JPH10115968A - Electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of electrification unevenness even though the distance is made >=0.1mm on a section where an electrification member comes nearest to an photoreceptor. SOLUTION: This device is capable of preventing a leak caused by a pin hole on the photoreceptor 1 by composing an outside layer part 2b, on the electrification member 2 opposing corresponding to the photoreceptor 1 in a state that the electrification surface 2c is held in non-contact therewith, of a material provided with conductivity in adding ionized compound while making the layer provided with medium resistance. In the case the outside layer part 2b is composed by the above material, the electrification unevenness becomes liable to occur, when the electrification member 2 is arranged apart from the photoreceptor 1, however an area in which the electrification occurs is made so as not to flare on the part coated by an insulating material by partially coating the electrification surface 2c, and making the area of the coated part beyond 70% corresponding to the whole area of the electrification surface 2c. In such a manner, the gap between the electrification member 2 and the photoreceptor 1 can be made >=0.1mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as an electrostatic copying machine or a laser printer has a corona charging device such as a scorotron or a charging member directly contacting a photosensitive member to be charged. There is a contact charging device that performs charging. The former corona charging device has a drawback that the amount of generated ozone is large and the applied voltage is large, for example, 5 to 7 KV. The latter contact charging device can improve the above-mentioned disadvantages of the corona charging device, and has recently been widely used in low-speed and medium-speed electrophotographic image forming device charging devices.

FIG. 7 shows an example of the contact charging device. The contact charging device includes a photosensitive member 51 that is a member to be charged, and a charging roller 52 that is a charging member.
1 is rotated in the direction indicated by the arrow A so that the charging roller 52 rotates in the direction indicated by the arrow B along with the photosensitive member 51. 51 is charged. The applied voltage is, for example, -1.5 to -2.0 KV in direct current.

The charging roller 52 has a diameter of, for example, 5 to 20.
mm and a roller formed to have a length of about 300 mm in the axial direction, and has an elastic layer 52b formed on the surface of the conductor 52a. The elastic layer 52b has a resistivity of 10 ⁷ to 10 ^9.
It is formed of a material of Ωcm. And the elastic layer 5
In some cases, a surface protective layer having a thickness of about 10 to 20 μm is formed on the surface of 2b. Also, the photoconductor 51
Is formed in a drum shape having a diameter of 30 to 80 mm and a length of about 300 mm, and a photosensitive layer 51 is formed on the surface of the conductor 51a.
b is formed.

[0005] The contact charging device configured as described above has the advantages described above as compared with the corona charging device.
Since the charging member (charging roller) is configured to be in contact with the photoconductor, there are the following disadvantages. 1. There is a reduction in charging performance caused by the transfer of deposits such as toner attached to the surface of the photoreceptor to the surface of the charging member. 2. In some cases, the material constituting the charging member oozes out on the surface and adheres to the surface of the photoreceptor, thereby staining the photoreceptor. 3. When the charging member is left in contact with the surface of the photoconductor for a long time, the elastic layer of the charging member undergoes permanent deformation.

Therefore, in order to solve such a problem, a proximity charging device has been proposed in which a charging member is arranged in a position where the charging member does not come into contact with the photosensitive member but comes close to the photosensitive member (for example, Japanese Patent Publication No. Hei 6 (1994)). -90568, JP-A-7-3
01973). Such a proximity charging device,
At a position where the charging member comes closest to the photoconductor, the distance between them is set to be 0.005 to 0.30 mm, and the photoconductor is charged by applying a voltage to the charging member in this state.

In this proximity charging device, since the charging member is not brought into contact with the photoreceptor, as described in the case of the contact charging device, the "adhesion of the substance constituting the charging member to the photoreceptor" or the " The problem of "permanent deformation of the elastic layer of the charging member when left for a long time" can be solved. In addition, since the amount of transfer of the adhered matter such as toner adhered to the surface of the photoreceptor to the charging member is reduced, the deterioration of the charging performance caused thereby is almost eliminated.

FIG. 8 shows an example of a conventional proximity charging device. In this proximity charging device, the roller-shaped charging member 62 has an outer diameter of 5 to 20 mm and an axial length of about 300 mm.
mm. The charging member 62 has a resistance layer 62b formed on the surface of the conductor portion 62a. The resistance layer 62b
Is formed of a material having a resistivity of 10 ⁷ to 10 ⁹ Ωcm. The photoreceptor 61 is formed in a drum shape having a diameter of 30 to 80 mm and a length of about 300 mm.
A photosensitive layer 61b is formed on the surface of 1a.

