JPH09138543A - Electrostatic charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charger of an electrostatic charging system for electrostatically charging an electrostatic latent image carrier such as a photoreceptor, etc., in a non-contact state, with less unevenness in electrostatic charging. SOLUTION: As for the electrostatic charger, an electrostatic charging member 2 made of a resistance member is arranged in non contact with the electrostatic latent image carrier 1, and by applying a bias voltage V1 on the upstream side in the electrostatic latent image carrier rotating direction of the electrostatic charging member 2, and applying a bias voltage V2 on the downstream side so as to generate a discharge, the electrostatic latent image carrier 1 is electrostatically charged. Thus, the electrostatic charger for electrostatically charging the carrier 1 in non contact with the electrostatic charging member 2, also, with less unevenness in electrostatic charging is obtained. And also, in addition to the constitution, by constituting the charger so that |V1|<|V2| may be established as for the relation between the bias voltage V1 and the bias voltage V2, the discharge is always realized stably little by little between the electrostatic charging member 2 and the electrostatic latent image carrier 1.

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 for charging an electrostatic latent image carrier in an electrophotographic image forming apparatus such as a copying machine, a facsimile and a printer.

[0002]

2. Description of the Related Art A corona charging system has been conventionally used as a charging device used for charging an electrostatic latent image carrier such as a photoconductor in an electrophotographic image forming apparatus. The corona charging system has advantages such as non-contact and simple structure, and is widely used. However, there are problems that ozone is generated during corona discharge, efficiency is low, and a high voltage must be applied. A contact charging method has been proposed as a method for improving this problem. In the contact-type charging, there are rollers, brushes, blades, etc. as contact members. However, in these methods, since the photoconductor and the charging member are literally used in contact with each other, residual toner on the photoconductor is charged to the charging member. Due to stains and the like caused by adhesion to the surface, uneven charging occurs, which adversely affects the image.

Japanese Patent Publication No. 6-90568 discloses that
A method is disclosed in which an electric resistor having a volume resistance of 10 ⁶ to 10 ¹³ Ωcm and a surface resistance of 10 ⁶ Ω or more is brought into close contact with the photoconductor in a non-contact manner to apply a bias voltage to charge the photoconductor. In this invention, charging unevenness is reduced by bringing the electric resistor and the photoconductor closer to 500 μm or less, but discharge is generated at a place where the gap between the electric resistor on the inlet side and the photoconductor is 500 μm or more. Easy,
There is a risk of uneven charging. Further, the resistance value is strictly controlled, and uneven charging occurs due to changes in the environment.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is a charging method for charging an electrostatic latent image carrier such as a photoconductor in a non-contact manner, and a method of less charging unevenness. It is an object to provide a charging device, and the object of each claim is shown below.

It is an object of the present invention to provide a charging type charging device in which the electrostatic latent image carrier and the charging member are not in contact with each other and the charging unevenness is small. It is an object of the invention of claim 2 to constantly and stably generate a discharge between the charging member and the electrostatic latent image carrier. It is an object of the invention of claim 3 to stabilize the first discharge between the charging member and the electrostatic latent image carrier. According to a fourth aspect of the invention, when the electrostatic latent image carrier is cylindrical and has a small diameter, a large void area exists when the charging member is a flat plate, and discharge is unstable in a large void area. Therefore, it is an object to prevent this unstable discharge by providing the charging member with a curvature. A fifth aspect of the present invention has a problem that when a defect such as a pinhole is present on the electrostatic latent image carrier, an excessive current flows and an abnormal discharge occurs, which is to be prevented. It is an object of the present invention to reliably charge the entire image forming area of the electrostatic latent image carrier. The invention of claim 7 is intended to prevent this abnormal discharge because abnormal discharge is likely to occur at the edge portion of the charging member.

[0006]

In order to achieve the above object, the charging device according to claim 1 is arranged such that a charging member made of a resistance member is arranged in non-contact with an electrostatic latent image carrier such as a photoconductor. By applying a bias voltage V1 on the upstream side of the charging member in the rotation direction of the electrostatic latent image carrier and a bias voltage V2 on the downstream side of the charging member, discharge is generated to charge the electrostatic latent image carrier.

