JPH0378629B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic brush cleaning device for electrophotographic copying machines, etc., and in particular, toner is collected with high efficiency from a magnetic carrier, which is a cleaning agent, and the carrier is always used in a clean state. This paper proposes a magnetic brush cleaning device that improves cleaning efficiency and extends the life of the carrier.

In an electrophotographic copying machine, an electrostatic latent image corresponding to the original image is formed on the surface of a photoreceptor, which is an image carrier, and then developed with toner to make it visible, and this toner image is transferred to a transfer material. Untransferred toner remaining on the surface of the photoreceptor without being transferred to the transfer material is removed by a cleaning device. FIG. 2 is a schematic diagram of a conventional magnetic brush cleaning device. The photosensitive drum 20 rotates at a constant speed in the direction of the arrow, and a magnetic brush 21 is arranged near the photosensitive drum 20.
has a built-in magnet 22 inside the cylindrical body, and is rotatably provided in the direction of the arrow so that a magnetic carrier attached to the circumferential surface of the cylindrical body rubs the circumferential surface of the photosensitive drum 20. Further, a bias roller 23 is provided rotatably in the direction of the arrow at a position where the magnetic brush 21 rubs, and a blade 24 is provided so as to rub the circumferential surface of the roller 23. A magnetic carrier such as iron powder is attached to the circumferential surface of the cylindrical body of the magnetic brush 21 by the magnetic force of the magnet 22, and untransferred toner on the circumferential surface of the photosensitive drum 20 is removed by the sliding of the magnetic brush 21. Due to the friction, it adheres to the circumferential surface of the carrier which is frictionally charged, and reaches the location of the roller 23 together with the carrier. Then, the toner on the carrier circumferential surface is transferred to the circumferential surface of the roller 23 to which a bias voltage having a polarity opposite to that of the toner is applied, and the toner adhering to this circumferential surface is scraped off by the blade 24.

However, conventionally, the toner adhering to the carrier surface is not removed, so the toner accumulates on the carrier surface in a short period of time, and the carrier loses its ability to attach new toner, resulting in a short carrier life. There was an inconvenience. Further, due to the accumulation of toner, the triboelectric charging ability of the carrier is reduced, resulting in low cleaning efficiency and low toner recovery efficiency. Furthermore, the carrier is roller 2
3, and this has the disadvantage that a large amount of carrier is mixed into the collected toner, resulting in problems such as increased carrier consumption, the inability to reuse the collected toner, and unstable cleaning performance. It had been pointed out.

In addition to the above-mentioned cleaning device using a magnetic brush, there are also cleaning devices that use a blade, web, or fur brush. However, in blade and web cleaning, the blade or web comes into sliding contact with the surface of the photoconductor. The surface is severely damaged, and fur brush cleaning has the disadvantage that toner remains as a thin film on the surface of the photoreceptor after passing through the cleaning device, which tends to cause so-called toner filming.

The present invention has been made in view of the above points, and includes a circulation path for the magnetic carrier that collects substantially all of the magnetic carrier after rubbing the image carrier from the magnetic brush and returns it to the magnetic brush. The object of the present invention is to provide a magnetic brush cleaning device that removes toner from the carrier while the carrier is conveyed through this path, thereby removing toner with high efficiency, improving cleaning efficiency, and extending the life of the carrier. do.

