JPH1184822A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of positive ghost by constituting a contact member of a material by which toner is electrified to the polarity opposite to a normal polarity. SOLUTION: The acrylic fiber of a fixed brush 6 used as the contact member imparts a positive charge to the toner having a polyester surface layer for instance by triboelectrification. In other words, the fixed brush 6 used as the contact member is made of the material by which the toner is electrified to the polarity (positive) opposite to the normal polarity (in this case, a negative) by a troboelectrification series. Further, for instance, a DC bias voltage of +200 V having the polarity (positive) opposite to the normal polarity (negative) of the toner is applied to the fixed brush 6 as the contact member from a bias applying power source S4. Thus, the charge quantity of the toner remaining after a transfer is uniformed and the temporary recovery rate of the toner in an electrifying part 2a is increased to reduce the occurrence of the positive ghost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging system, a transfer system, and a cleanerless image forming apparatus.

[0002]

[Prior art]

a) Transfer-Type Image Forming Apparatus The transfer-type image forming apparatus forms a transferable image on a first image carrier by an appropriate image forming process, and transfers the transferable image to a second image carrier. The first image carrier to be transferred is an apparatus of a system and a structure that is repeatedly used for image formation.

For example, an image forming apparatus such as a copying machine or a laser beam printer using a transfer type electrophotographic process includes:
Basically, an electrophotographic photoreceptor generally having a rotary drum type as a first image carrier, a charging unit for uniformly charging the surface of the rotary photoreceptor to a predetermined polarity and potential, and Image exposure means for forming an electrostatic latent image on the charged surface of the photoconductor, developing means for developing the electrostatic latent image as a toner image,
Transfer means for transferring the toner image from the photoconductor surface side to transfer paper as a second image carrier (recording medium); fixing means for fixing the toner image transferred to the transfer paper side as a permanent fixed image; Photoreceptor cleaning means (cleaner) is provided for removing transfer residual toner from the surface of the rotating photoreceptor after transferring the toner image to the paper side and cleaning the photoreceptor surface. The transfer paper subjected to the image fixing process by the fixing unit is discharged as an image formed product (copy, print). The photoreceptor surface cleaned by the cleaning means is repeatedly used for image formation.

B) Contact Charging Means A corona charger has conventionally been used as charging means for uniformly charging the surface of a photoreceptor to a predetermined polarity and potential.
The corona charger is disposed so as to face the member to be charged in a non-contact manner, and charges the surface of the member to be charged to a predetermined polarity and potential by exposing the surface of the member to a corona shower emitted from the corona charger to which a high voltage is applied.

In recent years, a contact charging device has been put to practical use instead of this. In this method, a conductive charging member (contact charging member, contact charger) such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type is brought into contact with a photoreceptor as a member to be charged. It applies a predetermined charging bias to the contact charging member to charge the photoreceptor surface to a predetermined polarity and potential, and has advantages such as low ozone and low power as compared with a corona charger.

As a charging bias application method for the contact charging member, there are a DC bias method in which only a DC bias is applied and an AC bias method in which a DC bias is applied while being superimposed on an AC bias.

[0007] The contact charging mechanism (charging mechanism,
The charging principle) includes two types: a corona charging system and a contact injection charging system.
Types are mixed, and each characteristic appears depending on which is dominant.

The corona charging system uses a discharge phenomenon such as corona discharge generated in a minute gap between the contact charging member and the member to be charged, and charges the surface of the member with the discharge product. Since the essential charging mechanism of this corona charging system uses the discharge phenomenon from the contact charging member to the member to be charged,
A very small amount of ozone is generated, though much less than with a corona charger.

The contact injection charging system is a system in which the surface of a member to be charged is charged by directly injecting electric charge from a contact charging member to the member to be charged. It is also called direct charging or injection charging. Japanese Patent Application Laid-Open No. Hei 6-3921 discloses that charge is injected into a charge holding member such as a trap level on the surface of a photoreceptor or conductive particles of a charge injection layer by a contact charging member such as a charging roller, a charging brush or a charging magnetic brush. There has been proposed a method of performing contact injection charging by using the method.

Since contact injection charging does not use a discharge phenomenon,
The voltage required for charging is only the desired surface potential of the photoreceptor, and is an ozone-less low-power charging method that does not generate ozone.

C) Cleanerless (Cleanerless Process, Toner Recycling Process) For a transfer type image forming apparatus, in order to reduce the size, cost, and ecology of the apparatus, it is not necessary to provide a special photoconductor cleaner. There has been proposed a method of performing cleaning (removal) of post-transfer residual toner (transfer residual toner) on a body using a charging device or a developing device (simultaneous charging cleaning or simultaneous developing cleaning).

That is, in a general transfer type image forming apparatus, the transfer residual toner remaining on the photoreceptor after transfer is removed from the photoreceptor surface by a dedicated cleaner to become waste toner. It is desirable not to come out from the aspect of protection.

In view of the above, a cleaner-less image forming apparatus having a structure in which the cleaner is eliminated, and the transfer residual toner on the photoreceptor after transfer is removed from the surface of the photoreceptor by simultaneous development and cleaning by the developing device and is collected and reused in the developing device. Has also appeared. That is, the developing device also serves as a cleaner for collecting the transfer residual toner remaining on the photosensitive member after the transfer of the toner image to the recording medium.

In the simultaneous cleaning with development, the toner remaining on the photoreceptor after the transfer is subjected to a fog removal bias (a fog removal potential difference Vback, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoreceptor) during the subsequent development. ). According to this method, the transfer residual toner is collected in the developing device and reused in the subsequent steps, so that waste toner can be eliminated and troublesome maintenance can be reduced. In addition, the cleaner-less has a great advantage in terms of space, so that the size and cost of the image forming apparatus can be reduced.

