JP3359202B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image
An image carrier that can be charged by injecting a charge, a charging member that comes into contact with the image carrier and injects and charges the image carrier, and an electrostatic latent image on the image carrier that is charged by the image carrier. The present invention relates to an image forming apparatus having a developing unit that develops with a toner having the same polarity as the charging polarity of the toner and collects the toner on the image carrier, and a transfer unit that transfers a toner image on the image carrier to a transfer material.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus of an electrophotographic system or an electrostatic recording system, an image bearing member (a member to be charged) such as an electrophotographic photosensitive member or an electrostatic recording dielectric is charged (including a charge removing process). For this purpose, a corona charger has been frequently used.

[0003] In this method, a corona charger is disposed in contact with a member to be charged in a non-contact manner, and the surface of the member is charged to a predetermined polarity and potential by exposing the surface of the member to a discharge corona generated by the corona charger. It is.

In recent years, a contact charging device (direct charging device) has been put to practical use because it has advantages such as lower ozone and lower power than a corona charger.

In this method, a charging member to which a voltage is applied is brought into contact with a member to be charged, and the surface of the member to be charged is charged to a predetermined polarity and potential.

A contact charging device using a magnetic brush as a charging member is preferably used in terms of charging, contact stability and the like. In this magnetic brush type contact charging device, the conductive magnetic particles are magnetically constrained and held directly as a magnetic brush on a magnet or a sleeve containing a magnet, and the magnetic brush of the magnetic particles is stopped on the surface of the member to be charged. Alternatively, the object to be charged is started to be charged by applying a voltage to the contact while rotating.

[0007] A brush made of conductive fibers (fur brush) or a conductive rubber roll made of conductive rubber in a roll shape is also preferably used as a contact charging member.

In contact charging, a surface to be charged is provided with a charge injection layer, and a charging member to which a voltage is applied is brought into contact with the surface of the member to be charged, thereby injecting charges into the charge injection layer and causing the surface of the member to be charged to a predetermined surface. Injection charging method to charge to polarity and potential,
Irrespective of the presence or absence of the superimposition of the AC voltage (AC bias) on the charging member, a surface potential of the member to be charged that is substantially equal to the applied DC voltage (DC bias) can be obtained. Since a discharge phenomenon such as that performed by using an electric field is not used, complete ozone-less and low-power-consumption charging is possible.

[0009]

However, in the contact charging method, since the charging member is brought into contact with the member to be charged, the charging member easily picks up the deposits on the member to be charged and becomes dirty. Excessive contamination of the contact charging member causes charging unevenness and the like, thereby lowering charging performance.

An object to be charged (image carrier) is charged by contact charging, an electrostatic latent image corresponding to the target image information is formed on a charged surface of the object to be charged, and the electrostatic latent image is formed. In an image forming apparatus in which a toner image is visualized as a toner image by a developing unit and an image is formed, the toner adheres to and mixes with the contact charging member and accumulates as the image is formed.

Normally, toner particles having a relatively high electric resistance are used. Therefore, if toner adheres or mixes into the charging member excessively, uneven charging due to an increase in resistance of the charging member may occur, and the charging member may be used. When a magnetic brush is used, magnetic particles are extruded due to excessive mixing of toner and decrease over time, resulting in uneven charging due to contact instability, and mixing of magnetic particles detached from the magnetic brush into developing means. There is a problem that abnormal images such as streaks are generated due to the above.

In particular, when the image forming apparatus is a cleanerless system apparatus which does not have a cleaning device for removing transfer residual toner from the surface of the member after transfer of the toner image to the transfer material, the transfer residue on the member to be charged is removed. This is more remarkable because the toner directly reaches the contact charging member and adheres to and mixes with the charging member.

Accordingly, the present invention provides an electrostatic latent image ,
Carrier that can be charged by injecting the image carrier, a charging member that contacts the image carrier and injects and charges the image carrier, and charges the electrostatic latent image on the image carrier with the charge polarity of the image carrier. An image forming apparatus having a developing unit that develops with a toner having the same polarity and that can collect toner on the image carrier, and a transfer unit that transfers a toner image on the image carrier to a transfer material.
Eliminates the occurrence of uneven charging and the occurrence of abnormal images due to excessive adhesion and mixing of toner to the charging member, and when the charging member is a magnetic brush, contact instability due to the temporal decrease of magnetic particles constituting the magnetic brush The purpose of the present invention is to maintain good image formation for a long period of time by eliminating problems such as irregularity of charging caused by the toner, and the occurrence of abnormal images such as streaks due to mixing of magnetic particles detached from the magnetic brush into the developing means. I do.

