JP3223837B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photosensitive member.
A step of uniformly charging the image carrier such as an electrostatic recording dielectric to a predetermined polarity and potential, an image information writing step of forming an electrostatic latent image on the charged surface, An image forming process is performed by applying an image forming process including a step of developing an electro-latent image as a toner image with toner and a step of transferring the toner image to a recording medium, and the image carrier repeatedly performs image forming. Related to the device.

More specifically, as a charging means for uniformly charging the image carrier to a predetermined polarity and potential, a contact charging means for performing contact by applying a contact charging member to which a voltage is applied to the image carrier is used. Also, the present invention relates to a so-called cleanerless system image forming apparatus which also serves as a cleaning unit that collects residual toner particles remaining on the image carrier after the developing unit transfers a toner image to a recording medium (simultaneous development cleaning method).

[0003]

2. Description of the Related Art FIG. 8 is a schematic diagram showing an example of a transfer type electrophotographic apparatus (copier, printer, facsimile, etc.) as a conventional example of an image forming apparatus.

Reference numeral 101 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier, which is driven to rotate at a predetermined peripheral speed in a clockwise direction indicated by an arrow.

The photosensitive drum 101 undergoes a uniform charging process of a predetermined polarity and potential by a corona charger 102 as a charging means in the course of its rotation, and then to an image exposure means (not shown). Means, laser beam scanning exposure means, etc.), the uniformly charged surface is selectively neutralized (or attenuated in potential) corresponding to the exposed image pattern to form an electrostatic latent image. Then, the formed electrostatic latent image is developed as a toner image by a toner developing device 103 as a developing unit.

On the other hand, a transfer material (transfer paper) P as a recording medium is fed between a photosensitive drum 1 and a transfer corona charger 104 as a transfer means at a predetermined control timing from a paper feed mechanism (not shown). The toner image on the surface of the photosensitive drum 101 is electrostatically transferred to the front surface of the transfer material P by charging the back surface of the transfer material P with a polarity opposite to that of the toner.

Next, the transfer material P is supplied to the separation corona charger 105.
Accordingly, the toner image is electrostatically separated from the surface of the rotating photosensitive drum 101, introduced into the fixing device 108 by the transport device 107, subjected to the fixing process of the toner image, and output as an image formed product (copy, print).

After the transfer of the toner image onto the transfer material P, the surface of the photosensitive drum 101 is cleaned by a cleaning means (cleaner) 106.
The toner is cleaned by receiving the transfer residual toner, and is repeatedly used for image formation.

In the above, a photoreceptor as an image carrier,
There are various configurations and methods for each means and device for an image forming process such as charging, exposure, development, transfer, fixing, and cleaning.

1) For example, as the charging means 102, a corona charger has been widely used. In this method, a corona charger is disposed opposite to a photosensitive drum in a non-contact manner, and the surface of the photosensitive drum is exposed to the corona discharged from the corona charger to charge the photosensitive drum surface to a predetermined polarity and potential.

Recently, a contact-charging type charging device has been put into practical use because it has advantages such as low ozone and low power as compared with the above-described corona charger of a non-contact type. In this method, a contact charging member to which a voltage is applied is brought into contact with the photosensitive drum to charge the surface of the photosensitive drum to a predetermined polarity and potential.

As the contact charging member, a magnetic brush member having magnetic particles magnetically constrained, and a magnetic brush member for bringing the magnetic brush portion into contact with the photosensitive drum is preferably used from the viewpoint of charging contact stability. .

The magnetic brush member has a magnetic brush portion formed by magnetically restraining conductive magnetic particles directly on a magnet or on a sleeve containing the magnet. The magnetic brush member is stopped or rotated. The magnetic brush is brought into contact with the photosensitive drum, and a voltage is applied to the photosensitive brush to start charging the photosensitive drum.

Further, a brush formed of conductive fibers in a brush shape (fur brush member) or a conductive rubber roller (charge roller) made of conductive rubber in a roll shape is also preferably used as a contact charging member.

[0015] In particular, using such a contact charging member, a photosensitive drum of a photosensitive drum as a member to be charged has a surface layer (charge injection layer) in which conductive fine particles are dispersed on a normal organic photosensitive member. When an amorphous silicon photoreceptor is used, it is possible to obtain a charging potential on the photoreceptor surface substantially equivalent to a DC component of a bias applied to the contact charging member (Japanese Patent Application Laid-Open No. 6-3921).

Such a charging method (charging of an object to be charged by direct injection of charges) is referred to as "injection charging". If this injection charging is used, the charging of the member to be charged does not use a discharge phenomenon that is performed using a corona charger.
Complete ozone-less and low power consumption type charging becomes possible,
It is getting attention.

2) In general, toner development methods for electrostatic latent images are roughly classified into the following four types a to d.

A. Non-magnetic toner is coated on the sleeve with a blade or the like, and magnetic toner is coated by magnetic force, transported, 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. Method of Developing the Two-Component Developer in a Non-Contact State (Two-Component Non-Contact Development) Among these, the two-component contact development method of c is often used from the viewpoint of high image quality and high stability. ing.

3) In recent years, the miniaturization of such an image forming apparatus has been advanced, but as described above, charging, exposure, development,
Each means of image forming process such as transfer / fixing / cleaning
Just reducing the size of each device has limited the overall miniaturization of the image forming apparatus.

Further, as described above, the transfer residual toner on the photosensitive drum 101 after the transfer is collected by the cleaner 106 to become waste toner, but it is preferable that the waste toner does not come out from the viewpoint of environmental protection. Therefore, the cleaner 106 is removed, and the untransferred toner on the photosensitive drum 101 is removed from the photosensitive drum 101 by "developing simultaneous cleaning" by the developing device 103 and collected and reused in the developing device 103. Image forming apparatuses of the "less system" have also appeared.

Simultaneous development cleaning refers to a fogging bias (fogging which is a potential difference between a DC voltage applied to a developing device and a surface potential of the photosensitive drum) at the time of development after the next step. This is a method of recovering by taking a potential difference Vback). According to this method, since the transfer residual toner is collected in the developing device 103 and used in the next step and thereafter, 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.

Further, in order to improve the cleaning efficiency in the simultaneous development cleaning method, the toner used for developing the electrostatic latent image is a toner having a very excellent releasability, such as a toner produced by a polymerization method. It is very effective to use.

4) The transfer material P from the photosensitive drum 101 side
The transfer means of the toner image to the side is also a transfer corona charger 104.
Instead, there are various methods such as a method using a transfer roller or a transfer belt.

[0024]

In the image forming apparatus of this type, when a contact charging means is used as a charging means for an image carrier such as a photoreceptor, one of the problems is that the contact charging means which is in contact with the image carrier is used. The member picks up dirt and foreign matter on the image carrier surface side, and the accumulation tends to cause a contamination state.

Normally, since the electrical resistance of toner particles is relatively high, if a relatively large amount of such toner particles adhere to and mix in the contact charging member and accumulate unacceptably excessively, the contact charging member may be damaged. The resistance of the entire or part of the image carrier increases, and the image carrier cannot be charged to a desired potential, or charging unevenness occurs, resulting in image defects.

