JP2005331822A - Image forming apparatus - Google Patents

Abstract

In an image forming apparatus in a cleaner-less system using contact charging, an image capable of maintaining a high-quality image for a longer period without fogging due to reversal toner regardless of the recording material used. Providing a forming device.
A charged member is charged by applying a bias voltage to a charging member opposite to the member to be charged, and a latent image is formed by image exposure by an image exposure unit, and is carried on a developer carrier. A developing unit that develops the latent image with the developed developer to form a toner image, and a cleaning unit that collects residual toner particles remaining on the image carrier after the developing unit transfers the toner image to a transfer material. The image forming apparatus also serves as means for collecting the developer having a charge opposite to the normal polarity by the developing device.
[Selection] Figure 1

Description

  The present invention relates to a transfer-type image forming apparatus using a cleaner-less process. More specifically, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric, and a charging member facing the image carrier, and a charging bias is applied to the charging member to charge the image carrier. A charging device, an image information writing device that forms an electrostatic latent image on the charging surface of the image carrier, a developing device that visualizes the electrostatic latent image with a developer, and a surface of the image carrier. A transfer device that moves the developer to the transfer material, and an image of a copying machine, a printer, or the like that uses the transfer device to recollect the developer remaining on the surface of the image carrier without being transferred to the transfer material by the transfer device The present invention relates to a forming apparatus.

(A) Contact charging:
In an electrophotographic or electrostatic recording image forming apparatus, as a charging means for charging an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric, and other charged objects to a predetermined polarity and potential, Conventionally, a corona charger has been generally used. This is done by placing a corona charger in contact with the image carrier (hereinafter referred to as a photoreceptor) in a non-contact manner, exposing the photoreceptor surface to the corona discharged from the corona charger, and charging the photoreceptor surface to a predetermined polarity and potential. It is something to be made. In recent years, since it has advantages such as low ozone and low power compared to the case of the above non-contact type corona charger, as described above, a voltage (charging bias) is applied to the photosensitive member as the member to be charged. A contact-type charging device has been put to practical use in which a charged member (contact charging member) is brought into contact to charge the surface of a photosensitive member to a predetermined polarity and potential. In particular, a roller charging apparatus using a conductive roller (charging roller) as a charging member is preferably used from the viewpoint of charging stability.

  Further, as the contact charging member, a magnetic brush charging member (charged magnetic brush, hereinafter referred to as a magnetic brush charger) provided with a magnetic brush portion in which magnetic particles are magnetically restrained on a carrier is used. A magnetic brush charging type device in which the magnetic brush portion is brought into contact with the photosensitive member is also preferably used from the viewpoint of the stability of the charging device. The magnetic brush charger has a magnetic brush portion formed by magnetically constraining conductive magnetic particles directly on a magnet or on a sleeve containing the magnet, and is stopped or rotated. The magnetic brush unit is brought into contact with the photoconductor, and a voltage is applied to the photoconductor to start charging the photoconductor.

  In addition, a conductive fiber formed in a brush shape (fur brush charging member, charging fur brush), a conductive rubber blade (charging blade) having a conductive rubber blade shape, etc. are preferably used as the contact charging member. ing.

  The contact charging mechanism (charging mechanism, charging principle) has two types of charging mechanisms, a corona charging system and a charge injection (direct charging) system, and each characteristic appears depending on which is dominant. .

  The corona charging system is a system in which the surface of the photosensitive member is charged with a discharge product due to a corona discharge phenomenon generated in a minute gap between the contact charging member and the photosensitive member. In corona charging, the contact charging member and the photosensitive member have a certain discharge threshold value, and therefore it is necessary to apply a voltage larger than the charging potential to the contact charging member. In addition, compared with a corona charger, the generated amount is not so small, but a discharge product is generated.

  The charge injection charging system is a system in which the surface of the photoreceptor is charged by directly injecting charges from the contact charging member to the photoreceptor. More specifically, a medium-resistance contact charging member comes into contact with the surface of the photoreceptor, and charge is directly injected into the surface of the photoreceptor without going through a discharge phenomenon, that is, basically without using discharge. Therefore, even when the applied voltage to the contact charging member is an applied voltage that is equal to or lower than the discharge threshold, the photosensitive member can be charged to a potential corresponding to the applied voltage. This charge injection charging system does not involve the generation of ions.

  However, because of charge injection charging, the contact property of the contact charging member to the photosensitive member greatly affects the charging property. Therefore, it is necessary to adopt a structure in which the contact charging member is more densely configured and has a large speed difference from the photoconductor, and more frequently contacts the photoconductor. The device can perform stable charging.

  Charge injection charging by a magnetic brush charger can be regarded as equivalent to a series circuit of a resistor and a capacitor. In an ideal charging process, the time during which a point on the surface of the photoreceptor is in contact with the magnetic brush (charging nip × The capacitor is charged to the peripheral speed of the photoconductor, and the surface potential of the photoconductor becomes almost equal to the applied voltage.

  There is a method in which a voltage is applied to a conductive contact member and a charge is injected into a trap level on the surface of the photoreceptor to charge the photoreceptor. Further, when a photosensitive member having a surface layer (electric injection layer) in which conductive fine particles are dispersed on an ordinary organic photosensitive member or an amorphous silicon photosensitive member is used, a direct current of the bias applied to the contact charging member is used. It is possible to obtain a charged surface with a charging potential substantially equal to that of the component (Patent Document 1).

The injection charging method is not only less environmentally dependent, but also uses no discharge, so that the voltage applied to the contact charging member is sufficient to be about the same as the photoreceptor potential, and has the advantage of not generating ozone. Ozone-less and low power consumption type charging becomes possible.
(B) Cleanerless process (toner recycling process):
In recent years, the size of image forming apparatuses has been reduced. However, the overall size of the image forming apparatus can be reduced only by reducing the size of each means and device for the image forming process such as charging, exposure, development, transfer, fixing, and cleaning. There was a limit to the size reduction. Further, the untransferred toner (residual developer) on the photoconductor after the transfer is recovered by a cleaning means (cleaner) and becomes waste toner, but it is preferable that this waste toner does not come out from the viewpoint of environmental protection.