[0014]

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

(1) It carries an electrostatic latent image and is charged with electric charge.
An image carrier that can be charged by charging the image carrier, a charging member that contacts the image carrier, and injects and charges the image carrier, and an electrostatic latent image on the image carrier that has the same polarity as the charge polarity of the image carrier. When an image is not formed in an image forming apparatus, the image forming apparatus includes a developing unit that develops with the toner and collects the toner on the image carrier, and a transfer unit that transfers the toner image on the image carrier to a transfer material. An image forming apparatus which performs charging at a potential lower than that at the time of image formation by charging a region which has been subjected to transfer charging by means with a charging member.

(2) The image forming apparatus according to (1), wherein the transfer charging performed during non-image formation is performed under conditions different from those during image formation.

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

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

(5) The image carrier has a surface layer made of silicon amorphous (1) or (2).
An image forming apparatus according to claim 1.

(6) The image carrier has a resistance of 10 ⁹ to 10 on the surface.
The image forming apparatus according to (1) or (2), further comprising a layer made of a material of ¹⁴ Ω · cm.

(7) The image forming apparatus according to any one of (1) to (6), wherein the charging member is made of conductive magnetic particles.

(8) The image forming apparatus according to any one of (1) to (6), wherein the charging member is a conductive fiber.

(9) Any one of (1) to (9), wherein the developing means is a contact developing system for developing a latent image by bringing a developer into contact with the image carrier. An image forming apparatus according to claim 1.

(10) The developer contained in the developing means is
The image forming apparatus according to (9), wherein the developer is a developer including toner particles and magnetic particles.

<Effect> Even if toner adheres to and mixes with the contact charging member, the potential contrast between the DC bias component applied to the charging member and the surface potential of the image bearing member is increased, so that the toner adheres to and mixes with the charging member.
It can be discharged entrained toner from the charging member side to the image bearing member side.

According to the present invention, the potential contrast is increased when necessary during non-image formation, thereby discharging the charging member to purify the charging member. The present invention utilizes transfer charging as a means for increasing the potential contrast. That is, when the non-image formation is necessary, the above-described potential contrast is increased by transferring and charging the image carrier . This is because the transfer potential is directly transferred to the image carrier immediately before charging, so that the surface potential of the image carrier before charging is charged to the opposite side of the charging polarity, so that the charging ability is reduced. The toner attached to and mixed with the charging member is discharged to the charged body side and reaches the developing unit,
It is collected by the developing means.

[0027] Thus, the adhesion-mixed toner even toner charging member adheres to and mixed image bearing at the non-image-forming
Since the charging member is purified (toner discharge) by being discharged to the body and collected by the developing unit, the charging member is prevented from being excessively contaminated by toner adhesion and mixing even after long-term image formation, and The magnetic brush hardly reduces the magnetic particles, so that a good image can be stably obtained over a long period of time.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 4) (1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this embodiment is a printer or a copying machine using a transfer type electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier (charged member), which has a predetermined peripheral speed (process speed) in a clockwise direction A shown by an arrow. Is driven to rotate.

During the rotation of the photosensitive drum 1, the peripheral surface of the photosensitive drum 1 is exposed to a uniform primary charging process of a predetermined polarity and potential by a charging unit 2 and then to image exposure L by an image exposure unit (not shown). An electrostatic latent image corresponding to the image information is formed.

The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed and visualized as a toner image by the developing means 6, and the toner image is transferred at a nip portion between the photosensitive drum 1 and a transfer belt device 7 as a transfer means. The recording medium P is sequentially transferred onto a transfer material P as a recording medium conveyed at an appropriate timing in synchronization with the rotation of the photosensitive drum 1 from a sheet feeding / conveying unit (not shown).

