JPH09171282A - Charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the charge unevenness of a charged surface with a noncontact charger by providing a charge member having a high-resistant layer and a charge induction member arranged in a part nearer the upstream side than the closest proximity part of the charge member and facing it. SOLUTION: This charger has the charging member 2 which is provided with a conductor 2b facing a photoreceptor 1a and the high-resistant layer 2a in contact with the conductor 2b, between it and the photoreceptor 1a and constituted so that at least a face confronting the photoreceptor 1a is moved and the charge induction member 9 which is arranged in the part nearer the upstream side than the closest proximity parts A/B of the charge member 2 with the photoreceptor 1a, in a moving direction and faces the charge member 2. Thus, the resistance of the charge member 2 is made high to reduce the variance of the surface potential of the photoreceptor 1a. Further, a charge work surface is moved and the charge induction member 9 is arranged, so that an electric charge required for charging the surface of the photoreceptor 1a to a desired potential can be applied, even if an applied voltage is not high. Therefore, the charge unevenness never occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for charging a body to be charged in a non-contact manner with a small gap. This charging device is used, for example, in an electrophotographic copying machine or printer that charges a photoconductor, exposes a charged surface with image light, develops an electrostatic latent image formed by the exposure, and transfers the electrostatic latent image to a recording medium. Used for charging or transferring a visible image to a recording medium.

[0002]

2. Description of the Related Art FIG. 5 is a schematic view of an image forming apparatus using an electrophotographic process. The photoconductor drum 1 is formed by applying the photoconductor 1a onto the surface of the conductor 1b.
Rotate in the direction of the arrow inside. The image forming apparatus forms an image by the following procedure: 1. The charging roller 2 (charging device) charges the surface of the photoconductor 1a to a desired potential; The exposure device ED projects image light onto the photoconductor 1a,
2. An electrostatic latent image corresponding to a desired image is formed on the photoconductor 1a; The developing device 4 develops the electrostatic latent image with toner,
3. Toner image (visual image) is formed on the photoconductor 1a; 4. The transfer roller 5 transfers the toner image on the photoconductor 1a onto a transfer paper 6 such as paper conveyed by a conveying means (not shown); 5. The cleaning device 7 cleans the toner that has not been transferred and remains on the photoconductor 1a; The transfer paper 6 on which the toner image has been transferred by the transfer roller 5 is conveyed to a fixing device (not shown). The fixing device heats and pressurizes the toner to fix it on the transfer paper; since the photosensitive drum 1 rotates in the direction of the arrow in FIG. From 6. A desired image is formed on each of the transfer papers by repeating the above procedure.

Although a charging roller 2 is used as a charging device in FIG. 1, a corona charging device such as a scorotron has been conventionally used as a means for charging the photosensitive member 1a.

However, in the corona charging device: A lot of ozone is generated, 2. There are problems such as difficulty in miniaturization. Therefore, in recent years, in addition to the corona charging device, a contact charging device such as the charging roller 2 has been used as a charging device of the image forming apparatus. The contact charging device has an advantage over the corona charging device in that ozone is hardly generated and the device is smaller than the corona charging device.

In the contact charging device, a charging member is brought into contact with a photosensitive member (hereinafter, simply referred to as a photosensitive member) which is a member to be charged,
The photoreceptor is charged by applying a voltage to the charging member. FIG. 6 shows a cross section of a conventional contact charging device. The charging roller 2 has a roller shape and a diameter of 5 to 20 [m.
m], a length of about 300 [mm], and an elastic resistance layer 2a is formed on the conductor 2b. The photoconductor drum 1 has a diameter of 30 to 80 [mm] and a length of about 300 [mm], and the photoconductor 1a is formed on the conductor 1b. Charging roller
The roller 2 contacts the rotating photosensitive drum 1 and is driven to rotate. The resistance layer 2a of the charging roller 2 has a resistivity of 10 ⁷
It is composed of a material of 10 ⁹ [Ωcm]. A voltage is applied to the charging roller 2 by the charging power source 3 to apply the voltage to the photoconductor 1a.
Is charged. Applied voltage is direct current -1 to -5 [kV]
It is.

