JP2002365885A - Contact type electrifying unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that it is difficult to uniformly electrify a photoreceptor surface by an electrifying system having an electrifying roller to hold a carbon nanotube on the surface. SOLUTION: When electrification start voltage at the time of electrifying a body to be electrified 15 from a contact electrifying unit 9 is set as V1, and electrification start voltage at the time of carrying out reverse discharging from the body to be electrified 15 to the contact electrifying unit 9 is set as V2 and the peak-to-peak voltage of AC voltage Vac applied between the contact electrifying unit 9 and the body to be electrified 15 is set as Vpp, the relations of |V1|<|V2| and Vpp>=|V2-V1| are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a contact type charger and a proximity type charger for charging an object to be charged such as a photoreceptor or a recording medium, an electrophotographic copying machine, a printer or a facsimile. The present invention relates to a process cartridge used and an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art A conventional charging system has mainly been a corotron or scorotron, which charges a photosensitive member or the like by corona discharge. However, in this Corotron and Scorotron,
Applying an electric field in the air generates a large amount of harmful substances such as ozone and NOx, consumes a large amount of power due to low charging efficiency, and requires a high-voltage power supply of 4 to 6 kV, resulting in high cost. And there is a drawback that there is danger to the human body. From recent environmental considerations,
Improving such a charging system is urgently required, and the charging system is being shifted from corotron and scorotron to a roller charging system.

[0003] The roller charging method is a method in which a conductive rubber roller (charging roller) is brought into contact with a photoreceptor to cause a discharge in a minute gap between the photoreceptor and the charging roller to charge the surface of the photoreceptor. Thus, ozone is significantly reduced (reduced to 1/100 to 1/500).

FIG. 17 shows an example of the charging potential of the photoconductor when a DC voltage is applied between the charging roller and the photoconductor in the roller charging system. When the photoconductor is negatively charged, the photoconductor is charged when a DC voltage (hereinafter referred to as an applied voltage) applied between the charging roller and the photoconductor becomes equal to or lower than a charging start voltage Vth (−550 V in FIG. 17), The charging potential of the photoconductor shows a charging potential proportional to the applied voltage. However, in the voltage application system (DC charging system) in which a DC voltage is applied between the charging roller and the photosensitive member, uneven charging occurs due to uneven contact between the charging roller and the photosensitive member and uneven resistance on the surface of the charging roller. In addition, the photoconductor surface cannot be charged uniformly.

In Japanese Patent Publication No. Hei 3-52058, a voltage obtained by superimposing an AC voltage having a peak-to-peak voltage Vpp twice or more of the charging start voltage Vth on a DC voltage Vdc corresponding to the charging potential Vs of the photosensitive member is used. An AC charging method has been proposed in which a photosensitive member is charged by applying a voltage between the member and a charging member such as a charging roller to improve the uniformity of charging on the surface of the photosensitive member.

The principle of the AC charging system will be described with reference to FIG. FIG. 18 shows a time change of the DC voltage Vdc applied to the charging roller, the applied voltage (Vdc + Vac), and the charging potential Vs of the photoconductor when a sine wave is used as the AC voltage. When an AC voltage Vac having a DC voltage Vdc and a peak-to-peak voltage Vpp that is twice or more of the charging start voltage Vth is applied between the photoconductor and the charging roller in a superimposed manner, the application between the photoconductor and the charging roller is performed. The voltage is represented by the sum of the DC voltage Vdc and the AC voltage Vac (Vdc + Vac).

At time t1 to t2, the AC voltage Vac decreases, so that the applied voltage (Vdc + Vac) decreases.
Here, since the peak-to-peak voltage Vpp of the AC voltage Vac exceeds the charging start voltage Vth, the discharge from the charging roller to the photosensitive member occurs at least before time t2, and the applied voltage (Vdc + Vac) decreases. The charging potential Vs of the photoconductor decreases, and the negative charging of the photoconductor increases (in FIG. 18, discharge from the charging roller to the photoconductor occurs between times t1 and t2).

In the period from time t2 to time t3, the AC voltage Vac changes to increase, so that the applied voltage (Vdc + Vac) also increases. As a result, the potential difference between the applied voltage (Vdc + Vac) and the charging potential Vs of the photoconductor does not exceed the charging start voltage Vth, the discharge from the charging roller to the photoconductor stops, and the charging potential Vs of the photoconductor is constant (Vs). (Minimum value).

In time t3 to t4, AC voltage Va
Since c further increases, the applied voltage (Vdc + Vac) increases. As a result, the potential difference between the charging potential Vs of the photoconductor and the applied voltage (Vdc + Vac) exceeds the charging start voltage Vth, reverse discharge occurs from the photoconductor to the charging roller, and negative charges move. As a result, the charging potential Vs of the photoconductor increases, and the negative charging of the photoconductor decreases. This is because when a discharge occurs in a minute gap between the photoconductor and the charging roller, the charging start voltage Vth when charging the photoconductor from the charging roller and the charging starting voltage when reverse discharging from the photoconductor to the charging roller are performed. This is a phenomenon that occurs because Vth is almost the same.

During time t4 to t5, AC voltage Va
Since c changes to decrease, the applied voltage (Vdc + Vac) decreases. As a result, the potential difference between the charging potential Vs of the photoconductor and the applied voltage (Vdc + Vac) does not exceed the charging start voltage Vth, the reverse discharge from the photoconductor to the charging roller stops, and the charging potential Vs of the photoconductor becomes constant (Vs Is the maximum value).

At time t5 to t6, the AC voltage Va
Since c further decreases, the applied voltage (Vdc + Vac) decreases. Therefore, the potential difference between the applied voltage (Vdc + Vac) and the charging potential Vs of the photoconductor exceeds the charging start voltage Vth, discharge occurs from the charging roller toward the photoconductor, and the negative charge moves to move the charging potential of the photoconductor. Vs decreases, and the negative charge of the photoconductor increases.

After time t6, the AC voltage Vac changes to increase again, so that the applied voltage (Vdc + Vac) increases. As a result, the potential difference between the applied voltage (Vdc + Vac) and the charging potential Vs of the photoconductor does not exceed the charging start voltage Vth, the discharge from the charging roller to the photoconductor stops, and the charging potential Vs of the photoconductor is constant (Vs). (Minimum value). As described above, the charging potential Vs of the photoconductor repeats oscillation between the minimum value and the maximum value of the charging potential Vs before and after the DC voltage Vdc, thereby improving the charging uniformity of the photoconductor surface. The charging potential of the photoconductor is apparently a DC voltage V
dc.

Also in the charging roller system, since a discharge is generated in a minute gap between the photosensitive member and the charging roller, generation of ozone and NOx cannot be completely eliminated, and a charging system capable of further reducing ozone and NOx is desired. ing. In view of this, the present inventor has proposed a contact type charger such as a charging roller 3, a charging brush, a magnetic brush or the like, which holds the carbon nanotubes 2 on the surface in contact with the surface of the photoreceptor 1, as shown in FIG.

The carbon nanotube has a very large aspect ratio cylindrical structure composed of carbon atoms of SP2 hybrid orbital.
There are multi-walled carbon nanotubes with nested cylinders, both of which have a fibrous shape with a very small diameter. When a negative voltage is applied to the carbon nanotube, the electric field is concentrated at the tip of the carbon nanotube, and the carbon nanotube emits a field at a relatively low voltage.
Since carbon nanotubes cause field emission even in the atmosphere, when a negative voltage is applied from the DC power supply 4 to the charging roller 3, an electric field concentrates on the tip of the carbon nanotubes 2, and mainly due to charges (electrons) due to field emission. The photoconductor 1 can be negatively charged. This method is
Since no discharge is used to charge the photoconductor 1, ozone, NO
This is a method that can reduce x.

When the organic photoreceptor (hereinafter referred to as OPC) 1 is charged by using the charging roller 3 holding the multi-walled carbon nanotubes 2 having a diameter of about 10 to 20 nm on the surface, the distance between the charging roller 3 and the OPC 1 Applied voltage and OPC
FIG. 20 shows the relationship of the charging potential of No. 1. When a negative voltage is applied from the DC power supply 4 to the charging roller 3 holding the carbon nanotubes 2 on the surface, an electric field is concentrated on the tip of the carbon nanotubes 2 and field emission occurs at about -200 V. Is negatively charged. Here, the organic photoreceptor 1 has an organic photosensitive layer 6 provided on a support 5, and a charging roller 3 has a conductive rubber 8 on a metal core 7.
Is formed and the carbon nanotubes 2 are held thereon. Since a general charging roller has a charging start voltage for OPC of about -550 V, it was confirmed that carbon nanotubes have an effect of lowering the charging start voltage.

On the other hand, when a positive voltage is applied to the charging roller holding the carbon nanotubes on the surface, no field emission occurs from the tip of the carbon nanotubes, and the carbon nanotubes do not contribute to the reverse discharge from the OPC to the charging roller. The charging roller holding the carbon nanotubes on the surface had a reverse discharge charging start voltage of about 550 V, similarly to the conventional charging roller.

[0017]

The electric field strength at the tip of the carbon nanotube is affected by the gap between the photoconductor and the carbon nanotube and the density of the carbon nanotubes. Since it is difficult at present, the charging method that has a charging roller that holds carbon nanotubes on the surface causes uneven air gaps with the photoconductor, uneven carbon nanotube density on the charging roller surface, and uneven threshold voltage for field emission. It has been difficult to uniformly charge the surface of the photoreceptor only with a negative DC voltage.

As a charging method for uniformly charging the surface of the photoreceptor, a DC voltage Vdc and an AC voltage Vac are applied to a charger having carbon nanotubes on the surface, similarly to the AC charging method used in the conventional roller charging method. Is applied, and charging and reverse discharging are repeated between the charger and the photoreceptor.

However, in the charging device having the carbon nanotubes held on its surface, the charging start voltage when charging the photoreceptor greatly differs from the charging start voltage when reverse discharging from the photoreceptor. 52058
As in the case of the AC charging system proposed in Japanese Patent Application Laid-Open Publication No. H10-209, the peak-to-peak voltage of the AC voltage cannot be uniquely determined to be twice or more the charging start voltage.

Even in a charger having carbon nanotubes on its surface, when an AC voltage having a relatively large peak-to-peak voltage is applied to the charger by superimposing it on a DC voltage,
It is easy to imagine that the charging uniformity of the photoconductor is improved, but the minimum peak-to-peak voltage remains unclear.