The transfer material P that has passed through the transfer section is separated from the surface of the rotary photosensitive drum 1 and introduced into fixing means (not shown), where the toner image is subjected to a fixing process and discharged as an image formed product (print, copy). Or in the double-sided image forming mode or the multiple image forming mode, the sheet is conveyed to the re-conveying section to the transfer section.

The residual toner (transfer residual toner) is removed by the cleaning means 9 from the surface of the photosensitive drum 1 after the transfer of the toner image to the transfer material, and is repeatedly used for image formation. Reference numeral 30 denotes a pre-exposure device.

A) Photosensitive Drum 1 In this embodiment, a photosensitive drum 1 as an image carrier has a conductive drum base 1a made of aluminum and the following first surface on its peripheral surface.
An OPC photoreceptor (OCL photoreceptor) having a diameter of 30 mm and a length of 300 mm, which is composed of a photoreceptor layer 1 b formed by sequentially forming the fifth to fifth layers, and is rotated at a process speed of 100 mm / sec. .

First layer: a subbing layer having a thickness of 20 provided for smoothing out defects and the like of the aluminum substrate 1a.
μm conductive layer.

A second layer, which is a positive charge injection preventing layer, which serves to prevent positive charges injected from the aluminum substrate 1a from canceling out negative charges charged on the surface of the photoreceptor;
10 with Amilan resin and methoxymethylated nylon
^This is a medium resistance layer having a thickness of 1 μm and a resistance adjusted to about ⁶ Ω · cm.

Third layer: a charge generation layer, which generates positive and negative charge pairs by exposure to light in a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin.

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

Fifth layer: a charge injection layer, which is a coating layer of a material in which ultrafine SnO ₂ particles are dispersed as conductive fine particles in a binder of an insulating resin. Specifically, SnO ₂ having a particle diameter of 0.03 μm is obtained by doping antimony, which is a light-transmitting conductive filler, into an insulating resin to reduce the resistance (make it conductive).
This is a coating layer of a material in which particles are dispersed in a resin by 70% by weight. The coating liquid prepared in this way is dipped coating method, spray coating method, roll coating coating method,
Approximately 3μm in thickness using an appropriate coating method such as beam coating
To form a charge injection layer.

Alternatively, a photosensitive member having an amorphous silicon surface layer (amorphous silicon drum, aS
i-drum) is similarly used.

The photosensitive member as the member to be charged has a surface resistance of 10 ⁹
It may have a low resistance layer of 10 to 10 ¹⁴ Ω · cm.

B) Charging Means 2 The charging means 2 is a magnetic brush contact charging member in this embodiment, and has a fixed magnet roller 2 having a diameter of 16 mm and two poles each of S and N (each having a magnetic flux density of about 1000 gauss).
a, a non-magnetic SUS sleeve 2b rotatably fitted on the magnet roller, and a magnetic brush layer 2c of magnetic particles adhered and held on the outer peripheral surface of the sleeve by the magnetic force of the magnet roller 2a. Was used.

The magnetic particles constituting the magnetic brush layer 2c have an average particle diameter of 10 to 100 μm and a saturation magnetization of 20 μm.
２５０250 emu / cm ³ , resistance 1 × 10 ² -1 × 10
It is preferably ¹⁰ Ω · cm. Considering that there is an insulation defect such as a pinhole in the photosensitive drum 1, it is 1 ×
It is preferable to use one of 10 ⁶ Ω · cm or more.

The resistance value of the magnetic particles has a bottom area of 228 mm.
After placing 2g of the magnetic particles in the ^second metal cell, 6.6kg /
The weight was measured in cm ² and a voltage of 100 V was applied for measurement.

In order to improve the charging performance, it is better to use one having as small a resistance as possible. In this embodiment, the average particle diameter is 25 μm, the saturation magnetization is 200 emu / cm ³ , and the resistance is 5 μm.
A magnetic brush layer 2c was formed by magnetically attaching 40 g of the material having a density of 10 ⁶ Ω · cm to the outer peripheral surface of the sleeve 2b.

The structure of the magnetic particles is as follows. A magnet is dispersed as a magnetic material in a resin to make the resin conductive, and carbon black is dispersed to adjust the resistance. There are used those which have been subjected to a reduction treatment to adjust the resistance or those obtained by coating the surface of a single magnetite such as ferrite with a resin and adjusting the resistance.

