JPH10207186A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the sticking of electrifying magnetic grains to the end part of an image carrier in a contact electrifying system using an electrifying fying auxiliary member and the cleaner system image forming device. SOLUTION: This image forming device is of a cleanerless system image forming device in which a developing means is used as an image carrier cleaning means for recovering toner grains remaining on the image carrier, after the last image formation. As an image carrier electrifying means, plural contact electrifying members of at least a first contact electrifying member and a second contact electrifying member in a position nearer to the downstream side in the rotational direction of the image carrier than the first contact electrifying member are arranged on the image carrier. A bias applied to the first contact electrifying member has a polarity opposite to that the of the normal charge of the image carrier and the bias applied to the second contact electrifying member as an electrifying means for finally electrifying the image carrier has the polarity of the normal charge of the image carrier. The electrifying width L31 in the longitudinal direction of the first contact electrifying member is shorter than the electrifying width L32 in the longitudinal direction of the second contact electrifying member and longer than the developing region width L4 in the longitudinal direction of the developing means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step of charging an image carrier on an image carrier, a step of forming an electrostatic latent image on the charged surface, and a step of developing the electrostatic latent image as a toner image. The present invention relates to an image forming apparatus in which image formation is performed by applying an image forming process having an image bearing member, and an image carrier is repeatedly used for image formation.

More specifically, a "cleanerless system" in which developing means for developing the electrostatic latent image with toner also serves as image carrier cleaning means for recovering toner particles remaining on the image carrier during previous image formation. Related to an image forming apparatus.

[0003]

2. Description of the Related Art FIG. 7 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 1 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 1 receives a uniform charging process of a predetermined polarity and potential by a charging roller 3 as a charging unit during the rotation process, and receives an image exposure unit (not shown) such as a projection image exposure unit for an original image. (E.g., laser beam scanning exposure means) to receive an image exposure L so that the uniformly charged surface is selectively neutralized (or potential attenuated) corresponding to the exposed image pattern.
As a result, an electrostatic latent image is formed. Then, the formed electrostatic latent image is developed as a toner image by a toner developing device 4 as a developing unit.

On the other hand, a transfer material P as a recording material is fed from a paper feed mechanism (not shown) to a transfer nip portion, which is a contact portion between the photosensitive drum 1 and a transfer roller 5 as transfer means, at a predetermined control timing. Then, the toner image on the photosensitive drum 1 surface side is electrostatically transferred to the front surface side of the transfer material P by charging the back surface of the transfer material P to the opposite polarity to the toner.

Next, the transfer material P is separated from the surface of the rotating photosensitive drum 1, introduced into the fixing device 6, subjected to a fixing process of the toner image, and outputted 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 1 is cleaned by removing the untransferred toner by a cleaning means (cleaner) 8, and is repeatedly used for image formation.

In recent years, the size of such an apparatus has been reduced. However, there is a limit to the miniaturization of each of the charging, exposure, development, transfer, fixing, and cleaning process devices described above.

[0010] The transfer residual toner is collected as waste toner by the cleaner 8, but it is preferable that the waste toner is not environmentally friendly.

1) Therefore, an image forming apparatus of a "cleaner-less system" in which the above-mentioned cleaner 8 is removed and cleaning (collection of residual toner after transfer) is performed simultaneously with development by the developing device 4 has appeared.

Simultaneous development cleaning is fogging, which is a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1 at the time of development after the next step. This is a method of collecting by the potential difference Vback.

According to this method, since the transfer residual toner is collected in the developing device 4 and used in the subsequent steps, waste toner can be eliminated. In addition, the cleaner-less has a great advantage in terms of space, and can greatly reduce the size of the image forming apparatus.

2) By the way, in recent years, charging means for charging a charged object such as an image carrier has advantages such as low ozone and low electric power. An apparatus of a system in which a charged member (contact charging member) is brought into contact with the charged member to charge the member to be charged has been put to practical use.

As a contact charging member in such a contact charging system, a magnetic brush charger is preferably used from the viewpoint of stability of charging contact.

In the magnetic brush charger, the conductive magnetic particles are magnetically constrained as a magnetic brush directly on a magnet or a sleeve containing the magnet, and the magnetic brush is stopped or rotated to contact the member to be charged. The object to be charged is charged by applying a voltage thereto.

Further, a conductive fiber formed on a brush (fur brush charger) or a conductive rubber roller formed by rolling conductive rubber (roller charger, charging roller) is preferably used as the contact charging member. Have been.

3) In particular, when such a contact charging member is used, a member having a surface layer in which conductive fine particles are dispersed on a normal organic photoreceptor or an amorphous silicon photoreceptor is used as a member to be charged. It is possible to obtain, on the surface of the member to be charged, a charging potential substantially equal to the DC component of the bias applied to the member.

Such a charging method is referred to as "injection charging".
Called. The use of this injection charging does not utilize a discharge phenomenon in which charging of the member to be charged is performed using a corona charger, so that complete ozone-less and low-power-consumption charging becomes possible, and has been attracting attention. .

