JPH09311526A - Noncontact roller electrifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a noncontahct roller electrifer at a level that there is no electrication unevenness and practical trouble while keeping such excellent characteristic that the electric characteristic is stable with time and there is no sticking of foreign matter. SOLUTION: An electrifying roller 1 is constituted of middle and high resistance layer parts 1a, a low resistance layer part 1b, and a core shaft 1c, and a large number of tooth-shaped sharp projections 10 are provided on the outer periphery of the low resistance layer part 1b at fixed pitches. When the electrifying roller 1 electrifies a photoreceptor 2, in a state where the top ends of the projection 10 of the low resistance layer part 1b come closet to the surface of the photoreceptor 2, a voltage is applied by a power source 3, to such a degree that the voltage of the gap between the surface of the high resistance layer part 1a as the surface of the electrifying roller 1 and the surface of the photoreceptor 2 exceeds the breakdown voltage of air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roller charging device, and more particularly to a non-contact roller charging device suitable for use in an image forming apparatus such as a printer, a facsimile and a copying machine.

[0002]

2. Description of the Related Art A conventional charging device of this type is of a contact type. For example, in a charging roller and a charging device disclosed in Japanese Patent Laid-Open No. 6-348110, an elastic layer and a surface layer containing a pressure-sensitive conductive rubber are laminated on a core metal, and a pressing force is adjusted for a long period of time. It is possible to control the charging of the member to be charged to a desired charging voltage. Further, in the electrophotographic process disclosed in Japanese Patent Laid-Open No. 6-348112, in the direct direct charging method, charging is performed by setting the photoconductor dark potential to a specific range (relatively low potential, for example, 300 to 650 V range). It is intended to obtain a uniform image without any image defects such as streaks. Further, the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 6-348114 detects a change in the electrical characteristics of the charging roller when it corresponds to the non-image area of the charged member, even if the electrical characteristic of the charging roller changes. When the area corresponding to the image forming area of the body to be charged corresponds to the above-mentioned detection characteristic, the DC voltage application control is performed so that there is always no insufficient charging.

[0003]

All of the conventional roller charging devices as described above are of the contact charging type, and are individually designed for uniform stabilization of the charging potential.
It is inevitable that foreign matter remaining on the surface of the photoconductor, which is the member to be charged (residual toner components that could not be removed by cleaning, paper powder, talc, and other paper constituents), will stick to the charging roller, causing uneven charging over time. Occurs and the life is short,
Due to this short life, commercialization of electrophotographic copying machines of a class that requires high speed and high reliability has not been realized. To solve this problem, a charging device using a non-contact charging roller has been studied, but the present inventors have found that the charging unevenness is severe and it has not reached a practical level.

In view of the above, the present invention has the advantage that the non-contact charging roller does not have foreign matter sticking and the electric characteristics can be kept stable over time, and the charging unevenness can be practically maintained at a level without any problem. The purpose is to do.

[0005]

A non-contact roller charging device of the present invention according to claim 1 is characterized in that the rotating charging roller is always kept in a non-contact state with a member to be charged, and the charging roller is used to cover the charging member. A device for charging a charging member, wherein a height difference of electric resistance is provided on a surface of the charging roller and a portion in the vicinity of the surface, and the height difference of the electric resistance is made larger in a rotation direction thereof than an axial direction of the charging roller, In addition, the material of the charging roller, the gap between the charging roller and the member to be charged, and the charging are set so that the discharge to the member to be charged does not occur at the highest resistance portion but mainly to the low resistance portion. It is characterized in that the voltage applied to the rollers is combined.

According to a second aspect of the present invention, the gap between the charging roller and the member to be charged is set to be larger than at least the maximum particle size of the coarse particles of toner particles to be adhered to the member to be charged during development.

According to a third aspect of the present invention, the discharge charge of the charging roller is always applied to the surface to be charged during the charging process of the member to be charged.

According to a fourth aspect of the present invention, a cleaning member that comes into contact with the charging roller is provided.

