JPH10312098A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect contaminants such as paper dust on a first contact charging member 6 as a charging auxiliary member in an image forming apparatus of a contact charging system and a cleaner-less system using a charging auxiliary member. And positive ghosts are less likely to occur, so that a good image can be output for a long period of time. SOLUTION: The first contact charging member 6 is rotatable, the first contact charging member 6 rotates intermittently, and the first contact charging member 6 is a rotary type fur brush charger. And that the second contact charging member 2 is a magnetic brush charger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

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

[0003]

[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 photosensitive member or an electrostatic recording dielectric. This is a method in which a corona charger is disposed in a non-contact manner on an image carrier as a member to be charged, and the surface of the image carrier is exposed to a corona shower emitted from the corona charger to which a high voltage is applied, and is charged to a predetermined polarity potential. It is to let.

[0004] In recent years, a contact charging device has been put to practical use instead. This is a method in which a conductive charging member (contact charging member) is brought into contact with a member to be charged, and a voltage is applied to the contact charging member to charge the surface of the member to be charged to a predetermined polarity and potential. There are advantages such as low ozone, low power, etc.

Among them, a roller charging method using a conductive roller as a contact charging member is preferably used in view 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 thereto to charge the member to be charged.

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

In order to obtain a surface potential Vd required for a photoreceptor as an image carrier in electrophotography, a charging roller serving as a contact charging member needs a DC of Vd + Vth equal to or higher than a required photoreceptor surface potential Vd. It is necessary to apply a voltage. The method in which only the DC voltage is applied to the contact charging member to perform charging in this manner is called a DC charging method.

As disclosed in Japanese Patent Application Laid-Open No. 63-149669, a DC voltage corresponding to a desired surface potential Vd of a member to be charged has a peak-to-peak voltage of 2 × Vth or more.
An AC charging system in which a voltage in which a C component is superimposed is applied to a contact charging member has been proposed and has been put to practical use. This is A
The smoothing effect of the potential by C makes it possible to further uniform the charging compared to 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, and the disturbance of the environment and the like. Is not affected.

Also in the contact charging device, the essential charging mechanism uses the phenomenon of discharge from the contact charging member to the member to be charged. 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 a charge into a photoreceptor is disclosed in JP-A-6-3921. In this charging method, a voltage is applied to a contact conductive member such as a charging roller, a charging brush, a charging magnetic brush, and a charge is injected into a float electrode on a photoconductor provided with a charge injection layer on the surface to perform contact injection charging. Is the way. In this charging system, since the discharge phenomenon is not used, the voltage required for charging is a DC voltage of only the desired photoconductor surface potential, and has the advantage that almost no ozone is generated.

2) On the other hand, in order to reduce the size of the image forming apparatus, cleaning of residual toner after transfer (hereinafter referred to as transfer residual toner) on the image carrier is performed by simultaneous cleaning or simultaneous charging with a charging device or a developing device. A method of performing simultaneous development and cleaning has been proposed (image forming apparatus of cleanerless system).

[0012] The image forming apparatus of the cleanerless system includes a dedicated image carrier cleaning means (cleaner).
, The size of the device can be reduced.
The toner particles remaining on the image carrier in the previous image formation are collected by the developing means and reused as a developer, and are advantageous in that they do not emit waste toner, and thus are environmentally friendly.

The simultaneous cleaning with development by the developing means includes
This is a method in which the toner slightly remaining on the image carrier after transfer is recovered by a fog removal potential difference Vback, which is a potential difference between a DC voltage applied to the developing means and a surface potential of the image carrier at the time of development after the next step. Since the residual toner is collected by the developing means and used in the next and subsequent steps, waste toner can be eliminated. In addition, the cleaner-less has a great advantage in terms of space, and can greatly reduce the size of the image forming apparatus.

[0014]

By the way, in an image forming apparatus using a contact charging system as a charging means for an image carrier, the image forming apparatus is not provided with a cleaner means, and the developing means collects the image at the same time. Is repeated, "positive ghost" occurs in which the previous image remains thin because the transfer residual toner cannot be collected by the developing means.

