JP3507277B2 - 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. Image forming process by applying an image forming process having a
The present invention relates to an image forming apparatus such as a printer or a facsimile.

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]

[Prior art]

1) Conventionally, in an image forming apparatus such as a copying machine, a printer or a facsimile, a corona charger has been used as a means for charging an image carrier such as an electrophotographic photoreceptor or an electrostatic recording dielectric. This is a corona charger that is placed in non-contact with the image carrier as the member to be charged, and the surface of the image carrier is exposed to the corona shower discharged from the corona charger to which a high voltage is applied to charge it to a predetermined polarity potential. It is what makes me.

In recent years, a contact charging device has been put into practical use in place of this. This is a method in which a conductive charging member (contact charging member) is brought into contact with an object to be charged, and a voltage is applied to the contact charging member to charge the surface of the object to be charged to a predetermined polarity and potential. Compared with, it has advantages such as low ozone and low electric power.

Of these, the roller charging method using a conductive roller as the contact charging member is particularly preferably used from the viewpoint of charging stability. In roller charging, a conductive elastic roller (charging roller) is brought into pressure contact with a member to be charged, and a voltage is applied to the member to charge the member to be charged.

In roller charging, charging is mainly performed by discharging from a contact charging member to a member to be charged, and therefore charging is started by applying a voltage equal to or higher than a certain threshold voltage. This threshold voltage is the charging start voltage Vth
It is defined as

In order to obtain the surface potential Vd required for the photoconductor as an image carrier in electrophotography, the charging roller as a contact charging member has a DC of Vd + Vth which is higher than the required photoconductor surface potential Vd. It is necessary to apply a voltage. A method of applying only the DC voltage to the contact charging member in this way to perform charging is called a DC charging method.

As disclosed in Japanese Patent Laid-Open No. 63-149669, a DC voltage corresponding to a desired surface potential Vd of the member to be charged has a peak-to-peak voltage of 2 × Vth or more.
An AC charging method in which a voltage in which a C component is superimposed is applied to a contact charging member has been proposed and put into practical use. This is A
Due to the leveling effect of the potential by C, the charging can be made more uniform than in the DC charging method, and the potential of the charged body substantially converges to Vd, which is the center of the peak of the AC voltage, to prevent disturbances such as the environment. Is not affected.

In the contact charging device as well, the essential charging mechanism uses the discharge phenomenon from the contact charging member to the member to be charged, so that the voltage required for charging is the charged member as described above. A value higher than the body surface potential is required, and a small amount of ozone is generated.

As a new charging method that does not use the discharge phenomenon, a charging method by directly injecting charges into the photoconductor is disclosed in Japanese Patent Application Laid-Open No. 6-3921. In this charging method, a voltage is applied to a contact conductive member such as a charging roller, a charging brush, and a charging magnetic brush, and charges are injected into a float electrode on a photoconductor having a charge injection layer on the surface to perform contact injection charging. Is the way. In this charging method, since the discharge phenomenon is not used, the voltage required for charging is a DC voltage of only the desired photoreceptor surface potential, and there is an advantage that ozone is hardly generated.

2) On the other hand, in order to reduce the size of the image forming apparatus or the like, the cleaning of the residual toner after transfer (hereinafter referred to as transfer residual toner) on the image carrier is carried out simultaneously with the charging apparatus or the developing apparatus. A method of performing simultaneous development cleaning has been proposed (cleaner-less system image forming apparatus).

The image forming apparatus of the cleanerless system is a dedicated image carrier cleaning means (cleaner).
Since the device is not provided, the device can be downsized.
The toner particles remaining on the image bearing member in the previous image formation are collected by the developing means and reused as a developer, which is advantageous in that the waste toner is not emitted and the environment is protected.

Simultaneous development cleaning by the developing means is
This is a method for recovering the toner slightly remaining on the image carrier after transfer by a fog-removal potential difference Vback, which is a potential difference between the DC voltage applied to the developing means and the surface potential of the image carrier during development in the subsequent steps. Since the residual toner is collected by the developing means and used in the subsequent steps, 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.

