JP3507265B2 - Image forming device - Google Patents

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 bearing member on the image bearing member, 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 an image is formed by applying an image forming process having the above, and an image carrier is repeatedly used for image formation.

More specifically, the "cleanerless system" in which the developing means for developing the electrostatic latent image with toner also serves as the image carrier cleaning means for collecting the toner particles remaining on the image carrier in the previous image formation. Image forming apparatus.

[0003]

2. Description of the Related Art FIG. 7 is a schematic diagram of an example of a transfer type electrophotographic apparatus (copying machine, printer, facsimile, etc.) as a conventional example of an image forming apparatus.

Reference numeral 1 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed.

In the course of its rotation, the photosensitive drum 1 is subjected to uniform charging processing of a predetermined polarity and potential by a charging roller 3 as a charging means, and an image exposure means (not shown) (projection / image formation exposure means of original image, The uniformly charged surface is selectively neutralized (or the potential is attenuated) in accordance with the exposure image pattern by receiving the image exposure L by the laser light scanning exposure means or the like).
As a result, an electrostatic latent image is formed. Then, the formed electrostatic latent image is developed as a toner image by the toner developing device 4 as developing means.

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 a transfer means at a predetermined control timing. Then, the back surface of the transfer material P is charged with a polarity opposite to that of the toner, so that the toner image on the surface of the photosensitive drum 1 is electrostatically transferred to the front surface side of the transfer material P.

Next, the transfer material P is separated from the surface of the rotary photosensitive drum 1, introduced into a fixing device 6, subjected to a fixing process of a toner image, and output as an image formed product (copy, print).

The surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is cleaned by the cleaning means (cleaner) 8 to remove the transfer residual toner, and is repeatedly used for image formation.

In recent years, such devices have been downsized, but there has been a limit only to downsizing the charging, exposing, developing, transferring, fixing, and cleaning process devices as described above.

Although the above-mentioned transfer residual toner is collected as waste toner by the cleaner 8, it is preferable that this waste toner is not environmentally friendly.

1) Therefore, an image forming apparatus of "cleanerless system" has also appeared in which the cleaner 8 is removed and the developing device 4 performs cleaning (collection of residual toner after transfer) simultaneously with development.

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

According to this method, the transfer residual toner is collected by the developing device 4 and used in the subsequent steps, so that the waste toner can be eliminated. Further, the cleaner-less structure has a great advantage in terms of space, and the image forming apparatus can be significantly downsized.

2) By the way, in recent years, as a charging means for charging an object to be charged such as an image bearing member, since it has advantages such as low ozone and low power, a voltage is applied to the contact charging device, that is, the object to be charged. An apparatus of the type in which the charged member (contact charging member) is brought into contact to charge the charged body has been put into 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.

The magnetic brush charger magnetically restrains conductive magnetic particles as a magnetic brush directly on a magnet or a sleeve containing the magnet, and contacts the charged body while stopping or rotating the magnetic brush. 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 (roller charger, charging roller) made of conductive rubber in a roll is preferably used as the contact charging member. Has been.

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

This charging method is called "injection charging".
Called. By using this injection charging, since the charging phenomenon is not performed by using the corona charger, charging to the body to be charged is completely ozoneless and low power consumption type charging is possible. .

[0020]

However, in an image forming apparatus using such a contact charging system, a cleaner means is not provided, and the developing means simultaneously collects the development, and when the image formation is repeated, the transfer is performed. Since the residual toner cannot be collected by the developing means, a “positive ghost” in which the previous image remains thin occurs.

This positive ghost is a phenomenon that occurs when the transfer residual toner cannot pass through the contact charging member at the position of the contact charging member, and the surface portion of the image carrier below the transfer residual toner cannot be charged.

Therefore, when the surface of the image bearing member is charged by the contact charging member, the surface portion of the image bearing member below the transfer residual toner is also charged. Therefore, the residual toner after transfer is stripped from the surface of the image bearing member and returned to the surface of the image bearing member after charging. It is important that the toner is discharged from the contact charging member to the image carrier and collected by the developing means.

Further, with respect to toner stains on the contact charging member, toner particles having a relatively high electric resistance are usually used, so that the toner particles are mixed in the contact charging member.
If the mixed toner particles cannot be sufficiently discharged to the image carrier, the resistance of the whole or a part of the contact charging member rises, and the image carrier cannot be charged to a desired potential, or the charging is performed. There is a drawback that unevenness occurs and an image defect occurs.