In addition to the above configuration, the charging device according to the second aspect is configured such that the relationship between the bias voltage V1 and the bias voltage V2 is | V1 | <| V2 |.

In addition to the above structure, the charging device according to a third aspect of the present invention is such that a bias voltage V1 of 0 volt and a bias voltage V2 of the same polarity as the charging potential Vs of the electrostatic latent image carrier are applied. Configured to.

According to a fourth aspect of the present invention, in addition to the above configuration, the surface of the charging member facing the electrostatic latent image carrier has a curvature, and the distance between the charging member and the electrostatic latent image carrier is small. It is configured to be substantially equal at any position on the circumference.

In addition to the above structure, the charging device according to the present invention has a surface protective layer on the surface of the charging member facing the electrostatic latent image carrier, and the resistivity of the surface protective layer is The volume resistivity and the surface resistivity were both higher than those of the charging member.

According to a sixth aspect of the present invention, in addition to the above configuration, the length of the charging member in the longitudinal direction is longer than the length of the image forming area of the electrostatic latent image carrier.

According to a seventh aspect of the present invention, in addition to the above configuration, the charging device has a rounded edge or a high resistance member on each side of the surface of the charging member facing the electrostatic latent image carrier. The structure is covered with.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of the configuration of the charging device according to the present invention. In the figure, reference numeral 1 denotes a drum-shaped photosensitive member which is an electrostatic latent image carrier for forming a latent image and rotates clockwise in the illustrated example. Reference numeral 2 denotes a plate-shaped charging member made of a high resistance member. A bias voltage V1 is applied to the upstream side of the charging member 2 in the rotation direction of the photosensitive member, and a bias voltage V2 is applied to the downstream side thereof. The volume resistance value of the charging member 2 is preferably 10 ⁶ Ωcm or more, and if it is less than that, the current flowing from the upstream side to the downstream side of the charging member 2 becomes large, resulting in an increase in power consumption. The material forming the charging member 2 may be rubber, plastic, ceramics, glass or the like as long as it satisfies the resistance value.

FIG. 2 is an enlarged view of a portion where the photosensitive member 1 and the charging member 2 shown in FIG. 1 are close to each other. Some point 1-a on the photoconductor
When the gap width between a point 2-a on the charging member and the charging member is ga, and the potential at the point 2-a on the charging member is V2a, V2a
Is the air discharge limit voltage V of Paschen in the air gap ga
If pa is exceeded, discharge will occur. This discharge slightly charges point 1-a on the photoconductor. In FIG. 2,
In order to avoid complication, only the discharge at the point 1-a of interest is shown, and the discharge at other places is omitted.

Next, FIG. 3 is a view showing a state in which the point 1-a of interest is moved to 1-b by the rotation of the photosensitive member 1. At this time, if the potential difference ΔVb between the point 2-b on the charging member 2 and the point 1-b on the photoconductor 1 exceeds the discharge limit in the gap width gb, discharge occurs, and a small amount of charge is exposed again. Move to point 1-b on the body. In this way, the points on the photoconductor are gradually charged while moving under the charging member 2. In order to proceed with the charging as the photoconductor 1 moves, the bias voltage applied to the charging member 2 is lower than the bias voltage V1 on the upstream side with respect to the bias voltage V1 on the upstream side in the rotation direction of the photoconductor. The absolute value is larger (| V1 | <| V2 |), and in order to charge the photoconductor 1 to a desired charging potential, sufficient discharge occurs at the shortest distance between the charging member 2 and the photoconductor 1. Should be just the voltage. The upstream bias voltage V1 may be 0V,
In this case, only one power supply is needed for the downstream bias voltage V2, which simplifies the device and is convenient.