The magnetic brush contact charging member 2 is provided with the magnetic brush layer 2c in contact with the surface of the photosensitive drum 1. The width of the contact nip n (charging nip) between the magnetic brush layer 2c and the photosensitive drum 1 was 6 mm.

Then, a predetermined charging bias Vdc is applied to the sleeve 2b from the charging bias applying power source S1, and the sleeve 2b is brought into a contact nip portion n with the photosensitive drum 1 in a counter direction (reverse direction) to the rotation direction of the photosensitive drum 1. By rotating the photosensitive drum 1 in the clockwise direction B at a peripheral speed of 150 mm / sec, the surface of the rotating photosensitive drum 1 is rubbed by the magnetic brush layer 2c to which the charging bias is applied, and the photosensitive layer of the photosensitive drum 1 is rotated. The surface of 1b is uniformly charged to a desired potential by an injection charging method.

Vdc = -7 is applied to the sleeve 2b of the charging member 2.
00V DC constant voltage is applied, and the photosensitive drum surface potential V
Vs = −690 V was obtained as s. That is, the potential contrast ΔV at this time is ΔV = | Vdc−Vs
| = 10V.

C) Image Exposure Means The image exposure means may be a laser beam scanning exposure system, a slit exposure system for original image light, or the like. In this example, an image exposure means of a laser beam scanning exposure system is used. Photosensitive drum 1
Is subjected to the laser beam scanning exposure L, the surface potential of the exposed portion of the photosensitive drum surface is attenuated, and an electrostatic latent image is formed.

D) Developing Means 6 As the developing means 6 for the electrostatic latent image on the image carrier 1, non-magnetic toner is generally coated on a sleeve with a blade or the like, and magnetic toner is coated by magnetic force. One-component non-contact developing method for developing the toner in a non-contact state with the image carrier, and developing the toner with the toner coated as described above in contact with the image carrier. A contact developing method, a two-component contact developing method in which a mixture of toner particles and a magnetic carrier is used as a developer and conveyed by magnetic force to develop the image carrier in a contact state, and the two-component developing method And a two-component non-contact development method in which the developer is developed in a non-contact state. The developing means 6 may be any of these. The two-component contact developing method is often used from the viewpoint of high image quality and high stability.

In this embodiment, a two-component magnetic brush developing device is used. 11 is a developing sleeve, 12 is a magnet roller fixedly arranged in the developing sleeve 11, and 13.1
4 is a stirring screw, 15 is a developing sleeve,
A regulating blade arranged to form a thin layer on the surface, 1
6 is a developing container, and 17 is a toner supply hopper. At least at the time of development, the developing sleeve 11 is arranged so that the area closest to the photosensitive drum 1 is about 500 μm, and is set so that the developer T can be developed while being in contact with the photosensitive drum 1. I have.

In the two-component developer T used in this example, the toner particles were prepared by externally adding 1% by weight of titanium oxide having an average particle diameter of 20 nm to a negatively charged toner having an average particle diameter of 6 μm manufactured by a pulverizing method. The carrier used was a magnetic carrier having a saturation magnetization of 205 emu / cm ^{3 and} an average particle diameter of 35 μm. A mixture of the toner and the carrier at a weight ratio of 6:94 was used as the developer T.

The developing sleeve 11 is driven to rotate at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow. The developer T pumped up by the N ₂ pole of the magnet roller 12 with the rotation of the developing sleeve 11 is regulated vertically disposed with respect to the developing sleeve 11 in the process of being transported from the S ₂ pole to the N ₁ pole. The thin layer is formed on the developing sleeve 11 by being regulated by the blade 15. Here, a thin developer layer Ta is formed.
However, when they are transported to the developing main pole S ₁ , ears are formed by magnetic force. The electrostatic latent image is developed by the spike-shaped developer, and the developer on the developing sleeve 11 is returned to the developing container 16 by the repulsive magnetic field of the N ₃ pole and the N ₂ pole.

