JP2000029282A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make output of an excellent image quality possible to be stably maintained over a long period by preventing deterioration of a contact charging member and the image defect as a result of the wear on the image carrier surface layer, with regard to an image forming device adopting a contact charging device. SOLUTION: In this image forming device capable of performing the image formation by an image formation processing means incorporating a charging means 2 charging the image carrier by holding a voltage applied charging member 20 in contact with the image carrier 1, the device is provided with means 24 to 26 for detecting the electric current value made to flow to the contact member for respectively charging the image exposed part and the unexposed part, and the means 26 to 28 and S1 for changing the voltage value applied to the contact charging member 20, in accordance with a detecting signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which an image is formed by an image forming process means including a charging means for charging an image carrier by applying a voltage to the image carrier. About.

[0002]

2. Description of the Related Art FIG. 14 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 rotated at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow.

[0004] In the course of rotation of the photosensitive drum 101, the entire surface of the photosensitive drum 101 is subjected to pre-exposure by an pre-exposure device (eraser lamp) 102, and the electrical memory remaining in the previous image forming process is erased. Table 103
And then uniformly charged with a predetermined polarity and potential, and then image exposure means (not shown)
Upon receiving image exposure L by a laser beam scanning exposure unit, the uniformly charged surface is selectively neutralized (or attenuated in potential) corresponding to the exposed image pattern, thereby forming an electrostatic latent image. Then, the formed electrostatic latent image is developed as a toner image by a toner developing device 104 as a developing unit.

On the other hand, a transfer material (transfer paper) P as a recording medium is fed between a photosensitive drum 101 and a transfer corona charger 105 as 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 106.
Thus, the toner image is electrostatically separated from the surface of the rotating photosensitive drum 101, is introduced into a fixing device (not shown), undergoes a fixing process of a toner image, and is 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 device (cleaner) 107.
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.

For example, as the charging means 103, a corona charger has been widely used conventionally. 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-type charging device has been put into practical use because it has advantages such as low ozone and low power as compared with the non-contact type corona charger. In this method, a contact charging member to which a voltage is applied is brought into contact with a photosensitive drum as a member to be charged, and the surface of the photosensitive drum is charged to a predetermined polarity and potential.

As the contact charging member, a magnetic brush contact charging member having a magnetic brush portion in which magnetic particles are magnetically constrained, and the magnetic brush portion is brought into contact with the photosensitive drum is preferably used from the viewpoint of charging contact stability. ing.

The magnetic brush contact charging member is formed by magnetically constraining conductive magnetic particles directly on a magnet or on a sleeve containing a magnet to form a magnetic brush portion. Then, the magnetic brush unit 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 provided with conductive fibers in the form of a brush (fur brush member contact charging member) or a conductive rubber roller (charging roller) formed of conductive rubber in a roll shape is also preferably used as the contact charging member. ing.

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 a member 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.

In recent years, such image forming apparatuses have been miniaturized. However, 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.

As described above, the photosensitive drum 101 after the transfer
The upper transfer residual toner is collected by the cleaner 107 to become waste toner, but it is preferable that this waste toner does not come out from the viewpoint of environmental protection. Therefore, the above cleaner 1
07, the transfer residual toner on the photosensitive drum 101 is removed from the photosensitive drum 101 by “developing simultaneous cleaning” by the developing device 104, and is collected by the developing device 104.
An image forming apparatus of a “cleanerless system” having an apparatus configuration for reuse has also appeared.

Simultaneous development cleaning refers to a fog removal bias (a potential difference between the DC voltage applied to the developing device and the 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 104 and used in the subsequent process, 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.

[0019]

One of the problems in the contact charging device is that the contact charging member in contact with the member to be charged picks up dirt and foreign matter on the surface of the member to be charged and becomes contaminated by the accumulation thereof. If the contact member is easily contaminated (deterioration of the contact charging member) and becomes in an unacceptable contaminated state, the member to be charged cannot be charged to a desired potential or uneven charging occurs, resulting in a decrease in charging ability.

In an image forming apparatus using a contact charging device as a charging means for an image carrier such as a photoreceptor, an image forming apparatus having a dedicated cleaner for removing transfer residual toner on the image carrier after transfer. Even so, while the image formation is repeated, toner particles and so-called external additives such as silica contained in the developer, which somewhat pass through the cleaner, may cause the contact charging member to move due to the continuous movement of the image carrier. The contact charging member is likely to be contaminated because it is carried to the position and adheres to and mixes with the contact charging member to accumulate.

Normally, the electrical resistance of toner particles and silica is relatively high, so if such toner particles or silica adheres to or mixes with the contact charging member and becomes in an unacceptable contaminated state, the contact charging member as a whole may be damaged. Alternatively, a part of the resistance increases, so that the image carrier cannot be charged to a desired potential, or charging unevenness occurs, resulting in an image defect.

