JP3261027B2 - Charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for performing a charging process by bringing a charging roller into contact with the surface of a photoreceptor in an apparatus such as a printer, a copying machine, a facsimile or the like using an electrophotographic system. About.

[0002]

2. Description of the Related Art Conventionally, a scorotron system using corona discharge has been generally employed as a means for performing a charging process on a member to be charged such as a photoconductor in an image forming apparatus using an electrophotographic system. Was. This scorotron method is a very effective means to uniformly charge the surface to be charged, but requires a high-voltage power supply and generates a large amount of ozone by corona discharge. There is also concern about the impact on the environment.

Therefore, at present, attention has been paid to a contact charging system which generates a small amount of ozone and can obtain a predetermined potential even at a relatively low voltage, instead of the scorotron system. This contact charging method is a method in which a charging member to which a bias voltage is applied is brought into direct contact with a member to be charged and then relatively moved, thereby charging the surface to be charged to a predetermined potential. Generally, an elastic roller is used.

[0004]

As described above, the contact charging system is a useful charging means, but has a drawback that the charging member is in contact with the surface to be charged, which is contaminated at an early stage. Therefore, some measures are required to use the charging device for a long time. For example, if a high-resistance foreign substance such as polyvinylidene fluoride used as a lubricant for the cleaning blade or toner that slips through the cleaning blade adheres to the charging member, poor charging occurs at that portion, and image defects such as vertical stripes occur. Occurs. Alternatively, if a low-resistance foreign substance such as paper dust adheres, it causes abnormal discharge under high humidity or image deletion. Further, if these foreign substances remain on the charging member for a long period of time, the charging member and the surface of the drum will be scratched over time, and streak-like image defects will occur. Therefore, when the charging device is used for a long time, effective cleaning of the charging member is always indispensable.

However, when the charging member is cleaned, the cleaning is performed while the cleaning member such as a cleaning blade is in contact with the charging member so as to rub the charging member. It is easy to be charged, and the charged particles such as toner and paper powder are adsorbed, so that the cleaning performance is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a charging device capable of performing stable cleaning of a charging roller under any environment. And

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a charging roller which rotates in contact with a photosensitive member which is driven in rotation, and a charging roller which elastically contacts a charging surface of the charging roller. A cleaning roller that cleans the charging surface by contacting and rotating the cleaning roller.
Conductivity of resistivity 10 ⁶ Ω · cm or more and 10 ⁸ Ω · cm or less
The charging roller and the cleaning roller, which are covered with a porous sponge member and are electrically grounded from the metal core via the conductive porous sponge member , and rotate relative to each other. The rotation driving of the elastic roller is controlled so as to have a constant peripheral speed difference at the position. By setting the conductive member to the above value,
The outer peripheral surface of the charging roller
Can suppress the triboelectric charge generated when rubbing
You.

[0008]

[0009]

[0010]

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be illustratively described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the mechanical components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Not just.

FIG. 1 shows an image forming apparatus to which the present invention is applied.
In particular, a basic configuration diagram of a process unit around the photosensitive drum 1 of the printer is shown, and an electricity removing means 2 including an LED unit 8, a developing unit 60, a transfer roller 7, a cleaning blade 3, and an eraser is arranged along the drum rotating direction (clockwise). , A charging roller 4 is disposed, and as is well known, the charge removing means 2
After the charge is removed, an exposure latent image is written by the LED unit 8 on the photosensitive drum 1 uniformly charged by the charging roller 4, and the exposed latent image is visualized as a toner image by the developing unit 60 by reversal development. After transferring the toner image to the recording medium 10 by the transfer roller 7, the residual toner is removed by the cleaning blade 3. The residual toner removed by the cleaning blade 3 is stored in a waste toner bottle (not shown) by a screw (not shown).

Next, the respective process means will be described. The photoconductor drum 1 uses an OPC drum (organic photoconductor) having a diameter of 30φ and a negative charging polarity, and is configured to be rotatable at a predetermined peripheral speed in a direction of an arrow by a motor (not shown). Then, the thickness (GG) of the photosensitive layer of the photosensitive drum 1
(Total thickness of L, CTL, etc.) is set to 25 μm, and a photoconductor having high viscoelastic properties is used for the CTL layer.
It is preferable to use a defect-less photoreceptor in which the coating surface of the photoreceptor has irregularities regulated.

The LED units 8 are arranged in a row as is well known in the art.
It consists of an LED head with D elements arranged and a focusing lens,
An exposure latent image corresponding to image information can be written on the photosensitive drum 1.