[0026] Such toner contamination of the contact charging member,
The occurrence of image defects due to this is caused by a contactless charging unit as a charging unit for the photoreceptor, and an image forming apparatus of a cleanerless system which does not have a dedicated cleaner for removing transfer residual toner on the image carrier after transfer. Is particularly noticeable.

That is, in the case of the image forming apparatus of the cleaner-less system, a relatively large amount of untransferred toner on the image carrier after transfer is carried to the position of the contact charging member as the image carrier continues to move. This is because a large amount of toner adheres to and mixes with the contact charging member, and the contact charging member quickly and excessively becomes in a toner-contaminated state.

In the case of the image forming apparatus of the cleaner-less system, since the untransferred toner on the image carrier after the transfer exists in a form (pattern) in which the previous image is left as it is, it passes through the charging device portion as it is. However, only the remaining image portion has a reduced charging potential or interrupts the exposure for the next image formation, affecting the next development process as it is, and the previous image portion on the next image becomes thinner. A so-called "ghost phenomenon" occurs, such as becoming darker or appearing densely.

Therefore, a brush-shaped uniformizing member for uniformly dispersing the transfer residual toner having the image shape as it is on the image carrier before reaching the charging device portion, a simple cleaning member using a temporary bias effect, and the like. However, any of these methods is disadvantageous for further miniaturization and simplification of the apparatus, and causes wear and deterioration of the image carrier, and improvement in durability cannot be expected. Further, eventually, the toner is mixed into the contact charging member when passing through the position of the contact charging member, so that the charging ability is inevitably reduced.

The present invention has been made in view of the above, and relates to an image forming apparatus of a cleanerless system using a contact charging means as a charging means for an image carrier such as a photoreceptor.
The purpose of the present invention is to prevent toner contamination of the contact charging member, erase the trace of the previous image of the transfer residual toner, and prevent the transfer ability of the transfer residual toner from lowering when passing through the charging means.

[0031]

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

(1) The image carrier is brought into contact with a contact charging member having a voltage applied to the image carrier so that the image carrier has a predetermined polarity.
Contact charging means for uniformly charging to an electric potential, image information writing means for forming an electrostatic latent image on a charged surface of an image carrier, and developing means for developing the electrostatic latent image as a toner image with toner particles And a transfer unit for transferring the toner image to a recording medium. The developing unit also serves as a cleaning unit for collecting residual toner particles remaining on the image carrier after transferring the toner image to the recording medium. In the image forming apparatus in which the body is repeatedly subjected to image formation, the contact charging member
Temporarily captures residual toner particles and carries the image after transfer
The average charge amount of the residual toner remaining on the body
To the opposite polarity of the charge polarity from the average charge amount of
Conductive part that enhances capture of residual toner particles by charging member
The remaining toner remaining on the image carrier after the transfer of the toner image from the image carrier to the recording medium has an average charge amount before reaching the charging means, which is larger than the average charge amount of the toner during development. The bias applied to the charging means is opposite to the charging polarity,
Further, the average charge amount of the residual toner adhered or mixed into the contact charging member is on the charging polarity side of the average charge amount of the residual toner remaining on the image carrier after transfer before reaching the charging unit. Image forming apparatus.

[0033]

(2) The image forming apparatus according to (1) , wherein the conductive member is provided near an image carrier.

(3) The image forming apparatus according to (2) , wherein a bias having a polarity opposite to a charging polarity is applied to the conductive member.

(4) The image forming apparatus according to (2) or (3) , wherein the conductive member is not in contact with the image carrier.

(5) The image forming apparatus according to any one of (1) to ( 4) , wherein the frictional charging series of the toner is on the charging polarity side with respect to the contact charging member.

(6) The contact charging member has a magnetic brush portion in which magnetic particles are magnetically constrained, and is a magnetic brush contact charging member in which the magnetic brush portion is brought into contact with an image carrier. The image forming apparatus according to any one of (1) to ( 5) .

(7) The contact charging member is a fur brush contact charging member having a fur brush portion made of a conductive fiber and bringing the fur brush portion into contact with an image carrier. The image forming apparatus according to any one of ( 1 ) to (5) .

(8) The image according to any one of (1) to (7) , wherein the image carrier is a photosensitive member having a charge injection layer on a surface and charged and injected. Forming equipment.

[0041] (9) in any one of (1), wherein (8) the image information writing means for forming an electrostatic latent image on the charged surface of the image bearing member is an image exposure means The image forming apparatus as described in the above.

<Operation> The present invention relates to an image forming apparatus of a cleanerless system using a contact charging means as a charging means for an image carrier. The contact charging member once collects the residual toner remaining on the image carrier after the transfer and carried to the position of the contact charging member once, so that the history of the previous image of the residual toner is erased, that is, a ghost phenomenon. To prevent the occurrence of Also, the toner collected by the contact charging member is positively re-discharged onto the image carrier at a polarity that can be collected by the developing means, thereby preventing excessive toner contamination of the contact charging member itself and effectively developing the toner by the developing means. This enables toner recovery.

After the transfer of the toner image from the image carrier to the recording medium, the average charge amount of the residual toner remaining on the image carrier before reaching the charging means is greater than the average charge amount of the toner during development. And the average charge amount of the residual toner adhered or mixed into the contact charging member reaches the charging means for the residual toner remaining on the image carrier after transfer. By being on the charging polarity side than the previous average charging amount, the transfer residual toner to the contact charging member is collected, and the toner collected by the contact charging member is discharged again to the image carrier. The collection by the developing means can be effectively performed.

As a result, there is no decrease in charging ability due to excessive toner contamination of the contact charging member, and no decrease in charging ability when passing untransferred toner. The output of high-quality images without images was stably maintained for a long period of time.

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment (FIGS. 1 to 6) (1) Schematic Configuration of Example of Image Forming Apparatus (FIG. 1) FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention.

The image forming apparatus of this embodiment is a laser beam printer utilizing a transfer type electrophotographic process, and uses a magnetic brush charging device of a contact charging type as a charging device of a photosensitive drum as an image carrier, and develops by a developing device. This is an image forming apparatus of a cleanerless system that performs simultaneous cleaning.

A is a laser beam printer, and B is an image reading device (image scanner) mounted on the printer.

A) Image Reading Apparatus B In the image reading apparatus B, reference numeral 10 denotes an original platen glass fixedly arranged on the upper surface of the apparatus, and is mounted on the upper surface of the original platen glass with the original G to be copied facing downward. And a document pressure plate (not shown) is placed thereon.

Reference numeral 9 denotes an image reading unit provided with a document irradiation lamp 9a, a short focus lens array 9b, a CCD sensor 9c, and the like. When a copy button (not shown) is pressed, the unit 9 is driven forward along the lower surface of the platen glass 10 from the home position indicated by the solid line on the right side of the glass to the left side along the lower surface of the glass. When the forward movement end point is reached, it is driven backward and returned to the home position indicated by the solid line.

