JPH103197A - Image forming device - Google Patents

Abstract

(57) [Summary] Contact charging means 2 as charging means for image carrier 1
For an image forming apparatus using an image forming apparatus, even if the image forming apparatus is a cleaner-less process apparatus that easily causes toner contamination on the contact charging member 2a, an allowable level at which toner contamination on the contact charging member 2a does not adversely affect an output image. The contact charging member 2 can be maintained in the following state.
(a) To solve problems such as a decrease in charging ability, the appearance of a positive ghost, and a decrease in durability of a contact charging member caused by excessive toner contamination of (a), and to stably maintain high-quality image output for a long period of time. And a toner capturing means for recovering the toner attached to the charging member 2a brought into contact with the image carrier 1 from the charging member and discharging the recovered toner to the charging member. An image forming apparatus wherein the toner discharged to the image carrier is discharged to the image carrier and collected by the 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 rotating image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric, such as an electrophotographic device such as a copying machine or a laser beam printer, or an electrostatic recording device. An image forming process including a charging unit for charging, an electrostatic latent image forming unit for forming an electrostatic latent image on the surface of the charged image carrier, and a developing unit for attaching a toner of a developer to the electrostatic latent image for development The image bearing member includes means for repeatedly forming an image.

More specifically, the present invention relates to an image forming apparatus using contact charging means for charging an image carrier by bringing a charging member into contact with the image carrier as a means for charging the image carrier.

[0003]

2. Description of the Related Art For convenience, a transfer type electrophotographic apparatus will be described as an example.

Conventionally, a transfer type electrophotographic apparatus generally has the following means configuration and image forming process. That is,
An electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) generally having a rotating drum type is used as an image carrier, and the surface of the rotating photosensitive drum is uniformly charged to a predetermined polarity and potential by a charging means. The surface of the photosensitive drum is image-exposed by an image exposure unit to form an electrostatic latent image corresponding to the exposed image, and a developing unit attaches a toner of a developer to the electrostatic latent image and develops as a toner image. The toner image is transferred to a transfer material 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 generally used as a means for charging the photosensitive drum. In this method, a corona charger is disposed in non-contact with the photosensitive drum, and the surface of the photosensitive drum is charged to a predetermined polarity and potential by exposing the surface of the photosensitive drum to a corona shower generated from the corona charger to which a high voltage is applied. It is to let.

In recent years, contact charging means has been put to practical use because it has advantages such as lower ozone and lower power than corona chargers.

The contact charging means includes a conductive member having a resistance value adjusted as a charging member, which is provided in contact with a photosensitive drum as a member to be charged, and a predetermined charging bias is applied to the charging member to rotate the member. The surface of the photosensitive drum is charged to a predetermined polarity and potential.

As the contact charging member, various types such as a roller type (charging roller), a blade type (charging blade), a magnetic brush type (charging magnetic brush), and a fur brush type (charging brush) can be used.

There are a DC bias application method in which the charging bias applied to the charging member is a DC voltage only, and an AC bias application method in which an oscillation voltage having a DC bias component and an alternating bias component is applied.

In contact charging, a system in which charging by a discharge phenomenon is dominant as disclosed in Japanese Patent Publication No. 3-52058 and the like, and a method for charging an object to be charged as disclosed in Japanese Patent Application Laid-Open No. Hei 6-3921. There is a system in which charging by direct injection (charging) of charges is dominant (charge injection charging method).

Since the charge injection charging method does not use a discharge phenomenon, there are advantages such that the applied charging bias required for charging is only the desired surface potential of the member to be charged and no ozone is generated. In this case, as the contact charging member, charging,
From the viewpoint of contact stability and the like, a charged magnetic brush or a charged brush is preferably used.

The charging magnetic brush has a magnetic brush portion of conductive magnetic particles (charge carrier) magnetically constrained and supported by a supporting member also serving as a power supply electrode, and the magnetic brush portion is brought into contact with a member to be charged. The power is supplied to the supporting member.

The charging fur brush has a conductive fiber brush portion carried on a carrying member also serving as a power supply electrode, and the conductive fiber brush portion is brought into contact with a member to be charged to supply power to the carrying member. .

As an image forming apparatus, the size of the apparatus can be reduced.
From the viewpoints of cost reduction, ecology, and the like, apparatuses of a cleanerless process (cleanerless system) have been proposed. The image forming apparatus of this cleaner-less system omits a dedicated cleaning device that is disposed between the transfer unit and the charging unit and that removes residual toner from the surface of the image carrier after the transfer. Transfer residual toner remaining on the body surface is removed by developing means using a fogging potential.
It is to be collected (so-called simultaneous development and cleaning). . By omitting the provision of a dedicated cleaning device, the size and cost of the image forming apparatus can be reduced. The toner collected by the developing means contributes to the development again and is used so that no waste toner is produced (ecology). When the charging means of the image carrier is a contact charging means, the image-like pattern of the transfer residual toner is scattered (disturbed) by the charging member in contact with the image carrier before the transfer residual toner reaches the developing section. ), Even if there is a recovery failure of the transfer residual toner by the developing unit, it is possible to suppress the occurrence of a positive ghost in the output image due to the image-like pattern of the transfer residual toner.
. Since there is no cleaning device, there is no damage to the charge injection layer in the image carrier surface due to the rubbing of the cleaning element such as a cleaning blade and the image carrier in a certain case, and the charge injection chargeable image carrier. There are advantages such as.

[0015]

One of the problems in the contact charging is that the charging ability is reduced due to contamination due to the durability of the contact charging member. In other words, the contact charging member is contaminated by picking up foreign substances and dirt present on the surface of the member to be charged due to being in contact with the member to be charged. Occurs.

In the case of an image forming apparatus, even if there is a cleaning device for removing transfer residual toner from the surface of a rotating photosensitive drum as an image carrier after transfer, the toner that continues to pass through the cleaning device to some extent continues. Is carried to the contact charging member and picked up by the charging member, and the charging member is contaminated with toner due to its durability. As a result, a change in the resistance value of the contact charging member (increase in the resistance of the charging portion, which is the contact nip portion between the photosensitive drum and the contact charging member) occurs, and the charging ability decreases. The lowering of the charging ability lowers the quality of the output image.