  Therefore, the “cleaner-less process” image forming apparatus is configured such that the cleaner is removed, and the transfer residual toner on the photosensitive member is removed from the photosensitive member by “development simultaneous cleaning” by the developing unit and collected and reused in the developing unit. Has also appeared. Simultaneous development cleaning is a fog removal bias (fogging potential difference Vback which is a potential difference between the DC voltage applied to the developing means and the surface potential of the photosensitive member) during the development after the next process for the toner slightly remaining on the photosensitive member after transfer. It is a method to collect by. According to this method, since the transfer residual toner is collected by the developing means and used after the next step, waste toner can be eliminated and the trouble of maintenance can be reduced. Further, since the cleaner is not required, there is a great advantage in terms of space, and the image forming apparatus can be greatly downsized. Further, when the charging device of the photoconductor is contact charging, the transfer residual toner is once collected by the charging member that is in contact with the photoconductor, and then discharged onto the photoconductor again to be collected by the developing device.

  In a system that does not have a cleaning device for removing the transfer residual toner from the object to be charged, a so-called cleaner-less system, a large amount of transfer residual toner is mixed or adhered to the contact charging member. The resistance value of the contact charging member varies. Therefore, a method is known in which charging member cleaning bias corresponding to the number of durable sheets and the image ratio is applied at the time of non-image formation, for example, to delay the deterioration of the charging member. That is, in the contact charging, there are bias conditions and hardware configuration conditions that make it easy to discharge the toner mixed in the magnetic brush or adhering to the roller onto the photoreceptor, and the life of the charger can be extended.

  In particular, in the case of a magnetic brush injection charging device, the transfer residual toner that is considered to have positive and negative polarity toners is once recovered by a magnetic brush to erase the history of the previous image, and the toner by contact friction between the magnetic particles and the recovered toner. Can be controlled to return the toner to the drum again.

  Further, since the toner discharged from the magnetic brush portion to the photosensitive drum is in a very uniform distribution state, and the amount thereof is small, it does not substantially adversely affect the next image exposure process. Further, there is no ghost image due to the transfer residual toner pattern, and normal polarity toner can be reliably recovered in the non-image area due to the difference between the development bias and the charging potential.

  In the case of charging using a conductive roller, there is a method of bringing a sheet in consideration of a friction series into contact with the roller in order to return the opposite polarity toner attached to the roller to the normal polarity.

JP-A-6-003921

  However, the following problems have occurred in the cleanerless image forming apparatus using such a contact charging method.

  As described above, the transfer residual toner is collected by development with a regular polarity, that is, the same polarity as the charging polarity in the charging device, but is slightly but has little or no polarity. (Hereinafter referred to as reversal toner) may exist. Usually, the toner of this reverse polarity is extremely small, and even if it is not recovered by development and is carried around on the drum, it is not transferred under normal transfer conditions, and many reversal toners are charged. Since normal polarity can be obtained again by contact with the member, there is no particular problem on the image.

  However, depending on the thickness and surface properties of the recording material used, it may occur as a fog on a white background on the image. Although the reason for this is not clear, it is considered that when the recording paper is thick, the contact pressure of the transfer blade or the transfer roller in the transfer portion is increased, so that the transfer is performed with the pressure of the opposite polarity. In addition, in recording paper with high smoothness such as coated paper, the adhesion between the recording paper and the photosensitive member is increased, so that there is no gap to avoid the toner being pressed against the recording paper at the same time. Is considered to be transferred by pressure.

  The toner of the opposite polarity or the toner having almost no polarity may exist at a certain ratio from the beginning. However, the toner is not likely to have a normal charging polarity under high humidity, or the amount of toner in the charger is temporarily It is noticeable when the amount of deteriorated toner increases, such as when it is in a state where contact charging is difficult to increase, or external additives are embedded while it circulates around the drum without being transferred for a long period of time. Occurs. These reversal toners accumulate without being discharged from the charging device, and when a certain amount is accumulated, they gradually leak onto the drum and may be pressure-transferred without being collected by development.

  In particular, in the case of using thick paper or coated paper, in the case of an apparatus having a mode in which the process speed is slowed down in order to maintain the fixability, the pressure is applied to the transfer portion for a long time. It becomes.

  Furthermore, when used over a long period of time, not only for thick paper, the reversal toner that is not collected by development and not transferred is accumulated, and any of these exceeds the allowable amount, and image defects due to charging member contamination, scattering, and device contamination. Cause the life of the device itself to be determined.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to maintain a high-quality image for a long period of time in an image forming apparatus in a cleaner-less system using contact charging without causing any fogging due to reversal toner regardless of the recording material used. It is an object of the present invention to provide an image forming apparatus capable of doing so.

  The said subject is solved by taking the following structures.

  A developer charged on a developer carrying member is formed by applying a bias voltage to a charging member facing the member to be charged to charge the member to be charged, and performing image exposure by an image exposure unit to form a latent image. And developing means for developing the latent image to form a toner image, and an image forming apparatus that also serves as a cleaning means for collecting residual toner particles remaining on the image carrier after the developing means transfers the toner image to a transfer material , The developer having a charge opposite to the normal polarity is collected by the developing device.

  It is preferable that the charging member is contact charging in contact with an object to be charged.

  The charging member is preferably composed of magnetic particles and a magnetic particle carrier.

  The charging member is preferably made of a conductive brush.

  The charging member is preferably made of a conductive rubber roller.

  The charging method is preferably a contact charging method in which charging is performed by bringing a conductive member having a voltage applied into contact with a photoreceptor having a charge injection layer on the surface.

  The developer having a charge opposite to the normal polarity is preferably a developer attached to the contact charging device.

  The developer having a charge opposite to the normal polarity is preferably a developer collected or mixed in the contact charging device.

  It is preferable that the means for collecting the developer having a charge opposite to the normal polarity by the developing device changes the potential difference between the charging potential and the developing bias.

  Preferably, the means for collecting the developer having a charge opposite to the normal polarity by the developing device reduces the potential difference between the charging potential and the developing bias.

  It is preferable that the means for collecting the developer having a charge opposite to the normal polarity by the developing device changes the waveform of the AC component of the developing bias.

  It is preferable that the means for collecting the developer having a charge opposite to the normal polarity by the developing device changes the amplitude of the AC component of the developing bias.

  It is preferable that the means for collecting the developer having a charge opposite to the normal polarity by the developing device increases the amplitude of the AC component of the developing bias.

  It is preferable to have a developer return bias different from that at the time of image formation applied to the charging member for returning the collected developer from the charging member onto the member to be charged.

  The charging bias is preferably a DC bias or a bias in which an AC bias is superimposed on a DC bias.

  The developer return bias different from that at the time of image formation preferably changes the amplitude of the AC bias.

  It is preferable that the developer return bias different from that at the time of image formation changes the waveform of the AC bias.

  It is preferable to change the process speed in accordance with the selected recording material.

  It is preferable to change the process speed in accordance with the selected recording material.