Therefore, at least two contact charging members contacting the image carrier are provided in the image carrier rotation direction, and the contact charging member located upstream of the other in the image carrier rotation direction is the 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 that finally charges 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 of the bias applied to the second charging member is applied to the first charging member so that the transfer residual toner is normally charged to the image carrier by the first charging member. In the second charging member as the final charging means that is charged in the opposite polarity, when the contact charging member using magnetic particles is used as the second charging member to charge the image carrier to the normal charging polarity. Transfer residual toner is collected at the time of charging (since the charging potential is generally lower than the applied bias, toner of the opposite polarity is more likely to be collected), and the image carrier surface area under the transfer residual toner is also uniformly charged. Further, the triboelectric charging characteristic of the magnetic particles of the second charging member charges the toner particles to the normal polarity, so that the toner particles collected by the second charging member are charged to the normal charging polarity. On the image carrier Spit (in accordance with the principles of reverse within the parentheses) it becomes possible.

Further, since the toner discharged from the second charging member to the image carrier in this way is charged to the normal charging polarity, the developing means collects it at the fog removing potential (Vback) at the time of development. It is possible to prevent the generation of positive ghosts, and it is possible to sufficiently discharge the toner mixed in the second charging member which is the final contact charging means, so that the toner contamination of the second charging member can be prevented. .

For the sake of convenience, the image forming apparatus having the above-mentioned structure is referred to as an image forming apparatus of a contact charging type using a charging auxiliary member and a cleaner system.

However, in such an image forming apparatus of a contact charging system or a cleaner system using a charging assisting member, there is a problem that 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]

The present invention is an image forming apparatus having the following configuration.

(1) A step of charging the image bearing member with respect to the image bearing member, a step of forming an electrostatic latent image on the charged surface,
An image forming process having a step of developing the electrostatic latent image as a toner image is applied to execute image formation, and a developing unit for developing the electrostatic latent image as a toner image is formed on the image carrier in the previous image formation. The image bearing member is an image forming apparatus of a cleanerless system that also serves as an image bearing member cleaning unit for collecting the remaining toner particles and is repeatedly used for image formation. At least a first contact charging member and a plurality of contact charging members of a second contact charging member downstream of the contact charging member in the rotation direction of the image carrier are disposed, and a bias applied to the first contact charging member. Is a polarity opposite to the normal charging polarity of the image carrier, and the bias applied to the second contact charging member, which is a charging means for finally charging the image carrier, is the normal charging polarity of the image carrier, second Contact charging member is a magnetic brush charger
The image forming apparatus is characterized in that the charging width in the longitudinal direction of the first contact charging member is shorter than the charging width in the longitudinal direction of the second contact charging member and longer than the developing area width in the longitudinal direction of the developing means.

(2) The magnetic brush charger is the developer
The developer and clean the developer by rubbing against the magnetic brush.
The image formation according to (1), which is charged to a regular charge.
apparatus. (3) The surface of the image bearing member is 10 ⁹ to 10 ¹⁴ Ω · cm
(1) characterized by having a layer made of the material
Is the image forming apparatus according to (2) .

(4) The image bearing member has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles, (1) to (3). Image forming device.

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

(6) The image forming apparatus according to (1) or (2), wherein the image carrier is composed of a surface layer containing amorphous silicon.

[0034]

(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 1.

(8) One of (1) to (7), wherein the developing method of the developing means is a contact developing method in which the developer is brought into contact with the image carrier. The image forming apparatus according to item 1.

(9) The electrostatic latent image forming means for the charged surface of the image carrier is an image exposing means for the image carrier, according to any one of (1) to (8). Image forming apparatus.

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

<Operation> By making the longitudinal charging width of the first contact charging member longer than the developing width in the longitudinal direction of the developing means, the effect of preventing positive ghosts from occurring in all the maximum image area width dimensions of the image carrier Will be good.

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 and the second contact charging member is charged. It is possible to eliminate a region where the member is not charged. When a region is generated which is charged by the first contact charging member and is not charged by the second contact charging member, the surface potential of the image carrier at the longitudinal end portion of the second contact charging member becomes the first contact charging member. When the magnetic brush portion at the longitudinal end portion of the second contact charging member protrudes into the area even a little, the magnetic particles forming the magnetic brush portion easily adhere to the image carrier surface due to the potential difference. Become.

Therefore, by making the longitudinal charging width of the first contact charging member shorter than the longitudinal charging width of the second contact charging member and longer than the longitudinal developing width of the developing means, the image bearing can be carried out. It is possible to prevent adhesion of magnetic particles to the body.

