JP2004029114A - Contact charger and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact charger which prevents a body to be charged from being charged ununiformly also decreases wear of the body to be charged, and also to provide an image forming apparatus which avoids an image quality defect, as in the form of a white streak, and ununiform image quality. <P>SOLUTION: The contact charger which comes into contact with a moving body 5 to be charged and charges the body 5 comprises: a charging member 10 in the form of a cylinder or endless belt, which has a pressure-sensitive, anisotropic and conductive layer which decreases in electric resistance with pressure and an anisotropic conductive layer overlaied further outside than the pressure-sensitive anisotropic and conductive layer and made anisotropic in the direction of its thickness; a conductive roll 11 which stretches the charging member 10 and brings the charging member into contact with the conductive roll 11; and a stretch roll 12 which stretches the charging member 10 upward at an angle in the direction of the movement of the body 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a contact charger for charging a member to be charged by contact, and an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, and the like using the contact charger.
[0002]
[Prior art]
Conventionally, a corotron has been widely used as a charger for charging an image carrier. However, a corotron is effective as a means for uniformly charging the image carrier, but requires a high-voltage power supply for applying a voltage to the corotron in order to charge the image carrier to a predetermined potential. Further, since ozone is generated by the corona discharge, not only the deterioration of the rubber parts and the image carrier is promoted but also the environment may be adversely affected.
[0003]
Therefore, as a charging means replacing the corotron, a contact charger has been developed in which a conductive member such as a roll, a brush, a blade, a film or a belt is brought into contact with the image carrier, and a voltage is applied to charge the image carrier. .
[0004]
The contact charger has the advantage that the generation of ozone is extremely small and a low-voltage power source is sufficient as compared with a corotron. As a voltage applied to the contact charger, a DC superimposed AC voltage application method in which DC is superimposed on AC or the like is widely used.
[0005]
For example, Japanese Patent Application Laid-Open No. 10-198123 discloses a conductive charging film that forms a predetermined nip region and is movable in the same direction as the moving direction of a member to be charged, and an AC voltage in which a DC voltage is superimposed on the conductive charging film. A contact charger is provided which has a bias power supply for applying a voltage and applies a minute concave portion capable of discharging at a portion facing a nip region of the conductive charging film.
[0006]
This method has the advantages that the charge uniformity is excellent, that the image carrier is hardly stained with toner or the like, and that even if toner adheres, poor charging hardly occurs.
However, when the process speed of the photoconductor is high, the potential unevenness (AC ripple) corresponding to the AC component becomes large and the image quality becomes uneven. Therefore, when the frequency of the AC component is increased, discharge occurs many times in both polarities. As a result, the photoconductor is easily damaged, and the life is shortened. Therefore, this method has a drawback that it cannot be mounted on a medium / high speed copying machine.
[0007]
On the other hand, a DC voltage application method has been developed which aims at suppressing the wear of the photoconductor, extending the life of the photoconductor and reducing the power supply cost.
[0008]
In JP-A-10-111584 and JP-A-11-258888, a charging member to which a DC voltage is applied is pressed against a photosensitive member by sandwiching a flexible cylindrical charging member between the charging member and the charging member. There is disclosed a technique in which a minute gap is formed between the photosensitive member and the photosensitive member by charging the photosensitive member by causing a discharge at an upstream side in a rotation direction of the photosensitive member.
[0009]
This method has the advantages of less damage due to discharge of the photoconductor, less abrasion, and lower power supply costs than the DC superimposed AC voltage application method.
[0010]
However, the charging device is easily contaminated by toner and the like, and poor charging is likely to occur due to the contamination. In addition, there is a disadvantage that white horizontal stripe-shaped image defects are likely to occur due to uneven charging from the beginning of use.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and in a DC voltage application method, an object to be charged is prevented from being charged unevenly, and in a DC superimposed AC voltage application method, the object to be charged is reduced from being worn. It is an object of the present invention to provide an image forming apparatus capable of avoiding the occurrence of white horizontal streak-like image defects and image quality unevenness by using the contact charger, and using the contact charger.
[0012]
[Means for Solving the Problems]
A contact charger according to a first aspect of the present invention that achieves the above object is a contact charger that contacts a moving member to be charged and charges the member to be charged.
A cylindrical or endless belt having a pressure-sensitive anisotropic conductive layer whose electric resistance is reduced by pressurization, and an anisotropic conductive layer having anisotropy in a thickness direction laminated outside the pressure-sensitive anisotropic conductive layer. Shaped charging member,
Along with stretching the charging member, a conductive roll for bringing the charging member into contact with the member to be charged,
And a stretching roll that inclines and stretches the charging member toward an upstream side in a moving direction of the charged body.