According to a fifth aspect of the present invention, the charging roller is kept in a rotating state during the charging step.

According to a sixth aspect of the present invention, the charging roller is kept stationary during the charging step.

According to a seventh aspect of the present invention, the charging roller is rotated at a predetermined timing in a non-charging step other than the charging step.

According to an eighth aspect of the present invention, in the charging step, the electric resistance of the surface of the charging roller that comes closest to the member to be charged and the portion near the surface is the lowest in the rotating direction of the charging roller. It is characterized by doing.

According to a ninth aspect of the present invention, means for performing a cleaning step is provided as means for performing a series of electrophotographic image forming steps provided around the member to be charged, for performing charging, exposure, development and transfer steps. Characterized by not being.

According to a tenth aspect of the present invention, the surface of the charging roller forms substantially the same circumferential surface.

The eleventh aspect of the present invention is characterized in that the surface of the charging roller is coated with a lubricant or a substance containing a lubricant.

According to a twelfth aspect of the present invention, the surface roughness of the charging roller is equal to or less than the volume average particle diameter of the toner.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional conceptual view showing an embodiment of a non-contact roller charging device according to the present invention. In the figure, 1 is a charging roller, 2 is a photoconductor which is a member to be charged, 3 is a power source for the charging roller, 4 is a cleaning section for the charging roller, 4a is a cleaning blade thereof, 5 is exposure for forming an electrostatic latent image, 6 Is a developing device, 7 is a transfer unit, and 8 is a charge removing / separating unit. Further, 9 is a transfer paper. Since the charging roller 1 is in non-contact with the photoconductor 2 to obtain a uniform discharge in the direction of the rotation axis of the photoconductor 2, the tip is sharp in a sawtooth shape, but a very small curvature (0.05 mmR or less is preferable. A discharge part having a) is exposed on the surface or provided near the surface.

Specifically, the charging roller 1 shown in FIG. 1 has an outermost middle-high resistance layer portion (hereinafter simply referred to as a high resistance layer portion for the sake of simplicity) 1a and a low resistance layer on the inner periphery thereof. Part 1b,
It is composed of the innermost core shaft 1c. The resistance value ρ1 (Ω · cm) of the high resistance layer portion 1a is preferably ρ1> 10 ^5, and the thinnest portion may be 0 to 10 μm. As shown in an enlarged view in FIG. 2, the low resistance layer portion 1b has a large number of sawtooth sharp projections 10 provided at a constant pitch on the outer peripheral surface, and its resistance value ρ2 (Ω · cm) is Let ρ2 <ρ1. The protrusion 10 extends like a gear in the axial direction.
Since a voltage is applied from the power source 3 to the core shaft 1c, a conductive metal is used for the core shaft 1c.

When the photoreceptor 2 is charged, the high resistance layer portion forming the surface of the charging roller in the most protruding portion of the low resistance layer portion 1b, that is, in the state where the tip of the protrusion 10 is closest to the surface of the photoreceptor 2. Power source 3 so that the voltage in the gap between the surface of 1a and the surface of the photoconductor exceeds the breakdown voltage of air.
To apply voltage.

A solid line A in FIG. 3 is a breakdown voltage curve of air under atmospheric pressure according to Paschen's law.
If the gap between the charging roller 1 and the photoconductor 2 is 6 to 48 μm, the applied voltage at the tip of the protrusion 10 is around 800 V (curve B shown by the broken line in FIG. 3), and stable photoconductor charging without unevenness is achieved. You can do it. At that time, in the concave portion (valley portion) of the low resistance layer portion 1b, the void voltage is low as indicated by the alternate long and short dash line C in FIG. 3, and no discharge occurs.

The minimum level of the gap between the charging roller 1 and the photosensitive member 2 is a coarse toner particle size in order to avoid toner sticking due to pressure contact between the toner and the charging roller 1 even in the case of a cleaningless system and there is a transfer residue. Powder-side classification cut level (for example, if the volume average particle size is around 10 μm, 2
It is better to make it wider than 5 μm on the coarse powder side.

