JP2000284570A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a stabilized excellent image formation to be successively performed by letting recovery of transfer residual toner by an electrostatic charging device efficiently performed, uniform property of charge potential on the image carrier improved, stable charge even with regard to the low humidity environment, and the fast image carrier peripheral speed, with respect to the transfer type image forming device of the contact electrostatic charge method-cleaner less processing. SOLUTION: When assuming the electrostatic charging member 2A of the electrostatic charging device performing the charge of the image carrier 1 by applying charge bias on the charging member 2A held in contact with the image carrier 1 as the first charging member, provided with the charging member 2A held in contact with the image carrier 1 as the first charging member, the device is made so that the image carrier surface potential Vs at the time of rushing to the charging part N by applying voltage on the second charging member 12, the DC voltage Vdc1 applied on the first charging member 2A of the charging device the same polarity, and provided with the second charging member 12 held in contact with the image carrier between a transfer part T and a charging part N provided, so as to satisfy the next relation, |Vs|>=|Vdc1|.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type image forming apparatus of a contact charging type and a cleanerless process.

More specifically, an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric, and a charging member (charging device) in contact with the image bearing member are provided, and a charging bias is applied to the charging member. A contact type charging device (contact charging device, direct charging device) for charging an image carrier by using an image information writing device for forming an electrostatic latent image on a charged surface of the image carrier; A developing device for visualizing the image with a developer, and a transfer device for moving the developer image on the surface of the image carrier to a material to be transferred, and the surface of the image carrier without moving to the material to be transferred by the transfer device The developer remaining in the charging device is once collected by a charging member in contact with the image carrier of the charging device, and the collected developer is discharged from the charging member to the image carrier and collected again by the developing device.
The present invention relates to an image forming apparatus such as a copying machine and a printer of a contact charging type and a cleanerless process.

[0003]

2. Description of the Related Art a) Contact charging In an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric, and other charged members have a predetermined polarity. As a charging means for charging to a potential, a corona charger has generally been used conventionally.

In this method, a corona charger is disposed opposite to an image carrier (hereinafter, referred to as a photoreceptor) in a non-contact manner, and the surface of the photoreceptor is exposed to a corona discharged from the corona charger, thereby causing the surface of the photoreceptor to have a predetermined polarity.・ Electricity is charged.

In recent years, since there are advantages such as low ozone and low power as compared with the non-contact type corona charger described above, a voltage (charging bias) is applied to the photoreceptor as a member to be charged as described above. ) Is applied to contact the charging member (contact charging member, contact charger) so that the surface of the photoreceptor has a predetermined polarity.
A contact-type charging device for charging to a potential has been put to practical use.

In particular, a roller charging system using a conductive roller (charging roller) as a contact charging member is preferably used in terms of charging stability.

In addition, a magnetic brush charging member (a charged magnetic brush, hereinafter referred to as a magnetic brush charger) having a magnetic brush portion in which magnetic particles are magnetically constrained on a carrier is used as the contact charging member. A magnetic brush charging type device in which a magnetic brush portion of a brush charger is brought into contact with a photoreceptor is also preferably used from the viewpoint of charging contact stability.

The magnetic brush charger is provided with a magnetic brush portion formed by magnetically restraining conductive magnetic particles directly on a magnet or on a sleeve containing a magnet. The magnetic brush unit is brought into contact with the photoreceptor, and a voltage is applied to the photoreceptor to start charging the photoreceptor.

[0009] Also, as a contact charging member, a member having conductive fibers formed in a brush shape (a fur brush charging member, a charging fur brush), a conductive rubber blade having a conductive rubber blade shape (a charging blade), and the like are also used. It is preferably used.

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

The corona charging system is a system in which the surface of the photoconductor is charged with a discharge product due to a corona discharge phenomenon generated in a minute gap between the contact charging member and the photoconductor. Since corona charging has a certain discharge threshold value for the contact charging member and the photoconductor, it is necessary to apply a voltage higher than the charging potential to the contact charging member. In addition, although the amount of generation is significantly smaller than that of the corona charger, a discharge product is generated.

The charge injection charging system is a system in which a charge is directly injected from a contact charging member to a photosensitive member to charge the surface of the photosensitive member. More specifically, the contact charging member having a medium resistance comes into contact with the surface of the photoreceptor, and charges are directly injected into the surface of the photoreceptor without using a discharge phenomenon, that is, basically without using discharge. Therefore, even if the applied voltage to the contact charging member 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 generation of ions.

However, because of the charge injection charging, the contact property of the contact charging member to the photoreceptor greatly affects the charging property. Therefore, it is necessary to form the contact charging member more densely, and to have a structure in which there is a large difference in speed from the photosensitive member and contact the photosensitive member with higher frequency. Can perform stable charging.

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

There is a method in which a voltage is applied to a conductive contact charging member to inject a charge into a trap level on the surface of the photoreceptor to perform contact charging of the photoreceptor. When a photosensitive member having a surface layer (charge injection layer) in which conductive fine particles are dispersed on a normal organic photosensitive member or an amorphous silicon photosensitive member is used, the direct current of the bias applied to the contact charging member is reduced. It is possible to obtain a charging potential substantially equivalent to the components on the surface of the member to be charged (JP-A-6-3921).

The injection charging method has the advantage that the voltage applied to the contact charging member is substantially the same as the potential of the photoreceptor and does not generate ozone because not only the environment dependency is low but also no discharge is used. Complete ozone-free and low power consumption type charging becomes possible.

B) Cleanerless Process (Toner Recycling Process) In recent years, the size of an image forming apparatus has been reduced, but each means and equipment for an image forming process such as charging, exposure, development, transfer, fixing, and cleaning are required. There is a limit to the overall size reduction of the image forming apparatus just by reducing the size.

Further, the transfer residual toner (residual developer) on the photoreceptor after the transfer is collected by a cleaning means (cleaner) to become waste toner. It is preferable that the waste toner does not come out from the viewpoint of environmental protection. .

Therefore, the cleaner is removed, and the transfer residual toner on the photoreceptor is removed from the photoreceptor by "development simultaneous cleaning" by the developing means, and is recovered and reused in the developing means. Image forming apparatuses have also appeared. Simultaneous development cleaning means fogging 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 photoconductor) at the time of development after the next step. It is a method of collecting 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 troublesome maintenance can be reduced. In addition, the cleaner-less system has a great advantage in terms of space, and can greatly reduce the size of the image forming apparatus.