This positive ghost causes the surface of the image bearing member where the transfer residual toner exists to be charged if the transfer residual toner remains on the image carrier when the transfer residual toner passes through the contact charging member position. The potential difference (Vback) for recovering toner is applied to this portion in the developing section
Is a phenomenon that occurs because the contact charging member cannot be secured, and becomes more remarkable when the contact charging member is deteriorated (contaminated).

Therefore, when the surface of the image carrier is charged by the contact charging member, the portion of the image carrier below the transfer residual toner is also charged. Therefore, the toner remaining after transfer is peeled off from the surface of the image carrier during charging, and is returned to the surface of the image carrier after charging. (Discharge of toner from the contact charging member to the image carrier), it is important to collect the toner by the developing means.

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

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

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

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

However, in such an image forming apparatus of a contact charging system using a charging auxiliary member and a cleanerless system, when a fixed fur brush or the like is used as a first contact charging member as a charging auxiliary member. Due to durability, paper dust and the like accumulate in the first contact charging member of the fixing system, and the first contact charging member corresponding to the accumulation of the paper dust and the like cannot contact the image carrier and the transfer residual toner. The charging current became difficult to flow, and as a result, a positive ghost sometimes occurred.

Accordingly, the present invention eliminates the accumulation of contaminants such as paper dust in the first contact charging member as a charging auxiliary member in a contact charging system using a charging auxiliary member and a cleanerless system image forming apparatus. Therefore, it is possible to output a good image over a long period of time without generating positive ghost.

[0023]

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

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

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

[0026] (3) 10 ^9-10 on the image bearing member surface
The image forming apparatus according to (1), further comprising a layer made of a material of ¹⁴ Ω · cm.

(4) The image carrier according to any one of (1) to (3), wherein the image carrier has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles. Image forming apparatus.

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

(6) The image forming apparatus according to any one of (1) to (3), wherein the image carrier is formed of a surface layer having 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. )
The 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 (1) to (7). The image forming apparatus according to any one of the above.

(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) The method of any one of (1) to (9), wherein the developing method of the developing means is a contact developing system in which the developer is in contact with the image carrier. An image forming apparatus according to claim 1.

(11) The apparatus according to any one of (1) to (10), wherein the means for forming an electrostatic latent image on the charged surface of the image carrier is an image exposure means for the image carrier. Image forming device.

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

<Operation> That is, in an image forming apparatus of a contact charging system using a charging auxiliary member and a cleanerless system, the first contact charging member as a charging auxiliary member is made rotatable so that the first charging member is rotatable. Since the same portion of the contact charging member does not always contact the image carrier, paper dust and the like are less likely to be clogged, and a good image free of positive ghost can be obtained for a long period of time.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION

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

The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process and a cleanerless system.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image carrier. 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 chargeability, and negative charge, and a process speed of 100 mm / sec in a clockwise direction indicated by an arrow around a central support shaft. (Peripheral speed).

Reference numeral 6 denotes a first contact charging member as a charging auxiliary member, which is disposed in contact with the surface of the photosensitive drum 1;
This example is a rotary type fur brush charger. S4 is a charging bias application power source for the fur brush charger 6.

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

During the rotation process of the photosensitive drum 1, the photosensitive drum 1
The polarity opposite to the normal charging polarity, in this example, the positive bias is the power supply S
4, a charging action is applied by the fur brush charger 6 as a first contact charging member, and then the normal charging polarity of the photosensitive drum 1, in this example, a negative bias is applied to the power supply S1.
Is applied by the magnetic brush charger 2 as a second contact charging member, and finally has a negative polarity,
It receives a uniform charging process at a predetermined potential.

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, etc., is applied to the uniformly charged surface of the rotating photosensitive drum 1. 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 rotating 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 the developing device 3 using an insulating toner in the case of the present embodiment. S2 is a power supply 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 from a paper feed unit (not shown) is pressed against the photosensitive drum 1 and a transfer roller 4 as a contact transfer member brought into contact with 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 a power source S3. In this example, a roller resistance of 5 × 10 ⁸ Ω is used and a D of +2000 V is used.
Transfer was performed by applying a voltage C.