The problems of lowering the charging ability and lowering the quality of an output image due to toner contamination of the contact charging member are particularly remarkable in a cleanerless image forming apparatus. That is, in the image forming apparatus of the cleanerless process, there is no dedicated cleaning device for removing the transfer residual toner from the surface of the image carrier after the transfer. Therefore, the untransferred toner on the image carrier after the transfer is carried to the contact charging member as it is, so that toner contamination of the contact charging member is more likely to occur than in an image forming apparatus having a cleaning device.

In the case where the contact charging member is a charged magnetic brush, toner is mixed into a magnetic brush portion formed of a charged carrier, and the magnetic brush is contaminated with toner. The transfer residual toner remaining on the surface of the rotating photosensitive drum as an image carrier includes a toner whose charging polarity has been inverted from a normal polarity due to discharge or the like at the time of transfer. Of such transfer residual toner, the toner of normal polarity is carried to the charging part which is the contact part of the photosensitive drum and the charging magnetic brush as a charging member, and the toner from the photosensitive drum generated in the charging part to the charging magnetic brush is The electric field basically passes through the charging unit, rides on the surface of the rotating photosensitive drum, reaches the developing unit, and is collected by the developing unit by the fogging potential of the developing unit. However, the toner whose polarity has been reversed is mixed into the magnetic brush unit at the charging unit, and causes the magnetic brush to be in a toner-contaminated state. The polarity reversal toner mixed in the magnetic brush part is normalized again by frictional charging with the charged carrier of the magnetic brush, is released to the photosensitive drum by the electric field generated in the charged part, and reaches the developing site on the photosensitive drum surface. The toner is collected by the developing means by the fogging potential of the developing means.

The toner mixed in the magnetic brush portion causes an increase in the resistance of the charged carrier, a decrease in contact between the photosensitive drum surface and the charged carrier of the magnetic brush, a contamination of the charged carrier by a toner binder or an external additive, and the like. Although this is a factor that lowers the charging ability, there is no problem as long as the amount of toner mixed into the magnetic brush is maintained at an allowable small level that does not adversely affect the output image quality, but a large amount of toner is required. When outputting a high-density image with a large image area or a decrease in transfer efficiency, the toner discharge from the magnetic brush unit to the photosensitive drum may not be able to keep up with the amount of toner mixed into the magnetic brush unit. is there.

If such a state continues, the amount of toner mixed in the magnetic brush portion increases and exceeds the allowable level, and the charging ability decreases and a positive ghost appears. Further, if the charged magnetic brush is continuously used with a large amount of toner mixed therein, the toner tends to be spent (fused) on the charged carrier, which is a factor of reducing the durability of the charged carrier.

The present invention has been proposed in view of the above,
Regarding an image forming apparatus using a contact charging unit as a charging unit for an image carrier, even if the image forming apparatus is a device of a cleanerless process that easily causes toner contamination on the contact charging member, the toner contamination of the contact charging member is output. It is possible to maintain the state below an allowable level that does not adversely affect the image, so that the charging ability is reduced, a positive ghost appears, the durability of the contact charging member is reduced due to excessive toner contamination of the contact charging member. And to stably maintain high-quality image output for a long period of time.

[0022]

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

(1) Charging means for charging a rotating image carrier, electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier surface, and applying toner of developer to the electrostatic latent image The image forming apparatus includes an image forming process unit including a developing unit that attaches and develops the image. In the image forming apparatus, the charging unit of the image carrier contacts the charging member with the image carrier. A contact charging means for charging the toner by adhering to the image carrier, collecting toner attached to the charging member from the charging member, and discharging the collected toner to the charging member. An image forming apparatus wherein the toner discharged from the toner capturing unit to the charging member is released to the image carrier and collected by the developing unit.

(2) Charging means for charging the rotating image carrier, electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier surface, and applying a developer toner to the electrostatic latent image The image forming apparatus includes an image forming process unit including a developing unit that attaches and develops the image. In the image forming apparatus, the charging unit of the image carrier contacts the charging member with the image carrier. A contact charging means for charging the toner by contacting the image bearing member with the image bearing member; and a toner capturing means for collecting the toner attached to the charging member from the charging member, and removing the captured toner from the toner capturing means. An image forming apparatus comprising a cleaning unit.

(3) The image forming apparatus according to (1) or (2), further comprising a transfer unit for transferring the toner image formed on the image carrier to a transfer material.

(4) Transfer means for transferring the toner image formed on the image carrier to a transfer material is provided, and the transfer residual toner remaining on the image carrier surface after the transfer of the toner image between the transfer means and the charging means is provided. The image forming apparatus according to any one of (1) to (3), further including an image carrier cleaning unit for removing the image carrier.

(5) A cleaner-less process apparatus comprising a transfer unit for transferring the toner image formed on the image carrier to a transfer material, and recovering the transfer residual toner remaining on the image carrier surface after the transfer of the toner image by a developing unit. The image forming apparatus according to (1) or (2), wherein

(6) The electrostatic latent image forming means is an image exposing means for forming an electrostatic latent image by imagewise exposing the surface of the image carrier after charging (1) to (5). The image forming apparatus according to any one of the above.

(7) The toner capturing means generates an electric field between itself and the charging member, and the electric field collects the toner adhered to the charging member from the charging member, and discharges the collected toner to the charging member. The image forming apparatus according to (1), wherein

(8) The toner capturing means collects the toner adhered to the charging member when charging the image area of the image carrier, and discharges the collected toner to the charging member when charging the non-image area. The image forming apparatus according to (1).

(9) The non-image area is charged by a charging bias having a smaller voltage amplitude than the image area when charging the image carrier. An image forming apparatus according to any one of the preceding claims.

(10) The image forming apparatus according to any one of (1) to (9), wherein the image carrier is charge-injectable and chargeable.

(11) The charging member brought into contact with the image carrier has a brush portion of conductive magnetic particles carried on the carrier member, and the brush portion is in contact with the image carrier. The image forming apparatus according to any one of (1) to (10).

(12) The charging member in contact with the image carrier has a conductive fiber brush portion carried on the carrier member, and the brush portion is in contact with the image carrier. The image forming apparatus according to any one of (1) to (10).

(13) The image forming apparatus according to any one of (1) to (12), wherein the developing means is a reversal developing device.