The magnetic brush cleaning device according to the present invention includes:
A magnetic brush with a built-in magnet inside the cylindrical body and a magnetic carrier attached to the circumferential surface of the cylindrical body so as to be rotatable so as to rub the surface of the image carrier; a supply means for supplying the carrier to the circumferential surface of the magnetic brush; a circulation means for once collecting the magnetic carrier after rubbing the surface of the image carrier from the circumferential surface of the magnetic brush and returning it to the supply means; The present invention is characterized by comprising a toner removing means that is interposed in a circulation path of the magnetic carrier in the circulation means and removes toner from the magnetic carrier. In this case,
The toner removing means may include a bias roller to which a bias voltage having a polarity opposite to the charged polarity of the toner is applied to electrostatically attract and remove the toner from the circumferential surface of the magnetic carrier. . Further, the circulation means has a magnetic roller having a built-in magnet inside a cylindrical body and rotatably provided in the vicinity of the magnetic brush with its axial direction coincident with the magnetic roller to magnetically transfer the magnetic carrier from the circumferential surface of the magnetic brush. The magnetic carrier may be transferred to the supply means by being magnetically attracted by a roller.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an embodiment in which the present invention is applied to an electrophotographic copying machine. A photosensitive drum 1 (in the figure, only the circumferential surface near the cleaning device according to the present invention is shown) is a drum-shaped photosensitive member formed by forming a photosensitive layer on the circumferential surface of a cylindrical conductive substrate. , is rotated at a constant speed in the direction of the arrow. The photosensitive layer is made of a photoconductive material such as amorphous selenium or a selenium-based alloy, and the conductive substrate is grounded. Near the circumferential surface of the photosensitive drum 1, a charging device, an image exposure device, a phenomenon device, a transfer device (all not shown), and a static eliminator 2 are arranged in this order in the rotational direction. A magnetic brush cleaning device according to the present invention having a magnetic brush 3 is disposed between the charging device and the charging device. The photosensitive layer of the photosensitive drum 1 is uniformly charged to, for example, positive polarity by a charging device, the original image is exposed to light by an image exposure device to form an electrostatic latent image, and then uniformly charged by a phenomenon device. Toner charged with a negative polarity opposite to the polarity is supplied to form a toner image. Approximately 80% of the amount of attached toner in this toner image is transferred to a transfer material by a transfer device, and the transferred image is subjected to a fixing process in a subsequent process. Thus, the circumferential surface of the photosensitive drum 1 reaches the position where the static eliminator 2 is disposed with the untransferred toner remaining thereon. The static eliminator 2 is, for example, a corona discharger connected to a power source with a positive polarity opposite to the charged polarity of the toner. After the amount of charge is reduced and the electrostatic adhesion to the circumferential surface of the photosensitive drum 1 is weakened, the position where the magnetic brush cleaning device according to the present invention is installed is reached.

Each element of the magnetic brush cleaning device is housed as a whole in a housing 17, and a magnetic brush 3 is disposed near the circumferential surface of the photosensitive drum 1. The cylindrical body 4 of the magnetic brush 3 is provided near the circumferential surface of the photoconductor drum 1 with its longitudinal direction aligned with the longitudinal direction of the photoconductor drum 1 so as to rotate in a direction opposite to the moving direction of the circumferential surface. . A plurality of (four in the illustrated example) magnets 5 are fixedly installed inside the cylinder 4. The magnet 5 is N in the vicinity of the cylinder 4.
The magnets 5 are arranged so that poles and south poles appear alternately, and the lines of magnetic force formed near the circumferential surface of the cylinder 4 cause magnetic particles such as iron powder to be applied to the outer circumferential surface of the cylinder 4. The body carrier is attached in a brush-like manner. This carrier is charged with a polarity opposite to that of the toner by frictional charging, etc., and magnet 5
Due to the magnetic force of the toner, the toner adheres to the outer peripheral surface of the cylindrical body 4 and rotates to the peripheral surface of the photoreceptor drum 1, and the toner is rubbed against the peripheral surface to separate the toner adhering to the peripheral surface and adhere to the surface of the carrier. The toner is removed from the circumferential surface of the photoreceptor drum 1.

A magnetic roller 6 is disposed at a suitable distance from the magnetic brush 3 on the downstream side in the rotational direction of the magnetic brush 3 when viewed from the photosensitive drum 1, and a magnetic roller 8 is disposed above the magnetic roller 6. 6 with an appropriate length interval between them. The magnetic rollers 6 and 8 are rotatably provided inside a cylindrical body with their axial directions aligned with the axial direction of the magnetic brush 3.
A plurality of magnets 7 and 9 (two in the illustrated example) are fixedly installed. Magnet 7 or 9 is N on the cylinder side
The magnets 5 and 7 and the magnetic roller 6 and the magnetic roller 8 are arranged in such a manner that the magnetic brush 3 and the magnetic roller 6 face each other. The magnets 7 and 9 at opposite positions are arranged so that they have different polarities. Further, the cylindrical bodies of the magnetic rollers 6 and 8 are both driven so that their circumferential surfaces rotate in the same direction at positions where the magnetic brush 3 and the magnetic roller 6 face each other, and at positions where the magnetic rollers 6 and 8 face each other. And magnets 5 and 7
and 9, the cylinder body 4 and the magnetic roller 6, respectively.
The magnetic carrier adhering to the circumferential surface of the magnetic roller 8 is caused by the magnetic fields between the magnets 5 and 7 and between the magnets 7 and 9, which are located opposite each other, to increase the magnetic field on the circumferential surface of the cylinder 4. The body carrier is transferred to the circumferential surface of the magnetic roller 6, and the magnetic carrier on the circumferential surface of the magnetic roller 6 is transferred to the circumferential surface of the magnetic roller 8.