[0014]

By the way, in an image forming apparatus using a contact charging system as a charging processing means of an image bearing member, a cleaner means is not provided, and a developing means performs simultaneous recovery of development to form an image. When the above procedure is repeated, the untransferred toner cannot be collected by the developing means, so that a “positive ghost” in which the previous image remains thin occurs.

In this positive ghost, when the transfer residual toner remains on the image carrier when the transfer residual toner passes through the contact charging member position, the surface part of the image carrier where the transfer residual toner exists is charged. Due to this, the potential difference (Vback) for toner recovery is applied to this portion in the developing unit.
Is a phenomenon that occurs when the contact charging member deteriorates (contaminates) and becomes more prominent.

Therefore, when the surface of the image carrier is charged by the contact charging member, the surface of the image carrier below the transfer residual toner is also charged. Therefore, the residual toner after transfer is stripped from the surface of the image carrier and returned to the surface of the image carrier 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, since toner particles having a relatively high electric resistance are usually used for toner contamination of the contact charging member, 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 rotating direction, and the contact charging member located upstream of the other in the image carrier rotating 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 manner is charged to the normal charging polarity, the developing means recovers the fog removal potential (Vback) during 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 configuration is referred to as a contactless charging system using a charging auxiliary member (first contact charging member) or a cleanerless system image forming apparatus.

However, in such an image forming apparatus of the contact charging system using the charging assisting member or the cleanerless system, when a fixed type fur brush or the like is used as the first contact charging member as the charging assisting member. Since paper dust or the like accumulates on the first contact charging member of the fixed system due to durability, the first contact charging member portion corresponding to the accumulated portion of the paper dust or the like cannot contact the image carrier and the transfer residual toner. It became difficult for the charging current to flow, and as a result, positive ghosts sometimes occurred.

Therefore, the present invention eliminates the accumulation of contaminants such as paper dust in the first contact charging member as the charging assisting member in the image forming apparatus of the contact charging system and the cleanerless system using the charging assisting member. Therefore, it is an object of the present invention to prevent positive ghosts from occurring, and thus to output a good image for a long period of time.

[0023]

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

(1) A charging unit that charges the image carrier, and a static image forming electrostatic latent image on the charging surface of the image carrier.
Latent image forming means, the electrostatic latent image by applying an image forming process with a developing means for developing as a toner image by executing the image formation, remaining on the image bearing member in the current image means the image before forming The image bearing member is an image forming apparatus of a cleanerless system that also serves as an image bearing member cleaning unit that collects the remaining toner particles, and is repeatedly used for image formation. at least
A rotatable 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 image carrier rotation direction and upstream of the developing unit are disposed. The contact charging member sets the applied bias to the opposite polarity to the normal charging polarity of the image bearing member, so that the residual toner particles are normally charged.
It is charged in the opposite polarity to the electrode property, and finally charges the image carrier.
That the second contact charging member is a magnetic brush charger, by a bias applied to the second contact charging member to the normal charging polarity of the image bearing member, the residual toner charged to the opposite polarity
-Collect the particles on the second contact charging member and collect the collected residual toner.
The rubbing of the toner particles with the magnetic brush part makes the image carrier normal.
An image forming apparatus comprising to Rukoto the charge polarity.

(2) The image forming apparatus according to (1), wherein the first contact charging member rotates intermittently.

(3) The image bearing member has a surface of 10 ⁹ to 10
The image forming apparatus according to (1), which has a layer made of a material of ¹⁴ Ω · cm.

(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 described in any one of (1) to (3), characterized in that the image carrier comprises a surface layer containing amorphous silicon.

(7) 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 (6). )
The image forming apparatus according to any one of 1.

(8) 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 (7). The image forming apparatus according to any one of 1.

(9) The image forming apparatus according to any one of (1) to (7), wherein the contact charging member moves with a peripheral speed difference with respect to the image carrier.

(10) One of (1) to (9), wherein the developing method of the developing means is a contact developing method in which a developer is brought into contact with the image carrier. The image forming apparatus according to item 1.

(11) 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 (10). Image forming apparatus.

(12) The image forming apparatus described in any one of (1) to (11), wherein the toner image formed on the image carrier is transferred onto a transfer material by a transfer means.