The transfer material P introduced into the transfer portion T is conveyed by nipping the transfer portion, and the toner image formed and carried on the surface of the photosensitive drum with respect to the surface of the transfer material facing the photosensitive drum 1. Is sequentially transferred by electrostatic force and pressing force.

The transfer material to which the toner image has been transferred in the transfer unit T is separated from the surface of the rotating photosensitive drum 1 and introduced into a fixing device 5 such as a heat fixing system, where the toner image is fixed and the image forming material (print) , Copy) out of the apparatus.

Since the printer of this embodiment is cleaner-less, a dedicated cleaning device for collecting the transfer residual toner remaining on the surface of the rotary photosensitive drum 1 after the transfer material is separated is not provided. The transfer residual toner on the surface is collected by the developing and cleaning at the same time in the developing device 3, and the surface of the rotating photosensitive drum 1 is repeatedly used for image formation.

That is, the transfer residual toner is charged by a first contact charging member as a charging auxiliary member, in this embodiment, a fur brush charger 6 to which a voltage having a polarity opposite to the normal charging polarity of the photosensitive drum is applied. Then, the transfer residual toner having the inverted polarity 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 transferred from the magnetic brush portion to the surface of the rotating photosensitive drum 1. (Discharge) uniformly, and it is cleaned (collected) at the same time as development in the developing section of the developing device 3.

In the printer of this embodiment, the four process devices of the photosensitive drum 1, the first and second contact charging members 6, 2 and the developing device 3 are contained in the cartridge 10 and are collectively attached to and detached from the printer main body. -It is a process cartridge type device that can be freely replaced, but is not limited to this.

(2) Photosensitive Drum 1 (FIG. 2) The photosensitive drum 1 as an image carrier used in the present embodiment is a negatively charged OPC photoreceptor. As shown in the layer configuration model diagram of FIG.
This is a charge-injection-chargeable photosensitive drum in which the following first to fifth functional layers are provided in order from the bottom on a 30 mm aluminum drum base (Al drum base) 11.

The first layer 12 is a subbing layer, and is a conductive layer having a thickness of about 20 μm provided to smooth defects of the Al drum base 11 and to prevent occurrence of moire due to reflection of laser exposure. It is.

The second layer 13 is a positive charge injection preventing layer,
It serves to prevent positive charges injected from the drum substrate 11 from canceling out negative charges charged on the surface of the photoreceptor, and the resistance is adjusted to about 1 × 10 ⁶ Ω · cm by amylan resin and methoxymethylated nylon. About 1μm thick
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 which generates positive and negative charge pairs by being subjected to laser exposure.

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

Fifth layer 16: a charge injection layer, which is a coating layer of a material in which SnO ₂ ultrafine particles as conductive particles 16a are dispersed in a binder of an insulating resin, for example, a photocurable acrylic resin. Specifically, it is a coating layer of a material in which antimony-doped SnO ₂ particles having a particle diameter of about 0.03 μm and having a reduced resistance are dispersed in a resin by 70% by weight. In addition, by dispersing 26% of a tetrafluoroethylene resin (trade name: Teflon) and improving the slip, the carrier (conductive) constituting the magnetic brush portion in the magnetic brush charger 2 as the second contact charging member is formed. Magnetic particles).

The coating solution thus prepared was applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coating method, beam coating method, etc. to form a charge injection layer. The surface resistance is 10 ¹³ Ωcm. By controlling the surface resistance in this manner, the chargeability is directly improved and a high-quality image can be obtained.

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

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

(3) First and second contact charging members 6.2
(FIG. 3) FIG. 3 is an enlarged model diagram of the first and second contact charging members 6.2.