[0020]

However, in such an image forming apparatus using the contact charging method, when the image formation is repeated by performing the simultaneous recovery by the developing means without providing the cleaner means, the transfer is performed. Since the residual toner cannot be collected by the developing means, a "positive ghost" in which the previous image remains thinly has occurred.

This positive ghost is a phenomenon that occurs when the transfer residual toner passes through the position of the contact charging member and thus the surface of the image bearing member under the transfer residual toner cannot be charged, and becomes more conspicuous when the contact charging member is contaminated.

Therefore, when the surface of the image bearing member is charged by the contact charging member, the portion of the image bearing member below the untransferred toner is also charged. (Discharge of toner from the contact charging member to the image carrier), it is important to collect the toner by the developing means.

Further, since toner particles having a relatively high electric resistance are generally used for toner contamination of the contact charging member, toner particles are mixed into the contact charging member,
If the mixed toner particles cannot be discharged sufficiently to the image carrier, the resistance of the contact charging member as a whole or a part thereof increases, and the image carrier cannot be charged to a desired potential or is charged. There is a disadvantage that unevenness occurs and an image defect occurs.

Therefore, at least two contact charging members that contact the image carrier are provided in the rotation direction of the image carrier, and the contact charging member located upstream of the other in the rotation direction of the image carrier is a first charging member. When the contact charging member located on the downstream side is the second charging member, the second charging member has a charging polarity for finally charging the image carrier (normal charging polarity of the image carrier).
Is applied to the first charging member, and a bias having a polarity opposite to that applied to the second charging member is applied to the first charging member. When charging the image carrier to the normal charging polarity by using a contact charging member using magnetic particles as the second charging member in the second charging member as the final charging means Transfer residual toner is collected at the time of charging (the charging potential is generally lower than the applied bias, so that toner of the opposite polarity is more likely to be recovered), and the surface of the image carrier under the transfer residual toner is also uniformly charged. Further, the frictional charging characteristics of the magnetic particles of the second charging member charge the toner particles to the normal polarity, thereby charging the toner particles collected by the second charging member to the normal charging polarity. On the image carrier Spit (in accordance with the principles of reverse within the parentheses) it becomes possible.

Since the toner discharged from the second charging member to the image carrier in this way is charged to the normal charging polarity, it is collected by the developing means at the fogging potential (Vback) during development by the developing means. And the occurrence of positive ghosts can be prevented, and the toner mixed in the second charging member, which is the final contact charging means, can be sufficiently discharged, so that toner contamination of the second charging member can also be prevented. .

For convenience, the image forming apparatus having the above-described configuration is referred to as a contact charging system using a charging auxiliary member or an image forming apparatus of a cleaner system.

However, in such an image forming apparatus of the contact charging system and the cleaner system using the charging auxiliary member, there is a problem that the charged magnetic particles adhere to the image carrier from the end of the second charging member. Occurred. The present invention aims to solve this problem.

[0028]

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

(1) An image having a step of charging the image carrier with respect to the image carrier, a step of forming an electrostatic latent image on the charged surface, and a step of developing the electrostatic latent image as a toner image A developing means for applying an image forming process to form an image and developing the electrostatic latent image as a toner image also serves as an image carrier cleaning means for collecting toner particles remaining on the image carrier in the previous image formation, The image carrier is an image forming apparatus of a cleanerless system for repeatedly providing image formation,
As charging means for charging the image carrier, the image carrier includes a plurality of contact charging members of at least a first contact charging member and a second contact charging member downstream of the contact charging member in the image carrier rotation direction. Disposed, the bias applied to the first contact charging member has a polarity opposite to the normal charging polarity of the image carrier,
The bias applied to the second contact charging member, which is a charging unit for finally charging the image carrier, is the normal charging polarity of the image carrier, and the longitudinal charging width of the first contact charging member is An image forming apparatus, wherein the width of the charging member in the longitudinal direction of the contact charging member is shorter than the width of the developing region in the longitudinal direction of the developing means.

[0030] (2) the image 10 ^9-10 carrying member to the surface
The image forming apparatus according to (1), further comprising a layer made of a material of ¹⁴ Ω · cm.

(3) The image forming apparatus according to (1) or (2), wherein the image carrier has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles.

(4) The image forming apparatus according to (3), wherein the conductive fine particles are SnO ₂ .

(5) The image forming apparatus according to (1) or (2), wherein the image carrier comprises a surface layer having amorphous silicon.

(6) The second contact charging member has a magnetic brush portion of conductive magnetic particles, and the magnetic brush portion is in contact with the image carrier (1) to (5). )
The image forming apparatus according to any one of the above.

(7) The first contact charging member has a conductive fiber brush portion, and the conductive fiber brush portion is in contact with the image carrier (1) to (6). The image forming apparatus according to any one of the above.

(8) The method according to any one of (1) to (7), wherein the developing method of the developing means is a contact developing method in which the developer is in contact with the image carrier. An image forming apparatus according to claim 1.

(9) The method according to any one of (1) to (8), wherein the means for forming an electrostatic latent image on the charged surface of the image carrier is an image exposure means for the image carrier. Image forming device.

