JP2000066492A - Method and device for developing, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of preventing the second color from the hue change, at the time of forming laminated images on the image carrier, and obtaining the image of the excellent hue, in furnishing satisfactory reflection density, and moreover to provide a developing device and the image forming device capable of obtaining the excellent image, provided with supreme developing property and developing stability, being made possible to restrain the absorption or the void caused the non-contact development, and to obtain the satisfactory density. SOLUTION: As for this developing method for developing the electrostatic latent image formed on a photoreceptor by making the developer possible to be carried/transported by a developing sleeve in a state of non-contact with regard to a photoreceptor, and applying the developing bias voltage consisting of AC voltage being superimposed with the DC voltage on the developing sleeve, the processing stage for forming an electric field capable attract/returning back the traveling developer from the photoreceptor to the developing sleeve is set at least, twice or more in cycle of the developing bias voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for forming a visible image by developing an electrostatic latent image on an image carrier, and a copying machine, a printer, a facsimile machine, etc., having the developing device for forming an image. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a developer is carried on the surface of a developer carrier, and the developer is conveyed to a development area facing an image carrier carrying an electrostatic latent image. 2. Description of the Related Art There is known an image forming apparatus that develops an electrostatic latent image to form a visible image while continuously superimposing an AC voltage on a voltage and applying the AC voltage.

Further, when developing an electrostatic latent image, a contact developing method such as a magnetic brush development in which a developer layer carried on a developer carrier is rubbed against the image carrier to develop the image, and There is known a non-contact developing method in which toner particles are caused to fly in an air layer from a developer carrier toward an image carrier to develop an electrostatic latent image. In this non-contact developing method, the voltage applied to the developer carrier is obtained by superimposing a symmetrical AC voltage on a DC voltage.

[0004]

On the image carrier, Y, M,
When a color image is formed by superimposing four color toners of C and K, it is necessary to use the non-contact developing method as described above. However, the voltage waveform applied to the developer carrier is in the case of a symmetric waveform AC voltage is applied to the symmetrical, in order to increase the developability by the toner, increasing the AC voltage V _AC, the toner which has been previously developed on the image bearing member, different in the next development step In some cases, the developer returned to the developer carrying member carrying the color toner, causing color mixing in the developing device.

In order to eliminate the toner return, it is effective to reduce the _AC voltage VAC, but at this time, there is a disadvantage that the toner developability is also reduced. Therefore, means for improving the toner developability without causing color mixing in the developing device has been desired.

The DC voltage _VDC and the AC voltage V
_{When AC} is superimposed and applied, the AC waveform changes the developing drive direction in which the toner moves from the developer carrier to the image carrier,
The asymmetrical voltage waveform in which the toner returns from the image carrier to the developer carrier in the returning direction is asymmetric, the electric field in the developing driving direction is increased, and the electric field in the returning direction is reduced, so that the toner developability is improved. Patents have been filed in recent years (Japanese Patent Application Laid-Open Nos. 8-286677 and 7-333).
957 publications).

[0007] This asymmetrical voltage waveform has a DC voltage V unless the integral values of the waveforms in the developing drive direction and the return direction are the same.
_{Since DC} substantially fluctuates, it is necessary to make the waveform integration values in the developing drive direction and the return direction the same.

Accordingly, in the asymmetrical voltage waveform, the electric field in the return direction decreases the absolute value, the application time increases, and the electric field in the developing driving direction increases by the absolute value.
The application time is shortened to improve the toner developability without substantially changing the DC voltage _VDC .

The movement of the toner flying from the developer carrier to the image carrier and the movement of the toner returning from the image carrier to the developer carrier are related to the electric field and time.

In order to improve developability without causing toner return (peeling) from the image carrier to the developer carrier,
It is most effective to reduce the absolute value of the electric field in the return direction and to shorten the time for applying the electric field in the return direction. However, when the duty is increased in the asymmetric waveform compared to the symmetric waveform, the electric field in the return direction is applied. The time required for the cleaning was relatively long, and peeling occurred, so that the maximum effect in improving the developing property could not be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the developability in a non-contact developing method without causing a peeling phenomenon in which a toner image formed on an image carrier is pulled back to a developer carrier side. is there.