D) Contact charging type / transfer type / cleanerless image forming apparatus In a transfer type / cleanerless image forming apparatus, when a contact charging means is adopted as a charging means for a photosensitive member as an image carrier, Positive ghost due to poor transfer residual toner collection in the developing device can be suppressed by the effect of scattering the residual transfer toner by the contact charging member in contact with the photoconductor. Since it is cleaner-less, there is an advantage that there is no damage to the photoreceptor surface due to a cleaning member such as a cleaning blade that rubs in contact with the photoreceptor surface, for example, there is no damage to the charge injection layer of a photoreceptor having a charge injection layer as a surface layer. is there.

Among the contact charging means, magnetic brush charging using a magnetic brush charger having a magnetic brush portion in which conductive magnetic particles are magnetically constrained into a brush as a contact charging member is performed by a magnetic brush as a contact charging member. The brush charger is less susceptible to toner contamination than other contact charging members such as a conductive rubber roller and a fixed or rotating fur brush, and is suitably used in a cleanerless process.

Here, a cleanerless process using magnetic brush charging will be briefly described. In the cleanerless process, with the rotation of the photoconductor as an image carrier,
A transfer carried from a transfer portion of the photoreceptor by the transfer means (hereinafter, referred to as a transfer portion of the photoreceptor) to a charge portion of the photoreceptor by a magnetic brush charger (hereinafter, referred to as a charge portion of the photoreceptor) to enter. The remaining toner includes both a toner whose charging polarity is a normal polarity and a toner whose charging polarity has been inverted due to discharge or the like at the time of transfer.

Of these, the toner of normal polarity passes through the charging portion of the photoreceptor while being rubbed by the magnetic brush, and is developed by the developing device of the photoreceptor (hereinafter referred to as a developing portion of the photoreceptor).
And is collected by the developing device.

The normal polarity toner passes through the charged portion of the photoreceptor because the surface of the photoreceptor is usually charged only to a potential slightly lower than the charging bias voltage applied to the contact charging member. This is because an electric field that is pressed toward the photoconductor is generated. Then, the toner pattern having the normal polarity is disturbed to some extent by the rubbing of the magnetic brush of the magnetic brush charger, which is a contact charging member, so that the toner is easily collected by the developing device.

On the other hand, the toner whose polarity has been reversed generates an electrostatic force in the direction of the contact charging member, and is once collected in the magnetic brush of the magnetic brush charger as the contact charging member.

The polarity of the toner, once inverted and collected in the magnetic brush, is normalized by frictional charging with magnetic particles (charged carriers) constituting the magnetic brush, so that the polarity of the toner is normalized again. The magnetic brush is discharged from the magnetic brush side to the photoreceptor surface by the electrostatic force in the direction, adheres to the photoreceptor surface, reaches the developing section of the photoreceptor, and is collected by the developing device.

However, even in this method, a positive ghost is generated due to a large amount of toner having a normal polarity in the transfer residual toner due to environmental fluctuations, poor charging and insufficient dispersion of the transfer residual toner due to a decrease in transfer efficiency. There was a thing.

Therefore, a contact member such as a fur brush is brought into contact with the photoreceptor between the transfer portion and the charging portion of the photoreceptor, and the transfer residual toner is also disturbed by the contact member. There has been proposed a method for improving the scattering effect of the residual toner.

Further, by applying a voltage of about 500 V having a polarity opposite to the normal polarity of the toner to the fur brush as the contact member, the normal brush toner of the transfer residual toner is captured by the fur brush. The polarity of the captured toner is inverted by charge injection or discharge into the toner by an electric field generated between the fur brush and the photoconductor, and the toner is discharged again to the photoconductor surface. As a result, the transfer residual toner reaching the charging portion of the photoreceptor has substantially the only inverted polarity, and substantially all of the toner is charged by the charging portion of the photoreceptor to a magnetic brush charger which is a contact charging member. A method has also been devised in which the toner is once collected in a magnetic brush, the polarity is normalized again by frictional electrification with magnetic particles constituting the magnetic brush, and the magnetic brush is discharged from the magnetic brush side to the photoreceptor surface and collected by a developing device. .

The transfer on the photoreceptor is performed by disturbing, temporarily collecting, and discharging the transfer residual toner by the fur brush as the contact member and disturbing, temporarily collecting, and discharging the transfer residual toner by the magnetic brush charger as the contact charging member. The residual toner image pattern is effectively erased.

The same effect can be obtained by the electric field generated between the fur brush as the contact member and the photosensitive member even when the fur brush is grounded. However, a higher effect can be obtained by applying a voltage.

In this manner, the amount of charge of the transfer residual toner is made uniform, and the temporary recovery rate of the toner at the charging portion of the photosensitive member is increased, so that the occurrence of the positive ghost can be greatly reduced.

[0028]

SUMMARY OF THE INVENTION An image forming apparatus of a contact charging type, a transfer type, and a cleanerless type, wherein a transfer residue on an image carrier is transferred between a transfer portion of the image carrier and a charging portion as described above. Even in the case of an image forming apparatus provided with a contact member that comes into contact with the toner, if the charging ability decreases due to the durability deterioration of the contact charging member or the like, the charging section, which is the contact section between the image carrier and the contact charging member, is used. May cause a positive ghost due to slippage of the transfer residual toner.

This is because the toner whose polarity is not sufficiently inverted by the contact member is collected by the contact charging member due to a decrease in the potential difference between the contact charging member and the image carrier in the image area due to a decrease in the charging ability of the contact charging member. It is because it disappears.