(10) The image forming apparatus according to any one of (1) to (9), wherein the toner image formed on the image carrier is transferred to a transfer material by a transfer unit.

<Operation> By making the longitudinal charging width of the first contact charging member longer than the developing width of the developing means in the longitudinal direction, the effect of preventing the occurrence of a positive ghost in all of the maximum image area width dimensions of the image carrier is obtained. Becomes better.

By making the longitudinal charging width of the first contact charging member shorter than the longitudinal charging width of the second contact charging member, the first contact charging member is charged by the first contact charging member and the second contact charging member is charged. It is possible to eliminate a region where the member is not charged. When an area charged by the first contact charging member and not receiving the charge of the second contact charging member occurs, the image carrier surface potential at the longitudinal end of the second contact charging member is changed to the first contact charging member. When the magnetic brush portion at the longitudinal end of the second contact charging member slightly protrudes into the area, the magnetic particles constituting the magnetic brush portion easily adhere to the image carrier surface due to the potential difference. Become.

Accordingly, the first contact charging member has a configuration in which the charging width in the longitudinal direction is shorter than the charging width in the longitudinal direction of the second contact charging member and longer than the developing width in the longitudinal direction of the developing means. Adhesion of magnetic particles to the body can be prevented.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION

(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, is an injection charging system using a magnetic brush charger, uses a fur brush charger as an auxiliary member, and uses a developing means. This is an image forming apparatus of a cleanerless system that performs cleaning simultaneously with development.

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

1) Image Reading Apparatus B In the image reading apparatus B, reference numeral 10 denotes an original platen glass fixedly disposed on the upper surface of the apparatus. 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 from the home position on the left side of the original table glass 10 to the right side along the lower surface of the original table glass 10 by pressing a copy button. When it reaches the end point, it is driven backward and returned to the initial home position.

In the forward drive process of the unit 9, the downward image surface of the placed set document G on the platen glass 10 is sequentially illuminated and scanned by the document irradiation lamp 9a of the unit 9 from the left side to the right 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 original G is photoelectrically read by the image reading device B as a time-series electric digital pixel signal (image signal).

2) Printer A In the printer A, reference numeral 1 denotes a rotating drum type, charge injection chargeable, negatively charged electrophotographic photosensitive member (photosensitive drum) as an image carrier. The photosensitive drum 1 is rotationally driven clockwise as indicated by an arrow at a predetermined peripheral speed about a central support shaft, in this example, a rotation speed of 100 mm / sec in this example. Finally, a uniform negative charging treatment is performed.

In this embodiment, the charging means 3 comprises a first and a second
This is a contact charging device in which two contact charging members 31 and 32 are brought into contact with the photosensitive drum 1. S1 and S2 are power supplies for applying a predetermined charging bias to the first and second contact charging members 31 and 32, respectively.

The uniformly charged surface of the rotating photosensitive drum 1 is modulated according to an image signal output from the laser scanning unit (laser scanner) 2 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 electrostatic latent image formed on the surface of the rotating photosensitive drum 1 is successively developed as a toner image by the developing device 4 in the case of the present embodiment, and is reversely developed. S3 is a power supply for applying a predetermined developing bias to the developing sleeve of the developing device 4.

On the other hand, a transfer material P as a recording material stored in the paper feed cassette 5 is fed out one by one by a paper feed roller 51, and is transferred to a predetermined position by a path of a sheet path 52 → a pair of registration rollers 52 → a sheet path 53. At the control timing, paper is fed to a transfer unit 75 which is a contact nip portion between the photosensitive drum 1 and a transfer belt 71 of a transfer belt device 7 as a transfer unit, and the toner image on the photosensitive drum 1 side is transferred to the transfer material It is electrostatically transferred to the side. That is, the transfer material P is conveyed from the paper feeding and conveying device to the transfer section 75 formed by the photosensitive drum 1 and the transfer belt 71 at an appropriate timing in synchronization with the rotation of the photosensitive drum 1.

The transfer belt 71 is an endless belt made of a dielectric material. The transfer belt 71 is suspended between a driving roller 72 and a driven roller 73 and rotates at a peripheral speed substantially equal to the peripheral speed of the photosensitive drum 1 in the direction of the arrow. Driven. Reference numeral 74 denotes a transfer charging blade provided in contact with the back side of the transfer belt 71 in the transfer section 72, and also serves as a pressing member for pressing the transfer belt 71 against the photosensitive drum 1 in a predetermined manner.
As a result, a predetermined transfer bias is applied, and charging of a polarity opposite to that of the toner is performed from the back surface of the transfer material. As a result, the toner image on the photosensitive drum 1 side is electrostatically transferred to the transfer material side in the transfer unit 75.

The transfer material to which the toner image on the photosensitive drum 1 side has been transferred in the transfer unit 75 is separated from the surface of the photosensitive drum 1 and is subsequently conveyed to the fixing device 6 by the rotation of the transfer belt 71 to thermally fix the toner image. Then, with the paper discharge roller 6a,
The data is output as a copy or print to the paper discharge tray 6b outside the apparatus.