A) First Contact Charging Member 6 The fur brush charger 6 serving as the first contact charging member in this embodiment is composed of a 6 denier · 10
This fur brush roll is formed by winding a fur brush 62 of 10,000 pieces / inch ² to φ10 mm, and has a longitudinal length (effective length) of 200 mm. In addition, the fur brush section 62
Is 6 × 10 ³ Ω · cm.

The fur brush portion 62 has a thickness of 30 denier or less and a density of 100,000 to 500,000 pieces / inch ² so that the fur brush portion 62 can uniformly contact the photosensitive drum surface and the transfer residual toner.
The above is preferred.

A constant current of +20 μA is passed through the fur brush roll 6 so that the fur brush roll 6 comes into contact with the photosensitive drum at an intrusion amount of 1 mm.
In this embodiment, the photosensitive drum 1 is 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-Fashiro roll peripheral speed−Photosensitive drum peripheral speed) / Photosensitive drum peripheral speed × 100 Therefore, −100% is a state in which the fur brush roll is stopped. If the direction of rotation of the fur brush roll is opposite to the direction of the photosensitive drum 1, the transfer residual toner is scraped off.

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 is as large as possible. However, as the rotation speed of the fur brush roll increases, toner scattering increases. Therefore, the peripheral speed ratio of the fur brush roll is preferably from 0% to -100%, and more preferably as close as possible to -100%.

The number of revolutions of the fur brush roll 6 can be adjusted by the amount of the hair of the fur brush portion 62 entering the photosensitive drum 1 and the contact pressure. Alternatively, it may be driven by a motor or the like and adjusted.

B) Second Contact Charging Member 2 The magnetic brush charger 2 as a second contact charging member is of a rotary sleeve type in this embodiment, and includes a fixedly supported magnet roll 21 and a magnet The outer diameter is 16mm, which is fitted around the outer circumference of the roll freely and freely.
Of a nonmagnetic conductive sleeve 22 and conductive magnetic particles (magnetic carrier for charging, hereinafter referred to as a carrier) formed by being attracted and held (constrained) on the outer peripheral surface of the sleeve by the magnetic force of a magnet roll 21 inside the sleeve. It consists of a magnetic brush part 23. 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 binding force on the carrier.

The magnetic brush charger 2 is connected to the photosensitive drum 1
Substantially in parallel with the above, the magnetic brush portion 23 was brought into 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 diameter of 30 μm, a maximum magnetization of 60 Am ² / kg, 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 attaching spacer rollers to both ends of the sleeve 22. When the amount of the carrier on the sleeve 22 is set to 15 g, the entire width of the charging nip including the carrier pool is about 6 mm. The carrier resistance at this nip width is 5 × 1 when DC 100 V is applied.
It was 0 ⁶ Ω.

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

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

Circumferential speed ratio (%) = (Magnetic flash charger peripheral speed−
(Photosensitive drum peripheral speed) / Photosensitive drum peripheral speed × 100 The peripheral speed of the magnetic brush charger 2 is a negative value when the rotation direction of the photosensitive drum 1 is opposite. Carrier and photosensitive drum 1 constituting magnetic brush portion 23 of magnetic brush charger 2
Considering the chance of contact with the surface, the absolute value of the peripheral speed ratio is desirably 100% or more, but -100% is a state where the magnetic brush charger 2 is stopped. Where the magnetic brush portion 23 does not sufficiently contact the surface of the photosensitive drum, charging failure occurs, and the stopped shape appears on the image as it is.

In the forward rotation, if the same peripheral speed ratio as that in the reverse direction is to be obtained, the number of rotations of the magnetic brush charger 2 becomes high, so that the carrier scatters from the magnetic brush portion 23 and the like. Disadvantageous. In this example, the peripheral speed ratio is -150%.

The sleeve 22 of the magnetic brush charger 2 is supplied with DC-700V, AC1
A charging bias of kHz and a peak-to-peak voltage of 700 V was applied. In this embodiment, the rotary photosensitive drum 1 is charged and charged to approximately -700 V by the magnetic brush charger 2.

