JP3630998B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copier / facsimile / printer of a contact charging system / cleanerless system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image bearing member (hereinafter referred to as a photoreceptor) such as a rotating drum type electrophotographic photosensitive member or electrostatic recording dielectric is charged (charge elimination). Corona chargers have often been used as means for processing).
[0003]
In this method, a corona charger is disposed in contact with the photoreceptor in a non-contact manner, and the surface of the photoreceptor is exposed to a discharge corona generated by the corona charger to charge the photoreceptor surface to a predetermined polarity and potential.
[0004]
In recent years, the “contact charging device” (direct charging device) has been put into practical use because it has advantages such as low ozone and low power over the corona charger.
[0005]
In this method, a charging member to which a voltage (charging electric field) is applied is brought into contact with the photosensitive member to charge the surface of the photosensitive member to a predetermined polarity and potential.
[0006]
A contact charging device using a magnetic brush as the contact charging member is preferably used from the viewpoint of charging, contact stability, and the like. In this magnetic brush type contact charging device, conductive magnetic particles are directly magnetically constrained and held as a magnetic brush on a magnet or a sleeve containing the magnet, and the magnetic brush is stopped or rotated on the surface of the photoreceptor. The photosensitive member is started to be charged by bringing it into contact and applying a voltage thereto.
[0007]
A conductive rubber roll made of a conductive fiber (fur brush) or a conductive rubber roll made of conductive rubber in a roll shape can also be used as the contact charging member.
[0008]
In contact charging, a charge injection layer is provided on the photoconductor, and a charging member to which a voltage is applied is brought into contact with the photoconductor to inject charge into the charge injection layer so that the surface of the photoconductor has a predetermined polarity and potential. The injection charging method for charging the surface of the photosensitive member can obtain a surface potential of the photosensitive member almost equal to the applied DC voltage (direct current bias) regardless of whether the AC voltage (alternating bias) is superimposed on the charging member. For this reason, since a discharge phenomenon in which the photosensitive member is charged using a corona charger is not used, ozone is not generated and low power consumption type charging is possible.
[0009]
Further, in recent years, so-called “cleanerless system” image forming apparatuses have also been put into practical use for the purpose of reducing the size and simplification of the image forming apparatus and preventing waste toner from being emitted.
[0010]
This eliminates the dedicated cleaning device (cleaner) that removes the transfer residual toner from the surface of the photoconductor after the toner image is transferred to the recording material, and after the transfer residual toner on the photoconductor is once collected by the contact charging device, It is discharged from the contact charging device at the time of non-image formation and collected by the developing device (development simultaneous cleaning).
[0011]
In the simultaneous development cleaning, the residual toner on the photoconductor is developed after the next step, that is, the photoconductor is continuously charged to form a latent image, and the latent image is developed. This is a method of collecting by a fog removal potential difference Vback, which is a potential difference between the voltage and the surface potential of the photoreceptor. Residual toner on the photosensitive member is collected by the developing device and reused in the subsequent steps. Therefore, waste toner can be eliminated, and maintenance work can be reduced. Further, the cleaner-less has a great space advantage, and the image forming apparatus can be greatly downsized.
[0012]
By adopting such a cleaner-less system and the contact charging method described above, it is possible to obtain an image forming apparatus that is small and simple, does not generate ozone, consumes low power, and does not generate waste toner.
[0013]
[Problems to be solved by the invention]
However, in the simple and small image forming apparatus of the contact charging method / cleanerless system, the transfer residual toner may increase due to the difference in transfer efficiency due to the high image ratio or the type / thickness of the recording material, When such a state continues for a long time, the recovery capability of the contact charging device and the recovery capability of the developing device may not be able to catch up. Then, the residual toner that could not be collected on the photoreceptor appears at the next image formation, resulting in an image defect.
[0014]
Therefore, the present invention provides a contact charging type / cleanerless system image forming apparatus that has a high image ratio or a transfer efficiency that varies depending on the type / thickness of the recording material, even if the residual toner increases. An object of the present invention is to provide an image forming apparatus that maintains the recovery capability of the charging device and prevents image defects.
[0015]
[Means for Solving the Problems]
The present invention is an image forming apparatus having the following configuration.
[0016]
(1) An image carrier that carries an image, a charging unit that charges the image carrier, an image information writing unit that forms an electrostatic latent image on a charging surface of the image carrier, and the electrostatic latent image A developing unit that develops the toner image as a toner image; and a transfer unit that transfers the toner image on the image carrier to a recording material. The developing unit uses the transfer unit to transfer the toner image on the image carrier to the recording material. It also serves as an image carrier cleaning means for removing residual toner on the image carrier after being transferred to the image carrier, and the image carrier is an image forming apparatus of a cleanerless system that is repeatedly used for image formation,
The charging means is a contact charging means having a charging member that contacts the image carrier and to which a charging electric field is applied,
The transfer means has a transfer member to which a transfer electric field is applied, forms an image carrier and a transfer nip, and transfers a toner image from the image carrier to the recording material at the transfer nip,
An image forming apparatus, wherein when the recording material is not in the transfer nip portion, an output of an applied transfer electric field to the transfer unit is made higher than that at the time of toner image transfer.
