JP3990810B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer.
[0002]
[Prior art]
FIG. 9 shows a schematic configuration of an electrophotographic copying machine as a conventional image forming apparatus.
[0003]
In the figure, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) as an image carrier, which is rotationally driven in the direction of arrow R1 with a predetermined peripheral speed (process speed). In the rotation process, the photosensitive drum 1 is subjected to static elimination exposure by a pre-exposure lamp 2, and is subjected to uniform charging processing of a predetermined polarity and potential by a corona charger 3 as a charging means, and an image exposure means (not shown) (original document). By receiving image exposure L by an image projection imaging exposure means, a laser beam scanning exposure means, etc., the uniformly charged surface is selectively neutralized (or potential attenuated) corresponding to the exposure image pattern, and the electrostatic latent image Is formed. The electrostatic latent image is developed as a toner image by the developing device 4 as a developing means.
[0004]
On the other hand, a transfer material P as a transfer member is fed from a sheet feeding mechanism (not shown) between the photosensitive drum 1 and a corona charger 7 as a transfer unit at a predetermined control timing, and the back surface of the transfer material P The toner image on the photosensitive drum 1 is electrostatically transferred onto the surface of the transfer material P by being charged with a polarity opposite to that of the toner.
[0005]
Next, the transfer material P is electrostatically separated from the surface of the photosensitive drum 1 by the separation charger 8, introduced into the fixing unit 6, subjected to toner image fixing processing, and output as a copy or print.
[0006]
After the toner image has been transferred to the transfer material P, the toner remaining on the surface without being transferred to the transfer material P (hereinafter referred to as “residual toner”) is removed by a cleaning unit (cleaner) 5 to form the next image. To be served.
[0007]
In the above-described image forming apparatus, the charging unit 3 for temporarily charging the photosensitive drum 1 may be a contact charging type charger (magnetic brush charging, fur brush charging, roller charging, etc.) instead of a corona charger. . The contact charging type charger has an advantage that generation of ozone or the like can be reduced. The transfer charger 7 can also be a transfer roller. Basically, as described above, an image is formed through a series of image forming processes of charging, exposure, development, transfer, fixing, and cleaning.
[0008]
Recently, such image forming apparatuses have been downsized. However, it is only necessary to downsize each device that performs the image forming processes such as charging, exposure, development, transfer, fixing, and cleaning as described above. There was a limit to downsizing as a whole. The residual toner is collected as waste toner by the cleaner 5, but it is preferable that the waste toner does not occur from the viewpoint of environmental protection.
[0009]
Therefore, an image forming apparatus of a so-called cleanerless system in which the above-described cleaner 5 is removed and simultaneous development cleaning (residual toner recovery) is performed by the developing device 4 has appeared.
[0010]
The simultaneous development cleaning is the difference between the direct current voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1 for the residual toner slightly remaining on the photosensitive drum 1 after the transfer of the toner image onto the transfer material P. The potential difference V is the fog removal potential difference V_backIt is a method to collect by.
[0011]
According to this method, since the residual toner is collected and reused after the next step, waste toner can be eliminated. In addition, since there is no need to provide a cleaner 5 dedicated to cleaning, there is a great advantage in terms of space, and the overall size can be greatly reduced.
[0012]
[Problems to be solved by the invention]
However, in the above-described image forming apparatus, when the cleaner 5 was removed and simultaneous development cleaning by the developing device 4 was attempted, a positive ghost of the previous image occurred in the photosensitive drum cycle in a portion where there was no image.
[0013]
This positive ghost is because the residual toner of the previous image could not be collected in the development area or was insufficiently collected, so that the residual toner reached the transfer portion T, and originally the white background portion of the surface of the transfer material P. It is a phenomenon that occurs by being transferred to the place.
[0014]
One of the measures for preventing this positive ghost is as follows.
[0015]
As a charging means, a contact charging device is used in place of the corona charger 3, and a DC voltage is applied to the contact charging member brought into contact with the photosensitive drum 1, so that the photosensitive drum 1 is primarily charged to a predetermined polarity and a predetermined potential. At the same time, the residual toner on the photosensitive drum 1 passing through the contact charging member is aligned with the normal charging polarity to reach the developing device 4, whereby the residual toner is advantageous in the toner recoverability during development of the developing device 4. Image defects (positive ghost) can be prevented.
[0016]
However, also in this case, when a DC voltage was applied to the contact charging member and image output was performed, charging failure due to toner contamination of the contact charging member occurred just by passing several sheets. The quality of the output image has deteriorated.
[0017]
Further, when a contact transfer member (for example, a transfer roller) disposed in contact with the surface of the photosensitive drum 1 is used as a transfer unit, the contact occurs when the above-described positive ghost, cleaning failure, or jam of the transfer material P occurs. The transfer member may be contaminated with toner and cause image defects. Conventionally, in such a case, a method of transferring the contaminated toner to the photosensitive drum 1 by the cleaning bias and cleaning the contact charging member is generally performed. However, as described above, since the capability of the simultaneous development cleaning is not sufficient, the developing device There was also a problem that the toner that could not be collected in No. 4 contaminated the contact charging member again.
[0018]
In view of this, the present invention provides an image forming apparatus that performs cleaning simultaneously with development, and prevents toner contamination of the contact charging member so that it can be charged satisfactorily over a long period of time, thereby preventing deterioration in output image quality. It is intended to do.
[0019]
Another object of the present invention is to provide an image forming apparatus for performing simultaneous development cleaning, which prevents toner contamination of the contact transfer member and performs good transfer over a long period of time, thereby preventing deterioration in output image quality. It is to provide.
[0020]
[Means for Solving the Problems]
  In order to achieve the above-mentioned object, the invention according to claim 1 includes a charging means for discharging and charging the surface of the image carrier with a contact charging member, and information writing for forming an electrostatic latent image on the surface of the image carrier after charging. A toner image on the image carrier by forming an electric field between the image carrier and the developing means for developing the electrostatic latent image as a toner image with a developer carried on the developer carrier. A transfer means for transferring the toner to a transfer material, wherein the developing means serves as a cleaning means for collecting residual toner remaining on the image carrier. A power supply for applying a DC bias voltage and an asymmetrical alternating voltage in a superimposed manner, and the developing method of the developing means is a reversal developing method using toner having the same polarity as the charged polarity of the image carrier, and the alternating voltage When the ratio of turning on the charging polarity identical to the polarity side bias of the image bearing member to the duty ratio of the alternating voltage, and scope the duty ratio of 60% to 90%Then, the electric potential of the image carrier is charged to an almost intermediate value between the maximum value and the minimum value of the charging bias voltage.It is characterized by that.
