JP2000047504A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the recovering ability of a contact electrifying device and to prevent image defect even when transfer efficiency is different according to the kind or the thickness of recording material and toner left after transfer is increased by making the output applied transfer electric field higher when the recording material does not exist at a transfer nip part than that when a toner image is transferred. SOLUTION: Transfer bias fed from a transfer bias applying power source S3 to a transfer electrifying blade 74 is set to a higher value than at ordinary image forming time and applied to the part of a photoreceptor 1 where image forming has been finished or the part of the photoreceptor 1 where image forming is not performed between the recording material carried in the midst of consecutive paper passing with discharging sequence. By applying the transfer bias in such a way, most of toner on the photoreceptor 1 which is not completely recovered by a developing device 4 at the time of discharging sequence is transferred to a transfer belt 71 where the recording material does not exist. The transferred toner passes through a transfer belt discharger 91 further and is eliminated by a transfer belt cleaner 92.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copier, a facsimile, a printer, etc. of a contact charging type and a cleanerless system.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image carrier such as an electrophotographic photosensitive member of a rotating drum type or an electrostatic recording dielectric (hereinafter referred to as a photosensitive member). As a means for performing a charging process (including a static elimination process), a corona charger has been frequently used.

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

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 technique, a charging member to which a voltage (charging electric field) is applied is brought into contact with a photosensitive member to charge the surface of the photosensitive member to a predetermined polarity and potential.

A contact charging device using a magnetic brush as a contact 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 is stopped or rotated on the surface of the photoreceptor. The photosensitive member is started to be charged by applying a voltage thereto while contacting the photosensitive member.

A brush made of conductive fibers (fur brush) or a conductive rubber roll made of conductive rubber in a roll shape can also be used as the contact charging member.

In contact charging, a charge injection layer is provided on a photoreceptor, and a charging member to which a voltage is applied is brought into contact with the photoreceptor, thereby injecting charge into the charge injection layer and causing the surface of the photoreceptor to have a predetermined surface. In the injection charging method of charging to a polarity and a potential, a surface potential of the photoconductor substantially equal to the applied DC voltage (DC bias) can be obtained regardless of the presence or absence of the AC voltage (alternating bias) superimposed on the charging member. For this reason,
Since a discharge phenomenon in which charging of the photoreceptor is performed using a corona charger is not used, ozone is not generated and charging with low power consumption can be performed.

Further, in recent years, a so-called "cleanerless system" image forming apparatus has been put into practical use for the purpose of reducing the size and simplification of the image forming apparatus, or not generating waste toner from the viewpoint of environmental protection.

In this method, a dedicated cleaning device (cleaner) for removing transfer residual toner from the surface of the photoreceptor after transferring the toner image to the recording material is omitted, and the transfer residual toner on the photoreceptor is once collected by a contact charging device. After that, when the image is not formed, the toner is discharged from the contact charging device and collected by the developing device (simultaneous cleaning with development).

In the simultaneous cleaning with development, the residual toner on the photoreceptor is charged at the time of subsequent development, that is, the photoreceptor is successively charged to form a latent image. This is a method of recovering by a fog removal potential difference (Vback) which is a potential difference between the applied DC voltage and the surface potential of the photoconductor. Since the residual toner on the photoreceptor is collected by the developing device and reused in the subsequent steps, the waste toner is eliminated, and the trouble of maintenance can be reduced. In addition, the cleaner-less system has a great advantage in terms of space, and can greatly reduce the size of the image forming apparatus.

By employing such a cleanerless system or the above-described contact charging method, it is possible to obtain an image forming apparatus which is compact, simple, generates no ozone, consumes low power, and generates no waste toner.

[0013]

However, in a simple and compact image forming apparatus of a contact charging type and a cleanerless system, the transfer ratio is high due to a high image ratio or a difference in transfer efficiency due to the type and thickness of the recording material. The remaining toner may increase, and if such a state continues for a long time, the collecting ability of the contact charging device and the collecting ability of the developing device may not be able to keep up. Then, the residual toner that cannot be completely collected on the photoconductor appears at the time of the next image formation, resulting in an image defect.

Therefore, the present invention relates to an image forming apparatus of a contact charging type / cleanerless system, in which the image ratio is high, or the transfer efficiency differs depending on the type and thickness of the recording material, and even if the transfer residual toner increases. It is still another object of the present invention to provide an image forming apparatus that maintains the collecting ability of the contact charging device and prevents image defects.

[0015]

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

(1) An image carrier for carrying an image, charging means for charging the image carrier, image information writing means for forming an electrostatic latent image on a charged surface of the image carrier, and Developing means for developing the latent image as a toner image, and transfer means for transferring the toner image on the image carrier to a recording material, wherein the developing means uses the transfer means to transfer the toner image on the image carrier. Is a cleanerless system image forming apparatus that also serves as an image carrier cleaning unit that removes residual toner on the image carrier after the image carrier is transferred to a recording material, and the image carrier is repeatedly used for image formation. The charging means contacts the image carrier,
A contact charging unit having a charging member to which a charging electric field is applied, wherein the transfer unit is applied with a transfer electric field, forms an image carrier and a transfer nip portion, and forms the recording material from the image carrier at the transfer nip portion. A transfer member for transferring the toner image to the
An image forming apparatus, wherein when the recording material is not in the transfer nip portion, the output of the transfer electric field applied to the transfer unit is made higher than that during toner image transfer.