Japanese Unexamined Patent Publication (Kokai) No. 4-336556 discloses a contact charging device in which a charging roller is used as a charging member and the charging roller is brought into contact with a photosensitive member. The surface of the charging roller is a dielectric, and the rotation direction of the charging roller is the same as the rotation direction of the photoconductor (the moving direction at the closest portion between the charging roller and the photoconductor is opposite). Since the surface of the charging roller is a dielectric, even if there are pinholes on the photoconductor, there will be no charge on the surface around the pinhole of the opposing charging member, and the uncharged portion of the photoconductor due to this Does not occur. Further, by rotating the charging roller in the above-mentioned direction, even if the photoconductor and the dielectric are charged, the photoconductor comes into contact with the dielectric having a lower charging potential in sequence, so that the photoconductor is exposed at a low applied voltage. It allows the body to be charged to a desired potential.

Japanese Unexamined Patent Publication (Kokai) No. 5-216326 discloses a charging device in which a charging roller is used as a charging member and the charging roller is brought into contact with a photosensitive member. The resistance layer of the charging roller is
It is a layer in which the low resistance portion and the high resistance portion are dispersed and mixed.
The resistance layer of the charging roller has low resistance (10 ⁷ [Ωcm] or less)
In this case, the potential of the charging roller is lowered due to a pinhole or the like on the photoconductor, and charging failure occurs. On the other hand, when the resistance layer has a high resistance (10 ¹¹ [Ωcm] or more), the surface potential of the charging roller is low and the charging efficiency is low. Therefore, the resistance layer of the charging roller has a medium resistance (10 ⁸
10 to 10 ¹⁰ [Ωcm]) is desirable, but even in this region, there is a problem that the surface potential of the photoreceptor depends on environmental conditions. In the charging roller disclosed in Japanese Unexamined Patent Publication No. 5-216326, the resistance layer is a layer in which the low resistance part and the high resistance part are dispersed and mixed, so that the charging efficiency does not decrease and the environment condition is maintained. Enables a charging device that does not depend on it.

However, the contact charging device has the following two problems: Trace of charging roller, 2. Charging noise, 3. 3. Decrease in charging performance due to toner on the photoconductor adhering to the charging member. 4. Adhesion of substances constituting the charging member to the photoconductor, Permanent deformation of the charging member that occurs when the photoreceptor is stopped for a long time.

The trace of the charging roller occurs because the substance forming the charging member oozes out from the charging member and adheres to and transfers to the surface of the charged body during the stop period of the charged body. Further, the charging sound occurs because the charging member in contact with the member to be charged vibrates when an AC voltage is applied to the charging member.

As a method of solving such a problem, a proximity charging device has been devised in which a charging member is brought into contact with a photoconductor in a non-contact manner. In the proximity charging device, the charging device is opposed to the photosensitive member so that the distance at the closest portion to the photosensitive member is 0.005 to 0.3 [mm], and a voltage is applied to the charging member, whereby A charging device for charging. In the proximity charging device, since the charging device and the photoconductor are not in contact with each other, there is a problem in the contact charging device such as "adhesion of the substance forming the charging member to the photoconductor" and "the photoconductor is stopped for a long time". "Permanent deformation that sometimes occurs" is not a problem. In addition, regarding the “deterioration of charging performance due to toner or the like on the photoreceptor adhering to the charging member”, the proximity charging device is superior because the amount of toner adhering to the charging member is reduced.

FIG. 7 shows an example of a proximity charging device which has been conventionally considered, and shows a cross section thereof. The charging roller 2, which is a charging member, has a roller shape and a diameter of 5 to 20 [mm],
The length is about 300 mm, and the resistance layer 2a is formed on the conductor 2b. The photosensitive drum 1 has a diameter of 30 to 80
[Mm] and length of about 300 [mm], and the photoconductor 1a is formed on the conductor 1b. The charging roller 2 may or may not be rotated. The charging roller 2 is located at the closest distance to the rotating photosensitive drum 1 (see FIG. 7).
The distance between the middle A / B) is 0.005 to 0.3 [mm]. Resistance layer 2a of charging roller 2
Is composed of a material having a resistivity of 10 ⁷ to 10 ⁹ [Ωcm]. A voltage is applied to the charging roller 2 by the charging power source 3 to charge the photoconductor 1a. The applied voltage is-
It is 1 to -5 [kV].