In order to prevent this positive ghost, it is effective to increase the voltage applied to the contact member and sufficiently reverse the polarity of the transfer residual toner by the contact member.
However, the contact member not only inverts the polarity of the toner, but also charges the image carrier to the opposite polarity. Therefore, by increasing the voltage applied to the contact member, the image carrier is charged to the opposite polarity, so that the contact charging member having reduced charging ability cannot fill the history of the potential difference between the image area and the non-image area, After all, a positive ghost occurs. This is more remarkable as the voltage applied to the contact member is higher.

That is, when the voltage applied to the contact member is grounded and in a low voltage range, a positive ghost occurs due to slippage of the transfer residual toner in the charging unit, and when the voltage is high, a positive ghost occurs due to poor charging. At the time of durability deterioration, it was impossible to suppress ghost by the contact member.

Therefore, the present invention relates to a contact charging type, transfer type, and cleanerless image forming apparatus, wherein a contact between a transfer portion of the image bearing member and a charging portion contacts a transfer residual toner on the image bearing member. An object of the present invention is to prevent the occurrence of a positive ghost which is remarkable at the time of deterioration of the durability of the contact charging member as described above in an image forming apparatus provided with the member.

[0033]

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

(1) The image carrier is charged by a contact charging member, and the transfer residual toner remaining on the image carrier after the transfer of the toner image to the recording medium is collected by a developing device. A contact charging system, a transfer system, and a cleaner-less image forming apparatus, comprising: a contact member that contacts a transfer residual toner remaining on the image carrier between a transfer site by the transfer unit and a charged site by the contact charging member. The image forming apparatus according to claim 1, wherein the contact member is made of a material that charges the toner to a polarity opposite to the normal polarity.

(2) The image carrier, charging means for charging the image carrier to a predetermined polarity, information writing means for forming an electrostatic latent image on the charged surface of the image carrier, and the electrostatic latent image Developing means for developing the image as a toner image, and transfer means for transferring the toner image to a recording medium, wherein the developing means collects transfer residual toner remaining on the image carrier after transferring the toner image to the recording medium. The image carrier is a transfer type / cleanerless image forming apparatus that is repeatedly used for image formation, and the charging unit contacts a charging member with the image carrier to perform charging. Charging means,
A contact member is provided between the transfer portion of the image carrier by the transfer means and the charged portion of the contact charging member, the contact member being in contact with the transfer residual toner remaining on the image carrier. An image forming apparatus comprising a material which is charged to a polarity opposite to the polarity.

(3) The image forming apparatus according to (1) or (2), wherein the contact member is made of a conductive fiber.

(4) The image forming apparatus according to (1) or (2), wherein the contact member is a rotatable conductive elastic body.

[0038] (5) 10 ^9-10 on the image bearing member surface
The image forming apparatus according to any one of (1) to (4), further including a layer made of a material of ¹⁴ Ω · cm.

(6) The image carrier according to any one of (1) to (5), wherein the image carrier has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles. An image forming apparatus according to claim 1.

(7) The image forming apparatus according to (6), wherein the conductive fine particles are SnO ₂ .

(8) The image forming apparatus according to any one of (1) to (5), wherein the image carrier comprises a surface layer having amorphous silicon.

(9) The developing device according to any one of (1) to (8), wherein the developing device is a contact developing system in which a latent image is developed while a developer is in contact with the image carrier. The image forming apparatus according to one of the above.

(10) The image forming apparatus according to any one of (1) to (9), wherein a voltage can be applied to the contact member.

<Operation> That is, an image forming apparatus of a contact charging type, a transfer type, and a cleaner-less type, in which a transfer residual toner on an image carrier is brought into contact between a transfer portion and a charging portion of the image carrier. With respect to an image forming apparatus having a contact member, by using the contact member that charges the toner to the polarity opposite to the normal polarity by frictional charging with the toner, the contact charging member is remarkably deteriorated in durability. Positive ghosts were prevented from occurring.

The main function of the contact member is to invert the polarity of the transfer residual toner, which is usually performed by applying a voltage to the contact member and injecting or discharging a charge into the toner. However, by using a contact member made of a material that charges the toner to a polarity opposite to the normal polarity by frictional charging, the charge polarity of the toner can be reversed by sliding friction between the transfer residual toner and the contact member. For this reason, the polarity of the toner can be inverted at a relatively low voltage by the synergistic effect of the charge application by the frictional charge and the charge application by the voltage application. In this voltage range, the image carrier is less charged in the opposite polarity, so that even a contact charging member having a somewhat reduced charging ability can be uniformly charged without leaving the history of the previous image.

On the other hand, if the contact member is made of a material that charges the toner to a normal polarity by frictional charging, the polarity reversal of the toner is performed by charge injection or discharge. It is necessary to increase the applied voltage, but in that case, the image carrier is also strongly charged to the opposite polarity, so that there is no area where the positive ghost disappears.

Thus, the contact member is made of a material that charges the toner to a polarity opposite to the normal polarity by frictional charging, thereby preventing a positive ghost that is remarkable at the time of durability deterioration of the contact charging member. be able to.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 (FIGS. 1 to 3) (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, a contact charging system, and a cleaner.

A) Reference numeral 1 denotes a rotating 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 embodiment has a charge injection charging property,
It is a negatively charged OPC photoconductor (organic photoconductor), and is driven to rotate at a process speed (peripheral speed) of 100 mm / sec in a clockwise direction indicated by an arrow around a central support shaft. More specifically, the photosensitive drum 1 has a charge generating layer in which a disazo pigment is dispersed in a resin and a charge transporting layer in which hydrazone is dispersed in a polycarbonate resin. Has an organic photosensitive layer composed of a charge injection layer in which SnO ₂ is dispersed.