Also, the apparent charging potential Vss of the photosensitive member is
, The apparent charging potential Vss becomes the charging potential Vs
Is considered to be a charging potential obtained by averaging over time, and the AC voltage V
When ac is superimposed on the DC voltage Vdc and applied to the charger, in the AC charging system described in Japanese Patent Publication No. 3-52058, the apparent charging potential Vss of the photoconductor coincides with the DC voltage Vdc applied to the charger. However, in the charging device holding the carbon nanotubes on the surface, the charging potential oscillates around a potential different from the DC voltage Vdc, so that the apparent charging potential Vss does not match the DC voltage Vdc, so When applying the desired charging potential, the DC voltage V
DC voltage and AC voltage Vac are superimposed and applied to the charger to measure the charging potential of the photoreceptor. The data is stored in a memory or the like, and the data is called up in the charging process to control the voltage applied to the charger. This complicates the control system of the charger.

An object of the present invention is to provide a contact-type charger and a proximity-type charger which can uniformly charge an object to be charged. Another object of the present invention is to provide a contact-type charger and a proximity-type charger that can maintain the relationship of | V1 | <| V2 | even when the electrophotographic process is repeated. Another object of the present invention is to provide an image forming apparatus capable of outputting a good image. Another object of the present invention is to provide a process cartridge including a contact-type charger and a proximity-type charger that can uniformly charge a photosensitive member.

[0023]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 contacts the surface of the member to be charged,
DC voltage Vdc and AC voltage Vac
In the contact-type charger for applying a predetermined charging potential to the member to be charged by applying an oscillating voltage on which the member to be charged is superimposed, the charging start voltage for charging the member to be charged from the contact-type charger is V1, The charging start voltage at the time of reverse discharge from the charged body to the contact type charger is V2, and the AC voltage Vac is
V1 | <| V2 | Vpp ≧ | V2-V1 | where the peak-to-peak voltage is Vpp.

According to a second aspect of the present invention, in the contact-type charger according to the first aspect, a nanotube having at least carbon atoms as a constituent element is held on a surface in contact with the object to be charged.

According to a third aspect of the present invention, in the contact-type charger according to the first aspect, a whisker having at least carbon atoms as a constituent element is held on a surface in contact with the member to be charged.

According to a fourth aspect of the present invention, there is provided an image forming apparatus for forming an image by an electrophotographic process including a step of charging a photoreceptor by a charger, wherein the charger is any one of the first to third aspects. Having a contact-type charger.

According to a fifth aspect of the present invention, there is provided a process cartridge detachably mountable to a main body of an image forming apparatus for performing image formation by applying an electrophotographic process including a step of charging a photosensitive member. And charging means for charging the photoreceptor, wherein the charging means comprises:
3. The contact-type charger according to any one of 1. to 3.

According to a sixth aspect of the present invention, the object to be charged is applied with an oscillating voltage obtained by superimposing a DC voltage Vdc and an AC voltage Vac between the object and the object to be charged. In a proximity charger that applies a predetermined charging potential, the charging start voltage when charging the charged object from the proximity charger is V1, and charging when reverse discharging from the charged object to the proximity charger is performed. Assuming that the starting voltage is V2 and the peak-to-peak voltage of the AC voltage Vac is Vpp, the relationship of | V1 | <| V2 | Vpp ≧ | V2-V1 | is satisfied.

According to a seventh aspect of the present invention, in the proximity charger of the sixth aspect, a nanotube having at least carbon atoms as a constituent element is held on a surface adjacent to the object to be charged.

According to an eighth aspect of the present invention, in the proximity type charger according to the sixth aspect, a whisker having at least carbon atoms as a component is held on a surface adjacent to the object to be charged.

According to a ninth aspect of the present invention, there is provided an image forming apparatus for forming an image by an electrophotographic process including a step of charging a photoreceptor by a charging device, wherein the charging device is any one of the sixth to eighth aspects. And a proximity charger described in (1).

According to a tenth aspect of the present invention, there is provided a process cartridge detachably mountable to a main body of an image forming apparatus for executing image formation by applying an electrophotographic process including a step of charging a photosensitive member. And a charging unit for charging the photosensitive member, wherein the charging unit is the proximity type charger according to any one of claims 6 to 8.

[0033]

FIG. 1 shows a first embodiment of the present invention. In the first embodiment, a contact-type charging roller 9 is used as a contact-type charging device.
The carbon nanotubes 10 are held on the surface of. The contact type charging roller 9 is connected to a DC voltage Vdc from a DC power supply 11.
(Where Vdc is a negative voltage) and an AC voltage Vac from the AC power supply 12 are applied.

The contact type charging roller 9 of the first embodiment has a structure in which a conductive rubber 14 is formed on a metal core 13, and a carbon nanotube 10 is held on the surface of the conductive rubber 14. The contact type charging roller 9 is mainly composed of carbon nanotubes 10 and an organic photoconductor (OPC) 15.
And makes the OPC 15 negatively charged.

The OPC 15 comprises a drum-shaped base 16 made of Al and an organic photosensitive layer 1 formed on the base 16.
7, and a charge injection blocking layer is provided between the base 16 and the organic photosensitive layer 17 as necessary. Substrate 16
Is grounded.

The carbon nanotube includes a single-walled carbon nanotube and a multi-walled carbon nanotube. The single-walled carbon nanotube has a diameter of 0.7 to 5 nm and an axial length (hereinafter abbreviated as length) of 10 nm to 1 μm. On the other hand, the multi-walled carbon nanotube has a diameter of 1 to 5
It is 00 nm, the length is 10 nm to several mm, and the more easily synthesized size is a diameter of 2 to 100 nm and a length of 1 μm or more. Both single-walled and multi-walled carbon nanotubes have a very fine fiber shape with a very large aspect ratio.

Therefore, when a negative voltage is applied to the carbon nanotube, an electric field concentrates on the tip of the carbon nanotube, and the carbon nanotube emits a field at a relatively low voltage. The threshold voltage of field emission of carbon nanotubes is reported to be several V / μm or less.

Since carbon nanotubes cause field emission even in the atmosphere, when the charging roller 9 holding the carbon nanotubes 10 on the surface is brought into contact with the OPC 15 and a negative voltage is applied to the charging roller 9, the OP of the charging roller 9 is reduced.
The electric field concentrates on the tip of the carbon nanotube 10 in the contact surface with the C15 or in the region close to the OPC 15, and the field emission occurs, and the OPC 15 can be negatively charged mainly by negative charges (electrons) due to the field emission.

The experimental results of the present inventor show that the diameter is 10 to 20.
When the contact type charging roller 9 holding the multi-walled carbon nanotubes 10 of about nm on the surface is used, the charging start voltage of the OPC 15, that is, the charging start voltage V 1 when the OPC 15 is charged mainly by the field emission from the carbon nanotube 10 is It is about -200 V (see FIG. 20), and the discharge starting voltage of the conventional charging roller (about -550 V)
The value of the negative voltage became smaller (that is, −550 <V1 <0). If the charging start voltage at the time of reverse discharge from the OPC 15 to the contact type charging roller 9 is V2, V2 is about 5
50V (see FIG. 20), and | V1 | <| V2
|

Next, conditions for repeating charging and reverse discharge between the contact type charging roller 9 and the OPC 15 will be described with reference to FIG. FIG. 2 shows changes in the DC voltage Vdc applied to the charging roller 9, the applied voltage (Vdc + Vac), and the charging potential Vs of the OPC 15 (Time) when a sine wave is used as the AC voltage Vac.

Assuming that the peak-to-peak voltage of the AC voltage Vac is Vpp, the applied voltage (Vdc + Vac) is described as follows. Vdc + Vac = Vdc + Vpp × sin (kt) where Vdc ≦ 0, Vpp> 0, k: constant Here, the applied voltage (Vdc + Vac) becomes the minimum value Vmin at time t2, and the applied voltage (Vdc + Va) at time t4.
c) becomes the maximum value Vmax, and the applied voltage (Vdc + Vac) again becomes the minimum value Vmin at time t6.

The maximum value Vmax and the minimum value Vmin of the applied voltage (Vdc + Vac) are as follows. Vmax = Vdc + 0.5 × Vpp Vmin = Vdc−0.5 × Vpp In order to repeat charging and reverse discharge between the contact-type charging roller 9 and the OPC 15, the applied voltage (Vdc + Vac) increases during the time t <b> 2 to t <b> 4. , Applied voltage (Vdc + V
Due to the increase in ac), the potential difference between the charging potential Vs of the OPC 15 and the applied voltage (Vdc + Vac) exceeds the charging start voltage V2 at the time of reverse discharge from the OPC 15 to the contact type charging roller 9, and the reverse from the OPC 15 to the contact type charging roller 9 It is necessary that the discharge starts to occur and the charging potential Vs of the OPC 15 starts to increase (negative charging decreases), and the applied voltage (Vdc + Va)
During the period from t4 to t6 when c) decreases, the applied voltage (Vdc + Vac) decreases due to the decrease in the applied voltage (Vdc + Vac).
ac) and the potential difference between the charged potential Vs of the OPC 15 is OPC
Exceeds the charging start voltage V1 when charging the OLED 15 and the OPC mainly due to the field emission from the carbon nanotubes 10.
15 starts to be negatively charged, and the charged potential Vs of the OPC 15 needs to decrease.

Here, the potential difference between the charging potential Vs of the OPC 15 and the applied voltage (Vdc + Vac) is the charging start voltage V2.
Time t3, the potential difference between the applied voltage (Vdc + Vac) and the charging potential Vs of the OPC 15 becomes the charging start voltage V1.
Is defined as t5. Next, the applied voltage (Vdc
+ Vac) OP at maximum value Vmax and minimum value Vmin
The charging potentials Vsmax and Vsmin of C15 are obtained.

Since the charging start voltage for charging the OPC 15 is V1 (V1 ≒ −200 V), Vsmin is as follows. Vsmin = Vmin−V1 = Vdc−0.5 × Vpp
−V1 Further, the charging start voltage at the time of causing the reverse discharge is V2 (V2 ≒).
550 V), Vsmax is as follows.

Vsmax = Vmax−V2 = Vdc +
0.5 × Vpp−V2 Next, the time t3 to t4 when the charging potential Vs of the OPC 15 increases due to the reverse discharge from the OPC 15 will be considered.

In time t2 to t3, the applied voltage (V
dc + Vac), the applied voltage (Vdc + V
The potential difference between ac) and the charging potential Vs of the OPC 15 becomes equal to or less than V1, the field emission from the carbon nanotube 10 stops, and the charging potential Vs of the OPC 15 remains constant at Vsmin. Therefore, the charging potential Vs (t3) of the OPC 15 at the time t3 is Vsmin, and Vs (t3) = Vsmin = Vdc−0.5 × Vpp−
V1.