(14) The method according to (13), wherein a bias voltage having a potential between the potential of the exposed portion and the potential of the non-exposed portion of the image carrier is applied to the developer carrying member of the developing device. The image forming apparatus as described in the above.

<Operation> By collecting the toner adhering to the contact charging member from the contact charging member by the toner capturing means to the side of the toner capturing means in a timely manner, for example, at the time of charging the image area on the surface of the image carrier, the contact charging member can be used. Irrespective of the attached toner, the degree of toner contamination of the contact charging member can be maintained at a level lower than an allowable level which does not adversely affect the output image by the toner collecting operation of the toner capturing means.

The toner collected by the toner capturing means is re-emitted from the toner capturing means to the contact charging member when the non-image area on the image carrier is charged, and the re-emitted toner is released to the image carrier. Then, the toner is collected by the developing unit (simultaneous cleaning with development), so that the contact charging member after the toner is discharged to the image carrier side is in a state in which the degree of toner contamination is small. Further, the toner collected by the developing unit is reused for developing the electrostatic latent image, and no waste toner is generated.

In addition to the configuration in which the toner captured from the contact charging member toward the toner capturing means is released onto the image carrier as described above and collected by the developing means, the toner capturing means may be, for example, a roller electrode or the like. A toner collecting container which is a rotating body, captures toner adhered to the contact charging member by the rotating body, and removes the toner captured by the rotating body from the rotating body by a re-cleaning means such as a blade provided on the rotating body. Even with a configuration in which the toner is collected, the toner contamination of the contact charging member can be maintained at an allowable level or less.

Therefore, regarding an image forming apparatus using a contact charging means as a charging means for an image carrier, even if the image forming apparatus is a cleaner-less process apparatus in which toner contamination easily occurs in the contact charging member, the contact charging member may be used. Can be maintained at a level below an allowable level that does not adversely affect the output image, and the charging ability is reduced, a positive ghost appears, and the durability of the contact charging member is caused by excessive toner contamination of the contact charging member. Thus, it is possible to solve the problems such as a decrease in image quality and to stably maintain high-quality image output for a long period of time.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 4) (1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration 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 using a transfer type electrophotographic process, a charged magnetic brush-contact charging system, a reversal developing system, and a cleanerless process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as an image carrier. Photosensitive drum 1 of this example
Is a charge generation layer in which a disazo pigment is dispersed in a resin,
It has a charge transport layer in which hydrazone is dispersed in a polycarbonate resin, and further has an organic photosensitive layer in which the outermost layer has a charge injection layer in which ultrafine particles of SnO ₂ are dispersed in a photocurable acrylic resin. (OPC-
OCL drum), 100 mm / sec in the counterclockwise direction of the arrow
It is rotationally driven at a peripheral speed (process speed) of c.

Reference numeral 2 denotes charging means for uniformly charging the outer peripheral surface of the rotary photosensitive drum 1 to a predetermined polarity and potential. The charging means 2 of this embodiment is a magnetic brush charger in which a charged magnetic brush 2a is brought into contact with the photosensitive drum 1 as a contact charging member. In this embodiment, the outer peripheral surface of the rotary photosensitive drum 1 is charged and charged to approximately -700 V by the magnetic brush charger 2.
The magnetic brush charger 2 will be described later in detail in (2).

The surface of the rotating photosensitive drum 1 which has been charged by the magnetic brush charger 2 receives an image exposure L corresponding to target image information by the image exposure means 3. The image exposure means 3 of the present embodiment is a laser beam scanner, which comprises a semiconductor laser, a polygon mirror 3a, an F-.theta. Lens 3b, a deflection mirror 3c, etc., and corresponds to a time-series electric digital pixel signal of target image information. The modulated laser beam is output, and the surface of the rotary photosensitive drum 1 is scanned and exposed with the laser beam. The potential on the photosensitive drum 1 is reduced when the laser is irradiated, that is, the potential of the exposed portion drops (bright portion potential), and when the laser is not irradiated, that is, the potential of the non-exposed portion (dark portion potential) is increased. An electrostatic latent image corresponding to the pattern is formed.

Reference numeral 4 denotes a document reading device (image scanner) provided on the upper surface of the printer body. Document loading glass 4
The original O is placed and set on the document a in accordance with a predetermined placing reference with the image surface to be read facing downward. An original pressing plate (not shown) is placed on the original O. Then, in response to a document reading start signal, a photoelectric reading unit 4b including a document illumination lamp, a short focus lens array (cell hook lens array), a solid-state image sensor array such as a CCD, and the like is moved from one end along the lower surface of the document placing glass 4a. By being reciprocated to the other end, the image information on the downward image surface of the document O is subjected to photoelectric reading processing as a time-series electric digital pixel signal, and the signal is output to the laser beam scanner 3 via the control circuit.

Reference numeral 5 denotes developing means for developing the electrostatic latent image formed on the rotary photosensitive drum 1 as a toner image. The developing means of this embodiment is a reversal developing device, which reversely develops the electrostatic latent image by attaching a negative toner to a bright portion potential portion of the electrostatic latent image. The developing device 5 will be described in detail in the section (3) below.

Reference numeral 6 denotes a transfer roller as transfer means.
The transfer nip portion T is formed by pressing the rotating photosensitive drum 1 with a predetermined pressing force.

Reference numeral 7 denotes a paper feed cassette in which transfer materials P are loaded and stored. When the paper feed roller 8 is driven to rotate based on the paper feed start signal, the transfer material P is fed out one by one from the paper feed cassette 7, and is controlled at a predetermined control timing via the sheet path 9 and the registration roller pair 10. That is, when the leading end of the toner image formed on the surface of the rotating photosensitive drum 1 reaches the transfer nip T, the leading end of the transfer material P just reaches the transfer nip T at the registration timing.
Is sent to

The transfer material P fed to the transfer nip T is nipped and conveyed by the transfer nip T. A predetermined transfer bias is applied to the transfer roller 6 from a transfer bias power supply (not shown) while the transfer material P is nipped and conveyed through the transfer nip portion T. The transfer bias is a bias having a polarity opposite to the polarity of the toner charge of the toner image on the rotating photosensitive drum 1.
The toner image on the surface side is electrostatically transferred to the surface side of the transfer material P sequentially.