[0017]
(2) The image forming apparatus according to (1), wherein the transfer member of the transfer unit carries a recording material, conveys the recording material to the transfer nip portion, and contacts the toner image on the image carrier.
[0018]
(3) The image forming apparatus according to (1) or (2), further comprising a transfer member cleaning unit that removes toner adhering to the transfer member of the transfer unit.
[0019]
(4) Any of (1) to (3), wherein the image carrier has a photosensitive layer and a surface layer thereon, and the surface layer includes a resin and conductive fine particles. The image forming apparatus according to one.
[0020]
(5) The conductive fine particles are SnO ₂ (4) The image forming apparatus as described in (4) above.
[0021]
(6) The image carrier has a volume resistivity of 10 ⁹ -10 ¹⁴ The image forming apparatus according to any one of (1) to (3), wherein the image forming apparatus has a surface layer made of a material of Ωcm.
[0022]
(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.
[0023]
(8) The image forming apparatus according to any one of (1) to (7), wherein the charging member includes magnetic particles, and the magnetic particles are in contact with the image carrier.
[0024]
(9) The image forming apparatus according to any one of (1) to (7), wherein the charging member includes conductive fibers, and the conductive fibers are in contact with the image carrier. .
[0025]
(10) Any one of (1) to (9) is characterized in that 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 claim 1.
[0026]
(11) The image forming apparatus according to (10), wherein the developer includes toner particles and magnetic particles.
[0027]
<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 brought into contact with the image carrier and the contact charging means from the transfer nip portion along with the subsequent movement of the image carrier. It is carried to the charging area, which is a part, and taken into the contact charging means (temporary recovery of toner to the contact charging means).
[0028]
The transfer residual toner taken into the contact charging unit is converted into a regular charged toner by rubbing with the contact charging unit even if the charging polarity is reversed.
[0029]
The transfer residual toner taken into the contact charging unit and sufficiently converted into a regular charged toner is gradually discharged from the contact charging unit onto the image carrier.
[0030]
Regularly charged toner discharged from the contact charging unit onto the image carrier reaches the development area as the image carrier moves, and is collected by the developing unit.
[0031]
In this case, even if the toner collecting capability of the developing unit cannot catch up, and the toner to be collected by the developing unit cannot be completely collected by the developing unit and is carried to the transfer nip portion, the output of the applied transfer electric field to the transferring unit is changed to the toner. By setting the height higher than that at the time of image transfer, most of the toner on the image carrier carried to the transfer nip portion without being sufficiently collected by the developing means is transferred onto the transfer means having no recording material and transferred to the image. It is removed from the carrier. Most of the toner transferred onto the transfer means is removed from the transfer means by the cleaning means.
[0032]
On the other hand, since a transfer bias higher than that at the time of normal image formation acts on the transfer nip portion, the toner that reaches the transfer nip portion is not transferred onto the transfer device without being collected by the developing device. Further, the toner remaining on the image carrier after passing through the transfer nip portion is in a charged state having a polarity opposite to the normal charging polarity, and is subsequently collected by the contact charging means when it reaches the charged region portion. .
[0033]
Therefore, even if a large amount of toner is mixed into the contact charging unit due to continuous images having a high image ratio, and the state where the toner cannot be collected by the developing unit in the discharge sequence, the image carrier is used in the next image formation. It is possible to prevent problems such as image defects due to the presence of extra toner on the top, and good image formation can be performed over a long period of time.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
<Example 1>
FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process, and is an apparatus of a cleanerless system using a magnetic brush type contact charging device as charging means for an image carrier (photosensitive member).
[0035]
A is a laser beam printer, and B is an image reading device (image scanner) mounted on the printer.
[0036]
(1) Image reading device B
In the image reading apparatus B, reference numeral 10 denotes a fixed original platen glass. The original platen glass is placed on the upper surface of the original platen glass with the surface on which the original G is to be copied facing down. set.
[0037]
An image reading unit 9 is 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 along the lower surface of the glass from the home position on the left side of the glass to the right side on the lower side of the platen glass 10 to obtain a predetermined forward movement. When it reaches the end point, it is driven back and returned to the first home position.
[0038]
In the forward drive process of the unit 9, the downward image surface of the set original G on the platen glass 10 is illuminated and scanned sequentially from the left side to the right side by the document irradiation lamp 9 a of the unit 9. Light reflected from the original surface is imaged and incident on the CCD sensor 9c by the short focus lens array 9b.
