JP2001109236A - Electrifying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of image failure due to deterioration of electrifying function caused by soiling of a magnetic brush 24a over a long period of time, to make the device small and simple and to facilitate maintenance in an image forming device provided with a magnetic brush electrifying device 2. SOLUTION: In this device, a magnetic particle detaching means 26 detaching magnetic particles forming the magnetic brush 24a from a magnetic brush carrying member 22 in the magnetic brush electrifying device 2 electrifying an image carrier 1, a magnetic particle recovering means recovering the detached magnetic particles and a magnetic particle feeding means 21a feeding new magnetic particles 24 to the carrying member from which the magnetic particles are detached, are provided. In this case, a magnetic brush renewal operation mode to have the carrying member above carry the magnetic brush with new magnetic particles is provided and a recovering container 95 recovering toner that is eliminated from the image carrier 1 at a cleaning means 9 is shared as the magnetic particles recovering means above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a magnetic brush charging device (charging device) for charging a magnetic brush of magnetic particles supported on a supporting member by bringing the magnetic brush into contact with a member to be charged, and the charging device. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, for example, a dry electrophotographic apparatus generally has the following construction and image forming process.

[0003] That is, an electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) generally of a rotary drum type is used as a first image carrier, and the surface of the rotary photosensitive drum is set to a predetermined polarity and potential by charging means. The photosensitive drum surface after uniform charging is image-exposed by an image exposing means to form an electrostatic latent image corresponding to the exposed image, and a developer toner is adhered to the electrostatic latent image by a developing means. To develop the toner image, and transfer the toner image to a transfer material as a second image carrier by a transfer unit. The transfer material onto which the toner image has been transferred is subjected to a fixing process of the toner image by a fixing unit, and is discharged as an image formed product (copy, print). Further, after the transfer of the toner image to the transfer material, the rotating photosensitive drum is subjected to the image formation repeatedly after the removal of the transfer residual toner by the cleaning means.

Conventionally, a corona charger has been used as a charging device for electrophotography. This is because a corona charger is disposed opposite to a photosensitive drum as a member to be charged in a non-contact manner, and the surface of the photosensitive drum is exposed to a corona shower generated by the corona charger to which a high voltage is applied, thereby causing the photosensitive drum surface to have a predetermined polarity.・ Electricity is charged.

In recent years, a contact charging device has been put to practical use instead. This is intended for low ozone and low power, and among them, a roller charging method using a conductive roller as a contact charging member is preferable in terms of charging stability,
Widely used.

In the roller charging, a conductive elastic roller is brought into pressure contact with a member to be charged, and a voltage is applied thereto to charge the member to be charged.

There are two types of bias applied to the contact charging device: a DC type in which only a DC bias is applied, and an AC type in which a DC bias is superimposed on an AC bias and applied. When the DC method is used, since the resistance value of the contact charging member fluctuates due to environmental fluctuations and the like, and Vth fluctuates when the film thickness changes due to shaving of the photoconductor, the potential of the photoconductor is set to a desired value. It was difficult.
The AC method is not affected by disturbances such as the environment due to the smoothing effect of the AC bias, but has a problem that the deterioration of the photosensitive member surface due to discharge becomes more remarkable than the DC method. In addition, in both the DC charging method and the AC charging method, a very small amount of ozone is generated because the essential charging mechanism uses a discharge phenomenon from the contact charging member to the photosensitive member.

Therefore, as a new charging method, an injection charging method by directly injecting electric charge to a photosensitive member has been devised.
This charging method is a method in which a voltage is applied to a contact conductive member such as a charging roller, a charging brush, a charging magnetic brush or the like, and charge is injected into a charge injection layer on the surface of the photoreceptor to perform contact injection charging. In this charging method, since the discharge phenomenon is not used, the voltage required for charging is only the desired photoconductor surface potential and no ozone is generated. Further, even when an AC bias is applied, discharge is suppressed, so that generation of ozone is small, and deterioration of the surface of the photoreceptor can be significantly reduced. As the charge injection layer, a material in which conductive fine particles such as tin oxide are dispersed in a resin, amorphous silicon, or the like is used.

The magnetic brush charging device has a magnetic brush portion made of conductive magnetic particles (charge carriers, hereinafter referred to as magnetic particles) magnetically constrained and supported by a supporting member also serving as a power supply electrode. This is to contact the member to be charged and supply power to the supporting member. Compared to other contact charging members, the magnetic brush charging has advantages such as excellent charging uniformity and less susceptibility to contamination by the residue on the photosensitive drum.

FIG. 5 is a schematic structural diagram of an example of a conventional magnetic brush charging device. Magnetic brush charging device 2 of this example
Is a sleeve rotation type.

Reference numeral 1 denotes a rotating photosensitive drum as a member to be charged, which is rotated at a predetermined peripheral speed in a clockwise direction indicated by an arrow.

Reference numeral 21 denotes a housing of the magnetic brush charging device 2, and reference numeral 22 denotes a non-magnetic sleeve (charging sleeve, charging roller) as a magnetic brush holding member.
1 is rotatably disposed with a part thereof exposed to the outside.

Reference numeral 23 denotes a magnet roller as a magnetic field generating means, which is inserted into the sleeve 22 and fixed so as not to rotate. The sleeve 22 rotates around the fixed magnet roller 23 in a clockwise direction indicated by an arrow. At a predetermined peripheral speed.

Reference numeral 24 denotes magnetic particles accommodated in the housing 21. The amount of the magnetic particles is an amount obtained by adding a margin to the amount of the magnetic particles carried on the peripheral surface of the sleeve 22 as a magnetic brush.

