JP2001109347A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of a defective image due to decline in chargeability caused by the permanent pollution of magnetic particles constituting a magnetic brush part for a long period in an image forming device using a magnetic brush charging device as the charging processing means of an image carrier. SOLUTION: This image forming device has a recovering means 3 for recovering conductive magnetic particles stuck to an image carrier 1 from a magnetic brush changing device 2 on the downstream side in the image carrier moving direction of the device 2 and on the upstream side in the image carrier moving direction compared with a developing means 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging means (magnetic brush charger) for charging an image carrier by bringing conductive magnetic particles into contact with an image carrier and applying a voltage to the conductive magnetic particles. The present invention relates to an image forming apparatus having means for forming an electrostatic latent image on a charged surface of an image carrier and developing means for developing the electrostatic latent image formed on the image carrier as a toner image.

[0002]

2. Description of the Related Art a) Transfer-Type Image Forming Apparatus A transfer-type image forming apparatus forms a transferable image on a first image carrier by an appropriate image forming process, and transfers the transferable image to a second image bearing member. The first image carrier is an apparatus having a system and a structure that is repeatedly used for image formation.

For example, an image forming apparatus such as a copying machine or a laser beam printer utilizing a transfer type electrophotographic process is basically an electrophotographic photosensitive member generally using a rotary drum type as a first image carrier. Charging means for uniformly charging the surface of the rotating photoreceptor to a predetermined polarity and potential; image exposure means for forming an electrostatic latent image on a charged surface of the rotating photoreceptor; Means for developing the toner image as a toner image, transfer means for transferring the toner image from the photoreceptor surface to a transfer paper as a second image carrier (recording medium), and permanently fixing the toner image transferred to the transfer paper side The image forming apparatus includes a fixing unit that fixes the image as an image, and a photoconductor cleaning unit (cleaner) that removes untransferred toner from the surface of the rotating photoconductor after transferring the toner image to the transfer paper and cleans the photoconductor surface.

The transfer paper on which the image has been fixed by the fixing means is discharged as an image formed product (copy, print).

The photoreceptor surface cleaned by the cleaning means is repeatedly used for image formation.

B) Contact Charging Means Corona charging has conventionally been used as charging means for uniformly charging the surface of a photoreceptor to a predetermined polarity and potential. The corona charger is disposed so as to face the member to be charged in a non-contact manner, and charges the surface of the member to be charged to a predetermined polarity and potential by exposing the surface of the member to a corona shower emitted from the corona charger to which a high voltage is applied.

In recent years, a contact charging device has been put into practical use instead. That is, a predetermined charging bias is applied to a conductive member such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type to a photoreceptor to be charged, and a predetermined polarity of a photoreceptor surface is applied. -It is charged to a potential, and has advantages such as low ozone and low power as compared with a corona charger.

As a method of applying a charging bias to the contact charging member, there are a DC bias method in which only a DC bias is applied and an AC bias method in which a DC bias is applied while being superimposed on an AC bias.

[0009] Contact charging mechanism (charging mechanism,
The charging principle) includes two types of corona charging system and contact injection charging system, and each characteristic appears depending on which is dominant.

The corona charging system uses a discharge phenomenon such as corona discharge generated in a minute gap between the contact charging member and the member to be charged, and charges the member to be charged with the discharged product. This corona charging system generates a very small amount of ozone although it is much less than the corona charger.

A contact injection charging system is a system in which a surface of a member to be charged is charged by injecting charges directly from a contact charging member to the member to be charged. It is also called direct charging or injection charging.

Japanese Patent Application Laid-Open No. 6-3921 and the like disclose that a charge holding member such as a trap level on the surface of a photoreceptor or conductive particles of a charge injection layer is charged by a contact charging member such as a charging roller, a charging brush, or a charging magnetic brush. Has been proposed to perform contact-injection charging.

Since contact injection charging does not use a discharge phenomenon,
The voltage required for charging is only the desired surface potential of the photoreceptor, and is an ozone-less low-power charging method that does not generate ozone.

C) Cleanerless (Cleanerless Process, Toner Recycling Process) Regarding the transfer type image forming apparatus, in order to reduce the size of the apparatus, reduce the cost, ecology, etc., it is not necessary to provide a special cleaner especially on the photosensitive member. A method of cleaning (removing) residual toner (transfer residual toner) after transfer using a charging device or a developing device (simultaneous charging cleaning or simultaneous developing cleaning) has been proposed.

That is, in a general transfer type image forming apparatus, transfer residual toner remaining on the photoreceptor after transfer is removed from the surface of the photoreceptor by a dedicated cleaner to become waste toner. It is preferable not to come out from the aspect of protection.

Therefore, the cleaner-less image forming apparatus is constructed such that the cleaner is eliminated, and the transfer residual toner on the photoreceptor after the transfer is removed from the photoreceptor surface by simultaneous development and cleaning by the developing device, and is collected and reused in the developing device. Has also appeared. That is, the developing device also serves as a cleaner for collecting the transfer residual toner remaining on the photosensitive member after the transfer of the toner image to the recording medium.