[0039]
The CCD sensor 9c includes a light receiving unit, a transfer unit, and an output unit. The optical signal is converted into a charge signal in the CCD light receiving unit, and sequentially transferred to the output unit in synchronization with the clock pulse in the transfer unit. The charge signal is converted into a voltage signal in the output unit, amplified and reduced in impedance, and output. 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.
[0040]
That is, the image information of the original G is photoelectrically read as a time-series electric digital pixel signal (image signal) by the image reading device B.
[0041]
(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. The photosensitive member 1 is driven to rotate in a clockwise direction a indicated by an arrow with a predetermined peripheral speed (process speed) around a central support shaft, and in the rotation process, the charging device 3 in this example has a uniform negative polarity. Receive proper charging treatment. The charging device 3 in this example is a magnetic brush as contact charging means.
[0042]
Then, the uniformly charged surface of the photoreceptor 1 is modulated in accordance with the image signal output from the exposure device (laser scanning device, laser scanner) 100 and sent from the image reading device B to the laser beam printer A side. By performing the scanning exposure L with the laser beam, an electrostatic latent image corresponding to the image information of the original G photoelectrically read by the image reading device B is sequentially formed on the photoreceptor 1.
[0043]
The electrostatic latent image formed on the photosensitive member 1 is sequentially developed as a toner image by the developing device 4 and is reversely developed in this embodiment.
[0044]
On the other hand, a recording material (transfer material) P such as paper stored in the paper feed cassette 41 is fed out and fed by the paper feed roller 42 and is fed to the photosensitive member 1 by a registration roller 43 at a predetermined timing. The toner image on the photosensitive member 1 is transferred to the recording material P by being fed to a transfer nip portion (transfer site) 70 between the transfer belt device 7 and the transfer belt 71 as a transfer means.
[0045]
The recording material P that has been transferred with the toner image through the transfer nip 70 is sequentially separated from the surface of the photoreceptor 1 and conveyed to the fixing device 6, and is subjected to thermal fixing of the toner image and is output as a copy or print. .
[0046]
The surface of the rotating photoreceptor 1 after the transfer of the toner image to the recording material P is repeatedly used for image formation.
[0047]
(3) Photoconductor 1
As the photoreceptor 1 as an image carrier, a commonly used organic photoreceptor can be used. Preferably, the resistance is 10 on the organic photoreceptor. ⁹ To 10 ¹⁴ Using a surface layer having a material of Ω · cm or an amorphous silicon (amorphous silicon) photoconductor can realize charge injection charging, and is effective in preventing ozone generation and reducing power consumption. . In addition, the chargeability can be improved.
[0048]
In this embodiment, the photoreceptor 1 is a negatively charged organic photoreceptor, in which a photoreceptor layer 1b is formed on an aluminum drum base 1a (FIG. 2) having a diameter of 30 mm, and a predetermined process speed (for example, 100 mm / cec).
[0049]
In the present embodiment, the photosensitive layer 1b is provided with the following first to fifth layers in order from the bottom.
[0050]
(1). First layer: an undercoat layer, which is a conductive layer having a thickness of 20 μm and provided for leveling defects of the drum base 1a.
[0051]
(2). Second layer: a positive charge injection preventing layer, which serves to prevent the positive charge injected from the drum substrate 1a from canceling the negative charge charged on the surface of the photoreceptor 1, and is formed by amylan resin and methoxymethylated nylon. 10 ⁶ This is a medium resistance layer having a thickness of 1 μm, whose resistance is adjusted to about Ω · cm.
[0052]
(3). 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]
(4). Fourth layer: a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, the negative charge charged on the surface of the photoreceptor 1 cannot move through this layer, and only the positive charge generated in the third layer (charge generation layer) can be transported to the surface of the photoreceptor 1.
[0054]
(5). 5th layer (outermost surface); charge injection layer, SnO as conductive fine particles in binder of insulating resin ₂ It is a coating layer of a material in which ultrafine particles are dispersed. Specifically, SnO having a particle size of 0.03 μm is obtained by reducing the resistance (conducting) by doping an insulating resin with antimony which is a light-transmissive conductive filler. ₂ It is a coating layer of a material in which particles are dispersed by 70 weight percent with respect to the resin. The coating solution thus prepared was applied to a thickness of about 3 μm by an appropriate coating method such as a dipping coating method, a spray coating method, a roll coating method, or a beam coating method to form a charge injection layer.
[0055]
(4) Charging device 3 (FIG. 2)
The charging device 3 in this example is a contact charging type magnetic brush charging device (magnetic brush). As shown in FIG. 2, the magnetic brush 3 of this example includes a fixed magnet roller 3a having a diameter of 16 mm, a nonmagnetic SUS sleeve 3b that is rotatably fitted around the magnet roller 3a, and an outer peripheral surface of the sleeve 3b. The sleeve rotation type comprises a magnetic brush layer 3c of magnetic particles (magnetic carrier) adhered and held by the magnetic force of the magnet roller 3a.