In the forward drive of the unit 9, the downward image surface of the placed set original G on the original platen glass 10 is sequentially illuminated and scanned by the original irradiation lamp 9 a of the unit 9 from the right side to the left side. The reflected light from the original surface of the illumination scanning light is image-formed on the CCD sensor 9c by the short focus lens array 9b.

The CCD sensor 9c includes a light receiving section, a transfer section, and an output section. The light signal is converted into a charge signal in the CCD light receiving unit, and the transfer unit sequentially transfers the light signal to the output unit in synchronization with the clock pulse. The output unit converts the charge signal into a voltage signal, amplifies the signal, reduces the impedance, and outputs the voltage signal. The analog signal obtained in this way is converted into a digital signal by performing known image processing, and
Send to

That is, the image information of the document G is photoelectrically read by the image reading device B as a time-series electric digital pixel signal (image signal).

B) Printer A In the printer A, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as an image carrier. The photosensitive drum 1 of this example is an OPC photosensitive member having a charge injection layer on the surface. The photoreceptor 1 will be described in detail in section (2) below.

The photosensitive drum 1 has a predetermined peripheral speed in the clockwise direction indicated by an arrow about the center support shaft, and in this example, a rotational speed of 100 mm /.
is driven to rotate in seconds, and in the rotation process,
In the case of this example, the charging means 2 receives a uniform negative polarity charging process.

The charging means 2 in this embodiment is a contact charging type magnetic brush charging device. The charging device 2 will be described later in detail in (3).

The uniformly charged surface of the rotating photosensitive drum 1 is modulated according to the image signal output from the laser scanning unit (laser scanner) 3 and sent from the image reading device B to the printer A. The scanning exposure L is performed by the laser light, and the document G photoelectrically read by the image reading device B is formed on the surface of the rotating photosensitive drum 1.
The electrostatic latent images corresponding to the image information are sequentially formed. The laser scanning unit 3 will be described later in detail in (4).

The electrostatic latent image formed on the surface of the rotating photosensitive drum 1 is sequentially developed as a toner image by the developing device 4 in reverse in the case of this embodiment. The developing device 4 of this embodiment is a two-component contact developing type device. The developing device 4 will be described later in detail in (5).

On the other hand, a transfer material P as a recording medium stored in the paper feed cassette 5 is fed out one by one by a paper feed roller 5a, fed into the printer A, and registered with a registration roller 5b.
Thus, at a predetermined control timing, the sheet is fed to a transfer portion T which is a contact nip portion between the photosensitive drum 1 and a transfer belt type transfer device 6 as a transfer unit.

The toner image on the side of the rotating photosensitive drum 1 is sequentially electrostatically transferred to the surface of the transfer material P fed to the transfer portion T by the transfer charging blade 6d disposed inside the transfer belt 6a . The transfer device 6 will be described later in detail in (6).

The transfer material P, to which the toner image has been transferred through the transfer portion T, is sequentially separated from the surface of the photosensitive drum 1 and is conveyed to the fixing device 8 by the conveyance device 7, where the toner image is thermally fixed and copied. Or output as a print.

Since the printer of this embodiment is a cleanerless system device, the rotary photosensitive drum 1 after the transfer material is separated
There is no dedicated cleaning device (cleaner) for collecting the transfer residual toner remaining on the surface of the rotating photosensitive drum 1, and the transfer residual toner on the surface of the rotating photosensitive drum 1 is rotated as will be described in detail in (7) below. The developing device 4 passes through the position of the electrode member 27 which is disposed in non-contact proximity to the photosensitive drum 1 and the position of the magnetic brush charger 20 which is a contact charging member of the magnetic brush charging device 2.
, And is collected by the simultaneous cleaning with development by the developing device 4, and the surface of the rotating photosensitive drum 1 is repeatedly provided for image formation.

(2) Photosensitive Drum 1 (FIG. 2) As the photosensitive drum (photosensitive member) 1 as an image carrier, a commonly used organic photosensitive member or the like can be used.
Further, a photosensitive member using an inorganic semiconductor such as CdS, Si, or Se can also be used. Preferably, when an organic photoreceptor having a surface layer having a material having a resistance of 10 ⁹ to 10 ¹⁴ Ω · cm or an amorphous silicon photoreceptor is used, charge injection charging can be realized and ozone generation can be prevented. , And power consumption. Further, the chargeability can be improved.

The photosensitive drum 1 used in this example is a negatively charged organic photosensitive member provided with a charge injection layer on its surface, and is formed on an aluminum drum substrate (hereinafter referred to as an aluminum substrate) having a diameter of 30 mm. Are provided in order from the bottom. FIG. 2A is a model diagram of the layer structure.

A first layer 12 which is an undercoat layer and has a thickness of 20 μm provided for smoothing defects of the aluminum base 11;
m of the conductive layer.

A second layer 13; a positive charge injection preventing layer, which prevents positive charges injected from the aluminum substrate 11 from canceling out negative charges charged on the surface of the photoreceptor; 1 × 1
0 is the resistance layer in the ⁶ Omega · cm about the resistance adjusted thickness 1 [mu] m.

The third layer 14 is a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates positive and negative charge pairs upon exposure.

Fourth layer 15; a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, negative charges charged on the surface of the photoreceptor cannot move through this layer, and only positive charges generated in the charge generation layer 14 can be transported to the surface of the photoreceptor.

Fifth layer 16: a charge injection layer, which is a coating layer of a material in which ultrafine SnO ₂ particles as conductive particles 16a are dispersed in a binder of an insulating resin. Specifically, a particle diameter of about 0.03 μm obtained by doping an insulating resin with antimony, which is a light-transmitting insulating filler, to reduce the resistance (to make it conductive).
This is a coating layer of a material in which m SnO ₂ particles are dispersed in a resin by 70% by weight.

The coating solution prepared as described above was applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coating method, beam coating method, etc. to form a charge injection layer.

(3) Charging Device 2 (FIGS. 3 and 4) The charging device 2 in this embodiment is a magnetic brush charging device of a contact charging type. FIG. 3 is a schematic configuration diagram thereof. Reference numeral 20 denotes a magnetic brush charger as a contact charging member disposed in contact with the photosensitive drum 1.

The magnetic brush charger 20 of this embodiment is of a rotary sleeve type, and has a magnet roll 21 fixedly supported in a non-rotating manner and an outer diameter which is concentrically and rotatably fitted around the outer periphery of the magnet roll. A 16-mm non-magnetic sleeve (non-magnetic, conductive, charging electrode sleeve) 22;
A magnetic brush portion 23 of conductive magnetic particles (magnetic carrier for charging) and the like formed by being attracted and held on the outer peripheral surface of the non-magnetic sleeve 22 by the magnetic force of the magnet roll 21 inside the sleeve.

The magnetic brush charger 20 is disposed substantially parallel to the photosensitive drum 1 with the magnetic brush portion 23 in contact with the surface of the photosensitive drum 1. In this case, the magnetic brush charger 20 was arranged so that the contact nip width (charging area) N of the magnetic brush portion 23 formed on the photosensitive drum 1 was about 6 mm.