In the proximity charging device, when a voltage is applied to the charging member, the surface potential of the photosensitive member becomes a straight line having an inclination of 1 as shown in FIG. Vth is a voltage at which discharge occurs between the charging member and the photoconductor and the surface of the photoconductor starts to be charged, and the distance between the charging member and the photoconductor at the closest portion (A- in FIG. 3).
(Distance between B). Vth depends on the distance at the closest point between the charging member and the photoconductor according to "Pashen's law" by assuming that the charging member and the photoconductor are parallel electrode pairs.

Japanese Unexamined Patent Publication (Kokai) No. 6-148923 discloses this type of proximity charging device, and as an experimental fact, the proximity gap between the charging member and the photoconductor is 5 μm or more and 300 μm.
The following is explained.

[0014]

However, although the proximity charging device has the above-mentioned advantages over the corona charging device and the direct charging device, it is difficult to put into practical use due to the following two problems. There are: 1. Ensuring the uniformity of the distance at the closest point between the charging member and the photoconductor, Uneven charging due to a large distance between the charging member and the photoconductor at the closest position. When uneven charging occurs, image defects such as toner adhered to a white background occur during image formation.

As for "ensuring the uniformity of the distance at the closest portion between the charging member and the photosensitive member", when the photosensitive member is charged by the proximity charging device, an image defect due to uneven charging occurs when an image is formed. In order not to do so, it is necessary to suppress the variation in the distance (variation in the longitudinal direction of the charging member) at the closest portion between the charging member and the photoconductor to about 0.01 [mm].
Therefore, it is difficult to mechanically arrange the charging member and the photoconductor with such accuracy.

With respect to "uniform charging due to an increase in the distance between the charging member and the photosensitive member at the closest portion", uneven charging means a state in which the photosensitive member is not uniformly charged. The surface potential becomes higher depending on the location,
It is in a state of becoming low. Uneven charging
Even if the distance between the charging member and the photoconductor is closest to each other, it tends to occur when the distance between the charging member and the photoconductor becomes large. Therefore, in the proximity charging device, uneven charging is more likely to occur than in the contact charging device. The occurrence of uneven charging is
It is known to depend on the resistivity of the charging member, and when the resistivity of the charging member is set to 10 ⁷ to 10 ⁹ [Ωcm],
Uneven charging is less likely to occur. However, at the moment,
The detailed mechanism of uneven charging has not been clarified.

An object of the present invention is to suppress uneven charging on a surface to be charged by a proximity charging device. More specifically, it is an object to solve the above two problems of the proximity charging device at the same time.

[0018]

DISCLOSURE OF THE INVENTION The present invention is a charging device for charging a movable object to be charged in close proximity to the surface to be charged, the conductor facing the surface to be charged, and the conductor. A charging member that has a high resistance layer between the charged surfaces and is in contact with the conductor, and at least a surface facing the charged surface moves, and a charging member for the charged surface with respect to the direction of the movement. A charge inducing member arranged upstream of the contact portion and facing the charging member.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

[0020]

1 shows a cross section of a first embodiment of the present invention.
The first embodiment differs from the conventional proximity charging device in that: the resistance layer 2a of the charging roller 2 has a high resistance; A point at which a surface of the charging roller 2 (hereinafter, simply referred to as a charging surface) facing 1a moves. The charging roller 2 is closest to the photoconductor 1a in the moving direction of the charging surface. The points are the point where the charge inducing member 9 is arranged on the upstream side of the section (A / B) so as to face the charging surface.