[0056]
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 250 emu / cm. ³ , Resistance 1 × 10 ² ~ 1x10 ¹⁰ The resistance is preferably Ω · cm. Considering the existence of an insulation defect such as a pinhole in the photosensitive member 1, the resistance is 1 × 10. ⁶ It is preferable to use one having Ω · cm or more.
[0057]
The resistance value of magnetic particles has a bottom area of 228 mm. ² After putting 2 g of magnetic particles in a metal cell of 6.6 kg / cm ² And measured by applying a voltage of 100V.
[0058]
The average particle diameter of the magnetic particles is indicated by the maximum horizontal chord length, and the measurement method is a microscopic method, randomly selecting 300 or more magnetic particles, measuring the diameter and taking the arithmetic average to obtain the average particle diameter. .
[0059]
For measurement of the magnetic properties of the magnetic particles, a direct-current magnetization BH characteristic automatic recording device BHH-50 manufactured by Riken Electronics Co., Ltd. can be used. At this time, a cylindrical container having a diameter (inner diameter) of 6.5 mm and a height of 10 mm is filled with magnetic particles with a load of about 2 g weight, and the magnetic particles do not move in the container, and saturation magnetization is obtained from the BH curve. Measure.
[0060]
In order to improve the charging performance, it is better to use a material having as small a resistance as possible. ³ , Resistance 5 × 10 ⁶ A magnetic brush layer 3c was formed by magnetically adhering 40 g to the outer peripheral surface of the sleeve 3b.
[0061]
The magnetic particles are composed of a resin carrier formed by dispersing a magnet as a magnetic material in the resin to make it conductive, and carbon black dispersed for resistance adjustment, or the surface of a magnetite simple substance such as ferrite is oxidized and reduced. For example, a material whose resistance is adjusted by coating the surface of a magnetite single body such as ferrite with a resin can be used.
[0062]
The magnetic brush 3 is disposed so that the magnetic brush layer 3c is in contact with the surface of the photoreceptor 1, and the width of the contact nip n (charging nip portion) between the magnetic brush layer 3c and the photoreceptor 1 is 6 mm. .
[0063]
Then, a predetermined charging bias is applied to the sleeve 3b from the charging bias application power source S1, and the sleeve 3b is in a counter nip (reverse direction) with respect to the rotation direction a of the photosensitive member 1 at the contact nip n with the photosensitive member 1. In the clockwise direction shown in the figure, for example, by rotating the photosensitive member at a peripheral speed of 150 mm / sec with respect to a rotating speed of 100 mm / sec, the surface of the photosensitive member 1 is rubbed with the magnetic brush layer 3c to which a charging bias is applied. The surface of the photoreceptor layer 1b of the photoreceptor 1 is uniformly subjected to primary charging to a desired potential by an injection charging method. At this time, by increasing the rotation speed of the sleeve 3b, the chance of contact between the untransferred toner on the photoconductor 1 and the magnetic brush 3 is increased, so that the recovery to the magnetic brush is also improved.
[0064]
FIG. 3 shows the relationship between the applied bias amplitude and the first-round charging potential when a rectangular alternating voltage (alternating voltage) Vpp is applied to the magnetic brush 3 at a frequency of 1000 Hz. By doing so, the difference between the DC (direct current) component of the applied bias and the first round charging potential is reduced.
[0065]
More specifically, assuming that the DC component of the bias applied to the magnetic brush 3 is Vdc and the surface potential on the photosensitive member 1 charged at this time is Vs, the potential contrast ΔV = | Vdc−Vs | Is approximately 40 V or less, the charging uniformity is also improved.
[0066]
Also in this case, by applying an alternating voltage to the magnetic brush 3, the transfer residual toner can be taken into the magnetic brush 3 by the vibration effect due to the electric field between the photoconductor 1 and the magnetic brush 3.
[0067]
Therefore, in this embodiment, it was possible to obtain good chargeability by applying to the magnetic brush 3 a bias in which a rectangular 800 Vpp alternating voltage having a frequency of 1000 Hz and a DC voltage of −700 V was superimposed.
[0068]
(5) Exposure apparatus 100 (FIG. 4)
FIG. 4 is a schematic block diagram of an exposure apparatus (laser scanner) 100 of a laser beam scanning exposure method.