The maximum level of the gap between the charging roller 1 and the photosensitive member 2 is that at least one of the protrusions 10 of the low resistance layer portion 1b must be in a discharged state at least during the charging process.
In order to perform the discharge most efficiently, the position where the charging roller 1 is stopped is preferably the position where the protrusion 10 of the charging roller 1 and the photoconductor 2 are closest to each other. In the case shown in FIG. 3, the gap between the surface of the charging roller 1 and the surface of the photoconductor 2 is 48 at the portion where the protrusion 10 facing the photoconductor 2 is located.
It is preferable that the thickness is less than μm (applied voltage is 800V level).

In the case of a cleaningless system, etc.,
If the pressure contact state can be avoided as in the above condition, there will be no strong dirt, but a slight amount of foreign matter adheres due to the dust collection effect of the electric field. Therefore, cleaning can further reduce uneven charging.

When the charging roller 1 is rotated during the charging process, the discharge position can be constantly changed before uneven charging occurs on the surface cleaned by cleaning or the like, and extreme deterioration of the charging roller can be prevented. Like During the charging process, the charging roller 1 is basically kept stationary and at least 1
If the gap between the protrusion 10 of the low resistance layer portion 1b and the photoconductor 2 is kept constant during the charging process, the charging unevenness can be further prevented. Of course, the charging roller 1 is rotated and cleaned during the non-charging process, and another protrusion 1 is used during the next charging process.
By stopping so that the gap between 0 and the photoconductor 2 becomes equal, there is no uneven charging and the charge potential level can be maintained.

In the image forming apparatus of FIG. 1, assuming the case of reversal development (forming a toner image on the low potential portion of the photoconductor), the photoconductor cleaning process is omitted during the series of image forming processes. is there. However, as in the case of positive development in which toner is attached to the high potential portion, it may be better to provide a cleaning step.

4A to 4D show other configurations of the charging roller. The charging roller 1A of (A) has a wire 10a similar to the charge wire on the surface of the low resistance layer portion 1b.
And a plurality of those having a diameter of about 30 to 100 μm are provided as the discharge part. Of course, the wire 10a is located in the high resistance layer portion 1a. Further, the charging roller 1B of (B) is
The base end is embedded in the low resistance layer portion 1b so that the tip of the bar-shaped discharge member 10b having a sharp tip is located at or near the surface of the high resistance layer portion 1a. Further, in the charging roller 1C of (C), the discharge member 10c made of a thin plate-shaped rigid metal is radially arranged with the base end on the low resistance layer part 1b so that the tip is located at or near the surface of the high resistance layer part 1a. It is buried. The charging roller 1D of (D) is
A discharge member 10d similar to the discharge member 10c of the charging roller 1C of (C) is embedded not obliquely but in a tilted manner, and the tip is not easily chipped even when slidingly contacting the cleaning blade 4a. In either case, of course, regarding the surface shape of the charging roller, when the cleaning means is brought into contact with or slidably contacts, the same circumferential surface is formed in order to keep the pressure constant and to make the cleaning performance good and stable. It is advisable to adopt a mode that does.

The embodiment of FIG. 5 is an example in which a lubricant application blade 11 is provided in order to maintain a good cleaning performance of the charging roller 1 and to apply a lubricant for reducing the friction coefficient of the surface of the charging roller 1. Of course, the entire surface of the charging roller 1 may be thinly coated with a substance having a low friction coefficient such as a fluorine resin so that the discharge is not hindered extremely. Further, as another means for maintaining good cleaning performance, it is also very effective to make the surface roughness of the charging roller 1 not more than the volume average particle diameter of the toner.