The toner contamination of such a contact charging member,
The occurrence of image defects due to the above-mentioned problem is caused by the above-described “cleanerless method” which uses a contact charging means as a charging means for the photoconductor and does not have a dedicated cleaner for removing transfer residual toner on the image carrier after transfer. This is particularly noticeable in the image forming apparatus of the “system”.

That is, in the case of the image forming apparatus of the cleanerless system, the untransferred toner on the image carrier after the transfer is carried to the position of the contact charging member by the continuous movement of the image carrier, so that the contact charging member is moved. This is because the contact charging member is quickly and excessively contaminated with toner.

Further, in the image forming apparatus of the cleanerless system, when the contact charging member is a first contact charging member in order to improve the recoverability of the untransferred toner in the developing device, the first contact charging member is used. Also, when a second contact charging member as an auxiliary member is disposed in contact with the image carrier on the upstream side in the image carrier moving direction (between the transfer section and the first contact charging member), the first and the second contact charging members are provided. Contamination of both of the contact charging member 2 reduces the recoverability of the transfer residual toner in the developing device,
An image defect occurs.

In some cases, an external additive such as silica contained in the developer acts as a so-called polishing agent to scrape the surface of the photoreceptor. In particular, when a charge injection layer in which conductive fine particles are dispersed on the surface of the photoreceptor is used, there are problems such as a change in the amount of light transmitted through the charge injection layer, a change in an exposed portion potential, and a change in density.

Accordingly, the present invention provides an image forming apparatus using a contact charging device, which prevents image deterioration due to deterioration of the contact charging member and scraping of the surface layer of the image carrier, and stably outputs a good quality image for a long period of time. The purpose is to maintain.

[0027]

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

(1) An image exposing unit in an image forming apparatus in which an image is formed by an image forming process unit including a charging unit for charging the image carrier by bringing a charging member to which a voltage is applied into contact with the image carrier. And means for detecting a current value flowing through the contact charging member when charging each of the unexposed portions, and means for changing a voltage value applied to the contact charging member in accordance with the detection signal. An image forming apparatus comprising:

(2) Charging means for charging the image carrier by bringing a charging member, to which a voltage is applied, into contact with the image carrier, and an electrostatic latent image corresponding to target image information on a charged surface of the image carrier. The image is formed by image forming means including image information writing means for forming an image and developing means for developing the electrostatic latent image with a developer. Forming equipment.

(3) Charging means for charging the image carrier by bringing a charging member, to which a voltage is applied, into contact with the image carrier, and an electrostatic latent image corresponding to target image information on a charged surface of the image carrier. Image formation is performed by image forming means including image information writing means for forming an image, developing means for developing the electrostatic latent image with a developer, and transfer means for transferring the developer image to a recording medium. (1) wherein the developing unit also serves as a unit for collecting a transfer residual developer remaining on the image carrier after the developer image is transferred to a recording medium by the transfer unit. Image forming apparatus.

(4) Charging means for charging the image carrier by bringing a charging member to which a voltage is applied into contact with the image carrier, and an electrostatic latent image corresponding to target image information on a charged surface of the image carrier. Image formation is performed by image forming means including image information writing means for forming an image, developing means for developing the electrostatic latent image with a developer, and transfer means for transferring the developer image to a recording medium. In the image forming apparatus, the developing unit also serves as a unit for collecting a transfer residual developer remaining on the image carrier after transferring the developer image to the recording medium by the transfer unit. When a first contact charging member is used, a second contact charging member brought into contact with the image carrier between the transfer unit and the first contact charging member, and the first contact charging member and the second contact charging member Means for detecting a current value flowing through each of the members; A current value flowing through the contact charging member when at least one of the first and second contact charging members charges the image-exposed portion and the unexposed portion is detected, and contact charging is performed in accordance with the detection signal. An image forming apparatus comprising means for changing a voltage value applied to a member.

(5) The detection signal of the current value flowing through the first contact charging member is corrected using the current value detection signal flowing through the second contact charging member, and the first signal is corrected according to the corrected value. The image forming apparatus according to (4), further comprising means for changing a voltage value applied to the contact charging member.

(6) The image forming method according to (4) or (5), wherein the voltage applied to the second contact charging member is opposite in polarity to the voltage applied to the first contact charging member. apparatus.

(7) The surface layer resistance of the image carrier is 10 ⁹ to 1
0 ¹⁴ Ω · cm (1) to (6)
The image forming apparatus according to any one of the above.

(8) The image information writing means for forming an electrostatic latent image corresponding to the target image information on the charged surface of the image carrier is an image exposure means (2) to (7). The image forming apparatus according to any one of the above.