In the simultaneous cleaning with development, the toner remaining on the photoreceptor after transfer is subjected to a fogging bias (a fog removing potential difference Vback which is a potential difference between a DC voltage applied to the developing device and a surface potential of the photoreceptor) at the time of subsequent development. ). According to this method, since the transfer residual toner is collected in the developing device and reused in the subsequent steps, the waste toner is eliminated, and the trouble of maintenance can be reduced. In addition, the cleaner-less has a great advantage in terms of space, and can reduce the size and cost of the image forming apparatus.

D) Contact charging type / transfer type / cleanerless image forming apparatus In a transfer type / cleanerless image forming apparatus, when a contact charging means is adopted as a charging means for a photosensitive member as an image carrier, Positive ghost due to poor transfer residual toner collection in the developing device can be suppressed by the effect of scattering the transfer residual toner by the contact charging member in contact with the photoconductor.

[0019] Since it is cleaner-less, there is an advantage that the photosensitive member surface is not damaged by a cleaning member rubbing in contact with the photosensitive member surface.

Among the contact charging members, as a contact charging member,
Magnetic brush charger (magnetic brush charger) having a magnetic brush portion in which conductive magnetic particles are magnetically constrained to form a brush
The magnetic brush as a contact charging member is less susceptible to toner contamination than other contact charging members such as a conductive rubber roller and a fixed or rotating fur brush, and is preferably used in a cleanerless process.

[0021]

The magnetic brush as a contact charging member in a magnetic brush charging device is less susceptible to toner contamination than other contact charging members, but it is still used for a long time and its durability is improved. As a result, the magnetic particles constituting the magnetic brush portion are gradually contaminated with toner and other image-bearing materials, and the resistance is increased due to the increase in resistance, and the charging capability is reduced in the image forming apparatus. There is a problem that ground fog and electrified ghosts occur due to the above.

Therefore, the present invention relates to an image forming apparatus using a magnetic brush charging device as a charging means for an image bearing member. It is intended to prevent the occurrence of defects for a long time.

[0023]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) Charging means for bringing the conductive magnetic particles into contact with the image carrier and applying a voltage to the conductive magnetic particles to charge the image carrier, and electrostatically charging the charged surface of the image carrier. In an image forming apparatus having a unit for forming a latent image and a developing unit for developing the electrostatic latent image formed on the image carrier as a toner image, on the downstream side in the image carrier moving direction of the charging unit,
An image forming apparatus further comprising a recovery means for recovering conductive magnetic particles adhered to the image carrier from the charging means at a position upstream of the developing means in the image carrier movement direction.

(2) The image forming apparatus according to (1), wherein the collecting means recovers the conductive magnetic particles by a magnetic force.

(3) The image forming apparatus according to (1), wherein the collecting means mechanically collects the conductive magnetic particles by bringing the collecting member into contact with the image carrier.

(4) Any one of (1) to (3), wherein a bias different from that at the time of charging the image carrier is applied to the charging means so that the conductive magnetic particles adhere to the image carrier. An image forming apparatus according to claim 1.

(5) The image forming apparatus according to any one of (1) to (4), wherein the charging by the conductive magnetic particles is performed by injecting a charge into the image carrier.

(6) The developing means also serves as means for collecting the transfer residual toner remaining on the image carrier after transferring the toner image on the image carrier onto the transfer material (1).
The image forming apparatus according to any one of (1) to (5).

(7) The image carrier comprises a surface layer having amorphous silicon (1) to (6).
The image forming apparatus according to any one of the above.

(8) The image forming apparatus according to any one of (1) to (7), wherein the developing means is a developing device using a two-component developer composed of toner and magnetic particles.

(9) The image carrier has a surface of 10 ⁹ to 10 ¹⁴ Ω
The image forming apparatus according to any one of (1) to (8), further comprising a layer made of a material of cm.

The image forming apparatus according to any one of claims 1 to 9, wherein the image carrier has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles.

(11) The image forming apparatus according to (10), wherein the conductive fine particles are SnO ₂ .

(12) The image forming apparatus according to any one of (1) to (11), wherein the means for forming an electrostatic latent image on the charged surface of the image carrier is an image exposure means.

<Operation> That is, in an image forming apparatus using a magnetic brush charging device, contamination due to durability of magnetic particles constituting the magnetic brush gradually progresses, and image defects due to an unacceptable decrease in charging ability occur. Before this occurs, the magnetic brush of the magnetic brush, which has been increased in resistance due to contamination, is detached and adhered to the image carrier by applying a bias to the magnetic brush so as to detach and adhere to the image carrier, and detached to the image carrier. The attached magnetic particles are collected by a magnetic particle collecting means provided on the image carrier moving direction downstream side from the magnetic brush charging device,
The magnetic brush charging device in which the magnetic particles are detached and adhered to the image carrier is supplied with new magnetic particles to reconfigure the magnetic brush with the new magnetic particles. It is intended to extend the life.