  According to the present invention, in the cleanerless image forming apparatus, the charging bias amplitude is increased, the potential difference between the charging potential and the DC bias applied to the developing device is reduced, and the mode for collecting the reversal toner by the developing device is set. As a result, it is possible to prevent fogging due to the reversal toner peculiar to thick paper and coated paper and toner having no polarity.

(1) Example of image forming apparatus (FIG. 1):
FIG. 1 is a schematic configuration diagram of an image forming apparatus. The image forming apparatus according to the present embodiment is a laser beam printer using a transfer type electrophotographic process, a charge injection charging method, and a cleaner-less process.

  Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. The photosensitive drum 1 according to the present embodiment is an OPC photosensitive member (organic photoconductive photosensitive member) having a negative charging property and a charge injection charging property, and has a process speed (peripheral speed) of 150 mm / sec in the clockwise direction a indicated by an arrow. Driven by rotation.

  A contact charging device 2 uniformly charges the surface of the photosensitive drum 1 with a predetermined polarity and potential. In this embodiment, it is a magnetic brush charging device, and the surface of the rotating photosensitive drum 1 is uniformly charged by the magnetic brush charging device 2 to approximately −700 V by a charge injection charging method.

  Reference numeral 3 denotes an image information exposure means (exposure device), which is a laser beam scanner in the present embodiment. The laser beam scanner 3 includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and inputs from an unillustrated host device such as a document reading device, an electric computer, or a word processor having a photoelectric conversion element such as a CCD. The laser beam L modulated in accordance with the time-series electric digital image signal of the target image information is emitted, and the uniformly charged surface of the rotating photosensitive drum 1 is subjected to laser beam scanning exposure. By this laser beam scanning exposure, an electrostatic latent image corresponding to target image information is formed on the peripheral surface of the rotary photosensitive drum 1.

  Reference numeral 4 denotes a developing device. In the present embodiment, a two-component contact developing type developing device using a developer prepared by mixing a highly releasable spherical toner with a small amount of transfer residual toner produced by a polymerization method and a magnetic carrier is used. The electrostatic latent image on the surface of the rotating photosensitive drum 1 is reversely developed as a toner image.

  Reference numeral 5 denotes a transfer device disposed below the photosensitive drum 1, and the transfer device of the present embodiment is a transfer belt type. Reference numeral 5a denotes an endless transfer belt (for example, a polyimide belt having a film thickness of 75 μm). The transfer belt 5a is suspended between the driving roller 5b and the driven roller 5c, and extends in the forward direction in the rotation direction of the photosensitive drum 1. The photosensitive drum 1 is rotated at the same peripheral speed as that of the photosensitive drum 1. Reference numeral 5d denotes a conductive blade disposed inside the transfer belt 5a, and the upper belt portion of the transfer belt 5a is pressed against the lower surface portion of the photosensitive drum 1 to form a transfer nip portion T as a transfer portion.

  Reference numeral 6 denotes a paper feed cassette in which a transfer material P such as paper is stacked and stored. One sheet of transfer material P loaded and stored in the sheet cassette 6 is separated and fed by the drive of the sheet feed roller 7, passes through the sheet path 9 including the conveyance roller 8 and the like, and the photosensitive drum 1 at a predetermined control timing. And a transfer nip T between the transfer device 5 and the transfer belt 5a of the transfer device 5.

  The material P to be transferred fed to the transfer nip T is nipped and conveyed between the rotating photosensitive drum 1 and the transfer belt 5a, and during that time, a predetermined transfer bias is applied to the conductive blade 5d from the transfer bias application power source E5. As a result, the reverse polarity of the toner is charged from the back surface of the transfer material P. As a result, the toner image on the surface side of the rotary photosensitive drum 1 is sequentially electrostatically transferred onto the surface side of the transfer material P passing through the transfer nip T.

  The transfer material P that has received the transfer of the toner image through the transfer nip T is sequentially separated from the surface of the rotary photosensitive drum 1 and is introduced into the fixing device (for example, a heat roller fixing device) 11 through the sheet path 10. The toner image is fixed and printed out.

  The printer according to the present embodiment is a cleaner-less process, and a dedicated cleaner for removing toner remaining on the surface of the rotating photosensitive drum 1 without being transferred to the transfer material P at the transfer nip T is not provided. As will be described later, the untransferred toner reaches the position of the magnetic brush charging device 2 by the subsequent rotation of the photosensitive drum 1, and the magnetic brush portion of the magnetic brush charger 2 </ b> A as a contact charging member in contact with the photosensitive drum 1. The collected toner is discharged to the surface of the photosensitive drum 1 again and finally collected by the developing device 4, and the photosensitive drum 1 is repeatedly used for image formation.

Reference numeral 12 denotes a conductive drum which is brought into contact with the photosensitive drum between the transfer device 5 and the magnetic brush charging device 2 and applied with an AC bias, a DC bias having a polarity opposite to that of charging, or a DC bias having a polarity opposite to that obtained by superimposing the AC bias. The brush of the magnetic brush charger 2A is used to level the surface potential of the photosensitive drum immediately before charging by the magnetic brush charging device 2 and at the same time removes the transfer residual toner or charges it with a polarity opposite to that of the photosensitive drum. Easy collection with the magnetic brush unit.
(2) Cleanerless process:
Since the printer of this embodiment is a cleaner-less process, the toner (transfer residual toner) remaining on the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is held in the charging nip portion N of the photosensitive drum 1. It is carried and mixed in the magnetic brush portion 2c of the magnetic brush charger 2A of the magnetic brush contact charging device 2 and temporarily recovered. The transfer residual toner on the photosensitive drum 1 often has a mixture of positive and negative polarity due to peeling discharge during transfer. The transfer residual toner in which the polarity is mixed reaches the magnetic brush charger 2A, is mixed in the magnetic brush portion 2c, and is temporarily collected. The transfer residual toner is taken into the magnetic brush portion 2c of the magnetic brush charger 2A by applying an AC component to the magnetic brush charger 2A, thereby causing an oscillating electric field effect between the magnetic brush charger 2A and the photosensitive drum 1. This can be done more effectively.

  Then, the transfer residual toner taken into the magnetic brush unit 14 is charged negatively in all polarities and discharged onto the photosensitive drum 1. The untransferred toner discharged on the photosensitive drum 1 with the same polarity reaches the developing section m and is collected by the developing 4b of the developing device 4 by the simultaneous development cleaning by the fog removing electric field at the time of development. When the image area in the rotation direction is longer than the peripheral length of the photosensitive drum 1, the simultaneous collection of the transfer residual toner is performed simultaneously with other image forming processes such as charging, exposure, development, and transfer. As a result, the transfer residual toner is collected in the developing device 4 and is used after the next step, so that waste toner can be eliminated. Further, the advantage in terms of space is great, and the image forming apparatus can be greatly downsized.