Reference numeral 25 denotes a magnetic brush layer thickness regulating member (regulating blade, regulating plate) provided at the opening of the housing 21 and is attached to the sleeve 22 with a predetermined small gap (SB gap). Have been. This regulating member 2
Numeral 5 is magnetically constrained and held as a magnetic brush by the magnetic field of a magnet roller 23 in the sleeve 22 on the sleeve 22, and the amount of magnetic particles (magnetic brush Of the magnetic brush coat layer 24a of an appropriate amount of magnetic particles by regulating the thickness of the magnetic brush coat layer 24a.

The magnetic brush charging device 2 is provided with a sleeve 22 in parallel and close to the photosensitive drum 1. The sleeve 22 and the photosensitive drum 1 are opposed to each other with a predetermined small gap (SD gap). The SD gap is set to be narrower than the SB gap, and in this SD gap, the regulating member 25 as described above is used.
The magnetic brush portion 24a on the sleeve 22, whose layer thickness is regulated by the SB gap, comes into contact with the photosensitive drum 1, and the surface of the photosensitive drum 1 is rubbed by the magnetic brush. N is the magnetic brush contact nip (charging nip).

Then, a predetermined charging bias is applied from the charging bias applying power source S1 to the magnetic brush unit via the sleeve 22, and the surface of the photosensitive drum 1 is contact-charged to a predetermined polarity and potential at the charging nip N.

[0018]

Although magnetic brush charging is less susceptible to the effects of deposits and residues on a member to be charged than other contact charging, magnetic brushes of magnetic particles can be used over a long period of time. Part is gradually contaminated, the charging ability decreases,
In an image forming apparatus, an image defect occurs due to a decrease in charging ability.

Accordingly, the present invention relates to a magnetic brush charging device and an image forming apparatus provided with the charging device, in which the charging ability is reduced due to the contamination of the magnetic brush. It is an object of the present invention to prevent the occurrence of an image defect due to a decrease in charging ability due to the above for a long time. It is another object of the present invention to reduce the size and simplification of an image forming apparatus using a magnetic brush charging device, and to further simplify maintenance.

[0020]

According to the present invention, there is provided a charging device and an image forming apparatus characterized by the following means.

(1) In a charging device for charging by bringing a magnetic brush of magnetic particles carried on a supporting member into contact with an object to be charged, magnetic particles for releasing magnetic particles forming the magnetic brush from the supporting member Separation means, and magnetic particle collection means for collecting the magnetic particles detached from the support member,
Magnetic particle supply means for supplying new magnetic particles to the carrier member from which the magnetic particles have been detached, and detaching the magnetic particles forming the magnetic brush from the carrier member to form a magnetic brush using the new magnetic particles. A charging device having a magnetic brush renewal operation mode for carrying.

(2) It has a detecting means for detecting the charging ability of the magnetic particles of the magnetic brush carried by the carrying member, and the magnetic brush updating operation mode is executed according to the detection information of the detecting means. The charging device according to (1), wherein

(3) The charging device according to (2), wherein the charging ability of the magnetic particles of the magnetic brush carried on the carrying member is detected by measuring the resistance of the magnetic particles.

(4) The carrier according to any one of (1) to (3), wherein the carrier is a rotating body, and the magnetic particle detaching means is a scraper that is controlled to contact and separate from the carrier. Charging device.

(5) The magnetic particle collecting means is a container for collecting the magnetic particles separated from the supporting member by the magnetic particle separating means, according to any one of (1) to (4). Charging device.

(6) The charging device according to any one of (1) to (5), wherein the magnetic particle supply means is a hopper storing magnetic particles.

(7) In an image forming apparatus for performing image formation by applying an image forming process including a charging step of charging the image carrier to the image carrier, the charging means for charging the image carrier includes (1) An image forming apparatus, which is the charging device according to any one of (6) to (6).

(8) A first image carrier, charging means for charging the image carrier, means for forming a toner image on the image carrier charged by the charging means, and 2
A charging unit for charging the first image carrier in an image forming apparatus having a transfer unit for transferring the image to the image carrier and a cleaning unit for removing transfer residual toner remaining on the first image carrier after the transfer. Is a charging device that performs charging by bringing a magnetic brush of magnetic particles carried by a carrier member into contact with the first image carrier, and a magnetic device that detaches the magnetic particles forming the magnetic brush from the carrier member. Particle detachment means,
A magnetic particle collection means for collecting magnetic particles detached from the support member, and a magnetic particle supply means for supplying new magnetic particles to the support member from which the magnetic particles have been detached, forming a magnetic brush from the support member An image forming apparatus having a magnetic brush update operation mode in which a magnetic brush is detached and a magnetic brush made of new magnetic particles is carried.

(9) A first image carrier, charging means for charging the image carrier, means for forming a toner image on the image carrier charged by the charging means, and 2
A charging unit for charging the first image carrier in an image forming apparatus having a transfer unit for transferring the image to the image carrier and a cleaning unit for removing transfer residual toner remaining on the first image carrier after the transfer. Is a charging device that performs charging by bringing a magnetic brush of magnetic particles carried by a carrier member into contact with the first image carrier, and a magnetic device that detaches the magnetic particles forming the magnetic brush from the carrier member. Particle detachment means,
A magnetic particle collection means for collecting magnetic particles detached from the support member, and a magnetic particle supply means for supplying new magnetic particles to the support member from which the magnetic particles have been detached, forming a magnetic brush from the support member A magnetic brush renewal operation mode in which the magnetic particles are detached and a magnetic brush of new magnetic particles is carried, and a collection container for collecting the toner removed from the first image carrier by the cleaning means is provided with the magnetic container. An image forming apparatus, which also serves as a particle collection unit.