<Operation> That is, in the image forming apparatus of the contact charging system and the cleanerless system using the charging assisting member, the first contact charging member as the charging assisting member is made rotatable so Since the same portion of the contact charging member is not always in contact with the image bearing member, paper dust or the like is less likely to be clogged, and a good image free from positive ghosts can be obtained for a long period of time.

[0037]

DETAILED DESCRIPTION OF THE INVENTION

<Embodiment 1> (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 and a cleanerless system.

Reference numeral 1 is a rotary drum type electrophotographic photosensitive member as an image bearing member. Hereinafter, it is referred to as a photosensitive drum. The photosensitive drum 1 of this example is an OPC photosensitive member (organic photoconductor) having a diameter of about 30 mm, charge injection charging property, and negative charging property, and a process speed of 100 mm / sec in the clockwise direction of the arrow centering on the central support shaft. It is driven to rotate at (peripheral speed).

Reference numeral 6 denotes a first contact charging member as a charging assisting member, which is arranged in contact with the surface of the photosensitive drum 1.
This example is a rotary type fur brush charger. S4 is a power supply for applying a charging bias to the fur brush charger 6.

Reference numeral 2 denotes a second contact charging member arranged in contact with the surface of the photosensitive drum 1 on the downstream side of the fur brush charger 6 as the first contact charging member in the rotation direction of the photosensitive drum. An example is a sleeve rotation type magnetic brush charger. S1 is a charging bias application power source for the magnetic brush charger 2.

The photosensitive drum 1 is
The polarity opposite to the normal charging polarity, in this example, the positive bias is the power source S.
4, a fur brush charger 6 serving as a first contact charging member applies a charging action, and then the normal charging polarity of the photosensitive drum 1, a negative bias in this example, is the power source S1.
The magnetic brush charger 2 serving as the second contact charging member applies a charging action by the
It is subjected to uniform charging treatment of a predetermined potential.

Then, with respect to the uniformly charged surface of the rotating photosensitive drum 1, the intensity corresponding to the time series electric digital pixel signal of the target image information output from the laser beam scanner 7 including a laser diode, a polygon mirror and the like. Scanning exposure L is performed by the modulated laser beam, and an electrostatic latent image corresponding to target image information is formed on the peripheral surface of the rotary photosensitive drum 1.

The electrostatic latent image formed on the surface of the rotating photosensitive drum 1 is successively developed as a toner image by reversal development by the developing device 3 using an insulating toner. S2 is a power source for applying a predetermined developing bias to the developing sleeve 31 of the developing device 3.

On the other hand, a transfer material P as a recording material is fed from a paper feeding section (not shown) to the photosensitive drum 1 and a transfer roller 4 as a contact transfer member abutting the photosensitive drum 1 with a predetermined pressing force. It is introduced into the transfer section T which is a section at a predetermined timing. The transfer roller 4 is a medium resistance member, and a predetermined transfer bias voltage is applied from the power source S3. In this example, a roller resistance of 5 × 10 ⁸ Ω is used, and D of + 2000V is used.
Transfer was performed by applying C voltage.

The transfer material P introduced into the transfer portion T is nipped and conveyed through the transfer portion, and a toner image is formed and carried on the surface of the transfer material, which is the surface of the transfer material facing the photosensitive drum 1. Are sequentially transferred by electrostatic force and pressing force.

The transfer material on which the toner image has been transferred at the transfer portion T is separated from the surface of the rotary photosensitive drum 1 and is introduced into a fixing device 5 such as a heat fixing system to be fixed with the toner image, and an image formed product (print , Copy) is ejected outside the device.

Since the printer of this embodiment is cleaner-less, no dedicated cleaning device for collecting the transfer residual toner remaining on the surface of the rotary photosensitive drum 1 after transfer material separation is provided, and the rotary photosensitive drum 1 is not provided. The transfer residual toner on the surface is collected by the developing device 3 by cleaning at the same time as development, and the surface of the rotary photosensitive drum 1 is repeatedly used for image formation.