[0042]

DETAILED DESCRIPTION OF THE INVENTION

(1) Schematic configuration of an example of an 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, and uses a fur brush charger as an auxiliary member, and a developing means. This is an image forming apparatus of a cleanerless system that simultaneously performs development and cleaning.

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, 10 is a document table glass fixedly arranged on the upper surface of the apparatus, and the document G is placed on the upper surface of the document table glass with the surface to be copied down. Then, the original document pressure plate (not shown) is placed thereon and set.

An image reading unit 9 is provided with an original irradiation lamp 9a, a short focus lens array 9b, a CCD sensor 9c and the like. When a copy button (not shown) is pressed, the unit 9 is driven forward along the glass lower surface from the home position on the left side of the glass under the platen glass 10 to the right side, and a predetermined forward movement is performed. When it reaches the end point, it is driven back and returned to the initial home position.

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

The CCD sensor 9c comprises a light receiving section, a transfer section and an output section. An optical signal is converted into a charge signal in the CCD light receiving unit, and sequentially transferred to the output unit in synchronization with a clock pulse in the transfer unit, and the charge signal is converted into a voltage signal in the output unit, amplified, reduced in impedance, and output. The analog signal thus obtained is subjected to well-known image processing to be converted into a digital signal, and the printer A
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, 1 is a rotary drum type, charge injection charging type, negatively charging electrophotographic photosensitive member (photosensitive drum) as an image bearing member. The photosensitive drum 1 is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed about a central support shaft, in this example, a rotational speed of 100 mm / sec, and in the course of the rotation, in the case of this example, the charging means 3 is used. Finally, it is uniformly charged with negative polarity.

The charging means 3 in this example is composed of the first and second charging means 3.
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 that apply predetermined charging biases to the first and second contact charging members 31 and 32, respectively.

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) 2 and sent from the image reading device B to the printer A side. The scanning exposure L is performed by the laser light that has been generated, so that the original G that is photoelectrically read by the image reading device B on the surface of the rotary photosensitive drum 1
Electrostatic latent images corresponding to the image information of are sequentially formed.

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 reversal development. S3 is a power source 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 housed in the paper feed cassette 5 is fed out by a paper feed roller 51, and a predetermined path is formed by a path of sheet path 52 → registration roller pair 52 → sheet path 53. At the control timing, the toner image on the side of the photosensitive drum 1 is fed to the transfer portion 75, which is a contact nip portion between the photosensitive drum 1 and the transfer belt 71 of the transfer belt device 7 as the transfer means, and the toner image on the side of the photosensitive drum 1 is transferred onto the transfer material at the transfer portion 75. It is electrostatically transferred to the side. That is, the transfer material P is conveyed from the paper feeding / conveying device to the transfer portion 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, and is stretched between the driving roller 72 and the driven roller 73 so as to rotate in the direction of the arrow at a peripheral speed substantially equal to the peripheral speed of the photosensitive drum 1. Driven. Reference numeral 74 denotes a transfer charging blade provided in contact with the back surface side of the transfer belt 71 in the transfer section 72, which also functions as a pressing member for pressing the transfer belt 71 against the photosensitive drum 1 in a predetermined manner, and a power source S4.
As a result, a predetermined transfer bias is applied, and the reverse surface of the transfer material is charged with a polarity opposite to that of the toner. As a result, the toner image on the photosensitive drum 1 side is electrostatically transferred to the transfer material side on the transfer portion 75.

The transfer material that has received the toner image on the photosensitive drum 1 side in the transfer portion 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, and the toner image is thermally fixed. Then, the paper discharge roller 6a receives
It is output as a copy or a print on the discharge tray 6b outside the machine.

Since the printer of this example is cleaner- less, no 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 provided. The transfer residual toner on the surface is collected by the developing device 4 by cleaning at the same time as development, and the surface of the rotary 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 photoconductor or the like can be used, but it is desirable that a resistance is provided on the organic photoconductor. By using a material having a surface layer having a material of 10 ⁹ to 10 ¹⁴ Ω · cm, an amorphous silicon photoconductor, or the like, charge injection charging can be realized, which is effective in preventing ozone generation and reducing power consumption.
In addition, it becomes possible to improve the charging property.

Therefore, in this example, as the photosensitive drum 1, as shown in the layer structure model of FIG. 2, a negatively charged organic photosensitive member is used, and the following first layer is formed on an aluminum base (Al drum base) 11 having a diameter of 30 mm. A charge-injection chargeable photosensitive drum in which the fifth to fifth functional layers are provided in order from the bottom was used.