In the charge injection charging, charge is injected into the surface of a member to be charged (photosensitive drum) having a medium-resistance contact resistance by a medium-resistance contact charging member. Instead of injecting a charge to the potential, the conductive particles (SnO ₂ ) 16 of the charge injection layer 16
a charge is charged by charging the charge transport layer 15a, and the charge transport layer 15 is made of a dielectric material;
This is considered to be based on the theory of charging a small capacitor using the conductive particles 16a in the charge injection layer 16 as both electrode plates with a contact charging member. At this time, the conductive particles 16a are electrically independent of each other and form a kind of minute float electrode. For this reason, macroscopically, the photosensitive drum surface appears to be charged and charged to a uniform potential, but in reality, SnO ₂ , a myriad of minutely charged conductive particles, covers the photosensitive drum surface. It is in such a situation. For this reason, even if the image exposure L is performed by the laser beam, each SnO ₂ particle 16a is expected to be able to hold an electrostatic latent image since it is electrically independent.

The magnetic carrier for charging constituting the magnetic brush portion 23 of the magnetic brush charger 2 has an average particle diameter 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.・ Cm 2 is preferred.

Considering the existence of insulation defects such as pinholes in the photosensitive drum 1, the resistance is 1 × 10 ⁶ Ω.
・ It is preferable to use one having a diameter of not less than cm. In order to improve the charging performance, it is better to use one having as small a resistance as possible.

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

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

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

(4) Developing Apparatus 3 In general, the method of developing an electrostatic latent image is such that non-magnetic toner is coated on a sleeve with a blade or the like, and magnetic toner is coated by a magnetic force and conveyed to a photosensitive drum. A non-contact development method (one-component non-contact development), a method of developing the toner coated as described above in contact with the photosensitive drum (one-component contact development), and a method of developing the toner particles. A method in which a mixture of magnetic carriers is used as a developer and conveyed by magnetic force to develop the photosensitive drum in contact with the photosensitive drum (two-component contact development); And two-component non-contact development. The two-component contact development method is often used from the viewpoints of high image quality and high stability.

In this embodiment, a mixture of non-magnetic toner particles and magnetic carrier particles is used as a developer.
A two-component magnetic brush contact development system in which the developer is held on a developer carrier as a magnetic brush layer by magnetic force, transported to a developing unit, and brought into contact with the surface of the photosensitive drum 1 to develop an electrostatic latent image as a toner image is used. Used. The two-component magnetic brush contact development is very suitable for collecting residual toner on the photosensitive drum 1 in an image forming apparatus of a 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 a developing bias applying power source S2.

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 in the thin layer of the developer magnetic brush on the developing sleeve 31 side selectively adheres to the electrostatic latent image on the photosensitive drum 1 side in the developing section, so that the electrostatic latent image becomes a toner image. Developed.

In general, in the two-component developing method, when an alternating voltage is applied, the developing efficiency is increased, and the quality of an image becomes high. On the contrary, there is a risk that fogging is likely to occur. For this reason, fog is generally prevented by providing a potential difference between the DC voltage applied to the developing device 3 and the surface potential of the photosensitive drum 1.

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

(5) Collection and discharge of transfer residual toner by contact charging member Cleaning at the same time as development by the developing device Transfer residual toner remains on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P. As for the transfer residual toner, there are those whose charge polarity is inverted due to peeling discharge or the like at the time of transfer, and those whose charge polarity is not inverted. Here, the toner in the polarity-reversed state is collected by the magnetic brush charger 2, which is the second contact charging member, while the toner whose polarity is not reversed is collected by the magnetic brush charger 2. This is difficult (because the charging potential is generally lower than the bias applied to the charger).

Therefore, a first contact charging member as a charging auxiliary member, in this example, the fur brush roll 6 as described above, is provided between the transfer portion T and the magnetic brush charger 2, and the photosensitive drum 1 A voltage having a polarity opposite to the normal charging polarity is applied, and the transfer residual toner is charged with the opposite polarity to the normal charging polarity, thereby improving the collection efficiency in the magnetic brush charger 2. Only when the charging polarity of the toner is opposite to the normal charging polarity, the transfer residual toner in the magnetic brush charger 2 is sufficiently collected, and the positive ghost is improved.