[0012]

According to the present invention, there is provided a developing method for carrying out the present invention, wherein a developer is carried on an image carrier in a non-contact state, and the developer is carried on the image carrier. A developing bias voltage comprising an AC voltage in which a DC voltage is superimposed on a developer carrier to develop an electrostatic latent image formed on the image carrier, wherein the developer is transferred from the image carrier to the developer. The step of forming a pull-back electric field in which the developer moves on the carrier is set at least twice or more within one cycle of the developing bias voltage (claim 1).

According to another aspect of the present invention, there is provided a developing device having a developer carrier for carrying a developer in a non-contact state with an image carrier, and a DC electric field is superimposed on the developer carrier. Applying a developing bias voltage composed of the obtained AC voltage,
A developing device for developing an electrostatic latent image formed on the image carrier with a developer carried by the developer carrier, wherein a developer is transferred from the image carrier to the developer carrier. The step of forming the moving pull-back electric field is controlled by a waveform control circuit that is set at least twice within one cycle of the developing bias voltage (claim 3).

Further, in an image forming apparatus for forming an image of a plurality of colors by superimposing them on an image carrier, a plurality of the developing devices according to claim 3 or 4 are provided for each color of the image of the plurality of colors. By forming an electrostatic latent image on the image carrier for each color of a plurality of color images and developing the electrostatic latent image by the developing device, a plurality of colors are superimposed on the image carrier. A combined image is formed (claim 5).

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of an embodiment of the present invention, the structure of a color printer as an example of the image forming apparatus of the present invention and its operation will be described with reference to the sectional view of FIG.

In this color printer, each color toner image sequentially formed on an image carrier is superimposed, then transferred once on a recording sheet by a transfer section to form a color image, and then separated by a separating means. This is a color image forming apparatus that separates recording paper from the surface of a carrier.

In FIG. 1, reference numeral 1 denotes a photosensitive drum (photosensitive member) serving as an image bearing member, which is formed by applying an OPC photosensitive member (organic photosensitive member) on a drum base, and is grounded in a clockwise direction shown in FIG. Rotate. 2 is a scorotron charger (hereinafter, referred to as a charger), a uniform charging of the photosensitive member charge potential V _H on the high potential to the peripheral surface of the photosensitive member 1, and the grid, which is the potential held at grid potential V _G Provided by corona discharge with corona discharge wire. Prior to charging by the charger 2,
In order to eliminate the history of the photoreceptor 1 up to now, the peripheral surface of the photoreceptor 1 is discharged by performing exposure by a pre-charging static eliminator (PCL) 8 using a light emitting diode or the like. The history on the photoreceptor 1 refers to an electrostatic latent image pattern remaining on the photoreceptor 1 formed by charging and image exposure during preceding image formation.

After the photosensitive member 1 is uniformly charged, image exposure based on an image signal is performed by the image exposing means 3, and the photosensitive member 1 is charged.
An electrostatic latent image is formed on the upper surface. The image exposure means 3 performs a main scan through a polygon mirror, an fθ lens, a cylindrical lens, and a reflection mirror which rotate by using a laser diode (not shown) as a light emitting light source. The latent image is formed by the rotation (sub-scan) of the photoconductor 1. It is formed. In this embodiment, the portion where the toner is to be adhered is exposed, and the absolute potential of the latent image potential _VL of the image portion (exposed portion) on the photoconductor 1 is changed to the photoconductor charge on the photoconductor 1. An inverted latent image having a potential lower than the absolute potential of the potential V _H is formed (│V _H │>
│V _L │).

A plurality of developing devices each including a two-component developer including a toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier are provided on the periphery of the photosensitive member 1. 4Y, 4M, 4C, 4K developing device 4
Is provided.

First, development of the first color yellow is performed by a developer carrier (developing sleeve) 41 which contains a magnetic field generating means 42 composed of a plurality of magnets and rotates while holding the developer. The developer consists of a carrier with magnetite as the core and an insulating resin coated around it, and a toner with a pigment and a charge control agent according to the color with polyester as the main material, silica, titanium oxide, etc.
The developer is regulated to a developer layer thickness of 100 to 600 μm on the developing sleeve 41 by a later-described developer layer regulating member 43, and is conveyed to the developing area.