(2) The image forming apparatus according to (1), wherein the transfer member of the transfer means carries a recording material, and conveys the recording material to the transfer nip portion so as to contact the toner image on the image carrier. apparatus.

(3) The image forming apparatus according to (1) or (2), further comprising a transfer member cleaning unit for removing toner attached to the transfer member of the transfer unit.

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

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

(6) The image bearing member has a volume resistivity of 10 ⁹
The image forming apparatus according to any one of (1) to (3), further including a surface layer made of a material having a thickness of 10 to 10 ¹⁴ Ωcm.

(7) The image forming apparatus according to any one of (1) to (3), wherein the image carrier has a surface layer made of amorphous silicon.

(8) The image forming apparatus according to any one of (1) to (7), wherein the charging member has magnetic particles, and the magnetic particles are in contact with the image carrier.

(9) The charging member according to any one of (1) to (7), wherein the charging member has conductive fibers, and the conductive fibers are in contact with the image carrier. Image forming device.

(10) The developing means is a contact developing system in which a developer is brought into contact with the image carrier to develop an electrostatic latent image as a toner image. The image forming apparatus according to any one of the above.

(11) The image forming apparatus according to (10), wherein the developer has toner particles and magnetic particles.

<Operation> The transfer residual toner on the surface of the image carrier after the transfer of the toner image from the image carrier side to the recording material surface in the transfer nip portion is transferred from the transfer nip portion side to the image carrier as the image carrier continues to move. And is taken into the contact charging means (temporary collection of toner by the contact charging means).

The transfer residual toner taken into the contact charging means is converted into a normally charged toner by rubbing with the contact charging means even if the charging polarity is reversed.

The transfer residual toner which has been taken into the contact charging means and sufficiently converted into a normally charged toner is gradually discharged from the contact charging means onto the image carrier.

The normally charged toner discharged from the contact charging means onto the image carrier reaches the developing area as the image carrier moves and is collected by the developing means.

In this case, even if the toner collecting ability of the developing means cannot keep up and the toner to be collected by the developing means cannot be completely collected by the developing means and is carried to the transfer nip portion, the transfer electric field applied to the transferring means can be reduced. By making the output higher than that at the time of transfer of the toner image, most of the toner on the image carrier carried to the transfer nip portion without being sufficiently collected by the developing means is transferred to the transfer means where there is no recording material. And removed from the image carrier. Most of the toner transferred onto the transfer unit is removed from the transfer unit by the cleaning unit.

On the other hand, since a higher transfer bias is applied to the transfer nip than during normal image formation, the toner that cannot be completely recovered by the developing means and reaches the transfer nip is deposited on the transfer means. Even after passing through the transfer nip portion without being transferred, the toner remaining on the image carrier is in a charged state having a polarity opposite to the normal charging polarity. Collected.

Therefore, even if a large amount of toner is mixed into the contact charging means due to continuous images having a high image ratio and cannot be collected by the developing means in the discharge sequence, the next image formation is not performed. It is possible to prevent a problem such as an image defect due to extra toner on the image carrier, and it is possible to form a good image over a long period of time.

[0034]

FIG. 1 is a schematic structural view of an example of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process, and is a cleaner-less system device using a magnetic brush type contact charging device as a charging unit of an image carrier (photoconductor).

A is a laser beam printer, and B is an image reading device (image scanner) mounted on the printer.

(1) Image Reading Device B In the image reading device B, reference numeral 10 denotes a fixed platen glass, which is placed on the upper surface of the platen glass with the surface on which the document G is to be copied facing downward, and Is set with a document pressing plate (not shown).

Reference numeral 9 denotes an image reading unit provided with a document irradiation lamp 9a, a short focus lens array 9b, a CCD sensor 9c, and the like. When a copy button (not shown) is pressed, the unit 9 is driven forward from the home position on the left side of the original table glass 10 to the right side along the lower surface of the original table glass 10 by pressing a copy button. When it reaches the end point, it is driven backward and returned to the initial home position.

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

The CCD sensor 9c includes a light receiving section, a transfer section, and an output section. The light signal is converted into a charge signal in the CCD light receiving unit, and the transfer unit sequentially transfers the light signal to the output unit in synchronization with the clock pulse. The output unit converts the charge signal into a voltage signal, amplifies the signal, reduces the impedance, and outputs the voltage signal. The analog signal thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to the laser beam printer A.

That is, the image information of the original G is photoelectrically read by the image reading device B as a time-series electric digital pixel signal (image signal).