When the charging device for the photoreceptor is a contact charging device, the transfer residual toner is once collected by a contact charging member that is in contact with the photoreceptor, discharged again onto the photoreceptor, and collected by the developing device. .

[0021]

As described above, in the transfer type image forming apparatus of the contact-electric type and the cleanerless process, the contact charging device for charging the photosensitive member to the normal charging polarity for forming an electrostatic latent image is used. The transfer residual toner is once collected by a contact charging member (hereinafter, referred to as an injection charger) that is in contact with the photoreceptor, discharged again onto the photoreceptor, and collected by the developing device. In this case, If the toner remaining on the surface of the photoreceptor without being transferred is completely recovered by an injection charger, and thereafter the toner is not charged to a predetermined potential, it appears as a positive ghost on the next circumference of the photoreceptor.

Therefore, a method for improving the recovery efficiency of the transfer residual toner in the injection charger is disclosed in Japanese Patent Application Laid-Open No. Hei 10-31346. In this method, an auxiliary contact charging member such as a conductive brush is provided between a transfer device and an injection charger in contact with the photoconductor, and a bias having a polarity opposite to the normal charging polarity of the photoconductor is provided on the auxiliary contact charging member. Is applied, the transfer residual toner is charged to the opposite polarity, and is easily collected by the injection charger to which the voltage of the normal charging polarity is applied.

However, in this method, charges of the opposite polarity are also injected into the photosensitive member by the auxiliary contact charging member provided between the transfer device and the injection charger. The photoreceptor charged to the opposite polarity is charged to the normal charging polarity again by the injection charger, but the injection charger is, for example, a magnetic brush charger, and has a low humidity, and the electric resistance of the magnetic brush or the injection layer of the photoconductor is low. In an environment where the amount of charge increases, the photoconductor may not be completely charged to the normal charging polarity. In particular, when the auxiliary contact charging member is a conductive brush, a streak-shaped reverse-polarity charging area is formed on the surface of the photoconductor, and when charging cannot be completely performed by injection charging, a potential difference between a charging bias and a potential of the photoconductor,
Since the toner is discharged from the injection charger and a sufficient fog removal potential difference Vback cannot be obtained by development, the toner is developed in that area, and appears as a stripe-like fog on the next circumferential image.

Further, when the peripheral speed of the photosensitive member is increased, the time required for the photosensitive member to pass through the area where the magnetic brush of the magnetic brush charger as an injection charger is in contact with the photosensitive member is shortened.
The time required for charging the portion of the photoreceptor charged to the opposite polarity to the normal charging polarity is not sufficient, and the same stripe fog as in a low humidity environment occurs.

In order to compensate for the lack of time, the amount of the magnetic particles of the magnetic brush coated on the charging sleeve or the like is increased.
There is also a method of expanding the area where the magnetic brush and the photoreceptor are in contact. It becomes easy to adhere. As a result, the charging magnetic particles on the side of the magnetic brush charger are carried and mixed into the developing device, thereby hindering stable development.

Accordingly, the present invention is directed to a transfer type image forming apparatus of a contact charging type and a cleanerless process, which makes it possible to efficiently collect transfer residual toner by using an injection charger without the above-mentioned problems. Improves the uniformity of the charging potential of the image carrier in the charger, enables stable charging even in a low-humidity environment and a high peripheral speed of the image carrier, and continuously performs stable and good image formation. The purpose is to:

[0027]

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

(1) An image bearing member, a charging device having a charging member in contact with the image bearing member, and charging the image bearing member by applying a charging bias to the charging member; An image information writing device that forms an electrostatic latent image on the charged surface, a developing device that visualizes the electrostatic latent image with a developer,
A transfer device for moving the developer image on the surface of the image carrier to the material to be transferred; and the developer remaining on the surface of the image carrier without moving to the material to be transferred by the transfer device is transferred to the image carrier of the charging device. In the image forming apparatus of the type in which the charging member is once collected by the charging member, and the collected developer is discharged from the charging member to the image carrier and collected again by the developing device, the charging member of the charging device is charged by the first charging device. When the member is used, the image carrier is located downstream of the position of the developer image transfer portion from the image carrier to the transfer material in the image carrier rotation direction, and is higher than the position of the contact portion between the first charging member and the image carrier. A second charging member that is brought into contact with the image carrier between the upstream sides in the rotation direction, and by applying a voltage to the second charging member, a contact portion between the first charging member and the image carrier is formed. The image carrier surface potential Vs at the time of intrusion and the DC applied to the first charging member In pressure Vdc1 is the same polarity, and | Vs
An image forming apparatus satisfying a relationship of | ≧ | Vdc1 |.

(2) DC voltage Vdc2 applied to the second charging member and DC voltage Vdc1 applied to the first charging member
Has the same polarity and satisfies the relationship of | Vdc2 | ≧ | Vdc1 |.

(3) The first charging member comprises magnetic particles and a magnetic particle carrier (1) or (2).
An image forming apparatus according to claim 1.

(4) The image forming apparatus according to any one of (1) to (3), wherein the second charging member is a conductive roller.

(5) The voltage applied to the second charging member is a superimposed bias of DC and AC. (1)
The image forming apparatus according to any one of (1) to (4).

(6) The method according to any one of (1) to (5), wherein the end of the charged region of the second charging member is located outside the end of the charged region of the first charging member. Image forming apparatus.

(7) The image forming apparatus according to any one of (1) to (6), wherein the image carrier is an electrophotographic photosensitive member.

(8) The image forming apparatus according to any one of (1) to (7), wherein the image carrier is charge-injectable and chargeable.

(9) The image carrier according to any one of (1) to (8), wherein the image carrier is an electrophotographic photosensitive member having a charge injection layer in which conductive fine particles are dispersed in an insulating binder. An image forming apparatus according to any one of the preceding claims.

(10) The image information writing device for forming an electrostatic latent image on the charged surface of the image carrier is an exposure device, wherein the image information writing device is an exposure device. Image forming device.