That is, the transfer residual toner is charged by the first contact charging member as a charging assisting member, in this example, the fur brush charger 6 to which a voltage having a polarity opposite to the normal charging polarity of the photosensitive drum is applied. The transfer residual toner of which the polarity is reversed is collected by the second contact charging member, in this example, the magnetic brush portion of the magnetic brush charger 2, and the collected toner is collected from the magnetic brush portion to the surface of the rotary photosensitive drum 1. Are uniformly discharged (discharged), and are simultaneously cleaned (collected) in the developing unit of the developing device 3 during development.

In the printer of this embodiment, the cartridge 10 contains the four process devices including the photosensitive drum 1, the first and second contact charging members 6 and 2, and the developing device 3, and is collectively attached to and detached from the printer body. -Although it is a process cartridge type device that can be exchanged, it is not limited to this.

(2) Photosensitive drum 1 (FIG. 2) The photosensitive drum 1 as an image carrier used in this example is a negatively charged OPC photosensitive member, and as shown in the layer structure model diagram of FIG.
A charge-injection chargeable photosensitive drum, which comprises a 30 mm aluminum drum base (Al drum base) 11 on which the following five first to fifth functional layers are sequentially provided.

The first layer 12 is an undercoat layer, and is a conductive layer having a thickness of about 20 μm, which is provided to smooth defects such as the Al drum substrate 11 and to prevent moire due to reflection of laser exposure. Is.

Second layer 13: a positive charge injection prevention layer, A
It plays a role of preventing the positive charge injected from the drum body 11 from canceling out the negative charge charged on the surface of the photoconductor, and the resistance is adjusted to about 1 × 10 ⁶ Ω · cm by the amylan resin and methoxymethylated nylon. Thickness about 1 μm
It is a medium resistance layer.

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 by being subjected to laser exposure.

Fourth layer 15: a charge transport layer, which is a polycarbonate resin in which hydrazone is dispersed, and is a P-type semiconductor. 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 is a charge injection layer, and 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, for example, a photocurable acrylic resin. Specifically, it is a coating layer made of a material in which antimony-doped SnO ₂ particles having a low resistance and a particle size of about 0.03 μm are dispersed in a resin in an amount of 70% by weight. In addition, a carrier (conductivity) that constitutes the magnetic brush portion of the magnetic brush charger 2 which is the second contact charging member is obtained by dispersing 26% of a tetrafluoroethylene resin (trade name: Teflon) to improve sliding. Magnetic particles) are made easy to move.

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 or 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.

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 the organic photoconductor has a resistance of 10 ⁹ to 10 ^{14 on it.}
When a material having a surface layer having a material of Ω · cm, an amorphous silicon photoconductor, or the like is used, 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.

Here, the volume resistance of the surface layer 16 was measured by arranging metal electrodes at intervals of 200 μm, injecting a preparation liquid for 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) First and second contact charging members 6.2
(FIG. 3) FIG. 3 is an enlarged model view of the first and second contact charging members 6 and 2.

A) First contact charging member 6 The fur brush charger 6 as the first contact charging member of this example has a core metal 61 of 4 mm in diameter, 6 denier.
This is a fur brush roll having a diameter of 10 mm by winding a fur brush 62 of ten thousand / inch ² , and the length in the longitudinal direction (effective length) is 200 mm. In addition, the fur brush portion 62
Has a resistance of 6 × 10 ³ Ω · cm.

The fur brush portion 62 has a thickness of 30 denier or less and a density of 1 to 500,000 / inch ² so that it can uniformly contact the surface of the photosensitive drum and the transfer residual toner.
The above is preferable.

A constant current of +20 μA was applied to the fur brush roll 6 to bring it into contact with the photosensitive drum with an intrusion amount of 1 mm,
In this example, the photosensitive drum 1 was driven to rotate.

Here, the peripheral speed ratio between the fur brush roll 6 and the photosensitive drum 1 is defined by the following equation.

Peripheral speed ratio (%) = (far brasil roll peripheral speed-photosensitive drum peripheral speed) / photosensitive drum peripheral speed × 100 Therefore, -100% is the state where the fur brush roll is stopped. If the fur brush roll is rotated in the opposite direction to the photosensitive drum 1, the transfer residual toner may be scraped off. Therefore, the same direction as the rotation of the photosensitive drum 1 is desirable.