B) The photosensitive drum 1 is subjected to contact injection charging at -700 V in the case of the present embodiment by the magnetic brush charging device 2 during the rotation process. This magnetic brush charging device 2 will be described in detail in section (2) below.

C) Next, the charged surface of the rotating photosensitive drum 1 is subjected to laser beam scanning exposure L of target image information by a laser beam scanner (not shown).
An electrostatic latent image of target image information is formed on the rotating photosensitive drum surface.

The laser beam scanner has a laser diode, a polygon mirror and the like, outputs a laser beam modulated in accordance with a time-series potential digital pixel signal of target image information, and outputs the laser beam to the rotating photosensitive drum 1 using the laser beam. Scanning exposure L is performed on the uniformly charged surface.

The potential of the laser beam scanning exposure portion (light exposure portion) on the uniformly charged surface of the rotary photosensitive drum 1 drops, and an electrostatic latent image is formed with a potential contrast with the potential of the exposure dark portion.

D) Next, the electrostatic latent image is developed by the developing device 3 as a toner image. In the present embodiment, the developing device 3 is a reversal developing device, and a negative toner (negative toner) adheres to the exposed portion of the electrostatic latent image so that the electrostatic latent image is reversibly developed. This developing device 3 will be described later in detail in section (3).

E) The toner image is transferred to a transfer portion (transfer portion, transfer nip portion) 4a which is a contact nip portion between the photosensitive drum 1 and a transfer roller 4 as a transfer device. The image is sequentially transferred onto a transfer material P as a recording medium fed at a predetermined timing from a sheet feeding mechanism.

The transfer roller 4 in this example is an elastic roller having a medium resistance foam layer formed on a core metal and having a roller resistance value of 5 × 10 ⁸ Ω.
The transfer bias voltage was applied to the core metal at a predetermined timing for a predetermined period to perform the transfer.

The transfer material P introduced into the transfer section 4a is conveyed by nipping the transfer section 4a, and the toner image formed and carried on the surface of the rotary photosensitive drum 1 on its surface side is sequentially subjected to electrostatic force and pressing force. Is transcribed.

F) Photosensitive drum 1 fed to transfer section 4a
The transfer material P having received the transfer of the toner image on the side thereof is separated from the surface of the rotary photosensitive drum 1 and introduced into a fixing device 8 such as a heat fixing method, and is subjected to a fixing process of the toner image to form an image formed material (print, copy). ) Is discharged outside the apparatus. 7 is a transfer unit 4
1 is a transfer material conveying device disposed between the fixing device 8 and the fixing device 8.

G) Since the printer of this embodiment is cleaner-less, a dedicated cleaner 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, and the rotary photosensitive drum is not provided. The transfer residual toner on one surface reaches the developing device 3 via the contact member 6 and the magnetic brush charging device 2 by the subsequent rotation of the photosensitive drum 1, and is collected by the developing device 3 at the same time as the development, and is collected. Are repeatedly provided for image formation.

The structure and operation of the contact member 6 and the simultaneous cleaning with development will be described in detail in the section (4).

(2) Magnetic Brush Charging Device 2 (FIG. 2) FIG. 2 is an enlarged cross-sectional model view of the magnetic brush charging device 2 used in this embodiment.

Reference numeral 21 denotes a rotating sleeve (charging sleeve) as a holding member for the magnetic brush of the conductive magnetic particles. The sleeve 21 of the present example is a non-magnetic sleeve, and also serves as a power supply electrode, and is made of, for example, aluminum. Both ends are rotatably supported in the device casing 25. The front side of this sleeve 21 is the device casing 2.
5 is exposed to the outside from the front opening.

Numeral 22 denotes a magnet roller as magnetic field generating means which is substantially concentrically inserted into and contained in the sleeve 21. This example is a four-pole magnet roller,
The roller is fixed non-rotating. N ₁ · S ₁ · N ₂ · S
₂ is a magnetic pole part.

The sleeve 21 is driven to rotate around the fixed magnet roller 22 in a clockwise direction indicated by an arrow at a peripheral speed of 200 mm / sec by a drive system (not shown).

Reference numeral 23 denotes conductive magnetic particles (magnetic carriers, hereinafter referred to as magnetic particles) or magnetic brushes of the magnetic particles, which are magnetically constrained on the outer surface of the sleeve 21 by the magnetic force of the magnet roller 22 inside the sleeve. . In this example, the conductive magnetic particles have an average particle size of 25 μm, a resistance value of 5 × 10 ⁶ Ω / cm, and a saturation magnetization of 200 emu / cm ^2.
Was used.

Reference numeral 24 denotes a regulating plate as regulating means for regulating the amount of magnetic particles carried on the sleeve 21.
In the present embodiment, the regulating plate 24 is a non-magnetic rigid blade. The regulating plate 24 is fixedly provided on the front wall on the upper side of the front opening of the device casing 25 with a predetermined gap set between the lower side of the regulating plate and the outer surface of the sleeve 21.

A predetermined gap between the sleeve portion exposed to the outside from the front opening of the apparatus casing 25 and the photosensitive drum 1 (the gap dimension at the closest position of the two 21.1)
Are set to face each other. In this example, the gap is 50
It is set to 0 μm.

The magnetic particles 23 adhered by being magnetically restrained to the outer surface of the sleeve 21 are conveyed in the same direction as the sleeve 21 rotates in the clockwise direction. A large pool portion is formed and held in a space defined by the back surface portion and the back surface portion of the front wall of the device casing 25.

