _B is, as shown in Table 1, since the photosensitive drum 1 is set to a charging potential value close to be charged by the charging member 21, to evaluate the uniformity of the charging potential by the white solid image printing An image for evaluating the state of charge was prepared. The toner used in the developing device was the same as described above. The surface potential Vo of the photosensitive drum 1 before charging by the charging member 21 is 0 V here.
In Table 1, Vo1 denotes the drum 1 after passing through the charging member 21.
This is the charged potential of the surface.

The following four types of films A, B, C and D were used for the film constituting the experimental charging member. A: stainless steel film, thickness 20 μm, surface resistance ρs 1 × 10 ⁻⁵ Ω / □ B: film in which conductive carbon powder is dispersed in polyimide, thickness 30 μm, surface resistance ρs 1 × 10 ³ Ω / □ C: Film in which conductive carbon powder is dispersed in polyimide, thickness 30 μm Surface resistance ρs 1 × 10 ⁵ Ω / □ D: Film in which conductive carbon powder is dispersed in polyimide, thickness 30 μm Surface resistance ρs 1 × 10 ⁷ Ω / □ In addition, when scale-like uneven charging occurs, scale-like noise also appears in the image for evaluating the state of charge. Therefore, the charging performance was evaluated by looking at the scale-like noise on this image. Here, a method of evaluating scale-like noise on an image based on scale-like uneven charging on the surface of the photosensitive drum 1 will be described. Developing bias potential V _B of the developing device 3 of the (squamous noise evaluation method) printer, the photosensitive drum 1 is set to a charge potential approximately the same potential that is charged by the charging member 21, the white solid image printing (without exposure) By doing so, so-called bias development was performed with the potential charged by the charging member, an image for evaluating the state of charge for evaluating the uniformity of the charged potential was created, and the image was printed on transfer paper. At this time, in the charged state evaluation image, if it is a uniformly charged state,
A uniform image in which toner is uniformly adhered to the entire transfer paper is obtained, and in a non-uniformly charged state, a non-uniform image is obtained in which the highly charged portion is white and the lowly charged portion is black. The image for evaluating the charged state on the transfer paper was visually observed and ranked as follows. "○" indicates that it is acceptable, "△" and "×"
The mark means unacceptable.

: No scaly noise (no scaly charge; uniform electrification) △: Partially scaly noise (partially scaly uneven charging) ×: Scaling noise entirely (no scaly uneven charging)

[0029]

[Table 1]

From the above experimental results, it was found that the film charging member 2
The surface resistance ρs of the charge-contributing surface of No. 1 is 1 × 10 ⁻⁵ Ω / □ or more 1
Even under the condition of × 10 ⁵ Ω / □ or less, the potential difference ΔV between the voltage Vc applied to the charging member 21 and the surface potential Vo of the surface of the photosensitive drum 1 before charging by the charging member 21 is set to be 550 V or more and 750 V or less. It can be seen that when set, the occurrence of scale-like uneven charging is sufficiently suppressed. Although not shown here, the surface resistance ρs of the charge contributing surface is 1 ×
The above potential difference Δ is applied to a charging member smaller than 10 ⁻⁵ Ω / □.
When V is regulated to 550 V or more and 750 V or less, scale-like uneven charging is suppressed. In the above experiment, the film D was not evaluated in the case of the potential difference ΔV 550 V to 800 V. Also, in the comparative experiment example 2, no scale-like uneven charging was generated because the surface resistance of the film D was 1 × 10 ^This is because, as large as ⁷ Ω / □, scaly uneven charging does not or does not occur from the beginning regardless of the potential difference.

Next, another example of the contact charging device according to the present invention will be described with reference to FIG. Charging device 20A shown in FIG.
In this example, the charging device shown in FIG. 2 is provided in two stages along the photosensitive drum surface moving direction a. The charging unit 20A1 on the upstream side in the moving direction a of the surface of the drum 1 cantileverly supports one end of the film FA1 cut into a predetermined size to be the film charging member 201 with the support member 202, and raises the free end of the film upward. The free end portion is bent and placed in contact with the surface of the photosensitive drum 1, and a DC voltage VCA1 is applied to the charging member 201.