(9) 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 contacts an image carrier. The image forming apparatus according to any one of 1) to 8).

(10) 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 (8).

<Operation> In the present invention, the difference between the potential of the exposed portion and the charged potential (so-called latent image contrast) is assured and controlled, and the change in the current value of the bias voltage applied to the contact charging member is detected. Thus, the resistance value accompanying the deterioration of the contact charging member is obtained, and the bias value applied to the contact charging member is changed so that the potential of the image carrier becomes a desired value. This makes it possible to prevent image defects due to the shaving of the carrier surface layer and to stably maintain good image quality output for a long period of time.

According to the present invention, a change in the current value with respect to the DC bias voltage applied to the contact charging member is detected using the image carrier for injection charging without providing the charge removing means for the image carrier, and a certain reference value is obtained. By changing the DC bias voltage so as to maintain the image quality, it is possible to prevent poor charging of the image carrier, uneven charging and image defects due to scraping of the surface layer of the image carrier, and maintain a stable output of a good quality image for a long time. It became possible to make it.

Further, even if an auxiliary member (second contact charging member) is used to improve the recoverability of transfer residual toner in an image forming apparatus of a cleanerless system utilizing simultaneous development and cleaning, the auxiliary member is deteriorated. To correct the influence on the contact charging member current value, prevent the exposure section potential fluctuation due to the shaving of the image carrier surface layer, prevent poor charging and uneven charging of the image carrier, and output good quality images. It has become possible to maintain stability for a long time.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (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 using a transfer type electrophotographic process and a cleanerless system.

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

A) Image reading device B In the image reading device B, reference numeral 31 denotes an original platen glass fixedly arranged on the upper surface of the apparatus, and is placed on the upper surface of the original platen glass with the original G to be copied facing downward. Then, a document pressure plate (not shown) is placed over the document and set.

Reference numeral 32 denotes an image reading unit provided with a document irradiation lamp 32a, a short focus lens array 32b, a CCD sensor 32c, and the like. When a copy button (not shown) is pressed, the unit 32 opens the platen glass 3.
1 is moved forward from the home position indicated by the solid line on the left side of the glass to the right side along the lower surface of the glass, and is driven backward when the predetermined forward end point is reached, and the first home position indicated by the solid line Is returned to.

In the forward drive of the unit 32,
The downward image surface of the set original G on the original platen glass 31 is sequentially illuminated and scanned from the left side to the right side by the original irradiation lamp 32a of the unit 32, and the original surface reflected light of the illumination scanning light is a short focal length lens. An image is incident on the CCD sensor 32c by the array 32b.

The CCD sensor 32c includes a light receiving section, a transfer section,
It consists of an output unit. 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 thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to the printer A.

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 has a negatively charged O
It is a PC photoreceptor. This photoreceptor 1 will be described later (2)
The details will be described in the section. The photosensitive drum 1 has a predetermined peripheral speed in the counterclockwise direction indicated by an arrow around the center support shaft, and a rotation speed of 100 m in this example.
In this case, the charging means 2 receives a uniform charging process of negative polarity in the case of the present embodiment.

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 in accordance with 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 includes a light emission signal generator, a solid laser element, a collimator lens system, a rotating polygon mirror (polygon mirror), and the like.

When the laser scanning unit 3 performs laser scanning exposure L on the surface of the rotating photosensitive drum, first, the solid-state laser element blinks (ON / OFF) at a predetermined timing by a light emission signal generator based on the input image signal. Let it. The laser light emitted from the solid-state laser element is converted into a substantially parallel light beam by a collimator lens system, and further scanned in the direction of the arrow by a rotating polygonal mirror that rotates at a high speed in the counterclockwise direction of the arrow, and by the fθ lens group. An image is formed on the photosensitive drum surface 1 in a spot shape. By such laser light scanning, an exposure distribution for one scan of an image is formed on the photosensitive drum surface 1, and the rotation of the photosensitive drum 1 causes the photosensitive drum surface to scroll by a predetermined amount perpendicular to the scanning direction for each scan. Thus, an exposure distribution according to the image signal is obtained on the rotating photosensitive drum surface.

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 the case of the present embodiment, and is reversely developed. 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 section (4).

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 surface 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 a transfer charging blade 6 d disposed inside the transfer belt 6. This transfer device 6 will be described later in detail in (5).

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 conveying device 7, where the toner image is thermally fixed and copied. Or output as a print.

The transfer residual toner on the photosensitive drum 1 is carried to the developing unit via the charging unit with the subsequent rotation of the photosensitive drum, and is removed, collected, and reused from the photosensitive drum 1 by simultaneous cleaning with the developing unit 4. Is done.