[0021]
  The invention according to claim 2A charging means for discharging and charging the surface of the image carrier by a contact charging member; an information writing means for forming an electrostatic latent image on the surface of the image carrier after charging; and the electrostatic latent image is carried on the developer carrier. Developing means for developing a toner image with the developer, and transfer means for forming an electric field between the image carrier and transferring the toner image on the image carrier to a transfer material. In the image forming apparatus that also serves as a cleaning unit that collects residual toner remaining on the image carrier, a power source that applies a DC bias voltage and an asymmetrical alternating voltage as a charging bias voltage to the contact charging member is superimposed. The developing means is a normal developing system using toner having a polarity opposite to the charging polarity of the image carrier, and the bias having the same polarity as the charging polarity of the image carrier of the alternating voltage is turned on. When the that ratio and the duty ratio of the alternating voltage, characterized in that the range of the duty ratio of 10-40%.
[0022]
  The invention according to claim 33. The image forming apparatus according to claim 1, wherein the toner particles stored in the developing unit are toner generated by a polymerization method.
[0023]
  According to a fourth aspect of the present invention, there is provided charging means for discharging and charging the surface of the image carrier with a contact charging member, information writing means for forming an electrostatic latent image on the surface of the image carrier after charging, and the electrostatic latent image. A developing means for developing a toner image with a developer carried on the developer carrying member, a contact transfer member is pressed against the image carrier, and an electric field is formed between the image carrying member and the contact transfer member. A transfer unit that transfers the toner image on the image carrier to a transfer material, and the developing unit also serves as a cleaning unit that collects residual toner remaining on the image carrier.SaidThe developing method of the developing unit is a reversal developing method using toner having the same polarity as the charged polarity of the image carrier, and the residual toner remaining on the contact transfer member is removed from the contact at a predetermined timing during non-image formation. A first step of transferring to the image carrier side by forming an electric field between the transfer member and the image carrier, and a DC bias voltage and an asymmetrical alternating current as a charging bias voltage for the contact charging member When the ratio of turning on the same polarity side bias as the charging polarity of the image carrier of the alternating voltage is a duty ratio of the alternating voltage, the duty ratio is in the range of 60 to 90%. Applying the alternating voltage to the contact charging member, And charging the potential of the image carrier to an intermediate value between the maximum value and the minimum value of the charging bias voltage,And a second step of collecting the residual toner by the developing unit.
[0024]
  The invention according to claim 5A charging means for discharging and charging the surface of the image carrier by a contact charging member; an information writing means for forming an electrostatic latent image on the surface of the image carrier after charging; and the electrostatic latent image is carried on the developer carrier. A developing unit that develops a toner image with the developer, and a contact transfer member is pressed against the image carrier and an electric field is formed between the image carrier and the contact transfer member to form a toner on the image carrier. A transfer unit that transfers an image to a transfer material, wherein the developing unit also serves as a cleaning unit that collects residual toner remaining on the image carrier. This is a normal development method using toner having a polarity opposite to the charged polarity of the carrier, and the residual toner remaining on the contact transfer member at a predetermined timing during non-image formation is transferred to the contact transfer member and the image carrier. And a power source for applying a DC bias voltage and an asymmetrical alternating voltage as a charging bias voltage to the contact charging member in a superimposed manner by forming an electric field between the first charging step and the contact charging member. When the ratio of turning on the same polarity side bias as the charged polarity of the image carrier of the alternating voltage is the duty ratio of the alternating voltage, the alternating voltage with the duty ratio in the range of 10 to 40% is And a second step of charging the residual toner by applying it to a contact charging member and collecting the residual toner by the developing means..
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0026]
<Embodiment 1>
(1) Schematic configuration and operation of the entire image forming apparatus
FIG. 1 shows an example of an image forming apparatus according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of an electrophotographic laser beam printer. In the laser beam printer (hereinafter referred to as "image forming apparatus") shown in the same figure, a contact charging device is used as a charging means for charging the surface of an image carrier, and a cleanerless system that performs simultaneous development cleaning as a developing means. Is adopted.
[0027]
In the figure, A indicates a printer unit, and B indicates an image reading unit (image scanner).
[0028]
In the image reading unit B, reference numeral 13 denotes a platen glass fixedly disposed on the upper part of the image reading unit B. The original G is placed on the upper surface of the original platen glass 13 with the image surface to be copied facing downward, and is set by covering an original pressing plate (not shown) thereon. An image reading unit 14 is provided with a document irradiation lamp 14a, a short focus lens array 14b, a CCD sensor 14c, and the like. When the copy button (not shown) is pressed, the image reading unit 14 moves in the direction of the arrow K1 from the home position indicated by a solid line on the right end side in FIG. When the predetermined forward end point indicated by the broken line is reached, it is driven backward to move in the direction of the arrow K2 and return to the initial home position.
[0029]
In the forward drive process of the image reading unit 14, the downward image surface of the original G on the original platen glass 13 is sequentially illuminated and scanned in the direction of the arrow K1 by the original irradiation lamp 14a of the image reading unit 14. The document surface reflected light of the scanning light is imaged and incident on the CCD sensor 14c by the short focus lens eye 14b.
[0030]
The CCD sensor 14c 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 known image processing to be converted into a digital signal and sent to the printer unit A.
[0031]
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 unit B.
[0032]
The printer unit A includes a rotating drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image carrier. The photosensitive drum 1 is rotationally driven in the direction indicated by the arrow R1 at a predetermined peripheral speed around the central support shaft, in this embodiment at a rotational speed of 150 mm / s, and in the rotational process, first, a charging roller that constitutes a charging means. (Contact charging member) 2 is subjected to a uniform negative charging process. The charging roller 2 is disposed in contact with the photosensitive drum 1, forms a charging nip portion N between the charging roller 2 and the photosensitive drum 1, and rotates following the direction of the arrow R <b> 1 of the photosensitive drum 1 in the direction of arrow R <b> 2. Further, a predetermined charging bias is applied to the charging roller 2 from the charging bias application power source S1, whereby the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and a predetermined potential.