The gap between the developing sleeve 41 and the photosensitive member 1 in the developing area is 0.5 to 1.0, which is larger than the thickness of the developer layer.
As mm, an AC voltage V _AC and the DC voltage V _DC is applied to overlap therebetween. DC voltage V _DC and the photosensitive member charge potential V _H, for charging the toner are the same polarity, the AC voltage V _AC
Toner given the opportunity to leave from the carrier by did not attach to the high portion of the photosensitive member charge potential V _H absolute potential than the DC voltage V _DC, low image portion of the DC voltage V _{D C} than the absolute potential (exposure And the latent image potential _VL of the portion (image portion), and visualization (reversal development) is performed.

After the visualization of the first color is completed, the image forming process for the magenta of the second color is started, and the scorotron charger 2 is again turned on.
, And a latent image based on the image data of the second color is formed by the image exposure unit 3. At this time, the charge elimination by the PCL 8 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to a sharp decrease in the surrounding potential.

[0023] Among the photosensitive surface which is charged to the charging potential V _H over the entire surface of the photosensitive member 1 the circumferential surface again, one for the portion having no color image similar latent image and the first color is made development However, in the portion where the image of the first color is developed again for the portion where the image of the first color is present, the latent image potential _VL of the exposed portion of the first color is reduced by the influence of the light shielding by the toner attached to the first color and the charge of the toner itself. also a latent image of a slightly higher voltage V _M is formed, developed in accordance with the voltage of the DC bias voltage V _DC and the potential V _M is performed.

For the third color cyan and the fourth color black, an image forming process similar to that for the second color magenta is performed, and four color toner images are formed on the peripheral surface of the photosensitive member 1.

The developing units 4Y, 4M, 4C, and 4K include:
New toner of each color is supplied from the toner cartridge 5 (Y, M, C, K).

On the other hand, the half moon roller 2
1 recording medium (transfer paper, etc.) P unloaded through
Is temporarily stopped in the vicinity of the registration sensor position via the intermediate sheet feeding roller pairs 22A and 22B, and is fed to the transfer area by the rotation operation of the registration roller pair 23 of the sheet feeding unit when the transfer timing is adjusted. You.

In the transfer area, a transfer roller 6 for applying a voltage for transferring a toner image to the peripheral surface of the photosensitive member 1 is pressed against the peripheral surface of the photoconductor 1 in synchronization with the transfer timing, and the fed recording medium P is pinched. Then, the four color toner images are collectively transferred to the recording medium P.

Next, the recording medium P is neutralized by the sawtooth electrode 7 and separated from the peripheral surface of the photoreceptor 1 to form the fixing device 2.
4, and the toner transferred by heating and pressing of the heat roller (upper roller) 241 and the pressure roller (lower roller) 242 is welded, and then the paper discharge roller pair 25A, 25
B and 25C, and are discharged onto a discharge tray 26 outside the apparatus. After passing through the recording medium P, the transfer roller 6 is retracted from the peripheral surface of the photoreceptor 1 to prepare for the formation of the next toner image.

On the other hand, the photosensitive member 1 from which the recording medium P is separated is
The residual toner is removed and cleaned by the pressure contact of the blade 91 of the cleaning device 9, and is again subjected to the charge removal by the PCL 8 and the charge by the scorotron charger 2 to enter the next image forming process. The blade 91 moves immediately after cleaning the surface of the photoconductor 1 and retracts from the peripheral surface of the photoconductor 1. The waste toner scraped into the cleaning device 9 by the blade 91 is discharged by a screw 92 and then stored in a waste toner collecting container (not shown).

FIG. 2 shows a plurality of sets of developing units 4Y and 4Y according to the present invention.
FIG. 4 is a sectional view of a developing device 4 including 4M, 4C, and 4K.
In these developing units 4Y, 4M, 4C, and 4K, the respective developing sleeves 41Y, 41M, 41C, and 41K are arranged in parallel in the vertical direction so as to face the photosensitive surface of the photosensitive member 1.