The charging portion 20A2 on the downstream side in the moving direction a of the surface of the drum 1 is configured to support one end of the film FA2 cut into a predetermined size to be the film charging member 203 by the supporting member 20.
4, the free end of the film is bent upward, and the free end is placed in contact with the surface of the photosensitive drum 1;
A DC voltage VCA2 is applied to the charging member 203.

In each of the films FA1 and FA2, the surface resistance ρs of the charge contributing surfaces fsA1 and fsA2 is greater than 0Ω / □ and 1 × 10 ⁵ Ω / □ or less, but here 1 × 10 ⁻⁵ Ω / □.
The material is selected from materials that fall within the range of 1 × 10 ⁵ Ω / □ or less. Further, the DC voltage VCA1 applied to the charging member 201 is a potential difference Δ from a potential V0A (here, 0 V) of the photosensitive drum surface 1 before charging by the member 201.
V = | VCA1−V0A | is set to be 550V or more and 750V or less, and the DC voltage VCA2 applied to the charging member 203 is different from the potential V0A1 on the surface of the photosensitive drum 1 before charging by the member 203. ΔV = | VCA2−V
0A1 | is set to be 550V or more and 750V or less.

Also in the charging device 20A, generation of scale-like uneven charging on the surface of the photosensitive drum 1 is sufficiently suppressed.
Next, each of the charging members 201 and 203 in the charging device 20A
Table 2 shows Experimental Examples 5 and 6, which show that if the surface resistances of the charging contributing surfaces fsA1 and fsA2 and the voltages applied to the charging members 201 and 203 are as described above, the scale-like uneven charging is suppressed. Table 2 also shows Comparative Experimental Examples 3 and 4 performed for comparison.

In these experiments, the charging member 201 was composed of the film A (made of stainless steel) adopted in the above-mentioned Experimental Example 1 and the like, and the applied voltage VCA1 was -70.
0V, thereby setting the charging potential V0A1 of the surface of the drum 1 by the charging member 201 to a constant value of V0A1 = -170 V. The charging member 203 is the same as that of the films A, B, and C used in Experimental Example 1 and the like. We adopt each kind,
The voltage VCA2 applied to them was varied.

All experiments were performed using the printer. Developing bias voltage V _B is, as shown in Table 2, a uniform charging potential by the photosensitive drum 1 is set to a value close to the charging potential V0A2 of the drum 1 surface after passing the rear stage charging member 203, and the white solid image printing An image for evaluating the state of charge for evaluating the chargeability was prepared. The toner used in the developing device was the same as described above. Image evaluation (Electrical unevenness evaluation)
Is the same as in Experimental Example 1 above.

[0037]

[Table 2]

From the above experimental results, even when the charging members are provided in a plurality of stages, the surface resistance ρs of the surface contributing to charging is 1 × 10 ⁻⁵ Ω / □ or more and 1 × 10 ⁵ Ω / square for each charging member. □
The potential difference between the DC voltage applied to each charging member and the potential before charging of the surface of the photosensitive drum 1 by the charging member is 550 V or more and 75
It is understood that when the voltage is 0 V or less, the scale-like uneven charging can be sufficiently suppressed. Although not shown here, even for a charging member having a surface resistance ρs of the charging-contributing surface smaller than 1 × 10 ⁻⁵ Ω / □, if the potential difference ΔV is regulated to 550 V or more and 750 V or less, scale-like charging unevenness occurs. Is suppressed.

When a voltage is applied so as to satisfy the condition of the potential difference of 550 V or more and 750 V or less, when the surface potential of the member to be charged cannot reach a practically predetermined potential with only one stage charging member, the following procedure is performed. A plurality of charging members can be provided, and the surface potential of the member to be charged can be made to reach a predetermined potential stepwise by the charging members. The contact charging device according to the present invention and the contact charging device using a corona charging device or a high-resistance charging member may be used as long as the surface potential of the member to be charged gradually reaches a desired potential. It is also conceivable to use a conventional charging device such as a device together. For example, it is conceivable to arrange a contact charging device using a high-resistance charging member in a stage preceding the contact charging device according to the present invention.
In this way, the streak-like charging unevenness that tends to occur in the contact charging device in the preceding stage is canceled by the contact charging device according to the present invention in the subsequent stage, so that uniform charging can be obtained.