Also, the magnetic particle collecting means is provided downstream of the magnetic brush charger in the image carrier moving direction and upstream of the developing means in the image carrier moving direction, so that the magnetic brush charger is separated from the magnetic brush charger to the image carrier. The deposited magnetic particles do not enter the developing means, and can prevent problems such as fluctuations in the amount of charge of the toner in the developing means caused by mixing of the magnetic particles for charging into the developing means. It is.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (FIGS. 1 to 6) (1) Overall Schematic Description of Example of Image Forming Apparatus FIG. 1 is a schematic structural model 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 3
On a 0 mm conductive drum substrate made of aluminum or the like, a charge generation layer in which a disazo pigment is dispersed in a resin, a charge transport layer in which hydrazone is dispersed in a polycarbonate resin, and a photocurable acrylic resin on the outermost layer. Has an organic photosensitive layer composed of a charge injection layer in which ultrafine particles of SnO ₂ are dispersed, and is driven to rotate in the clockwise direction of the arrow at a peripheral speed of 100 mm / sec.

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

Reference numeral 3 denotes a magnetic particle collecting device disposed downstream of the magnetic brush charging device 2 in the photosensitive drum rotation direction. This magnetic particle recovery device 3 will be described in detail in section (4).

Reference numeral 4 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 5 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). The two-component contact developing device 5 will be described in detail in section (3).

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 pressure contact nip portion is a transfer portion (transfer portion) T. At a predetermined control timing, a transfer material P as a second image bearing member is guided by a pre-transfer guide (not shown) and fed to a transfer portion T from a paper feed unit (not shown).

The transfer material P fed to the transfer site T is conveyed while being sandwiched between the rotary photosensitive drum 1 and the transfer roller 6.
In the meantime, a predetermined transfer bias is applied to the transfer roller 6 from the transfer bias application power source S4, and the back surface of the transfer material P is charged with a polarity opposite to that of the toner. As a result, 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 portion 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 guide or a conveying device 7. Then, the toner image is subjected to a fixing process and printed out.

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

The cleaning device 9 of this embodiment is of a blade type, is disposed in a cleaner container 91, and is provided in the cleaner container 91. The leading edge of the cleaning device 9 abuts on the surface of the photosensitive drum 1 and is adhered to and supported by a support plate. It comprises a cleaning blade (silicon-modified polyurethane rubber blade) 92, a screw shaft 93 disposed at the bottom in a cleaner container 91, and the like.

The transfer residual toner remaining on the rotating photosensitive drum 1 is scraped off by the cleaning blade 92 and falls to the bottom in the container 91, and is conveyed to one end side of the cleaner container by rotation of the screw shaft 93, and is not illustrated. And is conveyed to a waste toner container (not shown) and collected.

FIG. 5 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 stopped once, the rotation of the photosensitive drum is stopped, and the printer stands by until an image forming (printing) start signal is input. Held in state.

C) Pre-rotation process This is a period in which the main motor is restarted by the input of the image formation start signal, the photosensitive drum 1 is driven to rotate again, and the printer executes 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 case of the continuous image forming mode, the above-described image forming process is repeated, and image forming processes for a predetermined set number n are sequentially executed.

E) Paper-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 site T and the time when the front end of the next transfer material P reaches the transfer site T is reached. This is a transfer material non-sheet passing state period at the transfer portion T.

F) Post-rotation process The main motor continues to be driven for a while after the end of the last n-th image forming process 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 after a predetermined time, 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.

When 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 for 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.

Reference numeral 21 denotes a housing of the magnetic brush charging device 2, and reference numeral 22 denotes a non-magnetic charging sleeve as a magnetic brush holding member, the lower surface of which is exposed to the outside and rotatably disposed in the housing 21. .

Reference numeral 23 denotes a magnet roller as a magnetic field generating means, which is inserted into the charging sleeve 22 and fixed so as not to rotate.
The charging sleeve 22 is rotationally driven at a predetermined peripheral speed in the clockwise direction indicated by the arrow around the outer circumference of FIG.

The inside of the housing 21 is a magnetic particle storage hopper as a means for supplying conductive magnetic particles (charge carriers) to the charging sleeve 22. In this embodiment, 300 g of the magnetic particles 24 are stored.

Reference numeral 25 denotes a magnetic brush layer thickness regulating member (regulating blade, regulating plate) provided at the opening of the housing 21.
B gap). The regulating member 25 is magnetically constrained and carried as a magnetic brush by the magnetic field of the magnet roller 23 in the charging sleeve 22, and is carried by the rotation of the charging sleeve 22, and is rotatably conveyed and taken out of the housing 21. (The thickness of the magnetic brush) is regulated in a predetermined manner, and serves to form a magnetic brush coat layer 24a of an appropriate amount of magnetic particles.

The magnetic brush charging device 2 is disposed above the photosensitive drum 1 with the lower surface of the charging sleeve 22 parallel to and near the photosensitive drum 1. The charging sleeve 22 and the photosensitive drum 1 are opposed to each other with a small gap (SD gap). This SD gap is the above-mentioned SB
The gap is set to be smaller than the gap.
m. In this SD gap, the magnetic brush portion 24 a on the charging sleeve 22, whose layer thickness is regulated by the SB gap of the regulating member 25 as described above, comes into contact with the photosensitive drum 1 and the surface of the photosensitive drum 1 is moved. It is rubbed with the magnetic brush. N is a charged portion (charging portion) which is the magnetic brush contact nip portion.

