JP2000075602A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge developer (toner) to an image carrier from a contact type electrifying member without causing developing fogging and attaching developing carrier in a contact electrifying system and cleanerless process transfer type image forming device. SOLUTION: One part or all of the DC component and the AC component of electrifying bias applied to the contact type electrifying member 2A of a contact type electrifying device 2 and the DC component of developing bias applied to the developing member 4a of a developing device 4 are different in an image formation or in an image non-formation. When the bias in the image formation on that of the image non-formation is switched, one part or all of them are switched by taking previously decided time.

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 in contact with the image bearing member are provided, and a charging bias is applied to the charging member to form the image bearing member. Contact type charging device (contact charging device,
A direct charging device), 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 electrostatic latent image with a developer, and a surface of the image carrier. A transfer device for moving the developer image to the transfer material, and a developer remaining on the surface of the image carrier without moving to the transfer material by the transfer device is a charging member that contacts the image carrier of the charging device. The present invention relates to an image forming apparatus, such as a copying machine or a printer, of a type in which the collected developer is discharged once from a charging member and collected again by a developing device.

[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 photoreceptor surface 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. ) Has come into practical use as a contact-type charging device that contacts a charging member (contact charging member) to which the photosensitive member surface is charged to a predetermined polarity and potential.

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.

A magnetic brush charging member (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. Magnetic brush charging type devices in which the magnetic brush portion of the charger is brought into contact with the photoreceptor are 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]

In a transfer type image forming apparatus of a contact charging type and a cleanerless process, the transfer residual toner once collected by the contact charging member adheres to and mixes with the contact charging member. The electric resistance value will change. For example, if the contact charging member is a magnetic brush charger (injection charger), toner is mixed into the magnetic brush portion, and the electric resistance of the toner gradually increases.
For this reason, sufficient charge transfer is not performed during the passage through the charging nip, and the surface potential of the photoconductor after passing through the charging nip becomes smaller than the applied voltage. Hereinafter, the potential difference between the photoconductor surface potential and the applied voltage is defined as ΔV.

When the toner taken into the magnetic brush charger is charged with the same polarity as the photoconductor potential by contact with the magnetic brush carrier (magnetic particles, charged carrier), the toner is mixed by the electric field generated by the potential difference ΔV. The toner is discharged from the magnetic brush to the surface of the photoreceptor. As disclosed in Japanese Patent Application Laid-Open No. 9-96949 and the like, the amplitude Vpp of the AC component (AC component) of the charging bias is reduced during non-image formation (non-image formation) by utilizing this phenomenon. There is known a method in which the application of components is stopped to increase the potential difference ΔV, thereby positively discharging toner to suppress a rise in resistance of the magnetic brush.

The toner discharged from the magnetic brush charger onto the photoreceptor by the electric field generated by the potential difference ΔV is carried to the developing unit by the movement of the photoreceptor surface, and is collected by the developing unit. This principle is shown in FIG. The DC component (DC component) Vdc of the developing bias applied to the developing member (developing sleeve, developing roller, etc.) of the developing device is set lower than the photoconductor potential when the magnetic brush charger discharges toner. The toner discharged on the photoreceptor is collected in the developing device by the potential difference Vback between the photoreceptor potential and the DC value of the developing bias and the mechanical frictional force.

However, in order to discharge toner from the magnetic brush charger to the photosensitive member, the amplitude Vpp of the AC component of the charging bias applied to the magnetic brush charger is reduced, or the application is stopped to reduce the potential of the photosensitive member. If it is lowered too much, fogging may occur at the developing position. To prevent this, the potential of the photoconductor is measured and calculated by a potential sensor or the like, and the DC component of the charging bias is increased or the development is performed so that fogging and the development carrier do not adhere to the photoconductor (developing carrier adhesion). Bias DC
There is a method of lowering the component. At that time, the timing of switching these biases becomes important.

FIG. 13 to FIG. 13 show the possible cases of the bias switching timing and the change of the potential difference Vback at that time.
As shown in FIG.

[0026] The case of FIG. 13 is a case where the developing bias is constant, and the change of the AC component of the charging bias is DC.
If it is faster than the change of the component, the potential difference Vback
And the development carrier may be attached.

[0027] In the case of FIG. 14, the charging bias is constant, and the amplitude V of the AC component of the charging bias is used.
If the DC component of the developing bias decreases before the photoreceptor position at which the pp decreases or stops reaches the developing position, the potential difference Vback increases by the time difference, and the development carrier adheres.
In the reverse order, the potential difference Vback becomes small and fog may occur.