  By using a highly releasable spherical toner prepared by a polymerization method as the toner t of the developer, the amount of transfer residual toner can be reduced, and the development of the toner discharged from the magnetic brush charger 2A can be reduced. The recoverability to the apparatus 4 can be improved. The use of the two-component contact developing type developing device 4 also improves the recoverability of the toner discharged from the magnetic brush charger 2A to the developing device 4. Here, since the toner usually has a relatively high electric resistance, the mixing of such toner particles into the magnetic brush portion 14 of the magnetic brush charger 2A increases the electric resistance of the magnetic brush portion 2c and increases the charging ability. When the amount of mixed toner is relatively large, good charge can be maintained by discharging a large amount of toner during non-image formation.

  Here, the toner discharge will be briefly described.

  When toner is mixed into the magnetic brush part, its electric resistance gradually increases, so that sufficient charge movement is not performed while passing through the charging nip, and the photoreceptor surface potential after passing through the charging nip is smaller than the applied voltage. turn into. Hereinafter, the potential difference between the photoreceptor surface potential and the applied voltage is represented by ΔV. When the toner taken in the magnetic brush charger is charged with the same polarity as the photosensitive member potential by contact with the magnetic brush carrier, the mixed toner is transferred from the magnetic brush to the photosensitive member surface by the electric field generated by the potential difference ΔV. Exhaled. As disclosed in Japanese Patent Laid-Open No. 9-0096949 and the like, this phenomenon is used to reduce the amplitude Vpp of the AC component (AC component) of the charging bias during non-image formation (non-image formation) or AC By stopping the application of the component, the potential difference ΔV is increased, and the toner is actively discharged to suppress an increase in the electric resistance of the magnetic brush.

  The discharge at the time of non-image formation is performed by inter-paper or post-rotation after completion of the image formation operation, so that the amount of toner mixed in the magnetic brush can be kept below a certain level for long-term use.

Further, since the toner discharged from the magnetic brush portion 14 to the photosensitive drum 1 is in a very uniform distribution state and the amount thereof is small, it does not substantially adversely affect the next image exposure process. . Further, no ghost image is generated due to the residual toner pattern.
(3) Operation sequence (FIG. 2):
Next, an operation sequence will be described.

a. Pre-multi-rotation process:
This is a printer start-up operation period (start-up operation period, warming period). When the main power switch is turned on, the main motor of the apparatus is driven to rotate the photosensitive drum, and a predetermined operation of the process equipment is executed.

b. Pre-rotation process:
This is the period during which the pre-print operation is executed. The individual pre-rotation steps are executed subsequent to the pre-multi-rotation step when a print signal is input during the pre-multi-rotation step. When the print signal is not input, the drive of the main motor is temporarily stopped after the completion of the previous multi-rotation process, the rotation of the photosensitive drum is stopped, and the printer is kept in a standby (standby) state until the print signal is input. It is. When the print signal is input, the pre-rotation process is executed.

c. Printing process (image forming process, image forming process):
When the predetermined pre-rotation process is completed, an image forming process for the rotating photosensitive drum is subsequently performed, and the toner image formed on the surface of the rotating photosensitive drum is transferred to the transfer material, and the toner image is fixed by the fixing unit. The image formation is printed out. In the case of the continuous printing (continuous printing) mode, the above printing process is repeated for a predetermined set number of prints.

d. Inter-sheet process:
In the continuous printing mode, after the trailing edge of one transfer material passes through the transfer nip, the transfer material in the transfer nip until the leading edge of the next transfer material reaches the transfer nip. This is a non-paper passing period. During this period, while the area of the rotating photoconductor passing through the transfer nip passes through the charging nip portion, the AC component amplitude of the charging bias is changed, and the transfer residual toner temporarily collected by the magnetic brush charging member Is discharged to the surface of the rotating photosensitive drum and collected by a developing device.

e. Post-rotation process:
This is a period during which a predetermined post-operation is executed by continuing to drive the main motor for a while after the printing process of the last transfer material is completed and rotating the photosensitive drum. Also during this period, by changing the amplitude of the AC component of the charging bias in the same manner as the inter-sheet process, the transfer residual toner temporarily collected by the magnetic brush charging member is discharged to the surface of the rotating photosensitive drum and collected by the developing device. .

f. stand-by:
When the predetermined post-rotation process is completed, the driving of the main motor is stopped, the rotation of the photosensitive drum is stopped, and the printer is kept in a standby state until the next print start signal is input.

  In the case of printing only one sheet, after the printing is finished, the printer goes into a standby state through a post-rotation process. When a print start signal is input in the standby state, the printer shifts to a pre-rotation process.

  The printing process of c is the time of image formation, and the pre-multi-rotation process of a, the pre-rotation process of b, the paper gap process of d, and the post-rotation process of e are non-image formation (non-image formation).

Note that details regarding toner ejection and collection during non-image formation will be described later.
(4) Photosensitive drum (FIG. 3):
The photosensitive drum 1 of the present embodiment is a negatively chargeable / charge-injecting OPC photosensitive member as described above, and the first to fifth functional layers are arranged in order from the bottom on a φ30 mm aluminum drum base. It is provided.

  First layer: an undercoat layer, which is a conductive layer having a thickness of about 20 μm, which is provided for leveling defects on the aluminum drum substrate and preventing the occurrence of moire due to reflection of laser exposure.

Second layer: a positive charge injection preventing layer that serves to prevent the positive charge injected from the aluminum drum substrate 1a from canceling the negative charge charged on the surface of the photoreceptor, and is formed by amylan resin and methoxymethylated nylon. This is a medium resistance layer having a thickness of about 1 μm, the resistance of which is adjusted to about 10 ⁶ Ω · cm.

  Third layer: a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates positive and negative charge pairs upon receiving laser exposure.

  Fourth layer: a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, the negative charge charged on the surface of the photoconductor cannot move through this layer, and only the positive charge generated in the charge generation layer 1d can be transported to the surface of the photoconductor.