(2) Laser Beam Printer A In the laser beam printer A, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image carrier. This photoconductor 1
Is a predetermined peripheral speed (process speed) about the center support shaft
In the case of this example, the charging device 3 receives a uniform charging process of negative polarity in the case of the present embodiment. The charging device 3 in this example is a magnetic brush as a contact charging unit.

The image signal output from the exposure device (laser scanning device, laser scanner) 100 and transmitted from the image reading device B to the laser beam printer A on the uniformly charged surface of the photosensitive member 1 corresponds to the image signal. The scanning exposure L is performed by the modulated laser light, so that the original G that has been photoelectrically read by the image reading device B
The electrostatic latent images corresponding to the image information are sequentially formed.

The electrostatic latent image formed on the photoreceptor 1 is sequentially developed as a toner image by the developing device 4 and is reversely developed in this embodiment.

On the other hand, a recording material (transfer material) P such as paper stored in a paper feed cassette 41 is fed one by one by a paper feed roller 42 and fed, and is exposed by a registration roller 43 at a predetermined timing. The paper is fed to a transfer nip (transfer site) 70 between the body 1 and a transfer belt 71 of a transfer belt device 7 as a transfer unit, and the toner image on the photoconductor 1 is transferred to the recording material P.

The recording material P to which the toner image has been transferred through the transfer nip 70 is sequentially separated from the surface of the photoreceptor 1 and is conveyed to the fixing device 6, where the toner image is thermally fixed to be copied or printed. Is output.

After the transfer of the toner image onto the recording material P, the surface of the rotating photosensitive member 1 is repeatedly subjected to image formation.

(3) Photoreceptor 1 As the photoreceptor 1 as an image carrier, a commonly used organic photoreceptor or the like can be used.
If an organic photoreceptor having a surface layer having a material having a resistance of 10 ⁹ to 10 ¹⁴ Ω · cm or an amorphous silicon (amorphous silicon) photoreceptor is used, charge injection charging can be realized, and ozone It is effective in preventing occurrence and reducing power consumption. Further, the chargeability can be improved.

In the present embodiment, the photosensitive member 1 is a negatively charged organic photosensitive member, which is formed by forming a photosensitive layer 1b on a 30 mm-diameter aluminum drum base 1a (FIG. 2). Speed (for example, 100 mm / ce
It is rotationally driven in c).

In the present embodiment, the photosensitive layer 1b is provided with the following first to fifth layers in this order from the bottom.

[0050] First layer: a subbing layer, which has a thickness of 20 μm and is provided to smooth defects and the like of the drum substrate 1a.
m of the conductive layer.

[0051] A second layer; a positive charge injection preventing layer, which serves to prevent positive charges injected from the drum substrate 1a from canceling out negative charges charged on the surface of the photoreceptor 1,
With Amilan resin and methoxymethylated nylon,
0 is the resistance layer in the ⁶ Omega · cm about the resistance adjusted thickness 1 [mu] m.

[0052] Third layer: a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates positive and negative charge pairs upon exposure.

[0053] 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 surface of the photoreceptor 1 cannot move through this layer, and only the positive charges generated in the third layer (charge generation layer) can be transported to the surface of the photoreceptor 1.

[0054] Fifth layer (outermost surface); a charge injection layer, and Sn as conductive fine particles in a binder of an insulating resin.
This is a coating layer of a material in which O ₂ ultrafine particles are dispersed. Specifically, an insulating resin is doped with antimony, which is a light-transmissive conductive filler, to reduce the resistance (conductivity) to a particle size of 0.0.
This is a coating layer of a material in which 3 μm of SnO ₂ particles are dispersed in a resin by 70% by weight. The coating solution thus prepared was applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coat coating method, beam coat coating method, etc. to form a charge injection layer.

(4) Charging Device 3 (FIG. 2) The charging device 3 in this embodiment is a contact-type magnetic brush charging device (magnetic brush). The magnetic brush 3 of this example is
As shown in FIG. 2, a fixed magnet roller 3a having a diameter of 16 mm, a non-magnetic SUS sleeve 3b rotatably fitted on the magnet roller 3a, and a sleeve 3b
Is a sleeve rotating type comprising a magnetic brush layer 3c of magnetic particles (magnetic carrier) adhered and held on the outer peripheral surface by the magnetic force of a magnet roller 3a.

The magnetic particles constituting the magnetic brush layer 3c have an average particle diameter of 10 to 100 μm and a saturation magnetization of 20 to 2 μm.
50 emu / cm ³ , resistance 1 × 10 ² to 1 × 10 ¹⁰ Ω
cm is preferable, and considering that the photoconductor 1 has an insulation defect such as a pinhole, the resistance is 1 × 10
It is preferable to use one of 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 the measurement was performed by applying a voltage of 100 V.

The average particle size of the magnetic particles is represented by the maximum chord length in the horizontal direction. The measuring method is as follows: 300 or more magnetic particles are randomly selected by a microscopic method, the diameters are measured, and the arithmetic average is taken to obtain the average particle size. Diameter.