The transfer material P to which the toner image has been transferred through the transfer nip portion T is separated from the surface of the rotating photosensitive drum 1 and is conveyed to the fixing device 12 by the conveying means 11 to receive the heat and pressure of the toner image and fix the image. The paper is discharged onto the paper discharge tray 13 as a formed product.

After the transfer of the toner image onto the transfer material P, the photosensitive drum 1 is repeatedly subjected to image formation. In this case, transfer residual toner is present on the photosensitive drum 1, and in a cleanerless process apparatus such as the image forming apparatus of this embodiment, if the transfer residual toner is carried as it is to the next transfer step. The untransferred toner is transferred to a place where no recording signal is present on the transfer material, resulting in image contamination. However, the cleaner-less process apparatus collects the untransferred toner in the developing device 5 and cleans the photosensitive drum 1. (Simultaneous development cleaning). That is, in the developing step, a fog removing electric field is applied to the white background so that the toner pulls the toner toward the developing means, thereby cleaning the photosensitive drum 1.

(2) Magnetic Brush Charger 2 FIG. 2 is a schematic configuration diagram of the magnetic brush charger 2 in this embodiment. The magnetic brush charger 2 of this embodiment is of a sleeve rotation type.

Reference numeral 2a denotes a charged magnetic brush 2a as a contact charging member, a conductive sleeve 2b of non-magnetic SUS, aluminum or the like as a magnetic brush portion carrying member, and a magnetic field generating means inserted and disposed in the sleeve 2b. The magnet roller 2c magnetized with two poles of S and N (S ₁ · S ₂ · N ₁ · N ₂ ) was held on the outer peripheral surface of the sleeve 2b by the magnetic binding force of the magnet roller 2c inside the sleeve. Magnetic brush part 2 of conductive magnetic particles (charge carrier)
d.

Reference numeral 2e denotes a charger casing, and the charging magnetic brush 2a is disposed in the casing 2e with its front half surface exposed to the outside. Reference numeral 2f denotes a magnetic brush portion layer thickness regulating blade fixedly disposed on the front side of the casing 2e so that the lower side thereof is in a predetermined proximity to the upper surface of the sleeve 2b.

Magnet roller 2 of charged magnetic brush 2a
Reference numeral c denotes a non-rotating fixing member, and a sleeve 2b is provided with a predetermined peripheral speed by a driving mechanism (not shown) in a counterclockwise direction indicated by an arrow (counter direction with respect to the rotation of the photosensitive drum 1) concentrically around the outer periphery of the magnet roller 2c. In this example, 200 mm / sec
Is driven to rotate. The sleeve 2b is a rotating photosensitive drum 1
They are arranged close to each other in a non-contact manner with a predetermined gap, 500 μm in this example, from the surface.

In this embodiment, the charged carrier constituting the magnetic brush portion 2d has an average particle diameter of 25 μm and a resistance value of 5 × 10 ^6.
Ω / cm and a saturation magnetization of 200 emu / cm ² were used.

The magnetic brush portion 2d is rotated and conveyed in the same direction together with the sleeve 2b with the rotation of the sleeve 2b, and its layer thickness is regulated to a predetermined value by the blade 2f. The magnetic brush portion 2d forms a nip portion A by contacting the photosensitive drum surface with a predetermined width in the approach facing gap portion between the sleeve 2b and the photosensitive drum 1. The nip A is a charging unit. Therefore, the surface of the rotating photosensitive drum 1 is rubbed at the charging portion A by the magnetic brush portion 2d which is rotated and conveyed in the same direction together with the sleeve 2b as the sleeve 2b rotates.
The magnetic flux density by the magnet roller 2c on the sleeve 2b of the charging section A is 800 × 10 ⁻⁴ T.

A predetermined charging bias is applied to the sleeve 2b from a charging bias power supply S1. In this example, the amplitude 7
A charging bias in which a DC voltage of -700 V is superimposed on an alternating electric field of 00 V _PP and a frequency of 1 kHz is applied. As a result, the surface of the rotating photosensitive drum 1 is substantially at -70
It is uniformly charged to 0 V by a charge injection charging method. Applying an alternating electric field to the charging bias improves the charging property,
Effective for preventing positive ghosts.

Reference numeral 2g denotes a toner capturing electrode as a toner capturing means capable of temporarily recovering the toner mixed in the magnetic brush portion 2d from the magnetic brush portion 2d and discharging the recovered toner to the magnetic brush portion 2d. is there.

The toner capturing electrode 2g of this embodiment is a metal plate electrode having a constant concave curvature on the front side in a transverse section and having a longitudinal direction extending in the longitudinal direction of the charged magnetic brush 2a. Magnet roller 2 on the rear side
c conveyance is pole opposed located S ₂ of the front as lightly rubbing the surface of the magnetic brush portion 2d lightly the contacted to the surface of the magnetic brush portion 2d are arranged. In the present embodiment, the toner capture electrode 2g is provided with a 1.5 mm gap at regular intervals with respect to the surface of the sleeve 2b.

The toner capture electrode 2g is connected to a bias power source S
2, a toner collection bias of -850 V from the power source S2 to the toner capture electrode 2g, and -5V.
A toner discharge bias of 50 V can be switched and applied according to a predetermined image forming sequence. The collection and re-emission of toner by the toner capture electrode 2g will be described in detail in the section (4) below.

(3) Developing Unit 4 FIG. 3 is a schematic structural view of the developing unit 5 in this embodiment. The developing device 5 of this embodiment is a two-component magnetic brush developing device of a sleeve rotation type.

Reference numeral 5a denotes a conductive sleeve (developing sleeve) made of non-magnetic aluminum or the like as a developer carrying member, and 5b denotes a magnet roller as a magnetic field generating means inserted and arranged in the developing sleeve 5a.

Reference numeral 5e denotes a developing device casing, and the developing sleeve 5a with the built-in magnet roller 5b is disposed on the casing 5e with its front half surface exposed to the outside. Reference numeral 5f denotes a developer layer thickness regulating blade fixedly disposed on the front side of the casing 5e so that the lower side thereof is in close proximity to the upper surface of the developing sleeve 5a.

The magnet roller 5b is a non-rotating fixing member, and the developing sleeve 5a is concentrically arranged around the outer periphery of the magnet roller 5b in a clockwise direction indicated by an arrow (forward with respect to the rotation of the photosensitive drum 1) by a driving mechanism (not shown). At a predetermined peripheral speed, in this example, 150 mm / sec. The developing sleeve 5a is disposed close to the surface of the rotating photosensitive drum 1 in a non-contact manner with a predetermined gap.