A DC voltage and an AC voltage are applied to the developing sleeve 11 from a developing bias applying power source S2. In this example, the DC voltage is -500 V and the AC voltage is Vpp.
= 1500 V, Vf = 2000 Hz.
In general, in the two-component developing method, when an AC voltage is applied, the developing efficiency is increased, and the quality of an image is high. On the contrary, there is a risk that fogging is likely to occur. Because of this,
By providing a potential difference between the DC voltage applied to the developing device 6 and the surface potential of the photosensitive drum 1, fog can be prevented.

E) Transfer Device 7 The transfer device 7 in this embodiment is a belt transfer device, and transfers the endless transfer belt 71 to the driving roller 72 and the driven roller 7.
The photosensitive drum 1 is driven to rotate in a counterclockwise direction indicated by an arrow at substantially the same peripheral speed as the rotational speed of the photosensitive drum 1. A transfer charging blade 74 is provided inside the endless transfer belt 71, and the transfer nip 70 is formed by bringing a substantially intermediate portion of the belt portion on the ascending side of the belt 71 into contact with the surface of the photosensitive drum 1 with the blade.

The transfer material P is conveyed to the transfer nip 70 on the upper surface of the ascending belt portion of the belt 71. When the leading end of the transfer material P enters the transfer nip 70, the transfer bias applying power supply S
3 is supplied with a predetermined transfer bias, so that the transfer material P
The toner image on the photosensitive drum 1 is sequentially transferred onto the upper surface of the transfer material P by being charged from the back side of the toner with the polarity opposite to that of the toner.

In this embodiment, the belt 71 has a film thickness of 7
A polyimide resin having a thickness of 5 μm was used. The material of the belt 71 is not limited to a polyimide resin, but may be a polycarbonate resin, a polyethylene terephthalate resin, a polyvinylidene fluoride resin, a polyethylene naphthalate resin, a polyetheretherketone resin, a polyethersulfone resin, a polyurethane resin, or the like. Plastic, fluorine-based, or silicon-based rubber can be suitably used. The thickness is not limited to 75 μm, and a thickness of about 25 to 2000 μm, preferably 50 to 150 μm can be suitably used.

The transfer charging blade 74 has a resistance of 1 × 10 ⁵ to 1 × 10 ⁷ Ω, a thickness of 2 mm, and a length of 3 mm.
The thing of 06 mm was used. The transfer was performed by applying a bias of +15 μmA to the transfer charging blade 74 under constant current control.

The toner image thus formed on the photosensitive drum 1 is electrostatically transferred onto the transfer material P by the transfer charging blade 74.

F) Cleaning Means 9 This embodiment is a blade-type cleaning device (cleaner), and the surface of the photosensitive drum 1 is wiped off by the cleaning blade 9a contacting the surface of the photosensitive drum 1, and the rotation after the transfer of the toner image is performed. Residual toner is removed from the surface of the photosensitive drum 1.

The image forming apparatus of this embodiment is a process cartridge in which the photosensitive drum 1, the charging member 2, the developing device 6, the cleaning device 9, and the lamp of the pre-charging device 30 are collectively attached to and detached from the image forming apparatus main body. There is a PC. The combination of the process devices used as the process cartridge is not limited to the above, and is appropriate. An image forming apparatus other than the process cartridge type may be used.

(2) Control of Transfer Charging A) The transfer bias is applied to the transfer charging blade 74 of the transfer device 7 only during the period when the transfer material P passes through the transfer nip 70 during image formation, and the non-image At the time of formation, image formation was performed without applying a bias to the transfer charging blade 74. Vdc = −700 for the charging member 2
A DC constant voltage of V was applied to perform primary charging of the photosensitive drum 1. At this time, as the photosensitive drum surface potential Vs, Vs = −
690 V was obtained. That is, the potential contrast ΔV at the time of image formation in this case is ΔV = | Vdc−Vs | = | (−700) − (− 69)
0) | = 10V.

In this system, a streak began to appear on the output image at about the time when 50,000 sheets of image were formed by A4 horizontal feed.

This is because the untransferred toner on the photosensitive drum in the portion having a relatively high image density is gradually removed from the cleaning device 9.
The charging member 2 is excessively contaminated with the toner by mixing into the magnetic brush layer 2c of the charging member 2, and the resistance of the magnetic brush layer portion where the toner is excessively mixed increases, thereby causing a partial decrease in the photosensitive drum potential Vs. This is because the toner coating on the developing sleeve 6b is disturbed due to the magnetic particles generated and dislodged from the charging member 2 entering the developing device 6.