The first layer 12 is an undercoat layer and has a thickness of 2 provided to smooth defects such as the Al drum base 11.
It is a conductive layer of 0 μm.

Second layer 13: a positive charge injection prevention layer, A
The positive charge injected from the drum base 11 prevents the negative charge charged on the surface of the photoconductor from being canceled, and the resistance is adjusted to about 1 × 10 ⁶ Ω · cm by the amylan resin and methoxymethylated nylon. It is a medium resistance layer having a thickness of 1 μm.

Third layer 14: 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 when exposed to light.

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

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, the insulating resin is doped with antimony, which is a light-transmitting insulating filler, to reduce the resistance (conductivity), and the particle size is about 0.03μ.
m is a coating layer of a material in which 70 wt% of SnO ₂ particles are dispersed in a resin.

The coating solution thus prepared was applied to a thickness of about 3 μm by a suitable coating method such as a dipping coating method, a spray coating method, a roll coating method and a beam coating method to form a charge injection layer. The surface resistance is 10 ¹³ Ωcm. By controlling the surface resistance in this way, the direct charging property is improved and a high quality image can be obtained. Photoconductor is OPC
Not limited to, a-Si (amorphous silicon) drum, a-
It can be realized even by using a surface layer having Si, and higher durability can be realized.

Here, the volume resistance of the surface layer 16 was measured by arranging metal electrodes at intervals of 200 μm, injecting a preparation liquid of the surface layer between them to form a film, and applying a voltage of 100 V between the electrodes. It is a value. Measurement temperature 23 ℃, humidity 50% RH
It is the value measured under the condition of.

(3) Contact Charging Device (FIG. 3) The charging means 3 in this example 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 example, the first contact charging member 31 is a fixed brush type fur brush charger using conductive fibers, and the second contact charging member 32 is a rotating sleeve type magnetic brush charger using a magnetic carrier. First contact charging member 3
Reference numeral 1 is arranged upstream of the second contact charging member 32 in the rotation direction of the photosensitive drum 1.

1) Fur brush charger 31 The fixed brush type fur brush charger 31 as the first contact charging member has a horizontally long supporting metal plate 3 as an electrode plate.
A conductive fiber brush portion 31b is formed on 1a. 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 / inch ² , a brush diameter of 2 to 12 denier, and a brush resistance of 10 ^-2 to 10 ¹² Ω · cm, and charging. It can be used by controlling the current value flowing occasionally to about 5 to 50 μA.

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

Then, a charging bias of +20 is applied from the power source S1 to the supporting metal plate 31a as the electrode plate of the charger 31.
DC bias (+200 to +200) with μA constant current control
0 V) was applied.

2) Magnetic brush charger 32 A rotary sleeve type magnetic brush charger 32 as a second contact charging member is provided with a fixedly supported magnet roll 32a and a magnet roll 32a which is concentrically rotated around the outer periphery of the magnet roll to freely rotate. The non-magnetic conductive charging sleeve 32b having an outer diameter of 16 mm and the conductive magnetic particles formed by being attracted and held by the magnetic force of the magnet roll 32a inside the charging sleeve to the outer peripheral surface of the charging sleeve. The magnetic brush portion 32c of the carrier).

The magnetic brush charger 32 is arranged substantially in parallel with 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. It was arranged.

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

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

As the charging sleeve 32b rotates, the magnetic brush portion 32c rotates in the same direction and rubs against the surface of the photosensitive drum 1, and electric charges are applied onto the photosensitive drum 1 from the charging magnetic carrier forming the magnetic brush portion 32c. The surface of the photosensitive drum is charged to a potential corresponding to the charging voltage. In the case of this example, the photosensitive drum 1 is charged and charged to approximately -650V. The charging sleeve 32b tends to have better charging uniformity as the rotation speed increases.

The charging magnetic carrier constituting the magnetic brush portion 32c has 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.
It is preferably × 10 ¹⁰ Ω · cm. Considering that the photosensitive drum 1 has an insulating defect such as a pinhole, it is preferable to use one having a resistance of 1 × 10 ⁶ Ω · cm or more. In order to improve the charging performance, it is better to use the one with the smallest possible resistance, so in this example, the average particle size 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. The charging magnetic carrier used in this example oxidizes the surface of the phyllite,
The one that has undergone reduction treatment and resistance adjustment is used.

Here, the resistance value of the magnetic carrier is as follows after 2 g of the carrier is put into a metal cell having a bottom area of 228 mm ² .
The measurement is performed by applying a weight of 6.6 kg / cm ² and applying a voltage of 100V.