<Operation> a) That is, in the transfer type image forming apparatus of the contact charging type and the cleanerless process, the voltage of the normal charging polarity of the image carrier is applied to the second charging member. ,
At the same time that the polarity of the transfer residual developer on the image carrier is aligned with the normal charging polarity, the surface potential of the image carrier before entering the contact portion between the first charging member and the image carrier is changed to the first charging member. By setting the DC voltage applied to the first charging member or higher, the transfer residual toner can be easily collected by the first charging member.

B) The difference between the surface potential of the image carrier before entering the contact portion between the first charging member and the image carrier and the DC voltage value applied to the first charging member is reduced. This facilitates the convergence of the image carrier surface potential at the first charging member, improves the uniformity of the potential, and enables stable charging even in a low-humidity environment and a high peripheral speed of the image carrier. Thus, stable and good image formation can be continuously performed.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (1) Example of Image Forming Apparatus (FIG. 1) FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this embodiment is a laser beam printer of a transfer type electrophotographic process, a charge injection charging system, and a cleanerless 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 of this embodiment has a negative charging property and a charge injection charging property of O.
PC photoconductor (organic photoconductive photoconductor), 150 mm / sec. At the process speed (peripheral speed).

Reference numeral 2 denotes a contact charging device for uniformly charging the surface of the photosensitive drum 1 to a predetermined polarity and potential. In this embodiment, a magnetic brush charging device is used, and the surface of the rotating photosensitive drum 1 is substantially −700 by the magnetic brush charging device 2.
v is uniformly charged by a charge injection charging method.

Reference numeral 3 denotes an image information exposure means (exposure device), which in this embodiment is a laser beam scanner. The laser beam scanner 3 includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and receives input from a host device (not shown) such as a document reading device having a photoelectric conversion element such as a CCD, an electronic computer, a word processor, and the like. A laser beam L modulated according to a time-series electric digital pixel signal of 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, the rotating photosensitive drum 1
An electrostatic latent image corresponding to the target image information is formed on the peripheral surface of the image.

Reference numeral 4 denotes a developing device. In this embodiment, a developing device of a two-component contact developing system using a developer obtained by mixing a highly releasable spherical non-magnetic toner with a small amount of residual toner and a magnetic carrier, which is formed by a polymerization method, is used. Then, 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 this embodiment is of a transfer belt type. 5a is an endless transfer belt (for example, a film thickness of 75
μm of a polyimide belt), which is suspended between the driving roller 5b and the driven roller 5c, and has a circumferential speed substantially equal to the circumferential speed of the photosensitive drum 1 in the forward direction of the rotating direction of the photosensitive drum 1. Is turned. Reference numeral 5d denotes a conductive blade disposed inside the transfer belt 5a.
Is pressed against the lower surface of the photosensitive drum 1 to form a transfer nip T as a transfer portion. 5e is a cleaning device for the outer surface of the transfer belt 5a.

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

The transfer material P fed to the transfer nip portion T is nipped and conveyed between the rotating photosensitive drum 1 and the transfer belt 5a, during which a predetermined transfer bias is applied to the conductive blade 5d from a transfer bias applying power source E5. Is applied, and 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 of the rotating photosensitive drum 1 is electrostatically transferred to the surface of the transfer material P passing through the transfer nip portion T sequentially.

The transfer material P to which the toner image has been transferred through the transfer nip portion T is sequentially separated from the surface of the rotating photosensitive drum 1 and passes through a sheet path 10 to a fixing device (for example, a heat roller fixing device) 11. And subjected to the fixing process of the toner image, and printed out.

The printer of this embodiment is a cleanerless process, and a dedicated cleaner for removing toner remaining on the surface of the rotary photosensitive drum 1 without being transferred to the transfer material P at the transfer nip portion T is provided. However, as will be described later, the transfer residual toner reaches the position of the magnetic brush charging device 2 by the subsequent rotation of the photosensitive drum 1, and the magnetic brush as the first charging member in contact with the photosensitive drum 1 The collected toner is temporarily collected by the magnetic brush portion of the charger 2A, and the collected toner is again discharged to the surface of the photosensitive drum 1 and finally collected by the developing device 4, and the photosensitive drum 1 is repeatedly used for image formation. You.

Reference numeral 12 denotes a conductive roller as a second charging member, which is disposed between the transfer device 5 and the magnetic brush charging device 2 in contact with the surface of the photosensitive drum 1. In the present embodiment, the conductive roller 12 is a roller having a diameter of 9 and a volume resistance of 1 × 10 ⁵ Ωcm, and rotates following the rotation of the photosensitive drum 1. This conductive roller 12 has a power source E
From 6, a DC bias of the normal charging polarity (negative in this example) of the photosensitive drum 1 or a bias obtained by superimposing an AC bias on the DC bias is applied. As a result, the surface potential of the photosensitive drum immediately before charging by the magnetic brush charger 2A as the first charging member is set to −700 V or more, and the charging polarity of the transfer residual toner is made equal to the normal charging polarity (negative in this example). This facilitates the collection of the transfer residual toner in the magnetic brush portion of the magnetic brush charger 2A. This will be described in detail in section (7).

(2) Operation Sequence of Printer (FIG. 2) FIG. 2 is an operation sequence diagram of the printer.

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

B. Pre-rotation step This is a period during which the pre-print operation is performed. This pre-rotation step is 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 drive of the photosensitive drum is stopped, and the printer is kept in a standby state until a print signal is input. It is. When a print signal is input, a pre-rotation step is performed.

C. Printing Step (Image Forming Step, Image Forming Step) When the predetermined pre-rotation step is completed, an image forming process is subsequently performed on the rotating photosensitive drum, and the toner image formed on the rotating photosensitive drum surface is transferred onto the transfer material. Then, the toner image is fixed by the transferring and fixing means, and the image formed matter is printed out.

In the case of the continuous printing (continuous printing) mode, the above printing process is repeatedly executed for a predetermined set number of prints n.

D. In the continuous printing mode, in the continuous printing mode, after the rear end portion of one transfer material passes through the transfer nip portion, until the leading end portion of the next transfer material reaches the transfer nip portion, the transfer nip portion This is a non-sheet passing state period of the transfer target material.

E. Post-rotation process This is a period in which the main motor continues to be driven for a while to rotate the photosensitive drum to perform a predetermined post-operation even after the last n-th printing process is completed.

F. Standby When the predetermined post-rotation process is completed, the drive of the main motor is stopped, the rotation drive of the photosensitive drum is stopped, and the printer is kept in the standby state until the next print start signal is input.