[0033]
Then, a laser beam output from a laser scanning unit (laser scanner) 3 serving as information writing means on the uniformly charged surface of the photosensitive drum 1, that is, an image sent from the image reading unit B side to the printer unit A side. By performing scanning exposure L with a laser beam modulated in accordance with the signal, the charge at the laser-light irradiated portion is removed. Thus, electrostatic latent images corresponding to the image information of the original G photoelectrically read by the image reading unit B are sequentially formed on the surface of the photosensitive drum 1.
[0034]
The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by a developing device (developing unit) 4. The developing device 4 has a rotatable developing sleeve 42 disposed opposite to the surface of the photosensitive drum 1, and a developing bias is applied to the developing sleeve 42 by a developing bias applying power source S 2, thereby generating an electrostatic latent image. The toner is attached and developed as a toner image. The development in the present embodiment is so-called reversal development in which toner is attached to a portion from which charges have been removed by the above-described exposure.
[0035]
On the other hand, the transfer material P stored in the paper feed cassette 6 is fed one by one by the paper feed roller 7 and fed into the printer unit A, and transferred to the photosensitive drum 1 by the registration roller 8 at a predetermined timing. It is supplied to a transfer nip T between the roller (transfer means) 5. A transfer bias having a polarity opposite to that of the toner on the photosensitive drum 1 is applied to the transfer roller 5 from a transfer bias application power source S3 at a predetermined timing, and the photosensitive drum 1 is applied to the surface of the transfer material P supplied to the transfer nip T. The toner image on the surface is electrostatically transferred.
[0036]
The transfer material P that has received the transfer of the toner image through the transfer nip T is sequentially separated from the surface of the photosensitive drum 1 and conveyed to the fixing device 10 by the conveying device 9, where the toner image is heated and pressurized. After being fixed on the surface, the paper is output as a copy or print on the paper discharge tray 12 by the discharge roller 11.
[0037]
On the other hand, the toner (transferred toner) remaining on the surface of the photosensitive drum 1 after the toner image transfer without being transferred to the transfer material P is removed by the developing device 4 as described later, and is used for the next image formation.
[0038]
Above, description of the schematic structure and operation | movement of the whole image forming apparatus is finished, and it explains in full detail for every member next.
[0039]
(2) Photosensitive drum (image carrier)
In the present embodiment, as described above, the photosensitive drum 1 is used as the image carrier. As the surface layer of the photosensitive drum 1, an organic photoreceptor or the like can be used. As an example, in the present embodiment, a function-separated OPC photosensitive drum is used, the charge generation layer uses a phthalocyanine compound having a thickness of 0.2 μm, and the charge transport layer on the surface layer side has a thickness of about 22 μm. A polycarbonate in which the hydrazone compound was dispersed was used.
[0040]
(3) Laser scanning section
FIG. 2 shows a schematic configuration of the laser scanning unit 3. When the laser scanning unit 3 performs laser scanning exposure on the surface of the photosensitive drum 1 as a surface to be scanned, first, the solid-state laser element 32 is blinked at a predetermined timing by the light emission signal generator 31 based on the input image signal ( ON / OFF). The laser light emitted from the solid-state laser element 32 is converted into a substantially parallel light beam by the collimator lens system 33, and further main-scanned in the arrow K3 direction by the rotating polygon mirror 34 that rotates at high speed in the arrow R34 direction. An image is formed in a spot shape on the surface of the photosensitive drum 1 by the fθ lens groups 35a, 35b, and 35c. By such laser beam scanning, an exposure distribution for one image scan is formed on the surface of the photosensitive drum 1, and the surface of the photosensitive drum 1 can be scrolled by a predetermined amount perpendicular to the main scanning direction for each scan. For example, an exposure distribution corresponding to the image signal is obtained on the surface of the photosensitive drum 1.
[0041]
(4) Charging roller
The charging roller 2 as a contact charging member is based on a well-known contact charging method. As an example, an elastic conductive rubber having a thickness of 3 mm has a volume resistivity of 10 to 200 mm.⁶ A medium resistance layer of about Ω · cm was provided, and an anti-adhesion layer (nylon resin or the like) of several tens of μm was further provided thereon. At this time, a metal rod such as stainless steel (SUS) was used as the core material, and the outer diameter of the charging roller itself was configured to be 12 mm in total. The charging roller 2 is brought into contact with the photosensitive drum 1 with a linear pressure of about 20 to 50 g / cm so that a charging nip portion N of about 1 to 2 mm is formed. The charging roller 2 is configured to be driven to rotate in the direction of arrow R2 as the photosensitive drum 1 rotates in the direction of arrow R1. Further, a charging bias obtained by superimposing an asymmetrical alternating voltage on a −600 V DC voltage is applied to the charging roller 2 by a charging bias power source S1.
[0042]
Here, the asymmetrical alternating voltage is a waveform in which the duty of the rectangular wave is changed as shown in FIG. 3A, and two voltages having different frequencies on the positive side and the negative side of the voltage as shown in FIG. An asymmetrical alternating voltage such as a waveform combining sine waves, a triangular pulse waveform as shown in (c), or a trapezoidal pulse waveform as shown in (d). In these figures, when minus is taken upward, V_max Is the negative maximum voltage, V_min Is the minimum negative value, V_centerIs the above-mentioned maximum value V_max And the minimum value V_min And the average value, V_rms Indicates an effective value, and by applying an asymmetrical alternating voltage, the effective value V_rms Is the average value V_centerIt is deviated (shifted to the minus side in these figures). In FIGS. 3A to 3B, all are shifted to the minus side. In any of the waveforms (a) to (d), the time T during which the voltage is negative with respect to the effective value with respect to one period T._- The duty ratio is set so as to exceed 50%, where the duty ratio is the duty ratio.
[0043]
By applying the charging bias as described above, the following can be achieved.
(1) The surface of the photosensitive drum 1 is uniformly charged to approximately -600V. At this time, since the potential history before charging is made uniform, pre-exposure can be omitted.