The plural sets of developing units 4Y, 4M, 4C,
Since 4K has almost the same structure, the following description will be made on behalf of the developing device 4Y.

FIG. 3 is a sectional view of the developing unit 4Y.

In the figure, reference numeral 40 denotes a developer accommodating portion for accommodating a two-component developer composed of a toner and a carrier; 41, a developer carrying member (developing sleeve) for carrying and transporting the developer; A magnetic field generating means (hereinafter, referred to as a magnet roll) having a plurality of fixed magnets disposed therein, and a developer layer 43 formed of a non-magnetic round bar for regulating the thickness of the developer layer on the developing sleeve 41 to a predetermined amount A regulating member (a member that regulates the rising of the developer). 44 is a scraper for removing the developer adhered on the developing sleeve 41 after development, and 45 is a scraper for removing the developing sleeve 4 from the developing sleeve 41.
A paddle wheel-shaped developer conveying roller for conveying the developer removed from the peripheral surface of the developing device 1 to the developer stirring section, and a paddle wheel-shaped developer 46 for supplying the developer to the developing sleeve 41 from the developer stirring section Supply roller, 47A, 47
B is a developer stirring screw for stirring the developer in the developer stirring section. The illustrated arrows indicate the direction of rotation of each roller.
Note that, instead of the scraper 44 that is in pressure contact with the developing sleeve 41, a magnet may be disposed as a developer removing unit in close proximity without contacting the outer periphery of the developing sleeve 41.

In the developing sleeve 41, a plurality of N poles,
A magnet roll 42 in which N1, N2, and N3 and a plurality of S poles and S1 and S2 are alternately arranged is fixed (five pole arrangement). Of these plural magnetic poles, two magnetic poles N2 and N3 arranged adjacent to each other have the same polarity, and the adjacent magnetic poles N2 and N3 having the same polarity form a repulsive magnetic field. Of the developer is removed. The magnetic pole S1 faces the developer layer regulating member 43. The tip of the scraper 44 is pressed against the peripheral surface of the developing sleeve 41 near the intermediate position Nu between the magnetic poles N2 and N3 of the same polarity.

The outer diameter of the developing sleeve 41 is preferably not less than φ8 mm and not more than φ60 mm. When the outer diameter is 8 mm or more, it is easy to form the magnet roll 42 having at least five magnetic poles required for image formation.

The outer diameter of the developing sleeve 41 is φ60 m.
m or less, the developing device is easily reduced in size. In particular, in a color printer (see FIG. 1) having a plurality of sets of developing devices (developing units 4Y, 4M, 4C, 4K), the developing device 4
Is smaller, the outer diameter of the photoconductor 1 can be reduced.
After the transfer to the recording medium P and the charge elimination, the recording medium P is
Can be separated from the peripheral surface by the curvature. Further, the image forming apparatus can be made compact by downsizing the developing device 4 and the photoconductor 1.

The image forming apparatus according to the present invention includes:
A modified Konica KL-2010 color printer (manufactured by Konica Corporation) was used. The outer diameter of the developing sleeve 41 was 18 mm and the outer diameter of the photoconductor 1 was 100 mm.

The developer layer regulating member 43 is formed by a round bar made of a magnetic member such as magnetic stainless steel (SUS).

The developer stirring screw 47A and the developer stirring screw 47B are connected to a first stirring chamber 40b formed on both sides of a partition wall 40a standing upright from the bottom of the developing device housing (developer accommodating portion) 40, Second stirring chamber 4
0c, and rotate in opposite directions to each other. The upper portions of the first stirring chamber 40b and the second stirring chamber 40c are closed by a lid 40A.

The toner replenished from the toner cartridge 5 is fed into a first stirring chamber 40b of the developing device housing 40 from a toner replenishing port (not shown) formed in the lid 40A and replenished. , A developer stirring screw 47 in the first stirring chamber 40b and the second stirring chamber 40c.
A and 47B mix and agitate the developer, and are supplied to the developing sleeve 41 by the developer supply roller 46. The developer supplied on the rotatable developing sleeve 41 containing the magnet roll 42 is regulated in the thickness of the developer layer by the developer layer regulating member, and is conveyed to a development area facing the photoreceptor 1 for non-contact development. Is performed.