Considering the chance of contact between the transfer residual toner and the surface of the photosensitive drum, it is desirable that the peripheral speed difference be as large as possible, but toner scattering increases as the rotational speed of the fur brush roll increases. Therefore, the peripheral speed ratio of the fur brush roll is preferably 0% to -100%, and as close as possible to -100%.

The number of revolutions of the fur brush roll 6 can be adjusted by the amount of bristles of the fur brush portion 62 entering the photosensitive drum 1, the contact pressure, and the like. It may also be adjusted by driving from a motor or the like.

B) Second Contact Charging Member 2 The magnetic brush charger 2 as the second contact charging member is of the rotating sleeve type in this example, and has a fixed and supported magnet roll 21 and this magnet. Outer diameter of 16 mm, which is concentrically and externally fitted around the outer circumference of the roll.
Of the non-magnetic conductive sleeve 22 and conductive magnetic particles (charging magnetic carrier, hereinafter referred to as carrier) formed on the outer peripheral surface of the sleeve by being attracted and held (restricted) by the magnetic force of the magnet roll 21 inside the sleeve. The magnetic brush unit 23 is included. The length (effective length) of the magnetic brush charger 2 in the longitudinal direction is 230 mm.

The magnetic flux density at the magnetic pole position on the sleeve surface was 0.1 T (tesla). The magnetic flux density is preferably 0.03 T or more in consideration of the magnetic restraining force on the carrier.

This magnetic brush charger 2 is connected to the photosensitive drum 1
In parallel with the above, the magnetic brush portion 23 was placed in contact with the surface of the photosensitive drum 1 to form a charging nip portion having a predetermined width.

The carrier used in this example is a ferrite carrier having an average particle size of 30 μm, a maximum magnetization of 60 Am ² / kg, and a density of 2.2 g / cm ^{2 and} a medium resistance.

The gap from the sleeve 22 to the surface of the photosensitive drum 1 is maintained at 500 μm by mounting spacer rollers on both ends of the sleeve 22. When the amount of carrier on the sleeve 22 is 15 g, the entire width of the charging nip including the carrier pool is about 6 mm. The carrier resistance in this nip width is 5 × 1 when DC100V is applied.
It was 0 ⁶ Ω.

The sleeve 22 is rotated in the charging nip portion in the clockwise direction indicated by the arrow, which is the opposite direction to the rotation direction of the photosensitive drum 1. As the sleeve 22 rotates, the magnetic brush portion 23 rotates in the same direction and rubs the surface of the photosensitive drum 1.

Here, the peripheral speed ratio between the magnetic brush charger 2 and the photosensitive drum 1 is defined by the following equation.

Peripheral speed ratio (%) = (magnetic brush charger peripheral speed−
(Photosensitive drum peripheral speed) / photosensitive drum peripheral speed × 100 The peripheral speed of the magnetic brush charger 2 has a negative value in the direction opposite to the rotating direction of the photosensitive drum 1. The carrier forming the magnetic brush portion 23 of the magnetic brush charger 2 and the photosensitive drum 1
Considering the chance of contact with the surface, the absolute value of the peripheral speed ratio is preferably 100% or more, but -100% is the state in which the magnetic brush charger 2 is stopped. Where the magnetic brush portion 23 and the surface of the photosensitive drum are not in sufficient contact, charging is defective, and the stopped shape appears in the image as it is.

In the forward rotation, if the same peripheral speed ratio as in the reverse direction is to be obtained, the rotation speed of the magnetic brush charger 2 will be high, and carrier scattering from the magnetic brush portion 23 will occur. Will be disadvantageous. In this example, the peripheral speed ratio is -150%.

From the charging bias applying power source S1 to the sleeve 22 of the magnetic brush charger 2, DC-700V, AC1
A charging bias having a frequency of 700 kHz and a peak-to-peak voltage of 700 V was applied. In this example, the rotary photosensitive drum 1 is charged and charged by the magnetic brush charger 2 to approximately -700V.