The average particle diameter of the magnetic carrier is shown by the maximum chord length in the horizontal direction, and the measuring method was calculated by randomly selecting 300 or more particles by a microscopic method, measuring the diameter, and taking the arithmetic mean.

To measure the magnetic characteristics of the magnetic carrier, a DC magnetization BH characteristic automatic recording apparatus BHH-5 manufactured by Riken Denshi Co., Ltd.
0 can be used. At this time, the diameter (inner diameter) 6.5
A magnetic carrier is loaded into a cylindrical container having a size of 10 mm and a height of 10 mm with a load of about 2 g, and the saturation magnetization is measured from the BH curve 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 surface to be scanned 1 (rotary 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) Then, 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 the arrow b
The scanning is performed in the direction of arrow c by the rotary polygon mirror 24 which rotates at high speed in the direction of f and the fθ lens group 25
25c) forms an image in a spot on the surface to be scanned 1.
An exposure distribution for one scan of an image is formed on the surface to be scanned 1 by such laser light scanning, and the surface to be scanned 1 is further scanned for each scan.
By scrolling by a predetermined amount in a direction perpendicular to the scanning direction, an exposure distribution corresponding to an image signal can be obtained on the surface to be scanned 1.

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

In this example, a mixture of non-magnetic toner particles and magnetic carrier particles is used as a developer,
A two-component magnetic brush contact developing method in which the developer is held as a magnetic brush layer by a magnetic force on a developer carrier and is conveyed to a developing portion to contact the surface of the photosensitive drum 1 to develop an electrostatic latent image as a toner image I am using. The two-component magnetic brush contact development is very suitable for collecting the 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 example. 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 is a thin layer of the developer on the surface of the developing sleeve. For controlling the developer layer thickness, 45 is a developer stirring and conveying screw, and 46 is a developer container 41
It is a component developer and is a mixture of non-magnetic toner particles t and magnetic carrier particles c.

The developing sleeve 42 has a closest distance (gap) to the photosensitive drum 1 of about 5 at least during development.
The developer magnetic brush thin layer 46a 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 portion m between the developer magnetic brush layer 46a and the photosensitive drum 1
Is a developing area (developing section).

The developing sleeve 42 is driven around the fixed magnet roller 43 in the counterclockwise direction indicated by an arrow at a predetermined rotation speed, and the magnetic force of the magnet roller 43 causes the developer 46 to be applied to the outer surface of the sleeve inside the developing container 41. A magnetic brush is formed. The developer magnetic brush is sleeve 4
It is conveyed along with the rotation of 2 and is subjected to a layer thickness regulation by the blade 44 and is taken out of the developing container as a developer magnetic brush thin layer 46a having a predetermined layer thickness and conveyed to the developing portion to contact the surface of the photosensitive drum 1 and continue. When the sleeve 42 rotates, it is returned to the developing container 41 and conveyed again.

That is, first, the developer 46 drawn up by the N ₂ pole of the magnet roller 43 along with the rotation of the developing sleeve 42 is perpendicular to the developing sleeve 42 in the process of being conveyed from the S ₂ pole to the N ₁ pole. A thin layer 46 a of the developer 46 is formed on the developing sleeve 42 by being regulated by the regulating blade 44 disposed in the. When the thin-layered developer layer 46a is conveyed to the main developing electrode S ₁ of the developing section, the magnetic force causes the formation of ears. An electrostatic latent image on the photosensitive drum 1 by the developing agent layer 46a formed on the spikes is developed as a toner image, the developer on the developing sleeve 42 by a repulsive magnetic field of the subsequent N ₃ pole · N ₂ pole developing container 41
Returned inside.

Between the developing sleeve 42 and the conductive drum base of the photosensitive drum 1, a developing bias applying power source S3 applies a developing bias of a DC voltage and an alternating voltage.

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 46a on the developing sleeve 42 side selectively adheres to the electrostatic latent image on the photosensitive drum 1 side in the developing section, and the electrostatic latent image becomes toner. It is developed as an image.

Generally, in the two-component developing method, when an alternating voltage is applied, the developing efficiency is increased and the image is of high quality, but on the contrary, there is a risk that fogging is likely to occur. Therefore, normally, by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1, it is possible to prevent fogging.