A separator 10 is provided near the outer circumferential surface of the magnetic roller 8 on the opposite side of the magnet 9, and the magnetic carrier on the circumferential surface of the magnetic roller 8 is located at a position where the separator 10 is disposed where the magnetic force from the magnet 9 is weakened. It separates from the circumferential surface of the magnetic roller 8, is guided by the separator 10, and falls. On the other hand, a hopper 13 is disposed above the magnetic roller 3 to temporarily store the carrier that has fallen on the separator 10 and then supply it to the circumferential surface of the magnetic brush 3. The partition plate on the downstream side in the rotational direction of the magnetic brush 3 in the hopper 13 is a doctor blade 13a, and its lower end is spaced at an appropriate length (approximately 3 mm) from the circumferential surface of the magnetic brush 3.
The carrier on the circumferential surface of the magnetic brush 3 is placed so as to be separated from the doctor blade 1.
The thickness is regulated by 3a.

The bias roller 11 is placed in the area where the magnetic carrier falls from the separator 10.
and two opposing electrodes 12 are provided. The bias roller 11 and the counter electrode 12 are arranged to face each other across the falling path of the carrier, and the bias roller 11 is driven to rotate at a constant speed in the direction of the arrow by applying a bias voltage having a polarity opposite to the charging polarity of the toner. The counter electrode 12 is grounded. This bias roller 11 and counter electrode 12
Due to the electric field formed between the two, toner adhering to the surface of the carrier falling between the two is electrostatically attracted to the bias roller 11 and adheres to the circumferential surface thereof. A toner receiver 14 having a U-shaped cross section is installed between the hopper 13 and the housing 17, and a screw conveyor 1 is disposed inside the toner receiver 14.
6 are arranged. A pick-off 15 is attached to the upper end of the side edge of the toner receiver 14 on the hopper 13 side with its upper end slidingly in contact with the circumferential surface of the bias roller 11. The toner adhering to the circumferential surface of the bias roller 11 is scraped off by the pick-off 15, falls into the toner receiver 14, and is discharged from the apparatus by the screw conveyor 16.

Next, the operation of the apparatus of the present invention having such a configuration will be explained. In the present invention, the untransferred toner remaining on the circumferential surface of the photoconductor drum 1 has its electrostatic adhesion with the circumferential surface of the photoconductor drum 1 weakened by the static eliminator 2 as the photoconductor drum 1 rotates. The location of the magnetic brush cleaning device is reached.
The untransferred toner is then removed from the circumferential surface of the photosensitive drum 1 by a magnetic brush 3 having a magnetic carrier attached to its circumferential surface. That is, the untransferred toner is rubbed by a magnetic carrier that is magnetically attached to the circumferential surface of the cylindrical body 4 and whose layer thickness is regulated by the doctor blade 13a, so that the untransferred toner is transferred to the carrier that is charged to the opposite polarity to the toner. It is electrostatically attracted and transferred from the circumferential surface of the photoreceptor drum 1 to the surface of the carrier.
Then, the carrier to which the toner is attached is transferred to the cylindrical body 4.
With the rotation of the magnetic roller 5, it rotates to an area facing the magnetic roller 5, and due to the magnetic field formed between the magnets 5 and 7 in the opposing area, the magnetism is generated by drawing a trajectory as shown by the dashed line in the figure. It is transferred from the brush 3 to the magnetic roller 6. Next, as the magnetic roller 6 rotates, the carrier rotates to an area facing the magnetic roller 8, and the magnetic field formed between the magnets 7 and 9 in the opposing area causes the carrier to move from the magnetic roller 6 to the magnetic roller 8. Transfer to 8. Then, the carrier rotates the separator 10 as the magnetic roller 8 rotates.
The separator 10 is rotated to the position where the separator 10 is disposed, and the separator 10 is separated from the circumferential surface of the magnetic roller 8 at the position where the magnetic force from the magnet 9 is weakened. The detached carrier is guided by the separator 10 and falls into the hopper 13 while tracing a trajectory between the bias roller 11 and the counter electrode 12 as shown by the dashed line in the figure. Then, when the carrier falls between the bias roller 11 and the counter electrode 12, the bias roller 11 and the counter electrode 1
2, the toner on the carrier surface is transferred to the bias roller 11,
It adheres to its peripheral surface and is removed from the carrier. Therefore, the carrier that falls into the hopper 13 and is stored and is repeatedly used as a cleaning agent for the magnetic brush 3 always has a toner concentration of a predetermined value (for example,
5% by weight) or less. On the other hand, the toner attached to the circumferential surface of the bias roller 11 is removed by the pick-off 1.
5 scrapes off the peripheral surface of the toner receiver 1.
4 and is discharged to the outside of the apparatus by the screw conveyor 16.