Since the printer of this embodiment is cleanerless, a dedicated cleaning device for collecting the transfer residual toner remaining on the surface of the rotary photosensitive drum 1 after the transfer material is separated is not provided. The untransferred toner on the surface is collected by simultaneous cleaning with the developing device 4, and the surface of the rotating photosensitive drum 1 is repeatedly used for image formation.

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

Therefore, in the present embodiment, as shown in the schematic diagram of the layer structure in FIG. 2, the following first photosensitive drum 1 is formed on an aluminum substrate (Al drum substrate) 11 having a diameter of 30 mm and made of a negatively charged organic photosensitive member. To 5th functional layers were provided in order from the bottom, and a charge-injection chargeable photosensitive drum was used.

The first layer 12 is an undercoat layer and has a thickness of 2 provided for smoothing defects or the like of the Al drum base 11.
It is a conductive layer of 0 μm.

The second layer 13 is a positive charge injection preventing layer,
It serves to prevent positive charges injected from the drum substrate 11 from canceling out negative charges charged on the surface of the photoreceptor, and the resistance is adjusted to about 1 × 10 ⁶ Ω · cm by the amylan resin and methoxymethylated nylon. This is a medium resistance layer having a thickness of 1 μm.

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 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 thus prepared coating liquid 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 Ωcm. By controlling the surface resistance in this manner, the chargeability is directly improved and a high-quality image can be obtained. Photoconductor is OPC
A-Si (amorphous silicon) drum, a-
It can also be realized with a surface layer having Si, and can achieve higher durability.

Here, the volume resistance of the surface layer 16 was measured by arranging metal electrodes at an interval of 200 μm, flowing a preparation liquid for the surface layer during the film formation, and applying a voltage of 100 V between the electrodes. Value. Measurements were made at a temperature of 23 ° C and a humidity of 50% RH
Is a value measured under the conditions of

(3) Contact Charging Device (FIG. 3) The charging means 3 in this embodiment is a contact charging device in which the first and second contact charging members 31 and 32 are brought into contact with the photosensitive drum 1 as described above. is there. FIG. 3 is an enlarged cross-sectional model view of the first and second two contact charging members 31 and 32. In this embodiment, the first contact charging member 31 is a fixed brush type fur brush charger made of conductive fibers, and the second contact charging member 32 is a rotary sleeve type magnetic brush charger using a magnetic carrier. First contact charging member 3
Numeral 1 is disposed upstream of the second contact charging member 32 in the rotation direction of the photosensitive drum 1.

1) Fur brush charger 31 A fixed brush type fur brush charger 31 serving as a first contact charging member is provided with a horizontally long supporting metal plate 3 serving as an electrode plate.
1a, a conductive fiber brush portion 31b is formed. The conductive fiber brush portion 31b has a brush length of 4 mm, a brush density of 100,000 brushes / inch ² , a brush diameter of 6 denier, and a brush resistance of 10 ⁶ Ω · cm. The conductive fiber brush portion 31b is preferably one having a brush length of 1 to 10 mm, a brush density of 1 to 500,000 brushes / inch ² , a brush diameter of 2 to 12 denier, and a brush resistance of 10 ^-2 to 10 ¹² Ω · cm. It can be used by controlling the current value that flows sometimes to about 5 to 50 μA.

The fixed brush type fur brush charger 31 as the first contact charging member has a contact nip width (charging area) n1 of the conductive fiber brush portion 31b formed on the photosensitive drum 1 of about 5 mm. It was arranged so that it became.

The power supply S1 applies +20 as a charging bias to a supporting metal plate 31a as an electrode plate of the charger 31.
DC bias (+200 to +200) with μA constant current control
(About 0 V).

2) Magnetic Brush Charger 32 The rotary sleeve type magnetic brush charger 32 as the second contact charging member is rotatably and coaxially rotatable around the magnet roll 32a fixed and supported. A nonmagnetic conductive charging sleeve 32b having an outer diameter of 16 mm fitted therein, and conductive magnetic particles (magnetic for charging) formed by being attracted and held on the outer peripheral surface of the charging sleeve by the magnetic force of a magnet roll 32a inside the charging sleeve. (A carrier) magnetic brush portion 32c.

The magnetic brush charger 32 is adjusted substantially parallel to the photosensitive drum 1 so that the contact nip width (charging area) n2 of the magnetic brush portion 32c formed on the photosensitive drum 1 is about 6 mm. And arranged.

The charging sleeve 32b was rotated at a speed of 150 mm / sec in the charging area n2 in a clockwise direction indicated by an arrow opposite to the rotation direction of the photosensitive drum 1 with respect to a rotational peripheral speed of the photosensitive drum 1 of 100 mm / sec.

The charging sleeve 32 of the charger 32
A DC bias of -650 V was applied to b from a power source S2 as a charging bias.