The contact charging device in which the charging member is a film charging member has been described above, but the form of the charging member is not limited to a film-shaped charging member. In this regard, another example of the contact charging device according to the present invention will be described below.
The charging device 20B shown in FIG. 6 is provided with blade charging members 205, 206, and 207 formed of thick blades in three stages along the photosensitive drum surface moving direction a. The power supply PWB is provided with a DC voltage from a power source PWB.

The charging device 20C shown in FIG. 7 has two roller charging members 208 and 209 provided in two stages along the photosensitive drum surface moving direction a. The drum is arranged so as to partially contact the surface, and can rotate as the drum surface moves. Charging member 20
8 from the power supply PWC1, and the charging member 209 from the power supply PWC2.
, A DC voltage is applied.

In the charging device shown in FIGS. 6 and 7,
The surface resistance ρs of the charging contributing surface of each charging member is set to be greater than 0Ω / □ and 1 × 10 ⁵ Ω / □ or less, and the surface potential of the drum 1 before charging by each charging member and the DC voltage applied to the charging member are determined. By regulating the potential difference to 550 V or more and 750 V or less, scale-like uneven charging can be suppressed to a level that causes no practical problem.

[0043]

As described above, according to the present invention, there is provided a charging member provided in contact with a member to be charged, and a contact charging device for applying a DC voltage from a power source to the charging member to charge the member to be charged. It is possible to provide a contact charging device which can select a charging member material from a wide range and can suppress the occurrence of scale-like charging unevenness to a practically acceptable level.

[Brief description of the drawings]

FIG. 1 is a sectional view of a printer provided with an example of a contact charging device according to the present invention.

FIG. 2 is a side view of a contact charging device in the printer shown in FIG.

FIG. 3 is an explanatory diagram of a film material constituting a film charging member.

FIG. 4 is an explanatory diagram of a halftone image.

FIG. 5 is a side view of another example of the charging device according to the present invention.

FIG. 6 is a side view of still another example of the charging device according to the present invention.

FIG. 7 is a side view of still another example of the charging device according to the present invention.

FIG. 8 shows an example of an image for evaluating a charged state in which only scaly noise is present.
It is a figure showing an example.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (charged body) a surface moving direction of drum 1 2 contact charging device 21 film charging member 22 film support member PW charging device power supply F film f1 one end of film f f2 free end of film F fs charging contribution Surface 20A Contact charging device 20A1 Upstream charging section 201 Film charging member FA1 Film fsA1 Charging contribution surface 202 Support member 20A2 Downstream charging portion 203 Film charging member FA2 film fsA2 Charging contribution surface 204 Support member 20B Contact charging device 205, 206 , 207 Blade charging member PWB power supply 20C Contact charging device 208, 209 Roller charging member PWC1, PWC2 Power supply

Claims (2)

[Claims] 1. A contact charging device comprising a charging member disposed in contact with a member to be charged and applying a DC voltage from a power source to the charging member to charge the member to be charged, wherein the charging member contributes to charging of the charging member. The surface resistance ρs of the surface to be charged is greater than 0Ω / □ and 1 × 10 ⁵ Ω / □ or less, and the potential difference between the surface potential of the member to be charged before charging by the charging member and the DC voltage applied to the charging member. Is not less than 550 V and not more than 750 V. 2. The method according to claim 1, wherein a plurality of charging members are provided, and each of the charging members has a surface resistance ρs of a surface contributing to charging of more than 0Ω / □ and 1 × 10 ⁵ Ω / □ or less. The potential difference between the surface potential of the charged body before charging by the charging member and the DC voltage applied to the charging member is 550 V
The contact charging device according to claim 1, wherein the voltage is not less than 750V.