[0028] In the case of FIG.
In this case, each of the C component, the DC component, and the DC component of the developing bias changes. However, depending on the switching timing of each bias, fogging or the possibility of developing carrier adhesion may occur.

However, in an actual apparatus, it is very difficult to synchronize the respective switching timings.
When they are mixed into the charger, the charging efficiency of the charger is significantly reduced.

Further, the above description is based on image formation (at the time of image formation).
In this case, the bias is switched to a bias for discharging the toner from the charger to the photosensitive member during non-image formation (non-image formation), and the same decrease occurs in the reverse process.

Accordingly, the present invention relates to a transfer type image forming apparatus of a contact charging type and a cleanerless process, wherein a developer (a developer) from a contact charging member to an image carrier without causing the above-mentioned problem of developing fog and developing carrier adhesion. The purpose is to cause toner to be discharged.

[0032]

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 collected developer is once collected by the charging member in contact with the developer and the collected developer is discharged from the charging member and collected again by the developing device, the charging of the charging device during image formation and non-image formation is performed. Some or all of the DC component and AC component of the charging bias applied to the member, and some or all of the DC component of the developing bias applied to the developing member of the developing device are different, and a part thereof is used in bias switching between image formation and non-image formation. Alternatively, the image forming apparatus performs all of the operations over a predetermined time.

(2) The image forming apparatus according to (1), wherein the charging member comprises magnetic particles and a magnetic particle carrier.

(3) The absolute value of the DC component of the charging bias is smaller during image formation than during non-image formation, and the amplitude of the charging bias AC component is larger during image formation than during non-image formation. (1) or (2), wherein the absolute value of the charging bias DC component is changed over a certain period of time in the bias switching during non-image formation, and the switching of the amplitude of the charging bias AC component is performed instantaneously. The image forming apparatus as described in the above.

(4) The absolute value of the charging bias DC component is smaller during image formation than during non-image formation, and the amplitude of the charging bias AC component is larger during image formation than during non-image formation. (1) or (2), wherein the amplitude of the charging bias AC component is changed over a certain period of time in the bias switching at the time of non-image formation, and the absolute value of the charging bias DC component is switched instantaneously. The image forming apparatus as described in the above.

(5) The absolute value of the developing bias DC component is smaller during image formation than during non-image formation, and the amplitude of the charging bias AC component is larger during image formation than during non-image formation. And (2) wherein the absolute value of the developing bias DC component is changed over a certain period of time in the bias switching during non-image formation, and the amplitude of the charging bias AC component is switched instantaneously. The image forming apparatus as described in the above.

(6) The absolute value of the developing bias DC component is smaller during image formation than during non-image formation, and the amplitude of the charging bias AC component is larger during image formation than during non-image formation. And (2) wherein the amplitude of the charging bias AC component is changed over a certain period of time in the bias switching during non-image formation, and the absolute value of the developing bias DC component is switched instantaneously. The image forming apparatus as described in the above.

(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 (7), 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. The image forming apparatus as described in the above.

(10) The image forming apparatus according to any one of (1) to (9), wherein the image information writing device for forming an electrostatic latent image on the charged surface of the image carrier is an exposure device. apparatus.

<Operation> To discharge the developer (toner) mixed in the contact charging member (charger) to the image carrier during non-image formation (non-image formation), and collect the discharged developer by the developing device. In addition, since switching between the charging bias and the developing bias is not performed instantaneously, fog at the developing section and adhesion of the developing carrier can be prevented.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (FIGS. 1 to 8) (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 using 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.

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 rotary 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 charger as a contact charging member in contact with the photosensitive drum 1. 2
The toner is temporarily collected by the magnetic brush portion A, and the collected toner is discharged again 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.

Reference numeral 12 denotes a transfer device 5 and a magnetic brush charging device 2
A pre-exposure lamp for exposing the entire surface of the photoconductor drum 1 between the photoconductor drum 1 and the pre-exposure lamp 12 removes the surface potential of the photoconductor drum immediately before charging by the magnetic brush charger 2 to about 0 V by the entire exposure process. You.

Instead of the pre-exposure lamp 12, a conductive member which is brought into contact with a photosensitive drum and has an AC bias, a DC bias having a polarity opposite to that of charging, or a DC bias having a polarity opposite to that of charging, which is obtained by superimposing an AC bias. A similar effect can be obtained with a brush or the like.