Fifth layer: a charge injection layer, tin oxide SnO having a particle size of 0.03 μm, which has been reduced in resistance (conductivity) by doping light-curing acrylic resin as a binder with antimony as a light-transmitting conductive filler _This is a coating layer of about 3 μm made of a material in which 70% by weight of ₂ ultrafine particles are dispersed with respect to the resin. The electric resistance value of the electrification injection layer 1f needs to be 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ω · cm, which is a sufficient charging property and does not cause image flow. In this embodiment, a photosensitive drum having a surface resistance of 1 × 10 ¹¹ Ω · cm is used.
(5) Developing device 4 (FIG. 7):
In general, toner development methods for electrostatic latent images are roughly classified into the following four types a to d.

  a. A non-magnetic toner is coated on the sleeve with a blade or the like, and the magnetic toner is coated with a magnetic force and conveyed and developed in a non-contact state with respect to the photoreceptor (one-component non-contact development).

  b. A method in which the toner coated as described above is developed in contact with a photoreceptor (single component contact development).

  c. A method in which toner particles mixed with a magnetic carrier are used as a developer, conveyed by magnetic force boiling, and developed in contact with a photosensitive pair (two-component contact development).

  d. A method of developing the above two-component development with the agent in a non-contact state (two-component non-contact development).

  Among these, the two-component contact development method c is often used from the viewpoint of high image quality and high stability.

  The developing device 4 in the present embodiment uses, as a developer, a mixture of a highly releasable spherical non-magnetic toner prepared by a polymerization method and a magnetic carrier (developing magnetic particles, developing carrier), and the developer is used as a developer. A two-component magnetic brush contact development system in which a carrier (developing member, developer) is held as a magnetic brush layer by magnetic force, conveyed to a developing unit, and brought into contact with the surface of a photosensitive drum to develop an electrostatic latent image as a toner image. The reversal developing device.

  4a is a developing container, 4b is a developing sleeve as a developer carrying member, 4c is a magnet (magnet roller) as magnetic field generating means fixedly disposed in the developing sleeve 4b, and 4d is a thin layer of developer on the surface of the developing sleeve. 4e is a developer agitating / conveying screw, 4f is a two-component developer accommodated in the developer container 4a, and the nonmagnetic toner t and the developing carrier c as described above are formed. It is a mixture.

  At least during development, the developing sleeve 4b is disposed so that the closest distance (gap) to the photosensitive drum 1 is about 500 μm, and the developer magnetic brush thin layer carried on the outer surface of the developing sleeve 4b is photosensitive. It is set to come into contact with the surface of the body drum 1. A contact nip m between the developer magnetic brush thin layer 4 and the photosensitive drum 1 is a development region (development unit).

  The developing sleeve 4b is driven at a predetermined rotational speed in the counterclockwise direction indicated by an arrow around the outside of the internal fixed magnet 4c, and a magnetic brush of the developer 4f (t + c) is applied to the outer surface of the sleeve within the developing container 4a by the magnetic force of the fixed magnet 4c. It is formed. The developer magnetic brush is conveyed with the rotation of the sleeve 4b, is subjected to the layer thickness regulation by the blade 4d, is taken out of the developing container as a developer magnetic brush thin layer 4 having a predetermined layer thickness, and is conveyed to the developing unit m. The photosensitive drum comes into contact with the surface of the photosensitive drum 1 and is conveyed back into the developing container 4a by the subsequent rotation of the sleeve 4b.

  A predetermined developing bias in which a DC component and an AC component are superimposed is applied to the developing sleeve 4b by a developing bias applying power source E4. As for the development characteristics in the present embodiment, fogging occurs when the difference between the charged potential of the photosensitive drum 1 and the DC component value of the developing bias is 200 V or less, and when it is 350 V or more, the developing carrier c is transferred to the photosensitive drum 1. Adhesion occurred.

The toner concentration (mixing ratio with the developing carrier c) of the developer 4f (t + c) in the developing container 4a is consumed successively as the toner is consumed for developing the electrostatic latent image. When the toner concentration of the developer 4f in the developing container 4a is detected by a detection unit (not shown) and decreases to a predetermined allowable lower limit concentration, the toner t is supplied from the toner supply unit 4g to the developer 4f in the developing container 4a. Thus, toner replenishment control is performed so that the toner concentration of the developer 4f in the developing container 4a is always kept within a predetermined allowable range.
(6) Magnetic brush charging device (FIGS. 1 and 4):
FIG. 4 is an enlarged cross-sectional model view of the magnetic brush charging device 2. The magnetic brush charging device 2 of the present embodiment is roughly divided into a magnetic brush charging member (magnetic brush charger) 2A, a container containing the magnetic brush charger 2A and conductive magnetic particles (charge carrier) 14 ( Housing) 2 and a charging bias application power source E4 for the magnetic brush charger 2A.

  The magnetic brush charger 2A of this embodiment is a sleeve rotation type, and includes a magnet roll (magnet) 12 and a non-magnetic stainless steel sleeve (electrode sleeve, conductive sleeve, charging sleeve, etc.) fitted on the magnet roll. 13) and a magnetic brush portion of magnetic particles 14 formed and held on the outer peripheral surface of the sleeve 13 by being magnetically restrained by the magnetic force of the magnet roll 12 inside the sleeve.

  The magnet roll 12 is a non-rotating fixed member, and the sleeve 13 rotates around the magnet roll 12 in the direction of the arrow b by a drive system (not shown) at a predetermined peripheral speed, in this embodiment, a peripheral speed of 225 mm / sec. Is driven to rotate. The sleeve 13 is disposed with a gap of about 500 μm with respect to the photosensitive drum 1 by means of a spacer roller or the like.

  2e is a magnetic brush layer thickness regulating blade made of non-magnetic stainless steel attached to the container 2, and is arranged so that the gap with the surface of the sleeve 2b is 900 μm. A part of the magnetic particles 14 in the container 2B is magnetically constrained on the outer peripheral surface of the sleeve 13 by the magnetic force of the magnet roll 12 inside the sleeve 13 and held as the magnetic brush portion 2c. The magnetic brush portion 2 rotates in the same direction as the sleeve 13 together with the sleeve 13 as the sleeve 13 rotates. At this time, the layer thickness of the magnetic brush portion is regulated to a uniform thickness by the blade 15. Since the regulation layer thickness of the magnetic brush portion is larger than the gap between the facing gap portion between the sleeve 13 and the photosensitive drum 1, the magnetic brush portion is placed on the photosensitive drum 1 at the facing portion between the sleeve 13 and the photosensitive pair drum 1. A nip portion having a predetermined width is formed and contacted. This contact nip portion is a charging nip portion N.

  Accordingly, the rotating photosensitive drum 1 is rubbed at the charging nip portion N by the magnetic brush portion that rotates as the sleeve 13 of the magnetic brush charger 2A rotates. In this case, in the charging nip portion N, the moving direction of the photosensitive drum 1 and the moving direction of the magnetic brush portion are opposite, and the relative moving speed is increased. A predetermined charging bias is applied to the sleeve 13 and the magnetic brush layer thickness regulating blade 15 from the power supply E4.