When the image formation of 70,000 sheets has passed, an image having an image quality out of an allowable range was generated, and it was necessary to clean or replace the charging member and the developing device 6.

At this time, the magnetic brush layer 2c of the charging member 2
Was reduced by about 5 grams from the initial 40 grams.

B) Then, at the time of non-image formation, in this example, as shown in the timing chart of FIG. 2, the transfer charging blade 74 only has +30 μA
, And the image forming apparatus was operated to form an image.

The photosensitive drum potential Vs at the time of image formation is Vs =
−690 V, but Vs = −64 during post-rotation
It became 0V. That is, the potential contrast ΔV = 60V.

This is because the transfer potential is directly transferred to the photosensitive member immediately before charging, and the surface potential of the photosensitive drum before charging is charged to the opposite side (+) to the charging polarity (-in this example). It is because it falls. As shown in FIG. 3, ΔV increases by increasing the transfer current.

According to the study of the present inventors, in the system of this example, the discharge of the toner from the charging member 2 to the photosensitive drum 1 starts remarkably when the potential contrast ΔV exceeds about 50 V. FIG. 4 shows the relationship between the potential contrast ΔV and the toner discharge amount. The toner discharged from the charging member 2 to the photosensitive drum 1 is collected by the developing device 6.

Therefore, even if the toner that has passed through the cleaning device 9 is mixed into the charging member 2, the mixed toner is discharged to the photosensitive drum 1 during non-image formation (in this example, after every rotation), and the developing device 6 Because it is collected, the charging member is prevented from becoming excessively contaminated with toner, and even after long-term image formation, there is almost no charge unevenness, and the magnetic brush has almost no decrease in magnetic particles, and is stable for a long time A good image can be obtained.

Actually, in this embodiment, no streak is generated on the output image even when the image formation of 50,000 sheets is performed in the A4 landscape mode, and a good image can be obtained even after 100,000 sheets. Was. At the time of 100,000 sheets, the amount of the magnetic particles constituting the magnetic brush layer 2c was reduced by only 0.3 g from the initial 40 g.

In this example, the reason why the potential contrast ΔV is not set to 40 V or more during image formation is that the larger the ΔV is,
This is because charging uniformity is deteriorated. More specifically, in the system of the present example, in a halftone image such as a halftone, a minute charge unevenness (density unevenness) due to uneven charging may occur from a potential contrast ΔV exceeding 40 to 50 V. Was. Therefore, it was necessary to reduce the potential contrast ΔV during image formation.

However, the magnitude of the potential contrast ΔV at which density unevenness starts to occur is not limited to the value of this embodiment, but includes the process speed, the type of the photosensitive member, the resistance of the magnetic particles, the width of the contact nip n, and the like. And does not apply to all systems.

Embodiment 2 (FIG. 5) In this embodiment, as shown in FIG. 5, an image forming apparatus of a cleanerless system in which a cleaning device for cleaning a surface of a photosensitive drum 1 after a toner image is transferred onto a transfer material P is omitted. It is. FIG.
5 is different from the device of FIG. 5 only in that the device of FIG. 5 does not have the cleaning device (9), and the other device configuration is the same as that of the device of FIG.

In the image forming apparatus of this cleanerless system, as in B) of the first embodiment, as shown in the timing chart of FIG. The image forming apparatus was operated by controlling the application of a voltage to form an image.

In this case, a slight streak started to appear on the output image at a time when the A4 horizontal feed exceeded 70,000 sheets of image formation.

Thereafter, an image outside the allowable range was produced at 90,000 sheets. At this time, the magnetic brush layer 2 of the charging member 2
The amount of magnetic particles forming c was reduced by about 5 grams from the initial 40 grams.

This is because the transfer residual toner always mixes into the charging member 2 because there is no cleaning device.
This is because the amount of toner discharged from the charging member 2 toward the photosensitive drum 1 during the post-rotation cannot keep up with the system.

Accordingly, in this embodiment, the current value applied to the transfer charging blade 74 at the time of post-rotation (non-image formation) at the end of image formation is controlled to +40 μA, and once every ten images are formed. The image was formed by applying a current of +10 μA to the transfer charging blade 74 also during pre-rotation (non-image formation).