The charging roller 2 (charging member of the first embodiment) is roller-shaped, has a diameter of 5 to 20 [mm] and a length of about 300 [mm], and has a "high resistance" on the conductor 2b. The resistance layer 2a is formed. Its thickness is about 1 to 5 [mm]. In the present specification, "high resistance" has the following contents. That is, as described in the section of the prior art, in the conventional proximity charging device (FIG. 7), when the photoconductor 1a is charged, the relationship between the applied voltage and the surface potential becomes a straight line shown in FIG. . However, when the resistance value of the resistance layer 2a is increased,
The relationship between the surface potential and the applied voltage has a slope as shown by the solid line in FIG. 2 in the case of the conventional resistance layer (solid line in FIG. 8 = FIG.
The dotted line is smaller than the straight line. In the present invention, the relationship between the surface potential and the applied voltage has a slope smaller than that of the conventional case (solid line in FIG. 8 = dotted line in FIG. 2), and arrow range AA in FIG.
The case of 1 is defined as the resistance layer 2a having a high resistance. Conversely, the relationship between the applied voltage and the surface potential is
In the case of the conventional resistance layer (solid line in FIG. 8 = dotted line in FIG. 2) or larger, it is defined that the resistance layer 2a has medium resistance or low resistance. According to the experiments conducted by the inventors, when the resistance layer 2a is made of a material having a uniform resistivity, a material having a resistivity of 10 ⁹ or more is “high resistance” and 10 ⁹ to 10 ¹² [Ω].
It was found that the effect of suppressing charging unevenness described later can be obtained in the range of [cm].

The resistance layer 2a of the first embodiment shown in FIG. 1 is made of a material having a uniform resistivity, and the resistivity of the material is 10%.
^{It is 9} to 10 ¹² [Ωcm]. Resistivity is 10 ⁹ to 10
^{As a} method of producing a material having a resistance of ¹² [Ωcm], there is a method of mixing conductive particles such as carbon with an insulating resin or rubber to adjust the dispersion state or orientation state. There is also a method of mixing insulating particles with a conductive resin or rubber. The charging member having the "high resistance" resistance layer 2a is the charging roller 2 in the first embodiment, but it may be belt-shaped or the like.

FIG. 3 shows a second embodiment in which the charging member has a belt shape. In the charging belt 2 of this embodiment, a “high resistance” resistance layer 2a is formed on an endless belt-shaped conductor 2b. In the first and second embodiments,
Although the resistance layer 2a is composed of a material having a uniform resistivity, the resistance layer 2a may be composed of a plurality of layers 2a1, 2a2, 2a3 as shown in FIG. 4 showing the third embodiment.

In any of the embodiments, the charging roller or the charging belt 2 is rotationally driven in the direction of the arrow in the figure by a driving source (not shown) when charging the photoconductor 1a.

That is, the charging surface moves. further,
The charging roller or charging belt 2 and the photosensitive member 1a are arranged so that the moving speed of the charging surface and the moving speed of the photosensitive member surface at the closest position (A / B) between the photosensitive member 1a are different from each other. Alternatively, the rotational driving speed of the charging belt 2 is set. That is,
At the closest point (A / B), set the moving speed of the charging surface to V
The rotation driving speed of the charging roller or charging belt 2 is set so that V _A ≠ V _B , where _A (vector) and the moving speed of the photosensitive member surface are V _B. An appropriate value of the moving speed of the charging surface depends on the resistivity of the resistance layer 2a and the like.
It is 00 to 1000 [mm / sec]. The rotation direction of the charging roller or the charging belt 2 may be opposite to that shown by the arrow. However, even in that case, the position of the charge inducing member 9 is arranged upstream of the closest portion (A / B) with respect to the moving direction of the charging surface.

Further, the charging roller or the charging belt 2 is arranged at a position where the distance at the closest portion (A / B) to the photosensitive drum 1 is 0.005 to 0.3 [mm]. To do. The charging roller or the conductor 2b of the charging belt 2 has a charging power source 3
A charging voltage is applied to charge the photoconductor 1a.
The applied voltage is DC -1 to -5 [kV].