[0069]
When the exposure apparatus 100 performs laser scanning exposure L on the surface of the photoreceptor 1, first, the solid-state laser element 102 is blinked (ON / OFF) at a predetermined timing by the light emission signal generator 101 based on the input image signal. The laser light emitted from the solid-state laser element 102 is converted into a substantially parallel light beam by the collimator lens system 103, scanned in the arrow d direction by the rotating polygon mirror 104 that rotates at high speed in the arrow c direction, and an fθ lens. Images are formed in spots on the surface of the photosensitive member 1 by the 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 if the surface of the photoconductor 1 is scrolled by a predetermined amount perpendicular to the scanning direction for each scan, An exposure distribution corresponding to the image signal is obtained on the surface of the photoreceptor 1.
[0070]
That is, the surface of the rotating photoreceptor 1 is scanned on the surface of the rotating photoreceptor 1 by scanning the light of the solid-state laser element 102 that emits light ON / OFF corresponding to the image signal by the rotating polygon mirror 104 at high speed. An electrostatic latent image corresponding to the scanning exposure pattern is sequentially formed.
[0071]
(6) Developing device 4 (FIG. 5)
In general, the electrostatic latent image is developed by coating non-magnetic toner on a sleeve with a blade or the like, and magnetic toner is coated by magnetic force and conveyed and developed 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), and a mixture of toner particles and a magnetic carrier. A method of developing as a developer by conveying with magnetic force and developing it in contact with the photosensitive drum (two-component contact development), and a method of developing the two-component developer in a non-contact state (two-component non-contact) Development) is roughly divided into four types. A two-component contact development method is often used from the viewpoint of high image quality and high stability.
[0072]
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, 11 is a developing sleeve that is rotationally driven in the direction of arrow e, 12 is a magnet roller fixedly arranged in the developing sleeve 11, 13 and 14 are stirring screws, and 15 is a developer T on the surface of the developing sleeve 11. A regulating blade arranged to form a thin layer, 16 is a developing container, and 17 is a replenishing toner hopper.
[0073]
The developing sleeve 11 is arranged so that a region closest to the photosensitive member 1 is about 500 μm at least during development, and a thin layer Ta of the developer T formed on the surface of the developing sleeve 11 is disposed on the photosensitive member 1. Are set so that they can be developed in contact with each other.
[0074]
In the two-component developer T used in this example, toner particles t were externally added with 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 pulverization method. And the carrier c has a saturation magnetization of 205 emu / cm. ³ A magnetic carrier having an average particle size of 35 μm was used. Further, a mixture of toner t and carrier c at a weight ratio of 6:94 was used as developer T.
[0075]
Here, a developing process for visualizing the electrostatic latent image on the surface of the photoreceptor 1 by the two-component magnetic brush method using the developing device 4 and a circulation system of the developer T will be described. First, as the developing sleeve 11 rotates, N ₃ Developer T pumped up at the pole is S ₂ Pole → N ₁ In the process of being conveyed to the pole, the thin layer Ta of the developer T is formed on the developing sleeve 11 by being regulated by the regulating blade 15 disposed perpendicular to the developing sleeve 11. The developer T on which the thin layer Ta is formed is the developing main electrode S. ₁ When it is conveyed to the pole, the head is formed by the magnetic force. The electrostatic latent image is developed with the developer T formed into the spike shape, and then N ₂ Pole, N ₃ The developer T on the developing sleeve 11 is returned into the developing container 16 by the repulsive magnetic field of the pole.
[0076]
A direct current (DC) voltage and an alternating current (AC) voltage are applied to the developing sleeve 11 from the power source S2. In this embodiment, a DC voltage of −500 V and an AC voltage of 1500 V at a frequency of 2000 Hz are applied.
[0077]
In general, in the two-component development method, when an AC voltage is applied, the development efficiency increases and the image becomes high-quality, but conversely, fogging easily occurs. For this reason, it is possible to prevent fogging by providing a potential difference between the DC voltage normally applied to the developing device 4 and the surface potential of the photoreceptor 1.
[0078]
(7) Transfer device 7 (FIG. 1)
The transfer device 7 of this embodiment is a belt transfer device, and an endless transfer belt 71 is suspended between a driving roller 72 and a driven roller 73, and at a peripheral speed substantially the same as the rotational peripheral speed of the photoreceptor 1 in the direction of arrow f. Drive to rotate. A transfer nip portion 70 which is a transfer portion is formed by bringing the middle portion of the ascending belt portion of the transfer belt 71 into contact with the surface of the photoreceptor 1. A transfer charging blade 74 is disposed in contact with a position corresponding to the transfer nip portion 70 on the inner surface side of the upstream belt portion of the transfer belt 71.
[0079]
The recording material P rides on the upper surface of the ascending belt portion of the transfer belt 71 and is conveyed to the transfer nip portion 70. When a predetermined transfer bias is supplied from the transfer bias applying power source S3 to the transfer charging blade 74, the reverse polarity of the toner is charged from the back side of the recording material P, and the toner images on the surface of the photoreceptor 1 are sequentially transferred to the recording material P. It is transferred to the upper surface.