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

The toner concentration (mixing ratio with the carrier) of the developer 46 in the developing container 41 is gradually decreased 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 drops to a predetermined lower limit concentration, toner is replenished to the developer 46 in the developing container from a toner replenishing unit (not shown) for development. Toner replenishment control is performed 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 a toner particle t; a negatively charged toner having an average particle size of 6 μm, to which titanium oxide having an average particle size of 20 nm is externally added by 1% by weight. Carrier c: saturation magnetization Of 205 emu / cm ³ mixed with a magnetic carrier having an average particle diameter of 35 μm in a weight ratio of 6:94. At this time, the toner in the developer has a triboelectric charge amount of about 25 × 10 ⁻³ c / kg.
Met.

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

A Coulter counter T is used as a measuring device.
An A-II type (manufactured by Coulter) is used, an interface (manufactured by Nikkaki) that outputs a number average distribution and a volume average distribution, and a CX-i personal computer (manufactured by Canon) are connected, and a primary sodium chloride is used as an electrolytic solution. 1% NaC
l Prepare an aqueous solution.

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

The electrolytic solution in which the sample was suspended was subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and a particle size distribution of particles of 2 to 40 μm was obtained using a 100 μm aperture as an aperture by the Coulter Counter TA-II type. To determine the volume distribution. The volume average particle diameter of the sample is obtained from the obtained volume distribution.

As the toner particles t, it is more preferable to use spherical toner particles produced by a suspension method and having an average particle size of about 6 μm. Since the toner produced by the polymerization method has a shape close to a sphere, the external additive is uniformly coated. Therefore, the releasability from the photosensitive drum 1 is extremely good. In addition, the fog is also better than that of the pulverized toner, and since the transfer residual toner is in an extremely small amount and has a high releasability, there is no cleaner and a cleanerless device that collects the transfer residual toner at the time of development by the developing means. When the system image forming device configuration is adopted, the collectability is improved, which is even better.

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

Further, as the transfer charging blade 74, one having a resistance of 1 × 10 ⁵ to 1 × 10 ¹⁷ Ω was used. A bias of +15 μA was applied to the transfer charging blade 74 by constant current control to perform transfer.

(7) Charge Injection Charging Charge injection charging is to inject charges to the surface of the member to be charged (photosensitive drum) having a medium resistance surface resistance with a medium resistance contact charging member. This is a method of charging the conductive particles (SnO ₂ ) 16a of the charge injection layer 16 with electric charges, instead of injecting charges into the trapping potential of the drum surface material, and using the charge transport layer 15 as a dielectric. , Aluminum drum substrate 11 and charge injection layer 1
It is considered to be based on the theory that the contact charging member 32 charges the minute capacitor having the conductive particles 16a in 6 as both electrode plates. At this time, the conductive particles 16
a is electrically independent from each other and forms a kind of minute float electrode. For this reason, the surface of the photosensitive drum seems to be charged and charged to a uniform potential on a macroscopic scale, but in reality SnO _2, which is a myriad of charged conductive particles, covers the surface of the photosensitive drum. The situation is as follows. Therefore, image exposure L by laser light
Even if the above is performed, each SnO ₂ particle 16a is electrically independent, so it is expected that an electrostatic latent image can be held.

(8) Collection and discharge of transfer residual toner by the contact charging member, cleaning at the same time as the transfer residual toner remains on the surface of the photosensitive drum 1 after the toner image is transferred to the transfer material P. There are some transfer residual toners whose charging polarity is reversed and those which are not reversed due to peeling discharge during transfer. Here, the toner whose polarity is reversed is collected by the magnetic brush charger 32 which is the second contact charging member, but the toner whose polarity is not reversed is collected by the magnetic brush charger 32. It is difficult to do (because the charging potential is generally lower than the bias applied to the charger).

Therefore, in this example, the transfer portion (transfer area portion) 7
5 and the magnetic brush charger 32, a first contact charging member as an auxiliary member, a fixed brush type fur brush charger 31 using conductive fibers in this example, is provided, and the photosensitive drum 1 is normally charged. A voltage having a polarity opposite to the charging polarity of No. 1 is applied to charge the transfer residual toner in the opposite polarity to the normal charging polarity, thereby enhancing 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, the polarity of the transfer residual toner is easily reversed by increasing the transfer voltage, and the transfer residual toner in the magnetic brush charger 32 is easily changed. Collectability is improved.

However, as the average toner charge amount, even if the polarity is reversed, some toner remains with the normal charging polarity, so that the positive ghost cannot be completely erased. Further, it is not preferable to make the transfer voltage stronger than an appropriate value, because the transfer efficiency is lowered.

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

In this example, the bias applied to the magnetic brush charger 32 was only the DC voltage.
In order to further improve the collectability of the transfer residual toner and the charging uniformity, it is desirable to superimpose an alternating voltage on the DC voltage. Specifically, the effect is obtained by setting the alternating voltage of about 200 to 8000 Hz as the frequency and about 200 to 1500 V as the amplitude.