A part of the magnetic particles in the pool is
With the rotation of 1, it passes through the gap between the lower side of the regulating plate 24 and the outer surface of the sleeve 21, escapes outside the device casing 25, is held on the sleeve 21 as a magnetic brush whose layer thickness is regulated, and The sheet is conveyed to a position facing the photosensitive drum 1.

The magnetic brush of the magnetic particles transported to the position where the sleeve 21 and the photosensitive drum 1 are opposed to each other is raised by the magnetic force of the magnetic pole N ₁ on the magnet roller 22 which is positioned substantially corresponding to the opposed position. The rotating photosensitive drum 1 comes into contact with the surface of the rotating photosensitive drum 1 and is rubbed with a magnetic brush of magnetic particles. At a position where the sleeve 21 and the photosensitive drum 1 are opposed to each other, a contact area of the magnetic particles (magnetic brush) with respect to the surface of the photosensitive drum 1 is a charged portion (charged portion) 2a. In this example, the magnet roller 22 on the sleeve of the charging unit 2a
Is 800 × 10 ⁻⁴ T (tesla).

The magnetic particles that have passed through the gap at the opposing position are magnetically restrained and held on the sleeve 21 and are transported back into the apparatus casing 25 by the subsequent rotation of the sleeve 21 and are cyclically transported and used.

The sleeve 21 has a charging bias application power source S
1, a predetermined charging bias voltage is applied, and the surface of the rotating photosensitive drum 1 is subjected to contact charging processing to a predetermined polarity and potential at a charging section 2a by rubbing of magnetic particles by a magnetic brush and an applied charging bias.

In this embodiment, the sleeve 21 is supplied from the power source S1.
As a charging bias, a DC voltage: -700 V, an alternating electric field: a superposition bias having an amplitude of 700 Vpp and a frequency of 1 kHz was applied.

In the present embodiment, the photosensitive drum 1 as a member to be charged has a charge injection layer on the outermost layer as described above, and therefore, the photosensitive drum 1 has the above-mentioned D of the applied charging bias.
Contact charging is performed at approximately -700 V in accordance with the C bias by an injection charging method.

By applying an alternating electric field to the charging section,
It is effective in improving the charging ability and preventing a positive ghost.

(3) Developing Device 3 (FIG. 3) FIG. 3 is an enlarged cross-sectional model view of the developing device 3 used in this embodiment.

The developing device 3 of this embodiment uses the developer 36
A toner t (negative toner) having an average particle diameter of 8 μm having negative chargeability and a magnetic carrier having a chargeability of 50 μm having weight average toner concentration of 5 μm
% Of the two-component developer mixed with
A two-component magnetic brush contact developing system in which the developer is held as a magnetic brush layer by a magnetic force on a developer carrier, transported to a developing unit 3a, and brought into contact with the surface of the photosensitive drum 1 to reversely develop an electrostatic latent image as a toner image It is.

The toner used in this embodiment is a spherical toner manufactured by a suspension polymerization method, and its surface layer is made of a polyester resin. Since the spherical toner has a very high releasability, the transfer efficiency is high and the amount of the transfer residual toner can be reduced, so that the spherical toner is suitably used in a cleanerless image forming apparatus.

Reference numeral 31 denotes a developing container; 32, a developing sleeve as a developer carrier; 33, a magnet roller as magnetic field generating means fixedly arranged in the developing sleeve 32;
Reference numeral 34 denotes a developer layer thickness regulating blade for forming a thin layer 36a of the developer 36 on the surface of the developing sleeve, and 35 denotes a developer stirring / conveying screw.

At least at the time of development, the developing sleeve 32 is disposed so as to have a gap of about 500 μm with respect to the photosensitive drum 1. The developer magnetic brush thin layer 36a carried on the outer surface of the developing sleeve 32 is Is set so as to contact the surface. The contact nip portion between the developer magnetic brush layer 36a and the photosensitive drum 1 is a developing portion (developing portion) 3a.

The developing sleeve 32 moves around the outer periphery of the fixedly disposed magnet roller 33 in the counterclockwise direction indicated by the arrow in this example to a position of 15 degrees.
Driven at a peripheral speed of 0 mm / sec, a magnetic brush of the developer 36 is formed on the outer surface of the sleeve 32 in the developing container 31 by the magnetic force of the magnet roller 33. The developer magnetic brush is conveyed with the rotation of the sleeve 32,
The layer thickness is regulated by the blade 34 and is taken out of the developing container as a developer magnetic brush thin layer 36a having a predetermined thickness, is conveyed to the developing unit 3a, comes into contact with the surface of the photosensitive drum 1, and is again rotated by the subsequent rotation of the sleeve 32. It is transported back into the developing container 31.

A predetermined developing bias voltage is applied between the developing sleeve 32 and the conductive drum substrate of the photosensitive drum 1 by a developing bias applying power source S2.

In this example, a DC voltage; -500 V, an alternating electric field;

In the developing section 3a, the toner t in the developer magnetic brush thin layer 36a on the developing sleeve 32 side selectively adheres to the electrostatic latent image on the photosensitive drum 1 side, and the electrostatic latent image is developed as a toner image. To go.

In general, in the two-component developing method, when an alternating voltage is applied, the developing efficiency is increased, and the quality of the image is high, but 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 fog removing potential (Vback). This potential difference prevents toner from adhering to a non-image area of the photosensitive drum 1 during development.

The toner concentration (mixing ratio with the magnetic carrier) of the developer 36 in the developing container 31 gradually decreases as the toner is consumed for developing the electrostatic latent image. The toner concentration of the developer 36 in the developing container 31 is detected by an optical toner concentration sensor (not shown), and when the toner concentration decreases to a predetermined allowable lower limit concentration, the toner supply unit 37 supplies the toner 36 to the developer 36 in the developing container. The developer 36 in the developing container 31 is
Is controlled so as to always keep the toner concentration within a predetermined allowable range.