Normally, in the non-contact charging method, unstable discharge is likely to occur, and it is necessary to reduce the gap width between the photosensitive member 1 and the charging member 2. However, according to the main charging method, stable discharge is achieved. Occurs continuously, the charging unevenness is small, and it is not always necessary to reduce the width of the gap with the photoconductor 1. Further, even if the resistance value of the resistance member that constitutes the charging member 2 changes due to the environment or the like, the potential distribution on the resistance member does not change, so that there is an advantage that the charging characteristic is not affected.

By the way, in recent years, the diameter of the drum-shaped photosensitive member 1 has been reduced along with the downsizing of the apparatus. When the diameter of the photoconductor 1 becomes smaller, when the charging member 2 is a flat plate as shown in FIG. 1, the change in the gap between the photoconductor 1 and the charging member 2 in the photoconductor rotating direction is large, and the photoconductor 1 moves. At this time, the change in void becomes large, and stable charging is not performed.
In such a case, it is preferable that the charging member 2 has a curvature so that the gap does not change much even if the photosensitive member moves. The best shape is the gap width between the photoconductor 1 and the charging member 2 in which the surface of the charging member 2 facing the photoconductor 1 is formed in an arc shape along the peripheral surface of the photoconductor 1 as in the example shown in FIG. Has a substantially constant shape. With the shape shown in FIG. 4, since the void is always constant, the only factor that governs the discharge is the potential at each point on the charging member 2, and a stable discharge occurs as the photoreceptor 1 moves. It occurs continuously.

Next, when there is a defect such as a pinhole or a scratch on the photoconductor, the discharge concentrates on the spot and a large current flows, thereby exceeding the capacity of the power source and paralleling the photoconductor axial direction. A region that is not charged is generated. In order to prevent this, as in the example shown in FIG. 5, the surface protection layer 3 formed of a high resistance member on the surface of the charging member 2 facing the photoreceptor 1.
Should be provided. Note that FIG. 5 is a cross-sectional view showing a configuration example of the charging member. Both the volume resistivity and the surface resistivity of the surface protective layer 3 need to be higher than the resistivity of the material of the resistance member forming the charging member 2, and are increased by two digits or more if possible. Is desirable. This is because if the volume resistivity of the surface protective layer 3 is small, a current easily flows in the thickness direction of the charging member 2, and if the surface resistivity is small, the current flows from the power source side through the surface and the photoconductor 1 This is because a large current will flow when there is a defect or the like.

Next, in order to charge the entire image forming area of the photosensitive member, the length of the charging member 2 in the axial direction of the photosensitive member must be longer than that of the image forming area. Also, if the four sides of the surface of the charging member facing the photoconductor 1 are angled, abnormal discharge may occur from there, so it is necessary to round the edges or cover them with the high resistance member 4. There is.
The high resistance member 4 is still effective if it is an insulator. Here, FIG. 6 is a diagram showing an example of the configuration of the charging member.
Is a cross-sectional view showing an example in which the corners of the charging member 2 are rounded,
(B) is a cross-sectional view showing an example in which four sides of the charging member 2 are covered with the high resistance member 4, and (c) shows the charging member 2 coated with the high resistance surface protective layer 3 shown in FIG. It is sectional drawing which shows the example which covered the edge | side with the high resistance member 4. FIG.
6D is a plan view of the charging member 2 of FIG. 6C as seen from the photoconductor side. If the bias voltage V1 applied to the upstream side of the charging member 2 in the direction of rotation of the photoconductor is sufficiently small, for example, 0 V, on the side parallel to the photoconductor axis on the upstream side,
Since abnormal discharge does not occur, it is not necessary to perform the rounding process or the process of covering with a high resistance member as described above, but for safety, it is preferable to perform the above process on this side as well.