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

A. Multi-rotation process before: 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: a period during which a 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 process (image forming process, image forming process): When the predetermined pre-rotation process is completed, an image forming process is subsequently performed on the rotating photosensitive drum, and a transfer material of the toner image formed on the rotating photosensitive drum surface Then, the toner image is fixed by the transfer unit and the fixing unit, and the image formed matter is printed out.

In the case of the continuous printing (continuous printing) mode, the above-described printing process is repeatedly performed 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, and the multi-rotation process of a, the pre-rotation process of b, the paper interval process of d, and the post-rotation process of e are during non-image formation (non-image formation). become.

In the pre-multi-rotation step a and the post-rotation step e, a cleaning bias having the same polarity as the charge polarity of the toner is applied to the conductive blade 5d of the transfer device 5, so that the transfer belt 5a is contaminated. Is transferred to the photosensitive drum surface side, and the transfer belt 5a is cleaned.

In the paper interval step d, a paper interval bias different from the transfer bias in the printing step c is applied to the conductive blade 5d of the transfer device 5.

(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.

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

A second layer 1c; a positive charge injection preventing layer, which serves to prevent positive charges injected from the aluminum drum substrate 1a from canceling out negative charges 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.

The fourth layer 1e is 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-transmitting conductive filler to reduce the resistance (conductivity) to a particle size of 0.03 μm Is a coating layer of about 3 μm of 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 diagram 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 magnet roll 2a in a clockwise direction as indicated 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 constrained on the outer peripheral surface of the sleeve 2b by the magnetic force of the magnet roll 2a inside the sleeve and 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 nip portion having a predetermined width and contacts the photosensitive drum 1 at an opposing portion between the sleeve 2b and 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 part 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.

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 is 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 in the rotation direction of the photosensitive drum to 10 ° downstream. 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 the charging nip portion N does not have a magnetic pole, it is apparent that the binding force acting on the magnetic particles on the sleeve 2b is weakened, and the magnetic particles easily adhere to the photosensitive drum 1.

The charging nip N described herein 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 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 during 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 in 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.

[0095] 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 rotational speed in the counterclockwise direction indicated by an 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 Since the printer of this embodiment is a cleanerless process, the toner (transfer residual toner) remaining on the photosensitive drum 1 after the transfer of the toner image onto the material P to be transferred is removed.
And is temporarily collected by being mixed into the magnetic brush portion 2c of the magnetic brush charger 2A of the magnetic brush contact charging device 2 by being carried to the charging nip portion N.

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. The transfer residual toner having the mixed polarity reaches the magnetic brush charger 2A, enters the magnetic brush portion 2c, and is temporarily collected.

Magnetic brush charger 2A for transfer residual toner
Is taken into the magnetic brush unit 2c by applying an AC component to the magnetic brush charger 2A.
This can be performed more effectively by the oscillating electric field effect between the A-photoconductor drum 1.

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 same polarity and discharged onto the photosensitive drum 1 reaches the developing section m and is collected by the developing and cleaning unit 4b of the developing device 4 by the fog removal electric field during the developing and simultaneous cleaning.

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.

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.
The transfer residual toner which is generated in a normal image forming process and carried to the charging nip N and mixed into the magnetic brush portion 2c of the magnetic brush charging member 2A. Since the amount is very small, the mixed toner is smoothly discharged from the magnetic brush portion 2c, and the allowable amount of toner mixed into the magnetic brush portion 2c is relatively large, so that there is no practical problem.

Further, the photosensitive drum 1 is moved from the magnetic brush portion 2c to the photosensitive drum 1.
The discharged toner 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.

(7) Control when Switching Bias (FIG. 8) As described above, the magnetic brush charger 2 used in this embodiment is
The resistance value of A was 1 × 10 ⁶ Ω · cm, and the surface potential of the photosensitive drum 1 was also −700 V by applying −700 V as a DC component of charging bias (charging DC).

From this state, when about 5,000 sheets of an original having an image ratio of 10% were formed, the surface potential of the photosensitive drum 1 became -650 V, and the superposition of the AC component of the charging bias (charging AC) was stopped. When charging was performed only by applying the DC component of −700 V, the surface potential of the photosensitive drum 1 became −450 V.

The slope time of the charged DC without causing fogging and adhesion of the developing carrier will be described below with reference to FIG.

When the absolute value of the charging DC is gradually increased from the point (a) in FIG. 8, the absolute value of the photoconductor potential increases along the upper oblique line, and the ACVpp is increased at the point (c). 0v
(Point (f)). Thereafter, the final discharge potential and the bias state are reached along the lower oblique line (point (g) → point (h)).