Then, a predetermined charging bias is applied from the charging bias applying power source S1 to the magnetic brush section 24a via the charging sleeve 22, and the surface of the photosensitive drum 1 is contact-charged to a predetermined polarity and potential at the charging portion N. .

The charging sleeve 22 is driven to rotate in the clockwise direction of the arrow at a peripheral speed of 200 mm / sec. The magnetic flux density by the magnet roller 23 on the charging sleeve 22 at the charging site N is 800 × 10 ⁻⁴ T.

The average particle diameter of the magnetic particles 24 is 25 μm.
m, resistance value is 5 × 10 ⁶ Ω / cm, saturation magnetization is 200 e
mu / cm ² was used. The loading amount of the magnetic particles as the magnetic brush 24a on the charging sleeve 22 is 150 mg.
/ Cm ² .

The alternating electric field of 700 Vpp · 1 kHz from the charging bias applying power source S 1 is applied to the charging sleeve 22.
The switch SW is controlled by the control circuit 100 to switch between the charging bias on which the 700 V DC voltage is superimposed and the recovery bias of the +350 V DC voltage from the power supply S2, and can be switched by the switch SW1. The application of an alternating electric field as a charging bias is effective in improving the charging ability and preventing a positive ghost.

The magnetic particles 2 stored in the housing 21
4 shows that only the magnetic particles in the vicinity of the outer surface of the charging sleeve 22 are magnetically constrained as a magnetic brush layer by the magnetic force of the magnet roller 23 in the charging sleeve 22 so that the charging sleeve 2
Although the magnetic particles 24 are conveyed along with the rotation of 2, the remaining most of the magnetic particles 24 form an immobile layer that hardly moves even when the charging sleeve 22 rotates.

(3) Developing Device 5 FIG. 4 is an enlarged model diagram of the developing device 5. Reference numeral 51 denotes a developing container, and reference numeral 52 denotes a non-magnetic developing sleeve having a diameter of 16 mm. The developing sleeve 52 is rotatably disposed in the developing container 51 with a part of its outer peripheral surface being exposed to the outside.
Reference numeral 53 denotes a magnet roller fixed to the non-rotation and inserted into the developing sleeve 52; 54, a developer coating blade; 55, a two-component developer contained in the developing container 51;
Reference numeral 57 denotes a developer stirring member disposed on the bottom side in the developing container 51, and reference numeral 58 denotes a toner hopper disposed on an upper portion in the developing container 51, in which replenishment toner t is stored.

The two-component developer 55 in the developing container 51 has a weight toner concentration of 5 μm between a toner t having a negatively chargeable average particle diameter of 8 μm and a magnetic carrier c having a positively chargeable average particle diameter of 50 μm.
% Of the mixture, and is stirred by the developer stirring members 56 and 57.

The developing sleeve 52 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 55 is attracted and held as a magnetic brush layer on the outer peripheral surface of the developing sleeve 52 by the magnetic force of the magnet roller 53 in the sleeve, and is conveyed in rotation with the rotation of the sleeve. Thereby, the layers are adjusted to a predetermined thin layer 55a. The developing sleeve 52 is opposed to the photosensitive drum 1 with an interval of 500 μm, and a facing portion between the developing sleeve 52 and the photosensitive drum 1 is a developing portion (developing portion) A. At the development site A, the developer thin layer 55a formed on the development sleeve 52
Are set in such a manner that development is performed in a state of contact with the photosensitive drum 1. The developing sleeve 52 is supplied with an alternating electric field of 2 kV and 2 kHz from the developing bias application power source S3.
A developing bias on which a DC voltage of 500 V is superimposed is applied.

The toner in the developer coated on the surface of the rotating developing sleeve 52 as a thin layer 55a and conveyed to the developing site A is separated by the developing bias AC + DC.
The electrostatic latent image is developed as a toner image by selectively adhering to the surface of the photosensitive drum 1 corresponding to the electrostatic latent image by the electric field due to 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 52 that has passed through the developing site A is returned to the developer reservoir in the developing container 51 as the developing sleeve 52 continues to rotate.

In order to maintain the toner concentration of the two-component developer 55 in the developing container 51 within a predetermined substantially constant range, the toner concentration of the two-component developer 55 in the developing container 51 is, for example, an optical toner (not shown). The toner is detected by the density sensor, and the toner supply roller 58a of the toner hopper 58 is drive-controlled in accordance with the detection information, and the toner t in the toner hopper is supplied to the two-component developer 55 in the developing container 51. The toner supplied to the two-component developer 55 is
Stir evenly with 6.57.

(4) Magnetic Particle Recovery Apparatus 3 FIG. 3 is an enlarged model view of the magnetic particle recovery apparatus 3. The magnetic particle recovery device 3 of the present embodiment recovers the magnetic particles 24b attached on the photosensitive drum 1 by a magnetic force.