The charging member 62 may or may not be rotated. Then, at a position where the charging member 62 comes closest to the photoconductor 61, the charging member 62 is opposed to the photosensitive member 61 so that the distance therebetween becomes 0.005 to 0.30 mm. A voltage of up to -5 KV is applied to the photosensitive member 61.
Is charged.

[0010]

In such a proximity charging device, the distance between the charging member and the photoconductor at the position where the charging member is closest to the photoconductor is important. That is, when the distance between the charging member and the photoconductor becomes large, there is a problem that the charging unevenness occurs accordingly. Therefore, in the case where the charging member is formed using a material having conductivity by adding an ionic compound, the charging member is at least 0.1 mm from the surface of the photoreceptor in spite of being a close proximity charging device. There was a problem that the advantage as a proximity charging device was reduced because it could not be located at a distant position.

Hereinafter, this point will be described in detail. FIG. 9 is a diagram showing a voltage Vth at which a discharge occurs between the charging member and the photoconductor when a voltage is applied to the charging member, and the surface of the photoconductor starts to be charged. This voltage Vth depends on the distance between the charging member and the photoconductor at the closest part thereof. That is,
The voltage Vth depends on the distance between the charging member and the photosensitive member at the closest part between the charging member and the photosensitive member according to the so-called Paschen's law, assuming that the charging member and the photosensitive member are a pair of electrodes facing each other in parallel. .

As the distance between the charging member and the photoreceptor is increased, the surface of the photoreceptor is not uniformly charged, and so-called charging unevenness occurs. When the charging unevenness occurs, the potential of the surface of the photoconductor increases or decreases depending on the location. Since the pitch (spatial period) of the charging unevenness appearing in the proximity charging device is as small as about 0.1 to 1.0 mm, such a small charging unevenness is averaged in a normal surface voltmeter having a spatial resolution of about 5 mm. Therefore, it cannot be detected.

Therefore, as far as measured by the surface voltmeter, a linear relationship having a slope of 1 is established between the applied voltage and the surface potential of the photosensitive member as shown in FIG. 9, and the photosensitive member is uniformly charged. Observed as if. However,
When a photosensitive member is actually charged using a proximity charging device and an image is formed on the charged surface, spot-like charging unevenness appears on the image. Further, when reversal development (negative / positive) is performed, toner adheres to a white background portion, or a portion of the black background portion where toner adheres little is formed.

Also in such a proximity charging device, in order to prevent a so-called leak caused by a pinhole on the photoreceptor, the material of the charging member is made of a material similar to that of the contact charging device. Is 10 ⁷ to 10 ⁹ Ωc
It is preferable to use one having a medium resistance within the range of m. As described above, in order to prepare a material having a resistivity of 10 ⁷ to 10 ⁹ Ωcm, for example, a method of adding an ionic compound (a material for making ionic conductive) to a polymer material such as a resin or a rubber, And a method of dispersing carbon (a material for making it electrically conductive) in the above polymer material.

However, when such an ionic conductive material or an electronic conductive material is used for a charging member of a proximity charging device, the following problems arise. <When the charging member is formed of a material having ionic conductivity> When the distance between the charging member and the photoconductor is increased, fine charging unevenness that cannot be detected by a surface voltmeter is likely to occur. Therefore, when the distance at the portion where the charging member comes closest to the photoconductor becomes 0.1 mm or more, charging unevenness clearly appears on the image.

Therefore, when the charging member is formed of a material having ionic conductivity, the distance between the charging member and the photosensitive member at the portion closest to the photosensitive member cannot be made 0.1 mm or more. There is a problem that the advantage as an apparatus is reduced. Therefore, when mechanical vibration is applied to the charging member or the photoconductor, the charging member and the photoconductor come into contact with each other, so that the toner on the photoconductor side adheres to the surface of the charging member, and is easily stained.

<When the charging member is formed of an electronic conductive material> When an electronic conductive material is used, there is a problem that it is difficult to control the dispersion of a conductive material such as carbon. Therefore, the resistance tends to be different for each location of the charging member. As a result, there arises a problem that the potential of the surface of the photoconductor varies when charging is performed due to the variation in resistance of the charging member. In addition, when a material having electronic conductivity is used, there is also a problem that when an applied voltage exceeds a certain value, a current easily flows rapidly due to dielectric breakdown. This problem is particularly important in proximity charging devices.