(4) Contact Member 6, Cleaning Simultaneous Development The contact member 6 includes a transfer portion 4a and a charging portion 2a of the photosensitive drum 1.
Is a member that comes into contact with the transfer residual toner remaining on the photosensitive drum 1.

The contact member 6 used in this embodiment is
It is a fixed brush made of acrylic fiber whose resistance has been adjusted, and has a brush length of 4 mm, a brush density of 100,000 brushes / inch ² , a brush diameter of 6 denier, and a brush resistance of 10 ⁶ Ω · cm.

The brush is adhered on a conductive support plate, and a voltage can be applied to a power supply portion from a power source S4.

The fixed brush made of fibers used as the contact member 6 has a brush length of 1 to 10 mm, a brush density of 100,000 brushes / inch ² , a brush diameter of 2 to 12 denier,
A brush resistance of 10 ⁻² to 10 ¹² Ω · cm is also preferable.

The acrylic fiber of the fixed brush 6 used as the contact member in the present embodiment is to impart a positive charge to the toner t having a polyester surface layer used in the present embodiment by frictional charging.

That is, the fixed brush 6 used as the contact member
Is a material which charges the toner c to the polarity (plus) opposite to the normal polarity (minus in this example) in the triboelectric series.

In this embodiment, the fixed brush 6 as the contact member is supplied from the bias applying power source S4 with the toner c.
A DC bias voltage of +200 V having a polarity (plus) opposite to the normal polarity (minus) is applied.

[0096] The transfer residual toner remaining on the photosensitive drum 1 after the transfer of the toner image to the transfer material P reaches the contact portion 6a between the brush 6 as a contact member and the photosensitive drum 1 by the subsequent rotation of the photosensitive drum 1, and the sliding of the brush 6 Due to the rubbing, the image pattern of the transfer residual toner is scattered to some extent (disturbance of the transfer residual toner).

The transfer residual toner is charged to a positive polarity by frictional charging due to contact with the brush 6. In this example, since +200 V is applied to the brush 6, the applied voltage causes the toner of normal polarity (minus) of the transfer residual toner to be captured by the brush 6, and the toner is positively charged by charge injection or discharge. And the toner is again discharged onto the surface of the photosensitive drum. Originally, the positive polarity toner of the transfer residual toner passes through the contact member contact portion 6a.

Therefore, the transfer residual toner from the contact member contact portion 6a of the photosensitive drum 1 to the charging portion 2a is disturbed, and substantially all of the charge polarity is opposite to the normal polarity (minus) (positive). It is the one that is inverted.

[0099] Since the pattern is disturbed as described above and the transfer residual toner in a state where the charging polarity is substantially all inverted to the opposite polarity to the normal polarity reaches the charging portion 2a of the photosensitive drum 1, the charging portion 2a is charged. In 2a, substantially all of the toner is once collected in the magnetic brush of the magnetic brush charger as the contact charging member (improvement of the toner collection rate in the charging section).

The polarity of the toner once recovered in the magnetic brush, whose polarity is reversed to the opposite polarity to the normal polarity, is normalized (minus) again by frictional charging with the magnetic particles constituting the magnetic brush. Due to the electric field between the magnetic brush and the photosensitive drum, the magnetic brush is uniformly discharged (emitted) from the magnetic brush side to the photosensitive drum surface side.

. The toner discharged from the magnetic brush side to the photosensitive drum surface side reaches the developing unit 3a of the photosensitive drum 1 via the image exposure unit by the subsequent rotation of the photosensitive drum 1.

The toner discharged from the magnetic brush side to the photosensitive drum side is in a very uniform scattered state and its amount is small, so that it does not substantially adversely affect the next image exposure process.

The toner that has been discharged from the magnetic brush side to the photosensitive drum surface side and has reached the developing section 3a has substantially all the normal charging polarity (minus), and has been discharged to the photosensitive drum surface in the developing process. Of the toner, toner adhering to a white background portion is collected by the fogging electric field in the developing device 3 (simultaneous development and cleaning), and part of the toner adhering to the image portion is used for the next image formation. .

In this way, the amount of charge of the transfer residual toner is made uniform, and the temporary recovery rate of the toner in the charging section 2a is increased, so that the occurrence of a positive ghost can be greatly reduced.

[0105] In the present invention, the contact member 6 is made of a material that charges the toner to a polarity opposite to the normal polarity, thereby preventing the occurrence of a positive ghost that is remarkable when the contact charging device 2 is deteriorated in durability. .

Specifically, in this embodiment, as described above,
The acrylic fiber used for the fixed brush 6 as the contact member 6 gives a positive charge by frictional charging to the toner t (normally negatively charged polarity) having a polyester surface layer. The effect is described below.

Tables 1 to 4 show the relationship between the voltage applied to the contact member 6 and the state of occurrence of a positive ghost.

The experimental conditions at this time are described below. That is, the transfer bias is 2 kV, and the transfer residual toner amount is 0.0
The charging bias is 7 mg / cm ² , and the charging bias is obtained by superimposing a -700 DC voltage on an AC voltage having an amplitude of 1 kV. The magnetic particles 23 of the magnetic brush charger 2 used had a higher resistance value of 5 × 10 ⁻⁷ Ω · cm in order to clarify the effect of the contact member 6. The structure of the brush used for the contact member 6 was the same as that of the acrylic fiber.

Under these conditions, the occurrence of ghost in the middle density range was evaluated in five stages. The evaluation criteria are shown below.