If the charge inducing member 9 can generate a larger inductive charge on the charging surface,
Anything may be used. The charge inducing member 9 of the first to third embodiments has a structure in which a film 9a of an insulator is formed on the surface of a curved conductor 9b, and the conductor 9b is grounded. The installation position of the charge inducing member 9 is a position facing the charging surface, upstream of the closest portion (A / B) in the moving direction of the charging surface. In addition, the charge induction member 9 is
Although not in contact with the charging member (2) and the photoreceptor 1a,
It may be in contact with one or both of the charging member and the photoconductor.

In the first to third embodiments (FIGS. 1, 3 and 4), the surface of (the insulating film 9a of) the charge inducing member 9 is
Larger induced charges are generated than the charging surface (surface of the resistance layer 2a). On the other hand, when the charge inducing member 9 is not placed, the induced charge generated on the charging surface is small where the distance between the charging surface and the photoconductor 1a is large. This is because when the electrode (1b) facing the charging surface is far, the capacitance between the charging surface and the counter electrode (1b) is small, and thus the induced charge is also small. Here, the “distance between the charging surface and the photoconductor 1a” means the distance from a point on the charging surface to the surface of the nearest photoconductor. On the other hand, the distance at the closest portion (A / B) is “the distance at the closest portion between the charging member (2) and the photoconductor”.
To be distinguished.

FIG. 9 shows "distance between charging surface and photoconductor".
Is explained. The distance between the charging surface and the photosensitive member 1a at the point X on the charging surface is the distance from X to the surface Y of the photosensitive member 1a that is the shortest.

By the way, the charge inducing member 9 is replaced by the charge inducing member 9 shown in FIGS.
When arranged in the position as shown in FIG. 4, a discharge occurs between the charging surface and the charge inducing member 9, and the surface of the insulating film 9a constituting the charge inducing member 9 is charged. If the surface of the insulator film 9a is charged, the effect of inducing charges on the charging surface is reduced, but even in this case, the charge roller or the charging belt 2 and the charge inducing member 9 may not be electrically charged. ,
A voltage corresponding to the discharge start voltage is applied. The discharge starting voltage here is a discharge starting voltage between the charging roller or charging belt 2 and the charge inducing member 9, and the charging starting voltage.
Or the closest portion of the charging belt 2 and the charge induction member 9 (A
/ B) depending on the distance.

The discharge starting voltage becomes the smallest when the charging roller or charging belt 2 and the charge inducing member 9 are in contact with each other, but is still about 500 [V]. Therefore, even if the induction charge member 9 is charged, in the charging devices of the first to third embodiments, the induction charge on the charging surface becomes larger than in the case where the charge induction member 9 is not placed. In the charging devices of the first to third embodiments, the induction charge generated by the charge induction member 9 is moved on the charging action surface to move the charging roller or the charging belt 2 and the closest portion of the photoconductor 1a. (A / B) to discharge. In order to generate the induced charges on the charging surface, a method of placing a conductor near the charging surface can be considered. However, in this case, when discharge occurs between the charging roller or the charging belt 2 and the conductor which is the charge induction member, the discharge roller or the charging belt 2 and the charge induction member are not limited to each other. Instead, the current will begin to flow. For this reason, when the charge inducing member 9 is made of only the conductor 9b, an extra current flows through the charge inducing member, which deteriorates the charging efficiency. In the case where the insulator film 2a is present, the surface potential of the insulator rises, so that no discharge occurs between the charging roller or charging belt 2 and the charge induction member 9. In addition, the first to third
In the charging device of the embodiment, by applying an appropriate voltage to the conductor 9b of the charge inducing member 9, it is possible to prevent the discharge from occurring between the charge roller or the charging belt 2 and the charge inducing member 9. it can. In this case, even a current for charging the charge inducing member 9 does not flow between the charging roller or the charging belt 2 and the charge inducing member 9, so that the charging effect is further improved.