In the charge injection charging, a contact charging member having a medium resistance is used to inject charges to the surface of the charged body (photosensitive drum) having a medium resistance surface resistance. In this example, the trap of the surface material of the photosensitive drum is used. Instead of injecting charges into the electric potential, the conductive particles (SnO ₂ ) 16 of the charge injection layer 16
This is a method of charging by charging a to a. The charge transport layer 15 is a dielectric, and the aluminum drum substrate 11 is
This is considered to be based on the theory that a contact charging member charges electric charge to a minute capacitor having conductive particles 16a in the charge injection layer 16 as both electrode plates. At this time, the conductive particles 16a are electrically independent of each other and form 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, even if the image exposure L is performed with the laser light, each SnO ₂ particle 16a is electrically independent, so that it is expected that the electrostatic latent image can be held.

The charging magnetic carrier constituting the magnetic brush portion 23 of the magnetic brush charger 2 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 × 10 ¹⁰ Ω.・ The one with cm 3 is preferable.

Considering that the photosensitive drum 1 has an insulating defect such as a pinhole, the resistance is 1 × 10 ⁶ Ω.
-It is preferable to use one having a size of cm or more. In order to improve the charging performance, it is better to use the one with the smallest possible resistance.

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 measurement 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 device 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) Developing Device 3 Generally, in a method of developing an electrostatic latent image, 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 to a photosensitive drum. In contrast, a method of developing in a non-contact state (one-component non-contact development), a method of developing the toner coated as described above in a state of contact with the photosensitive drum (one-component contact development), and a method of developing toner particles A method in which a mixture of magnetic carriers is used as a developer and is conveyed by magnetic force to develop in contact with the photosensitive drum (two-component contact development), and the above two-component developer is brought into non-contact state. The method is roughly classified into four types, i.e., a method of developing by means of 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 the image forming apparatus of the cleanerless system.

A developing bias of a DC voltage and an alternating voltage is applied between the developing sleeve 31 and the conductive drum substrate of the photosensitive drum 1 by the developing bias applying power source S2.

In this example, DC voltage: -480V Alternating voltage: Amplitude Vpp = 1500V, Frequency Vf = 30
A developing bias of 00 Hz is applied, and the toner in the developer magnetic brush thin layer on the developing sleeve 31 side selectively adheres to the electrostatic latent image on the photosensitive drum 1 side in the developing section, and the electrostatic latent image becomes a toner image. It will be developed.

Generally, in the two-component developing method, when an alternating voltage is applied, the developing efficiency is increased and the quality of the image is high, but conversely 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 3 and the surface potential of the photosensitive drum 1, it is possible to prevent fogging.

The potential difference for preventing fog is called a fog 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.

(5) Collection and discharge of transfer residual toner by contact charging member Simultaneous development cleaning by developing device The transfer residual toner remains on the surface of the photosensitive drum 1 after the toner image is transferred onto 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 2 which is the second contact charging member, but the toner whose polarity is not reversed is collected by the magnetic brush charger 2. It is difficult to do (because the charging potential is generally lower than the bias applied to the charger).

Therefore, a first contact charging member as a charging assisting member, which is the fur brush roll 6 in this example as described above, is provided between the transfer portion T and the magnetic brush charger 2, and the photosensitive drum 1 is attached to the first contact charging member. By applying a voltage having a polarity opposite to the normal charging polarity, the transfer residual toner is charged in the opposite polarity to the normal charging polarity, and the recovery efficiency in the magnetic brush charger 2 is improved. 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 2 and the positive ghost is improved.

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 roll 6 as the charging assisting member, the transfer residual toner of which the polarity is reversed is transferred to the magnetic brush charger 2 Will be collected.

In this example, in order to further improve the collectability of the transfer residual toner and the charging uniformity of the bias applied to the magnetic brush charger 2, an alternating voltage is superimposed on the DC voltage. There is.