In this case, point (c) is equivalent to point (b) and point (d).
The fog occurs earlier (to the left of point (b)) and later (to the right of point (d)).
Development carrier adhesion occurs.

Therefore, the maximum deviation time from the charging AC bias application start target is Tace, the maximum deviation time Tdce of the center time of the charging DC bias slope is from point (b) to point (d), or from point (b) to point. Assuming that the time required for the change up to (d) is T1, by changing the DC bias so as to satisfy the following equation 2 · (Tace + Tdce) <T1, fog and development carrier adhesion can be prevented.

In the apparatus of this embodiment, the errors Tace and T
dce is about 50 msec. Therefore, T1 is set to 50, 1
00, 150, 200, 250 msec. 1 in the case of
Dirt on the transfer belt after passing 00 sheets was observed.

In this embodiment, the sequence is set so that the bias switching is always performed during non-image formation.
The fogging and the adhesion of the developing carrier accompanying the switching are attached to the transfer belt.

As a result, 50, 100, 150 ms
c. In contrast, the transfer belt and the back stain of the paper (transferred material) occurred, while 200 and 250 msec. In this case, neither transfer belt stain nor paper back stain occurred.

When the bias is switched from the non-image portion bias to the image portion bias, the above-described process is performed in the reverse direction. Therefore, it is apparent that the same effect can be obtained by switching the bias over the same time. It is.

The above-described bias control is performed by an image forming apparatus control unit (CPU) (not shown).

<Second Embodiment> (FIG. 9) In this embodiment, while the charging DC bias is instantaneously switched, the amplitude of the charging AC bias is gradually changed.

The slope time of the charging AC that does not cause fogging or adhesion of the developing carrier will be described below with reference to FIG.

When the charging AC is gradually reduced from the point (a), the absolute value of the photoconductor potential decreases along the lower oblique line, and the charging DC switches at the point (c) (point (f)). ). Thereafter, the final discharge potential and the bias state are reached along the upper oblique line (point (g) → point (h)). In this case, the point (c) must be located between the points (b) and (d). If the point is earlier (to the right of the point (b)), development carrier adhesion occurs. (Left of (d)) Fog occurs.

Therefore, the maximum deviation time from the charging DC bias application start target time is Tdce, the maximum deviation time Tace of the center time of the charging AC bias slope, from point (b) to point (d), or from point (b). Assuming that the time required for the change up to the point (d) is T2, changing the AC bias so as to satisfy the following equation 2 · (Tdce + Tace) <T2 can prevent fog and development carrier adhesion.

As in the first embodiment, the error Tdce, Tace of the start and stop timings of the application of the AC bias and the DC bias in the apparatus of this embodiment is about 50 msec. Therefore, T2 is set to 50, 100, 150, 200, 250
msec. In the case of (1), dirt on the transfer belt after passing 100 sheets was observed.

In this embodiment, since the sequence is set so that the bias switching is always performed during non-image formation, the fog and the development carrier attached to the switching are attached to the transfer belt.

As a result, 50, 100, 150 ms
c. In contrast, the transfer belt stained and the paper back stain occurred, whereas 200 and 250 msec. Then transfer belt dirt,
Neither did the paper back stain occur.

When the bias is switched from the non-image portion bias to the image portion bias, the above-described process is performed in the reverse direction. Therefore, it is apparent that the same effect can be obtained by switching the bias over the same time. It is.

The above-described bias control is performed by an image forming apparatus control unit (CPU) (not shown).

<Third Embodiment> (FIG. 10) In this embodiment, the charging bias DC component is constant, and the application of the charging bias AC component is stopped between sheets or during post-rotation, and the photoconductor potential is changed by AC switching. The developing bias was gradually switched in accordance with the decrease.

The slope time of the developing DC which does not cause fogging or development carrier adhesion will be described below with reference to FIG.

When the development DC is gradually decreased from the point (a), Vback increases along the upper oblique line, and the charging AC is switched at the point (c) (point (f)). Thereafter, the final discharge potential and the bias state are reached along the lower oblique line (point (g) → point (h)). in this case,
The point (c) must be between the points (b) and (d). If it is earlier, fog occurs (to the right of point (b)), and if it is later (to the left of point (d)). ) Development carrier adhesion occurs.