Reference numeral 10 denotes a fur brush as an auxiliary member provided upstream of the charging means 2 in the rotation direction of the photosensitive drum in order to improve the recoverability of the transfer residual toner to the developing device 4. This will be described in detail in (6) below.

(2) Photosensitive Drum 1 (FIG. 2) As the photosensitive drum (photosensitive body) 1 as an image carrier, a commonly used organic photosensitive body or the like can be used.
Use of an organic photoreceptor having a surface layer having a material having a resistance of 10 ⁹ to 10 ¹⁴ Ω · cm can realize charge injection charging, which is effective in preventing ozone generation and reducing power consumption. . Further, the chargeability can be improved.

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

The first layer 12 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 functions to prevent 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.

The fourth layer 15 is 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 SnO ₂ ultrafine 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 thus prepared 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.

The surface resistance is 10 ¹³ Ω · cm. By controlling the surface resistance in this manner, the chargeability is directly improved and a high-quality image can be obtained. Photoreceptor is O
It can be realized not only with a PC but also with an a-Si drum, and further high durability can be realized.

Here, the volume resistance of the surface layer was measured by arranging metal electrodes at intervals of 200 μm, flowing a preparation liquid for the surface layer between the electrodes to form a film, and applying a voltage of 100 V between the electrodes. Value. The measurement is a value measured under the conditions of a temperature of 23 ° C. and a humidity of 50% RH. (3) Charging Device 2 (FIG. 3) The charging device 2 in this example 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 in parallel with 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 such that the contact nip width (charging area) n of the magnetic brush portion 23 formed on the photosensitive drum 1 was about 5 mm.

The charging magnetic particles constituting the magnetic brush portion 23 have an average particle size of 10 to 100 μm, a saturation magnetization of 20 to 250 emu / cm ³ , and a resistance of 1 × 10 ² to 1 × 10 ^2.
It is preferably ¹⁰ Ω · cm. Considering that the photosensitive drum 1 has an insulation defect such as a pinhole, it is preferable to use a photosensitive drum having a resistance of 1 × 10 ⁶ Ω · cm or more. In order to improve the charging performance, it is better to use a material having as small a resistance as possible.
5 μm, saturation magnetization 200 emu / cm ³ , resistance 5 × 10 ⁶ Ω
Cm magnetic particles were used.

The resistance value of the magnetic particles has a bottom area of 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 diameter of the magnetic particles is represented by the maximum chord length in the horizontal direction, and the measurement was performed by microscopically selecting 300 or more particles at random, measuring the diameter, and taking the arithmetic average.

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. In the present embodiment, a ferrite surface whose resistance has been adjusted by oxidizing and reducing is used.

Non-magnetic sleeve 2 of magnetic brush charger 20
Reference numeral 2 denotes a counterclockwise direction of an arrow (counter direction) opposite to the rotation direction of the photosensitive drum 1 in the charging area n, which is 15 with respect to the rotational peripheral speed of the photosensitive drum 1 of 100 mm / sec.
It was rotated at 0 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.

Reference numerals 24 to 28 denote a bias control which detects a current value flowing through the magnetic brush charger 20 as a contact charging member and changes a voltage value applied to the magnetic brush charger 20 according to the detection signal. System. This will be described in detail in section (6).

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

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.

FIG. 4 shows a schematic configuration of the developing device 4 used in this embodiment. 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 The electrostatic latent image is developed as a toner image by being transported and brought into contact with the surface of the photosensitive drum 1 2
It is a component magnetic brush contact development type device.

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 disposed 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) of about 5 to the photosensitive drum 1 at least during 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 the 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 again.

That is, first, the developer 46 pumped 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 a process of being conveyed vertically 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: -400 V alternating voltage; amplitude Vpp = 1500 V, frequency Vf = 30
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 increases, and the quality of the image becomes high. On the contrary, there is a risk that fogging is liable 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 referred to as fogging potential (Vback). This potential difference prevents toner from adhering to a non-image area of the photosensitive drum 1 during development. 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 detection unit (not shown) and decreases to a predetermined allowable lower limit concentration, the toner t is supplied from the toner replenishing unit 47 to the developer 46 in the developing container to perform development. 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.

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

(5) 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, polyether ether ketone resin, polyether sulfone 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.

(6) Applied bias control for contact charging member a) FIG. 5 shows a contact charging member (contact charger) in this embodiment.
Is a charged object when the weight ratio of the toner mixed into the magnetic brush portion 23 to the weight of the magnetic carrier (magnetic particles) constituting the magnetic brush portion 23 of the magnetic brush charger 20 is changed. The charged potential of the photosensitive drum 1 is represented by a broken line,
The DC current flowing through the magnetic brush charger 20 is shown by a solid line.

From this, it can be seen that the charging potential and the current value change with a correlation according to the weight ratio of the mixed toner.