That is, generally, in the case of the proximity charging device, it is necessary to increase the applied voltage as compared with the case of the contact charging device. Specifically, every time the distance at the portion where the charging member comes closest to the photoconductor increases by 0.1 mm, about 5 mm
The applied voltage of 00V must be increased. Therefore, when the charging member of the proximity charging device is formed of a material having electronic conductivity, leakage due to pinholes or the like on the photoconductor is more likely to occur than in the case of the contact charging device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a medium resistance by forming a charging member from a material having ionic conductivity, so that a portion where the charging member comes closest to the photoreceptor is provided. It is an object of the present invention to prevent charging unevenness from occurring even if the distance therebetween is 0.1 mm or more.

[0020]

According to the present invention, in order to achieve the above object, a charging surface of a charging member faces a surface to be charged of a member to be charged in a non-contact state, and a voltage is applied to the charging member. In a charging device that charges the surface to be charged by causing a direct discharge between the surface to be charged and the surface to be charged by applying, an ionic compound is added to at least a part of the surface of the charging member that becomes a surface to be charged. The charged surface is partially covered with an insulating material, and the area of the portion covered with the insulating material is set to 70% or more of the total area of the charged surface. In addition, the distance between the charged surface and the charged surface is set to 0.1 mm or more at the position where they are closest to each other.

The insulating material has a resistivity of 10 ¹⁰ Ω.
cm or more, and the relative permittivity is preferably 5 or less. Further, the charging surface of the charging member may have a surface roughness of 10 μm or less as a 10-point average roughness. The insulating material has a dielectric breakdown resistance of 10 ⁸ V /
m or more.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a charging device according to the present invention, and FIG. 2 is a schematic diagram showing the periphery of an image forming unit of an image forming apparatus provided with the charging device. The image forming apparatus shown in FIG. 2 shows the vicinity of an image forming unit. The image forming apparatus includes a roller-shaped charging member 2 that charges a drum-shaped photosensitive member 1 in a non-contact state. By applying a voltage from the power supply 3 to the conductor portion 2a, the surface to be charged of the photoconductor 1 is uniformly charged to a predetermined potential.

The photosensitive member 1 has a diameter of, for example, 30 to 80.
The photosensitive layer 1b is formed on the outside of the conductor 1a as shown in FIG. 1, and is formed by a drum driving timing belt and a drum driving pulley (both shown in FIG. 1). ) Is rotated in the direction of arrow C by a motor that is rotationally driven through As shown in FIG. 2, a developing device 6, a transfer roller 7 constituting a transfer device, and a cleaning unit 8 are provided around the photoreceptor 1 as shown in FIG. From the photosensitive member 1 is incident on the surface of the photoreceptor 1, and the charging member 2
The surface of the photoreceptor 1 uniformly charged by the exposure is exposed to form an electrostatic latent image thereon, which is developed with toner supplied by a developing sleeve 6a of the developing device 6 to form a toner image (visible image). ).

On the other hand, the transfer paper P, which is a paper housed in a paper feed cassette (not shown), is sent out one by one by a paper feed roller rotating at a predetermined timing, and the paper is pressed against the registration roller 13. After being temporarily stopped between the rotating pressure roller 14 and timing adjustment, the sheet is conveyed toward the transfer section provided with the transfer roller 7 at an accurate timing coincident with the toner image on the photoconductor 1. .

The transfer sheet P has a toner image transferred to the upper surface side in FIG. 2 and is separated from the photoreceptor 1 and is conveyed to a fixing device (not shown). It is discharged to a tray or the like. After the transfer is completed, foreign matters such as residual toner and paper dust remaining on the photoconductor 1 are removed by a cleaning blade 8a provided in the cleaning unit 8, and the residual potential remaining on the photoconductor 1 is not shown. It is removed by the charge removing lamp to prepare for the next charging by the charging member 2.

As shown in FIG. 1, the charging member 2 has an outer layer 2b integrally mounted on the outside of a conductor (conductive core) 2a serving as a shaft made of, for example, stainless steel (SUS). is there. Then, the thickness of the outer layer portion 2b is set to 1
５5 mm. The roller-shaped charging member 2 has an outer diameter (diameter) of 5 to 20 mm and an axial length of about 300 mm.