Note that by applying a bias voltage having a polarity opposite to the charged polarity of the toner to the cylinder 4 of the magnetic brush 3, the untransferred toner on the circumferential surface of the photoreceptor drum 1 can be removed with higher efficiency. Further, a collection means for collecting a part of the carrier falling on the separator 10 is provided in the fall area of the carrier, and the collected carrier is introduced into a toner concentration sensor to detect the toner concentration, It is preferable to change the conditions for applying the bias voltage to the bias roller 11 based on the detection result. That is, when the toner concentration is high, the bias voltage is set high to increase the recovery efficiency of toner from the carrier, and conversely, when the toner concentration is low, the bias voltage is set low. This is because the carrier exhibits conductivity, so if the toner concentration is low, leakage is likely to occur between the bias roller 11 and the counter electrode 12 via the carrier, so the bias voltage is set to a low value to prevent the occurrence of leakage. This is to avoid it. Further, even in this case, since the toner concentration of the carrier is low, the carrier in the hopper 13 is maintained at a predetermined toner concentration or less. On the other hand, when the toner concentration of the carrier falling on the separator 10 is high, the resistance value of the entire carrier is high, so there is no risk of leakage occurring between the bias roller 11 and the counter electrode 12, and the toner is strongly For recovery, the voltage applied to the bias roller 11 is set to a high value. As described above, in this embodiment, a space necessary for moving the carrier containing magnetic toner upward and then separating the magnetic toner from the carrier via the toner removing means is provided.

As described in detail above, in the case of the present invention, magnetic toner is distributed between the magnetic brush 3 and the magnetic brush 3.
between the hopper 13, which is a carrier supply means for
The magnetic rollers 6 and 8 transport the toner along a circulation path as shown by the dashed line in the figure, and during this transport, the toner is collected and removed from the carrier by a bias roller serving as toner removing means. Therefore, since substantially the entire amount of the carrier is once collected from the magnetic brush 3 to remove toner, the toner removal efficiency is high and the toner concentration of the carrier, which is a cleaning agent, can be maintained at an extremely low value. Therefore, the magnetic brush cleaning device according to the present invention has high cleaning efficiency, and the life of the carrier is dramatically extended. Note that the present invention should not be limited to the above-described specific embodiments, and various modifications can be made within the technical scope of the present invention.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing one embodiment of the present invention, Figure 2 is a schematic diagram showing one embodiment of the present invention;
The figure is a schematic diagram of a conventional magnetic brush cleaning device. (Explanation of symbols), 1: Photosensitive drum, 3: Magnetic brush, 4: Cylindrical body, 5, 7, 9: Magnet, 6, 8:
Magnetic roller, 11: bias roller, 13: hopper, 13a: doctor blade.

Claims (1)

[Claims] 1. A magnet is built into the cylindrical body, and a magnetic carrier is attached to the circumferential surface of the cylindrical body so as to be rotatable so as to rub the surface of the image carrier, and is provided above a horizontal line passing through the center of the image carrier; a magnetic brush that rotates in the same direction as the rotational direction of the image carrier; a supply means provided above the magnetic brush for supplying a magnetic carrier to the circumferential surface of the magnetic brush; a circulation means for once collecting the body carrier from the circumferential surface of the magnetic brush and returning it to the supply means; and a toner removal means for removing toner from the magnetic carrier by being interposed in the circulation path of the magnetic carrier in the circulation means. A magnetic brush cleaning device comprising means.