Then, in the charging area of the magnetic brush charger 2, the transfer residual toner collected and mixed in the magnetic brush portion 23 of the charger 2 is made into a normally charged toner by rubbing against the magnetic brush portion 23, and at the same time alternating By the voltage, the history of the transfer residual toner remaining in the state of the previous image is erased by the vibration effect due to the electric field between the photosensitive drum 1 and the magnetic brush charger 2, and the normally charged toner is transferred from the magnetic brush portion 23 to the photosensitive drum 1. Exhaled in a uniform condition on top.

The toner which has been normally charged and discharged onto the photosensitive drum 1 is carried to a developing area and is cleaned (collected) at the same time by the two-component developing device 3.

That is, since the toner discharged from the second charging member 2 to the image carrier 1 is charged to the normal charging polarity, the DC voltage applied to the developing means 3 and the image at the time of developing in the developing means 3 It is possible to collect at the fogging removal potential (Vback) which is the potential difference between the surface potentials of the carrier 1. 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. The occurrence of positive ghost can be prevented, and the toner mixed in the second charging member 2 which is the final contact charging means can be sufficiently discharged, so that the toner contamination of the second charging member 2 can be prevented.

(6) Effect of Rotation of First Charging Member 6 In the printer of this example, the fur brush roll 6 as the first contact charging member, which is a charging assisting member, was fixed to non-rotation and an endurance experiment was conducted. As a result, in the case of the first contact charging member of this fixed system, the paper dust is partially clogged after about 10,000 prints, and a positive ghost is generated in the portion corresponding to the fur brush portion of the paper dust clogging part. I got it.

On the other hand, when the fur brush roll 6 that rotates is used as the first contact charging member as in this example, 5
Even after 10,000 sheets, it became possible to obtain a good image without a positive ghost caused by the occurrence of paper dust clogging.

<Second Embodiment> This embodiment is the same as the first embodiment.
In this printer, the fur brush roll 6 as the first contact charging member is intermittently rotated.

That is, the fur brush roll 6 serving as the first contact charging member is stopped during image formation (during printing), and is rotated by rotation of the photosensitive drum 1 in the non-image area (during non-image formation). It was

As a result of a durability test with this configuration, paper dust clogging did not occur even after 50,000 sheets, and toner scattering could be suppressed.

When the fur brush roll 6 rotates quickly, the toner attached to the fur brush roll 6 is scattered. Therefore, when the image area passes through the fur brush as in this example, the brush is stopped to prevent the paper jam. It has become possible to realize a configuration that does not generate toner and has little toner scattering.

FIG. 4 is an operation process diagram of the printer.

.. By turning on the main power switch of the printer during the pre-multi-rotation period, the main motor of the printer is driven to rotate the photosensitive drum 1,
This is a start-up (start-up) operation period (warming period) of the printer in which the heater of the fixing device 5 is energized to start heating and other necessary process devices are started up.

.. When multiple rotation period previous stand-by period the ends, rotation of the photosensitive drum 1 the main motor is temporarily stopped is stopped, until the pre-<br/> te print start signal is input Standby Held in a state. During this time, the fixing device 5 is temperature-controlled to a predetermined temperature.

.. Pre-rotation period This is a period in which the main motor is re-driven to re-rotate the photosensitive drum 1 in response to the input of the print start signal, and the printer performs a predetermined pre-printing operation for a while.

When the print start signal has already been input at the end of the previous multi-rotation period, the process proceeds to the previous rotation period without the standby period.

.. Printing period When the predetermined pre-rotation period ends, the image forming process (image forming process) of a predetermined sequence such as charging, image exposure, development and transfer on the rotating photosensitive drum is subsequently executed to print the first sheet. Be done.

In the continuous print mode, the image forming process for the predetermined number n is repeatedly executed. FIG. 4 shows an example of continuous printing of two sheets. In the continuous print mode, after the trailing edge of one transfer material P passes through the transfer section T and before the leading edge of the next transfer material P reaches the transfer section T, the transfer material in the transfer section T is not passed. There is a paper condition period, which is called the paper interval.

.. The main motor continues to be driven for a while to rotate the photosensitive drum 1 for a predetermined post-operation of the printer even after the end of the printing period of one sheet in the post-rotation period or the last n-th sheet in the continuous print mode. This is the period to be executed.