  Thus, the photosensitive drum 1 is rotationally driven, the sleeve 13 of the magnetic brush charger 2A is rotationally driven, and a predetermined charging bias is applied from the power source E4, so that the peripheral surface of the rotational photosensitive drum 1 becomes the main surface. In the case of the embodiment, the contact charging process is uniformly performed to a predetermined polarity and potential by an injection charging method. The magnet roll 12 fixedly arranged in the sleeve 13 has an angle θ between the sleeve 13 and the closest position c of the photosensitive drum 1 in a range from 20 ° upstream to 10 ° downstream of the photosensitive drum rotation direction. It is desirable that the upstream side is 15 ° to 0 °. If it is downstream, the magnetic particles are attracted to the position of the main pole, and the magnetic particles are likely to stay on the downstream side of the charging nip portion N in the rotation direction of the photosensitive drum. The transportability of magnetic particles is deteriorated, and retention is likely to occur. Further, when there is no magnetic pole in the charging nip portion N, it is clear that the binding force acting on the sleeve 13 acting on the magnetic particles becomes weak and the magnetic particles easily adhere to the photosensitive drum 1. The charging nip portion N described here indicates a region where the magnetic particles of the magnetic brush portion are in contact with the photosensitive drum 1 during charging. In this embodiment, a magnetic pole of about 900 G is arranged at a position 10 ° upstream.

In this embodiment, the magnetic particles 14 constituting the magnetic brush portion are obtained by reducing the sintered ferromagnetic material (ferrite), but the particles are also obtained by kneading resin and ferromagnetic powder. The one formed into a shape, or the one mixed with conductive carbon or the like for adjusting the resistance value, or the one subjected to the surface treatment can be similarly used. The magnetic particles 14 of the magnetic brush portion have a role of favorably injecting charges into the trap level on the surface of the photosensitive drum, and that the charging current is concentrated on defects such as pinholes generated on the drum on the photosensitive drum. It must also have a role of preventing the energization destruction of the charging member and the photosensitive member caused by the cause. Therefore, the electric resistance value of the magnetic brush charger 2A is preferably from ^{1 × 10 4 Ω~1 × 10 9} Ω, and particularly preferably from ^{1 × 10 4 Ω~1 × 10 7} Ω. If the electric resistance value of the magnetic brush charger 2A is less than 1 × 10 ⁴ Ω, pinhole leakage tends to occur, and if it exceeds 1 × 10 ⁹ Ω, good charge injection tends to be difficult. In order to control the resistance value within the above range, the volume resistance value of the magnetic particle 2d is desirably 1 × 10 ⁴ Ω · cm to 1 × 10 ⁹ Ω · cm, and in particular, 1 It is more preferable that it is × 10 ⁴ Ω · cm to 1 × 10 ⁷ Ω · cm.

The electric resistance value of the magnetic brush charger 2A used in this embodiment is 1 × 10 ⁶ Ω · cm, and by applying −700 V as the DC component of the charging bias, the surface potential of the photosensitive drum 1 is also increased. It became -700V.

The volume resistance value of the magnetic particles 14 was measured with an apparatus schematically shown in FIG. That is, the cell A is filled with the magnetic particles 2 d, the main electrode 17 and the upper electrode 18 are arranged so as to be in contact with the filled magnetic particles 14, and a voltage is applied from the constant voltage power supply 22 between the electrodes 17 and 18. The current flowing at that time was obtained by measuring with an ammeter 20. 19 is an insulator, 21 is a voltmeter, and 24 is a guide ring. The measurement conditions were: 23 ° C., 65% environment, contact area S = 2 cm ² of the filled magnetic particle 2d cell, thickness d = 1 mm, load of upper electrode 18 10 kg, applied voltage 100 V average of magnetic particles 14 The peak in the particle size and particle size distribution measurement is preferably in the range of 5 to 100 μm from the viewpoint of preventing charging deterioration due to contamination of the particle surface and preventing adhesion of magnetic particles to the surface of the photosensitive drum 1. The average particle diameter of the magnetic particles 14 is indicated by the maximum horizontal chord length. As the measurement method, 300 or more magnetic particles are randomly selected by a microscopic method, and the diameter is measured to obtain an arithmetic average.

  The charging bias is applied to the sleeve 13 and the regulating blade 15 by the power source E2. In this embodiment, a bias in which an AC component is superimposed on a DC component is used.

  In the charging nip portion N, the surface of the photosensitive drum 1 is rubbed by the magnetic brush portion of the magnetic brush charger 2A and a charging bias is applied to the magnetic brush charger 2A. Electric charges are applied from the particles 14 onto the photosensitive drum 1, and the surface of the photosensitive drum 1 is uniformly contact-charged to a predetermined polarity and potential. In the case of this example, as described above, since the photosensitive drum 1 is provided with the charge injection layer on the surface, the photosensitive drum 1 is charged by charge injection charging. That is, the surface of the photosensitive drum 1 is charged to a potential corresponding to the DC component of the charging bias DC + AC. The sleeve 13 tends to have better charging uniformity as the rotational speed increases.

  The charge injection charging of the photosensitive drum 1 by the magnetic brush charger 2A can be regarded as a series circuit of a resistor R and a capacitor C as shown in the equivalent circuit of FIG. In such a circuit, assuming that the resistance value is r, the electrostatic capacity of the photosensitive member is Cp, the applied voltage is V0, and the charging time (the time for a certain point on the surface of the photosensitive drum to pass through the charging nip portion N) is T0. The surface potential Vd of the photosensitive drum is expressed by the formula (1).

Vd = V0 (1-exp (T0 / (Cp · r))) Equation (1)
In the charging bias DC + AC, the DC component is set to the same value as the required surface potential of the photosensitive drum 1, which is −700 V in this embodiment.

  The AC component during image formation (image formation) has little effect on charging uniformity and potential convergence when the peak-to-peak voltage is small, and when it is too large, the retention of magnetic particles and the adhesion level to the photosensitive drum Gets worse. Further, the upper and lower limits of Vpp vary depending on the amount of toner remaining after transfer, the deterioration state of magnetic particles, or the external environment when the sheet passing durability is continued. That is, when the toner is mixed in a large amount, or when the toner is deteriorated due to adhesion of toner or external additives to the magnetic particles due to long-term paper passing durability, the resistance value of the magnetic particles increases when the external environment is low humidity. Therefore, in order to perform proper charging, it is necessary to increase Vpp and increase the amount of current.