Therefore, the maximum deviation time from the charging AC bias application start target time is Tace, the maximum deviation time Tddce of the center time of the developing DC bias slope, and the charging AC bias application start target position due to uneven rotation of the photosensitive member reaches the developing position. Assuming that an error Tme of the time to perform, and a time taken to change from the point (b) to the point (d) or from the point (b) to the point (d) is T3, the following equation 2 · (Tace + Tdce + Tme) <T3 is satisfied. By changing the AC bias as described above, fog and development carrier adhesion can be prevented.

In the apparatus of this embodiment, the error Tddce between the start and stop timing of the application of the charging AC bias and the start and stop timing of the application of the developing DC bias is 50 ms.
c, the error Tme in the time required for the charging AC bias application start target position to reach the developing position due to uneven rotation of the photoconductor is about 3
0 msec. Therefore, T3 is set to 150, 200, 25
0, 300, 350 msec. In the case of (1), dirt on the transfer belt after passing 100 sheets was observed.

In this embodiment, since the sequence is set so that the bias switching is always performed during non-image formation, the fog and the development carrier attached to the switching are attached to the transfer belt.

As a result, 150, 200, 250 mse
c. In contrast, the transfer belt was stained and the back of the paper was stained, whereas 300 and 350 msec. In this case, neither the transfer belt nor the paper back was stained.

When the bias is switched from the non-image portion bias to the image portion bias, the above-described process is performed in the reverse direction, so that the same effect can be obtained by switching the bias over the same time. It is.

The above-described bias control is performed by an image forming apparatus control unit (CPU) (not shown).

<Fourth Embodiment> (FIG. 11) In this embodiment, the charging bias DC component is constant and the developing D
The application of the charging AC was gradually stopped in accordance with the switching of the C bias.

The slope time of the charging AC that does not cause fogging or adhesion of the developing carrier will be described below with reference to FIG.

When the charging AC is gradually reduced from the point (a), Vback decreases along the lower oblique line, and the developing DC bias switches at the point (c) (point (f)).
After that, the final discharge potential along the upper diagonal line,
The bias state is reached (point (g) → point (h)). In this case, the point (c) must be located between the points (b) and (d). If it is earlier (to the right of the point (b)), development carrier adhesion occurs, and if it is later (the point (b)). (Left of (d)) Fog occurs.

Accordingly, the maximum deviation time from the target time for starting the application of the development DC bias is Tddce, the maximum deviation time Tace of the center time of the charging AC bias slope, and the target position for starting the application of the charging AC bias due to the uneven rotation of the photosensitive member reaches the development position. Assuming that a time error Tme, and a time required to change from point (b) to point (d) or from point (b) to point (d) is T4, the following equation 2 · (Tddce + Tace + Tme) <T4 is satisfied. By changing the developing DC bias as described above, fog and development carrier adhesion can be prevented.

In the apparatus of this embodiment, the error Tace of the start and stop timings of the application of the charging AC bias and the error Tdce of the start and stop timings of the application of the developing DC bias are five.
0 msec. Error T in the time required for the charging AC bias application start target position to reach the developing position due to uneven rotation of the photoconductor.
me is about 30 msec. Therefore, T4 is set to 150, 2
00, 250, 300, 350 msec. 1 in the case of
Dirt on the transfer belt after passing 00 sheets was observed.

As a result, 150, 200, 250 mse
c. In contrast, the transfer belt was stained and the back of the paper was stained, whereas 300 and 350 msec. In this case, neither the transfer belt nor the paper back was stained.

When the bias is switched from the non-image portion bias to the image portion bias, the above-described process is performed in the reverse direction, so that the same effect can be obtained by switching the bias over the same time. It is.

As described above, in the first to fourth embodiments of the four types, the case where two types are switched among the three types of biases has been described. It is clear that fogging and development carrier adhesion can be prevented by switching each bias so that the development carrier adhesion NG potential does not occur.

The above-described bias control is performed by an image forming apparatus control unit (CPU) (not shown).

<Others> 1) The magnetic brush charger 2A as a contact charging member is not limited to a sleeve rotating type, but may be a type in which a magnet roll rotates or a surface of the magnet roll may be electrically conductive as a power supply electrode as necessary. After the treatment, the magnetic brush portion may be formed by magnetically constraining the conductive magnetic particles directly on the outer peripheral surface of the magnet roll, and the configuration may be such that the magnet roll is rotated. A non-rotating type magnetic brush charging member may be used.

The contact charging member may be a fur brush charging member, a charging roller using conductive rubber or conductive sponge, or a non-rotating structure.