As described in the section of the prior art, in order to prevent uneven charging, in the conventional proximity charging device, the resistivity of the charging member was set in the medium resistance region of 10 ⁷ to 10 ⁹ [Ωcm]. . However, when the resistivity of the charging member is set in this range, the variation of the distance at the closest portion (A / B) between the charging member and the photoconductor (variation in the longitudinal direction of the charging member) causes There was a problem that the surface potential changed. Specifically, in order not to cause a defect when an image is formed, it is necessary to suppress the variation in the distance at the closest portion between the charging member and the photosensitive member to about 0.01 [mm].
This is because in FIG. 8, Vth depends on the distance at the closest point between the charging member and the photoconductor. Vth is “Pa
According to the "Shen's law", it becomes large at a rate of about 5000 [V / mm] with respect to the change in the distance between the charging member and the photoconductor. Therefore, if the variation in the distance between the charging member and the photoconductor is set to about 0.01 [mm], the variation in the surface potential of the photoconductor at the time of charging will be about 50 [V].

On the other hand, according to the experiments conducted by the inventors, when the resistivity of the charging member is set to a high resistance region of 10 ⁹ to 10 ¹² [Ωcm], the relationship between the applied voltage and the surface potential of the photoconductor is as follows. This is different from the case where the resistivity of the charging member is set in the medium resistance region of 10 ⁷ to 10 ⁹ [Ωcm]. When the resistivity of the charging member is set to a high resistance region of 10 ⁹ to 10 ¹² [Ωcm], the relationship between the surface potential and the applied voltage is a straight line with a slope of 1 (solid line in FIG. 8 = broken line in FIG. 2). However, the slope becomes a straight line with a slope smaller than 1 (solid line in FIG. 2). Further, at this time, the voltage Vth at which charging is started depends only on the distance at the closest portion (A / B) between the charging member and the photoconductor, and does not depend on the resistivity of the resistance layer 2a of the charging member. (Vth has almost the same value for medium resistance and high resistance). That is,
The resistivity of the resistance layer 2a of the charging member is 10 ⁹ to 10 ¹² [Ωc
m] in the high resistance region, the relationship between the applied voltage and the surface potential is as shown by the solid line in FIG. Therefore,
The resistivity of the resistance layer 2a of the charging member is 10 ⁹ to 10 ¹² [Ωc
m] in the high resistance region, the resistivity is 10 ⁷ to
Compared with the case where the medium resistance region is set to 10 ⁹ [Ωcm], the variation in the surface potential of the photoconductor due to the variation in the distance at the closest portion (A / B) between the charging member and the photoconductor is reduced. be able to. This is because when the charging member has a high resistance, the relationship between the applied voltage and the surface potential becomes a straight line having an inclination smaller than 1.

However, according to the experiments conducted by the inventors, uneven charging occurs when the resistivity of the charging member is set in the high resistance region of 10 ⁹ to 10 ¹² [Ωcm]. That is, when the resistance of the charging member is increased and the relationship between the surface potential and the applied voltage becomes smaller than 1, this uneven charging is likely to occur. However, this charging unevenness has a different form from the charging unevenness that occurs when the resistivity of the charging member is 10 ⁷ [Ωcm] or less. The mechanism of uneven charging generated when the resistivity of the charging member is set to a high resistance region of 10 ⁹ to 10 ¹² [Ωcm] has not been clarified, but it is expected to be as follows. .