  However, the adhesion level of the magnetic particles, which is considered to be harmful when Vpp is increased, tends to decrease as the resistance value increases. This is because the larger the amount of charge injected into the magnetic particles, the more easily affected by the potential difference between the applied bias and the photoreceptor, and the more easily attached. That is, depending on the amount of current, the proper AC bias amplitude shifts in the same direction for both upper and lower limits. Accordingly, when the resistance value is low, the adhesion of the magnetic particles tends to increase. However, even if Vpp is set smaller, a sufficient amount of current can be obtained for charging.

  The frequency is preferably 100 Hz to 5000 Hz, particularly preferably 500 Hz to 2000 Hz. Below that, the effect of improving the adhesion of magnetic particles to the photosensitive drum and improving the charging uniformity and potential rise properties become diminished, and the effect of improving the charging uniformity and potential rise properties becomes difficult to obtain even more. The AC waveform is preferably a rectangular wave, a triangular wave, a sin wave, or the like.

  Here, characteristics of the bias applied to the charging device during image formation and non-image formation will be described.

  When only the DC electric field is applied to the charging device, the discharge property of the toner mixed in the charging device to the photoreceptor is improved and the carrier is maintained for a long time without deteriorating, but is slightly smaller than when the AC electric field is applied. The chargeability also decreases with respect to carrier deterioration. For example, even if 700 V is initially applied to the charging potential target of 700 V, the photosensitive member is charged only to about 690 V. As the durability of the magnetic brush deteriorates, the potential further decreases, and the difference from the case where an AC electric field is applied gradually widens. Therefore, the reverse potential necessary for the DC value of the developing bias is not maintained, and the development bias is applied. Further, if the potential drop exceeds a certain value with respect to the initial set potential, the change in density of the output image exceeds the allowable level due to the fluctuation of the exposure portion potential.

  The level of the potential drop that causes a constant density change is more severe as a condition than the level of the potential drop that normally starts to appear. That is, even if it is not fogged, the development contrast may change due to a decrease in the charging potential, and the density and color appearance of the output image may exceed allowable levels. In particular, when an image with a high image ratio such as a solid image is output continuously, the toner density in the charging member temporarily increases and the charging ability decreases, and a ghost is generated in the image portion. Since there may be a situation where the reverse potential is not maintained, it is desirable to continue to apply the AC bias with an appropriate amplitude at least in the paper passing portion through which the paper passes.

As described above, the image portion is required to maintain at least stable AC charging, and the discharge needs to be performed between the sheets and during the front to rear rotation. However, if it is covered even between papers or after rotation, transfer residual toner is generated between papers and after rotation, which leads to an increase in toner mixed in the charger. Therefore, it is necessary to maintain a charge level at which fog does not occur. . At that time, it is desirable to set the bias in consideration of the charging property and discharging property depending on the environment. In the present embodiment, in a normal environment, the amplitude of the applied bias is set to 600 V during image formation and 400 V during non-image formation.
(7) Reverse toner discharge recovery mode:
However, as described above, there is toner having no polarity or reversal toner on the drum, in the magnetic brush of the charging charger or in the developing machine, and when it reaches the transfer section, it is pressure transferred to cardboard or coated paper. There is a problem that it ends up.

  Non-polar toner and reversal toner present on the drum are usually accumulated in the magnetic brush of the injection charger because there are few opportunities to be removed by the action of transfer bias and development bias. The toner discharged from the injection charger onto the drum includes both the reversal toner and the normal polarity toner. The normal polarity toner is collected by the developing unit in the non-image area, and therefore has little influence on the image, and is always processed by the discharge bias during non-image formation.

  On the other hand, when the reversal toner is discharged at the time of image formation, it is not collected by the developing unit, and thus fogging occurs on thick paper or coated paper. It has been found that this occurs even when a very small amount of reversal toner is present. Therefore, when using thick paper or coated paper, it is necessary to provide a mechanism for processing reversal toner. When the use of cardboard is rare, it is possible to set a bias so that the reverse toner is not discharged during image formation.

  However, when thick paper is frequently used, the reversal toner exhibits a behavior opposite to that of the normal toner with respect to the bias setting, and thus cannot be compatible with the above-described bias setting for processing the normal toner. Therefore, it is necessary to reduce the reversal toner mixed in the charger in advance.

  Therefore, in the present embodiment, the reverse toner discharge / collection mode for 5 seconds is set for every 100 A4 size sheets after the 100th sheet is discharged. Details will be described below.

  The AC amplitude of the charging bias in this mode was set to 750 V, which is higher than that at the time of image formation. This is because the reversal toner is better as ΔV is smaller, and the convergence of the charged potential is further improved. The reverse toner accumulated by this setting is discharged.

  Next, the recovery in the developing device is performed by bringing the developing bias closer to the charging potential. Specifically, the charging potential is −700 V, and in the normal setting, the developing bias is set to −500 V, whereas in this mode, it is set to −650 V. As a result, regular negative polarity toner may adhere to the photoconductor from the developing device due to the action of an electric field, but they can be collected again in the normal paper-passing mode and are collected more than before. The reversal toner without toner is separated from the photosensitive member by the AC component of the developing bias, and is finally scraped off and collected by the magnetic particle ears of the two-component developing device.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  In the present embodiment, a cleanerless system using the magnetic brush injection charging method similar to that of the first embodiment is adopted, and by simultaneously controlling the bias applied to the auxiliary charging brush arranged upstream of the charging device. Thus, the reversal toner discharge performance is improved.

  As described above, in FIG. 1, reference numeral 12 denotes a photosensitive drum between the transfer device 5 and the magnetic brush charging device 2, and an AC bias, a DC bias having a polarity opposite to that of charging, or a charging in which an AC bias is superimposed. This is a conductive brush to which a DC bias of reverse polarity is applied. At the same time as the surface potential of the photosensitive drum just before charging by the magnetic brush charging device 2 is discharged, the transfer residual toner is discharged or charged to the opposite polarity to the charging of the photosensitive drum. Thus, recovery at the magnetic brush portion of the magnetic brush charger 2A is facilitated. In a room temperature and normal humidity environment, a DC bias of about 500 V is applied and the value is controlled according to the environment.

  Here, non-polar toner or reversal toner mixed in the magnetic brush could be discharged by increasing the amplitude Vpp of the AC component (AC component) of the charging bias and decreasing the potential difference ΔV. Since a bias having a polarity opposite to the charging polarity is always applied to the auxiliary brush, even after charging by the magnetic brush, a poorly charged portion remains in a minute region where the reverse charge is injected, such as a brush tip passage portion. It may end up. That is, it means that ΔV has a certain value in that region, and it can be said that the reverse toner is not easily discharged.