At time t3 to t4, the OPC 15
OPC1 at time t3 because the reverse discharge from
It is considered that the potential difference between the charging potential of No. 5 (that is, Vsmin) and the applied voltage at time t4 (that is, Vmax) exceeds the charging start voltage V2 of the reverse discharge. Therefore, it is necessary to satisfy the following expression. Vmax−Vsmin ≧ V2 (Vdc + 0.5 × Vpp) − (Vdc−0.5 × Vpp−V1) ≧ V2∴Vpp ≧ V2-V1, where Vpp> 0, V2 ≒ 550V, V1 ≒ −200
Since it is V, the equation can be transformed as the following equation.

Vpp ≧ | V2-V1 | On the other hand, OPC1
Consider times t5 to t6 when the charging potential Vs of No. 5 decreases. During time t4 to t5, the applied voltage (Vdc + V
ac) decreases, the potential difference between the charging potential Vs of the OPC 15 and the applied voltage (Vdc + Vac) becomes equal to or lower than the charging start voltage V2 of the reverse discharge, the reverse discharge stops, and the charging potential Vs of the OPC 15 remains constant at Vsmax. . Therefore,
The charging potential Vs (t5) of the OPC 15 at time t5 is V
Vs (t5) = Vsmax = Vdc + 0.5 × Vpp−
V2.

Here, from time 5 to t6, the charging from the contact type charging roller 9 (that is, the inflow of negative charges) causes the OP
Since the negative charge of C15 increases (the charge potential decreases), the applied voltage at time t6 (that is, Vmin) and the charge potential of OPC 15 at time t5 (that is, Vsmax)
Is the charging start voltage V1 for charging the OPC 15
Must be exceeded. Therefore, it is necessary to satisfy the following expression.

Vmin−Vsmax ≦ V1 (Vdc−0.5 × Vpp) − (Vdc + 0.5 × Vpp−V2) ≦ V1 {Vpp ≧ (V2−V1) where Vpp> 0, V2 ≒ 550V, V1} −200
Since it is V, the equation can be transformed as the following equation.

Vpp ≧ | V2−V1 | Since the expressions match, in order to repeat charging and reverse discharging between the OPC 15 and the contact type charging roller 9, the peak-to-peak voltage Vpp of the AC voltage Vac is expressed by the following expression. Should be satisfied.

Vpp ≧ | V2-V1 | Next, the apparent charging potential Vss of the OPC 15 is considered. Although the charging potential Vs of the OPC 15 oscillates around a certain value and improves the charging uniformity on the surface of the OPC 15, it is not microscopically constant, but the average value can be obtained. The value obtained by averaging the charging potential Vs over time is defined as the apparent charging potential Vss of the OPC 15.

In the AC charging system described in Japanese Patent Publication No. 3-52058, the charging potential Vs oscillates around a DC voltage.
However, in the first embodiment, the apparent charging potential Vss does not match the DC voltage Vdc because the central value of the oscillation of the charging potential Vs is different from the DC voltage Vdc.

FIG. 3 shows a DC voltage V applied to the contact type charging roller 9 when a sine wave is used as the AC voltage Vac.
3 shows a change in time (Time) of dc, applied voltage Vdc + Vac, charging potential Vs of OPC 15 and apparent charging potential Vss of OPC 15.

Here, the charging potential Vs can be described as follows. t2 to t3 Vs = Vsmin = Vdc−0.5 × Vp
p−V1 t3 to t4 Vs = Vsmin + ｛Vdc + Vpp × s
in (kt) −Vsmin−V2｝ = Vdc + Vpp ×
sin (kt) -V2 t4 to t5 Vs = Vsmax = Vdc + 0.5 × Vp
p-V2 t5 to t6 Vs = Vsmax + ｛Vdc + Vpp × s
in (kt) −Vsmax−V1｝ = Vdc + Vpp ×
sin (kt) -V1 From the above equation and FIG. 3, also in the first embodiment, the charging potential Vs is equal to the period k / 2π similarly to the charging potential of the AC charging method.
It can be seen that it is vibrating with. Therefore, the charging potential V
The center of oscillation of s is considered to be the center of the amplitude of the charging potential Vs, and the maximum value Vsmax and the minimum value Vsmi of the charging potential Vs are considered.
It is given by the average value of n. Therefore, the apparent charging potential Vss is as follows. Vss = 0.5 × (Vsmin + Vsmax) = 0.5 × {(Vdc−0.5 × Vpp−V1) + (Vdc + 0.5 × Vpp−V2)} = 0.5 × {2Vdc− (V1 + V2)} = Vdc−0.5 × (V1 + V2) From the above results, it came into contact with the surface of the photoconductor (OPC15),
A contact-type charger (contact-type charging roller 9) for applying a predetermined charging potential to the photosensitive member by applying an oscillating voltage obtained by superimposing a DC voltage Vdc and an AC voltage Vac between the contact-type charger and the photosensitive member Assuming that the charging start voltage when charging the photoreceptor is V1, the charging start voltage when reverse discharging from the photoreceptor to the contact type charger is V2, and the peak-to-peak voltage of the AC voltage Vac is Vpp, | V1 | <| V2 If | Vpp ≧ | V2-V1 |, the charging and the reverse discharging can be repeated between the contact-type charger and the photoconductor, and the charging potential of the photoconductor can be made uniform. When a voltage is applied to the contact-type charger as described above, the apparent charging potential V
Since ss can be considered to be a value averaged over time, it can be obtained by Vss = Vdc−0.5 × (V1 + V2).

Next, when the above relationship of the first embodiment, that is, the relationship of | V1 | <| V2 | Vpp ≧ | V2-V1 | is not satisfied, the contact type charger holding the carbon nanotube on the surface is In order to investigate that charging and reverse discharging cannot be repeated between photoconductors, a simulation was performed under the following conditions.

The contact type charging roller 9 has a negative DC voltage Vd
Applying an oscillating voltage obtained by superimposing an AC voltage Vac consisting of c (−1000 V) and a sine wave, Vdc = −1000 V Vac = Vpp × sin (kt), and charging when the OPC 15 is charged from the contact-type charging roller 9. Starting voltage V1 = −200 V, charging start voltage V2 when reverse discharging from OPC 15 to contact type charging roller 9
= 550 V, and the peak-to-peak voltage V of the AC voltage Vac
The charging potential Vs of the OPC 15 was determined using pp as a parameter.

The conditions used in the simulation are shown in Table 1 below, where DC voltage Vdc, applied voltage Vdc + Vac,
FIG. 4 to FIG. 7 show the change over time of the charging potential Vs. | V2-
V1 | = 750 V, so that the conditions A and B satisfy the above relationship of the first embodiment, and the conditions C and D do not satisfy the above relationship.

[0059]

[Table 1]

From FIGS. 4 to 7, OPC1 only under conditions A and B
It can be seen that the charging potential Vs of No. 5 vibrates, that is, charging and reverse discharging are repeated. In the conditions A and B, the center of the oscillation of Vs, that is, the apparent charging potential Vss is −117.
5 V, which was consistent with Vss = Vdc−0.5 × (V1 + V2) = − 1000−0.5 × (−200 + 550) = − 1175 (V).

On the other hand, in the AC charging system proposed in Japanese Patent Publication No. 3-52058, the charging start voltage V2 is used as a reference, considering that the peak-to-peak voltage of the AC voltage is twice or more the charging start voltage. In the case, Vpp ≧ 1100V
It is expected that the charging potential Vs of the OPC oscillates only under the condition A.

Also, considering the charging start voltage V1 as a reference, Vpp ≧ 400 V, and it is expected that Vs will oscillate under the conditions A, B and C, but these do not agree with the results of FIGS. | V1 | <| V2 |, where V1 is the charging start voltage when charging the photoreceptor from the contact type charging roller and V2 is the charging start voltage when reverse discharging from the photoreceptor to the contact type charger. Sometimes, the peak-to-peak voltage Vpp of the AC voltage Vac
Is not more than twice the charging start voltage, and must satisfy the following conditions.

Vpp ≧ | V2−V1 | In the first embodiment, V1 ≒ −200V, V2 ≒ 55
Although described as 0V, the charging start voltage V1 at the time of charging the photoreceptor from the contact type charger changes depending on the diameter of the carbon nanotube, the state of the open and closed tubes at the tip, the density, and the like. However, at least when the OPC 15 is negatively charged mainly due to the field emission from the carbon nanotube 10, the discharge starting voltage of the conventional charging roller (−55) is used.
Negative voltage (ie, −550 <V).
1 <0) means that the charging start voltage V1 is present, and it can be considered that | V1 | <| −550 |.

On the other hand, when the reverse discharge from the photoconductor to the contact-type charging device is performed, the charging start voltage V2 is set such that when the OPC 15 reversely discharges to the contact-type charging roller 9, the carbon nanotubes 10 on the surface of the contact-type charging roller 9 are subjected to the reverse discharge. 550 V as in the case of the conventional charging roller.

Therefore, when a contact-type charger holding carbon nanotubes on the surface is used, the electric field is easily concentrated at the tip of the carbon nanotubes at the time of charging, and field emission easily occurs. Also, the relationship | V1 | <| V2 | is maintained.

In charging the OPC 15 by the electric field emission from the carbon nanotube 10, the charging start voltage V1 is a negative voltage larger than -550V (that is, V1 <-55).
0), the OPC 15 is actually-
At 550 V, the electric field starts to be negatively charged by the discharge, so that the field emission hardly contributes to the negative charging of the OPC 15, and V1 ≒ −5
50V, which does not satisfy | V1 | <| V2 |. That is, it is excluded from the present invention.

Next, the contact type charging roller 9 of the first embodiment
Will be described. The metal core 13 is made of Fe, A
A vibration voltage is applied to the carbon nanotubes 10 on the surface of the contact type charging roller 9 by being connected to external power sources 11 and 12 and made of a metal or alloy such as l, Cu, stainless steel, or the like.

As the conductive rubber 14, rubber obtained by adding a conductive filler or carbon nanotube to EPDM, polyurethane, NBR, silicone rubber or the like can be used. Further, the conductive rubber 14 may have a three-layer structure of a protective layer / medium resistance layer / elastic layer as in the conventional charging roller.

The carbon nanotubes 10 are held on the surface of the conductive rubber 14. The carbon nanotubes 10 include single-walled carbon nanotubes and multi-walled carbon nanotubes. The single-walled carbon nanotube has a diameter of 0.7 to 5 nm and an axial length (hereinafter abbreviated as length) of 10 nm to 1 μm. On the other hand, the multi-walled carbon nanotube has a diameter of 1 to 500 nm and a length of 10 n.
m to several mm, and as a size that can be more easily synthesized, the diameter is 2 to 100 nm, the length is 1 μm or more, and the single-walled carbon nanotube and the multi-walled carbon nanotube have an extremely fine fiber shape having an extremely large aspect ratio. are doing.