In the case of printing only one sheet, after the printing is completed, 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 step.

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

(3) Photoreceptor Drum 1 (FIG. 3) The photoreceptor drum 1 of this embodiment has a negative charging property as described above.
As shown in FIG. 3, a first to fifth functional layers 1b to 1f are provided in order from the bottom on an aluminum drum base 1a having a diameter of 30 mm. It is a thing.

A first layer 1b; an undercoat layer, a conductive layer having a thickness of about 20 μm provided to smooth defects of the aluminum drum base 1a and to prevent the occurrence of moire due to reflection by laser exposure. It is.

The second layer 1c is a layer for preventing positive charge injection, and 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. Approximately 1μ in thickness adjusted to about 10 ⁶ Ω · cm by methylated nylon
m is a medium resistance layer.

Third layer 1d: 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 which generates positive and negative charge pairs when subjected to laser exposure.

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

Fifth layer 1f: a charge injection layer, a photocurable acrylic resin as a binder doped with antimony as a light transmissive conductive filler to reduce the resistance (conductivity) to a particle diameter of 0.03 μm Is a coating layer having a thickness of about 3 μm and a material in which 1 g of ultrafine particles of tin oxide SnO ₂ are dispersed in a resin by 70% by weight. The electric resistance value of the charge injection layer 1f needs to be 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ω · cm, which is a condition that does not cause sufficient chargeability and image deletion. In this embodiment, a photosensitive drum having a surface resistance of 1 × 10 ¹¹ Ω · cm was used.

(4) Magnetic Brush Charging Device 2 (FIGS. 4 to 6) FIG. 4 is an enlarged cross-sectional model view of the magnetic brush charging device 2. The magnetic brush charging device 2 of this embodiment is roughly divided into a magnetic brush charging member (magnetic brush charger) 2A, a container (housing) containing the magnetic brush charger 2A and conductive magnetic particles (charge carrier) 2d. 2B) and a power supply E2 for applying a charging bias to the magnetic brush charger 2A.

The magnetic brush charger 2A of this embodiment is a sleeve rotating type, and a magnet roll (magnet)
2a, a non-magnetic stainless steel sleeve (referred to as an electrode sleeve, a conductive sleeve, a charging sleeve, etc.) 2b externally fitted to the magnet roll, and the magnetic force of the magnet roll 2a inside the sleeve on the outer peripheral surface of the sleeve 2b. The magnetic brush portion 2c of the magnetic particles 2d is formed by magnetically constraining and holding the magnetic particles.

The magnet roll 2a is a non-rotating fixing member, and the sleeve 2b is rotated around the outer periphery of the magnet roll 2a in a clockwise direction shown by an arrow b by a driving system (not shown) at a predetermined peripheral speed, 225 mm / sec in this embodiment. . Is driven to rotate at a peripheral speed of. The sleeve 2b is disposed so as to face the photosensitive drum 1 with a gap of about 500 μm kept by means such as a spacer roller.

Reference numeral 2e denotes a magnetic brush layer thickness regulating blade made of non-magnetic stainless steel, which is attached to the container 2B, and is arranged so that the gap with the surface of the sleeve 2b is 900 μm.

A part of the magnetic particles 2d in the container 2B is magnetically restrained on the outer peripheral surface of the sleeve 2b by the magnetic force of the magnet roll 2a inside the sleeve, and is held as the magnetic brush portion 2c. The magnetic brush portion 2c rotates together with the sleeve 2b in the same direction as the sleeve 2b with the rotation of the sleeve 2b. At this time, the layer thickness of the magnetic brush portion 2c is regulated to a uniform thickness by the blade 2e. The thickness of the regulating layer of the magnetic brush portion 2c is the same as that of the sleeve 2b and the photosensitive drum 1.
Larger than the gap of the opposing gap with the magnetic brush part 2
Reference numeral c denotes a portion where the sleeve 2b and the photosensitive drum 1 are opposed to each other and forms a nip portion having a predetermined width with respect to the photosensitive drum 1. This contact nip is the charging nip N. Therefore, the rotating photosensitive drum 1 is rubbed at the charging nip portion N by the rotating magnetic brush portion 2c accompanying rotation of the sleeve 2b of the magnetic brush charger 2A. In this case, in the charging nip N, the moving direction of the photosensitive drum 1 and the moving direction of the magnetic brush portion 2c are opposite to each other, and the relative moving speed is increased.

A predetermined charging bias is applied from the power source E2 to the sleeve 2b and the magnetic brush layer thickness regulating blade 2e.

Thus, the photosensitive drum 1 is driven to rotate,
The sleeve 2b of the magnetic brush charger 2A is driven to rotate,
By applying a predetermined charging bias from the power supply E2,
In the case of the present embodiment, the peripheral surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charge injection charging method.

The magnet roll 2a fixed in the sleeve 2b has a magnetic pole (main pole) of about 900 G at a position 10 ° upstream from the closest position c between the sleeve 2b and the photosensitive drum 1 in the rotation direction of the photosensitive drum. N1 is arranged.

It is desirable that the main pole N1 be set so that the angle θ between the sleeve 2b and the closest position c of the photosensitive drum 1 is within the range of 20 ° from the upstream side to 10 ° downstream in the rotation direction of the photosensitive drum. It is even better if the angle is 15 ° to 0 ° on the upstream side. If it is further downstream, the magnetic particles are attracted to the main pole position, so that the magnetic particles tend to stay on the downstream side of the charging nip N in the rotation direction of the photosensitive drum, and if too upstream, the magnetic particles pass through the charging nip N. The transportability of the magnetic particles deteriorates, and stagnation tends to occur.

When there is no magnetic pole in the charging nip portion N, it is apparent that the binding force acting on the magnetic particles on the sleeve 2b is weakened, and the magnetic particles tend to adhere to the photosensitive drum 1.

The charging nip N described here indicates a region where the magnetic particles of the magnetic brush portion 2c are in contact with the photosensitive drum 1 during charging.

The charging bias is applied to the sleeve 2b and the regulating blade 2e by the power source E2. In this embodiment, D
A bias in which an AC component is superimposed on a C component is used.