Non-magnetic sleeve 2 of magnetic brush charger 20
Reference numeral 2 denotes a clockwise rotation of the photosensitive drum 1 in the charging area N which is opposite to the rotation direction of the photosensitive drum 1 (counter direction).
It was rotated at mm / sec.

A predetermined charging bias was applied to the non-magnetic sleeve 22 from a charging bias applying power source S1.

With the rotation of the non-magnetic sleeve 22, the magnetic brush portion 23 rotates in the same direction and rubs the surface of the photosensitive drum 1 in the charging area N, so that electric charges are generated from the charging magnetic particles constituting the magnetic brush portion 23. The photosensitive drum 1 is provided on the photosensitive drum 1, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential.

In the case of this example, as described above, the photosensitive drum 1
Has a charge injection layer 16 on the surface thereof, so that the photosensitive drum 1 is charged by charge injection charging. That is, by applying a predetermined charging bias voltage to the non-magnetic sleeve 22, electric charges are given to the photosensitive drum 1 from the magnetic particles constituting the magnetic brush portion 23,
The surface of the photosensitive drum 1 is charged to a potential corresponding to the charging bias voltage. The non-magnetic sleeve 22 tends to have better charging uniformity as the rotation speed is higher.

A) Magnetic Particles The charging magnetic particles constituting the magnetic brush portion 23 have an average particle diameter of 10 to 100 μm and a saturation magnetization of 20 to 2 μm.
50 emu / cm ³ , resistance 1 × 10 ² to 1 × 10 ¹⁰ Ω · cm
Are preferred. Considering the existence of insulation defects such as pinholes in the photosensitive drum 1, the resistance is 1 × 10
It is preferable to use one of ⁶ Ω · cm or more. In order to improve the charging performance, it is better to use a material having a resistance as small as possible. In this example, magnetic particles having an average particle size of 25 μm, a saturation magnetization of 200 emu / cm ³ , and a resistance of 5 × 10 ⁶ Ω · cm are used. Was.

The resistance value of the magnetic particles is such that the bottom area is 228 mm.
After placing 2g of the magnetic particles in the ^second metal cell, 6.6Kg /
The weight was measured in cm ² and a voltage of 100 V was applied for measurement.

The average particle size of the magnetic particles is represented by the maximum chord length in the horizontal direction, and the measurement was carried out by microscopically selecting 300 or more particles at random, measuring the diameter, and taking the arithmetic mean.

For the measurement of the magnetic characteristics of the magnetic particles, a DC magnetization BH characteristic automatic recording device BHH-50 manufactured by Riken Denshi Co., Ltd. can be used. At this time, the diameter (inner diameter) is 6.5 m
m, magnetic particles in a cylindrical container with a height of 10 mm
The filling is carried out at about g weight, and the saturation magnetization is measured from the BH curve while keeping the particles from moving in the container.

As the magnetic particles, a resin carrier formed by dispersing magnetite as a magnetic material in a resin and dispersing carbon black for conductivity and resistance adjustment;
Alternatively, a material in which the surface of a single magnetite such as ferrite is oxidized and reduced to adjust the resistance, or a material in which the surface of a single magnetite such as ferrite is coated with a resin and the resistance is adjusted may be used.

B) Charging Bias With respect to the charging bias applied to the magnetic brush charger 20, the amplitude of the applied bias and the charging potential in the first cycle when a rectangular alternating voltage is applied at a frequency of 1000 Hz are shown in FIG.

By increasing the amplitude, the difference between the DC component of the applied bias and the charged potential in the first cycle becomes smaller. More specifically, assuming that the DC component of the bias applied to the charger 20 is Vdc and the surface potential of the charged photosensitive drum 1 at this time is Vs, the difference between them is ΔΔ.
When V = | Vdc-Vs | is approximately 40 V or less, the uniformity of charging is also improved.

Therefore, in this example, DC voltage; -700 V alternating voltage; rectangular amplitude Vpp 800 V frequency Vf 1
By applying a bias superimposed on 000 Hz to the charger 20, good charging properties could be obtained. c) Charge Injection Charging In the charge injection charging, charge is injected into the surface of a member to be charged (photosensitive drum) having a medium-resistance contact resistance by a medium-resistance contact charging member. Instead of injecting charge into the trapping potential, the charge is charged by charging the conductive particles (SnO ₂ ) 16 a of the charge injection layer 16, as shown in the equivalent circuit diagram of FIG. In addition, for a small capacitor in which the charge transport layer 15 is a dielectric, the aluminum drum base 11 and the conductive particles 16a in the charge injection layer 16 are both electrode plates,
This is considered to be based on the theory of charging the electric charge by the contact charging member 20.

At this time, the conductive particles 16a are electrically independent of each other and form a kind of minute float electrode. For this reason, macroscopically, the photosensitive drum surface appears to be charged and charged to a uniform potential, but in reality, SnO ₂ , a myriad of minutely charged conductive particles, covers the photosensitive drum surface. It is in such a situation. For this reason, even if the image exposure L is performed by the laser beam, each SnO ₂ particle 16a is electrically independent, and it is expected that the electrostatic latent image can be held.

(4) Laser Scanning Section 3 (FIG. 5) FIG. 5 shows a schematic configuration of the laser scanning section (laser scanner) 3. When laser scanning exposure L is performed on the surface 1 to be scanned (the surface of the rotating photosensitive drum) by the laser scanning unit 3, first, the solid-state laser element 32 blinks at a predetermined timing by the light emission signal generator 31 based on the input image signal. (ON / OFF). The laser light emitted from the solid-state laser element 32 is converted into a substantially parallel light beam by a collimator lens system 33, and is further scanned in the direction of the arrow by a rotating polygon mirror 34 rotating at high speed in the counterclockwise direction of the arrow, and fθ Lens group 35 (35a · 3
5b and 35c), an image is formed on the scanned surface 1 in a spot shape.

The scanning surface 1 is scanned by such laser beam scanning.
An exposure distribution for one scan of an image is formed. Further, if the scanned surface 1 is scrolled by a predetermined amount perpendicularly to the scanning direction for each scan, an image signal corresponding to the image signal is formed on the scanned surface 1. An exposure distribution is obtained.

(5) Developing Device 4 (FIG. 6) FIG. 6 shows a schematic configuration of the developing device 4. The developing device 4 of the present embodiment uses a mixture of non-magnetic toner particles and magnetic carrier particles as a developer, causes the developer to be held as a magnetic brush layer by a magnetic force on a developer carrying member, and This is a two-component magnetic brush contact development type apparatus that transports and contacts the surface of the photosensitive drum 1 to develop an electrostatic latent image as a toner image. The two-component magnetic brush contact developing device is very suitable for collecting residual toner on the photosensitive drum 1 in an image forming apparatus of a cleanerless system.

Reference numeral 41 denotes a developing container; 42, a developing sleeve as a developer carrier; 43, a magnet roller as a magnetic field generating means fixedly arranged in the developing sleeve 42;
44 is a developer layer thickness regulating blade for forming a thin layer of the developer on the surface of the developing sleeve, 45 is a developer stirring and conveying screw, 46 is a two-component developer housed in the developing container 41, and is a non-magnetic developer. Toner particles t and magnetic carrier particles c
Are mixed.