The size of the carbon nanotube 10 according to the first embodiment is not limited to the above range, and any carbon nanotube having a diameter of less than 1 μm can be used in the first embodiment.

The carbon nanotubes 10 are made of conductive rubber 1
4 is held on the surface.
The carbon nanotubes 10 may be adhered to the conductive rubber 14 by a conductive paste, or a part of the carbon nanotubes 10 may be fixed in a state of being embedded in the conductive rubber 14. There is no limitation, and it is sufficient that the carbon nanotubes 10 hardly fall off upon contact with the OPC 15.

Next, an example of a method for producing the carbon nanotube 10 will be described. Single-walled carbon nanotubes are made of Fe, Co, Ni, Ru, Rh, P
Using a composite rod mixed with a metal catalyst such as d, Os, Ir, Pt, La, and Y, a graphite rod is used as a cathode, and synthesis is performed by arc discharge in a He atmosphere at 100 to 700 Torr. The single-walled carbon nanotube exists in soot on the inner wall of the chamber (chamber soot) or soot on the cathode surface (cathode soot) depending on the type of the metal catalyst.

Further, the above composite rod was heated to 1000 to 1400 ° C. in an electric furnace, and was heated to 500 Torr of Ar.
A single-walled carbon nanotube may be synthesized by irradiating an Nd: YAG pulse laser in an atmosphere. Since the synthesized single-walled carbon nanotubes contain various impurities, they are preferably purified by a hydrothermal method, a centrifugal separation method, an ultrafiltration method, or the like.

On the other hand, for the multi-walled carbon nanotube, graphite rods were used for both
Synthesis is performed using arc discharge in an atmosphere such as He of orr. Multi-walled carbon nanotubes are present in the core of the columnar deposit on the cathode. Multi-walled carbon nanotubes can also be obtained by thermally decomposing hydrocarbons such as benzene, ethylene, and acetylene under an H ₂ gas flow. According to the above method, the multi-walled carbon nanotube contains various impurities after the synthesis, and thus, after being dispersed in an aqueous solution to which an organic solvent or a surfactant is added, a high purity is obtained by centrifugation or ultrafiltration. It is good to refine.

Further, metals such as Fe, Co, and Ni, alloys,
Using an oxide as a catalyst, acetylene, ethylene, methane, or the like may be decomposed by thermal CVD, plasma CVD, or the like to produce carbon nanotubes. This method does not require purification because the purity of carbon nanotubes is high, and facilitates the process. The tip of the carbon nanotube 10 may have either a closed tube or an open tube.

Next, the OPC 15 charged in the first embodiment
Is described. A hole injection preventing layer in which titanium oxide fine particles are dispersed in a binder resin is formed on a drum-shaped substrate 16 made of Al by dip coating to a thickness of 1 to 3.
A 5 μm-thick layer was formed, and then a laminated organic photosensitive layer 17 composed of a charge generation layer (hereinafter abbreviated as CGL) and a charge transport layer (hereinafter abbreviated as CTL) was formed.

CGL is made of a charge generating material (hereinafter abbreviated as CGM) made of a petalal resin, a thermosetting modified acrylic resin,
It is made of a material dispersed in a binder resin such as a phenol resin, and has a thickness of 0.
It was formed in a thickness of 1-1 μm. As CGM, the wavelength 740 to
Squarylium dye, metal-free phthalocyanine, metal phthalocyanine, azurenium salt dye, azo pigment, etc. having sensitivity around 780 nm, and thiapyrylium salt, polycyclic quinone, perylene or azo pigment etc. having sensitivity around 635-650 nm Can be used.

The CTL is formed by dispersing a hole carrier transporting material (hereinafter abbreviated as CTM) in a binder resin such as a bisphenol-based polycarbonate resin, and has a film thickness of about 10 to 40 μm and is formed by a dipping coating method. CTMs include oxadiazole derivatives, pyrarizone derivatives, triphenylmethane derivatives, oxazole derivatives, triarylamine derivatives,
Butadiene derivatives and the like are used.

In the first embodiment, a function-separated type OPC
Although the description has been made taking the example of the OPC 15 as an example, the OPC 15 is not limited to the function-separated type, and may be a single-layer type OPC. The OPC 15 is a drum-shaped OPC in the first embodiment, but may be a belt-shaped OPC using a belt having a conductive layer formed on the surface instead of the base 16, or may be a sheet-shaped OPC.

Further, the present invention is not limited to the contact type charger used for charging the OPC, and the same contact type charger can be used as long as the photosensitive member is negatively charged. It does not limit the invention. Further, the present invention can also be used for charging an object to be charged such as a recording medium other than the photoreceptor.

Next, the contact-type charging roller 9 of the first embodiment
An example of a method for fabricating is described. Metal core 1 made of SUS
3 is a multi-walled carbon nanotube (diameter 10 to 20 nm)
Was covered with a conductive rubber (NBR) 14 in which the resin was dispersed by a molding method. The thickness of the conductive rubber 14 was 2 mm.
Thereafter, the surface of the conductive rubber 14 was roughly ground by cylindrical grinding, and the surface was further polished with free alumina abrasive grains or the like. This polishing process has a particle size of 10 μm, 5 μm, 1 μm.
m and the roller surface (the surface of the conductive rubber 14) was polished, and the carbon nanotubes 10 were projected from the roller surface. By controlling the amount of polishing, the carbon nanotube 1
The protrusion length of 0 was set to 0.2 μm to 2 μm. Then, the contact-type charging roller 9 is connected to the external power supplies 11 and 12 so that a vibration voltage in which a DC voltage and an AC voltage are superimposed can be applied.

The contact-type charging roller 9 manufactured by the above method
Is mounted as a charger in an electrophotographic copying machine, a solid black image is copied under the conditions shown in Table 2 below, and the in-plane uniformity of the copied solid black image (hereinafter referred to as an analog halftone image) is visually observed. Was evaluated.

[0083]

[Table 2]

When Vpp is set to 400 V, the analog halftone image is similar to the case where only the DC voltage is applied to the contact-type charging roller 9.
At 1600 V, it was confirmed that the in-plane uniformity of the analog halftone image was improved and the charging uniformity of the OPC 15 was improved as compared with the case where only the DC voltage was applied to the contact type charging roller 9.

The developing unit was removed from the copying machine, a surface voltmeter was installed near the OPC 15, and a DC voltage was applied to the contact type charging roller 9 to measure the charging potential of the OPC 15 with the surface voltmeter. From the charging roller 9
The charging start voltage V1 when charging the PC 15 is -210.
V, the charging start voltage V2 at the time of reverse discharge from the OPC 15 to the contact type charging roller 9 is 570 V, and the peak-to-peak voltage Vpp of the AC voltage superimposed on the DC voltage is 780 V or more. Was consistent.

In the first embodiment, the AC voltage applied to the contact charger 9 has been described as a sine wave, but the AC voltage is not limited to a sine wave, but may be a square wave, a sawtooth wave, or the like. Any AC voltage that periodically fluctuates as described above can be used. In the first embodiment, the carbon nanotube 10 has been described as an example. However, any structure may be used as long as an electric field can be concentrated at the tip, and the surface of the carbon nanotube is modified by attaching an atom having a small work function, such as Li. Alternatively, the carbon nanotube may have a reduced field emission threshold voltage.

FIG. 8 shows another embodiment 2 of the present invention. In the second embodiment, a contact-type charging blade 18 is used as a contact-type charging device.
A surface of the surface 8 that comes into contact with the OPC 19 as a photoreceptor holds a carbon whisker 20 which is a whisker containing carbon atoms as a constituent element.
Is applied with an oscillating voltage in which a DC voltage Vdc from the DC power supply 11 (where Vdc is a negative voltage) and an AC voltage Vac from the AC power supply 12 are superimposed.

The contact type charging blade 18 of the second embodiment
Has a structure in which a conductive rubber 22 is attached to one surface of a metal plate 21, and a carbon whisker 20 is held on the surface of the conductive rubber 22. Then, the contact type charging blade 18 mainly comes into contact with the OPC 19 with the carbon whisker 20 to charge the OPC 19 negatively.

The OPC 19 comprises a drum-shaped substrate 23 made of Al and an organic photosensitive layer 24, and a charge injection blocking layer is provided between the substrate 23 and the organic photosensitive layer 24 as needed. The base 23 is grounded.

The carbon whiskers 20 are in the form of thin fibers having carbon atoms as constituent elements, similarly to the carbon nanotubes. The carbon whisker 20 has a diameter of several tens nm to several μm and a length of several μm to several mm.
It is. When a negative voltage is applied to the carbon whiskers 20, an electric field concentrates on the tip similarly to the carbon nanotubes, and a field emission occurs at a relatively low voltage. When the blade 18 is brought into contact with the OPC 19 and a negative voltage is applied, an electric field is concentrated on the contact surface of the contact-type charging blade 18 with the OPC 19 or on the tip of the carbon whisker 18 in a region close to the OPC 19, and electric field emission occurs. The OPC 19 can be negatively charged by negative charges (electrons) due to field emission.

Here, a contact-type charger for applying a predetermined charging potential to the photosensitive member by applying an oscillating voltage obtained by superimposing the DC voltage Vdc and the AC voltage Vac from the power supplies 11 and 12 to the photosensitive member (OPC 19). (Contact type charging blade 1
8) In the contact type charging blade 18 to the OPC 19
Is a charging start voltage when charging is performed, and V2 is a charging start voltage when performing reverse discharge from the OPC 19 to the contact type charging blade 18.

When the OPC 19 reversely discharges electricity to the contact type charging blade 18, electric field emission from the tip of the carbon whisker 20 on the surface of the contact type charging blade 18 does not occur. Charging start voltage V2 is about 550V like blade
(The discharge start voltage V2 is around -550 V for both the conventional charging roller and charging blade).

Therefore, the second embodiment has | V1 | <| V2
In order to satisfy the condition of |
The charging start voltage V1 for charging the PC 19 is -550 V
What is necessary is just to select the diameter, length, and density of the carbon whiskers 20 so that the negative voltage becomes smaller (that is, −550 <V1 <0).

Since the diameter and length of the carbon whiskers 20 can be controlled by the synthesis method, and the density of the carbon whiskers 20 can be controlled by the method of manufacturing the contact-type charging blade 18, the charging start voltage V1 is set to -550.
It is relatively easy to make the negative voltage smaller than V (that is, -550 <V1 <0).

Generally, the carbon whisker 20 is
As the tip diameter becomes smaller, the electric field concentration is promoted, and therefore, a relatively thin carbon whisker may be used. For example, several tens to 100 diameters slightly larger than carbon nanotubes
A carbon whisker on the order of nm is suitable for the carbon whisker 20 of the second embodiment. −550 <V1 <
If the charging start voltage V1 is set in the region of 0, the charging start voltage V2 is about 550 V, so that the second embodiment satisfies the relationship | V1 | <| V2 | as in the first embodiment.