The magnetic brush portion 2c is formed by rubbing the surface of the photosensitive drum 1 by the magnetic brush portion 2c of the magnetic brush charger 2A in the charging nip portion N and applying a charging bias to the magnetic brush charger 2A. A charge is applied to the photosensitive drum 1 from the charged magnetic particles 2d, 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 has the charge injection layer 1f on the surface thereof, the charging process of the photosensitive drum 1 is performed by charge injection charging. That is, the photosensitive drum 1 surface is charged DC + AC DC
It is charged to a potential corresponding to the component. The sleeve 2b tends to have better charging uniformity as the rotation speed is higher.

The charge injection charging of the photosensitive drum 1 by the magnetic brush charger 2A can be regarded as a circuit of a resistor R and a capacitor C as shown in an equivalent circuit of FIG. In the case of such a circuit, the resistance value is r and the capacitance of the photoconductor is C.
Assuming that p is p, the applied voltage is V ₀ , and the charging time (the time during which a certain point on the photosensitive drum passes through the charging nip N) is t ₀ , the surface potential Vd of the photosensitive drum is expressed by equation (1).

Vd = V ₀ (1−exp (t ₀ / (Cp · r))) Expression (1) In the charging bias DC + AC, the DC component is equal to the required surface potential of the photosensitive drum 1. Equivalent, in this embodiment-
700v.

The AC component at the time of image formation (at the time of image formation) has a peak-to-peak voltage Vpp of 100 V or more and 2000 V or more.
v or less, especially 300 v or more and 1200 v or less.
If the peak-to-peak voltage Vpp is lower than this, the effect of improving the charging uniformity and the rise of potential is weak, and if it is higher, the retention of the magnetic particles and the adhesion to the photosensitive drum deteriorate.

The frequency is preferably from 100 Hz to 5000 Hz, particularly preferably from 500 Hz to 2000 Hz.
Below this, the effect of improving the adhesion of the magnetic particles to the photosensitive drum, the uniformity of charge, and the effect of improving the rise property of the electric potential become thin, and the effect of improving the uniformity of charge, the improvement of the rise property of the electric potential becomes difficult to obtain. .

The waveform of the AC component is a rectangular wave, a triangular wave, sin
Waves are good.

Magnetic particles 2 constituting magnetic brush portion 2c
d is a sintered ferromagnetic material (ferrite) in this embodiment.
Was used, but a resin and ferromagnetic powder were kneaded and shaped into particles, or a mixture of conductive carbon etc. to adjust the resistance value, and surface treatment Can be similarly used.

The role of the magnetic particles 2d of the magnetic brush portion 2c to inject charges well into the trapping order on the surface of the photosensitive drum and the fact that the charging current is concentrated on defects such as pinholes formed on the photosensitive drum. Therefore, the charging member and the photosensitive drum must also have a role of preventing the electrical breakdown of the photosensitive member and the photosensitive member caused by the above.

[0088] Accordingly, the 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 resistance value of the magnetic brush charger 2A is less than 1 × 10 ⁴ Ω, pinhole leakage tends to occur easily.
If it exceeds × 10 ⁹ Ω, good charge injection tends to be difficult. Further, in order to control the resistance value within the above range, the volume resistance value of the magnetic particles 2d must be 1 × 10 ⁴ Ω · cm.
１1 × 10 ⁹ Ω · cm, particularly 1
It is preferably from × 10 ⁴ Ω · cm to 1 × 10 ⁷ · cm.

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

The volume resistance of the magnetic particles 2d was measured as shown in FIG. That is, the cell A is filled with the magnetic particles 2d, the main electrode 17 and the upper electrode 18 are arranged so as to be in contact with the filled magnetic particles 2d, and a voltage is applied between the electrodes 17 and 18 from the constant voltage power supply 22. When the current flowing, ammeter 2
It was determined by measuring at 0. 19 is an insulator, 21 is a voltmeter, and 24 is a guide ring.

The measurement conditions were as follows: the contact area S of the filled magnetic particles 2d with the cell was 2 cm in an environment of 23 ° C. and 65%.
^{2. The} thickness d is 1 mm, the load on the upper electrode 18 is 10 kg, and the applied voltage is 100 V.

The peak in the measurement of the average particle size and the particle size distribution of the magnetic particles 2d is in the range of 5 to 100 μm.
It is preferable from the viewpoint of preventing charging deterioration due to contamination of the particle surface.

The average particle size of the magnetic particles 2d is represented by the maximum chord length in the horizontal direction. The measuring method is to randomly select 300 abnormal magnetic particles by a microscopic method, measure the diameter, and take the arithmetic average.

(5) Developing device 4 (FIG. 7) As a toner developing method for an electrostatic latent image, the following a to d are generally used.
Are roughly divided into four types.

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

B. A method in which the toner coated as described above is developed in contact with the photoreceptor (one-component contact development).

C. A method in which a mixture of toner particles and a magnetic carrier is used as a developer and conveyed by magnetic force to develop in contact with a photoreceptor (two-component contact development).

D. A method of developing the above two-component developer in a non-contact state (two-component non-contact development).

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

FIG. 7 is an enlarged cross-sectional model view of the developing device 4 used in this embodiment. The developing device 4 in the present embodiment includes:
A mixture of a highly releasable spherical non-magnetic toner prepared by a polymerization method and a magnetic carrier (magnetic particles for development, a development carrier) is used as a developer, and the developer is used as a developer carrier (a developing member, a developing device). Is a two-component magnetic brush contact development type reversal developing device in which the toner is held as a magnetic brush layer by a magnetic force, transported 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.

4a is a developing container, 4b is a developing sleeve as a developer carrier, 4c is a magnet (magnet roller) as a magnetic field generating means fixedly arranged in the developing sleeve 4b, and 4d is a developer on the surface of the developing sleeve. The developer layer thickness regulating blade 4e for forming a thin layer of the developer, a developer stirring and conveying screw 4e, a two-component developer housed in a developing container 4a, and a non-magnetic toner t and a developing carrier c.

The developing sleeve 4b is arranged so that the closest distance (gap) to the photosensitive drum 1 is about 500 μm at least at the time of development.
The developer magnetic brush thin layer 4f 'carried on the outer surface of the photosensitive drum 1 is set in contact with the surface of the photosensitive drum 1. The contact nip m between the developer magnetic brush thin layer 4f 'and the photosensitive drum 1 is a developing area (developing section).