Reference numeral 31 denotes a housing of the magnetic particle recovery device 3,
Reference numeral 32 denotes a non-magnetic recovery sleeve having a diameter of 16 mm. The recovery sleeve 32 is rotatably disposed in the housing 31 with a part of its outer peripheral surface being exposed to the outside.

Reference numeral 33 denotes a four-pole magnet roller serving as a magnetic field generating means, which is inserted into the collection sleeve 32 and is fixed so as to be non-rotatable. Are driven to rotate at a predetermined peripheral speed in the counterclockwise direction of the arrow.

Numeral 34 denotes a flexible scraper disposed in the housing 31 with its leading edge contacting the counter of the surface of the collecting sleeve 31, and numeral 35 denotes a screw shaft disposed at the bottom of the housing 31. .

The magnetic particle collecting device 3 is located at a position downstream of the magnetic brush charging device 2 in the direction of rotation of the photosensitive drum, upstream of the developing device 5 in the direction of rotation of the photosensitive drum, and a laser scanning exposure position for the photosensitive drum 1. A collection sleeve 32 is provided facing the photosensitive drum 1 in a non-contact manner at a distance of 200 μm on the upstream side in the photosensitive drum rotation direction. The magnetic flux density of the magnetic pole of the magnet roller 33 in the collection sleeve 32 facing the photosensitive drum 1 is 800 × 10 ⁻⁴ T.

In the magnetic brush charging device 2, the magnetic particles (charge carriers) 24 b detached from the magnetic brush portion 24 a of the charging sleeve 22, adhere to the surface of the photosensitive drum 1, and are carried to the development site A as the photosensitive drum 1 rotates. On the way, the magnetic particles are transferred to and adhered to the outer surface of the collecting sleeve 32 by the magnetic force of the magnet roller 33 in the collecting sleeve at the portion where the collecting sleeve 32 of the magnetic particle collecting device 3 and the photosensitive drum 1 are close to each other. The magnetic particles 24b transferred to and adhered to the outer surface of the collecting sleeve 32 by magnetic force are carried into the housing 31 as the collecting sleeve 32 rotates, and scraped off from the outer surface of the collecting sleeve 32 to the bottom of the housing 31 by the scraper 34. , Screw shaft 35
Is transported to one end side of the housing 31 by rotation of the housing 31, and is transported and collected through a duct (not shown) to a waste toner container (not shown) of the cleaning device 9 in this case.

The collecting sleeve 32 of the magnetic particle collecting device 3 is constantly rotating during the image forming process.
The magnetic particles that slightly detach from and adhere to the surface of the photosensitive drum 1 from the magnetic brush portion 24a are also collected.

(5) Magnetic brush renewal operation mode The magnetic brush portion 24a of the charging sleeve 22 of the magnetic brush charging device 2 forms an image with toner or toner external additives that have passed through the cleaning blade 92 of the cleaning device 9. Adheres gradually every time. These deposits are mainly insulators, and the electrical resistance of the magnetic particles constituting the magnetic brush increases by attaching to the magnetic brush. If the resistance of the magnetic particles constituting the magnetic brush portion is too high, sufficient charge is not applied to the photosensitive drum, resulting in poor charging.

Therefore, in this embodiment, the magnetic particles having a high resistance constituting the magnetic brush portion 24a of the charging sleeve 22 of the magnetic brush charging device 2 are intentionally applied to the surface of the photosensitive drum 1 every time a fixed number of images are output. And collects them in the magnetic particle collection device 3 described above.
The magnetic brush portion 24a is formed and supported by new magnetic particles (refreshing of magnetic particles, magnetic brush renewal operation) to prevent charging failure beforehand and to improve the durability of the magnetic brush charging device 2. is there.

After completion of image formation after the image output of the image forming apparatus has exceeded a certain number, the above-described magnetic brush update operation mode is executed. The steps will be described.

[0088] At the time of the post-rotation process after completion of image formation after the image output of the image forming apparatus exceeds a certain number, only the charging bias applied to the charging sleeve 22 of the magnetic brush charging device 2 is switched from the power source S1 by the switch SW1 to the power source S2. Change to + 300V by switching. Switch SWl
Is automatically controlled by the control circuit 100.

Thus, the magnetic particles constituting the magnetic brush 24 a on the charging sleeve 22 are separated from the charging sleeve 22 and adhere to the photosensitive drum 1.

When the photosensitive drum 1 of this embodiment is negatively charged and a positive polarity bias is applied to the charging sleeve 22, the photosensitive drum 1 is hardly charged, and there is a gap between the charging sleeve 22 and the photosensitive drum 1. A potential difference of about 250 V occurs. Due to this potential difference, + charges are injected into the magnetic particles constituting the magnetic brush 24 a on the charging sleeve 22, and the magnetic particles constituting the magnetic brush 24 a are formed by an electrostatic force caused by an electric field generated between the charging sleeve 22 and the photosensitive drum 1. Adhere to the photosensitive drum 1.