As described above, by applying a voltage having a polarity opposite to the normal charging polarity of the photosensitive drum 1 to the fur brush roll 6 serving as a charging auxiliary member, the transfer residual toner having the inverted polarity is transferred to the magnetic brush charger 2. Will be collected.

In this embodiment, in order to increase the bias applied to the magnetic brush charger 2 to improve the recoverability of the transfer residual toner and the charging uniformity in the charger 2, an alternating voltage is superimposed on the DC voltage. I have.

Then, in the charging area of the magnetic brush charger 2, the transfer residual toner collected and mixed into the magnetic brush portion 23 of the charger 2 is converted into a normally charged toner by rubbing with the magnetic brush portion 23, and alternately changed. The history of the transfer residual toner remaining 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 2 by the voltage, and the normally charged toner is removed from the magnetic brush unit 23 by the photosensitive drum 1. It is exhaled in a uniform state on the top.

The toner that has been charged normally and is discharged onto the photosensitive drum 1 is carried to the developing area, and is subjected to simultaneous cleaning (recovery) 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 unit 3 and the Recovery at the fog removal potential (Vback), which is the potential difference between the surface potentials of the carrier 1, is possible. As a result, it is possible to prevent the appearance of a positive ghost in the previous image, and the toner discharged in a thin layer is advantageous in terms of recoverability during development. The occurrence of a positive ghost can be prevented, and the toner mixed in the second charging member 2, which is the final contact charging means, can be sufficiently discharged. Therefore, 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 the present example, a durability test was performed with the fur brush roll 6 as the first contact charging member, which is a charging auxiliary member, fixed to non-rotation. As a result, in the case of the first contact charging member of the fixed system, paper dust is partially clogged after about 10,000 prints, and a positive ghost is generated in a portion corresponding to the fur brush portion of the paper dust clogged portion. I have.

On the other hand, by forming the first contact charging member into the rotating fur brush roll 6 as in the present embodiment, 5
Even after 10,000 sheets, it was possible to obtain a good image without a positive ghost caused by the occurrence of paper dust clogging.

<Embodiment 2> This embodiment is the first embodiment of the present invention.
In this printer, the fur brush roll 6 as the first contact charging member is rotated intermittently.

That is, the fur brush roll 6 as the first contact charging member is stopped during image formation (during printing), and is driven to rotate by rotation of the photosensitive drum 1 in a non-image area (during non-image formation). Was.

As a result of an endurance test with this configuration, no paper dust was clogged even after 50,000 sheets, and scattering of toner could be suppressed.

When the rotation of the fur brush roll 6 is fast, the toner attached to the fur brush roll 6 is scattered. Therefore, when the image area passes through the fur brush as in the present embodiment, the brush is stopped so that a paper jam is prevented. It is possible to realize a configuration in which no toner is generated and toner scattering is small.

FIG. 4 is a diagram showing the operation process of the printer.

[0104] Multi-rotation period before When the main power switch of the printer is turned on, 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 to execute a start-up operation of other necessary process equipment.

[0105] Standby (standby) period When the preceding multi-rotation period ends, the driving of the main motor is temporarily stopped, the rotation of the photosensitive drum 1 is stopped, and the printer is kept in the standby state until a print start signal is input. During this time, the temperature of the fixing device 5 is adjusted to a predetermined temperature.

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

If the print start signal has already been input at the end of the previous multi-rotation period, the operation shifts to the pre-rotation period without the standby period.

. Printing Period When a predetermined pre-rotation period is completed, an image forming process (image forming process) of a predetermined sequence of charging, image exposure, development, transfer, and the like is performed on the rotating photosensitive drum, and the first sheet is printed. It is.

In the continuous print mode, an image forming process for a predetermined number n is repeatedly executed. FIG. 4 shows an example of continuous printing of two sheets. In the continuous print mode, after the rear end of one transfer material P has passed through the transfer portion T and before the leading end of the next transfer material P reaches the transfer portion T, the transfer material is not passed through the transfer portion T. There is a paper state period, referred to as the paper interval.