(2) When a small amount of residual toner is present, the charged charge (tribo) polarity and the charge amount can be controlled to predetermined values, and the residual toner adheres to the charging roller 2 Will not get dirty or splash around.
[0044]
The reason for the above (1) is that the charging to the photosensitive drum 1 by the charging roller 2 is in the air in accordance with Paschen's law, which occurs in the minute gap G near the charging nip N as shown in FIG. It is conceivable that the ratio depending on the discharge is large. That is, according to the air discharge, once the discharge is generated and the photosensitive drum 1 is charged, a charged area having a certain width is formed. Therefore, the DC voltage is not applied to the charging roller 2 without applying an alternating voltage. When only voltage is applied, rotation of the photosensitive drum 1 weakens the electric field near the charging nip N until the charged area passes through the air discharge area near the charging nip N, and the next discharge occurs. A so-called discharge relaxation time occurs. On the other hand, when the alternating voltage is superimposed on the charging roller 2, the discharge threshold value in the vicinity of the charging nip N is exceeded every time the voltage alternates. Therefore, if the alternating cycle is set shorter than the discharge relaxation time, the photosensitive drum The amount of charge by the charging roller 2 to 1 is the number of alternating times and the upper and lower peaks of the alternating voltage (V_max , V_min ) Intermediate value (= V_center) Only depends on T and T_- No longer depends on the ratio (duty ratio). Where V_max And V_min As a result, the surface potential of the photosensitive drum 1 is approximately V._centerIt seems to converge to the value, that is, -600V.
[0045]
On the other hand, the reason for the above-mentioned (2) is that the charge imparted to the residual toner t remaining on the photosensitive drum 1 is not the air discharge as in (1) but exclusively in the charging nip portion N in FIG. This is considered to be caused by charge injection. That is, in this case, the charge injection amount is V which is an effective value of the bias voltage applied to the charging roller 2._rms The tribo of the residual toner t is the application time of the alternating voltage, T and T_- Can be controlled by the ratio (duty ratio). Although the reason why the charging roller 2 is not contaminated or scattered by the residual toner t has not been fully clarified, as a comparative example, when the duty ratio of the alternating electric field is 50% (that is, plus and minus the same amount), The residual toner t adheres to the charging roller 2 to cause contamination, and a phenomenon occurs in which the toner is scattered like a cloud around the charging roller 2. From this point, the electric field action of pulling the residual toner t away from the charging roller 2 at the charging nip N and keeping it on the photosensitive drum 1 is T_- This seems to be caused by taking a long time. Specific charging bias conditions will be described in detail later.
[0046]
(5) Developer
In general, the electrostatic latent image is developed by coating non-magnetic toner on a developing sleeve with a blade or the like, and magnetic toner is coated by magnetic force and conveyed to be developed in a non-contact state with respect to the photosensitive drum. A method (one-component non-contact development), a method in which the toner coated as described above is developed in contact with a photosensitive drum (one-component contact development), and a magnetic carrier mixed with toner particles. Is used as a developer and conveyed by magnetic force and developed in contact with the photosensitive drum (two-component contact development), and the above-mentioned two-component developer is developed in a non-contact state (two-component non-development). And contact development).
[0047]
In the present embodiment, a mixture of non-magnetic toner particles and magnetic carrier particles is used as a developer, and this developer is held as a magnetic brush or the like by a magnetic force on a developing sleeve 4a as a developing carrier. A two-component contact development method is used in which the electrostatic latent image is developed as a toner image by being conveyed to the developing unit and brought into contact with the surface of the photosensitive drum 1.
[0048]
This is because it is advantageous in terms of improving the image quality and stability of the image and in terms of mechanical recovery by the magnetic brush when recovering the residual toner on the photosensitive drum 1.
[0049]
FIG. 5 is a longitudinal sectional view showing a schematic configuration of the developing device 4 of the two-component contact development method (two-component magnetic brush development) used in the present embodiment.
[0050]
In the figure, 41 is a developing container, 42 is a developing sleeve as a developer carrying member, 43 is a magnet roller as magnetic field generating means fixedly arranged in the developing sleeve 42, and 44 is carried on the surface of the developing sleeve 42. A regulating blade for regulating the layer thickness of the developer, 45 is a developer agitating and conveying screw, 46 is a two-component developer accommodated in the developing container 41, and includes nonmagnetic toner particles t, magnetic carrier particles c, Are mixed. Reference numeral 47 denotes a toner replenishing unit.
[0051]
At least during development, the developing sleeve 42 is disposed so that the closest distance (gap) to the photosensitive drum 1 is about 500 μm, and the developer magnetic brush thin layer 46 a carried on the outer surface of the developing sleeve 42 is photosensitive. It is set so as to contact the surface of the drum 1. A contact portion between the developer magnetic brush thin layer 46 a and the photosensitive drum 1 is a developing portion (developing region) D.
[0052]
The developing sleeve 42 is rotationally driven around the fixedly arranged magnet roller 43 in the direction of arrow R4 at a predetermined rotational speed, and the magnetic brush of the developer 46 is applied to the outer surface of the developing sleeve 42 in the developing container 41 by the magnetic force of the magnet roller 43. It is formed. The magnetic brush is conveyed along with the rotation of the developing sleeve 42 in the direction of the arrow R4, is subjected to the layer thickness regulation by the regulating blade 44, and is taken out of the developing container 41 as a developer magnetic brush thin layer 46a having a predetermined layer thickness to be developed D To the surface of the photosensitive drum 1, and subsequently returned to the developing container 41 by the rotation of the developing sleeve 42.
[0053]
A developing bias in which a DC voltage and an alternating voltage are superimposed is applied between the developing sleeve 42 and the conductive drum base 1a of the photosensitive drum 1 by a developing bias applying power source S2. In the present embodiment, the potential setting of the photosensitive drum 1 is set to a dark portion of −600 V and a light portion of −150 V, and a developing bias for the dark portion is set to
DC voltage; -450V,
Alternating voltage; amplitude V_PP= 1500V, frequency V_f = 2000Hz
In the developing portion D, the toner particles t in the developer magnetic thin layer 46a on the developing sleeve 42 side are selectively attached to the electrostatic latent image on the photosensitive drum 1 in the developing portion D, and the electrostatic latent image is formed. It is developed as a toner image.