For the measurement of the magnetic properties of the magnetic particles, a DC magnetization BH characteristic automatic recording apparatus BHH-50 manufactured by Riken Denshi Co., Ltd. can be used. At this time, the diameter (inner diameter) is 6.5 m
m, magnetic particles in a cylindrical container with a height of 10 mm
The filling is performed at about g weight, and the saturation magnetization is measured from the BH curve while keeping the magnetic particles from moving in the container.

In order to improve the charging performance, it is better to use one having the smallest possible resistance. In this embodiment, the average particle diameter is 25 μm, the saturation magnetization is 200 emu / cm ³ ,
Used as the resistor 5 × 10 ⁶ Ω · cm, which 40g magnetic deposited allowed by the magnetic brush layer 3c on the outer circumferential surface of the sleeve 3b
Was formed.

The structure of the magnetic particles is as follows. A magnet is dispersed in a resin as a magnetic material to make it conductive, and a resin carrier formed by dispersing carbon black for resistance adjustment, or a surface of magnetite alone such as ferrite is oxidized. A material which has been subjected to a reduction treatment to adjust the resistance or a material obtained by coating the surface of a single magnetite such as ferrite with a resin and adjusting the resistance may be used.

The magnetic brush 3 is disposed such that the magnetic brush layer 3c is in contact with the surface of the photoreceptor 1, and the magnetic brush layer 3c
Contact nip n between c and photoconductor 1 (charging nip)
Was 6 mm in width.

Then, a predetermined charging bias is applied to the sleeve 3b from the charging bias applying power source S1, and the sleeve 3
b at the contact nip portion n with the photoconductor 1 in a clockwise direction b as indicated by an arrow which is a counter direction (reverse direction) to the rotation direction a of the photoconductor 1, for example, a rotation speed of the photoconductor of 100 mm / sec.
By rotating the photosensitive member 1 at a peripheral speed of 150 mm / sec, the surface of the photosensitive member 1 is rubbed with the magnetic brush layer 3c to which the charging bias is applied, and the surface of the photosensitive member 1b of the photosensitive member 1 has a desired potential. The primary charging process is uniformly performed by an injection charging method. At this time, by increasing the rotation speed of the sleeve 3b, the chance of contact between the transfer residual toner on the photoreceptor 1 and the magnetic brush 3 is increased, and the recoverability to the magnetic brush is also improved.

FIG. 3 shows that the magnetic brush 3 has a frequency of 1000H.
This figure shows the relationship between the amplitude of the applied bias and the charging potential in the first cycle when a rectangular alternating voltage (AC voltage) Vpp is applied at z. By increasing the amplitude, the DC ( The difference between the (DC) component and the charged potential in the first cycle becomes smaller.

More specifically, assuming that the DC component of the bias applied to the magnetic brush 3 is Vdc and the surface potential on the charged photosensitive member 1 at this time is Vs, the potential contrast ΔV = | Vdc, which is the difference between them, −Vs |
Is about 40 V or less, the uniformity of charging is improved.

Also in this case, the alternating voltage is
, The effect of taking in the transfer residual toner into the magnetic brush 3 is improved by the vibration effect due to the electric field between the photoreceptor 1 and the magnetic brush 3.

Therefore, in this embodiment, a rectangular 800 Vp at a frequency of 1000 Hz is applied to a DC voltage of -700 V.
By applying a bias on which the alternating voltage of p was superimposed to the magnetic brush 3, good charging properties could be obtained.

(5) Exposure Apparatus 100 (FIG. 4) FIG. 4 is a schematic configuration diagram of an exposure apparatus (laser scanner) 100 of a laser beam scanning exposure system.

When the surface of the photoreceptor 1 is subjected to laser scanning exposure L by the exposure apparatus 100, the solid-state laser element 102 is turned on and off at a predetermined timing by the light emission signal generator 101 based on the input image signal (ON / OFF). ). The laser light emitted from the solid-state laser element 102 is converted into a substantially parallel light beam by a collimator lens system 103, and the rotating polygon mirror 1 rotates at a high speed in the direction of arrow c.
In addition, scanning is performed in the direction of arrow d by an arrow 04, and an image is formed in the form of a spot on the surface of the photoconductor 1 by the fθ lens groups 105a, 105b, and 105c. By such laser beam scanning, an exposure distribution for one image scan is formed on the surface of the photoconductor 1 and, further, by scrolling the surface of the photoconductor 1 by a predetermined amount perpendicular to the scanning direction for each scan, An exposure distribution according to the image signal is obtained on the surface of the photoconductor 1.

That is, the solid-state laser element 102 which emits ON / OFF light corresponding to an image signal on the uniformly charged surface of the photosensitive member 1
Is scanned by the rotating polygon mirror 104 rotating at a high speed, an electrostatic latent image corresponding to the scanning exposure pattern is sequentially formed on the surface of the rotating photoconductor 1.