[0080]
In this embodiment, a transfer belt 71 made of polyimide resin having a film thickness of 75 μm was used. The material of the transfer belt 71 is not limited to polyimide resin, but other than this, for example, polycarbonate resin, polyethylene terephthalate resin, polyvinylidene fluoride resin, polyethylene naphthalate resin, polyether ether ketone resin, polyether. Plastics such as sulfone resin and polyurethane resin, and fluorine-based and silicon-based rubbers can be suitably used. Further, the thickness is not limited to 75 μm, and a thickness of 25 to 2000 μm, preferably 50 to 150 μm can be suitably used.
[0081]
Further, the transfer charging blade 74 has a resistance of 1 × 10. ⁵ ~ 1x10 ⁷ A plate with a thickness of 2 mm and a length of 306 mm was used. In this embodiment, transfer was performed by applying a bias of 10 μA to the transfer charging blade 74 by constant current control.
[0082]
In this manner, 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.
[0083]
The transfer belt 71 also serves as means for conveying the recording material P from the transfer nip portion 70 to the fixing device 6, and the recording material P that has passed through the transfer nip portion 70 is separated from the surface of the photoreceptor 1 and transferred. The belt 71 is conveyed to the fixing device 6.
[0084]
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 off at the transfer belt suspension portion of the transfer belt drive roller 72.
[0085]
The transfer belt neutralizer 91 is composed of a grounded conductive fur brush, and the pair of the transfer belt drive roller 72 that is also grounded removes the front and back surface potentials of the transfer belt 71.
[0086]
The transfer belt cleaner 92 is composed of a urethane rubber blade, and removes adhering foreign matters such as residual toner and paper dust on the surface of the transfer belt 71.
[0087]
(8) Cleanerless system
The transfer residual toner on the surface of the photoconductor 1 after the toner image is transferred from the photoconductor 1 side to the recording material P surface in the transfer nip portion 70 is contact-charged with the photoconductor 1 from the transfer nip portion 70 side as the photoconductor 1 continues to rotate. It is carried to a charging region n that is a contact portion with the magnetic brush 3 that is means, and is taken into the magnetic brush layer 3c of the magnetic brush 3 (temporary recovery of toner to the contact charging means).
[0088]
In this case, when an alternating voltage is applied to the magnetic brush 3, the toner can be easily taken into the magnetic brush layer 3c of the magnetic brush 3 by the vibration effect due to the electric field between the photoconductor and the magnetic brush.
[0089]
The transfer residual toner taken into the magnetic brush 3 is converted into a regular charged toner (negatively charged in this embodiment) by rubbing with the magnetic brush layer 3c even if the charging polarity is reversed.
[0090]
The transfer residual toner taken into the magnetic brush 3 and sufficiently converted into a regular charged toner is gradually discharged from the magnetic brush layer 3c onto the photosensitive member 1 by an electric repulsive force with an applied voltage to the magnetic brush 3.
[0091]
Regularly charged toner discharged from the magnetic brush 3 onto the photoconductor 1 reaches the developing area as the photoconductor 1 rotates, and is collected by the developing device 4.
[0092]
In this embodiment, the photosensitive member 1 that does not form an image between the portion of the photoreceptor 1 that has finished image formation (the non-image forming surface portion) or between the recording material and the recording material conveyed during continuous paper feeding. As for the portion of the body 1 (non-image forming surface portion), the toner is discharged from the magnetic brush 3 and the toner is collected by the developing device 4 by the discharge sequence as described below.
[0093]
That is, as shown in the control timing chart of FIG. 6, in the discharge sequence, the output of the magnetic brush 3 that is the contact charging unit is configured not to apply an alternating voltage (AC voltage) superimposed during normal image formation, The DC component of the developing bias applied to the developing sleeve 11 is applied to about 1450 V so that its absolute value is slightly lower than the value −500 V during normal image formation.
[0094]
When such a discharge sequence is performed, the collected toner, which has been stirred with the magnetic particles in the magnetic brush 3 until then, is negatively charged by frictional charging, and the alternating voltage is not applied. Since there is a potential difference between the charged potential of the body 1 and the magnetic brush 3, it is effectively discharged onto the photoreceptor 1.
[0095]
Further, since the negatively charged toner discharged onto the photosensitive member 1 is changed in accordance with the charging potential on the photosensitive member 1 in the developing device 4 as well, a sufficient fog removal potential is generated and the magnetic brush 3 The toner discharged and conveyed on the photoreceptor 1 is collected by the developing device 4.
[0096]
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 collected by the developing device 4. After passing through the transfer nipping unit 70, the photosensitive member 1 is transported to the magnetic brush 3 again.