[0054]
In general, in the two-component development method, when an alternating voltage is applied, the development efficiency increases and the image becomes high-quality, but conversely, there is a risk that fog is likely to occur. For this reason, normally, a fog is prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1.
[0055]
The toner concentration (mixing ratio of the toner to the carrier) of the developer 46 in the developing container 41 is gradually decreased as the toner is consumed for developing the electrostatic latent image. When the toner concentration of the developer 46 in the developing container 41 is detected by a detecting means (not shown) and falls to a predetermined allowable lower limit concentration, the toner is replenished from the toner replenishing unit 47 to the developer 46 in the developing container 41 and developed. The toner supply control is performed so that the toner concentration of the developer 46 in the container 41 is always kept within a predetermined allowable range.
[0056]
The two-component developer 46 used in this embodiment is
Toner particles t; a negatively charged toner having an average volume particle diameter of 6 μm manufactured by a pulverization method and titanium oxide added externally at a weight ratio of 1%.
Carrier c; saturation magnetization is 205 emu / cm^Three Magnetic carrier with an average particle size of 35 μm
In a weight ratio of 6:94.
[0057]
Here, a method for measuring the toner particle size distribution in the present invention will be described.
[0058]
As a measuring device, a Coulter counter TA-2 type (manufactured by Coulter Co.) was used, and an interface (manufactured by Nikkiki) and CX-1 personal computer (manufactured by Canon) for outputting the number average distribution and volume average distribution were connected, and The solution is adjusted to a 1% NaCl aqueous solution using primary sodium chloride.
[0059]
As a measuring method, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the above-mentioned electrolytic aqueous solution, and 0.5 to 50 mg of a measurement sample is further added.
[0060]
The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the particle size distribution of particles of 2 to 40 μm is obtained by using the above-mentioned Coulter counter TA-2 type using a 100 μ aperture as the aperture. Measure to obtain a volume average distribution. The volume average particle diameter is obtained from the obtained volume average distribution.
[0061]
The developer circulation system in the developing device 4 will be described. First, as the developing sleeve 42 rotates, the N of the magnet roller 43 is increased._Three The developer 46 pumped up at the pole is S₂ Pole → N₁ In the process of being conveyed to the pole, the developer magnetic brush thin layer 46 a is formed on the developing sleeve 42 by being regulated by the regulating blade 44 arranged perpendicular to the developing sleeve 42. The thin developer magnetic brush thin layer 46a is formed into the developing main pole S of the developing section D.₁ When it is transported to the head, the head is formed by the magnetic force. The electrostatic latent image on the photosensitive drum 1 is developed as a toner image by the developer magnetic brush thin layer 46a formed in the shape of a spike, and also remains on the photosensitive drum 1 as a residual toner in the image forming process described above. The toner that is normally charged (negative) by 2 is collected in the developer magnetic brush thin layer 46 a on the developing sleeve 42. Then N₂ Pole and N_Three The developer on the developing sleeve 42 is returned into the developing container 41 by the repulsive magnetic field of the pole.
[0062]
(6) Transfer roller (transfer means)
In the present embodiment, the transfer roller 5 is used as the transfer means. The transfer roller 5 is in predetermined contact with the photosensitive drum 1 to form a transfer nip portion T as a transfer portion. The transfer roller 5 in the present embodiment is composed of a cored bar made of a conductive rigid material such as a metal having an outer diameter of 8 mm, and a conductive elastic layer surrounding its outer peripheral surface, that is, urethane, EPDM (ethylene propylene dimethyl rubber), or the like. Disperse a conductive material such as carbon to make the resistance value 10^Five -10^TenThe outer diameter of the conductive elastic layer is 16 mm. The conductive elastic layer is formed of a foamed elastic body adjusted to about 20 to 50 degrees in Ω · cm and Asker C hardness. The transfer roller 5 is driven to rotate at a constant speed in the direction of the arrow R5 as the photosensitive drum 1 rotates in the direction of the arrow R1. At the time of transfer, a negative polarity toner that forms a toner image between the photosensitive drum 1 and the transfer roller 5 by applying a DC voltage of about +4 kV as a transfer bias to the core of the transfer roller 5 from the transfer bias application power source S3. Electrostatic transfer is performed by forming a transfer electric field in the direction in which the particles are transferred to the transfer material P.
[0063]
(7) Simultaneous development cleaning by developing device 4 (residual toner recovery)
Residual toner remains on the surface of the photosensitive drum 1 after the transfer of the toner image to the transfer material P. This residual toner not only reverses the charging polarity due to peeling discharge or transfer charge injection during transfer, but also charges the surface of the photosensitive drum 1 after transfer slightly positively (about + several tens of volts). It often ends up.
[0064]
It is difficult for the developing device 4 to simultaneously collect the development of the toner whose polarity is reversed in this way. Further, since the photosensitive drum 1 whose potential is reversed in this way is to be charged, the difference between the voltage applied to the transfer roller 5 and the charging potential of the photosensitive drum 1 becomes large, and the charging ability is lowered.
[0065]
On the other hand, according to the present invention, as described above in the charging roller 2, the duty ratio of the alternating electric field, that is, the duty ratio that is the ratio of turning on the bias on the same polarity side as the photosensitive drum charging polarity is adjusted. In addition, while maintaining good uniform chargeability, it is possible to control the residual toner tribo to an optimum state, and the above-described simultaneous development and recovery can be performed satisfactorily. As an example, a rectangular charging bias as shown in FIG. 3A is used, the frequency is 2 kHz, and V_centerIs set to −600 V as described above, and the amplitude voltage V_PP(V_max , V_min Potential difference) is 2000V, that is, V_max -1600V, V_min + 400V, duty ratio (T to T_- ) Is 70%, the surface potential on the photosensitive drum 1 is uniformly charged to approximately −600 V, and the residual toner tribo after passing through the charging roller 2 (directly from the surface of the photosensitive drum 1 by the suction method). (Measured by suction) was controlled to about −10 to −70 μC / g, and the development device 4 could easily collect the development simultaneously. In this state, about 5000 prints were repeatedly performed, but there was almost no contamination due to the toner adhering to the charging roller 2, and toner scattering to the surroundings did not occur.