The developing sleeve 42 has a closest distance (gap) to the photosensitive drum 1 at least at the time of development.
The developer magnetic brush thin layer 46 a carried on the outer surface of the developing sleeve 42 is set to be in contact with the surface of the photosensitive drum 1. The contact nip m between the developer magnetic brush layer 46a and the photosensitive drum 1
Is a development area (developing part).

The developing sleeve 42 is driven around the fixedly disposed magnet roller 43 at a predetermined rotation speed in the counterclockwise direction as indicated by an arrow, and the developer 46 is applied to the outer surface of the sleeve in the developing container 41 by the magnetic force of the magnet roller 43. A magnetic brush is formed. The developer magnetic brush is sleeve 4
2 is conveyed together with the rotation of the roller 2, and is regulated by the blade 44 so as to be taken out of the developing container as a developer magnetic brush thin layer 46a having a predetermined thickness, conveyed to the developing section, and contacts the surface of the photosensitive drum 1 and continues. The rotation of the sleeve 42 returns the developer to the inside of the developing container 41 and is conveyed.

That is, first, the developer 46 pumped up by the N ₃ pole of the magnet roller 43 with the rotation of the developing sleeve 42 is transported from the S ₂ pole to the N ₁ pole in the process of being perpendicular to the developing sleeve 42. The thin layer 46 a of the developer 46 is formed on the developing sleeve 42 by being regulated by the regulating blade 44 disposed at the position. Developer layer 46a which is a thin layer formed brush is formed by the conveyed to the developing main pole S ₁ of the developing unit magnetic force. The electrostatic latent image on the photosensitive drum 1 is developed as a toner image by the developer layer 46a formed in a spike shape, and then the developer on the developing sleeve 42 is changed to a developing container 41 by a repulsive magnetic field of N ₃ pole and N ₂ pole.
Will be returned within.

A developing bias of a DC voltage (DC) and an alternating voltage (AC, AC voltage) is applied between the developing sleeve 42 and the conductive drum substrate of the photosensitive drum 1 by a developing bias applying power source S2.

In this example, DC voltage: -500 V alternating voltage; amplitude Vpp = 1500 V, frequency Vf = 20
A developing bias of 00 Hz is applied, and the toner t in the developer magnetic brush thin layer 46 a on the developing sleeve 42 side selectively adheres to the electrostatic latent image on the photosensitive drum 1 side in the developing section, so that the electrostatic latent image is It is developed as an image.

In general, in the two-component developing method, when an alternating voltage is applied, the developing efficiency is increased, and the quality of an image is high. On the contrary, there is a risk that fogging is likely to occur. For this reason, fog is generally prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1.

The potential difference for preventing fogging is called a fog removing potential (Vback). This potential difference prevents toner from adhering to a non-image area of the photosensitive drum 1 during development, and a transfer residue in a cleanerless system. We also collect toner.

The toner concentration (mixing ratio with the carrier) of the developer 46 in the developing container 41 gradually decreases as the toner is consumed for developing the electrostatic latent image. When the toner concentration of the developer 46 in the developing container 41 is detected by a detecting unit (not shown) and decreases to a predetermined allowable lower limit concentration, toner is supplied from the toner replenishing unit (not shown) to the developer 46 in the developing container and development is performed. The toner supply is controlled so that the toner concentration of the developer 46 in the container 41 is always kept within a predetermined allowable range.

The two-component developer 46 used in this example is composed of toner particles t; negatively charged toner having an average particle diameter of 6 μm and titanium oxide having an average particle diameter of 20 nm externally added by 1% by weight. Carrier c; saturation magnetization Is a mixture of 205 emu / cm ³ of magnetic carrier having an average particle diameter of 35 μm in a weight ratio of 6 to 94. At this time, the toner in the developer has a triboelectric charge amount of about 25 × 10 ⁻³ c / kg.
Met.

For the volume average particle diameter of the toner, for example, the one measured by the following measuring method is used.

As a measuring device, Coulter Counter T
Using an A-II type (manufactured by Coulter), an interface (manufactured by Nikkaki) for outputting a number average distribution and a volume average distribution and a CX-i personal computer (manufactured by Canon) are connected, and primary electrolyte is sodium chloride. 1% NaC
Adjust the aqueous solution.

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

The electrolytic solution in which the sample was suspended was subjected to dispersion treatment for about 1 to 3 minutes using an ultrasonic disperser, and the particle size distribution of particles of 2 to 40 μm was measured using the Coulter Counter TA-II with a 100 μm aperture. Is measured to determine the volume distribution. From these determined volume distributions, the volume average particle size of the sample is obtained.

(6) Transfer Device 6 The transfer device 6 (FIG. 1) is of the transfer belt type in this embodiment as described above. Reference numeral 6a denotes an endless transfer belt, which is suspended between a driving roller 6b and a driven roller 6c, and has a circumferential speed substantially equal to the circumferential speed of the photosensitive drum 1 in the forward direction of the photosensitive drum 1. It is turned. Reference numeral 6d denotes a transfer charging blade disposed inside the transfer belt 6a, which presses the ascending-side belt portion of the transfer belt 6a against the photosensitive drum 1 to form a transfer nip T, and transfers a transfer bias from a transfer bias applying power source S3 to the transfer bias. Is applied, 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 rotating drum 1 side is sequentially electrostatically transferred onto the surface of the transfer material P passing through the transfer portion T.

In this example, the belt 6a has a thickness of 75
A resin made of a μm polyimide resin was used.

The material of the belt 6a is not limited to polyimide resin, but may be polycarbonate resin,
Plastics such as polyethylene terephthalate resin, polyvinylidene fluoride resin, polyethylene naphthalate resin, polyetheretherketone resin, polyethersulfone resin, and polyurethane resin, and fluorine-based and silicon-based rubbers can be suitably used. The thickness is not limited to 75 μm, but is
000 μm, preferably 50 to 150 μm can be suitably used.

Further, as the transfer charging blade 6d, one having a resistance of 1 × 10 ⁵ to 1 × 10 ⁷ Ω, a plate thickness of 2 mm and a length of 306 mm was used. This transfer charging blade 6d
Was transferred by applying a bias of +15 μA under constant current control.

(7) Function of Electrode Member 27 Capturing and discharging (discharging) transfer residual toner of magnetic brush charger 20 Simultaneous development cleaning by developing device 4 a) As described above, toner for transfer material P as a recording medium Transfer residual toner remains on the surface of the photosensitive drum 1 after the image transfer, and in a cleanerless system image forming apparatus, the transfer residual toner is used as a contact charging member in this case. When the transfer residual toner passes through the position of the charger 20 as it is, a previous image ghost of the transfer residual toner occurs.

Even when the transfer residual toner passes through the contact portion between the photosensitive drum 1 and the magnetic brush charger 20, in most cases the shape of the previous image is maintained, and under the setting of the magnetic brush charger under appropriate charging conditions. Did not appear to be uniformly dispersed.