With the rotation of the charging sleeve 32b, the magnetic brush portion 32c rotates in the same direction and rubs the surface of the photosensitive drum 1, and charges are given to the photosensitive drum 1 from the charging magnetic carrier constituting the magnetic brush portion 32c. Then, the photosensitive drum surface is charged to a potential corresponding to the charging voltage. In the case of the present example, the photosensitive drum 1 is charged and injected at approximately -650 V. The charging sleeve 32b tends to have better charging uniformity as the rotation speed is higher.

As the charging magnetic carrier constituting the magnetic brush portion 32c, the average particle diameter is 10 to 100 μm, the saturation magnetization is 20 to 250 emu / cm ³ , and the resistance is 1 × 10 ² to 1
× 10 ¹⁰ Ω · cm is preferred. 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 one having as small a resistance as possible. In this example, the average particle diameter is 25 μm, the saturation magnetization is 200 emu / cm ³ , and the resistance is 5 ×.
Magnetic particles of 10 ⁶ Ω · cm were used. In addition, the magnetic carrier for charging used in this example oxidizes the surface of the philite,
The one that has undergone a reduction treatment to adjust the resistance is used.

Here, the resistance value of the magnetic carrier is determined by placing 2 g of the carrier in a metal cell having a bottom area of 228 mm ² ,
The measurement was performed by applying a load of 6.6 kg / cm ² and applying a voltage of 100 V.

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

For measuring the magnetic characteristics of the magnetic carrier, a DC magnetization BH characteristic automatic recording device BHH-5 manufactured by Riken Denshi Co., Ltd. was used.
0 can be used. At this time, the diameter (inner diameter) is 6.5.
A magnetic container is filled with a load of about 2 g in a cylindrical container having a diameter of 10 mm and a height of 10 mm, and the saturation magnetization is measured from the BH curve of the particle while keeping the particles from moving in the container.

(4) Laser Scanning Section 2 (FIG. 4) FIG. 4 shows a schematic configuration of the laser scanning section (laser scanner) 2. When the scanned surface 1 (the rotating photosensitive drum surface) is subjected to laser scanning exposure by the laser scanning unit 2, first, the solid-state laser element 22 is blinked at a predetermined timing by the light emission signal generator 21 based on the input image signal. ON / OFF). The laser light emitted from the solid-state laser element 22 is converted into a substantially parallel light flux by the collimator lens system 23, and further converted into an arrow b
The lens is scanned in the direction of arrow c by the rotating polygon mirror 24 which rotates at high speed in the direction, and the fθ lens group 25 (25a, 25b.
By 25c), a spot-like image is formed on the surface 1 to be scanned.
By such laser beam scanning, an exposure distribution for one scan of an image is formed on the surface 1 to be scanned.
Is scrolled by a predetermined amount perpendicular to the scanning direction, an exposure distribution according to the image signal is obtained on the surface 1 to be scanned.

(5) Developing Apparatus 4 (FIG. 5) In general, the method of developing an electrostatic latent image is such that non-magnetic toner is coated on a sleeve with a blade or the like, and magnetic toner is coated by magnetic force and conveyed. A method of developing in a non-contact state with respect to the photosensitive drum (one-component non-contact development), a method of developing the toner coated as described above in contact with the photosensitive drum (one-component contact development), A method in which a mixture of toner particles and a magnetic carrier is used as a developer and transported by magnetic force to develop the photosensitive drum in contact with the photosensitive drum (two-component contact development); The method is broadly classified into four types: a method of developing in a non-contact state (two-component non-contact development). The two-component contact development method is often used from the viewpoints of high image quality and high stability.

In this embodiment, a mixture of non-magnetic toner particles and magnetic carrier particles is used as a developer.
A two-component magnetic brush contact development system in which the developer is held on a developer carrier as a magnetic brush layer by magnetic force, transported to a developing unit, and brought into contact with the surface of the photosensitive drum 1 to develop an electrostatic latent image as a toner image is used. Used. The two-component magnetic brush contact development is very suitable for collecting residual toner on the photosensitive drum 1 in a cleanerless image forming apparatus.

FIG. 5 is a schematic view of the two-component magnetic brush developing device 4 used in this embodiment. 41 is a developing container, 42 is a developing sleeve as a developer carrying member, 43 is a magnet roller as a magnetic field generating means fixedly arranged in the developing sleeve 42, and 44 forms a thin layer of developer on the surface of the developing sleeve. 45 is a developer stirring / conveying screw, and 46 is a blade for regulating the thickness of the developer contained in the developing container 41.
Component developer, which is a mixture of non-magnetic toner particles t and magnetic carrier particles c.

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 at a predetermined rotation speed in a counterclockwise direction indicated by an arrow around the outer periphery of the fixedly disposed 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 up by the N ₂ pole of the magnet roller 43 with the rotation of the developing sleeve 42 is conveyed vertically from the S ₂ pole to the N ₁ pole, and is 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 and an alternating 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 S3.

In this example, DC voltage: -480 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 is increased, 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 called a fogging 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 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 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.