[0013]
In this manner, the charging member on which the pressure-sensitive anisotropic conductive layer whose electric resistance is reduced when pressurized is tilted and stretched by the stretching rolls, so that the pressure-sensitive anisotropic conductive layer of the charging member is formed. Since the pressure is applied in the downstream gap of the conductive roll, the resistance value is reduced, and the discharge occurring between the charging member and the member to be charged can be limited to only the downstream gap.
[0014]
A contact charger of the second invention that achieves the above object is a contact charger that contacts a moving member to be charged and applies a voltage to the member to be charged to charge the member to be charged.
Having an anisotropic conductivity having anisotropy in the thickness direction, a cylindrical or endless belt-shaped charging member,
A conductive roll having a pressure-sensitive anisotropic conductive layer in which the charging member is stretched and the charging member is brought into contact with the object to be charged, and the electric resistance is reduced by pressurization,
And a stretching roll that inclines and stretches the charging member upstream in a moving direction of the charged body.
[0015]
As described above, by stretching the charging member by inclining it with the stretching roll, the pressure-sensitive anisotropic conductive layer laminated on the conductive roll is pressed at the downstream gap of the conductive roll, so that the resistance value decreases. In addition, discharge occurring between the charging member and the member to be charged can be limited to only the downstream gap.
[0016]
An image forming apparatus according to a first aspect of the present invention, which achieves the above object, forms an electrostatic latent image on a moving photoconductor by charging and exposing the photoconductor, and develops the electrostatic latent image with toner. In an image forming apparatus for forming an image composed of the toner image fixed on the recording medium by finally transferring and fixing the toner image on the recording medium,
A cylindrical or endless belt having a pressure-sensitive anisotropic conductive layer whose electric resistance is reduced by pressurization, and an anisotropic conductive layer having anisotropy in a thickness direction laminated outside the pressure-sensitive anisotropic conductive layer. Shaped charging member,
Along with stretching the charging member, a conductive roll for bringing the charging member into contact with the member to be charged,
A stretching roll that stretches the charging member by inclining it to the upstream side in the moving direction in which the member to be moved moves,
A voltage application unit for applying a voltage to the conductive roll.
In this way, the charging member on which the pressure-sensitive anisotropic conductive layer is laminated is stretched while being inclined by the stretching roll, so that the discharge occurring between the charging member and the photoconductor is limited to only the downstream gap. Since the contact charger is provided, it is possible to suppress a horizontal streak-shaped image quality defect and abrasion of the photoconductor caused by unstable discharge occurring in an upstream gap of a contact portion between the charging member and the photoconductor.
[0017]
According to a second aspect of the present invention, there is provided an image forming apparatus which forms an electrostatic latent image on a photosensitive member by charging and exposing a moving photosensitive member, and develops the electrostatic latent image with toner. In an image forming apparatus for forming an image composed of a toner image fixed on the recording medium by finally transferring and fixing the image on the recording medium,
Having an anisotropic conductivity having anisotropy in the thickness direction, a cylindrical or endless belt-shaped charging member,
Along with stretching the charging member, the charging member is brought into contact with the photoreceptor, a conductive roll having a pressure-sensitive anisotropic conductive layer whose electric resistance is reduced when pressed,
A stretching roll that stretches the charging member by inclining it to the upstream side in the moving direction in which the member to be moved moves,
A voltage application unit for applying a voltage to the conductive roll.
[0018]
In this manner, the charging member is tilted and stretched by the stretching roll, and the downstream side gap of the conductive roll on which the pressure-sensitive anisotropic conductive layer is laminated is pressed, thereby causing a gap between the charging member and the photoconductor. Since a contact charger whose discharge is limited only to the downstream gap is provided, a horizontal streak-like image defect caused by unstable discharge occurring in the upstream gap of the contact portion between the charging member and the photoconductor, and the photoconductor Wear can be suppressed.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
First, a description will be given of a mechanism of discharge generated between the contact-type charging member and the member to be charged in the DC voltage application method and the DC superimposed AC voltage application method.
[0020]
For the sake of simplicity, it is assumed that the contact-type charging member is a charging roll and the member to be charged is a planar photosensitive member.
[0021]
FIG. 1 is a diagram showing a contact charger using a charging roll and a power supply.
[0022]
In the contact charger shown in FIG. 1, a charging roller 3 in which a conductive charging member 2 is coated on a power supply shaft 1 rotates in the direction of arrow B, and is in contact with the photoconductor 5 moving in the direction of arrow A. When a voltage is applied from the power supply 4 to the power supply shaft 1, the photoconductor 5 is charged to a predetermined voltage.