[0097]
At this time, if the discharge sequence from the magnetic brush 3 still continues, the toner that has made one turn on the photosensitive member 1 is naturally not collected by the magnetic brush 3, but is further combined with the discharged toner to be exposed to the photosensitive drum. Continue on body 1.
[0098]
As a result of the above, if there is toner that could not be collected once by the developing device 4, the residual toner on the photoreceptor 1 will continue to increase, resulting in an image defect during the next image formation.
[0099]
In order to prevent this from occurring, in the present embodiment, as shown in the control timing chart of FIG. The transfer bias supplied to the transfer charging blade 74 from the transfer bias application power source S3 is slightly higher than 10 μA at the time of normal image formation for the portion of the photosensitive member 1 where image formation is not performed between the recording material to be recorded. Set to a value of 14 μA and apply.
[0100]
By applying the transfer bias in this way, 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 is present. Is done.
[0101]
Most of the toner transferred onto the transfer belt 71 further passes through the transfer belt neutralizer 91 and is removed by the transfer belt cleaner 92.
[0102]
On the other hand, a transfer bias higher than that at the time of normal image formation is applied to the transfer nip portion 70, and therefore, transfer of the negatively charged toner that reaches the transfer nip portion 70 without being completely collected by the developing device 4. The toner remaining on the photosensitive member 1 after passing through the transfer nip portion 70 without being transferred onto the belt 71 is in a positively charged state (FIG. 7). The result is collected by the brush 3.
[0103]
As described above, in the image forming apparatus according to the present exemplary embodiment, a large amount of toner is mixed into the magnetic brush 3 serving as the contact charging unit by continuously printing images with a high image ratio, and the toner can be completely collected by the developing device 4 in the discharge sequence. The magnetic brush is again applied by applying a transfer high voltage that causes the residual toner to be positively charged, which has a polarity opposite to the normal charging polarity of the toner, even if a non-existent state occurs. A configuration is adopted in which when 3 is reached, it is collected again.
[0104]
Accordingly, it is possible to prevent defects such as image defects due to the presence of excess toner on the photoreceptor 1 in the next image formation, and good image formation can be performed over a long period of time.
[0105]
<Example 2>
In this embodiment, the portion of the photoconductor 1 that has completed image formation in Embodiment 1, or the portion of the photoconductor 1 that does not perform image formation between the recording material conveyed during continuous paper passing, In particular, the ejection sequence from the magnetic brush 3 is not actively performed. That is, the bias applied to the magnetic brush 3 as the contact charging unit and the developing device 4 during continuous image formation or even when the photoreceptor 1 and the transfer belt 71 are still rotating after image formation is completed. Does not change during image formation.
[0106]
However, the transfer bias supplied from the transfer bias application power source S3 to the transfer charging blade 74 is set to a value 14 μA that is slightly higher than 10 μA during normal image formation, as in the first embodiment.
[0107]
In other words, the toner should not actively exist on the photoconductor in the non-image portion, but when “fogging” occurs, the toner is attached to the transfer belt 71 side to be photosensitive. By removing it from the body, it is prevented from being mixed in a large amount in the magnetic brush 3 as the contact charging means, and the residual toner that has passed through the transfer nipping portion 70 is also charged with a polarity opposite to the normal charging polarity. It is promoted to be collected by the brush 3.
[0108]
<Others>
1) The magnetic brush 3 as the contact charging means has been described in the non-magnetic sleeve rotation system in which the magnet roller 3a is fixed. However, the present invention is not limited to this configuration. For example, a system in which the magnet roller 3a rotates in the same configuration, Even in a system in which the magnet roller itself rotates with the configuration of only the magnet roller, it can be realized by conducting the conductive treatment on the roller surface.
[0109]
2) The contact charging means may be a charging roller or fur brush using conductive rubber or conductive sponge.
[0110]
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 a core metal roller 3d having an outer diameter of 10 mm, a bristle length of 3 mm, and a flocking density of 100,000 / inch. ² Resistance value is 1 × 10 ⁶ An Ω conductive fiber brush layer (fur brush layer) 3e is formed and has a total outer diameter of 16 mm.
[0111]
The fur brush 3A is disposed with the conductive fiber brush layer 3e in contact with the surface of the photoreceptor 1. The width of the contact nip n between the conductive fiber brush layer 3e and the photoreceptor 1 was 7 mm. The fur brush 3A is configured to rotate in the counter direction with respect to the photosensitive member 1 at 200 mm / sec with respect to the rotational peripheral speed of the photosensitive member 1 of 100 mm / sec.
[0112]
Then, by applying a predetermined charging bias from the charging bias applying power source S1 to the fur brush 3A and rotating the fur brush 3A, the surface of the rotary photosensitive member 1 is rubbed with the conductive fiber brush layer 3e to which a charging voltage is applied, and photosensitive. The surface of the photoreceptor layer 1b of the body 1 is subjected to primary charging uniformly at a desired potential by an injection charging method.