2) It is desirable that the photoreceptor as an 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, and may be a contact charging system in which a discharge phenomenon is dominant.

3) Although the developing device has been described only for the two-component developing method, 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 an ordinary 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, after the dielectric surface is uniformly charged to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head or an electron gun to write and form a desired electrostatic latent image.

6) The transfer material on 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 multi-color 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 collectively 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.

[0176]

As described above, according to the present invention, in a transfer type image forming apparatus of a contact charging type and a cleanerless process, a developer (toner) mixed in a contact charging member is applied to an image carrier during non-image formation. In order to discharge and collect the discharged developer in the developing device, the charging bias and the developing bias are not instantaneously switched, so that the contact charging member is transferred from the charging member to the image carrier without causing the development fog and the adhesion of the developing carrier. Developer discharge, and stable contact charging performance over a long period of time.
Good output image quality can be maintained.

[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 photoconductor.

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 a diagram showing a change relationship of a photoconductor potential or a potential difference Vback due to bias switching.

FIG. 9 is a diagram showing a change relationship of a photoconductor potential or a potential difference Vback due to bias switching in the second embodiment.

FIG. 10 is a diagram showing a change relationship of a photoconductor potential or a potential difference Vback due to bias switching in the third embodiment.

FIG. 11 is a diagram showing a change relationship of a photoconductor potential or a potential difference Vback due to bias switching in a fourth embodiment.

FIG. 12 is a view for explaining the principle of discharging toner from a charging device and collecting toner to a developing device.

FIG. 13 is a timing chart of switching biases (case 1).

FIG. 14 is a timing chart of switching biases (Case 2)

FIG. 15 is a timing chart of switching biases (Case 3).

[Explanation of symbols]

 Reference Signs List 1 image carrier (photosensitive drum) 2 developing device 3 laser beam scanner (exposure device) 4 developing device 5 transfer device 6 paper feed cassette 11 fixing device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Atsushi Takeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Fumiko Gomi 3-30-2 Shimomaruko, Ota-ku, Tokyo Non-corp. F term (reference) 2H003 AA12 BB04 BB11 CC06 DD03 EE11 EE19 2H034 EA01

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 transfer material A developer remaining on the surface of the image carrier without being transferred 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. An image forming apparatus of a type in which the toner is discharged from the developing device and collected again by the developing device, wherein a DC component and an AC component of a charging bias applied to a charging member of the charging device during image formation and non-image formation, and development of the developing device D of developing bias applied to member Some of the components or all are different, the image forming apparatus and performs over time which is predetermined a part or all the bias switching at the time of image formation and non-image formation. 2. The image forming apparatus according to claim 1, wherein the charging member comprises magnetic particles and a magnetic particle carrier. 3. An image forming apparatus according to claim 1, wherein the absolute value of the charging bias DC component is smaller during image formation than during non-image formation.
The amplitude of the component is larger during image formation than during non-image formation, and the absolute value of the charging bias DC component is changed over a certain period of time during bias switching between image formation and non-image formation, and the charging bias AC component is changed. 3. The image forming apparatus according to claim 1, wherein the switching of the amplitude is performed instantaneously. 4. An image forming apparatus according to claim 1, wherein the absolute value of the charging bias DC component is smaller during image formation than during non-image formation.
The amplitude of the component is larger during image formation than during non-image formation, and the amplitude of the charging bias AC component is changed over a certain period of time during the bias switching between image formation and non-image formation, and the absolute value of the charging bias DC component is changed. The image forming apparatus according to claim 1, wherein the switching of the value is performed instantaneously. 5. An image forming apparatus according to claim 1, wherein the absolute value of the developing bias DC component is smaller during image formation than during non-image formation.
The amplitude of the component is larger during image formation than during non-image formation, and the absolute value of the developing bias DC component is changed over a certain period of time during bias switching between image formation and non-image formation, and the charging bias AC component is changed. 3. The image forming apparatus according to claim 1, wherein the switching of the amplitude is performed instantaneously. 6. An image forming apparatus according to claim 1, wherein the absolute value of the developing bias DC component is smaller during image formation than during non-image formation.
The amplitude of the component is larger during image formation than during non-image formation, and the amplitude of the charging bias AC component is changed over a certain period of time during bias switching between image formation and non-image formation, and the absolute value of the developing bias DC component is changed. The image forming apparatus according to claim 1, wherein the switching of the value is performed instantaneously. 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 charge-chargeable. 9. The image according to claim 1, 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. Forming equipment. 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.