[0023]
FIG. 2 is a conceptual diagram in which the time course of the surface potential of the photoreceptor by the contact charger shown in FIG. 1 is obtained by simulation. FIG. 2A shows a case where a DC voltage applying power supply is used. ) Is a case where a power supply for applying a DC superimposed AC voltage is used.
[0024]
2A, the surface of the charging roll 3 in each of the upstream discharge region 5A and the downstream discharge region 5B in the moving direction A of the photoconductor 5 has a potential corresponding to the voltage applied to the power supply shaft 1. Since the gap in the upstream discharge area 5A gradually narrows with the movement of the charging roll 3 and the photoconductor 5, a discharge is generated in the narrowed area, and the photoconductor 5 is charged by the discharge. Now, when a certain point X on the photoconductor 5 reaches the upstream discharge region 5A, a discharge occurs, and the photoconductor 5 is gradually charged, and ends when a certain voltage is reached. Therefore, no discharge occurs in the downstream discharge region 5B. Discharge occurs less frequently in an area where the gap is relatively large, and the discharge is also unstable. Therefore, in the upstream discharge area 5A, uneven charging is increased due to unstable discharge, and white horizontal stripe-shaped image defects are likely to occur. Conceivable.
[0025]
FIG. 2B is a conceptual diagram in which the time transition of the surface potential of the photoconductor is obtained by simulation when the power supply in FIG. 1 is a power supply for applying a DC superimposed AC voltage.
[0026]
In FIG. 2B, discharge occurs on the surface of the charging roll 3 in the discharge region 5A on the upstream side in the moving direction A of the photoconductor 5 as the gap between the charging roll 3 and the photoconductor 5 becomes narrower. The voltage gradually rises in a relatively wide area, and changes greatly when the gap becomes equal to or less than a certain value. Then, the voltage is maintained at a constant value in the nip portion 6, but when passing through the nip portion 6 and reaching the downstream-side discharge region 5 </ b> B, the voltage changes greatly again. This indicates that in the upstream discharge region 5A and the downstream discharge region 5B, discharges at both poles are generated alternately many times. Unlike the direct current method, the discharge by the alternating current method is alternately repeated in both the gaps on the upstream side and the downstream side over a long area in both poles, so that the photoreceptor 5 is damaged and the photoreceptor 5 is worn. Is considered to be promoted.
[0027]
Therefore, if it is possible to generate only the discharge in the downstream discharge region 5B without generating the discharge in the upstream discharge region 5A, it is possible to improve the image quality defect in the DC voltage application method, and to further improve the image quality in the DC superimposed AC voltage application method. Wear of the photoconductor 5 can be reduced by half.
[0028]
Hereinafter, embodiments of the present invention will be described.
[0029]
The first embodiment corresponds to the embodiment of the contact charger of the first invention.
[0030]
FIG. 3 is a schematic configuration diagram illustrating the contact charger of the first embodiment.
[0031]
The contact charger shown in FIG. 3 includes an endless belt-shaped charging member 10, a conductive roll 11 and a stretching roll 12 that stretch the endless belt-shaped charging member 10, and a power source 13 that applies a voltage to the conductive roll 11. And contacts the photoconductor 5 moving in the direction of the arrow to charge the photoconductor 5.
[0032]
The charging member 10 has a pressure-sensitive anisotropic conductive layer whose electric resistance decreases when pressed, has a larger elastic coefficient than the pressure-sensitive anisotropic conductive layer, is hardly stretched, and has anisotropy in the thickness direction. An anisotropic conductive layer is laminated on the outside to form an endless belt.
The conductive roll 11 is made of a metal shaft and brings the charging member 10 into contact with the photoconductor 5.
[0033]
The stretching roll 12 applies tension to the charging member 10 to be stretched, and is located on the upstream side in the direction of arrow A in which the photosensitive member 5 moves from a normal line 5C of the photosensitive member 5 at a position where the charging member 10 contacts the photosensitive member 5. The charging member 10 is tilted and stretched.
[0034]
As described above, when the charging member 10 is inclined and stretched upstream of the normal 5C at the contact position where the charging member 10 contacts the photoconductor 5 in the direction of the arrow A in which the photoconductor 5 moves, the charging member 10 Pressure is applied to the charging member 10 wound around the downstream gap 15 formed by the photoconductor 5 and the photosensitive member 5. For this reason, in the downstream gap 15, the pressure is applied to the pressure-sensitive anisotropic conductive layer of the charging member 10 due to the anisotropic conductive layer and the conductive roll 11 in which the elastic coefficient of the charging member 10 is large and difficult to extend, and the volume resistance decreases. I do. On the other hand, in the upstream gap 14 formed by the charging member 10 and the photoconductor 5, no pressure is applied to the pressure-sensitive anisotropic conductive layer of the charging member 10, so that the volume resistance does not decrease.