As the toner particles t, it is more preferable to use a spherical toner having an average particle diameter of about 6 μm produced by a suspension method. Since the toner produced by the polymerization method has a nearly spherical shape, the external additive is uniformly coated. Therefore, the releasability from the photosensitive drum 1 is extremely good. In addition, the fog is better than the pulverized toner. In addition to the very small amount of transfer residual toner and the high releasability, there is no cleaner. When the configuration of the image forming apparatus of the system is adopted, the retrievability is further improved, which is even better.

(6) Transfer Device 7 The transfer device 7 is of the transfer belt type in this embodiment as described above. In this example, a belt 71 made of a polyimide resin having a film thickness of 75 μm was used. The material of the belt 71 is not limited to polyimide resin,
It is preferable to use a plastic such as a polycarbonate resin, a polyethylene terephthalate resin, a polyvinylidene fluoride resin, a polyethylene naphthalate resin, a polyether ether ketone resin, a polyether sulfone resin, a polyurethane resin, or a fluorine-based or silicon-based rubber. it can. The thickness is not limited to 75 μm, but is 25 to 2000 μm, preferably 50 to 1 μm.
Those having a size of 50 μm can be suitably used.

Further, a transfer charging blade 74 having a resistance of 1 × 10 ⁵ to 1 × 10 ¹⁷ Ω was used. Transfer was performed by applying a bias of +15 μA to the transfer charging blade 74 under constant current control.

(7) 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 with a medium-resistance contact charging member. Instead of injecting charge into the trapping potential of the drum surface material, the charge is charged by charging the conductive particles (SnO ₂ ) 16 a of the charge injection layer 16. The charge transport layer 15 is made of a dielectric material. , Aluminum drum substrate 11 and charge injection layer 1
It is considered that this is based on the theory that the contact charging member 32 charges the minute capacitor using the conductive particles 16a in 6 as both electrode plates. At this time, the conductive particles 16
a 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. Therefore, image exposure L by laser light
It is anticipated that even if the above process is performed, each of the SnO ₂ particles 16a is electrically independent, so that an electrostatic latent image can be held.

(8) Collecting and discharging the transfer residual toner by the contact charging member, and cleaning at the same time as development The transfer residual toner remains on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P. As for the transfer residual toner, there are those whose charge polarity is inverted due to peeling discharge or the like at the time of transfer, and those whose charge polarity is not inverted. Here, the toner whose polarity has been inverted is collected by the magnetic brush charger 32 as the second contact charging member, while the toner whose polarity is not inverted is collected by the magnetic brush charger 32. This is difficult (because the charging potential is generally lower than the bias applied to the charger).

Therefore, in this example, the transfer section (transfer area section) 7
5 and a magnetic brush charger 32, a first contact charging member as an auxiliary member, in this example, a fixed brush type fur brush charger 31 using a conductive fiber is provided. A voltage having a polarity opposite to the charging polarity is applied to charge the transfer residual toner in the opposite polarity to the normal charging polarity, thereby improving the collection efficiency in the magnetic brush charger 32. Only when the charging polarity of the toner is opposite to the normal charging polarity, the transfer residual toner is sufficiently collected by the magnetic brush charger 32, and the positive ghost is improved.

For example, even when the fur brush charger 31 as the auxiliary member is not used, if the transfer voltage is increased, the polarity of the transfer residual toner is likely to be inverted, and the transfer residual toner in the magnetic brush charger 32 is removed. Recovery is improved.

However, as the average amount of toner charge, even if the polarity is reversed, a small amount of toner remains at the normal charge polarity, so that the positive ghost cannot be completely eliminated. Further, it is not preferable to increase the transfer voltage to an appropriate value or more, since this causes a decrease in transfer efficiency and the like.

As described above, by applying a voltage having a polarity opposite to the normal charging polarity of the photosensitive drum 1 to the fur brush charger 31 as an auxiliary member, the transfer residual toner having the reversed polarity is transferred to the magnetic brush charger 32. Will be collected.

In this embodiment, the bias applied to the magnetic brush charger 32 is only the DC voltage.
It is desirable to superimpose an alternating voltage on the DC voltage in order to further improve the recoverability of the transfer residual toner and the uniformity of the charging. More specifically, the effect can be obtained by setting an alternating voltage having a frequency of about 200 to 8000 Hz and an amplitude of about 200 to 1500 V.

Further, by increasing the amplitude of the alternating voltage (about 700 V or more), even when no voltage is applied to the fur brush charger 31, the prevention of a positive ghost may be realized in some cases. However, when the toner is fused to the magnetic carrier for charging due to long-term durability (10000 sheets or more) and the charging ability is reduced, a positive ghost occurs without the fur brush charger 31. By applying a bias having a polarity opposite to the normal charging polarity of the photosensitive drum 1 to the device 31, it is possible to prevent a positive ghost with respect to a certain reduction in charging ability.

Therefore, in the case where the alternating voltage is superimposed on the magnetic brush charger 32 as the second contact charging member, the charging means 31 to which a voltage having a polarity opposite to the normal charging polarity is applied as the second contact charging member. By providing
The recoverability of transfer residual toner and the charging uniformity in the magnetic brush charger 32 as the second contact charging member can be further improved, and a good image can be obtained for a longer period.