When the predetermined post-rotation period ends, the drive of the main motor is stopped and the rotation of the photosensitive drum 1 is stopped.
The printer is held in the standby state again until the next print start signal is input.

In the above description, the printing period is the image forming period, and the pre-multi-rotation period, the pre-rotation period, the sheet interval, and the post-rotation period are the non-image forming periods in the printer driving state.

<Others> 1) The image exposing means as the information writing means for the charged surface of the image carrier is not limited to the laser scanning means of the embodiment.
For example, a solid-state light emitting element such as an LED may be provided close to the image carrier 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 bearing member 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 2 as the second contact charging member is not limited to the sleeve rotation type of the embodiment, but the magnet roll 21 and the surface of the magnet roll 21 may be rotated as required. It is also possible to use a structure in which the magnet roll 21 is rotated by conducting conductivity treatment as a power supply electrode and magnetically binding the conductive magnetic particles directly to the outer peripheral surface of the magnet roll 21 to form the magnetic brush portion 23. it can. A non-rotating type magnetic brush member can also be used.

5) The first contact charging member may be of a rotary type other than the fur brush charger.

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 contact 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 roller transfer, but may be belt transfer or corona discharge transfer. 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.

10) The image forming apparatus, after transferring the toner image formed on the image bearing member to the image display portion without displaying it on the recording material for display / reading, 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.

[0123]

As described above, according to the present invention, in the image forming apparatus of the contact charging system or the cleanerless system using the charging assisting member, the first contact charging member as the charging assisting member is rotatable. By doing so, the same portion of the first contact charging member is not always in contact with the image bearing member, so that paper dust or the like is less likely to be clogged, and a good image in which positive ghost does not occur can be obtained for a long period of time. It became so.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus (laser beam printer) according to the present invention.

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

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

FIG. 4 is an operation process diagram of the image forming apparatus.

[Explanation of symbols]

1 Photosensitive drum (image carrier) 6 Fur brush charger as the first contact charging member 2 Magnetic brush charger as the second contact charging member

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 13/02 G03G 15/02

Claims (12)

(57) [Claims] 1. A charging unit for charging an image bearing member to the image bearing member, and an electrostatic latent image forming an electrostatic latent image on the charging surface.
Forming means , development for developing the electrostatic latent image as a toner image
By applying the image forming process having means to execute the image formation, it serves as an image carrier cleaning means for recovering the residual toner particles present image unit remaining on an image bearing member in the previous image formation, the image bearing member Is an image forming apparatus of a cleanerless system that is repeatedly used for image formation. As charging means for charging the image carrier, at least the rotatable first contact charging member and the image more than the contact charging member are provided on the image carrier. A plurality of contact charging members of a second contact charging member on the downstream side of the carrier rotation direction and on the upstream side of the developing means are disposed,
The normal charging polarity of the image bearing member to bias the first contact charging member is applied to the residual toner particles by reversed polarity
The normal charging polarity is charged to the opposite polarity, the second contact charging member you charge the image bearing member Eventually magnetic brush charger der
By setting the bias applied to the second contact charging member to the normal charging polarity of the image bearing member, it is charged to the opposite polarity.
Residual toner particles are collected on the second contact charging member and collected.
Image bearing by rubbing residual toner particles against the magnetic brush
An image forming apparatus comprising to Rukoto to the normal charging polarity of the body. 2. The image forming apparatus according to claim 1, wherein the first contact charging member rotates intermittently. 3. The surface of the image carrier is 10 ⁹ to 10 ¹⁴ Ω
The image forming apparatus according to claim 1, further comprising a layer made of a material of cm. 4. 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. apparatus. 5. The image forming apparatus according to claim 4, wherein the conductive fine particles are SnO ₂ . 6. The image forming apparatus according to claim 1, wherein the image carrier comprises a surface layer containing amorphous silicon. 7. 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. An image forming apparatus according to any one of the above. 8. 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. 9. The image forming apparatus according to claim 1, wherein the contact charging member moves with a peripheral speed difference with respect to the image carrier. 10. 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, which is a contact developing method. Image forming apparatus. 11. 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. . 12. 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.