[0035]
As a result, the voltage between the charging member 10 and the photoreceptor 5 due to the voltage applied from the power supply 13 is higher in the downstream gap 15 than in the upstream gap 14, so that the discharge is performed in the downstream gap 15. Only at the upstream gap 14 and not at the upstream gap 14.
[0036]
Here, the power supply 13 may apply a DC voltage or may apply an AC voltage on which a DC is superimposed.
[0037]
FIG. 4 is a schematic sectional view showing the structure of the charging member.
[0038]
As shown in FIG. 4, the charging member has a pressure-sensitive anisotropic conductive layer 10a whose electric resistance is reduced when pressurized. Anisotropic conductive layer 10b having anisotropy is laminated, and anisotropic conductive layer 10b is laminated outside pressure-sensitive anisotropic conductive layer 10a.
[0039]
The pressure-sensitive conductive elastic layer 10a is made of a rubber material in which conductive particles 10c such as conductive carbon black and ferrite are linearly dispersed at appropriate intervals in the thickness direction. Since the contact area between the particles 10c increases or the distance between adjacent particles decreases, the volume resistance decreases. In addition, since the conductive particles 10c are dispersed in a linear shape, the conductive particles 10c are not limited to pressurized and non-pressurized, and exhibit insulating properties in a direction perpendicular to the thickness.
[0040]
The anisotropic conductive layer 10b is made of a resin material such as polyester, polyamide, polyethylene, polycarbonate, and polyvinylidene fluoride in which conductive particles such as conductive carbon black and ferrite are linearly dispersed at appropriate intervals in the thickness direction. It is not distorted even when pressed, and hardly expands or contracts as compared with the elastic body. However, since the conductive particles are linearly dispersed, the conductive particles have conductivity in the thickness direction, but exhibit insulation in the direction perpendicular to the thickness.
[0041]
The charging member 10 generates a discharge only when the pressure-sensitive conductive elastic layer 10a is pressurized and the volume resistance is reduced, and is different from the pressure-sensitive conductive elastic layer 10a so that no discharge occurs when no pressure is applied. The resistance value with the one conductive layer 10b is adjusted respectively.
[0042]
As described above, since the charging member 10 is provided with not only the pressure-sensitive anisotropic conductive layer 10a but also the anisotropic conductive layer 10b, when the charging member 10 is stretched by applying tension, it is wound around the downstream gap. It is possible to prevent the pressure-sensitive anisotropic conductive layer 10a of the charging member other than the portion where the pressure-sensitive anisotropic conductive layer 10a expands and contracts from being reduced in volume resistance. In addition, the strength can be increased, and the pressure can be applied to the pressure-sensitive anisotropic conductive layer 10a in the downstream gap to reliably reduce the resistance value. Furthermore, since the anisotropic conductive layer 10b also has anisotropy, the lateral flow of the current can be eliminated, so that it is possible to prevent discharge from occurring in the upstream gap due to the lateral flow current.
[0043]
Here, in the contact charger of the present embodiment, the case where the member to be charged is a photosensitive member has been described, but the member to be charged does not necessarily need to be a photosensitive member. Or a cleaning member.
[0044]
Next, a second embodiment will be described.
[0045]
The second embodiment corresponds to the embodiment of the contact charger of the second invention.
[0046]
FIG. 5 is a schematic configuration diagram showing a contact charger of the second embodiment.
[0047]
The contact charger of the second embodiment is different from the contact charger of the first embodiment in that the anisotropic conductive layer is laminated but the pressure-sensitive anisotropic conductive layer is not laminated, but the charging member is The difference is that a conductive roll to which a voltage is applied is covered with a pressure-sensitive anisotropic conductive layer. However, since other configurations are common, the same components are denoted by the same reference numerals and description thereof will be omitted.
[0048]
The contact charger shown in FIG. 5 applies a voltage to an endless belt-shaped charging member 20, a conductive roll 21 and a stretching roll 12 that stretch the endless belt-shaped charging member 20, and a power supply member 21a of the conductive roll 21. A power supply 13 for applying the voltage is provided, and the power supply 13 contacts the photoconductor 5 moving in the direction of arrow A to charge the photoconductor 5.