The outer layer 2b is made of a so-called ionic conductive material which is made conductive by adding an ionic compound such as a halide or an alkali metal salt to various polymer materials such as rubber and resin. It is formed. Specifically, epichlorohydrin rubber, urethane,
Thermoplastic extomers and the like. The charging surface 2c on the surface of the outer layer portion 2b is partially covered with an insulating material, as will be described in detail later. Here, the charging surface 2 c refers to a portion of the entire surface of the charging member 2 which faces the photoconductor 1 and is used for charging the photoconductor 1.

As shown in the schematic diagram of FIG. 3, the charged surface 2c has a portion 4 covered by an insulating material (a portion shown by hatching) and a portion 5 not covered by the insulating material (a portion shown by white). And formed. The proportion of the area of the portion 4 covered with the insulating material occupies 70% or more of the entire area of the charged surface 2c. Further, the portions 5 not covered with the insulating material are arranged so as to be substantially uniformly dispersed on the charging surface 2c shown in FIG. The size (maximum diameter portion) of each uncoated portion 5
Is desirably 0.1 to 0.01 mm.

As the insulating material used for the portion 4 covered with the insulating material, any material can be used as long as it can prevent discharge from occurring directly from the charging member 2 to the photosensitive member 1. You may. For example, various insulating polymer materials such as polycarbonate, polyamide, fluororesin, and silicone resin, as well as insulating metal oxides such as ceramics may be used.

As a method for coating the charged surface 2c of the charging member 2 with the insulating material, for example, a method by spraying, printing, vapor deposition, thermal spraying, etc., the charged surface 2c is coated with the insulating material as shown in FIG. Any method may be used as long as the portion 4 and the portion 5 not covered with the insulating material can be formed. In this way,
The charging member 2 having the charging surface 2c formed on the surface of the roller is adjusted so that the distance L between the charging member 2 and the photosensitive member 1 is 0.1 mm or more at a position (closest point) closest to the photosensitive member 1 as shown in FIG. A voltage can be applied thereto by the power supply 3. When charging the photosensitive member 1 by the charging member 2, a DC voltage of −2 to −5 KV is applied from the power supply 3 to the charging member 2.

The charging member 2 is rotatable in a state where the closest portion to the photosensitive member 1 is kept at a position separated by 0.1 mm or more.
The shaft portions formed at both ends of the conductor portion 2a are rotatably supported by bearings, and charging is performed while rotating the shaft portions by a motor (not shown) or the like. However, the rotation may not be performed. When the charging member 2 is rotated in this way, the charging surface 2c used for discharging between the charging member 2 and the photoconductor 1 can be relatively large. This is advantageous in that the life of the charging member 2 is extended as compared with the case where the charging member 2 is not rotated.

In the proximity charging device constructed as described above, the outer layer 2b of the charging member 2 is formed of an ionic conductive material. No problem. That is, since the resistance differs for each location of the charging member, it is possible to prevent the resistance of the charging member from varying and the potential on the surface of the photoconductor from varying when charging is performed.

Further, when a material for electronic conductivity is used for the charging member, when the applied voltage exceeds a certain value, there is a disadvantage that a current easily flows rapidly due to dielectric breakdown.
Further, in the case of a proximity charging device, it is generally necessary to increase the applied voltage as compared with the case of a contact charging device. For this reason, when a material having an electronic conductivity is used for the charging member, the distance of the portion where the charging member comes closest to the photoconductor increases by about 500 mm every time the distance increases by 0.1 mm.
Since the V applied voltage must be increased, in the case of such a proximity charging device, a leak due to a pinhole or the like on the photosensitive member is more likely to occur than in the case of the contact charging device. By using an ionic conductive material for the outer layer portion 2b of the charging member 2, it can be prevented.

Even when an ionic conductive material is used for the charging member, if the charging member is arranged at a position closest to the photosensitive member and separated by more than 0.1 mm, it cannot be detected by the surface voltmeter. Fine charging unevenness is likely to occur, and the charging unevenness may clearly appear on an image. However, in the proximity-type charging device according to the present invention, as described with reference to FIG. 3, the charging surface 2c of the charging member 2 is covered with an insulating material covering an area of 70% or more of the entire area with the insulating material. The above-mentioned problem is solved by making the other part a part 5 which is not covered with the insulating material, whereby the charging member 2 is moved to the photosensitive member 1 at a position closest to the photosensitive member 1. It can be arranged at a distance of 0.1 mm or more from 1.