However, this measurement was performed during the rotation of the photosensitive drum 1 when -550 V was applied to the magnetic brush charger 20 as the contact charger after the photosensitive drum 1 as the member to be charged was set to substantially zero potential. It is what went. To set the photosensitive drum 1 to substantially zero potential, the sleeve 22 of the magnetic brush charger 20 was rotated, the DC bias value was set to 0 V, and the photosensitive drum 1 was rotated. This is because a charging potential substantially equal to the DC bias value applied to the contact charger, which is a feature of the injection charging, is obtained on the surface of the member to be charged, and the contact charger has a charge removing ability. Therefore, in this example, a new charge removing means is not necessarily required. To stabilize the charging potential, the DC bias applied to the contact charger is preferably a constant voltage power supply.

In FIG. 6, after the photosensitive drum 1 is set to substantially zero potential,
The graph shows the charging potential of one rotation of the photosensitive drum 1 when a current of −17 μA flows through the magnetic brush charger 20. Accordingly, the charging potential is constant irrespective of the weight ratio of the toner mixed in the magnetic brush portion 23 to the weight of the magnetic carrier constituting the magnetic brush portion 23 of the magnetic brush charger 20. I understand.

Therefore, in this embodiment, for example, prior to image formation, the photosensitive drum 1 and the sleeve 2 of the magnetic brush charger 20 are used.
3 is rotated, and 0 V is applied to the magnetic brush charger 20 to make the surface potential of the photosensitive drum 1 substantially 0 V.

Next, for a place where the photosensitive drum 1 is at 0 V, for example, -500 V, -600 V,
A plurality of different DC biases are applied, the DC current value is detected by the ammeter 24 (FIG. 3), and is taken into the CPU 26 via the A / D converter 25.

The CPU 26 calculates and determines a DC bias value to be applied to the magnetic brush charger 20 so that a reference current value flows so as to obtain a desired charging potential according to the sensed detected DC current value. The driver 28 of the power supply S1 is controlled via the D / A converter 27 so that the computed and determined DC bias is applied from the charging bias application power supply S1 to the magnetic brush charger 20.

As a result, even if the magnetic brush portion 23 of the magnetic brush charger 20 as a contact charger becomes contaminated due to the adhesion, mixing and accumulation of toner and the like, and the charging property is reduced, the magnetic brush charger 20 is not affected. By appropriately correcting the applied charging voltage value, a desired charging potential of the photosensitive drum 1, which is a member to be charged, is guaranteed without a potential sensor.

That is, the charging device 20 using a carrier, particularly a charging device for injecting a charge into a photosensitive member as a member to be charged, has a high resistance due to the durability and has a low chargeability. In this embodiment, the charged potential is guaranteed without a potential sensor. As described above, the photoreceptor is neutralized by using the injection charger 20, and a predetermined voltage is applied to detect the DC current value. The current is fed back to the DC value of the injection charger so as to have a predetermined current value, and is applied at a constant voltage during image formation.

In addition, each time a plurality of different DC biases are applied, the charge of the photosensitive drum 1 as the member to be charged may be removed each time.

Further, a reference current value is applied to a place where the photosensitive drum 1 as a member to be charged has a voltage of about 0 V,
The DC bias value at that time may be used at the time of image formation.

B) In the image forming apparatus of this embodiment, a fur brush as the auxiliary member 10 is provided upstream of the injection charger 20 because it is cleanerless. The value of the current flowing through the fur brush is related to the injection charger current. Detects a change in current due to the deterioration of the fur brush, corrects the injection charging current value, feeds back to the injection charging device DC value so that a predetermined current value is obtained, and applies a constant voltage at the time of image formation. Obtain a charged potential.

After transfer of the toner image to the transfer material P, the transfer residual toner remains on the photosensitive drum 1. These transfer residual toners have both positive and negative polarities due to peeling discharge at the time of transfer. The transfer residual toner having a mixed polarity reaches the magnetic brush charger 20 as a contact charger. Particularly, the transfer residual toner having a positive polarity is collected in the magnetic brush portion 23 of the magnetic brush charger 20, and friction with the magnetic carrier is caused. It becomes negative due to charging and the like, and is discharged onto the photosensitive drum 1,
It reaches the developing section m of the developing device 4 and is collected by the fog removing electric field during development. An alternating electric field may be superimposed on the DC bias applied to the magnetic brush charger 20 in order to improve the recovery of toner in the magnetic brush charger 20.