(10) There is a detecting means for detecting the charging ability of the magnetic particles of the magnetic brush carried on the carrying member, and the magnetic brush updating operation mode is executed according to the detection information of the detecting means. (8) or (9).

(11) The charging device according to (10), wherein the charging ability of the magnetic particles of the magnetic brush carried by the carrying member is detected by measuring the resistance of the magnetic particles.

(12) The detection by the detecting means of the charging ability of the magnetic particles of the magnetic brush carried by the supporting member, and the execution of the magnetic brush updating operation mode in accordance with the detection information of the detecting means, make the predetermined number of image outputs. The image forming apparatus according to (10) or (11), wherein the image forming is performed after the image formation at the time of exceeding.

(13) The magnetic recording medium according to any one of (8) to (12), wherein the carrier is a rotating body, and the magnetic particle detaching means is a scraper that is controlled to contact and separate from the carrier. Charging device.

(14) The magnetic particle supply means is a hopper storing magnetic particles (8).
The charging device according to any one of (13) to (13).

(15) The means for forming a toner image on the image carrier charged by the charging means forms an electrostatic latent image on the image carrier charged by the charging means by the image exposure means, and carries toner particles. (8) The image forming apparatus according to any one of (8) to (14), wherein the developing device forms a toner image corresponding to the electrostatic latent image.

<Operation> Before the contamination of the magnetic brush due to endurance gradually progresses to cause an unacceptable decrease in the charging ability or an image defect due to the decrease in the charging ability, the magnetic brush is held by the magnetic particle detaching means. The magnetic particles of the magnetic brush with advanced contamination are separated from the member, collected by the collecting means as used magnetic particles, and new magnetic particles are supplied from the magnetic particle supply means to the supporting member from which the magnetic particles have been separated and supported. By executing the magnetic brush renewal operation mode in which the member carries the magnetic brush with the new magnetic particles, the occurrence of a reduction in charging ability due to the contamination of the magnetic brush and the contamination of the magnetic brush in the image forming apparatus are reduced. It is possible to prevent the occurrence of an image defect due to a reduction in charging ability due to a long period of time.

In the transfer type image forming apparatus, the transfer residual toner remaining on the first image carrier after the transfer of the toner image from the first image carrier to the second image carrier is removed. The size of the apparatus can be reduced by using the collecting container for collecting the toner removed from the first image carrier of the cleaning means to be used as the used magnetic particle collecting means for collecting the magnetic particles detached from the magnetic brush supporting member. , Simplification, and further, simplification of maintenance.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Overall Schematic Description of Example of Image Forming Apparatus FIG. 1 is a schematic structural diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer of a transfer type electrophotographic process, a magnetic brush charging type, and a reversal developing type.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as a first image carrier. This example is a negatively chargeable and charge injection chargeable organic photoreceptor having a diameter of 30 mm.
And a commonly used photoreceptor layer on a conductive drum substrate made of aluminum or the like, and a charge injection layer is provided on the outermost layer. The photosensitive drum 1 moves 10 times clockwise as indicated by the arrow.
It is driven to rotate at a process speed of 0 mm / sec.

Reference numeral 2 denotes a sleeve rotation type magnetic brush charging device. The surface of the rotating photosensitive drum 1 is uniformly injected and charged to approximately -700 V by the magnetic brush charging device 2. The magnetic brush charging device 2 will be described in detail in section (2).

Reference numeral 3 denotes an image information exposure means (exposure device), which in this embodiment is a laser beam scanner. A laser L modulated corresponding to a time-series electric digital pixel signal of image information input from a host device (not shown) such as a document reading device having a photoelectric conversion element such as a CCD, an electronic computer, a word processor, etc. The uniformly charged surface of the drum 1 is scanned and exposed. By this scanning exposure, the potential of the surface of the photosensitive drum 1 irradiated with the laser L drops, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

Reference numeral 4 denotes a two-component contact developing device, which reversely develops an electrostatic latent image as a toner image using a two-component developer composed of toner and a magnetic carrier (developing carrier).

More specifically, FIG. 3 is an enlarged model diagram of the developing device 4. Reference numeral 41 denotes a developing container, and reference numeral 42 denotes a non-magnetic developing sleeve. The developing sleeve 42 is rotatably disposed in the developing container 41 with a part of its outer peripheral surface being exposed to the outside. 43 is a magnet roller fixed in a non-rotating manner and inserted in the developing sleeve 42, 44 is a developer coating blade, 45 is a two-component developer contained in the developing container 41, 46 and 47 are bottom sides in the developing container 41 Is a developer stirring member, and a toner hopper 48 is provided at an upper portion in the developing container 41, and accommodates a supply toner t.

The two-component developer 45 in the developing container 41 is composed of a toner t having a negative chargeability of 8 μm in average particle diameter and a magnetic carrier c having a positive chargeability of 50 μm in average particle diameter.
% Of the mixture, and is stirred by the developer stirring members 46 and 47.