The developing unit 60 includes a developing container 61 containing a multi-component developer composed of a carrier and a toner, and a developing roller 62 containing a fixed magnet assembly (not shown). A DC development bias Vg of -450 V is connected to perform reversal development with a low electric field. Then, the carrier is formed by fixing conductive fine particles on the surface of carrier base particles in which a magnetic substance is uniformly dispersed in a binder resin,
As for the magnetic force, a developer having a maximum magnetization of 55 to 80 emu / g in a magnetic field of 5 kOe (Oersted), an average central particle size of the carrier of 35 μm, and a particle size distribution containing particles of 35 μm or less, particularly 15 wt% or more, is used. As the toner, a normal high-resistance or insulating toner is used. For example, a magnetic substance is added to a binder resin, a colorant, a charge control agent, an offset preventing agent, and the like, and the average central particle size is 5 to 15 μm.
For example, the proper mixing ratio of the carrier and the toner is 85 to 90:15 to 10% by weight.
Set to.

The transfer roller 7 has a resistivity of 10 ⁵ Ω · cm.
The following conductive elastic roller, specifically, a urethane rubber roller, is used, and the transfer bias 70 is set to +250 V to 2000 V having a polarity opposite to the surface potential of the photoconductor 1 and the polarity of the toner image charge.
Set to.

On the other hand, the cleaning blade 3 is
1, a plate-like polyurethane elastomer material having a wedge-shaped cross section at its tip is attached to a support member (not shown), and the corner of the tip abuts on the photosensitive drum 1 almost in line contact. .

The charging roller 4 is driven and rotated in synchronization with the photosensitive drum 1 to add a conductive component to the periphery of a roller shaft 41 composed of a solid stainless steel shaft of 6φ to make the resistivity 1.
It is formed by molding a polyurethane rubber 42 set to not more than 0 ⁷ Ω · cm, and molding it into a 12φ roller shape, and performing a nylon resin coating on the surface. The roller surface roughness is set to Rz <7 μm, preferably 4 to 6 μm.

The polyurethane rubber 42 constituting the charging roller 4 has a different molecular weight distribution and a different degree of crosslinking, and the rubber hardness of the rubber layer is set in the range of 40 to 50 ° by Asker-C measurement. If the surface rubber layer is within the rubber hardness range, the surface layer of the rubber layer 42 of the charging roller 4 may be subjected to a hardening treatment if necessary. The molecular weight distribution and the degree of crosslinking may be changed in the radial direction toward the rubber surface layer.

A cleaning roller 5 composed of a sponge roller is disposed in contact with the back side of the charging roller 4. The cleaning roller 5 is formed by covering a metal roller shaft (metal core) 52 with a sponge (conductive member) 51 of urethane foam, which has been subjected to a conductive treatment, in a cylindrical shape. Is set to 12.5φ, which is slightly larger than the diameter of the charging roller 4. The conductive treatment of the urethane foam may be performed by adjusting the resistance value by adding carbon, but is not limited thereto. Further, the resistivity of the conductive member is set to 10
^It is set to ⁶ to 10 ⁸ Ω · cm, and the metal roller shaft 52 is grounded to prevent the charging roller surface from being frictionally charged.

The surface of the cleaning roller 5 is formed with 20 to 60 cells per inch in order to efficiently clean attached matter such as toner. In this case, if a cell having a large number of cells is used, the scraped foreign matter cannot be taken into the elastic member, and the foreign matter remaining on the surface of the elastic member is rubbed against the charging roller, which has an adverse effect. Therefore, when this elastic member is used stably for a long time, the elastic member having a large space for storing the scraped foreign matter and having a small number of cells (20 to 40) is used.
Is more preferred.

As shown in FIG. 1, the surroundings of the cleaning roller 5 and the charging roller 4 on the back side thereof are disposed around the collection container 4.
0, and rotating the cleaning roller 5 with a peripheral speed difference, the skeleton of the urethane foam sponge scrapes foreign substances on the surface of the charging roller 4 by the peripheral speed difference between the sponge roller 5 and the charging roller 4, and removes the foreign matter. By storing the foreign matter in the cells in the sponge, foreign substances adhering to the surface of the charging roller 4 can be reliably removed. Moreover, even in a low-temperature environment where frictional charging is likely to occur, the cleaning roller 5 is a conductive member and is grounded, so that the surface of the charging roller 4 and the surface of the cleaning roller are not frictionally charged.