[0091] Magnetic brush part 24 of charging sleeve 22
a, the magnetic particles 24b adhered to the surface of the photosensitive drum 1 and carried to the downstream side in the rotation direction of the photosensitive drum as the photosensitive drum 1 rotates. At the opposing portion facing the photosensitive drum 1, the magnetic force of the magnet roller 33 in the collecting sleeve transfers and adheres to the outer surface of the collecting sleeve 32.
Picked up from the surface.

The magnetic particles 24b transferred and attached to the outer surface of the collecting sleeve 32 by magnetic force are carried into the housing 31 with the rotation of the collecting sleeve 32, and are scraped from the outer surface of the collecting sleeve 32 to the bottom of the housing 31 by the scraper 34. In the case of this example, the toner is scraped off, transported to one end side of the housing 31 by rotation of the screw shaft 35, transported to a waste toner container (not shown) of the cleaning device 9 in this case through a duct (not shown), and collected.

[0093] On the other hand, in the magnetic brush charging device 2, as the magnetic particles constituting the magnetic brush 24 a on the charging sleeve 22 adhere to the photosensitive drum 1 and are carried to reduce the amount, the housing 21 is placed on the charging sleeve 22. The unused magnetic particles 24 stored therein are supplied, and the magnetic brush layer 24a is formed by the unused new magnetic particles. That is, the magnetic brush layer 24a is updated.

Experimental Example: Here, a durability test of image output was performed to examine the effect of suppressing the reduction in charging ability and the effect of suppressing ghosting of the magnetic brush charging device 2 in the first embodiment. FIG. 6 shows the result.

Comparative Example 1 is one in which the magnetic particle collection step by the magnetic particle collection device 3 is omitted in the above-mentioned magnetic brush update operation (system in which the magnetic brush is not updated at all). Therefore, in the case of Comparative Example 1, every time the magnetic brush renewal operation is performed, the magnetic particles 24b detached and attached to the photosensitive drum 1 from the charging sleeve 22 of the magnetic brush charging device 2 reach the developing site A and enter the developing device 5 It is taken in and mixed into the two-component developer 55.

The loading amount of the magnetic particles 24 in the housing 21 of the magnetic brush charging device 2 is 300 g for both the embodiment 1 and the comparative example 1, and the amount of the magnetic particles 24 as the magnetic brush 24a on the charging sleeve 22 is 170mg / sec
It is. Endurance test is continuous 100 sheets mode, image ratio 8%
Using an A4 original.

The vertical axis of the graph of FIG. 6 indicates the charging ability, which is represented by ΔV here. △ V is 0V photosensitive drum-
This is a value obtained by subtracting the saturation potential from the potential in the first round when charging to 700V. The smaller this value is, the higher the charging ability is. The horizontal axis is the number of durable sheets.

The execution of the magnetic brush update operation mode was performed every 10,000 output sheets. Photosensitive drum 1 and charging sleeve 2
The peripheral speed of No. 2 was the same as that during image formation, and approximately 15 g of magnetic particles could be collected by performing the magnetic brush update operation for 20 seconds.

As in the first embodiment, in the case of the above-described magnetic brush update operation mode, it can be seen that the deterioration of the charging ability due to the durability is very small as compared with the comparative example 1.

In Comparative Example 1 in which the magnetic particle collecting step by the magnetic particle collecting apparatus 3 was omitted, a ghost occurred due to a decrease in charging ability in about 15,000 sheets. Was not seen at all.

In the case of the magnetic brush charging, the magnetic particles constituting the magnetic brush 24a slightly adhere to the photosensitive drum 1 even during normal image formation. The magnetic particles used for charging have a lower electrical resistance than the magnetic carrier (development carrier) c of the two-component developer 55 of the developing device 5, so that when the charging magnetic particles are mixed into the developer, the charge amount of the toner is stable. Without
This may cause toner scattering and fog on the ground.

However, in the first embodiment, the developing device 5
The charging magnetic particles were hardly mixed into the developer 55, and the charge amount of the toner was stable throughout.

<Embodiment 2> (FIG. 7) In this embodiment 2, the magnetic particle collecting device 3 is brought into contact with the photosensitive drum 1 with the collecting member 36 as shown in FIG. It was of a type for collecting 24b. Other configurations of the printer and the image forming process are the same as those in the first embodiment, and a description thereof will be omitted.

In the magnetic particle collecting apparatus 3 of the second embodiment, the collecting member 36 is a blade-shaped member made of silicon-modified polyurethane rubber, and its tip is disposed in contact with the counter of the rotating photosensitive drum 1 on the surface thereof. I have.

Charging Sleeve 22 of Magnetic Brush Charging Device 2
The magnetic particles 24b detached from the magnetic brush portion 24a, adhered to the surface of the photosensitive drum 1 and carried downstream of the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 with the rotation of the photosensitive drum 1 before the magnetic particle collection device 3 The blade-shaped collecting member 36 scrapes off the photosensitive drum 1 from the surface of the photosensitive drum 1 to the bottom in the housing 31, and is conveyed to one end of the housing 31 by rotation of the screw shaft 35, and passes through a duct (not shown). It is transported to a waste toner container (not shown) and collected.