A: None at all B: Ghost at high density part faintly generated C: Ghost at high density part vividly generated D: Ghost at medium density part slightly generated E: Ghost at medium density part vivid Occurrence Table 1 shows a case where a brush made of the same acrylic fiber as in the present embodiment was used as the contact member 6. The acrylic fiber gives a positive charge to the toner t (normally charged polarity minus) composed of a polyester surface layer.

On the other hand, Table 2 shows the results obtained by using a brush made of a nylon fiber which gives a negative charge by frictional charging to a toner having a polyester surface layer.

In the case where a brush made of acrylic fiber is used as the contact member 6, no positive ghost is generated in the range of the applied voltage of +100 to + 300V. Also, +4
Above 00V, the history of the high density area of the previous image slightly occurs as a positive ghost.

On the other hand, when nylon fibers are used, the
Positive ghosts become best at around 0 V, but do not disappear, and there is a large difference in the occurrence of positive ghosts compared to acrylic fibers. This can be explained as follows.

That is, the main function of the contact member 6 is to invert the polarity of the transfer residual toner. Usually, this is performed by applying a voltage to the contact member 6 and injecting or discharging a charge from the brush to the toner. Done. However, by using, as the contact member 6, a brush that applies a positive charge by frictional charging to the toner t composed of a polyester surface layer such as an acrylic fiber, the charge polarity of the toner can be inverted by rubbing of the transfer residual toner and the brush. Can be. For this reason, when acrylic fibers are used as shown in Table 1, the polarity of the toner can be inverted at a relatively low voltage due to the synergistic effect of the charge application by frictional charging and the charge application by voltage application. In this voltage range, the charging device 2 has a slightly reduced charging ability because the photosensitive drum has less charging of the opposite polarity.
However, it is possible to charge uniformly without leaving the history of the previous image.

On the other hand, when the nylon fiber is used, since the polarity reversal of the toner is performed by charge injection or discharge, it is necessary to increase the applied voltage in order to completely reverse the polarity. Since it is strongly charged to the opposite polarity, there is no region where the positive ghost disappears as shown in Table 2.

Next, Table 3 shows the state of occurrence of ghost when a brush made of polypropylene (hereinafter referred to as PP) fiber and a brush made of polyethylene terephthalate (hereinafter referred to as PET) are used as the contact member 6. ,
See Table 4. The experimental conditions are the same as those in Tables 1 and 2.

PP is a toner having a polyester surface layer.
To a positive charge.

Further, PET gives a negative charge to a toner having a polyester surface layer.

Here, as in Tables 1 and 2, it can be seen that a positive ghost is less likely to be generated in the contact member 6 made of PP having the positive application property than in PET having the negative application property. Also, the effect is higher for acrylic than for PP.

In nylon, ghost is most likely to occur, followed by PET. The permutation of this effect is roughly along the charging sequence.

Rayon, PET, etc., in addition to acryl and PP, are also effective for a toner whose surface layer is made of styrene acryl.

In this embodiment, the fixed contact member 6 is used. However, the present invention is not limited to this.
For example, the brush may be vibrated in the generatrix direction of the photosensitive drum,
Alternatively, the same effect can be obtained even when the brush roller, which is planted in a roll, is brought into contact with the roller while rotating.

The voltage applied to the contact member 6 is not limited to a DC voltage, and an AC voltage may be superimposed thereon.

As described above, since the brush used for the contact member 6 is made of a material that charges the toner to the polarity opposite to the normal polarity by frictional charging, this is remarkable when the durability of the contact charging device is deteriorated. Positive ghost can be prevented.

[0125]

[Table 1]

[0126]

[Table 2] <Embodiment 2> (FIG. 4) FIG. 4 is a schematic configuration diagram of an image forming apparatus of the present embodiment. The image forming apparatus of the present embodiment differs from the image forming apparatus of the first embodiment (FIG. 1) in that an elastic roller 6A is used as a contact member, and other configurations are the same.
The same reference numerals are given to common constituent members and portions, and the description thereof will not be repeated.

The elastic roller 6 a serving as a contact member is made of nitrile rubber in which carbon is dispersed and whose resistance is controlled to 10 ⁻⁶ Ω · cm, and is in contact with the photosensitive drum 1. The elastic roller 6A is not driven, but follows the rotation of the photosensitive drum 1.

The occurrence state of the positive ghost in the image forming apparatus having such a configuration was examined by the same method as in the first embodiment.

The toner t used is a spherical toner having a polyester resin on the surface layer manufactured by a suspension polymerization method.

Table 5 shows the results.

Table 6 also shows the results when silicon rubber was used as the elastic roller 6A as a comparative example.

Positive ghosts were generated with silicon rubber at any applied voltage, whereas no ghost was generated with nitrile rubber in the range of +100 to +200 V applied voltage. The cause of this difference is Example 1.
Similarly to the above, it is considered that the nitrile rubber gives a positive charge to the toner t whose surface layer is made of polyester by frictional charging. Conversely, silicone rubber imparts a negative charge to the polyester, causing ghosting.

In addition to nitrile rubber, a material in which Teflon particles are dispersed in a surface layer is also effective.

In this embodiment, the elastic roller 6A as a contact member is driven by the photosensitive drum 1. However, the same effect can be obtained by driving the photosensitive drum 1 in the same or opposite direction as the rotation of the photosensitive drum 1.

Further, the voltage applied to the elastic roller 6A is not limited to a DC voltage, and an AC voltage may be superimposed thereon.

As described above, even when the elastic roller 6A is used as the contact member, the surface layer of the contact roller is made of a material that charges the toner to the opposite polarity to the normal polarity by frictional charging. Positive ghost which was remarkable at the time of durability deterioration of No. 2 can be prevented.