The developing sleeve 4b is driven at a predetermined rotation speed in the counterclockwise direction indicated by the arrow around the outer periphery of the internal fixed magnet 4c, and is fixed to the outer surface of the sleeve in the developing container 4a.
A magnetic brush of the developer 4f (t + c) is formed by the magnetic force of c. The developer magnetic brush is transported together with the rotation of the sleeve 4b, is regulated by the blade 4d, is taken out of the developing container as a developer magnetic brush thin layer 4f 'having a predetermined thickness, and is transported to the developing unit m. It comes into contact with the surface of the photosensitive drum 1 and is transported back into the developing container 4a again 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. In the developing characteristics of the present embodiment, fog occurs when the difference between the charging potential (-700 V) of the photosensitive drum 1 and the DC component value of the developing bias is 200 V or less,
If it is 350 V or more, the photosensitive drum 1 of the developing carrier c
, The DC component of the developing bias is -4.
00v.

The toner concentration (mixing ratio with the developing carrier c) of the developer 4f (t + c) in the developing container 4a gradually decreases 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 replenishing unit 4g to the developer 4f in the developing container 4a. 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) Cleanerless Process The printer of this embodiment is a cleanerless process.
Although a cleaner dedicated to removing toner remaining on the surface of the rotating photosensitive drum 1 without being transferred to the transfer material P in the transfer nip portion T is not provided, the remaining transfer toner is continuously rotated by the rotation of the photosensitive drum 1. To the position of the magnetic brush charging device 2, and is temporarily collected by the magnetic brush portion of the magnetic brush charger 2A as a contact charging member that is in contact with the photosensitive drum 1, and the collected toner is returned to the photosensitive drum 1 again. And is finally collected by the developing device 4 and is
Are repeatedly provided for image formation.

The transfer residual toner on the photosensitive drum 1 often has both positive and negative polarities due to peeling discharge at the time of transfer. In the present embodiment, the normal charge polarity (negative in this example) while the transfer residual toner having the mixed polarity passes through the conductive roller 12 as the second charging member.
To the magnetic brush charger 2A, which is the first charging member, mixed into the magnetic brush unit 2c and 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. It can be performed more effectively.

Then, the transfer residual toner taken into the magnetic brush portion 2c is discharged to the photosensitive drum 1 with the polarity being all negatively charged. The transfer residual toner having the polarity adjusted to be negative and discharged onto the photosensitive drum 1 reaches the developing unit m and is collected by the developing unit 4b of the developing device 4 by the fog removing electric field at the time of development by simultaneous cleaning with development.

When the image area in the rotation direction is longer than the circumferential length of the photosensitive drum 1, the simultaneous development and recovery of the transfer residual toner proceeds simultaneously with other image forming steps such as charging, exposure, development and transfer. Done in

As a result, the transfer residual toner is collected in the developing device 4 and used after the next step, so that waste toner can be eliminated. Further, there is a great advantage in terms of space, and the size of the image forming apparatus can be significantly reduced.

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 toner discharged from the magnetic brush charger 2A can be reduced. Can be recovered in the developing device 4. The use of the developing device 4 of the two-component contact developing system also improves the recoverability of the toner discharged from the magnetic brush charger 2A to the developing device 4.

The toner discharged from the magnetic brush portion 2c to the photosensitive drum 1 is in a very uniform scattered state and its amount is small, so that it does not substantially adversely affect the next image exposure process. . Also, there is no occurrence of a ghost image due to the transfer residual toner pattern.

Here, since the toner generally has a relatively high electric resistance, it is difficult for such toner particles to enter the magnetic brush portion 2c of the magnetic brush charger 2A.
is a factor that increases the resistance of c and reduces 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.

Therefore, in the present embodiment, the area of the rotary photosensitive drum 1 passing through the transfer nip T during the inter-sheet process during non-image formation passes through the charging nip before that, and During the post-rotation step during image formation, the application of the AC component of the charging bias applied to the magnetic brush charger 2A is stopped, and at the same time, the application of the voltage to the conductive roller 12 is stopped. The potential difference ΔV from the voltage is increased to increase the magnetic brush portion 2c of the magnetic brush charger 2A.
A large amount of toner is positively discharged from the inside to keep the amount of toner mixed in the magnetic brush portion 2c below a certain level for a long period of time so as to suppress an increase in electric resistance of the magnetic brush.

(7) Potential of Photoconductor Before Injection Charging and Recovery of Transfer Residual Toner (FIG. 8) In this embodiment, the photoconductor drum 1 as an image carrier is brought into contact between the transfer nip T and the charging nip N. Then, a conductive roller 12 as a second charging member is provided, and a voltage is applied to the conductive roller 12 so that a contact portion between the magnetic brush charger 2A as the first charging member and the photosensitive drum 1 is provided. And the DC voltage Vdc1 applied to the magnetic brush charger 2A has the same polarity as the photoconductor surface potential Vs (photoconductor potential before injection charging) when entering the charging nip N,
In addition, the relationship of | Vs | ≧ | Vdc1 | is satisfied.

The DC voltage Vdc2 applied to the conductive roller 12 and the DC voltage Vdc1 applied to the magnetic brush charger 2A have the same polarity, and | Vdc2 | ≧ | Vdc1 |
Is satisfied.

That is, by applying a voltage of the normal charging polarity of the photosensitive drum 1 to the conductive roller 12, the polarity of the transfer residual toner on the photosensitive drum 1 is adjusted to the normal charging polarity, and at the same time, the charging is performed. By setting the surface potential of the photosensitive member before entering the nip portion N to be equal to or higher than the DC voltage value applied to the magnetic brush charger 2A, the transfer residual toner can be easily collected by the magnetic brush charger 2A. Also, by reducing the difference between the photoconductor surface potential before entering the charging nip N and the DC voltage value applied to the magnetic brush charger 2A, the photoconductor surface potential at the magnetic brush charger 2A is reduced. Convergence is facilitated, the uniformity of potential is improved, stable charging can be performed even in a low humidity environment and a high peripheral speed of the photosensitive drum, and stable and good image formation can be continuously performed.