The transfer residual toner collected and mixed into the magnetic brush portion 32c of the magnetic brush charger 32 in the charging area n2 is mixed into the magnetic brush portion 32c of the conductive magnetic particles of the air brush charger 32 and The toner image is transferred to the normally charged toner by the rubbing, and the transfer voltage remaining in the previous image is erased by the alternating voltage due to the vibration effect of the electric field between the photosensitive drum 1 and the magnetic brush charger 32. The charged toner is discharged from the magnetic brush layer 32c onto the photosensitive drum 1 in a uniform state.

The toner that has been charged normally and discharged onto the photosensitive drum 1 is carried to the developing area, and is subjected to simultaneous cleaning (collection) by the two-component developing device 4.

That is, since the toner discharged from the second charging member to the image carrier is charged to the normal charging polarity, the DC voltage applied to the developing device 4 and the photosensitive drum 1 at the time of development by the developing means are changed. Recovery at the fog removal potential (Vback), which is the potential difference between the surface potentials, becomes possible. As a result, it is possible to prevent the appearance of a positive ghost in the previous image, and the toner discharged in a thin layer is advantageous in terms of recoverability during development. The occurrence of a positive ghost can be prevented, and the second charging member 3 which is the final contact charging means
Because the toner mixed in 2 can be sufficiently discharged,
The toner contamination of the second charging member can also be prevented.

(9) Prevention of Adhesion of Magnetic Particles to Photosensitive Drum 1 (FIG. 6) FIG. A width dimension (length dimension) L ₁ of the photosensitive drum 1 as an image carrier, b. The maximum image area width dimension L of the photosensitive drum 1
₂ , c. Fur brush charger 3 as first contact charging member
1, the longitudinal charging width L ₃₁ , d. Magnetic brush charger 32 as second contact charging member
In the longitudinal charging width L ₃₂ , e. FIG. _{5 is} a dimensional relationship diagram of a longitudinal developing width L4 of the developing device 4;

The longitudinal developing width L ₄ of the developing device 4 is the longitudinal dimension of the area where the developer is coated on the developing sleeve 42, and is almost the effective image area width L ₂ as shown in FIG. The longitudinal charging width L ₃₁ of the fur brush charger 31 as the first contact charging member is shorter than the longitudinal charging width L ₃₂ of the magnetic brush charger 32 as the second contact charging member. Longitudinal development width L ₄
It has a longer configuration.

[0114] by increasing the longitudinal charge width L ₃₁ of the fur brush charger 31 as a first contact charging member than the longitudinal development width L ₄ of the developing device 4, the photosensitive drum 1
Maximum image area width L ₂ all effect of preventing the positive ghost is improved by at.

[0115] Then, be less than the magnetic brush charger 32 in the longitudinal direction charge width L ₃₂ of the longitudinal charge width L ₃₁ of the fur brush charger 31 as a first contact charging member as the second contact charging member Accordingly, it is possible to eliminate a region which is charged by the fur brush charger 31 as the first contact charging member and is not charged by the magnetic brush charger 32 as the second contact charging member. When an area charged by the fur brush charger 31 serving as the first contact charging member and not receiving the charge of the magnetic brush charger 32 serving as the second contact charging member is generated, a magnetic field serving as the second contact charging member is generated. The photosensitive drum potential at the longitudinal end of the brush charger 32 becomes positive, and the magnetic brush charger 32
If the magnetic brush portion 32c at the longitudinal end of the magnetic brush portion 32c protrudes even slightly to the plus region, the magnetic particles constituting the magnetic brush layer 32c tend to adhere to the surface of the photosensitive drum 1 due to the potential difference.

Therefore, as in this example, the longitudinal charging width L ₃₁ of the fur brush charger 31 as the first contact charging member is equal to the longitudinal charging width L ₃₁ of the magnetic brush charger 32 as the second contact charging member. shorter than L _32, by the longer configuration than the longitudinal development width L ₄ of the developing device 4, it is possible to prevent the adhesion of the magnetic particles to the photosensitive member.

(10) Others 1) In addition to the laser scanning means of the embodiment, the image exposure means as the information writing means for the charged surface of the image carrier may be, for example, a solid light emitting element such as an LED. A latent image may be formed in the vicinity and formed by the light emission. An analog image exposure unit using a halogen lamp, a fluorescent lamp, or the like as a light source may be used. Any device that can form an electrostatic latent image corresponding to image information may be used.

2) The image carrier may be an electrostatic recording dielectric or the like. In this case, after uniformly charging the dielectric surface,
The charged surface is selectively discharged by a discharging means such as a discharging needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information.

3) The method and means for developing the electrostatic latent image with toner are arbitrary. A reversal development system or a regular development system may be used.

4) The magnetic brush charger 32 as the second contact charging member is not limited to the sleeve rotating type of the embodiment, but may rotate the magnet roll 32a or change the surface of the magnet roll 32a as required. A configuration may be adopted in which a conductive process is performed as a power supply electrode, the conductive magnetic particles are magnetically constrained directly on the outer peripheral surface of the magnet roll 32a to form the magnetic brush portion 32c, and the magnet roll 32a is rotated. it can. A non-rotating type magnetic brush member may be used.