FIG. 4 shows a configuration of a bias circuit for performing the charging and development. Reference numeral 30 denotes a high-voltage power supply circuit that supplies a DC voltage V of 1200 V to a voltage adjustment circuit; 31 denotes a voltage adjustment circuit; An assembly adjustment volume and a user adjustment volume for adjusting the charging bias voltage and the developing bias voltage, respectively, are provided. The charging bias Vt adjusted by the volumes is supplied to the roller shaft of the charging roller 5 via a correction resistor, and to the developing roller 62. Are applied with a developing bias, respectively. In this case, the charging bias is -800 to -1000 V
Is applied to the charging roller 4 and constant voltage control is performed so that a constant voltage is always applied. Therefore, load fluctuation of the charging roller, the cleaning roller, and the like is not applied as compared with the constant current control. Development bias is -350 to -4
A DC voltage of 50 V is applied to the charging roller 4 and about 170 V
It is configured such that a developing current of １７173 μm flows.

FIG. 3 shows the construction of a drive system around the charging roller 4. The transmission is transmitted from the shaft gear M1 of the motor M to the shaft gear 1A of the photosensitive drum 1 via the relay gear 59 and then to the shaft gear 1A. The shaft gear 4 </ b> A of the charging roller 4 meshes with the charging roller 4 so that the charging roller 4 rotates synchronously with the rotation of the photosensitive drum 1. The shaft gear 5A of the cleaning roller 5 meshes with the shaft gear M1 of the motor M via the relay gears 58,58. In this case, the number of gears is set so that the direction of rotation of the cleaning roller 5 is in the direction of rotation (forward direction) with respect to the charging roller 4 at the contact position with the charging roller 4. The peripheral speed between the charging rollers 4 is varied so that the relative peripheral speed difference is 1.1 or more and less than 2, preferably 1.1 to 1.5.
It is good to set in the range of. If the ratio is 1.1 or less, a load is applied to the charging roller 4 that is driven and rotated by the photoconductor 1, and if the ratio is more than 2 not only the driving mechanism of the cleaning roller 5 but also the friction of the charging roller 4 is increased. This is because charging is promoted, which is not preferable. Therefore, in order to set the cleaning roller 5 to rotate forward with respect to the charging roller 4, that is, to set the charging roller 4 in a counterclockwise rotation direction with respect to the clockwise direction, the two relay gears 58, 58 are interposed and the diameter ratio is adjusted. Thus, the relative peripheral speed difference is set in a range of 1.1 to 1.5.

The charging roller 4 is, as shown in FIG.
The charging roller shaft 41 is fitted into a guide groove 20A recessed in the drum support frame 20, and a pressure is movably applied to both ends of the roller shaft 41 toward the center of the photosensitive drum shaft 1a using springs 49. Energize. In this embodiment, the length of the charging roller 4 is set to 226 mm, the distance from the roller end to the spring contact position is set to 7.2 mm, and the A4 size recording paper is configured to be chargeable. On the other hand, the cleaning roller 5 and the charging roller 4 are controlled by the housing of the collection container 40 of the charging roller 4 so that the interval between them is constant. As a result, the sponge layer 51 of the cleaning roller 5 is always pressed against the charging roller 4 at a predetermined nip and the contact pressure thereof is almost constant, so that the load applied to the charging roller 4 by the cleaning roller 5 becomes zero. ing. As a result, the load of the cleaning roller 5 is not applied to the photosensitive drum 1, and the total pressure of the charging roller 4 toward the photosensitive drum 1 is determined only by the load of the spring 49. In this embodiment, the load of the spring 49 is increased by 250 V at the end of the charging roller shaft 41 toward the photosensitive drum.
６００600 g, specifically 300 g. The interval between the cleaning roller 5 and the charging roller 4 is set to 10 to 11 mm, preferably 10.5 mm, and the compression amount of the sponge layer 51 constituting the cleaning roller 5 is set to 0.5 to 1.5 mm, preferably 1 mm. I do.

[0026]

Next, in order to confirm the effect of the present invention, while the cleaning roller 5 and the charging roller 4 are set to a forward rotation, the peripheral speed ratio is 1 (synchronous rotation with the charging roller).
Image formation was performed at a printing rate of 5% for each of 20,000 sheets, which were different from 1, 1.5, and 3, respectively.