The embodiment of FIG. 6 shows an example of a means for maintaining a minute gap between the charging roller 1 and the photosensitive member 2, and the spacer rollers 12, 12 are abutted against the photosensitive member 2 at the shaft end of the charging roller 1. In this example, the gap is set to half the difference between the diameter of the spacer roller 12 and the diameter of the charging roller 1. The gap may be on the order of tens to hundreds of μm. The smaller the gap, the easier it is to stabilize the discharge efficiency and the smaller the amount of ozone generated. However, when the charging roller 1 and the photoconductor 2 are too close to each other, the toner is pressed and moved from the photoconductor 2 to the charge roller 1. Therefore, it is possible to easily maintain the minute gap to the extent that this does not occur. Further, the discharge from the charging roller 1 causes
The gap with other adjacent conductors or low resistance members may be set to several millimeters or more so that they do not occur in areas where they do not face each other.

[0029]

As described above, in the non-contact roller charging device according to the first aspect of the present invention, a difference in electric resistance is provided on the surface of the charging roller and a portion in the vicinity of the surface so that the discharge to the member to be charged has the highest resistance. Since it does not occur at the parts corresponding to the parts, but mainly at the low resistance part, there is no foreign matter sticking which is the advantage of the non-contact charging roller, and the electric characteristics are stable over time, while charging There is an effect that unevenness can be practically maintained at a level with no problem.

A non-contact roller charging device according to claim 2 is
Since the gap between the charging roller and the member to be charged is made larger than the maximum particle size of the coarse particles of the toner particles, in addition to the effect common to claim 1,
There is no effect that the toner on the charging roller and the toner on the member to be charged are brought into pressure contact with each other, and therefore, it is possible to further prevent the strong toner adhesion on the surface of the charging roller.

The non-contact roller charging device according to claim 3 is
Since the discharge charge of the charging roller is always applied to the surface to be charged during the step of charging the member to be charged, the effect is the same as that of claim 1, and the members are intermittently arranged in the rotating direction. There is an effect that uneven charging can be reduced by the discharging portion of the charging roller.

A non-contact roller charging device according to a fourth aspect is
Since the cleaning member that comes into contact with the charging roller is provided, in addition to the same effect as in claim 1, even if the charging roller becomes dirty, it can be cleaned and restored to a good state by cleaning, and the life of the charging roller is greatly extended. The effect is that you can.

A non-contact roller charging device according to a fifth aspect is
Since the charging roller is kept in the rotating state during the charging step, in addition to the effect common to claim 1, uneven charging can be reduced by the discharging portion of the charging roller which is intermittently arranged in the rotating direction. effective.

A non-contact roller charging device according to a sixth aspect of the present invention is
Since the discharging portion of the charging roller is kept stationary during the charging step, in addition to the effect common to the third aspect, there is an effect that the charging level of the photoconductor during that time can be kept constant.

The non-contact roller charging device according to claim 7 is
Since the charging roller is rotated at a predetermined timing of the non-charging step, in addition to the effect common to claim 6, in the next charging step, after the charging roller is restored to a good state via the charging roller cleaning step. You can use the unused discharge part,
There is an effect that it is possible to always use the discharged portion in a good state at the time of charging.

The non-contact roller charging device according to claim 8 is
During the charging process, the electric resistance of the surface of the charging roller that is closest to the member to be charged during the charging process and the vicinity of the surface is the lowest part in the direction of rotation of the charging roller, and the part where the discharge of the charging roller is most likely occurs during the charging process. In addition to the effect common to the sixth aspect, there is an effect that the stability and uniformity of charging are good.

A non-contact roller charging device according to claim 9 is
The means for performing a cleaning step as a series of electrophotographic image forming steps provided around the member to be charged is omitted.
In addition to the effects that are common with, cost reduction of the entire imaging system,
There is an effect that space saving becomes easy.

In the non-contact roller charging device according to the tenth aspect, the charging roller surface forms substantially the same circumferential surface. Therefore, in addition to the effect common to the fourth aspect, the charging roller and the cleaning member therefor are contacted with each other. The contact pressure can be kept constant, and the cleaning performance of the charging roller can be kept stable.