[0049]
The charging member 20 has an anisotropic conductive layer 10b having a larger elasticity coefficient than the pressure-sensitive anisotropic conductive layer, hardly extending, and having anisotropy in the thickness direction, and forms an endless belt.
[0050]
The conductive roll 21 is formed by a metal power supply member 21a to which a voltage is applied, and a pressure-sensitive anisotropic conductive layer 10a coated on the power supply member 21a and having a reduced electric resistance when pressed. The member 20 is brought into contact with the photoconductor 5.
[0051]
The stretching roll 12 applies tension to the charging member 20 to be stretched, and is located on the upstream side in the arrow A direction where the photosensitive member 5 moves from the normal line 5C of the photosensitive member 5 at a position where the charging member 20 contacts the photosensitive member 5. First, the charging member 20 is inclined.
[0052]
As described above, when the charging member 20 is inclined and stretched upstream of the normal 5C at the contact position where the charging member 20 comes into contact with the photoconductor 5 in the arrow A direction in which the photoconductor 5 moves, the charging member 20 Pressure is applied to the charging member 10 wound around the downstream gap 15 formed by the photoconductor 5. For this reason, in the downstream gap 15, the elasticity of the charging member 20 is larger than that of the pressure-sensitive anisotropic conductive layer, and it is difficult to expand. The anisotropic conductive layer 10 b exerts pressure on the pressure-sensitive anisotropic conductive layer 10 a of the conductive roll 21. Is added, the volume resistance value of the pressure-sensitive anisotropic conductive layer 10a decreases. On the other hand, in the upstream gap 14 formed by the charging member 20 and the photoconductor 5, no pressure is applied to the pressure-sensitive anisotropic conductive layer 10a of the conductive roll 21, so that the volume resistance does not decrease. As a result, the surface potential of the charging member 20 due to the voltage applied from the power source 13 is higher in the downstream gap 15 than in the upstream gap 14, so that the discharge occurs only in the downstream gap 15 and It does not occur in the gap 14.
[0053]
Here, the power supply 13 may apply a DC voltage or may apply an AC voltage on which a DC is superimposed.
[0054]
As described above, in the present embodiment, unlike the first embodiment, the pressure-sensitive anisotropic conductive layer 10 a is provided on the conductive roll 21 side, but the charging member 20 wound around the conductive roll 21 and the conductive roll The action by 21 is the same. Further, since the lateral flow of the current can be eliminated, it is possible to prevent the discharge from occurring between the charging member and the photosensitive member in the upstream gap due to the lateral flow current. Further, when the charging member is stretched by applying tension, the pressure can be applied to the pressure-sensitive anisotropic conductive layer of the conductive roll in the downstream gap to reliably reduce the resistance value.
[0055]
Here, in the contact charger of the present embodiment, the case where the member to be charged is a photosensitive member has been described, but the member to be charged does not necessarily need to be a photosensitive member. Or a cleaning member.
[0056]
Next, a third embodiment will be described.
[0057]
The third embodiment corresponds to the embodiment of the image forming apparatus of the second invention.
[0058]
The image forming apparatus of the present embodiment uses the contact charger of the second embodiment described with reference to FIG. 5 as a contact charger for charging a photoconductor.
[0059]
FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to the third embodiment.
[0060]
The image forming apparatus shown in FIG. 6 rotates in the direction of arrow A to expose a photoreceptor 31 on which a toner image is formed, a contact charger 30 for uniformly charging the photoreceptor 31, and a uniformly charged photoreceptor 31. An exposure device 33 for irradiating light to form an electrostatic latent image; a developing device 34 for developing the electrostatic latent image formed on the photoconductor 31 with toner to form a toner image; A transfer roll 35 for transferring the formed toner image to a sheet P conveyed from a sheet tray 36; a fixing device 37 for heating and pressing the toner image transferred on the sheet P to fix the toner image on the sheet P; A cleaner 38 for cleaning the toner remaining on the photoconductor 31 after the transfer to the P is provided, and a discharging lamp 39 for discharging the charge remaining on the photoconductor 31.
[0061]
The contact charger 30 further includes an endless belt-shaped charging member 20, a conductive roll 21 and a stretching roll 12 that stretch the endless belt-shaped charging member 20, and a DC voltage that applies a voltage to the conductive roll 21. And a power source 13 to which an AC voltage on which is superimposed is applied. The power source 13 contacts the photosensitive member 31 moving in the direction of arrow A to charge the photosensitive member 31.