However, of the transfer residual toner, the toner having a negative polarity and a large charge amount is not recovered by the magnetic brush charger 20 and is conveyed to the transfer portion T again without being recovered by the developing device 4, and is transferred to the transfer material P. The image was transferred and sometimes caused an image defect. In order to prevent this, in this example, the magnetic brush charger 20 (first contact charging member), which is a contact charger, is upstream of the photosensitive drum rotation direction and downstream of the transfer unit T in the rotation direction of the photosensitive drum (magnetic brush). A conductive fiber brush having a bristle length of 6 mm, a penetration amount of about 1 mm, and a contact nip of about 3 mm with the photosensitive drum 1 (between the charger 20 and the transfer section T) (flocking density 1
100,000 / inch ² , resistance value 5 × 10 ⁶ Ω) was disposed as the auxiliary member 10 (second contact charging member).

The auxiliary member 10 as the second contact charging member is supplied with a power supply S of plus 500 V opposite to the DC charging polarity of the magnetic brush charger 20 as the first contact charging member.
4 was applied.

As a result, the transfer residual toner having a particularly large negative charge is primarily captured in the auxiliary member 10,
After being neutralized or charged to the positive electrode, it is sent out onto the photosensitive drum 1 again and collected by the magnetic brush charger 20 or collected by the developing device 4. Therefore, the above-described image defects can be prevented.

FIG. 7 shows the charging potential of the photosensitive drum 1 when the weight ratio of the toner mixed in the magnetic brush charger 20 to the weight of the magnetic carrier in the magnetic brush charger 20 is indicated by a broken line. The absolute value of the DC current flowing through the brush charger 20 is indicated by a solid line, and the DC current flowing through the auxiliary member 10 is indicated by a chain line.

Thus, the charging potential of the photosensitive drum 1 according to the weight ratio of the toner mixed into the magnetic brush charger 20, the DC current value flowing through the magnetic brush charger 20, and the DC current value flowing through the auxiliary member 10 Changes.

Also, the D which has flowed into the magnetic brush charger 20
It can be seen that the absolute values of the C current value and the DC current value flowing through the auxiliary member 10 are substantially equal.

The experimental conditions at this time were as follows.
The peak-to-peak voltage Vpp700 as an alternating electric field at 0
V, frequency 1 kHz, rectangular waveform AC voltage to DC voltage-
The voltage was superimposed on 500 V, and a positive voltage of 500 V was applied to the auxiliary member 10. In addition, the measurement was performed after the bias was applied to the magnetic brush charger 20 and the auxiliary member 10 and then the photosensitive drum 1 was measured.
Was rotated one or more times.

In FIG. 8, the same measurement is performed using auxiliary members 10 having different durability levels, and the charging potential of the photosensitive drum is indicated by a broken line with respect to the current value flowing through the auxiliary members 10 to the magnetic brush charger 20. The flowing DC current value is shown by a solid line.

From this, it can be seen that the DC current value flowing through the magnetic brush charger 20 changes according to the current value of the auxiliary member 10, although the charging potential of the photosensitive drum does not change. That is, the value of the current flowing through the magnetic brush charger 20 changes due to the deterioration of the auxiliary member 10. The cause of the deterioration of the auxiliary member 10 is considered to be transfer residual toner, external additives, paper powder, and the like that cannot be discharged from the auxiliary member.

FIG. 9 shows that the bias value applied to the auxiliary member is set to 5 using the auxiliary members 10 having different durability levels as described above.
The amount of change in current when the voltage is changed from 00 V to 0 V, for example, is 5
This is shown for the current value when 00V is applied. This indicates that the current value of the auxiliary member 10 has a correlation.
That is, the amount of change in current when the bias value applied to the auxiliary member is changed from 500 V to, for example, 0 V has a correlation with the deterioration of the auxiliary member 10.

In order to better understand this phenomenon, FIG. 10 shows, with a solid line, an auxiliary member that has not deteriorated the value of the current flowing through the auxiliary member with respect to the difference between the charged member (photosensitive drum) potential and the applied bias value of the auxiliary member 10. The broken auxiliary members are indicated by broken lines.

C) In this example, the current flowing through each of the magnetic brush charger 20 as the first contact charging member and the auxiliary member 10 as the second contact charging member is detected, and the current is detected in accordance with the detection signal. The voltage value applied to the magnetic brush charger 20 as the first contact charging member is changed.

FIG. 3 shows an example of the control system. Reference numerals 24 to 28 denote control systems for the magnetic brush charger 20, which are as described above. 29 to 32, 26 are auxiliary members 1
0 is a control system, and 29 is an ammeter for detecting a current flowing through the auxiliary member 10, and its detection information is A / D
The data is captured by the CPU 26 via the converter 30. The applied bias power source S4 for the auxiliary member 10 is
Is controlled via the D / A converter 31 and the driver 32.