Therefore, the transfer residual toner that has reached the charging area N with the rotation of the photosensitive drum 1 is charged with the magnetic brush charger 2.
It is necessary to temporarily erase the history of the pre-capture image to 0. At this time, the DC voltage is applied to the magnetic brush charger 20.
, The transfer residual toner is not sufficiently taken into the charger 20. However, when the alternating voltage is applied to the magnetic brush charger 20, the vibration effect due to the electric field between the photosensitive drum 1 and the charger 20 causes Incorporation of the toner into the charger 20 is relatively easy.

However, there is a case where it is very difficult to take in the magnetic brush charger 20 depending on the charge amount of the transfer residual toner that has reached the charging area N. That is, as long as the transfer residual toner is charged, the potential difference between the magnetic brush charger 20 and the photosensitive drum 1 and the mirror force between the toner and the photosensitive drum greatly affect the toner take-up property of the magnetic brush charger 20. is there.

Here, it is ideal that the surface potential of the photosensitive drum 1 passing therethrough is equal to the applied voltage of the magnetic brush charger 20, but actually the contact portion of the magnetic brush charger 20 is also charged. Even if it has a width and is eventually charged to almost the same potential, a sufficient charge is not obtained in the initial stage of passage through the contact portion, and a potential difference between the charger 20 and the photosensitive drum 1 is generated there. . In the case of this example, since Vdc of the magnetic brush charger 20 is set to -700 V, the positively charged toner is easily taken in the direction of the magnetic brush in a region where the surface potential of the photosensitive drum is lower at the initial stage of the passage of the contact portion. The negatively charged toner is not taken in. Further, even if the amount of charge of the transfer residual toner is extremely large and the mirror power with the photosensitive drum is too large, the toner remains on the photosensitive drum.

Therefore, although the toner is originally a negatively chargeable toner,
It is desirable that the transfer residual toner is positively charged. However, even if the magnetic brush charger 20 is not positively charged, the effect of being forcibly scraped off by the magnetic brush charger 20 can be expected if the absolute value of the charge amount is sufficiently small.

In practice, the charge polarity of the transfer residual toner is often reversed due to the peeling discharge at the time of transfer, but even if the transfer efficiency is the same, the charge amount distribution of the transfer residual toner greatly differs depending on the transfer current. Further, if the developer is used for a long period of time, the developer itself deteriorates and the transfer efficiency decreases, so that the ratio of the toner remaining on the photosensitive drum while being negatively charged increases. Therefore, it is preferable to have a means for increasing the transfer current or charging the transfer residual toner to the opposite polarity.

B) Therefore, in this embodiment, the transfer device 6
(Transfer section) and magnetic brush charger 20 as a contact charging member
A metal plate 27 as an electrode member (conductive member) was disposed in non-contact proximity to the photosensitive drum 1 between the (charging portions), and a bias of +500 V was applied to the metal plate 27 by a bias applying power source S4. The distance between the metal plate 27 and the photosensitive drum 1 was 100 to 500 μm.

Since a positive bias is applied to the metal plate 27, the transfer residual toner carried from the transfer unit to the charging unit passes through the position of the metal plate 27, of the transfer residual toner. The transfer residual toner passes through, and the negative transfer residual toner is temporarily captured on the surface of the metal plate 27, is discharged, and is then sent out onto the photosensitive drum 1 again. At this time, even if a bias or the like for positively sending the photosensitive drum 1 is not applied, if the toner accumulates on the surface of the metal plate, the amount of the toner reaches the limit, and the toner is discharged one after another from the discharged toner. It is returned to drum 1.

That is, the metal plate 27 sets the average charge amount of the residual toner remaining on the surface of the photosensitive drum 1 (image carrier) after the transfer to be opposite to the charge polarity of the average charge amount of the toner during development. It functions as a means to make it more polar.

Therefore, the toner that enters the contact portion N between the magnetic brush charger 20 and the photosensitive drum 1 is limited to a toner having a polarity opposite to the charging polarity or a toner having a low charge amount after being discharged. It will be almost recovered. At this point, the history of the previous image is lost, and the direct cause of the ghost is removed.

C) If the transfer residual toner once collected in the magnetic brush charger 20 remains positively charged, the relationship between the potential difference between the magnetic brush charger 20 and the photosensitive drum 1 is as described above. Therefore, it is accumulated in the magnetic brush unit 23 without being discharged from the magnetic brush charger 20,
Although it depends on the resistance value of the toner and the like, if a predetermined amount or more of toner is mixed into the magnetic brush charger 20, the charging ability is reduced even when the alternating voltage is superimposed. Even if the toner is discharged onto the photosensitive drum 1 by the centrifugal force of the charger 20 or the like, the toner is not collected simultaneously with the developing device 4 in the non-image area unless the toner is of a regular negative charge, and the toner remains. I will.

That is, the untransferred toner is transferred to the magnetic brush charger 2
Once the toner has been taken in the toner, the toner is converted to a regular negatively charged toner, and a long-term stable cleanerless process is completed. This can be realized by setting a combination in which the frictional charging series of the toner and the magnetic brush carrier (magnetic particles) is closer to the negative polarity for the toner.

In this example, the magnetic brush charger 2 was used for the negative toner using polyester as the binder resin.
As the magnetic particles constituting the magnetic brush portion 23 of No. 0, those obtained by coating the surface of a single magnetite such as ferrite with a resin and adjusting the resistance were used.

D) The toner discharged from the magnetic brush charger 20 onto the photosensitive drum 1 is carried to the developing area m, and is simultaneously cleaned (collected) by the developing device 4.
Is done.

That is, since the toner discharged in a thin layer from the inside of the magnetic brush charger 20 onto the photosensitive drum 1 is charged to the normal charging polarity, the developing device 4 applies the DC voltage applied during development to the photosensitive drum 1. Recovery at the fog removal potential (Vback), which is the potential difference between the surface potentials, becomes possible. The toner discharged into a thin layer is advantageous in terms of recoverability during development.

From the inside of the magnetic brush charger 20, the photosensitive drum 1
The toner discharged above, that is, the transfer residual toner, is
Since the toner is collected 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.

E) As a result of performing the image output durability test in the above configuration, the magnetic brush charger 20 continuously collects and discharges the transfer residual toner for 100,000 sheets for a long period of time. There is no decrease in the charging ability due to excessive toner contamination of the charger 20 and no decrease in the charging ability when the transfer residual toner passes, and the previous image trace of the transfer residual toner is also erased, and a high-quality image free of a ghost phenomenon. Output was kept stable.

F) That is, according to the present invention, the average charge amount of the residual toner remaining on the image carrier after the transfer of the toner image from the image carrier (photosensitive drum) 1 to the recording medium P before reaching the charging means 2 Is the opposite of the charging polarity of the bias applied to the charging means from the average charging amount of the toner at the time of development, and the average charging amount of the residual toner adhered or mixed into the contact charging member 20 is the image bearing capacity after transfer. It is characterized in that the residual toner remaining on the body is on the charging polarity side of the average charging amount before reaching the charging means.

More specifically, before the transfer residual toner enters the contact point between the contact charging member 20 and the image carrier 1, the average charge amount of the transfer residual toner is larger than the average charge amount after development. Wherein the average charge amount of the toner collected by the contact charging member 20 is higher on the charging polarity side than the average charge amount of the transfer residual toner before reaching the contact charging member. It is.