[0020]

EXAMPLES Next, specific examples of the present invention will be shown. (Embodiment 1) Chloroprene rubber having a thickness of 1 mm and a length of 1 cm is used as a charging member 2 and is arranged at a position facing the photoconductor 1 in a non-contact manner. The width of the charging member 2 is substantially the same as the axial length of the photoconductor 1. The four sides of the surface of the charging member 2 facing the photoconductor 1 are covered with insulating members as shown in FIG. 6B. The chloroprene rubber has a volume resistivity of 10 ⁷ Ωcm and a surface resistivity of 10 ⁵ Ω / □. Further, as shown in FIG. 4, the charging member 2 has a curvature so that the distance between the charging member 2 and the photoconductor 1 is approximately 500 μm at any place.
Electrodes are provided at both ends of the charging member 2, and V1 = 0
A bias voltage of V and V2 = -4 kV is applied.
As a result of rotating the photoconductor 1 at a linear velocity of 60 mm / s with the above configuration, a charging potential of about -600 V was obtained for the photoconductor 1. When the photosensitive member 1 was developed with a positively charged toner, the image was uniform and almost no uneven charging was observed.

(Embodiment 2) With the same construction as in Embodiment 1, charging was carried out by applying a bias voltage of V1 = -4 kV and V2 = -4 kV to the charging member 2. The charging potential of the photoconductor 1 is about −
At 650 V, almost the same potential as in Example 1 was obtained. Next, when the image was developed with positively charged toner, fine scale-like unevenness was observed in the image.

(Embodiment 3) With the same construction as in Embodiment 1, charging was carried out by applying a bias voltage of V1 = 0 V and V2 = -4 kV to the charging member 2. When the photoreceptor 1 after the image formation of 50,000 sheets was used in an actual machine, uneven charging potential was observed. When the image was developed by developing with a positively charged toner, several streaky, non-charged portions were found parallel to the axial direction of the photoconductor. Then, when the photoconductor 1 was examined, small scratches were found at the corresponding places, and it is considered that abnormal discharge occurred due to the scratches, the power supply voltage dropped due to the flow of a large current, and there were places where no charge occurred. .

(Embodiment 4) The same constitution as that of Embodiment 3 was used, but the same photosensitive member was used. The surface of the charging member 2 facing the photoconductor 1 was coated with high-resistance Teflon as a surface protective layer 3. Further, insulating layers 4 were provided on four sides to form the structure shown in FIG. The volume resistivity of the surface protective layer 3 is 10 ¹² Ωc.
m, and the surface resistivity was 10 ¹⁰ Ω / □. When charging was carried out with the above-mentioned constitution, only spotted portions of the photoconductor were found to be spot-like non-charged portions, but no streak-like charging unevenness as seen in Example 3 was observed.

[0024]

As described above, according to the present invention, it is possible to provide a charging type charging device for charging the electrostatic latent image carrier in a non-contact manner. That is, in the charging device according to claim 1, a charging member made of a resistance member is arranged in non-contact with the electrostatic latent image carrier such as a photoconductor, and the charging member is provided on the upstream side in the rotation direction of the electrostatic latent image carrier. By applying the bias voltage V1 and the bias voltage V2 to the downstream side to generate the discharge and charge the electrostatic latent image carrier, the electrostatic latent image carrier and the charging member are brought into non-contact with each other. Further, it is possible to provide a charging type charging device with less uneven charging.

In the charging device according to the second aspect, in addition to the above structure, the relationship between the bias voltage V1 and the bias voltage V2 is such that | V1 | <| V2 | The discharge between the latent image carriers can always be generated stably and in small steps.

In the charging device according to the third aspect of the present invention, in addition to the above configuration, a bias voltage V1 of 0 volt and a bias voltage V2 of the same polarity as the charging potential Vs of the electrostatic latent image carrier are applied. Since it is configured, it is possible to stabilize the initial discharge between the charging member and the electrostatic latent image carrier, and reduce uneven charging.

According to a fourth aspect of the present invention, in addition to the above structure, the surface of the charging member facing the electrostatic latent image carrier has a curvature, and the distance between the charging member and the electrostatic latent image carrier is circular. Since the electrostatic latent image carrier is cylindrical and has a small diameter, there is a large void area when the electrostatic latent image bearing member is a flat plate and the void is large. Discharge in a large place was sometimes unstable, but this unstable discharge can be prevented.