(6) Developing Apparatus 4 (FIG. 5) In general, the method of developing an electrostatic latent image is such that non-magnetic toner is coated on a sleeve with a blade or the like, and magnetic toner is coated by magnetic force and conveyed. A method of developing in a non-contact state with respect to the photosensitive drum (one-component non-contact development), a method of developing the toner coated as described above in contact with the photosensitive drum (one-component contact development), A method in which a mixture of toner particles and a magnetic carrier 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); The method is broadly classified into four types: a method of developing in a non-contact state (two-component non-contact development). The two-component contact developing method is often used from the viewpoints of high image quality and high stability.

The developing device 4 in this embodiment is a two-component contact developing device (two-component magnetic brush developing device), and FIG. 5 is a schematic diagram thereof. In this figure, reference numeral 11 denotes a developing sleeve which is driven to rotate in the direction of arrow e, and 12 denotes a developing sleeve.
1, a magnet roller 13 and 14 are agitating screws, 15 is a regulating blade arranged to form a thin layer of the developer T on the surface of the developing sleeve 11, 1
Reference numeral 6 denotes a developing container, and 17 denotes a replenishing toner hopper.

The developing sleeve 11 is arranged so that the area closest to the photosensitive member 1 is at least about 500 μm at least at the time of development, and the thin layer Ta of the developer T formed on the surface of the developing sleeve 11 is 1 is set so as to be able to be developed in a state of contact.

In the two-component developer T used in the present embodiment, the toner particles t have an average particle diameter of 20 n with respect to a negatively charged toner having an average particle diameter of 6 μm manufactured by a pulverization method.
A magnetic carrier having an external particle size of 1% by weight of titanium oxide and a carrier having a saturation magnetization of 205 emu / cm ^{3 and} an average particle diameter of 35 μm was used as the carrier c. Also, the toner t
And a carrier c mixed at a weight ratio of 6:94 was used as the developer T.

Here, the developing step of visualizing the electrostatic latent image on the surface of the photoconductor 1 by the two-component magnetic brush method using the developing device 4 and the circulation system of the developer T will be described. First, in the process in which the developer T pumped at the N ₃ pole with the rotation of the developing sleeve 11 is transported from the S ₂ pole to the N ₁ pole,
A thin layer Ta of the developer T is formed on the developing sleeve 11 by being regulated by a regulating blade 15 arranged perpendicularly to the developing sleeve 11. When the developer T on which the thin layer Ta is formed is conveyed to the main development pole S ₁ , ears are formed by magnetic force. Developing the electrostatic latent image by the developer T formed on the spikes, then, N ₂ poles, N
The developer T on the developing sleeve 11 is generated by the repulsive magnetic field of _three poles.
Is returned into the developing container 16.

A direct current (DC) voltage and an alternating current (AC) voltage are applied to the developing sleeve 11 from a power source S2. In this embodiment, a DC voltage of -500 V and a frequency of 2000 Hz
, An AC voltage of 1500 V is applied.

In general, in the two-component developing method, when an AC voltage is applied, the developing efficiency increases, and the image becomes high quality.
Conversely, there is a problem that fogging easily occurs.
For this reason, fogging can be prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photoconductor 1.

(7) Transfer Apparatus 7 (FIG. 1) The transfer apparatus 7 of this embodiment is a belt transfer apparatus, and transfers an endless transfer belt 71 to a driving roller 72 and a driven roller 73.
The photosensitive member 1 is rotated in the direction indicated by the arrow f at a peripheral speed substantially equal to the rotational peripheral speed of the photosensitive member 1. The transfer nip 70, which is a transfer portion, is formed by bringing a part of the ascending-side belt portion of the transfer belt 71 into contact with the surface of the photoconductor 1. The transfer nip portion 70 on the inner surface side of the ascending belt portion of the transfer belt 71
A transfer charging blade 74 is provided in contact with the corresponding position.

The recording material P is conveyed to the transfer nip 70 on the upper surface of the ascending belt portion of the transfer belt 71.
When a predetermined transfer bias is supplied from the transfer bias applying power source S3 to the transfer charging blade 74, charging of the opposite polarity to that of the toner is performed from the back side of the recording material P, and the toner image on the surface of the photoconductor 1 is sequentially printed on the recording material P. It is transferred to the upper surface.

In this embodiment, a transfer belt 71 made of a polyimide resin having a thickness of 75 μm was used. The material of the transfer belt 71 is not limited to a polyimide resin, and may be, for example, a polycarbonate resin, a polyethylene terephthalate resin, a polyvinylidene fluoride resin, a polyethylene naphthalate resin, a polyether ether ketone resin, or a polyether. Plastics such as sulfone resins and polyurethane resins, and fluorine-based and silicon-based rubbers can be suitably used. Also, the thickness is not limited to 75 μm, but is 25 to 2000 μm, preferably 50 μm.
Those having a thickness of up to 150 μm can be suitably used.