The resistivity of the charging member is 10 ⁹ to 10 ¹² [Ωc
In the high resistance region [m], it is considered that the next discharge is unlikely to occur once the discharge occurs between the charging member and the photoconductor. That is, when discharge occurs between the charging member and the photoconductor, the potential at the place where the discharge occurs on the surface of the charging member decreases. However, since the resistivity of the charging member is large, it takes a long time for the potential thus lowered to be restored to the potential before the electric charge is supplied from the charging power supply 3 and the discharge. Therefore, the resistivity of the charging member is 10 ⁷ to 10 ⁹
Just by applying the voltage of the same value as in the case of the medium resistance region of [Ωcm], the charge necessary for charging the surface potential of the photoconductor to the desired value cannot be supplied to the surface of the charging member.
(It takes a long time for the electric potential of the surface of the charging member, which has been lowered by the discharge, to recover to the value before the discharging, and the photosensitive member moves and passes through the charging device during that time.) Therefore, the resistance of the charging member In the case of a high resistance region having a rate of 10 ⁹ to 10 ¹² [Ωcm], the relationship between the surface potential and the applied voltage is a straight line with a slope smaller than 1. In order to charge the surface of the photoconductor to the desired potential, increase the applied voltage,
A method of speeding up the recovery of the potential on the surface of the charging member can be considered. However, in this case, by increasing the applied voltage, the amount of charge transferred from the charging member to the photosensitive member by one discharge increases, and uneven charging occurs.
(Because the applied voltage is large, the discharge does not uniformly occur on the entire surface of the charging member, but is locally concentrated.) In contrast, the resistivity of the charging member is 10 ⁷ to 10 ⁹ [Ωc
In the case of a medium resistance region such as m], it takes a short time for the potential on the surface of the charging member, which has been lowered by the discharge, to recover to the value before the discharge, and the distance the photoreceptor moves during that time is not so large. Therefore, the electric charge necessary for charging the surface of the photosensitive member to a desired value is supplied to the surface of the charging member without increasing the applied voltage so much. That is, 1
The amount of charge transferred from the charging member to the photoconductor by the discharge once does not increase, and uneven charging does not occur.

In the charging devices of the first to third embodiments, although the charging member has a high resistance region of 10 ⁹ to 10 ¹² [Ωcm], uneven charging does not occur. This is because the charging surface moves, and the closest portion (A / B) between the charging member (2) and the photoconductor (1a) in the moving direction of the charging surface.
This is because the charge inducing member 9 is provided at a position facing the charging surface on the upstream side. Due to the charge inducing member 9, a larger induced charge is generated on the charging surface as compared with the absence thereof, and this charging surface moves to move to the closest portion (A / B). Therefore, even though the resistivity of the charging member is in the high resistance region of 10 ⁹ to 10 ¹² [Ωcm], the closest portion (A / B) between the charging member and the photosensitive member can be obtained without increasing the applied voltage. It is possible to supply the charge amount necessary for charging the photoconductor to a desired potential on the charging surface of (1).

Therefore, in the charging devices of the first to third embodiments, the charging member (2) has a resistivity of 10 ⁹ to 10 ¹² [Ωc.
In the high resistance region of [m], uneven charging, which is a problem, does not occur. This is because, in the charging devices of the first to third embodiments, it is not necessary to increase the applied voltage, and therefore the amount of charge that moves by one discharge does not increase. Furthermore, in the charging devices of the first to third embodiments, the moving speeds of the charging surface and the surface of the photoconductor differ at the closest portion (A / B) between the charging member (2) and the photoconductor 1a. Therefore, even if a single discharge occurs between the charging member and the photoconductor, the photoconductor surface is sequentially changed to a different place on the charge action surface due to the difference in the moving speed of the charge action surface and the photoconductor surface. opposite. Therefore, even if there is a place where the potential is lowered (a place where the amount of electric charge is reduced) on the charging surface due to discharge, the place where the potential is sequentially higher (the amount of electric charge is large) due to the movement of the charging surface. Location) faces the surface of the photoconductor. In other words, the larger area of the charging surface used to charge the surface of the photoconductor per unit area means that the surface of the charging surface and the surface of the photoconductor are larger than the case where the moving speed of the surface of the charging surface is the same as that at the same speed. This is the case where the moving speed of the surface is different. In the charging devices of the first to third embodiments, since the moving speeds of the charging surface and the photosensitive member surface at the closest portion (A / B) are different as described above, it is possible to further reduce the applied voltage. is there. Therefore, uneven charging is less likely to occur, which is a problem when the charging member has a high resistance region of 10 ⁹ to 10 ¹² [Ωcm].