In FIG. 3, 48 is an AC power source E1, D
A bias voltage applying means 49 including a C power source E2 and the like are waveform control means 49. The waveform control means 49 outputs a pause portion (blank portion) time T _B , a pulse portion time T _P , and a time ratio between the pulse portion and the pause portion (T _P / (T _P +
T _B )), the pulse amplitude, the pulse frequency (f) and the like are controlled.

Therefore, the present inventor studied improvement of the developing property of the blank pulse.

FIG. 4 is a diagram showing a conventional developing bias voltage waveform and image defects.

[0044] FIG. 4 (a), yellow toner Yt on the developing sleeve 41Y is in the developing area, an AC voltage V _AC and the DC voltage V _DC and flying to the peripheral of the photosensitive member 1 by being applied to the developing sleeve 41Y It is a schematic diagram which shows that it adheres to a surface.

[0045] The developing sleeve 41Y, and an AC voltage V _AC and DC voltage V _DC is superimposed applied. An AC voltage V _AC 28
Assuming that 00 V and the DC voltage _VDC are −600 V, the superimposed applied voltage is +800 V [(+1400 V) + (− 600 V).
V)] to -2000V [(-1400V) + (-60
0V)].

The latent image potential _VL of the image area on the photosensitive member 1 is -5.
In the case of a high density of 0 V, during development by the developing device 4Y, the yellow toner Yt is applied with a DC voltage _VDC of -600V to a developing sleeve 41Y having a sleeve potential of -2000V.
Photoconductor 1 having latent image potential V _L (−50 V) of image portion from above
Fly over the surface (in the direction of the arrow shown).

[0047] To increase the amount of toner adhered onto the photoreceptor 1, an AC voltage V _AC during the application of the AC bias voltage, further from said 2800V 3800V~48
By increasing the voltage to 00 V, the force for peeling the toner from the carrier increases, and the amount of toner adhered on the developing sleeve 41 can be increased. However, in this case, the potential difference between the developing sleeve 41 and the photoconductor 1 periodically increases, and the latent image potential V _L (−50)
V), a discharge breakdown (lightning phenomena) occurs between the developing sleeve 41Y and the photoconductor 1, and a so-called ring mark that generates a ring-shaped crater on the photoconductor 1 is generated. Therefore, there is a limit in increasing the toner adhesion amount by increasing the _AC voltage value VAC.

FIG. 4B shows that the yellow toner Yt previously formed on the photoreceptor 1 is applied to the photoreceptor 1 in a developing area when a plurality of toner images are superimposed on the photoreceptor 1.
FIG. 4 is a schematic view showing that the toner is peeled off from the top and re-attached to a developing sleeve.

When the magenta image is developed by the developing unit 4M, the yellow toner Yt is adhered onto the photoreceptor 1 by a preceding yellow image forming process including charging, exposure and development. The magenta image by the developing device 4M during development, increasing the AC voltage V _AC as described above, the yellow toner Yt adhering on the photosensitive member 1 of the re-charged photoreceptor potential (-750 V) photosensitive power take off from on the body 1 also will be increased, and the AC voltage V _AC applied to the developing sleeve 41M, the DC voltage V _DC, a yellow toner Yt is stripped from the developing sleeve 41Y, further sleeve potential (+ 800 V ) Developing sleeve 4
In some cases, the yellow toner Yt flies toward 1M and mixes with the magenta toner Mt on the developing sleeve 41M (hereinafter, this phenomenon is referred to as peeling).

[0050] In summary, increasing the AC voltage V _AC, the toner adhesion amount (developability) is increased, and generation exceeds a certain voltage value, the discharge breakdown (lightning phenomena), the photosensitive member 1 In an image forming apparatus that damages the toner or superimposes a plurality of toner images on the photoconductor 1,
The peeling is caused to cause the mixing of different color toners. Therefore, in order to improve the toner adhesion amount (developability), it is necessary to devise a method of preventing discharge breakdown and suppressing occurrence of peeling.