Further, the transfer charging blade 74 has a resistance of 1 × 10 ⁵ to 1 × 10 ⁷ Ω, a plate thickness of 2 mm and a length of 3 × 10 ⁵ Ω.
The thing of 06 mm was used. In the present embodiment, transfer was performed by applying a bias of 10 μA to the transfer charging blade 74 by constant current control.

The toner image formed on the surface of the photoreceptor 1 is transferred onto the recording material P by the transfer electric field applied to the transfer charging blade 74.

The transfer belt 71 is connected to the transfer nip 7
The recording material P that has passed through the transfer nip 70 is also separated from the surface of the photoconductor 1 and is conveyed to the fixing device 6 by the transfer belt 71. .

Reference numerals 91 and 92 denote a transfer belt static eliminator and a transfer belt cleaner, which act on the outer surface of the transfer belt from which the recording material P has been peeled at the transfer belt suspension portion of the transfer belt driving roller 72.

The transfer belt static eliminator 91 is constituted by a grounded conductive fur brush, and the pair of the transfer belt drive roller 72 and the ground is used to remove the front and rear surface potentials of the transfer belt 71.

The transfer belt cleaner 92 is constituted by a urethane rubber blade and removes foreign matters such as residual toner and paper dust on the surface of the transfer belt 71.

(8) Cleanerless system The transfer residual toner on the surface of the photoconductor 1 after the transfer of the toner image from the photoconductor 1 side to the recording material P surface in the transfer nip 70 is transferred nip as the photoconductor 1 continues to rotate. From the 70 side, the photoconductor 1 is carried to a charging area n which is a contact portion between the photoconductor 1 and the magnetic brush 3 as the contact charging means, and is taken into the magnetic brush layer 3c of the magnetic brush 3 (temporary transfer of toner to the contact charging means). Target).

In this case, when the alternating voltage is applied to the magnetic brush 3, the toner is easily taken into the magnetic brush layer 3c of the magnetic brush 3 by the vibration effect of the electric field between the photosensitive member and the magnetic brush.

The transfer residual toner taken into the magnetic brush 3 is converted into a normally charged toner (negatively charged in this embodiment) by rubbing against the magnetic brush layer 3c even if the charging polarity is inverted.

The transfer residual toner, which is taken into the magnetic brush 3 and sufficiently converted into the normally charged toner, is gradually discharged from the magnetic brush layer 3c onto the photosensitive member 1 by an electric repulsive force against the voltage applied to the magnetic brush 3.

The normally charged toner discharged from the magnetic brush 3 onto the photoreceptor 1 reaches the developing area with the rotation of the photoreceptor 1, and is collected by the developing device 4.

In this embodiment, the photosensitive member 1 on which image formation has been completed
(A non-image forming surface portion) or a portion (non-image forming surface portion) of the photoreceptor 1 where image formation is not performed between recording materials conveyed during continuous paper feeding (between recording materials). As described below, toner is ejected from the magnetic brush 3 and toner is collected by the developing device 4 according to the ejection sequence.

That is, as shown in the control timing chart of FIG. 6, in the discharge sequence, the output of the magnetic brush 3 serving as the contact charging means does not apply the alternating voltage (AC voltage) superimposed during normal image formation. The DC component of the developing bias applied to the developing sleeve 11 is applied at about 450 V, whose absolute value is slightly lower than -500 V during normal image formation.

When such a discharging sequence was performed, the recovered toner that had been stirred with the magnetic particles in the magnetic brush 3 was charged to the negative polarity by frictional charging, and that no alternating voltage was applied. The photoreceptor 1
Since the potential difference between the charged potential and the magnetic brush 3 is generated, the magnetic brush 3 is effectively discharged onto the photosensitive member 1.

Further, since the negatively charged toner discharged onto the photoreceptor 1 is also changed in the developing device 4 in accordance with the charged potential on the photoreceptor 1, a sufficient fogging potential is generated, and The toner discharged from the brush 3 and conveyed on the photoconductor 1 is collected by the developing device 4.

However, when a large amount of toner is accumulated in the magnetic brush 3 by continuously outputting images with a high image ratio, the toner to be collected by the developing device 4 is At 4, the toner is passed through the transfer nip 70 without being completely collected, and is again conveyed on the photoconductor 1 to the magnetic brush 3.

At this time, if the ejection sequence from the magnetic brush 3 is still continued, the toner that has made one round on the photoreceptor 1 is not collected by the magnetic brush 3 as a matter of course.
Further, the toner continues to rotate on the photosensitive member 1 in combination with the discharged toner.

As a result of the above, if there is any toner that has not been completely collected by the developing device 4, the remaining toner on the photosensitive member 1 will continue to increase, and an image defect will occur at the time of the next image formation. .

In order to prevent such a problem from occurring, in this embodiment, as shown in the control timing chart of FIG. 6, a portion of the photosensitive member 1 where image formation has been completed or a continuous For the portion of the photoconductor 1 where no image is formed between the recording materials conveyed in the recording material, the transfer charging blade 7
The transfer bias supplied to 4 is set to 10 at the time of normal image formation.
A value 14 μA, which is slightly higher than μA, is set and applied.