The reason why the charging surface 2c is configured so that charging unevenness does not occur even when the charging member 2 is separated from the photosensitive member 1 by 0.1 mm or more will be described below. For example, if the charging layer of the charging member is simply formed of an ionic conductive material without any ingenuity,
Fine charging unevenness (hereinafter, referred to as fine charging unevenness) that cannot be detected by the surface voltmeter easily occurs.
The reason why the fine charging unevenness is likely to occur is as follows.
The following can be considered.

In the ionic conductive material, it is considered that ions such as halides and alkali metal salts which transfer electric charges are uniformly dispersed in the insulating polymer. That is, the distance between the individual ions is about the same as the size of the molecule. Therefore, discharge can occur between the charging member and the photoconductor at any location on the surface of the charging member.

That is, on the surface of the charging member in which the ions are dispersed in the same order of magnitude as the size of the molecule, there are places where discharge is likely to occur and places where discharge is unlikely to occur at the same interval as the size of the molecule. doing. Thus, because of the very fine pitch, discharge can occur anywhere on the surface of the charging member.

In such a case, when a discharge occurs between a charging member and a photosensitive member starting from a certain place, it is considered that the discharge easily spreads around the starting point. That is, since the discharge spreads along the surface of the charging member, the range in which the discharge is performed is widened. In this case, the amount of charge that moves from the charging member to the photosensitive member by one discharge increases, and as a result, fine charging unevenness occurs.

On the other hand, in the charging member 2 of the proximity charging device described with reference to FIG. 1, the outer layer portion 2b is formed of an ionic conductive material.
As described in the above, the discharge between the charging surface 2c of the charging member 2 and the photoreceptor 1 does not occur in the portion 4 covered with the insulating material, but the discharge occurs between the charging surface 2c of the charging member 2 and the insulating material. Occurs only in the uncoated part 5. Therefore, the range in which the discharge occurs is limited to the portion 5 not covered with the insulating material, and does not extend to the portion 4 covered with the insulating material.

Since the area ratio of the portion 4 covered with the insulating material is 70% or more of the total surface area of the charging surface 2c, the charging layer of the charging member is simply formed of the ionic conductive material. As a result, the range of discharge is not widened as compared with the case where a portion covered with an insulating material is not formed on the surface. Therefore, since the amount of electric charge moving from the charging member 2 to the photoconductor 1 does not become so large, it is possible to prevent the occurrence of fine charging unevenness.

As described above, according to the proximity charging device using the charging member 2, the outer layer 2b of the charging member 2 is formed of the ionic conductive material, and the charging member 2 is
Even if the charging member 2 is set at a position (closest point) closest to the photosensitive member 1 at a distance of 0.1 mm or more from the photosensitive member 1, fine charging unevenness can be prevented. Therefore, a good image can be obtained.

FIG. 4 is a schematic structural view similar to FIG. 1 showing an embodiment of a proximity charging device in which a charging member is formed in a belt shape, and portions corresponding to FIG. 1 are denoted by the same reference numerals. . This proximity charging device is provided with a belt-shaped charging member 12 which is stretched between rollers 15 and 16 and rotates. The charging member 12 has an outer layer portion 12b formed on the surface of a conductor portion 12a, and an ionic conductive material which is made conductive by adding an ionic compound (the embodiment described with reference to FIG. 1). And the outer layer 1
2b. Then, the distance between the charging member 12 and the photoconductor 1 is set to 0.
It is 1 mm or more.

The charging surface 12c of the charging member 12
Also, 70% or more of the entire surface area is a portion covered with an insulating material, and the other portion is a portion not covered with an insulating material. As described above, even when a belt-shaped charging member 12 is used, the same operation and effect as those of the proximity charging device of FIG. 1 are obtained.

As shown in FIG. 5, the charging member 22 is formed in a blade shape, and the charging member 22 is connected to the conductor 22a.
May be formed by forming an outer layer portion 22b on the surface of the substrate. Even in this case, the outer layer 2
2b is formed of an ionic conductive material similarly to the embodiment of FIGS. Then, the distance between the charging member 22 and the photoconductor 1 is set to 0.
It is 1 mm or more. In the charging member 22, 70% or more of the entire surface area of the charging surface 22c is covered with an insulating material, and the other portions are not covered with the insulating material. As described above, even if the charging member 22 is formed in a blade shape, the same operation and effect as those of the proximity charging device of FIGS.