Thus, the present inventors have conducted intensive studies and as a result,
By making the waveform of the AC voltage application part of the blank pulse waveform an asymmetric waveform in one cycle of the AC voltage,
It has been found that a decrease in developability in the blank pulse portion can be prevented.

FIG. 5 is a diagram showing an astigmatic waveform of the developing bias voltage. In the figure, the broken line indicates a symmetric waveform,
The solid line shows an astigmatic waveform according to the invention. This waveform
In one cycle of the AC voltage, the waveform has no symmetry point, that is, an asymmetry waveform. Preferably, the astigmatism symmetrical waveform includes an integral value on the developing drive side (area of a hatched portion on the upper side in the drawing) in which toner moves from the developing sleeve 41 onto the photosensitive member 1 and a developing sleeve 41 from the photosensitive member 1. The integral value on the return side where the toner moves to the side (the area of the hatched portion on the lower side in the figure) is equal to a constant value (effective voltage level is constant), and the peak value of the asymmetry waveform is effectively applied. The absolute value of the difference from the DC voltage value is different between the high and low DC voltage values. The ratio between the applied voltage and time is changed.

T _{1 in the} figure is the application time on the developing drive side, and T ₂ is the application time on the return side. The waveform shown is Dut.
y ratio: T ₂ / (T ₁ + T ₂ ) is set to 0.6 (T ₂ > T ₁ ). Further, it is desired that the effectively applied DC voltage V ′ _DC is equal to the actually applied DC potential difference V _DC .

As shown in FIG. 5, by making the AC voltage of the developing bias voltage a non-point symmetrical waveform, the absolute value of the applied voltage on the developing drive side increases as compared with the symmetrical waveform. This can be compensated for by the AC voltage applying unit, and the amount of toner adhering to the photoreceptor 1 from the developing sleeve 41 increases as a whole, thereby improving the developing property. In addition, since the absolute value of the applied voltage on the return side also becomes small, the above-described stripping can be suppressed.

The following is a comparison of the developability of the symmetric blank pulse waveform and the astigmatic symmetric blank pulse waveform. Note that the charging potential V _{H of} the photoconductor 1 is −750 V, the latent image potential V _L on the photoconductor 1 is −50 V, the DC voltage _{VDC is} −600 V, and the closest distance d between the photoconductor 1 and the developing sleeve 41 is d = 0.57m
m, developer transport amount DWS of the developing sleeve 41 = 9 mg /
cm ² and frequency f = 6 kHz. Further, two wavelengths of the pulse portion and then a portion corresponding to two wavelengths of the blank portion were applied.

(1) Symmetrical blank pulse waveform development: At this time, the maximum AC voltage at which stripping does not occur is V _AC =
At 2.4 kV, the toner adhesion amount (M / A) on the photoconductor 1 was 0.56 mg / cm ² .

(2) Duty ratio: astigmatic blank pulse waveform development with T ₂ / (T ₁ + T ₂ ) set to 0.6: At this time, the maximum AC voltage at which peeling does not occur is V _AC =
It is improved to 2.6 kV, and the toner adhesion amount on the photoreceptor 1 is 0.3 kV.
Increased to 78 mg / cm ² .

By making the waveform of the pulse portion of the blank pulse a non-point symmetric waveform (a non-point symmetric blank pulse), it is possible to suppress a decrease in developability which was a problem with the blank pulse, and to suppress a decrease in developability. As a result, the potential of the high-density portion is likely to be saturated, so that there is also an effect that the above-described suction and white spots are less likely to occur.

Here, the stripping will be discussed.

In the case of the astigmatism symmetrical waveform as shown in FIG. 5, the DC voltage _VDC substantially fluctuates unless the waveform integration value in the developing drive direction is equal to that in the return direction. The waveform integration values in the return direction must be the same.

[0061] Therefore, minute electric field in the return direction to decrease the absolute value, the time for applying long, minute electric field in the developing drive direction to increase the absolute value, to shorten the time applied, the DC voltage V _DC is It does not substantially fluctuate.