By applying the transfer bias in this manner, most of the toner (about 90%) on the photoreceptor 1 that has not been sufficiently collected by the developing device 4 during the discharge sequence.
%) Is transferred onto the transfer belt 71 where no recording material exists.

Most of the toner transferred on the transfer belt 71 further passes through the transfer belt static eliminator 91 and is removed by the transfer belt cleaner 92.

On the other hand, since a higher transfer bias is applied to the transfer nip 70 than in normal image formation, the negatively charged toner that cannot be completely collected by the developing device 4 and reaches the transfer nip 70 Of the toner, the toner remaining on the photoreceptor 1 even after passing through the transfer nip 70 without being transferred onto the transfer belt 71 is in a positively charged state (FIG. 7), and thereafter reaches the magnetic brush 3 Sometimes, the result is collected by the magnetic brush 3.

As described above, in the image forming apparatus of this embodiment,
Even if a large amount of toner is mixed into the magnetic brush 3 serving as the contact charging means due to continuous images having a high image ratio, and a state where the toner cannot be completely collected in the developing device 4 in the discharge sequence occurs, normal image formation is performed. By applying a transfer high voltage such that the charge of the residual toner becomes higher than the normal charge, which is the polarity opposite to the normal charge polarity of the toner, the toner is collected again when it reaches the magnetic brush 3 again. .

Therefore, it is possible to prevent a problem such as an image defect due to extra toner on the photoreceptor 1 in the next image formation, and it is possible to form a good image over a long period of time.

<Embodiment 2> In this embodiment, an image is formed between the portion of the photosensitive member 1 where the image formation has been completed or the recording material conveyed during continuous paper feeding in the first embodiment. For the portion of the photosensitive member 1 that is not
Does not perform the discharge sequence. That is, even when the photosensitive member 1 and the transfer belt 71 are still rotating after the image formation is completed or after the image formation is completed, the bias applied to the magnetic brush 3 as the contact charging unit and the developing device 4 Does not change during image formation.

However, the transfer bias supplied from the transfer bias application power source S3 to the transfer charging blade 74 is set to 14 μA, which is slightly higher than 10 μA during normal image formation, as in the first embodiment.

That is, the toner should not positively exist on the photoreceptor in the non-image area. However, when "fogging" occurs, the toner adheres to the transfer belt 71 side. Then, the toner is removed from the photoreceptor to prevent the toner from being mixed in a large amount into the magnetic brush 3 serving as the contact charging means, and the residual toner that has passed through the transfer nip 70 is also charged to a polarity opposite to the normal charging polarity. This facilitates the collection by the magnetic brush 3.

<Others> 1) The magnetic brush 3 as the contact charging means has been described in the non-magnetic sleeve rotating system in which the magnet roller 3a is fixed. However, the present invention is not limited to this configuration. Even a system in which the magnet 3a rotates or a system in which the magnet roller itself rotates with only the magnet roller can be realized by performing a conductive treatment on the roller surface.

2) The contact charging means may be a charging roller or fur brush using conductive rubber or conductive sponge.

FIG. 8 shows an example of a fur brush. The fur brush 3A as the contact charging means of this example has an outer diameter of 10 m.
m core metal roller 3d, the bristle length is 3 mm, the flocking density is 100,000 / inch ² , and the resistance value is 1 × 10 ⁶ Ω.
The conductive fiber brush layer (fur brush layer) 3e is formed and has a total outer diameter of 16 mm.

The fur brush 3A is provided with its conductive fiber brush layer 3e in contact with the surface of the photoreceptor 1. The width of the contact nip portion n between the conductive fiber brush layer 3e and the photoconductor 1 was 7 mm. The fur brush 3A is moved in the counter direction with respect to the photoconductor 1 so that the peripheral speed of the photoconductor 1 is 100 mm.
/ Sec at a speed of 200 mm / sec.

Then, a predetermined charging bias is applied to the fur brush 3A from a charging bias applying power source S1 to rotate the fur brush 3A, whereby the surface of the rotating photoreceptor 1 is rubbed with the conductive fiber brush layer 3e to which the charging voltage is applied. Then, the surface of the photoreceptor layer 1b of the photoreceptor 1 is uniformly charged to a desired potential by an injection charging method.

3) It is also desirable that the photosensitive member as the image carrier has a low resistance layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm from the viewpoint of realizing charge injection and preventing ozone generation. Organic photoreceptor or the like, or a dielectric or the like in electrostatic recording.

4) As the developing method, only the two-component developing method has been described in the embodiment, but other developing methods are also effective. Preferably, one-component contact development or two-component contact development in which the developer is developed in contact with the photoreceptor is effective in increasing the simultaneous recovery effect during development.

5) When a polymerized toner is used as the toner particles in the developer, the above-described one-component contact development,
A sufficient recovery effect can be obtained not only in component contact development but also in development methods such as one-component non-contact development and two-component non-contact development.