[0066]
As for the aforementioned duty ratio, good results were obtained at 60 to 90% in the present embodiment. On the other hand, when the duty ratio is 60% or less, the toner recovery to the developing device 4 is not performed satisfactorily, and the ghost image and the toner scattering in the charging unit (near the charging roller 2) occur. On the other hand, when the duty ratio is 90% or more, the charging potential of the photosensitive drum 1 is shifted to the minus side, and the potential convergence effect is deteriorated.
[0067]
<Embodiment 2>
In the above-described first embodiment, a so-called reversal development method for developing the image exposure portion (light irradiation portion) in the electrostatic latent image on the photosensitive drum 1 has been described. In the second embodiment, the non-exposure portion is used. A case where the present invention is applied to a so-called regular development method for development will be described.
[0068]
This regular development method is a method generally used in a so-called analog copying machine that directly forms an image by reflected light from the image surface of the original G when the original G is exposed, and is also used in some laser beam printers. However, the main difference in configuration with the first embodiment is that the charging polarity of the photosensitive drum 1 and the charging polarity of the toner, which were the same polarity in the first embodiment, are opposite in the second embodiment. It is a point that becomes polar.
[0069]
Therefore, in the present embodiment, only this point will be described in detail, and description of other parts will be omitted.
[0070]
In order to carry out the regular development method described above, only one of the polarity of the photosensitive drum 1 and the polarity of the toner in the first embodiment should be reversed. Here, a case where the polarity of the photosensitive drum 1 is reversed (plus) will be described.
[0071]
Specifically, an amorphous silicon drum having a positive charge polarity was used as the photosensitive drum 1, and a layer structure having a Si—C protective layer provided on the surface of the amorphous silicon layer was used. .
[0072]
The same toner as in Embodiment 1 was used, and the charging potential of the photosensitive drum was set to about + 450V. Further, the bright portion potential (which becomes the background potential) which is the exposed portion was set to + 50V.
[0073]
Since the polarity of the toner is the same as that of the first embodiment, the same polarity as that of the first embodiment can be used as the transfer bias, but the developing bias is set to +150 V by reversing the polarity of the DC voltage. Further, the value of the transfer bias was increased by about 300 V to a DC bias voltage of about +4.3 kV.
[0074]
Next, regarding the bias applied to the charging roller 2, the polarity of the DC bias voltage was reversed to + 500V. This takes into account dark decay until the development position is reached after the amorphous silicon is charged.
[0075]
On the other hand, for the asymmetrical alternating voltage, as shown in FIGS. 6A to 6D, plus is taken above the vertical axis, and the positive maximum value of the voltage is V_max , The minimum value is V_min And V_center, V_rms (Effective value) The time during which the voltage is positive for one period T is T₊ And the like are defined following the first embodiment.
[0076]
Here, in regular development, since the polarity of the toner is negative in this embodiment, the time T with respect to T₊ Is set to be smaller than 50%. Thus, according to the same principle as described in the first embodiment, the charging performance is always V._centerAccording to this value, a uniform dark potential is formed on the surface of the photosensitive drum 1, while the residual toner tribos are aligned to a predetermined negative value according to the duty ratio, and good simultaneous development recovery can be performed in the developing unit.
[0077]
As an example, the rectangular wave bias shown in FIG._PP= V_max -V_min 2000V, V_max + 1500V, V_min By setting the voltage to −500 V and the duty ratio to 30%, good simultaneous recovery of development can be performed, and at this time, contamination of the charging roller 2 and toner scattering due to durability at the charged portion did not occur.
[0078]
The above-described duty ratio was 10% to 40% in the present embodiment, and good results were obtained. On the other hand, when the duty ratio is 40% or more, the toner recovery to the developing device 4 is not performed satisfactorily, and the ghost image and the toner scattering in the charging portion occur. Further, if it is 10% or less, the charged potential of the photosensitive drum 1 is shifted to the negative side, and the potential convergence effect is deteriorated.
[0079]
<Embodiment 3>
Embodiment 3 is shown below. In the present embodiment, in the image forming apparatuses of the first and second embodiments described above, the toner of the developer to be used is a toner generated by a polymerization method. It is the same. The repetitive description of similar parts is omitted.
[0080]
In the image forming apparatuses according to the first and second embodiments, the toner produced by the pulverization method is used as the toner particles t of the developer 46. In this example, the average particle size produced by the suspension polymerization method is 6 μm. Titanium oxide having an average particle diameter of 20 mm and 1% by weight added to the spherical toner was used.
[0081]
The magnetic carrier c has a saturation magnetization of 205 emu / cm.^Three A magnetic carrier having an average particle size of 35 μm was used.
[0082]
A mixture of the above toner particles t and carrier particles c in a weight ratio of 6:94 was used as the developer 46. Since the toner produced by the polymerization method has a nearly spherical shape, the external additive is uniformly coated. For this reason, the releasability from the photosensitive drum 1 is very good. Further, recharging by the charging roller 2 can be performed more stably and uniformly. Therefore, for example, when the transfer efficiency (the amount of toner per unit area transferred onto the transfer material P / the amount of toner per unit area on the photosensitive drum 1) is compared between the pulverized toner and the polymerized toner, the pulverized toner is 90%. When the polymerized toner was used, the efficiency was as high as 97%. Further, the fog is also better than the pulverized toner._backThe fogging could be prevented even at 50V.
[0083]
Using such a polymerized toner, the same examination as in Embodiments 1 and 2 was conducted. In this embodiment, in addition to the extremely small amount of residual toner, it is highly releasable. When the cleanerless system / development simultaneous cleaning configuration is adopted, the residual toner recoverability is further improved, and image defects do not occur at all.
[0084]
Note that the use of spherical toners including those produced by the polymerization method has an effect of making the coating of the external additive uniform on the toner and facilitating toner movement by an electric field. For this reason, the present invention can be effectively carried out other than the two-component development method using the magnetic carrier particles c used in the present embodiment. For example, even in a one-component development method that does not use a carrier, a toner is coated on a developing sleeve having a conductive elastic body provided on the surface, and this is brought into contact with the photosensitive drum 1. By using the spherical toner manufactured by this method, the simultaneous development and recovery system using the present invention can be effectively operated.