As a mechanism for controlling the charge amount of the transfer residual toner before reaching the contact charging member, a conductive member (electrode member) to which a bias having a polarity opposite to the charging polarity is applied. Is more opposite to the charging polarity than the toner.

Here, in this example,. Average charge amount of transfer residual toner before reaching transfer means 2. Average charge amount of toner during development. Each measurement of the average charge amount of the transfer residual toner adhered or mixed into the contact charging member 20 is performed by using an Espart analyzer (trade name) of Hosokawa Micron Corporation, and blowing the toner with nitrogen gas to measure the measurement unit ( The measurement was performed by introducing the sample into the measurement cell) through the sampling hole.

In this measuring device, sample particles are introduced into a detecting section (measuring section) in which an electric field and an acoustic field are simultaneously formed, and the moving speed of the particles is measured by a laser Doppler method to measure the particle diameter and the charge amount. The sample particles that enter the measuring section are affected by the acoustic and electric fields, fall while deviating in the horizontal direction, and the beat frequency of this horizontal velocity is counted.The count value is sent to the computer. The data is input by interruption, and is displayed on a computer screen in real time as a particle size distribution or a charge amount distribution per unit particle size. When a predetermined number is measured, the screen stops, and thereafter, a three-dimensional distribution of the charge amount and the particle size, a charge amount distribution for each particle size, an average charge amount (coulomb / weight), and the like can be displayed.
By introducing the toner as sample particles into the measuring section of the apparatus, the charge amount of the toner can be measured, and the relationship between the particle size and the charge amount can be evaluated from the charge performance of the toner.

The measurement principle of this measuring apparatus, that is, the simultaneous measurement of the particle size and the charge amount by the laser Doppler method is described in, for example,
It is described in detail in Journal of the Society of Powder Technology, Vol. 31, No. 3 (1994).

<Embodiment 2> (FIG. 7) In this embodiment, the charging device 2 for charging the photosensitive drum 1 in the image forming apparatus (printer) of Embodiment 1 described above.
As a contact charging type fur brush charging device. Since there is no change in the configuration of the other image forming apparatuses, the description will not be repeated.

In FIG. 7, reference numeral 20A denotes a fur brush charger as a contact charging member disposed in contact with the photosensitive drum 1. Reference numeral 24 denotes a core bar having an outer diameter of 10 mm, and reference numeral 25 denotes a fur brush portion planted on the core bar. The fur brush portion 25 is formed by implanting conductive fibers having a bristle length of 3 mm and a resistance value of 1 × 10 ⁶ Ω at a density of 100,000 fibers / inch ² .

The fur brush charger 20A is disposed substantially in parallel with the photosensitive drum 1 with the fur brush portion 25 in contact with the surface of the photosensitive drum 1. In this case, the fur brush charger 20A is set so that the contact nip width (charging area) N of the fur brush portion 25 formed with respect to the photosensitive drum 1 is about 7
mm.

In the charging area N, the core metal 24 of the fur brush charger 20A is rotated clockwise by an arrow opposite to the rotation direction of the photosensitive drum 1 (counter direction) with respect to the rotational peripheral speed of the photosensitive drum 1 at 100 mm / sec. 200mm
/ Sec.

A predetermined charging bias was applied to the metal core 24 from the charging bias applying power source S1.

As the core 24 rotates, the fur brush 2
5 rotate in the same direction to rotate the photosensitive drum 1 in the charging area N.
The surface is rubbed, and charges are given to the photosensitive drum 1 from the conductive fibers constituting the fur brush portion 25, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential. In the case of this example, the photosensitive drum 1 is provided with the charge injection layer 16 on the surface thereof.
Is performed.

The contact charging member is a fur brush charger 20A
In the case of (1), the fur brush charger was excessively contaminated due to the mixing and accumulation of toner, so that the charging performance was reduced, causing non-uniform charging and causing a defective image.

In this embodiment, a brush member 28 made of rayon made of conductive fiber and having a bristle length of 6 mm as an electrode member (conductive member) is provided between the transfer device 6 and the fur brush charger 20A. It was arranged in contact with. The contact nip width between the brush member 28 and the photosensitive drum 1 is 7 mm.
Met.

The rayon brush member 28 is supplied from the bias applying power source S4 with a voltage of plus 5 having a polarity opposite to the charging polarity.
A DC voltage of 00 V was applied.

Since a positive bias is applied to the rayon brush member 28, the negative transfer residual toner on the surface of the rotating photosensitive drum 1 after the transfer reaches the fur brush charger 20A before the transfer. Temporarily this brush member 2
After being captured by the brush No. 8 and being neutralized, it is sent out onto the photosensitive drum 1 again.

Therefore, the toner entering the contact portion N between the fur brush charger 20A and the photosensitive drum 1 is only the plus toner or the negatively charged toner having a low charge amount, and is collected by the fur brush charger 20A. It is easy to be.

The toner collected in the fur brush charger 20A again takes a negative charge due to the contact friction with the fur brush, and is uniformly discharged onto the photosensitive drum 1.

The toner uniformly discharged from the fur brush charger 20A onto the photosensitive drum 1 is simultaneously cleaned (collected) by the developing device 4 in the developing area m.

In the above-described configuration, as a result of performing the image output durability test, the fur brush charger 20A continuously collects and discharges the transfer residual toner over a long period of 100,000 sheets. There is no reduction in charging ability due to excessive toner contamination and no reduction in charging ability when passing residual toner, and the previous image trace of residual toner is also erased. Maintained stable.

<Embodiment 3> In Embodiments 1 and 2, the toner generated by the pulverization method is used as the toner particles t of the developer 46 (t + c) of the developing device 4, but in this embodiment, Average particle size 6 produced by suspension polymerization
A 1% weight ratio of titanium oxide having an average particle diameter of 20 nm was externally added to a μm spherical toner.

The magnetic carrier c has a saturation magnetization of 2
A magnetic carrier having an average particle size of 35 μm of 05 emu / cm ³ was used.

A mixture of the toner t and the carrier c at a weight ratio of 7:93 was used as the developer 46.

Since the toner produced by the polymerization method has a nearly spherical shape, the external additive is uniformly coated. For this reason,
The releasability from the photosensitive drum 1 is extremely good. For example, when the transfer efficiency (toner amount per unit area transferred onto paper / toner amount per unit area on the photosensitive drum) of the above-mentioned ground toner and polymerized toner is compared, the ground toner is 90%. On the other hand, when the polymerized toner was used, the efficiency was as high as 97%.

The fogging is also better than that of the pulverized toner, and when the polymerized toner is used, V _back =
Even at 50 V, fogging could be prevented.

In this example, in addition to the fact that the amount of the transfer residual toner is extremely small, and because of the high releasability, there is no cleaner, and when the transfer residual toner is collected during development,
The recoverability is further increased, and no image defects occur.