[0062]
The charging member 20 has an anisotropic conductive layer having a larger elasticity coefficient than the pressure-sensitive anisotropic conductive layer, is difficult to expand, and has anisotropy in the thickness direction, and forms an endless belt.
[0063]
The conductive roll 21 is formed by a metal power supply member to which a voltage is applied, and a pressure-sensitive anisotropic conductive layer coated on the power supply member and having a reduced electric resistance when pressed. The photosensitive member 31 is brought into contact.
[0064]
The stretching roll 12 applies tension to the charging member 20 to be stretched, and is located on the upstream side in the direction of arrow A where the photosensitive member 31 moves from the normal line of the photosensitive member 31 at the position where the charging member 20 contacts the photosensitive member 31. The charging member 20 is inclined.
[0065]
When an image is formed on a sheet of paper P using the image forming apparatus of the present embodiment, first, the photoconductor 31 is uniformly charged by the contact charger 30, and the image read from the original is read onto the uniformly charged photoconductor 31. The exposure device 33 emits an exposure light based on a signal or an image signal input from the outside to form an electrostatic latent image. The toner of the developing unit 34 is adhered to the electrostatic latent image and developed to form a toner image. Then, the toner image is transferred to the sheet P using a transfer roll, and the toner image on the sheet P is further fixed by the fixing device 37.
[0066]
Here, in the present embodiment, an AC voltage on which a DC voltage is superimposed is applied to the contact charger 30, but a DC voltage may be applied. The operation of the contact charger 30 is the same as the operation described with reference to FIG. 5, and a duplicate description will be omitted.
[0067]
As described above, in the contact charger used in the image forming apparatus of the present embodiment, discharge occurs only in the downstream gap in the rotation direction of the photoconductor 31, and no discharge occurs in the upstream gap. And the unevenness of image quality can be prevented, and the wear of the photoconductor 31 is reduced by half even when an AC voltage is applied, so that the life can be extended.
[0068]
Although the image forming apparatus of the present embodiment has been described based on the direct transfer type image forming apparatus, the present invention can be applied to an indirect transfer type image forming apparatus. Further, the photoreceptor is not necessarily required to be one, and may be applied even if a plurality of photoreceptors are arranged.
[0069]
Next, a fourth embodiment will be described.
[0070]
The fourth embodiment corresponds to the embodiment of the image forming apparatus of the first invention.
[0071]
The image forming apparatus of the present embodiment uses the contact charger of the first embodiment described with reference to FIG. 3 as a contact charger for charging a photosensitive member, as compared with the image forming apparatus of the third embodiment. However, the other points are common. Therefore, overlapping drawings and descriptions are omitted.
[0072]
【Example】
(Example 1)
The present example is an example of the contact charger of the first embodiment and the contact charger used in the image forming apparatus of the fourth embodiment.
[0073]
The pressure-sensitive conductive elastic layer is formed of a rubber material such as silicon rubber, EPDM, or fluorine rubber in which conductive particles such as conductive carbon black and ferrite are linearly dispersed at appropriate intervals in the thickness direction. When pressure is applied to the particles, the contact area between the internally added conductive particles increases, and the volume resistance decreases due to the decrease in the distance between adjacent particles. The thickness may be about 0.05 to 3 mm.
[0074]
In this example, ferrite particles were dispersed in silicon rubber having a thickness of 200 μm.
[0075]
The volume resistivity at the time of pressurization is preferably set in the range of about 3 to 9 log Ωcm in consideration of charging performance and pressure resistance, and the volume resistivity at no pressurization is set so as not to cause discharge. The dispersion amount of the conductive particles is appropriately adjusted so as to be about 6 log Ωcm or more.
[0076]
In this embodiment, the volume resistivity under no pressure is set at about 10 log Ωcm, and the volume resistivity under pressure is set at about 5 log Ωcm.
[0077]
The anisotropic conductive layer is formed of a resin material such as polyester, polyamide, polyethylene, polycarbonate and polyvinylidene fluoride in which conductive particles such as conductive carbon black and ferrite are linearly dispersed at appropriate intervals in the thickness direction. The thickness may be about 0.01 to 3 mm.
[0078]
In the present example, ferrite particles were dispersed in polyvinylidene fluoride having a thickness of 30 μm.
[0079]
The volume resistivity is preferably set in a range of about 3 to 9 log Ωcm in consideration of its charging performance, pressure resistance performance, and the like, and is appropriately adjusted according to the amount of conductive particles dispersed.
The volume resistivity in this example was set to about 6 log Ωcm.
[0080]
The conductive roll is made of a conductive material such as a metal or alloy such as aluminum, copper alloy or SUS, iron plated with chromium or nickel, or a synthetic resin. The conductive roll is positioned by fixing its central axis, and the charging member contacts the member to be charged with an appropriate nip width or nip pressure.