Here, the contact type charging blade 18
Assuming that the charging start voltage V1 for charging C19 is -350 V, the charging potential V of the OPC 19 is the same as in the first embodiment.
The time change of s was determined. The contact-type charging blade 18
Are supplied from the power supplies 11 and 12 to the negative DC voltage Vdc (−100
0V) and an AC voltage Vac consisting of a sine wave were applied, and Vdc = −1000 V Vac = Vpp × sin (kt). In addition, the contact type charging blade 18
The charging start voltage V2 at the time of reverse discharge was set to 550V.

The conditions used in the simulation are shown in Table 3 below, where the DC voltage Vdc and the applied voltage (Vdc + Va
c), the change over time of the charging potential Vs is shown in FIGS.
Since | V2−V1 | = 900 V, the condition E falls under the condition of the second embodiment, and the conditions F and G correspond to the second embodiment.
Not included in the conditions.

[0098]

[Table 3]

9 to 11, the OPC 19 only under the condition E
It can be seen that the charging potential Vs of the sample oscillates, that is, charging and reverse discharging are repeated. The center of oscillation of the charging potential Vs under the condition E, that is, the apparent charging potential Vss of the OPC 19
Was -1100 V, and Vss = Vdc−0.5 × (V1 + V2) = − 1000−0.5 × (−350 + 550) = − 1100 (V).

Therefore, in the same manner as in the first embodiment, also in the carbon whisker 20, the charging start voltage when charging the photoconductor (OPC 19) from the contact type charger (contact type charging roller 18) is V1, and the charging start voltage is V1 from the photoconductor. When the charging start voltage at the time of reverse discharging to the charger is V2, when | V1 | <| V2 |, the alternating voltage Vac is required to repeat charging and reverse discharging between the OPC and the contact type charger. Peak-to-peak voltage V
It can be seen that pp is not more than twice the charging start voltage and it is necessary to satisfy the following conditions.

Vpp ≧ | V2-V1 | Next, the components of the contact type charging blade 18 of the second embodiment will be described. The metal plate 21 is made of Fe, Al, C
u, a metal such as stainless steel or an alloy, connected to external power supplies 11 and 12, and applies an oscillating voltage to the conductive
Is applied.

As the conductive rubber 22, rubber obtained by adding a conductive filler or carbon whisker to EPDM, polyurethane, NBR, silicone rubber or the like can be used.
Further, the conductive rubber 22 may have a three-layer structure of a protective layer / medium resistance layer / elastic layer as in the conventional charging blade. Then, a carbon whisker 20 is provided on the surface of the conductive rubber 22.
Is held.

Next, an example of a method for manufacturing the contact type charging blade 18 of Embodiment 2 will be described. One of the metal plates 21 made of SUS has carbon whiskers (50 to 200 in diameter).
(NB, length 20 μm or less) dispersed conductive rubber (NB
R) 22 was formed by a molding method. Conductive rubber 2
The thickness of 2 was 2 mm. Thereafter, the surface of the conductive rubber 22 was roughly ground by grinding, and the surface was further polished with free alumina abrasive grains or the like. This polishing process,
The surface of the charging blade 18 was polished by changing the particle diameter to 10 μm, 5 μm, and 1 μm, and the carbon whiskers 20 were projected from the surface of the charging blade 18. By controlling the polishing amount, the protrusion length of the carbon whisker 20 is set to 5 to 15 μm.
And The contact-type charging blade 18 is connected to the external power supplies 11 and 12, and has a structure capable of applying a vibration voltage in which DC and AC are superimposed.

The contact-type charging blade 18 produced by the above method is mounted as a charger in an electrophotographic copying machine, and an analog halftone image is output under the copying conditions shown in Table 4 below as in the first embodiment. The in-plane uniformity was visually evaluated.

[0105]

[Table 4]

When the peak-to-peak voltage Vpp is 400 V, 850 V
In this case, the same analog halftone image was obtained as when only the DC voltage was applied to the contact-type charging blade 18, but when the peak-to-peak voltage Vpp was 1600 V,
It was found that the in-plane uniformity of the analog halftone image was improved and the OPC 19 was more uniformly charged than when only a DC voltage was applied to the contact type charging blade 18.

The charging start voltages V1 and V2 were measured in the same manner as in the first embodiment.
The charging start voltage V1 when charging the OPC 19 from 8 is-
At 380 V, the charging start voltage V2 at the time of reverse discharge from the OPC 19 to the contact type charging roller 18 is 560 V, and the peak-to-peak voltage Vp of the AC voltage Vac superimposed on the DC voltage Vdc.
It was found that the lower limit of p was 940 V, which was consistent with the experimental results.

In the second embodiment, the carbon whisker 20 has been described as an example. However, the whisker may have a structure in which an electric field can be concentrated at the tip. It does not matter if the carbon atom of is replaced by a boron or nitrogen atom.

FIG. 12 shows another embodiment 3 of the present invention.
The third embodiment uses a contact-type charging film 25 as a contact-type charger. The surface of the contact-type charging film 25 that contacts the OPC 26 contains carbon, and at least one of boron and nitrogen. And the contact type charged film 25 is applied with an oscillating voltage in which a DC voltage Vdc from the DC power supply 11 (where Vdc is a negative voltage) and an AC voltage Vac from the AC power supply 12 are superimposed.

In the contact type charging film 25 of the third embodiment, a conductive film 29 is held on a metal plate 28.
Further, the above-mentioned hetero nanotube 27 is held on the surface of the conductive film 29 which is in contact with the OPC 26. The contact-type charged film 25 is mainly curved by the above-described hetero nanotube 27 while being curved.
6 and makes the OPC 26 negatively charged. OPC26
Are a drum-shaped substrate 30 made of Al and an organic photosensitive layer 3
1, and a charge injection blocking layer is provided between the base 30 and the organic photosensitive layer 31 as necessary. Substrate 30
Is grounded.

The hetero nanotube containing carbon and containing at least one of boron and nitrogen is also in the form of a fiber having a small diameter like the carbon nanotube, and the diameter and size are almost the same as those of the carbon nanotube. The composition ratio of carbon, boron and nitrogen can take various values depending on the synthesis method. Furthermore, boron and nitrogen may be unevenly distributed in the carbon skeleton. When a negative voltage is applied to a hetero nanotube containing carbon and at least one of boron and nitrogen, an electric field is concentrated at the tip similarly to the carbon nanotube, and a field emission occurs at a relatively low voltage. In the above-mentioned hetero nanotube 27
OPC 26
When a negative voltage is applied to the contact-type charged film 25 by contact with the OPC 26, the electric field concentrates on the contact surface with the OPC 26 or on the tip of the hetero nanotube 27 in the region close to the OPC 26, and the field emission mainly occurs. OPC 26 can be negatively charged by negative charges (electrons) due to emission.

Here, a contact type charger for applying a predetermined charging potential to the photosensitive member by applying an oscillating voltage obtained by superimposing a DC voltage Vdc and an AC voltage Vac from the power supplies 11 and 12 to the photosensitive member (OPC 26). (Contact type charged film 2
In 5), the contact-type charged film 25 to the OPC 26
Is a charging start voltage when charging is performed, and a charging start voltage when reverse discharging from the OPC 26 to the contact-type charging film 25 is V2.

When the OPC 26 reversely discharges to the contact type charging film 25, the field emission from the tip of the hetero nanotube 27 on the surface of the contact type charging film 25 does not occur.
The charging start voltage V2 when the reverse discharge is performed from C26 to the contact type charging film 25 is about 550 like the conventional charging film.
V.

On the other hand, when the voltage applied to the contact-type charging film 25 is the charging start voltage V1, the OPC 26 is negatively charged mainly by the negative charge due to the field emission from the hetero nanotube 27. V1 | <| V2
In order to satisfy the condition of |, it is necessary to set the field emission threshold so that the charging start voltage V1 becomes a negative voltage smaller than -550 V (that is, -550 <V1 <0).

Here, the current J due to the field emission is expressed by the following F
It is given by the equation of Owler-Nordheim.

[0116]

(Equation 1)

Therefore, if the diameter, length, and density of the hetero nanotube 27 are selected in consideration of the difference between the work function of the hetero nanotube 27 and the work function of the carbon nanotube,
The charging start voltage V1 can be a negative voltage smaller than -550V.

Further, in general, the hetero nanotube 27
Since the electric field concentration is promoted when the tip diameter is small, the charging start voltage V1 can be set to a negative voltage smaller than -550 V (that is, -550 <V1 <0) by using a relatively thin hetero nanotube. . If the charging start voltage V1 is set in the range of -550 <V1 <0 by the above method, the relationship of | V1 | <| V2 | is obtained because the charging start voltage V2 is about 550V.

Therefore, in the third embodiment, the first and second embodiments
Similarly, the following conditions can be derived. That is, the contact type charging film 25 as the contact type charger holding the hetero nanotubes 27 containing carbon and at least one of boron and nitrogen on the surface is changed from the OPC as the photosensitive member.
Assuming that the charging start voltage when charging the OPC 26 is V1 and the charging start voltage when the OPC 26 is reversely discharged to the contact type charging film 25 is V2, when | V1 | <| V2 | In order to repeat charging and reverse discharging with the charging film 25, the AC voltage Vac
Needs to satisfy the following conditions.

Vpp ≧ | V2-V1 | Next, the components of the contact type charging film 25 of the third embodiment will be described. The metal plate 28 is made of Fe, Al, C
u, a metal such as stainless steel, or an alloy, is connected to external power supplies 11 and 12, and an oscillating voltage is applied to the hetero nanotube 27 on the surface of the contact-type charging film 25.

As the conductive film 29, a film obtained by adding a conductive filler, the above-mentioned hetero nanotube, or the like to a film of polycarbonate, polyethylene, polypropylene or the like can be used. The surface of the conductive film 29 holds the hetero nanotube 27 containing carbon and at least one of boron and nitrogen.

Next, an example of a method for producing the contact-type charged film 25 of Embodiment 3 will be described. After dissolving the polycarbonate resin in tetrahydrofuran, a BCN heterotube (diameter 10 to 50 nm, length 10 μm or less) containing carbon containing boron and nitrogen is dispersed, and then formed into a film shape by a doctor blade and heated at 100 to 130 ° C. The conductive film 29 was completed. The film 29 has a thickness of 40 to 60 μm. Thereafter, the surface of the film 29 was roughly polished with a 1500 sandpaper, and the surface was further polished with free alumina abrasive grains or the like. This polishing process has a particle size of 10 μm, 5 μm
and the surface of the film 29 is polished by changing the
The CN hetero nanotube 27 protruded from the surface of the film 29. The polishing amount was controlled so that the protrusion length of the BCN hetero nanotube 27 was 5 μm or less. Thereafter, the conductive film 27 was fixed to one side of a metal plate 28 made of Al 2 with screws (not shown) to complete the contact type charging film 25. Then, the contact-type charging film 25 is connected to the external power supplies 11 and 12 so that a vibration voltage in which the DC voltage Vdc and the AC voltage Vac are superimposed can be applied.