The cleaning roller 5 used in this experiment was a porous sponge layer 51 made of conductive urethane foam, and the number of cells on the outer peripheral surface of the sponge layer 51 was set to 40 cells / 1 inch. I have.

Investigation of the above configuration shows that, when the peripheral speed ratio is 1 (Comparative Example 1), black streaks begin to appear in the image from about 1000 sheets after the image formation, and the black streaks occur until 20,000 sheets are printed. When the charging roller was disassembled after printing, contamination such as adhesion of foreign matter to the charging roller occurred.

In the case where the peripheral speed ratio is 1 (Example 1), 1.5
In each case (Example 2), an extremely clear image could be obtained even after printing 20,000 sheets, and the surface was extremely clean when the charging roller was disassembled. Further, in the case of the peripheral speed ratio of 3 (Comparative Example 2), disturbance such as slight density unevenness occurred from the beginning of the image formation, but the disturbance did not increase much after printing 20,000 sheets. When the charging roller was disassembled, the surface was clean.

Next, when the peripheral speed ratio was set to 1.5, the number of cells on the surface of the sponge layer 42 was 10/1 inch (Comparative Example 3), 60/1 inch (Example 3), and 10%.
Using the cleaning rollers set at 0/1 inch (Comparative Example 4), images were formed at a printing rate of 5% for each of 20,000 sheets.

As a result, in Comparative Example 4 in which the number of cells is large, a black streak smaller than about 10000 sheets was generated, and after printing 20,000 sheets, a slight vertical streak was increased so that it could be visually confirmed. When the charging roller was disassembled, foreign matter was found to adhere to the surface of the charging roller.

In the third embodiment in which the number of cells is 60, 2
Although no image distortion was confirmed after printing 10,000 sheets,
When the charging roller was disassembled, foreign matter was slightly attached to the surface of the charging roller.

Further, in Comparative Example 3 in which the number of cells is as small as 10, a slight vertical streak was generated from around 6000 sheets, and the vertical streak increased so that it could be visually confirmed after printing 20,000 sheets. When the charging roller was disassembled, a large number of foreign substances adhered to its surface.

Accordingly, it was found that the number of cells of the sponge layer 51 of the elastic roller is preferably 20 to 60 cells / 1 inch, preferably 20 to 40 cells / 1 inch.

In the above state, the spring pressure of the spring 49 applied to both ends of the charging roller 4 was 200 g (Comparative Example 5), 300 g (Example 2)
When the charged state was confirmed to be different from 700 g (Comparative Example 6), charging unevenness occurred in Comparative Example 3 in which the spring pressure was 200 g, and when the spring pressure was 700 g, the voltage on both sides of the charging roller 4 became higher than the central portion. Again, uneven charging occurs in the axial direction.

[0036]

As described above, a conductive elastic member is used as a cleaning member for a charging member such as a charging roller, the conductive elastic member is grounded, and the roller-shaped conductive elastic member is charged. By adhering to the charged surface of the member and constantly rubbing the charged surface while generating a peripheral speed difference between the charging roller and the cleaning roller with a driving device, the adhering matter on the outer peripheral surface of the charging roller under any environment Can be reliably removed, and the occurrence of image defects and damage to the charging roller can be reduced. Furthermore, by suppressing the occurrence of scratches on the charging roller, the durability of the charging device can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus applied to the present invention.

FIG. 2 shows a configuration of a drive system around a charging roller 4 of the apparatus shown in FIG.

FIG. 3 shows a fitting state of a charging roller and a photosensitive drum.

FIG. 4 shows a configuration of a bias circuit for performing charging and development of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 1A shaft drum of photoconductor drum 4 charging roller 4A shaft gear of charging roller 5 cleaning roller 5A shaft gear of cleaning roller 49 spring 51 sponge layer (conductive member) 52 metal roller shaft (metal core)

Claims (1)

(57) [Claims] A charging roller that contacts and rotates the photosensitive member that is driven to rotate, and a cleaning roller that elastically contacts the charged surface of the charging roller and cleans the charged surface by rotating the charged roller. The cleaning roller has a resistance around the metal core.
Conductivity of 10 ⁶ Ω · cm or more and 10 ⁸ Ω · cm or less
And Tsutsumihi porous sponge member, said guide from said metal core
The elastic roller is configured so as to be electrically grounded through an electrically conductive porous sponge member , and has a constant peripheral speed difference at a contact position between the charging roller and the cleaning roller that rotate with each other. A charging device characterized by controlling the rotation drive.