[0081]
As the tension roll, a roll made of the same material as the conductive roll, or a roll further coated with various resin materials is used. Further, by rotating the tension roll, the charging member can be positively rotated. In this case, the surface of the stretching roll is coated with a surface material having an appropriate coefficient of friction so that the charging member moves without slipping.
[0082]
In the present embodiment, a charging member having a diameter of 20 mm is stretched by an aluminum conductive roll having a diameter of 8 mm and a stretching roll having a diameter of 10 mm, and the pressure-sensitive anisotropic conductive layer of the charging member wound around the downstream gap portion. About 1.47 N / cm ² Pressure was applied.
[0083]
Further, in the present embodiment, the tension roll is rotationally driven so that the charging member rotates at the same speed as the photoconductor of the image forming apparatus of the fourth embodiment, and a DC voltage of -1100 V is supplied from the power supply to the conductive roll. And the photoreceptor was charged to about -500V. The rotation speed of the photoconductor (hereinafter, process speed) was 120 mm / s.
[0084]
Next, an image having a halftone of 20% was formed on the image forming apparatus of the fourth embodiment using the contact charger of this example, and the initial image quality and the uneven charging were evaluated. As a comparative example, the same evaluation was performed on an image forming apparatus using a conventional contact charger disclosed in JP-A-10-111584.
[0085]
The image forming apparatus using the contact charger of the conventional example has many white horizontal streak-like image quality defects and the charging unevenness is about 50 V, but the image forming apparatus using the contact charger of the present embodiment has a white image. No horizontal streak-like image quality defect occurred, and the uneven charging was about 10 V, which was a level that was not a problem in use.
(Example 2)
This example is an example of the contact charger of the second embodiment and the contact charger used in the image forming apparatus of the third embodiment. The members used for each component of the contact charger of the present embodiment are the same as those of the first embodiment except for the conductive roll and the charging member.
[0086]
The conductive roll formed a power supply member having a diameter of 8 mm using the same member as the conductive roll in Example 1, and was formed using the same material as that used for the pressure-sensitive anisotropic conductive layer of the charging member to have a thickness of 200 μm. A pressure-sensitive anisotropic conductive layer was formed.
[0087]
Further, as the charging member, an anisotropic conductive layer having a thickness of 50 μm was formed using the same material as that used for the anisotropic conductive layer of the charging member in Example 1.
[0088]
Next, an image having a halftone of 20% was formed on the image forming apparatus of the third embodiment using the contact charger of the present example, and the initial image quality and uneven charging were evaluated.
[0089]
As a result, as in Example 1, no white horizontal streak-like image quality defect occurred, and the charging unevenness was about 10 V, which was a level having no problem in use.
(Example 3)
In the present embodiment, a contact charger for charging a photoconductor is a contact charger having the same configuration as that of the second embodiment and applying a DC superimposed AC voltage to the image forming apparatus of the third embodiment. This is an embodiment of the present invention.
[0090]
Using a power supply that outputs a voltage of 1.3 KHz, 1.5 KVP-P and a DC voltage of -550 V superimposed on the contact charger, a print test is performed until the photoconductor rotates 100,000 times. The amount of wear of the photosensitive drum was measured. As a comparative example, a similar test was performed on a conventional contact charger of the DC superimposed AC voltage application system disclosed in Japanese Patent Application Laid-Open No. 10-198123.
[0091]
FIG. 7 is a diagram illustrating a print test result in the image forming apparatus according to the present embodiment.
[0092]
In FIG. 7, the vertical axis indicates the amount of wear (μm) of the photoconductor, and the horizontal axis indicates the number of rotations (1000 rotations) of the photoconductor.
[0093]
As can be seen from the figure, the amount of wear (μm) of the photoconductor is substantially proportional to the number of rotations (1000 rotations) of the photoconductor. When the contact charger of the present embodiment is used, the conventional contact charger is used. It can be seen that the amount of wear is reduced by 30% to 40% as compared with the case, and is greatly improved.
[0094]
【The invention's effect】
As described above, according to the contact charger of the present invention, the pressure-sensitive anisotropic conductive layer is provided on the charging member or the conductive roll, and the charging member and the conductive roll in the downstream gap of the conductive roll to which a voltage is applied are provided. Therefore, discharge is limited in the upstream gap regardless of whether the applied voltage is a DC voltage or a DC superimposed AC voltage. Body wear is reduced. Further, according to the image forming apparatus of the present invention using this contact charger, when the applied voltage is DC, the horizontal streak caused by the unstable discharge occurring in the upstream gap between the contact portion of the charging member and the photosensitive member is generated. The image quality defect can be avoided, and when the applied voltage is an AC voltage on which a DC voltage is superimposed, abrasion of the photoreceptor can be reduced and its life can be extended.