However, even if the absolute value of the electric field in the return direction is small, if the continuous application time is long, stripping occurs in the same manner, which is a problem.

The inventor of the present invention divided the process of forming the electric field in the return direction into two or more times within one cycle of the developing bias voltage to prevent peeling.

The reason is that a certain time is required for the toner on the photoreceptor 1 to return to the developing sleeve 41 of the next color. However, if the electric field in the return direction is switched before reaching the time, the toner returns. This is because it does not occur.

When this method is applied to an asymmetry waveform, the developability can be further improved.

(Embodiment 1) FIG. 6A shows a short drive voltage application time (short time) in a return electric field of a symmetrical voltage waveform in which a voltage in which an AC component is superimposed on a DC component is applied. is a diagram showing an embodiment containing the resting portion) T _4.

[0067] Rather than continuously applying a return side voltage portion shown in FIG. 6, by interposing a brief pause portion T ₄ during, stripping is switched electric field before the stripping occurs Does not occur.

Further, since the AC component can be increased to the limit at which peeling occurs, the developability is improved.

As shown in FIG. 6A, the T ₄ interposed between the portions where the electric field in the return direction is formed is not only a DC component as shown in FIG. 6A, but also a developing drive as shown in FIG. The voltage in the return direction may be applied, or the voltage in the return direction may be applied as shown in FIG.

However, the waveform integral value in the hatched upper developing drive direction is the same as the waveform integral value in the application time T ₃ , T _{5 in the} two lower hatched return directions.

The application times T _{1 to} T ₅ are determined by the waveform control means 4.
9 formed.

The application time T _{2 in} the return direction is:
Has been divided by T ₄ brief drive voltage application time to 2 times a cycle intermediate, the present invention is not limited to this, even if the divided waveform to three or more of the plurality of times Good.

(Embodiment 2) FIG. 7 shows an astigmatic type (Va> V) in which a voltage obtained by superimposing an AC component on a DC component is applied.
the voltage waveform b), a diagram showing an embodiment of applying a brief pause portion T _4.

In FIG. 7, a short pause T ₄ is applied within the operation time T ₂ on the return side in the step of forming a pull-back electric field in the direction in which the toner travels from the photoreceptor 1 to the developing sleeve 41. Thus, the pull-back electric field was divided into two to form T ₃ and T ₅ .

As a result, the developability is improved with an asymmetry waveform,
The stripping was reduced, and the stripping margin was further increased, so that the AC component could be increased and the developability was further improved.

The waveform for dividing the pull-back electric field by the short drive voltage application time T ₄ is set at least twice within one cycle (1 / f) of the developing bias voltage.

As a result, the return of the toner was eliminated, and the developability was further improved.

(Embodiment 3) FIG. 8 shows the application times T ₆ and T in the return direction before and after the normal developing drive direction application time T _1.
7 is provided, and shows another embodiment of the point-asymmetrical blank pulse waveform having a rest portion time T _B.

By providing the application times T ₆ and T ₇ in the return direction divided by the application time T ₁ of the short drive voltage, toner return can be eliminated. The developing device of the present invention and this developing device The image forming apparatus provided with is not limited to the above embodiment, and may be a color image forming apparatus provided with a belt photoreceptor, a color image forming apparatus provided with a transparent photoreceptor, or a tandem type color image forming apparatus. And so on.

The developer used in the developing device of the image forming apparatus of the present invention is not limited to a two-component developer, but can be applied to a one-component developer.

[0081]

According to the developing method, the developing apparatus and the image forming apparatus of the present invention, the step of forming a pull-back electric field in which the toner moves from the photoreceptor to the developing sleeve includes one step of the developing bias voltage.
The method is characterized in that the voltage in the return direction is switched for a short time before a predetermined time before the toner on the photoreceptor starts to return to the developing sleeve of the next color, since it is set at least twice in the cycle. Therefore, peeling due to toner return from the photoreceptor did not occur, there was no change in secondary color hue, a sufficient reflection density was obtained, and an image with good hue was obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color printer on which a plurality of sets of a developing device of the present invention are mounted.