The developing sleeve 42 is moved counterclockwise by 1
It is driven to rotate at a peripheral speed of 50 mm / sec. A part of the two-component developer 45 is attracted and held as a magnetic brush layer on the outer peripheral surface of the developing sleeve 42 by the magnetic force of the magnet roller 43 in the sleeve, and is rotated and conveyed with the rotation of the sleeve. Thereby, the layers are adjusted to a predetermined thin layer 45a. The developing sleeve 42 is opposed to the photosensitive drum 1 at a predetermined small interval, and a facing portion between the developing sleeve 42 and the photosensitive drum 1 is a developing section A. In the developing section A, the development is performed such that the developer thin layer 45 a formed on the developing sleeve 42 is in contact with the photosensitive drum 1. The developing sleeve 42 has a developing bias application power source S2.
And a developing bias in which a DC voltage of -500 V is superimposed on an alternating electric field of 2 kV and 2 kHz.

The toner in the developer which is coated as a thin layer 45a on the surface of the rotating developing sleeve 42 and is conveyed to the developing section A is charged on the surface of the photosensitive drum 1 by the electric field by the developing bias AC + DC. The electrostatic latent image is developed as a toner image by selectively adhering to the image. In the case of this example, the toner adheres to the light-exposed portion on the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.

The developer thin layer on the developing sleeve 42 that has passed the developing section A is returned to the developer reservoir in the developing container 41 as the developing sleeve 42 continues to rotate.

In order to maintain the toner concentration of the two-component developer 45 in the developing container 41 within a predetermined substantially constant range, the toner concentration of the two-component developer 45 in the developing container 41 is, for example, an optical toner (not shown). The toner is detected by the density sensor, and the toner supply roller 48a of the toner hopper 48 is drive-controlled in accordance with the detected information, and the toner t in the toner hopper is supplied to the two-component developer 45 in the developing container 41. The toner supplied to the two-component developer 45 is
Stir evenly with 6.47.

Reference numeral 6 denotes a transfer device, and in this embodiment, a transfer roller. The transfer roller 6 is pressed against the photosensitive drum 1 with a predetermined pressing force, and the pressing nip portion is a transfer portion T. A transfer material P as a second image carrier is guided by a pre-transfer guide 6 and fed to a transfer unit T from a paper supply unit (not shown) at a predetermined control timing. The transfer material P fed to the transfer unit T is conveyed while being sandwiched between the rotating photosensitive drum 1 and the transfer roller 6, during which a predetermined transfer bias is applied to the transfer roller 6 from a transfer bias application power source S 3. The reverse polarity of the toner is charged from the back surface of the transfer material P. Thus, the toner image on the surface of the rotating photosensitive drum 1 is sequentially electrostatically transferred to the surface of the transfer material P passing through the transfer portion T.

The transfer material P to which the toner image has been transferred through the transfer section T is sequentially separated from the surface of the rotating photosensitive drum 1 and introduced into a fixing device 8 (for example, a heat roller fixing device) by a conveyor belt device 7. The image is printed out after the toner image is fixed.

After the transfer of the toner image onto the transfer material P (after the transfer material is separated), the transfer residual toner (including paper dust and other residual contaminants remaining on the surface of the rotating photosensitive drum 1) remaining by the cleaning device (cleaner) 9 is also included. ), The surface is cleaned and repeatedly subjected to image formation.

The cleaning device 9 of this embodiment is a blade type, and includes a cleaner container 91, a cleaning blade (rubber blade) 92 disposed in the cleaner container 91, and having a leading edge portion in contact with the surface of the photosensitive drum 1. It comprises a screw shaft 93 and the like disposed at the bottom in the cleaner container 91.

The transfer residual toner remaining on the rotating photosensitive drum 1 is scraped off by the cleaning blade 92. The scraped transfer residual toner falls to the bottom in the cleaner container 91, is conveyed to one end side of the cleaner container by the rotation of the screw shaft 93, is conveyed to the waste toner container 95 through the duct 94, and is collected.

FIG. 4 is an operation process diagram of the printer of this embodiment.

A) Pre-multi-rotation process Printer startup (startup) operation period (warming period)
It is. When the main power switch is turned on, a main motor (not shown) of the printer is driven to rotate the photosensitive drum 1 to execute a preparation operation for required process equipment.

B) Standby After the predetermined start period, the drive of the main motor is temporarily stopped, the rotation of the photosensitive drum is stopped, and the printer stands by until an image formation (printing) start signal is input. Held in state.

C) Pre-rotation process This is a period in which the main motor is restarted to drive the photosensitive drum 1 to rotate again in response to the input of the image formation start signal, and the printer performs a predetermined pre-image formation operation for a while.

D) Image Forming Step When a predetermined pre-rotation step is completed, an image forming process is subsequently performed on the rotating photosensitive drum 1, and the transfer material P to which the toner image has been transferred is conveyed to the fixing device 8.
The first image forming process is performed.

In the continuous image forming mode, the above-described image forming process is repeated, and the image forming processes for a predetermined set number n are sequentially performed.

E) Sheet-to-paper stroke In the continuous image forming mode, the interval between the time when the rear end of one transfer material P passes through the transfer portion T and the time when the front end of the next transfer material P reaches the transfer portion T is reached. This is a transfer material non-sheet passing state period in the transfer unit T.

F) Post-rotation process After the end of the last n-th image forming process, the main motor continues to be driven for a while to rotate the photosensitive drum 1, and the printer performs a predetermined post-operation. It is a period to let.

G) Standby When the post-rotation process is completed, the drive of the main motor is stopped and the rotation of the photosensitive drum 1 is stopped, and the apparatus is kept in the standby state again until the next image formation start signal is input. Is done.

If an image forming signal is input immediately after the previous multi-rotation process, the image forming process is subsequently executed through the pre-rotation process. In the case of forming only one image, after the image forming process is completed, the printer enters a standby state via a post-rotation process.