Reference numeral 5d denotes a two-component developer containing a mixture of the magnetic carrier (magnetic particles) C and the toner t, housed in the developing device casing 5e. Two-component developer 5d of this example
The toner t has a negatively chargeable average particle diameter of 8 μm and a magnetic carrier C having a positively chargeable average particle diameter of 50 μm at a toner concentration of 5% by weight. The toner t used in this example is a toner produced by a polymerization method, and has a spherical shape and very good fluidity than a toner produced by a pulverization method usually used in this type of apparatus.

Reference numerals 5h and 5h denote developer stirring members for uniformly stirring the developer 5d and transporting the inside of the developing device casing 5e to the developing sleeve 5a side.

The developer 5d in the developing device casing 5e is carried as a developer magnetic brush layer 5c on the outer peripheral surface of the rotating developing sleeve 5a by the magnetic restraining force of the magnet roller 5b inside the developing sleeve. Accordingly, it is rotated and conveyed in the same direction together with the sleeve 5a, and its layer thickness is regulated to a predetermined thin layer by the blade 5f. The developer magnetic brush layer 5c contacts the surface of the photosensitive drum at a predetermined width in the approaching gap between the developing sleeve 5a and the photosensitive drum 1 to form a nip portion B. Or facing non-contact. The nip portion B or the non-contact facing portion is a developing portion.

The developing sleeve 5a has a developing bias power source S
From 3, a predetermined developing bias (a bias voltage between the potential of the exposed portion and the potential of the non-exposed portion of the photosensitive drum) is applied. In this example, an alternating electric field of 2 kV _PP and 2 kHz
Developing bias (AC +
DC) is applied, and the developing sleeve 5
The negatively charged toner (negative toner) in the developer magnetic brush layer 5c on the a side adheres to the bright portion potential portion of the electrostatic latent image on the rotating photosensitive drum 1, and the electrostatic latent image is sequentially developed as a toner image in reverse development. Will be done.

Since the toner density of the developer 5d in the developing device casing 5e decreases as the toner is consumed for developing the electrostatic latent image, the toner density state is detected by an optical toner density sensor (not shown). When the toner concentration falls below the allowable lower limit, the supply toner t is supplied to the developer 5d in the developing device casing 5e by the supply roller from the toner hopper portion 5g, and mixed into the developer 5d by the stirring member 5h. Thus, control is performed to always maintain the toner concentration of the developer 5d within a predetermined allowable range.

(4) Recovery and Re-emission of Toner by Toner Capture Electrode 2g a) As described above, in the image forming apparatus of the cleanerless process, the transfer residue remaining on the surface of the rotating photosensitive drum after the transfer of the toner image onto the transfer material P The toner is transferred to the photosensitive drum 1 and the charged magnetic brush 2 by the subsequent rotation of the photosensitive drum 1.
It is carried as it is to the charging portion A which is the contact portion of a.

B) Photosensitive drum 1 carried to charging section A
The upper transfer residual toner is disturbed by the sliding force of the magnetic brush portion 2d of the charged magnetic brush 2a in contact with the photosensitive drum 1, and the image-like pattern is erased. This suppresses the occurrence of positive ghosts in the output image due to the image-like pattern of the transfer residual toner even when the transfer residual toner is not properly collected by the developing device 5.

C) Of the transfer residual toner on the photosensitive drum 1 carried to the charging section A and disturbed as described above,
The toner of normal polarity (negatively charged toner in this example) passes through the charging section A and reaches the developing section B of the developing device 5 in principle, and is collected by the developing device 5 by the fogging potential (simultaneous development cleaning). . The toner collected in the developing device 5 is reused for developing the electrostatic latent image.

The transfer residual toner that passes through the charging section A and reaches the developing section B of the developing device 5 passes through the image exposure section on the way. In this case, the transfer residual toner on the photosensitive drum 1 is finely disturbed and dispersed. Since the transfer residual toner is in a state in which the toner remains untransferred and the amount thereof is small, it is practically not a problem that the transfer residual toner becomes an exposure obstacle.

On the other hand, the toner (positively charged toner in this example) whose polarity is inverted due to the transfer bias in the transfer process is
Since an electric field is generated in the charging portion A in the direction of the sleeve 2b, the electric field is mixed into the magnetic brush portion 2d of the charging magnetic brush 2a. When the amount of toner mixed into the magnetic brush portion 2d becomes a certain level or more, adverse effects such as a reduction in charging ability of the charging portion A (amount of toner mixed in the magnetic brush portion) occur.

D) Therefore, in this embodiment, while the image area of the rotary photosensitive drum 1 passes through the charging section A, the above-described toner collection bias (−850 V) is applied from the bias power source S2 to the toner capture electrode 2g as a toner capture means. ) Is applied.

As a result, in the charging section A, the polarity reversal toner mixed into the magnetic brush section 2d of the charging magnetic brush 2a is electrically attracted to the surface of the toner capturing electrode 2g and is adhered to and held by the magnetic brush section 2d. Temporarily collected from inside.

From the surface of the rotating photosensitive drum 1 to the magnetic brush portion 2d
The polarity of the polarity-reversed toner immediately after being mixed therein is not normalized (negatively charged) immediately because the friction with the charged carrier of the magnetic brush portion 2d is not sufficient, and thus the toner is applied to the toner capturing electrode 2g. Due to the electric field effect of the toner collecting bias, the toner is adhered and held on the toner capturing electrode 2g.

That is, regardless of the polarity reversal toner, the magnetic brush portion 2d is kept at a small amount of toner by the toner collecting action of the toner capture electrode 2g, and at least the charging portion A is rotated by the rotating photosensitive drum. While the first image area is passing, the charged magnetic brush 2a does not hinder the charging due to the mixed toner, and a sufficient charging ability is secured.

E) In this example, while the non-image area of the rotary photosensitive drum 1 passes through the charging section A, the above-described toner discharge bias (-550 V) is applied to the toner capture electrode 2g from the bias power source S2. .

As a result, the toner adhered and collected on the toner capturing electrode 2g is separated (released) from the toner capturing electrode 2g, and the magnetic brush portion 2d of the charged magnetic brush 2a is released.
Re-mix in.