FIG. 2 is a sectional view of a developing device including a plurality of sets of developing devices according to the present invention.

FIG. 3 is a cross-sectional view of the developing device of the present invention.

FIG. 4 is a diagram showing a developing bias voltage waveform and an image defect.

FIG. 5 is a diagram showing an astigmatic symmetric continuous waveform of a developing bias voltage according to the present invention.

FIG. 6 is a diagram showing a symmetrical, return-portion divided waveform according to the first embodiment;

FIG. 7 is a diagram showing a non-point symmetric type, return portion divided waveform according to the second embodiment.

FIG. 8 is a diagram showing a non-point symmetric type, return-portion divided waveform according to the third embodiment.

[Explanation of symbols]

Reference Signs List 1 image carrier (photosensitive drum, photosensitive body) 2 scorotron charger (charger) 4 developing device 4Y, 4M, 4C, 4K developing device 40 developing device housing (developer accommodating portion) 41, 41Y, 41M, 41C, 41K developer carrier (developing sleeve) 42 magnetic field generating means (magnet roll) 43 developer layer regulating member 48 bias voltage applying means 49 waveform control means Vs peripheral speed of developing sleeve Vp peripheral speed of photoreceptor V _AC applied to developing sleeve AC voltage V _DC applied to the developing sleeve DC voltage V _L the latent image potential of the image portion on the photosensitive member (latent image potential of the exposed portion) V _H photoreceptor charging potential T ₁ developing drive side of the application time T ₂ to, T _3, T ₅ the return side of the application time T ₄ be applied to the short time of the driving voltage application time pulse unit time T _B developing sleeve of the AC component applied to the (short pause portion) T _P developing sleeve The pause time of the alternating current component f The pulse frequency of the alternating current component applied to the developing sleeve d The closest distance between the developing sleeve and the photoconductor

Claims (5)

[Claims] 1. A developing bias comprising an AC voltage in which a DC voltage is superimposed on a developer carrying member, wherein the developer carrying the developer is carried in a non-contact state with respect to the image carrying member. A voltage is applied, a developing method of developing an electrostatic latent image formed on the image carrier, wherein a step of forming a pull-back electric field in which a developer moves from the image carrier to the developer carrier, A developing method characterized by being set at least twice or more within one cycle of the developing bias voltage. 2. The developing method according to claim 1, wherein the developing bias voltage satisfies the following relational expression. Va ≧ Vb: Va: Absolute value of the difference between the maximum bias voltage at which the developer driving electric field at which the developer moves from the developer carrier to the image carrier and the average of the developing bias and the average value of the developing bias, Vb: Image carrier The absolute value of the difference between the maximum bias voltage at which the withdrawal electric field at which the developer moves from the developer to the developer carrying member and the average value of the developing bias. 3. A developer carrying member for carrying a developer in a non-contact state with respect to an image carrying member, wherein a developing bias voltage composed of an AC voltage on which a DC voltage is superimposed is applied to the developer carrying member. A developing device for developing the electrostatic latent image formed on the image carrier with a developer carried by the developer carrier, wherein the developer is transferred from the image carrier to the developer carrier. Forming a withdrawing electric field in which
A developing device controlled by a waveform control circuit that is set at least twice within one cycle of the developing bias voltage. 4. The developing device according to claim 3, wherein the developing bias voltage satisfies the following relational expression. Va ≧ Vb: Va: Absolute value of the difference between the maximum bias voltage at which the developer driving electric field at which the developer moves from the developer carrier to the image carrier and the average of the developing bias and the average value of the developing bias, Vb: Image carrier The absolute value of the difference between the maximum bias voltage at which the withdrawal electric field at which the developer moves from the developer to the developer carrying member and the average value of the developing bias. 5. An image forming apparatus for superimposing and forming a plurality of color images on an image carrier, comprising a plurality of the developing devices according to claim 3 for each color of the plurality of color images. By forming an electrostatic latent image on the image carrier for each color of a plurality of color images and developing the electrostatic latent image by the developing device, a plurality of colors are superimposed on the image carrier. An image forming apparatus for forming a combined image.