Hereinafter, this will be described more specifically. FIG. 8 shows a case where a conductive brush (second charging member) to which a bias of a reverse polarity (positive in this case) is applied between a conventional transfer unit and an injection charger (first charging member) is used, The photoconductor surface potential when a conductive roller (second charging member) to which a bias of a normal charging polarity (here, a negative electrode) used in this embodiment is applied and a toner collecting mechanism in the injection charger 2A are shown. .

(A) is a case where +500 V is applied to the conductive brush, and the transfer residual toner charged to the positive electrode by the conductive brush is applied with a bias of -700 V from the surface of the photosensitive member charged to about +400 V. Is electrically attracted to the charged charging device 2A and collected.

At this time, the amount of change in the potential of the photoconductor is 1200 V. As described above, in a low humidity environment where the electrical resistance of the charging member and the photoconductor increases or when the peripheral speed of the photoconductor is high, sufficient charging is not achieved. This is likely to occur, and fogging occurs during development.

(B) shows that the conductive roller 12
In this case, the transfer residual toner charged to the negative electrode by the roller 12 is electrically attracted from the surface of the photoreceptor charged to about -900 V to the injection charger 2A to which the bias of -700 V is applied. Is collected.

At this time, since the amount of change in the potential of the photosensitive member is 200 V, the convergence of the potential is facilitated, and the occurrence of fogging during development can be prevented.

(C) is a case where −600 V is applied to the conductive roller 12, and the transfer residual toner charged to the negative electrode by the roller 12 is approximately −500 V from the injection charger 2 A to which a bias of −700 V is applied. Since the toner is electrically attracted to the surface of the photoreceptor charged with the toner, the transfer residual toner is not sufficiently collected by the injection charger 2A, and appears as a positive ghost on the next circumference of the photoreceptor drum 1.

As described above, by setting the potential of the photosensitive member immediately before entering the charging nip portion N higher than the charging DC bias applied to the injection charger 2A as the first charging member, the recovery of transfer residual toner can be improved. To prevent ghosting and at the same time to achieve uniform charging.

It is desirable that the potential of the photoconductor immediately before entering the charging nip N is smaller than the potential of the photoconductor after passing through the charging nip N causing the development carrier to adhere to the developing unit. It is preferable that the voltage can be converged to the applied DC voltage.

Further, even if the photoconductor potential just before entering the charging nip portion N is the same as the charging bias applied to the injection charger 2A, the transfer residual toner remains between the magnetic brush rubbing force and the magnetic particles and the toner. It is collected by the magnetic brush by the working mirror.

The second charging member 12 is not limited to a roller, but may be a blade, a sheet, a brush, or the like.

<Second Embodiment> In this embodiment, in the image forming apparatus of the first embodiment, an AC bias is superimposed on a DC bias applied to the conductive roller 12 as a second charging member.

By doing so, the potential of the photosensitive member immediately before entering the charging nip portion N can be stabilized, so that the difference between the DC voltage applied to the conductive roller 12 and the charged potential of the photosensitive member can be reduced. At the same time, it is possible to prevent the resistance of the conductive roller 12 from increasing due to the adhesion of the transfer residual toner, thereby preventing the chargeability from being deteriorated.

Further, when the AC bias is superimposed, when excessive transfer residual toner adheres to the surface of the conductive roller, the difference between the DC component of the applied bias and the potential of the photosensitive member after passing through the conductive roller causes the adhered toner to the photosensitive member. This has the effect of facilitating attraction.

A of the bias applied to the conductive roller 12
When the amplitude of the C component was 0 V, 200 V, 400 V, and 600 V, the presence or absence of a ghost was confirmed after 10,000 sheets of 10% original were formed.

The target potential of the photosensitive member after charging was -700 V, and the DC voltage applied to the conductive roller 12 was -800 V.

AC amplitude (v) 0 200 400 600 Ghost Yes Slight Yes No No Ghost is generated even when residual toner adheres to conductive roller 12 by image formation by superimposing AC bias as described above. Can be prevented. The AC bias amplitude is 200
v or more, 2000 v or less, especially 500 v or more, 1200
v or less is preferable. Below that, the effect of AC bias superimposition is thin, and above that, there is a possibility of leakage of the photoconductor and conductive roller.

<Third Embodiment> When a positive bias is applied to the conductive brush as the second charging member as in the case of FIG. 8A described above, the injection as the first charging member is performed. The surface potential of the photoconductor rapidly changes at a boundary between a region where the magnetic brush portion 2c of the charger 2A is in contact with the photoconductor 1 and a region where the magnetic brush portion 2c is not. Therefore, magnetic particles adhere to the surface of the photoconductor at the end of the magnetic brush portion 2c. In order to prevent this, a method is known in which the surface of the charging sleeve near the end of the magnetic brush is insulated to make the surface potential change at the boundary gentle.

However, as shown in this embodiment, the conductive roller 1 as a second charging member to which a negative bias is applied is used.
By making the length 2 longer than that of the magnetic brush portion 2c of the injection charger 2A, which is the first charging member, the surface potential of the photoconductor becomes as shown in FIG. Will not occur.

Further, when a positive bias is applied to the conductive brush, the mixed toner is likely to be discharged to the adjacent low potential region at the end of the magnetic brush 2c, and it is difficult to collect the toner again with the magnetic brush 2c. , And it follows the photoreceptor surface. When the conductive roller 12 to which the negative bias is applied is used, since the potential of the region where the magnetic brush 2c is not in contact is high, the mixed toner is not discharged,
No rotation of the toner occurred.

<Others> 1) The magnetic brush charger 2A as the first charging member is
Not only the sleeve rotating type, but also the one where the magnet roll rotates or the surface of the magnet roll is conductively treated as a power supply electrode if necessary, and the conductive magnetic particles are magnetically bound directly on the outer peripheral surface of the magnet roll Then, a magnetic brush portion may be formed, and a configuration in which a magnet roll is rotated may be used. A non-rotating type magnetic brush charging member may be used.

Further, a fur brush charging member, a charging roller using a conductive rubber or a conductive sponge, or the like may be used. In this case, a non-rotating structure may be used.

2) It is desirable that the photosensitive member as the image carrier has a low resistance layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm from the viewpoint of realizing charge injection charging and preventing ozone generation. Organic photoreceptors other than the above may be used. That is, the contact charging is not limited to the charge injection charging system of the embodiment, but may be a contact charging system in which a discharge phenomenon is dominant.