FIG. 6 is a schematic structural view similar to FIG. 1 showing an example of a proximity charging device using a charging member in which the outer layer portion is composed of a plurality of layers having different resistivity. Parts are given the same reference numerals. The charging member 32 used in this proximity charging device includes an outer layer portion formed outside the conductor portion 32a and a first member having three different resistances.
It is composed of a layer 32b, a second layer 32c and a third layer 33d. Then, the first layer 32b, the second layer 32c and the third
All of the layer 33d is formed of the ionic conductive material described above.

The distance between the charging member 32 and the photosensitive member 1 is set to 0.1 mm or more at the position where they are closest. The charging member 32 covers the charging surface 32e, which is the surface of the outermost first layer 32b, with an insulating material covering 70% or more of the entire surface area, and the other portions are coated with an insulating material. The part is not covered. Even in this case, the same operation and effect as those of the proximity charging device of FIG. 1 can be obtained.

In each of the above embodiments, each of the charging surfaces 2c, 1 of the charging members 2, 12, 22, and 32 respectively.
As the insulating material covering 70% or more of each of 2c, 22c and 32e, a material having a resistivity of 10 ¹⁰ Ωcm or more is preferably used. Thus, the insulating material has a resistivity of 10 ¹⁰ Ωc
By using a material having a length of m or more, the spread of discharge can be suppressed, and thus charging unevenness can be prevented.

According to the experimental results, it was confirmed that the resistivity of the insulating material was different from that of the insulating material for partially covering the surface of the charging member for insulation. As a result, the resistivity of the insulating material was 10 ¹⁰ Ω.
When it was smaller than 1.0 cm, uneven charging became noticeable. This is considered to be because when the resistivity is smaller than 10 ¹⁰ Ωcm, the discharge occurring between the charged surface and the photoreceptor spreads to the portion where the surface is covered with the insulating material.

On the other hand, the resistivity of the insulating material is set to 10 ¹⁰ Ω.
cm or more, charging unevenness hardly caused a problem. Therefore, in general, the resistivity is 10 ¹² Ωc
m or more is considered an insulating material,
In the proximity-type charging device according to the present invention, it is sufficient if the resistivity of the insulating material is 10 ¹⁰ Ωcm or more, so that the charging device has a high degree of freedom because the material can be selected in a wide range.

Examples of the insulating material include various insulating polymer materials such as polycarbonate, polyamide, fluorine resin, and silicone resin, and insulating metal oxides such as ceramics, and various insulating materials such as chloroprene and silicone. Rubber may be used. Further, even if the insulating material is various kinds of glass, various kinds of plastics such as acrylic, epoxy, polyvinyl chloride, Teflon, nylon, polyethylene, polystyrene, and other materials, even if the resistivity is 10 ¹⁰ Ωcm or more. If so, it does not matter. However, since a high voltage of -2 to -5 KV is applied as a direct current from a power source to the conductor portion of the charging member, the above resistivity is maintained at 10 ¹⁰ Ωcm or more under actual use conditions. It is necessary.

Further, it is preferable that the insulating material has a relative dielectric constant of 5 or less. In this case, as the insulating material, in addition to various insulating polymer materials such as polycarbonate, polyamide, fluororesin, and silicone resin, insulating metal oxides such as ceramics may be used. Of course, other materials may be used. However, any material having a relative dielectric constant of 5 or less may be used.

According to the results of the experiment, when the relative dielectric constant of the used insulating material was 5 or less, no charging unevenness that could be visually confirmed was generated. On the other hand, when the relative dielectric constant of the insulating material was larger than 5, uneven charging was noticeable. This is presumably because the manner in which the discharge spreads between the charged surface and the photoconductor varies depending on the material covering the surface. That is, it is considered that the magnitude of the rise in the potential of the charged surface differs depending on the material that covers the surface of the charging member, and the stop of the discharge is different. As described above, by setting the relative dielectric constant of the insulating material covering the surface of the charging member to 5 or less, the charging unevenness can be reduced as compared with the charging member using the insulating material having the relative dielectric constant larger than 5. Is less likely to occur.