6) The transfer means 7 is not limited to the belt transfer device, but may be a transfer roller or the like. Further, the present invention can be applied not only to the formation of a single-color image using a transfer drum, a transfer belt, an intermediate transfer member or the like, but also to an apparatus for forming a multi-color or full-color image by multiple transfer or the like.

7) The image carrier is not limited to the electrophotographic photosensitive member.
It may be a dielectric or the like in electrostatic recording.

8) The image exposure means as the information writing means on the charged surface of the image carrier is not limited to the laser scanning exposure means for forming a digital latent image as shown in the embodiment, but may be an ordinary analog exposure means. Image exposure and LED
Other light-emitting elements may be used as long as they can form an electrostatic latent image corresponding to image information, such as a combination of a light-emitting element such as a fluorescent lamp and a liquid crystal shutter.

When the member to be charged is not a photosensitive member but an electrostatic recording dielectric or the like, its surface is uniformly charged to a predetermined polarity and potential, and then charged by a discharging means such as a discharging needle head or an electron gun. By selectively removing the charge, an electrostatic latent image of the target image information is written and formed.

9) As the waveform of the alternating voltage, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Alternatively, a rectangular wave formed by periodically turning on / off a DC power supply may be used. As described above, a bias whose voltage value periodically changes can be used as the waveform of the alternating voltage.

[0121]

As described above, according to the present invention, in the image forming apparatus of the contact charging type / cleanerless system, a large amount of toner is mixed into the contact charging means by, for example, continuously arranging images having a high image ratio. However, even if a state occurs in which the developing unit cannot collect the toner in the discharging sequence, it is possible to prevent a defect such as an image defect due to extra toner on the image carrier in the next image formation.
Good image formation can be performed over a long period of time.

[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 a schematic diagram of a magnetic brush as a contact charging device.

FIG. 3 is a diagram showing a relationship between an applied alternating voltage to a magnetic brush and a charging potential.

FIG. 4 is a schematic view of an exposure apparatus (laser scanner).

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

FIG. 6 is a control timing chart.

FIG. 7 is a diagram illustrating a transfer bias and a toner charge amount.

FIG. 8 is a schematic diagram of a fur brush as a contact charging device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor (image carrier) 3 magnetic brush (contact charging device) 4 developing device (developing device) 6 fixing device 7 transfer device 71 transfer belt (recording material carrier) 91 transfer belt static eliminator 92 transfer belt cleaner (recording material) Carrier cleaning means) 100 Exposure device

Claims (11)

[Claims] An image carrier for carrying an image; a charging unit for charging the image carrier; an image information writing unit for forming an electrostatic latent image on a charged surface of the image carrier; Developing means for developing the image as a toner image, and transfer means for transferring the toner image on the image carrier to a recording material, wherein the developing means transfers the toner image on the image carrier by the transfer means. An image forming apparatus of a cleanerless system, which also serves as an image carrier cleaning means for removing residual toner on the image carrier after being transferred to a recording material, and the image carrier is repeatedly provided for image formation. The charging unit is a contact charging unit that has a charging member that is in contact with the image carrier and to which a charging electric field is applied.The transfer unit is configured to be applied with a transfer electric field and form a transfer nip portion with the image carrier. At the transfer nip, the toner is transferred from the image carrier to the recording material. An image forming apparatus having a transfer member for transferring an image, wherein when the recording material is not in the transfer nip portion, the output of a transfer electric field applied to the transfer means is made higher than at the time of toner image transfer. . 2. The image forming apparatus according to claim 1, wherein the transfer member of the transfer unit carries a recording material, and conveys the recording material to the transfer nip portion so that the transfer material comes into contact with the toner image on the image carrier. . 3. The image forming apparatus according to claim 1, further comprising a transfer member cleaning unit that removes toner attached to the transfer member of the transfer unit. 4. The image carrier according to claim 1, wherein the image carrier has a photosensitive layer and a surface layer thereon, and the surface layer has a resin and conductive fine particles. The image forming apparatus according to one of the above. 5. The image forming apparatus according to claim 4, wherein the conductive fine particles are SnO ₂ . 6. The image bearing member has a volume resistivity of 10 ⁹ to 1.
The image forming apparatus according to claim 1, further comprising a surface layer made of a material of 0 ¹⁴ Ωcm. 7. The image forming apparatus according to claim 1, wherein the image carrier has a surface layer made of amorphous silicon. 8. The image forming apparatus according to claim 1, wherein the charging member has magnetic particles, and the magnetic particles contact the image carrier.
8. The image forming apparatus according to any one of items 1 to 7, 9. The image forming apparatus according to claim 1, wherein the charging member has conductive fibers, and the conductive fibers are in contact with the image carrier. . 10. The developing device according to claim 1, wherein said developing means is of a contact developing type in which a developer is brought into contact with said image carrier to develop an electrostatic latent image as a toner image.
The image forming apparatus according to any one of the above. 11. The image forming apparatus according to claim 10, wherein said developer has toner particles and magnetic particles.