The toner re-mixed in the magnetic brush portion 2d is normalized by frictional charging of the magnetic brush portion 2d with the charge carrier, and is discharged onto the rotating photosensitive drum 1 by the action of the electric field in the charging portion A. After the toner is released, the magnetic brush portion 2d is held in a state where the amount of mixed toner is small.

The toner normalized and discharged from the magnetic brush unit 2d onto the photosensitive drum 1 reaches the developing unit B of the developing unit 5 with the rotation of the photosensitive drum 1, and is collected by the developing unit 5 by the fogging potential. . The toner collected in the developing device 5 is reused for developing the electrostatic latent image.

Incidentally, due to the temporary re-emission of the collected toner from the toner capturing electrode 2g to the magnetic brush portion 2d, the amount of toner mixed in the magnetic brush portion 2d increases at that time, and the charged magnetic brush 2a is charged by the toner. Although the performance is impaired, the surface portion of the photosensitive drum 1 corresponding to the charging section A is a non-image area and does not affect the quality of an output image.

F) In this embodiment, while the non-image area of the rotating photosensitive drum 1 passes through the charging section A as described above, the toner collected from the magnetic brush section 2d by the toner capturing electrode 2g is again magnetized. In order to discharge into the brush part 2d at once,
The toner concentration in the magnetic brush portion of the charging portion A in the non-image area on the surface of the rotating photosensitive drum 1 is higher than that in the conventional example, and the charging ability is greatly reduced. Accordingly, the electric field intensity generated in the charging section A is higher than in the conventional example, and the toner discharging ability to the photosensitive drum 1 is higher than in the conventional example. That is, in the present embodiment, the steady toner mixing amount can also be reduced.

This effect will be described with reference to FIG.
FIG. 4 shows an output image ratio of 8% to 90%, and 90% to 8%.
Represents the amount of toner mixed into the magnetic brush unit 2d with respect to the number of image outputs when the value is changed to.

The toner mixing amount in this example is represented by a curve a, and the toner mixing amount in the conventional example is represented by a curve c.

In the conventional example, when the image ratio was set to 90%, an increase in the amount of toner mixed in with an increase in transfer residual toner was observed, and ghost occurred.

On the other hand, in this example, although the increase in the amount of mixed toner is observed, it is slight, and no ghost is generated. In addition, by always keeping the toner mixing amount at a low level, it is possible to reduce the contamination of the charged carrier due to toner spent or an external additive of the toner, and to maintain a good charging ability for a long period of time.

The shape of the toner capturing electrode 24 is not limited to that of the present embodiment, but is a semi-cylindrical electrode and a magnetic brush portion 2.
The same effect can be obtained with a shape that covers the rear surface side of d or a metal flat plate having no curvature.

As described above, in this embodiment, by providing the toner capturing electrode 2g, an image requiring a large amount of toner is continuously output, and the transfer efficiency is reduced, and the contact charging member is reduced. Even when the amount of toner mixed into the magnetic brush portion 2d of the charged magnetic brush 2a increases, a high-quality image free from ghosts and fogging could be output.

<Embodiment 2> In this embodiment, the charging of the surface of the rotating photosensitive drum 1 by the charging magnetic brush 2a is performed in the image forming apparatus of Embodiment 1 described above, and the charging of the image area is performed when the non-image area is charged. It is characterized in that the charging is performed with a charging bias having a smaller voltage amplitude than at the time. Other device configuration,
Since the control and the like are the same as those in the first embodiment, the description will not be repeated.

That is, in the image forming apparatus according to the first embodiment, the charging bias applied to the charging magnetic brush 2a at the time of charging the image area and the non-image area on the surface of the rotary photosensitive drum 1 is set to 700 V amplitude. In this example, an alternating electric field having a frequency of 1 kHz and a DC voltage of -700 V are superimposed. In this example, the charging bias applied to the charging magnetic brush 2a at the time of charging the non-image area is a DC voltage of -700V.
Switch to only. Then, when the non-image area is charged, the temporarily collected toner is released from the toner capturing electrode 2g to the magnetic brush portion 2d of the charged magnetic brush 2a.

The charging ability with only the DC bias is lower than the charging ability with the AC bias. Therefore, the electric field generated in the charging section A when charging the non-image area is increased by the charging with the DC bias, and the toner discharge ability from the magnetic brush section 2d of the charged magnetic brush 2a to the photosensitive drum 1 is increased.

By doing so, the toner capturing electrode 2g
Then, the toner discharged to the magnetic brush portion 2d from the first portion is further efficiently discharged to the photosensitive drum 1, and the steady toner mixing ratio to the magnetic brush portion 2d can be further reduced.

The curve b in the graph of FIG. 4 represents the amount of toner mixed in the magnetic brush portion with respect to the number of output images when the output image ratio is changed from 8% to 90% and from 90% to 8% in this example. It is shown.

In this example, it can be seen that the amount of mixed toner can be further reduced as compared with the curve a in the case of the first embodiment, and the durability of the charged carrier can be further improved.

In this embodiment, only the DC voltage is used as the charging bias when charging the non-image area on the surface of the photosensitive drum 1. However, the charging bias is not limited to this, and any charging bias having a voltage amplitude smaller than 700 V can be used. Similar effects can be obtained.

In particular, when a charged carrier having a low chargeability is used or the chargeability is abnormally lowered, the development fog may occur because the potential of the non-image portion is too low. Under such conditions, it is more preferable to use a charging bias having a certain voltage amplitude.

As described above, in this embodiment, the non-image area on the surface of the photosensitive drum 1 is charged by the DC bias, and the toner collected from the toner capturing electrode 2g to the magnetic brush section 2d is temporarily charged during the charging of the non-image area. By discharging the toner, the mixing ratio of the toner into the magnetic brush portion 2d can be further reduced, and the durability of the charged carrier can be further improved.

<Embodiment 3> (FIG. 5) This embodiment is characterized in that a fur brush charger is used in place of the magnetic brush charger 2 in the image forming apparatus of Embodiment 1. The other device configuration, control, and the like are the same as those in the first embodiment, and a description thereof will not be repeated.

The fur brush charger used in this example has a core bar having an outer diameter of 10 mm, a bristle length of 3 mm, a flock density of 100,000 / inch ² , a resistance value of 1 × 10 ⁶ Ω,
The outer diameter of the fur brush is made by planting conductive fibers of
A 6 mm cylindrical member used as a contact charging member (fur brush charging member) was used.