In this embodiment as well, the magnetic brush charging device 2
The magnetic particles 24b detached from the magnetic brush portion 24a of the charging sleeve 22 and carried and adhered to the surface of the photosensitive drum 1 can be reliably collected. By providing a magnetic particle collecting step, defective charging is prevented. Example 1 can be performed without the charging magnetic particles being mixed into the developer 55.
A stable image could be obtained over a long period of time in the same manner as in the above.

<Embodiment 3> (FIGS. 8 and 9) Embodiment 3 is a printer of a cleanerless process (cleanerless system). FIG. 8 is a schematic structural model diagram of the printer in the present embodiment. Example 1 (FIG. 1)
Since the configuration is almost the same as the printer configuration except that the cleaning device 9 is omitted, a detailed description of the configuration is omitted here.

In the cleanerless process, the transfer residual toner that is carried from the transfer portion T to the charged portion N due to the absence of the cleaning device (9) includes the toner having the normal charge polarity and the toner having the normal charge polarity. And the toner whose charging polarity has been inverted due to the discharge of the toner.

Of these, the toner of normal polarity passes through the charging portion N to the developing portion A while being rubbed by the magnetic brush 24a, and is collected by the developing device 5 at the same time as the development.

Normal toner passes through the charging portion N because the surface of the photosensitive drum 1 is normally charged only to a potential slightly lower than the charging bias voltage applied to the contact charging member. This is because an electric field that is pressed in the direction is generated. The image pattern of the transfer residual toner is disturbed to some extent by the rubbing of the toner of the normal polarity by the magnetic brush 24 a as the contact charging member, and the toner is easily collected by the developing device 5.

On the other hand, the toner whose polarity has been reversed generates an electrostatic force in the direction of the contact charging member, and is once collected in the magnetic brush 24a as the contact charging member. The polarity-reversed toner once collected in the magnetic brush 24a is re-normalized in polarity by frictional charging with the magnetic particles constituting the magnetic brush 24a, so that electrostatic force toward the photosensitive drum is generated. Is discharged from the magnetic brush 24a onto the surface of the photosensitive drum, adheres to the surface of the photosensitive drum, reaches the developing site A, and is collected by the developing device 5.

Experimental Example: FIG. 9 shows the result of an endurance test of an image output performed by the cleanerless process printer of the third embodiment.

In the cleaner-less process, transfer residual toner on the surface of the photosensitive drum enters the charged portion N without being scraped off by the cleaner, so that the contamination of the magnetic particles of the magnetic brush 24a of the magnetic brush charger is further promoted. Is done.

Therefore, in the third embodiment, the execution of the magnetic brush update operation mode is performed every 8,000 output sheets. Other experimental conditions are the same as in the first embodiment.

In Comparative Example 2, the magnetic particle collecting step by the magnetic particle collecting apparatus 3 was omitted (system in which the magnetic brush was not renewed at all). Therefore, in the case of this comparative example, every time the magnetic brush renewal operation is performed, the magnetic particles 24b detached and attached to the photosensitive drum 1 from the charging sleeve 22 of the magnetic brush charging device 2 reach the developing site A and are taken into the developing device 5. And mixed into the two-component developer 55.

From the experimental results, it is understood that the use of the third embodiment suppresses a decrease in the charging ability.

In this image forming step, by applying the same magnetic particle collecting step as in Example 1, charging failure was prevented, the toner charge amount of the developer was stabilized, and a good image could be obtained over a long period of time. .

<Others> a) The magnetic particle detaching means for detaching the magnetic particles constituting the magnetic brush 24a from the magnetic brush holding member 22 is a scraper that is controlled to swing toward and away from the magnetic brush holding member and the magnetic brush. Mechanical means such as the above.

B) A means for detecting the charging ability of the magnetic particles of the magnetic brush 24a carried by the magnetic brush carrying member 22 is provided, and the magnetic brush updating operation mode is executed in accordance with the detection information of the detecting means. You can also.

The charging ability of the magnetic particles of the magnetic brush can be detected, for example, by measuring the resistance of the magnetic particles of the magnetic brush.

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.

C) In the case of the injection charging system, the image carrier preferably has a layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm. In addition to the OCL photoconductor in which a surface layer (charge injection layer) in which conductive particles such as SnO ₂ are dispersed on the OPC photoconductor of the embodiment, a surface layer of α-Si (amorphous silicon, amorphous silicon) A material having charge injecting and charging properties, such as a photoreceptor having a Further, the image carrier as the member to be charged may be one in which the discharge charging mechanism is dominant.

D) The magnetic brush charging device 2 of the sleeve rotation type used in the embodiment is an example. For example, a magnetic brush attached magnetic particles to a fixed magnet bar that does not rotate, or a rotating or non-rotating magnetic brush. An apparatus of a type in which a multi-pole magnet is rotated in a sleeve to convey a magnetic brush of magnetic particles may be used.

The charging bias applied to the magnetic brush charging device may be a DC bias alone. It is also possible to superimpose an AC bias on a DC bias to further promote adhesion. As an AC bias waveform when applying an AC bias, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Alternatively, a rectangular wave formed by periodically turning on / off a DC power supply may be used. As described above, a bias whose voltage value periodically changes can be used as the waveform of the AC bias.