In the above description, the image forming process d) is the time of image forming, and the multi-rotation process before a), the pre-rotation process c), the inter-paper stroke e), and the post-rotation process during non-image formation. It is time.

(2) Magnetic Brush Charging Device 2 FIG. 2 is an enlarged model diagram of the magnetic brush charging device 2. The magnetic brush charging device 2 of this embodiment is basically the same as the device 2 of FIG.
This is the same type of sleeve rotation type as. The same components and parts as those of the apparatus 2 of FIG. 4 are denoted by the same reference numerals, and the description thereof will not be repeated.

In the magnetic brush charging device 2 of this embodiment,
The housing 21 is extended upward to form a large-capacity magnetic particle storage hopper section (magnetic particle storage section) 21a as magnetic particle supply means for the upper surface of the charging sleeve 22. In this embodiment, the magnetic particle storage hopper section 21a. 280 g of magnetic particles 24 are filled and stored in advance.

The lower part of the housing 21 communicates with the upper part of the cleaner container 91 of the cleaning device 9 described above.
9 is connected.

The non-magnetic charging sleeve 22 has a diameter of 25 mm.
And is driven to rotate at a peripheral speed of 200 mm / sec in the clockwise direction of the arrow. The non-rotating fixed magnet roller 23 inserted in the sleeve is a four-pole magnet roller having four magnetic poles, and the magnetic flux density on the sleeve 22 is 800
Gauss. The carrying amount of the magnetic particles as the magnetic brush 24a on the sleeve 22 is 150 mg / cm ² . The gap (SD gap) between the photosensitive drum 1 and the sleeve 22 was 0.05 cm (500 μm).

The sleeve 22 has a charging bias application power source S
1 to a DC bias of -700 V and an amplitude of 1000
V, a charging bias having a frequency of 1 kHz is applied.

Reference numeral 26 denotes the magnetic brush 2 from the surface of the sleeve 22.
This is a scraper as a magnetic particle releasing means for releasing the magnetic particles forming 4a. This scraper 26
Is located downstream of the charging nip N in the sleeve rotation direction,
The magnetic particle storage hopper 21 a is disposed in the lower part of the housing 21 on the upstream side in the sleeve rotation direction with respect to the rotation direction of the sleeve, and is controlled to swing toward and away from the surface of the sleeve 22.

Reference numeral 27 designates this scraper 26 as a sleeve 22
(For example, a solenoid). The driving device 27 is a control circuit (CPU) 1
On / off control is performed by 00. The scraper 26 is always separated from the sleeve 22 and is retracted and held at a position shown by a solid line which does not act on the magnetic brush 24a on the surface of the sleeve 22. In the magnetic brush renewal operation mode described later, the magnetic particles constituting the magnetic brush 24a carried on the sleeve 22 by being moved so as to contact the surface of the sleeve 22 as shown by the broken line can be scraped off.

Reference numeral 28 denotes a sensor for detecting the remaining amount of the magnetic particles 24 in the magnetic particle storage hopper 21a, and detects that the magnetic particles 24 in the magnetic particle storage hopper 21a have reached the lower limit. The detection signal is transmitted to the control circuit 100
To enter.

Reference numeral 101 denotes a DC current amount detection device interposed in a charging bias application circuit for the sleeve 22. The detected DC current amount information is input to the control circuit 100.

Here, the following are preferably used as the magnetic particles 24.

[0075] A resin and magnetic powder such as magnetite are kneaded and molded into particles, or mixed with conductive carbon or the like to adjust the resistance value. Sintered magnetite, ferrite, or those whose resistance has been adjusted by reducing or oxidizing them. The above magnetic particles are coated with a coating material (such as phenol resin in which carbon is dispersed) whose resistance is adjusted or plated with a metal such as Ni so as to have an appropriate resistance value.

If the resistance value of these magnetic particles is too high, charges cannot be uniformly injected into the photoreceptor, resulting in a fog image due to minute charging failure. If the temperature is too low, when there is a pinhole on the surface of the photoreceptor, current concentrates on the pinhole and the charging voltage drops, so that the surface of the photoreceptor cannot be charged, resulting in charging nip-shaped charging failure. Therefore, the resistance value of the magnetic particles is desirably 1 × 10 ⁴ to 1 × 10 ⁷ Ω.

[0077] The magnetic characteristics of the magnetic particles, it is better to increase the magnetic binding force in order to prevent the magnetic particles adhered to the photosensitive Doramuhe, saturation magnetization 50A · m ² / kg or more.

Actually, the magnetic particles used in this example had a volume average particle size of 30 μm, an apparent density of 2.0 g / cm ³ ,
The resistance value was 1 × 10 ⁶ Ω and the saturation magnetization was 58 A · m ² / kg.

Further, the particle size of the magnetic particles affects the charging ability and the uniformity of charging. In other words, if the particle size is too large, the contact ratio with the photosensitive drum decreases, causing charging unevenness. When the particle size is small, both the charging ability and the uniformity are improved, but the adhesion to the photosensitive drum 1 is easily caused. Therefore, a magnetic particle having a diameter of 5 to 100 μm is preferably used.

The resistance value of the magnetic particles was measured by placing 2 g of the magnetic particles in a metal cell (bottom area: 228 mm ² ) to which a voltage could be applied, applying a load, and applying a voltage of 1 to 1000 V.

The volume average particle diameter of the magnetic particles is represented by the maximum chord length in the horizontal direction, and the measurement was carried out by randomly selecting 300 or more magnetic particles by microscopy, measuring the diameter, and taking the arithmetic average. .