It is considered that the toner having the charge of the normal charge polarity is almost completely transferred due to the high transfer efficiency, and the transfer residual toner is almost completely charged to the opposite polarity. The magnetic brush charger 20 and the fur brush charger 20A, which are contact charging members, are also significantly advantageous in recoverability.

Further, since the mixed toner has good releasability from the magnetic brush portion magnetic particles and the fur brush conductive fiber,
Discharge of toner from the charger 20 or 20A is also performed better than in the case of pulverized toner.

In the above configuration, an image endurance test was performed. As a result, the magnetic brush charger 20 or the fur brush charger 20A continued to collect and discharge the transfer residual toner successively for 100,000 sheets for a long period of time. There is no decrease in charging ability due to excessive toner contamination of the charger 20 or 20A, and no decrease in charging ability when passing the transfer residual toner. Also, the previous image trace of the transfer residual toner is erased, and there is no ghost phenomenon.
High quality image output was maintained stably.

<Others> 1) The configuration of the present invention is not limited to the above-described first, second, and third embodiments. In an image forming apparatus in which the developing device 4 also serves as a cleaner, for example, the contact charging member is ,
It may be a charging roller using conductive rubber or conductive sponge, a magnetic brush charger 20, a fur brush charger 20A or a non-rotating charger, and is applicable to all contact-type charging devices. it can.

2) The photosensitive member 1 as an image carrier also has a low resistance layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm so that charge injection charging can be realized and ozone generation can be prevented. Although desirable from the point of view, other organic photoreceptors and the like can provide a sufficient effect for preventing contamination of the charger. That is, the contact charging of the image carrier 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) In the first, second and third embodiments, only the two-component developing method has been described as the developing device 4, but other developing methods are also effective. 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 the polymerized toner is used as the toner particles in the developer as in Embodiment 3, the above-mentioned 1
A sufficient recovery effect can be obtained by other developing methods such as one-component non-contact development and two-component non-contact development as well as the two-component contact development and the two-component contact development.

4) The charging bias applied to the charger may be only a DC voltage.

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

6) 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 is a general analog type. Other light-emitting elements such as an image exposure or LED may be used, and any device that can form an electrostatic latent image corresponding to image information, such as a combination of a light-emitting device such as a fluorescent lamp and a liquid crystal shutter, may be used.

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.

7) The recording medium that receives the transfer of the toner image from the image carrier may be an intermediate transfer member such as a transfer drum.

[0163]

As described above, according to the present invention, as the charging means for uniformly charging the image carrier to a predetermined polarity and potential, a contact charging member applying a voltage to the image carrier is brought into contact. The image forming apparatus of a so-called cleaner-less system, which uses a contact charging unit that performs the cleaning operation, and also serves as a cleaning unit that collects residual toner particles remaining on the image carrier after the developing unit transfers the toner image to the recording medium. That is, the contact charging member is effectively prevented from being contaminated by the contact charging member, elimination of a trace of the previous image of the transfer residual toner, and prevention of a reduction in the charging ability of the transfer residual toner when passing through the charging means. No decrease in charging ability due to excessive toner contamination and no decrease in charging ability when passing residual toner, no trace of the previous image of the residual toner is erased, and there is no ghost phenomenon. The output of the image is maintained stably for a long term.

[Brief description of the drawings]

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

2A is a schematic diagram of a layer structure of a photosensitive drum as an image carrier, and FIG. 2B is an equivalent circuit diagram of a photosensitive drum having a charge injection layer and a magnetic brush charger as a contact charging member (charge injection charging). Illustration of

FIG. 3 is a schematic configuration diagram of a magnetic brush charging device.

FIG. 4 is a graph showing the amplitude of the applied bias and the charging potential in the first cycle when a rectangular alternating voltage is applied at a frequency of 1000 Hz with respect to the applied charging bias to the magnetic brush charger;

FIG. 5 is a schematic configuration diagram of a laser scanning unit (laser scanner).

FIG. 6 is a schematic configuration diagram of a developing device.

FIG. 7 is a schematic configuration diagram of a main part (a fur brush charging device part) of an image forming apparatus according to a second embodiment.

FIG. 8 is a schematic diagram illustrating an example of a transfer type electrophotographic apparatus as a conventional example of an image forming apparatus.

[Explanation of symbols]

 Reference Signs List A Printer section B Image reading device (image scanner) 1 Image carrier (photosensitive drum) 2 Contact charging device 20 Magnetic brush charger as contact charging member 20A Fur brush charger as contact charging member 27/28 Electrode member (conductive) 3) Laser scanning unit (laser scanner) 4 Developing device 5 Paper cassette 6 Transfer device 7 Transport device 8 Fixing device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/08-15/095 G03G 15/02-15/02 103 G03G 21/10

Claims (9)

(57) [Claims] An image bearing member; a contact charging means for contacting a contact charging member to which a voltage is applied to the image bearing member to uniformly charge the image bearing member to a predetermined polarity and potential; Image information writing means for forming an electrostatic latent image on the charged surface of the
Developing means for developing the electrostatic latent image as a toner image with toner particles, and transfer means for transferring the toner image to a recording medium, wherein the developing means transfers the toner image to the recording medium, and then an image carrier In the image forming apparatus in which the image carrier is repeatedly used for image formation, the contact charging member temporarily captures the remaining toner particles.
In both cases, the average charge amount of residual toner remaining on the image carrier after transfer
Is opposite to the average charge amount of the toner during development.
Toward the polarity, capture remaining toner particles by contact charging member
The average charge amount of the residual toner remaining on the image bearing member after the transfer of the toner image from the image bearing member to the recording medium before reaching the charging means is determined by The average charge amount of the residual toner adhered to or mixed with the contact charging member is the opposite of the charge polarity of the bias applied to the charging unit than the average charge amount, and the residual toner remaining on the image carrier after transfer is An image forming apparatus characterized in that it is on the charging polarity side of the average charge amount before reaching the charging means. 2. The image forming apparatus according to claim 1 , wherein the conductive member is provided near the image carrier. 3. An image forming apparatus according to claim 2 , wherein a bias having a polarity opposite to a charging polarity is applied to said conductive member. 4. An image forming apparatus according to claim 2 or 3, characterized in that said conductive member is a said image bearing member and a non-contact. 5. The method according to claim 1, wherein the frictional charging series of the toner is on the charging polarity side with respect to the contact charging member.
5. The image forming apparatus according to any one of 4 . Wherein said contact charging member has a magnetic brush portion of the magnetic particles are magnetically bound, characterized in that said magnetic brush portion is a magnetic brush contact charging member in contact with the image bearing member according Item 6. The image forming apparatus according to any one of Items 1 to 5 . 7. The contact charging member according to claim 1, wherein said contact charging member has a fur brush portion made of conductive fibers, and is a fur brush contact charging member in which said fur brush portion is brought into contact with an image carrier. 5. The image forming apparatus according to any one of 5 . 8. The image forming apparatus according to any one of claims 1 to 7, wherein said image bearing member is a photosensitive member to be charge injection charging a charge injection layer on the surface. 9. The image according to the image information writing means for forming an electrostatic latent image on the charged surface of the image bearing member is any one of claims 1 to 8, characterized in that an image exposure means Forming equipment.