  Therefore, in the present embodiment, a DC bias of minus 1000 V is applied to the auxiliary brush application bias in the reverse toner discharge recovery mode in the first embodiment. At this time, the drum surface potential after passing through the auxiliary brush is charged to about −800 V, which is higher on the charging polarity side than the charging DC bias of the original magnetic brush charging. At this time, the charged potential converges to −700 V by the AC bias applied to the magnetic brush after passing through the charging of the magnetic brush, so there is no problem in controlling the charging potential. The dischargeability of the reversal toner is improved because ΔV does not remain but rather a negative portion occurs.

<Embodiment 3>
In the present embodiment, the present invention is applied to a cleanerless system using a charging roller. FIG. 1 is a configuration diagram around a drum in the present embodiment.

  2 is a charging roller, 4 is a developing device, and 5a is a transfer roller. A DC bias of −800 V is applied to the auxiliary brush A shown in 7 during operation, and a DC bias of +400 V is applied to the auxiliary brush B shown in 8. The auxiliary brush B is applied with a bias having a polarity opposite to the charging polarity in order to erase the history of the drum surface potential after the transfer, and the auxiliary brush A uniformly applies the charged charge of the transfer residual toner to the normal polarity, that is, It has a negative effect and an auxiliary charging function.

On the other hand, in a normal environment, the charging roller 2 is superposed with a DC bias of −700 V and an AC bias subjected to constant current control for maintaining an AC current of 2000 μA. The transfer residual toner passing through the auxiliary brush A ideally has a negative polarity and converges to about −30 μC / cm ² suitable for development recovery by AC discharge received when passing through the charging roller 5. Part of the toner adheres to the charging roller and causes charging failure. The toner adhering to the charging roller is mostly reversible toner, and it is desirable to return it to the photoreceptor as appropriate.

  Therefore, in the present embodiment, a reverse toner discharge recovery mode is provided as in the second embodiment. The high pressure setting in the discharge recovery mode is OFF for the auxiliary brush B, -1000 V for the auxiliary brush A, and normal charging roller.

As for the developing bias in the reverse toner discharge and recovery mode, the DC bias is set to −650 V as in the first and second embodiments, and the AC component amplitude is changed from 1.8 kV to 2.2 kV. Normally, an optimal amplitude is set to ensure the linearity of the developing toner amount with respect to the developing contrast, but it is desirable to improve the recoverability with as high an amplitude as possible while aiming only at this toner recovery.
The fog could be effectively prevented over a long period of time. In addition, scattering from the charger and the occurrence of charging failure, which are the effects of reversal toner mixed in the charger, can be prevented for a longer period.

  The present invention has been particularly described with reference to a magnetic brush injection charging device. However, the present invention can be applied to other various charging devices, and the high voltage condition can be replaced with any DC component, frequency, waveform, etc. It is obvious.

1 is a schematic configuration diagram of an image forming apparatus according to Embodiment 1 of the present invention. It is process explanatory drawing explaining the sequence control in Embodiment 1 of this invention. 1 is a schematic configuration diagram of a photoconductor used in first and second embodiments of the present invention. It is a schematic block diagram of the charging device used in Embodiments 1 and 2 of the present invention. It is an equivalent circuit diagram of the charging circuit in the first and second embodiments of the present invention. It is explanatory drawing of the measurement point of the electrical resistance value (volume resistance value) of a magnetic particle (charging carrier). 1 is a schematic configuration diagram of a developing device used in an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Magnetic brush charging device 3 Laser beam scanner 4 Developing device 5 Transfer device 6 Paper feed cassette 7 Paper feed roller 8 Conveyance roller 9,10 Sheet path 11 Fixing device 12 Conductive brush 14 Magnetic brush part

Claims (18)

A developer charged on a developer carrying member is formed by applying a bias voltage to a charging member facing the member to be charged to charge the member to be charged, and performing image exposure by an image exposure unit to form a latent image. And developing means for developing the latent image to form a toner image, and an image forming apparatus that also serves as a cleaning means for collecting residual toner particles remaining on the image carrier after the developing means transfers the toner image to a transfer material In
An image forming apparatus comprising: a developer that collects a developer having a charge opposite to a normal polarity by the developing device.   The image forming apparatus according to claim 1, wherein the charging member is contact charging that contacts a member to be charged.   The image forming apparatus according to claim 1, wherein the charging member includes magnetic particles and a magnetic particle carrier.   3. The image forming apparatus according to claim 1, wherein the charging member is made of a conductive fiber brush.   3. The image forming apparatus according to claim 1, wherein the charging member is made of a conductive rubber roller.   5. The charging method according to claim 1, wherein the charging method is a contact charging method in which charging is performed by bringing a conductive member applied with a voltage into contact with a photoreceptor having a charge injection layer on a surface thereof. Image forming apparatus.   The image forming apparatus according to claim 5, wherein the developer having a charge opposite to the normal polarity is a developer attached to a contact charging device.   The image forming apparatus according to claim 3, wherein the developer having a charge opposite to the normal polarity is a developer collected or mixed in a contact charging device. apparatus.   9. The means for collecting a developer having a charge opposite to the normal polarity by the developing device is by changing a potential difference between a charging potential and a developing bias. The image forming apparatus according to any one of the above.   10. The means for collecting a developer having a charge opposite to the normal polarity by the developing device is by reducing a potential difference between a charging potential and a developing bias. The image forming apparatus according to any one of the above.   11. The means for collecting the developer having a charge opposite to the normal polarity by the developing device is by changing the waveform of the AC component of the developing bias. The image forming apparatus according to any one of the above.   12. The means for collecting the developer having a charge opposite to the normal polarity by the developing device is by changing the amplitude of the AC component of the developing bias. The image forming apparatus according to any one of the above.   12. The means for collecting the developer having a charge opposite to the normal polarity by the developing device is by increasing the amplitude of the AC component of the developing bias. The image forming apparatus according to any one of the above.   14. A developer returning bias different from that at the time of image formation applied to the charging member for returning the collected developer from the charging member onto the member to be charged. Image forming apparatus.   15. The image forming apparatus according to claim 14, wherein the charging bias is a DC bias or a bias in which an AC bias is superimposed on a DC bias.   16. The image forming apparatus according to claim 15, wherein the developer return bias different from that at the time of image formation changes the amplitude of the AC bias.   16. The image forming apparatus according to claim 15, wherein the developer return bias different from that at the time of image formation changes a waveform of an AC bias.   The image forming apparatus according to claim 1, wherein the process speed is changed according to the selected recording material.

Images