By increasing the amplitude of the alternating voltage (about 700 V or more), positive ghost may be prevented even if the voltage is not applied to the fur brush charger 31. However, if the toner is fused to the charging magnetic carrier due to long-term durability (10,000 sheets or more) and the charging ability is reduced, positive ghosts will occur if the fur brush charger 31 is not provided. By applying a bias having a polarity opposite to the normal charging polarity of the photosensitive drum 1 to the container 31, it is possible to prevent positive ghost even if the charging capability is lowered to some extent.

Therefore, in the case where an alternating voltage is superposed on the magnetic brush charger 32 as the second contact charging member, the charging means 31 applying the voltage of the opposite polarity of the normal charging polarity as the second contact charging member. By providing
The magnetic brush charger 32 serving as the second contact charging member can further improve the collectability of the transfer residual toner and the charging uniformity, and a good image can be obtained for a longer period of time.

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

The toner which has been normally charged and discharged onto the photosensitive drum 1 is carried to the developing area and is cleaned (collected) by the two-component developing device 4 simultaneously with development.

That is, since the toner discharged from the second charging member to the image bearing member is charged to the regular charging polarity, the DC voltage applied to the developing device 4 and the photosensitive drum 1 at the time of developing in the developing means. It is possible to collect at the fog-removing potential (Vback), which is the potential difference between the surface potentials. This makes it possible to prevent the appearance of positive ghosts in the previous image, and the toner discharged in a thin layer is also advantageous in the collectability during development. Then, generation of positive ghost can be prevented, and the second charging member 3 which is the final contact charging means.
Since the toner mixed in 2 can be discharged sufficiently,
Toner contamination of the second charging member can also be prevented.

(9) Prevention of Attachment of Magnetic Particles to Photosensitive Drum 1 (FIG. 6) FIG. 6 shows a. Width dimension (length dimension) L ₁ of the photosensitive drum 1 as an image carrier, b. Maximum image area width dimension L on 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
Longitudinal charging width L ₃₂ , e. A dimensional relationship diagram in the longitudinal direction the developing width L ₄ of the developing device 4.

[0113] longitudinal development width L ₄ of the developing device 4 is that the longitudinal dimension of the area is coated a developer on the developing sleeve 42, as shown in FIG. Is almost effective image area width L ₂ The longitudinal charging width L ₃₁ of the fur brush charger 31 serving as the first contact charging member is shorter than the longitudinal charging width L ₃₂ of the magnetic brush charger 32 serving as the second contact charging member. Longitudinal development width L ₄
It has a longer configuration.

By making the longitudinal charging width L ₃₁ of the fur brush charger 31 as the first contact charging member longer than the longitudinal developing width L _{4 of the} developing device 4, the photosensitive drum 1
In all of the maximum image area width dimension L _{2 in the above} , the positive ghost generation preventing effect is improved.

The longitudinal charging width L ₃₁ of the fur brush charger 31 as the first contact charging member is made shorter than the longitudinal charging width L ₃₂ of the magnetic brush charger 32 as the second contact charging member. As a result, 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 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 is generated, the magnetic force as the second contact charging member is generated. The photosensitive drum potential at the end of the brush charger 32 in the longitudinal direction 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 into the positive region, the magnetic particles forming the magnetic brush layer 32c easily adhere to the surface of the photosensitive drum 1 due to the potential difference.

Therefore, as in the present example, the longitudinal charging width L ₃₁ of the fur brush charger 31 as the first contact charging member is 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 exposing means as the information writing means for the charged surface of the image carrier is, for example, a solid light emitting element such as an LED as the image carrier. It may be provided in close proximity to form a latent image by the light emission. It may be an analog image exposure means using a halogen lamp, a fluorescent lamp or the like as a light source. Anything can be used as long as it can form an electrostatic latent image corresponding to image information.

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 neutralized by a neutralizing means such as a neutralizing needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information.

3) The toner developing system / means for the electrostatic latent image is arbitrary. The reversal development method or the regular development method may be used.

4) The magnetic brush charger 32 as the second contact charging member is not limited to the sleeve rotation type of the embodiment, but the magnet roll 32a rotates or the surface of the magnet roll 32a may be changed as necessary. It is also possible to use a structure in which the power supply electrode is subjected to a conductivity treatment, the conductive magnetic particles are magnetically bound directly to 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 can also be used.