In addition, in the charging devices of the first to third embodiments, there was a problem in the conventional proximity charging device, that is, "the variation of the distance between the charging member and the photoconductor at the closest portion is 0.01 [. m
m]]. In the conventional proximity charging device, the relationship between the applied voltage (V ₀ ) and the surface potential (V _S ) of the photoconductor is a straight line with an inclination of 1. This is because when the surface potential (V _S ) of the photoconductor reaches a value of V _S = V ₀ −Vth (Vth is the voltage at which charging starts), no further discharge occurs between the charging member and the photoconductor, and This is because the surface potential of does not increase. Vth is the closest point between the charging member and the photoconductor (A / B)
Since it greatly depends on the distance at
The distance at the closest point between the charging member and the photoconductor has to be strictly limited. On the other hand, in the charging devices of the first to third embodiments, the surface potential of the photoconductor is determined by the amount of charge supplied from the charging member to the photoconductor. (Before the surface potential of the photoconductor reaches the saturation value (V ₀ -Vth), the photoconductor moves and passes through the charging device.)
In the charging device of the third embodiment, the amount of charge transferred from the charging member to the photoconductor is determined by the resistivity of the charging member, the relative movement speed of the charging surface with respect to the photoconductor surface, and the charge guiding member 9 on the charging surface. It is determined by the magnitude of the induced charge generated. Therefore, the value of the surface potential when the photoreceptor is charged is
It is not so much affected by the variation in the distance at the closest portion (A / B) between the charging member and the photoconductor. That is, the first to the third
In the charging device of the embodiment, like the conventional proximity charging device,
The variation in the surface potential of the photoconductor can be reduced without strictly limiting the variation in the distance at the closest portion between the charging member and the photoconductor to 0.01 [mm].

As described above, in the charging devices of the first to third embodiments, by making the charging member have a high resistance, the distance at the closest portion between the charging member and the photoconductor is larger than that in the conventional proximity charging device. Variations in the surface potential of the photoconductor due to variations in
Can be made smaller. Furthermore, since the charging surface is moved and the charge inducing member 9 is arranged,
Even if the applied voltage is not increased, the electric charges necessary for charging the surface potential of the photoconductor to a desired potential can be supplied. Therefore, uneven charging does not occur. As described above, the charging devices of the first to third embodiments simultaneously solve the two problems that have been encountered in the conventional proximity charging device.

[Brief description of the drawings]

FIG. 1 is a cross sectional view of a first embodiment of the present invention.

2 is a graph showing the relationship (charging characteristics) between the applied voltage and the surface potential of the photoconductor 1a of the charging roller 2 shown in FIG. 1 by a solid line.

FIG. 3 is a transverse sectional view of a second embodiment of the present invention.

FIG. 4 is a cross sectional view of the third embodiment of the present invention.

FIG. 5 is a transverse sectional view of an image forming apparatus using a conventional charging roller 2.

6 is an enlarged cross-sectional view of the charging roller 2 shown in FIG.

FIG. 7 is a cross-sectional view of a conventional proximity charging type charging roller 2.

8 is a graph showing the relationship (charging characteristics) between the charging voltage of the proximity charging type charging roller 2 shown in FIG. 7 and the potential formed on the surface of the photoconductor 1a by the charging voltage.

9 is the closest position A, B of the charging roller 2 of the proximity charging system and the photosensitive member 1a shown in FIG. 7, and an arbitrary point X on the charging surface of the charging roller 2 and the closest point to this point. FIG. 3 is a cross-sectional view showing a point Y on the surface of the photoconductor.

Claims (4)

[Claims] 1. A charging device for charging a movable object to be charged so as to approach the surface to be charged in a non-contact manner, and a conductor facing the surface to be charged and the conductor between the conductor and the surface to be charged. A charging member having a high-resistance layer in contact with the charging surface, at least the surface facing the surface to be charged moves, and with respect to the direction of the movement, the charging member is arranged upstream from the closest portion of the charging member to the surface to be charged. A charging device, comprising: a charge inducing member facing the member. 2. The high resistance layer has a resistivity of 10 ⁹ to 10 ^9.
The charging device according to claim 1, wherein the charging device has a resistance of ¹² [Ωcm]. 3. The charging device according to claim 1, wherein the moving speed of the moving surface of the charging member at the closest portion is different from the moving speed of the surface to be charged. 4. The charge inducing member includes a conductor to which a ground or a voltage is applied and a film of an insulator laminated on a surface of the conductor facing the charging member. The charging device described.