The contact nip width (charging portion) between the photosensitive drum 1 and the fur brush portion is about 7 mm, the rotating direction of the fur brush charging member is the counter direction with respect to the photosensitive drum 1, and the rotating speed of the photosensitive drum 1 is 100 mm. / Sec, the fur brush charging member was rotated at 200 mm / sec.

The toner capturing electrode has the same shape as that of the toner capturing electrode 2g of the first embodiment, and is in contact with the fur brush charging member with a penetration amount of 0.5 mm.

The bias applied to the fur brush charging member and the toner capture electrode and the application sequence are the same as in the first embodiment.

FIG. 5 shows the amount of toner mixed into the fur brush portion with respect to the number of image outputs in this example. In the drawing, the amount of toner mixed into the fur brush unit in this example is represented by a curve d, and the amount of toner mixed into the fur brush unit when no toner capture electrode is provided is represented by a curve e.

The output images and their order are the same as in FIG. In this example, it can be seen that the amount of mixed toner is reduced and the occurrence of ghost is suppressed.

As described above, according to the present embodiment, it is possible to reduce the amount of toner mixed in the fur brush charging, and it is extremely effective in preventing positive ghost, lowering the charging potential, and improving the durability of the fur brush. It was effective.

<Embodiment 4> (FIG. 6) In the present embodiment, as shown in FIG.
Then, the roller electrode 2h is disposed in contact with or close to the magnetic brush portion 2d of the charging magnetic brush 2a as a contact charging member, and the above-described toner collecting bias is applied to the roller electrode 2h from the bias power source S2. As a result, the toner adhering and mixing into the magnetic brush portion 2d from the surface of the photosensitive drum 1 is adhered and collected on the surface of the rotating roller electrode 2h. Then, the toner is scraped off from the surface of the rotating roller electrode 2h by a blade member (scraper) 2i as a re-cleaning unit brought into contact with the rotating roller electrode 2h, and is collected in the charging casing 2e as a toner collecting container. You. With this configuration, toner contamination of the magnetic brush 2a as the contact charging member can be maintained at an allowable level or less. Needless to say, the contact charging member may be other than the magnetic brush 2a.

<Others> 1) The application control sequence of the toner collecting bias and the toner releasing bias to the toner capturing electrode 2g as the toner capturing means is not limited to the embodiment, and may be appropriately determined in consideration of the degree of toner contamination of the contact charging member. A sequence such as thinning-out can also be used.

2) The charging magnetic brush 2a as the contact charging member is not limited to the sleeve rotating type of the embodiment, and the surface of the magnet roller 2c can be electrically conductive as a power supply electrode if necessary. do it,
Further, if necessary, a resistive layer may be applied, and the charge carrier may be directly magnetically restrained on the surface of the magnet roller to form and hold the magnetic brush portion 2d, and the magnet roller may be rotated. it can. A fixed type magnetic brush that does not rotate can also be used.

The fur brush charging member may be of a fixed type that does not rotate.

Further, the contact charging member may be in a form other than the charging magnetic brush or the fur brush charging member.

3) A photoreceptor having an amorphous silicon (α-Si) surface layer (amorphous silicon photoreceptor) is also charge-chargeable. In the case of the injection charging system, the image carrier desirably has a low resistance layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm.

The image carrier may be one in which charging by discharge is dominant.

The charging bias applied to the contact charging member is D
A C bias application method or an AC bias application method may be used. However, in the case of the DC bias application type charging method, the resistance value of the contact charging member fluctuates due to environmental fluctuation or the like,
When the film thickness changes due to scraping of the member to be charged (photosensitive member, etc.), the charging start voltage value Vth of the member to be charged changes, so that the charging potential is unstable. There are advantages such as being unaffected by disturbances such as the environment due to the effect.

As the contact charging means of the AC bias application method, as disclosed in Japanese Patent Publication No. 3-52058, which was previously proposed by the present applicant, a predetermined DC voltage component and a predetermined alternating voltage component are applied to the contact charging member. The method of applying an oscillating voltage having an (alternating voltage having a peak-to-peak voltage that is twice or more the charging start voltage value of the member to be charged when a DC voltage is applied to the contact charging member) is excellent in uniform charging property.

As the alternating voltage component (AC bias component), one having an appropriate waveform such as a sine wave, a square wave (rectangular wave), a triangular wave, and a sawtooth wave can be used. It also includes a rectangular wave formed by periodically turning on and off a DC power supply.

In contact charging in which charging by discharge is dominant, the charging member does not necessarily have to be in contact with the member to be charged, and the charging member and the member to be charged can be discharged between them by the gap voltage and the corrected Paschen curve. Charging is performed (proximity charging) as long as they face each other in a non-contact manner with a small gap (gap) satisfying the conditions. In the present invention, such a proximity charging mode is also included in the category of contact charging.

4) Regarding the image forming apparatus, the image forming process is optional. The image forming apparatus is not limited to the image forming apparatus of the cleanerless process, and may be an image forming apparatus provided with a dedicated cleaning device for removing a transfer residual toner after transferring a toner image to a transfer material. This is because, even in such an apparatus, toner contamination of the contact charging member is caused by toner that slips through the cleaning device at all.

The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly charged to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head or an electron gun to write and form a desired electrostatic latent image.

The method and means for developing an electrostatic latent image are arbitrary.
A reversal development system or a regular development system may be used.

The transfer method is not limited to the roller transfer shown in the embodiment, but may be a blade transfer or other contact transfer charging method. Needless to say, the present invention can be applied to an image forming apparatus that forms a multi-color or full-color image by multiple transfer or the like.

[0125] Arbitrary process equipment such as an image carrier, a charging member, a developing device and the like may be configured so as to be detachably attachable to and detachable from the image forming apparatus main body.

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

5) In the charged magnetic brush, the resistance value of the charged carrier (magnetic particles) constituting the magnetic brush portion is 6.6 kg / after putting 2 g of the carrier into a metal cell (bottom area 228 mm ² ) to which a voltage can be applied. cm ² was applied, and a voltage of 100 V was applied for measurement.

The average particle size of the carrier is represented by the maximum chord length in the horizontal direction. The measurement was performed by microscopically selecting at least 300 carriers, measuring the diameter, and taking the arithmetic average.