5) The fur brush charger 31 as the first contact charging member may be a rotary type instead of a fixed type. It is also possible to use a contact charging member of a type other than the fur brush, such as a roller body or a flat plate body made of a conductive elastic member.

6) Three or more contact charging members may be arranged 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 appropriately used. It may be a rectangular wave formed by periodically turning the DC power supply on and off. In this way, the alternating voltage can be biased so that its voltage value changes periodically.

8) The transfer means is not limited to belt transfer, but may be roller transfer, corona discharge transfer, or the like. Further, by using an intermediate transfer body such as a transfer drum or a transfer belt, it can be applied not only to a single color image but also to an image forming apparatus for forming a multicolor or full color image by multiple transfer.

9) The image forming process of the image forming apparatus is not limited to that of the embodiment and is arbitrary. Also, other auxiliary process equipment may be added if necessary.

It is also possible to have an apparatus structure in which arbitrary process equipment such as the image carrier 1, the charging members 31 and 32, the developing device 4 and the like are collectively detachable from the main body of the image forming apparatus.

10) The image forming apparatus places the toner image formed on the image bearing member on the image display section without transferring it to the recording material for display / reading, and then simultaneously collects it from the surface of the image bearing member for development. The image carrier may be an image display device that is repeatedly used for image formation.

[0128]

As described above, according to the present invention, it is possible to suppress the adhesion of magnetic particles to the end portion of the image carrier in the image forming apparatus of the contact charging system and the cleaner system using the charging assisting member. It is possible to realize an image forming apparatus with extremely stable quality.

[Brief description of drawings]

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

[Fig. 2] Model diagram of layer structure of photosensitive drum

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

FIG. 4 is an explanatory diagram of a configuration of a laser scanning unit.

FIG. 5 is a schematic diagram of the configuration of the developing device.

FIG. 6 is a dimensional relationship diagram of a photosensitive drum, an image area width, a charging width by two 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]

A laser beam printer B image reading device (image scanner) 1 photosensitive drum (image carrier) 31 fur brush charger 32 as a first contact charging member magnetic brush charger L ₁ as a second contact charging member L ₁ photosensitive drum Width dimension (length dimension) L ₂ Maximum image area width dimension on photosensitive drum L ₃₁ Longitudinal charging width of fur brush charger L ₃₂ Longitudinal charging width of magnetic brush charger L ₄ Longitudinal developing width of developing device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ identification code FI G03G 15/16 G03G 15/08 507B 21/10 21/00 312 (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 13/02 G03G 15/02

Claims (10)

(57) [Claims] 1. An image forming method comprising: a step of charging an image bearing member with respect to the image bearing member; a step of forming an electrostatic latent image on a charged surface thereof; and a step of developing the electrostatic latent image as a toner image. A developing unit that applies a process to execute image formation and develops an electrostatic latent image as a toner image also serves as an image carrier cleaning unit that collects toner particles remaining on the image carrier in the previous image formation. The carrier is an image forming apparatus of a cleanerless system that is repeatedly used for 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 carrier 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 arranged, and the bias applied to the first contact charging member is opposite to the normal charging polarity of the image carrier,
The bias applied to the second contact charging member, which is the charging means for finally charging the image carrier, has the normal charging polarity of the image carrier, and the second contact charging member is the magnetic brush charger.
The image forming apparatus is characterized in that the first contact charging member has a longitudinal charging width that is shorter than the longitudinal charging width of the second contact charging member and longer than the longitudinal developing area width of the developing unit. 2. A magnetic brush charger collects the developer.
The developer is normally charged by rubbing against the magnetic brush.
The image forming apparatus according to claim 1, wherein
Place 3. The image carrier has a surface of 10 ⁹ to 10 ¹⁴
A contract characterized by having a layer made of a material of Ω · cm
The image forming apparatus according to claim 1 or 2 . Wherein said image bearing member has a photosensitive layer and a surface layer, the image formation as claimed in any one of claims 1 to 3, characterized in that the surface layer has a resin and conductive fine particles apparatus. 5. An image forming apparatus according to claim 4, wherein the conductive fine particles are characterized by a SnO _2. 6. The image forming apparatus according to claim 1 or 2, wherein the image bearing member is characterized by comprising a surface layer having an amorphous silicon. 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. The image forming apparatus according to one. 8. The developing method of said developing means is a contact developing method in which a developer is brought into contact with an image bearing member, and the developing method is a contact developing method. Image forming apparatus. 9. The image forming apparatus according to claim 1, wherein the electrostatic latent image forming unit for the charged surface of the image carrier is an image exposing unit 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.