At this time, the bias Vd applied to the charging member 2
When c is Vdc = −720 V, the photosensitive drum potential Vs during image formation is Vs = −690 V, the potential contrast ΔV is ΔV = 30 V, and the photosensitive drum potential Vs during post-rotation is Vs = −640 V, and the potential contrast ΔV. Is Δ
V = 80V.

When an image was formed in this way,
A good image without streaks could be obtained even after 100,000 sheets. At the time of 100,000 sheets, the amount of the magnetic particles constituting the magnetic brush layer 2c was reduced by only 0.3 g from the initial 40 g.

This is not remarkable at the time of image formation, but discharges the toner mixed into the charging member 2 little by little, discharges more toner at the time of post-rotation, and as a whole, from the charging member 2 to the photosensitive drum 1 side. This is because the toner discharge can catch up.

<Embodiment 3> (FIG. 6) In this embodiment, as a contact charging member of the photosensitive drum 1, a brush 2A made of conductive fiber as shown in FIG. 6 (hereinafter referred to as a fur brush)
Was used.

The fur brush 2A of this example has an outer diameter of 10 m.
m on the outer peripheral surface of the cored roller 2d, the bristle length is 3 mm, the flocking density is 100,000 / inch ² , and the resistance value is 1 × 10 ⁶ Ω.
Brushed 2e of conductive fiber of 2e, total outer diameter 16mm
The is also the in.

The fur brush 2A is provided with the conductive fiber brush portion 2e in contact with the surface of the photosensitive drum 1. The width of the contact nip portion n between the conductive fiber brush portion 2e and the photosensitive drum 1 was 7 mm. The fur brush 2A is configured to rotate in the counter direction with respect to the photosensitive drum 1 at a rotational speed of 200 mm / sec with respect to the rotational speed of the photosensitive drum 1 of 100 mm / sec.

Then, a predetermined charging bias Vdc is applied to the fur brush 2A from the charging bias applying power source S1 to rotate the fur brush 2A, whereby the surface of the rotating photosensitive drum 1 is slid by the conductive fiber brush portion 2e to which the charging voltage is applied. As a result, the surface of the photosensitive layer 1b of the photosensitive drum 1 is uniformly charged to a desired potential by an injection charging method.

In the fur brush 2A, unlike the case of the magnetic brush contact charging member 2, there is no adverse effect on the developing device 6 due to the lack of the magnetic particles constituting the magnetic brush layer 2c. The incorporation of toner into the brush portion 2e has caused an abnormality in an output image.

Also in the case where the fur brush 2A is used as the contact charging member, a transfer current is applied to the transfer charging blade 74 at an appropriate timing during non-image formation, as in the case of Embodiments 1 and 2. When the toner mixed in the fur brush 2A was discharged so as to generate the potential contrast ΔV, a good image could be obtained even after the formation of 100,000 sheets. Further, in the fur brush 2A, since the magnetic particles are not missing as in the magnetic brush, the life of the charging member can be extended.

<Others> 1) The image forming apparatus of the first embodiment is a cleaning device 9
In the second embodiment, the cleaner-less system is used. However, the present invention is not limited to this. Any embodiment can be applied to all systems by changing the intensity and application timing of the transfer current. It is. It is of course possible to use two or more embodiments at the same time.

2) Purification of charging member 2 (toner discharge)
The transfer current is applied to the transfer charging blade 74 during non-image formation (pre-multi-rotation, pre-rotation, paper interval, post-rotation, etc.)
May be performed at any timing.

[0093] 3) transfer means 7 is not limited to the belt transfer device may be a transfer roller or a transfer corona charger or the like.

4) In each embodiment, the charging members 2
Although the bias applied to A is only the DC voltage, the same effect can be obtained by superimposing an appropriate AC voltage on the DC voltage.

5) The magnetic brush contact charging member is not a sleeve rotating type, but a magnet rotating type in which conductive magnetic particles are magnetically attracted and held as a magnetic brush layer directly on a rotating magnet roller or via a conductive coating layer. It can also be.