The contact-type charged film 25 produced by the above method is mounted as a charger in an electrophotographic copying machine, and an analog halftone image is output in the same manner as in the first and second embodiments, and the in-plane uniformity is improved. It was evaluated visually. As a result, in the third embodiment, | V1 | <| V2 |, Vpp ≧ | V2-V
An image having excellent uniformity was obtained under the condition of 1 |.

In the first to third embodiments, carbon nanotubes, carbon whiskers, and hetero nanotubes having carbon atoms as constituent elements have been described as examples. However, these materials can be converted into carbon atoms by selecting synthesis conditions. A very thin fiber shape can be easily produced. Graphite has a work function of about 5 eV, but an electric field can be concentrated at the tip by forming it into an extremely thin fiber shape as in the above-mentioned materials, so that field emission can be caused at a low voltage.

Further, carbon nanotubes, carbon whiskers, and hetero nanotubes containing carbon atoms as constituents have good crystallinity and therefore high mechanical strength. Young's modulus of carbon whisker by vapor phase growth is 800 GPa,
The multi-walled carbon nanotube has a Young's modulus of 1.8 TPa,
It is reported that the single-walled carbon nanotube has a Young's modulus of 4 to 5 TPa. Similarly, a large Young's modulus can be expected for a hetero nanotube having carbon atoms as a constituent element. Further, the carbon nanotube is a material that can be relieved by buckling when a large stress is applied, and is hardly broken.

As described above, carbon nanotubes, carbon whiskers, and hetero nanotubes having carbon atoms as constituent elements have large mechanical strength. Therefore, the photosensitive member is slid by a contact-type charger holding the above-mentioned material on the surface. In this case, the above-mentioned material is not easily broken. Therefore, the contact-type charger can maintain the relationship | V1 | <| V2 | even in long-term use.

A material having both an extremely fine shape and a large mechanical strength as described above is suitable for a contact-type charger satisfying the following relationship: | V1 | <| V2 | Vpp ≧ | V2-V1 | At present, nanotubes composed of atoms and whiskers composed of carbon atoms are materials that can be relatively easily manufactured.

FIG. 13 shows a fourth embodiment of the present invention. The image forming apparatus according to the fourth embodiment includes an OPC3
2, a charger 33 as a charging unit for uniformly charging the OPC 32, an exposure device 34 for forming an electrostatic latent image, and a developing device for visualizing the electrostatic latent image to form a toner image. 35 and recording paper 36 using the toner image as a recording medium
The transfer device 37 for transferring the image to the recording paper 36 and the charge of the recording paper 36 are removed.
A static eliminator 38 for separating the recording paper 36 from the PC 32;
A cleaning device 39 for removing toner remaining on the PC 32 is provided.

[0129] The transfer device 37 includes a recording medium 3 serving as a recording medium.
6 and a charge providing material 41 for supplying transfer charges to the transfer belt 40. Charger 33
The contact type charging roller 9 according to the first embodiment includes power supplies 11 and 12 for applying an oscillating voltage to the contact type charging roller 9. The contact type charging roller 9 includes the metal core 13 as described above,
The conductive rubber 14 covers the metal core 13 and the carbon nanotubes 10 held on the surface of the conductive rubber 14.

The operation of this image forming apparatus will be described.
The PC 32 is driven to rotate in the direction of the arrow by a drive unit (not shown), is uniformly charged to about -800 V by the contact-type charging roller 33, and is subjected to raster exposure by the exposure device 34 based on an image signal. OP by this raster exposure
The charge on C32 disappears, the potential of the exposed portion on OPC32 drops from -800V to about -40V, and an electrostatic latent image is formed. The OPC 32 comes into contact with toner having a negative charge on the developing roller of the developing device 35,
The toner does not adhere to the portion where the charge remains, and the toner adheres to the portion without the charge, that is, the exposed portion, and a toner image similar to the electrostatic latent image is formed.

The toner image on the OPC 32 is charged on the recording paper 36 conveyed by the transfer belt 40 which is driven at a constant speed in contact with the OPC 32, from the brush-like charge applying material 41, which has an electric charge of the opposite polarity to the toner particles. The image is transferred by an electric field formed by being supplied to the transfer belt 40. The recording paper 36 is sent to a fixing device (not shown) by the transfer belt 40, and the toner image is fixed by the fixing device. The brush-shaped charge applying material 41 is in contact with the transfer belt 40 to supply the charge.

Here, the toner remaining on the OPC 32 without being transferred is cleaned by the cleaning device 39. Also, the OPC 32 is provided by a static eliminator (not shown).
The charge remaining on the top is removed.

In the image forming apparatus of the fourth embodiment, at least the photosensitive member (OPC 32) and the contact-type charging roller 33 as a contact-type charger are configured as a process cartridge, and the process cartridge is used as the main body of the image forming apparatus (other than the process cartridge). And an image forming apparatus that forms an image by an electrophotographic process including a step of charging a photoconductor (OPC 32) by a contact-type charging roller 33.

In the fourth embodiment, when the process cartridge is mounted on the image forming apparatus main body and an image is output, a good image is obtained. This is because the contact type charging roller 9 and the OPC 32 included in the process cartridge
When the charging start voltage when charging the OPC 32 from the contact charging roller 9 is V1, the charging starting voltage when reverse discharging from the OPC 32 to the contact charging roller 9 is V2, and the peak-to-peak voltage of the AC voltage Vac is Vpp. Since the relationship of V1 | <| V2 | Vpp ≧ | V2-V1 | is satisfied, it is expected that the OPC 32 could be charged more uniformly than when only the DC voltage was applied to the contact type charging roller 9.

FIG. 14 shows a fifth embodiment of the present invention. The fifth embodiment uses a proximity charging roller 42 as the shape of the proximity charger. A carbon nanotube 43 is held on the surface of the proximity type charging roller 42. The proximity type charging roller 42 has a DC voltage Vdc (where Vdc is a negative voltage) from the DC power supply 11 and an AC voltage Va from the AC power supply 12.
An oscillation voltage on which c is superimposed is applied.

The proximity charging roller 42 of the fifth embodiment has a structure in which a conductive rubber 45 is formed on a metal core 44, and a carbon nanotube 43 is held on the surface of the conductive rubber 45. Organic photosensitive layer 48 of OPC 46
Installed close to the surface. The OPC 46 includes a drum-shaped substrate 47 made of Al and an organic photosensitive layer 48, and a charge injection blocking layer is provided between the substrate 47 and the organic photosensitive layer 48 as necessary. The base 47 is grounded.

As described in the description of the first embodiment, when a contact-type charging roller holding multi-walled carbon nanotubes having a diameter of about 10 to 20 nm on the surface is used, the charging of the OPC with the contact-type charging roller is not performed. Charging start voltage V1
Was about -200 V, but the carbon nanotubes 43
When the OPC 46 is charged by the proximity type charging roller 42 holding the OPC on the surface, the carbon nanotube 43 and the OPC 46 are charged.
Since the distance 46 is large, the electric field applied to the tip of the carbon nanotube 43 decreases, and the threshold voltage of the field emission shifts to the negative high voltage side. As a result, the negative value of the charging start voltage V1 when charging the OPC 46 becomes larger than -200V (that is, V1 <-200V).

However, the discharge breakdown voltage Vb of the gap between the OPC 46 and the proximity type charging roller 42 is one of the gap Z.
Because of the following function, even when reverse discharge is performed from the OPC 46 to the proximity type charging roller 42, as the distance between the OPC 46 and the carbon nanotube 43 increases, the charging start voltage V2 becomes higher than about 550V.

The discharge breakdown voltage Vb of the gap Z is calculated according to Paschen's rule. Further, since the voltage applied between the OPC 46 and the proximity charging roller 42 is distributed to the OPC 46 and the gap Z, the charging start voltage V2 can be estimated by determining the film thickness and the relative permittivity of the OPC 46. Using a conventional proximity charging roller, the thickness of the OPC 46 is set to 19 μm.
m, the relative permittivity ratio was 3, and the relationship between the gap Z between the OPC 46 and the proximity charging roller and the charging start voltage V2 was estimated. The result is shown in FIG.

When the gap Z is about 20 μm or less, since the actual discharging distance is about 20 to 25 μm, the charging start voltage V2 becomes a constant value (≒ 550 V). In the case of 30 μm or more, the charging start voltage V2
Increases monotonically according to the gap Z. Even in the proximity type charging roller 42 holding the carbon nanotubes 43 on the surface, since the carbon nanotubes 43 do not contribute to the reverse discharge, the charging start voltage V2 is considered to exhibit the same behavior as in FIG.

Therefore, in order for the fifth embodiment to satisfy the condition of | V1 | <| V2 | Vpp ≧ | V2-V1 |, the charging start voltage V1 is applied to the proximity type charging roller 42 holding the carbon nanotubes 43 on the surface. Then, the proximity charging roller 42 may be installed in a section of the gap Z where | V1 | <| V2 | is measured in consideration of FIG.
The proximity charging device may be a proximity charging blade or the like having carbon nanotubes on the surface instead of the proximity charging roller 42.

Actually, a negative DC voltage was applied to a proximity charging blade holding multi-walled carbon nanotubes having a diameter of about 10 to 20 nm on the surface, and the gap Z was used as a parameter to make OP
The charging start voltage V1 when charging C46 was measured.
The measurement results are shown in Table 5 below. In addition, since the proximity type charger has a blade shape, the gap Z can be accurately adjusted.

[0143]

[Table 5]

From Table 5, if at least the gap Z is 19 μm or less, the charging start voltage V1 is a negative value (that is, −550 <V1 <0) smaller than the charging start voltage of the conventional charging blade (about −550 V). ), The relationship of | V1 | <| V2 | is satisfied when at least the gap Z is set to 19 μm or less in the proximity-type charging roller, and the proximity-type charging roller 42 satisfying the above condition of the fifth embodiment can be realized. understood.

In the fifth embodiment, however, the gap Z is 19 μm.
m is not limited, and there is no problem if the relationship of | V1 | <| V2 | is satisfied even when it is larger than 19 μm. As described above, the upper limit of the gap Z is determined by measuring the relationship between the charging start voltage V1 and the gap Z in the proximity type charging roller 42 in detail, and determining the maximum Z that maintains the relationship | V1 | <| V2 | Just do it.