[0085]
<Embodiment 4>
In the first embodiment, an embodiment in which the charging roller 2 that is a roller-type contact charging member is used has been described. However, as shown in FIG. 7, a fixed blade-type charging member is used as the contact charging member. Can be used. The charging blade 20 is a phosphor bronze plate having a free length (rotating direction of the photosensitive drum 1) of 20 mm and a thickness of 120 μm as a back plate 21, an elastic conductive rubber layer having a thickness of about 1 mm thereon, and a further 100 to 200 μm thereon. Thickness, volume resistivity 10⁶ A medium resistance layer of about Ω · cm and a surface layer provided with a charging layer 22 made of an anti-adhesion layer (nylon-based resin or the like) of several tens of μm were used. The contact direction was the forward direction with respect to the rotation direction of the photosensitive drum 1 (the direction of the arrow R1), and the linear pressure was set to several g / cm. Also in this method, the charging nip N and the discharge region G in the vicinity of the charging nip₁ , G₂ Can be formed.
[0086]
Therefore, charging of the photosensitive drum 1 is performed in the discharge region G.₁ , G₂ In addition, the charge application to the residual toner can be performed in the charging nip portion N.
[0087]
In the present embodiment, the width of the charging nip portion N (the length in the direction along the rotation direction of the photosensitive drum 1) is formed approximately 1 to 2 mm, and the charging bias application condition by the transfer bias application power source S1 is as follows. Good results were obtained under the same conditions as in the first embodiment.
[0088]
According to the configuration of the present embodiment, the entire image forming apparatus can be configured more compactly than in the case of the charging roller 2, and charging can be performed by the spring force of the back plate 21 and the contact method. Nip part N, discharge area G₁ , G₂ There is an advantage that can be freely adjusted to some extent. Although FIG. 7 of the present embodiment shows an example in which the charging blade 20 is contacted in the forward direction, the distance between the charging nip portion N and the contact end is ensured to some extent (about several mm). In this case, even if the contact is made in the counter direction, the toner can be scraped without accumulating, and the contact pressure can be stabilized.
[0089]
Further, in the fourth embodiment, particularly when used in combination with the polymerized (spherical) toner of the third embodiment, the toner can be easily rubbed off at the charging nip portion N, and good results can be obtained. it can.
[0090]
<Embodiment 5>
The present embodiment relates to a method for cleaning the transfer roller 5 when the transfer roller 5 is contaminated with residual toner in the event of a jam or the like. Here, the basic configuration will be described according to the first embodiment.
[0091]
In FIG. 1, the transfer roller 5 may be directly subjected to toner contamination without the transfer material P due to, for example, a paper feed jam. In this case, the residual toner of normal polarity and the residual toner whose polarity is reversed by a partial transfer electric field or the like are mixedly attached on the transfer roller 5.
[0092]
Therefore, when the power is turned on again after the jam processing, as shown in FIG. 8, first, the positive and negative transfer biases are transferred to the transfer roller 5 using the transfer bias application power source S3 in the rotation state of the photosensitive drum 1, respectively. By providing the first step of alternately applying the roller 5 over one rotation, the contaminated toner having positive and negative charges is transferred from the transfer roller 5 to the photosensitive drum 1. Here, the surface of the photosensitive drum 1 is charged to a normal dark potential (background potential in reversal development) by the charging roller 2 in advance, so that the asymmetrical alternating voltage described in the first embodiment causes the positive and negative. The contaminated toner having the electric charge is uniformly recharged to the negative polarity. Next, by providing a second step in which the developing device 4 is operated under normal image forming conditions, the recharged contaminated toner is developed by the potential difference between the potential of the photosensitive drum 1 and the potential of the developing sleeve 42. It is collected in the device 4.
[0093]
Finally, the DC bias voltage is turned off as the bias voltage of the charging roller 2, the surface of the photosensitive drum 1 is neutralized to about 0 V by an alternating bias, and the cleaning process is completed.
[0094]
In this embodiment, based on the first embodiment, the charging potential of the photosensitive drum 1 is approximately −600 V during cleaning, the DC voltage of the developing bias is −450 V, and an AC bias is applied thereto. As the cleaning bias applied to 5, −2 kV is used as the transfer (−) bias and +2 kV is used as the transfer (+) bias, so that the contaminated toner on the transfer roller 5 is collected in the developing device 4 via the photosensitive drum 1. We were able to.
[0095]
Note that various combinations other than the above can be used for the above-described bias value. For example, the DC bias voltage to the charging roller 2 is set to -150 V, the development DC bias voltage is set to 0 V, or the like. The DC bias voltage to the charging roller 2 may be 0V, the development DC bias voltage may be + 150V, or the like.
[0096]
In the present embodiment, the case of the reversal development method has been described, but it goes without saying that the present embodiment can be similarly applied to the case of the regular development method as in the second embodiment.
[0097]
Further, this cleaning process can be executed at the time of non-image formation such as between the transfer materials, for example, at the time of jamming and when the power is turned on, for example, during the pre-printing process at the time of printing or at the time of idling in the post-printing process .
[0098]
In the above-described embodiment, the case where the polarity of the residual toner is controlled to the negative polarity that is the normal polarity by the charging roller 2 has been described. However, the first process and the second process described above are non-images. Since it is performed in the formed state, it is not necessary to perform simultaneous development at the time of collection by the developing device 4. Therefore, for example, by setting the duty ratio of the alternating bias applied to the charging roller 2 to 10 to 40%, charging the residual toner to the positive polarity, and appropriately adjusting the values of the development DC bias voltage and the charging DC bias voltage. The residual toner in the developing device 4 may be collected by shifting the developing DC bias voltage largely in the minus direction from the photosensitive drum potential.
[0099]
【The invention's effect】
As described above, according to the present invention, a DC bias voltage and an asymmetrical alternating bias voltage with different duty ratios are applied as a charging bias voltage to a contact charging member disposed in contact with the image carrier. With a simple configuration, it is possible to uniformly charge the surface of the image carrier and to apply a stable tribo with a predetermined polarity to the residual toner, so that good simultaneous development cleaning can be performed. As a result, it is possible to prevent a charging failure caused by the contact charging member being contaminated by the residual toner, and to form a good image over a long period of time.