E) The magnetic particle collecting means 3 is not limited to the embodiment. A recovery container may be provided to store the recovered magnetic particles therein.

F) 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, but is usually used. Any of those which can form an electrostatic latent image corresponding to image information, such as an analog image exposure unit, a device using a light emitting element such as an LED, and a device using a combination of a light emitting device such as a fluorescent lamp and a liquid crystal shutter. I just need.

F) 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.

G) 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.

H) 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.

I) Using an intermediate transfer member such as a transfer drum or a transfer belt as the second image carrier, not only for forming a single-color image but also for an image forming apparatus for forming a multi-color or 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.

[0132]

As described above, according to the present invention, in an image forming apparatus provided with a magnetic brush charging device, contamination due to durability of magnetic particles constituting a magnetic brush gradually progresses, and unacceptable charging occurs. Before an image defect due to a decrease in performance occurs, a bias is applied to the magnetic brush to cause the magnetic particles of the magnetic brush having increased resistance due to contamination to be detached and adhered to the image carrier. A magnetic brush, wherein the magnetic particles detached and attached to the image carrier are collected by magnetic particle collection means provided on the downstream side in the image carrier moving direction from the magnetic brush charging device, and the magnetic particles are detached and attached to the image carrier. The charging device is supplied with new magnetic particles to reconfigure the magnetic brush using the new magnetic particles. It is. As a result, it is possible to prevent a reduction in charging ability due to contamination of the magnetic brush and an image defect due to the reduction in charging ability for a long period of time.

By providing the magnetic particle collecting means downstream of the magnetic brush charger in the image carrier moving direction and upstream of the developing means in the image carrier moving direction, the magnetic brush collecting device is separated from the magnetic brush charger to the image carrier. The adhered magnetic particles do not enter the developing unit, and it is possible to prevent the adverse effects such as fluctuations in the amount of charge of the toner in the developing unit caused by mixing of the magnetic particles for charging into the developing unit. is there. The life of the developer can be extended.

[Brief description of the drawings]

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

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

FIG. 3 is an enlarged model diagram of a magnetic particle collecting device part.

FIG. 4 is an enlarged model diagram of a developing device part.

FIG. 5 is an operation process diagram of the printer.

FIG. 6 is a graph showing experimental results in Example 1.

FIG. 7 is a schematic diagram illustrating a configuration of a magnetic particle recovery apparatus according to a second embodiment.

FIG. 8 is a schematic diagram illustrating a schematic configuration of an image forming apparatus according to a third embodiment.

FIG. 9 is a graph showing experimental results in Example 3.

[Explanation of symbols]

1. First image carrier (photosensitive drum), 2. Magnetic brush charging device, 3. Magnetic particle collection device, 4. Laser beam scanner, 5. Development device, 6, Transfer roller,
8. Fixing device, 9 Cleaning device, P. 2nd
Image carrier (transfer material)

Claims (12)

[Claims] A charging means for bringing the conductive magnetic particles into contact with the image carrier and applying a voltage to the conductive magnetic particles to charge the image carrier; In an image forming apparatus having a means for forming an image and a developing means for developing an electrostatic latent image formed on an image carrier as a toner image, the image forming apparatus is provided at a downstream side of a charging means in a moving direction of the image carrier and an image from the developing means. An image forming apparatus, further comprising a collection unit configured to collect conductive magnetic particles attached to an image carrier from a charging unit on an upstream side in a carrier moving direction. 2. An image forming apparatus according to claim 1, wherein said collecting means recovers the conductive magnetic particles by a magnetic force. 3. The image forming apparatus according to claim 1, wherein the collection unit mechanically collects the conductive magnetic particles by bringing the collection member into contact with the image carrier. 4. The charging device according to claim 1, wherein a bias different from that for charging the image bearing member is applied to the charging means for attaching the conductive magnetic particles to the image bearing member. Image forming device. 5. The image forming apparatus according to claim 1, wherein the charging by the conductive magnetic particles is performed by injecting a charge into the image carrier. 6. The image forming apparatus according to claim 1, wherein said developing means also serves as a means for collecting a transfer residual toner remaining on the image carrier after transferring the toner image on the image carrier onto the transfer material. The image forming apparatus according to any one of the above. 7. An image forming apparatus according to claim 1, wherein said image carrier comprises a surface layer having amorphous silicon. 8. An image forming apparatus according to claim 1, wherein said developing means is a developing device using a two-component developer comprising toner and magnetic particles. 9. An image carrier having a surface having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm.
The image forming apparatus according to any one of claims 1 to 8, further comprising a layer made of the above material. 10. The image forming apparatus according to claim 1, wherein the image carrier has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles. 11. The image forming apparatus according to claim 10, wherein the conductive fine particles are SnO ₂ . 12. A device according to claim 1, wherein said means for forming an electrostatic latent image on the charged surface of said image carrier is an image exposure means.
12. The image forming apparatus according to any one of claims 11 to 11.