Therefore, if the relation of | V1 | <| V2 | is satisfied also in the proximity type charging roller 42, the following relation can be derived as in the first embodiment. That is,
Proximity type in which a predetermined charging potential is applied to the photoconductor by applying an oscillating voltage obtained by superimposing a DC voltage Vdc and an AC voltage Vac from the power supplies 11 and 12 between the photoconductor and the photoconductor (OPC 46). Charger (proximity type charging roller 4
2 and the proximity charging blade), the charging start voltage when charging the photoconductor from the proximity charger is V1, the charging start voltage when reverse discharging from the photoconductor to the proximity charger is V2,
Assuming that the peak-to-peak voltage of the AC voltage Vac is Vpp, if | V1 | <| V2 | Vpp ≧ | V2-V1 |, the charging and the reverse discharging are repeated between the OPC and the proximity charger, and Charge uniformity can be improved.

When the above oscillating voltage is applied between the proximity charger and the photosensitive member, the apparent charging potential Vss of the photosensitive member can be considered to be a value averaged over time. Vss = Vdc−0.5 × (V1 + V2) The charging roller actually manufactured in the first embodiment is used as a proximity charging roller whose distance from the OPC is set to 10 μm, and is mounted on an electrophotographic copying machine as a charging device. Was output, and the in-plane uniformity was visually evaluated. In addition,
The DC voltage Vdc is -1000V, the AC voltage Vac is a sine wave, and the peak-to-peak voltage Vpp is 400V, 700V.
V, 800 V, and 1600 V. The peak-to-peak voltage Vpp of the AC voltage Vac applied to the proximity charging roller is 400
When the voltage was set to V to 800 V, there was no change from the case where only the DC voltage Vdc was applied between the charging roller and the OPC, but when the peak-to-peak voltage Vpp was set to 1600 V, an image having improved charging uniformity was obtained. In addition, charging start voltage V
1, when V2 was measured, V1 = −320 V, V2 =
570 V, and the lower limit of the peak-to-peak voltage Vpp is 8
It was found that the voltage was about 90 V, which was in good agreement with the above result.

The AC voltage Vac that can be used in the fifth embodiment is a sine wave, a square wave,
An alternating voltage such as a sawtooth wave can be used. Further, in the fifth embodiment, the proximity type charging roller holding the carbon nanotubes on the surface has been described. However, a hetero nanotube or a carbon atom having carbon atoms including boron or suffocation as a component. Even in proximity chargers (while charging rollers, proximity blades, etc.) that hold whiskers on the surface, the electric field concentrates at the tips of hetero nanotubes and whiskers that have carbon atoms as components, and the electric field at a relatively low voltage Since the discharge occurs, the charging start voltage when charging the photoconductor from the proximity charger is V1 and the charging start voltage when reverse discharging from the photoconductor to the proximity charger is V2. By controlling the diameter, density, etc., | V1 | <| V
2 | can be satisfied, so that charging and reverse discharging are repeated between the OPC and the proximity charger by setting the peak-to-peak voltage Vpp of the AC voltage Vac applied to the proximity charger as follows. And the charging uniformity of the OPC can be improved.

Vpp ≧ | V2-V1 | FIG. 16 shows a sixth embodiment of the present invention. The image forming apparatus according to the sixth embodiment includes an OPC 49 as a photoreceptor,
A charging device 50 as a charging unit for uniformly charging the PC 49; and an exposure device 51 for forming an electrostatic latent image.
Developing device 52 that visualizes the electrostatic latent image to form a toner image
And a transfer device 54 for transferring the toner image on the OPC 49 to a recording paper 53 as a recording medium, and a static eliminator 55 for discharging the recording paper 53 and separating the recording paper 53 from the OPC 49
And a cleaning device 56 for removing the toner remaining on the OPC 49.

[0150] The transfer device 54 includes a recording medium 5 serving as a recording medium.
3 and a charge providing material 58 for supplying transfer charges to the transfer belt 57. Charging device 50
Comprises a proximity charging roller 42 according to the fifth embodiment and power supplies 11 and 12 for applying an oscillating voltage to the proximity charging roller 42. The proximity charging roller 42 includes a metal core 44, a conductive rubber 45 covering the metal core 44, and a carbon nanotube 43 held on the surface of the conductive rubber 45.

Next, the operation of the image forming apparatus will be described. The OPC 49 is rotationally driven by a driving unit (not shown), is uniformly charged to about −800 V by the charging device 50, and is subjected to raster exposure by the exposure device 51 based on an image signal. Due to this raster exposure, the charge on the OPC 49 is lost, the potential of the exposed portion on the OPC 49 is reduced from -800 V to about -40 V, and an electrostatic latent image is formed.

The OPC 49 is configured such that when a toner having a negative charge contacts the developing roller of the developing device 52, the toner does not adhere to a portion where the charge remains, and a portion having no charge, that is, an exposed portion. The toner is attracted, and a toner image similar to the electrostatic latent image is formed. The toner image on the OPC 49 is transferred onto a recording paper 53 conveyed by a transfer belt 57 that is driven at a constant speed in contact with the OPC 49, and a charge having a polarity opposite to that of the toner particles is transferred from the brush-like charge applying material 58 to the transfer belt. Transfer is performed by an electric field formed by being supplied to 57.

The recording paper 53 is sent to a fixing device (not shown) by the transfer belt 57, and the toner image is fixed by the fixing device. The brush-like charge applying material 58 is in contact with the transfer belt 57 to supply charges. Here, the toner remaining on the OPC 49 without being transferred is cleaned by the cleaning device 56. In addition, OPC4
The electric charges remaining on 9 are removed by a static eliminator (not shown).

The sixth embodiment has a process cartridge including at least an OPC 49 as a photosensitive member and a proximity charger 42, and this process cartridge can be attached to and detached from an image forming apparatus main body (a part other than the process cartridge). It is composed. Therefore, when the process cartridge is replaced, the gap between the OPC 49 as the photosensitive member and the proximity type charging roller 42 is predetermined, and | V1 | <| V2 | can be satisfied without adjusting the gap. it can. The sixth embodiment is an image forming apparatus that performs image formation by an electrophotographic process including a step of charging an OPC 49 as a photoconductor by a proximity type charging roller 42.

In the sixth embodiment, when a process cartridge is mounted on the image forming apparatus main body and an image is output, a good image is obtained. This is because the proximity charging roller 42 and the OPC 49 included in the process cartridge
The charging start voltage when charging the OPC 49 from the proximity charging roller 42 was V1, the charging starting voltage when reverse discharging from the OPC 49 to the proximity charging roller 42 was V2, and the peak-to-peak voltage of the AC voltage Vac was Vpp. In the case of | V1 | <| V2 | Vpp ≧ | V2-V1 |, it is expected that the OPC 49 could be charged more uniformly than when only the DC voltage Vdc was applied to the proximity type charging roller 42. .

As described above, in the contact-type charger of the embodiment of the present invention, the vibration voltage in which the DC voltage Vdc and the AC voltage Vac are superimposed is applied between the contact type charger and the photoreceptor. In the contact-type charger that applies a predetermined charging potential to the photoreceptor, the charging start voltage when charging the photoreceptor from the contact-type charger is V1, and the charging start voltage when reverse discharging from the photoreceptor to the contact-type charger. To V2 and the AC voltage Va
Assuming that the peak-to-peak voltage of c is Vpp, there is a relationship of | V1 | <| V2 | Vpp ≧ | V2-V1 |.

Therefore, assuming that the applied voltage between the contact type charger and the photosensitive member becomes minimum at time t2, the applied voltage becomes maximum at time t4, and the applied voltage becomes minimum again at time t6. Between the time t2 to t4 and the time t4 to t6, a time t3 at which the potential difference between the charging potential Vs of the photoconductor and the applied voltage matches the charging start voltage V2, and a potential difference between the applied voltage and the charging potential Vs of the photoconductor starts charging. There is a time t5 that matches the voltage V1.

As a result, during the period from time t3 to time t4, the potential difference between the charging potential Vs of the photosensitive member and the applied voltage becomes the charging start voltage V2
, A reverse discharge occurs from the photoconductor toward the contact type charger. On the other hand, during time t5 to t6, the potential difference between the applied voltage and the charging potential Vs of the photoconductor exceeds the charging start voltage V1, and the negative charging of the photoconductor proceeds. Therefore, on the surface of the photoconductor, charging and reverse discharge of the photoconductor are repeated in time. As a result, charging unevenness of the photoconductor can be reduced, and charging uniformity of the photoconductor can be improved.

Further, in the contact-type charger of the embodiment of the present invention, at least a nanotube having carbon atoms as a component is held on the surface in contact with the photoreceptor. Since nanotubes composed of carbon atoms are in the form of extremely thin fibers, the electric field concentrates on the tips of the nanotubes,
Nanotubes emit fields at relatively low negative voltages.
Therefore, the relationship of | V1 | <| V2 | can be realized by selecting the diameter and density of the nanotube. In addition, since nanotubes containing carbon atoms have high mechanical strength, nanotubes containing carbon atoms are not destroyed even when they slide on the photoreceptor. However, the relationship | V1 | <| V2 | is maintained.

In the contact-type charger of the embodiment of the present invention, whiskers containing at least carbon atoms are held on the surface in contact with the photosensitive member. Since whiskers containing carbon atoms as components are in the form of extremely thin fibers, an electric field is concentrated on the whisker tips, and the whiskers emit a field at a relatively low negative voltage. for that reason,
By choosing the whisker diameter, density, etc. |
The relationship of V1 | <| V2 | can be realized. In addition, since whiskers containing carbon atoms have high mechanical strength, whiskers containing carbon atoms are not destroyed even when they slide on the photoreceptor. However, the relationship | V1 | <| V2 | is maintained.

The image forming apparatus according to the embodiment of the present invention forms an image by an electrophotographic process including a step of charging a photoreceptor by the contact type charger. Therefore, the photosensitive member is uniformly charged, so that a good image can be output.

Further, the detachable process cartridge according to the embodiment of the present invention includes at least the photosensitive member and charging means for charging the photosensitive member, and the charging means is the above-mentioned contact type charger. Therefore, when the process cartridge is mounted on the image forming apparatus main body, | V1 | <| V2 |, and the peak-to-peak voltage Vpp of the AC voltage applied to the contact-type charger is set to the following voltage so that the photosensitive member can be made uniform. Can be charged.