The magnetic characteristics of the carrier can be measured using a DC magnetization BH characteristics automatic recording device BHH-50 manufactured by Riken Denshi Co., Ltd. At this time, the diameter (inner diameter) is 6.5 m
Approximately 2 weights of a carrier in a cylindrical container with a height of 10 mm
g Filled at a medium level, and measure the saturation magnetization from its BH curve while keeping the carrier from moving in the container.

An example of a method for measuring the toner particle size distribution will be described.
Interface (manufactured by Nikkaki) and CX that output the number average distribution and volume average distribution using a mold (manufactured by Coulter)
-1 Connect a personal computer (Canon),
As the electrolytic solution, a 1% NaCl aqueous solution is adjusted using primary sodium chloride.

The measuring method is as follows.
A surfactant as a dispersant in 150 ml, preferably
0.1 to 5 ml of an alkylbenzene sulfonate is added, and 0.5 to 50 mg of a measurement sample is further added.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and the particle size of 2 to 40 μm was measured using the Coulter Counter TA-2 using a 100 μ aperture as an aperture. The distribution is measured to determine the volume average distribution. The volume average particle size is obtained from the obtained volume average distribution.

[0133]

As described above, according to the present invention, in an image forming apparatus using a contact charging means as a charging means for an image carrier, the image forming apparatus easily causes toner contamination on a contact charging member. Even in a cleaner-less process device, the toner contamination state of the contact charging member can always be maintained at a level below an allowable level that does not adversely affect the output image, and due to excessive toner contamination of the contact charging member, Problems such as a decrease in charging ability, the appearance of a positive ghost, and a decrease in durability of a contact charging member can be solved, and high-quality image output can be stably maintained for a long period of time.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram of a charger.

FIG. 3 is a schematic configuration diagram of a developing device.

FIG. 4 is a graph showing the relationship between the number of output images and the amount of toner mixed in the magnetic brush portion of the charged magnetic brush in the first and second embodiments.

FIG. 5 is a graph showing the relationship between the number of output images and the amount of toner mixed in the fur brush portion of the fur brush charging member according to the third embodiment.

FIG. 6 is a schematic configuration diagram of a charger in Embodiment 4;

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier, charged body) 2 charger 2a charged magnetic brush 2b rotating sleeve 2c fixed magnet roller 2d magnetic brush section 2g toner capturing electrode 2h rotating roller electrode as toner capturing electrode 2i toner scraping blade S1 S3 Bias power supply 3 Laser beam scanner 4 Image reading device (image scanner) 5 Developing device 6 Transfer roller 7 Paper cassette 12 Fixing device

Claims (14)

[Claims] A charging means for charging a rotating image carrier;
An electrostatic latent image forming unit for forming an electrostatic latent image on the surface of the charged image carrier, and an image forming process unit including a developing unit for developing by attaching toner of a developer to the electrostatic latent image; The image carrier is an image forming apparatus that is repeatedly provided for image formation, wherein the charging means of the image carrier is contact charging means for charging the image carrier by bringing a charging member into contact with the image carrier. The image forming apparatus further includes a toner capturing unit configured to collect the toner attached to the charging member from the charging member and to release the collected toner to the charging member. The toner released from the toner capturing unit to the charging member is transferred to the image carrier. An image forming apparatus, which is released and collected by a developing unit. 2. A charging means for charging a rotating image carrier,
An electrostatic latent image forming unit for forming an electrostatic latent image on the surface of the charged image carrier, and an image forming process unit including a developing unit for developing by attaching toner of a developer to the electrostatic latent image; The image carrier is an image forming apparatus that is repeatedly provided for image formation, wherein the charging means of the image carrier is contact charging means for charging the image carrier by bringing a charging member into contact with the image carrier. An image forming apparatus comprising: a toner capturing unit that collects toner attached to a charging member from the charging member; and a toner capturing unit recleaning unit that removes the captured toner from the toner capturing unit. 3. The image forming apparatus according to claim 1, further comprising a transfer unit configured to transfer a toner image formed on the image carrier to a transfer material.
Or the image forming apparatus according to 2. 4. A transfer device for transferring a toner image formed on an image carrier to a transfer material, and removing transfer residual toner remaining on the surface of the image carrier after the transfer of the toner image between the transfer device and the charging device. The image forming apparatus according to claim 1, further comprising an image carrier cleaning unit that performs cleaning. 5. A cleaner-less process apparatus comprising a transfer unit for transferring a toner image formed on an image carrier to a transfer material, and recovering transfer residual toner remaining on the surface of the image carrier after transfer of the toner image by a developing unit. The image forming apparatus according to claim 1, wherein: 6. The electrostatic latent image forming means according to claim 1, wherein said electrostatic latent image forming means is an image exposing means for forming an electrostatic latent image by imagewise exposing the charged image carrier surface. The image forming apparatus according to one of the above. 7. The toner capturing means generates an electric field between the toner and the charging member, and recovers the toner adhered to the charging member from the charging member by the electric field, and discharges the collected toner to the charging member. The image forming apparatus according to claim 1, wherein: 8. The toner capturing means collects toner adhering to the charging member when the image area of the image carrier is charged, and discharges the collected toner to the charging member when charging the non-image area. The image forming apparatus according to claim 1. 9. The image carrier according to claim 1, wherein the non-image area is charged by a charging bias having a smaller voltage amplitude than that of the image area when the image carrier is charged. Image forming apparatus. 10. The image forming apparatus according to claim 1, wherein the image carrier is charge-chargeable. 11. A charging member brought into contact with an image carrier has a brush portion of conductive magnetic particles carried on the carrying member,
The image forming apparatus according to claim 1, wherein the brush is in contact with the image carrier. 12. The image forming apparatus according to claim 12, wherein the charging member brought into contact with the image carrier has a brush portion made of conductive fibers carried on the carrier member, and the brush portion is in contact with the image carrier. Item 11. The image forming apparatus according to any one of Items 1 to 10. 13. The image forming apparatus according to claim 1, wherein the developing unit is a reversal developing device. 14. The image forming apparatus according to claim 13, wherein a bias voltage having a potential between an exposed portion and an unexposed portion of the image carrier is applied to the developer carrying member of the developing device. Image forming apparatus.