In addition to the above structure, the charging device according to claim 5 has a surface protective layer on the surface of the charging member facing the electrostatic latent image carrier, and the resistivity of the surface protective layer is Since both the resistivity and surface resistivity are higher than that of the charging member, when an electrostatic latent image carrier has defects such as pinholes, it prevents excessive current from flowing and abnormal discharge to occur. It is possible to prevent uneven charging.

In the charging device according to the sixth aspect, in addition to the above structure, the length of the charging member in the longitudinal direction is longer than the length of the image forming area of the electrostatic latent image carrier. It is possible to reliably charge the entire image forming area of the electrostatic latent image carrier.

According to a seventh aspect of the present invention, in addition to the above configuration, the edges of each side of the surface of the charging member facing the electrostatic latent image carrier are rounded or are made of a high resistance member. Since the structure is covered, abnormal discharge is likely to occur at the edge portion of the charging member, but this abnormal discharge can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a charging device according to the present invention.

FIG. 2 is an enlarged view of a portion where the photoconductor shown in FIG. 1 and a charging member are close to each other.

3 is an enlarged view of a portion where the photoconductor shown in FIG. 1 and a charging member are close to each other, and is a diagram showing a state in which a point of interest due to rotation of the photoconductor is moved from the position shown in FIG.

FIG. 4 is a diagram showing another configuration example of the charging device according to the present invention.

FIG. 5 is a cross-sectional view showing a configuration example of a charging member used in the charging device of the present invention.

6A and 6B are views showing another configuration example of the charging member used in the charging device of the present invention, FIG. 6A is a sectional view showing an example in which the corners of the charging member are rounded, and FIG. Sectional view showing an example in which four sides of the member are covered with a high resistance member, (c) is an example in which the charging member is coated with the high resistance surface protective layer shown in FIG. 5, and further four sides are covered with a high resistance member. Sectional view showing (d)
FIG. 7A is a plan view of the charging member in (c) as viewed from the photoconductor side.

[Explanation of symbols]

1 electrostatic latent image carrier (photoreceptor) 2 charging member 3 surface protective layer 4 high resistance member V1 bias voltage applied to the upstream side in the rotational direction of the electrostatic latent image carrier V2 downstream side in the rotational direction of the electrostatic latent image carrier Bias voltage applied to

Claims (7)

[Claims] 1. A charging device used for charging an electrostatic latent image bearing member, wherein a charging member composed of a resistance member is arranged in non-contact with the electrostatic latent image bearing member, and the electrostatic latent image of the charging member. A charging device characterized in that by applying a bias voltage V1 on the upstream side in the rotational direction of the carrier and a bias voltage V2 on the downstream side, discharge is caused to charge the electrostatic latent image carrier. 2. The charging device according to claim 1, wherein the relationship between the bias voltage V1 and the bias voltage V2 is | V1 | <| V2 |. 3. The charging device according to claim 1, wherein 0 volt is applied to the bias voltage V1 and a voltage having the same polarity as the charging potential Vs of the electrostatic latent image carrier is applied to the bias voltage V2. Charging device. 4. The charging device according to claim 1, wherein:
A charging device, wherein a surface of the charging member facing the electrostatic latent image carrier has a curvature, and a distance between the charging member and the electrostatic latent image carrier is substantially equal at any position on the circumference. 5. The charging device according to claim 1, wherein:
The charging member has a surface protective layer on the surface facing the electrostatic latent image carrier, and the surface protective layer has a resistivity higher than that of the charging member in terms of both volume resistivity and surface resistivity. Charging device. 6. The charging device according to claim 1, wherein:
The charging device is characterized in that the length of the charging member in the longitudinal direction is longer than the length of the image forming area of the electrostatic latent image carrier. 7. The charging device according to claim 6, wherein the edges of each side of the surface of the charging member facing the electrostatic latent image carrier are rounded or covered with a high resistance member. Charging device characterized in that