Vpp ≧ | V2-V1 | In the proximity type charger of the embodiment of the present invention, the oscillation voltage obtained by superimposing the DC voltage Vdc and the AC voltage Vac between the photosensitive member and the photosensitive member surface. Is applied to apply a predetermined charge potential to the photoreceptor, the charging start voltage when charging the photoreceptor from the proximity type charger is V1, and when the reverse discharge is performed from the photoreceptor to the proximity type charger. Is the charging start voltage of V2 and the peak-to-peak voltage of the AC voltage Vac is V2.
pp, | V1 | <| V2 | Vpp ≧ | V2-V1 |

Therefore, assuming that the applied voltage between the proximity charger and the photosensitive member becomes minimum at time t2, the applied voltage becomes maximum at time t4, and the applied voltage becomes minimum again at time t6. Between the time t2 to t4 and the time t4 to t6, a time t3 when the potential difference between the charging potential Vs of the photoconductor and the applied voltage matches the charging start voltage V2, and a potential difference between the applied voltage and the charging potential Vs of the photoconductor is charged. There is a time t5 that coincides with the start voltage V1.

As a result, during the period from time t3 to time t4, the potential difference between the charging potential Vs of the photosensitive member and the applied voltage becomes the charging start voltage V2.
, A reverse discharge occurs from the photoconductor toward the proximity charger. On the other hand, during time t5 to t6, the potential difference between the applied voltage and the charging potential Vs of the photoconductor exceeds the charging start voltage V1, and the negative charging of the photoconductor proceeds.

Therefore, on the photosensitive member surface, charging and reverse discharge of the photosensitive member are repeated in terms of time. as a result,
Charge unevenness of the photoreceptor can be reduced, and charge uniformity of the photoreceptor can be improved.

Further, in the proximity type charger of the embodiment of the present invention, at least a nanotube having carbon atoms as a component is held on the surface in contact with the photoreceptor. Since a nanotube containing carbon atoms as a component is in an extremely fine fiber shape, an electric field is concentrated at the tip of the nanotube, and the nanotube emits a field at a relatively low negative voltage. Therefore, by appropriately selecting the diameter and density of the nanotubes and the gap between the photoconductor and the proximity charger, | V
The relationship of 1 | <| V2 | can be realized.

In the contact-type charger of the embodiment of the present invention, whiskers containing at least carbon atoms are held on the surface in contact with the photosensitive member. Since whiskers containing carbon atoms as components are in the form of extremely thin fibers, an electric field is concentrated on the whisker tips, and the whiskers emit a field at a relatively low negative voltage. for that reason,
By properly selecting the diameter and density of the whiskers and the gap between the photoconductor and the proximity charger, | V1 | <| V
2 | can be realized.

Further, in the image forming apparatus according to the embodiment of the present invention, an image is formed by an electrophotographic process including a step of charging a photosensitive member by the proximity type charger. Therefore, the photosensitive member is uniformly charged, so that a good image can be output.

Further, the detachable process cartridge according to the embodiment of the present invention includes at least the photosensitive member and charging means for charging the photosensitive member, and the charging means is the above-mentioned proximity charger. Therefore, when this process cartridge is mounted on the image forming apparatus main body, | V1 | <| V2 |
The peak-to-peak voltage Vpp of the AC voltage applied to the proximity charger
Can be charged uniformly as described below.

Vpp ≧ | V2−V1 | Further, since the proximity charger and the photosensitive member are incorporated in the process cartridge, the gap between the proximity charger and the photosensitive member can be determined in advance. As a result, the relationship | V1 | <| V2 | can be realized without adjusting the gap. Note that the present invention is not limited to the above-described embodiment, and can be applied to, for example, a charger for charging a member to be charged such as a recording medium other than the photosensitive member.

[0172]

As described above, according to the first aspect of the present invention, the charging unevenness of the member to be charged can be reduced, and the charging uniformity of the member to be charged can be improved. According to the invention of claim 2, |
The relationship of V1 | <| V2 | can be realized, and the relationship of | V1 | <| V2 | can be maintained even during long-term use. According to the third aspect of the present invention, the relationship of | V1 | <| V2 | can be realized, and | V1 | <| V2 even in long-term use.
| Relationship can be maintained.

According to the fourth aspect of the present invention, the photosensitive member can be uniformly charged, and a good image can be output. According to the fifth aspect of the present invention, the photoconductor can be uniformly charged. According to the invention of claim 6, it is possible to reduce charging unevenness of the member to be charged and to improve charging uniformity of the member to be charged.

According to the seventh aspect of the invention, | V1 | <
| V2 | can be realized. According to the invention of claim 8, it is possible to realize the relationship | V1 | <| V2 |. According to the ninth aspect, a good image can be output. According to the tenth aspect, the photoconductor can be uniformly charged, and the relationship | V1 | <| V2 | can be realized without adjusting the gap with the photoconductor.

[Brief description of the drawings]

FIG. 1 is a sectional view showing Embodiment 1 of the present invention.

FIG. 2 shows a DC voltage Vd applied to a charging roller when a sine wave is used as the AC voltage Vac in the first embodiment.
c is a characteristic diagram showing a change over time of the applied voltage (Vdc + Vac) and the charging potential Vs of the OPC.

FIG. 3 is a graph showing a change in DC voltage Vdc applied to a contact-type charging roller, a change in applied voltage (Vdc + Vac), a change in OPC charging potential Vs with time, and an apparent OPC in the first embodiment when a sine wave is used as AC voltage Vac. FIG. 4 is a characteristic diagram illustrating a charging potential Vss.

FIG. 4 is a diagram showing a temporal change of a DC voltage Vdc, an applied voltage (Vdc + Vac), and a charging potential Vs under a simulation condition A of the first embodiment.

FIG. 5 is a diagram showing a temporal change of a DC voltage Vdc, an applied voltage (Vdc + Vac), and a charging potential Vs under a simulation condition B of the first embodiment.

FIG. 6 is a diagram illustrating a temporal change of a DC voltage Vdc, an applied voltage (Vdc + Vac), and a charging potential Vs under a simulation condition C of the first embodiment.

FIG. 7 is a diagram showing a time change of a DC voltage Vdc, an applied voltage (Vdc + Vac), and a charging potential Vs under a simulation condition D of the first embodiment.

FIG. 8 is a sectional view showing another embodiment 2 of the present invention.

FIG. 9 is a diagram showing a time change of a DC voltage Vdc, an applied voltage (Vdc + Vac), and a charging potential Vs under a simulation condition E of the second embodiment.

FIG. 10 is a diagram showing a time change of a DC voltage Vdc, an applied voltage (Vdc + Vac), and a charging potential Vs under a simulation condition F of the second embodiment.

FIG. 11 is a diagram showing a time change of a DC voltage Vdc, an applied voltage (Vdc + Vac), and a charging potential Vs under a simulation condition G of the second embodiment.

FIG. 12 is a sectional view showing another embodiment 3 of the present invention.

FIG. 13 is a sectional view showing Embodiment 4 of the present invention.

FIG. 14 is a sectional view showing Embodiment 5 of the present invention.

FIG. 15 is a characteristic diagram illustrating a relationship between a gap between a proximity type charging roller and an OPC and a charging start voltage V2.

FIG. 16 is a sectional view showing Embodiment 6 of the present invention.

FIG. 17 is a characteristic diagram illustrating an example of a charging potential of a photoconductor when a DC voltage is applied between a charging roller and a photoconductor in a roller charging method.

FIG. 18 is a diagram for explaining the principle of the AC charging system.

FIG. 19 is a cross-sectional view illustrating an example of a contact-type charger holding carbon nanotubes.

FIG. 20 is a characteristic diagram illustrating a relationship between an applied voltage between a charging roller holding carbon nanotubes and an OPC and a charging potential of the OPC.

[Explanation of symbols]

 Reference Signs List 9 contact charging roller 10 carbon nanotube 11 DC power supply 12 AC power supply 18 contact charging blade 20 carbon whisker 25 contact charging film 27 hetero nanotube 32 OPC 33, 50 charger 34, 51 exposure device 35, 52 developing device 36, 53 Recording paper 37, 54 Transfer device 38, 55 Static eliminator 39, 56 Cleaning device 42 Proximity type charging roller 43 Carbon nanotube

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yukie Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. HB47 HB48 LC03 LC08 MA03 MA14 MA20 MB01 MC16 NA06 NA09

Claims (10)

[Claims] 1. A predetermined charging potential is applied to a member to be charged by contacting the surface of the member to be charged and applying an oscillating voltage obtained by superimposing a DC voltage Vdc and an AC voltage Vac between the member and the member to be charged. In the contact type charger, the charging start voltage when charging the charged object from the contact type charger is V1,
When the charging start voltage at the time of reverse discharge from the charged body to the contact type charger is V2 and the peak-to-peak voltage of the AC voltage Vac is Vpp, | V1 | <| V2 | Vpp ≧ | V2-V1 | The contact type charger characterized by satisfying the following relationship. 2. The contact-type charger according to claim 1, wherein a nanotube having at least carbon atoms as a component is held on a surface in contact with the member to be charged. 3. The contact-type charger according to claim 1, wherein a whisker having at least carbon atoms as a component is held on a surface in contact with the member to be charged. 4. An image forming apparatus for performing image formation by an electrophotographic process including a step of charging a photoreceptor by a charger, wherein said charger is a contact-type charging device according to claim 1. An image forming apparatus comprising a container. 5. A process cartridge detachably mountable to an image forming apparatus main body for performing image formation by applying an electrophotographic process including a step of charging a photosensitive member, wherein at least the photosensitive member and the photosensitive member are charged. A process cartridge, comprising: a charging unit that performs charging, wherein the charging unit is the contact-type charger according to claim 1. 6. A predetermined charging potential is applied to the member to be charged by applying an oscillating voltage obtained by superimposing a DC voltage Vdc and an AC voltage Vac between the member and the member to be charged. In the proximity charger, the charging start voltage when charging the charged object from the proximity charger is V1,
When a charging start voltage when the object to be charged is reversely discharged to the proximity type charger is V2, and a peak-to-peak voltage of the AC voltage Vac is Vpp, | V1 | <| V2 | Vpp ≧ | V2-V1 | A proximity charger characterized by satisfying the following relationship: 7. The proximity-type charger according to claim 6, wherein a nanotube having at least carbon atoms as a component is held on a surface adjacent to the object to be charged. 8. The proximity charging device according to claim 6, wherein a whisker having at least carbon atoms as a component is held on a surface adjacent to the member to be charged. 9. An image forming apparatus for performing image formation by an electrophotographic process including a step of charging a photoreceptor by a charger, wherein said charger is a proximity-type charging device according to claim 6. An image forming apparatus comprising a container. 10. A process cartridge detachably mountable to an image forming apparatus main body for performing image formation by applying an electrophotographic process including a step of charging a photosensitive member, wherein at least the photosensitive member and the photosensitive member are charged. A process cartridge, comprising: a charging unit that performs charging, wherein the charging unit is the proximity type charging device according to claim 6.