[0110] Post-rotation period After the printing period of one sheet or the last n-th sheet in the continuous print mode is completed, the main motor is driven for a while to rotate the photosensitive drum 1 to perform a predetermined post-operation of the printer. This is the period for execution.

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

In the above, the printing period is the time of image formation, and the pre-multi-rotation period, the pre-rotation period, the paper interval, and the post-rotation period are non-image formation in the printer driving state.

<Others> 1) The image exposure means as the information writing means on 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, and a latent image may be formed by the light emission.
An analog image exposure unit using a halogen lamp, a fluorescent lamp, or the like as a light source may be used. Any device that can form an electrostatic latent image corresponding to image information may be used.

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

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

4) The magnetic brush charger 2 serving as the second contact charging member is not limited to the sleeve rotating type of the embodiment, but may be one in which the magnet roll 21 rotates or the surface of the magnet roll 21 may be changed as required. A configuration in which the magnetic brush portion 23 is formed by magnetically constraining the conductive magnetic particles directly on the outer peripheral surface of the magnet roll 21 by conducting a conductive process as a power supply electrode, and rotating the magnet roll 21 may be employed. it can. A non-rotating type magnetic brush member may be used.

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

6) A plurality of three or more contact charging members may be arranged in the plane moving direction of the image carrier 1.

7) As a 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 on / off the DC power supply. As described above, the alternating voltage can use a bias whose voltage value changes periodically.

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

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

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

[0123]

As described above, according to the present invention, the first contact charging member as a charging auxiliary member is rotatable in an image forming apparatus of a contact charging system using a charging auxiliary member and a cleanerless system. By doing so, since the same portion of the first contact charging member is not always in contact with the image carrier, paper dust and the like are hardly clogged, and a good image free of positive ghost for a long period of time can be obtained. It became so.

[Brief description of the 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 is a schematic diagram of a layer configuration of a photosensitive drum.

FIG. 3 is an enlarged schematic diagram of a first and a second contact charging member.

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

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 6 fur brush charger as first contact charging member 2 magnetic brush charger as second contact charging member

Claims (12)

[Claims] 1. An image forming method comprising: charging an image carrier with respect to the image carrier; forming an electrostatic latent image on a charged surface of the image carrier; and developing the electrostatic latent image as a toner image. The developing means for applying the process to form an image and developing the electrostatic latent image as a toner image also serves as an image carrier cleaning means for collecting toner particles remaining on the image carrier in the previous image formation, and The carrier is an image forming apparatus of a cleanerless system for repeatedly performing image formation. As a charging unit for charging the image carrier, the image carrier has at least a first contact charging member and an image bearing member which is more than the contact charging member A plurality of contact charging members of the second contact charging member on the downstream side in the body rotation direction are provided, and the bias applied to the first contact charging member is opposite in polarity to the normal charging polarity of the image carrier,
The bias applied to the second contact charging member, which is a charging unit for finally charging the image carrier, is a normal charging polarity of the image carrier, and the first contact charging member is rotatable. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the first contact charging member rotates intermittently. 3. An image carrier having a surface having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω.
The image forming apparatus according to claim 1, further comprising a layer made of a material having a size of about cm. 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 said image bearing member comprises a surface layer having amorphous silicon. 7. The image forming apparatus according to claim 1, wherein the second contact charging member has a magnetic brush portion of conductive magnetic particles, and the magnetic brush portion is in contact with the image carrier. The image forming apparatus according to any one of the above. 8. The method according to claim 1, wherein the first contact charging member has a conductive fiber brush portion, and the conductive fiber brush portion is in contact with the image carrier. The image forming apparatus according to one of the above. 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 method according to claim 1, wherein a developing method of said developing means is a contact developing method in which a developer is in contact with an image carrier. Image forming device. 11. The image forming apparatus according to claim 1, wherein the electrostatic latent image forming means for the charged surface of the image carrier is an image exposing means for the image carrier. . 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.