[0113]
3) The surface resistance of the photoreceptor as an image carrier is 10 ⁹ -10 ¹⁴ Having a low resistance layer of Ω · cm is desirable from the viewpoint of realizing charge injection and preventing the generation of ozone. However, it may be an organic photoreceptor other than the above or a dielectric in electrostatic recording.
[0114]
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 more effective in enhancing the simultaneous recovery effect during development.
[0115]
5) When polymerized toner is used as the toner particles in the developer, not only the above-mentioned one-component contact development and two-component contact development but also development methods such as one-component non-contact development and two-component non-contact development. A sufficient recovery effect can be obtained.
[0116]
6) The transfer means 7 is not limited to a belt transfer device, and may be a transfer roller or the like. Furthermore, the present invention can be applied not only to the formation of a single color image by using a transfer drum, a transfer belt, an intermediate transfer body, etc., but also to an apparatus for forming a multicolor, full color image by multiple transfer or the like.
[0117]
7) The image bearing member is not limited to the electrophotographic photosensitive member, and may be a dielectric member in electrostatic recording.
[0118]
8) The image exposure means as the information writing means for the charged surface of the image carrier is not limited to the laser scanning exposure means for forming a digital latent image shown in the embodiment, but a normal analog image. Other light emitting elements such as exposure and LED may be used, and any combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter may be used as long as it can form an electrostatic latent image corresponding to image information. .
[0119]
If the object to be charged is not a photoconductor but an electrostatic recording dielectric, the surface is uniformly charged to a predetermined polarity and potential, and then selectively electrified by a static elimination means such as a static elimination head or an electron gun. The electrostatic latent image of the target image information is written and formed by discharging.
[0120]
9) As a waveform of the alternating voltage, a sine wave, a rectangular wave, a triangular wave or the like can be used as appropriate. Further, it may be a rectangular wave formed by periodically turning on / off a DC power source. In this way, a bias that changes the voltage value periodically can be used as the waveform of the alternating voltage.
[0121]
【The invention's effect】
As described above, according to the present invention, in the contact charging type / cleanerless system image forming apparatus, a large amount of toner is mixed in the contact charging unit by, for example, continuously printing images with a high image ratio. Even if the developing unit cannot be fully collected, it is possible to prevent defects such as image defects due to excess toner on the image carrier in the next image formation, and good image formation over a long period of time. Can be done.
[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 alternating voltage applied 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 showing a transfer bias and a toner charge amount.
FIG. 8 is a schematic view of a fur brush as a contact charging device.
[Explanation of symbols]
1 Photoconductor (image carrier)
3 Magnetic brush (contact charging means)
4 Developing device (Developing means)
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 equipment

Claims (11)

An image carrier that carries an image, a charging unit that charges the image carrier, an image information writing unit that forms an electrostatic latent image on a charging surface of the image carrier, and the electrostatic latent image as a toner image A developing unit that develops the image and a transfer unit that transfers the toner image on the image carrier to the recording material, and the developing unit transfers the toner image on the image carrier to the recording material by the transfer unit; It also serves as an image carrier cleaning means for removing the residual toner on the subsequent image carrier, and the image carrier is an image forming apparatus of a cleanerless system that is repeatedly used for image formation,
The charging means is a contact charging means having a charging member that contacts the image carrier and to which a charging electric field is applied,
The transfer means has a transfer member to which a transfer electric field is applied, forms an image carrier and a transfer nip, and transfers a toner image from the image carrier to the recording material at the transfer nip,
An image forming apparatus, wherein when the recording material is not in the transfer nip portion, an output of an applied transfer electric field to the transfer unit is made higher than that at the time of toner image transfer. The image forming apparatus according to claim 1, wherein a transfer member of the transfer unit carries a recording material, conveys the recording material to the transfer nip portion, and contacts a toner image on the image carrier. 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 bearing member according to claim 1, wherein the image carrier has a photosensitive layer and a surface layer thereon, and the surface layer includes a resin and conductive fine particles. Image forming apparatus. The image forming apparatus according to claim 4, wherein the conductive fine particles are SnO ₂ . The image forming apparatus according to claim 1, wherein the image carrier has a surface layer made of a material having a volume resistivity of 10 ⁹ to 10 ¹⁴ Ωcm. 4. The image forming apparatus according to claim 1, wherein the image carrier has a surface layer made of amorphous silicon. The image forming apparatus according to claim 1, wherein the charging member includes magnetic particles, and the magnetic particles are in contact with the image carrier. 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 contact developing method according to claim 1, wherein the developing unit 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. Image forming apparatus. The image forming apparatus according to claim 10, wherein the developer includes toner particles and magnetic particles.

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