[Brief description of the drawings]
FIG. 1 is a diagram showing a contact charger using a charging roll and a power supply.
FIG. 2 is a conceptual diagram showing a time course of a surface potential of a photoconductor by a contact charger shown in FIG. 1 obtained by simulation.
FIG. 3 is a schematic configuration diagram illustrating a contact charger of the first embodiment.
FIG. 4 is a schematic sectional view showing a structure of a charging member.
FIG. 5 is a schematic configuration diagram illustrating a contact charger of a second embodiment.
FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to a third embodiment.
FIG. 7 is a diagram illustrating a print test result in the image forming apparatus according to the present exemplary embodiment.
[Explanation of symbols]
1 Power supply shaft
2,10,20 charging member
3 Charging roll
4,13 power supply
5,31 Photoconductor
5A Upstream discharge area
5B Downstream discharge area
5C normal
6 Nip section
10a Pressure-sensitive anisotropic conductive layer
10b Anisotropic conductive layer
10c conductive particles
11,21 conductive roll
12 tension roll
14 Upstream gap
15 Downstream gap
21a Power supply member
30 Contact charger
33 Exposure equipment
34 Developer
35 Transfer Roll
36 paper tray
37 Fixing unit
38 Cleaner
39 Static elimination lamp

Claims (6)

In a contact charger that contacts a moving member to be charged and charges the member to be charged,
A cylindrical or endless belt having a pressure-sensitive anisotropic conductive layer whose electric resistance is reduced by pressurization, and an anisotropic conductive layer having anisotropy in a thickness direction laminated outside the pressure-sensitive anisotropic conductive layer. Shaped charging member,
Along with stretching the charging member, a conductive roll for bringing the charging member into contact with the member to be charged,
And a stretching roll which inclines and stretches the charging member toward an upstream side in a moving direction of the object to be charged. In a contact charger that contacts the moving object to be charged by applying a voltage to the object to be charged and charging the object to be charged,
Having an anisotropic conductive layer having anisotropy in the thickness direction, a cylindrical or endless belt-shaped charging member,
A conductive roll having a pressure-sensitive anisotropic conductive layer in which the charging member is stretched and the charging member is brought into contact with the member to be charged, and the electric resistance is reduced by pressurization,
And a stretching roll which inclines and stretches the charging member toward an upstream side in a moving direction of the object to be charged. 3. The contact charger according to claim 1, further comprising a power supply for applying a DC voltage to the conductive roll. The contact charger according to claim 1, further comprising a power supply that applies an AC voltage in which a DC voltage is superimposed on the conductive roll. An electrostatic latent image is formed on the moving photoconductor by charging and exposing the photoconductor, and a toner image obtained by developing the electrostatic latent image with toner is finally transferred and fixed on a recording medium. An image forming apparatus for forming an image composed of a toner image fixed on the recording medium,
A pressure-sensitive anisotropic conductive layer whose electric resistance is reduced by pressurization, and an elongation smaller than the pressure-sensitive anisotropic conductive layer laminated outside the pressure-sensitive anisotropic conductive layer, and anisotropy in a thickness direction. Having an anisotropic conductive layer having, a cylindrical or endless belt-shaped charging member,
Along with stretching the charging member, a conductive roll for bringing the charging member into contact with the member to be charged,
A stretching roll that stretches the charging member by inclining it to the upstream side in the moving direction in which the member to be charged moves,
An image forming apparatus comprising: a voltage applying unit that applies a voltage to the conductive roll. An electrostatic latent image is formed on the photoconductor by charging and exposing the moving photoconductor, and a toner image obtained by developing the electrostatic latent image with toner is finally transferred and fixed on a recording medium. In an image forming apparatus for forming an image composed of a toner image fixed on a recording medium,
Having an anisotropic conductive layer having anisotropy in the thickness direction, a cylindrical or endless belt-shaped charging member,
A conductive roll having a pressure-sensitive anisotropic conductive layer in which the charging member is stretched and the charging member is brought into contact with the member to be charged, and the electric resistance is reduced by pressurization,
A stretching roll that stretches the charging member by inclining it to the upstream side in the moving direction in which the member to be charged moves,
An image forming apparatus comprising: a voltage applying unit that applies a voltage to the conductive roll.

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