[0100]
Even when the contact transfer member is contaminated with residual toner, after transferring the residual toner on the contact transfer member to the image carrier, the contact charging member is charged with a DC bias voltage and a duty ratio as a charging bias voltage. A simple configuration in which asymmetrical alternating bias voltages having different voltages are applied in a superimposed manner makes it possible to uniformly charge the surface of the image carrier and to apply a stable tribo with a predetermined polarity to the residual toner, thus providing good simultaneous development cleaning. It can be performed. As a result, it is possible to effectively prevent image defects and stains on the back side of the transfer material due to the contact transfer member being contaminated by residual toner.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.
2 shows a configuration of an optical system in Embodiment 1. FIG.
3A, 3B, 3C, and 3D are diagrams showing asymmetric charging biases in Embodiment 1. FIG.
FIG. 4 is a diagram for explaining the application of electric charge to residual toner in the first embodiment.
FIG. 5 is a longitudinal sectional view showing a schematic configuration of a developing device according to the first embodiment.
6A, 6B, 6C, and 6D are diagrams showing asymmetrical electric band biases in Embodiment 2. FIGS.
FIG. 7 is a diagram for explaining the application of electric charge to residual toner in Embodiment 4.
FIG. 8 illustrates an operation in Embodiment Mode 5;
FIG. 9ConventionalFIG. 2 is a longitudinal sectional view showing a schematic configuration of the image forming apparatus.
[Explanation of symbols]
1 Image carrier (photosensitive drum)
2 Charging means (contact charging member, charging roller)
3 Information writing means (laser operation part)
4 Development means (developing device)
5 Transfer means (contact transfer member, transfer roller)
20 Charging means (contact charging member, charging blade)
46 Developer
P transfer material
S1 power supply (charging bias application power supply)
S2 Development bias application power supply
S3 Transfer bias application power supply

Claims (5)

A charging means for discharging and charging the surface of the image carrier by a contact charging member; an information writing means for forming an electrostatic latent image on the surface of the image carrier after charging; and the electrostatic latent image is carried on the developer carrier. Developing means for developing a toner image with the developer, and transfer means for forming an electric field between the image carrier and transferring the toner image on the image carrier to a transfer material. In the image forming apparatus that also serves as a cleaning unit that collects residual toner remaining on the image carrier,
A power supply that superimposes and applies a DC bias voltage and an asymmetrical alternating voltage as a charging bias voltage to the contact charging member,
The developing method of the developing means is a reversal developing method using a toner having the same polarity as the charged polarity of the image carrier,
When the ratio of turning on the same polarity side bias as the charging polarity of the image carrier of the alternating voltage is the duty ratio of the alternating voltage, the duty ratio is in the range of 60 to 90%, and the potential of the image carrier is An image forming apparatus , wherein the charging bias voltage is charged to an intermediate value between a maximum value and a minimum value . A charging means for discharging and charging the surface of the image carrier by a contact charging member; an information writing means for forming an electrostatic latent image on the surface of the image carrier after charging; and the electrostatic latent image is carried on the developer carrier. Developing means for developing a toner image with the developer, and transfer means for forming an electric field between the image carrier and transferring the toner image on the image carrier to a transfer material. In the image forming apparatus that also serves as a cleaning unit that collects residual toner remaining on the image carrier,
A power supply that superimposes and applies a DC bias voltage and an asymmetrical alternating voltage as a charging bias voltage to the contact charging member,
The developing method of the developing means is a regular developing method using a toner having a polarity opposite to the charged polarity of the image carrier.
An image forming apparatus characterized in that the duty ratio is in the range of 10 to 40%, where the duty ratio of the alternating voltage is the ratio of turning on the same polarity side bias as the charging polarity of the image carrier of the alternating voltage. .   The image forming apparatus according to claim 1, wherein the toner particles contained in the developing unit are toner generated by a polymerization method. A charging means for discharging and charging the surface of the image carrier by a contact charging member; an information writing means for forming an electrostatic latent image on the surface of the image carrier after charging; and the electrostatic latent image is carried on the developer carrier. A developing unit that develops a toner image with the developer, and a contact transfer member is pressed against the image carrier and an electric field is formed between the image carrier and the contact transfer member to form a toner on the image carrier. An image forming apparatus including a transfer unit that transfers an image to a transfer material, and the developing unit also serves as a cleaning unit that collects residual toner remaining on the image carrier.
The developing system of developing means is a reverse developing method using the toner charging polarity and same polarity of the image bearing member,
A first toner is transferred to the image carrier side by forming an electric field between the contact transfer member and the image carrier at a predetermined timing during non-image formation by forming an electric field between the contact transfer member and the image carrier. Process,
A power supply that superimposes and applies a DC bias voltage and an asymmetrical alternating voltage as a charging bias voltage to the contact charging member,
When the ratio of turning on the same polarity side bias as the charging polarity of the image carrier of the alternating voltage is the duty ratio of the alternating voltage, the alternating voltage having the duty ratio in the range of 60 to 90% is set to the contact charging member. And a second step of charging the potential of the image carrier to an approximately intermediate value between the maximum value and the minimum value of the charging bias voltage, and collecting the residual toner by the developing unit. An image forming apparatus. A charging means for discharging and charging the surface of the image carrier by a contact charging member; an information writing means for forming an electrostatic latent image on the surface of the image carrier after charging; and the electrostatic latent image is carried on the developer carrier. A developing unit that develops a toner image with the developer, and a contact transfer member is pressed against the image carrier and an electric field is formed between the image carrier and the contact transfer member to form a toner on the image carrier. An image forming apparatus including a transfer unit that transfers an image to a transfer material, and the developing unit also serves as a cleaning unit that collects residual toner remaining on the image carrier.
The developing method of the developing means is a regular developing method using a toner having a polarity opposite to the charged polarity of the image carrier.
A first toner is transferred to the image carrier side by forming an electric field between the contact transfer member and the image carrier at a predetermined timing during non-image formation by forming an electric field between the contact transfer member and the image carrier. Process,
A power supply that superimposes and applies a DC bias voltage and an asymmetrical alternating voltage as a charging bias voltage to the contact charging member,
When the ratio of turning on the same polarity side bias as the charging polarity of the image carrier of the alternating voltage is the duty ratio of the alternating voltage, the alternating voltage having the duty ratio in the range of 10 to 40% is used as the contact charging member. And a second step of charging the residual toner by the developing means and collecting the residual toner by the developing means.

Images