6) The present invention is effective not only for charge injection charging but also for contact charging using a magnetic brush or fur brush as a contact charging member and charging by a discharge phenomenon.

7) The contact charging members 2 and 2A may be rotated in the same direction as the image carrier at the contact nip n with the image carrier 1, or may be fixed stop members.

8) The image carrier as the member to be charged is not limited to the electrophotographic photosensitive member, but may be a dielectric or the like in electrostatic recording.

[0099]

As described above, according to the present invention, an image carrier that carries an electrostatic latent image and can be charged by injecting a charge, and is in contact with the image carrier to form an image carrier Charging means for injecting and charging the toner, developing means for developing the electrostatic latent image on the image carrier with toner having the same polarity as the charging polarity of the image carrier, and recovering the toner on the image carrier; an image forming apparatus having a transfer unit that transfers the toner image on the transfer material, and during non-image formation, an image bearing than during image formation by charging the area which received the transfer charging by the transfer means in the charging member Large potential contrast between body and charged potential
So that the potential of the image carrier is lower than that during image formation.
By charging the charging member, the potential contrast between the DC bias component applied to the charging member and the surface potential of the image carrier is made larger than that at the time of image formation, and the toner adhering to and mixed with the charging member is discharged. It is possible to eliminate the occurrence of uneven charging and the occurrence of an abnormal image due to excessive toner adhesion and mixing with the member. When the charging member is a magnetic brush, contact failure due to a decrease in magnetic particles constituting the magnetic brush over time occurs. It is possible to eliminate problems such as uneven charging due to stability and occurrence of abnormal images such as streaks due to mixing of magnetic particles detached from the magnetic brush into the developing means. Image formation can be maintained.

[Brief description of the drawings]

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

FIG. 2 is a control timing chart.

FIG. 3 is a correlation diagram between a transfer current and a potential contrast.

FIG. 4 is a correlation diagram between a potential contrast and a toner discharge amount.

FIG. 5 is a schematic configuration model diagram of an image forming apparatus according to a second embodiment.

FIG. 6 is a schematic diagram illustrating a configuration of a main part (a fur brush portion) of an image forming apparatus according to a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) as a charged body 2.2A Magnetic brush or fur brush as a contact charging member 6 Developing device 7 Transfer device 9 Cleaning device PC Process cartridge P Transfer material

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-61270 (JP, A) JP-A-7-5748 (JP, A) JP-A-62-175780 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) G03G 15/02 G03G 15/16 G03G 15/00 303

Claims (10)

(57) [Claims] 1. An image forming apparatus , comprising: an electrostatic latent image carrying an electric charge;
An image carrier that can be charged by the above, a charging member that comes into contact with the image carrier and injects and charges the image carrier, and an electrostatic latent image on the image carrier that has the same polarity as the charging polarity of the image carrier. An image forming apparatus comprising: developing means for developing with toner and collecting toner on the image carrier; and transfer means for transferring the toner image on the image carrier to a transfer material. Charges the area charged with the transfer by the charging member with an image, so that the image is carried more than during image formation.
Image so that the potential contrast between the body and the charged potential is large
An image forming apparatus, wherein a charge of a potential lower than that at the time of image formation is applied to a carrier . 2. The image forming apparatus according to claim 1, wherein the transfer charging performed during non-image formation is performed under a condition different from that during image formation. 3. The image forming apparatus according to claim 1, wherein the image carrier has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles. 4. The image forming apparatus according to claim 3, wherein the conductive fine particles are SnO ₂ . 5. The image carrier according to claim 1, wherein the image carrier has a surface layer made of amorphous silicon.
An image forming apparatus according to claim 1. 6. An image carrier having a surface having a resistance of 10 ⁹ to 10 ¹⁴ Ω.
The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus has a layer of (cm). 7. The image forming apparatus according to claim 1, wherein the charging member is a conductive magnetic particle. 8. The image forming apparatus according to claim 1, wherein the charging member is a conductive fiber. 9. The image forming apparatus according to claim 1, wherein said developing means is a contact developing system for developing a latent image by bringing a developer into contact with an image carrier. The image forming apparatus as described in the above. 10. The image forming apparatus according to claim 9, wherein the developer contained in the developing unit is a developer including toner particles and magnetic particles.