In the non-contact roller charging device according to the eleventh aspect, since the surface of the charging roller is coated with the lubricant or the substance containing the lubricant, in addition to the effect common to the fourth aspect, the surface friction coefficient of the charging roller is low. By keeping it, there is an effect that the cleaning property can be always kept excellent.

In the non-contact roller charging device according to the twelfth aspect of the present invention, the surface roughness of the charging roller is set to be equal to or less than the volume average particle diameter of the toner. Since the toner is hardly buried in the concave portion, there is an effect that the cleaning property of the charging roller is good and the toner fixation can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a non-contact roller charging device according to the present invention.

FIG. 2 is an enlarged perspective partial view of a low resistance layer portion of the charging roller of FIG.

FIG. 3 is a diagram showing a gap voltage-gap width curve between a charging roller and a photoconductor in the apparatus of FIG. 1;

FIG. 4 is a sectional view showing another configuration of the charging roller.

FIG. 5 is a schematic sectional view showing an embodiment in which a lubricant is applied to the surface of the charging roller.

FIG. 6 is a cross-sectional conceptual diagram showing an embodiment including means for maintaining a minute gap between a charging roller and a photoconductor.

[Explanation of symbols]

 1, 1A, 1B, 1C, 1D Charging roller 1a Medium to high resistance layer part 1b Low resistance layer part 1c Core shaft 2 Photoconductor 3 Charging roller power supply 4 Charging roller cleaning part 4a Cleaning blade 5 Forming electrostatic latent image Exposure 6 developing device 7 transfer part 8 static elimination separation part 9 transfer paper 10 projection of low resistance layer part 10a wire 10b discharge member 10c discharge member 10d discharge member 11 lubricant coating blade 12 spacer roller

Claims (12)

[Claims] 1. A device for charging a rotating charging roller in a non-contact state with a member to be charged at all times to charge the member to be charged by the charging roller, wherein an electric resistance is provided on a surface of the charging roller and a portion in the vicinity of the surface. With the height difference of
The height difference of the electric resistance is made larger in the rotation direction than the axial direction of the charging roller, and the discharge to the member to be charged does not occur at the highest resistance portion, but mainly at the low resistance portion. 2. A non-contact roller charging device comprising: a material for the charging roller, a gap between the charging roller and the member to be charged, and a voltage applied condition to the charging roller. 2. The non-contact roller according to claim 1, wherein the gap between the charging roller and the member to be charged is at least larger than the maximum particle size of coarse particles of toner particles to be adhered to the member to be charged during development. Charging device. 3. The non-contact roller charging device according to claim 1, wherein the discharge charge of the charging roller is always applied to the surface to be charged during the step of charging the charged member. 4. The non-contact roller charging device according to claim 1, further comprising a cleaning member that contacts the charging roller. 5. The non-contact roller charging device according to claim 3, wherein the charging roller is kept in a rotating state during the charging step. 6. The non-contact roller charging device according to claim 3, wherein the charging roller is kept stationary during the charging step. 7. The non-contact roller charging device according to claim 6, wherein the charging roller is rotated at a predetermined timing of a non-charging step other than the charging step. 8. The electric resistance of the surface of the charging roller that comes closest to the member to be charged and the portion near the surface during the charging step is the lowest portion in the rotating direction of the charging roller. The non-contact roller charging device according to claim 6. 9. A means for performing a series of electrophotographic image forming steps provided around the member to be charged is a means for performing charging, exposing, developing and transferring steps, and is not provided with a means for performing a cleaning step. The non-contact roller charging device according to claim 1. 10. The non-contact roller charging device according to claim 4, wherein the charging roller surface forms substantially the same circumferential surface. 11. The non-contact roller charging device according to claim 4, wherein the surface of the charging roller is coated with a lubricant or a substance containing a lubricant. 12. The non-contact roller charging device according to claim 10, wherein the surface roughness of the charging roller is not more than the volume average particle diameter of the toner.