5) The fur brush charger 31 as the first contact charging member may be of a rotary type instead of a fixed type. A contact charging member of a type other than the fur brush, such as a roller or a flat plate made of a conductive elastic member, can also be used.

6) Three or more contact charging members may be provided in the surface moving direction of the image carrier 1.

7) As the waveform of the alternating voltage applied to the charging member and the developing member, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It may be a rectangular wave formed by periodically turning on / off the DC power supply. As described above, the alternating voltage can use a bias whose voltage value changes periodically.

8) The transfer means is not limited to belt transfer, but may be any transfer such as roller transfer or corona discharge transfer. Further, the present invention can be applied not only to a single-color image but also to an image forming apparatus that forms a multi-color or full-color image by multiple transfer or the like using an intermediate transfer member such as a transfer drum or a transfer belt.

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

It is also possible to adopt an apparatus configuration in which any process equipment such as the image carrier 1, the charging members 31 and 32, and the developing device 4 is collectively detachable from the image forming apparatus main body.

10) The image forming apparatus, after transferring the toner image formed on the image carrier to the image display section without transferring it to the recording material and displaying and reading the image, simultaneously collects the development from the surface of the image carrier simultaneously. The image carrier may be an image display device that repeatedly provides images.

[0128]

As described above, according to the present invention, in the image forming apparatus of the contact charging system and the cleaner system using the charging auxiliary member, the adhesion of the magnetic particles to the end portion of the image carrier can be suppressed. Thus, an image forming apparatus of very stable quality can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention.

FIG. 2 is a schematic diagram of a layer configuration of a photosensitive drum.

FIG. 3 is an enlarged cross-sectional model view of the first and second contact charging members.

FIG. 4 is a diagram illustrating a configuration of a laser scanning unit.

FIG. 5 is a structural model diagram of a developing device.

FIG. 6 is a dimensional relationship diagram of a photosensitive drum, an image area width, a charging width by the first and second contact charging members, and a developing width.

FIG. 7 is a schematic configuration diagram of a conventional example of an image forming apparatus.

[Explanation of symbols]

Reference Signs List A laser beam printer B image reading device (image scanner) 1 photosensitive drum (image carrier) 31 fur brush charger as first contact charging member 32 magnetic brush charger as second contact charging member L ₁ photosensitive drum the width dimension (length dimension) L ₂ longitudinal development width of the maximum image area width L ₃₁ fur brush charging assembly in the longitudinal direction charge width L ₃₂ magnetic brush charging assembly longitudinally charging width L ₄ developing device on the photosensitive drum

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03G 21/10 G03G 21/00 312

Claims (10)

[Claims] 1. An image forming method comprising: charging an image carrier with respect to the image carrier; forming an electrostatic latent image on a charged surface of the image carrier; and developing the electrostatic latent image as a toner image. The developing means for applying the process to form an image and developing the electrostatic latent image as a toner image also serves as an image carrier cleaning means for collecting toner particles remaining on the image carrier in the previous image formation, and The carrier is an image forming apparatus of a cleanerless system for repeatedly performing image formation. As a charging unit for charging the image carrier, the image carrier has at least a first contact charging member and an image bearing member which is more than the contact charging member A plurality of contact charging members of the second contact charging member on the downstream side in the body rotation direction are provided, and the bias applied to the first contact charging member is opposite in polarity to the normal charging polarity of the image carrier,
The bias applied to the second contact charging member, which is a charging unit for finally charging the image carrier, is the normal charging polarity of the image carrier, and the longitudinal charging width of the first contact charging member is An image forming apparatus, wherein the width of the charging member in the longitudinal direction of the contact charging member is shorter than the width of the developing region in the longitudinal direction of the developing means. 2. The image carrier has a surface having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω.
The image forming apparatus according to claim 1, further comprising a layer made of a material having a size of about cm. 3. The image forming apparatus according to claim 1, wherein the image carrier has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles. 4. The image forming apparatus according to claim 3, wherein the conductive fine particles are SnO ₂ . 5. The image forming apparatus according to claim 1, wherein the image carrier is formed of a surface layer having amorphous silicon. 6. The image forming apparatus according to claim 1, wherein the second contact charging member has a magnetic brush portion of conductive magnetic particles, and the magnetic brush portion is in contact with the image carrier. The image forming apparatus according to any one of the above. 7. The image forming apparatus according to claim 1, wherein the first contact charging member has a conductive fiber brush portion, and the conductive fiber brush portion is in contact with the image carrier. The image forming apparatus according to one of the above. 8. The method according to claim 1, wherein a developing method of said developing means is a contact developing method in which a developer is in contact with an image carrier. Image forming device. 9. The image forming apparatus according to claim 1, wherein the electrostatic latent image forming means for the charged surface of the image carrier is an image exposing means for the image carrier. . 10. The image forming apparatus according to claim 1, wherein the toner image formed on the image carrier is transferred to a transfer material by a transfer unit.