[0137]

[Table 3] <Others> 1) The surface of the image carrier has a volume resistivity of 10 ⁹ to 10 ¹⁴ Ω ·
The presence of a layer made of a material having a thickness of 10 cm makes contact injection charging dominant.

Even when the charge injection layer is not used, the same effect can be obtained, for example, when the charge transport layer is in the above resistance range. The same effect can be obtained even when the image carrier is made of a surface layer having amorphous silicon.

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

3) 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.

4) The magnetic brush charging device 2 as the contact charging means is not limited to the sleeve rotating type of the embodiment, but may be a device in which a magnet roll rotates, or the surface of the magnet roll may be subjected to a conductive treatment as a power supply electrode as necessary. Then, a magnetic brush portion may be formed by magnetically constraining the conductive magnetic particles directly on the outer peripheral surface of the magnet roll, and a configuration in which the magnet roll is rotated may be employed. A non-rotating type magnetic brush member may be used.

A contact charging means other than the magnetic brush charging device may be used. The contact charging member may be a charging roller, a fur brush, a felt, a material such as cloth, a material such as a cloth, or a contact charging unit using a material obtained by laminating them and adjusting the elasticity and conductivity more appropriately. .

5) In general, 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 be in non-contact with the photosensitive drum. A method of developing in a state (one-component non-contact development), a method of developing a toner coated as described above in contact with a photosensitive drum (one-component contact development), and a method of developing a magnetic carrier for toner particles. A method in which the mixture of the two is used as a developer and transported by magnetic force to develop the photosensitive drum in contact with the photosensitive drum (two-component contact development), and a method of developing the two-component developer in a non-contact state. 4 with (two-component non-contact development)
Broadly classified into types.

The two-component contact developing method is often used from the viewpoint of improving the image quality and the stability of the image.

In the image forming apparatus of the embodiment, a mixture of non-magnetic toner particles t and magnetic carrier particles c is used as a developer, and the developer is applied to a developer carrier as a magnetic brush layer by a magnetic force. A two-component magnetic brush contact development system is used in which the toner is held, transported to the developing unit 3a, and brought into contact with the surface of the photosensitive drum 1 to develop the electrostatic latent image as a toner image. 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.

6) The transfer means is not limited to roller transfer, but may be any of belt transfer, corona discharge transfer and the like. 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.

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 used as appropriate. It may be a rectangular wave formed by periodically turning on / off the DC power supply. As described above, the alternating voltage can use a bias whose voltage value changes periodically.

8) Two or more contact charging members and two or more contact members may be provided in the plane moving direction of the image carrier.

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.

[0150]

As described above, according to the present invention, there is provided an image forming apparatus of a contact charging type, a transfer type, and a cleanerless type, wherein an image bearing member is provided between a transfer portion and a charging portion of the image bearing member. For an image forming apparatus provided with a contact member that comes into contact with the transfer residual toner, the contact member is configured to charge the toner to a polarity opposite to the normal polarity by frictional charging with the toner, so that the contact charging member is Positive ghost, which was remarkable at the time of durability deterioration, could be prevented.

[Brief description of the drawings]

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

FIG. 2 is an enlarged cross-sectional model diagram of the magnetic brush charging device used.

FIG. 3 is an enlarged cross-sectional model diagram of the developing device used.

FIG. 4 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 2 magnetic brush charging device 3 two-component contact developing device 4 transfer roller 5.5A contact member (fixed brush, elastic roller) 6 transport device 7 fixing device L laser beam P transfer material (recording medium) S1-S4 bias application power supply

Claims (10)

[Claims] An image carrier is charged by a contact charging member, and a transfer residual toner remaining on the image carrier after transfer of a toner image to a recording medium is collected by a developing device. A contact charging system, a transfer system, and a cleaner-less image forming apparatus including a contact member that contacts a transfer residual toner remaining on an image carrier between a transfer site and a charging site by a contact charging member; An image forming apparatus, wherein the contact member is made of a material that charges the toner to a polarity opposite to the normal polarity. 2. An image carrier, a charging unit for charging the image carrier to a predetermined polarity, an information writing unit for forming an electrostatic latent image on a charged surface of the image carrier, and the electrostatic latent image Developing means for developing the toner image as a toner image, and a transfer means for transferring the toner image to a recording medium, wherein the developing means collects transfer residual toner remaining on the image carrier after the transfer of the toner image to the recording medium. The image carrier is a transfer-type / cleanerless image forming apparatus that also serves as a cleaning unit and is repeatedly used for image formation. The charging unit contacts the charging member to the image carrier to perform charging. A contact member for contacting the transfer residual toner remaining on the image carrier between a transfer portion of the image carrier by the transfer device and a charged portion of the contact charging member; , Regular toner An image forming apparatus comprising a material which is charged to a polarity opposite to the polarity. 3. The image forming apparatus according to claim 1, wherein the contact member is made of a conductive fiber. 4. The image forming apparatus according to claim 1, wherein the contact member is a rotatable conductive elastic body. 5. The method according to claim 1, wherein the surface of the image carrier has a surface resistance of 10 ⁹ to 10 ¹⁴ Ω.
The image forming apparatus according to any one of claims 1 to 4, further comprising a layer made of a material having a size of about cm. 6. The image carrier 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. Image forming device. 7. The image forming apparatus according to claim 6, wherein the conductive fine particles are SnO ₂ . 8. The image forming apparatus according to claim 1, wherein said image bearing member comprises a surface layer having amorphous silicon. 9. The image forming apparatus according to claim 1, wherein the developing device is a contact developing system in which a latent image is developed while a developer is in contact with the image carrier. The image forming apparatus as described in the above. 10. The image forming apparatus according to claim 1, wherein a voltage can be applied to the contact member.