3) Although only the two-component developing method has been described for the developing device, other developing methods may be used. Preferably, one-component contact development or two-component contact development in which a developer is brought into contact with a photoreceptor to develop a latent image is effective in further enhancing the simultaneous recovery effect of the developer.

When polymerized toner is used as the toner particles in the developer, other developing methods such as one-component non-contact development and two-component non-contact development as well as one-component contact development and two-component contact development described above are used. , A sufficient recovery effect can be obtained.

The developing device may be a reversal developing system or a regular developing system.

4) As an AC (alternating voltage, alternating voltage) waveform, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Further, there may be a rectangle formed by periodically turning on / off the DC power supply. As described above, a bias whose voltage value periodically changes can be used as the waveform of the alternating voltage.

5) The image forming process of the image forming apparatus is not limited to the embodiment but is optional. Further, other auxiliary process equipment may be added as needed.

The image exposing means for forming an electrostatic latent image is not limited to the laser scanning exposing means for forming a digital latent image as in the embodiment, but may be a normal analog image exposing means. Any other light-emitting element such as a light-emitting element such as an LED or an LED may be used as long as an electrostatic latent image corresponding to image information can be formed, such as a combination of a light-emitting element such as a fluorescent lamp and a liquid crystal shutter.

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

6) The transfer material to which the toner image is transferred from the image bearing member may be an intermediate transfer member such as a transfer drum.

7) The transfer means is not limited to the transfer belt device of the embodiment, but may be any type such as corona discharge transfer, roller transfer, and blade transfer.

8) The image forming apparatus of the embodiment is for forming a black and white image. A photosensitive member, a charging device, a developing device, and an exposing device are provided for each color of yellow, magenta, cyan, and black. A full-color image can be obtained by sequentially transferring the toner image on the body to a transfer material on a belt or a cylindrical transfer material holding member.

That is, the present invention can be applied not only to the formation of a single-color image using an intermediate transfer member such as a transfer drum or a transfer belt, but also to an image forming apparatus for forming a multicolor or full-color image by multiple transfer or the like.

9) Image Carrier 1, Charging Device 2, Developing Device 4
It is also possible to adopt a process cartridge detachable type device configuration in which an arbitrary process device such as the above can be detachably exchanged at a time with respect to the image forming apparatus main body.

10) 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 image information is formed thereon by a charging / electrostatic latent image forming / 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. In the present invention, the image forming apparatus includes such an image display device.

[0153]

As described above, according to the present invention, in a transfer type image forming apparatus of a contact charging type and a cleanerless process, the transfer residual toner is efficiently collected by a charger, To improve the uniformity of the charging potential of the image carrier in the above-mentioned manner, thereby enabling stable charging even in a low-humidity environment and a high peripheral speed of the image carrier, and to continuously perform stable and good image formation. it can.

[Brief description of the drawings]

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

FIG. 2 is an operation sequence diagram of the image forming apparatus.

FIG. 3 is a schematic diagram of a layer configuration of a photoreceptor.

FIG. 4 is an enlarged schematic cross-sectional view of a magnetic brush charging device.

FIG. 5 is an equivalent circuit diagram of a charging circuit.

FIG. 6 is an explanatory view of a procedure for measuring the electric resistance (volume resistance) of magnetic particles (charged carriers).

FIG. 7 is an enlarged cross-sectional model diagram of the developing device.

FIG. 8 is an explanatory diagram of the photoreceptor potential before injection charging and the transfer residual toner recovery property

FIG. 9 is a diagram showing a potential in an end region of the injection charger in the third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging device 2A Magnetic brush charger (injection charger) as a first charging member 3 Laser beam scanner (exposure device) 4 Developing device 5 Transfer device 6 Paper feed cassette 11 Fixing device 12 Conductive roller as second charging member N Charging nip T Transfer nip

Claims (10)

[Claims] A charging device that has an image carrier, a charging member that contacts the image carrier, and charges the image carrier by applying a charging bias to the charging member; and a charging device that charges the image carrier. An image information writing device that forms an electrostatic latent image on a processing surface, a developing device that visualizes the electrostatic latent image with a developer, and a transfer that moves a developer image on the surface of the image carrier to a material to be transferred A developer remaining on the surface of the image carrier without moving to the material to be transferred by the transfer device, is once collected by a charging member in contact with the image carrier of the charging device, and the collected developer is charged by the charging member. In the image forming apparatus of the type in which the toner is discharged from the image carrier to the image carrier and collected again by the developing device, when the charging member of the charging device is a first charging member,
On the downstream side in the image carrier rotation direction from the position of the developer image transfer portion from the image carrier to the transfer material, and on the upstream side in the image carrier rotation direction from the contact portion position between the first charging member and the image carrier. A second charging member that is in contact with the image carrier between the first charging member and an image when the first charging member and the image carrier rush into a contact portion between the first charging member and the image carrier by applying a voltage to the second charging member; An image forming apparatus, wherein a carrier surface potential Vs and a DC voltage Vdc1 applied to a first charging member have the same polarity and satisfy a relationship of | Vs | ≧ | Vdc1 |. 2. A DC voltage Vd applied to a second charging member.
2. The image forming apparatus according to claim 1, wherein c2 and the DC voltage Vdc1 applied to the first charging member have the same polarity and satisfy a relationship of | Vdc2 | ≧ | Vdc1 |. 3. The image forming apparatus according to claim 1, wherein the first charging member includes magnetic particles and a magnetic particle carrier. 4. The image forming apparatus according to claim 1, wherein the second charging member is a conductive roller. 5. The image forming apparatus according to claim 1, wherein the voltage applied to the second charging member is a DC and AC superimposed bias. 6. The image forming apparatus according to claim 1, wherein an end of the charging area of the second charging member is located outside an end of the charging area of the first charging member. apparatus. 7. The image forming apparatus according to claim 1, wherein the image carrier is an electrophotographic photosensitive member. 8. The image forming apparatus according to claim 1, wherein the image carrier is chargeable and chargeable. 9. The image bearing member according to claim 1, wherein the image bearing member is an electrophotographic photosensitive member having a charge injection layer in which conductive fine particles are dispersed in an insulating binder.
An image forming apparatus according to any one of the preceding claims. 10. The image forming apparatus according to claim 1, wherein the image information writing device that forms an electrostatic latent image on the charged surface of the image carrier is an exposure device. .