In this embodiment, the magnetic brush charger 20 and the auxiliary member 10 are operated, for example, between sheets during continuous copying, and a current It flowing through the magnetic brush charger 20 at that time and 500 V applied to the auxiliary member 10 are applied. Current values Ih500 and 0
The current value Ih0 when V is applied is detected and taken into the CPU 26.

When the auxiliary member 10 is not deteriorated, the difference between the current value when 500 V is applied to the auxiliary member and the current value when 0 V is applied is determined by a reference value δIhth (a preset value or a CPU value for each image forming apparatus). May be taken in). Here, assuming that δIh = δIhth− (Ih500−Ih0), CδIh multiplied by a certain coefficient C is a variation due to deterioration of the auxiliary member with respect to the current value It flowing through the magnetic brush charger 20.

Here, the coefficient C is used to correct that the current value fluctuation due to the deterioration of the auxiliary member 10 is different due to the potential difference between the photosensitive drum 1 and the auxiliary member 10.

Therefore, if the sum of the absolute values of It and CδIh is equal to or less than the reference value Ith, it is determined that the magnetic brush charger 20 has deteriorated, and the DC voltage applied to the magnetic brush charger 20 is set to a desired current value. Apply feedback to the bias value.

In this example, C = 1.5 and δIhth = 15
μA, Ith = 32 μA. Further, the DC bias value applied to the magnetic brush charger 20 and the auxiliary member 10
The values of C, δIhth, and Ith may be changed in accordance with the bias value applied to.

D) FIG. 11 shows the potential change when the exposure amount is constant when the thickness of the charge injection layer as the photosensitive member surface layer is changed.

It is understood from this that the lower the film thickness, the lower the potential. This is conceivably because the effect of light scattering and light absorption of the curing agent differs depending on the film thickness when conductive fine particles for forming the charge injection layer or particularly a photocurable resin is used as the charge injection layer.

FIG. 12 shows a change in density when development is performed under the conditions of FIG. 11, and it can be seen that the density increases as the film thickness decreases.

FIG. 13 shows the current value and film thickness flowing through the magnetic brush charger 20 when the auxiliary member 10 is electrically floated and the exposed surface of the photoreceptor is charged without performing the developing and transferring operations. It shows an example of the relationship with.

As a result, it is found that there is a correlation between the current value and the film thickness.

The current detecting method is as described above (FIG. 3). The detected current value is similarly taken into the CPU 26,
If the current value is not the predetermined current value, for example, the exposure amount is controlled so that the current value becomes the predetermined current value. The exposure control method is
For example, control of the amount of light emitted from the light emitting element, the emission time, and the like. Alternatively, the charging potential may be changed. In this case, it is desirable that the current value is the target value for determining the magnetic brush application bias. The auxiliary member 10
A similar effect can be obtained by applying a bias and using the value obtained when the surface of the exposed portion is charged by the above-described current detection method. Note that, in this case, it is desirable to perform the correction after correcting the charging potential due to the deterioration of the magnetic brush charger 20 or the auxiliary member 10. Further, the image data may be corrected so as to be equivalent to the exposure amount correction.

<Others> 1) The configuration of the present invention is not limited to the above-described embodiment. For example, the contact charging member may be a fur brush charger, a charging roller using conductive rubber or conductive sponge, or the like. Or a non-rotating contact charging member or the like.

2) The photosensitive member as the member to be charged (image carrier) also has a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm.
It is desirable to have a low-resistance layer in order to realize charge injection charging and to prevent generation of ozone, but an organic photoreceptor other than the above may be used. That is, the contact charging is not limited to the charge injection charging system of the embodiment, but may be a contact charging system in which a discharge phenomenon is dominant.

3) As the developing device, only the two-component developing method has been described in the embodiment, 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, other developing methods such as one-component non-contact development and two-component non-contact development as well as the one-component contact development and the two-component contact development described above are used. , A sufficient recovery effect can be obtained.

4) The charging bias applied to the contact charging member 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. 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.

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 may be a general analog exposing means. 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 for receiving the transfer of the toner image from the image carrier may be an intermediate transfer member such as a transfer drum.

[0148]

As described above, according to the present invention, in an image forming apparatus using a contact charging device, poor charging or poor charging can occur regardless of deterioration of the contact charging member, that is, regardless of progress of contamination of the contact charging member due to durability. Prevents the occurrence of unevenness and stably maintains good contact charging performance for a long period of time.Prevents image defects due to scraping of the surface layer of the image carrier, and maintains stable output of good quality images for a long period of time. It is possible to achieve the intended purpose well.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of a layer configuration of a photoreceptor.

FIG. 3 is a schematic diagram of a magnetic brush charger, an auxiliary member, and a control system thereof.

FIG. 4 is a structural model diagram of a developing device part.