For the measurement of the magnetic characteristics of the magnetic particles, a DC magnetization BH characteristic automatic recording device BHH-50 manufactured by Riken Denshi Co., Ltd. can be used. At this time, the diameter (inner diameter) is 6.5 m
m, magnetic particles in a cylindrical container with a height of 10 mm
The filling is performed at about g weight, and the saturation magnetization is measured from the BH curve of the container while keeping the magnetic particles from moving in the container.

The apparent density of the magnetic particles is JISZ2504
This was performed according to the method described in 1.

(3) Magnetic brush update operation mode In this embodiment, the charging ability of the magnetic particles constituting the magnetic brush 24a carried on the sleeve 22 is detected by measuring the resistance of the magnetic particles. When it is detected that the charging capability has dropped to the lower limit, the magnetic brush update (exchange) operation mode is automatically executed.

That is, the magnetic particles (used magnetic particles) having a reduced charging ability, which constitute the magnetic brush 24 a carried on the sleeve 22, are scraped off by the scraper 26, and a new magnetic particle is placed on the sleeve 22. By supplying the particles and forming and carrying a magnetic brush using the new magnetic particles, the durability of the charging device is improved.

Here, a mechanism for updating (exchanging) the magnetic brush (magnetic particles) on the sleeve 22 will be described.

The scraper 26 is separated from the sleeve 22 at the time of image formation, but the drive device 27 is turned on by the control circuit 100 to replace the sleeve 22 when the magnetic particles are replaced.
Is moved to contact the In this state, the sleeve 22
Is rotated, the magnetic particles on the sleeve 22 are scraped off by the scraper 26, pass through the communication opening 29 between the lower part of the housing 21 and the upper part of the cleaner container 91,
It falls to the bottom of the cleaner container 91. Then, new magnetic particles 24 are supplied from the magnetic particle storage hopper 21a onto the sleeve 22 from which the magnetic particles have been scraped off. The scraper 26 contacts the sleeve 22 before the sleeve 2
At the time point when 2 has completed one rotation, it is separated from the sleeve 22. As a result, the magnetic brushes on the entire peripheral surface of the sleeve 22 are updated to the magnetic brushes 24a made of new magnetic particles, and normal image formation becomes possible. The used magnetic particles scraped off from the sleeve 22 and dropped into the cleaner container 91 are transported together with the waste toner to the waste toner container 95 by the screw 93.
Collected inside.

New magnetic particles are supplied only by peeling off the magnetic particles on the sleeve 22. The magnetic particles carried on the sleeve 22 as the magnetic brush 24a and the magnetic particle storage hopper are used for normal image formation. This is because there is almost no mixing of the magnetic particles 24 stored in 21a. This is because the amount of magnetic particles per unit time which is regulated by the magnetic brush layer thickness regulating member 25 and supplied to the photosensitive drum 1 is equal to the amount of magnetic particles per unit time entering the magnetic particle storage hopper 21a. Also, this is because the magnetic particles on the sleeve 22 are restrained on the sleeve 22 by a magnetic force. Therefore, the magnetic particles 24 in the magnetic particle storage hopper portion 21a are always kept unused except for a part of the magnetic particles on the sleeve 22. Therefore, by removing the magnetic particles on the sleeve 22, new magnetic particles 24 are supplied onto the sleeve 22 from the magnetic particle storage hopper 21a.

The amount of magnetic particles scraped off the sleeve 22 is determined by the number of revolutions of the sleeve 22. In this embodiment, the sleeve 22 is rotated once while the scraper 26 is in contact. It was possible to replace 80% or more of the magnetic particles on the sleeve 22 based on the amount of the magnetic particles dropped at this time.

Next, a method for detecting the charging ability of the charging device will be described. A charging bias in which an AC bias having an amplitude of 1 kV and a frequency of 1 kHz is superimposed on a DC bias of -700 V from a charging bias applying power source S1 is applied to the magnetic brush charging device S1.
Flowing through the magnetic particles between the magnetic brush charging device 1 and the magnetic brush charging device 2
A DC current amount detecting device 101 for detecting a current amount is provided.

The current amount detection is performed after image formation when the number of image forming operations (image output) of the image forming apparatus exceeds a predetermined number. In this embodiment, the current amount is detected every 1500 image outputs.

In the current amount detection, in order to accurately measure the resistance of the magnetic brush, the potential difference of the magnetic brush with respect to the photosensitive drum 1 needs to be constant. Therefore, during image formation, since the image ratio and transfer voltage change, the potential difference from the photoconductor at the time of charging is not constant, so that detection is not performed, and non-image formation is performed (for example, during the pre-rotation step or post-rotation step). Current detection is performed while the potential on the photoconductor is kept constant.

In this embodiment, during non-image formation, the entire surface of the photosensitive member is exposed by the laser L, the developing bias application power source S2 and the transfer bias application power source S3 are turned off, and the exposure portion potential VL to the charging potential VD is kept constant. DC at potential difference
The current was measured. The ratio of the measured current amount to the reference current is obtained, and if it is less than the standard, the magnetic brush update operation mode described above is executed to supply new magnetic particles to the sleeve 22. The current amount after the supply is also measured and compared with the value before the supply. If the ratio of these two values is within a certain range and the charging ability is not improved, it is regarded as a change in the amount of current due to environmental fluctuations, and supply of magnetic particles is not performed thereafter.

The magnetic particle storage hopper 21a is provided with a sensor 28 for detecting the remaining amount of the magnetic particles, and confirms that the remaining amount of the magnetic particles 24 in the magnetic particle storage hopper 21a has reached a predetermined lower limit. If detected, the magnetic brush update operation mode is not executed thereafter.