Further, the surface roughness of the charging surface of the charging member is preferably set to 10 μm or less in terms of 10-point average roughness. As a method of making the charged surface of the charging member such a surface roughness, for example, the charged surface of the surface of the charging member formed of an ionic conductive material is 10 μm or less in 10-point average roughness by polishing or grinding. I do. Then, the above-mentioned insulating material is attached thereon by spraying, printing, vapor deposition, thermal spraying, etc.
Even if other methods are used, any method may be used as long as the surface property of the charged surface can be reduced to 10 μm or less in terms of 10-point average roughness.

If the surface roughness of the charged surface of the charging member is set to 10 μm or less in terms of the 10-point average roughness as described above, variations in the surface potential of the photoconductor at the time of charging due to unevenness of the charged surface may cause problems in practical use. It can be reduced to a level without any.
Further, the insulating material preferably has a dielectric breakdown resistance (dielectric breakdown field) of 10 ⁸ V / m or more. In this case,
As the insulating material, vinyl chloride, polystyrene, glass or the like may be used. Of course, other materials may be used as long as they have a dielectric breakdown resistance of 10 ⁸ V / m or more.

As described above, if an insulating material having a set dielectric breakdown resistance is used for the charging surface of the charging member, the insulating property of the insulating material is destroyed even when a high voltage is applied to the charging member. Therefore, it is possible to prevent the occurrence of fine charging unevenness as described above. Further, even when the thickness of the insulating material is reduced to about 10 μm, the insulating property is not destroyed, so that the surface roughness of the charged surface of the charging member is easily reduced to 10 μm or less in terms of 10-point average roughness. As a result, the variation in the surface potential of the photoconductor at the time of charging can be reduced to a level at which there is no problem in practical use.

[0056]

As described above, according to the present invention, the charging member is made of an ionic conductive material to have a medium resistance, and the charging member is closest to the photoreceptor at the portion where the charging member is closest to the photosensitive member. Even when the distance is set to 0.1 mm or more, the spread of discharge can be limited by partially covering the surface of the charging member with an insulating material. The substance constituting the charging member can be prevented from adhering to the photoreceptor, and the charging member can be prevented from being permanently deformed when left for a long time.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram showing the periphery of an image forming unit of an image forming apparatus provided with the charging device.

FIG. 3 is a schematic diagram schematically showing a charging member provided in the charging device and a charging surface thereof.

FIG. 4 is a schematic configuration diagram similar to FIG. 1, showing an embodiment of a proximity charging device in which a charging member is formed in a belt shape.

FIG. 5 is a schematic configuration diagram showing an embodiment in which a charging member is formed in a blade shape and an outer layer formed on the surface thereof is formed of an ionic conductive material.

FIG. 6 is a schematic configuration diagram similar to FIG. 1 showing an example of a proximity charging device using a charging member in which an outer layer portion is configured by a plurality of layers having different resistivity.

FIG. 7 is a schematic configuration diagram illustrating an example of a conventional contact charging device.

FIG. 8 is a schematic configuration diagram illustrating an example of a conventional proximity charging device.

FIG. 9 is a diagram illustrating a relationship between an applied voltage and a surface potential of a photoconductor in a proximity charging device.

[Explanation of symbols]

1: Photoconductor (charged body) 1b: Photosensitive layer (charged surface) 2, 12, 22, 32: Charging member 2c, 12c, 22c, 32e: Charging surface 4: Portion covered with insulating material 5: Insulating material Part not covered with

Claims (5)

[Claims] 1. A charging member faces a charging surface of a member to be charged in a non-contact state, and a voltage is applied to the charging member so that a voltage is applied between the charging surface and the charging surface. In the charging device for charging the surface to be charged by causing direct discharge in, at least a portion of the charging member to be a charged surface of the surface is formed of a material having conductivity by adding an ionic compound, The charged surface is partially covered with an insulating material, the area of the portion covered with the insulating material is 70% or more of the total area of the charged surface, and the distance between the charged surface and the charged surface is At the location where they are closest.
A charging device having a thickness of 1 mm or more. 2. The insulating material has a resistivity of 10 ¹⁰ Ωcm.
The charging device according to claim 1, wherein: 3. The charging device according to claim 1, wherein the insulating material has a relative dielectric constant of 5 or less. 4. A charging surface of the charging member has a surface roughness of 1
2. The charging device according to claim 1, wherein the zero point average roughness is 10 [mu] m or less. 5. The insulating material has a dielectric breakdown resistance of 10 ^8.
The charging device according to claim 1, wherein the charging device is not less than V / m.