FIG. 5 is a diagram for explaining the relationship between the deterioration of the magnetic brush charger, the charging potential and the charger current value (part 1)

FIG. 6: Same as above (part 2)

FIG. 7 is a characteristic diagram for explaining the embodiment (part 1);

FIG. 8: Same as above (part 2)

FIG. 9 is the same as FIG.

FIG. 10 Same as above (part 4)

FIG. 11 (part 5)

FIG. 12 is the same as FIG.

FIG. 13 (No. 7)

FIG. 14 is a schematic diagram illustrating an example of an image forming apparatus.

[Explanation of symbols]

 Reference Signs List A laser beam printer B image reading device (image scanner) 1 member to be charged (image carrier, photosensitive drum) 2 contact charging means 20 magnetic brush charger (contact charging member) 3 laser scanning unit (laser scanner) 4 developing device 5 Paper feed cassette 6 Transfer device 8 Fixing device 9 Cleaning device 10 Auxiliary member (second contact charging member)

Continuing on the front page (72) Inventor Koichi Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shimitsu Gomi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F term (reference) 2H003 BB11 CC04 CC06 DD03 DD06 2H027 DA01 DE10 EA01 EC06 EC07 ED03 ED08 ED10 ZA01 2H077 AA37 AD06 AD13 AD18 AD31 AD36 DB12 DB22 EA01 EA14 EA15 EA16

Claims (10)

[Claims] 1. An image forming apparatus in which an image is formed by an image forming process means including a charging means for charging a charged member applied with a voltage to the image bearing member to charge the image bearing member. Means for detecting a value of a current flowing through the contact charging member when charging each of the unexposed portions; and means for changing a voltage value applied to the contact charging member in accordance with the detection signal. Characteristic image forming apparatus. 2. A charging means for charging an image carrier by bringing a charging member to which a voltage is applied into contact with the image carrier, and an electrostatic latent image corresponding to target image information on a charged surface of the image carrier. 2. The image forming apparatus according to claim 1, wherein the image forming is performed by an image forming process unit including an image information writing unit that forms the image and a developing unit that visualizes the electrostatic latent image with a developer. apparatus. 3. A charging means for charging an image carrier by bringing a charging member to which a voltage is applied into contact with the image carrier, and an electrostatic latent image corresponding to target image information on a charged surface of the image carrier. An image is formed by image forming means including image information writing means for forming the image, developing means for visualizing the electrostatic latent image with a developer, and transfer means for transferring the developer image to a recording medium. 2. The image forming apparatus according to claim 1, wherein the developing unit also serves as a unit for collecting a transfer residual developer remaining on the image carrier after the developer image is transferred to a recording medium by the transfer unit. Image forming device. 4. A charging means for charging an image carrier by bringing a charging member to which a voltage is applied into contact with the image carrier, and an electrostatic latent image corresponding to target image information on a charged surface of the image carrier. An image is formed by image forming means including image information writing means for forming the image, developing means for visualizing the electrostatic latent image with a developer, and transfer means for transferring the developer image to a recording medium. An image forming apparatus in which a developing unit also serves as a unit for collecting a transfer residual developer remaining on an image carrier after a developer image is transferred to a recording medium by a transfer unit, wherein a charging member of the charging unit is A first contact charging member, a first contact charging member, and a second contact charging member that are in contact with the image carrier between the transfer means and the first contact charging member; Means for detecting a current value flowing through each of the A current value flowing through the contact charging member when at least one of the first and second contact charging members charges the image-exposed portion and the unexposed portion is detected, and the contact charging is performed in accordance with the detection signal. An image forming apparatus comprising means for changing a voltage value applied to a member. 5. A correction is made to a detection signal of a current value flowing through the first contact charging member using a current value detection signal flowing through the second contact charging member, and the first signal is corrected according to the corrected value. The image forming apparatus according to claim 4, further comprising a unit that changes a voltage value applied to the contact charging member. 6. The image forming apparatus according to claim 4, wherein the voltage applied to the second contact charging member has a polarity opposite to that of the voltage applied to the first contact charging member. 7. The image bearing member has a surface layer resistance of 10 ⁹ to 10 ^14.
The image forming apparatus according to claim 1, wherein the value is Ω · cm. 8. The image exposure means according to claim 2, wherein the image information writing means for forming an electrostatic latent image corresponding to the target image information on the charged surface of the image carrier is an image exposure means. The image forming apparatus according to one of the above. 9. A magnetic brush contact charging member having a magnetic brush portion in which magnetic particles are magnetically constrained, and wherein the magnetic brush portion is brought into contact with an image carrier. 9. The image forming apparatus according to any one of 1 to 8. 10. A contact charging member having a fur brush portion made of a conductive fiber, wherein the fur brush portion is in contact with an image carrier. The image forming apparatus according to any one of the above.