As described above, while the magnetic particles having the reduced charging ability are peeled off from the sleeve and new magnetic particles are supplied onto the sleeve, while the waste toner container 95 of the cleaning device 9 is peeled off from the sleeve, the charged toner is removed. By also serving as a container for storing magnetic particles having a reduced capacity (used magnetic particle collection means), the size and simplification of the apparatus and the simplification of maintenance could be achieved.

(4) Others a) The magnetic brush update operation mode can be executed at the time of image formation. The current amount detection for detecting the charging ability of the charging device may be performed during non-image formation, and the magnetic brush update operation may be performed during image formation.

B) The waste toner container 95 is the cleaner container 9
1, and the magnetic particles peeled off from the sleeve 22 may be collected in the cleaner container 91.

C) The method of peeling off the magnetic particles from the sleeve 22 is not limited to the embodiment. A movable magnet is provided in the housing of the charging device, and the magnetic particles are contained in the sleeve when the magnetic particles are peeled off. Magnetic particles may be peeled off by forming a repulsive magnetic field by bringing a movable magnet close to the magnetic pole of the magnet 23.

D) The charging device of the present invention is not limited to the charging process of the image carrier in the image forming apparatus of the embodiment, but is naturally effective as a charging device for the charged object.

E) In the case of the injection charging system, the member to be charged preferably has a layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm. As the image carrier, in addition to the OCL photoconductor obtained by coating the surface layer (charge injection layer) in which conductive particles such as SnO ₂ are dispersed on the OPC photoconductor of the embodiment, α-S
A photoreceptor having a surface layer of i (amorphous silicon, amorphous silicon) or the like having charge injection and charging properties can be used. Further, the member to be charged (image carrier) may be one whose discharge charging mechanism is dominant.

F) The magnetic brush charging device is not limited to the sleeve rotating type of the embodiment, and the magnetic brush is conveyed along the outer peripheral surface of the sleeve by rotating the sleeve 22 and rotating the magnet roller 23. thing,
Conducting the surface of the magnet roller as necessary as a power supply electrode by conducting electrical treatment, directly constraining magnetic particles on the surface to form and carry a magnetic brush layer, and rotating the magnet roller. Can also. A non-rotating type magnetic brush charging device may be used.

G) The charging bias applied to the magnetic brush charging device may be a DC bias only. AC
As an AC bias waveform for applying a bias, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Also,
It may be a rectangular wave formed by periodically turning on / off a DC power supply. As described above, a bias whose voltage value periodically changes can be used as the waveform of the AC bias.

H) The image exposure means as the information writing means on the charged surface of the first image carrier in the image forming apparatus is not limited to the digital laser scanning exposure means as in the embodiment. Normal analog image exposure means and those using light emitting elements such as LEDs,
Any device that can form an electrostatic latent image corresponding to image information, such as a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter, may be used.

I) The first image carrier may be an electrostatic recording dielectric or the like. In this case, the dielectric surface is uniformly charged to a predetermined polarity / potential, and then selectively neutralized by a static elimination means such as a static elimination needle head or an electron gun to write and form a target electrostatic latent image.

J) The method and means for developing the electrostatic latent image are arbitrary. Instead of the reversal development of the embodiment, a regular development system may of course be used.

K) The transfer means is not only the roller transfer of the embodiment, but also a blade transfer and other contact transfer charging systems,
A non-contact transfer charging system using a corona charger may be used.

L) Using an intermediate transfer member such as a transfer drum or a transfer belt as a second image carrier, not only a single-color image formation but also an image forming apparatus for forming a multi-color, full-color image by multiple transfer or the like. Applicable.

An electrophotographic photosensitive member or an electrostatic recording dielectric as an image carrier is formed into a rotating belt type, and a charging / latent image forming /
A toner image corresponding to required image information is formed by a developing process means, the toner image forming section is positioned at a reading / displaying section, and an image is displayed, and an image carrier is repeatedly used for forming a display image. There is also a device (display device). The image forming apparatus of the present invention includes such an image display device.

[0109]

As described above, according to the present invention, with respect to the magnetic brush charging device and the image forming apparatus provided with the charging device, the contamination of the magnetic brush due to durability gradually progresses, and the unacceptable charging occurs. Before the deterioration of the performance or the image failure due to the reduction of the charging ability, the magnetic particles of the magnetic brush which has been contaminated from the magnetic brush holding member are separated by the magnetic particle separating means and collected as used magnetic particles. The magnetic brush renewal operation mode in which new magnetic particles are supplied from the magnetic particle supply means to the carrier member from which the magnetic particles have been separated and the magnetic particles are detached, and the carrier member carries the magnetic brush using the new magnetic particles. As a result, the deterioration of the charging ability due to the contamination of the magnetic brush, and the occurrence of image defects due to the decrease of the charging ability due to the contamination of the magnetic brush in the image forming apparatus for a long time. Over it can be prevented.

In the transfer type image forming apparatus, the transfer residual toner remaining on the first image carrier after the transfer of the toner image from the first image carrier to the second image carrier is removed. The size of the apparatus can be reduced by using the collecting container for collecting the toner removed from the first image carrier of the cleaning means to be used as the used magnetic particle collecting means for collecting the magnetic particles detached from the magnetic brush supporting member. , Simplification, and further, simplification of maintenance.

[Brief description of the drawings]

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

FIG. 2 is an enlarged model diagram of a magnetic brush charging device.

FIG. 3 is an enlarged model diagram of a developing device part.

FIG. 4 is an operation process diagram of the printer.

FIG. 5 is a schematic configuration diagram of a conventional example of a magnetic brush charging device.

[Explanation of symbols]

1. First image carrier (charged object), 2. Magnetic brush charging device, 3. Laser beam scanner, 4. Development device, 6. Transfer roller, 8. Fixing device, 9. A cleaning device, a second image carrier (transfer material), 21
..Charging device housing, 21a..Magnetic particle storage hopper (magnetic particle supply means), 22..Sleeve, 23
..Magnet rollers, 24..Magnetic particles, 24a ..
Magnetic brush part, 25 ... Magnetic brush layer thickness regulating member, 26
..Scraper (magnetic particle peeling means), 27..Scraper driving device, 28..Remaining magnetic particle detection sensor, 1
00: Control circuit, 101: DC current amount detection device, S
1. Power supply for applying charging bias, 91. Cleaner container, 95 .. Waste toner container (also used as used magnetic particle collecting means)

Claims (15)

[Claims] 1. A charging device for charging by bringing a magnetic brush of magnetic particles carried on a carrier member into contact with a member to be charged, wherein the magnetic particles detaching the magnetic particles forming the magnetic brush from the carrier member. Means, a magnetic particle collecting means for collecting the magnetic particles detached from the support member, and a magnetic particle supply means for supplying new magnetic particles to the support member from which the magnetic particles have been detached. A charging device having a magnetic brush renewal operation mode in which magnetic particles forming a brush are detached and a magnetic brush of new magnetic particles is carried. 2. A magnetic brush renewal operation mode is performed according to detection information of the magnetic brush carried by the carrier member, the detecting means detecting a charging ability of magnetic particles of the magnetic brush. The charging device according to claim 1, wherein: 3. The charging device according to claim 2, wherein the charging ability of the magnetic particles of the magnetic brush carried on the carrying member is detected by measuring the resistance of the magnetic particles. 4. The charging device according to claim 1, wherein the carrier is a rotating body, and the magnetic particle detaching unit is a scraper controlled to be in contact with and separated from the carrier. . 5. The charging device according to claim 1, wherein the magnetic particle collecting means is a container for collecting the magnetic particles separated from the supporting member by the magnetic particle separating means. . 6. The charging device according to claim 1, wherein said magnetic particle supply means is a hopper storing magnetic particles. 7. An image forming apparatus for performing image formation by applying an image forming process including a charging step of charging the image carrier to the image carrier, wherein a charging unit for charging the image carrier is provided. 7. An image forming apparatus, which is the charging device according to any one of 6. 8. A first image bearing member, charging means for charging the image bearing member, means for forming a toner image on the image bearing member charged by the charging means, A charging unit for charging the first image carrier, the transfer unit transferring the first image carrier to the first image carrier, and a cleaning unit for removing transfer residual toner remaining on the first image carrier after the transfer. Is a charging device that performs charging by bringing a magnetic brush of magnetic particles carried by a carrier member into contact with the first image carrier, and a magnetic device that separates the magnetic particles forming the magnetic brush from the carrier member. A particle detaching means, a magnetic particle collecting means for collecting the magnetic particles detached from the support member, and a magnetic particle supply means for supplying new magnetic particles to the support member from which the magnetic particles have been detached. Shape magnetic brush from To the magnetic particles are detached and the image forming apparatus characterized by having a magnetic brush updating operation modes of carrying a magnetic brush by the new magnetic particles. 9. A first image carrier, a charging unit for charging the image carrier, a unit for forming a toner image on the image carrier charged by the charging unit, and a second unit for transferring the toner image to a second unit. A charging unit for charging the first image carrier, the cleaning unit removing transfer residual toner remaining on the first image carrier after the transfer. Is a charging device that performs charging by bringing a magnetic brush of magnetic particles carried by a carrier member into contact with the first image carrier, and a magnetic device that separates the magnetic particles forming the magnetic brush from the carrier member. A particle detaching unit, a magnetic particle collecting unit that collects the magnetic particles detached from the support member, and a magnetic particle supply unit that supplies new magnetic particles to the support member from which the magnetic particles have been detached. Shape magnetic brush from A magnetic brush renewal operation mode in which the magnetic particles are removed and a magnetic brush made of new magnetic particles is carried, and a collection container for collecting the toner removed from the first image carrier by the cleaning means is provided in the magnetic container. An image forming apparatus, which also serves as a particle collection unit. 10. A magnetic brush renewal operation mode is performed according to detection information of the magnetic brush carried by the carrier member, the detecting means detecting a charging ability of magnetic particles of the magnetic particles. The charging device according to claim 8, wherein the charging device is used. 11. The charging device according to claim 10, wherein the charging ability of the magnetic particles of the magnetic brush carried on the carrying member is detected by measuring the resistance of the magnetic particles. 12. The detection of the charging ability of the magnetic particles of the magnetic brush carried by the carrying member by the detection means, and the execution of the magnetic brush update operation mode in accordance with the detection information of the detection means exceeds a predetermined number of image outputs. The image forming apparatus according to claim 10, wherein the image forming is performed after the image is formed. 13. The charging device according to claim 8, wherein the carrier is a rotating body, and the magnetic particle detaching unit is a scraper that is controlled to contact and separate from the carrier. . 14. The charging device according to claim 8, wherein said magnetic particle supply means is a hopper storing magnetic particles. 15. A device for forming a toner image on an image carrier charged by a charging device, comprising: forming an electrostatic latent image on an image carrier charged by the charging device by an image exposure device; 15. The image forming apparatus according to claim 8, wherein the developing device forms a toner image corresponding to the electrostatic latent image.